CA1075837A - Arrangement for processing auxiliary signals in a frequency multiplex transmission system - Google Patents
Arrangement for processing auxiliary signals in a frequency multiplex transmission systemInfo
- Publication number
- CA1075837A CA1075837A CA255,477A CA255477A CA1075837A CA 1075837 A CA1075837 A CA 1075837A CA 255477 A CA255477 A CA 255477A CA 1075837 A CA1075837 A CA 1075837A
- Authority
- CA
- Canada
- Prior art keywords
- signals
- arrangement
- digital
- output
- signal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J1/00—Frequency-division multiplex systems
- H04J1/02—Details
- H04J1/14—Arrangements providing for calling or supervisory signals
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J1/00—Frequency-division multiplex systems
- H04J1/02—Details
- H04J1/04—Frequency-transposition arrangements
- H04J1/05—Frequency-transposition arrangements using digital techniques
Abstract
P?? 75550 ABSTRACT:
The arrangement for converting in an FDM format spatially separated signalling signals and pilot signals, comprises a digital filter bank for bringing the signals in the FDM format. The arrangements for separating the signalling signals and pilot signals from the FDM signal comprises for that purpose also a digital filter bank with which the signals are simultaneously obtained in baseband position. These filter banks have a transfer characteristic formed by a number of passband curves which are derived from a characteristic low-pass filter.
The arrangement for converting in an FDM format spatially separated signalling signals and pilot signals, comprises a digital filter bank for bringing the signals in the FDM format. The arrangements for separating the signalling signals and pilot signals from the FDM signal comprises for that purpose also a digital filter bank with which the signals are simultaneously obtained in baseband position. These filter banks have a transfer characteristic formed by a number of passband curves which are derived from a characteristic low-pass filter.
Description
I,OOl'/'YMU/KOOI
13-~-1976 ~775~ ~7 ' I
"Arrangement for processing auxillary signals in a frequency multiplex transmisslon system".
, ._ 7 (A) Background of the invention '~! ( ~ of the i vention :~ The invention :relates to an arrangement for pro-eessing auxiliary signals in the form of spatially separated signalling signals and pilot signals ~or a given number of main in~ormation signals for transmitting these auxiliary signals together with the main informat~on signals in an :; FDM format.
:
, The invention also relates to an arrangement for proeessing auxiliary signals o~ a given number of main infor-: mation signals, ~or spatially separating and reeovering these :: auxiliary signals in the form of signalling signals and pilot signals, whieh are applied to the arrangement together :~ with the main in~ormation signals in an FDM ~ormat.
(A~) Deserip~
. As known, an FDM signal for speech signals is com-posed of a plurality of FDM channels which each cover a . bandwidth o~ 4 KHzo Each of these channels aeeommodates a ~: speech channel ~or ~le transmission of a speech signal~ Eerein . 20 this speech signal has a bandwidth of 3.1 k~z and the distance .
. between two SUecQsSive speeeh ehannels in the FDM signal is : 900 Hz. The ~requene~ spaees of 900 Hz whieh are eaeh time .~ present between two suceessive speech ehannels are utilized ~ for transmitting signal~ng signals-~nd, possibly, pilo-t :1 25 signals.
' ':' . -2- ~
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P~ 75550 .
758;~7 . ~
¦ More in particular an auxiliary channel is added to each speech channel for transmitting the signalling signals associat-~ ed with this speech channel. It should be noted that the 1 bandwidth of such signalling signals is only a few tens of ¦ 5 hertz (for example 20 Hz).
The location describ0d above of the signalling signals with respect to the associated speech signal is also ` indlcated by out of band signalling. This in contrast with the so-called in-band signalling in which the signalling Aignals are located within the frequency band of the speech signal.
The ~ignalling signals used ~ practice are all in the form of a series of pulses having a repetition ~requency of, for example, 10 Hz. To accommodate these signals in the auxiliary channels of the FDM signal each of these signalIing signals is filtered by means of a low-pass filter and there-'~` after modulated on a carrier of a suitably chosen freq~ency.
In the reverse case, to separate the signalling signals spatially again from the FDM signal and to~obtain the signal-~ng signals in base band~ the FDM signal is applied to a - plurality of parallel channels. In each of these channels the FDM slgnal is demodulated with a carrier of a suitably chosen frequency. From each of the demodulated signals ob-~;
tained in this way a signalling signal is again selected by means of a low~pass filter. For the proper operation of both arrangements the cut-off ~requencies of the low-pass ~ilters ;'`.'.
used must be low7 for exampla 50 Hz. However, this results -~ in very bulky and expensive filters.
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Pl~` 7555 ~ 37S~37 J
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With an FDM signal one or more pllot signals are also transmitted together ~ith the signalling signals. For a primary FDM group 1~hich is located in the frequency band of ¦ 60 - 108 kHz one or more pilot signals are acco~nodated with ! the frequencies 8~,080 kHz, 84.140 k~Iz or 104.80 kH~ res-pectively, ~t the raceiver slde of the FDM transmission system the level of such a pilot signal is used ~or automatic volume ~ control of the speech signals. In view of the accuracy which is required for this volume control both the frequency and the ¦ 10 amplitudes of these pilot signals must ba very s~able whilst at the receiving side of the FDM transmission system extreme-ly selective filters must be used to select these pilot signals from the FDM signal. Such a filter has~ for example, a band wid$h of 20 Hz, whereas lts intermediate frequency coincides with the pilot frequency, In practice quartz oscillators are used for producing the pilot signals whilst very expensive ¦ quartz filters are used for selecting the pilot signals from ;~ the F~M signal, In prac$ice the above means that approximately 40%
of the costs of an FDM multiplexer or demul~iplexer is deter~
mined by the necessary transmission of signalling signals ¦ and pilot signals.
- . ".
(B) Summary of the invention ¦ It is an object of the present invention to pro-1 25 vide another concept of the arrangements described above ~
with which a considerable cost reduction is-obtained.
! It is also an object of the present invention to provide arrangements of the kind defined above which can be ': ~ , .
.'.~
.' , . . '-:~' ' ' .
Pl~` 7555 fully constructed in d~gital techniques.
, The arrangemont for processing spatially separated a~xiliary signals in the form of spatially separated signalling . 1 signal~ for a given number of main information signals for ¦ 5 transmltting these auxiliary signals together with the maln ~-¦ information signals in an FDM format, and which comprises a )?.
¦ plurality of input circuits which is equal to the plurality of main information signals and w~*h an output clrcuit.further ¦ comprisas, according to the inventlon:
- means for digiti~ing the auxiliary signals;
- means ~hich are coupled to said digitizing means for limit-in~ng the bandwidth of each of the auxiliary signals;
- a digital filter bank to which said digital auxiliary signals are applied and which has a passband characteristic which ls characteristic for each of the auxiliary signals, the 1~-_.termediate frequency of this passband characteristic coin-c ~id~ngiw~th the intermediate frequency of the auxiliary channel for the relevant auxiliary signal.
'.
The arrangement for processing auxiliary signals in the form of signalling signals o~ a given number of main information signals, for spatially separating and recovering these slgnalling signals which are offered together with the main information signals in an FDM format, and which comprises an input circuit to which said FDM signal is applied and a ?, plurality of output circuits which is equal to the plurality of main i.nformation signals further comprises according to the invention:
!
` - .
., j ,~ , : .' . .
. i I ~l~ 75550 ~ ~75837 13-5-1976 - means for digitizing the FDM signal ~ - a first digital fllter bank to which said digltized FDM
-~ signal i9 applied and which has a band-pass characteristic which is characteristic for each of the signalling signals, the intermediate frequency of one of the passbands coincid-ing with the intermediate frequency of the relevant auxi-liary channel;
l~ - a second digital filter bank to which the digital output signals of the first digital filter bank are applied and which has a low-pass characteristic for each of the auxi-liary signals.
In what follows hereinafter the said first arrange-¦ ment which is arranged for converting the spatially separated signalling signals in an FDM format will be indicated b~
¦ 15 FDM modulation arrangements. The second arrangement which is arranged for recovering and spatiall~ separating signalling signals offered in an FDM format will be indicated by ~DM
demodula~on arrangement.
: In one embodiment, in the FDM modulation arrange-ment, the sampling frequency of the auxiliary signals is equal to the channel signal bandwidth of 4 kHz. Furthermore the digital filter banks are mainly constituted in the FDM modulation and demodulation arrangements by the cascade B circuit o~ a discrete Fourier trans~ôrmer and a ~ ~ ~e net-work. In this embodiment the computing speed in all computing devices is equal to 4 kHz.
. In another embodiment the computing speed in a large part o~ the computi~g arrangements is considerably .
..
0~` 7555 13-5-1~76 ~ S837 !
reduced because the al~iliary si~lals are sampled with a con-, siderably lower sampling ~requoncy (-fo~ xample;cwith,500 Hz).
! To increase the sampling frequency an interpolating digital filter is included in the FDM modulation arrangemffnt between each of the pol~phase network and tha assoclated output o~
the Fourier transformer. In the FDM demodulation arrangement ! a decimation filter is included between each polyphase network and the associated input o~ the Fourier transformer to reduoe I the sampl~ng ~requency. In this embodiment the Fourier trans-¦ 10 formers operate at a lower computing speed and, consequently, ~¦ also the second digital filter bank, (C). Short descr ~ ~ res The Figures 1 and 2 show an FDM modulation arrange-ment and an FDM demodulation arrangement according to the invention rospeotively;
- Fig. 3 shows the spectrum of the multiplex signal ~or a primary group of 12 telephone signals.
In Fig. 4 diagram 4a shows the attenuation i characteristic of a lowpass ~ilter and the diagrams 4b ~ 4f inclusive show various attenuation characteristics of band-pass filters which together constitute the transmission f characteristic o~ a digital ~ilter bank, the diagram 4g shows the spectrum of the multiplexed auxiliary signals.
In Fig~ 5 the diagram 5a shows the spectrum o~ the signal at the output of the digital filter bank in the FDM de-modulation arrangement and diagram 5b shows the characteristic o~ the filter for selacting the signalling signals. Diagram 5c shows the characteristic of the ~ilter ~or selecting a : .,' . ~.
~7 :
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P~. 75-550.
~ 07S837 pilot signal.
Fig. 6 shows an embodiment of a digital phase shifter, Figs. 7 and 8 respectively shcw another embodlment of the FDM modulation and dem~ulation arrangement acoording ~o the invention.
Figs. 7 and 8 show modifications of the circuits shown in Figs. 1 and 2.
Fig. 9 shows waveforms useful in explaining the oper~
ation of the control devioe and Fig. ga shows a pulse of signal-ling signal.
Y Fig. 10 shcws an ~miodim~nt of the control and store devices of Fig. 1.
;; (D) Description of the e~bodiments.
Fig. l~shows an FDM modulation arrang~nent according ; - 15 to the invention. This arrangement is arranged for transmitting control and signalling auxiliary signals which are added to a group of telephone signals to be transmitted in frequency divi~
sion n~ltiplex. Here belcw it is asisumed that the F~M signal is constituted by a primary group of 12 telephone signals.
The spectrum of such a primary group is shcwn in ~` Fig. 3. This spectrum camprises the speech channels Tl to T12inclusive, which correspond to the 12 telephone signals and which each occupy a frequency band having a width of 3100 Hz.
me æ speech channels are each time situated between the multiples of 4 k~Iz in the frequency band from 60 - 108 kHz.
The intervals Il to I12 inclusi~e, having a width of 900 Hz !~ which are situated outside the speech channels are used as transmissi~n channels for the auxiliary signals.
m e signalling signals belong to these auxiliary signals. These signallLng signals are logic signals havlng a ~ B ~ 8 - ~ ~
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~75837 PHF. 75-550, frequency of 10 Elz which are each associated with a char~el signal for controlling the con~nication in this c~nnel.
Tb be able to intrcduce the sic~alling signals in the inter-.
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i I'~rl~' 75550 7~37 vals between speech channels the bandwidth of each of those signalling signals is limlted to some tens of Hz, ~lereafter the signals thus limited are modulated on a carrier. In, for ~- ¦ example, the so-callecl dc signalling systems carrier fre-¦ 5 quencies are used which are in the frequency band of 6~-108 ~ kHz and which are each a multiple of 4 k~Iz. These carrier ; ¦ frequencies have been indicated in Fig. 3 by means o~ the solid l ~ arrows S1 to S12 inclusive.
5;,1 Added to a group of channel signals are also one ;' 1 10 or more control signals in the form o~ pilot signals having a very stable frequency and a very stable amplitude. This amplitude is used in the FDM demodulation arrangement for the automatic control of the speech channel level. A pilot signal having a ~requency of 84.140 Hz is used in a primary group of 12 channel signals with d.c. signalling. In Fig. 3 this l~ pilot signal is indicated by means of $he solid arrow X. From ,:
~: ~ig. 3 it appears that a signalling signal and a pilot signal is present in the interval I6 which i9 situated around the frequency of 84 kHz.
~ 20 In Fig. 1 the sources ~or logic signallingsignals ,.~ .
are represented by contacts C1 to Cl2 inclusive which are ~ed by a d.c. voltage V and which are operated with a frequency of 10 Hz by means not further shown in the Figure. Reference numeral 1 indlcates a pilot signal generator. The circuit 2 which performs filter and carrier modulation operations on the control and signalling signals supplies the auxiliary i: signals in an FDM format which~ in an ampli~ier-adder 3 is ~:
superimposed on the multiplex signal ~ormed by the speech signals ST, which multiplex signal is assumed to have been ~:~ . ~ .
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Pl~` 7555 :~07S~3~
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formed by mealls not shown in the Figure. The complete multiplex ~, signal of the speoch channels thus ~ormod and tho auxiliary `1 signals are transmitted thl~ough the lead 4.
¦ The FDM demodulation arrangement of Fig. 2 is provided with an amplifier 5 to which the FDM signal which is transmitted through the lead 4is applied. This amplifier 5 has a variabl0 gain ~actor and is controlled by the received pilot signal which is appliad to the control terminal 6 of this amplifier. The FDM signal which is produced at the output of the amplifier 5 is applied to the terminal 7 for spatially separating the speech channels in a manner which is not further indicated in Fig. 2. This FDM signal is also applied to a cir-1 , cuit 8 in ~rhich tho demodulation and filtering processes are performed for spatially separatin~ the received auxiliary .
signals. The signalling signals are derived from the leads ~1 to ~12 respectively and are used for actuating the con-tacts C~l to C~12 inclusive which correspond to the contacts Cl to C12 of Fig. 1. The transmitted pilot signal is deri~ed from the lead ~p for suppl~ to the control terminal 7 of the ~ 20 amplifier 6.
`¦ At present, in frequency multiplex transmission ::! systems the filtering and modulation processes and the de-modulation and filtering processes for the auxiliary signals I - are still per~ormed by means of analog signal processing techniques~ As has already been indicated these arrangements are consequently bulky and expensive. By means of the arrangement according to the invention it is possibly to ¦ mitigate these drawbacks to a considerable extent.
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1 3_ 5--1 9 7 6 1~:97~837 The FD~I modulation arrangement according to the invention (Flg. 1) comprises to that ond means for producing digital signals which correspond to the base band auxiliary signals. ' -As regards the sign~llingsignals these means are constituted by a control device 9 and a storage device 10. The signalling si~lals s1 to s12 inclusive are applied to the con~
~;¦ trol device 9. As remarked above these signalling signals ~ are ~ormed by series of pulses which occur with a frequency ¦ 10 o~ 10 Hz. To introduce these signals in the intervals between ~ the speech channels these signals must be ~iltered in order ,1 to limit their bandwidth to some tens o~ Hz. This might be ~, e~ected by digital low-pass filters having a suitably chosen impulse response. In Fig. 1 this ~iltering process-is per- -~ormed in a simpler manner. The samples of the stap response , , o~ the required low-pass ~ilter are stored in digltal ~orm in - the storage device 10~ In response to each o~ the signalllngpulses, samples o~ the stap response are read from the sto-rage device 10 by the control device 9 in a manner which will be further explained with re~erence to Fig. 9. In particular, in response to a signalling pulse at the input S1 o~ the con-, trol device a series o~ samples is produced at the output b1 ': o~ the storage device 10, in response to a signalling pulse at the input~;S~ a series o~ samples is produced atthe output b6 etc. Thle ~requency with which the samples o~ the stap response occur at, for example, the ou-,tput b1 of the storage ! device 10 is determined by the time base 11.
I The pilot signal which must be inserted into .'~ .
.
. ~ .
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P}n` 75550 13_~-197~
~ccommodated tho FD~I sig~ l and which has~ ~or exarnple, a frequenc~ o~ 84~1~tO llz iS generatQd by procossing ,a base band pilot signal sp having a frequency of 1l~0 ~Iz. This slgnal is produced in digital form b3r the generator 1~ This generator ` i 5 is, for oxample, consti-tuted by a ROM~ in which the samples of a sinusoidal signal having a frequency o~ 140 Hz are j stored in digltal form. These samples are applied to the output .
. ~ .
of the memory with a frequency which is determined by the time ~`. `:.1 '~ ' base 1~. ' '~ 10 To insert this pilot signal into the FDM signal the- 3 arrangement of Fig. 1 further comprises an adder circuit 12 an input of which is connected to the output a6 of the storag~
device 10 and whos~a other input is conneoted to the output of ~'~ ' the storage de'vice 1. The signallingsignal s6 and the pilot '~ 15 signal sp are auxiliary signals which must be transmitted in the same channel. In particular these signals are transmitted ` ~ in *he lnterval I6 of Fig. 3. ~onsoquently the digital signal S6 ~ sp occurs at the output of the adder 12, ~ ' The FDM modulation arrangemant of Fig. 1 further i;l 20 comprises a digital filter bank 13 for converting the auxiliarysignals into the FDM format. In particular the 12 intervals I1...~I12 of Fig. 3 contain the digital signals s1, r~
S6 ~ sp, ....s12 respectively. The filter bank 13 has a ~j transfer characteristic which is formed by bandpass character-istics whose intermediate ~requencies 'coincide wi'th the inter-, ~;' mediate frequencies o~ the auxiliary channels which accommo-t ~ date the au~iliary signals. These characteristics are derived rom the characteristic of a low~pass filter which ensures the transmission of the auxiliary signals in the base band.
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~ ~ ~ S ~ ~ ~ Pl-IF. 75-550.
Diagram 4a of Fig. 4 shcws the attenuation charac-teristic of this lcw-pass filter. It appears from this characteristic that around the frequency 0 a very slight attenuation is exercised on a signalling signal. This signal-ling signal, having a bandwidth of, for example, 50 Hz is represented in this diagram 4a by means of ha~ched triangle.
In this diagram 4a also the tw~) base band pilot signals having respectively the frequencies + 140 Hz are indicated by tw~
arrows. As this diagram 4a shows the attenuation curve of the filter is infinitely high for all multiples of 4 kHz.
m e attenuation curve of the various bandpass char-acteristics of the filter bank 13 is shcwn in the diagrams 4b to 4f inclusive. me characteristics of the diagra~s 4b, 4c,....4d, ... 4e, 4f are obtained from the characteristic 4a by shifts over 12 x 4 kHz, 11 x 4 kHz, ... 7 x 4 kHz,
13-~-1976 ~775~ ~7 ' I
"Arrangement for processing auxillary signals in a frequency multiplex transmisslon system".
, ._ 7 (A) Background of the invention '~! ( ~ of the i vention :~ The invention :relates to an arrangement for pro-eessing auxiliary signals in the form of spatially separated signalling signals and pilot signals ~or a given number of main in~ormation signals for transmitting these auxiliary signals together with the main informat~on signals in an :; FDM format.
:
, The invention also relates to an arrangement for proeessing auxiliary signals o~ a given number of main infor-: mation signals, ~or spatially separating and reeovering these :: auxiliary signals in the form of signalling signals and pilot signals, whieh are applied to the arrangement together :~ with the main in~ormation signals in an FDM ~ormat.
(A~) Deserip~
. As known, an FDM signal for speech signals is com-posed of a plurality of FDM channels which each cover a . bandwidth o~ 4 KHzo Each of these channels aeeommodates a ~: speech channel ~or ~le transmission of a speech signal~ Eerein . 20 this speech signal has a bandwidth of 3.1 k~z and the distance .
. between two SUecQsSive speeeh ehannels in the FDM signal is : 900 Hz. The ~requene~ spaees of 900 Hz whieh are eaeh time .~ present between two suceessive speech ehannels are utilized ~ for transmitting signal~ng signals-~nd, possibly, pilo-t :1 25 signals.
' ':' . -2- ~
. , .
P~ 75550 .
758;~7 . ~
¦ More in particular an auxiliary channel is added to each speech channel for transmitting the signalling signals associat-~ ed with this speech channel. It should be noted that the 1 bandwidth of such signalling signals is only a few tens of ¦ 5 hertz (for example 20 Hz).
The location describ0d above of the signalling signals with respect to the associated speech signal is also ` indlcated by out of band signalling. This in contrast with the so-called in-band signalling in which the signalling Aignals are located within the frequency band of the speech signal.
The ~ignalling signals used ~ practice are all in the form of a series of pulses having a repetition ~requency of, for example, 10 Hz. To accommodate these signals in the auxiliary channels of the FDM signal each of these signalIing signals is filtered by means of a low-pass filter and there-'~` after modulated on a carrier of a suitably chosen freq~ency.
In the reverse case, to separate the signalling signals spatially again from the FDM signal and to~obtain the signal-~ng signals in base band~ the FDM signal is applied to a - plurality of parallel channels. In each of these channels the FDM slgnal is demodulated with a carrier of a suitably chosen frequency. From each of the demodulated signals ob-~;
tained in this way a signalling signal is again selected by means of a low~pass filter. For the proper operation of both arrangements the cut-off ~requencies of the low-pass ~ilters ;'`.'.
used must be low7 for exampla 50 Hz. However, this results -~ in very bulky and expensive filters.
' `~
':
~: . -3-..
. .
. `.. ..
Pl~` 7555 ~ 37S~37 J
I .
With an FDM signal one or more pllot signals are also transmitted together ~ith the signalling signals. For a primary FDM group 1~hich is located in the frequency band of ¦ 60 - 108 kHz one or more pilot signals are acco~nodated with ! the frequencies 8~,080 kHz, 84.140 k~Iz or 104.80 kH~ res-pectively, ~t the raceiver slde of the FDM transmission system the level of such a pilot signal is used ~or automatic volume ~ control of the speech signals. In view of the accuracy which is required for this volume control both the frequency and the ¦ 10 amplitudes of these pilot signals must ba very s~able whilst at the receiving side of the FDM transmission system extreme-ly selective filters must be used to select these pilot signals from the FDM signal. Such a filter has~ for example, a band wid$h of 20 Hz, whereas lts intermediate frequency coincides with the pilot frequency, In practice quartz oscillators are used for producing the pilot signals whilst very expensive ¦ quartz filters are used for selecting the pilot signals from ;~ the F~M signal, In prac$ice the above means that approximately 40%
of the costs of an FDM multiplexer or demul~iplexer is deter~
mined by the necessary transmission of signalling signals ¦ and pilot signals.
- . ".
(B) Summary of the invention ¦ It is an object of the present invention to pro-1 25 vide another concept of the arrangements described above ~
with which a considerable cost reduction is-obtained.
! It is also an object of the present invention to provide arrangements of the kind defined above which can be ': ~ , .
.'.~
.' , . . '-:~' ' ' .
Pl~` 7555 fully constructed in d~gital techniques.
, The arrangemont for processing spatially separated a~xiliary signals in the form of spatially separated signalling . 1 signal~ for a given number of main information signals for ¦ 5 transmltting these auxiliary signals together with the maln ~-¦ information signals in an FDM format, and which comprises a )?.
¦ plurality of input circuits which is equal to the plurality of main information signals and w~*h an output clrcuit.further ¦ comprisas, according to the inventlon:
- means for digiti~ing the auxiliary signals;
- means ~hich are coupled to said digitizing means for limit-in~ng the bandwidth of each of the auxiliary signals;
- a digital filter bank to which said digital auxiliary signals are applied and which has a passband characteristic which ls characteristic for each of the auxiliary signals, the 1~-_.termediate frequency of this passband characteristic coin-c ~id~ngiw~th the intermediate frequency of the auxiliary channel for the relevant auxiliary signal.
'.
The arrangement for processing auxiliary signals in the form of signalling signals o~ a given number of main information signals, for spatially separating and recovering these slgnalling signals which are offered together with the main information signals in an FDM format, and which comprises an input circuit to which said FDM signal is applied and a ?, plurality of output circuits which is equal to the plurality of main i.nformation signals further comprises according to the invention:
!
` - .
., j ,~ , : .' . .
. i I ~l~ 75550 ~ ~75837 13-5-1976 - means for digitizing the FDM signal ~ - a first digital fllter bank to which said digltized FDM
-~ signal i9 applied and which has a band-pass characteristic which is characteristic for each of the signalling signals, the intermediate frequency of one of the passbands coincid-ing with the intermediate frequency of the relevant auxi-liary channel;
l~ - a second digital filter bank to which the digital output signals of the first digital filter bank are applied and which has a low-pass characteristic for each of the auxi-liary signals.
In what follows hereinafter the said first arrange-¦ ment which is arranged for converting the spatially separated signalling signals in an FDM format will be indicated b~
¦ 15 FDM modulation arrangements. The second arrangement which is arranged for recovering and spatiall~ separating signalling signals offered in an FDM format will be indicated by ~DM
demodula~on arrangement.
: In one embodiment, in the FDM modulation arrange-ment, the sampling frequency of the auxiliary signals is equal to the channel signal bandwidth of 4 kHz. Furthermore the digital filter banks are mainly constituted in the FDM modulation and demodulation arrangements by the cascade B circuit o~ a discrete Fourier trans~ôrmer and a ~ ~ ~e net-work. In this embodiment the computing speed in all computing devices is equal to 4 kHz.
. In another embodiment the computing speed in a large part o~ the computi~g arrangements is considerably .
..
0~` 7555 13-5-1~76 ~ S837 !
reduced because the al~iliary si~lals are sampled with a con-, siderably lower sampling ~requoncy (-fo~ xample;cwith,500 Hz).
! To increase the sampling frequency an interpolating digital filter is included in the FDM modulation arrangemffnt between each of the pol~phase network and tha assoclated output o~
the Fourier transformer. In the FDM demodulation arrangement ! a decimation filter is included between each polyphase network and the associated input o~ the Fourier transformer to reduoe I the sampl~ng ~requency. In this embodiment the Fourier trans-¦ 10 formers operate at a lower computing speed and, consequently, ~¦ also the second digital filter bank, (C). Short descr ~ ~ res The Figures 1 and 2 show an FDM modulation arrange-ment and an FDM demodulation arrangement according to the invention rospeotively;
- Fig. 3 shows the spectrum of the multiplex signal ~or a primary group of 12 telephone signals.
In Fig. 4 diagram 4a shows the attenuation i characteristic of a lowpass ~ilter and the diagrams 4b ~ 4f inclusive show various attenuation characteristics of band-pass filters which together constitute the transmission f characteristic o~ a digital ~ilter bank, the diagram 4g shows the spectrum of the multiplexed auxiliary signals.
In Fig~ 5 the diagram 5a shows the spectrum o~ the signal at the output of the digital filter bank in the FDM de-modulation arrangement and diagram 5b shows the characteristic o~ the filter for selacting the signalling signals. Diagram 5c shows the characteristic of the ~ilter ~or selecting a : .,' . ~.
~7 :
. ~ ... ..
` . ` , `
P~. 75-550.
~ 07S837 pilot signal.
Fig. 6 shows an embodiment of a digital phase shifter, Figs. 7 and 8 respectively shcw another embodlment of the FDM modulation and dem~ulation arrangement acoording ~o the invention.
Figs. 7 and 8 show modifications of the circuits shown in Figs. 1 and 2.
Fig. 9 shows waveforms useful in explaining the oper~
ation of the control devioe and Fig. ga shows a pulse of signal-ling signal.
Y Fig. 10 shcws an ~miodim~nt of the control and store devices of Fig. 1.
;; (D) Description of the e~bodiments.
Fig. l~shows an FDM modulation arrang~nent according ; - 15 to the invention. This arrangement is arranged for transmitting control and signalling auxiliary signals which are added to a group of telephone signals to be transmitted in frequency divi~
sion n~ltiplex. Here belcw it is asisumed that the F~M signal is constituted by a primary group of 12 telephone signals.
The spectrum of such a primary group is shcwn in ~` Fig. 3. This spectrum camprises the speech channels Tl to T12inclusive, which correspond to the 12 telephone signals and which each occupy a frequency band having a width of 3100 Hz.
me æ speech channels are each time situated between the multiples of 4 k~Iz in the frequency band from 60 - 108 kHz.
The intervals Il to I12 inclusi~e, having a width of 900 Hz !~ which are situated outside the speech channels are used as transmissi~n channels for the auxiliary signals.
m e signalling signals belong to these auxiliary signals. These signallLng signals are logic signals havlng a ~ B ~ 8 - ~ ~
, , .
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~75837 PHF. 75-550, frequency of 10 Elz which are each associated with a char~el signal for controlling the con~nication in this c~nnel.
Tb be able to intrcduce the sic~alling signals in the inter-.
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i I'~rl~' 75550 7~37 vals between speech channels the bandwidth of each of those signalling signals is limlted to some tens of Hz, ~lereafter the signals thus limited are modulated on a carrier. In, for ~- ¦ example, the so-callecl dc signalling systems carrier fre-¦ 5 quencies are used which are in the frequency band of 6~-108 ~ kHz and which are each a multiple of 4 k~Iz. These carrier ; ¦ frequencies have been indicated in Fig. 3 by means o~ the solid l ~ arrows S1 to S12 inclusive.
5;,1 Added to a group of channel signals are also one ;' 1 10 or more control signals in the form o~ pilot signals having a very stable frequency and a very stable amplitude. This amplitude is used in the FDM demodulation arrangement for the automatic control of the speech channel level. A pilot signal having a ~requency of 84.140 Hz is used in a primary group of 12 channel signals with d.c. signalling. In Fig. 3 this l~ pilot signal is indicated by means of $he solid arrow X. From ,:
~: ~ig. 3 it appears that a signalling signal and a pilot signal is present in the interval I6 which i9 situated around the frequency of 84 kHz.
~ 20 In Fig. 1 the sources ~or logic signallingsignals ,.~ .
are represented by contacts C1 to Cl2 inclusive which are ~ed by a d.c. voltage V and which are operated with a frequency of 10 Hz by means not further shown in the Figure. Reference numeral 1 indlcates a pilot signal generator. The circuit 2 which performs filter and carrier modulation operations on the control and signalling signals supplies the auxiliary i: signals in an FDM format which~ in an ampli~ier-adder 3 is ~:
superimposed on the multiplex signal ~ormed by the speech signals ST, which multiplex signal is assumed to have been ~:~ . ~ .
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Pl~` 7555 :~07S~3~
.
formed by mealls not shown in the Figure. The complete multiplex ~, signal of the speoch channels thus ~ormod and tho auxiliary `1 signals are transmitted thl~ough the lead 4.
¦ The FDM demodulation arrangement of Fig. 2 is provided with an amplifier 5 to which the FDM signal which is transmitted through the lead 4is applied. This amplifier 5 has a variabl0 gain ~actor and is controlled by the received pilot signal which is appliad to the control terminal 6 of this amplifier. The FDM signal which is produced at the output of the amplifier 5 is applied to the terminal 7 for spatially separating the speech channels in a manner which is not further indicated in Fig. 2. This FDM signal is also applied to a cir-1 , cuit 8 in ~rhich tho demodulation and filtering processes are performed for spatially separatin~ the received auxiliary .
signals. The signalling signals are derived from the leads ~1 to ~12 respectively and are used for actuating the con-tacts C~l to C~12 inclusive which correspond to the contacts Cl to C12 of Fig. 1. The transmitted pilot signal is deri~ed from the lead ~p for suppl~ to the control terminal 7 of the ~ 20 amplifier 6.
`¦ At present, in frequency multiplex transmission ::! systems the filtering and modulation processes and the de-modulation and filtering processes for the auxiliary signals I - are still per~ormed by means of analog signal processing techniques~ As has already been indicated these arrangements are consequently bulky and expensive. By means of the arrangement according to the invention it is possibly to ¦ mitigate these drawbacks to a considerable extent.
. j .
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p~[~i` 7~5.~
1 3_ 5--1 9 7 6 1~:97~837 The FD~I modulation arrangement according to the invention (Flg. 1) comprises to that ond means for producing digital signals which correspond to the base band auxiliary signals. ' -As regards the sign~llingsignals these means are constituted by a control device 9 and a storage device 10. The signalling si~lals s1 to s12 inclusive are applied to the con~
~;¦ trol device 9. As remarked above these signalling signals ~ are ~ormed by series of pulses which occur with a frequency ¦ 10 o~ 10 Hz. To introduce these signals in the intervals between ~ the speech channels these signals must be ~iltered in order ,1 to limit their bandwidth to some tens o~ Hz. This might be ~, e~ected by digital low-pass filters having a suitably chosen impulse response. In Fig. 1 this ~iltering process-is per- -~ormed in a simpler manner. The samples of the stap response , , o~ the required low-pass ~ilter are stored in digltal ~orm in - the storage device 10~ In response to each o~ the signalllngpulses, samples o~ the stap response are read from the sto-rage device 10 by the control device 9 in a manner which will be further explained with re~erence to Fig. 9. In particular, in response to a signalling pulse at the input S1 o~ the con-, trol device a series o~ samples is produced at the output b1 ': o~ the storage device 10, in response to a signalling pulse at the input~;S~ a series o~ samples is produced atthe output b6 etc. Thle ~requency with which the samples o~ the stap response occur at, for example, the ou-,tput b1 of the storage ! device 10 is determined by the time base 11.
I The pilot signal which must be inserted into .'~ .
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. ~ .
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P}n` 75550 13_~-197~
~ccommodated tho FD~I sig~ l and which has~ ~or exarnple, a frequenc~ o~ 84~1~tO llz iS generatQd by procossing ,a base band pilot signal sp having a frequency of 1l~0 ~Iz. This slgnal is produced in digital form b3r the generator 1~ This generator ` i 5 is, for oxample, consti-tuted by a ROM~ in which the samples of a sinusoidal signal having a frequency o~ 140 Hz are j stored in digltal form. These samples are applied to the output .
. ~ .
of the memory with a frequency which is determined by the time ~`. `:.1 '~ ' base 1~. ' '~ 10 To insert this pilot signal into the FDM signal the- 3 arrangement of Fig. 1 further comprises an adder circuit 12 an input of which is connected to the output a6 of the storag~
device 10 and whos~a other input is conneoted to the output of ~'~ ' the storage de'vice 1. The signallingsignal s6 and the pilot '~ 15 signal sp are auxiliary signals which must be transmitted in the same channel. In particular these signals are transmitted ` ~ in *he lnterval I6 of Fig. 3. ~onsoquently the digital signal S6 ~ sp occurs at the output of the adder 12, ~ ' The FDM modulation arrangemant of Fig. 1 further i;l 20 comprises a digital filter bank 13 for converting the auxiliarysignals into the FDM format. In particular the 12 intervals I1...~I12 of Fig. 3 contain the digital signals s1, r~
S6 ~ sp, ....s12 respectively. The filter bank 13 has a ~j transfer characteristic which is formed by bandpass character-istics whose intermediate ~requencies 'coincide wi'th the inter-, ~;' mediate frequencies o~ the auxiliary channels which accommo-t ~ date the au~iliary signals. These characteristics are derived rom the characteristic of a low~pass filter which ensures the transmission of the auxiliary signals in the base band.
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~ ~ ~ S ~ ~ ~ Pl-IF. 75-550.
Diagram 4a of Fig. 4 shcws the attenuation charac-teristic of this lcw-pass filter. It appears from this characteristic that around the frequency 0 a very slight attenuation is exercised on a signalling signal. This signal-ling signal, having a bandwidth of, for example, 50 Hz is represented in this diagram 4a by means of ha~ched triangle.
In this diagram 4a also the tw~) base band pilot signals having respectively the frequencies + 140 Hz are indicated by tw~
arrows. As this diagram 4a shows the attenuation curve of the filter is infinitely high for all multiples of 4 kHz.
m e attenuation curve of the various bandpass char-acteristics of the filter bank 13 is shcwn in the diagrams 4b to 4f inclusive. me characteristics of the diagra~s 4b, 4c,....4d, ... 4e, 4f are obtained from the characteristic 4a by shifts over 12 x 4 kHz, 11 x 4 kHz, ... 7 x 4 kHz,
2 x 4 kHz, 1 x 3 kHz.
In the embodiment of Fig. 1 the sampling frequency of the signals applied to the'filter bank 13 is equal to ~'~
4 kHz and this filter bank is reaIized in the manner as extenr ~' 20 sively described'in Applicant's U.S. Patent Specification No. 3,89I,803 (PHN. 6554) and Canadian Patent 1,025,135 -January 24, 1978 tPHN 7416~. In particular the 12 digital signals sl~ --- s6 ~ sp,.... sl2 are applied to inputs bl to bl2 inclusive of an inverse discrete Fourier transformer 14.
This Fourier'transformer 14 is provided with 28 real outputs do to d27 inclusive and the digital signals at these outputs are applied to the 28 branches'of a polyphase netw~rk. Each branch ca~prises in cascade a digital phase shifter ~ 0~
.
.
" ' ~"
,~ I'lr~i` 7555 , 13 ~-1976 5~337 i l ~ 27 and a d~lay circuit ~o9 ~1~ O~R27~ rhese delay clr-,, 0~ R1 ~ R27 introduce a clelay o~ 0, ~ T 1 T
I ' = ~ respectively. The digital phase shifters y o~
I ~ 27 have a phase-frequency characteristic having a ~saw-I 5 ~*oothed" shape, whose slopes are equal in absolute value but f are of opposite direction to the phase-*requency character ! istics o~ the delay circuits Ro~ 27~ which are con-nected in cascade to these phase shi~ters. All digital phase shi~ters have the same amplitude-frequency characteristic which is equal to the amplitudo-~requency characteristic o~
the baseband filter shown in diagram 4a. The outputs o~ the ~ 28 branches of the polyphase network are connected to the :~:! output lead 15 o~ the digital ~ilter bank 13. As explained in detail in the above-mentioned patent speoi~ication and said ~¦ patent application a multiplex signal is obtained in digital ¦ ~orm at the output 15 which signal may be considered as having been produced by sampling each of the 12 digital *nput signals ¦ S1~ S2~ S6 -~ S10~ Sll~ s12~ with a frequency o~ 4 kHz, thereafter by digital ~iltering o~ this digital signal by ~¦ 20 means o~ a digital ~ilter having a cut-o~ ~requency o~
~1 approximately 50 IIz and thereafter selecting those spectrum -~ 'repetitions which have the desired location, This se~ction '¦ may be considered as the ~iitering action with the character ¦ istics 4b, 4c, .... 4e~ 4~ shown in Fig. 4. In this manner a j 25 multiplex signal is obtained which has a sampling frequency ' o~ 4 x 28 ~ 112 kHz, The spectrum o~ $his multiplex signal ~, located in the band ~rom ~requency 0 to half the sampling ~requency,56 k~Iz, is shown in diagram 4g. It comprises the ' '~ ''' ' ., " -~ - - - .
, '` :
1~75837 spectra of the 12 signa]llng signals 91 to S1z inclusive around tho 12 frequoncies which are ~ach a multiple o~ 4 k~Iz and a , , pilot signal at the ~requency 28 kllz - 140 ~
I The output signal of the polyphase network 13 can j 5 now be converted in a slmpl0 manner into an FDM slgnal o~ the l usual construction. To this end this digital FDM signal is ¦ converted into an analog signal by means of the digital-to-analog converter 16. A9 lcnown the spectrum o~ this signal consists o~ the original spectrum and repetitions of this spectrum at multiples of the sampling ~requency of 112 kHz.
By means o~ the bandpass filter 17 the band ~rom 64-108 kHz is selected. Now thls band comprises the spectra of the 12 signalling signals in a sequence which is the reverse of that of the diagram 3g and tha pilot signal having the desired ¦- 15 ~requency o~ 84.1L~0 k~ as indicated in Fig. 3~
The FDM demodulation arrangement shown in Fig~ 2 comprises the circuit 8 f'or spatia]ly separating and recover-ing the auxiliary signals which are applied to the demodulation ¦ arrangement in an FDM format. This circuit 8 comprises a samp~
ling device 18 which, under the control o~ a local clock 19 ~I which produces sampling pulses having a frequency o~ 112 k~
I samples the multiplex signal. It should be noted that the mul-¦ tiplex signal applied to the sampling device 18 comprises both the speech channels and the au~iliary channels. The samoled' signal is oonverted into a digital signal by means of the ana~og-to-digital converter 20. Via the input lead 21 this digital signal is applied to the digital Pilter bank 22 for separating the 12 a~iliary channels. This filter bank i~
. .
: :' ' .
, .~. . ' .
~07s83~ p~. 75,550.
again oonstructed in -~le nanner as ex*ensively described in the above-mentioned U.S. and Canadian Patent Specifications and comprises ele~,ents wh~se operation is the inverse of the operation of the Eilter ba~ 13 of the FDM modulation arrangement. This filter bank 22 comprises a series-to-parallel converter 23 with 28 outputs which produces at each output digital signals whose oode words occur wQth 4 kHz. These outputs are connected to the 28 branches of a polyphase netwDrk. Each branch comprises in cascade a delay circuit Rlo, R'l ..... R'27 having delay times of 0, ~ T, 27 T respectively where T = -3-~ and a digital phase filter ~ o Y'l .... Y 27 each having a phase~ frequency char~
acteristic having a "saw-toothed" shape. Also here the slope of a phase-frequency characteristic is equal in absolute value but is of opposite sign as regards the phase-frequency cha~
` acteristic of the associated delay circuits R~o~ R'l or R'27.
'' All the æ digital phase shifters have the same amplitude-~requency characteristic which is again equal to the amplitude-frequency characteristic of the baseband filter shown in dia-gram 4a. me'signals at the'output of the'phase shifters y 'O
to Y 27 respectively are fed to the inputs d'o to d'27 respec-tively of a discrete Fourier transformer 24 which camprises 12 ocmplex pairs of outputs which are indicated by b'l to b'l2 respectively.
As extensively explained'in the above-mentioned patent application and patent specification the output signals which are produced at the'outputs b'l to b'l2 respect;vely of the Fourier transformer'24 may be considered as .., .~ ., ' ', , ' .. ,., .,:. ~ ., ~ , ,, ., -.. .
~: .
P I r~! 7 5 5 5 ~5~37 having b0en obtainod by ~iltering the multiplex signal with filters whosc passband characteristics are shown in the diagrams 4b to 4f respectively and b~ therea~ter demodulating these signals to the base band, Now these base band signals i 5 are digital signals which are c~mpled with a frequency oP
i 4 kHz.
! It should be noted tha-t although real auxiliary ! signals are applied to the inputs b1 to b12 inclusive of the Fourierr transformer 14 o~ the FDM modu~tion arrang0ment~ the l 10 Fourier transformer 24 of the FDM demodulation arrangemen-tt ! produces complex signals. This is nec0ssary, because the ~¦ transmitting medium introduces phase shi~ts which are ~ot equal for all signals.
B The spectrum of the signals which ~r~ occur in ¦ 15 digital form at the various outputs o~ the Fourier trans-former 24 is shown in the diagram 5a o~ Fig. 5 ~around the ~ero frequency, For all outputs b71 to b712 inclusive this spectrum comprises the spectrum of a signalling signal which is represented b~ the hatch0d triangle which is si-tuated around the zero ~requency and the spectrum of the speech signals of1he adjacent channels. These speech signals ¦ are not appreciably attenu~ted by the ~ tering acffDn which ¦ is not so severe in the filter bank 22. For this ~iltering action is per~ormed with the characteristic, shown in diag~am 4a o~ the base band ~ilter and mainly serves to separate auxiliar~ channels. The spectrum o~ the telephone signals , is represented by the ~o double hatched portions which I extend to above the ~requency o~ 3000 Hz for the uppermost !
. . .
rlr:F 75550 , ~ .
1~, 5837 ~t ~
j tolepllone channel and to below -tho ~roq~lerlcy o~ -600 1l~ ~or t ~' the bottol~nost telephone channe~O The spectrwn o:~ tho signal "~t at the ~utput b'6 ~urthermore comprises a pllot signal having , ~ a ~requency o:~ 140 Hz as shown in Fig. 5a.
! 5 To separato the sigialling signals ~rom the
In the embodiment of Fig. 1 the sampling frequency of the signals applied to the'filter bank 13 is equal to ~'~
4 kHz and this filter bank is reaIized in the manner as extenr ~' 20 sively described'in Applicant's U.S. Patent Specification No. 3,89I,803 (PHN. 6554) and Canadian Patent 1,025,135 -January 24, 1978 tPHN 7416~. In particular the 12 digital signals sl~ --- s6 ~ sp,.... sl2 are applied to inputs bl to bl2 inclusive of an inverse discrete Fourier transformer 14.
This Fourier'transformer 14 is provided with 28 real outputs do to d27 inclusive and the digital signals at these outputs are applied to the 28 branches'of a polyphase netw~rk. Each branch ca~prises in cascade a digital phase shifter ~ 0~
.
.
" ' ~"
,~ I'lr~i` 7555 , 13 ~-1976 5~337 i l ~ 27 and a d~lay circuit ~o9 ~1~ O~R27~ rhese delay clr-,, 0~ R1 ~ R27 introduce a clelay o~ 0, ~ T 1 T
I ' = ~ respectively. The digital phase shifters y o~
I ~ 27 have a phase-frequency characteristic having a ~saw-I 5 ~*oothed" shape, whose slopes are equal in absolute value but f are of opposite direction to the phase-*requency character ! istics o~ the delay circuits Ro~ 27~ which are con-nected in cascade to these phase shi~ters. All digital phase shi~ters have the same amplitude-frequency characteristic which is equal to the amplitudo-~requency characteristic o~
the baseband filter shown in diagram 4a. The outputs o~ the ~ 28 branches of the polyphase network are connected to the :~:! output lead 15 o~ the digital ~ilter bank 13. As explained in detail in the above-mentioned patent speoi~ication and said ~¦ patent application a multiplex signal is obtained in digital ¦ ~orm at the output 15 which signal may be considered as having been produced by sampling each of the 12 digital *nput signals ¦ S1~ S2~ S6 -~ S10~ Sll~ s12~ with a frequency o~ 4 kHz, thereafter by digital ~iltering o~ this digital signal by ~¦ 20 means o~ a digital ~ilter having a cut-o~ ~requency o~
~1 approximately 50 IIz and thereafter selecting those spectrum -~ 'repetitions which have the desired location, This se~ction '¦ may be considered as the ~iitering action with the character ¦ istics 4b, 4c, .... 4e~ 4~ shown in Fig. 4. In this manner a j 25 multiplex signal is obtained which has a sampling frequency ' o~ 4 x 28 ~ 112 kHz, The spectrum o~ $his multiplex signal ~, located in the band ~rom ~requency 0 to half the sampling ~requency,56 k~Iz, is shown in diagram 4g. It comprises the ' '~ ''' ' ., " -~ - - - .
, '` :
1~75837 spectra of the 12 signa]llng signals 91 to S1z inclusive around tho 12 frequoncies which are ~ach a multiple o~ 4 k~Iz and a , , pilot signal at the ~requency 28 kllz - 140 ~
I The output signal of the polyphase network 13 can j 5 now be converted in a slmpl0 manner into an FDM slgnal o~ the l usual construction. To this end this digital FDM signal is ¦ converted into an analog signal by means of the digital-to-analog converter 16. A9 lcnown the spectrum o~ this signal consists o~ the original spectrum and repetitions of this spectrum at multiples of the sampling ~requency of 112 kHz.
By means o~ the bandpass filter 17 the band ~rom 64-108 kHz is selected. Now thls band comprises the spectra of the 12 signalling signals in a sequence which is the reverse of that of the diagram 3g and tha pilot signal having the desired ¦- 15 ~requency o~ 84.1L~0 k~ as indicated in Fig. 3~
The FDM demodulation arrangement shown in Fig~ 2 comprises the circuit 8 f'or spatia]ly separating and recover-ing the auxiliary signals which are applied to the demodulation ¦ arrangement in an FDM format. This circuit 8 comprises a samp~
ling device 18 which, under the control o~ a local clock 19 ~I which produces sampling pulses having a frequency o~ 112 k~
I samples the multiplex signal. It should be noted that the mul-¦ tiplex signal applied to the sampling device 18 comprises both the speech channels and the au~iliary channels. The samoled' signal is oonverted into a digital signal by means of the ana~og-to-digital converter 20. Via the input lead 21 this digital signal is applied to the digital Pilter bank 22 for separating the 12 a~iliary channels. This filter bank i~
. .
: :' ' .
, .~. . ' .
~07s83~ p~. 75,550.
again oonstructed in -~le nanner as ex*ensively described in the above-mentioned U.S. and Canadian Patent Specifications and comprises ele~,ents wh~se operation is the inverse of the operation of the Eilter ba~ 13 of the FDM modulation arrangement. This filter bank 22 comprises a series-to-parallel converter 23 with 28 outputs which produces at each output digital signals whose oode words occur wQth 4 kHz. These outputs are connected to the 28 branches of a polyphase netwDrk. Each branch comprises in cascade a delay circuit Rlo, R'l ..... R'27 having delay times of 0, ~ T, 27 T respectively where T = -3-~ and a digital phase filter ~ o Y'l .... Y 27 each having a phase~ frequency char~
acteristic having a "saw-toothed" shape. Also here the slope of a phase-frequency characteristic is equal in absolute value but is of opposite sign as regards the phase-frequency cha~
` acteristic of the associated delay circuits R~o~ R'l or R'27.
'' All the æ digital phase shifters have the same amplitude-~requency characteristic which is again equal to the amplitude-frequency characteristic of the baseband filter shown in dia-gram 4a. me'signals at the'output of the'phase shifters y 'O
to Y 27 respectively are fed to the inputs d'o to d'27 respec-tively of a discrete Fourier transformer 24 which camprises 12 ocmplex pairs of outputs which are indicated by b'l to b'l2 respectively.
As extensively explained'in the above-mentioned patent application and patent specification the output signals which are produced at the'outputs b'l to b'l2 respect;vely of the Fourier transformer'24 may be considered as .., .~ ., ' ', , ' .. ,., .,:. ~ ., ~ , ,, ., -.. .
~: .
P I r~! 7 5 5 5 ~5~37 having b0en obtainod by ~iltering the multiplex signal with filters whosc passband characteristics are shown in the diagrams 4b to 4f respectively and b~ therea~ter demodulating these signals to the base band, Now these base band signals i 5 are digital signals which are c~mpled with a frequency oP
i 4 kHz.
! It should be noted tha-t although real auxiliary ! signals are applied to the inputs b1 to b12 inclusive of the Fourierr transformer 14 o~ the FDM modu~tion arrang0ment~ the l 10 Fourier transformer 24 of the FDM demodulation arrangemen-tt ! produces complex signals. This is nec0ssary, because the ~¦ transmitting medium introduces phase shi~ts which are ~ot equal for all signals.
B The spectrum of the signals which ~r~ occur in ¦ 15 digital form at the various outputs o~ the Fourier trans-former 24 is shown in the diagram 5a o~ Fig. 5 ~around the ~ero frequency, For all outputs b71 to b712 inclusive this spectrum comprises the spectrum of a signalling signal which is represented b~ the hatch0d triangle which is si-tuated around the zero ~requency and the spectrum of the speech signals of1he adjacent channels. These speech signals ¦ are not appreciably attenu~ted by the ~ tering acffDn which ¦ is not so severe in the filter bank 22. For this ~iltering action is per~ormed with the characteristic, shown in diag~am 4a o~ the base band ~ilter and mainly serves to separate auxiliar~ channels. The spectrum o~ the telephone signals , is represented by the ~o double hatched portions which I extend to above the ~requency o~ 3000 Hz for the uppermost !
. . .
rlr:F 75550 , ~ .
1~, 5837 ~t ~
j tolepllone channel and to below -tho ~roq~lerlcy o~ -600 1l~ ~or t ~' the bottol~nost telephone channe~O The spectrwn o:~ tho signal "~t at the ~utput b'6 ~urthermore comprises a pllot signal having , ~ a ~requency o:~ 140 Hz as shown in Fig. 5a.
! 5 To separato the sigialling signals ~rom the
3 ad~acent speech signals di.gital low-pass ~ilt0rs F1 to F12 t, ' ', respectively are connected to all pairct of OtltpUtS b~1 to bl12 t ~ respectively o~ the Fourier transformer 24. These ~ilters act 3 on complex signals and are composed o~ two filter cells which , in the ~igure are not depictod as two separate cells but which ~; process the real part and the imaginary part o~ the complex t signals respectively. The frequency attenuation characteris ¦ tic o~ each cell varies as shown in ~iagram 5b~ Each cell may be realized as a second order filter.
, ~ 15 Tocobtain the pilot signal with the ~requency o~
~ 140 Hz a bandpass filter Fp is fur-thermore connected to the `, ~ pair of outputs b'6 of the Four.ier transformer 24. This ~
t'~ ter Fp is also constituted by two ~ilter cells, not shown in 3 ~ detail, which again process the real part ana the imaginary part of the complex signal respectively at the pair o~ outputs ¦ b~6. The ~requency attenuation characteristic o~ this filter Fp varies as shown in diagram 5c. The passband o~ this ~ilter r l I centres around 140 Hz and has a bandwidth in the order o~
,f~j ' 20 ~z, ~3 25 At the outputs of the signalling filters Fl to F12 inclusive complox signals are produced, in digital form, ;l which correspond to the received signalling signals. For ~, actuating the contactct C~1 to C~12 inclusive, however~ only . ~31 `''1 .
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.~ ~'`,``' , ' ' ': ' ' ' :
' ~` .
PIU~` 75~
the ~mplLtudes of thosa slgnals are required. To this end tll~ pairs of outpu-ts of tho ~ilters F1 to F12 are connected to detectors Dl to Dl2 inclusive which each produce as an output ~lgnal the modules of the complex output signal of 3 5 the preceding filter~ Such detectors have alroady been des-¦ cribed in an article by Blaser and Braun "Schnelle digitale Amplitudenbildung von Quadraturpaaren" pages 20 to 26 in-clusive and which was published in the periodical A G E N -- Zurich, No~ 17, Decembor 1974. Consequently logic signals ' 10 a~e produced at the output~ ~1 to ~12 inclusive of the de-3 tectors Dl to D12 for controlling the signalling contacts to C~12 inclusive~
~ As al50 ~or controlling the level o~ the input - FDM signal only the amplitude o~ the ~ilot signal is used ¦ 15 a detector Dp is connected to the output o~ the pilot ~
ter Fp. This de-tector Dp produces a digital signal which is i applied to a digital-to-analog converter 25. The latter ;i' applies the control signal to the lead ~p for controlling ~ the gain of the ampli~ier 5.
¦ 20 The digital system according to the i~vention for transmitting the auxiliary signals has considerable advantages ~! - with respect to the analog systems used so ~ar. So9 for example in the FDM modulation arrangement the analog low-¦ pass ~ilters for limiting tho bandwidth of the signalling ~¦ 25 ~ signals are completely eliminated~ This ~iltering function I is now realized by means of the storagQ device 10 in which I the coefficients ~or all signalling signals are stored. The ., ~ ~ase band pilot 4ignal (ll~0 Hz) is also produced by a storage . ' .
-19~
'' : ' . :
P~[l~' 7555 , 13-5 1976 ~C~7S~337 .
, , device '1. Conver-ting the plLot si~lrll into its definLte ~re-..
quency (84,1l~0 ~Iz) in the multiplex signal ls peformod s:L-~ multaneously with converting the signalling slgnals 'by means ! 0~ the digltal filtor bank 13. In the system clescribod it,is extremely simple to use a pilo-t signal having another fre-quency than 84.140 kTIz. If a pilot signal having a ~r~quoncy i of 84.080 lcHz is deslred then it is su~ficient to replace the COe~iCiQntS of the storago device 1, To change ~rom the frequency 84,080 kHz to -the -~requency o~ 104.840 kHz it ' ' 10 sufflces to insert the adder 12 at a~other input (bl1) of the ,~ ~ Fourier trans~ormer 1~.
j In the FDM demodulatlon arrangement the use o~
, ' bulky analog filters for selectlng the signalling si~als , ¦ have been avoided whilst furthermore no expensive quartz Y~¦ 15 filters, which are difficult to realize~ are needed anymore for selecting the pilot signals. The digital filter processing ¦ which is performed to separate the au~ciliary signals spa-j tially and to con~ert them to baseband position can be realized ;~1 in a si~ple manner and is perfo~med in two steps~ In a f~rst' ~ 20 step which is performed in the digital filter bank 24 the ~1 auxiliary channels are separated and the signals in these " I channels are brought in baseband position, In a second step ,:' . WhlCh i8 performed in the filters Fl to F12 inclusive and inthe ~llter Fp the signalling signa~s are separated from the ,~ 2~ pilot signals and the speech channels. ~s these digital ; filters F1 to F12 inclusive and Fp are arranged ~or processing ; ~ , .
~ low frequency signals -they are simple to realize. The latter . .
applies particularly to the pilot filter Fp which is centr~d-l ', around 1l~0 Hz and which has a bandwidth of 20 Ez.
~20-' .~ ' '`~, ' . ' ~ ' '.' Pl[L` 75550 . 13-5~197G
~75837 ~s alroady relrlarlced bo~ore~ no stringent re-qulro~llont-s are ITlaCIe on the digita]. f.Llter ban1cs 13 anc1 22~
T~e dl~ltal phase shlfters ~ 0 to ~ 27 inclugive and y ~0 to ~ '27 inclusive can th0refore be realized in a particular-ly simple manner. ~lg. 6 shows an ombodimen-t o~ such a phase shifter. This phase shi~ter is o~ the conven-tional non-recur-sive type in which -two coe~icients are used. Two delay ~G~ SCa~
j B cireuits 61 and 62 are connected~ in o~i~se, to the lnput 60 of this phaso shifter. Multlpllors 63 and 64 with the coefficients k1 and k2 are connected to the outputs o~ 61 ~ and 62, which coe~ficients correspond to the attenuation ¦ eharacteristic o~ the phase shifter. The outputs o~ the ¦ multipliers 63, 64 are con~ected to the inputs o~ the adder ~j circuit 65 whose output constitutes the output o~ the phase -~ 15 shifter.
In the FDM modulation arrangements according to the invention described so ~ar9 digi-tal signals are applied ¦ to the digital ~ilter bank 13 ~ith a sampling ~requency o~
! 4 kHz, being the distance between two successive channel ¦ 20 signals; in the same manner the digital ~ilter bank 22 o:~
.
. the FDM demddulation arrangement produces digital signals having a sampling ~requency o~ also 4 kHz. Consequently, in these ~ilter banlcs calculations are per~ormed by all eomputing devices, such as ~ourier trans~ormers 1l~ and 24 ancl P Y ~ 27 inclusive, ~y 0 to y 27 inclusive at a rate of 4 kHz. ~lso in the digital filters ' F1 to F12 inclusive a~d Fp calculations must consequently be : performed at a rate o~ 4 kHz. ~s known it is always ad vantageous when realizing digital arrangements, especially ~or their integration, to decrease the numbor o~ calculations I ~ to be per~ormecl per second as much as possible~
~21 ,, . ~ .
- . .
iLa~75~337 ~. 75-550.
' Figs. 7 and 8 respectively show a variant of the FDM modulation and FDM demDdulation arrangement of Fig. 1 and 2 with which a oonsidercible decrease in the number of calculations per second is obtained. In these Figures 7 and 8 elements corresponding with Fig. 1 and Fig. 2 respectively are indicated with the same reference numerals. For a proper understanding of the arrangements shown in Fig. 7 and Fig. 8 it should be noted that the sampling frequency of the baseband auxiliary signals may be much lower than 4 kHz. For, the highest frequency which occurs in these auxiliary signals is not much higher than 50 Hz for the signalling signals whilst the ' pilot signal has a frequency of 140 Hz or 80 Hz. In the arrange-mer~ shown in the Figs. 7 and 8 the sanpling frequency of the M auxiliary signals is 500 Hz.
' 15 In the'FDM mDdNlation arrangement shcwn in Fig. 7 digit~l signals are applied to the'inputs bl to bl~ inclusive of the inverse Fourier transformer''l4 with a sampling fre-quency of O.S kHz. mis computing device'performs inverse Eburier calculations at a rate of 0.5 kHz. Consequently at , 20 the outputs do to d27 inclusive of the Fourier transformer digital signals are produced with a sampling frequency of 0.5 kHz. me output signals of the Fourier transformer 14 are - thereafter each applied to an interpolating digital filter toincrease the sampling frequency. mis interpolating filter ,' 25 is constructed in the manner as described in detail in Applicant's Canadian Patent 1,011,823 - June 7, 1977 (PE~ 6883) and in parti-cular oomprises three interpolation elements connected in cascade, `:~
B
`'~','. :.' ` :
~ P~. 75-550.
1~75~33~
, Ao to A27 inclusive, Bo to B27 inclusive, C0 to C27 inclusive.
Each interpolation element is a digital filter which is called half-bandpass filter in Canadian Patent 1,011,823 supra.
As indicated in said patent application a half-bandpass filter , S must be understood to mean a low-pass filter having a cut off '' frequency which is equal to ht~lf the input sampling frequency and which is arranged for supplying a digital signal having an output sampling frequency which is equal to twice the input sampling frequency. Fig. 7 shows the various sampling fre-quencies which occur at different points m the circuit. Mbre in particular the sampling frequency at the outputs of the elemEnts Ao to A27 inclusive is 1 kHz; this frequency is 2 kHz t at the outputs of the elements Bo to B27 inclusive and 4 kHz at the outputs of the elements C0 to C27 inclusive. m e digital ;~ signals at the'outputs of the interpolation elements C0 to C
inclusive are applied bo the same branches of the polyphase netw~rk as in Fig. 1, these branches'being oonstitut~d by the `' digital phase shifters ~ O to ~27 inclusive with which the delay circuits Ro to R27 inclusive are connected in series.
'These phase shifters and these delay circuits have exactly the ~me characteristics as that of Fig. 1 and, as in Fig. 1 the speed of computing in the phase ~hifters is 4 kHz. The ~- same FDM signal is obtained'at the output 15 as with the ~ "
arrangenæ~rt of Fig. 1.
, 25 In the FDM demDdulation arrangement of Fig. 8 the '-~ digital filter bank 22 oomprises, as in Fig. 2 at the ' `
' - 23 -`'`..... ~` ' ' ~ ~ '.
1~7583~7 outputs of the series-parallel converter 23 the same poly-phase network branches which are each provided with a series circuit of an R'o to R'27 inclusive and a digital phase shifter ~ '0 to Y'27 inclusive. The input sampling fre-quency of the delay circuits R'o to R'27 inclusive and the output sampling frequency of the phase shifters y '0 to Y'27 inclusive is 4 kHz. The outputs of the phase shift-ers ~ 'o ~ Y'27 are connected to the inputs of sampling frequency reduction filters. The latter filters which are also called "extrapolating" or "decimation" filters are constructed in a manner as described in detail in said Canadian patent 1,011,823 (PHN 6883). More in particular also now each of these filters comprises three elements C'0 to C'27 inclusive, B~o to B'27 inclusive, A~o to A'27 ;~ 15 inclusive, connected in cascade. In said Canad;an patent 1,011,823 each of these elements is indicated as half-band--~ pass dividing filter. The term half-bandpass dividing fil-ter must be understood to mean a low-pass filter having a cut-off frequency which is equal to one fourth of the in-put sampling frequency and which is arranged for producing a digital signal with an output sampling frequency which is half that of the input sampling frequency. As indicated in Fig. 8 the output sampling frequency of the elements C'0 to C'27 inclusive is 2 kHz. The output sampling frequency of the elements B~o to B'27 inclusive is also here 1 kHz and the output sampling frequency of the elements A~o to A'27 inclusive is 0.5 kHz. Now the Fourier transformer 24 is operated at a` rate of 0.5 kHz and at the pairs of outputs -bl',.. b'l2 of this :~ .
PllF. 75-550.
~75837 Fourier transformer 24 ~he sampling frequency is 0.5 kHz. The selection filters Fl - Fl2 ~or the signalling signals and the selection filter Fp ~or the pilot signal are now operated ~ith a rate of 0.5 kHz.
With respect to the arrangements indicated in the Figs. 1 and 2 the arrangements of the Figs. 7 and 8 comprise as additional material the interpolation elements A B C and the extrapolation elements C' B' A'. As indicated in said Canadian patent 1,011,823, these elements may be realized in a particularly simple manner. In particular each element can be constructed from a single m~ltiplier and two stores which constitute two delay circuits. However, as appears from the sampling frequencies indicated in various places in the Figs. 7 and 8 a considerable decrease (by a factor 8) has now, hcwever, been realized in the speed at which cal-culations in the two Fourier transformers 14 and 24 and in the separating filters Fl to F12 and Fp must be performed.
Furthermore these separating filters may be less co~plex. `i ' The separating filters for the'signalling signals, for example, may be realized with a single second order recur- -sive digital filter instead of with a cascade circuit of tw~ second order'recursive digital filters. It is possible to prove that in the'arrangements of the Figs. 7 and 8 with ~ ' respect to the arrangements of the'FigsO 1 and 2 a decrease in the'nu~ber'of calculations-per second ~m~inly multipli-cations~ by a factor of appr~ximately ~ can be reaIized ' whilst the required'number of stores is only increased by ;' approximately a factor of 2.
~ - 25 -. _ ,, , . .
":, ~ - ' :
. , , pll;T?'7~sO
13 5~ 6 ~ ~7S~3~7 - To oxplain the oporation ol' t]-le corltrol device 9 and t]1e store 10 ]?ig. 9a '3]10WS a pulse o~ ~ signalliIlg si~nal.
T]1ese pulses occur at a ~requenGy o~ 10 II~. The purpose of the control davice 9 and the storo 10 is to convert the pulse shown irl Fig. 9a into a ser:ias o~ binary coded samples which , ', , occur at a sampll~ ~requency of` l~ kllz or 0~5 k~Iz and which characterizo the filtered v0rsion of` thi3 puls~. More in ') particular9 in the described embodiments the pulses are iltered by means o~ a ~ilter which has a cut-o~`f ~requency of 50 Hz. The filtered version of` this pulse is shown in , ~ ~ig. 9b by means Or the dashed curve a Furthermor~ Fig. 9b 3 shows a number o~ sampl~s Or this riltered pulse, ~our o~
these sampl0s having boen indicated b~ b.
Flg. 10 shows an embodiment Or the control device 9 and the store 10. In this embodiment the control devicc 9 comprises twelve input leads through which the signalling , ; ~
"'1 signals s1 - s12 are appli0d to -the device 9. Each input lead comprises a two way counter 1001~ 1012 which are each provided with an input CD and an input H. Th-e r0levant signalling signal is applied to the input CD and clock pulses are applied to the input H said clock pulses being produced ~ by the clock pulse generator 11. Ir a signalling pulse is ¦ present at the input CD o~ a two-wa~ counter the clock pulsesapplied to the input II are count0d until the counter has 1 25 reached its maximum position whereafter an~ additionally '-~ applied clock pulse does not change the counter position~
Ir at a given moment th~ ~ig~nalling pulse a-t the input CD
the counter disappears then, owing to the clock pulses .' .
~ ~2~-'~ . ' .
~ ~ .
. . , . ' . .
I?J17? '~55,0 l3-5-19~jG
~75837 : th~ occurl:ing, tho counto:r COUlltS clo-rn ti.].L it hc~s roachcd i-ts minillluln countQr po~i.tion wllorea:~ter an~ ~urtller clock pulse caus2e no challge in the counte:r position anymoro. 'Nle clock pulse gonerc-ltor 11 produces pulses wit}L the clesired ~; 5 sampling :frequency; so wi1;h a freqllellcy of ~ldk. or 0.5 k~lz.
~ A decoding network is as.soclated with each o~ the - ~ countors 1001 - 1012~ In Fig. 10 these ne-tworks are indicated by means o:~ the hatchod areas 1013 - 1024, the outputs 1025 -1036 o~ which are applied tothe store 10. At these ou-tputs a code word in parallel ~orm is produced which is oharacteris-tic for the counter position. The decoding netlYo:rks 1025 1036 are furthermore each provided with an output l037 - 1 o48 at which a pulse is produced i~ the counter has reached its ~, lowQst counter position and with an output 1049 - 1060 at which a pulse is produced if the counter has reached its maximum counter position. These outputs are connected -to in-~, puts of the store 10 through AND-gates 1061- 1072 and through ,~, 2 AND-gates 1073 - 1084. Also the cloclc pulses o~ the clock pulse generator 11 are applied to these AND-gates 106-l - 1084.
In this embodiment the store 10 is cons-tltu-ted by l twelve storag~ elements 1085 - 1096~ each in the ~orm o~ a i ROM. Fach o~ these storage elements is associated in the , - manner shown in the Figure to one o~ the counters 1001 - 10120 If it is asswned that the counters 1001 - 1012 each need N
clock pulses to arrive from the minimum into the maximum counter position or vice versa then, in each of the storage elements 1085 - 1095 N code words are stored which each characterize a sample o~ the unit stap respcnse of the '~ ~
~ -27_ '1 ' ~ ' . .
.,., ,. , :
. . .:: .
.
1 3_ 5~ ) 7 G
Y~ '75~337 .~ . ~
dos:irecl lo~-pclss fi:ltor havillg~ a cut-o~ froquenc~ o~ 50 l~z, As a r~sul-t; ot' eacl- of tl~o code woTds producod by a docoding , net-~or~ a code word is roacl in paralle:L for1n f-rom the ;~ associated stora~e elomon-t a1ld applied for para:Llel-to-series conversion to a parallel-series convorter 1097 - 10108 which is provided with the outputs al - a12, ¦ The operation of the arrangemont shown in F:Lg, 10 is as follows, I~ a contact, for example C1 is closed at an instant that the counter 1001 has the minimum counter posi tion (for exa1nple the position 0) then the counter counts N clock pulses and reaches its maximum counter posltion, When ~;` counting these N clock pulses the counter passes throug}l N
; different counter positions. As a result of each of` these .
counter positions the storage element 1085 produces a code word whlch corresponds to a sample of tho ~iltered pulsc in the period of time T1 indicated in Fig. 9b. If, the maximum counter position is reached and the contact Cl remains closed, the counter 1001 remains iniits maximum counter position, ~- 3 the storage element 10~5 produces, as a result of the output pulses of the AND~gate 10~3, in the period of time T~ (see Fig, 9b) code words which characterize the maximum amplitude ¦ - of the filtered signalling pulse, If the contact C1 is opened after the period T2 then the counter 1001 counts down until it reaches its minimum counter position, In the -time T3 (see , 1 25 Fig, 9b) required ~or this purpose the storage element 1085 5 ~ supplies the same code words as in the period T1, howe~er, in reversed sequence, After the minimum counter position ~; ~ (the zero position) is reaches the storage element 1085 no r ! :
, ., ~ -28_ ", 1 , .
... ; .
r. ~
~.' '` ' " ' , '111` 75:37(~
~75837 : 10ng~r ~ro~uces code wo:rd~.
It shol:lld bc no-tod tllat a.l.though in tho ~mbodi.mcrlt . o~ Fig. lO tho store 10 i~ constitutod b~ tw~lvo separQ-te storag~c elen~ents a singlo sto:rago element will do. P'o:r all twelve storage eloments contain the samo codo words. This ~, single storage oleMent may then be oporated by moans o~ "t.imo ' sharillg" techniques, , I
, 1. .
.
r .
t ~ t .~
' i, .
'~ .
~ '~
'~ ~
~ .3 r'~
.) :
. :,~ .
. 1 . , .
. ~ ..
.,~ .
. ' i .
~! -2 9-. 1~ .
.. . . ..
, ~ 15 Tocobtain the pilot signal with the ~requency o~
~ 140 Hz a bandpass filter Fp is fur-thermore connected to the `, ~ pair of outputs b'6 of the Four.ier transformer 24. This ~
t'~ ter Fp is also constituted by two ~ilter cells, not shown in 3 ~ detail, which again process the real part ana the imaginary part of the complex signal respectively at the pair o~ outputs ¦ b~6. The ~requency attenuation characteristic o~ this filter Fp varies as shown in diagram 5c. The passband o~ this ~ilter r l I centres around 140 Hz and has a bandwidth in the order o~
,f~j ' 20 ~z, ~3 25 At the outputs of the signalling filters Fl to F12 inclusive complox signals are produced, in digital form, ;l which correspond to the received signalling signals. For ~, actuating the contactct C~1 to C~12 inclusive, however~ only . ~31 `''1 .
.
.~ ~'`,``' , ' ' ': ' ' ' :
' ~` .
PIU~` 75~
the ~mplLtudes of thosa slgnals are required. To this end tll~ pairs of outpu-ts of tho ~ilters F1 to F12 are connected to detectors Dl to Dl2 inclusive which each produce as an output ~lgnal the modules of the complex output signal of 3 5 the preceding filter~ Such detectors have alroady been des-¦ cribed in an article by Blaser and Braun "Schnelle digitale Amplitudenbildung von Quadraturpaaren" pages 20 to 26 in-clusive and which was published in the periodical A G E N -- Zurich, No~ 17, Decembor 1974. Consequently logic signals ' 10 a~e produced at the output~ ~1 to ~12 inclusive of the de-3 tectors Dl to D12 for controlling the signalling contacts to C~12 inclusive~
~ As al50 ~or controlling the level o~ the input - FDM signal only the amplitude o~ the ~ilot signal is used ¦ 15 a detector Dp is connected to the output o~ the pilot ~
ter Fp. This de-tector Dp produces a digital signal which is i applied to a digital-to-analog converter 25. The latter ;i' applies the control signal to the lead ~p for controlling ~ the gain of the ampli~ier 5.
¦ 20 The digital system according to the i~vention for transmitting the auxiliary signals has considerable advantages ~! - with respect to the analog systems used so ~ar. So9 for example in the FDM modulation arrangement the analog low-¦ pass ~ilters for limiting tho bandwidth of the signalling ~¦ 25 ~ signals are completely eliminated~ This ~iltering function I is now realized by means of the storagQ device 10 in which I the coefficients ~or all signalling signals are stored. The ., ~ ~ase band pilot 4ignal (ll~0 Hz) is also produced by a storage . ' .
-19~
'' : ' . :
P~[l~' 7555 , 13-5 1976 ~C~7S~337 .
, , device '1. Conver-ting the plLot si~lrll into its definLte ~re-..
quency (84,1l~0 ~Iz) in the multiplex signal ls peformod s:L-~ multaneously with converting the signalling slgnals 'by means ! 0~ the digltal filtor bank 13. In the system clescribod it,is extremely simple to use a pilo-t signal having another fre-quency than 84.140 kTIz. If a pilot signal having a ~r~quoncy i of 84.080 lcHz is deslred then it is su~ficient to replace the COe~iCiQntS of the storago device 1, To change ~rom the frequency 84,080 kHz to -the -~requency o~ 104.840 kHz it ' ' 10 sufflces to insert the adder 12 at a~other input (bl1) of the ,~ ~ Fourier trans~ormer 1~.
j In the FDM demodulatlon arrangement the use o~
, ' bulky analog filters for selectlng the signalling si~als , ¦ have been avoided whilst furthermore no expensive quartz Y~¦ 15 filters, which are difficult to realize~ are needed anymore for selecting the pilot signals. The digital filter processing ¦ which is performed to separate the au~ciliary signals spa-j tially and to con~ert them to baseband position can be realized ;~1 in a si~ple manner and is perfo~med in two steps~ In a f~rst' ~ 20 step which is performed in the digital filter bank 24 the ~1 auxiliary channels are separated and the signals in these " I channels are brought in baseband position, In a second step ,:' . WhlCh i8 performed in the filters Fl to F12 inclusive and inthe ~llter Fp the signalling signa~s are separated from the ,~ 2~ pilot signals and the speech channels. ~s these digital ; filters F1 to F12 inclusive and Fp are arranged ~or processing ; ~ , .
~ low frequency signals -they are simple to realize. The latter . .
applies particularly to the pilot filter Fp which is centr~d-l ', around 1l~0 Hz and which has a bandwidth of 20 Ez.
~20-' .~ ' '`~, ' . ' ~ ' '.' Pl[L` 75550 . 13-5~197G
~75837 ~s alroady relrlarlced bo~ore~ no stringent re-qulro~llont-s are ITlaCIe on the digita]. f.Llter ban1cs 13 anc1 22~
T~e dl~ltal phase shlfters ~ 0 to ~ 27 inclugive and y ~0 to ~ '27 inclusive can th0refore be realized in a particular-ly simple manner. ~lg. 6 shows an ombodimen-t o~ such a phase shifter. This phase shi~ter is o~ the conven-tional non-recur-sive type in which -two coe~icients are used. Two delay ~G~ SCa~
j B cireuits 61 and 62 are connected~ in o~i~se, to the lnput 60 of this phaso shifter. Multlpllors 63 and 64 with the coefficients k1 and k2 are connected to the outputs o~ 61 ~ and 62, which coe~ficients correspond to the attenuation ¦ eharacteristic o~ the phase shifter. The outputs o~ the ¦ multipliers 63, 64 are con~ected to the inputs o~ the adder ~j circuit 65 whose output constitutes the output o~ the phase -~ 15 shifter.
In the FDM modulation arrangements according to the invention described so ~ar9 digi-tal signals are applied ¦ to the digital ~ilter bank 13 ~ith a sampling ~requency o~
! 4 kHz, being the distance between two successive channel ¦ 20 signals; in the same manner the digital ~ilter bank 22 o:~
.
. the FDM demddulation arrangement produces digital signals having a sampling ~requency o~ also 4 kHz. Consequently, in these ~ilter banlcs calculations are per~ormed by all eomputing devices, such as ~ourier trans~ormers 1l~ and 24 ancl P Y ~ 27 inclusive, ~y 0 to y 27 inclusive at a rate of 4 kHz. ~lso in the digital filters ' F1 to F12 inclusive a~d Fp calculations must consequently be : performed at a rate o~ 4 kHz. ~s known it is always ad vantageous when realizing digital arrangements, especially ~or their integration, to decrease the numbor o~ calculations I ~ to be per~ormecl per second as much as possible~
~21 ,, . ~ .
- . .
iLa~75~337 ~. 75-550.
' Figs. 7 and 8 respectively show a variant of the FDM modulation and FDM demDdulation arrangement of Fig. 1 and 2 with which a oonsidercible decrease in the number of calculations per second is obtained. In these Figures 7 and 8 elements corresponding with Fig. 1 and Fig. 2 respectively are indicated with the same reference numerals. For a proper understanding of the arrangements shown in Fig. 7 and Fig. 8 it should be noted that the sampling frequency of the baseband auxiliary signals may be much lower than 4 kHz. For, the highest frequency which occurs in these auxiliary signals is not much higher than 50 Hz for the signalling signals whilst the ' pilot signal has a frequency of 140 Hz or 80 Hz. In the arrange-mer~ shown in the Figs. 7 and 8 the sanpling frequency of the M auxiliary signals is 500 Hz.
' 15 In the'FDM mDdNlation arrangement shcwn in Fig. 7 digit~l signals are applied to the'inputs bl to bl~ inclusive of the inverse Fourier transformer''l4 with a sampling fre-quency of O.S kHz. mis computing device'performs inverse Eburier calculations at a rate of 0.5 kHz. Consequently at , 20 the outputs do to d27 inclusive of the Fourier transformer digital signals are produced with a sampling frequency of 0.5 kHz. me output signals of the Fourier transformer 14 are - thereafter each applied to an interpolating digital filter toincrease the sampling frequency. mis interpolating filter ,' 25 is constructed in the manner as described in detail in Applicant's Canadian Patent 1,011,823 - June 7, 1977 (PE~ 6883) and in parti-cular oomprises three interpolation elements connected in cascade, `:~
B
`'~','. :.' ` :
~ P~. 75-550.
1~75~33~
, Ao to A27 inclusive, Bo to B27 inclusive, C0 to C27 inclusive.
Each interpolation element is a digital filter which is called half-bandpass filter in Canadian Patent 1,011,823 supra.
As indicated in said patent application a half-bandpass filter , S must be understood to mean a low-pass filter having a cut off '' frequency which is equal to ht~lf the input sampling frequency and which is arranged for supplying a digital signal having an output sampling frequency which is equal to twice the input sampling frequency. Fig. 7 shows the various sampling fre-quencies which occur at different points m the circuit. Mbre in particular the sampling frequency at the outputs of the elemEnts Ao to A27 inclusive is 1 kHz; this frequency is 2 kHz t at the outputs of the elements Bo to B27 inclusive and 4 kHz at the outputs of the elements C0 to C27 inclusive. m e digital ;~ signals at the'outputs of the interpolation elements C0 to C
inclusive are applied bo the same branches of the polyphase netw~rk as in Fig. 1, these branches'being oonstitut~d by the `' digital phase shifters ~ O to ~27 inclusive with which the delay circuits Ro to R27 inclusive are connected in series.
'These phase shifters and these delay circuits have exactly the ~me characteristics as that of Fig. 1 and, as in Fig. 1 the speed of computing in the phase ~hifters is 4 kHz. The ~- same FDM signal is obtained'at the output 15 as with the ~ "
arrangenæ~rt of Fig. 1.
, 25 In the FDM demDdulation arrangement of Fig. 8 the '-~ digital filter bank 22 oomprises, as in Fig. 2 at the ' `
' - 23 -`'`..... ~` ' ' ~ ~ '.
1~7583~7 outputs of the series-parallel converter 23 the same poly-phase network branches which are each provided with a series circuit of an R'o to R'27 inclusive and a digital phase shifter ~ '0 to Y'27 inclusive. The input sampling fre-quency of the delay circuits R'o to R'27 inclusive and the output sampling frequency of the phase shifters y '0 to Y'27 inclusive is 4 kHz. The outputs of the phase shift-ers ~ 'o ~ Y'27 are connected to the inputs of sampling frequency reduction filters. The latter filters which are also called "extrapolating" or "decimation" filters are constructed in a manner as described in detail in said Canadian patent 1,011,823 (PHN 6883). More in particular also now each of these filters comprises three elements C'0 to C'27 inclusive, B~o to B'27 inclusive, A~o to A'27 ;~ 15 inclusive, connected in cascade. In said Canad;an patent 1,011,823 each of these elements is indicated as half-band--~ pass dividing filter. The term half-bandpass dividing fil-ter must be understood to mean a low-pass filter having a cut-off frequency which is equal to one fourth of the in-put sampling frequency and which is arranged for producing a digital signal with an output sampling frequency which is half that of the input sampling frequency. As indicated in Fig. 8 the output sampling frequency of the elements C'0 to C'27 inclusive is 2 kHz. The output sampling frequency of the elements B~o to B'27 inclusive is also here 1 kHz and the output sampling frequency of the elements A~o to A'27 inclusive is 0.5 kHz. Now the Fourier transformer 24 is operated at a` rate of 0.5 kHz and at the pairs of outputs -bl',.. b'l2 of this :~ .
PllF. 75-550.
~75837 Fourier transformer 24 ~he sampling frequency is 0.5 kHz. The selection filters Fl - Fl2 ~or the signalling signals and the selection filter Fp ~or the pilot signal are now operated ~ith a rate of 0.5 kHz.
With respect to the arrangements indicated in the Figs. 1 and 2 the arrangements of the Figs. 7 and 8 comprise as additional material the interpolation elements A B C and the extrapolation elements C' B' A'. As indicated in said Canadian patent 1,011,823, these elements may be realized in a particularly simple manner. In particular each element can be constructed from a single m~ltiplier and two stores which constitute two delay circuits. However, as appears from the sampling frequencies indicated in various places in the Figs. 7 and 8 a considerable decrease (by a factor 8) has now, hcwever, been realized in the speed at which cal-culations in the two Fourier transformers 14 and 24 and in the separating filters Fl to F12 and Fp must be performed.
Furthermore these separating filters may be less co~plex. `i ' The separating filters for the'signalling signals, for example, may be realized with a single second order recur- -sive digital filter instead of with a cascade circuit of tw~ second order'recursive digital filters. It is possible to prove that in the'arrangements of the Figs. 7 and 8 with ~ ' respect to the arrangements of the'FigsO 1 and 2 a decrease in the'nu~ber'of calculations-per second ~m~inly multipli-cations~ by a factor of appr~ximately ~ can be reaIized ' whilst the required'number of stores is only increased by ;' approximately a factor of 2.
~ - 25 -. _ ,, , . .
":, ~ - ' :
. , , pll;T?'7~sO
13 5~ 6 ~ ~7S~3~7 - To oxplain the oporation ol' t]-le corltrol device 9 and t]1e store 10 ]?ig. 9a '3]10WS a pulse o~ ~ signalliIlg si~nal.
T]1ese pulses occur at a ~requenGy o~ 10 II~. The purpose of the control davice 9 and the storo 10 is to convert the pulse shown irl Fig. 9a into a ser:ias o~ binary coded samples which , ', , occur at a sampll~ ~requency of` l~ kllz or 0~5 k~Iz and which characterizo the filtered v0rsion of` thi3 puls~. More in ') particular9 in the described embodiments the pulses are iltered by means o~ a ~ilter which has a cut-o~`f ~requency of 50 Hz. The filtered version of` this pulse is shown in , ~ ~ig. 9b by means Or the dashed curve a Furthermor~ Fig. 9b 3 shows a number o~ sampl~s Or this riltered pulse, ~our o~
these sampl0s having boen indicated b~ b.
Flg. 10 shows an embodiment Or the control device 9 and the store 10. In this embodiment the control devicc 9 comprises twelve input leads through which the signalling , ; ~
"'1 signals s1 - s12 are appli0d to -the device 9. Each input lead comprises a two way counter 1001~ 1012 which are each provided with an input CD and an input H. Th-e r0levant signalling signal is applied to the input CD and clock pulses are applied to the input H said clock pulses being produced ~ by the clock pulse generator 11. Ir a signalling pulse is ¦ present at the input CD o~ a two-wa~ counter the clock pulsesapplied to the input II are count0d until the counter has 1 25 reached its maximum position whereafter an~ additionally '-~ applied clock pulse does not change the counter position~
Ir at a given moment th~ ~ig~nalling pulse a-t the input CD
the counter disappears then, owing to the clock pulses .' .
~ ~2~-'~ . ' .
~ ~ .
. . , . ' . .
I?J17? '~55,0 l3-5-19~jG
~75837 : th~ occurl:ing, tho counto:r COUlltS clo-rn ti.].L it hc~s roachcd i-ts minillluln countQr po~i.tion wllorea:~ter an~ ~urtller clock pulse caus2e no challge in the counte:r position anymoro. 'Nle clock pulse gonerc-ltor 11 produces pulses wit}L the clesired ~; 5 sampling :frequency; so wi1;h a freqllellcy of ~ldk. or 0.5 k~lz.
~ A decoding network is as.soclated with each o~ the - ~ countors 1001 - 1012~ In Fig. 10 these ne-tworks are indicated by means o:~ the hatchod areas 1013 - 1024, the outputs 1025 -1036 o~ which are applied tothe store 10. At these ou-tputs a code word in parallel ~orm is produced which is oharacteris-tic for the counter position. The decoding netlYo:rks 1025 1036 are furthermore each provided with an output l037 - 1 o48 at which a pulse is produced i~ the counter has reached its ~, lowQst counter position and with an output 1049 - 1060 at which a pulse is produced if the counter has reached its maximum counter position. These outputs are connected -to in-~, puts of the store 10 through AND-gates 1061- 1072 and through ,~, 2 AND-gates 1073 - 1084. Also the cloclc pulses o~ the clock pulse generator 11 are applied to these AND-gates 106-l - 1084.
In this embodiment the store 10 is cons-tltu-ted by l twelve storag~ elements 1085 - 1096~ each in the ~orm o~ a i ROM. Fach o~ these storage elements is associated in the , - manner shown in the Figure to one o~ the counters 1001 - 10120 If it is asswned that the counters 1001 - 1012 each need N
clock pulses to arrive from the minimum into the maximum counter position or vice versa then, in each of the storage elements 1085 - 1095 N code words are stored which each characterize a sample o~ the unit stap respcnse of the '~ ~
~ -27_ '1 ' ~ ' . .
.,., ,. , :
. . .:: .
.
1 3_ 5~ ) 7 G
Y~ '75~337 .~ . ~
dos:irecl lo~-pclss fi:ltor havillg~ a cut-o~ froquenc~ o~ 50 l~z, As a r~sul-t; ot' eacl- of tl~o code woTds producod by a docoding , net-~or~ a code word is roacl in paralle:L for1n f-rom the ;~ associated stora~e elomon-t a1ld applied for para:Llel-to-series conversion to a parallel-series convorter 1097 - 10108 which is provided with the outputs al - a12, ¦ The operation of the arrangemont shown in F:Lg, 10 is as follows, I~ a contact, for example C1 is closed at an instant that the counter 1001 has the minimum counter posi tion (for exa1nple the position 0) then the counter counts N clock pulses and reaches its maximum counter posltion, When ~;` counting these N clock pulses the counter passes throug}l N
; different counter positions. As a result of each of` these .
counter positions the storage element 1085 produces a code word whlch corresponds to a sample of tho ~iltered pulsc in the period of time T1 indicated in Fig. 9b. If, the maximum counter position is reached and the contact Cl remains closed, the counter 1001 remains iniits maximum counter position, ~- 3 the storage element 10~5 produces, as a result of the output pulses of the AND~gate 10~3, in the period of time T~ (see Fig, 9b) code words which characterize the maximum amplitude ¦ - of the filtered signalling pulse, If the contact C1 is opened after the period T2 then the counter 1001 counts down until it reaches its minimum counter position, In the -time T3 (see , 1 25 Fig, 9b) required ~or this purpose the storage element 1085 5 ~ supplies the same code words as in the period T1, howe~er, in reversed sequence, After the minimum counter position ~; ~ (the zero position) is reaches the storage element 1085 no r ! :
, ., ~ -28_ ", 1 , .
... ; .
r. ~
~.' '` ' " ' , '111` 75:37(~
~75837 : 10ng~r ~ro~uces code wo:rd~.
It shol:lld bc no-tod tllat a.l.though in tho ~mbodi.mcrlt . o~ Fig. lO tho store 10 i~ constitutod b~ tw~lvo separQ-te storag~c elen~ents a singlo sto:rago element will do. P'o:r all twelve storage eloments contain the samo codo words. This ~, single storage oleMent may then be oporated by moans o~ "t.imo ' sharillg" techniques, , I
, 1. .
.
r .
t ~ t .~
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'~ .
~ '~
'~ ~
~ .3 r'~
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. :,~ .
. 1 . , .
. ~ ..
.,~ .
. ' i .
~! -2 9-. 1~ .
.. . . ..
Claims (13)
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An arrangement for processing spatially separated auxiliary signals for a given number of main information sig-nals for transmitting these auxiliary signals together with the main information signals in an FCM format, said arrange-ment comprising a plurality of input circuit means for receiv-ing said auxiliary signals, which plurality is equal to the number of main information signals, an output circuit, wherein the arrangement further comprises:
means coupled to said input means for digitizing the auxiliary signals, whereby said digital signals have a given bandwidth;
means which are coupled to said digitizing means for limit-ing the bandwidth of each of the auxiliary signals to less than said given bandwidth; and a digital filter bank coupled to said limiting means and to said output means to which said digital auxiliary signals are applied and which has a passband char-acteristic which is characteristic for each of the auxiliary signals, the intermediate frequency of this characteristic coinciding with the intermediate frequency of the auxiliary channel for the relevant auxiliary signal.
means coupled to said input means for digitizing the auxiliary signals, whereby said digital signals have a given bandwidth;
means which are coupled to said digitizing means for limit-ing the bandwidth of each of the auxiliary signals to less than said given bandwidth; and a digital filter bank coupled to said limiting means and to said output means to which said digital auxiliary signals are applied and which has a passband char-acteristic which is characteristic for each of the auxiliary signals, the intermediate frequency of this characteristic coinciding with the intermediate frequency of the auxiliary channel for the relevant auxiliary signal.
2. An arrangement for processing auxiliary signals of a given number of main information signals and for spatially separating and recovering these signalling signals which are applied to the arrangement together with the main information signals in an FDM format, said arrangement comprising an input PHF. 75-550.
circuit means for receiving said signals to said FDM format having a plurality of output circuits which is equal to the number of main information signals, the arrangement further-more comprises:
means coupled to said input means for digitizing the FDM
signal, a first digital filter bank to which said digitized FDM
signal is applied and which has a bandpass characteristic which is characteristic for each of the signalling signals, the intermediate fre-quency of one of the passbands coinciding with the intermediate frequency of the relevant aux-iliary channel; and a second digital filter bank to which the digital output signals of the first digital filter bank are applied and which has a low-pass characteristic for each of the auxiliary signals.
circuit means for receiving said signals to said FDM format having a plurality of output circuits which is equal to the number of main information signals, the arrangement further-more comprises:
means coupled to said input means for digitizing the FDM
signal, a first digital filter bank to which said digitized FDM
signal is applied and which has a bandpass characteristic which is characteristic for each of the signalling signals, the intermediate fre-quency of one of the passbands coinciding with the intermediate frequency of the relevant aux-iliary channel; and a second digital filter bank to which the digital output signals of the first digital filter bank are applied and which has a low-pass characteristic for each of the auxiliary signals.
3. An arrangement as claimed in claim 1, wherein the means for digitizing the auxiliary signals produces output code words with a sampling frequency which is smaller than the fre-quency in erval between the main information signals in the FDM
format.
format.
4. An arrangement as claimed in claim 1, wherein said digital filter bank comprises an inverse discrete Fourier trans-former having a plurality of parallel outputs, and a polyphase network having a plurality of inputs coupled to said outputs respectively and an output coupled to the output circuit of the arrangement.
5. An arrangement as claimed in claim 4, wherein the polyphase network comprises a plurality of channels which are equal in number to the plurality of outputs of said Fourier PHF. 75-550.
transformer, each of these channels including a series arrange-ment of a digital phase shifting network and a digital delay device, the outputs of these delay devices being coupled to the output of the polyphase network.
transformer, each of these channels including a series arrange-ment of a digital phase shifting network and a digital delay device, the outputs of these delay devices being coupled to the output of the polyphase network.
6. An arrangement as claimed in claim 5, further com-prising a plurality of interpolating digital filters disposed bobbin each of the outputs of the Fourier transformer and the corresponding input of the polyphase network respectively.
7. An arrangement as claimed in claim 1, wherein the auxiliary signals comprise signalling signals and said means for limiting the bandwidth of the signalling signals has a plurality of output channels which correspond to the plurality of signalling signals, the arrangement further comprising a pilot signal generator means for producing a digital pilot sig-nal and in which one of the output channels of said limiting means comprises digital adder means for adding the pilot sig-nal to the signalling signal produced at the relevant output.
8. An arrangement as claimed in claim 2, wherein said first digital filter bank comprises a series-to-parallel con-verter having a plurality of output channels which is at most twice as large in number as the plurality of main information signals in the FDM signal, and a polyphase network couyled to said output channels.
9. An arrangement as claimed in claim 8, wherein said polyphase network comprises a plurality of series arrangements including a digital delay circuit and a digital phase shifting network coupled in each of the output leads of the series-to-parallel converter respectively.
10. An arrangement as claimed in claim 9, wherein said first digital filter bank comprises a discrete Fourier trans-PHF. 75-550.
former having inputs coupled to said output channels of the series-to-parallel converter and a plurality of output circuits which are equal in number to the plurality of main information signals in the FDM signal and which are coupled to inputs of the second digital filter bank.
former having inputs coupled to said output channels of the series-to-parallel converter and a plurality of output circuits which are equal in number to the plurality of main information signals in the FDM signal and which are coupled to inputs of the second digital filter bank.
11. An arrangement as claimed in claim 10, wherein said second digital filter bank has a plurality of channels each com-prising a digital filter, an input of each of said channels being coupled to an output circuit of the Fourier transformer.
12. An arrangement as claimed in claim 9, further com-prising a plurality of sampling frequency reduction extrapola-ting digital filters included in each of the output leads of the series-to-parallel converter in series with said phase shifting network respectively.
13. An arrangement as claimed in claim 11, further com-prising a second digital filter means coupled to at least one of the output circuits of the Fourier transformer for selecting a pilot signal which is co-transmitted in the FDM signal.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7519717A FR2315809A1 (en) | 1975-06-24 | 1975-06-24 | AUXILIARY SIGNAL TRANSMISSION SYSTEM OF A GROUP OF TELEPHONE CHANNELS OF A FREQUENCY DISTRIBUTED MULTIPLEX |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1075837A true CA1075837A (en) | 1980-04-15 |
Family
ID=9156933
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA255,477A Expired CA1075837A (en) | 1975-06-24 | 1976-06-23 | Arrangement for processing auxiliary signals in a frequency multiplex transmission system |
Country Status (12)
| Country | Link |
|---|---|
| US (1) | US4101738A (en) |
| JP (2) | JPS5210612A (en) |
| AU (1) | AU506733B2 (en) |
| BE (1) | BE843256A (en) |
| CA (1) | CA1075837A (en) |
| CH (1) | CH608670A5 (en) |
| DE (1) | DE2626122C2 (en) |
| DK (1) | DK277476A (en) |
| FR (1) | FR2315809A1 (en) |
| GB (1) | GB1550673A (en) |
| NL (1) | NL7606692A (en) |
| SE (1) | SE7607049L (en) |
Families Citing this family (25)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL180369C (en) | 1977-04-04 | 1987-02-02 | Philips Nv | DEVICE FOR CONVERTING DISCRETE SIGNALS TO A DISCREET SINGLE-BAND FREQUENCY-MULTIPLEX SIGNAL AND REVERSE. |
| US4199660A (en) * | 1977-11-07 | 1980-04-22 | Communications Satellite Corporation | FDM/TDM Transmultiplexer |
| JPS5820491B2 (en) * | 1978-04-12 | 1983-04-23 | 沖電気工業株式会社 | Double-sided frequency division multiplexing signal transmitter/receiver for dial signals |
| FR2427743A1 (en) * | 1978-05-29 | 1979-12-28 | Trt Telecom Radio Electr | TRANSMULTIPLEXER MONITORING DEVICE |
| DE2848494B2 (en) * | 1978-11-08 | 1980-08-28 | Siemens Ag, 1000 Berlin Und 8000 Muenchen | Arrangement for keying in an out-of-band signal frequency |
| US4221934A (en) * | 1979-05-11 | 1980-09-09 | Rca Corporation | Compandor for group of FDM signals |
| US4683471A (en) * | 1985-01-30 | 1987-07-28 | Hughes Aircraft Company | Data bus pilot tone |
| US5058107A (en) * | 1989-01-05 | 1991-10-15 | Hughes Aircraft Company | Efficient digital frequency division multiplexed signal receiver |
| SE467680B (en) * | 1990-12-19 | 1992-08-24 | Johan Hellgren | DIGITAL FILTER BANK WITH Diminished Power Consumption |
| US5444697A (en) * | 1993-08-11 | 1995-08-22 | The University Of British Columbia | Method and apparatus for frame synchronization in mobile OFDM data communication |
| US5526343A (en) * | 1994-01-19 | 1996-06-11 | Fujitsu Limited | Auxiliary service channel signal transmission system |
| US6334219B1 (en) | 1994-09-26 | 2001-12-25 | Adc Telecommunications Inc. | Channel selection for a hybrid fiber coax network |
| US5748683A (en) * | 1994-12-29 | 1998-05-05 | Motorola, Inc. | Multi-channel transceiver having an adaptive antenna array and method |
| US5754597A (en) * | 1994-12-29 | 1998-05-19 | Motorola, Inc. | Method and apparatus for routing a digitized RF signal to a plurality of paths |
| US5579341A (en) * | 1994-12-29 | 1996-11-26 | Motorola, Inc. | Multi-channel digital transceiver and method |
| US5668836A (en) * | 1994-12-29 | 1997-09-16 | Motorola, Inc. | Split frequency band signal digitizer and method |
| CA2181807C (en) * | 1994-12-29 | 1999-09-28 | Robert C. Elder | Wideband frequency signal digitizer and method |
| US5854813A (en) * | 1994-12-29 | 1998-12-29 | Motorola, Inc. | Multiple access up converter/modulator and method |
| US5602874A (en) * | 1994-12-29 | 1997-02-11 | Motorola, Inc. | Method and apparatus for reducing quantization noise |
| US7280564B1 (en) | 1995-02-06 | 2007-10-09 | Adc Telecommunications, Inc. | Synchronization techniques in multipoint-to-point communication using orthgonal frequency division multiplexing |
| USRE42236E1 (en) | 1995-02-06 | 2011-03-22 | Adc Telecommunications, Inc. | Multiuse subcarriers in multipoint-to-point communication using orthogonal frequency division multiplexing |
| US5710763A (en) * | 1995-07-31 | 1998-01-20 | Motorola, Inc. | Filtered fast Fourier transmultiplexer and method |
| FR2788869B1 (en) * | 1999-01-25 | 2001-04-13 | St Microelectronics Sa | ELECTRONIC DEVICE FOR CALCULATING THE DIRECT OR REVERSE FOURIER TRANSFORM OF THE PRODUCT OF A COMPLEX SYMBOL BY A COMPLEX SINUSOIDAL WAVEFORM, IN PARTICULAR WITH A PIPELINE ARCHITECTURE |
| US6505037B1 (en) * | 1999-06-29 | 2003-01-07 | Sharp Laboratories Of America, Inc. | Data unit detection including antenna diversity |
| US7072412B1 (en) | 1999-11-09 | 2006-07-04 | Maurice Bellanger | Multicarrier digital transmission system using an OQAM transmultiplexer |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3605019A (en) * | 1969-01-15 | 1971-09-14 | Ibm | Selective fading transformer |
| US3573380A (en) * | 1969-05-15 | 1971-04-06 | Bell Telephone Labor Inc | Single-sideband modulation system |
| US3676598A (en) * | 1970-06-08 | 1972-07-11 | Bell Telephone Labor Inc | Frequency division multiplex single-sideband modulation system |
| BE789239A (en) * | 1971-12-27 | 1973-01-15 | Western Electric Co | METHOD AND DEVICE FOR SIMULTANEOUSLY SEPARATING AND DEMODULATING A SIGNALMULTIPLEX |
| FR2188920A5 (en) * | 1972-06-15 | 1974-01-18 | Trt Telecom Radio Electr | |
| US3991277A (en) * | 1973-02-15 | 1976-11-09 | Yoshimutsu Hirata | Frequency division multiplex system using comb filters |
| DE2453441B2 (en) * | 1974-11-12 | 1976-12-16 | Siemens AG, 1000 Berlin und 8000 München | METHOD FOR PERFORMING A DIGITAL BROADBAND SIGNAL TRANSMISSION |
| US3971922A (en) * | 1974-11-29 | 1976-07-27 | Telecommunications Radioelectriques Et Telephoniques T.R.T. | Circuit arrangement for digitally processing a given number of channel signals |
-
1975
- 1975-06-24 FR FR7519717A patent/FR2315809A1/en active Granted
-
1976
- 1976-06-11 DE DE2626122A patent/DE2626122C2/en not_active Expired
- 1976-06-18 US US05/697,357 patent/US4101738A/en not_active Expired - Lifetime
- 1976-06-21 NL NL7606692A patent/NL7606692A/en not_active Application Discontinuation
- 1976-06-21 SE SE7607049A patent/SE7607049L/en not_active Application Discontinuation
- 1976-06-21 CH CH790076A patent/CH608670A5/xx not_active IP Right Cessation
- 1976-06-21 DK DK277476A patent/DK277476A/en unknown
- 1976-06-21 GB GB25648/76A patent/GB1550673A/en not_active Expired
- 1976-06-22 BE BE168188A patent/BE843256A/en unknown
- 1976-06-22 AU AU15117/76A patent/AU506733B2/en not_active Expired
- 1976-06-22 JP JP51072857A patent/JPS5210612A/en active Granted
- 1976-06-23 CA CA255,477A patent/CA1075837A/en not_active Expired
-
1980
- 1980-11-28 JP JP55166835A patent/JPS5821454B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CH608670A5 (en) | 1979-01-15 |
| DE2626122C2 (en) | 1982-06-09 |
| DE2626122A1 (en) | 1977-01-20 |
| JPS56128044A (en) | 1981-10-07 |
| AU1511776A (en) | 1978-01-05 |
| US4101738A (en) | 1978-07-18 |
| AU506733B2 (en) | 1980-01-24 |
| JPS5718736B2 (en) | 1982-04-19 |
| JPS5210612A (en) | 1977-01-27 |
| JPS5821454B2 (en) | 1983-04-30 |
| FR2315809A1 (en) | 1977-01-21 |
| DK277476A (en) | 1976-12-25 |
| SE7607049L (en) | 1976-12-25 |
| GB1550673A (en) | 1979-08-15 |
| NL7606692A (en) | 1976-12-28 |
| BE843256A (en) | 1976-12-22 |
| FR2315809B1 (en) | 1979-10-19 |
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