CA1320770C - Transmission system for sending two signals simultaneously on the same communications channel - Google Patents
Transmission system for sending two signals simultaneously on the same communications channelInfo
- Publication number
- CA1320770C CA1320770C CA000605188A CA605188A CA1320770C CA 1320770 C CA1320770 C CA 1320770C CA 000605188 A CA000605188 A CA 000605188A CA 605188 A CA605188 A CA 605188A CA 1320770 C CA1320770 C CA 1320770C
- Authority
- CA
- Canada
- Prior art keywords
- signal
- modulated
- spread spectrum
- pseudo
- random code
- 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 - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
- H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J13/00—Code division multiplex systems
- H04J13/0007—Code type
- H04J13/0022—PN, e.g. Kronecker
Abstract
ABSTRACT
TRANSMISSION SYSTEM FOR SENDING TWO SIGNALS
SIMULTANEOUSLY ON THE SAME COMMUNICATIONS CHANNEL
A transmission system in which a suitably modulated speech or data signal is combined with a low bit rate (100b/s) spread spectrum signal and transmitted simultaneously on the same channel.
At a receiver the modulated speech or data signal is demodulated and the modulated speech or data signal together with the spread spectrum signal are applied to a multiplier in which the spread spectrum signal is despread.
A code synchronising signal may be included in the modulated signal prior to transmission and when recovered in the receiver, the synchronising signal is applied to a pseudo-random code generating means. The transmission system may include a text transmission system in which case the low bit rate signal comprises pages of data. A number of pages may be transmitted simultaneously by spreading the data associated with each page by orthogonal psuedo-random codes.
TRANSMISSION SYSTEM FOR SENDING TWO SIGNALS
SIMULTANEOUSLY ON THE SAME COMMUNICATIONS CHANNEL
A transmission system in which a suitably modulated speech or data signal is combined with a low bit rate (100b/s) spread spectrum signal and transmitted simultaneously on the same channel.
At a receiver the modulated speech or data signal is demodulated and the modulated speech or data signal together with the spread spectrum signal are applied to a multiplier in which the spread spectrum signal is despread.
A code synchronising signal may be included in the modulated signal prior to transmission and when recovered in the receiver, the synchronising signal is applied to a pseudo-random code generating means. The transmission system may include a text transmission system in which case the low bit rate signal comprises pages of data. A number of pages may be transmitted simultaneously by spreading the data associated with each page by orthogonal psuedo-random codes.
Description
~ ~ ~ 0 7 ~ ~
~010~-~55~
The present invention relates to a transmission system ~or sending two signals simultaneously on the same channel.
In mobile radlo applications speech in the band 300Hz ~o 3.3Hz is frequently transmitted as an ~M signal on an allocated channel having a bandwid~h of 25k~z. If it is desired to send data then this is frequently done by frequency shl~t key signalling. If the mobile is onl~ allocated one channel then up to now only speech or data can be sent at any one time. However there is a desire to be able to present text information in a mobile as well as being able to conduct ~oice communications.
However this would normally require two channels if done simultaneously.
One technique for sequen~ially sending text in~ormation on the same channel as current information is teletext in which as known the text information is transmitted in the spare unused lines of a television transmission. However there are applications where there are not regularly occurring unused slots in the signals as transmitted.
According to one aspeGt of the present invention there is provided a method of transmitting first and second signals by the same transmltter on a single channel, comprising: multiplying signals from a first signal source with a pseudo-random code to produce a spread spectrum signal, producing a modulated second signal which is not a spread spectrum signal and which includes a synchronization signal for the pseudo-random code and other information, combining the spread spectrum signal and the modulated signal so that the modulated second siynal lies within the bandwidth occupied by the spread spectrum signal, and transmitting the combined signals on a s~ngle communications channel.
Spread spectrum signalling techniques are known per se but as far as is known the simultaneous ~ransmission of two signals, such as a data signal an~ a voice signal, on the same channel has not be sug~ested before. By sending data using a spread spectrum technique in combination with the modulated signal a more effective use is made of the available signalling spectrum.
'~ 1 :~32~7~) 20104-855~
Synchronisation of the pseudo-random code a~ the re~eiver is achievecl by the modulated signal includincl a code synchronisation signal. The data rate for the spread specl;rum signal ls t~pically between 10 and lOOb/s.
In order to be able to clistinguish hetween the spread spectrum and modulated siynals at ~he receiver, the spread spectrum signal is transmit~ed at a lower amplitude, for example 20dBs lower, than the modulated signal.
When transmitting text, each page of data may be encoded using a different orthogonal pseudo-random code and transmitted simultaneously with the other pages. However, as only llmited numbers of orthogonal codes are available then ~he system capacity is in consequence limited to a few tens of pages.
If the data to be transmitted is to be se~ure then it can be encrypted and further protected by changing the pseudo-random code. In any event the data is not discernable to a person equipped wi~h for example an FM receiver because the data as transmitted appears as noise. Additional security can be provided by using frequency hopping ~echniques.
According to a particular embodiment oE the present invention the method of the present invention, further comprises frequency down-converting the received signal to form an IF
signal, applying the IF signal to a demodulator for recoverlng the second signal, multiplying the IF signal wi~h the same pseudo-random code as was used to encode the data, in order to despread the signal and narrowband filtering the despread signal in order to recover the first signal.
Despreading the data signal to collapse it back to its original bandwidth has a processing gain which facilitates the recovery of the first and second signals.
According to another aspect of the presen~ invention there is provided a transmitting apparatus comprising a multiplier having a first input connected to a source of first signals; a second input connected to a source of a pseudo-random code and an ou~put for a spread spectrum first signal; means for producing a modulated second signal which is not a spread spectrum signal, and ,~. r~ 2 ~ 32~77~
2010~-8~5~
which includes a synchroni~ation signal for said pseuclo-random code and other information; and means for combining the spread spectrum first signal and the modulated second signal so that the modulated second signal lies within the bandwidth occupied by the spread spectrum signal and for -transmitting the combined signals on a single communications channel.
According to a fourth aspect of the present invention there is provided a receiving apparatus for recoverin~ a signal transmitted in accordan~e with the present invention~ the apparatus comprising an r.f. Eront end for producing an IF signal comprising a spread spectrum first signal and a modulated second signal, means for demodulating the IF signal, a multiplier having a first input for receiving the IF signal, a second input coupled to a source of the same pseudo-random code as was used to spread the spectrum of the first signal and an output for the despread signal, and narrowband filtering means for selecting the first signal coupled to the multiplier output.
The present invention will now ~e described, by way of example, with reference to the accompanying drawings, wherein2 Figure 1 is a block schematic diagram of a transmitter suitable for carrying out the method in accordance with the present invention, Figure 2 illustrates the frequency spectrum o~ the spread spectrum data signal and an FM voice signal, Figure 3 is a block schematic diagram of a receiver suitable for receiving the signal transmitted by the method in accordance with the present invention, and Yigure ~ illustrates a modification to the receiver in order to make it suitable for handling text data signals.
In the drawings the same reference numerals have been used -to indicate corresponding features.
For simplicity of description it will be assuMed that a lOOb/s ASCII encoded data signal will comprise the spread spectrum signal and the modulated signal is a frequency modulated speech signal. However~ the modulated signal may comprise a data signal having a bit rate of the order of 2.~ kbi~s/second or an ;;\ 3 i-132~
4 P~3347 AM, DSB-SC or SS~ speech signal.
In Figure 1 the speech s;gnaL hav;ng a band~;dth of the order of 3kHz ;s derived from a source 10 ~hich ~ay b~ a microphone and ampl;f;er. The data is derived from a source 12 whi~h may compr;se a message data source, a control ;nfor~ation source or a source of text data. The cpeech signal from the source 10 ;s applied to a frequency modulator 14 ~h;ch modulates the signal on an appropr;a~e carr;er frequency assoc;ated ~;th a designated rad;o channel hav;ng 25kHz band~idth ~see Figure 2).
The data signal ;s applied to a d;gital mult;pl;er 18 ;n ~h;ch ;t ;s mult;pl;ed by a pseudo-random code der;ved from a pseudo random b;t sequence source 18 on a l;ne 20 to form a spread spectrum signal extending across the entire channel band~;dth (Figure 2). The amplitude of the spread spectrum ~;gnal ;s of the order of 20d8 less than that of the FM s;gnal. The source 18 may also produce a synchron;sing signal on a l;ne 22 ~h;ch ;s connected to the frequency modulator 14 so that the FM s;gnal may also include the synchron;s;ng s;gnal. The FM s;gnal and the spread spectrum s;gnal are appl;ed to an r.f. output stage 24 for transmission by way of an antenna 26.
Referr;ng to F;gure 3, a rece;ver compr;ses an r.f. front end 32 connected to an antenna 30~ ~n IF s;gnal der;ved from the r.fO front end 32 ;s appl;ed to both an FM demodulator 34 and to a multipLier 36. In the FM demodulator 34 the speech ;s 2s reco~ered and a synchron;s;ng s;gnal may be obta;ned. The speech s;gnal ;s passed to an aud;o output stage 38 for reproduct;on and/or seorageO The synchron;s;ng s;gnalO if present9 is relayed on a l;ne 35 to a pseudo random bit sequence source 40 ~h;ch ;s arranged to produce an ;dent;cal pseudo-random code as used to spread the spectrum of the data s;gnal at the transmitter and ;n exact phase synchronisation ~;th that code. Synchron;sation ;s maintained by a code track;ng loop 45 connected between the output sf a lsw pass filter 42 and the pseudo-random b;t sequence source 40~ In the eYent of a synchron;s;ng s;gnal not be;ng transm;tted then synchronisation at the rece;ver can be pærformed ~2~7~(3 by for example a synchronous preamble or slid;ng correlator disclosed ~or example in "Spread Sp~ctrum Systems" Second Edition by Robert C. Dixon, published by Wiley ~nterscience. The IF
signal ;s multiplied ~ith the synchronous pseudo-random signal to despread the s;gnal. The lo~ pass filter 42 ~h;ch is connected to the output of the multipl;er 36 selects the 100b/s data s;gnal ~hich is passed to a suitable data output device 44 ~h;ch includes clock recovery.
Despreading the whole of the IF signal enables one to obtain a processing ga;n ;rrespective of ~hether or not there is a second signal present, uhich processing ga;n fac;l;tates the recovery of the data~ For example if 100b/s is spread o~er 25kHz a process;ng ga;n of the order of 27da ;s ach;eved. In the c8s2 of speech hav;ng been frequency modulated, the process;ng ga;n obta;ned during the demodulation reduces the no;se component due to the spread spectrum s;gnal.
If ;t is desired to protect the data signal further the pseudo-random code can be changed regularly or at irregular intervals and the synchronisation s;gnal could prov;de an 2D indication that the code has been changed to another one ;n a preset sequence or prov;de an ;nd;cat;on of the ne~ codeO An add;tional method for prov;ding security to the whole transm;ssion is frequency hopp;ng.
In the case of the data being a number of pages of text then each page can have a un;que orthogonal pseudo-random code ar,d the synchronising signal cvuld contain an ;nd;cat;on of the page be;ng transmitted so that at the rece;ver the appropr;ate orthogonaL code can be used to despread the s;gnal. If des;red all the pages could be transmitted s;multaneously and a predeterm;ned page despread by applying the appropr;ate pseudo-random code.
F;gure 4 is a block schemat;c d;agram o~ part of a rece;ver for recover;ng text data. In v;e~ of the fact that ;ndividual pages may be updated at different times~ the orthogonal pseudo-random codes are stored in a microprocessor 4S ~h;ch may ~32~0 6 PHB33~78 in response to an appropriate indication in the synchronising signal on the line 35 produce the relevant code N. This code N
is used, as in Figure 3~ to despread or operate on the entire signal from the IF front end 32 (Figure 3). The output from the multiplier 36 is passed to a lo~ pass filter 42 to recover the data signal ~hich is stored in a RAM 48 under the control of the microprocessor 46. A clock recovery stage 50 is coupled to the output of the filter 42 and recovered clock signals are applied to the RAM 48 to synchronise the data being stored. A text display device 52 is connected to the RAM 48 for displaying pages of text ~hich have been requested by ~ay of a control bus 54 connected to the microprocessor 46.
An amplitude difference of the order of 20d~ bet~een the FM
and spread spectrum s;gnals ;s considered desirabLe in order to m;nimise degradation of the FM s;gnal. However the amplitude of the spread spectrum s;gnal itself should be sufficiently large to enable the receiver to recover the data signal. In the event of having FM and spread spectrum signals of equal powers, then at ~he receiver one ~ould recover a good data signal but a degraded speech signal~
From reading the present disclosure, other mod;f;cat;ons ~ill be apparent to persons skilled in the art. Such modifications may ;nvolve other features ~hich sre already known in the field of transmission sys~ems and in the des;gn~
manufacture and use of transmitters and receivers and component par~s thereof and ~hich may be used instead of or in addition to features already described herein. ALthough claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein e;ther expl;citly or ;mpLici~ly or any ~eneralisation thereof~
~hether or not it relates to the same invention as presently claimed in any claim and whether or not ;t mitiga~es any or all of the same technical problems as does the present ;nvention.
:~21~7~
7 P~1~33~7 The applicants hereby g;ve notice that new claims may be formulated to such features and/or comb;nations of such features during the prosecut;on of the present application or of any further appl;cat;on der;ved therefrom.
s
~010~-~55~
The present invention relates to a transmission system ~or sending two signals simultaneously on the same channel.
In mobile radlo applications speech in the band 300Hz ~o 3.3Hz is frequently transmitted as an ~M signal on an allocated channel having a bandwid~h of 25k~z. If it is desired to send data then this is frequently done by frequency shl~t key signalling. If the mobile is onl~ allocated one channel then up to now only speech or data can be sent at any one time. However there is a desire to be able to present text information in a mobile as well as being able to conduct ~oice communications.
However this would normally require two channels if done simultaneously.
One technique for sequen~ially sending text in~ormation on the same channel as current information is teletext in which as known the text information is transmitted in the spare unused lines of a television transmission. However there are applications where there are not regularly occurring unused slots in the signals as transmitted.
According to one aspeGt of the present invention there is provided a method of transmitting first and second signals by the same transmltter on a single channel, comprising: multiplying signals from a first signal source with a pseudo-random code to produce a spread spectrum signal, producing a modulated second signal which is not a spread spectrum signal and which includes a synchronization signal for the pseudo-random code and other information, combining the spread spectrum signal and the modulated signal so that the modulated second siynal lies within the bandwidth occupied by the spread spectrum signal, and transmitting the combined signals on a s~ngle communications channel.
Spread spectrum signalling techniques are known per se but as far as is known the simultaneous ~ransmission of two signals, such as a data signal an~ a voice signal, on the same channel has not be sug~ested before. By sending data using a spread spectrum technique in combination with the modulated signal a more effective use is made of the available signalling spectrum.
'~ 1 :~32~7~) 20104-855~
Synchronisation of the pseudo-random code a~ the re~eiver is achievecl by the modulated signal includincl a code synchronisation signal. The data rate for the spread specl;rum signal ls t~pically between 10 and lOOb/s.
In order to be able to clistinguish hetween the spread spectrum and modulated siynals at ~he receiver, the spread spectrum signal is transmit~ed at a lower amplitude, for example 20dBs lower, than the modulated signal.
When transmitting text, each page of data may be encoded using a different orthogonal pseudo-random code and transmitted simultaneously with the other pages. However, as only llmited numbers of orthogonal codes are available then ~he system capacity is in consequence limited to a few tens of pages.
If the data to be transmitted is to be se~ure then it can be encrypted and further protected by changing the pseudo-random code. In any event the data is not discernable to a person equipped wi~h for example an FM receiver because the data as transmitted appears as noise. Additional security can be provided by using frequency hopping ~echniques.
According to a particular embodiment oE the present invention the method of the present invention, further comprises frequency down-converting the received signal to form an IF
signal, applying the IF signal to a demodulator for recoverlng the second signal, multiplying the IF signal wi~h the same pseudo-random code as was used to encode the data, in order to despread the signal and narrowband filtering the despread signal in order to recover the first signal.
Despreading the data signal to collapse it back to its original bandwidth has a processing gain which facilitates the recovery of the first and second signals.
According to another aspect of the presen~ invention there is provided a transmitting apparatus comprising a multiplier having a first input connected to a source of first signals; a second input connected to a source of a pseudo-random code and an ou~put for a spread spectrum first signal; means for producing a modulated second signal which is not a spread spectrum signal, and ,~. r~ 2 ~ 32~77~
2010~-8~5~
which includes a synchroni~ation signal for said pseuclo-random code and other information; and means for combining the spread spectrum first signal and the modulated second signal so that the modulated second signal lies within the bandwidth occupied by the spread spectrum signal and for -transmitting the combined signals on a single communications channel.
According to a fourth aspect of the present invention there is provided a receiving apparatus for recoverin~ a signal transmitted in accordan~e with the present invention~ the apparatus comprising an r.f. Eront end for producing an IF signal comprising a spread spectrum first signal and a modulated second signal, means for demodulating the IF signal, a multiplier having a first input for receiving the IF signal, a second input coupled to a source of the same pseudo-random code as was used to spread the spectrum of the first signal and an output for the despread signal, and narrowband filtering means for selecting the first signal coupled to the multiplier output.
The present invention will now ~e described, by way of example, with reference to the accompanying drawings, wherein2 Figure 1 is a block schematic diagram of a transmitter suitable for carrying out the method in accordance with the present invention, Figure 2 illustrates the frequency spectrum o~ the spread spectrum data signal and an FM voice signal, Figure 3 is a block schematic diagram of a receiver suitable for receiving the signal transmitted by the method in accordance with the present invention, and Yigure ~ illustrates a modification to the receiver in order to make it suitable for handling text data signals.
In the drawings the same reference numerals have been used -to indicate corresponding features.
For simplicity of description it will be assuMed that a lOOb/s ASCII encoded data signal will comprise the spread spectrum signal and the modulated signal is a frequency modulated speech signal. However~ the modulated signal may comprise a data signal having a bit rate of the order of 2.~ kbi~s/second or an ;;\ 3 i-132~
4 P~3347 AM, DSB-SC or SS~ speech signal.
In Figure 1 the speech s;gnaL hav;ng a band~;dth of the order of 3kHz ;s derived from a source 10 ~hich ~ay b~ a microphone and ampl;f;er. The data is derived from a source 12 whi~h may compr;se a message data source, a control ;nfor~ation source or a source of text data. The cpeech signal from the source 10 ;s applied to a frequency modulator 14 ~h;ch modulates the signal on an appropr;a~e carr;er frequency assoc;ated ~;th a designated rad;o channel hav;ng 25kHz band~idth ~see Figure 2).
The data signal ;s applied to a d;gital mult;pl;er 18 ;n ~h;ch ;t ;s mult;pl;ed by a pseudo-random code der;ved from a pseudo random b;t sequence source 18 on a l;ne 20 to form a spread spectrum signal extending across the entire channel band~;dth (Figure 2). The amplitude of the spread spectrum ~;gnal ;s of the order of 20d8 less than that of the FM s;gnal. The source 18 may also produce a synchron;sing signal on a l;ne 22 ~h;ch ;s connected to the frequency modulator 14 so that the FM s;gnal may also include the synchron;s;ng s;gnal. The FM s;gnal and the spread spectrum s;gnal are appl;ed to an r.f. output stage 24 for transmission by way of an antenna 26.
Referr;ng to F;gure 3, a rece;ver compr;ses an r.f. front end 32 connected to an antenna 30~ ~n IF s;gnal der;ved from the r.fO front end 32 ;s appl;ed to both an FM demodulator 34 and to a multipLier 36. In the FM demodulator 34 the speech ;s 2s reco~ered and a synchron;s;ng s;gnal may be obta;ned. The speech s;gnal ;s passed to an aud;o output stage 38 for reproduct;on and/or seorageO The synchron;s;ng s;gnalO if present9 is relayed on a l;ne 35 to a pseudo random bit sequence source 40 ~h;ch ;s arranged to produce an ;dent;cal pseudo-random code as used to spread the spectrum of the data s;gnal at the transmitter and ;n exact phase synchronisation ~;th that code. Synchron;sation ;s maintained by a code track;ng loop 45 connected between the output sf a lsw pass filter 42 and the pseudo-random b;t sequence source 40~ In the eYent of a synchron;s;ng s;gnal not be;ng transm;tted then synchronisation at the rece;ver can be pærformed ~2~7~(3 by for example a synchronous preamble or slid;ng correlator disclosed ~or example in "Spread Sp~ctrum Systems" Second Edition by Robert C. Dixon, published by Wiley ~nterscience. The IF
signal ;s multiplied ~ith the synchronous pseudo-random signal to despread the s;gnal. The lo~ pass filter 42 ~h;ch is connected to the output of the multipl;er 36 selects the 100b/s data s;gnal ~hich is passed to a suitable data output device 44 ~h;ch includes clock recovery.
Despreading the whole of the IF signal enables one to obtain a processing ga;n ;rrespective of ~hether or not there is a second signal present, uhich processing ga;n fac;l;tates the recovery of the data~ For example if 100b/s is spread o~er 25kHz a process;ng ga;n of the order of 27da ;s ach;eved. In the c8s2 of speech hav;ng been frequency modulated, the process;ng ga;n obta;ned during the demodulation reduces the no;se component due to the spread spectrum s;gnal.
If ;t is desired to protect the data signal further the pseudo-random code can be changed regularly or at irregular intervals and the synchronisation s;gnal could prov;de an 2D indication that the code has been changed to another one ;n a preset sequence or prov;de an ;nd;cat;on of the ne~ codeO An add;tional method for prov;ding security to the whole transm;ssion is frequency hopp;ng.
In the case of the data being a number of pages of text then each page can have a un;que orthogonal pseudo-random code ar,d the synchronising signal cvuld contain an ;nd;cat;on of the page be;ng transmitted so that at the rece;ver the appropr;ate orthogonaL code can be used to despread the s;gnal. If des;red all the pages could be transmitted s;multaneously and a predeterm;ned page despread by applying the appropr;ate pseudo-random code.
F;gure 4 is a block schemat;c d;agram o~ part of a rece;ver for recover;ng text data. In v;e~ of the fact that ;ndividual pages may be updated at different times~ the orthogonal pseudo-random codes are stored in a microprocessor 4S ~h;ch may ~32~0 6 PHB33~78 in response to an appropriate indication in the synchronising signal on the line 35 produce the relevant code N. This code N
is used, as in Figure 3~ to despread or operate on the entire signal from the IF front end 32 (Figure 3). The output from the multiplier 36 is passed to a lo~ pass filter 42 to recover the data signal ~hich is stored in a RAM 48 under the control of the microprocessor 46. A clock recovery stage 50 is coupled to the output of the filter 42 and recovered clock signals are applied to the RAM 48 to synchronise the data being stored. A text display device 52 is connected to the RAM 48 for displaying pages of text ~hich have been requested by ~ay of a control bus 54 connected to the microprocessor 46.
An amplitude difference of the order of 20d~ bet~een the FM
and spread spectrum s;gnals ;s considered desirabLe in order to m;nimise degradation of the FM s;gnal. However the amplitude of the spread spectrum s;gnal itself should be sufficiently large to enable the receiver to recover the data signal. In the event of having FM and spread spectrum signals of equal powers, then at ~he receiver one ~ould recover a good data signal but a degraded speech signal~
From reading the present disclosure, other mod;f;cat;ons ~ill be apparent to persons skilled in the art. Such modifications may ;nvolve other features ~hich sre already known in the field of transmission sys~ems and in the des;gn~
manufacture and use of transmitters and receivers and component par~s thereof and ~hich may be used instead of or in addition to features already described herein. ALthough claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein e;ther expl;citly or ;mpLici~ly or any ~eneralisation thereof~
~hether or not it relates to the same invention as presently claimed in any claim and whether or not ;t mitiga~es any or all of the same technical problems as does the present ;nvention.
:~21~7~
7 P~1~33~7 The applicants hereby g;ve notice that new claims may be formulated to such features and/or comb;nations of such features during the prosecut;on of the present application or of any further appl;cat;on der;ved therefrom.
s
Claims (16)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of transmitting first and second signals by the same transmitter on a single channel, comprising: multiplying signals from a first signal source with a pseudo-random code to produce a spread spectrum signal, producing a modulated second signal which is not a spread spectrum signal and which includes a synchronization signal for the pseudo-random code and other information, combining the spread spectrum signal and the modulated signal so that the modulated second signal lies within the bandwidth occupied by the spread spectrum signal, and transmitting the combined signals on a single communications channel.
2. A method as claimed in claim 1, in which the spread spectrum signal as transmitted is of lower amplitude than the modulated signal.
3. A method as claimed in claim 2, in which the amplitude of the spread spectrum signal is substantially 20dB lower than the amplitude of the modulated signal.
4. A method as claimed in any one of claims 1 to 3, in which the signal from the first signal source comprises data having a bit rate of substantially 100b/s.
5. A method as claimed in claim 4, wherein when the data comprises pages of text, each page having a different pseudo-random code.
6. A method as claimed in claim 5, wherein at least two pages of text are transmitted simultaneously.
7. A method as claimed in claim 4, wherein the data is encrypted by changing the pseudo-random code.
8. A method as claimed in claim 1, 2, 3, 5, 6 or 7, wherein the modulated second signal comprises a speech signal.
9. A method as claimed in claim 8, wherein the speech signal is frequency modulated.
10. A method as claimed in claim 1, 2, 3, 5, 6 or 7, in which the signal is transmitted using frequency hopping techniques.
11. A method of receiving a signal transmitted in accordance with the method as claimed in claim 1, comprising frequency down-converting the received signal to form an IF signal, applying the IF
signal to a demodulator for recovering the second signal, multiplying the IF signal with the same pseudo-random code as was used to encode the data, in order to despread the signal and narrowband filtering the despread signal in order to recover the first signal.
signal to a demodulator for recovering the second signal, multiplying the IF signal with the same pseudo-random code as was used to encode the data, in order to despread the signal and narrowband filtering the despread signal in order to recover the first signal.
12. A transmitting apparatus comprising a multiplier having a first input connected to a source of first signals; a second input connected to a source of a pseudo-random code and an output for a spread spectrum first signal; means for producing a modulated second signal which is not a spread spectrum signal, and which includes a synchronization signal for said pseudo-random code and other information; and means for combining the spread spectrum first signal and the modulated second signal so that the modulated second signal lies within the bandwidth occupied by the spread spectrum signal and for transmitting the combined signals on a single communications channel.
13. An apparatus as claimed in claim 12, in which the means for producing a modulated signal comprises a frequency modulator.
14. A receiving apparatus for use with a method as claimed in claim 11, comprising an r.f. front end for producing an IF signal comprising a spread spectrum first signal and a modulated second signal, means for demodulating the IF signal, a multiplier having a first input for receiving the IF signal, a second input coupled to a source of the same pseudo-random code as was used to spread the spectrum of the first signal and an output for the despread signal, and narrowband filtering means for selecting the first signal coupled to the multiplier output.
15. An apparatus as claimed in claim 14, in which the demodulating means comprises means for deriving a synchronising signal from the modulated second signal and the pseudo-random code source has a synchronising signal input connected to the demodulating means.
16. An apparatus as claimed in claim 15, in which the pseudo-random code source comprises processing means containing a plurality of orthogonal pseudo-random codes, the processing means being responsive to a code identifier contained in the synchronising signal to provide an appropriate code to the multiplier.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8816635.0 | 1988-07-13 | ||
| GB8816635A GB2220824A (en) | 1988-07-13 | 1988-07-13 | Transmission system for sending two signals simultaneously on the same communications channel |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1320770C true CA1320770C (en) | 1993-07-27 |
Family
ID=10640357
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000605188A Expired - Fee Related CA1320770C (en) | 1988-07-13 | 1989-07-10 | Transmission system for sending two signals simultaneously on the same communications channel |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US5073899A (en) |
| EP (1) | EP0351008B1 (en) |
| JP (1) | JPH02132939A (en) |
| CA (1) | CA1320770C (en) |
| DE (1) | DE68922347D1 (en) |
| FI (1) | FI893347A (en) |
| GB (1) | GB2220824A (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL6702874A (en) * | 1966-08-27 | 1968-08-26 | ||
| US3912722A (en) * | 1972-12-06 | 1975-10-14 | Shionogi & Co | Novel 6{62 -amino-steroids and production thereof |
| NL7403957A (en) * | 1974-03-22 | 1975-09-24 | Shape Technical Centre | Spread spectrum communication using multiple transmission and access - imparts additional modulating signal to carrier at sender producing sub carrier and code |
| GB1512700A (en) * | 1975-10-23 | 1978-06-01 | Standard Telephones Cables Ltd | Data transmission |
| US4313197A (en) * | 1980-04-09 | 1982-01-26 | Bell Telephone Laboratories, Incorporated | Spread spectrum arrangement for (de)multiplexing speech signals and nonspeech signals |
| CA1226914A (en) * | 1984-01-26 | 1987-09-15 | The University Of British Columbia | Modem for pseudo noise communication on a.c. lines |
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| JPS63275233A (en) * | 1987-05-06 | 1988-11-11 | Victor Co Of Japan Ltd | Spread spectrum communication system |
| JPH069348B2 (en) * | 1988-09-16 | 1994-02-02 | 日本ビクター株式会社 | Spread spectrum communication system |
-
1988
- 1988-07-13 GB GB8816635A patent/GB2220824A/en not_active Withdrawn
-
1989
- 1989-07-07 EP EP89201804A patent/EP0351008B1/en not_active Expired - Lifetime
- 1989-07-07 DE DE68922347T patent/DE68922347D1/en not_active Expired - Lifetime
- 1989-07-10 JP JP1177864A patent/JPH02132939A/en active Pending
- 1989-07-10 CA CA000605188A patent/CA1320770C/en not_active Expired - Fee Related
- 1989-07-10 FI FI893347A patent/FI893347A/en not_active IP Right Cessation
- 1989-07-12 US US07/378,886 patent/US5073899A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US5073899A (en) | 1991-12-17 |
| GB8816635D0 (en) | 1988-08-17 |
| EP0351008A3 (en) | 1990-12-12 |
| FI893347A (en) | 1990-01-14 |
| EP0351008B1 (en) | 1995-04-26 |
| EP0351008A2 (en) | 1990-01-17 |
| GB2220824A (en) | 1990-01-17 |
| FI893347A0 (en) | 1989-07-10 |
| JPH02132939A (en) | 1990-05-22 |
| DE68922347D1 (en) | 1995-06-01 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed | ||
| MKLA | Lapsed |
Effective date: 19960129 |