CA2497947C - Transmitting rf signals employing improved high-level combinations of analog fm and digital signals - Google Patents
Transmitting rf signals employing improved high-level combinations of analog fm and digital signals Download PDFInfo
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- CA2497947C CA2497947C CA2497947A CA2497947A CA2497947C CA 2497947 C CA2497947 C CA 2497947C CA 2497947 A CA2497947 A CA 2497947A CA 2497947 A CA2497947 A CA 2497947A CA 2497947 C CA2497947 C CA 2497947C
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- 239000002131 composite material Substances 0.000 claims abstract description 8
- 238000000034 method Methods 0.000 claims abstract description 8
- 230000008878 coupling Effects 0.000 description 21
- 238000010168 coupling process Methods 0.000 description 21
- 238000005859 coupling reaction Methods 0.000 description 21
- 238000002347 injection Methods 0.000 description 21
- 239000007924 injection Substances 0.000 description 21
- 230000003321 amplification Effects 0.000 description 12
- 238000003199 nucleic acid amplification method Methods 0.000 description 12
- 230000009977 dual effect Effects 0.000 description 9
- 238000004458 analytical method Methods 0.000 description 6
- 230000006870 function Effects 0.000 description 6
- 238000003780 insertion Methods 0.000 description 6
- 230000037431 insertion Effects 0.000 description 6
- 230000008901 benefit Effects 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 230000001427 coherent effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000005284 excitation Effects 0.000 description 2
- 238000009434 installation Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000000243 solution Substances 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
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Classifications
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- 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
- H04B1/02—Transmitters
- H04B1/04—Circuits
- H04B1/0483—Transmitters with multiple parallel paths
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- 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
- H04B1/38—Transceivers, i.e. devices in which transmitter and receiver form a structural unit and in which at least one part is used for functions of transmitting and receiving
- H04B1/40—Circuits
- H04B1/403—Circuits using the same oscillator for generating both the transmitter frequency and the receiver local oscillator frequency
- H04B1/406—Circuits using the same oscillator for generating both the transmitter frequency and the receiver local oscillator frequency with more than one transmission mode, e.g. analog and digital modes
Abstract
Apparatus and method are presented for broadcasting an RF signal comprised of analog FM and digital signals. An analog FM source provides an analog FM signal. A digital source provides a digital signal. A splitter splits the FM signal into a fractional portion and remainder portion. A summer combines the fractional portion with the digital signal to provide a first combined signal. A main FM transmitter amplifies the remainder portion to provide an amplified FM signal. A digital transmitter amplifies the first combined signal to provide an amplified combined signal. A combiner combines the amplified FM signal and the amplified combined signal to provide a composite RF signal to be broadcasted. -20-
Description
TRANSMITTING RF SIGNALS EMPLOYING IMPROVED HIGH-LEVEL
COMBINATIONS OF ANALOG FM AND DIGITAL SIGNALS
Background of the Invention It has been known in the radio broadcasting art to transmit a composite signal consisting of a frequency modulated (FM) analog signal and a digital signal, such as an in band on channel (IBOC) digital signal. The prior art includes, for example, the U.S. patents to Murphy et al.
5,315,583 and Papadopoulos et a1. 6,144,705.
The prior art also includes separate amplification of such signals, sometimes referred to as IBOC high-level combining. An example is illustrated in Fig. 1 herein. In this example, the output v2 of an existing FM transmitter 10, illustrated as a main FM transmitter, is combined with the output v3 from a digital transmitter referred to as a digital TX (linear) transmitter. The input to the main transmitter 10 is obtained from a conventional FM signal source 14 while the input to the digital transmitter 12 is obtained from a conventional IBOC source 16. The outputs vz and v3 of these transmitters are combined in a conventional coupler C, which typically is a 10 dB coupler. The coupler, which is sometimes known as an output coupler, provides an output v~ that is supplied to a transmitting antenna 20 for broadcasting the composite signal. The coupler C has ports l, 2, 3 and 4 with the voltages vz and v3 being applied to ports 2 and 3. The output at port 1 is supplied to the antenna 20. Port 4 is coupled to a reject load RL.
Because the outputs v~ and v2 are combined only after they have reached a high level of amplitude (because they have already been amplified by separate amplifiers) this is referred to in the art as "high-level combining" or "separate amplification". This type of combining results in high losses. This may be viewed as the penalty paid for the simplicity involved. In a 10 dB coupler, the problems that are noted include the following: the main FM transmitter needs to have enough headroom in order to increase its output power by 11% to overcome the combiner insertion loss. This can be very problematic in specific installations without additional headroom to spare. Major hardware upgrade could be necessary to overcome this issue, such as by replacing the existing main FM transmitter with a more powerful transmitter.
A second problem with this type of system is that the overall dissipation increases. Besides the power dissipated by digital transmitter 12, additional energy is wasted at this reject load RL where up to 10% of the main transmitter FM
output and up to 90% of the output of the digital transmitter will be dissipated. This inefficiency creates additional heat load for the air-conditioning equipment in the room containing the transmitter equipment.
The present invention is directed toward improvements in the combining of an output of an FM transmitter with that of a digital transmitter. The improvements are directed toward minimizing the FM and digital power losses in high level combining. The improved system provides various benefits including higher overall system efficiency and elimination of requirements for FM headroom.
Summnary of the Invention In accordance with one aspect of the present invention, an apparatus is provided for broadcasting an RF signal comprised of analog FM and digital signals. The apparatus includes a splitter that splits an FM signal received from an analog FM source into a fractional portion and a remainder portion. The summer combines the fractional portion with a digital signal obtained from a digital source to provide a
COMBINATIONS OF ANALOG FM AND DIGITAL SIGNALS
Background of the Invention It has been known in the radio broadcasting art to transmit a composite signal consisting of a frequency modulated (FM) analog signal and a digital signal, such as an in band on channel (IBOC) digital signal. The prior art includes, for example, the U.S. patents to Murphy et al.
5,315,583 and Papadopoulos et a1. 6,144,705.
The prior art also includes separate amplification of such signals, sometimes referred to as IBOC high-level combining. An example is illustrated in Fig. 1 herein. In this example, the output v2 of an existing FM transmitter 10, illustrated as a main FM transmitter, is combined with the output v3 from a digital transmitter referred to as a digital TX (linear) transmitter. The input to the main transmitter 10 is obtained from a conventional FM signal source 14 while the input to the digital transmitter 12 is obtained from a conventional IBOC source 16. The outputs vz and v3 of these transmitters are combined in a conventional coupler C, which typically is a 10 dB coupler. The coupler, which is sometimes known as an output coupler, provides an output v~ that is supplied to a transmitting antenna 20 for broadcasting the composite signal. The coupler C has ports l, 2, 3 and 4 with the voltages vz and v3 being applied to ports 2 and 3. The output at port 1 is supplied to the antenna 20. Port 4 is coupled to a reject load RL.
Because the outputs v~ and v2 are combined only after they have reached a high level of amplitude (because they have already been amplified by separate amplifiers) this is referred to in the art as "high-level combining" or "separate amplification". This type of combining results in high losses. This may be viewed as the penalty paid for the simplicity involved. In a 10 dB coupler, the problems that are noted include the following: the main FM transmitter needs to have enough headroom in order to increase its output power by 11% to overcome the combiner insertion loss. This can be very problematic in specific installations without additional headroom to spare. Major hardware upgrade could be necessary to overcome this issue, such as by replacing the existing main FM transmitter with a more powerful transmitter.
A second problem with this type of system is that the overall dissipation increases. Besides the power dissipated by digital transmitter 12, additional energy is wasted at this reject load RL where up to 10% of the main transmitter FM
output and up to 90% of the output of the digital transmitter will be dissipated. This inefficiency creates additional heat load for the air-conditioning equipment in the room containing the transmitter equipment.
The present invention is directed toward improvements in the combining of an output of an FM transmitter with that of a digital transmitter. The improvements are directed toward minimizing the FM and digital power losses in high level combining. The improved system provides various benefits including higher overall system efficiency and elimination of requirements for FM headroom.
Summnary of the Invention In accordance with one aspect of the present invention, an apparatus is provided for broadcasting an RF signal comprised of analog FM and digital signals. The apparatus includes a splitter that splits an FM signal received from an analog FM source into a fractional portion and a remainder portion. The summer combines the fractional portion with a digital signal obtained from a digital source to provide a
-2-first combined signal. The main FM transmitter amplifies the remainder portion to provide an amplified FM signal and a digital transmitter amplifies the first combined signal to provide an amplified combined signal. A combiner then combines the amplified FM signal with the amplified combined signal to provide a composite RF signal to be broadcast.
In accordance with another aspect of the present invention, a method is provided for broadcasting an RF signal that is comprised of analog FM and digital signals. The method includes the steps of extracting a fractional portion of an FM signal provided by an analog FM source and providing a remainder portion. The summer combines the fractional portion with a digital signal obtained from a digital source to provide a first combined signal. The remainder portion and the first combined signal are respectively amplified by a main FM transmitter and a digital transmitter. The amplified FM
signal and the amplified combined signal are then combined to provide a composite RF signal to be broadcast.
Brief Description of the Drawings The foregoing and other features of the present invention will become apparent to one skilled in the art for which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, wherein:
Fig. 1 illustrates a block diagram illustration of a prior art combining circuit;
Fig. 2 is a schematic-block diagram illustration of one embodiment of the present invention;
Fig. 3 is a graphical illustration that is helpful in understanding the invention;
Fig. 4 is a graphical illustration that is helpful in understanding the invention;
In accordance with another aspect of the present invention, a method is provided for broadcasting an RF signal that is comprised of analog FM and digital signals. The method includes the steps of extracting a fractional portion of an FM signal provided by an analog FM source and providing a remainder portion. The summer combines the fractional portion with a digital signal obtained from a digital source to provide a first combined signal. The remainder portion and the first combined signal are respectively amplified by a main FM transmitter and a digital transmitter. The amplified FM
signal and the amplified combined signal are then combined to provide a composite RF signal to be broadcast.
Brief Description of the Drawings The foregoing and other features of the present invention will become apparent to one skilled in the art for which the present invention relates upon consideration of the following description of the invention with reference to the accompanying drawings, wherein:
Fig. 1 illustrates a block diagram illustration of a prior art combining circuit;
Fig. 2 is a schematic-block diagram illustration of one embodiment of the present invention;
Fig. 3 is a graphical illustration that is helpful in understanding the invention;
Fig. 4 is a graphical illustration that is helpful in understanding the invention;
-3-Fig. 5 is a graphic illustration that is helpful in understanding the invention;
Fig. 6 is a graphical illustration that is helpful in understanding the invention; and Fig. 7 is a graphical illustration that is helpful in understanding the invention.
Description of Preferred Embodiments Reference is now made to Fig. 2. This illustrates an embodiment of the invention which is similar in structure to that of the prior art as illustrated in Fig. 1. To simplify the description herein, like components in Figs. 1 and 2 are identified with like character references with only the differences in the embodiment of Fig. 2 being described in detail below.
In the embodiment of Fig. 2, a splitter 30 is employed to split off a fractional portion 34 of the analog FM signal from the source 14 with the remainder portion 32 being supplied to the main transmitter 10. The fractional portion 34, which may be on the order of 1-10% of that obtained from source 14, is supplied by way of an adjustable phase adjuster 36 to a summer 40, the opposite of splitter 30. The phase adjusted fractional portion 34 from source 14 and digital IBOC signal obtained from source 16 are combined by summer 40 and the combined signal, as a first combined signal, is supplied to the digital transmitter 12. The fractional portion of the FM
signal has been phase adjusted so that it will properly match that generated by the FM transmitter 10 when combined at the output combiner C. The outputs v2 and v3 are supplied to the coupler C and are combined to provide a combined or composite output V~ for application to the broadcasting antenna 20.
It has been determined that the new and improved embodiment in Fig. 2 which may be considered as a dual FM
Fig. 6 is a graphical illustration that is helpful in understanding the invention; and Fig. 7 is a graphical illustration that is helpful in understanding the invention.
Description of Preferred Embodiments Reference is now made to Fig. 2. This illustrates an embodiment of the invention which is similar in structure to that of the prior art as illustrated in Fig. 1. To simplify the description herein, like components in Figs. 1 and 2 are identified with like character references with only the differences in the embodiment of Fig. 2 being described in detail below.
In the embodiment of Fig. 2, a splitter 30 is employed to split off a fractional portion 34 of the analog FM signal from the source 14 with the remainder portion 32 being supplied to the main transmitter 10. The fractional portion 34, which may be on the order of 1-10% of that obtained from source 14, is supplied by way of an adjustable phase adjuster 36 to a summer 40, the opposite of splitter 30. The phase adjusted fractional portion 34 from source 14 and digital IBOC signal obtained from source 16 are combined by summer 40 and the combined signal, as a first combined signal, is supplied to the digital transmitter 12. The fractional portion of the FM
signal has been phase adjusted so that it will properly match that generated by the FM transmitter 10 when combined at the output combiner C. The outputs v2 and v3 are supplied to the coupler C and are combined to provide a combined or composite output V~ for application to the broadcasting antenna 20.
It has been determined that the new and improved embodiment in Fig. 2 which may be considered as a dual FM
-4-(DFM) version, reduces the RF losses compared to that of the system in Fig. 1, making better use of the auxiliary transmitter 12. There is also a reduction of the FM odd mode excitation that is achieved by feeding the in-phase power into the coupler. A lower FM odd mode excitation brings about various benefits including a lower overall FM insertion loss, and a tighter coupler coefficient on the order of 6 dB or lower. The tighter coupling coefficient reduces the overall IBOC power generation and this reduces the overall IBOC power loss, enabling the injection of the FM signal through the auxiliary digital transmitter 12.
Fig. 2 presents a dual FM injection system in that it provides high-level combination of the FM and digital signals.
Thus, the digital transmitter 12 carries the IBOC signal and a fractional portion of the FM signal that has been phased so as to match and add at the output combiner C with the signal generated by the FM transmitter 10.
This system as shown in Fig. 2 provides a solution of upgrading to IBOC without impacting the output requirement of the main FM transmitter. This reduces by at least 50% the power lost in the reject load. These features, along with the increase in overall system efficiency is described in greater detail in the analysis that follows below.
Combining Analysis The combining analysis hereinafter involves significant equations and their explanation with respect to various graphical terms. It is believed that various definitions of terms and language employed should be defined to facilitate an understanding herein. Table 1, presented below, provides these definitions.
Table 1 - Definitions IBOC = In-Band-On-Channel, a system of digital audio broadcast that places digital information on
Fig. 2 presents a dual FM injection system in that it provides high-level combination of the FM and digital signals.
Thus, the digital transmitter 12 carries the IBOC signal and a fractional portion of the FM signal that has been phased so as to match and add at the output combiner C with the signal generated by the FM transmitter 10.
This system as shown in Fig. 2 provides a solution of upgrading to IBOC without impacting the output requirement of the main FM transmitter. This reduces by at least 50% the power lost in the reject load. These features, along with the increase in overall system efficiency is described in greater detail in the analysis that follows below.
Combining Analysis The combining analysis hereinafter involves significant equations and their explanation with respect to various graphical terms. It is believed that various definitions of terms and language employed should be defined to facilitate an understanding herein. Table 1, presented below, provides these definitions.
Table 1 - Definitions IBOC = In-Band-On-Channel, a system of digital audio broadcast that places digital information on
-5-frequencies immediately adjacent to the analog AM or FM signal, but still within the assigned channel.
Vet) - Instantaneous voltage at port 1, as a function of time V2(t) - Instantaneous voltage at port 2, as a function of time V3(t) - Instantaneous voltage at port 3, as a function of time rms = root mean square V~ - rms voltage at port 1 (rms) VZ = rms voltage at port 2 (rms) V3 - rms voltage at port 3 (rms) t = time T = period of integration Siz - scattering parameter, between port 1 and 2 scattering parameter, between port 1 and 3 p~ - power at port 1 2 - power at port 2 p'3 - power at port 3 - system impedance, usually 50 Ohm TPO = Transmitter Power Output, the licensed power a broadcast is allowed to transmit Kv = Voltage peak-to-average ratio, in linear terms IBOC/FM ratio = ratio between the IBOC and the FM signals
Vet) - Instantaneous voltage at port 1, as a function of time V2(t) - Instantaneous voltage at port 2, as a function of time V3(t) - Instantaneous voltage at port 3, as a function of time rms = root mean square V~ - rms voltage at port 1 (rms) VZ = rms voltage at port 2 (rms) V3 - rms voltage at port 3 (rms) t = time T = period of integration Siz - scattering parameter, between port 1 and 2 scattering parameter, between port 1 and 3 p~ - power at port 1 2 - power at port 2 p'3 - power at port 3 - system impedance, usually 50 Ohm TPO = Transmitter Power Output, the licensed power a broadcast is allowed to transmit Kv = Voltage peak-to-average ratio, in linear terms IBOC/FM ratio = ratio between the IBOC and the FM signals
-6-Tx = Transmitter dB = a logarithmic ratio between two signals dBc = a logarithmic ratio between a signal and a carrier Vs-iboc~eak = peak amplitude of the IBOC voltage at port 3 V3 fm = FM voltage at port 3 V3_peak = peak voltage at port 3 p3-peak = peak power at port 3 CW = Constant wave. A signal whose amplitude does not change over time. The FM signal is an example of a CW signal, as its amplitude is unchanged (the information is conveyed in the frequency modulation, not on the amplitude. .) Prefect = Total power dissipated in the reject load Prefect fm = FM power dissipated in the reject load Separate amplification = Prior art, where the FM
transmitter is combined with the output of an IBOC-only transmitter ~Isys - overall system efficiency ~2 = efficiency of transmitter connected at port 2 (FM transmitter) r/3 = efficiency of transmitter connected at port 3 (Digital transmitter) When two signals are combined, the instantaneous output voltage V~(t) is given by the sum of each coupled input voltage:
v~~t~ s~2 v2~ta+s~3 v3ct~
The average output power, pl, is obtained by averaging, over time, the square of the resultant output voltage:
~~12 y2\t/ + s13 y3~t~~ dt ToJ Zo In the case of coherent signals, the numerator can be simplified as the square of the sum of their rms voltages:
- _v1 = U.112 y2 + s13 y3) 2 1 Zo Zo Where V1, V2, and V3 are the corresponding rms values (vectors) for the waveforms V1 (t) , V2 (t) and V3 (t) .
However, for incoherent signals, as those at different frequencies (FM and IBOC), the total power is obtained by the sum of each coupled power. This can be proven by solving the square of the resultant instantaneous voltage.
s122 v2\t/2 + 2 s12 s13 v2~t~ v3~t~ + s132 v3\tJ 2 Due to orthogonality between V2(t) and V3(t), their multiplication averages over time to zero, amounting to no contribution to the average power at the output. The resulting term, to be averaged over time, has been reduced to:
s122 v2~t~ + s132 v3\t, 2 which means that the average power at the output, for non-coherent signals, is obtained by summing each coupled input power, _ 2 2 PI sl2 P2 + s13 P3 _8_ Important to note that this value is smaller than the value obtained by the square of the sum of their rms voltages (properly phased), and accordingly, some power is being lost.
In the following sections, the advantages are noted of adding some coherence between the signals v2 and v3, such that the mid term does not totally cancel.
How Much Dual FM Injection is Needed Partial coherence is obtained by adding some FM signal at port 3, along with IBOC. Let's now determine the minimum amount of dual FM injection that is needed so that the main FM
power can remain unchanged.
Assume that vl is the output voltage, V2 is the FM
voltage applied at the thru port (where the main FM
transmitter connects), and v3-fmis the FM voltage applied at the coupled port of the output combiner (where the Digital transmitter connects).
To further simplify the analysis, make Zo - 1, and the total coupled FM power into port 1 (output) - 1. Then at 100%
TPO, pl - 1 and V1 - l:
_~(~ ,2 _ P1 ~12 v2 + S13 v3_ fml Solving for v3 fm, the FM voltage needed at the coupled port 3 to achieve output power pl - 1:
1- Slz V2 v3_fm=
This expression is used for the condition of no impact on the main FM power. This condition forces _g_ Vz - 1~ and then the value V3 fm obtained is the FM voltage needed at port 3 that guarantees that the main FM transmitter power is not affected. In other ways, viewed from the main transmitter's port (port 2), the combiner has no loss.
If we now sweep a range of coupling factors, then we obtain the dual FM injection level that is needed, as a function of the coupler used, in order to make the main FM
path lossless.
Table 2 Coupling DFM injection level (dB) (% of TPO) -10 2.6%
- 9 3.4%
- 8 4.3%
transmitter is combined with the output of an IBOC-only transmitter ~Isys - overall system efficiency ~2 = efficiency of transmitter connected at port 2 (FM transmitter) r/3 = efficiency of transmitter connected at port 3 (Digital transmitter) When two signals are combined, the instantaneous output voltage V~(t) is given by the sum of each coupled input voltage:
v~~t~ s~2 v2~ta+s~3 v3ct~
The average output power, pl, is obtained by averaging, over time, the square of the resultant output voltage:
~~12 y2\t/ + s13 y3~t~~ dt ToJ Zo In the case of coherent signals, the numerator can be simplified as the square of the sum of their rms voltages:
- _v1 = U.112 y2 + s13 y3) 2 1 Zo Zo Where V1, V2, and V3 are the corresponding rms values (vectors) for the waveforms V1 (t) , V2 (t) and V3 (t) .
However, for incoherent signals, as those at different frequencies (FM and IBOC), the total power is obtained by the sum of each coupled power. This can be proven by solving the square of the resultant instantaneous voltage.
s122 v2\t/2 + 2 s12 s13 v2~t~ v3~t~ + s132 v3\tJ 2 Due to orthogonality between V2(t) and V3(t), their multiplication averages over time to zero, amounting to no contribution to the average power at the output. The resulting term, to be averaged over time, has been reduced to:
s122 v2~t~ + s132 v3\t, 2 which means that the average power at the output, for non-coherent signals, is obtained by summing each coupled input power, _ 2 2 PI sl2 P2 + s13 P3 _8_ Important to note that this value is smaller than the value obtained by the square of the sum of their rms voltages (properly phased), and accordingly, some power is being lost.
In the following sections, the advantages are noted of adding some coherence between the signals v2 and v3, such that the mid term does not totally cancel.
How Much Dual FM Injection is Needed Partial coherence is obtained by adding some FM signal at port 3, along with IBOC. Let's now determine the minimum amount of dual FM injection that is needed so that the main FM
power can remain unchanged.
Assume that vl is the output voltage, V2 is the FM
voltage applied at the thru port (where the main FM
transmitter connects), and v3-fmis the FM voltage applied at the coupled port of the output combiner (where the Digital transmitter connects).
To further simplify the analysis, make Zo - 1, and the total coupled FM power into port 1 (output) - 1. Then at 100%
TPO, pl - 1 and V1 - l:
_~(~ ,2 _ P1 ~12 v2 + S13 v3_ fml Solving for v3 fm, the FM voltage needed at the coupled port 3 to achieve output power pl - 1:
1- Slz V2 v3_fm=
This expression is used for the condition of no impact on the main FM power. This condition forces _g_ Vz - 1~ and then the value V3 fm obtained is the FM voltage needed at port 3 that guarantees that the main FM transmitter power is not affected. In other ways, viewed from the main transmitter's port (port 2), the combiner has no loss.
If we now sweep a range of coupling factors, then we obtain the dual FM injection level that is needed, as a function of the coupler used, in order to make the main FM
path lossless.
Table 2 Coupling DFM injection level (dB) (% of TPO) -10 2.6%
- 9 3.4%
- 8 4.3%
- 7 5.6%
- 6 7.2%
- 5 9.5%
- 4 12.6%
- 3 17.2%
Table 2, DFM level needed not to impact the main FM
transmitter output.
How Much IBOC Injection is Needed The peak IBOC voltage needed at the coupled port 3 (V3-=b~~) to achieve the proper injection at the output is:
_ o.l k V3 _ iboc _ peak S~3 where k~ is the IBOC voltage peak-to-average ratio, in linear terms, needed to comply with the RF mask. A value of 1.778 (5dB) will be considered throughout the analysis.
The ratio between the IBOC and FM through the digital transmitter is:
Iboc l fm ratio = 20 log 1 0.1 dBc - s~2 vz Using the case in which the main Tx remains at 100% TPO
(vz - 1), and considering a 6 dB coupler, the IBOC/FM ratio needed is -2.5dBc.
So far it is seen that the required amount of dual FM
injection at port 3 increases with the coupling factor, but in general it is a small fraction of the main FM service (or TPO).
On the other hand, the required generation of IBOC at port 3 is inversely proportional with the coupling coefficient. The smaller the coupling coefficient (the looser the coupling) the more IBOC power will need to be generated.
Considering both effects at once, tighter coupling coefficients require more DFM injection but less IBOC
generation. The optimum coupling value that minimizes the size of the digital transmitter is now considered.
Optimum Coupling Coefficient for Minimum Size of Digital Transmitter The peak voltage at port 3 is:
V3 _ peak v3 - fm + v3 _ iboc _ peak which generates a peak power of:
z _ 1 -S12 V2 + 0.1 kv P3 _ peak s13 s13 This value includes fast, highly compressed envelope peaks. It is the short duration of these peaks, much shorter than the amplifier thermal constant (its temperature will hardly change with modulation) that allows the device to reach higher levels than in a CW mode. Accordingly, in order to compare the size of a digital transmitter, whose envelope is being pulsed, to the corresponding 100% TPO (that is provided by a CW-operated FM transmitter), we need to adjust these peak levels to its equivalent maximum CW operation.
Based on peak power measurements, we rate the maximum CW
operation of a digital transmitter 0.5dB below its maximum pulsed level. As an example, a 11.22 kW peak-capable digital transmitter will be considered to be a lOkW CW unit (lOkW =
11.22kW - 0.5dB). This is the value that will be used to compare sizes between the FM and Digital transmitters.
The relative size of the digital transmitter, respect 100% TPO, can then be estimated by:
-O.Sdb Relative_size = 1 'S12 y2 -f- ~.1 kv 1 O '°
If we sweep a range of coupling coefficients, and graph three different values of ~Z (main FM output), we then obtain the results as seen in Fig. 3.
Several important conclusions can be extracted from Fig.
3. The optimum coupling coefficient (for size) is in the region of 5 to 6 dB, instead of the lOdB coupling used in separate amplification.
The digital transmitter needs to be 35% the size of the main transmitter's (or TPO), in order to provide the secondary FM injection level that is required to make the main FM-path lossless. It is important to note that this value (35%) is comparable to the size demanded for separate amplification.
In other words, with the same hardware (as the one used in prior art), we are now providing a "lossless" solution for the FM path, resolving the headroom problem.
Fig. 3 also shows that a bigger transmitter can afford to over-inject FM, resulting in gain at the main FM port. A
smaller transmitter, with less injection than the one required (not to impact the main FM path), will make the main FM to have to overcome some loss.
Finally, by using now this tighter coupling coefficient (6dB), the amount of IBOC that needs to be generated drops by 4 dB, of which 25% will get coupled to the output. As a result, the dissipated IBOC power into the reject load is about 30% of the amount dissipated in separate amplification.
The next section studies the reject power in more detail.
Optimum Coupling Coefficient for Minimum Reject Power The total reject power is composed of:
reject reject - jm + reject - iboc where, __~~ 1z reject- fm VJ t3 V2 -St2 v3- fm/
and, z __ o. l s12 2 5 Prefect - iboc To keep our analysis practical, let's select the same size transmitter as the one required for separate amplification (minimum size).
With this restriction, the total FM voltage supplied at port 3 will be limited to:
= 0.623 - 0~ 1778 v3_jm As the coupling coefficient is changed (or swept), and the digital transmitter size is now allowed to change, we will have to adjust the output of the main FM transmitter (vz) in order to guarantee 100% TPO at the output of the combiner (vl - 1)s.
The value of the voltage at port 2 then needs to be:
1 -Sl3 y3-jm v2 -Sl2 Fig. 4 shows the total reject power for the DFM system, and its FM and IBOC contributions. As a comparison, the straight line represents the reject power for a lOdB-coupler separate amplification system.
The minima in total reject power is found to be somewhere between 6 to 7 dB coupling, with a value equal to half of the power dissipated in separate amplification.
Output Po'ver of a Digital Traaemitter Operating with DFM
Considering signal clipping to be our limit (independent of their probability of occurrence), let's calculate the maximum average power at which a digital transmitter can be operated, for different IBOC injection levels.
P3 1 3 - jm + P3 _ iboc Substituting, we obtain:
z 1.06 -V3 fm P3 v3 _ jm +
kv The total output power of the digital transmitter, relative to its CW equivalent rating, has been plotted in Fig.
as a function of the IBOC/FM ratio.
The new operating average power, with a DFM injection of 5 -2.5dBc, is about the same than the IBOC-only rating.
We can already predict an improvement in the overall system efficiency, i.e., with the same generated average power of the digital transmitter (respect separate amplification), we have upgraded our system to FM IBOC without demanding 11%
more power out of the main FM transmitter.
$fficiency of a Digital Transmftter Operating with DP'M
The measured efficiency of a digital transmitter, operating at different levels of DFM injection is represented in Fig. 6.
For IBOC/FM ratios weaker than -lOdBc, the efficiency of a digital transmitter is very similar to the efficiency of common amplification. For stronger injection levels, the efficiency quickly improves (for the same average power) and approaches the efficiency of IBOC-only operation.
Overall System ~fficieacy Knowing that the output power (including IBOC) has to be 1.01, the overall system efficiency is:
1.01 ~Isys =
1.01 + pz 1 ~z + ps 1 ~3 + prej~t ~2 - I 3 We will assume a 60% efficiency for the FM transmitter r~z. The efficiency curve fit function used to generate the graph in Fig. 6 will be used to compute the value of Equations for the other terms have already been determined.
A graph of the overall efficiency for a DFM system implemented using the minimum size digital transmitter, is represented in Fig. 7.
With the new DFM implementation, the efficiency approaches 50%, as compared to separate amplification, whose efficiency would be 46%. The coupling coefficient for peak efficiency is found at 6.75dB.
We have described the Dual FM injection, an improved high-level combining method of upgrading to IBOC. This method uses a tighter coupling coefficient at the output combiner, which decreases the IBOC losses. Simultaneously, by injecting a small fraction of the FM signal, properly phased, at the coupled port, the total combining efficiency is increased, as both the main and the dual FM injection are partially summed at the output.
A coupling factor of 6dB is the optimum value to minimize the size required for the digital transmitter and to reduce the dissipation in the reject load, and as such boosting the overall system efficiency by 3 to 4%. Under these conditions, the total reject power is expected to be reduced by 50%.
All these benefits are added to the fact that with DFM
injection, the main FM transmitter does not have to increase its output level to overcome the coupler losses, an inconvenience at times unsurpassable for many installations in the field.
Finally, the system performance is dependent on the size of the digital transmitter in the following manner; the bigger the digital transmitter to be used, the stronger the FM
injection through it and the tighter the optimum coupling coefficient can be, this way obtaining a lower output power demanded of the main FM transmitter, a lower reject power and a higher overall system efficiency.
It has been determined that this system of high-level combining with dual FM injection achieves lower insertion loss for the FM transmitter. Instead of a 10% insertion loss known in the prior art, the typical insertion loss for the new system is 0 dB (no loss), if a 6 dB coupler is used. If tighter couplers are used, an actual gain is achieved, as more FM power is added through port 2. This improvement is fundamental to economically upgrade to IBOC in "difficult powers" where the FM insertion loss can not be tolerated if prior art is to be used. Overall efficiency of this new system can be as high as 52% using present broadcast technology, which results in a reduction of 20% in dissipated power. The RF combining efficiency can reach 98.5% with typical values of 95%. The equipment ratio to make the conversion is now 1.35. The small difference of 4% in size (minimum), in practice is enough to provide optimum configuration to broadcast customers.
- 6 7.2%
- 5 9.5%
- 4 12.6%
- 3 17.2%
Table 2, DFM level needed not to impact the main FM
transmitter output.
How Much IBOC Injection is Needed The peak IBOC voltage needed at the coupled port 3 (V3-=b~~) to achieve the proper injection at the output is:
_ o.l k V3 _ iboc _ peak S~3 where k~ is the IBOC voltage peak-to-average ratio, in linear terms, needed to comply with the RF mask. A value of 1.778 (5dB) will be considered throughout the analysis.
The ratio between the IBOC and FM through the digital transmitter is:
Iboc l fm ratio = 20 log 1 0.1 dBc - s~2 vz Using the case in which the main Tx remains at 100% TPO
(vz - 1), and considering a 6 dB coupler, the IBOC/FM ratio needed is -2.5dBc.
So far it is seen that the required amount of dual FM
injection at port 3 increases with the coupling factor, but in general it is a small fraction of the main FM service (or TPO).
On the other hand, the required generation of IBOC at port 3 is inversely proportional with the coupling coefficient. The smaller the coupling coefficient (the looser the coupling) the more IBOC power will need to be generated.
Considering both effects at once, tighter coupling coefficients require more DFM injection but less IBOC
generation. The optimum coupling value that minimizes the size of the digital transmitter is now considered.
Optimum Coupling Coefficient for Minimum Size of Digital Transmitter The peak voltage at port 3 is:
V3 _ peak v3 - fm + v3 _ iboc _ peak which generates a peak power of:
z _ 1 -S12 V2 + 0.1 kv P3 _ peak s13 s13 This value includes fast, highly compressed envelope peaks. It is the short duration of these peaks, much shorter than the amplifier thermal constant (its temperature will hardly change with modulation) that allows the device to reach higher levels than in a CW mode. Accordingly, in order to compare the size of a digital transmitter, whose envelope is being pulsed, to the corresponding 100% TPO (that is provided by a CW-operated FM transmitter), we need to adjust these peak levels to its equivalent maximum CW operation.
Based on peak power measurements, we rate the maximum CW
operation of a digital transmitter 0.5dB below its maximum pulsed level. As an example, a 11.22 kW peak-capable digital transmitter will be considered to be a lOkW CW unit (lOkW =
11.22kW - 0.5dB). This is the value that will be used to compare sizes between the FM and Digital transmitters.
The relative size of the digital transmitter, respect 100% TPO, can then be estimated by:
-O.Sdb Relative_size = 1 'S12 y2 -f- ~.1 kv 1 O '°
If we sweep a range of coupling coefficients, and graph three different values of ~Z (main FM output), we then obtain the results as seen in Fig. 3.
Several important conclusions can be extracted from Fig.
3. The optimum coupling coefficient (for size) is in the region of 5 to 6 dB, instead of the lOdB coupling used in separate amplification.
The digital transmitter needs to be 35% the size of the main transmitter's (or TPO), in order to provide the secondary FM injection level that is required to make the main FM-path lossless. It is important to note that this value (35%) is comparable to the size demanded for separate amplification.
In other words, with the same hardware (as the one used in prior art), we are now providing a "lossless" solution for the FM path, resolving the headroom problem.
Fig. 3 also shows that a bigger transmitter can afford to over-inject FM, resulting in gain at the main FM port. A
smaller transmitter, with less injection than the one required (not to impact the main FM path), will make the main FM to have to overcome some loss.
Finally, by using now this tighter coupling coefficient (6dB), the amount of IBOC that needs to be generated drops by 4 dB, of which 25% will get coupled to the output. As a result, the dissipated IBOC power into the reject load is about 30% of the amount dissipated in separate amplification.
The next section studies the reject power in more detail.
Optimum Coupling Coefficient for Minimum Reject Power The total reject power is composed of:
reject reject - jm + reject - iboc where, __~~ 1z reject- fm VJ t3 V2 -St2 v3- fm/
and, z __ o. l s12 2 5 Prefect - iboc To keep our analysis practical, let's select the same size transmitter as the one required for separate amplification (minimum size).
With this restriction, the total FM voltage supplied at port 3 will be limited to:
= 0.623 - 0~ 1778 v3_jm As the coupling coefficient is changed (or swept), and the digital transmitter size is now allowed to change, we will have to adjust the output of the main FM transmitter (vz) in order to guarantee 100% TPO at the output of the combiner (vl - 1)s.
The value of the voltage at port 2 then needs to be:
1 -Sl3 y3-jm v2 -Sl2 Fig. 4 shows the total reject power for the DFM system, and its FM and IBOC contributions. As a comparison, the straight line represents the reject power for a lOdB-coupler separate amplification system.
The minima in total reject power is found to be somewhere between 6 to 7 dB coupling, with a value equal to half of the power dissipated in separate amplification.
Output Po'ver of a Digital Traaemitter Operating with DFM
Considering signal clipping to be our limit (independent of their probability of occurrence), let's calculate the maximum average power at which a digital transmitter can be operated, for different IBOC injection levels.
P3 1 3 - jm + P3 _ iboc Substituting, we obtain:
z 1.06 -V3 fm P3 v3 _ jm +
kv The total output power of the digital transmitter, relative to its CW equivalent rating, has been plotted in Fig.
as a function of the IBOC/FM ratio.
The new operating average power, with a DFM injection of 5 -2.5dBc, is about the same than the IBOC-only rating.
We can already predict an improvement in the overall system efficiency, i.e., with the same generated average power of the digital transmitter (respect separate amplification), we have upgraded our system to FM IBOC without demanding 11%
more power out of the main FM transmitter.
$fficiency of a Digital Transmftter Operating with DP'M
The measured efficiency of a digital transmitter, operating at different levels of DFM injection is represented in Fig. 6.
For IBOC/FM ratios weaker than -lOdBc, the efficiency of a digital transmitter is very similar to the efficiency of common amplification. For stronger injection levels, the efficiency quickly improves (for the same average power) and approaches the efficiency of IBOC-only operation.
Overall System ~fficieacy Knowing that the output power (including IBOC) has to be 1.01, the overall system efficiency is:
1.01 ~Isys =
1.01 + pz 1 ~z + ps 1 ~3 + prej~t ~2 - I 3 We will assume a 60% efficiency for the FM transmitter r~z. The efficiency curve fit function used to generate the graph in Fig. 6 will be used to compute the value of Equations for the other terms have already been determined.
A graph of the overall efficiency for a DFM system implemented using the minimum size digital transmitter, is represented in Fig. 7.
With the new DFM implementation, the efficiency approaches 50%, as compared to separate amplification, whose efficiency would be 46%. The coupling coefficient for peak efficiency is found at 6.75dB.
We have described the Dual FM injection, an improved high-level combining method of upgrading to IBOC. This method uses a tighter coupling coefficient at the output combiner, which decreases the IBOC losses. Simultaneously, by injecting a small fraction of the FM signal, properly phased, at the coupled port, the total combining efficiency is increased, as both the main and the dual FM injection are partially summed at the output.
A coupling factor of 6dB is the optimum value to minimize the size required for the digital transmitter and to reduce the dissipation in the reject load, and as such boosting the overall system efficiency by 3 to 4%. Under these conditions, the total reject power is expected to be reduced by 50%.
All these benefits are added to the fact that with DFM
injection, the main FM transmitter does not have to increase its output level to overcome the coupler losses, an inconvenience at times unsurpassable for many installations in the field.
Finally, the system performance is dependent on the size of the digital transmitter in the following manner; the bigger the digital transmitter to be used, the stronger the FM
injection through it and the tighter the optimum coupling coefficient can be, this way obtaining a lower output power demanded of the main FM transmitter, a lower reject power and a higher overall system efficiency.
It has been determined that this system of high-level combining with dual FM injection achieves lower insertion loss for the FM transmitter. Instead of a 10% insertion loss known in the prior art, the typical insertion loss for the new system is 0 dB (no loss), if a 6 dB coupler is used. If tighter couplers are used, an actual gain is achieved, as more FM power is added through port 2. This improvement is fundamental to economically upgrade to IBOC in "difficult powers" where the FM insertion loss can not be tolerated if prior art is to be used. Overall efficiency of this new system can be as high as 52% using present broadcast technology, which results in a reduction of 20% in dissipated power. The RF combining efficiency can reach 98.5% with typical values of 95%. The equipment ratio to make the conversion is now 1.35. The small difference of 4% in size (minimum), in practice is enough to provide optimum configuration to broadcast customers.
Claims (7)
1. An apparatus for broadcasting an RF signal comprised of analog FM and digital signals and comprising:
an analog FM source for providing an analog FM
signal;
a digital source for providing a digital signal;
a splitter for splitting the FM signal into a fractional portion and remainder portion;
a summer for combining said fractional portion with said digital signal to provide a first combined signal;
a main FM transmitter for amplifying said remainder portion to provide an amplified FM signal;
a digital transmitter for amplifying said first combined signal to provide an amplified combined signal; and a combiner that combines said amplified FM signal and said amplified combined signal to provide a composite RF
signal to be broadcasted.
an analog FM source for providing an analog FM
signal;
a digital source for providing a digital signal;
a splitter for splitting the FM signal into a fractional portion and remainder portion;
a summer for combining said fractional portion with said digital signal to provide a first combined signal;
a main FM transmitter for amplifying said remainder portion to provide an amplified FM signal;
a digital transmitter for amplifying said first combined signal to provide an amplified combined signal; and a combiner that combines said amplified FM signal and said amplified combined signal to provide a composite RF
signal to be broadcasted.
2. An apparatus as set forth in claim 1 including a phase adjuster located intermediate said splitter and said summer for adjusting the phase of said fractional portion.
3. An apparatus as set forth in claim 1 wherein said digital source is an IBOC source and said digital signal is an IBOC digital signal.
4. An apparatus as set forth in claim 3 including a phase adjuster located intermediate said splitter and said summer for adjusting the phase of said fractional portion.
5. A method for broadcasting an RF signal comprised of:
analog FM and digital signals including the steps of:
providing an analog FM signal;
providing a digital signal;
extracting a fractional portion of said FM signal;
combining said fractional portion with said digital signal;
amplifying the FM signal portion remaining after said fractional portion has been extracted to provide an amplified FM signal;
amplifying said first combined signal to provide an amplified combined signal; and combining said amplified FM signal with said amplified combined signal to provide a composite RF signal to be broadcast.
analog FM and digital signals including the steps of:
providing an analog FM signal;
providing a digital signal;
extracting a fractional portion of said FM signal;
combining said fractional portion with said digital signal;
amplifying the FM signal portion remaining after said fractional portion has been extracted to provide an amplified FM signal;
amplifying said first combined signal to provide an amplified combined signal; and combining said amplified FM signal with said amplified combined signal to provide a composite RF signal to be broadcast.
6. A method as set forth in claim 5 including the step of adjusting the phase of said fractional portion.
7. A method as set forth in claim 6 including the step of adjusting the phase of said fractional portion.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US10/788,710 | 2004-02-27 | ||
| US10/788,710 US7477700B2 (en) | 2004-02-27 | 2004-02-27 | Transmitting RF signals employing improved high-level combinations of analog FM and digital signals |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2497947A1 CA2497947A1 (en) | 2005-08-27 |
| CA2497947C true CA2497947C (en) | 2010-06-29 |
Family
ID=34887058
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA2497947A Expired - Fee Related CA2497947C (en) | 2004-02-27 | 2005-02-22 | Transmitting rf signals employing improved high-level combinations of analog fm and digital signals |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US7477700B2 (en) |
| CA (1) | CA2497947C (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7272363B1 (en) * | 2004-02-06 | 2007-09-18 | Fluker Stephen M | HD digital radio combining methods and systems |
| US7623833B2 (en) | 2006-04-13 | 2009-11-24 | Harris Corporation | Dual output digital exciter |
| US8965290B2 (en) * | 2012-03-29 | 2015-02-24 | General Electric Company | Amplitude enhanced frequency modulation |
| CN103457615A (en) * | 2013-08-16 | 2013-12-18 | 奥维通信股份有限公司 | Audio broadcasting frequency modulation transmitter based on digital-analog networking |
Family Cites Families (22)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4507746A (en) * | 1982-07-28 | 1985-03-26 | The United States Of America As Represented By The Secretary Of The Army | Programmable matched filter for binary phase-coded signals |
| US4660192A (en) * | 1985-04-11 | 1987-04-21 | Pomatto Sr Robert P | Simultaneous AM and FM transmitter and receiver |
| US5029003A (en) * | 1989-12-18 | 1991-07-02 | General Electric Company | Apparatus for incorporating digital signals with a standard TV signal |
| US5315583A (en) * | 1991-04-11 | 1994-05-24 | Usa Digital Radio | Method and apparatus for digital audio broadcasting and reception |
| US5465396A (en) * | 1993-01-12 | 1995-11-07 | Usa Digital Radio Partners, L.P. | In-band on-channel digital broadcasting |
| US5436930A (en) * | 1993-06-14 | 1995-07-25 | At&T Corp. | Simultaneous analog and digital communications with a selection of different signal point constellations based on signal energy |
| JPH09504915A (en) * | 1993-09-10 | 1997-05-13 | アマティ・コミュニケーションズ・コーポレーション | Digital sound broadcasting using a dedicated control channel |
| IL114471A0 (en) * | 1994-07-12 | 1996-01-31 | Usa Digital Radio Partners L P | Method and system for simultaneously broadcasting and analog signals |
| US5956624A (en) * | 1994-07-12 | 1999-09-21 | Usa Digital Radio Partners Lp | Method and system for simultaneously broadcasting and receiving digital and analog signals |
| WO1996021291A1 (en) * | 1995-01-03 | 1996-07-11 | Northrop Grumman Corporation | Method and apparatus for improving am compatible digital broadcast analog fidelity |
| US5949793A (en) * | 1996-07-22 | 1999-09-07 | Cellularvision Technology & Telecommunications, L.P. | Transmission of digital and analog signals in the same band |
| US6144705A (en) * | 1996-08-22 | 2000-11-07 | Lucent Technologies Inc. | Technique for simultaneous communications of analog frequency-modulated and digitally modulated signals using precanceling scheme |
| US5991334A (en) * | 1996-11-12 | 1999-11-23 | Lucent Technologies Inc. | Technique for simultaneous communications of analog frequency-modulated and digitally modulated signals using postcanceling scheme |
| US6549242B1 (en) * | 1997-04-04 | 2003-04-15 | Harris Corporation | Combining adjacent TV channels for transmission by a common antenna |
| US6243424B1 (en) * | 1998-03-27 | 2001-06-05 | Ibiguity Digital Corporation | Method and apparatus for AM digital broadcasting |
| US6721337B1 (en) * | 1999-08-24 | 2004-04-13 | Ibiquity Digital Corporation | Method and apparatus for transmission and reception of compressed audio frames with prioritized messages for digital audio broadcasting |
| US6549544B1 (en) * | 1999-11-10 | 2003-04-15 | Ibiquity Digital Corporation | Method and apparatus for transmission and reception of FM in-band on-channel digital audio broadcasting |
| US7088740B1 (en) * | 2000-12-21 | 2006-08-08 | Bae Systems Information And Electronic Systems Integration Inc | Digital FM radio system |
| ATE242568T1 (en) * | 2001-07-11 | 2003-06-15 | Sony Int Europe Gmbh | DRM/AM SIMULCAST |
| US6882832B2 (en) * | 2002-09-10 | 2005-04-19 | Harris Corporation | Frequency verification of an amplitude modulated signal |
| US6898249B2 (en) * | 2002-12-17 | 2005-05-24 | Ibiquity Digital Corporation | Method and apparatus for AM digital audio broadcasting with amplitude scaled tertiary subcarriers |
| US6914579B2 (en) * | 2003-03-26 | 2005-07-05 | Spx Corporation | Apparatus and method for isolating in-channel FM antennas sharing common aperture space |
-
2004
- 2004-02-27 US US10/788,710 patent/US7477700B2/en not_active Expired - Fee Related
-
2005
- 2005-02-22 CA CA2497947A patent/CA2497947C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| US20050190851A1 (en) | 2005-09-01 |
| US7477700B2 (en) | 2009-01-13 |
| CA2497947A1 (en) | 2005-08-27 |
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