CA2374255A1 - Digital broadcast transmission system comprising a power control system using a pilot signal - Google Patents
Digital broadcast transmission system comprising a power control system using a pilot signal Download PDFInfo
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- CA2374255A1 CA2374255A1 CA002374255A CA2374255A CA2374255A1 CA 2374255 A1 CA2374255 A1 CA 2374255A1 CA 002374255 A CA002374255 A CA 002374255A CA 2374255 A CA2374255 A CA 2374255A CA 2374255 A1 CA2374255 A1 CA 2374255A1
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- signal
- pilot
- sample
- output
- gain
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Classifications
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
- H03G3/20—Automatic control
- H03G3/30—Automatic control in amplifiers having semiconductor devices
- H03G3/3036—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers
- H03G3/3042—Automatic control in amplifiers having semiconductor devices in high-frequency amplifiers or in frequency-changers in modulators, frequency-changers, transmitters or power amplifiers
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03G—CONTROL OF AMPLIFICATION
- H03G3/00—Gain control in amplifiers or frequency changers without distortion of the input signal
- H03G3/005—Control by a pilot signal
Abstract
A high definition television broadcast transmission system includes a feature of maintaining a constant transmission output power. A system includes components, such as a digital encoder (12), for providing an information signal. A pilot source (30) provides a pilot signal. A combiner (26) combines the information and pilot signals. A power amplifier (50) amplifies the combined information and pilot signals to a broadcast transmission power level. An automatic gain control (38), located upstream of the amplifier (50), increases gain of the information signal in response to a control signal. The broadcast transmission power level of the information signal is dependent upon the gain applied by the gain control. A sample signal contains the combined information and pilot signals, is derived from an output of the power amplifier (50). A pilot-indicative signal is isolated from the sample signal.
The control signal for the gain control (38) is determined using the pilot-indicative signal.
The control signal for the gain control (38) is determined using the pilot-indicative signal.
Description
POWER CONTROL VIA USE OF A PILOT SIGNAL WITHIN A DIGITAL BROADCAST
TRANSMISSION SYSTEM
The present invention relates to maintenance of a desired broadcast power level, and is particularly directed to maintenance of a broadcast power level of a digital TV ("DTV") transmission system.
In a broadcast communication system, such as a broadcast television or radio system, it is typically desirable to maintain a constant broadcast transmission power level. For example, in a broadcast transmission system which has an output power level of 50 kilowatts, it may be undesirable for the output to vary more than even a few watts of power.
1o Transmission power level is related to the power level of an amplified electrical signal provided to an antenna of the broadcast system. For analog broadcast transmission systems, it is known to monitor the amplified electrical signal provided to the antenna and adjust the system to maintain a desired transmission power level.
One type of analog system is a national television system committee ("NTSC") format system. A technique known as peak of synchronization is currently utilized within the NTSC
system to control the transmission power level of the system. Specifically, a peak amplitude level is monitored and is utilized to determine the power level of the transmission signal. Use of the peak of synchronization technique is possible within such a system because the output signal is rather repetitive and deterministic, thus determination of the output power and control of the output power are readily accomplished.
Digital-based transmission systems offer a marked improvement in quality and quantity of data that can be transmitted. For example, a high definition television ("HDTV") system is a digital (i.e., DTV) system that provides greater sound and picture quality compared to the known analog television systems. One aspect of HDTV systems is that the improvements in 2s sound and picture quality are associated with a need for greater detail information and an increase in the amount of transmitted information. Typically, the information is provided in a Trellis encoded frame format of information.
Contrary to the known analog systems, DTV (e.g., HDTV) systems provide an output that is generally not repetitive and not deterministic. The output of the system is pseudo so random, and in general the output cannot be predicted. Thus, it becomes difficult to utilize the output of the DTV system to control the transmission power level of the system. One approach is to utilize an average output power detector. However, such an approach has limited accuracy ability. The present invention includes a broadcast transmission system comprising signal provision means for providing an information signal and a pilot signal, amplifier means for amplifying the information and pilot signals, control means for controlling the amount amplification using the pilot signal characterized in that said amplifier means includes power amplifier means for amplifying the information and pilot signals to a broadcast transmission s power level gain means, located upstream of said power amplifier means, for increasing gain of the information signal in response to a control signal, the broadcast transmission power level of the information signal being dependent upon the gain applied by said gain means, said control means includes means for controlling said gain means to maintain the broadcast transmission power level constant, said means for controlling said gain means including sample 1o means for deriving a sample signal containing the information and pilot signals from an output of said power amplifier means, isolation means for isolating a pilot-indicative signal from the sample signal, and determination means for determining the control signal using the pilot-indicative signal.
Advantageously the present invention provides a broadcast transmission system that ~5 includes signal provision means for providing an information signal and a pilot signal.
Amplifier means amplify the information and pilot signals. Control means controls the amount of amplification using the pilot signal. The invention also includes a broadcast transmission system comprising information signal provision means for providing an information signal, pilot signal provision means for providing a pilot signal having predefined signal 2o characteristics, combiner means for combining the information and pilot signals, power amplifier means for amplifying the combined information and pilot signals to a broadcast transmission power level, gain means, located upstream of said power amplifier means, for increasing gain of the information signal in response to a control signal, the broadcast transmission power level of the information signal being dependent upon the gain applied by z5 said gain means, control means for controlling said gain means to maintain the broadcast transmission power level, said control means including sample means for deriving a sample signal containing the combined information and pilot signals from an output of said power amplifier means, isolation means for isolating a pilot-indicative signal from the sample signal and determination means for determining the control signal of said gain means using the pilot-3o indicative signal.
Conveniently, the present invention provides a broadcast transmission system that includes information signal provision means for providing an information signal. Pilot signal provision means provides a pilot signal having predetermined signal characteristics. Combiner means combines the information and pilot signals. Power amplifier means amplify the combined information and power signals to a broadcast transmission power level. Gain means, located upstream of the power amplifier means, increases gain of the information signal in response to a control signal. A broadcast transmission power level of the information signal is dependent upon the gain applied by the gain means. Control means controls the gain means to maintain the broadcast transmission power level. The control means includes sample means for deriving a sample signal containing the combined information and pilot signals from an output of the power amplifier means. The control means includes isolation means for isolating a pilot-indicative signal from the sample signal. The control means also includes determination means for determining the control signal of the gain means using the pilot-indicative signal.
1o The present invention will now be described by way of example, with reference to the accompanying drawings in which:
Fig. 1 is a block diagram of a first embodiment of a system in accordance with the present invention;
Fig. 2 is a block diagram of a second embodiment of a system in accordance with the present invention;
Fig. 3 is a block diagram of a third embodiment of a system in accordance with the present invention; and Fig. 4 is a block diagram of the overall DTV system of either the first or second embodiment.
2o One representation of the present invention is schematically shown in Fig.1 as a digital broadcast transmission system 10 that automatically controls its broadcast transmission power level. Preferably, the system 10 is a digital television ("DTV") system.
Further, the system 10 is preferably a high definition television ("HDTV") system.
The system 10 includes a digital encoder 12 and a digital baseband modulator 14 that are located along a signal stream that proceeds toward a broadcast transmission antenna 16 of the system 10. The encoder 12 is operatively connected to receive a clock signal 18 from a clock 20. Within the encoder 12, the clock signal 18 is used within a process to provide the information signal in digital format. The output ?2 of the encoder 12 is provided to the baseband modulator 14, and, in turn, the output 24 of the modulator is provided as a first input 3o to a summation device 26.
A number of components (not shown in Fig. l) are located upstream of the encoder 12.
Any known and/ or otherwise suitable components may be located upstream of the encoder 12 for generating, processing, and otherwise conveying an information signal to the portion of the system 10 illustrated within Fig. 1. These upstream components are not related to the present invention and are omitted for brevity. Herein, the encoder 22, the baseband modulator 14, and the upstream components are defined to be a means for providing the information signal as the first input to the summation device 26.
A second input 28 to the summation device 26 is a digital pilot signal from a pilot signal source 30. Preferably, the pilot signal 28 is digital representation of a signal at 8.07 MHz and a predetermined amplitude (i.e., its signal characteristics). A combination signal 32 is a digital combination of the information signal 24 (as provided by the baseband modulator 14) and the pilot signal 28. The combination signal 32 is output from the summation device 26 and is provided to a digital-to-analog converter (DAC) 34.
1o The analog combination signal 36 is then provided to an automatic gain control ("AGC" ) component 38. The AGC 38 is controllable via a control signal 40 to adjust the gain applied to the analog combination signal 36. In one embodiment, the control signal 40 has an amplitude value and the applied gain is dependent upon the amplitude value. The output 42 from the AGC 38 is provided to an up-converter 44 that is operatively connected to a local oscillator 45.
The up-converted signal 46 is passed through a bandpass filter 48 and is provided to a power amplifier circuit 50. The amount of amplification imposed by the power amplifier 50 is typically dependent upon the amount of gain imposed by the AGC 38. The output 52 of the power amplifier 50 is provided to the antenna 16.
An electromagnetic broadcast signal 54 that is transmitted from the antenna 16 has a 2o power level related to the power of the output 52 from the power amplifier 50. Thus, the power of the broadcast signal 54 is dependent upon the amplification applied by the power amplifier 50 (and thus the gain applied by the AGC 38). In one example, the desired output power of the broadcast signal 54 emitted from the antenna 16 is 50 (fifty) kilowatts.
1n order to maintain the power of the broadcast signal 54 at its desired value, the output 52 of the power amplifier 50 is sampled to permit determination of the control signal 40 for the AGC 38. Specifically, a sample signal 56 is coupled-off of the power amplifier output 52 and provided to a down-converter 58. The down-converter 58 is operatively connected to the local oscillator 45.
The output 60 of the down-converter 58 is an intermediate frequency signal that 3o represents the sample signal 56, and thus contains both the information signal and the pilot signal. Hereinafter, the intermediate frequency signal 60 is referred to as the IF sample signal 60. The IF sample signal 60 is indicative of the amount of gain/ amplification that has been applied to the information and pilot signals. Hereinafter, the gain/
amplification is referred to as amplification.
TRANSMISSION SYSTEM
The present invention relates to maintenance of a desired broadcast power level, and is particularly directed to maintenance of a broadcast power level of a digital TV ("DTV") transmission system.
In a broadcast communication system, such as a broadcast television or radio system, it is typically desirable to maintain a constant broadcast transmission power level. For example, in a broadcast transmission system which has an output power level of 50 kilowatts, it may be undesirable for the output to vary more than even a few watts of power.
1o Transmission power level is related to the power level of an amplified electrical signal provided to an antenna of the broadcast system. For analog broadcast transmission systems, it is known to monitor the amplified electrical signal provided to the antenna and adjust the system to maintain a desired transmission power level.
One type of analog system is a national television system committee ("NTSC") format system. A technique known as peak of synchronization is currently utilized within the NTSC
system to control the transmission power level of the system. Specifically, a peak amplitude level is monitored and is utilized to determine the power level of the transmission signal. Use of the peak of synchronization technique is possible within such a system because the output signal is rather repetitive and deterministic, thus determination of the output power and control of the output power are readily accomplished.
Digital-based transmission systems offer a marked improvement in quality and quantity of data that can be transmitted. For example, a high definition television ("HDTV") system is a digital (i.e., DTV) system that provides greater sound and picture quality compared to the known analog television systems. One aspect of HDTV systems is that the improvements in 2s sound and picture quality are associated with a need for greater detail information and an increase in the amount of transmitted information. Typically, the information is provided in a Trellis encoded frame format of information.
Contrary to the known analog systems, DTV (e.g., HDTV) systems provide an output that is generally not repetitive and not deterministic. The output of the system is pseudo so random, and in general the output cannot be predicted. Thus, it becomes difficult to utilize the output of the DTV system to control the transmission power level of the system. One approach is to utilize an average output power detector. However, such an approach has limited accuracy ability. The present invention includes a broadcast transmission system comprising signal provision means for providing an information signal and a pilot signal, amplifier means for amplifying the information and pilot signals, control means for controlling the amount amplification using the pilot signal characterized in that said amplifier means includes power amplifier means for amplifying the information and pilot signals to a broadcast transmission s power level gain means, located upstream of said power amplifier means, for increasing gain of the information signal in response to a control signal, the broadcast transmission power level of the information signal being dependent upon the gain applied by said gain means, said control means includes means for controlling said gain means to maintain the broadcast transmission power level constant, said means for controlling said gain means including sample 1o means for deriving a sample signal containing the information and pilot signals from an output of said power amplifier means, isolation means for isolating a pilot-indicative signal from the sample signal, and determination means for determining the control signal using the pilot-indicative signal.
Advantageously the present invention provides a broadcast transmission system that ~5 includes signal provision means for providing an information signal and a pilot signal.
Amplifier means amplify the information and pilot signals. Control means controls the amount of amplification using the pilot signal. The invention also includes a broadcast transmission system comprising information signal provision means for providing an information signal, pilot signal provision means for providing a pilot signal having predefined signal 2o characteristics, combiner means for combining the information and pilot signals, power amplifier means for amplifying the combined information and pilot signals to a broadcast transmission power level, gain means, located upstream of said power amplifier means, for increasing gain of the information signal in response to a control signal, the broadcast transmission power level of the information signal being dependent upon the gain applied by z5 said gain means, control means for controlling said gain means to maintain the broadcast transmission power level, said control means including sample means for deriving a sample signal containing the combined information and pilot signals from an output of said power amplifier means, isolation means for isolating a pilot-indicative signal from the sample signal and determination means for determining the control signal of said gain means using the pilot-3o indicative signal.
Conveniently, the present invention provides a broadcast transmission system that includes information signal provision means for providing an information signal. Pilot signal provision means provides a pilot signal having predetermined signal characteristics. Combiner means combines the information and pilot signals. Power amplifier means amplify the combined information and power signals to a broadcast transmission power level. Gain means, located upstream of the power amplifier means, increases gain of the information signal in response to a control signal. A broadcast transmission power level of the information signal is dependent upon the gain applied by the gain means. Control means controls the gain means to maintain the broadcast transmission power level. The control means includes sample means for deriving a sample signal containing the combined information and pilot signals from an output of the power amplifier means. The control means includes isolation means for isolating a pilot-indicative signal from the sample signal. The control means also includes determination means for determining the control signal of the gain means using the pilot-indicative signal.
1o The present invention will now be described by way of example, with reference to the accompanying drawings in which:
Fig. 1 is a block diagram of a first embodiment of a system in accordance with the present invention;
Fig. 2 is a block diagram of a second embodiment of a system in accordance with the present invention;
Fig. 3 is a block diagram of a third embodiment of a system in accordance with the present invention; and Fig. 4 is a block diagram of the overall DTV system of either the first or second embodiment.
2o One representation of the present invention is schematically shown in Fig.1 as a digital broadcast transmission system 10 that automatically controls its broadcast transmission power level. Preferably, the system 10 is a digital television ("DTV") system.
Further, the system 10 is preferably a high definition television ("HDTV") system.
The system 10 includes a digital encoder 12 and a digital baseband modulator 14 that are located along a signal stream that proceeds toward a broadcast transmission antenna 16 of the system 10. The encoder 12 is operatively connected to receive a clock signal 18 from a clock 20. Within the encoder 12, the clock signal 18 is used within a process to provide the information signal in digital format. The output ?2 of the encoder 12 is provided to the baseband modulator 14, and, in turn, the output 24 of the modulator is provided as a first input 3o to a summation device 26.
A number of components (not shown in Fig. l) are located upstream of the encoder 12.
Any known and/ or otherwise suitable components may be located upstream of the encoder 12 for generating, processing, and otherwise conveying an information signal to the portion of the system 10 illustrated within Fig. 1. These upstream components are not related to the present invention and are omitted for brevity. Herein, the encoder 22, the baseband modulator 14, and the upstream components are defined to be a means for providing the information signal as the first input to the summation device 26.
A second input 28 to the summation device 26 is a digital pilot signal from a pilot signal source 30. Preferably, the pilot signal 28 is digital representation of a signal at 8.07 MHz and a predetermined amplitude (i.e., its signal characteristics). A combination signal 32 is a digital combination of the information signal 24 (as provided by the baseband modulator 14) and the pilot signal 28. The combination signal 32 is output from the summation device 26 and is provided to a digital-to-analog converter (DAC) 34.
1o The analog combination signal 36 is then provided to an automatic gain control ("AGC" ) component 38. The AGC 38 is controllable via a control signal 40 to adjust the gain applied to the analog combination signal 36. In one embodiment, the control signal 40 has an amplitude value and the applied gain is dependent upon the amplitude value. The output 42 from the AGC 38 is provided to an up-converter 44 that is operatively connected to a local oscillator 45.
The up-converted signal 46 is passed through a bandpass filter 48 and is provided to a power amplifier circuit 50. The amount of amplification imposed by the power amplifier 50 is typically dependent upon the amount of gain imposed by the AGC 38. The output 52 of the power amplifier 50 is provided to the antenna 16.
An electromagnetic broadcast signal 54 that is transmitted from the antenna 16 has a 2o power level related to the power of the output 52 from the power amplifier 50. Thus, the power of the broadcast signal 54 is dependent upon the amplification applied by the power amplifier 50 (and thus the gain applied by the AGC 38). In one example, the desired output power of the broadcast signal 54 emitted from the antenna 16 is 50 (fifty) kilowatts.
1n order to maintain the power of the broadcast signal 54 at its desired value, the output 52 of the power amplifier 50 is sampled to permit determination of the control signal 40 for the AGC 38. Specifically, a sample signal 56 is coupled-off of the power amplifier output 52 and provided to a down-converter 58. The down-converter 58 is operatively connected to the local oscillator 45.
The output 60 of the down-converter 58 is an intermediate frequency signal that 3o represents the sample signal 56, and thus contains both the information signal and the pilot signal. Hereinafter, the intermediate frequency signal 60 is referred to as the IF sample signal 60. The IF sample signal 60 is indicative of the amount of gain/ amplification that has been applied to the information and pilot signals. Hereinafter, the gain/
amplification is referred to as amplification.
It is to be recalled that the information signal is pseudo random, and thus it is difficult to directly determine the amount of amplification that is applied to the information signal.
However, the amount of amplification that is applied to the pilot signal is readily determined.
Since the same amount of amplification is applied to both the information signal and the pilot signal (i. e., the information and pilot signals are combined within the summation device 26), the determination of the amount of amplification applied to the pilot signal is useful to control the amplification. The present invention provides for such determination and control.
In order to provide the correct system amplification, an appropriate voltage must be applied to the AGC 38. This control voltage is related to the pilot level in the return sample o signal 60. Specifically, the AGC control voltage should be inversely proportional to the pilot level. In the embodiment of Fig. l, the IF sample signal 60 contains 8VSB
modulation centered at the symbol rate of 10.76 MHz, with a pilot frequency of 8.07 MHz. The signal 60 can be described mathematically by:
F ~t ~ _ ~ p ~t ~ + s ~t ~~ cos ~2 ~ f o t + 8 where:
p(t) = the pilot signal;
s(t) = the baseband SVSB signal;
fp = pilot frequency (i.e., 8.07 MHz); and 8 = an arbitrary phase shift.
2o The IF sample signal must be processed so that the energy of the pilot signal p(t) can be isolated from the rest of the signal. This is accomplished by mvdng the signal with a phase-coherent and phase-aligned L.O. whose frequency is identical to the pilot frequency. In the embodiment of Fig.1, the IF sample signal 60 is provided as a first input to a mixer component 62.
A second input 64 to the mixer 62 is a signal that is associated with the pilot frequency (i.e., 8.07 MHz). In the example shown in Fig. 1, the signal 64 with the pilot associated frequency is derived from the clock 20 that is operatively connected to the encoder 12, the baseband modulator 14, and the digital pilot source 30. In one embodiment, the clock 20 provides a signal at 43.04 MHz. In order to provide the pilot frequency (i.e., 8.07 MHz), the so output of the clock 20 is provided to a phase lock loop ("PLL") component 66 that imposes a multiplication factor of three (3) and division factor of sixteen (16).
Further, the phase of the pilot-associated frequency signal 64 is phase-adjusted by a phase-adjust component 68 prior to provision of the signal 64 as the second input to the mixer 62. The signal 64 can be described mathematically by:
cos (2 ~z f o t +
where:
fo = pilot frequency (i.e., 8.07 MHz); and ~ = the phase angle controlled by the phase adjust component 68.
The output 70 of the mixer 62 is a signal that is given as:
~p ~t ) + s (t )~cos (6 - ~ ) + cos (2 ~ 2 f o t + B + ~ ~~
Because the information signal s(t) is pseudo-random signal whose average value is zero, 1o the DC component of the signal is indicative of the amount of amplification applied to the pilot signal as the pilot signal passes in combination with the information signal through the AGC
38 and the power amplifier 50. The mixer output 70 is provided to a low-pass filter 72. The low-pass filter 72 passes a range of very low frequencies. Specifically, it is desired that the low-pass filter 72 pass only a DC component. The resultant output of the low-pass filter is:
p (t )~os (e - ~ ) The pilot signal level p (t) is a slowly varying signal versus time due to thermal variations and within the AGC bandwidth of the system. For measurements over a short period of time relative to these long-term fluctuations, it can be considered as a DC signal.
Thus, the output 74 of the low-pass filter 72 is a DC signal proportional to the pilot amplification through the 2o system and scaled by a term proportional to the cosine of the phase difference of the mixer input signals 64 and 60. When the phase difference is zero (i.e., A = ~ ) , the low-pass filter output signal is maximized and is proportional only to the sample pilot level.
The output or DC signal 74 is provided to a hold circuit 76 whose output is the control signal 40. In other words, the DC signal 74 is utilized as a control for the AGC 38. The hold 25 circuit 76 latches the value of the DC signal 74 and utilizes the latched value for the control signal 40.
Control of the hold circuit 76 is provided by a maximum amplitude detection component 78 that is operatively coupled to receive the DC signal 74 that is the output of the low-pass filter 72. The maximum amplitude detection component 78 monitors the DC signal 74 to determine 3o the maximum DC value. This occurs when the pilot phase of the same signal and the pilot associated frequency signal are identical (i.e., B = ~) . When the maximum is detected, the maxinnum amplitude detection component 78 provides a command signal 80 that causes the hold circuit 76 to latch the value for use as the control signal 40.
In order to compensate for phase difference between the pilot component within the IF
sample signal 60 and the pilot-associated frequency signal 64 provided from the clock 20 via the PLL 66, the ma~cimum amplitude detection component 78 provides a control signal 82 to the phase-adjust component 68. Accordingly, the phase difference is negated. The result of negating the phase difference results in a true indication of the amount of amplification applied to the pilot.
The maximum amplitude detection component 78 routinely monitors the DC signal and makes a determination as to whether the amount of imposed amplification has deviated o from a desired amount. Any significant change in the amount of amplification results in the ma~cimum amplitude detection component 78 providing the command signal 80 to cause the hold circuit 76 to "update" the latched value from the DC signal 74.
Accordingly, the value of the control signal 40 is changed. In response to the change in the control signal 40, the gain provided by the AGC 38 is adjusted. The control signal 40 will be inversely proportional to the gain of AGC 38. When the value of the signal 40 goes up, the gain of the AGC
38 will go down and vice versa.
Fig 1 shows the control signal 40 (i.e., the signal indicative of the amount of amplification provided to the pilot signal) is done in an analog format. A second embodiment is shown in Fig. 2, but control of the amount of amplification (e.g., determination and use of a signal 2o indicative of amplification imposed upon a pilot signal) is done in a digital format.
Similar to the embodiment of Fig.1, the system 110 of the second embodiment (Fig. 2) has an information signal that is provided via a digital encoder 112 and a digital modulator 114 as a first input 118 of a summation device 120. A second input 122 to the summation device 120 is a pilot signal (a digital representation of a signal at 8.07 MHz and a predetermined amplitude - i.e., its signal characteristics) provided from a pilot source 124. The output 126 of the summation device 120 is a combination signal containing the information signal and the pilot signal and is provided as an input to an automatic gain control (AGC) component 128. The gain imposed upon the combined signal by the AGC 128 is controlled via a control signal 130. In one embodiment, the control signal 130 has an amplitude value and the imposed gain is dependent so upon the amplitude value.
The output 132 of the AGC 128 is provided to a digital-to-analog converter ("DAC") 134.
The analog signal 136 output from the DAC 134 is up-converted by an up-converter 138 driven by a local oscillator 150. The output 140 of the up-converter mixer 138 is applied to a bandpass filter 142. A power amplifier 152 amplifies the up-converted, filtered signal 144. The amplified electrical signal 156 (which contains both the information and pilot signals) is output to the broadcast antenna 158. In turn, the antenna transmits a broadcast signal 159.
In order to provide the control signal 130 for the AGC 128 (i.e., to control the power of the broadcast signal 159), the output 156 of the power amplifier 152 is coupled-off to provide a sample signal 160. The sample signal 160 is indicative of the amplified information and pilot signals. The sample signal 160 is provided to a coherent down-converter 162 that is driven by the local oscillator 150. The output 163 of the down-converter 162 is an intermediate frequency signal that is provided to a low-pass filter 164. In turn, the filter output 165 is provided to an analog-to-digital ("A/D") converter 166.
o The output 168 of the A/D converter 166 is a digital representation of the sample signal 160, and thus contains the information pilot signals. Hereinafter, the output 168 is referred to as the digital sample signal 168. Further, the digital sample signal 168 is indicative of the amount of gain/ amplification that has been applied to the information and pilot signals.
Hereinafter, the gain/ amplification is referred to as amplification.
The digital sample signal 168 is provided as a first input to a mixer component 170. A
second input 172 of the mixer 170 is provided by the pilot signal source 124.
A phase-adjust component 174 adjusts the phase to compensate for phase difference.
Like the analog version of Fig.1, the digital sample signal input to the mixer 170 contains 8VSB modulation centered at the symbol rate of 10.76 MHz, with a pilot frequency of 8.07 MHz.
2o The digital sample signal can be described mathematically by:
F~nT ~_ ~p~nT ~+s~nT ~~cos ~2~cfonT +B~
where:
T = the symbol period;
p(nT) = the pilot signal;
s(nT) = the baseband 8VSB signal;
fo = pilot frequency (i.e., 8.07 MHz); and 8 = an arbitrary phase shift.
The second input to the mixer 170 is the digital pilot signal with phase adjustment and can be described mathematically by:
so cos ~2 ~ f o nT + ~
where:
f0 = pilot frequency (i.e., 8.07 MHz); and = the phase angle controlled by the phase adjust component 174.
The output 176 of the mixer 170 contains the baseband 8VSB signal along with a DC
term that is proportional to the pilot level. The signal is given by:
s ~p ~nT ~ + s ~NT ~~cos ~B - ~ ~ + cos ~4 ~cfo nT + B + ~ ~~
Since the average energy of s(nT) is zero, the pilot level can be extracted from the signal by taking a long term average of the data stream. A moving average component 178 performs this averaging function. The resultant output of component 178 will only be proportional to the pilot scaled by the cosine of the phase difference between the digital sample signal and the 1o digital pilot signal. This is given by:
p o cos where:
po is the average value of the pilot level.
The phase of the digital pilot signal must be aligned before the correct pilot level po can 15 be obtained. This is accomplished by the AGC 128 and a controller 180, which receives the output 182 (average pilot value Po) of the moving average component 178. If the phase-adjust component 174 is implemented in a look-up-table (LUT), the controller 180 can increment the address until a maximum output from the moving average is obtained. This occurs when the phase difference is between the digital sample signal and the digital pilot signal is zero 20 (i.e., A = ~ ) . Algorithmic or digital synthesis can be used to generate the appropriate phase adjustment for the phase-adjustment component 174. Once a maximum output has been achieved from the phase-adjustment component 174, the average pilot value po is then compared to the known pilot level. If the level is too large the controller 180 reduces the gain of the AGC 128. If the level is too small, the AGC gain is increased.
25 Thus, the system 110 of Fig. 2 controls its output transmission power via use of the pilot signal. Further, it is to be appreciated that control of the AGC 128, and thus control of the transmission power, is performed in the digital format. Specifically, the AGC
128, the mixer 170, the moving average component 178, and the controller 180 are digital components.
Similar to the embodiment of Fig. 2, in the system 210 of the third embodiment control 3o is provided in a digital format. A digital encoder 212 outputs a signal 214 with symbols at a 10.76 MHz rate. A multiplier 216 multiplies the signal 214 with a complex vector 218 (e.g., 2.69 MHz). The vector 218 is provided via a clock 220 (e.g., 43.04 MHz) and a divider component 222 (e.g., divide by 4). The multiplication effectively down converts the signal 214 so that the output 224 is centered at DC.
The output signal 224 is filtered by a complex root-raised-cosine filter 226 (RRC-traditionally called a Nyquist filter). This sets the 3 dB shoulders of an output signal 228 at -2.69 MHz and +2.69MHz. A pilot tone 230 is added at -2.69 MHz (the negative frequency is accommodated using complex signal) via a component 232. An output signal 234 is interpolated via a component 236 to a complex data rate of 21.52 MHz. A non-linear corrector 238 provides correction. A complex up-conversion is provided using a half-band filter 240 and a complex up-converter 242 to provide a signal 244 with a real IF centered at 10.76 MHz, which places the pilot at 8.07 MHz (i.e.,10.76-2.69=8.07 MHz). The signal 244 is then provided to a 1o sequence of an equalizer 246, an AGC 248, a DAC 250, an up-converter 252, and a power amplifier 254.
On the return path, a sample signal 256 is provided to a down-converter 258 and the sample is digitized via an A/D converter 260. The digital output 262 is down-converted to baseband by a 10.76 MHz complex carrier via component 264. The output signal 266 is filtered via a half-band filter 268, which can also perform complex down conversion.
The baseband signal 270 is decimated by 2 (complex data rate is now 10.76 MHz) via component 272.
Finally, the down-converted decimated complex baseband signal 274 is up-converted with a complex -2.69 MHz tone 276 via component 278. This places the pilot at DC. The output signal 280 is low-pass filtered, via filter 282, sufficiently so that only the DC energy 284 is left (this is done by a long term average).
The DC value 284 is applied to a controller 286. In turn, control signals are provided to the AGC 248 and a phase control 288. The phase control 288 adjusts the phase of the -2.69 MHz complex earner 276 until the DC average of the pilot energy 284 is maximized.
The maximized DC pilot level is then used to control the AGC 248. If the pilot level is low, the AGC gain is increased (AGC is simply a multiplier). If the pilot level is high, the AGC
gain is decreased.
Fig. 4 is an example of the overall system for either the first embodiment (Fig. 1), the second embodiment (Fig. 2), or the third embodiment (Fig. 3). Specifically, the components of the systems shown within Figs. 1, 2, and 3 are components at the SVSB exciter 300 and the transmitter 302.
3o From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.
A high definition television broadcast transmission system includes a feature of maintaining a constant transmission output power. In one example, a system includes components, such as a digital encoder (12), for providing an information signal. A pilot source (30) provides a pilot signal. A combiner (26) combines the information and pilot signals. A
power amplifier (50) amplifies the combined information and pilot signals to a broadcast transmission power level. An automatic gain control (38), located upstream of the amplifier s (50), increases gain of the information signal in response to a control signal. The broadcast transmission power level of the information signal is dependent upon the gain applied by the gain control. In order to maintain the broadcast transmission power level, a sample signal, which contains the combined information and pilot signals, is derived from an output of the power amplifier (50). A pilot-indicative signal is isolated from the sample signal. The control 1o signal for the gain control (38) is determined using the pilot-indicative signal. The components for the isolation and determination may be either analog or digital components.
However, the amount of amplification that is applied to the pilot signal is readily determined.
Since the same amount of amplification is applied to both the information signal and the pilot signal (i. e., the information and pilot signals are combined within the summation device 26), the determination of the amount of amplification applied to the pilot signal is useful to control the amplification. The present invention provides for such determination and control.
In order to provide the correct system amplification, an appropriate voltage must be applied to the AGC 38. This control voltage is related to the pilot level in the return sample o signal 60. Specifically, the AGC control voltage should be inversely proportional to the pilot level. In the embodiment of Fig. l, the IF sample signal 60 contains 8VSB
modulation centered at the symbol rate of 10.76 MHz, with a pilot frequency of 8.07 MHz. The signal 60 can be described mathematically by:
F ~t ~ _ ~ p ~t ~ + s ~t ~~ cos ~2 ~ f o t + 8 where:
p(t) = the pilot signal;
s(t) = the baseband SVSB signal;
fp = pilot frequency (i.e., 8.07 MHz); and 8 = an arbitrary phase shift.
2o The IF sample signal must be processed so that the energy of the pilot signal p(t) can be isolated from the rest of the signal. This is accomplished by mvdng the signal with a phase-coherent and phase-aligned L.O. whose frequency is identical to the pilot frequency. In the embodiment of Fig.1, the IF sample signal 60 is provided as a first input to a mixer component 62.
A second input 64 to the mixer 62 is a signal that is associated with the pilot frequency (i.e., 8.07 MHz). In the example shown in Fig. 1, the signal 64 with the pilot associated frequency is derived from the clock 20 that is operatively connected to the encoder 12, the baseband modulator 14, and the digital pilot source 30. In one embodiment, the clock 20 provides a signal at 43.04 MHz. In order to provide the pilot frequency (i.e., 8.07 MHz), the so output of the clock 20 is provided to a phase lock loop ("PLL") component 66 that imposes a multiplication factor of three (3) and division factor of sixteen (16).
Further, the phase of the pilot-associated frequency signal 64 is phase-adjusted by a phase-adjust component 68 prior to provision of the signal 64 as the second input to the mixer 62. The signal 64 can be described mathematically by:
cos (2 ~z f o t +
where:
fo = pilot frequency (i.e., 8.07 MHz); and ~ = the phase angle controlled by the phase adjust component 68.
The output 70 of the mixer 62 is a signal that is given as:
~p ~t ) + s (t )~cos (6 - ~ ) + cos (2 ~ 2 f o t + B + ~ ~~
Because the information signal s(t) is pseudo-random signal whose average value is zero, 1o the DC component of the signal is indicative of the amount of amplification applied to the pilot signal as the pilot signal passes in combination with the information signal through the AGC
38 and the power amplifier 50. The mixer output 70 is provided to a low-pass filter 72. The low-pass filter 72 passes a range of very low frequencies. Specifically, it is desired that the low-pass filter 72 pass only a DC component. The resultant output of the low-pass filter is:
p (t )~os (e - ~ ) The pilot signal level p (t) is a slowly varying signal versus time due to thermal variations and within the AGC bandwidth of the system. For measurements over a short period of time relative to these long-term fluctuations, it can be considered as a DC signal.
Thus, the output 74 of the low-pass filter 72 is a DC signal proportional to the pilot amplification through the 2o system and scaled by a term proportional to the cosine of the phase difference of the mixer input signals 64 and 60. When the phase difference is zero (i.e., A = ~ ) , the low-pass filter output signal is maximized and is proportional only to the sample pilot level.
The output or DC signal 74 is provided to a hold circuit 76 whose output is the control signal 40. In other words, the DC signal 74 is utilized as a control for the AGC 38. The hold 25 circuit 76 latches the value of the DC signal 74 and utilizes the latched value for the control signal 40.
Control of the hold circuit 76 is provided by a maximum amplitude detection component 78 that is operatively coupled to receive the DC signal 74 that is the output of the low-pass filter 72. The maximum amplitude detection component 78 monitors the DC signal 74 to determine 3o the maximum DC value. This occurs when the pilot phase of the same signal and the pilot associated frequency signal are identical (i.e., B = ~) . When the maximum is detected, the maxinnum amplitude detection component 78 provides a command signal 80 that causes the hold circuit 76 to latch the value for use as the control signal 40.
In order to compensate for phase difference between the pilot component within the IF
sample signal 60 and the pilot-associated frequency signal 64 provided from the clock 20 via the PLL 66, the ma~cimum amplitude detection component 78 provides a control signal 82 to the phase-adjust component 68. Accordingly, the phase difference is negated. The result of negating the phase difference results in a true indication of the amount of amplification applied to the pilot.
The maximum amplitude detection component 78 routinely monitors the DC signal and makes a determination as to whether the amount of imposed amplification has deviated o from a desired amount. Any significant change in the amount of amplification results in the ma~cimum amplitude detection component 78 providing the command signal 80 to cause the hold circuit 76 to "update" the latched value from the DC signal 74.
Accordingly, the value of the control signal 40 is changed. In response to the change in the control signal 40, the gain provided by the AGC 38 is adjusted. The control signal 40 will be inversely proportional to the gain of AGC 38. When the value of the signal 40 goes up, the gain of the AGC
38 will go down and vice versa.
Fig 1 shows the control signal 40 (i.e., the signal indicative of the amount of amplification provided to the pilot signal) is done in an analog format. A second embodiment is shown in Fig. 2, but control of the amount of amplification (e.g., determination and use of a signal 2o indicative of amplification imposed upon a pilot signal) is done in a digital format.
Similar to the embodiment of Fig.1, the system 110 of the second embodiment (Fig. 2) has an information signal that is provided via a digital encoder 112 and a digital modulator 114 as a first input 118 of a summation device 120. A second input 122 to the summation device 120 is a pilot signal (a digital representation of a signal at 8.07 MHz and a predetermined amplitude - i.e., its signal characteristics) provided from a pilot source 124. The output 126 of the summation device 120 is a combination signal containing the information signal and the pilot signal and is provided as an input to an automatic gain control (AGC) component 128. The gain imposed upon the combined signal by the AGC 128 is controlled via a control signal 130. In one embodiment, the control signal 130 has an amplitude value and the imposed gain is dependent so upon the amplitude value.
The output 132 of the AGC 128 is provided to a digital-to-analog converter ("DAC") 134.
The analog signal 136 output from the DAC 134 is up-converted by an up-converter 138 driven by a local oscillator 150. The output 140 of the up-converter mixer 138 is applied to a bandpass filter 142. A power amplifier 152 amplifies the up-converted, filtered signal 144. The amplified electrical signal 156 (which contains both the information and pilot signals) is output to the broadcast antenna 158. In turn, the antenna transmits a broadcast signal 159.
In order to provide the control signal 130 for the AGC 128 (i.e., to control the power of the broadcast signal 159), the output 156 of the power amplifier 152 is coupled-off to provide a sample signal 160. The sample signal 160 is indicative of the amplified information and pilot signals. The sample signal 160 is provided to a coherent down-converter 162 that is driven by the local oscillator 150. The output 163 of the down-converter 162 is an intermediate frequency signal that is provided to a low-pass filter 164. In turn, the filter output 165 is provided to an analog-to-digital ("A/D") converter 166.
o The output 168 of the A/D converter 166 is a digital representation of the sample signal 160, and thus contains the information pilot signals. Hereinafter, the output 168 is referred to as the digital sample signal 168. Further, the digital sample signal 168 is indicative of the amount of gain/ amplification that has been applied to the information and pilot signals.
Hereinafter, the gain/ amplification is referred to as amplification.
The digital sample signal 168 is provided as a first input to a mixer component 170. A
second input 172 of the mixer 170 is provided by the pilot signal source 124.
A phase-adjust component 174 adjusts the phase to compensate for phase difference.
Like the analog version of Fig.1, the digital sample signal input to the mixer 170 contains 8VSB modulation centered at the symbol rate of 10.76 MHz, with a pilot frequency of 8.07 MHz.
2o The digital sample signal can be described mathematically by:
F~nT ~_ ~p~nT ~+s~nT ~~cos ~2~cfonT +B~
where:
T = the symbol period;
p(nT) = the pilot signal;
s(nT) = the baseband 8VSB signal;
fo = pilot frequency (i.e., 8.07 MHz); and 8 = an arbitrary phase shift.
The second input to the mixer 170 is the digital pilot signal with phase adjustment and can be described mathematically by:
so cos ~2 ~ f o nT + ~
where:
f0 = pilot frequency (i.e., 8.07 MHz); and = the phase angle controlled by the phase adjust component 174.
The output 176 of the mixer 170 contains the baseband 8VSB signal along with a DC
term that is proportional to the pilot level. The signal is given by:
s ~p ~nT ~ + s ~NT ~~cos ~B - ~ ~ + cos ~4 ~cfo nT + B + ~ ~~
Since the average energy of s(nT) is zero, the pilot level can be extracted from the signal by taking a long term average of the data stream. A moving average component 178 performs this averaging function. The resultant output of component 178 will only be proportional to the pilot scaled by the cosine of the phase difference between the digital sample signal and the 1o digital pilot signal. This is given by:
p o cos where:
po is the average value of the pilot level.
The phase of the digital pilot signal must be aligned before the correct pilot level po can 15 be obtained. This is accomplished by the AGC 128 and a controller 180, which receives the output 182 (average pilot value Po) of the moving average component 178. If the phase-adjust component 174 is implemented in a look-up-table (LUT), the controller 180 can increment the address until a maximum output from the moving average is obtained. This occurs when the phase difference is between the digital sample signal and the digital pilot signal is zero 20 (i.e., A = ~ ) . Algorithmic or digital synthesis can be used to generate the appropriate phase adjustment for the phase-adjustment component 174. Once a maximum output has been achieved from the phase-adjustment component 174, the average pilot value po is then compared to the known pilot level. If the level is too large the controller 180 reduces the gain of the AGC 128. If the level is too small, the AGC gain is increased.
25 Thus, the system 110 of Fig. 2 controls its output transmission power via use of the pilot signal. Further, it is to be appreciated that control of the AGC 128, and thus control of the transmission power, is performed in the digital format. Specifically, the AGC
128, the mixer 170, the moving average component 178, and the controller 180 are digital components.
Similar to the embodiment of Fig. 2, in the system 210 of the third embodiment control 3o is provided in a digital format. A digital encoder 212 outputs a signal 214 with symbols at a 10.76 MHz rate. A multiplier 216 multiplies the signal 214 with a complex vector 218 (e.g., 2.69 MHz). The vector 218 is provided via a clock 220 (e.g., 43.04 MHz) and a divider component 222 (e.g., divide by 4). The multiplication effectively down converts the signal 214 so that the output 224 is centered at DC.
The output signal 224 is filtered by a complex root-raised-cosine filter 226 (RRC-traditionally called a Nyquist filter). This sets the 3 dB shoulders of an output signal 228 at -2.69 MHz and +2.69MHz. A pilot tone 230 is added at -2.69 MHz (the negative frequency is accommodated using complex signal) via a component 232. An output signal 234 is interpolated via a component 236 to a complex data rate of 21.52 MHz. A non-linear corrector 238 provides correction. A complex up-conversion is provided using a half-band filter 240 and a complex up-converter 242 to provide a signal 244 with a real IF centered at 10.76 MHz, which places the pilot at 8.07 MHz (i.e.,10.76-2.69=8.07 MHz). The signal 244 is then provided to a 1o sequence of an equalizer 246, an AGC 248, a DAC 250, an up-converter 252, and a power amplifier 254.
On the return path, a sample signal 256 is provided to a down-converter 258 and the sample is digitized via an A/D converter 260. The digital output 262 is down-converted to baseband by a 10.76 MHz complex carrier via component 264. The output signal 266 is filtered via a half-band filter 268, which can also perform complex down conversion.
The baseband signal 270 is decimated by 2 (complex data rate is now 10.76 MHz) via component 272.
Finally, the down-converted decimated complex baseband signal 274 is up-converted with a complex -2.69 MHz tone 276 via component 278. This places the pilot at DC. The output signal 280 is low-pass filtered, via filter 282, sufficiently so that only the DC energy 284 is left (this is done by a long term average).
The DC value 284 is applied to a controller 286. In turn, control signals are provided to the AGC 248 and a phase control 288. The phase control 288 adjusts the phase of the -2.69 MHz complex earner 276 until the DC average of the pilot energy 284 is maximized.
The maximized DC pilot level is then used to control the AGC 248. If the pilot level is low, the AGC gain is increased (AGC is simply a multiplier). If the pilot level is high, the AGC
gain is decreased.
Fig. 4 is an example of the overall system for either the first embodiment (Fig. 1), the second embodiment (Fig. 2), or the third embodiment (Fig. 3). Specifically, the components of the systems shown within Figs. 1, 2, and 3 are components at the SVSB exciter 300 and the transmitter 302.
3o From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.
A high definition television broadcast transmission system includes a feature of maintaining a constant transmission output power. In one example, a system includes components, such as a digital encoder (12), for providing an information signal. A pilot source (30) provides a pilot signal. A combiner (26) combines the information and pilot signals. A
power amplifier (50) amplifies the combined information and pilot signals to a broadcast transmission power level. An automatic gain control (38), located upstream of the amplifier s (50), increases gain of the information signal in response to a control signal. The broadcast transmission power level of the information signal is dependent upon the gain applied by the gain control. In order to maintain the broadcast transmission power level, a sample signal, which contains the combined information and pilot signals, is derived from an output of the power amplifier (50). A pilot-indicative signal is isolated from the sample signal. The control 1o signal for the gain control (38) is determined using the pilot-indicative signal. The components for the isolation and determination may be either analog or digital components.
Claims (9)
1. A broadcast transmission system comprising information signal provision means (12, 14; 112, 114; 212, 214, 216) for providing an information signal (24; 118; 228), a pilot signal provision means (30; 124) for providing a pilot signal (28; 122; 230) having predefined signal characteristics, summation means (26; 120; 232) for combining the information signal (24; 118; 228) and pilot signal (28; 122; 230) into a combination signal (32; 126; 234), power amplifier means (50; 152; 254) for amplifying the combination signal (32; 126;
234) to a broadcast transmission power level, gain means (38; 128; 248) located upstream of the power amplifier means (50; 152; 254) for adjusting the gain applied to the combination signal (32; 126; 234), and control means for controlling the gain means (38; 128; 248) to maintain the broadcast transmission power level constant, the control means including sample means (45,58; 150, 162, 164, 166; 258, 260, 264, 268, 272) for deriving a sample signal (60; 168; 274) containing the combined information and pilot signals from an output (52; 156) of the power amplifier means (50; 152; 254), isolation means (58, 62, 72; 170, 178; 278, 282) for isolating a pilot-indicative signal (74; 182; 284) from the sample signal (60; 168; 274) and determination means (76, 78; 180; 286) for determining a control signal (40;130) of the gain means (38; 128; 248) using the pilot-indicative signal (74; 182; 284), which system is characterised in that: the pilot signal (28; 122; 230) has a predetermined pilot frequency; the isolation means (62, 72; 170, 178; 278, 282) includes combiner means (62; 170; 278) for combining the sample signal (60; 168; 274) with a signal (64; 172; 276) having the predetermined pilot frequency and for providing an output signal (70; 176; 280); and means (72; 178; 282) for filtering the output signal (70; 176; 280) of the combiner means (62; 170;
278) to provide the pilot-indicative signal (74; 182; 284) as a DC signal having a magnitude indicating the broadcast transmission power level.
234) to a broadcast transmission power level, gain means (38; 128; 248) located upstream of the power amplifier means (50; 152; 254) for adjusting the gain applied to the combination signal (32; 126; 234), and control means for controlling the gain means (38; 128; 248) to maintain the broadcast transmission power level constant, the control means including sample means (45,58; 150, 162, 164, 166; 258, 260, 264, 268, 272) for deriving a sample signal (60; 168; 274) containing the combined information and pilot signals from an output (52; 156) of the power amplifier means (50; 152; 254), isolation means (58, 62, 72; 170, 178; 278, 282) for isolating a pilot-indicative signal (74; 182; 284) from the sample signal (60; 168; 274) and determination means (76, 78; 180; 286) for determining a control signal (40;130) of the gain means (38; 128; 248) using the pilot-indicative signal (74; 182; 284), which system is characterised in that: the pilot signal (28; 122; 230) has a predetermined pilot frequency; the isolation means (62, 72; 170, 178; 278, 282) includes combiner means (62; 170; 278) for combining the sample signal (60; 168; 274) with a signal (64; 172; 276) having the predetermined pilot frequency and for providing an output signal (70; 176; 280); and means (72; 178; 282) for filtering the output signal (70; 176; 280) of the combiner means (62; 170;
278) to provide the pilot-indicative signal (74; 182; 284) as a DC signal having a magnitude indicating the broadcast transmission power level.
2. A system as claimed in claim 1, wherein the control means operates in analog format, the combiner means (62) mixes the pilot frequency signal (64) with the sample signal (60) to produce the output signal (70) of the combiner means (62), and the filtering means is a low-pass filter (72) which filters the output signal (70) of the combiner means (62) to provide the DC pilot-indicative signal (74).
3. A system as claimed in claim 2 wherein: the determination means (76, 78) includes detection means (78) for detecting the amplitude of the pilot-indicative signal (74) and hold means (76) controlled by the detection means (78) to provide the control signal (40) for the gain means (38) in response to detection of a maximum amplitude of the pilot-indicative signal by the detection means (78); the isolation means includes phase means (68) for adjusting the phase of the pilot frequency signal (64) prior to combination with the sample signal (60) by the combiner means (62); and the detection means {78) controls the phase means (68) in response to the detected amplitude of the pilot-indicative signal (74).
4. A system as claimed in claim 3 wherein the sample means includes a down converter (58) connected to a local oscillator (45) and coupled to sample the output (52) of the power amplifier (50) for providing an analog sample signal (60) to the combiner means (62).
5. A system as claimed in claim 1 wherein: the control means operates in digital format; the output signal (182; 284) of the filtering means (178; 282) is received by a controller (180; 286) which provides the control signal (130) for the gain means (128; 248); a phase-adjusting means (174; 288) adjusts the phase of the pilot frequency signal (172; 276) prior to combination thereof with the sample signal (168; 274) by the combiner means (170; 278); and the controller (180; 286) controls the phase-adjusting means (174; 288) to obtain a maximum output from the processing means (178; 282).
6. A system as claimed in claim 5 wherein the filtering means is a moving average means.(178).
7. A system as claimed in claim 5 wherein the filtering means is a long term averaging means (282).
8. A system as claimed in claim 4 wherein the sample means includes a down converter (162; 258) connected to a local oscillator (45) and coupled to sample the output (156) of the power amplifier (152, 254), a low-pass filter (164; 268) and an analogue to digital converter (166; 260) being connected between the down converter (162; 258) and the combiner means (170; 278) for providing a digital sample signal (168; 274) to the combiner means (170; 278).
9. A system as claimed in any preceding claim including clock means (20;
220) for providing a clock signal (18) for use in the information signal provision means (12, 14; 112, 114) and for use in providing the pilot frequency signal (64; 172; 276).
220) for providing a clock signal (18) for use in the information signal provision means (12, 14; 112, 114) and for use in providing the pilot frequency signal (64; 172; 276).
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US33834599A | 1999-06-22 | 1999-06-22 | |
US09/338,345 | 1999-06-22 | ||
PCT/US2000/017254 WO2000079713A2 (en) | 1999-06-22 | 2000-06-22 | Digital broadcast transmission system comprising a power control system using a pilot signal |
Publications (1)
Publication Number | Publication Date |
---|---|
CA2374255A1 true CA2374255A1 (en) | 2000-12-28 |
Family
ID=23324447
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002374255A Abandoned CA2374255A1 (en) | 1999-06-22 | 2000-06-22 | Digital broadcast transmission system comprising a power control system using a pilot signal |
Country Status (3)
Country | Link |
---|---|
AU (1) | AU5633600A (en) |
CA (1) | CA2374255A1 (en) |
WO (1) | WO2000079713A2 (en) |
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DE102018105040A1 (en) | 2017-07-31 | 2019-01-31 | Schaeffler Technologies AG & Co. KG | fluid arrangement |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
FR2532802B1 (en) * | 1982-09-07 | 1986-02-14 | Lignes Telegraph Telephon | INFORMATION TRANSMISSION SYSTEM COMPRISING A DEVICE FOR REGULATING INFORMATION LEVELS |
US5113525A (en) * | 1989-11-06 | 1992-05-12 | Mitsubishi Denki Kabushiki Kaisha | Linear-modulation type radio transmitter |
-
2000
- 2000-06-22 CA CA002374255A patent/CA2374255A1/en not_active Abandoned
- 2000-06-22 AU AU56336/00A patent/AU5633600A/en not_active Abandoned
- 2000-06-22 WO PCT/US2000/017254 patent/WO2000079713A2/en active Application Filing
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AU5633600A (en) | 2001-01-09 |
WO2000079713A3 (en) | 2001-06-14 |
WO2000079713A2 (en) | 2000-12-28 |
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