JP2011055125A - Signal compensation device, signal compensation method, signal compensation program, computer readable recording medium, and communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a signal compensation device which is capable of extracting a desired wave free from the influence of nonlinear distortion of a signal amplifier. <P>SOLUTION: A signal compensation device 8 is used for a communication system wherein a superposition signal wherein an IB signal transmitted from a first station and an OB signal different from the IB signal, which is transmitted from a second station, are superposed one over the other is transmitted to the second station from a relay station including TWTA, and the signal compensation device inputs a replica signal being a replica of the OB signal, to a nonlinear compensation model wherein input/output characteristics of an output signal to an input signal show input/output characteristics of TWTA including a linear region and a nonlinear region, to generate a compensated replica signal. Therefore, signal deterioration of the desired wave (the IB signal) is considerably reduced by the signal compensation device 8. The signal compensation device 8 is applicable to an unnecessary wave demodulation system as well as a delay detection system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  In the present invention, the first station transmission signal transmitted from the first station and the second station transmission signal which is a signal different from the first station transmission signal and transmitted from the second station are superimposed. The present invention relates to a signal compensator for receiving a superimposed signal from a relay station including a signal amplifier and obtaining a second-station transmission signal as a desired signal from the superimposed signal.

  In recent years, the use of satellite communication has increased with the increase in communication capacity and the increase in communication speed. However, geostationary satellites used for communication satellites orbit the earth's equator and the number thereof is limited, so effective use of frequencies in satellite communication is a very important issue.

  Therefore, in order to improve the frequency utilization efficiency, a transmission signal superposition method in a VSAT (Very Small Aperture Terminal) system or a normal opposed type system has been studied.

  In the transmission signal superposition method, the signal transmitted by the partner station (desired wave) and the signal transmitted by the own station (unnecessary wave) are transmitted in the same frequency band, so the unnecessary wave interferes with the desired wave. Therefore, an interference canceller for reproducing and removing the interference wave is required. Then, as its interference canceller, after transmitting its own transmission signal from its own station, it generates an accurate replica signal by demodulating the signal (unnecessary wave) that returns to its own station via the satellite. Then, a method of subtracting (cancelling) the replica signal from the superimposed signal is adopted (unnecessary wave demodulation method).

  Alternatively, a delay detection method has been studied as another transmission signal superposition method. The delay detection method is a method of measuring a delay time between one round trip of the satellite, generating a replica signal by delaying the transmission signal of the own station by the delay time, and subtracting the replica signal from the superimposed signal.

  References disclosing such a transmission signal superposition method include Patent Document 1 and Non-Patent Documents 1 to 6.

WO2007 / 102415 (International publication date September 13, 2007)

M. Dankberg, Paired Carrier Multiple Access (PCMA) for Satellite Communications, The ViaSat Inc. Presentation Material URL: http://www.viasat.com/_files/?view=pcma.pdf M. Ichikawa, T. Hara, M. Okada, H. Yamamoto and K. Andou "Fast and Accurate Canceller on Carrier Super-positioning for VSAT Frequency Reuse" IEEE-WCNC 2005, New Orleans, March, 2005. Takao hara, Michihiro Ichikawa, Minoru Okada, and Heiichi Yamamoto, "Canceller Design for Carrier Super-positioning Frequency Re-use of VSATsatellite Communications", IEIEC Transaction Vol.J88-B, No.7, pp1300-1309, July, 2005. Noriaki ISHIDA, "Commom-band Satellite Communication System", IEIEC Transactions Vol.J82-B, No.8, pp1531-1537, Aug.1999 B.R.Ebert, The Satellite Communication Application Handbook, Artech House, 1997 Nara Institute of Science and Technology, Takeshi Uraya, Master's thesis, "Effect of nonlinearity of satellite repeater amplifier on transmission characteristics of signal superposition system", 2008.2.7.

  However, the inventions described in Patent Document 1 and Non-Patent Documents 1 to 5 have the following problems.

  Specifically, a nonlinear amplifier is provided in a satellite in an actual satellite transmission system, and nonlinear distortion is added to an unnecessary wave from the satellite by this nonlinear amplifier. On the other hand, the interference canceller has a mechanism in which a replica signal of an unnecessary wave is generated by a receiver, and the replica signal is basically not affected by nonlinear distortion. Therefore, a difference occurs between the unnecessary wave and the replica signal, and nonlinear distortion remains in the signal (desired wave) after the unnecessary wave cancellation in the receiver. As a result, there arises a problem that interference noise is added to the desired wave and its signal waveform is different from the original waveform. In addition, when two signals of a desired wave and an unnecessary wave are input to the nonlinear amplifier, there is a concern that the BER (Bit Error Rate) characteristics of the signal may be significantly deteriorated due to intermodulation distortion between the two signals and cross modulation. The

  In this respect, none of the inventions of Patent Document 1 and Non-Patent Documents 1 to 5 considers the influence of signal distortion due to the nonlinear amplifier of the relay station mounted on the satellite. Therefore, in the inventions of Patent Document 1 and Non-Patent Documents 1 to 5, in particular, when two signals of a desired wave and an interference wave are input to the nonlinear amplifier, signal characteristics due to intermodulation distortion and intermodulation between the two signals. It is unlikely that the transmission signal superposition method will be optimally operated.

  On the other hand, the invention of Non-Patent Document 6 examines how the nonlinear region of the nonlinear amplifier affects the characteristics of the interference canceller. Specifically, by taking the input back-off (IBO (Input Back-off)) and indicating the total amount of BER degradation and power loss, an appropriate operating point of the satellite relay station is appropriately selected, and the interference canceller It is clarified by calculation simulation that it works even in a nonlinear system.

  The IBO is a saturation output amplitude at which the output of a nonlinear amplifier such as a traveling wave tube amplifier (TWTA) mounted on a satellite relay station becomes maximum, and the input amplitude at that time Is a saturation input amplitude, and the saturation input amplitude is used as a reference (0 dB), and how much the amplitude is suppressed therefrom is displayed in decibels.

  However, since the invention of Non-Patent Document 6 takes IBO sufficiently and operates the nonlinear amplifier in the linear region, there is a problem that the transmission power at the time of outputting a signal from the satellite decreases as the IBO increases. This is called power loss due to back-off. Usually, in order to use the power of the relay station mounted on the satellite as efficiently as possible, it is necessary to avoid taking too much IBO. In other words, there is a trade-off relationship between IBO and power loss. In the invention of Non-Patent Document 6, an increase in power loss is assumed due to excessive IBO. Therefore, transmission power when a signal is output from a satellite is assumed. There is concern about the problem of falling. That is, in the invention of Non-Patent Document 6, there is an extremely high risk that nonlinear distortion of a signal due to a nonlinear amplifier hinders optimal operation of the transmission signal superposition method.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a signal compensation device, a signal compensation method, and a signal compensation program that compensate for characteristic deterioration of a received signal caused by a nonlinear amplifier mounted on a relay station. Another object of the present invention is to provide a computer-readable recording medium and a communication device including the signal compensation device.

  In order to solve the above problems, the signal compensation apparatus according to the present invention is a signal different from the first station transmission signal transmitted by the first station and the first station transmission signal, and is transmitted by the second station. A signal compensator used in a communication system in which a superimposed signal on which a second-station transmission signal, which is a transmitted signal, is superimposed is transmitted from a relay station including a signal amplifier to the second station, is an output signal for an input signal Compensation replica that generates a compensation replica signal by inputting a replica signal that is a replica of the second station transmission signal to a nonlinear compensation model that shows the input / output characteristics of the signal amplifier including input and output characteristics of the signal amplifier including a linear region and a nonlinear region A signal generation means is provided.

  In addition, in order to solve the above-described problem, the signal compensation method according to the present invention is a signal different from the first station transmission signal transmitted from the first station and the first station transmission signal. A signal compensator used in a communication system in which a superimposed signal on which a second station transmission signal that is a signal transmitted from the relay station is superimposed is transmitted from a relay station including a signal amplifier to the second station, A replica replica signal, which is a replica of the second station transmission signal, is input to a nonlinear compensation model indicating the input / output characteristics of the signal amplifier including input and output characteristics of the output amplifier including a linear region and a nonlinear region to generate a compensation replica signal. A compensation replica signal generation step is included.

  According to the above configuration, the compensation replica signal generation means or the compensation replica signal generation step inputs a replica signal that is a replica of the second station transmission signal to the nonlinear compensation model, thereby allowing the signal amplifier including the linear region and the nonlinear region to A compensation replica signal including input / output characteristics can be generated. Therefore, by subtracting (cancelling) the compensation replica signal from the superimposed signal in which the first and second station transmission signals are superimposed, the influence of the nonlinear distortion due to the input / output characteristics remains, It is possible to extract the first station transmission signal (desired wave) transmitted by the first station whose influence has been offset. That is, it is possible to extract the first station transmission signal with the original signal waveform excluding the influence due to the nonlinear distortion of the signal amplifier.

  Thus, in the signal compensation apparatus and signal compensation method according to the present invention, the compensation replica signal generation means (step) compensates by inputting the replica signal to the nonlinear compensation model indicating the input / output characteristics of the signal amplifier of the relay station. A replica signal is generated. Therefore, as in the prior art, sufficient input back-off (IBO) is taken for the purpose of operating the nonlinear amplifier in the linear region, so that the transmission power when outputting a signal from the relay station is reduced. As a result, the characteristic deterioration of the received signal caused by the nonlinear amplifier mounted on the relay station can be suitably compensated.

Furthermore, in the signal compensation device according to the present invention,
The signal amplifier is a TWTA,
The compensation replica signal generation means generates an output u (t) obtained by using the replica signal as an input s (t) as the compensation replica signal based on the following equations (1) to (12). Is preferred.

u (t) = s (t) × G [s (t)] (1)
G [s (t)] = 1 / | s (t) |
× g (| s (t) |) × exp (jf (| s (t) |)) (2)
g (γ) = α _x · γ / (1 + β _x · γ ² ) (3)
f (γ) = α _φ · γ ² / (1 + β _φ · γ ² ) (4)

i _k = α × I _k (7)
q _k = α × Q _k (8)
s = i _k + jq _k (9)

However,
u (t): Output signal of TWTA s (t): Input signal to TWTA G [s (t)]: Gain of TWTA (gain)
g (r): AM / PM conversion characteristic of TWTA f (r): AM / AM conversion characteristic of TWTA AM: Amplitude Modulation (amplitude modulation)
PM: Phase Modulation
j: √ (−1)
α _x : small signal gain 1 / √β _x : saturation input amplitude α _φ : parameter for determining AM / PM conversion characteristic β _φ : parameter for determining AM / PM conversion characteristic I _k : k-th I component of input signal Q _k : K-th Q component of input signal N: number of data samplings Γ _IBO : IBO (dB)
i _k : I component of input complex amplitude to TWTA q _k : Q component of input complex amplitude to TWTA Amax: Maximum saturation amplitude (dB)

And

  As described above, the compensation replica signal generation means (step) generates the compensation replica signal by inputting the replica signal to the nonlinear compensation model. Therefore, the compensation replica signal can be generated by calculation processing by software. it can.

  Therefore, by using the equations (1) to (12), the compensation replica signal generation means can generate the I component and the Q component of the compensation replica signal as an output u (t) by calculation processing. .

  Therefore, the compensation replica signal generation means (step) can generate a desired compensation replica signal more quickly and accurately.

  Furthermore, in the signal compensation device according to the present invention, the replica signal may be the second signal as an undesired signal using a difference in power density between the first station transmission signal and the second station transmission signal. It is preferable that the signal is generated as a replica of the second station transmission signal by demodulating the station transmission signal.

  In the signal compensator according to the present invention, the replica signal is held in the second station until the second station transmission signal transmitted to the first station returns to the second station. It is preferable.

  In the signal compensation apparatus according to the present invention, the compensation replica signal generation means generates a compensation replica signal by inputting the replica signal input to itself into the nonlinear compensation model. In other words, in both the unnecessary wave demodulation method and the delay detection method, the input / output characteristics of the signal amplifier mounted on the satellite as the relay station can be modeled as a nonlinear compensation model, and the replica signal can be canceled from the superimposed signal. Therefore, the signal compensator according to the present invention is applicable to both a so-called unnecessary wave demodulation method and a delay detection method.

  That is, the signal compensation device according to the present invention can be incorporated into any transmission signal superposition method, and thus can be said to be a highly versatile device that can meet the needs of a wide range of consumers.

  The signal compensation apparatus may be realized by a computer. In this case, a signal compensation program for realizing the signal compensation apparatus by a computer by causing the computer to operate as the compensation replica signal generation unit, and A computer-readable recording medium on which is recorded also falls within the scope of the present invention.

  In this case, by generating a compensation replica signal by calculation processing by software, it is possible to reduce the size of the apparatus while reducing costs compared to a configuration in which the compensation replica signal is generated in hardware.

  In addition, a communication device provided with the signal compensation device also falls within the scope of the present invention. As a result, the communication apparatus can suitably compensate for the deterioration of the received signal characteristics caused by the nonlinear amplifier mounted on the relay station.

  As described above, the signal compensation apparatus according to the present invention includes the second station transmission signal in the nonlinear compensation model indicating the input / output characteristics of the signal amplifier including the input / output characteristics of the output signal with respect to the input signal including the linear region and the nonlinear region. Compensation replica signal generation means for generating a compensation replica signal by inputting a replica signal that is a replica of

  In addition, as described above, the signal compensation method according to the present invention is based on the nonlinear compensation model in which the input / output characteristics of the output signal with respect to the input signal indicate the input / output characteristics of the signal amplifier including the linear region and the nonlinear region. This is a configuration including a compensation replica signal generation step of generating a compensation replica signal by inputting a replica signal that is a replica of the station transmission signal.

  In addition, as described above, the signal compensation program according to the present invention adds the second compensation model to the nonlinear compensation model in which the input / output characteristics of the output signal with respect to the input signal indicate the input / output characteristics of the signal amplifier including the linear region and the nonlinear region. In this configuration, the computer executes a compensation replica signal generation step of generating a compensation replica signal by inputting a replica signal that is a replica of the station transmission signal.

  Therefore, there is an effect that it is possible to realize a signal compensation device, a signal compensation method, and a signal compensation program that compensate for the characteristic deterioration of the received signal caused by the nonlinear amplifier mounted on the relay station.

It is a block diagram which shows the structure of the communication apparatus provided with the signal compensation apparatus of this invention. It is a figure for demonstrating the PP system in which frequency reuse is possible. It is a figure for demonstrating the P-MP system in which frequency reuse is possible. It is a figure for demonstrating the replica signal generation method in a delay detection system. It is a figure for demonstrating the replica signal generation method in an unnecessary wave demodulation system. It is a figure which shows roughly the input-output characteristic of the amplifier in which the input-output characteristic of the output signal with respect to an input signal contains a linear region and a nonlinear region. It is a figure which shows a mode that the superimposed OB signal and IB signal were input into TWTA, and the OB signal received to the influence of the nonlinear distortion of the signal by TWTA. It is a graph which shows the AM / PM conversion characteristic and AM / AM conversion characteristic in TWTA. It is a figure which shows the simulation result of the characteristic evaluation by the output electric power spectrum in a linear area | region. It is a figure which shows the simulation result of the characteristic evaluation by the output electric power spectrum in a nonlinear area | region. It is a figure which shows the test result by hardware. It is a figure which shows the spectrum of the input signal and output signal by simulation. It is a figure which shows the error rate characteristic of the IB signal after signal cancellation in the case of IBO = 2dB. It is a figure which shows the error rate characteristic of the IB signal after signal cancellation in the case of IBO = 10 dB. It is a figure which shows the deterioration amount of the BER characteristic when IBO is changed in error rate ^10-4 . It is a figure which shows the example of the signal point arrangement | positioning of 8PSK system. It is a figure which shows the example of the signal point arrangement | positioning of 16QAM system.

  Hereinafter, an embodiment of a signal compensation device according to the present embodiment and a communication device including the signal compensation device will be described. For convenience of explanation, an embodiment in which the present invention is applied to a VSAT network will be described below, but the scope of the present invention is not limited to this.

[1. Basic overview of VSAT signal superposition method]
2 and 3 show two typical satellite communication systems in which frequency reuse is possible. Each of the two satellite communication systems shown in each figure transmits a signal (desired wave) transmitted by the partner station and a signal (unnecessary wave) transmitted by the own station in the same frequency band. Interference cancellers that interfere with the desired wave and regenerate and remove the interference wave are required. Each figure will be described below.

  FIG. 2 shows a point-to-point (PP) system. The PP system transmits two signals transmitted at the same signal level from the station A (second station) and the station B (first station) using the same size antenna and superimposed on the same frequency band. It is a system that performs. In this PP system, a replica signal is created by delaying the transmission signal of the own station (second station transmission signal) within the own station for a time equivalent to one round trip of the satellite, and the replica signal is subtracted (cancelled) from the superimposed signal. ) To perform interference canceller processing. In this case, it is necessary to accurately measure the delay for one round trip of the satellite, and it is necessary to cancel unnecessary waves at both stations. The cancellation of unnecessary waves by the above method is referred to as a delay detection method.

  FIG. 3 shows a P-MP (Point to Multi Point) system. This system is also referred to as a VSAT system, and is composed of a hub station A (Hub Station) (second station) having a large antenna diameter and a large number of micro earth stations B (Remote Station) (first station). . In the following description, as seen from the hub station side, the desired wave is an IB signal (Inbound Signal) (first station transmission signal), and the unnecessary wave is an OB signal (Outbound Signal) (second station transmission). Signal).

  The carrier of the OB signal transmitted from the hub station A to the remote station has a wide band and generally has a higher signal power density than the carrier of the narrow band IB signal. This is because there is a difference in reception performance between the hub station and the remote station (G / T: Gain to Noise Temperature Ratio, which represents the good antenna density of the earth station), so that the required transmission signal power differs from each other. It is. Therefore, when the signals are superimposed, the OB signal becomes larger than the IB signal when the received signal powers are compared with each other.

  For this reason, even if an IB signal that is an unnecessary wave exists in the same band, the remote station can demodulate an OB signal that is a desired wave without removing them. Thereby, in the VSAT system, it is not necessary to change the system of many remote stations. On the other hand, in the hub station, a signal having a large power with respect to the IB signal which is a desired wave causes interference. Therefore, in order to demodulate the IB signal, it is necessary to generate a replica of the OB signal and cancel the OB signal There is. The unnecessary wave cancellation method according to the above method is referred to as an unnecessary wave demodulation method.

[2. Replica signal generation method (delay detection method)
Next, a replica signal generation method in the PP system will be described with reference to FIG. FIG. 4 is a diagram for explaining a replica signal generation method in the delay detection method.

  In the figure, a signal (unwanted wave) transmitted from the station A is indicated by a broken line, and a signal (desired wave) transmitted by the station B is indicated by a solid line. Since station A and station B use antennas of the same size, unnecessary waves and desired waves may be considered to have the same signal level.

  As shown in the figure, a path 1 and a path 2 exist in the replica signal generation method in the delay detection method. In path 1, a superimposed signal in which an unnecessary wave and a desired wave are superimposed is transmitted, and in path 2, an unnecessary wave replica signal is generated and transmitted. The replica signal is generated by delaying the transmission signal (unnecessary wave) of the A station within the A station by the time (τ) for one round trip of the satellite, and generating the delayed unnecessary wave as a replica signal. Then, in the interference canceller, the replica signal is subtracted (cancelled) from the superimposed signal, and the canceled signal is output to the outside as a desired wave.

  Since the desired wave is acquired in this way, in the delay detection method, it is necessary to accurately and continuously measure the delay for one round trip of the satellite, and unnecessary waves are canceled at both stations.

[3. Replica signal generation method (unnecessary wave demodulation method)
Next, a replica signal generation method in the P-MP system will be described with reference to FIG. FIG. 5 is a diagram for explaining a replica signal generation method in the unnecessary wave demodulation method.

  As described above, in the VSAT system, even if there is an IB signal that is an unnecessary wave in the same band, the remote station can demodulate the OB signal that is a desired wave without removing them. Thereby, in the VSAT system, it is not necessary to change the system of many remote stations. On the other hand, in the hub station, a signal having a large power with respect to the IB signal which is a desired wave causes interference. Therefore, in order to demodulate the IB signal, a replica of the OB signal is generated. It is necessary to cancel the OB signal from the superimposed signal.

  Therefore, as shown in FIG. 5, in the unnecessary wave demodulation method, a superimposed signal of the IB signal and the OB signal is transmitted in path 1, and a replica of the OB signal is generated in the demodulator in path 2. Then, in the interference canceller, the replica signal is subtracted (cancelled) from the superimposed signal, and the canceled signal is output as a desired wave. The subtraction is delayed by a time required for generating the replica signal, and the replica signal is subtracted from the superimposed signal, thereby suppressing the influence of the fixed delay caused by demodulating the replica signal.

  Since the desired wave is acquired in this way, the unnecessary wave demodulation method is simple and can be suitably used for the VSAT system. However, the accuracy of the generated replica signal is affected by the error rate characteristics when demodulating unnecessary waves.

[4. (Satellite relay amplifier)
In satellite communications, a large number of signals are commonly amplified in a relay amplifier (signal amplifier) mounted on a satellite (relay station), and the amplitude and phase of each output signal are commonly amplified in an ideal linear amplifier. It is not affected by the signal.

  However, a high power amplifier (HPA) such as a solid state power amplifier (SSPA) or a traveling wave tube amplifier (TWTA) mounted on a satellite is linear while the input signal power is small. Although it operates, the effect of nonlinear amplification appears when the signal power increases. In particular, in the transmission signal superposition method, since a plurality of signals are transmitted and received in the same frequency band, the influence of nonlinear amplification becomes large.

  FIG. 6 is a diagram schematically showing input / output characteristics of an amplifier in which input / output characteristics of an output signal with respect to an input signal include a linear region and a nonlinear region.

  As shown in the figure, the nonlinear amplifier such as SSPA or TWTA mounted on the satellite has input / output characteristics including a linear region and a nonlinear region. In the linear region, the input level and the output level maintain linearity. However, in the nonlinear region, the input level and the output level lose linearity, and the output signal is distorted and output. Therefore, it is necessary to eliminate the influence of the nonlinearity of the satellite relay amplifier on the transmission characteristics of the communication system from the viewpoint of the optimum operation of the transmission signal superposition method.

  The signal compensation device 8 according to the present embodiment to be described next is intended to solve the above problems. In the following description, the signal compensator 8 is described as being applied to a VSAT system, but the scope of application of the present invention is not limited to this. Although details will be described later, the signal compensation device 8 applies predetermined processing to the replica signal of the generated OB signal, so any transmission signal superposition method for generating a replica signal can be used. It can also be applied to. Therefore, the signal compensator 8 is [2. The present invention can also be applied to the PP system described in “Replica Signal Generation Method (Delay Detection Method)”.

[5. Details of Communication Device 1 with Signal Compensation Device 8]
A communication device 1 in which the signal compensation device 8 according to the present embodiment is used will be described with reference to FIG.

  FIG. 1 is a block diagram showing a configuration of a communication device 1 including a signal compensation device 8 of the present invention. The communication device 1 is provided on the hub station side in the VSAT system. That is, the communication device 1 includes a signal receiving unit 2, a phase rotator 3, a first demodulating unit 4, a binarizing unit 5, a modulator 6, a filter 7, a signal, as shown in FIG. A compensation device 8, an automatic amplification circuit 9, a correlation calculation unit 10, a signal delay unit 11, a signal cancellation unit 12, and a second demodulation unit 13 are provided.

  The signal receiving unit 2 receives a superimposed signal (see FIG. 3) in which an OB (outbound) signal and an IB (inbound) signal are superimposed from a satellite. The signal receiving unit 2 converts the signal received from the satellite into a QPSK I / Q signal, and then outputs the I / Q signal to the phase rotator 3.

  The phase rotator 3 rotates the phase of the input signal to synchronize the carrier phase of the I / Q signal. Then, the phase rotator 3 outputs the phase-rotated I / Q signal to the signal delay unit 11 via the path 1 and to the first demodulation unit 4 via the path 2.

  The first demodulator 4 demodulates an undesired outbound signal by using the power density difference Δ between the outbound signal and the inbound signal output from the phase rotator 3. Further, the first demodulator 4 feeds back the phase difference between the received signal and its decision point to the phase rotator 3 by a QPSK Demap block (not shown) included therein. The phase rotator 3 receives the feedback and performs phase control of the I / Q signal.

  Note that the demodulation of the outbound signal using the power density difference Δ may follow a conventional method, and a detailed description thereof is omitted here.

  The binarization unit 5 converts the outbound signal demodulated by the first demodulation unit 4 into a pulse train composed of an I signal and a Q signal.

  The modulator 6 modulates the pulse train composed of the I signal and the Q signal using the carrier train output from the first demodulator 4. Then, by passing the modulated carrier train through the filter 7, a replica signal of the outbound signal before being affected by the nonlinear distortion of the signal by the nonlinear amplifier mounted on the satellite is reproduced.

  The signal compensation device 8 includes compensation replica signal generation means 8a. The compensation replica signal generation means 8a includes an I component acquisition unit 8b, a Q component acquisition unit 8c, and a nonlinear compensation model calculation unit 8d. The I component acquisition unit 8 b acquires the I component of the replica signal of the outbound signal from the filter 7. The Q component acquisition unit 8 c acquires the Q component of the replica signal from the filter 7.

  The nonlinear compensation model calculation unit 8d has a nonlinear compensation model in which the input / output characteristics of the output signal with respect to the input signal indicate the input / output characteristics of the nonlinear amplifier including the linear region and the nonlinear region. Then, the nonlinear compensation model calculation unit 8d inputs the I component and Q component of the replica signal acquired from the I component acquisition unit 8b and the Q component acquisition unit 8c to the nonlinear compensation model, and performs the calculation described later. A compensation replica signal indicated by an I component and a Q component is generated. The compensation replica signal is a signal in which the input / output characteristics of the nonlinear amplifier including the linear region and the nonlinear region are included in the replica signal.

  Next, the nonlinear compensation model calculation unit 8 d outputs the compensation replica signal to the automatic amplification circuit 9 and the correlation calculation unit 10. The input / output characteristics of the signal amplifier including the linear region and the nonlinear region, details of the nonlinear compensation model, and generation of the compensation replica signal will be described in detail later.

  The automatic amplifying circuit 9 is provided between the signal compensator 8 and the signal cancellation unit 12, and synchronizes the received signal from the satellite including the unnecessary wave signal and the generated replica signal, and adjusts the amplitude of both signals. The same level. In the output after the signal cancellation in the signal cancellation unit 12, the power difference between the generated replica signal and the unnecessary wave becomes an interference of a desired wave to be demodulated. For the purpose of preventing such a situation in advance An automatic amplifier circuit 9 is provided.

  The correlation calculation unit 10 calculates the correlation between the residual signal that is the output of the signal cancellation unit 12 and the replica signal. The amplitude control signal used in the automatic amplification circuit 9 is obtained based on the correlation calculated by the correlation calculation unit 10.

  The signal delay unit 11 delays the signal output from the phase rotator 3 via the path 1 by the time during which the replica signal is generated in the path 2. The time (τ) required for generating the replica signal in the path 2 is always constant, and is usually 10 symbols to a maximum of several tens of symbol periods.

  The signal cancellation unit 12 subtracts (cancels) the compensation replica signal output from the automatic amplification circuit 9 from the signal delayed by the signal delay unit 11. The signal cancellation unit 12 outputs the canceled signal to the correlation calculation unit 10 and also outputs it to the second demodulation unit 13. Note that the canceling process in the signal canceling unit 12 may follow a conventional method, and a detailed description thereof is omitted here.

  The second demodulation unit 13 obtains an inbound signal that is a desired signal by demodulating the signal that has been canceled by the signal cancellation unit 12.

[6. Nonlinear compensation model (TWTA model)]
In satellite communication, a plurality of signals are commonly amplified in a relay amplifier mounted on the satellite, and a high-power amplifier (HPA) such as a solid-state amplifier (SSPA) or traveling wave tube amplifier (TWTA) is used as the amplifier. In general, there are many cases where SSPA is used for terrestrial mobile communication and TWTA is mounted on a satellite. This is because TWTA can obtain a higher output than SSPA.

  Therefore, in the present embodiment, a method for generating a compensation replica signal in the signal compensator 8 is proposed in consideration of the case where the amplifier mounted on the satellite is TWTA. Therefore, the signal compensation device 8 adds a replica signal that is a replica of the OB signal (unnecessary wave) to the nonlinear compensation model in which the input / output characteristics of the output signal with respect to the input signal indicate the input / output characteristics of the TWTA including the linear region and the nonlinear region. It may be considered that a compensation replica signal is generated by inputting. Accordingly, in the following, TWTA input / output characteristics including a linear region and a nonlinear region, a nonlinear compensation model related to TWTA, a method of generating a compensation replica signal by inputting a replica signal of an OB signal into the nonlinear compensation model, and the method The effects obtained by will be described sequentially.

  Note that the present invention is not limited to TWTA. Similarly, in SSPA, an input / output characteristic of an output signal with respect to an input signal is a non-linear compensation model indicating an input / output characteristic of an SSPA including a linear region and a nonlinear region. It is also possible to generate a compensation replica signal by inputting a replica signal that is a replica of the signal (unnecessary wave).

[6-1. TWTA model)
First, the superimposed OB signal and IB signal are input to the TWTA, and the state in which the OB signal is affected by the nonlinear distortion of the signal due to the TWTA is shown in FIG. In FIG. 7, the horizontal axis represents the I component of the input signal, and the vertical axis represents the Q component of the input signal. The OB signal and the IB signal are expressed in a complex manner.

  (A), (b), and (c) of the same figure show the signal vector of the OB signal and IB signal input to TWTA, and the signal (IB signal + OB signal) which combined them. (D) shows an output vector of TWTA, which is a combined signal of an IB signal and an OB signal subjected to nonlinear distortion of the signal by TWTA. It should be noted that the influence of the non-linear distortion on the composite signal (c) affects only the OB signal transmitted by the hub station.

  The TWTA model to be described below is to generate a compensation replica signal in which the nonlinear distortion is included in the replica signal of the OB signal affected by the nonlinear distortion due to the TWTA shown in FIG.

  Therefore, first, the input / output characteristics of TWTA will be described, and then the nonlinear compensation model related to TWTA will be described. In this nonlinear compensation model, an input signal to TWTA is expressed by a complex function s (t). At this time, an equation for generating an output u (t) obtained using a replica signal as an input s (t) as the compensation replica signal is expressed by the following equation (1).

u (t) = s (t) × G [s (t)] (1)
here,
u (t): Output signal of TWTA s (t): Input signal to TWTA G [s (t)]: Gain of TWTA (gain)
And
Furthermore, G [s (t)], which is the gain of TWTA, is expressed by the following equation (2).

G [s (t)] = 1 / | s (t) |
× g (| s (t) |) × exp (jf (| s (t) |)) (2)
here,
g (r): AM / PM conversion characteristic of TWTA f (r): AM / AM conversion characteristic of TWTA AM: Amplitude Modulation (amplitude modulation)
PM: Phase Modulation
j: √ (−1)
And

  In TWTA, g (γ) is expressed by equation (3), and f (γ) is expressed by equation (4).

g (γ) = α _x · γ / (1 + β _x · γ ² ) (3)
f (γ) = α _φ · γ ² / (1 + β _φ · γ ² ) (4)
here,
α _x : Small signal gain 1 / √β _x : Saturation input amplitude α _φ : Parameter for determining AM / PM conversion characteristic β _φ : Parameter for determining AM / PM conversion characteristic

  Here, FIG. 8 is a graph showing AM / PM conversion characteristics and AM / AM conversion characteristics in TWTA. Table 1 shows parameter values used in the equations (3) and (4) to determine the TWTA characteristics. Each parameter in Table 1 is a typical numerical value suitable for TWTA. When these parameters are inserted into Equation (3) and Equation (4), g (γ) in Equation (3) Is known to suitably represent the AM / AM conversion characteristic of FIG. 8, and f (γ) in the equation (4) suitably represents the AM / PM conversion characteristic of FIG.

Further, when the saturation output amplitude is set to a point where the output of the TWTA is maximized, the input amplitude at that time is set as the saturation input amplitude (1 / √β _x ). Furthermore, input back-off (IBO) and output back-off (OBO) indicate how much the amplitude is suppressed from the saturation input amplitude and saturation output amplitude as a reference (0 dB). Defined as decibels.

  For example, in FIG. 8, the saturation input reference is 2 dB, which is the input amplitude when the output amplitude is maximum. With this as the IBO reference, when the input amplitude is halved (the input power is reduced by 6 dB), the output amplitude is 0.8, that is, 4/5 of the output amplitude 1.0 which is the OBO reference. In other words, the output power has decreased by 2 dB, and IBO and OBO at this time are 6 dB and 2 dB, respectively.

Subsequently, the k-th I component and Q component of the input signal are set as I _k and Q _k , respectively, and the average power of the input signal is calculated by the following equation (5).

here,
N: The number of data sampling.

  Next, the input power correction coefficient α is calculated by the following equation (6).

here,
Γ _IBO : IBO (dB)
And
Then, the I component and the Q component of the input complex amplitude to the nonlinear amplifier TWTA modeled by the equations (1) and (2) are given by the following equations (7) and (8).

i _k = α × I _k (7)
q _k = α × Q _k (8)
And in Formula (1) and Formula (2),
s = i _k + jq _k (9)
As a result, the output value of the nonlinear compensation model is calculated.
Therefore, the output value u is obtained by the following equation (10).

The obtained output value u is further multiplied by the saturation amplitude maximum value Amax and output. Therefore, the I component and Q component of the output signal are expressed by the following equations (11) and (12).

  In this way, the I component and Q component of the output signal are calculated based on the equations (1) to (12). That is, based on the equations (1) to (12), it is possible to realize a nonlinear compensation model in which the input / output characteristics of the output signal with respect to the input signal indicate the input / output characteristics of the TWTA including the linear region and the nonlinear region.

  When this is applied to the block diagram of FIG. 1, the I component acquisition unit 8 b and the Q component acquisition unit 8 c constituting the signal compensation device 8 filter the I component and the Q component related to the replica signal of the outbound signal as a filter 7. Get from. The I component and Q component of this replica signal become the input signal (s (t)) to the nonlinear compensation model. Then, the nonlinear compensation model calculation unit 8d receives the input signal s (t) as an input, performs calculation in the nonlinear compensation model expressed by the equations (1) to (12), and finally shows the I component and the Q component. To generate a compensated replica signal (Equation (11), Equation (12)). In this way, the compensation replica signal is generated by the equations (1) to (12), and the compensation replica signal includes the TWTA input / output characteristics including the linear region and the nonlinear region.

[6-2. (Results of simulation and verification test)
Laboratories using computer simulations and hardware prototypes based on Field Programmable Gate Arrays (FPGAs) were performed for compensation of interference degradation in the linear region and nonlinear region of TWTA. The power density ratio of the OB signal to the IB signal was set at 13 dB.

  FIG. 9 shows the simulation result of the characteristic evaluation by the output power spectrum in the linear region. The power spectrum of the received signal (including the 5 MHz OB signal and the 1 MHz IB signal) and the extracted IB signal are shown in FIG. It is shown. FIG. 10 shows the simulation result of the characteristic evaluation by the output power spectrum in the non-linear region. The simulation result for the non-linear region when IBO is 0 dB is shown.

  As can be seen by comparing FIG. 9 and FIG. 10, the IB signal (desired wave) is more reliably extracted in the linear region than in the nonlinear region. It can be seen that in the non-linear region, the power density ratio (D / U) between the residual OB signal (interference wave) and the IB signal is as small as 10 dB or less.

  FIG. 11 is a diagram showing a test result by hardware performed under the same conditions as in the simulation, and shows a received signal (OB signal + IB signal) and an extracted IB signal. As a result, the test result by hardware was inferior to the test result by simulation. In other words, the IB signal could not be sufficiently extracted in the hardware test. The D / U of the extracted IB signal was only 6-7 dB. This is thought to be due to the stronger non-linear influence in the experiment.

[6-3. (Cancer operation verification by simulation)
Next, the operation verification of the canceller by simulation will be described. In the simulation, the OB signal is a QPSK signal, the IB signal is a DQPSK signal, and the power density ratio of the OB signal to the IB signal is set to 13 dB. Other simulation specifications are as shown in Table 2.

  First, the effect of compensation for characteristic deterioration of the IB signal after signal cancellation will be described. FIG. 12 is a diagram showing the spectrum of the input signal (IB signal + OB signal) to the canceller and the output signal (IB signal) from the canceller by simulation. Note that the operating point of TWTA is the saturation input standard (IBO = 0 dB), and the power density ratio of the OB signal to the IB signal is set to 13 dB. Furthermore, the output signal was subjected to two types of simulation depending on whether compensation was performed.

  As shown in the figure, when compared with the presence or absence of compensation, the signal degradation of the IB signal is about 10 dB, that is, about 90% by canceling the compensation replica signal related to the OB signal from the superimposed signal of the IB signal and the OB signal. It is suppressed. This indicates that the effect of suppressing the characteristic deterioration of the IB signal due to the cancellation is extremely high.

  Next, the error rate characteristics of the IB signal after signal cancellation will be described. FIG. 13 is a diagram illustrating an error rate characteristic of an IB signal after signal cancellation in the case of IBO = 2 dB. FIG. 14 is a diagram illustrating an error rate characteristic of an IB signal after signal cancellation when IBO = 10 dB.

  As can be seen from FIG. 13, in the case of IBO = 2 dB, “with compensation” shows a numerical value with a lower error rate characteristic of the IB signal than “without compensation”. That is, it has been proved that the error rate characteristic of the IB signal is reduced by canceling the compensation replica signal related to the OB signal from the superimposed signal of the IB signal and the OB signal.

  On the other hand, as can be seen from FIG. 14, when IBO = 10 dB, there is no clear difference in the error rate characteristics of the IB signal between “with compensation” and “without compensation”, and the OB signal is determined from the superimposed signal of the IB signal and the OB signal. No significant effect was found by canceling the compensation replica signal. This is because by setting IBO = 10 dB, the input / output characteristics of the output signal with respect to the input signal approach from the nonlinear region to the linear region, and the degree of signal degradation is reduced.

Next, FIG. 15 is a diagram illustrating the deterioration amount of the BER characteristic when the IBO is changed at an error rate of 10 ⁻⁴ . The deterioration amount referred to here is a dB display of the deterioration amount from the “ideal value” described with reference to FIGS. 13 and 14.

  As shown in the figure, by canceling the compensation replica signal related to the OB signal from the superimposed signal of the IB signal and the OB signal, the amount of deterioration of the BER characteristic of the output signal (IB signal) after the cancellation process can be greatly suppressed. I understand that. In this simulation, cancel processing is performed under the same conditions as the nonlinear characteristics of TWTA used in an actual satellite relay station. Therefore, in order to suppress the characteristic deterioration in the nonlinear region of TWTA, a replica signal is input to the nonlinear compensation model to generate a compensation replica signal, and the compensation replica related to the OB signal from the superimposed signal of the IB signal and the OB signal It has been proved that the signal compensation method according to the present embodiment for canceling the signal can effectively reduce the signal degradation of the desired wave (IB signal).

  As described above, the compensation replica signal generation unit 8a generates a compensation replica signal by inputting the replica signal to the nonlinear compensation model indicating the input / output characteristics of the TWTA mounted on the satellite. Therefore, as in the prior art, sufficient input back-off (IBO) is taken for the purpose of operating in the linear region, so that the problem of reduced transmission power when signals are output from the satellite is greatly reduced. be able to.

  In addition, the compensation replica signal generation means 8a generates a compensation replica signal by inputting the replica signal to the nonlinear compensation model, and it is not always necessary to use hardware such as an amplifier (amplifier). A configuration in which a compensation replica signal is generated by arithmetic processing is also possible. Therefore, by generating the compensation replica signal in software, it is possible to simultaneously reduce the size of the communication device 1 while suppressing the cost for hardware.

  Furthermore, the signal compensation method proposed in this embodiment can be applied to both the unnecessary wave demodulation method and the delay detection method. This is because the compensation replica signal generating means 8a acquires the replica signal of the outbound signal from the filter 7, and the input / output characteristics of the output signal with respect to the input signal are the input / output characteristics of the TWTA including the linear region and the nonlinear region. This is to adopt a method of generating a compensation replica signal by inputting to a nonlinear compensation model indicating the characteristics.

  Therefore, when the signal compensation method according to this embodiment is applied to a delay detection method different from the above-described unnecessary wave demodulation method, a configuration in which the signal compensation device 8 is provided immediately before the interference canceller in the path 2 of FIG. And it is sufficient. As a result, the compensation replica signal generation means 8a (not shown) acquires a replica signal of an unnecessary wave (A station transmission signal), and the input / output characteristics of the output signal with respect to the input signal are in a linear region and A compensation replica signal can be generated by inputting to a nonlinear compensation model indicating the input / output characteristics of the TWTA including the nonlinear region. Then, the desired wave is extracted by the interference canceller subtracting the compensation replica signal from the superimposed signal.

  As described above, the signal compensation method according to the present embodiment can favorably compensate for the characteristic deterioration of the received signal caused by the nonlinear amplifier in both the unnecessary wave demodulation method and the delay detection method. Therefore, the signal compensation method according to the present embodiment is preferably applied to both the signal superposition method of the P-MP system employing the unnecessary wave demodulation method and the PP system employing the delay detection method. be able to.

  The PP system is a system that performs transmission by superimposing two signals transmitted at the same signal level from the stations A and B using the same size antenna on the same frequency band. Therefore, in the PP system, it is preferable to provide the signal compensation device 8 according to the present embodiment in both the station A and the station B.

  As described above, the signal compensation method according to the present embodiment can be incorporated in any transmission signal superposition method of the P-MP system and the P-P system, and therefore can meet the needs of a wide range of consumers.

  In addition, the signal compensation method proposed in this embodiment can be applied regardless of whether the signal modulation method is multilevel modulation. This will be described with reference to FIGS. FIG. 16 is a diagram illustrating an example of signal point arrangement of the 8PSK system, and FIG. 17 is a diagram illustrating an example of signal point arrangement of the 16QAM system.

  In general, in a digital wireless communication system such as a mobile communication system, data is transmitted by a modulation method that can obtain a desired communication quality (for example, an error rate of a predetermined value or less on the receiver side). . Among such modulation schemes, there is a multi-level modulation scheme as a scheme for transmitting a plurality of bits with one symbol as a modulation unit. The multi-level modulation method transmits information of a plurality of bits by one symbol which is a modulation unit. A QPSK (Quadri-Phase Shift Keying) method which transmits 2 bits of information by one symbol is 3 by one symbol. What transmits bit information is called 8PSK system, 16QAM (Quadrature Amplitude Modulation) which transmits 4 bits information by one symbol.

  As shown in FIGS. 16 and 17, the interval (distance) between signal points becomes smaller as the modulation signal becomes multilevel modulation. Therefore, the influence of nonlinear distortion due to the nonlinear amplifier mounted on the satellite increases as the modulation signal becomes multilevel modulation. That is, the 8PSK system is more affected by nonlinear distortion than the QPSK system, and the 16QAM system is more greatly affected by nonlinear distortion than the 8PSK system. Therefore, the deterioration of the received signal characteristics caused by the nonlinear amplifier also increases as the multi-level modulation is performed.

  In this regard, the signal compensation method proposed in the present embodiment gives the same characteristic as the nonlinear characteristic of TWTA used in an actual satellite relay station to the replica signal of the desired wave. Is expressed by I component and Q component. Therefore, the signal compensation method according to the present embodiment has the effect of nonlinear distortion caused by the nonlinear amplifier with respect to any of the multilevel modulation methods such as the QPSK method, the 8PSK method, and the 16QAM method expressed by the I component and the Q component. It can apply suitably, eliminating.

  On the other hand, the above-described invention of Non-Patent Document 6 takes a sufficient amount of IBO and operates the nonlinear amplifier in the linear region, thereby operating the interference canceller in the nonlinear system. That is, the invention of Non-Patent Document 6 takes IBO uniformly without considering the problem that the influence of nonlinear distortion due to the nonlinear amplifier becomes larger as multilevel modulation is performed, and without considering the signal modulation method. This eliminates the influence of nonlinear distortion caused by the nonlinear amplifier. Therefore, in the invention of Non-Patent Document 6, when the signal modulation method is a multi-level modulation method, it is difficult to reliably exclude the influence of non-linear distortion caused by a non-linear amplifier different for each multi-level modulation method.

  For these reasons, the signal compensation method proposed in the present embodiment can solve the problems of the invention of Non-Patent Document 6 that is a conventional invention, and is the signal modulation method a multi-level modulation method? It has the remarkable effect that it can be applied regardless of whether or not.

  In the present embodiment, the influence of signal distortion caused mainly by the nonlinear amplifier (TWTA) of the relay station mounted on the satellite has been described. However, the present invention can also be applied to a nonlinear amplifier used in a communication system performed via a terrestrial base station, and its application is not limited to a communication satellite.

  Finally, each block of the communication device 1, particularly the signal compensation device 8, may be configured by hardware logic, or may be realized by software using a CPU as follows.

  That is, the communication device 1 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, a RAM (random access memory) that expands the program, A storage device (recording medium) such as a memory for storing the program and various data is provided. An object of the present invention is to provide a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program of the communication device 1 which is software that realizes the above-described functions is recorded so as to be readable by a computer. This can also be achieved by supplying the communication apparatus 1 and reading and executing the program code recorded on the recording medium by the computer (or CPU or MPU).

  Examples of the recording medium include a tape system such as a magnetic tape and a cassette tape, a magnetic disk such as a floppy (registered trademark) disk / hard disk, and an optical disk such as a CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The communication device 1 may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available. Also, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  According to the present invention, in a transmission signal superposition method for transmitting a signal in the same frequency band, an inbound signal, which is a desired signal, is transmitted from a signal transmitted from the first station to the second station by the nonlinear amplifier of the relay station. Extraction can be performed while greatly reducing the influence of signal distortion.

DESCRIPTION OF SYMBOLS 1 Communication apparatus 2 Signal receiving part 3 Phase rotator 4 1st demodulation part 5 Binarization part 6 Modulator 7 Filter 8 Signal compensation apparatus 8a Compensation replica signal production | generation means 8b I component acquisition part 8c Q component acquisition part 8d Nonlinear compensation model Calculation unit 9 Automatic amplification circuit 10 Correlation calculation unit 11 Signal delay unit 12 Signal cancellation unit 13 Second demodulation unit

Claims (8)

A first station transmission signal transmitted from the first station and a superimposed signal on which a second station transmission signal that is a signal different from the first station transmission signal and transmitted from the second station is superimposed, A signal compensator used in a communication system transmitted from a relay station including a signal amplifier to the second station,
A replica signal that is a replica of the second station transmission signal is input to a nonlinear compensation model that shows the input / output characteristics of the signal amplifier including input and output characteristics of the output signal with respect to the input signal including a linear region and a nonlinear region. Compensation replica signal generation means for generating the signal compensation device. The signal amplifier is a traveling wave tube amplifier (TWTA: TWTA),
The compensation replica signal generation means generates an output u (t) obtained by using the replica signal as an input s (t) as the compensation replica signal based on the following equations (1) to (12). The signal compensator according to claim 1.
u (t) = s (t) × G [s (t)] (1)
G [s (t)] = 1 / | s (t) |
× g (| s (t) |) × exp (jf (| s (t) |)) (2)
g (γ) = α _x · γ / (1 + β _x · γ ² ) (3)
f (γ) = α _φ · γ ² / (1 + β _φ · γ ² ) (4)

i _k = α × I _k (7)
q _k = α × Q _k (8)
s = i _k + jq _k (9)

However,
u (t): Output signal of TWTA s (t): Input signal to TWTA G [s (t)]: Gain of TWTA (gain)
g (r): AM / PM conversion characteristic of TWTA f (r): AM / AM conversion characteristic of TWTA AM: Amplitude Modulation (amplitude modulation)
PM: Phase Modulation
j: √ (−1)
α _x : small signal gain 1 / √β _x : saturation input amplitude α _φ : parameter for determining AM / PM conversion characteristic β _φ : parameter for determining AM / PM conversion characteristic I _k : k-th I component of input signal Q _k : K-th Q component of input signal N: number of data samplings Γ _IBO : IBO (dB)
i _k : I component of input complex amplitude to TWTA q _k : Q component of input complex amplitude to TWTA Amax: Maximum saturation amplitude (dB)

And   The replica signal is obtained by demodulating the second station transmission signal as an undesired signal using a difference in power density between the first station transmission signal and the second station transmission signal. The signal compensation apparatus according to claim 1, wherein the signal compensation apparatus is generated as a replica of a two-station transmission signal.   The replica signal is held in the second station until the second station transmission signal transmitted to the first station returns to the second station. 2. The signal compensation device according to 2. A first station transmission signal transmitted from the first station and a superimposed signal on which a second station transmission signal that is a signal different from the first station transmission signal and transmitted from the second station is superimposed, A signal compensation method used in a communication system transmitted from a relay station including a signal amplifier to the second station,
A replica signal that is a replica of the second station transmission signal is input to a nonlinear compensation model that shows the input / output characteristics of the signal amplifier including input and output characteristics of the output signal with respect to the input signal including a linear region and a nonlinear region. Compensating replica signal generating step for generating a signal compensation method. A first station transmission signal transmitted from the first station and a superimposed signal on which a second station transmission signal that is a signal different from the first station transmission signal and transmitted from the second station is superimposed, A signal compensation program used in a communication system transmitted from a relay station including a signal amplifier to the second station,
A replica signal that is a replica of the second station transmission signal is input to a nonlinear compensation model that shows the input / output characteristics of the signal amplifier including input and output characteristics of the output signal with respect to the input signal including a linear region and a nonlinear region. Compensation signal generation program for causing a computer to execute a compensation replica signal generation step for generating.   A computer-readable recording medium on which the signal compensation program according to claim 6 is recorded.   The communication apparatus provided with the signal compensation apparatus of any one of Claim 1 to 4.

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