JP6743327B2 - Wireless communication system, wireless transmitter, and wireless receiver - Google Patents

Description

The present invention relates to a wireless communication system, a wireless transmission device, and a wireless reception device that perform phase error estimation using a pilot signal in a wireless communication system using an FBMC (Filter Bank Multi-Carrier) transmission method to which OQAM (Offset QAM) is applied. ..

In the next generation wireless communication system, the use of a high frequency band is newly noticed in order to accommodate the increasing data traffic. In addition, it is expected that various services and applications will spread. Therefore, in the next-generation wireless communication system, a flexible transmission method capable of supporting a wide frequency band and various applications is required. The FBMC (Filter Bank Multi-Carrier) transmission method, which has been drawing attention as a flexible transmission method, is a multi-carrier transmission method characterized by performing filter processing for each subcarrier using a filter bank. is there. Further, in the FBMC transmission system, it has been proposed to apply OQAM (Offset QAM) in order to have a high data rate (Non-Patent Document 1). Hereinafter, the FBMC transmission method to which OQAM is applied is referred to as FBMC/OQAM, and the FBMC transmission method to which OQAM is not applied is referred to as FBMC/QAM.

FIG. 1 shows the concept of FBMC/OQAM.
In FIG. 1, by applying OQAM, the real part and the imaginary part of the complex constellation modulation symbol are alternately arranged in the time domain with a shift of ½ symbol interval. Also, in the frequency domain, the real part and the imaginary part are arranged alternately. With such an arrangement, while OFDM has complex orthogonality, FBMC/OQAM has only orthogonality between real parts and between imaginary parts. That is, in FBMC/OQAM, real parts do not interfere with each other and imaginary parts do not interfere with each other, but signals adjacent to each other in the frequency domain (adjacent subcarriers) do not orthogonally interfere with each other. Since it does not, it interferes (Non-patent document 2). The arrow in FIG. 1 indicates that a signal that is not orthogonal to the desired signal interferes.

On the other hand, in the high frequency band, the influence of the phase error due to the frequency error of the local oscillator is large, and there is a problem that the characteristics deteriorate when the FBMC transmission system is used. In order to efficiently use the high frequency band, It is an important issue to reduce the characteristic deterioration due to the phase error. As a typical method for reducing the characteristic deterioration due to the phase error, there is a method of estimating the phase error using a pilot signal and compensating for the phase error. The phase error estimated by this method is characterized by giving equal phase fluctuations to all subcarriers in a symbol. From such a characteristic, the phase error is estimated by calculating the amount of phase fluctuation received by each pilot signal in the symbol and calculating the average thereof. Since the phase error changes with time, estimation accuracy can be improved by estimating for each symbol.

Examples of the pilot signal insertion method include a method of inserting a pilot symbol in the time domain, a method of inserting a pilot subcarrier in the frequency domain, and a method of inserting a pilot signal in a scattered type in the time and frequency domains. Among these, in the method of inserting the pilot symbol and the method of inserting the pilot signal in the scattered type, there is a symbol in which the pilot signal is not inserted, the time-varying phase error cannot be tracked, and the phase error can be accurately estimated. Can not. Therefore, the method of inserting pilot subcarriers in the frequency domain is suitable for tracking and estimating the time-varying phase error.

FIG. 2 shows the configuration of a wireless communication system to which the conventional FBMC/OQAM is applied.

FIG. 2(1) shows a configuration of a wireless transmission device, which includes a modulated signal generation unit 11 that performs coding processing and modulation processing on a generated data signal, a pilot generation unit 12 that generates a pilot signal from a known signal, A pilot insertion unit 13 that inserts the pilot signal output from the pilot generation unit 12 into the output signal of the modulation signal generation unit 11, an OQAM modulation unit 16 that performs OQAM modulation processing on the output signal of the pilot insertion unit 13, and an OQAM modulation unit. An IFFT unit 17 for performing an inverse Fourier transform on the output signal of 16 and a filter processing unit 18 for filtering the output signal of the IFFT unit 17.

FIG. 2(2) shows the configuration of the wireless reception device, which includes a filter processing unit 21 that filters the received signal, an FFT unit 22 that performs a Fourier transform on the output signal of the filter processing unit 21, and an output signal of the FFT unit 22. A phase for estimating a phase error using a pilot demultiplexing unit 23 that separates and outputs pilot subcarriers and data subcarriers, and a known signal shared by wireless transceivers and a pilot signal that is demultiplexed by the pilot demultiplexing unit 23. Output of the error estimator 25, the phase error compensator 26 that compensates the phase error of the data signal separated by the pilot separator 23 using the estimated phase error output from the phase error estimator 25, and the phase error compensator An OQAM demodulation unit 27 that performs OQAM demodulation processing on the signal, and a modulation signal restoration unit 28 that performs demodulation processing and decoding processing on the output signal of the OQAM demodulation unit 27.

M. Bellanger et al., "FBMC Physical Layer: A Primer," June 2010. T. Yoon et al., "Pilot Structure for High Data Rate in OFDM/OQAM-IOTA System," IEEE Vehicular Technology Conference, VTC 2008-Fall, Sept. 2008.

In a wireless communication system to which FBMC/OQAM is applied, a pilot signal receives interference from adjacent symbols in the time domain and interference from adjacent subcarriers in the frequency domain. This makes it difficult to accurately estimate the phase error.

Therefore, in a wireless communication system to which FBMC/OQAM is applied, one or more pilot signals are inserted in all symbols, and the phase error is accurately estimated without being affected by the interference components from the adjacent symbols and adjacent subcarriers. A possible pilot signal processing method is required.

The present invention, when performing phase error estimation using a pilot signal in a wireless communication system to which FBMC/OQAM is applied, accurately estimates the phase error without being affected by interference components from adjacent symbols and adjacent subcarriers. An object of the present invention is to provide a possible wireless communication system, wireless transmission device, and wireless reception device.

The present invention relates to a wireless communication system in which wireless communication is performed between a wireless transmission device and a wireless reception device by the FBMC/OQAM transmission system, and the wireless transmission device gives an arbitrary phase rotation to a known signal in a frequency domain. After that, a null subcarrier consisting of a null signal is inserted between a pilot subcarrier consisting of a pilot signal generated by performing BPSK modulation and a data subcarrier consisting of a data signal. removing the interference to the pilot sub-carrier, comprising a control means only to be due to symbol interference component included in the pilot signal received by the wireless reception device are adjacent in the time domain, the wireless receiver, the known adjacent symbols Phase error estimation means for generating a pilot signal including an interference component due to the reference signal as a reference signal, comparing the generated reference signal with the received pilot signal, and estimating a phase error for each symbol in consideration of interference from adjacent symbols. Equipped with.

The wireless transmission device of the wireless communication system of the present invention can perform a BPSK modulation after applying a phase rotation to a known signal and a modulation signal generation unit that performs coding processing and modulation processing on the generated data signal. A pilot generation unit that generates a pilot signal, a null generation unit that generates a null signal, and a pilot subcarrier composed of the pilot signal are inserted into the data subcarrier composed of the data signal, and further between the pilot subcarrier and the data subcarrier. , A pilot/null insertion unit for inserting a null subcarrier composed of a null signal, an OQAM modulation unit for performing OQAM modulation processing on the output signal of the pilot/ null insertion unit, and an IFFT for inverse Fourier transforming the output signal of the OQAM modulation unit. Section and a filter processing section for filtering the output signal of the IFFT section, and by inserting null subcarriers, interference from adjacent data subcarriers in the frequency domain to pilot subcarriers is removed.

A wireless reception device of a wireless communication system of the present invention includes a filter processing unit that filters a received signal, an FFT unit that performs a Fourier transform on an output signal of the filter processing unit, and an output signal of the FFT unit as a pilot subcarrier and a data sub A pilot separation unit that separates the carrier and null subcarriers and outputs a pilot signal and a data signal, a reference signal generation unit that generates a pilot signal containing an interference component due to a known adjacent symbol as a reference signal, a reference signal and a pilot A phase error estimator that compares the pilot signal separated by the separator and estimates the phase error for each symbol in consideration of interference from adjacent symbols included in the pilot signal of the received signal, and a phase error estimator A phase error compensating unit for compensating the phase error of the data signal separated by the pilot separating unit by using the estimated phase error output from the PQ, and an OQAM demodulating unit for performing OQAM demodulation processing on the output signal of the phase error compensating unit And a modulated signal restoration unit that performs demodulation processing and decoding processing on the output signal of the OQAM demodulation unit.

In the wireless reception device of the wireless communication system of the present invention, the reference signal generation unit inserts a known signal into a subcarrier in which a pilot subcarrier is inserted, and a signal sequence in which a null subcarrier is inserted into other subcarriers. The generated signal sequence is subjected to OQAM modulation, inverse Fourier transform, transmitting-side filter process, receiving-side filter process, and Fourier transform, and an interference component due to a known adjacent symbol is estimated to generate a reference signal.

A radio communication system to which the FBMC/OQAM of the present invention is applied limits an interference component included in a pilot signal to only known signals, so that a phase error can be accurately estimated using a pilot signal on the receiving side. As a result, the estimation accuracy of the phase error is significantly increased compared to the case where the conventional method is applied, and the effect of compensating the phase error is improved. As a result, it is possible to reduce the deterioration of the error rate characteristic and improve the system throughput.

It is a figure which shows the concept of FBMC/OQAM. It is a figure which shows the structure of the radio|wireless communications system which applied the conventional FBMC/OQAM. It is a figure which shows the Example structure of the wireless communication system to which FBMC/OQAM of this invention is applied. It is a figure which shows the simulation result explaining the effect of this invention.

A feature of the wireless transmission device of the wireless communication system of the present invention is that a null subcarrier is inserted between a pilot subcarrier and a data subcarrier in the frequency domain. By this means, it is possible to remove the interference from the data subcarrier to the pilot subcarrier, and the interference component contained in the pilot signal detected by the wireless reception device is limited to only the adjacent symbols. Here, since signals of symbols adjacent to each other in the time domain in the pilot subcarrier are known, the radio receiving apparatus can easily estimate the interference component remaining in the pilot signal.

A feature of the wireless reception device of the wireless communication system of the present invention is to generate a pilot signal including an interference component due to an adjacent symbol using a known signal as a reference signal, and compare the reference signal with the received pilot signal, The phase error is estimated in consideration of interference from adjacent symbols.

The configuration of the embodiment of the wireless communication system will be described below.
FIG. 3 shows an embodiment configuration of a wireless communication system to which the FBMC/OQAM of the present invention is applied.
FIG. 3(1) shows the configuration of the wireless transmission device, which includes a modulated signal generation unit 11, a pilot generation unit 12, a pilot insertion unit 13, a null generation unit 14, a null insertion unit 15, an OQAM modulation unit 16, an IFFT unit 17, and a filter. It is configured by the processing unit 18. The pilot insertion part 13 and the null insertion part 15 may be integrated.

The modulated signal generation unit 11 performs coding processing and modulation processing of an input data signal. The coding process here may be performed at any coding rate using any coding method such as a convolutional code or a turbo code. In addition, QAM modulation is generally used for the modulation processing, and modulation may be performed with an arbitrary multivalued number. The pilot generating unit 12 applies arbitrary phase rotation to the known signal and then performs BPSK modulation to generate a pilot signal. The modulated signal output from the modulated signal generation unit 11 and the pilot signal output from the pilot generation unit 12 are input to the pilot insertion unit 13.

The pilot inserting unit 13 inserts pilot subcarriers, which are pilot signals, into predetermined one or more subcarriers of a modulated signal shared between transmitting and receiving devices in the frequency domain. The output of the pilot insertion unit 13 is input to the null insertion unit 15. On the other hand, the null generator 14 generates and outputs a null signal. Here, the null signal is a signal located at the origin on the IQ plane. Null insertion section 15 inserts a null subcarrier composed of the null signal output from null generation section 14 between the pilot subcarrier output from pilot insertion section 13 and the data subcarrier in the frequency domain. The output of the null insertion unit 15 is input to the OQAM modulator 16.

The OQAM modulator 16 separates the input pilot subcarrier, data subcarrier, and null subcarrier complex number signals into a real part and an imaginary part, respectively, and shifts them by 1/2 symbol in the time domain and alternately arranges them. Further, by alternately applying the modulation in which the real part is arranged to be 1/2 symbol ahead and the modulation in which the imaginary part is arranged to 1/2 symbol ahead, for each subcarrier, the real part and the imaginary part are also formed in the frequency domain. Place them alternately. The signal subjected to the OQAM modulation processing by the OQAM modulation unit 16 is input to the IFFT unit 17. The IFFT unit 17 inverse Fourier transforms the input signal and inputs the signal to the filter processing unit 18. The filter processing unit 18 performs a filtering process for each subcarrier in the frequency domain and performs a parallel/serial conversion of the filtered signal (converts a parallel signal composed of a plurality of series into a serial signal). I do. In FBMC/OQAM, the polyphase configuration of the synthesis filter bank is applied to the filter processing unit 18. The filter is a prototype filter having the same frequency characteristics as the low-pass filter (PHYDYAS, "D5-1: Prototype filter and structure optimization," January 2009.).

Here, a processing example of the null insertion unit 15 will be described. If the number of all subcarriers is M and the subcarrier index is k (0 ≤ k ≤ M-1), and pilot subcarriers are inserted in k = n (1 ≤ n ≤ M-2), k = n-1 and k Insert a null subcarrier at =n+1. When inserting pilot subcarriers at the ends of data subcarriers (k=0, k=M−1), null subcarriers are inserted only at k=1 and k=M−2. By sharing the subcarrier in which the pilot signal is inserted between the transmitting and receiving devices, in the wireless receiving device, the nth subcarrier is a pilot subcarrier, the n-1 and n+1th subcarriers are null subcarriers, and the others. By using the subcarrier of as the data subcarrier, the pilot subcarrier, the data subcarrier, and the null subcarrier can be accurately separated, and the pilot subcarrier and the data subcarrier can be taken out. Similarly, when a plurality of m lines inserts pilot sub-carrier, k = n _1, n ₂ at the transmission side, ..., the pilot subcarriers _{n m, k = n 1 ±} 1, n 2 ± 1, ..., n _A null subcarrier is inserted in _m ±1, the radio receiving apparatus separates the pilot subcarrier, the null subcarrier, and the data subcarrier, and the phase error estimation is performed for each symbol using the signal of the pilot subcarrier.

When inserting pilot subcarriers into two or more continuous subcarriers, null subcarriers are inserted into only two subcarriers located between both ends of continuous pilot subcarriers and data subcarriers. Although the signals of the adjacent pilot subcarriers interfere with each other, the signals of the respective pilot subcarriers are known signals, so that the interference component can be easily estimated by the wireless reception device.

FIG. 3B shows the configuration of the wireless reception device, which includes a filter processing unit 21, an FFT unit 22, a pilot separation unit 23, a reference signal generation unit 24, a phase error estimation unit 25, a phase error compensation unit 26, and an OQAM demodulation unit 27. , Modulation signal restoration unit 28.

The filter processing unit 21 performs a process equivalent to performing a filter process for each subcarrier after serial/parallel conversion (converting a serial signal into a parallel signal composed of a plurality of series) of an input received signal. The filter processing unit 21 is applied with the polyphase configuration of the analysis filter bank paired with the filter processing unit 18 of the wireless transmission device. The filter used is also a pair with the prototype filter applied in the wireless transmission device.

The output signal of the filter processing unit 21 is Fourier transformed by the FFT unit 22 and input to the pilot separation unit 23. The pilot demultiplexing unit 23 demultiplexes the output signal of the FFT unit 22 into pilot subcarriers, data subcarriers, and null subcarriers based on the information of the insertion positions of the pilot subcarriers shared between the transmitting and receiving devices, Is input to the phase error estimation unit 25, and the data signal is input to the phase error compensation unit 26.

On the other hand, the reference signal generation unit 24 inserts the known signal into the subcarriers in which the pilot subcarriers are inserted and the null subcarriers into the other subcarriers, using the information of the known signal and the insertion location of the pilot subcarriers. The inserted signal sequence is generated and subjected to OQAM modulation, inverse Fourier transform, transmission side filter process, reception side filter process, and Fourier transform on this signal sequence, so that the inserted pilot subcarrier receives an interference component from an adjacent symbol. The considered pilot signal is generated as a reference signal and output. The phase error estimation unit 25 receives the pilot signal output from the pilot separation unit 23 and the reference signal output from the reference signal generation unit 24, and compares these signals to determine the phase received by each pilot signal. The error is estimated and output as an estimated phase error. When a plurality of pilot signals are inserted in the same symbol, the average of the phase errors received by the pilot signals in the same symbol is calculated, and this is output as the estimated phase error.

The phase error compensator 26 inputs the data signal separated by the pilot separator 23 and the estimated phase error output from the phase error estimator 25, compensates the phase error of the data signal for each symbol, and the OQAM demodulator 27. To enter. The OQAM demodulator 27 OQAM demodulates the input data signal for each subcarrier. At this time, OQAM demodulation processing corresponding to the modulation processing performed by the OQAM modulation unit 16 on the transmission side is performed on each subcarrier based on the information on the insertion location of the pilot subcarrier. The output signal of the OQAM demodulation unit 27 is input to the modulation signal restoration unit 28. The modulation signal restoration unit 28 performs decoding/demodulation processing corresponding to the coding/modulation performed by the modulation signal generation unit 11 on the transmission side, and restores the data signal.

The wireless communication system of the present invention configured by the wireless transmission device and the wireless reception device described above can be applied to a fixed communication system and a mobile communication system using radio.

The pilot signal processing method according to the present invention can also be applied to phase error estimation in MIMO (Multi-Input Multi-Output) transmission in which wireless communication is performed using a plurality of antennas.

Further, the effect of the pilot signal processing method according to the present invention does not depend on the used frequency, and can be applied to any frequency band used in a wireless communication system including a high frequency band. Further, the processing of the pilot signal between the wireless transmission/reception devices of the present invention can be used for phase error estimation regardless of the occupied bandwidth.

Further, the pilot signal processing method of the present invention can be applied to FBMC/QAM to which OQAM is not applied and multicarrier transmission such as OFDM. In this case, when the pilot generator 12 generates the pilot signal, it is not necessary to give an arbitrary phase rotation to the known signal. Further, when applied to the FBMC/QAM system, the OQAM modulator 16 of the radio transmitter and the OQAM demodulator 27 of the radio receiver shown in FIG. 3 are unnecessary, and the pilot subcarriers and the null subcarriers are not OQAM processed. To use. Further, the filter processing unit 18 and the filter processing unit 21 use filters suitable for FBMC/OAM signal formation. Further, when applied to the OFDM system, the OQAM modulator 16 and the filter processor 18 of the radio transmitter, the OQAM demodulator 27 and the filter 21 of the radio receiver are unnecessary, and the pilot subcarrier and the null subcarrier are OQAM. Used without processing and filtering.

Further, when the transmission characteristics of the frequency in which the pilot subcarrier is inserted are deteriorated due to the frequency selective fading, the subcarrier in which the pilot subcarrier is inserted may be changed. In this case, the symbol immediately before the pilot subcarrier insertion position is changed is used to notify the wireless reception device of the subcarrier in which the pilot signal is newly inserted. At this time, in the subcarrier insertion position notification symbol, a null signal is inserted in a subcarrier in which a pilot signal is newly inserted in null insertion section 15 of the wireless transmission device. Since the data signal of the notification symbol does not interfere with the next symbol by inserting the null signal, the pilot signal can be accurately restored in the wireless reception device. In the wireless reception device, after receiving the notification of the change of the insertion position of the pilot subcarrier, the reference signal generation unit 24 generates the reference signal in the new pilot subcarrier arrangement.

Further, although the phase error can be accurately estimated by using the pilot signal on the receiving side by the pilot signal processing method according to the present invention, the phase error can be similarly used for channel estimation.

FIG. 4 shows simulation results for explaining the effect of the present invention.
The simulation specifications used convolutional code with coding rate 3/4 and Viterbi decoding for encoding and decoding, 64QAM for modulation and demodulation, subcarrier spacing 312.5 kHz, phase error level 1 MHz offset -90 dBc/Hz. , The propagation environment is additive white gaussian noise (AWGN), the number of transmission subcarriers is 60, the number of data subcarriers is 56, the number of pilot subcarriers is 4, and the method of the present invention is data subcarriers. The number is 48, the number of pilot subcarriers is 4, and the number of null subcarriers is 8.

At Eb/No=20 dB, the conventional method has BER=0.41 and the invented method has BER=2.8×10 ^-4 . From these results, assuming that the transmission time of a 1500-byte data packet is 224 μs and the control signal is 146 μs per packet, the throughput is estimated to be 4.8 × 10 ^-12 Mbps for the conventional method and 32 Mbps for the invented method, and FBMC/OQAM. As a result of using the method of the invention in the wireless communication system to which is applied, it can be seen that the accuracy of estimation of the phase error is improved and the compensation effect of the phase error is improved, thereby reducing the deterioration of the error rate characteristic and improving the system throughput. .. This tendency becomes more remarkable as the packet length becomes longer.

11 Modulation Signal Generation Section 12 Pilot Generation Section 13 Pilot Insertion Section 14 Null Generation Section 15 Null Insertion Section 16 OQAM Modulation Section 17 IFFT Section 18 Filter Processing Section 21 Filter Processing Section 22 FFT Section 23 Pilot Separation Section 24 Reference Signal Generation Section 25 Phase Error estimation unit 26 Phase error compensation unit 27 OQAM demodulation unit 28 Modulated signal restoration unit

Claims (4)

In a wireless communication system in which wireless communication is performed between a wireless transmission device and a wireless reception device by an FBMC (Filter Bank Multi-Carrier) transmission method to which OQAM (Offset QAM) is applied, the wireless transmission device, in the frequency domain , A null subcarrier made up of a null signal is inserted between a pilot subcarrier made up of a pilot signal generated by applying arbitrary phase rotation to a known signal and then performing BPSK modulation and a data subcarrier made up of a data signal. to remove the interference to the pilot subcarrier from the data adjacent subcarriers in the frequency domain, comprises a control means for interference component included in the pilot signal received by the wireless receiving apparatus is only by symbols adjacent in the time domain ,
The radio receiving device generates a pilot signal including an interference component due to a known adjacent symbol as a reference signal, compares the generated reference signal and the received pilot signal, and considers interference from the adjacent symbol A wireless communication system comprising a phase error estimating means for estimating a phase error for each . The wireless transmission device of the wireless communication system according to claim 1,
A modulation signal generation unit that performs encoding processing and modulation processing on the generated data signal,
A pilot generation unit that generates a pilot signal by performing BPSK modulation after applying an arbitrary phase rotation to a known signal;
A null generator that generates a null signal,
A pilot/null insertion unit that inserts a pilot subcarrier composed of the pilot signal into a data subcarrier composed of the data signal, and further inserts a null subcarrier composed of the null signal between the pilot subcarrier and the data subcarrier. When,
An OQAM modulator for performing OQAM modulation on the output signal of the pilot/ null inserter;
An IFFT unit for performing an inverse Fourier transform on the output signal of the OQAM modulation unit,
A filter processing unit that filters the output signal of the IFFT unit;
A radio transmitting apparatus, characterized in that, by inserting the null subcarrier, interference from adjacent data subcarriers in the frequency domain to pilot subcarriers is removed. The wireless reception device of the wireless communication system according to claim 1,
A filter processing unit that filters the received signal,
An FFT unit for performing a Fourier transform on the output signal of the filter processing unit,
A pilot separation unit that separates the output signal of the FFT unit into pilot subcarriers, data subcarriers, and null subcarriers, and outputs a pilot signal and a data signal;
A reference signal generation unit that generates a pilot signal including an interference component due to a known adjacent symbol as a reference signal,
A phase error that compares the reference signal with the pilot signal separated by the pilot separation unit and estimates a phase error for each symbol in consideration of interference from adjacent symbols included in the pilot signal of the received signal. An estimation section,
A phase error compensator that compensates for each symbol the phase error of the data signal separated by the pilot separator using the estimated phase error output from the phase error estimator,
An OQAM demodulation unit that performs OQAM demodulation processing on the output signal of the phase error compensation unit;
And a modulated signal restoration unit that performs demodulation processing and decoding processing on the output signal of the OQAM demodulation unit. The radio receiver of the radio communication system according to claim 3,
The reference signal generation unit inserts the known signal into a subcarrier into which the pilot subcarrier is inserted, generates a signal sequence in which null subcarriers are inserted into other subcarriers, and OQAM-modulates the signal sequence. , An inverse Fourier transform, a transmitting side filtering process, a receiving side filtering process, and a Fourier transform are performed, and an interference component due to the known adjacent symbol is estimated to generate the reference signal. ..

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