JP2009065608A - Receiving apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate adjacent channel interference caused by a difference in frequency offset of a base station. <P>SOLUTION: A reception signal is input to a multiplier 13 for compensating for frequency offset of an OFDM signal 1 from a base station A and a multiplier 21 for compensating for frequency offset of an OFDM signal 2 from a base station B. Output of the multiplier 13 is input to a subtractor 15 via a GI elimination section 14. Output of the multiplier 21 is input to a Fourier transform section 23 via a GI elimination section 22, made into a component for each sub-carrier of the OFDM signal 2 from the base station B, and combined into a temporal waveform by an inverse Fourier transform section 24. The temporal waveform from the inverse Fourier transform section 24 is brought into the same frequency relation as the frequency offset of the base station A by a multiplier 25, then input to the subtractor 15, and subtracted from an output signal from the GI elimination section 14. Thus, the receiving signal from which an interference signal from the base station B is eliminated, is supplied to a Fourier transform section 16. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a receiving apparatus in a wireless communication system employing an OFDM method.

In order to improve cell-edge throughput in a wireless communication system such as a cellular system, frequency repetition (3 cell repetition, etc.), reuse partition (Non-patent Document 1), FFR (Fractional Frequency Reuse) (Non-Patent Document 2), etc. Frequency reuse techniques are known.
Halpern, SW "Reuse partitioning in cellular systems", Proceedings of IEEE Vehicular Technology Conference, VTC-83, pp.322-327, (1983). Nortel, "Adaptive Fractional Frequency Reuse", 3GPP TSG-RAN Working Group 1 Meeting # 44bis R1-060905, Mar.27-31,2006. <Http://www.3gpp.org/ftp/tsg_ran/WG1_RL1/TSGR1_44bis/ Docs / R1-060905.zip>

In recent years, a wireless communication system employing an OFDM (Orthogonal Frequency Division Multiplexing) scheme has attracted attention.
When frequency repetition, FFR, reuse partition, or the like is applied to a wireless communication system that employs such an OFDM system, an OFDM signal transmitted from the base station A to which the mobile station belongs and transmitted from the adjacent base station B There may be a frequency band adjacent to the OFDM signal to be processed. Each base station is controlled so as not to have a frequency offset, but it is difficult to eliminate the frequency offset, and the amount of the frequency offset may be different for each base station.
In such a case, the orthogonal relationship between the subcarriers transmitted from the base station A and the subcarriers transmitted from the base station B cannot be maintained, and adjacent channel interference becomes a problem.

FIG. 8 is a diagram showing a configuration of a wireless communication system employing the OFDM method.
In this figure, an OFDM signal 1 transmitted from the base station A and an OFDM signal 2 in a frequency band adjacent to the OFDM signal 1 transmitted from the base station B reach the mobile station C. Basically, signals from a plurality of base stations are orthogonal, but may interfere with each other due to the influence of frequency offset.

FIG. 9 is a diagram for explaining the influence of the difference in frequency offset between base stations.
In this figure, the vertical axis represents the received power, and the horizontal axis represents the subcarrier number. When a signal of subcarrier number −6 to 0 is transmitted from the base station A, the signal transmitted from the base station B The received power received in the band of subcarrier numbers 1 to 9 that is the band, that is, the interference power for the signal transmitted from the base station B by the signal transmitted from the base station A is expressed by the value of the normalized frequency offset α. It shows about each case of (alpha) = 0.01-1. Here, the subcarrier interval is 15 kHz, and the normalized frequency offset α is a value obtained by dividing the frequency offset by the subcarrier interval (15 kHz).
As is apparent from FIG. 9, it is shown that interference is exerted on the reception band from the adjacent base station due to the influence of the frequency offset difference between the base stations.

Thus, mutual interference (adjacent channel interference) between the received signals from each base station has occurred due to the difference in frequency offset between base stations.
Conventionally, since only the signal of the base station with which it communicates is received, there has been a problem that inter-frequency interference from adjacent frequencies cannot be removed and communication quality deteriorates.

  Therefore, the present invention provides a receiving apparatus capable of overcoming communication quality degradation due to mutual interference (adjacent channel interference) between received signals from each base station, which is caused by a difference in frequency offset between base stations. It is an object.

  In order to solve the above problems, a receiving apparatus according to the present invention is a receiving apparatus used in a wireless communication system in which OFDM signals in close frequency bands are transmitted from a plurality of base stations. First frequency offset compensation means for compensating and outputting the frequency offset of the OFDM signal from one base station, and receiving the received signal, compensating and outputting the frequency offset of the OFDM signal from the second base station Second frequency offset compensation means for inputting, and second Fourier transform means for receiving the output signal of the second frequency offset compensation means and decomposing the OFDM signal from the second base station into components for each subcarrier And an inverse Fourier transform means for synthesizing and outputting a component for each subcarrier decomposed by the Fourier transform means into a time waveform, and the inverse Fourier transform. A third frequency offset compensating means for receiving the output signal of the means and compensating and outputting the frequency offset so as to have the same frequency relationship as the output signal of the first frequency offset compensating means, and the first frequency offset Subtracting means for subtracting the output signal of the third frequency offset compensating means from the output signal of the compensating means, and the output signal of the subtracting means being input, and subtracting the OFDM signal from the first base station as a subcarrier And first Fourier transform means for decomposing each component.

Further, the demodulating means for demodulating the component for each subcarrier of the OFDM signal from the second base station output from the second Fourier transform means, and the data for each subcarrier demodulated by the demodulating means are modulated. Modulation means for outputting to the inverse Fourier transform means, and the inverse Fourier transform means synthesizes an output signal from the modulation means into a time waveform.
Further, the OFDM signal from the second base station has been subjected to error correction coding, an error correction decoding means for performing error correction decoding processing on the output signal of the demodulation means, and an error correction decoding means Error correction coding means for performing error correction coding on the output and outputting the result to the modulation means, the modulation means modulating the output signal from the error correction coding means to perform the inverse Fourier transform Output to the means.
Still further, the inverse Fourier transform means determines one or more subcarriers close to the frequency band of the OFDM signal from the first base station among the subcarriers included in the OFDM signal from the second base station. It is supposed to be synthesized into a time waveform and output.

  Furthermore, another receiving apparatus of the present invention is a receiving apparatus used in a wireless communication system in which OFDM signals in a frequency band close to each other are transmitted from a plurality of base stations. A first frequency offset compensating means for compensating and outputting a frequency offset of the OFDM signal from the station; and a second for receiving the received signal and compensating and outputting the frequency offset of the OFDM signal from the second base station. Frequency offset compensation means, first subtraction means for subtracting the output signal of the third frequency offset compensation means from the output signal of the first frequency offset compensation means, and the second frequency offset compensation means The second subtracting means for subtracting the output signal of the fourth frequency offset compensating means from the output signal of the output signal, and the output signal of the first subtracting means. A first Fourier transform means for decomposing and outputting an OFDM signal from the first base station into components for each subcarrier, and an output signal of the second subtraction means, and the second base station A second Fourier transform means for decomposing and outputting the OFDM signal from the station into components for each subcarrier; and for each subcarrier of the OFDM signal from the first base station decomposed by the first Fourier transform means The first inverse Fourier transform means for synthesizing and generating the components of the time waveform and outputting them, and the components for each subcarrier of the OFDM signal from the second base station decomposed by the second Fourier transform means are time waveforms And an output signal from the first inverse Fourier transform means and the same frequency as the output signal of the second frequency offset compensation means The output signal from the fourth frequency offset compensation means that compensates and outputs the frequency offset so as to be related and the output signal from the second inverse Fourier transform means are input, and the output signal of the first frequency offset compensation means The third frequency offset compensating means for compensating and outputting the frequency offset so as to have the same frequency relationship as the above.

Furthermore, the first demodulation means for demodulating the component for each subcarrier of the OFDM signal from the first base station output from the first Fourier transform means, and demodulated by the first demodulation means First modulation means for modulating the data for each subcarrier and outputting it to the first inverse Fourier transform means; and sub-signals of the OFDM signal from the second base station outputted from the second Fourier transform means A second demodulating means for demodulating a component for each carrier; a second modulating means for modulating the data for each subcarrier demodulated by the second demodulating means and outputting the data to the second inverse Fourier transform means; The first inverse Fourier transform means synthesizes an output signal from the first modulation means into a time waveform and outputs the time waveform; and the second inverse Fourier transform means comprises the second modulation means. Output from It is intended to synthesize and output the time waveform No..
Furthermore, the OFDM signals from the first base station and the second base station are error-correction-encoded, and an error correction decoding process is performed on the output signal of the first demodulation means. Error correction decoding means, second error correction decoding means for performing error correction decoding processing on the output signal of the second demodulation means, and error correction for the output of the first error correction decoding means First error correction coding means for performing coding and outputting to the first modulation means; and error correction coding for the output of the second error correction decoding means to perform the second modulation means. Second error correction coding means for outputting to the first error correction coding means, wherein the first modulation means modulates the output signal from the first error correction coding means and sends the modulated signal to the first inverse Fourier transform means. The second modulation means outputs the second error correction code Modulates the output signal from the means is intended to be output to the second inverse Fourier transform unit.
Furthermore, the first inverse Fourier transform means includes one or more of the subcarriers included in the OFDM signal from the first base station that are close to the frequency band of the OFDM signal from the second base station. Subcarriers are combined into a time waveform and output, and the second inverse Fourier transform means outputs subcarriers from the first base station out of subcarriers included in the OFDM signal from the second base station. One or more subcarriers close to the frequency band of the OFDM signal are combined into a time waveform and output.

  According to such a receiving apparatus of the present invention, by receiving a signal from an adjacent base station transmitted at a close frequency and removing it, inter-frequency interference is reduced and communication quality is improved. Can do.

FIG. 1 is a block diagram showing a configuration of an embodiment of a receiving apparatus 10 of the present invention.
The receiving apparatus 10 is provided in the mobile station C in FIG. 8, and as described above, the OFDM signal 1 from the first base station A and the OFDM signal 2 from the second base station B are Received by the antenna 11. Here, it is assumed that the received signal from the first base station A is the desired reception signal.
A signal received by the antenna 11 is multiplied by a signal having the same frequency as the carrier wave fc by a multiplier 12, down-converted to a baseband signal, and input to a multiplier 13 and a multiplier 21.
The received signal input to the multiplier 13 is compensated for the frequency offset f _{A of the} signal transmitted from the base station A and input to the guard interval removing unit 14. Note that the frequency offset of the signal transmitted from each base station can be measured, for example, by detecting the phase of a pilot signal included in the signal transmitted from the base station.
The signal output from the guard interval removing unit 14 is input to the subtractor 15, and the subtractor 15 subtracts the interference component (OFDM signal transmitted from the base station B) supplied from the multiplier 25 as will be described later. Then, the signal is supplied to the Fourier transform unit 16 where the OFDM signal transmitted from the base station A, which is a desired reception signal, is converted into a signal (data) for each subcarrier. This signal is supplied to a decoding unit (not shown) and decoded.

The signal down-converted to baseband by the multiplier 12 is also input to the multiplier 21 where the frequency offset f _{B of the} signal transmitted from the base station _B is compensated and input to the guard interval removal unit 22. Is done. The received signal from which the guard interval is removed by the guard interval removing unit 22 is input to the Fourier transform unit 23, where the OFDM signal 2 transmitted from the base station B is converted into a signal for each subcarrier.
The signal for each subcarrier of the OFDM signal 2 transmitted from the base station B output from the Fourier transform unit 23 is supplied to the inverse Fourier transform unit 24, where it is OFDM-modulated into a time domain signal. The OFDM signal 2 (interference component) transmitted from B is reproduced. The reproduced interference component is added with the frequency offset f _B of the base station B and compensated for the frequency offset of the base station A by the multiplier 25. Thereby, the frequency offset of the interference component (OFDM signal 2 of the adjacent channel transmitted from the base station B) with respect to the OFDM signal 1 transmitted from the base station A is the same as the signal whose frequency offset is compensated by the multiplier 13. It is considered a relationship.
The interference component output from the multiplier 25 is input to the subtractor 15, where the interference component is subtracted from the received signal from which the frequency offset has been compensated and the guard interval has been removed. The received signal from the base station A from which the inter-adjacent channel interference component (interference component) has been removed is supplied to the Fourier transform unit 16 and subjected to OFDM demodulation.
As described above, the multiplier 21, the guard interval removing unit 22, the Fourier transform unit 23, the inverse Fourier transform unit 24, the multiplier 25, and the subtractor 15 cause interference components (in this case, transmitted from the base station B) from the received signal. The interference canceller 20 for subtracting the (OFDM signal) is configured.

Processing relating to frequency offset removal performed using the multipliers 13, 21, and 25 will be described with reference to FIG.
FIG. 2A is a diagram showing a received signal received by the antenna 11 and down-converted to the baseband region by the multiplier 12. As shown in the figure, it is assumed that the received signal 1 from the base station A has a frequency offset of f _A and the received signal 2 from the base station B has a frequency offset of f _B.
As described above, since the frequency offset f _A included in the received signal 1 from the base station A is removed in the multiplier 13, the received signal 1 from the base station A output from the multiplier 13 is as shown in FIG. As shown in (b), the position has no frequency offset.
Further, since the frequency offset f _B included in the received signal 2 from the base station B is removed by the multiplier 21, the received signal 2 from the base station B output from the multiplier 21 is shown in ( As shown in c), the position has no frequency offset.

As described above, the received signal 2 from which the frequency offset shown in (c) of FIG. 2 is removed is converted into a signal for each subcarrier by the Fourier transform unit 23, and the signal in the time domain is again converted by the inverse Fourier transform unit 24. To reproduce the OFDM signal (interference component) transmitted from the base station B, and subtract it from the input signal to the Fourier transform unit 16 that demodulates the received signal from the base station A. The received signal 2 that is a component is subtracted. At this time, the output from the inverse Fourier transformer 24 is based on the signal from which the frequency offset is removed. There is a frequency shift corresponding to the offset.
Therefore, in the multiplier 25, the frequency of the interference component output from the inverse Fourier transform unit 24 is the same as the received signal 1 in the received signal shown in FIG. 2A (in the example shown, the received signal 1). The frequency is shifted so that the frequency D shifts between the highest frequency of the received signal 2 and the lowest frequency of the received signal 2). That is, the multiplier 25 performs a frequency shift of f _B −f _A.
As a result, as shown in FIG. 2D, the interference component output from the multiplier 25 is the same as the received signal 2 of the received signal output from the multiplier 13 and output from the guard interval removing unit 14. As shown in FIG. 2 (e), a reception signal 1 from which the reception signal 2 that is an interference component between adjacent channels is removed is obtained by subtracting the frequency band, and the interference is removed. The received signal can be input to the Fourier transform unit 16.

In the embodiment shown in FIG. 1, the signal after being Fourier-transformed by the Fourier transform unit 23 is a signal that has received interference or noise from an adjacent channel (adjacent base station).
That is, assuming that the received signal from the base station B is R _B , R _B is expressed as follows.
R _B = d _B H _B + I _A + N (1)
Here, d _{B is} a transmission signal of the base station B, H _B is a fluctuation in a propagation path with the base station B, I _A is interference from an adjacent channel (base station A), and N is noise.
Subtracting this reception signal R _B as it is from the receive signal as an interference component, so that the results in unnecessarily cancel the interference component I _A.
Therefore, a second embodiment of the present invention that can suppress interference components with higher accuracy by determining received data after Fourier transform will be described.

FIG. 3 is a block diagram showing a main configuration of a second embodiment of the receiving apparatus of the present invention in which received data is determined. In this figure, the same components as those in FIG.
As shown in FIG. 3, in this embodiment, a demodulator 26 and a modulator 27 to which the output of the demodulator 26 is input are provided between the Fourier transform unit 23 and the inverse Fourier transform unit 24. ing.
The subcarrier signal output from the Fourier transform unit 23 is demodulated by the demodulation unit 26 to determine the received data. The received data and D _B. When the data D _B after the determination is modulated by the modulation unit 27, if the determination is correct, the modulation signal d _B ′ = d _B is obtained. After multiplying this by the propagation path fluctuation H _B , the inverse Fourier transform unit 24 generates a time waveform, whereby an interference component not including interference I _A and noise N from the adjacent channel in the equation (1) is obtained. Can be played.
As described above, the determination by the demodulator 26 can cancel the interference component without being affected by interference or noise in the received signal, so that the accuracy of the interference canceller can be improved.

さらに、第１の基地局Ａからの信号との周波数関係を合わせるために周波数オフセットを補償すると補償後の信号ｃ'(k)は、次式となる。

ここで、ｆ_A、ｆ_Bは第１，第２の基地局の周波数オフセットを、Δｆはサブキャリア間隔を表す。
また、判定を行なう場合には、判定データに基づき変調を行った信号をｄ_B'(n)とすると、Ｒ(n)＝ｄ_B'(n)Ｈ_B(n)となり、キャンセル用の信号は、上記と同様に作成される。 Specific cancellation signals used in the interference canceller will be specifically described below using mathematical expressions.
In the embodiment shown in FIG. 1, the received signal of the nth subcarrier after the Fourier transform from the second base station B is R (n). At this time, the transmission signal of the second base station B is d _B (n), the propagation path fluctuation is H _B (n), the interference component due to the reception signal from the first base station A is I (n), If the noise is N (n), R (n) is expressed by the following equation.
R (n) = d _B (n) H _B (n) + I (n) + N (n)
When the number of all subcarriers is N and the second base station B performs transmission using subcarriers N / 2 to N−1, and the time sample number is k, the signal c (k after inverse Fourier transform) ) Can be expressed by the following equation.

Further, when the frequency offset is compensated for matching the frequency relationship with the signal from the first base station A, the compensated signal c ′ (k) is expressed by the following equation.

Here, f _A and f _B represent the frequency offsets of the first and second base stations, and Δf represents the subcarrier interval.
Further, in the determination, if the signal modulated based on the determination data is d _B ′ (n), R (n) = d _B ′ (n) H _B (n), and the cancel signal Is created as described above.

According to the second embodiment, interference can be canceled by eliminating the influence of interference and noise. However, when a determination error occurs in the demodulator 26, the wrong signal is canceled. As a result, communication quality deteriorates accordingly. In order to eliminate such inconvenience, a third embodiment of the present invention in which the accuracy of determination is improved using an error correction code will be described.
FIG. 4 is a block diagram showing a main configuration of the third embodiment of the present invention. In this embodiment, the data transmitted from the base station B is assumed to be error correction encoded.
As is clear from comparison between FIG. 4 and FIG. 3, in this embodiment, an error correction decoding unit 28 and an error correction encoding unit 29 are provided between the demodulation unit 26 and the modulation unit 27. The signal demodulated by the demodulator 26 is subjected to error correction, and the error-corrected data is subjected to error correction coding and supplied to the modulator 27.
That is, the reception signal (complex symbol such as 1 + j) for each subcarrier output from the Fourier transform unit 23 is demodulated by the demodulation unit 26 and the determination signal (1,0 data or reception level) for each subcarrier. Is weighted data). The determination signal for each subcarrier is the data (1,0 data) that has been error-corrected by the error correction decoding unit 28, and is input to the error correction encoding unit 29 and is again subjected to error correction encoding (1, 0 data). The error-corrected encoded data is input to the modulation unit 27 to be a signal for each subcarrier (complex symbol such as 1 + j), and the inverse Fourier transform unit 24 generates a time waveform.
By providing the error correction decoding unit 28 and the error correction encoding unit 29 in this manner, the possibility of a determination error can be reduced, and interference cancellation with higher accuracy can be performed.

  Furthermore, in the first to third embodiments, each subcarrier signal from the Fourier transform unit 23 (or a signal modulated after demodulating it, or error-correction-decoded after demodulation, and an error-correcting code) When the time-waveform is generated by inputting the signal after modulation into the inverse Fourier transform unit 24, it is not necessary to use the signals of all subcarriers, but signals of adjacent subcarriers that give large interference (for example, adjacent signals) Only a few subcarriers) may be inverse Fourier transformed by the inverse Fourier transform unit 24 to generate a time waveform. Thereby, the amount of signal processing can be reduced. Note that only a small number of subcarriers may be output from the Fourier transform unit 23, or only a small number of subcarrier components output from the Fourier transform unit 23 may be selected to perform the inverse Fourier transform. The signal may be input to the unit 24 (or the demodulator 26).

In each of the above-described embodiments, the signal from the first base station A is the desired signal, and the signal from the second base station B is the interference component. Next, an embodiment of the present invention applied when the mobile station C receives both the received signal 1 from the first base station A and the received signal 2 from the second base station B will be described.
A method for improving the throughput of a mobile station located near a cell boundary by synchronizing timing between a plurality of base stations and allowing OFDM signals from the plurality of base stations to be orthogonally multiplexed by frequency multiplexing and received by the mobile station C is also considered. It is done. When such a method is adopted, signals from the first base station A and the second base station B are both received by the mobile station C. At this time, as described above, if the frequency offset for each base station is different, the received signal from the second base station B becomes an interference component with respect to the received signal from the first base station A, and For the received signal from the second base station B, the received signal from the first base station A becomes an interference component.
Therefore, in this embodiment, the reception signal from the base station B is removed from the reception signal for decoding the signal from the base station A, and the base station A is converted from the reception signal for decoding the signal from the base station B. The received signal from is removed.

FIG. 5 is a principal block diagram showing the configuration of the fourth embodiment of the receiving apparatus of the present invention. In this figure, the same components as those in FIG.
As is clear from comparison between FIG. 1 and FIG. 5, in this embodiment, the output signal of the Fourier transform unit 16 that extracts the reception component for each subcarrier from the reception signal 1 from the first base station A. And the output of the Fourier transform unit 23 that extracts the received component for each subcarrier from the received signal 2 from the second base station B are input as a received signal (data) to a demodulator (not shown).

Further, an inverse Fourier transform unit 31 to which an output of the Fourier transform unit 16 corresponding to the received signal 1 from the base station A is input is provided, and the received signal 1 reproduced by the inverse Fourier transform unit 31 is provided. A time waveform that is an interference component is generated.
This time waveform is input to the multiplier 32, where the frequency shift (f _A −f _B ) is the same as the received signal 1 included in the received signal output from the guard interval removing unit 22. Is only frequency shifted.
A subtractor 33 is provided between the guard interval removing unit 22 and the Fourier transform unit 23. In the subtracter 33, the frequency offset f _B is compensated by the multiplier 21, and the guard interval removing unit 22 is provided. The interference component shifted in frequency by the multiplier 32 is subtracted from the received signal 2 from the base station B that is output through the base station B, and the received signal 1 from the base station A that causes interference between adjacent channels is subtracted. The received signal 2 is input to the Fourier transform unit 23, and the received component for each subcarrier is extracted.
The output of the Fourier transform unit 23 is output as a received signal data to a subsequent demodulating unit and also supplied to the inverse Fourier transform unit 24. Here, as described above, the received signal 1 from the base station A is received. Interference component to be subtracted from the input signal to the Fourier transform unit 16 for OFDM demodulation.

  Thus, according to this embodiment, signal components that cause interference between adjacent channels are removed from the received signal 1 from the first base station A and the received signal 2 from the second base station B, respectively. The Fourier transform unit 16 and the Fourier transform unit 23 can respectively obtain the corresponding subcarrier reception components.

In this embodiment as well, as in the embodiment of FIG. 3, a demodulator that demodulates each subcarrier component is demodulated by the demodulator between the Fourier transform unit and the inverse Fourier transform unit. Further, a modulation unit for modulating the data of each subcarrier component may be provided. That is, in this embodiment, each subcarrier component of the OFDM signal 2 from the second base station B is demodulated by the second demodulator supplied with the output of the Fourier transform unit 23, and each demodulated The subcarrier component data is modulated by the second modulation unit and supplied to the inverse Fourier transform unit 24 to reproduce the OFDM signal transmitted from the base station B. Further, the first demodulator supplied with the output of the Fourier transform unit 16 demodulates each subcarrier component of the OFDM signal 1 from the first base station A, and the demodulated data of each subcarrier component is converted into the first subcarrier component. The OFDM signal transmitted from the base station A is reproduced by being modulated by one modulation unit and supplied to the inverse Fourier transform unit 31.
Thereby, since interference can be canceled without being affected by interference or noise in the received signal, the accuracy of the canceller can be improved.

Further, as in the embodiment of FIG. 4, an error correction decoding unit and an error correction coding unit may be provided in addition to the demodulation unit and the modulation unit. That is, the second base station demodulates each subcarrier component of the OFDM signal 2 from the second base station B output from the Fourier transform unit 23 so as to transmit a signal subjected to error correction coding from each base station. A demodulator, a second error correction decoder for performing error correction decoding on the data of each subcarrier component demodulated by the second demodulator, and an error correction decoder by the second error correction decoder A second error correction encoder that performs error correction encoding on the data of each subcarrier component, and a second error correction encoder that modulates the error correction encoded data of each subcarrier component and outputs the modulated data to the inverse Fourier transform unit 24. 2 modulation units. Also, a first demodulator that demodulates each subcarrier component of the OFDM signal 1 from the first base station A output from the Fourier transform unit 16, and each subcarrier demodulated by the first demodulator A first error correction decoding unit that performs error correction decoding on the component data, and a first error that performs error correction encoding on the data of each subcarrier component that has been error correction decoded by the first error correction decoding unit A correction encoding unit and a first modulation unit for modulating the error correction encoded data of each subcarrier component and outputting the data to the inverse Fourier transform unit 31 are provided.
As a result, the possibility of a determination error can be reduced, and interference cancellation with higher accuracy can be performed.

  Further, similarly to the above, each subcarrier signal from the Fourier transform units 16 and 23 (or a signal modulated after being demodulated, or error-correction-decoded after demodulation and modulated after error-correction coding) Signal) is input to the inverse Fourier transform units 31 and 24 to generate the time waveform of the interference component, it is not necessary to use the signals of all the target subcarriers, only the signals of adjacent subcarriers that give large interference. May be inverse Fourier transformed to generate a time waveform. Thereby, the amount of signal processing can be reduced.

6 and 7 are diagrams showing the computer simulation results of the present invention. (A) of FIG. 6 shows the simulation specifications, and (b) is a diagram showing the simulation result regarding the interference power.
As shown in FIG. 6A, the simulation conditions are: subcarrier interval: 15 kHz, number of subcarriers: 64, guard interval length: 1/8 of the symbol length, number of OFDM symbols: 1, modulation scheme: QPSK, maximum Doppler frequency: 0 Hz. The path model used was an equidistant exponential function model with 5 paths and a slope of 3 dB. Each path was subject to independent Rayleigh fluctuation, and the delay spread was about 1 μs. Furthermore, timing synchronization, frequency synchronization for each base station, and channel estimation are ideal, and the average received power of adjacent channels (adjacent base stations) is increased by 10 dB assuming application of FFR and a reuse partition.

(B) of FIG. 6 is a figure which shows the evaluation result of average interference power, a vertical axis | shaft shows average interference power and a horizontal axis shows a subcarrier number. Analysis results are indicated by solid lines, and simulation results are indicated by points. α is a normalized frequency offset obtained by normalizing the frequency offset by the subcarrier interval (in this case, 15 kHz), and shows simulation results for each case of α = 0.01 to 0.50. Here, the interference canceller 20 having the configuration shown in FIG. 1 is used. In the figure, the left half area (subcarrier numbers 16 to 31) indicates the interference power from the adjacent channel when the interference canceller of the present invention is used, and the right half area (subcarrier numbers 32 to 47) in the figure. Shows the interference power from the adjacent channel without the interference canceller of the present invention.
As shown in this figure, it can be seen that the interference power caused by the frequency offset can be greatly reduced by applying the interference canceller of the present invention. It was also confirmed that the analysis results agreed well with the simulation results.

FIG. 7 is a diagram showing simulation results and analysis results of the BER characteristics for each subcarrier when SNR = 10 dB under the same conditions as FIG. In this figure, the vertical axis represents BER (Bit Error Rate), and the horizontal axis represents subcarrier numbers. The BER of each subcarrier in each case of the normalized frequency offset α = 0.01 to 0.50 described above is shown.
In the figure, the left half area (subcarrier numbers 16 to 31) is the BER when the interference canceller of the present invention is used, and the right half area (subcarrier numbers 32 to 47) is the case where the interference canceller of the present invention is not used. BER is shown.
As is apparent from this figure, it can be seen that the BER characteristics can be significantly improved by applying the interference canceller of the present invention. It was also confirmed that the analysis results agreed well with the simulation results.

  In the above description, it has been described that OFDM signals in adjacent frequency bands are transmitted from the adjacent base station A and base station B. However, the present invention is not necessarily adjacent frequency bands but inter-frequency interference. Can be used as it is in order to eliminate interference between OFDM signals transmitted in a frequency band close enough to cause the occurrence of.

It is a block diagram which shows the principal part structure of 1st Embodiment of the receiver of this invention. It is a figure for demonstrating compensation of a frequency offset. It is a block diagram which shows the principal part structure of 2nd Embodiment of the receiver of this invention. It is a block diagram which shows the principal part structure of 3rd Embodiment of the receiver of this invention. It is a block diagram which shows the principal part structure of 4th Embodiment of the receiver of this invention. It is a figure which shows the simulation result of interference electric power. It is a figure which shows the simulation result of BER. It is a figure which shows the structure of the radio | wireless communications system using OFDM. It is a figure for demonstrating the interference between adjacent channels resulting from the frequency offset of a base station.

Explanation of symbols

  1: received signal from base station A, 2: received signal from base station B, 10: receiving device, 11: antenna, 12, 13, 21, 25, 32: multiplier, 14, 22: guard interval removing unit 15, 33: Subtractor, 16, 23: Fourier transform unit, 24, 31: Inverse Fourier transform unit, 26: Demodulation unit, 27: Modulation unit, 28: Error correction decoding unit, 29: Error correction coding unit

Claims (8)

A reception device used in a wireless communication system in which OFDM signals in close frequency bands are transmitted from a plurality of base stations,
First frequency offset compensation means for receiving a received signal and compensating and outputting the frequency offset of the OFDM signal from the first base station;
Second frequency offset compensation means for receiving the received signal and compensating and outputting the frequency offset of the OFDM signal from the second base station;
Second Fourier transform means for receiving an output signal of the second frequency offset compensation means and decomposing the OFDM signal from the second base station into components for each subcarrier;
Inverse Fourier transform means for synthesizing and outputting a component for each subcarrier decomposed by the Fourier transform means into a time waveform;
A third frequency offset compensation unit that receives the output signal of the inverse Fourier transform unit and compensates and outputs the frequency offset so as to have the same frequency relationship as the output signal of the first frequency offset compensation unit;
Subtracting means for subtracting and outputting the output signal of the third frequency offset compensating means from the output signal of the first frequency offset compensating means;
And a first Fourier transform means for receiving the output signal of the subtracting means and decomposing the OFDM signal from the first base station into components for each subcarrier. Demodulating means for demodulating a component for each subcarrier of the OFDM signal from the second base station output from the second Fourier transform means;
Modulation means for modulating the data for each subcarrier demodulated by the demodulation means and outputting to the inverse Fourier transform means,
2. The receiving apparatus according to claim 1, wherein the inverse Fourier transform means synthesizes an output signal from the modulation means into a time waveform. The OFDM signal from the second base station is error correction encoded,
Error correction decoding means for performing error correction decoding processing on the output signal of the demodulation means;
Error correction coding means for performing error correction coding on the output of the error correction decoding means and outputting to the modulation means;
3. The receiving apparatus according to claim 2, wherein the modulating means modulates an output signal from the error correction coding means and outputs the modulated signal to the inverse Fourier transform means.   The inverse Fourier transform means uses one or a plurality of subcarriers close to the frequency band of the OFDM signal from the first base station among the subcarriers included in the OFDM signal from the second base station as a time waveform. The receiving apparatus according to claim 1, wherein the receiving apparatus combines and outputs. A reception device used in a wireless communication system in which OFDM signals in close frequency bands are transmitted from a plurality of base stations,
First frequency offset compensation means for receiving a received signal and compensating and outputting the frequency offset of the OFDM signal from the first base station;
Second frequency offset compensation means for receiving the received signal and compensating and outputting the frequency offset of the OFDM signal from the second base station;
First subtracting means for subtracting and outputting the output signal of the third frequency offset compensating means from the output signal of the first frequency offset compensating means;
Second subtracting means for subtracting and outputting the output signal of the fourth frequency offset compensating means from the output signal of the second frequency offset compensating means;
First Fourier transform means for receiving an output signal of the first subtracting means, decomposing the OFDM signal from the first base station into components for each subcarrier,
Second Fourier transform means for receiving an output signal of the second subtracting means, decomposing the OFDM signal from the second base station into components for each subcarrier,
First inverse Fourier transform means for combining the components for each subcarrier of the OFDM signal from the first base station decomposed by the first Fourier transform means into a time waveform and outputting it;
Second inverse Fourier transform means for synthesizing and outputting a component for each subcarrier of the OFDM signal from the second base station decomposed by the second Fourier transform means;
The fourth frequency offset compensation that receives the output signal from the first inverse Fourier transform means and compensates and outputs the frequency offset so as to have the same frequency relationship as the output signal of the second frequency offset compensation means. Means,
The third frequency offset compensation that receives the output signal from the second inverse Fourier transform means and compensates and outputs the frequency offset so as to have the same frequency relationship as the output signal of the first frequency offset compensation means. And a receiving device. First demodulation means for demodulating a component for each subcarrier of the OFDM signal from the first base station output from the first Fourier transform means;
First modulating means for modulating the data for each subcarrier demodulated by the first demodulating means and outputting the modulated data to the first inverse Fourier transform means;
Second demodulation means for demodulating a component for each subcarrier of the OFDM signal from the second base station output from the second Fourier transform means;
Second modulation means for modulating the data for each subcarrier demodulated by the second demodulation means and outputting the data to the second inverse Fourier transform means;
The first inverse Fourier transform means synthesizes an output signal from the first modulation means into a time waveform and outputs it,
6. The receiving apparatus according to claim 5, wherein the second inverse Fourier transform unit is configured to synthesize an output signal from the second modulation unit into a time waveform and output the synthesized signal. The OFDM signals from the first base station and the second base station are error correction encoded,
First error correction decoding means for performing error correction decoding processing on the output signal of the first demodulation means;
Second error correction decoding means for performing error correction decoding processing on the output signal of the second demodulation means;
First error correction coding means for performing error correction coding on the output of the first error correction decoding means and outputting to the first modulation means;
Second error correction coding means for performing error correction coding on the output of the second error correction decoding means and outputting to the second modulation means;
The first modulation means modulates an output signal from the first error correction coding means and outputs the modulated signal to the first inverse Fourier transform means,
7. The reception according to claim 6, wherein the second modulation means modulates an output signal from the second error correction coding means and outputs the modulated signal to the second inverse Fourier transform means. apparatus. The first inverse Fourier transform means selects one or more subcarriers close to the frequency band of the OFDM signal from the second base station among the subcarriers included in the OFDM signal from the first base station. It is synthesized and output to a time waveform,
The second inverse Fourier transform means calculates one or more subcarriers close to the frequency band of the OFDM signal from the first base station among the subcarriers included in the OFDM signal from the second base station. The receiving apparatus according to claim 5, wherein the receiving apparatus is combined with a time waveform and output.

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