JP5518636B2 - Multipath interference equalization filter and receiving apparatus - Google Patents

Description

  The present invention relates to a multipath interference equalization filter and a receiving apparatus.

  In an OFDM (Orthogonal Frequency Division Multiplexing) system that receives using a plurality of antennas, the timing of symbol synchronization of the ODFM symbol in the OFDM signal is determined from the received signal received by each of the plurality of antenna elements. Detection is performed using a preamble added to the signal packet. At the symbol synchronization timing, the timing of performing FFT (Fast Fourier Transform) on the ODFM symbol is synchronized with high accuracy to demodulate and decode the received signal (for example, Patent Document 1).

  When there is a high-power interference wave that interferes with the desired OFDM signal, the received signal is multiplied by a weighting factor, and the received signals multiplied by the weighting factor are combined to suppress the high-power interference wave. Thus, the timing is detected and the desired OFDM signal is demodulated. Here, the high-power interference wave is, for example, a radio wave transmitted from another communication system, and has a higher power than the received wave of the desired OFDM signal, D / U (Desirable signal / Undesirable signal) = − The radio wave is about 20 dB, and hereinafter referred to as a high power interference wave.

An example of a receiving apparatus that receives and demodulates a desired OFDM signal in an environment where a high-power interference wave exists as described above will be described.
FIG. 9 is a schematic block diagram illustrating a configuration of a reception device 9 that suppresses a high-power interference wave and receives and demodulates a desired OFDM signal. Here, a case where the number of antenna elements is two will be described. As shown in the figure, the receiving device 9 includes antenna elements 11-1 and 11-2, an interference removing unit 13, a synchronization detecting unit 14, FFT units 15-1 and 15-2, an interference removing unit 16, and a demodulating unit 17. And a P / S (Parallel / Serial) converter 18.

The interference removing unit 13 generates a combined signal in which the high-power interference wave is suppressed by multiplying the received signals X ₁ and X ₂ received by the antenna elements 11-1 and 11-2 by a weighting coefficient and combining them. . The synchronization detection unit 14 detects the timing at which FFT is performed using a preamble or the like included in the combined signal generated by the interference removal unit 13. The FFT units 15-1 and 15-2 each perform FFT on the received signals X ₁ and X ₂ based on the timing detected by the synchronization detection unit 14, and signals in the frequency domain for each of M subcarriers. Convert to

  The interference removal unit 16 combines the signals of the same subcarriers output from the FFT units 15-1 and 15-2 to output a signal in which the component of the high power interference wave is suppressed to the demodulation unit 17. The demodulation unit 17 demodulates the signal output from the interference removal unit 16 for each subcarrier. The P / S converter 18 performs parallel / serial conversion on the signal of each subcarrier demodulated by the demodulator 17 and outputs it as one signal string.

The interference removing unit 13 includes multipliers 131 and 132, an adder 133, and an MMSE (Minimum Mean Square Error) unit 134. Multipliers 131 and 132 multiply the received signals X ₁ and X ₂ by weighting factors calculated by the MMSE unit 134. The adder 133 adds the signals multiplied by the weighting coefficients calculated by the multipliers 131 and 132. The MMSE unit 134 calculates each of the weighting coefficients output to the multipliers 131 and 132 so that the power of the interference wave included in the signal calculated by the adder 133 is minimized.

For example, the MMSE unit 134 calculates the weighting factor input to the multiplier 132 by fixing the weighting factor input to the multiplier 131 to 1 so that the power of the signal output from the adder 133 is minimized. . In this case, the MMSE unit 134 weights the interference wave included in the signal output from the multiplier 132 into a signal having the same amplitude and opposite phase as the interference wave included in the signal output from the multiplier 131. Is calculated.
Here, the MMSE unit 134 includes algorithms such as LMS (Least Mean Square), RLS (Recursive Least Square), and SMI (Sample Matrix Inversion), which is a direct solution using sample values. Is used to calculate the weighting coefficients for the multipliers 131 and 132, respectively.

  The interference removal unit 16 includes multipliers 161 and 162, an adder 163, and an MMSE unit 164. Moreover, the interference removal part 16 synthesize | combines the signals of the same subcarrier output from FTT15-1, 15-2 in frequency space. The interference cancellation unit 16 calculates a weighting factor so that the MMSE unit 164 maximizes the signal-to-interference and noise power ratio (SINR) of each subcarrier signal, and a multiplier. The weighting coefficients calculated by 161 and 162 are multiplied to the input signal, and the signals multiplied by the adder 163 are combined to suppress the interference wave. Thereby, when the signal level of the interference wave is high, the interference wave suppression effect can be obtained, and when the signal level of the interference wave is low, the space diversity effect by the two antenna elements 11-1 and 11-2 is obtained. Can do.

The receiving device 9 suppresses high-power interference waves from the received signals X ₁ and X ₂ by the interference removing unit 13 having a 1-tap filter based on spatial diversity by two different antenna elements 11-1 and 11-2. The timing of performing FFT using the signal is detected, and the received signals X ₁ and X ₂ are converted into frequency domain signals based on the detected timing to obtain signals for each of M subcarriers. Then, the reception device 9 performs demodulation by suppressing the component of the high-power interference wave included in the signal of each subcarrier by the interference removal unit 16 having a 1-tap filter.
Thereby, the receiving device 9 demodulates and decodes a desired OFDM signal by removing the high power interference wave from the received signal even in an environment where the high power interference wave exists.

JP 2006-186421 A

However, when the above-described high-power interference wave exists in a multipath environment, the delayed wave of the high-power interference wave affects the OFDM signal to be demodulated / decoded like a different interference wave. That is, in a multipath environment, even when there is only one interference wave, the situation is the same as when there are a plurality of interference waves.
For example, in a multipath environment, when an interference wave reaches the reception device 9 via a plurality of paths, the reception device 9 receives interference from the plurality of interference waves, and two different antenna elements 11-1, It may be difficult to sufficiently suppress the interference wave using the spatial diversity according to 11-2, and the symbol synchronization timing may not be detected. Therefore, there is a problem that communication quality is deteriorated.

In order to solve the above-described problems, there is a method of suppressing interference waves by increasing the number of antenna elements and using space diversity. However, there is a problem that it is difficult to determine the appropriate number of antenna elements because the number of delayed waves differs depending on the place where the receiving device 9 is installed and the communication environment. In particular, when the receiving device 9 moves, it is more difficult to determine the number of antenna elements, and there is a problem that it is difficult to appropriately suppress interference waves.
That is, there is a problem that it is difficult to appropriately suppress the interference wave in a multipath environment where a plurality of delay waves of the interference wave are generated.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a multipath interference equalization filter capable of appropriately suppressing interference waves in a multipath environment, and a receiving apparatus including the filter. There is.

  In order to solve the above problem, the present invention is a first FIR filter unit to which a reference signal that is one of a plurality of reception signals received by each of a plurality of antennas is input, A first FIR filter provided corresponding to each received signal other than the reference signal; and a first subtraction provided corresponding to each received signal other than the reference signal among the plurality of received signals. A first subtracter that subtracts the output of the first FIR filter unit corresponding to the received signal from the received signal, and the first subtractor when the plurality of received signals include only interference waves. A tap coefficient that minimizes the power of the signal output from each of the subtracters is calculated for each of the first FIR filter units, and the first FIR filter unit receives the base that is not given a delay. A tap coefficient setting unit that sets a tap coefficient of a tap calculated with respect to a signal to 0 and sets a tap coefficient of another tap to the calculated tap coefficient to determine a tap coefficient of each of the first FIR filter units. This is a characteristic multipath interference equalization filter.

  Further, the present invention provides the multipath interference equalization filter according to the above invention, wherein the second FIR filter unit having the same number of taps as the number of taps provided in the first filter unit is input. A second subtracter for subtracting the output of the second FIR filter unit from the received signal, and a ratio of the received signal input to the second subtractor to the signal output from the second subtractor An input / output power ratio calculation unit that calculates the input / output power ratio, and a tap coefficient of a tap included in the second FIR filter unit that maximizes the input / output power ratio calculated by the input / output power ratio calculation. For a combination of two reception signals in which any one of the tap coefficient calculation unit and the plurality of reception signals is sequentially set as a first reception signal, and reception signals other than the first reception signal are sequentially set as second reception signals. The A process in which one received signal is input to the second FIR filter unit, the second received signal is input to a second subtractor, and the tap coefficient calculation unit calculates a tap coefficient of the second FIR filter unit In any one of the plurality of received signals based on the input / output power ratio calculated for each first received signal, the output of the second subtractor, or the calculated tap coefficient. A reference signal selection unit that selects the reference signal, and a reception signal selected by the reference signal selection unit as the reference signal is used as the first reception signal, and other reception signals are sequentially used as the second reception signal. Among the calculated tap coefficients, the tap coefficient of the tap calculated for the first received signal not given a delay is set to 0, and the first FIR filter unit corresponding to the received signal other than the reference signal No Characterized in that it comprises a tap coefficient selecting section for determining the up factor.

  In the multipath interference equalization filter according to the present invention, the reference signal selection unit may use the received signal as the first received signal for each of the plurality of received signals, and The sum of input / output power ratios when receiving signals other than the first received signal are sequentially used as the second received signal is calculated, and the received signal corresponding to the maximum sum among the calculated sums is selected as the reference signal. It is characterized by doing.

  In the multipath interference equalization filter according to the present invention, the reference signal selection unit may use the received signal as the first received signal for each of the plurality of received signals, and The standard deviation of the signal output from the second subtracter when the received signal other than the first received signal is sequentially used as the second received signal is calculated, and the minimum standard deviation among the calculated standard deviations is calculated. A corresponding received signal is selected as the reference signal.

  In the multipath interference equalization filter according to the present invention, the reference signal selection unit calculates the tap coefficient when the received signal is the first received signal for each of the plurality of received signals. The sum of the absolute values of the tap coefficients calculated by the unit is calculated, and the received signal corresponding to the minimum sum of the absolute values among the calculated absolute values is selected as the reference signal.

  Further, the present invention provides the multipath interference equalization filter according to the above invention, a synchronization detection unit that detects timing of symbol synchronization based on a signal output from the multipath interference equalization filter, and the synchronization detection unit. An FFT unit that performs FFT on a signal output from the multipath interference equalization filter based on the detected timing of symbol synchronization, and a demodulation unit that demodulates the signal FFTed by the FFT unit. This is a featured receiving apparatus.

According to the present invention, the tap coefficient setting unit calculates the tap coefficient of the FIR filter representing the channel response characteristic of the interference wave in the multipath environment, and calculates the tap coefficient of the tap to be calculated with respect to the reference signal to which no delay is given. By setting the tap coefficient to 0 and setting the tap coefficient of another tap to be a calculated tap coefficient, the signal calculated by the subtracter and the reference signal can be in a scalar multiplication relationship with complex as a constant.
As a result, the signal output from the multi-path interference equalization filter of the present invention is adjusted for phase and amplitude to be anti-phase synthesized, thereby causing interference even in a multi-path environment in which multiple interference waves are generated. Waves can be appropriately suppressed, and deterioration in communication quality can be prevented.

It is a schematic block diagram which shows the structure of the receiver in 1st Embodiment. It is a schematic block diagram which shows the structure of the multipath interference equalization filter in the same embodiment. It is a schematic block diagram which shows the structure of the FIR filter part in the embodiment. It is a figure which shows the structure of the multipath interference equalization filter in 2nd Embodiment. It is a schematic block diagram which shows the structure of the 1st FIR filter part in the embodiment. It is a flowchart which shows the tap coefficient setting process of the multipath interference equalization filter in the embodiment. It is a schematic block diagram which shows the structure of the multipath interference equalization filter in 3rd Embodiment. It is a schematic diagram which shows an example of the process by the multipath interference equalization filter in the embodiment. It is a schematic block diagram which shows the structure of the receiver which suppresses a high power interference wave and receives and demodulates a desired OFDM signal.

  Hereinafter, a multipath interference equalization filter and a receiving apparatus using the same according to an embodiment of the present invention will be described with reference to the drawings. In the following embodiments, a case will be described in which the receiving apparatus receives and demodulates an OFDM signal.

(First embodiment)
FIG. 1 is a schematic block diagram illustrating a configuration of the receiving device 1 according to the first embodiment. As shown in the figure, the receiving device 1 includes antenna elements 11-1, 11-2, a multipath interference equalization filter 12, an interference removing unit 13, a synchronization detecting unit 14, FFT units 15-1, 15-2, An interference removing unit 16, a demodulating unit 17, and a P / S (Parallel / Serial) converter 18 are provided.
The receiving apparatus 1 in the present embodiment is different from the receiving apparatus 9 shown in FIG. 9 in that it includes a multipath interference equalization filter 12. Since each part except for the multipath interference equalization filter 12 has the same configuration as each part described in FIG. 9, the same reference numerals are given to the corresponding parts and description thereof is omitted.

FIG. 2 is a schematic block diagram showing the configuration of the multipath interference equalization filter 12 in the present embodiment. As shown in the figure, the multipath interference equalization filter 12 includes FIR filter units 121 and 122 and subtractors 123 and 124.
FIR filter section 121 is input the received signal X ₁ received by the antenna element 11-1, a channel response characteristic up the antenna element 11-1 from the source of the interference wave, the antenna element 11 from the source of the interference wave performed on the received signal X ₁ that is input to the filter processing based on a channel response characteristic up -2.

The FIR filter unit 122 receives the reception signal X ₂ received by the antenna element 11-2, and, similarly to the FIR filter unit 122, the channel response characteristics from the interference wave transmission source to the antenna element 11-1 and the interference performed on the received signal X ₂ input filtering based on the channel response characteristic from a wave source to the antenna element 11-2.
Subtractor 123, from the signal received by the antenna elements 11-2 subtracts the signal output from the FIR filter 121 outputs an output signal _{Y 2.} Subtractor 124, from the signal received by the antenna elements 11-1, FIR filter 122 subtracts the output signal for outputting an output signal _{Y 1.}

Since the FIR filter unit 121 and the FIR filter unit 122 have the same configuration, the specific configuration of the FIR filter unit 122 will be described below, and the description of the FIR filter unit 121 will be omitted.
FIG. 3 is a schematic block diagram showing the configuration of the FIR filter unit 122 in the present embodiment. As shown in the figure, the FIR filter unit 122 includes an MMSE unit (tap coefficient calculation unit) 1221 and a filter unit 1222. The filter unit 1222 includes three delay elements 1223 b to 1223 d to which the reception signal X ₂ is input and connected in series, weight multipliers 1224 a to 1224 d that are four complex multipliers, and an adder 1225. .

The reception signal X ₂ is input to the FIR filter unit 122, and the filter unit 1222 performs a filtering process on the reception signal X ₂ based on the weighting coefficient calculated by the MMSE unit 1221.
Specifically, the weighting multiplier 1224a multiplies the tap coefficients w0 to MMSE 1221 was calculated for the received signal _{X 2} input. Weight multiplier 1224b multiplies the tap coefficients w1 to MMSE 1221 was calculated for the received signal _{X 2,} which delay element 1223b is delayed. Weight multiplier 1224c multiplies the delay element 1223b, tap coefficients w2 to MMSE 1221 was calculated for the received signal _{X 2} which 1223c is delayed. Weight multiplier 1224d multiplies the tap coefficient w3 of MMSE 1221 was calculated for the received signal _{X 2,} which delay elements 1223b~1223d is delayed. The adder 1225 adds the results calculated by the weight multipliers 1224a to 1224d, and outputs the addition result to the subtractor 124 outside the FIR filter unit 122. Note that the delay added to the signals input by the delay elements 1223b to 1223d is a delay of one delay unit with a predetermined time as a delay unit.

MMSE unit 1221 subtracts the signal obtained by filtering from the received signals _{X 1} to the reception signal _{X 2,} canceling the component of the interference wave tap coefficients w0~w3 as (suppress) calculate. For example, when only the interference wave is received in a period in which the OFDM signal demodulated by the receiving apparatus 1 is not transmitted, the MMSE unit 1221 has a tap coefficient that minimizes the power of the output signal Y ₁ output from the subtractor 124. w0 to w3 are calculated and set. Here, the tap coefficients w0 to w3 are numerical values represented by complex numbers. The MMSE unit 1221 uses algorithms such as LMS (Least Mean Square), RLS (Recursive Least Square), and SMI (Sample Matrix Inversion) which is a direct solution using sample values. Use to calculate the tap coefficients w0 to w3.

Returning to FIG. 2, the processing for the received signals X ₁ and X ₂ of the multipath interference equalization filter 12 of the present embodiment will be described.
The desired OFDM signal transmitted from the transmitting apparatus that is the communication partner of the receiving apparatus 1 is S, the interference wave signal is I, and the channel response characteristics from the transmitting apparatus to the antenna elements 11-1 and 11-2 are H _s1. (Z), H _s2 (z), and when the channel response characteristics from the interference wave transmission source to the antenna elements 11-1, 11-2 are H _u1 (z), H _u2 (z), the antenna element 11 -1 and 11-2, the received signals X ₁ and X ₂ are expressed by the following equation (1).

The FIR filter unit 122 is set so as to cancel the interference wave component included in the signal output from the subtractor 124 by the tap coefficient set by the internal MMSE unit 1221. That is, the FIR filter unit 122 operates as a filter having response characteristics expressed by FIR by expanding (H _u1 (z) / H _u2 (z)).
Here, channel response characteristics H _u1 (z) and H _u2 (z) in the multipath environment are expressed by the following equation (2).

Using equation (2), (H _u1 (z) / H _u2 (z)) can be expanded as shown in the following equation (3), and can be expressed as an FIR filter by approximation. it can.

Then, when the desired OFDM signal S is received, the output signal _{Y 1} from the subtracter 124 is output is represented by the formula (4).

Similarly to the FIR filter unit 122, the FIR filter unit 121 is set so as to cancel the interference wave component included in the signal output from the subtractor 123, and (H _u2 (z) / H _u1 (z) It operates as a filter having a response characteristic. Then, when the desired OFDM signal is received, the output signal _{Y 2} which subtractor 123 outputs are represented by the following formula (5).

With the above configuration, the FIR filter unit 122, based on the interference wave included in the received signal X _2, signals for canceling the interference wave and a delayed wave in a multi-path environment that is output from the filter unit 1222 included in the FIR filter section 122 Is generated. Subtractor 124 subtracts the signal is an FIR filter section 122 from the received signal X ₁ generated, cancel the interference wave and the delayed wave. Further, the FIR filter section 121, a subtracter 123, similarly, cancel the interference wave and the delayed wave included in the received signal _{X 2.}
Thereby, the multipath interference equalization filter 12 can cancel the interference wave in the multipath environment from the reception signals X ₁ and X ₂ . As a result, the receiving apparatus 1 of the present embodiment can suppress interference waves that reach through a plurality of paths in a multipath environment without increasing the number of antenna elements according to the number of delay waves of the interference waves. It is possible to prevent deterioration in communication quality.

In the present embodiment, the configuration in which the number of taps of the FIR filter units 121 and 122 is four has been described. It may be.
Further, in the present embodiment, the configuration including the two FIR filter units 121 and 122 so as to cancel the interference wave included in each of the reception signals X ₁ and X ₂ has been described, but the configuration including only one of them is employed. Also good. In this case, in the interference removal units 13 and 16, the MMSE units 134 and 164 may calculate a weighting factor that outputs only a signal in which the interference wave is canceled. For example, the weight coefficient for a signal including an interference wave may be set to zero.
Further, in the present embodiment, the configuration in which the interference wave included in the reception signals X ₁ and X ₂ is canceled using the FIR filter units 121 and 122 has been described. However, the reception signal X ₁ , X ₂ may be configured to cancel the interference wave included in one of the _two .

(Second Embodiment)
In the receiving apparatus according to the present embodiment, the configuration of the multipath interference equalization filter is different from the configuration of the multipath interference equalization filter 12 of the first embodiment. Since other configurations are the same as those of the first embodiment, the multipath interference equalization filter according to this embodiment will be described below.

FIG. 4 is a diagram showing a configuration of the multipath interference equalization filter 22 in the second embodiment. As shown in the figure, the multipath interference equalization filter 22 includes switch units 221a and 221b, a first FIR filter unit 223, a subtractor 224, and a tap coefficient setting unit 25.
Hereinafter, a case where the number of taps of the first FIR filter unit 223 is 4 (k = 4) will be described.

The switch unit 221a selects _{one of} the reception signals X ₁ and X ₂ received by the antenna elements 11-1 and 11-2 according to the control of the tap coefficient setting unit 25, and subtracts the selected reception signal. The signal is output to the subtracter 224 as the subtracted signal in the calculator 224. The switch unit 221b selects the other of the reception signals X ₁ and X ₂ according to the control of the tap coefficient setting unit 25, outputs the selected reception signal to the first FIR filter unit 223, and selects the selected reception signal and outputs to the FFT unit 15-2 as the output signal _{Y 2.}

The first FIR filter unit 223 receives the reception signal input from the switch unit 221b. The first FIR filter unit 223 performs a filtering process based on the tap coefficient set by the tap coefficient setting unit 25 on the input received signal and outputs the received signal to the subtractor 224. Subtractor 224 from the received signal inputted from the switch unit 221a, a signal first FIR filter unit 223 and outputs the subtraction, and outputs the subtraction result as an output signal _{Y 1} to FFT section 15-1.

FIG. 5 is a schematic block diagram showing the configuration of the first FIR filter unit 223 in the present embodiment. As shown in the figure, the first FIR filter unit 223 includes three delay elements 2232b to 2232d to which a reception signal is input from the switch unit 221b and connected in series, and a weight multiplier 2233a that is four complex multipliers. ˜2233d and an adder 2234.
In the weight multipliers 2233a to 2233d, tap coefficients w0 to w3 calculated by the tap coefficient setting unit 25 are set. The weight multiplier 2233a multiplies the received signal by the tap coefficient w0 set by the tap coefficient setting unit 25 and outputs the result. The weight multiplier 2233b multiplies the reception signal delayed by the delay element 2232b by the tap coefficient w1 and outputs the result.

The weight multiplier 2233c multiplies the reception signal delayed by the delay elements 2232b and 2232c by the tap coefficient w2 and outputs the result. The weight multiplier 2233d multiplies the reception signal delayed by the delay elements 2232b to 2232d by the tap coefficient w3 and outputs the result. The adder 2234 adds the multiplication results calculated by the weight multipliers 2233b to 2233d, and outputs the addition result to the subtractor 224.
Here, the tap coefficients w0 to w3 are numerical values represented by complex numbers. Further, the delay added to the input signal by the delay elements 2232b to 2232d is a delay of one delay unit.

Returning to FIG. 4, tap coefficient setting unit 25 based on the received signal X _1, X _2, selects the reception signal X _1, reference signal one of X _2, reference signal selected is the first The switch unit 221b is controlled so as to be input to the FIR filter unit 223. Further, the tap coefficient setting unit 25 sets the tap coefficient of the first FIR filter unit 223 that minimizes the power of the signal output from the subtractor 224 during the period in which only the interference wave is included in the reception signals X ₁ and X _2. calculate. Then, the tap coefficient setting unit 25 determines the tap coefficients w0 to w3 of the first FIR filter unit 223 based on the calculated tap coefficients.

The tap coefficient setting unit 25 includes second FIR filter units 252a and 252b, subtracters 253a and 253b, input / output power ratio calculation units 254a and 254b, a reference signal selection unit 255, and a tap coefficient selection unit 256. Yes.
The second FIR filter section 252a the received signal _{X 1,} and outputs to filter the received signal _{X 1} that is input. The second FIR filter section 252b the received signal _{X 2,} and outputs to filter the received signal _{X 2} input. The second FIR filter units 252a and 252b have the same configuration. The second FIR filter units 252a and 252b use their own tap coefficients using the signals input from the subtracters 253a and 253b, similarly to the FIR filter units 121 and 122 (FIG. 3) of the first embodiment. Set.

Subtractor 253a is corresponding to a combination of the received signal _{X 1} being input, the received signal _{X 2} of the received signal _{X 1} except that input to the second FIR filter portion 252a to the second FIR filter section 252a Is provided. Further, the subtractor 253b, the combination of the received signal _{X 2,} which is input to the second FIR filter section 252b, a reception signal _{X 1} other than the reception signal _{X 2,} which is input to the second FIR filter unit 252b It is provided corresponding to.
Subtractor 253a from the received signal _{X 2,} which subtracts the signal second FIR filter section 252a outputs. Subtractor 253b from the received signal _{X 1,} subtracts the signal second FIR filter unit 252b outputs.

Output power ratio calculating section 254a is provided corresponding to the subtracter 253a, and calculates the ratio of the received signal X ₂ being input to the subtraction result of the subtracter 253a. Output power ratio calculating unit 254b includes a subtractor 253b provided corresponding to, calculating the ratio of the received signal X ₁ being input to the subtraction result of the subtractor 253b.
The reference signal selection unit 255 selects _{one of} the reception signals X ₁ and X ₂ as a reference signal based on the ratio calculated by the input / output power ratio calculation units 254a and 254b. Then, the reference signal selection unit 255 switches the switch unit 221b so that the reception signal selected as the reference signal is input to the first FIR filter unit 223, and the reception signal other than the reference signal is input to the subtractor 224. The switch unit 221a is switched as described above.

The tap coefficient selection unit 256 selects the tap coefficient calculated by one of the second FIR filter units 252a and 252b to which the reference signal selected by the reference signal selection unit 255 is input, and sets the selected tap coefficient. Based on this, the tap coefficient set in the first FIR filter unit 223 is selected.
Since the second FIR filter units 252a and 252b have the same configuration as the FIR filter unit 122 (FIG. 3) of the first embodiment, description of the second FIR filter units 252a and 252b is omitted. Hereinafter, the tap coefficients calculated by the second FIR filter units 252a and 252b are w′0 to w′3.

  FIG. 6 is a flowchart showing tap coefficient setting processing of the multipath interference equalization filter 22 in the present embodiment.

In the multipath interference equalization filter 22, the MMSE unit included in each of the second FIR filter units 252a and 252b during a period in which a desired OFDM signal is not transmitted, that is, a period in which only the interference wave is received. 1221 repeatedly performs a calculation by a predetermined algorithm until the tap coefficients w′0 to w′3 of the respective filter units 1222 converge to calculate the tap coefficients w′0 to w′3 (step S102).
The input / output power ratio calculation units 254a and 254b calculate the input / output power ratio that is the ratio of the received signal input to the subtractor to the signal output from the corresponding subtractor 253a and 253b (step S104). .

The reference signal selection unit 255 is calculated for each of the reception signals X ₁ and X ₂ by the input / output power ratio calculation units 254a and 254b corresponding to the outputs of the second FIR filter units 252a and 252b to which the reception signal is input. A received signal corresponding to a large input / output power ratio in the input / output power ratio is selected as a reference signal (step S106).
Then, the tap coefficient selection unit 256 calculates the tap coefficient calculated by the second FIR filter unit to which the received signal selected as the reference signal is input among the tap coefficients calculated by the second FIR filter units 252a and 252b. Select w′0 to w′3. Then, the tap coefficient selection unit 256 performs a tap coefficient (w′0) of a tap that performs an operation on a received signal (reference signal) that is not given a delay among the selected tap coefficients w′0 to w′3. The tap coefficients (0, w′1, w′2, w′3) in which is set to 0 are determined as the tap coefficients (w0, w1, w2, w3) of the first FIR filter unit 223 (step S108).

  Hereinafter, the process in the tap coefficient setting by the tap coefficient selection unit 256 will be further described. Generally, the channel response characteristic of a multipath interference wave in which an interference wave and a delayed wave of the interference wave are combined can be expressed by an FIR filter, and can be expressed by, for example, the following equation (6). Here, the multipath interference wave refers to an interference wave with a delayed wave in a multipath environment.

Here, H _u1 (z) and H _u2 (z) are channel response characteristics from the generation source (transmission source) of the interference wave to the antenna elements 11-1 and 11-2.
At this time, if it contains only multipath interference wave in the received signal X _1, X _2, when a signal of the interference wave and I, received signal X _1, X ₂ are represented by the following formula (7).

Here, IIR filter multipath interference waves contained in the reception signal _{X 1} of the formula (7) is represented by the second FIR filter portion 252b of the portion _{(H u1 (z) / H} u2 (z)) Can be canceled. However, since it is difficult to set an appropriate tap coefficient of the IIR filter, an IIR filter that cancels the multipath interference wave is approximated by a finite FIR filter, for example, as shown in the following equation (8). The tap coefficient of the second FIR filter unit 252b is calculated.

Here, a subtractor 253b provided in the tap coefficient setting unit 25 subtracts the received signal _{X 2,} which is filtered by a second FIR filter unit 252b from the received signal _{X 1.} Signal Y _'1 output from the subtracter 253b is expressed by the following equation (9).

The second FIR filter unit 252b calculates tap coefficients γ _{0 to} γ ₃ that minimize the received power of the signal Y ′ ₁ represented by Expression (9). That is, the second FIR filter unit 252b calculates tap coefficients γ _{0 to} γ ₃ that minimize the power of the multipath interference wave of the reception signal X ₁ .
As can be seen from Expression (9), in the second FIR filter unit 252b, the antenna element 11-2 receives the interference wave (γ ₀ X ₂ (z)) received simultaneously with the antenna element 11-1 and the antenna element 11. -2 is included in the received signal X ₁ based on the interference wave ((γ ₁ z ⁻¹ + γ ₂ z ⁻² + γ ₃ z ⁻³ ) X ₂ (z)) received after the antenna element 11-1. It is shown to cancel the interference wave.

Next, processing for the received signals X ₁ and X ₂ by the first FIR filter unit 223 will be described. Here, as an example, the reference signal selection section 255 receives signals X ₂ selected reference signal, the tap coefficient selection unit 256 selects the tap coefficients gamma ₀ to? ₃ calculated by the second FIR filter unit 252b The case will be described.
The multipath interference wave represented by Expression (7) can be canceled by providing an IIR filter represented by (H _u1 (z) / H _u2 (z)) in the first FIR filter unit 223. it can. In the present embodiment, the tap coefficient setting unit 25 selects the tap coefficients γ _{0 to} γ ₃ calculated by the second FIR filter unit 252b, so that a finite FIR filter is obtained as shown in the following equation (10). Approximate as

However, (w0, w1, w2, w3) = (γ ₀ , γ ₁ , γ ₂ , γ ₃ ).
Here, from the equation (10), the channel response characteristic H _u1 can be expressed as the following equation (11) using the channel response characteristic H _u2 and the tap coefficients γ _{0 to} γ ₃ .

By the way, the channel response characteristic of the desired wave to be demodulated / decoded can also be expressed by the FIR filter in the same manner as the channel response characteristic of the interference wave expressed by the equation (6). The channel response characteristics H _s1 (z) and H _s2 (z) from the transmission source (transmission source) of the desired wave S to the antenna elements 11-1 and 11-2 can be expressed by, for example, the following equation (12). .

The received signals X ₁ and X ₂ including the interference wave I and the desired wave S are represented by the following equation (13).

Here, the tap coefficient selection unit 256 sets the tap coefficients of the first FIR filter unit 223 to (w0, w1, w2, w3) = (0, γ ₁ , γ ₂ , γ) by the process of step S108 in FIG. ₃ ) Set as The response characteristic FIR of the first FIR filter unit 223 is expressed by the following equation (14).

At this time, the output signal _{Y 1} is expressed by the following equation (15).

Here, using equation (11), by transforming Equation (15), the received signal _{Y 1} is expressed by the following equation (16).

On the other hand, the output signal _{Y 2} is expressed by the following equation (17).

Comparing Expression (16) and Expression (17), the preceding wave of the desired wave S included in each of the output signal Y ₁ and the output signal Y ₂ (term not including the delay z ⁻ⁿ ) has no correlation. I understand. That is, by the tap coefficients of taps for calculating the reference signal is not given a delay to 0, the reception apparatus receives at the same time, the desired wave S included in the received signal X _1, received signal X ₂ can be prevented from being combined with each other, and the desired wave S included in the output signal Y ₁ can be kept uncorrelated with the desired wave S included in the output signal Y ₂ . Thereby, the space diversity effect obtained by using the antenna elements 11-1 and 11-2 can be maintained.
On the other hand, the interference wave I included in the reception signal Y ₁ and the interference wave I included in the reception signal Y ₂ have a scalar multiplication relationship with a tap coefficient (γ ₀ : complex number) as a constant. it can. Since the output signal Y ₁ and the output signal Y ₂ for the interference wave I have a scalar multiplication relationship with a complex number as a constant, the phase and amplitude of the output signal Y ₁ and the output signal Y ₂ are adjusted. Multipath interference waves can be suppressed by performing reverse phase synthesis.

Using this relationship, the receiving apparatus according to the present embodiment suppresses multipath interference waves included in the output signals Y ₁ and Y ₂ using the interference removing units 13 and 16 (FIG. 1) having a one-tap configuration. be able to. Then, the receiving apparatus of this embodiment, suppresses the desired wave S received signals X _1, X ₂ is, in a case that includes a multipath interference waves even, the multipath interference wave included in the received signal X _1, X ₂ Thus, the desired wave S included in the output signals Y ₁ and Y ₂ can be demodulated and decoded.
Here, a case has been described in which the reference signal selector 255 selects the received signal X ₂ to the reference signal, also in case of selecting the reception signal X ₁ on the reference signal, maintaining a space diversity effect on the desired signal S In addition, multipath interference waves can be suppressed.

As described above, in the receiving apparatus according to the present embodiment, after the tap coefficient selection unit 256 calculates the tap coefficient by the second FIR filter units 252a and 252b, any _one of the reception signals X ₁ and X ₂ is used as a reference signal. The tap coefficient calculated by the second FIR filter unit to which the selected reference signal is input is selected. Then, the tap coefficient selection unit 256 sets the tap coefficient of the tap calculated with respect to the reference signal not given a delay in the first FIR filter unit 223 to 0 and selects the tap coefficient of another tap. I tried to do it.
Thus, as shown in equation (16) and (17), in the section corresponding to the preceding wave of the desired OFDM signal contained in the output signals Y ₁ and the output signal Y ₂ (desired wave S) The interference wave I can be made to have a scalar multiplication relationship with a complex number as a constant without causing a correlation. Then, in the interference removal unit 16 provided in the subsequent stage of the multipath interference equalization filter 22, the multipath interference wave can be suppressed by adjusting the phase and amplitude and performing anti-phase synthesis, thereby improving the communication quality. Can be prevented.

In the present embodiment, the reference signal selection unit 255 selects a received signal corresponding to a large input / output power ratio among the input / output power ratios calculated by the input / output power ratio calculation units 254a and 254b as a reference signal. explained. However, the present invention is not limited to this, and the reference signal selection unit 255 calculates the sum of absolute values of tap coefficients in the second FIR filter units 252a and 252b to which the received signals X ₁ and X ₂ are input, and calculates the calculated taps. _{One of} the received signals X ₁ and X ₂ having a small sum of the absolute values of the coefficients may be selected as the reference signal.
This is because the smaller the sum of absolute values of tap coefficients, the more likely to suppress interference waves. Therefore, the reference signal selection unit 255 increases the accuracy of interference wave suppression by using, as a reference signal, the received signal input to the smaller sum of the tap coefficients in the second FIR filter units 252a and 252b. Can do.

(Third embodiment)
In the third embodiment, a multipath interference equalization filter in the case where the reception apparatus includes three antenna elements will be described.
FIG. 7 is a schematic block diagram showing the configuration of the multipath interference equalization filter 32 in the present embodiment. As shown in the figure, the multipath interference equalization filter 32 receives the received signals X _{1 to} X ₃ and outputs output signals Y _{1 to} Y ₃ . The multipath interference equalization filter 32 includes switch units 321a to 321c, first FIR filter units 323a and 323b, subtracters 324a and 324b, and a tap coefficient setting unit 35. Here, a case where the number of taps k of the first FIR filter units 323a and 323b is four will be described.

Received signals X _{1 to} X ₃ received by antenna elements 11-1 to 11-3 are input to switch units 321 a to 321 c, and different received signals are selected according to control of tap coefficient setting unit 35. And output. The received signal selected as the reference signal by the tap coefficient setting unit 35 is output from the switch unit 321c.
The first FIR filter units 323a and 323b correspond to the switch units 321a and 321b that output received signals other than the reference signal, and a reference signal is input to each of them. In addition, the first FIR filter units 323a and 323b have the same configuration as the FIR filter unit 122 (FIG. 3) of the first embodiment, and thus description thereof is omitted.

The subtracters 324a and 324b correspond to the switch units 321a and 321b that output received signals other than the reference signal, and the first FIR filter corresponding to the received signal from the received signals output from the corresponding switch units 321a and 321b The signals output from the units 323a and 323b are subtracted to output a subtraction result.
The signals output from the subtracters 324a and 324b and the switch unit 321c are output signals Y ₁ , Y ₂ and Y ₃ of the multipath interference equalization filter 32, respectively.

Tap coefficient setting unit 35 based on the received signal _X 1 to X _3, selects one of the received signals _X 1 to X ₃ in the reference signal, the received signal selected in the reference signal is the first FIR filter The switch unit 321c is controlled so as to be input to the units 323a and 323b. Specifically, the tap coefficient setting unit 35, similarly to the tap coefficient setting unit 25 of the second embodiment, in a period that includes only the interference wave in the received signal _X 1 to X _3, subtractors 324a, 324b output The tap coefficients of the first FIR filter units 323a and 323b that minimize the power of the signals to be calculated are calculated, and the tap coefficients of the first FIR filter units 323a and 323b are determined based on the calculated tap coefficients.

Tap coefficient setting unit 35, in response to each received signal _X 1 to X ₃ 2 and a second FIR filter unit 352a~352f provided ((number of antennas elements) -1) or by the second FIR Subtractors 353a to 353f provided corresponding to the filter units 352a to 352f, input / output power ratio calculation units 354a to 354f provided corresponding to the subtractors 353a to 353f, and a reference signal selection unit, respectively. 355 and a tap coefficient selection unit 356.

  Similarly to the first FIR filter units 323a and 323b, the second FIR filter units 352a to 352f have k taps, and corresponding reception signals are input thereto. The second FIR filter units 352a to 352f have the same configuration as the FIR filter unit 122 (FIG. 3) of the first embodiment, and are provided in the second FIR filter units 352a to 352f. The MMSE unit 1221 calculates the tap coefficient.

Subtractor 353a~353f from the received signal _X 1 to X _3, subtracts the signal second FIR filter unit 352a~352f outputs. Further, the subtracters 353a to 353f respectively receive the received signals input to the second FIR filter units 352a to 352f and received signals other than the received signals input to the second FIR filter units 352a to 352f. It is provided for all combinations.
For example, subtractor 353a and subtractor 353b, the second FIR filter unit 352a, a reception signal _{X 1} that is input to the 352b, the received signal _X 2 other than the reception signal _{X 1, X 3} combination of the respective (reception Signal X ₁ , reception signal X ₂ ) and (reception signal X ₁ , reception signal X ₃ ) are provided. Subtractor 353a is a signal output from the second FIR filter unit 352b subtracts from the received signal _{X 2,} and outputs the subtraction result to the input-output power ratio calculating section 354a.

The input / output power ratio calculation units 354a to 354f calculate the ratio of the received signal input to the subtractor to the signal output by the corresponding subtractor 353a to 353f.
Similarly to the reference signal selection unit 255 of the second embodiment, the reference signal selection unit 355 is any of the received signals X _{1 to} X ₃ based on the input / output power ratios calculated by the input / output power ratio calculation units 354a to 354f. One of them is selected as a reference signal. The reference signal selection unit 355 switches the switch unit 321c so that the selected reference signal is input to the first FIR filter units 323a and 323b, and different received signals other than the reference signal are supplied to the subtracters 324a and 324b, respectively. Is switched between the switch units 321a and 321b.

  The tap coefficient selection unit 356 is based on the tap coefficient calculated by the second FIR filter unit to which the reception signal selected as the reference signal among the second FIR filter units 352a to 352f is input. The tap coefficients of the taps included in the FIR filter units 323a and 323b are determined. Specifically, the tap coefficient selection unit 356, like the tap coefficient selection unit 256 of the second embodiment, tap coefficients w′0 to w calculated by the second FIR filter unit to which the reference signal is input. The tap coefficients (0, w′1, w′2, w′3) in which the tap coefficients (w′0) for performing the operation on the reference signal to which no delay is given among “3” are set to the second The tap coefficients (w0, w1, w2, and w3) of the first FIR filter units 323a and 323b corresponding to the FIR filter unit are set.

Here, the 1st FIR filter part corresponding to a 2nd FIR filter part is a 1st FIR filter part with which the received signal used as the object which suppresses an interference wave corresponds. For example, the received signal _{X 1} is the reference signal, the switch unit 321a outputs the received signal _{X 2,} when the switch unit 321b outputs the received signal _{X 3,} in the second FIR filter unit 352a, the received signal X The first FIR filter unit 323a that suppresses the _second interference wave corresponds.
Then, the multipath interference equalization filter 32 performs a tap coefficient setting process similar to the tap coefficient setting process (FIG. 6) of the multipath interference equalization filter 22 of the second embodiment, and the first FIR filter unit 323a, A tap coefficient of 323b is set.

Hereinafter, processing on the received signals X _{1 to} X ₃ by the multipath interference equalization filter 32 will be described. Here, the output signals Y _{1 to} Y ₃ output from the multipath interference equalization filter 32 will be described in the case where the desired wave S is not received and the interference wave I is received. At this time, it is assumed that the received signal X ₂ is selected to the reference signal.
FIG. 8 is a schematic diagram illustrating an example of a process of suppressing the interference wave I by the multipath interference equalization filter 32 in the present embodiment. In the example shown in the figure, the tap coefficient selection unit 356 selects the tap coefficient calculated by the second FIR filter unit 352c and selects the tap coefficient calculated by the second FIR filter unit 352d. Show.
Here, if the channel response characteristics from the transmission source of the interference wave I to the antenna elements 11-1 to 11-3 are H _u1 (z), H _u2 (z), and H _u3 (z), each received signal X ₁ to X ₃ is expressed by the following equation (18).

The second FIR filter unit 352c calculates a tap coefficient for canceling the multipath interference wave contained multipath interference waves contained in the reception signal X ₁ to the reception signal X _2. The tap coefficient selection unit 356 selects the tap coefficient calculated by the second FIR filter unit 352c. The tap coefficient calculated by the second FIR filter unit 352c is expressed by the following equation (19).

The second FIR filter unit 352d calculates a tap coefficient for canceling the multipath interference wave contained multipath interference waves contained in the reception signal X ₃ to the reception signal X _2. The tap coefficient selection unit 356 selects the tap coefficient calculated by the second FIR filter unit 352d. The tap coefficient calculated by the second FIR filter unit 352d is expressed by the following equation (20).

At this time, the tap coefficient selection unit 356 uses the tap coefficients (0, α ₁ , α ₂ , α ₃ ) obtained by setting α ₀ in Expression (19) to 0 as tap coefficients (w0, w1) of the first FIR filter unit 323a. , W2, w3) are determined and assigned. Further, the tap coefficient selection unit 356 converts the tap coefficients (0, β ₁ , β ₂ , β ₃ ) obtained by setting β ₀ to 0 in Expression (20) to the tap coefficients (w 0, w 1, 1) of the first FIR filter unit 323b. It is set by determining and substituting as w2, w3).
Here, the output signals Y _{1 to} Y ₃ output from the multipath interference equalization filter 32 in the present embodiment are expressed by the following equation (21).

As shown in Expression (21), the output signal Y ₁ and the output signal Y ₂ have a scalar multiplication relationship with respect to the interference wave I, with the tap coefficient α ₀ as a constant. Also, and the output signal Y ₂ output signals Y _3, similarly, with respect to the interference wave I, is a scalar multiple of the tap coefficients β0 a constant.
As a result, the interference removal unit 16 provided at the subsequent stage of the multipath interference equalization filter 32 adjusts the amplitude and phase of the output signal Y ₁ and the output signal Y ₂ to perform antiphase synthesis, thereby producing the output signal Y _1. Can be suppressed. Moreover, by inversely phase synthesis by adjusting the amplitude and phase of the output signal Y ₃ and the output signal Y _2, it is possible to reduce interference signals I contained in the output signal Y _3. That is, by using the multipath interference equalization filter 32, it is possible to suppress the interference wave I reaching through a plurality of paths exceeding the degree of freedom of the antenna in a multipath environment without increasing the number of antenna elements. It is possible to prevent the communication quality from being lowered.
Further, as shown by the equations (16) and (17) in the second embodiment, the spatial diversity effect obtained by using the antenna elements 11-1 to 11-3 can be maintained also in the third embodiment. Therefore, it is possible to prevent the communication quality from being lowered.

In the second embodiment and the third embodiment, the signal input to the multipath interference equalization filter 12 (22, 32) is a received signal received by two or three different antenna elements. Although described, the present invention is not limited to this configuration, and reception signals received by four or more antenna elements may be input.
In the third embodiment, the configuration in which the reference signal selection unit 355 selects the reference signal based on the input / output power ratio has been described. However, the reception signal is input to each of the reception signals X _{1 to} X ₃ . calculating a sum of absolute values of the tap coefficients of taps provided in the second FIR filter unit 352A～352f, the sum of the absolute value of the calculated tap coefficients of the received signals X ₁ to X ₃ are the minimum received signal The reference signal may be selected.

  In the second embodiment and the third embodiment, the reference signal selection unit 255 (355) is configured to receive, for each received signal, the second FIR filter units 252a and 252b (352a to 352f) to which the received signal is input. You may make it calculate the standard deviation of the signal which subtractor 253a, 253b (353a-353f) using the output signal outputs. Then, the reference signal selection unit 255 (355) may select a received signal having the smallest calculated standard deviation as the reference signal among the received signals.

In each embodiment, the multipath interference equalization filter 12 (22, 32) may generate a signal in which the interference wave is suppressed, and output the generated signal to the synchronization detection unit 14.
As a result, the synchronization detection unit 14 detects the timing of symbol synchronization using the signal input from the multipath interference equalization filter 12 (22, 32) without providing the interference removal unit 13 for suppressing the interference wave. can do.
In each of the embodiments, the configuration of the receiving apparatus that demodulates the OFDM signal has been described. However, the multipath interference equalization filter 12 (22, 32) suppresses the interference wave in the time domain. Can be applied.
In each embodiment, the signal input to the multipath interference equalization filter 12 (22, 32) may be a quantized digital signal. In this case, the delay time in each delay element provided in each FIR filter may be set so that the sampling time at the time of quantization is a unit time.

  In the second and third embodiments, the tap coefficient setting unit 25 (35) corresponds to the combination of two received signals in a plurality of received signals, and the second FIR filter units 252a and 252b (352a to 352f). The configuration of providing the above has been described. However, the present invention is not limited to this configuration, and the tap coefficient setting unit 25 (35) is provided with one second FIR filter unit 252a (352a) and one subtractor 253a (353a), and a received signal input to each of them. May be switched to calculate k tap coefficients and input / output power ratios for all combinations of received signals. By configuring the tap coefficient setting unit 25 (35) in this way, the circuit scale of the tap coefficient setting unit 25 (35) can be reduced.

  Further, in the first FIR filter unit 223 (323a, 323b) in the second and second embodiments, the tap coefficient of the tap (weight multiplier 1224a) that performs an operation on the reference signal not given a delay is set. Since it is set to 0, the weight multiplier 1224a may not be provided.

  The above multipath interference equalization filter may have a computer system inside. In that case, a computer-readable program for causing a computer to execute the functions of the switch unit, delay element, first FIR filter unit, subtractor, and tap coefficient setting unit provided in the multipath interference equalization filter Each function may be realized by the computer by being stored in a recording medium and being read and executed by the computer. Here, the computer-readable recording medium means a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like. Alternatively, the computer program may be distributed to the computer via a communication line, and the computer that has received the distribution may execute the program.

DESCRIPTION OF SYMBOLS 1,9 ... Reception apparatus 11-1, 11-2 ... Antenna element 12, 22, 32 ... Multipath interference equalization filter 13, 16 ... Interference removal part 14 ... Synchronization detection part 15-1, 15-2 ... FFT part 17 ... demodulator 18 ... P / S converter 25, 35 ... tap coefficient setting unit 121, 122 ... FIR filter 123, 124, 224, 253a, 253b, 324a, 324b, 353a, 353b, 353c, 353d, 353e, 353f ... subtracters 131, 132, 161, 162 ... multipliers 134, 164, 1221 ... MMSE units 221a, 221b, 321a, 321b, 321c ... switch units 223, 323a, 323b ... first FIR filter units 252a, 252b, 352a, 352b, 352c, 352d, 352e, 352f... Filter unit 254a, 254b, 354a, 354b, 354c, 354d, 354e, 354f ... I / O power ratio calculation unit 255, 355 ... Reference signal selection unit 256, 356 ... Tap coefficient selection unit 1222 ... Filter unit 133, 163, 1225 2234 ... adders 1223b, 1223c, 1223d, 2232b, 2232c, 2232d ... delay elements 1224a, 1224b, 1224c, 1224d, 2233a, 2233b, 2233c, 2233d ... weight multipliers

Claims (6)

A first FIR filter unit to which a reference signal that is any one of a plurality of reception signals received by each of a plurality of antennas is input, provided corresponding to each of the reception signals other than the reference signal A first FIR filter unit being configured;
A first subtracter provided corresponding to each of the received signals other than the reference signal among the plurality of received signals, wherein the output of the first FIR filter unit corresponding to the received signal is the received signal A first subtractor for subtracting from
When each of the plurality of received signals includes only an interference wave, a tap coefficient that minimizes the power of the signal output from each of the first subtracters is calculated for each of the first FIR filter units. In the FIR filter unit, tap coefficients of taps calculated with respect to the reference signal not given a delay are set to 0, and tap coefficients of other taps are set to the calculated tap coefficients. A multipath interference equalization filter comprising: a tap coefficient setting unit that determines a tap coefficient. A second FIR filter unit having the same number of taps as the number of taps provided in the first filter unit;
A second subtracter for subtracting the output of the second FIR filter section from the input received signal;
An input / output power ratio calculator that calculates an input / output power ratio that is a ratio of a received signal input to the second subtractor to a signal output from the second subtractor;
A tap coefficient calculation unit that calculates a tap coefficient of a tap included in the second FIR filter unit that maximizes the input / output power ratio calculated by the input / output power ratio calculation; and one of the plurality of received signals. The first received signal is input to the second FIR filter unit for a combination of two received signals that are sequentially set as the first received signal and the received signals other than the first received signal are sequentially set as the second received signal. The input / output power calculated for each first received signal in the process of inputting the second received signal to the second subtracter and the tap coefficient calculating unit calculating the tap coefficient of the second FIR filter unit. A reference signal selection unit that selects any one of the plurality of reception signals as the reference signal based on any one of the ratio, the output of the second subtractor, or the calculated tap coefficient;
Of the tap coefficients calculated when the received signal selected as the reference signal by the reference signal selection unit is the first received signal and the other received signals are sequentially set to the second received signal, a delay is given. A tap coefficient selection unit that sets a tap coefficient of a tap calculated for the first received signal that is not set to 0 and determines a tap coefficient of the first FIR filter unit corresponding to a received signal other than the reference signal. The multipath interference equalization filter according to claim 1. The reference signal selector is
For each of the plurality of reception signals, the input / output power ratio when the reception signal is the first reception signal and the reception signals other than the first reception signal among the plurality of reception signals are sequentially used as the second reception signal. Calculate the sum,
The multipath interference equalization filter according to claim 2, wherein a reception signal corresponding to a maximum sum among the calculated sums is selected as the reference signal. The reference signal selector is
For each of the plurality of reception signals, the second subtraction when the reception signal is the first reception signal and the reception signals other than the first reception signal among the plurality of reception signals are sequentially used as the second reception signal. Calculate the standard deviation of the signal output from the instrument,
The multipath interference equalization filter according to claim 2, wherein a reception signal corresponding to a minimum standard deviation among the calculated standard deviations is selected as the reference signal. The reference signal selector is
For each of the plurality of reception signals, calculate a sum of absolute values of tap coefficients calculated by the tap coefficient calculation unit when the reception signal is the first reception signal;
The multipath interference equalization filter according to claim 2, wherein a reception signal corresponding to a minimum sum of absolute values among selected sums of absolute values is selected as the reference signal. The multipath interference equalization filter according to any one of claims 1 to 5,
A synchronization detector that detects a symbol synchronization timing based on a signal output from the multipath interference equalization filter;
An FFT unit that performs FFT on a signal output from the multipath interference equalization filter based on the timing of symbol synchronization detected by the synchronization detection unit;
And a demodulator that demodulates the signal FFTed by the FFT unit.

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