JP7486305B2 - Wireless receiving device - Google Patents

Description

The present invention relates to a wireless receiving device that receives waves arriving at multiple branches based on a space diversity method.

Regarding microwave radio reception in microwave wireless communication systems, a space diversity method using multiple antennas is known as a device for obtaining good reception signals even under fading conditions that occur in radio wave propagation. For example, a wireless communication technology that utilizes the diversity effect is known in which, in a wireless receiving device that realizes space diversity by providing a branch corresponding to each reception signal received by multiple antennas and combining the reception signals of each branch, when diversity combining the reception signals of each branch by weight processing based on a weighting coefficient, a correction matrix is generated such that the covariance matrix obtained from the reception signal vector of the reception signal to be weighted becomes a unit matrix, the reception signal is transformed by the correction matrix, an eigenvector corresponding to the maximum eigenvalue of the covariance matrix obtained from the reception signal vector of the transformed reception signal is calculated, and diversity combining is performed using the eigenvector as a weighting coefficient (Patent Document 1).

International Publication WO2013/018716

However, due to the demand for more efficient frequency utilization in response to an increase in wireless traffic, there is an increasing demand for high-speed transmission using a high-level QAM (Quadrature Amplitude Modulation) method in digital wireless transmission. On the other hand, when a conventional space diversity method (specifically, for example, a minimum amplitude deviation synthesis method or an in-phase synthesis method) aimed at improving reception performance is applied to a high-level QAM method, the effect of phase control error before diversity synthesis may lead to performance degradation when demodulating a signal after diversity synthesis. The technology described in the cited document 1 has the technical idea of reducing the effect of synthesis error by performing waveform equalization before diversity synthesis, and diversity synthesis is performed after performing waveform equalization on the received signal of each branch. In other words, the technology described in Reference 1 performs waveform equalization using the received signals of each branch before the effect of improving the received C/N ratio (Carrier to Noise ratio) due to diversity is obtained, so the equalization limit is equivalent to reception with a single antenna, and there is a problem that degradation of equalization performance due to a decrease in the received C/N ratio cannot be avoided.

The present invention aims to provide a wireless receiving device that can perform phase control of diversity combining with high precision.

In order to solve the above problem, the present invention provides an A/D converter provided for each of a plurality of branches corresponding to each of a plurality of antennas, performing analog-to-digital conversion processing on a baseband signal obtained based on a radio signal received by the antenna, and outputting a received signal; a tap processing unit provided for each of the plurality of branches, performing weight multiplication processing on the received signal based on a tap coefficient, outputting a tap output signal, and outputting a received signal vector of the received signal; an adaptive processing unit that outputs the tap coefficient based on the tap output signal and the received signal vector of each of the plurality of branches; and a diversity combining unit that performs diversity combining processing on the tap output signals of each of the plurality of branches. a combining unit that diversity combines the received signals of the respective branches and outputs a combined received signal, a power detection unit that outputs an amount of phase rotation when the combined signal has maximum power, a diversity combining unit that diversity combines the received signals of the respective branches and outputs a combined received signal, and a demodulation unit that performs demodulation processing on the combined received signal, wherein the amount of phase rotation is determined in the power detection unit from the combined signal obtained by diversity combining the tap output signal generated by multiplying the tap coefficients output from the adaptive processing unit, the phase of the received signal is rotated based on the amount of phase rotation and then diversity combined in the diversity combining unit to obtain the combined received signal, and the combined received signal is demodulated in the demodulation unit.

The invention described in claim 2 is characterized in that in the wireless receiving device described in claim 1, the modulation method of the wireless signal received by the antenna is quadrature phase shift keying.

The invention described in claim 3 is characterized in that in the wireless receiving device described in claim 1 or 2, the number of branches is two.

According to the invention described in claim 1 , adaptive equalization processing is incorporated into power detection for phase adjustment of diversity combining, and power detection is performed after combining the equalized signals, making it possible to perform highly accurate phase control that eliminates the influence of interference due to reflected waves, delay errors between antennas, etc. According to the invention described in claim 1, since the purpose is power detection, highly accurate equalization is not necessary, and an equalization algorithm that operates stably even when the receiving C/N ratio is low can be adopted.

According to the invention described in claim 2, it is possible to achieve the above-mentioned effects in wireless communication using the quadrature phase shift keying method.

According to the invention described in claim 3, it is possible to achieve the above-mentioned effect in diversity combining with two branches.

1 is a functional block diagram showing a schematic configuration of a wireless receiving device according to an embodiment of the present invention; 2 is a functional block diagram showing a schematic configuration of a circuit for verifying correlation detection characteristics of the wireless receiving device shown in FIG. 1. 3 is a graph showing correlation detection characteristics of the wireless receiving device shown in FIG. 1 using the circuit shown in FIG. 2;

The present invention will be described below based on the illustrated embodiment. Note that the following describes the characteristic configuration of the present invention, and omits a description of the conventional mechanism for communicating using the space diversity method.

Figure 1 is a functional block diagram showing the schematic configuration of a wireless receiving device 1 according to an embodiment of the present invention. This wireless receiving device 1 is a mechanism provided in a receiving fixed station to perform wireless communication (particularly microwave wireless communication) between a transmitting fixed station equipped with a single antenna and a receiving fixed station equipped with multiple antennas.

The wireless receiving device 1 according to this embodiment includes A/D converters 13A and 13B, which are provided for two branches (here, the first branch and the second branch) corresponding to the two antennas 11A and 11B, respectively, and which perform analog-to-digital conversion processing on baseband signals (I, Q) obtained based on wireless signals received by the antennas 11A and 11B, and output received signals (I_1, Q_1 and I_2, Q_2); tap processing units 14A and 14B, which are provided for each of the two branches, perform weight multiplication processing on the received signals (I_1, Q_1 and I_2, Q_2) based on tap coefficients (W_1 and W_2), and output tap output signals (Ti_1, Tq_1 and Ti_2, Tq_2) and output received signal vectors (V_1 and V_2) of the received signals; and and V_2), a combiner 16 that diversity combines the tap output signals of the two branches and outputs a combined signal (Ci, Cq), a power detector 17 that outputs the phase rotation amount Δθ when the combined signal (Ci, Cq) has maximum power, a diversity combiner 20 that diversity combines the received signals of the two branches (I_1, Q_1 and I_2, Q_2) and outputs a combined received signal (Ic, Qc), and a demodulator 21 that performs demodulation processing on the combined received signal (Ic, Qc). The phase of the received signal (I_2, Q_2) is rotated based on the phase rotation amount Δθ, and then the diversity combiner 20 diversity combines the received signal (Ic, Qc) to obtain a combined received signal (Ic, Qc), which is then demodulated by the demodulator 21.

The wireless receiving device 1 according to this embodiment has two branches corresponding to two antennas as space diversity branches, and each branch is provided with two mixers, two A/D converters, and two tap processors.

Antennas 11A and 11B receive radio signals transmitted from an antenna (not shown) of the transmitting fixed station and output a received wave signal corresponding to the received radio signal.

The mixers 12A and 12B receive the received wave signals output from the antennas 11A and 11B, perform quadrature demodulation processing on the received wave signals, and output an in-phase baseband signal I and a quadrature component baseband signal Q. In this embodiment, quadrature phase shift keying (QPSK: an abbreviation for Quadrature Phase Shift Keying) is used as the modulation method.

The A/D converter 13A of the first branch performs analog-to-digital conversion processing on the in-phase component baseband signal I output from the mixer 12A to output a received signal (in-phase component I_1), and performs analog-to-digital conversion processing on the quadrature component baseband signal Q to output a received signal (quadrature component Q_1).

The A/D converter 13B of the second branch performs analog-to-digital conversion processing on the in-phase component baseband signal I output from the mixer 12B to output a received signal (in-phase component I_2), and performs analog-to-digital conversion processing on the quadrature component baseband signal Q to output a received signal (quadrature component Q_2).

The tap processing unit 14A of the first branch performs weight multiplication processing on the received signal output from the A/D converter 13A based on a weighting coefficient (also called a tap coefficient or weight vector) corresponding to the signal on the first branch side output from the adaptive processing unit 15, and outputs an in-phase component signal and a quadrature component signal. Specifically, the tap processing unit 14A of the first branch multiplies the received signal (in-phase component I_1, quadrature component Q_1) output from the A/D converter 13A by the weighting coefficient W_1 output from the adaptive processing unit 15 to generate a tap output signal (in-phase component Ti_1, quadrature component Tq_1).

Then, the tap processing unit 14A of the first branch outputs the generated tap output signal (in-phase component Ti_1, quadrature component Tq_1) to the adaptive processing unit 15 and the combiner 16. The tap processing unit 14A of the first branch also supplies the received signal (in-phase component I_1, quadrature component Q_1) output from the A/D converter 13A to the adaptive processing unit 15 as the received signal vector V_1 of the first branch.

The tap processing unit 14B of the second branch performs weight multiplication processing on the received signal output from the A/D converter 13B based on the weighting coefficient (also called a tap coefficient or weight vector) corresponding to the signal on the second branch side output from the adaptive processing unit 15, and outputs an in-phase component signal and a quadrature component signal. Specifically, the tap processing unit 14B of the second branch multiplies the received signal (in-phase component I_2, quadrature component Q_2) output from the A/D converter 13B by the weighting coefficient W_2 output from the adaptive processing unit 15 to generate a tap output signal (in-phase component Ti_2, quadrature component Tq_2).

Then, the tap processing unit 14B of the second branch outputs the generated tap output signal (in-phase component Ti_2, quadrature component Tq_2) to the adaptive processing unit 15 and also outputs it to the combiner 16. The tap processing unit 14B of the second branch also supplies the received signal (in-phase component I_2, quadrature component Q_2) output from the A/D converter 13B to the adaptive processing unit 15 as the received signal vector V_2 of the second branch.

The adaptive processing unit 15 performs adaptive equalization processing to perform tap updating. Specifically, the adaptive processing unit 15 calculates a weighting coefficient W_1 corresponding to the signal on the first branch side and a weighting coefficient W_2 corresponding to the signal on the second branch side using the received signal vector V_1 and tap output signal (in-phase component Ti_1, quadrature component Tq_1) of the first branch output from the tap processing unit 14A of the first branch, and the received signal vector V_2 and tap output signal (in-phase component Ti_2, quadrature component Tq_2) of the second branch output from the tap processing unit 14B of the second branch.

Then, the adaptive processing unit 15 outputs the calculated weighting coefficient W_1 corresponding to the signal on the first branch side to the tap processing unit 14A of the first branch, and outputs the calculated weighting coefficient W_2 corresponding to the signal on the second branch side to the tap processing unit 14B of the second branch.

The combiner 16 performs diversity combining of the in-phase and quadrature components of the signal of the system on the first branch side and the in-phase and quadrature components of the signal of the system on the second branch side, and outputs a combined signal (in-phase component Ci, quadrature component Cq). The combiner 16 receives two signal series in parallel, combines the two signal series using a predetermined combining method, and outputs a combined signal series. In-phase combining is used as the combining method in the combiner 16.

The power detection unit 17 determines the amount of phase rotation Δθ when the combined signal has maximum power based on the signal level of the combined signal (in-phase component Ci, quadrature component Cq) output from the combiner 16. The power detection unit 17 then outputs the determined amount of phase rotation Δθ to the phase adjustment unit 18 and to the mixer 19.

The phase adjustment unit 18 rotates the phase of the tap output signal (in-phase component Ti_2, quadrature component Tq_2) output from the tap processing unit 14B of the second branch by the phase rotation amount Δθ output from the power detection unit 17 to generate a phase rotation signal (in-phase component Ri_2, quadrature component Rq_2) and outputs it to the combiner 16. In other words, the combiner 16 performs diversity combining of the tap output signal (in-phase component Ti_1, quadrature component Tq_1) output from the tap processing unit 14A of the first branch as a signal of the system on the first branch side, and the phase rotation signal (in-phase component Ri_2, quadrature component Rq_2) output from the phase adjustment unit 18 as a signal of the system on the second branch side.

The mixer 19 rotates the phase of the received signal (in-phase component I_2, quadrature component Q_2) output from the A/D converter 13B of the second branch by the phase rotation amount Δθ of the phase output from the power detection unit 17 to generate a phase adjustment signal (in-phase component Pi_2, quadrature component Pq_2) and outputs it to the diversity combining unit 20. Note that, although the mixer 19 is provided for the system on the second branch side in the example shown in the figure, the configuration is not limited to that shown in the figure as long as the phase of the signal on the system on the first branch side and the phase of the signal on the system on the second branch side rotate relatively by the phase rotation amount Δθ.

The diversity combining unit 20 diversity combines the received signal (in-phase component I_1, quadrature component Q_1), which is a signal sequence output from the A/D converter 13A of the first branch, and the phase adjustment signal (in-phase component Pi_2, quadrature component Pq_2), which is a signal sequence output from the mixer 19 provided in the system on the second branch side, to output a combined received signal (in-phase component Ic, quadrature component Qc). The diversity combining unit 20 receives two signal sequences in parallel, combines the two signal sequences using a predetermined combination method, and outputs a combined signal sequence. The combination method used in the diversity combining unit 20 is the same as that used in the combiner 16 (i.e., in-phase combination).

The demodulation unit 21 receives the combined received signal (in-phase component Ic, quadrature component Qc), which is the signal sequence output from the diversity combining unit 20, and performs demodulation processing on the combined received signal (in-phase component Ic, quadrature component Qc) using quadrature phase shift keying (QPSK: abbreviation for Quadrature Phase Shift Keying) as the modulation method, and outputs the signal sequence resulting from the demodulation.

Next, we will explain the function and operation of the wireless receiving device 1 configured in this way.

As processing related to the first branch, the antenna 11A outputs a received wave signal corresponding to the radio signal received to the mixer 12A, the mixer 12A performs quadrature demodulation processing on the received wave signal, and outputs an in-phase component baseband signal I and a quadrature component baseband signal Q to the A/D converter 13A, and the A/D converter 13A performs analog-to-digital conversion processing on the baseband signals I and Q, and outputs a received signal (in-phase component I_1, quadrature component Q_1) to the tap processing unit 14A. The tap processing unit 14A performs weight multiplication processing on the received signal (in-phase component I_1, quadrature component Q_1) using a weighting coefficient W_1 corresponding to the signal on the first branch side output from the adaptive processing unit 15, and outputs a tap output signal (in-phase component Ti_1, quadrature component Tq_1) to the adaptive processing unit 15 and the synthesis unit 16.

As processing related to the second branch, the antenna 11B outputs a received wave signal corresponding to the radio signal received to the mixer 12B, the mixer 12B performs quadrature demodulation processing on the received wave signal to output the in-phase component baseband signal I and the quadrature component baseband signal Q to the A/D converter 13B, the A/D converter 13B performs analog-to-digital conversion processing on the baseband signals I and Q to output the received signal (in-phase component I_2, quadrature component Q_2) to the tap processing unit 14B. The tap processing unit 14B performs weight multiplication processing on the received signal (in-phase component I_2, quadrature component Q_2) using the weighting coefficient W_2 corresponding to the signal on the second branch side output from the adaptive processing unit 15, and outputs the tap output signal (in-phase component Ti_2, quadrature component Tq_2) to the adaptive processing unit 15 and to the synthesis unit 16.

The tap processing unit 14A of the first branch supplies the received signal (in-phase component I_1, quadrature component Q_1) to the adaptive processing unit 15 as the received signal vector V_1 of the first branch, and the tap processing unit 14B of the second branch supplies the received signal (in-phase component I_2, quadrature component Q_2) to the adaptive processing unit 15 as the received signal vector V_2 of the second branch.

Next, the adaptive processing unit 15 calculates a weighting coefficient W_1 corresponding to the signal on the first branch side and a weighting coefficient W_2 corresponding to the signal on the second branch side using the tap output signal (in-phase component Ti_1, quadrature component Tq_1) and the received signal vector V_1 of the first branch, and the tap output signal (in-phase component Ti_2, quadrature component Tq_2) and the received signal vector V_2 of the second branch, and outputs them to the tap processing unit 14A of the first branch and the tap processing unit 14B of the second branch.

The combiner 16 diversity combines the signal of the system on the first branch side (specifically, the in-phase component Ti_1 and the quadrature component Tq_1 of the tap output signal) and the signal of the system on the second branch side (specifically, the in-phase component Ri_2 and the quadrature component Rq_2 of the phase rotation signal) to output the combined signal (in-phase component Ci, quadrature component Cq) to the power detector 17. The power detector 17 determines the phase rotation amount Δθ when the combined signal has maximum power based on the signal level of the combined signal (in-phase component Ci, quadrature component Cq) and outputs it to the phase adjuster 18 and the mixer 19. The phase adjuster 18 rotates the phase of the tap output signal (in-phase component Ti_2, quadrature component Tq_2) output from the tap processor 14B of the second branch by the phase rotation amount Δθ and outputs the phase rotation signal (in-phase component Ri_2, quadrature component Rq_2) to the combiner 16.

The mixer 19 then rotates the phase of the received signal (in-phase component I_2, quadrature component Q_2) by the phase rotation amount Δθ and outputs a phase adjustment signal (in-phase component Pi_2, quadrature component Pq_2) to the diversity combining unit 20. The diversity combining unit 20 diversity combines the received signal (in-phase component I_1, quadrature component Q_1), which is the signal series of the first branch side system, with the phase adjustment signal (in-phase component Pi_2, quadrature component Pq_2), which is the signal series of the second branch side system, and outputs a combined received signal (in-phase component Ic, quadrature component Qc) to the demodulation unit 21. The demodulation unit 21 demodulates the combined received signal (in-phase component Ic, quadrature component Qc) and outputs a signal series of the demodulation result.

According to the wireless receiving device 1 of this embodiment , adaptive equalization processing is incorporated into the power detection for phase adjustment of diversity combining, and the equalized signals are combined before power detection, so that highly accurate phase control can be performed that eliminates the influence of interference due to reflected waves, delay errors between antennas, etc. According to the wireless receiving device 1 of this embodiment, since the purpose is power detection, highly accurate equalization is not necessary, and an equalization algorithm that operates stably even when the reception C/N ratio is low can be adopted.

Next, the phase difference detection characteristics of the wireless receiving device 1 configured in this way will be verified using Figures 2 and 3.

As shown in Figure 2, when a signal transmitted from a single antenna 2 installed at a transmitting fixed station is received by two antennas 11A and 11B installed at a receiving fixed station, one antenna 11A receives only direct waves and outputs a received wave signal, while the other antenna 11B outputs a received wave signal in a situation where fading is occurring (i.e., it receives reflected waves in addition to direct waves), the difference in correlation detection characteristics depending on whether or not equalization processing is performed is verified.

Here, verification will be performed using the following specifications and conditions.
Modulation method
Quadrature Phase Shift Keying (QPSK)
<Fading conditions (minimum phase shift type)>
Delay time: 0.015T
Notch depth: 30 dB
Notch frequency: Modulation spectrum center frequency (equalization algorithm)
Godard's method (Godard's Kalman algorithm)

The correlation between the signal series of the first branch system based on the received wave signal of antenna 11A and the signal series of the second branch system based on the received wave signal of antenna 11B is calculated when the phase is rotated in the range of -180° to 180° with respect to the signal series of the second branch system, and this is called detection 1. Detection 1 is the correlation detection result when no equalization processing is performed.

On the other hand, equalization is performed on the signal series of the first branch system based on the received wave signal of antenna 11A and the signal series of the second branch system based on the received wave signal of antenna 11B, and the correlation between the signal series of the first branch system and the signal series of the second branch system is calculated when the phase is rotated in the range of -180° to 180° with respect to the signal series of the second branch system, and this is called detection 2. Detection 2 is the correlation detection result when equalization is performed.

The relationship between the amount of phase rotation (i.e., phase difference) and correlation for detection 1 and detection 2 is summarized in Figure 3. The vertical axis in Figure 3 uses the average value between the in-phase components and the quadrature components of the signal series on the first branch side and the signal series on the second branch side. Here, the correlation value is calculated by taking the complex conjugate of one of the data for which correlation is to be observed, and then complex multiplying it. According to this calculation, the imaginary number (IMG) component becomes 0 (zero) where the correlation is high.

From the results of detection 1 shown in Figure 3, it can be seen that in a situation where fading is occurring, if equalization processing is not performed, the phase difference will shift and the detection sensitivity will be low. On the other hand, from the results of detection 2, it can be seen that even in a situation where fading is occurring, by performing equalization processing, it is possible to detect the phase difference and the detection sensitivity is high.

Although the embodiment of the present invention has been described above, the specific configuration is not limited to the above embodiment, and even if there are design changes within the scope of the present invention, they are included in the present invention. Specifically, the gist of the present invention is to incorporate adaptive equalization processing into power detection for phase adjustment of diversity combining, combine the equalized signals, and then perform power detection, and even if there are design changes within the scope of the present invention, they are included in the present invention. For example, in the above embodiment, two branches, a first branch and a second branch, are provided as branches in space diversity, but the number of branches is not limited to two and can be any number greater than two.

1 Radio receiving device 11A Antenna (first branch)
11B Antenna (second branch)
12A Mixer (first branch)
12B Mixer (second branch)
13A A/D converter (first branch)
13B A/D converter (second branch)
14A Tap processing unit (first branch)
14B Tap processing unit (second branch)
15 Adaptive processing unit 16 Combining unit 17 Power detection unit 18 Phase adjustment unit 19 Mixer 20 Diversity combining unit 21 Demodulation unit

Claims (3)

an A/D converter provided for each of a plurality of branches corresponding to a plurality of antennas, the A/D converter performing analog-to-digital conversion processing on a baseband signal obtained based on a radio signal received by the antenna, and outputting a received signal;
a tap processing unit provided for each of the plurality of branches, which performs a weight multiplication process on the received signal based on a tap coefficient to output a tap output signal and outputs a received signal vector of the received signal;
an adaptive processor that outputs the tap coefficients based on the tap output signals of each of the plurality of branches and the received signal vector;
a combiner that performs diversity combining on the tap output signals of the respective branches and outputs a combined signal;
a power detector that outputs a phase rotation amount when the composite signal has a maximum power;
a diversity combining unit that diversity combines the received signals of the plurality of branches and outputs a combined received signal;
A demodulation unit that performs demodulation processing on the composite received signal,
the power detection unit determines the amount of phase rotation from the combined signal obtained by diversity combining the tap output signal generated by multiplying the tap coefficient output from the adaptive processing unit by the tap coefficient,
the phase of the received signal is rotated based on the amount of phase rotation, and then the diversity combining unit performs diversity combining to obtain the combined received signal, and the combined received signal is demodulated by the demodulation unit.
A radio receiving device comprising: The modulation method of the radio signal received by the antenna is quadrature phase shift keying.
2. The wireless receiving device according to claim 1, The number of branches is two.
3. The radio receiving device according to claim 1, wherein the first and second inputs are connected to the first and second inputs.

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