JPH06268559A - Diversity receiver - Google Patents

Abstract

PURPOSE:To attain the synthesis diversity for phase difference detection independently of the number of branches (reception system). CONSTITUTION:A detector 19 of each signal processing section 311(i=1,2,...k) detects a reception level W1 of a reception signal of each branch, a phase difference is detected by a phase difference detector 32, latched as a sample in sample latch circuits 33, 34 in a symbol timing, a phase difference detection output DELTAPSI1 is fed to adders 351, 352, 353, 354, in which a difference from phase differences 3pi/4, pi/4-pi/4,-3pi/4, taken by adjacent symbols is taken. The differences are sequentially extracted within one symbol period and absolute values are taken. A reception level W1 is multiplied by each absolute value at a multiplier 38 and the product is used for an output of the signal processing section 311. A synthesizer 39 synthesizes outputs of the signal processing sections 311-31k at each phase difference taken and the phase difference taken by a minimum output of the four synthesized outputs is discriminated by a data discrimination section 41, and the result is outputted as a code.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, in digital mobile communications to improve the deterioration of transmission quality due to multipath fading. The signals received from a plurality of antennas are weighted according to the reception level after phase difference detection. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a post-detection combining diversity receiver that combines signals by combining.

[0002]

2. Description of the Related Art In digital mobile communications, the amplitude and phase of a received signal fluctuate drastically due to multipath fading, and the transmission quality is greatly degraded. Diversity reception using two or more received waves is a technique for reducing the influence of fading. Diversity reception is a technique that uses a plurality of received waves having a small fading correlation so that even if the level of one received wave drops, the received waves of another level are used to achieve good quality. Diversity reception includes pre-detection synthesis and post-detection synthesis. Post-detection synthesis is more practical than pre-detection synthesis because it does not require the function of performing in-phase synthesis by following the high-speed phase fluctuation of the received signal due to fading.

For diversity reception after detection, there are a selective combining method and a maximum ratio combining method. The selective combining method selects the symbol determination result of the branch (reception system) having the highest reception level. In the selective combining method, only the signal of one branch having the highest reception level is always used for each symbol, whereas in the maximum ratio combining method, the received waves of each branch are weighted according to the reception level to be combined, so that a larger signal can be obtained. The effect of improving the transmission characteristics can be obtained. Reference [1] Adachi, F .;
and Ohno, K .; , "BER performance
nce of QDPSK with postdet
section diversity reception
in mobile radiochannel
s, "IEEE Trans. Veh. Techno
l. , Vol. 40, pp. 237-249, Feb.
1991. Then, for π / 4 shift QDPSK differential detection,
The error rate characteristics under Rayleigh fading when the diversity after detection is applied are analyzed, and the effect is described in [2] Adachi, F. et al. and Ohno, K .; "P
ostdetection MRC diversit
y for π / 4-shift QDPSK mob
ile radio, "Electron. Let
t. , Vol. 27, pp. 1642-1643, Au
g. 1991. Have been confirmed by experiments.

FIG. 3 shows the configuration of a conventional two-branch phase-combining diversity receiver when phase difference detection is performed on a QDPSK signal. Although not shown in the figure, the received signals from the two antennas are converted into intermediate frequency signals and input terminal 1
The signals 1 ₁ and 11 ₂ are input to the signal processing units 12 ₁ and 12 ₂ , respectively. The signal processing unit 12 ₁ limits the received signal to the limiter 1
The amplitude is limited by 3, and the signal of the local oscillator 14 is used to detect the phase by the phase detector 15. The detection output of the phase detector 15 is sampled at the symbol timing in the sampling circuit 16 and supplied to the adder 17 and the 1-symbol delay circuit 18. The adder 17 detects the phase difference between the phase detection output at the current symbol timing and the phase detection output one symbol before. The phase detector 15, the sampling circuit 16, and the delay circuit 18 constitute a phase difference detection circuit. The output W _K of the reception level detector 19 is multiplied by the multiplier 21 to weight the phase difference detection output. The outputs of the signal processing units 12 ₁ and 12 ₂ processed in this way are combined by the combiner 22. The data determiner 23 determines the sign according to the output of the combiner 22.

In the quadrature delay detection, the in-phase component and the quadrature component of the detection output of each branch are weighted at the reception level and vector-synthesized. In the phase synthesis, the phase difference detection output of each branch is weighted at the reception level [-π, Scalar synthesis is performed within the range of [π]. That is, t = nT (T:
The phase difference detection output of each branch in the symbol length)
If Ψ _k (n) and the weighting coefficient of each branch are W _k , the combined output ΔΨ (n) is given by the following equation.

ΔΨ (n) = ΣW _k ΔΨ _k (n) mod 2π (1) Σ is from k = 1 to 2 However, when | ΔΨ ₁ (n) −ΔΨ ₂ (n) |> π, the expression ( Combining the phase difference of each branch based on 1),
For example, as shown in FIG. 4, in the case of vector combination, the combined vector ΔΨ (n) has a direction indicated by a dotted line, but the combined vector ΔΨ (n) is combined in a phase opposite to the dotted line as shown by a solid line. . Therefore, ΔΨ ₂ (n)
Must be corrected before the synthesis according to equation (1).

When ΔΨ ₂ (n) + 2π, ΔΨ ₁ (n) −ΔΨ ₂ (n)> π When ΔΨ ₂ (n) -2π, ΔΨ ₁ (n) −ΔΨ ₂ (n) <− π ( 2) In this way, the phase difference detection output is calculated as | ΔΨ ₁ (n) −Δ
In the case of Ψ ₂ (n) |> π, ΔΨ ₂ (n) is corrected, and then weighted by the reception level and combined, whereby a two-branch diversity receiver can be constructed in phase difference detection.

[0008]

As described above, mobile communication requires a technique for improving the deterioration of transmission quality due to fading, and diversity reception is a practical method. From References [1] and [2], the improvement effect increases as the number of branches increases. However, although the synthesis by equation (1) constitutes scalar synthesis on the phase plane, the phase plane becomes discontinuous at ± π, so equation (1) after phase difference detection is used.
The combination of (2) can be applied only to two branches, and even if the number of branches is increased from this, improvement in transmission characteristics cannot be expected. Phase difference detection has a simpler high-frequency configuration than quadrature detection, and it is desired that the post-phase-difference detection combination effect can be improved according to the number of branches.

It is an object of the present invention to solve such a problem and to provide a diversity receiver capable of diversity combining regardless of the number of branches in phase difference detection.

[0010]

According to the present invention, each reception signal received by a plurality of antennas, that is, each reception signal of each diversity branch is subjected to phase difference detection by a phase difference detector, and each diversity branch (reception The reception level detector detects the difference between the ideal phase point and the phase difference detection output of each diversity branch, and the absolute value of each difference is calculated. The absolute value is weighted according to the detected reception level for each branch, the difference absolute value weighted for the same ideal phase point from each branch is combined by the combiner, and the ideal output that minimizes the combiner output. The data determination circuit outputs a code indicating the ideal phase point by determining the phase point.

[0011]

In the present invention, since the absolute value of the phase difference between the ideal phase point and the phase difference detection output is weighted by the reception level and combined as described above, the problem of discontinuity on the phase plane occurs. Absent. Therefore, combined diversity can be realized regardless of the number of branches, and transmission characteristics can be improved under fading.

[0012]

EXAMPLE The present invention is applied to π / 4 shift QDPSK.
Another embodiment is shown in FIG. In this example, n divers
Although not shown in the figure when a branch is provided, k pieces
The signals received from the antennas of
Input terminal 11₁~ 11 _kBased on this invention
Signal processing unit 31₁~ 31_kAre input respectively. signal
Processing unit 31₁~ 31_kHave the same configuration, and the signal processing unit 3
1₁Will be described. Input terminal 11₁Signal from
It is supplied to the signal level detector 19 and its reception level is detected.
Along with being output, it is branched and supplied to the limiter 13 as well.
Is limited and is supplied to the phase difference detector 32.

The phase difference detector 32 is the local oscillator 1 in FIG.
4, a phase detector 15, a sampling circuit 16, an adder 17, and a 1-symbol delay circuit 18. Phase difference detection output of phase difference detector 32 ΔΨ ₁ (n)
And the detected reception level of the reception level detector 19 are sample-held at the symbol timing in the sample-holding circuits 33 and 34, respectively. Phase difference detection output ΔΨ at the time point nT when the sample is held in the sample holding circuit 33
₁ (n) is the ideal phase point 3π / 4, π / 4, −π / in adders 35 ₁ , 35 ₂ , 35 ₃ , and 35 ₄ , respectively.
The difference between 4 and -3π / 4 is taken. In this example, since it is π / 4 shift QDPSK, the possible phase difference between adjacent symbols is any of 3π / 4, π / 4, -π / 4, and -3π / 4, and these are ideal phase points. Becomes

[0014] and the phase difference detection output from the adder 35 ₁ to 35 _4, the difference switch 36 between each ideal phase points, (fast at least 4 times or more) sufficiently higher than the symbol frequency 1 / T
The absolute values are sequentially switched by the high-speed clock and supplied to the absolute value circuit 37, and the respective absolute values are taken. These absolute value circuit 3
The output of 7 is the output W of the sample holding circuit 34 in the multiplier 38.
₁ (n) is multiplied and weighted, and W ₁ (n) · | Ψ
₁ (n) -3π / 4 |, W ₁ (n) · | Ψ ₁ (n) -π
/ 4 |, W ₁ (n) · | Ψ ₁ (n) + π / 4 |, W
₁ (n) · | Ψ ₁ (n) + 3π / 4 | is the signal processing unit 31.
It is output sequentially from ₁ .

Similarly, the signal processing unit 31_kTo W
_k(N) ・ | Ψ_k(N) -3π / 4 |, W _k(N) ・ |
Ψ_k(N) -π / 4 |, W_k(N) ・ | Ψ_k(N) + π
/ 4 |, W _k(N) ・ | Ψ_k(N) + 3π / 4 |
Is output. The signal processing unit 31 in the synthesizer 39₁~ 31_kOut
The corresponding ideal phase points of force are combined. That is, ideal
For the phase point 3π / 4, W₁(N) ・ | Ψ₁(N) -3
π / 4 | + W₂(N) ・ | Ψ ₂(N) -3π / 4 | + ...
+ W_k(N) ・ | Ψ_k(N) -3π / 4 |
The other ideal phase points are similarly combined.
These combined outputs are supplied to the data determination unit 41. Day
The data determination unit 41 uses four ideal phases for each symbol period.
The ideal position where the output value is the minimum in the composite output for the point
The phase point is determined and the code indicating the ideal phase point is output.

[0016]

As described above, according to the present invention, combined diversity can be realized in phase difference detection regardless of the number of branches. The effect of the present invention confirmed by computer simulation was confirmed by π / 4 shift QDPS.
The case of K is shown in FIG. The fading pitch f _D T normalized by the symbol length T is 1.9 × 10 ⁻³ .
The horizontal axis is the average E _b / N ₀ , and the vertical axis is the average error rate. Plots of □ are characteristics of the present invention, others are quadrature differential detection, plots of × are characteristics when diversity is not applied, plots of Δ are characteristics of selection diversity, and plots of ○ are maximum ratio combining diversity. Is a characteristic of. The solid line and the broken line are theoretical characteristic curves in QDPSK differential detection according to document [1], and L is the number of branches. From this figure, according to the diversity of the present invention, there is almost the same improvement effect as the maximum ratio combining diversity in the differential detection, a greater diversity gain than the selective diversity is obtained, and it is effective in improving the transmission quality under fading. is there. When the number of branches L is 3, the characteristic becomes better than when the number of branches is 2, and the greater the number of branches, the greater the diversity effect. The characteristics are almost the same as the theoretical characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a post-detection combining diversity receiver according to the present invention.

FIG. 2 is a diagram showing error rate characteristics with respect to an average E ₀ / N ₀ in each reception system.

FIG. 3 is a block diagram showing a conventional 2-branch phase-combining diversity receiver.

FIG. 4 is a signal vector diagram showing an example in which the direction is reversed from the actual state in the phase combined output.

Claims (1)

[Claims] 1. A diversity receiver for combining received signals received by a plurality of antennas with a phase difference detector, and combining the received signals after the phase difference detection, a reception level detector for detecting a reception level of each antenna, Means for obtaining the difference between the phase difference detection output from each phase difference detector and the ideal phase point, means for obtaining the absolute value of each difference, and weighting according to the detection reception level corresponding to the absolute value of each difference Means for adding, a synthesizer for synthesizing these weighted absolute values for each of the ideal phase points, and a code indicating the ideal phase point by determining the minimum ideal phase point in the output of the synthesizer. A diversity receiver, comprising: a data determination circuit for outputting as demodulated data.