JPS5935221B2 - Diversity reception method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a method for reducing the frequency of code errors caused by multi-bus fading in fixed or mobile radio communication systems using digital angle modulation. This relates to the reception method.

Conventionally, this type of diversity reception method is (I)
A method of selectively receiving the received signal of the branch that takes the maximum value by detecting the envelope level of the received signal of each branch and comparing them with each other (selective synthesis diversity reception method);
(l■) A method of comparing the phases of the received signals of each branch with each other, controlling the respective phase differences to be zero, and then combining and receiving them at the same level (equal gain combining diversity reception method), (Ili) A method in which the phases of the received signals of each branch are compared with each other, the respective phase differences are controlled to be zero, and then weighting is performed in proportion to the envelope level of each received signal, and then combined reception is performed (maximum Synthesizers, diversity reception systems), etc. have been adopted.

In either case, these methods not only require a circuit to detect the envelope level ((1) and (11))) or a circuit to detect the phase difference ((11) and (111)). , a circuit (1) that compares the envelope levels of each branch, determines the maximum value, and then selects that branch, and a control circuit that makes the phase difference zero ((11) and 011).
) and a circuit (111) for weighting the received signal of each branch according to the level ratio. This has not only been an obstacle to simplifying and downsizing the configuration of the diversity receiving device, but has also caused problems in terms of operational stability and economic efficiency.
SUMMARY OF THE INVENTION Accordingly, the present invention aims to improve the above-mentioned drawbacks of the prior art by reducing the frequency of code errors caused by multipath fading and the like by using a simple device.

The present invention is characterized by using the output of a local oscillator that performs angle modulation on the received signal of each branch using a specific waveform that is synchronized with the repetition period of the digital modulation signal waveform and satisfies a mutually complementary relationship. The method is a diversity reception method in which a plurality of signals obtained by frequency conversion using the above-mentioned specific waveform or direct angle modulation of the received signal itself using the specific waveform are synthesized and received, and then delayed detection and integral detection are performed. This will be explained below with reference to the drawings. FIG. 1 shows an embodiment in which the present invention is applied in the case of two-branch reception.
, 2 is a receiving antenna, 3 and 4 are frequency converters, 5 and 6 are angle modulators, 7 and 8 are input signal terminals for angle modulation, 9 is a local oscillator, 10 is a combiner, 11 is a delay detector, 12 13 is an integral detector, 13 is a clock synchronization circuit, 14 is a waveform generator, and 15 is a demodulated reproduction output signal terminal.

First, two signals received by receiving antennas 1 and 2 are applied to angle modulation input signal terminals 7 and 8 using specific waveforms (described later) that satisfy a mutually complementary relationship.
The two signals in the intermediate frequency band obtained by mixing the output of the local oscillator (9) which has been angularly modulated using the angle modulator (5, 6) and the frequency converter (3, 4) are converted into 10
After being synthesized and received by a synthesizer, 11 performs delayed detection, and using a clock signal regenerated by a clock synchronization circuit 13, integral detection is performed by 12, a desired signal is demodulated and reproduced, and is outputted from 15.

Note that the waveforms applied to the angle modulation input signal terminals 7 and 8 are specific waveforms that satisfy a mutually complementary relationship.
It is assumed that the clock signal regenerated by 13 is used to generate a waveform generator 14. The fact that the combined reception effect in such a diversity reception system matches that in the conventionally known maximum ratio combining diversity reception system will be explained below using a mathematical formula. Now, the received waves r1(t) and R2(t) by the two receiving antennas are received via a multipath propagation path modeled as a Z-l fading channel. Assuming that there is, it is expressed mathematically as follows.

However, Re{} in the above formula means taking the real part of {}, and ωo and ψ) indicate the center angular frequency of the carrier wave and the digital angle modulation signal, respectively.

Further, Z1 and Z2 are complex Gaussian variables, and are expressed as in the following equation using envelopes Rl and R2 according to the l-l distribution law and phases θ1 and θ2 according to the uniform distribution law. r1(t) and R2(t) expressed by formula (1),
When the frequency is converted using the output of a local oscillator that has been angularly modulated with specific waveforms ψ1(t) and ψ2(t) that satisfy the special relational expressions described below, the intermediate frequency band is displayed as the following equation. Two signals e1(t and E2(t)) are obtained.

However, it is assumed that ωo represents an angular frequency corresponding to the intermediate frequency.

By combining the two signals in equation (3), the input e(t) to the differential detector is expressed as shown in the following equation.

However, it is assumed that Z(t) is given by the following equation. Here, assuming that the noise level of the receiver is sufficiently small, the output v(t) of the differential detector is determined by the following equation. Here Z*
(t) is a symbol indicating the complex conjugate of Z(t), and T is the delay time in the delay line of the differential detector, which is generally selected to be equal to the repetition period of the digital angle modulation signal.

Assuming that the digital angle modulation signal to be considered is a two-phase differential phase modulation signal, ω0T and φm1(t) satisfy the following relationship.

Therefore, since the output of the delayed detector given by equation (6) t)
is the following formula.

By integrating this from t=(n-1)T to t=NT, we obtain the output of the integral detector. Here, using equation (5), Z ) by redisplaying, equation (10) becomes .

Therefore, if ψ1(t) and ψ2(t) are chosen to satisfy the following special relational expression (n is an integer, T is the repetition period of the digital signal), then the equation (
11) is obtained as follows using R1 and R2 defined by equation (2).

Equation (14) is consistent with the output of the delay detection integral detector when the conventionally known maximum ratio combining diversity reception method is introduced, and the combined reception effect of this diversity reception method is equal to the maximum ratio combination reception effect. It shows that you are getting used to it. From equation (12), φ1([) and ψ2(t) are periodic functions of T, so equation (13) can be expressed as the following equation. The following can be considered as a concrete solution that satisfies this equation. However, β and ω.

satisfies the following equation. The above is an explanation for a diversity reception system with two branches, but it is clear that the same thing can be extended to a case with two or more branches, and in that case, equation (12) and equation The relationship corresponding to (13) is as follows.

In addition, although the above explanation has been made using a two-phase differential phase modulation signal as an example, it goes without saying that it can be applied to multi-phase differential phase modulation signals such as 4-phase, 8-phase, 16-phase, etc., as well as continuous phase FSK signals, etc.
The present invention can be similarly applied to other general digital angle modulation signals to which the delay detection/integral detection method can be applied.
FIG. 2 is another embodiment of the invention, in which all symbols are the same as in FIG. 1, and the effect is the angular frequency ω of the intermediate frequency in equation (3).

It can be easily understood by setting ωc as ωc. In addition, in FIG. 2, the synthesizer may be placed after the frequency conversion to the intermediate frequency; this is a matter of which frequency band to perform the operations of delayed detection and integral detection, and is completely covered by the scope of this patent. .

Also, the detection method of delayed detection/integral detection used in the present invention is slightly inferior to the synchronous detection method in terms of noise margin, waveform distortion, interference resistance, etc., and as a measure to remedy this, two time slots are used. It is also possible to employ an auxiliary means of performing error correction using the differential detection outputs described above.

As is clear from the above description, according to the present invention, the clock synchronization signal regenerated from the demodulated signal is used to synchronize with the repetition period of the digital modulation signal waveform generated by the waveform generator and to establish a mutually complementary relationship. The conventional maximum ratio combining diversity reception method simply combines and receives multiple signals obtained by converting the frequency using the output of a local oscillator that has been angularly modulated with a "satisfactory specific waveform." The same improvement effect can be obtained.

In the conventional maximum ratio combining diversity reception system, it was not only necessary to synchronize the carrier phase of the received signals of each branch, but also to weight each branch Q received signal according to its respective envelope level. It was hot, but
The present invention eliminates the need for these complex and advanced techniques. That is, the present invention can achieve the same effect as the conventional maximum ratio combining diversity method with a simple device configuration, and is particularly advantageous when fading changes rapidly. The present invention is not only useful as a measure to improve reliability when transmitting signals using the digital angle modulation method in poor communication channels such as land mobile radio channels where multipath fading is always present, but also useful for improving the reliability of signal transmission using the digital angle modulation method. It is also useful as a fixed wireless transmission line using millimeter waves.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a diversity receiver according to the present invention, and FIG. 2 is a block diagram of another embodiment of the diversity receiver according to the present invention. 1, 2...Receiving antenna, 3, 4...
Frequency converter, 5, 6... Angle modulator, 7, 8
...Input signal terminal for angle modulation, 9...
Local oscillator, 10...Synthesizer, 11...
・Delay detector, 12... Integral detector, 13...
. . . Clock synchronization circuit, 14 . . . Waveform generator, 15 . . . Demodulation reproduction output signal terminal.

Claims (1)

[Claims] 1. In a multi-branch diversity reception system in a communication system using digital angle modulation, signals are synchronized with the repetition period of the digital modulation signal waveform and have a mutually complementary relationship, that is, ψ_i(t)−ψ_i(t− T)=0i
=1, 2, 3,...m, ∫^n^T_(_n_-_1
＿）＿Texp[−j{ψ_i(t)−ψ_j(t)}
] dt=0(i≠j, i, j=1, 2, 3,..., m
) (where n is an integer, T is the repetition period of the digital signal waveform, and m is the number of branches, a natural number of 2 or more). A diversity reception method characterized in that a plurality of signals obtained by frequency converting a received signal using the output of a local oscillator subjected to processing are synthesized and received, and then delay detection and integral detection are performed.