JPS6342456B2 - - Google Patents

Description

[Detailed Description of the Invention] (Technical Field) The present invention relates to a diversity communication method used to improve transmission characteristics in digital mobile communications where bit error rate characteristics are significantly degraded due to multipath fading, etc. be.

(Background technology) Conventionally, diversity communication methods include (1) spatial diversity method, (2) polarization diversity method,
(3) Directional diversity method, (4) Frequency diversity method, (5) Time diversity method, etc. are known. However, since the methods (1) to (3) use the receiving antenna as a diversity branch, they have the disadvantage of requiring multiple receiving antennas and receivers. Furthermore, since the method (4) uses multiple carrier waves as diversity branches, it requires multiple transceivers. Therefore, the methods (1) to (4) all have the disadvantage that they require large-scale mobile equipment and base station equipment, which is contrary to the miniaturization and economicalization of equipment that is important in mobile communications.

On the other hand, the time diversity method (5) has the advantage that a diversity communication method can be configured with one transmission/reception system, and the following methods have been proposed in the past.

(i) A method in which the transmitted data has a frame structure and is repeatedly transmitted for each frame.

(ii) A method in which transmission data is encoded by repeatedly arranging it in an interlaced pattern and transmitted using a binary modulation method.

However, method (i) requires a frame synchronization circuit on the receiving side, and has a fatal drawback in that if frame synchronization is lost, data demodulation becomes impossible. In addition, in method (ii), since data is arranged repeatedly, it is necessary to perform time slot synchronization, and if this is lost, diversity reception cannot be performed, which has the disadvantage of deteriorating transmission characteristics. Ta.

(Problem to be solved by the invention) In order to eliminate such drawbacks, the present invention uses a multilevel modulation/demodulation method to transmit multiple pieces of transmitted data that have a low correlation in reception level fluctuations and are delayed by different delay times. By transmitting and receiving sequences simultaneously, time diversity can be achieved without the need for frame synchronization or time slot detection.The feature is that in digital mobile communications, on the transmitting side, the correlation of reception level fluctuations is N ways that are low and different from each other (N
is a natural number of 2 or more), and the N transmission data sequences obtained in the same way are simultaneously encoded via the encoding means for the 2 ^N -value modulation method, and each transmission data sequence is is divided into N parts and transmitted, and on the receiving side, the data is repeated N times with the delay time interval, and the received data is regarded as a received signal appearing in the N diversity branches and selected.
It is a time diversity communication method such as combining.

(Structure and operation of the invention) FIG. 1 is an embodiment of a method for allocating time for transmitting and receiving signals in a time diversity communication system according to the present invention. For the sake of simplicity, a case will be described in which the diversity combining method is a selection method and the number of diversity branches is two, that is, a case where a four-level digital modulation method is used.

The data sequence 1 of the signal to be transmitted is {a _i } (i is an integer), the data sequence 2 of the signal actually sent from the transmitter is {I _i , Q _i }, and the demodulated output signal output from the receiver is Data series 3 is expressed as {b _i }. Both data series have the same clock frequency _c . {a _i } is encoded into {I _i , Q _i } in the following manner by an encoder in the transmitting device, which will be described later.

One sequence of {I _i , Q _i }, {I _i }, is directly assigned the data {a _i } that is input to the encoder at that time. That is, I _i =a _i . On the other hand, the other sequence {Q _i } is assigned a data sequence obtained by delaying the input data sequence {a _i } by n bits. That is, Q _i =a _io . The transmission data sequence {I _i , Q _i } obtained in this manner is transmitted using a four-level digital modulation method.

A method of setting the number of delay bits n will be explained below. In digital mobile communications, a plurality of signals received at intervals of about half a period of fading or more are subjected to fading that has little correlation with each other, so that the probability that code errors will occur at the same time is low. If the time for one bit is t=1/ _c , the above delay time can be expressed as nt. Therefore, if nt is set to a value greater than half the period of fading, {I _i }
and {Q _i } are two received data sequences with a low probability of simultaneously causing errors. In this way, when the number n of delay bits is expressed using the fading period τ and the time t for one bit, it may be set so as to satisfy the condition n≧τ/2t.

On the other hand, on the receiving side, the data sequence {I _i , Q _i } is demodulated and reception level 4 is detected. There is a close relationship between the reception level and the code error rate at that time, and the higher the level, the lower the code error rate. The diversity control circuit in the receiving device, which will be described later, is
A composite control signal is generated that instructs which of {I _i } and {Q _i } to select based on the reception level. In the case of FIG. 1, since the reception level at times T _o - _{T o+2} is higher than the reception level at times T _2o - T _2o+2 , I _o - _{I o+2} and Q _o - Q _o+2 is I _2o ~
It is expected that the bit error rate will be lower than I _2o+2 and Q _2o to Q _2o+2 . The data {a _i } to be transmitted is assigned twice to {I _i } and {Q _i } with a delay time nt. For example, _ao is assigned to _Io and _Q2o . As mentioned above, from the reception level, it is better than Q _2o .
Since I _o is more reliable, the received data output b _2o
select I _o and output. Similarly, b _2o+1 = I _o+1 ,
Choose b _2o+2 = I _o+2 .

As described above, by considering {I _i } and {Q _i } as received signals in two diversity branches and selecting them according to the reception level, code errors can be reduced compared to normal transmission. It is possible to configure a communication system with a good rate. In addition, since it uses a multilevel modulation method, time slot detection, which was required in conventional time diversity communication methods that use interlace transmission using a binary modulation method, is no longer necessary, simplifying the configuration and stabilizing the operation. There is. When the number of diversity branches is N, {I _i , {Q _i }
Although N data sequences such as the following are required, the transmission characteristics can be further improved.

FIG. 2 shows an embodiment of a transmitting/receiving system in the time diversity communication system of the present invention, where 5 is a transmitting device and 12 is a receiving device. The transmission signal input from the terminal 6 undergoes code conversion as described above at the encoder 7, and is then applied to the ^2N -value digital modulator 8 together with the carrier signal output from the carrier wave generator 10. It is modulated and amplified to the required transmission power by the power amplifier 9, and then transmitted to the transmitting antenna 1.
Sent from 1. The radio waves received by the receiving antenna 13 are detected and demodulated by the receiver 14, and the demodulated data is input to the synthesis circuit 16 and the reception level signal is input to the synthesis control circuit 15. The synthesis control circuit outputs a synthesis control signal according to the reception level to the synthesis circuit. A diversity composite output signal is obtained at terminal 17.

FIG. 3 shows an example of the configuration of the encoder 7. Transmission data input from input terminal 20 is output to N output terminals 24 through n-bit shift registers 21-23. In this way, the encoder has a very simple construction.

FIG. 4 shows an example of the configuration of the synthesis control circuit 15 and the synthesis circuit 16. The demodulated data applied to N input terminals 30 is transferred to n-bit shift registers 31 to 30.
After being delayed by 33, the signals are input to a combiner 34, combined according to a combination control signal 41, and output to a diversity output terminal 35. For example, in the case of the selection method, data corresponding to the highest reception level is selected and output. The synthesis control circuit passes the received level signal applied to the input terminal 36 through delay circuits 37 to 39, and generates a weighting coefficient, ie, a synthesis control signal 41, in a level comparison circuit 40.

As explained above, the time diversity communication system of the present invention uses a ^2N- value digital modulation method to arrange data to be transmitted on N data sequences with a delay time difference of n bits. As a result, N diversity branches can be obtained, and a diversity communication system can be constructed without a frame synchronization or time slot detection circuit required in conventional time diversity.

(Effects of the Invention) As explained above, the time diversity communication system of the present invention utilizes the fact that the bit error rate characteristics of signals received at different times in digital mobile communication have a low correlation with each other, and uses four-value This is a diversity communication method that uses the multilevel digital modulation method described above to send the signals to be transmitted multiple times with a delay time difference, and selects or combines these signals on the receiving side, considering them as diversity branches. A digital mobile communication system with extremely good transmission characteristics can be constructed with a single antenna, transmitting/receiving device, and frequency, and the equipment can be made smaller and more economical, which is an essential condition for mobile communication, and it is necessary for conventional time diversity. Since the conventional frame synchronization and time slot detection are not required, there are advantages in that the configuration can be simplified and the stability of operation can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the time allocation configuration of transmitted and received signals, FIG. 2 is a block diagram showing the configuration of an embodiment of a transmitting and receiving device in the time diversity communication system according to the present invention, and FIG. 3 is a configuration of an encoder. FIG. 4 is a block diagram showing an example of the configuration of a synthesis circuit and a synthesis control circuit. 1... Transmission data sequence, 2... Encoder output signal, 3
...Synthesizing circuit output signal, 4... Signal indicating reception level, 5... Transmitting device, 6... Transmitting data input terminal, 7
...Encoder, 8...Modulator, 9...Power amplifier, 10...
Carrier wave generator, 11... Transmitting antenna, 12... Receiving device, 13... Receiving antenna, 14... Receiver, 15
...Composition control circuit, 16...Composition circuit, 17...Diversity synthesis signal output terminal, 20...Transmission data input terminal, 21-23...Shift register, 24...Encoder output terminal, 30...Reception signal input terminal, 31-
33...Shift register, 34...Synthesizer, 35...Combined signal output terminal, 36...Reception level signal input terminal, 37-39...Delay circuit, 40...Level comparator, 41...Combined control signal.

Claims (1)

[Claims] 1. In digital mobile communications, on the transmitting side,
Each transmission data sequence is delayed by N different delay times (N is a natural number of 2 or more) in which the correlation of reception level fluctuations is low and different from each other, and the N transmission data sequences obtained in the same way are combined into 2 ^N- value modulation methods. Each transmission data sequence is divided into N parts and transmitted, and on the receiving side, the data received repeatedly with the delay time interval is outputted to the N diversity branches. A time diversity communication method that is characterized by selecting and combining received signals.