JPS6337540B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a diversity communication system used to improve transmission characteristics in digital mobile communications where bit error rate characteristics are significantly degraded due to multipath fading and the like.

(Background technology) Diversity communication systems set up multiple communication channels (diversity branches) with low correlation in received signal level fluctuations, and reduce the width of signal level fluctuations by selecting or combining the outputs of these channels. This is a communication method that aims to improve transmission characteristics.

As shown in Figure 1, a receiving device used in a diversity communication system in conventional digital mobile communication receives radio waves from a base station or a mobile device using m antennas A ₁ to _{A n} . The received radio waves are input to receivers _B1 to _Bn , respectively.
The receiver detects the received signal and outputs its output to the synthesis circuit 11, and also outputs a signal indicating the reception level (hereinafter referred to as a reception level signal) to the synthesis control circuit 12. The synthesis control circuit 12 determines a synthesis coefficient for the detected output signal based on the received level signal and outputs it to the synthesis circuit 11. The synthesis circuit 11 multiplies each detection output signal by a synthesis coefficient, synthesizes these signals, and outputs a synthesized signal to the identification determination circuit 13 and the clock recovery circuit 14. Clock regeneration circuit 14
Identification judgment circuit 1 based on the regenerated clock generated by
3 performs identification judgment on the composite signal and outputs the demodulated signal to the output terminal 15.

Conventionally, methods for obtaining antennas A ₁ to _{A n} that have low correlation in fluctuations in received signal strength are: a) spatial diversity method in which multiple antennas are installed at a distance of about half a wavelength or more from each other; There are polarization diversity methods that use multiple antennas to receive waves, but all of these methods require multiple antennas and receivers.

There is also a frequency diversity method that uses a plurality of carrier waves of different frequencies and uses these as diversity branches, but this method requires a plurality of transmitters to transmit the plurality of carrier waves. Therefore, in the conventional diversity communication system, the mobile equipment and the base station equipment are large-scale, which is disadvantageous in that it is contrary to the miniaturization and economicalization of equipment that is important in mobile communication.

(Summary of the Invention) In order to eliminate such drawbacks, the present invention interlacedly transmits codes two or more times at regular time intervals, and selects and combines the codes each time on the receiving side according to the respective reception levels. As a result, a highly reliable transmission path can be constructed using only one antenna, transmitter/receiver, and frequency.The drawings will be described in detail below.

(Embodiment) FIG. 2 is an embodiment of a method for allocating time for transmitted and received signals in the time diversity communication system of the present invention. For the sake of simplicity, a case will be described in which the number of interlaced transmissions is two.

The data sequence 20 of the signal to be transmitted, such as an encoded voice signal or facsimile signal, is {a _i } (i is an integer), and the data sequence 21 of the signal actually sent from the transmitter is {b _j } (j is an integer), and the data sequence 22 of the demodulated output signal output from the receiving device is {c _i }
Expressed as. {a _i } is a data series of clock frequency c, and when the number of interlaces is N, the clock frequency c' of {b _j } must be set to Nc. In this example, it is twice, so c′=2c
It is as follows. {a _i } is encoded into {b _j } in the following manner by an encoder in the transmitting device, which will be described later.
The data {a _i } input at that time is assigned as is to the even time slot {b _2i } of {b _j }. That is, b _2i =a _i . On the other hand, n-bit delay data {a _io } to be interlace transmitted is assigned to odd time slot {b _2i-1 } of {b _j }. That is, b _2i-1 = a _io . The delay amount n bits is set to an arbitrary value equal to or more than about half a period of fading. In this way, {a _i } is interlaced and then sent out. When the above encoding is performed _, as shown in the figure, a ₁ is assigned to the time slots of b ₂ and b _2o+1 , and a _o is assigned to b _2o and b _2o+2 on both sides of b 2o+1, respectively. , a _o+1 are assigned, and data without delay and data with delay are transmitted alternately.

On the other hand, in the receiving device, {b _j },
A recovered clock with a frequency of 2c is obtained from the clock recovery circuit output, and the data b _j at each clock timing is the same as the data b _{j -(2o-1)} obtained before 2 _o-1 bits and each reception level. The data are synthesized accordingly, and after passing through an identification/determination circuit, become demodulated data output {c _i }. {c _i }
are two pieces of data b _j whose bit error rates have low correlation with each other
Since it is obtained by selecting and synthesizing from and b _j-2o-1 ,
A lower coding error rate can be obtained than when {a _i } is transmitted as is. As can be seen from the figure, there are two combinations of {b _j }: even time slots and odd time slots, and a combination detection circuit described later detects which combination is correct.

The above explanation has been given for the case of two-time interlaced transmission, but in general, in the case of N-time interlaced transmission, {b _j } becomes a signal sequence of clock frequency Nc, and is transmitted within the time of one bit of {a _i }. It has a time slot of N bits. Each time slot contains N bits a _i , a _io , a _i-2o , ..., a _i-(N-1)o , and the receiving side selects one of the N combinations of time slots consisting of N bits. Detect and demodulate the correct combination. This combination detection can be realized by selecting the combination with the highest degree of matching among the N bits among N combinations. Combinations other than the correct combination result in different combinations of data bits, so 0s and 1s will not be combined randomly and the degree of matching will not be high, and it is unlikely that the combination will be detected incorrectly. Unless otherwise specified, the combination detection will not fail. Also, during the transient time until the combination detection works correctly, {b _j } is sampled every N bits,
By setting {c _i }, a correct demodulated output can be obtained. Therefore, the present invention can be expected to operate extremely stable and with high reliability.

FIG. 3 shows an embodiment of a transmitting/receiving system in the time diversity communication system of the present invention. The transmission signal input from the terminal 30 is converted into an interlaced signal repeated N times by the encoder 31, and then applied to the modulator 32 together with the carrier signal output from the carrier wave generator, where it is modulated by NSK or the like and sent to the power amplifier. 33, the signal is amplified to the required transmission power and sent out from the transmitting antenna 35. Radio waves received by the receiving antenna 40 are detected by the receiver 41 and input to the expansion circuit 42 and the clock regeneration circuit 14. The expansion circuit extracts N pieces of data assigned to each time slot from the interlaced signal and outputs them to the synthesis circuit 43. The combining circuit receives a combining coefficient corresponding to the reception level in each time slot from the combining control circuit 44, selects and combines N pieces of data, and outputs a combined signal. The composite signal is discriminated by a discrimination circuit 13 and a demodulated signal is outputted to an output terminal 45.

In this way, in the present invention, the bit error rate characteristics can be improved by using the interlaced signal repeated N times as the output signal from the N diversity branches and selectively combining them according to the reception level. . Moreover, a diversity communication system can be configured with a single transmitter/receiver and transmitting/receiving antenna, making it possible to realize a compact and economical system.

Furthermore, the larger the number of repetitions N is set, the greater the degree of improvement in the bit error rate characteristic can be achieved, so it can be easily applied to communications that require highly reliable transmission paths, such as facsimile and data communications.

FIG. 4 shows an example of the configuration of the encoder 31 in the embodiment of the present invention shown in FIG. Transmission data input from the input terminal 30 is applied to a gate circuit 57 having N input terminals through (N-1) n-bit shift registers 54 to 56. The shift register is shifted by the transmit clock (frequency c). The gate circuit sequentially switches N inputs based on a high speed clock of frequency Nc and outputs an encoder output signal to an output terminal 53. In order to synchronize the transmission data and the high-speed clock, the frequency of the high-speed clock is divided by N in the frequency divider 58, and the transmission clock is outputted to the output terminal 52. In this way, by using shift registers and gate circuits,
An N-times interlaced signal is obtained.

FIG. 5 shows an expansion circuit 42, a synthesis circuit 43, and a synthesis control circuit 44 in the embodiment of the present invention shown in FIG.
This is an example of a configuration. The received level signal input from the input terminal 62 passes through delay circuits 70 to 72, and then outputs the N signal corresponding to each bit of the interlaced signal.
The received level signals are applied to the composite control signal generation circuit 73 as individual reception level signals. The synthesis control signal generation circuit determines a synthesis coefficient according to the reception level according to a predetermined algorithm, and outputs it to the synthesis circuit 43 as a synthesis control signal 7. On the other hand, the receiver detection output is inputted from the received signal input terminal 60 and passed through (N-1) n-bit shift registers 65 to 67.
It is added to a combination detection circuit 68 and a combination circuit 43 having input terminals. The combination detection circuit detects a correct combination among the N time slot combinations and outputs a reset signal indicating this timing to the frequency divider 69. Using this reset timing, the frequency divider divides the frequency of the reproduced clock input from the input terminal 61 by N, and outputs the reception clock 8 synchronized with the synthesis circuit output signal, which will be described later, to the synthesis circuit 43 and the output terminal 64. The combining circuit combines the N received signals based on the combining control signal 7 at the receiving clock timing, and generates the combining circuit output signal 9.
is output to the output terminal 63. As can be seen from the above explanation, the circuit shown in this figure combines the interlace transmitted signals in N time slots according to the reception level of each, so the combined output signal is lower than any of the signals before combining. This results in a bit error rate.

As explained above, compared to the conventional diversity communication method, the time diversity communication method of the present invention requires only one transmitter/receiver and one transmitting/receiving antenna. The circuits shown in Figures 1 and 5 can be constructed almost entirely from digital circuits, and can be easily made smaller and more economical by converting them to LSI.) They do not require frame synchronization and the communication system has good stability.) Since the required bit error rate can be obtained by changing the number of interlaces, it has many advantages such as being easily applicable not only to encoded audio signals but also to facsimile, data communications, etc.

(Effects of the Invention) As explained above, the time diversity communication system of the present invention takes advantage of 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. Since this is a diversity communication method that selects or combines the following diversity branches, it is possible to construct a digital mobile communication system with extremely good transmission characteristics using a single antenna system, transmitter/receiver, and frequency, which is essential for mobile communication. The requirements are that the equipment can be made smaller and more economical, and that the diversity circuit can be constructed mostly of digital circuits, making it suitable for LSI implementation.In addition to normal voice communications, it also supports image communications such as facsimile, and data communications. This method has the advantage that it can be easily applied to communications that require a high-quality transmission path by setting the number of signal repetitions to a value that provides the required quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a conventional receiver for diversity communication system, FIG. 2 is a diagram showing an example of time allocation configuration of transmitted and received signals, and FIG. 3 is a transmitting/receiving device in time diversity communication system according to the present invention. FIG. 4 is a block diagram showing an example of the structure of an encoder, and FIG. 5 is a block diagram showing an example of the structure of an expansion circuit, a synthesis control circuit, and a synthesis circuit. A ₁ to _{A n} ...Antenna, B ₁ to _{B n} ... Receiver, 11...
Synthesis circuit, 12...Synthesis control circuit, 13...Identification determination circuit, 14...Clock regeneration circuit, 15...Demodulated signal output terminal, 16...Regenerated clock output terminal, 20...
Transmission data sequence, 21... Encoder output signal, 22...
Decoder output signal, 3... transmitting device, 4... receiving device,
30... Transmission data input terminal, 31... Encoder, 32
...Modulator, 33...Power amplifier, 34...Carrier wave generator, 35...Transmission antenna, 40...Reception antenna,
41...Receiver, 42...Development circuit, 43...Composition circuit, 44...Composition control circuit, 45...Demodulated signal output terminal, 51...High speed clock input terminal, 52...Transmission clock output terminal, 53...Encoder output terminal, 54 ~
56...Shift register, 57...Gate circuit, 58
... Frequency divider, 60... Received signal input terminal, 61... Regenerated clock input terminal, 62... Received level input terminal,
63...Composition circuit output signal terminal, 64...Reception clock output terminal, 65-67...Shift register, 68
...Combination detection circuit, 69...Frequency divider, 6...Reset signal, 7...Composition control signal, 8...Reception clock, 9
...Synthesizing circuit output signal, 70-72...Delay circuit, 7
3...Composition control signal generation circuit.

Claims (1)

[Claims] 1 In digital mobile communication that performs time diversity with N branches (N is a positive integer of 2 or more),
On the transmitting side, the input digital signal sequence A is speed-converted by N times to generate a signal sequence B, and this signal sequence _B is generated from the timeslot (b _i1 ,..., b _iN ) is determined by every n bits before a _i of the signal sequence A (a _i-(N-1)o ,..., a _i )
The receiving side detects N bits and the reception level at that time for every n bits of the received signal sequence B.
The bits appearing in each diversity branch are weighted and combined according to the reception level, or the bit with the maximum reception level is selected, and the speed of this combination or the selected bit is converted to 1/N. A time diversity communication method featuring: