JPH0131805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an error correction method in data transmission using a maximum likelihood function method.

Conventionally, in this type of method, for example, the transmitting side modulates each of five frequencies with the same data, the receiving side demodulates each of the five frequencies, and the five data obtained by demodulation are Since then, data transmission has been performed using a fixed number of transmissions and a fixed number of determinations, such as if there are three or more identical data, that data is output as a decoded output. In this way, in the conventional method, the above-mentioned decision is made by majority vote, regardless of the amount of errors, fading interference, etc., burst errors that fluctuate over time, etc. The problem with transmission was that the improvement rate did not improve much.

The present invention solves the drawbacks of these conventional techniques, and involves calculating a likelihood function or a likelihood function difference on the receiving side using a known maximum likelihood decoding method, and calculating the calculated likelihood function or likelihood function difference. Based on the value of the function difference, data with poor decoding quality is deleted from a plurality of received data of the same transmission data, and a majority decision is made among the remaining received data.

Embodiments of the present invention shown in the drawings will be explained in detail below.

Before going into the description of the embodiments, the basic principle of the maximum likelihood decoding method will be described first. First, on the transmitting side, transmission data is encoded using a convolutional code or the like, and then transmitted to the receiving side.

On the receiving side, the likelihood function LF is expressed by the following equation (1).
Calculate.

LF=P(〓｜〓)= 〓 ¹ (yi｜ai) ……(1) However, 〓 is the received data sequence vector〓=
(y ₁ , y ₂ ...y _i ...), 〓 is the l-th output data sequence vector determined by the transmitting encoder 〓=
(a ^l ₁ , a ^l ₂ … a ^l _i …).

Calculate the likelihood function of equation (1) for all data sequence vectors determined by the transmitter encoder,
All of the calculated likelihood function LF and its corresponding data series are stored. This is a type of error correction method in which a data sequence corresponding to the largest likelihood function LF among the stored LFs after a certain length is calculated is sequentially output as received data. In other words, the known maximum likelihood decoding method is to select the data sequence that is considered to be closest to the transmitted data sequence on the receiving side, and from equation (1), if there is an error in the received sequence 〓,
The likelihood function LF becomes smaller. Therefore, the likelihood function is a function that represents the decoding quality of received data. Among the likelihood function sequences calculated by equation (1), 1
The difference between the largest likelihood function and the second largest likelihood function has the property that the more errors there are, the smaller the difference is, and if the number of errors is constant, the difference is almost constant. The degree function difference (difference between the maximum value and the next largest value) is also a function representing the decoding quality of received data.

FIG. 1 is a drawing for explaining an embodiment of the present invention using the above-mentioned likelihood function LF or likelihood function difference.
A plurality of frequencies (six frequencies f ₁ to f ₆ in this embodiment) are modulated with the same data sequence. Consider a case where the receiving side performs the aforementioned maximum likelihood decoding and outputs data and a likelihood function or a likelihood function difference.

In FIG. 1, the horizontal axis represents time (bit sequence), and the vertical axis represents frequency as a type of frequency. If there is interference, or an error, in the shaded area, the likelihood function or likelihood function difference in the area with interference is smaller than that in the area without interference, so the likelihood function or likelihood function difference in the area with interference is smaller than that in the same time slot. 5
(in the example in Figure 1, 5 pieces from f ₂ to f ₆ ) are extracted (marked A in Figure 1), and if there are three or more identical pieces of data from the five extracted data, that data is received. Output as data. In addition, if there are many errors due to interference, etc., three pieces of data (f ₁ to f ₃ in the example of Fig. It is also possible to extract two or more pieces of the same received data from the data and output them as decoded outputs.

The circuit according to the embodiment of the present invention shown in FIG. 2 has a configuration corresponding to that in FIG. 4 is a transmitter, 4 is a receiver, 5 is a maximum likelihood decoder (six pieces corresponding to FIG. 1), and 6 is a majority decision device. In this operation, data is input from the input terminal on the transmitting side, the encoder 1 encodes it using a convolutional code, etc., the modulator 2 modulates it at frequencies f ₁ to f ₆ , and the transmitter 3 Send by. On the receiving side, receiver 4 transmits 6
The signals received for each type of frequency (f ₁ to f ₆ ) and separated are decoded by the maximum likelihood decoder 5 for each frequency slot of f ₁ to _{f 6} and calculated data and likelihood function LF or likelihood. The function difference is input to the majority decision device 6. The majority decision device 6 performs the operation described in FIG. 1, selects the top five or three pieces of data with the highest quality, performs a majority decision on these data, and outputs the data as received data. Here, the number of high-quality items to be selected is determined depending on the calculated likelihood function or the magnitude of the likelihood function difference.

The error correction method described above is a so-called transmission method with redundancy in terms of frequency, but it goes without saying that the same data can be transmitted multiple times in terms of time and a majority decision can be made in the same manner as described above.

As explained above, according to the present invention, even if the data line has errors that fluctuate from time to time, it is possible to delete data with poor decoding quality and always make a majority decision from among the best data at that time. , high-quality data transmission is possible even on lines with fading or interference.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the operation of the method of the present invention, and FIG. 2 is a block circuit diagram showing an embodiment of the method of the present invention. 1... Encoder, 2... Modulator, 3... Transmitter, 4... Receiver, 5... Maximum likelihood decoder, 6... Majority decider.

Claims (1)

[Claims] 1. An error correction method in which the same transmission data is transmitted through a plurality of channels, and the transmission data is selected from among the received data of the plurality of channels received at the receiving side using a majority decision method,
The same transmission data is encoded and then transmitted through a plurality of channels, and maximum likelihood decoding is performed on each received data of the plurality of channels received at the receiving side to calculate a likelihood function or a likelihood function difference. The received data of channels with high decoding quality are selected according to the likelihood function or the magnitude of the likelihood function difference, and a majority decision is made among the plurality of selected received data to determine the decoded data. An error correction method in data transmission characterized by obtaining the following.