JPH0410773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a line quality monitoring circuit for detecting the line quality status (for example, bit error rate) of a satellite communication channel.

[Technical background of the invention and its problems]

In satellite communication lines, the quality of the communication line fluctuates and deteriorates due to rain, etc., so it is necessary to constantly monitor the line status in the receiving state. Efforts are being made to improve the line unavailability rate by controlling the

By the way, in the past, in order to monitor the receiving line condition, the receiving condition was checked by inserting a specific signal for line quality inspection into the transmitted data and extracting that signal from the decoded data. The disadvantage was that the number of communication information areas decreased and transmission efficiency decreased when trying to detect line quality with good performance.

[Purpose of the invention]

The present invention was developed in view of the above-mentioned drawbacks of the prior art, and by utilizing a Viterbi error correction circuit installed on the receiving side, there is no need to insert a specific signal for line quality inspection. Therefore, it is an object of the present invention to provide a line quality monitoring circuit that can constantly estimate and detect line quality without degrading transmission efficiency at all.

[Summary of the invention]

The present invention applies statistical calculation processing to path metrics that appear during the algorithm processing of the Viterbi decoding method, and estimates line quality from the obtained results.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings. FIG. 1 is a basic configuration diagram of a line quality monitoring circuit according to the present invention, which is composed of a Viterbi decoding circuit 1 and an arithmetic circuit 2. In addition to the normal operation of inputting a received signal and outputting error-corrected decoded data, the Viterbi decoding circuit 1 also performs calculations on a path metric signal, which is the second output from the Viterbi decoding circuit. The signal is input to the circuit 2, and a line quality signal is output accordingly.

In explaining the principle of the present invention,
proceedings of the IEEE, Vol61, No.3, P268
I will summarize some key points about the Viterbi decoding method known from ~278, 1973, etc.

The Viterbi decoding method is known as a powerful error correction decoding method for convolutional codes, but its structure is closely related to the encoder itself that generates the code.

In other words, by specifying the parameters of the target encoder (i.e. coding rate, constraint length), the number of internal states of the encoder is uniquely determined. ) For each internal state, one surviving path and the path metric associated with that path (that is, the distance between the received signal sequence) are sequentially determined.

Therefore, at each time, a total of as many surviving paths as the number of internal states and the same number of path metrics corresponding to each path are stored, but among them, the surviving path with the minimum path metric (i.e. , the path closest to the received data sequence in a probabilistic sense) is called the maximum likelihood path at that time in the sense that it is the most likely transmission data, and is directly related to the determination of the decoding output.

However, the path metric selection method is arbitrary, and it is also possible to associate paths that are close to the received data with a large path metric.In such a case, the surviving path with the largest path metric is the most likely path. becomes.

Therefore, for the purpose of unifying the two, we will consider the maximum likelihood path determined regardless of the definition of the path metric as a standard, and here the path metric of that maximum likelihood path will be referred to as the maximum likelihood path metric.

It is known that the above-mentioned Viterbi decoding method can dramatically improve bit error rate characteristics, especially when used in combination with soft-decision demodulation, and is actually used in this manner.

In this case, the path metric is the symbol metric calculated for the soft decision data at each time according to the symbol metric table that defines the distance between the soft decision data and the transmitted symbol. Therefore, if the symbol metric is chosen to be non-negative, the path metric will have the property of increasing monotonically with time.

Let us return to the explanation of the principle of the present invention.

However, in order to make the following explanation accurate, the symbol metric is here assumed to be non-negative, and the maximum likelihood path metric is used in the sense of the minimum path metric. Under these assumptions, the relationship between the S/N (Eb/No) at the time of soft decision and the average increment <Γmin>ar (however, it represents the standard value based on the maximum increment) of the maximum likelihood pathmetric at that time is as follows. The results shown in Figure 2 are obtained, and as shown in the figure, it can be seen that there is a very specific and quantitative functional relationship.

Furthermore, as is clear from the above explanation, the maximum likelihood path metric is a quantity generated in the process of processing the algorithm itself, and therefore is independent of the specific transmission data.

Therefore, it can be seen that by using this relationship, communication quality can be estimated by focusing on a single quantity, the path metric, that appears in the decoding process, without depending on the actual transmitted data.

Figure 3 shows a concrete implementation of this principle, which consists of a Viterbi decoding circuit 1, an averaging circuit 5, and a conversion circuit 6, and calculates the bit error rate of the entire system including the encoder and decoder. It can be output from circuit 2. However, in FIG. 3, 4 is a path metric normalization circuit for keeping the path metric within a finite capacity.

Now, the maximum likelihood path metric output from the Viterbi decoding circuit 1 is input to the averaging circuit 5, and its output average value is input to the conversion circuit 6, where the bit error rate is output. The principle of operation of the circuit of FIG. 3 is explained as follows.

In Fig. 2, we have already shown the relationship between the S/N during soft decision and the average increment of the corresponding maximum likelihood path metric.
The relationship between the theoretical bit error rate of the entire system including the decoder (which can be calculated) can be considered to be known, so by combining them, we can find the relationship between <average increment of maximum likelihood pathmetric> vs. <bit error rate>. It can be given quantitatively as shown in FIG.

Therefore, the maximum likelihood pathmetrics output from the Viterbi decoding circuit 1 are input one after another to the averaging circuit 5 to extract the average value, and that value is input to the <average maximum likelihood pathmetric> to <bit error rate> conversion circuit 6. Then, the bit error rate of the entire system can be output. Obviously, since all of these operations can be processed in real time, it can be seen that by monitoring the output of the conversion circuit 6, the line quality can be constantly monitored in real time.

A digital filter can be used as the averaging circuit, and a ROM (read-only memory) can be used as the conversion circuit. By the way, in the configuration shown in Figure 3, it is possible to directly display the code error rate, but in some cases, it may not be the error rate itself, but the S/N of the received signal or other similar quantities. Then, since they have a quantitative functional relationship with each other, by appropriately configuring the conversion circuit,
It is also possible to extract these values according to the purpose.

〔Effect of the invention〕

As described above, according to the present invention, by utilizing the characteristics of the Viterbi decoding method itself,
To provide an extremely effective line quality monitoring circuit capable of estimating communication line quality in real time, and in which the derivation process effectively utilizes a quantity appearing in the middle of a decoding operation, so that the amount of additional calculation is small. I can do it.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of a line quality monitoring circuit according to the present invention, FIG. 2 is a characteristic diagram showing the relationship between the average increment of the maximum likelihood path metric and the S/N of a received signal, and FIG. 3 is an embodiment of the present invention. FIG. 4, which is a circuit diagram of the example, is a characteristic diagram showing the relationship between the bit error rate and the average maximum likelihood path metric. 1... Viterbi decoding circuit, 2... Arithmetic circuit, 3...
... Viterbi decoding circuit, 4... Path metric normalization circuit, 5... Averaging circuit, 6... Conversion circuit.

Claims (1)

[Scope of Claims] 1. A Viterbi decoding circuit which inputs a received signal and outputs maximum likelihood pathmetrics obtained by normalizing a pathmetric signal at predetermined time intervals and decoded data subjected to error correction; An averaging circuit that receives a path metric as an input and outputs an average value of the input maximum likelihood path metric, and a conversion circuit that converts the average value of the maximum likelihood path metric into a corresponding bit error rate. A line quality monitoring circuit featuring: