JP2000165359A - System and method for evaluating channel quality - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a channel quality evaluation system that can evaluate channel quality even during data transmission while keeping a data transmission efficiency. SOLUTION: A MODEM 50a applies Viterbi decoding to a convolution code, calculates a hamming distance 80 between a code stream given on a path of a trellis diagram corresponding to decoded data and a received code stream and gives the calculated distance to an arithmetic section 40a as a hamming distance. Then the arithmetic section 40a calculates a channel quality evaluation value on the basis of the hamming distance 80 and an AGC output voltage 60 outputted from a radio set 20 and outputs the value externally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for evaluating channel quality, and more particularly to a technique for evaluating channel quality while maintaining transmission efficiency at a high level in a receiver for Viterbi decoding of a convolutional code.

[0002]

2. Description of the Related Art In a frequency band having a poor line quality such as a short wave band, it is important how to perform communication at an optimum frequency.
Communication in the shortwave band is mainly performed using ionospheric reflection,
The state of the ionosphere changes every moment due to the influence of time, region, season, number of sunspots, and the like, and the optimum frequency for performing communication to a certain region constantly changes.

[0003] In this regard, the selection of the optimum frequency has conventionally been performed by human judgment, but in recent years, various techniques for automating the frequency selection have been proposed. ALE (Automati
c Link Establishment) is one of the technologies. The ALE periodically emits radio waves, evaluates the line quality on the receiving side based on the radio waves, and automatically selects an optimal frequency based on the evaluation. Conventionally, a method using a bit error rate or the like has been adopted for evaluating the line quality.

FIG. 3 is a diagram showing an example of the configuration of a line quality evaluation device according to the prior art. As shown in FIG. 1, the line quality evaluation device includes a radio device 20 to which an antenna 10 is connected, an ALE circuit 30, an arithmetic unit 40, and a modem 50.
And is configured. Radio 20 is antenna 1
0, demodulates the received radio wave, outputs the demodulated signal to the ALE circuit 30 and the modem 50, and outputs an AGC (Auto
matic Gain Control) The output voltage 60 is output to the calculation unit 40. The modem 50 decodes the demodulated signal and outputs digital data.

On the other hand, the ALE circuit 30 has a MIL-STD-
188-141A.
It has a QA (Link Quality Analysis) function. In the ALE circuit 30, the radio 2
The bit error rate value 70 is calculated based on the ALE signal included in the demodulated signal output from 0, and is output to the arithmetic unit 40. Then, the operation unit 40 calculates a line quality evaluation value based on the AGC output voltage 60 and the bit error rate value 70. The line quality evaluation value is output to the outside, where it is subjected to processing for automatic selection of the optimum frequency.

[0006]

However, when the line quality is evaluated by the above prior art, the line is monopolized for transmitting and receiving the ALE signal. Therefore, when the ALE is not used or the data transmission is performed. During that time, it was impossible to evaluate the ever-changing line quality in real time. This is because the line quality evaluation is AL
Due to being entrusted to E, ALE must be used when performing line quality evaluation, and there is a problem that data cannot be transmitted during this time.

Further, the inability to output the bit error rate from the modem 50 is one of the reasons that the ALE must be used. Although it is conceivable to insert dummy data for bit error rate measurement into communication data and measure the error rate during communication, there is a problem that the data transmission efficiency is reduced in this case.

The present invention has been made in view of the above problems, and has as its object to provide a line quality evaluation apparatus and method capable of evaluating the line quality even during data transmission while maintaining data transmission efficiency. Is to do.

[0009]

In order to solve the above problems, a channel quality evaluation apparatus according to the present invention provides a decoding means for Viterbi decoding of a convolutional code and a decoding means for providing a path on a trellis diagram corresponding to decoded data. Means for calculating a degree of similarity between the obtained code string and the received code string, and evaluation information calculation for calculating line quality evaluation information representing the quality of the line on which the convolutional code is transmitted based on the degree of similarity Means. For example, the similarity is calculated based on the Hamming distance between the decoded data and the received code string.

[0010] A line quality evaluation method according to the present invention comprises:
Viterbi-decoding the convolutional code, calculating a Hamming distance between a code string given to a path on the trellis diagram corresponding to the decoded data and a received code string, and transmitting the convolutional code based on the Hamming distance. Assess line quality,
It is characterized by the following.

That is, when the convolutional code is subjected to maximum likelihood decoding by Viterbi decoding, the similarity between the code string given to the path on the trellis diagram corresponding to the decoded data and the received code string depends on the degree of error mixing. Corresponding. For this reason, in the present invention, when performing Viterbi decoding, the similarity between the code sequence given to the path on the trellis diagram corresponding to the decoded data and the received code sequence is calculated by calculating the Hamming distance thereof. The line quality is evaluated based on the similarity. This eliminates the need to use a special line for evaluating the line quality, so that the line quality can be evaluated while maintaining data transmission efficiency even during data transmission.

[0012] In another aspect of the present invention, the apparatus further comprises a radio which receives the convolutional code and outputs an automatic gain control signal, wherein the evaluation information calculating means further comprises: Calculate line quality evaluation information. For example, the evaluation information calculation means calculates a signal level based on the automatic gain control signal output at the time of decoding by the decoding means, and outputs the noise level at a time other than at the time of decoding by the decoding means. The channel quality evaluation information is calculated based on the automatic gain control signal, and the line quality evaluation information is calculated based on the ratio between the two. In this case, the S / N ratio can be referred to when evaluating the line quality, so that the line quality can be more accurately evaluated.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a line quality evaluation apparatus according to an embodiment of the present invention. The line quality evaluation device shown in the figure includes a radio 20 to which the antenna 10 is connected,
It is configured to include an arithmetic unit 40a and a modem 50a, and does not include the ALE circuit 30 unlike the line quality evaluation device according to the related art shown in FIG.

In the line quality evaluation apparatus according to the present embodiment, the radio wave received by antenna 10 is demodulated by radio device 20, and the demodulated signal is input to modem 50a. In addition,
In this channel quality evaluation device, the radio wave received by the antenna 10 does not include special information for channel quality evaluation. The modem 50a decodes the digital data based on the demodulated signal and outputs it to the outside. The modem 50a performs Viterbi decoding for error correction when decoding digital data, and outputs a Hamming distance 80, which is information for evaluating line quality, to the arithmetic unit 40a at that time.

On the other hand, the AGC output voltage 60 is also output from the wireless device 20 to the arithmetic unit 40a.
In a, a line quality evaluation value is calculated based on the AGC output voltage 60 and the Hamming distance 80, and is output to the outside.

FIG. 2 is a diagram for explaining Viterbi decoding performed by the modem 50a, and shows a trellis diagram. Here, the information code is {1,1,0,0,1,
0} and the transmission code is {11,10,10,11,11,0
{00, 00, 01, 00, 00, 00} is mixed into the convolutional code (coding rate ２) which is 1
The case where {11, 10, 11, 11, 11, 01} is received will be described.

In FIG. 1, 00, 0 drawn at each node
Codes 1, 10, and 11 indicate the state of an encoder (not shown) provided on the transmitting side, and the number in parentheses indicates the Hamming distance from the received code. The path represented by the solid line corresponds to the input of the encoder 0, and the path represented by the broken line corresponds to 1. In the figure, the state transition “00 → 01 →
The sum of the Hamming distances of the path of “11 → 10 → 00” is 1, which is the minimum. Therefore, the path indicating this state transition is the surviving path. Then, based on the state transition, it is estimated that the original information code is {1,1,0,0,1,0}, and the estimated digital data is
a is output to the outside.

At this time, in the modem 50a, the path corresponding to the decoded data (the state transition "00 → 01 → 11 → 10 → 0
The sum of the hamming distances (ie, “0”) (ie, “1”) is output to the arithmetic unit 40a as the hamming distance 80. That is, the present line quality evaluation apparatus pays attention to the fact that the Hamming distance calculated at the time of Viterbi decoding by the modem 50a indicates the degree of error mixing mixed in the line, and outputs the Hamming distance 80 from the modem 50a to the arithmetic unit 40a. It is used to evaluate the line quality.

The operation unit 40a calculates the line quality evaluation value in the following manner.

That is, first, the arithmetic unit 40 a
S / N based on AGC output voltage 60 calculated from 0
Calculate the ratio. In the following, the value of the AGC output voltage 60 is
V is V _NP when the modem 50a is asynchronous, and V _N is the moving average of V _NP . Further, V when the modem 50a synchronizes is set to V _S. Note that the synchronization of the modem 50a means a state in which a Viterbi decoder (not shown) provided in the modem 50a finds the head of the convolutional code and performs Viterbi decoding with synchronization. In this case, V _S corresponds to the signal level, and V _N corresponds to the noise level. Then, the arithmetic unit 40a calculates the S / N ratio S at the time of synchronization of the modem 50a according to the following equation.

[0022]

S = f _SN (V _S , V _N ) Here, the function f _SN calculates the signal level and the noise level from the AGC output voltage 60 of the radio device 20,
The S / N ratio is calculated therefrom.

The arithmetic unit 40a calculates not only the S / N ratio S but also the channel quality Q. That is, the modem 50a
Assuming that the value of the Hamming distance 80 during Viterbi decoding is H, the arithmetic unit 40a calculates the channel quality Q according to the following equation.

[0024]

Q = f _PSO (S, H) Here, Q indicates that the larger the value, the better the channel quality. The function f _PSO is an increasing function for S and It is a decreasing function.

After performing the above operations, the operation unit 40a calculates a line quality evaluation value based on the calculated S / N ratio S and the line quality Q, and outputs it to the outside. The output line quality evaluation value is used by a control device (not shown) as a material for determining whether or not the frequency to be used should be changed.

According to the line quality evaluation device described above,
Since it is not necessary to use a special line for evaluating the line quality, the line quality can be evaluated even during data transmission while maintaining the data transmission efficiency.

For example, if 30 radio stations exist on one frequency, and 5 channels are used, and the line quality is evaluated once every 30 minutes, according to the conventional technology, 15 minutes per hour is used. The time during which data cannot be transmitted occurs. In contrast, if this line quality evaluation device is used,
Under the same conditions, there is no time during which data cannot be transmitted. Therefore, if the present line quality evaluation device is used, the time during which the line can be used can be increased by 33%.

The line quality evaluation device according to the present embodiment can be variously modified. For example, in the above-described channel quality evaluation device, the Hamming distance is used as a measure for finding the most likely code string in Viterbi decoding, but another measure may be used.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a line quality evaluation device according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of Viterbi decoding performed by a modem.

FIG. 3 is a diagram showing a configuration of a line quality evaluation device according to the related art.

[Explanation of symbols]

Reference Signs List 10 antenna, 20 radio, 40a arithmetic unit, 50
a Modem, 60 AGC output voltage, 80 Hamming distance.

Claims (5)

[Claims] A decoding means for performing Viterbi decoding of a convolutional code; a similarity calculating means for calculating a similarity between a code string given to a path on a trellis diagram corresponding to decoded data and a received code string; A channel quality evaluation device for calculating channel quality evaluation information indicating the quality of the channel through which the convolutional code is transmitted, based on the similarity. 2. The channel quality evaluation device according to claim 1, wherein the similarity is calculated based on a Hamming distance between the decoded data and a received code string. 3. The line quality evaluation device according to claim 1, further comprising: a radio that receives the convolutional code and outputs an automatic gain control signal, wherein the evaluation information calculating unit further includes the automatic gain control unit. A line quality evaluation device for calculating the line quality evaluation information based on a control signal. 4. The line quality evaluation device according to claim 1, wherein said evaluation information calculation means calculates a signal level based on said automatic gain control signal output at the time of decoding by said decoding means. And calculating the noise level based on the automatic gain control signal output at a time other than at the time of decoding by the decoding means, and calculating the line quality evaluation information based on a ratio between the two. Quality evaluation device. 5. A Viterbi decoding of a convolutional code, calculating a Hamming distance between a code string given to a path on a trellis diagram corresponding to decoded data and a reception code string, and based on the Hamming distance, A line quality evaluation method for evaluating the quality of a line through which a code is transmitted.