Method for controlling adaptive modulation system

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an adaptive modulation method control method used for mobile wireless communication such as a mobile wireless system or a mobile phone system, and particularly relates to an adaptive modulation method control method capable of improving line quality.

【0002】

[Conventional technology]

In mobile wireless communication, as a conventional technique related to an adaptive modulation method that transmits and receives by a modulation method according to the situation of line quality, Japanese Patent Application Laid-Open No. 9-200282 "Adaptive modulation method transmission / reception for TDD" published on July 31, 1997. There is a vessel (applicant: Kokusai Denki Co., Ltd., inventor: Tsutomu Takahashi, etc.). This conventional technique is based on a bit error rate detected when a radio signal to which an error correction code is added on the transmitting side, modulated by a selected modulation method, and transmitted is demodulated on the receiving side and error corrected. It is an adaptive modulation method transmitter / receiver for TDD that estimates the propagation path condition, specifies the modulation method to the modulation section on the transmission side based on the estimation result, and realizes adaptive modulation, which deteriorates the frame efficiency of information. The propagation path condition estimation method can be adopted without increasing the circuit scale of the receiving portion.

【0003】

Here, a communication system using the conventional adaptive modulation method control method will be described with reference to FIG. FIG. 8 is a block diagram of a conventional communication system. As shown in FIG. 8, the conventional communication system includes a transmission device 1'which adds information for estimating the propagation path condition on the receiving side, modulates it by a selected modulation method, and transmits a radio signal, and a radio. The signal is received, demodulated, the propagation path condition is estimated based on the information added on the transmitting side, and the transmitting device control signal that specifies the modulation method on the transmitting side is sent to the transmitting device 1'based on the estimation result. It is composed of a receiving device 2'for transmitting. Then, in the conventional communication system, the information for estimating the propagation path condition added by the transmitting device 1'is an error detection code (CRC code), and the receiving device 2'performs error detection by the CRC code. The propagation path condition is estimated based on the detected bit error rate.

【0004】

The inside of the transmission device 1'composed of a transmission data control unit 11, a CRC coding unit 12, a mapping unit 13, a modulation unit 14, and a demodulation unit 15, and the inside of the reception device 2'. Is composed of a demodulation unit 21, a demapping unit 22, a CRC error detection unit 23, a source control unit 24', and a modulation unit 25.

【0005】

Next, each part of the conventional transmission device 1'will be specifically described. The transmission data control unit 11 controls transmission of transmission data input from the outside, and particularly controls data retransmission in response to a data retransmission request from the receiving side. The CRC coding unit 12 adds an error detection code to the transmission data and outputs the coded data, and uses a CRC (Cyclic Redundancy Check) code as one of the error detection codes. The mapping unit 13 maps the encoded data with the selected mapping arrangement and outputs the mapping signal. As the mapping method, 64QAM (64-positions Quadrature Amplitude Modulation), 16QAM (16-positions Quadrature Amplitude Modulation), QPSK (Quadrature Phase Shift Keying), BPSK (Binary Phase Shift) Keying) etc. can be considered. In these mapping methods (modulation methods), the transmission speed increases by increasing the mapping arrangement, for example, 1200bps for BPSK, 2400bps for QPSK, 4800bps for 16QAM, and 19200bps for 64QAM.

【0006】

The modulation unit 14 modulates the carrier wave according to the mapped signal and outputs the transmission signal to the transmission line. The demodulation unit 15 demodulates the received signal and outputs a data retransmission request signal and a modulation method switching control signal.

【0007】

Next, each part of the conventional receiving device 2'will be specifically described. The demodulation unit 21 demodulates the received signal from the transmission line. The demapping unit 22 is a general demapping device that obtains a decoded output signal by demapping the demodulated signal corresponding to the mapping on the transmitting side. The CRC error detection unit 23 performs error detection based on the CRC code, outputs an error detection signal, and outputs decoded data.

【0008】

The source control unit 24'estimates the state of the transmission line (line quality) based on the presence / absence and frequency of errors based on the error detection signal from the CRC error detection unit 23, and requests data retransmission based on the estimated line quality. It outputs a transmitter control signal composed of a signal and a modulation method switching control signal that controls a modulation method on the transmitting side.

【0009】

Specifically, for example, when an error occurs, a data retransmission request signal requesting data retransmission is output. Furthermore, if the frequency of errors is high, the quality of the transmission line is degraded. Therefore, modulation that makes the mapping method on the transmitting side slower than the current one so that the quality is ensured even if the transmission efficiency is lowered. Outputs the method switching control signal. For example, if the current status is 64QAM, switch to 16QAM, if the current status is 16QAM, switch to QPSK, and if the current status is QPSK, switch to BPSK. On the contrary, when the frequency of error occurrence is low, the quality of the transmission line is improved. Therefore, in order to improve the transmission efficiency, a modulation method switching control signal that makes the mapping method on the transmitting side faster than the current one is used. Output. For example, if the current status is BPSK, switch to QPSK, if the current status is QPSK, switch to 16QAM, and if the current status is 16QAM, switch to 64QAM. The modulation unit 25 modulates the transmission device control signal and sends it to the transmission line.

【0010】

Next, the operation of the conventional communication system will be described with reference to FIG. In the conventional communication system, in the transmission device 1', the transmission data is output to the CRC coding unit 12 under the control of the transmission data control unit 11, and the CRC coding unit 12 adds an error detection code for mapping. It is mapped by the mapping arrangement selected by the section 13, modulated by the modulation section 14, and sent to the transmission line.

【0011】

Then, the received data is demodulated by the demodulation unit 21 of the receiving device 2', demapped by the demapping unit 22, error detected by the CRC error detection unit 23, and the decoded data without errors is output. At this time, when an error is detected by the CRC error detection unit 23, an error detection signal is output, the line quality is estimated by the source control unit 24', and the data retransmission request signal and the modulation method on the transmission side are controlled. A transmission device control signal including a modulation method switching control signal is output, modulated by the modulation unit 25, and transmitted to the transmission device 1'.

【0012】

In the transmission device 1', the transmission device control signal is received and demodulated by the demodulation unit 15, the data retransmission request signal is output to the transmission data control unit 11, and the transmission data control unit 11 makes a data retransmission request. If so, the data is retransmitted. Further, the modulation method switching control signal is output to the mapping unit 13, and when there is a request for switching the modulation method according to the control signal, the mapping method can be switched.

【0013】

[Problems to be Solved by the Invention]

However, in the above-mentioned conventional adaptive modulation method control method, since the transmission line condition (line quality) is estimated from the presence or absence of an error and its frequency, the line is controlled based on the error after it occurs. There was a problem that the detection of quality deterioration was delayed and it was difficult to ensure the quality of the transmission line. Further, the above-mentioned conventional adaptive modulation method control method has a problem that it is extremely difficult to detect when the transmission line condition is heading in a favorable direction.

【0014】

The present invention has been made in view of the above circumstances, and transmission is performed by detecting deterioration of the transmission line condition before an error occurs, detecting recovery of the transmission line condition, and selecting an appropriate modulation method. It is an object of the present invention to provide an adaptive modulation method control method capable of stably ensuring road quality.

【0015】

[Means for solving problems]

The present invention for solving the problems of the above-mentioned conventional example includes a transmitting device having a plurality of modulation methods corresponding to a transmission situation and a receiving device having a plurality of demographic methods corresponding to the plurality of modulation methods. This is an adaptive modulation method control method in which the receiving device selects a modulation method in the transmitting device according to the transmission status of the transmission line, and the transmitting device transmits by the modulation method selected by the receiving device. To determine the correction status of errors that can be made, two thresholds for specifying the appropriate range are set in advance in association with multiple modulation methods, and if the error is out of the appropriate range, the correction status is considered to be defective, and the error is out of the appropriate range. If it is good, the correction status is good, if it is within the appropriate range, the correction status is normal, and if no uncorrectable error is detected and the correction status of the correctable error is good, the currently selected modulation is used. If a modulation method corresponding to the case where the transmission condition is better than the method is selected and an uncorrectable error is detected, or if an uncorrectable error is not detected and the correction status of the correctable error is poor, Select a modulation method that corresponds to the case where the transmission status is poorer than the currently selected modulation method, and if an error that cannot be corrected is not detected and the correction status of the error that can be corrected is normal, it is currently selected. It is characterized by selecting the modulation method so as to maintain the modulation method. Before an uncorrectable error occurs, the deterioration of the transmission line condition is detected from the correction status of the correctable error, and the transmission line condition is recovered. By selecting an appropriate modulation method by detecting the above, stable transmission line quality can be ensured.

【0016】

Further, the present invention for solving the problem of the above-mentioned conventional example includes a transmission device having a plurality of modulation methods corresponding to a transmission situation and a receiving device having a plurality of modulation methods corresponding to the plurality of modulation methods. The receiving device is an adaptive modulation method control method in which the receiving device selects a modulation method in the transmitting device according to the transmission status of the transmission line, and the transmitting device transmits by the modulation method selected by the receiving device. In one case, the threshold for determining the correction status based on the error detection status and the correction status is adjusted so that the correction status of the error that can be corrected is poor and the detection frequency of the error that cannot be corrected is low. Or, when it occurs a specific number of times, the threshold value for determining the correction status corresponding to the currently selected modulation method is widened in the defective direction, and the correction status of the error that can be corrected is normal or good, and an error that cannot be corrected is detected. When the case occurs once or a specific number of times, the threshold value for determining the correction status corresponding to the currently selected modulation method is narrowed in a positive direction, and the current value is adjusted according to the adjustment of the threshold value. It is characterized by adjusting the threshold value in the modulation method corresponding to the case where the transmission status is worse than the selected modulation method, and the appropriate range of the correction status for each predetermined modulation method is set, the error detection status and the error detection status. By making adjustments based on the correction status, it is possible to flexibly respond to changes in the reception characteristics of the transmission line over the years, and by selecting an appropriate modulation method, stable transmission line quality can be ensured.

【0017】

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described with reference to the drawings. The function realizing means described below may be any circuit or device as long as it can realize the function, and a part or all of the function can be realized by software. is there. Further, the function realizing means may be realized by a plurality of circuits, or a plurality of function realizing means may be realized by a single circuit.

【0018】

In the adaptive modulation method control method according to the present invention, in the receiving device, transmission is performed according to the detection status of an error that cannot be corrected in the transmission path by CRC error detection or the like and the correction status of the error that can be corrected by the pathmetric value of bitabi decoding or the like. It is an adaptive modulation method control method that selects the modulation method in the device, and the determination of the correction status of errors that can be corrected is determined by associating with multiple modulation methods and setting two thresholds that specify the appropriate range in advance and setting the appropriate range. If the error is out of the proper range, the correction status is bad, if it is out of the proper range and good, the correction status is good, and if it is within the proper range, the correction status is normal. If the correction status is good, the modulation method corresponding to the case where the transmission status is better than the currently selected modulation method is selected, and if an error that cannot be corrected is detected, or an error that cannot be corrected is detected. If the correction status of the error that can be corrected is bad, the modulation method corresponding to the case where the transmission status is bad is selected from the currently selected modulation method, and the error that cannot be corrected is not detected and can be corrected. When the correction status of is normal, the modulation method is selected so as to maintain the currently selected modulation method, so that the transmission path is based on the correction status of the error that can be corrected before the error that cannot be corrected occurs. By detecting the deterioration of the situation, detecting the recovery of the transmission line condition, and selecting an appropriate modulation method, the transmission line quality can be stably ensured.

【0019】

Further, the adaptive modulation method control method according to the present invention is based on the detection status of uncorrectable errors in the transmission line by CRC error detection or the like and the correction status of errors that can be corrected by the pathmetric value of bitabi decoding in the receiving device. , It is an adaptive modulation method control method that adjusts the threshold value for judging the correction status, and there was a case where the correction status of the error that can be corrected is poor and the detection frequency of the error that cannot be corrected is low once or a specific number of times. In some cases, the threshold for determining the correction status corresponding to the currently selected modulation method is widened in the defective direction, and the correction status of the error that can be corrected is normal or good, and an error that cannot be corrected is detected. , Once or a certain number of times, the threshold for determining the correction status corresponding to the currently selected modulation method is narrowed in a positive direction, and is currently selected according to the adjustment of the threshold. Since the threshold value in the modulation method corresponding to the case where the transmission status is worse than the modulation method is adjusted, the appropriate range of the correction status for each predetermined modulation method is determined based on the error detection status and the correction status. By adjusting, the transmission line quality can be stably ensured by flexibly responding to changes in the reception characteristics of the transmission line over the years and selecting an appropriate modulation method.

【0020】

First, the outline of the Viterbi decoding algorithm will be described. Convolutional coding, which is one of error correction coding, has a feature that the most probable decoding, which estimates the original text stochastically transmitted, can be performed relatively easily. Among the most probable decoding, the Viterbi decoding is practically used in satellite communication and space communication because it has an extremely excellent error correction capability.

【0021】

The operation of the convolutional code encoder can be represented by a state transition diagram as shown in FIG. FIG. 1 is a state transition diagram of convolutional coding. FIG. 1 shows a transition from each state to the same or different state through a solid line or a broken line for each bit.

【0022】

Specifically, if the bit is specified to pass through a solid line when it is "0" and the bit is specified to pass through a dashed line when it is "1", then the solid line encoder If the next bit is "1" while in the state S0, it will move to the state S2 via the broken line. At that time, the code "11" shown in parentheses in FIG. 1 is output. In the following description, the reference numerals shown in parentheses are referred to as symbol metrics.

【0023】

This state transition diagram is usually described using a trellis diagram as shown in FIG. FIG. 2 is a trellis diagram showing the state transition of convolutional coding. A specific example of encoding "01101100" will be described with reference to FIG. First, if we start from the state S0, since the first bit is "0", "00" is output through the solid line, and the state stays at S0.

【0024】

Then, since the next bit is "1", "11" is output from the state S0 through the broken line, and the state becomes S2. In the same manner thereafter, the transition is made in the order of S3 S1 S2 S3 S1 S0, and as a result, the code 0011101000101011 is output.

【0025】

Next, the decoding method will be described with reference to FIG. FIG. 3 is a trellis diagram illustrating the Viterbi decoding. FIG. 3 is the same trellis diagram as in FIG. 2, except that the coded bits are shown in FIG. 2 and the Hamming distance between the code and the received code is shown in FIG.

【0026】

If the code "0011101000101011" corresponding to the original text "01101100" is transmitted and the received code is "1011111000001011", the path from the state S0 to the state S0 through the solid line is "00". Therefore, the Hamming distance is "1" compared to the first two bits "10" of the received code. Further, since the route from the state S0 to the state S2 through the broken line is "11", the Hamming distance is also "1".

【0027】

Therefore, the value of the grid point A and the value of the grid point B are set to "1", which is the minimum value of the Hamming distance, respectively. Next, for the next two bits received, "11", the Hamming distances from each route of "11", "10", "01", and "00" are "0" and "1", respectively. Note that, "1" and "2", at grid point C, the solid line from grid point A corresponds to "00", so "1" of grid point A is relative to "00". Adding the Hamming distance "2", the value of the grid point C becomes "3".

【0028】

The value of the grid point E is "1". Similarly, the values of the grid points D and the grid points F are "2". Here, considering the grid point H, at the grid point H, there are a path that passes through the solid line from the grid point E and a path that passes through the solid line from the grid point F, and the values obtained from each are , "2" and "3". In such a case, in the Viterbi decoding, the smaller value is used as the value of the grid point. Therefore, the value of the grid point H is "2".

【0029】

Similarly, the values of each grid point are obtained, and are as shown in FIG. Then, from the trellis diagram as shown in FIG. 3, a route that minimizes the value at the final grid point Y (hereinafter referred to as a survival route) is selected (indicated by a thick line in FIG. 3). Then, if the value corresponding to each line (solid line is "0", broken line is "1") is used as the decoding result, the transmitted code is reproduced, and therefore the original text "01101100" is reproduced.

【0030】

For more detailed explanations on Viterbi decoding, see Yo Shiozaki, "Basics of Information and Code Theory", Ohmsha, p82-86 published in April 1991, or "Solid Line Error Correction Technology", published by Trikeps Co., Ltd. , P131-166 supervised by Toru Inoue.

【0031】

In this way, when the decoding of one frame in the Viterbi decoding algorithm is completed, the value at the final grid point Y that follows the selected survival path is called the minimum path metric value, and the minimum path metric value is the transmission line. The value fluctuates depending on the situation (line quality). That is, as shown in FIG. 4, the BER (Bit Error Rate) characteristic becomes smaller as the signal energy per bit and the one-sided noise power density (Eb / No) become larger, that is, the line quality becomes better. At the same time, the minimum path metric value after the completion of 1-frame decoding becomes close to 0 (zero), and conversely, the minimum path metric value increases as the line quality deteriorates. FIG. 4 is an explanatory diagram showing the average value of the minimum path metric after the completion of Eb / No to 1 frame decoding and the BER characteristic in the QPSK modulation method soft determination Viterbi decoding.

【0032】

Therefore, in the adaptive modulation method control method of the present invention, the detection result of an error that cannot be corrected by the error detection code represented by the CRC error detection code, the minimum path metric value obtained when the received signal is viterbi-decoded, or the average thereof. The tendency of the line quality status is estimated from the error occurrence status that can be corrected by the value, the modulation method is selected and controlled according to the line status from the estimation result, and the trend of the line quality status is estimated from the minimum path metric average value. By adjusting the threshold value that specifies the appropriate range for this, the transmission line quality is stably ensured.

【0033】

The control method of the modulation method and the review method of the judgment threshold value will be specifically described with reference to FIG. FIG. 5 is an explanatory diagram showing an image of each modulation method and the optimum minimum path metric appropriate range. Note that FIG. 5 shows four modulation methods of BPSK, QPSK, 16QAM, and 64QAM. In FIG. 5, the order of modulation methods that are resistant to poor line quality, that is, have high interference resistance is BPSK, QPSK, 16QAM, 64QAM, and conversely, the transmission rates are higher in order. It is the order. Then, it is assumed that an appropriate range (threshold value is a black circle), which is a range of an appropriate minimum metric value (average value), is predetermined for each modulation method.

【0034】

In the specific modulation method selection control method in the adaptive modulation method control method of the present invention, first, when an error is detected by an error detection code, a data retransmission request is made to the source and the current state of the art. Since an error occurs in the received data in the modulation method, a switching request is made so as to select a modulation method that is resistant to poor line quality even if the transmission efficiency is lowered. That is, it is required to switch the modulation method to the right by one on the horizontal axis of FIG.

【0035】

If no error is detected by the error detection code and the minimum path metric average value obtained by Viterbi decoding is within the appropriate range shown in Fig. 5 of the current modulation method, the current modulation method is appropriate. As a modulation method, the current modulation method is maintained.

【0036】

Further, if an error is not detected by the error detection code, but the minimum path metric average value obtained by Viterbi decoding is larger than the appropriate range shown in FIG. 5 of the current modulation method (defective), the current modulation method is used. Then, although the error is within the correctable range, it is assumed that the line quality is prone to error, and a switching request is made so as to select a modulation method that is resistant to poor line quality. That is, it is required to switch the modulation method to the right by one on the horizontal axis of FIG.

【0037】

If no error is detected by the error detection code and the minimum pathmetric average value obtained by Viterbi decoding is smaller (good) than the appropriate range shown in FIG. 5 of the current modulation method, the current modulation method is used. Makes a request to switch to a modulation method that improves transmission efficiency, assuming that the line quality that is becoming better cannot be effectively used. That is, it is required to switch the modulation method to the left on the horizontal axis of FIG.

【0038】

When the state of the line quality changes suddenly, it may be possible to switch the modulation method in a plurality of stages at once. Further, in the error detection by the error detection code, one error may be included in the error at a specific time interval, or an error may be present when a predetermined number of errors occur in a predetermined number. Further, in the above description, the error correction status is determined using the average value of the minimum path metric, but it does not have to be the average value.

【0039】

On the other hand, the method of adjusting the threshold value in the adaptive modulation method control method of the present invention corrects based on the detection status of uncorrectable errors in the transmission line and the correction status of errors that can be corrected by the pathmetric average value of bitabi decoding. It adjusts the threshold value for judging the situation, and is currently selected when the correction status of the error that can be corrected is poor and the detection frequency of the error that cannot be corrected is low once or a specific number of times. The threshold for determining the correction status corresponding to the modulation method is widened in the defective direction, and the correction status of the error that can be corrected is normal or good, and the error that cannot be corrected is detected once or a specific number of times. If this is the case, the threshold for determining the correction status corresponding to the currently selected modulation method is narrowed in a positive direction, and the transmission status is worse than the currently selected modulation method according to the adjustment of the threshold. The threshold value in the modulation method corresponding to such a case is adjusted.

【0040】

Specifically, the minimum pathmetric average value obtained by Viterbi decoding is larger than the appropriate range shown in Fig. 5 of the current modulation method (defective direction), but no error is detected by the error detection code, or If the detection frequency is low, it is highly likely that the minimum pathmetric average value range of the current modulation method is not appropriate, and the upper limit threshold value of the minimum pathmetric average value range is corrected upward. If the minimum path metric average is within the appropriate range shown in Fig. 5 of the current modulation method, but an error is detected or the detection frequency is high, the minimum path metric average of the current modulation method is used. Correct the upper threshold of the minimum pathmetric mean range downwards, assuming that the value range is likely to be inappropriate.

【0041】

Then, when the correction (adjustment) of the above upper limit value is applied to the appropriate range in the current modulation method, the modulation method to the right of the correction (adjustment) is performed in the modulation method (modulation method corresponding to the case where the transmission condition is worse than the currently selected modulation method). Since the balance of the lower limit value of the appropriate range is lost, the appropriate range of the modulation method on the right side is corrected by the relative positional relationship.

【0042】

Explaining with the specific example of FIG. 5, when the upper limit threshold value of QPSK is A, the minimum path metric average is larger than A during QPSK communication method selection, but no error is detected or is detected. In the case of infrequent cases, the upper threshold A is corrected upward (up arrow of B), and conversely, the minimum pathmetric mean is lower than A, but an error is detected. Alternatively, if the detection frequency is high, the upper limit threshold value A is corrected downward (down arrow of B).

【0043】

In addition, in any modulation method, when the upper limit threshold value is reviewed and corrected, the lower limit threshold value of the modulation method located on the right side of the modulation method in FIG. 5 is also relatively corrected. .. Explaining with the specific example of FIG. 5, if the upper limit threshold value A of QPSK is corrected upward or downward, the lower limit threshold value C of BPSK is also corrected upward or downward accordingly.

【0044】

As a result, even if the relationship between the initially set line quality estimate and the threshold value for selecting the modulation method also changes due to the effect of changes in reception characteristics due to changes over the years. In the case where a line error occurs even though the line quality estimate is within the threshold range, it is possible to correct the threshold relationship and perform control in a state that matches the current situation. it can.

【0045】

Next, the configuration of the communication system that realizes the adaptive modulation method control method according to the present invention will be described with reference to FIG. FIG. 6 is a block diagram of a communication system that realizes the adaptive modulation method control method according to the present invention. The parts having the same configuration as that of FIG. 8 will be described with the same reference numerals.

【0046】

Similar to the conventional communication system, the communication system of the present invention (the present system) adds information for estimating the propagation path condition on the receiving side, modulates it by a selected modulation method, and transmits a radio signal. Device 1 and the transmitter control signal that receives the radio signal, demolishes it, estimates the propagation path condition based on the information added on the transmitting side, and specifies the modulation method on the transmitting side based on the estimation result. It is composed of a receiving device 2 that transmits to the transmitting device 1.

【0047】

However, in the communication system of the present invention, the information for estimating the propagation path condition added by the transmitting device 1 is a convolutional code and an error detection code (CRC code), and is added on the transmitting side in the receiving device 2. Conventional communication is to estimate the propagation path condition based on the average value of the path metric obtained as a result of Viterbi decoding from the convolutional code, error detection by the CRC code, and the detected bit error rate. It is different from the system. Further, the control method for switching the modulation method on the transmission side based on the estimation result of the propagation path condition is also different from the conventional control method.

【0048】

Then, inside the transmission device 1 of the present invention, in addition to the transmission data control unit 11, the CRC coding unit 12, the mapping unit 13, the modulation unit 14, and the demodulation unit 15, which have the same configuration as the conventional one. , A convolutional coding unit 16 is newly provided, and the inside of the receiving device 2 of the present invention includes a demodulation unit 21, a demapping unit 22, and a CRC error detecting unit 23, which have the same configuration as the conventional one. , In addition to the source control unit 24 and the modulation unit 25, a Viterbi decoding unit 26 is newly provided.

【0049】

A feature portion of the present invention will be described. The convolutional coding unit 16 in the transmission device 1 is a general coding unit that performs convolutional coding for error correction coding, and outputs coded data. The Viterbi decoding unit 26 in the receiving device 2 is a general decoding unit that performs Viterbi decoding, which is the most probable decoding method, for the convolutional coding performed on the transmitting side, and performs error-corrected decoding data. In addition to outputting, the minimum pathmetric average value is output after decoding one frame.

【0050】

The source control unit 24 in the receiving device 2 has roughly two control functions, one is a source control function for controlling a modulation method on the transmitting side, and the other is a transmitting function. This is a threshold control function that reviews the judgment threshold value for determining the modulation method on the side.

【0051】

First, the source control function will be described. The source control function of the source control unit 24 in the receiver 2 is based on the error detection signal from the CRC error detection unit 23 and the minimum path metric average value from the bitabi decoding unit 26, and the line quality of the transmission line. Is estimated, and a transmitter control process for outputting a transmitter control signal including a data retransmission request signal and a modulation method switching control signal for controlling a modulation method on the transmitting side is performed based on the estimated line quality. In the method of estimating the line quality of the transmission line, an appropriate range consisting of the upper limit threshold value and the lower limit threshold value of the minimum path metric average value corresponding to each modulation method as shown in FIG. 5 is set in advance. It is stored and estimated based on whether or not the minimum path metric average value output from the Viterbi decoding unit 26 is within an appropriate range corresponding to the current modulation method.

【0052】

Here, a specific flow of the source control process of the source control unit 24 will be described with reference to FIG. 7. FIG. 7 is a flowchart showing a flow of source control processing in the source control unit 24 of the receiver 2 that realizes the adaptive modulation method control method of the present invention. The source control process in the source control unit 24 of the receiver 2 that realizes the adaptive modulation method control method of the present invention first determines whether or not there is an error according to the error detection signal from the CRC error detection unit 23 (100). If there is an error (Yes), a data retransmission request signal to the source is output (102), and a switching request that shifts the modulation method from the current method to the right by one (104) is output. Terminate the source control process. If the current modulation method is BPSK, switching is not performed.

【0053】

On the other hand, if there is no error in the process 100 (No), it is determined whether the minimum path metric average value from the Viterbi decoding unit 26 is within the threshold range of the current communication method (110), and the range is determined. If it is inside (Yes), the communication method is assumed to maintain the current status (112), and the source control process is terminated.

【0054】

On the other hand, in the process 110, if it is not within the range (No), it is determined whether the minimum path metric average value is out of the value larger than the upper limit of the threshold range (120), and a large value is obtained. If it deviates from (Yes), a switching request for shifting the modulation method from the current method to the right by one is output (122), and the source control process is terminated. If the current modulation method is BPSK, switching is not performed.

【0055】

Also, in process 120, if it does not deviate to the larger value (No), that is, it deviates to the value smaller than the lower limit of the threshold range, so the modulation method is changed to the left from the current method. A switching request for shifting by one is output (124), and the source control process is terminated. If the current modulation method is 64QAM, switching will not be performed.

【0056】

When the state of the line quality changes suddenly, it may be possible to switch the modulation method in a plurality of stages at once. Further, in the error detection by the error detection code, one error may be included in the error at a specific time interval, or an error may be present when a predetermined number of errors occur in a predetermined number. Further, in the above description, the error correction status is determined using the average value of the minimum path metric, but it does not have to be the average value.

【0057】

Next, the threshold value control function will be described. The threshold control function of the source control unit 24 in the receiver 2 is an appropriate range consisting of the upper limit threshold and the lower limit threshold of the minimum pathmetric average value corresponding to each modulation method as shown in FIG. Is set and stored in advance, but the line quality of the transmission line estimated from the error detection signal from the CRC error detection unit 23 and the transmission estimated from the minimum path metric average value output from the Vitabi decoding unit 26. When the line quality of the channel is inconsistent, the appropriate range consisting of the upper limit threshold value and the lower limit threshold value of the minimum path metric average value corresponding to each stored modulation method is corrected.

【0058】

For example, if there are many cases where the minimum path metric is out of the appropriate range upward (defective direction), but no error is detected by the error detection code, the appropriate minimum path metric of the current modulation method is appropriate. Correct the upper threshold upwards as the range is likely to be inadequate. In addition, if the minimum path metric is within the appropriate range but errors are frequently detected, it is highly likely that the minimum path metric average value range of the current modulation method is not appropriate. Correct the upper threshold of the proper range of the minimum path metric downward. It should be noted that, when the above case occurs once, it is not immediately corrected, but it is more practical to correct it when a predetermined number of times (the number of times considered to be frequent) occur. Further, the correction width such as how much the upper limit threshold value is corrected is set in advance, and the correction is performed upward or downward within the set correction width.

【0059】

Then, if the correction is made to the appropriate range of the current modulation method, the lower limit value of the appropriate range in the modulation method on the right side (the modulation method corresponding to the case where the transmission condition is worse than the currently selected modulation method). Since the balance of the above is lost, the appropriate range of the modulation method on the right side is corrected by the relative positional relationship with a preset correction width.

【0060】

Next, the operation of the communication system that realizes the adaptive modulation method control method of the present invention will be described with reference to FIG. In the communication system of the present invention, in the transmission device 1, the transmission data is output to the CRC coding unit 12 under the control of the transmission data control unit 11, the CRC coding unit 12 adds an error detection code, and the tatami mat. Convolutional coding for error correction is performed by the embedded coding unit 16, the mapping is performed by the mapping arrangement selected by the mapping unit 13, the modulation is performed by the modulation unit 14, and the data is transmitted to the transmission line.

【0061】

Then, the received data is demodulated by the demodulation unit 21 of the receiving device 2, demapped by the demapping unit 22, the Viterbi decoding is performed by the Viterbi decoding unit 26, and the error-corrected data is output, and the CRC error detection unit Error is detected in 23 and the decrypted data without error is output. At this time, the bitabi decoding unit 26 outputs the minimum path metric average value after the completion of one-frame decoding, and the CRC error detection unit 23 outputs an error detection signal when an error is detected to control the source. In section 24, the line quality is estimated from the minimum pathmetric average value and the error detection signal, and a transmitter control signal consisting of a data retransmission request signal and a modulation method switching control signal that controls the modulation method on the transmitting side is output. It is modulated by the modulation unit 25 and transmitted to the transmission device 1. At this time, if the transmission line condition is in a state where the appropriate range in the current modulation method should be corrected, the threshold value of the stored appropriate range is corrected and updated.

【0062】

The transmission device 1 receives the transmission device control signal, demodulates it in the demodulation unit 15, outputs the data retransmission request signal to the transmission data control unit 11, and the transmission data control unit 11 receives a data retransmission request. If so, the data is retransmitted. Further, the modulation method switching control signal is output to the mapping unit 13, and when there is a request for switching the modulation method according to the control signal, the mapping method can be switched.

【0063】

According to the adaptive modulation method control method of the present invention, bitabi decoding and error detection are performed on the receiving side according to the error detection code and error correction code added on the transmitting side, and even if an uncorrectable error is not detected, the bitabi decoding is performed. If a poor tendency of line quality is detected by the minimum path metric average value indicating the error correction status by, the modulation method on the transmitting side is switched to the modulation method with high interference resistance, so before a fatal uncorrectable error occurs. In addition, it is possible to switch to an appropriate modulation method, stably improve the transmission line quality, reduce the number of retransmissions, and improve the transmission efficiency.

【0064】

Also, if no error is detected and a good tendency of line quality is detected by the minimum path metric average value by Viterbi decoding, the modulation method on the transmitting side is switched to the modulation method with a high transmission rate, so when the line quality improves. , It is possible to switch to a more efficient modulation method, and there is an effect that the characteristics of the transmission line can be effectively used.

【0065】

In addition, the threshold value for specifying the appropriate range for judging the tendency of line quality by the minimum path metric average value is set in advance, but the minimum path metric average by Viterbi decoding is performed even though no error is detected. If a bad tendency of line quality is frequently detected in the value, the upper limit threshold value that specifies the appropriate range is corrected to widen in the bad direction, so the change in reception characteristics due to aging changes is also included. , There is an effect that an appropriate modulation method can be selected according to the current state of transmission line quality.

【0066】

On the contrary, if it is frequently detected that the minimum path metric average value by Viterbi decoding is within the appropriate range even though an error is detected, the upper limit that specifies the appropriate range is specified. Since the threshold value is corrected so as to narrow it in a good direction, it has the effect of being able to select an appropriate modulation method that matches the current state of transmission line quality by incorporating changes in reception characteristics due to changes over the years.

【0067】

[Effect of the invention]

According to the present invention, in the receiving device, the modulation method in the transmitting device is determined according to the detection status of the error that cannot be corrected in the transmission line by CRC error detection or the like and the correction status of the error that can be corrected by the pathmetric value of bitabi decoding. It is an adaptive modulation method control method to be selected, and the judgment of the correction status of an error that can be corrected is determined by associating with a plurality of modulation methods, setting two thresholds for specifying an appropriate range in advance, and deviating from the appropriate range for defects. A case is regarded as a bad correction status, a case that is out of the appropriate range and is good is regarded as a good correction status, and a case that is within the appropriate range is regarded as a normal correction status. In some cases, the modulation method corresponding to the case where the transmission condition is better than the currently selected modulation method is selected, and when an uncorrectable error is detected, or an uncorrectable error is not detected and can be corrected. If the correction status of is bad, the modulation method corresponding to the case where the transmission status is bad is selected from the currently selected modulation method, and the error correction status that cannot be corrected is usually not detected and can be corrected. In the case of, since the modulation method is selected so as to maintain the currently selected modulation method, deterioration of the transmission line condition is detected from the correction status of the error that can be corrected before the error that cannot be corrected occurs. Further, by detecting the recovery of the transmission line condition and selecting an appropriate modulation method, there is an effect that the transmission line quality can be stably ensured.

【0068】

Further, according to the present invention, in the receiving device, the correction status is determined based on the detection status of the uncorrectable error in the transmission line by CRC error detection or the like and the correction status of the error that can be corrected by the path metric value of Vitabi decoding. It is an adaptive modulation method control method that adjusts the threshold value to be corrected, and is currently selected when the correction status of the error that can be corrected is poor and the detection frequency of the error that cannot be corrected is low once or a specific number of times. There is one case or specific case where the threshold value for determining the correction status corresponding to the modulation method used is widened in the defective direction, and the correction status of the error that can be corrected is normal or good and the error that cannot be corrected is detected. When the number of occurrences occurs, the threshold value for determining the correction status corresponding to the currently selected modulation method is narrowed in a favorable direction, and the transmission status is higher than that of the currently selected modulation method according to the adjustment of the threshold value. Since the threshold value in the modulation method corresponding to the case where is defective is adjusted, the appropriate range of the correction status for each predetermined modulation method is adjusted based on the error detection status and the correction status. By flexibly responding to changes in the reception characteristics of the transmission line over the years and selecting an appropriate modulation method, there is an effect that the quality of the transmission line can be stably ensured.

[Simple explanation of drawings]

[Figure 1]

It is a state transition diagram of convolutional coding.

[Figure 2]

It is a trellis diagram showing the state transition of convolutional coding.

[Fig. 3]

It is a trellis diagram explaining the Viterbi decoding.

[Fig. 4]

It is explanatory drawing which shows the average value of the minimum path metric after the completion of Eb / No to 1 frame decoding in QPSK modulation method soft judgment Viterbi decoding, and BER characteristic.

[Fig. 5]

It is explanatory drawing which shows the image of each modulation method and the optimum minimum path metric appropriate range.

[Fig. 6]

It is a block diagram of the structure of the communication system which realizes the adaptive modulation system control method which concerns on this invention.

[Fig. 7]

It is a flowchart which shows the flow of the source control processing in the source control part of the receiving apparatus which realizes the adaptive modulation system control method of this invention.

[Fig. 8]

It is a block diagram of the structure of the conventional communication system.

[Explanation of symbols]

1 ... Transmitter, 2 ... Receiver, 11 ... Transmit Data Control, 12 ... CRC Encoding, 13 ... Mapping, 14 ... Modulator, 15 ... Demodulation section, 16 ... Convolutional coding section, 21 ... Demodulation section, 22 ... Demapping section, 23 ... CRC error detection section, 24, 24'... Source control section, 25 ... Modulation section, 26 ... Bitabi decoding section