JP4918935B2 - Adaptive modulation method and data rate control method - Google Patents

Description

  The present invention relates to a method for controlling a modulation method and a data rate adapted to quality fluctuations for each propagation path in a wireless communication system that communicates through a plurality of propagation paths by using a plurality of carriers.

In order to increase the amount of transmission per time in a wireless communication system, a multi-level modulation technique for transmitting information of a plurality of bits per symbol is known.
In multilevel modulation technology, the maximum throughput increases when the channel quality is better as the number of bits per symbol increases, while the throughput increases when the channel quality decreases as the number of bits per symbol increases. In order to perform stable communication, an adaptive modulation technique that switches the modulation multi-level number in accordance with the quality of the propagation path has been proposed. Regarding this technology, the paper “Transmission characteristics of modulation multi-level variable adaptive modulation system” (The Institute of Electronics, Information and Communication Engineers B-II Vol.J78-B-II No.6 pp.435-444, June 1995) (Non-Patent Document 1) and the like.

  In addition, to cope with the difference in propagation path quality within the OFDM band, OFDM (Orthogonal Frequency Division Multiplexing) method is used to divide and transmit information into a number of orthogonal subcarriers as wireless communication becomes wider. In addition, an OFDM adaptive modulation scheme that switches the modulation scheme for each subcarrier has been proposed. For this technology, the paper “OFDM adaptive modulation using multi-level transmission power control for high-speed data communication” (The Institute of Electronics, Information and Communication Engineers B-II Vol.J84-B-II No.7 pp.1141-1150) , July 2001) (Non-Patent Document 2) and the like.

Shinya Ohtsuki et al., "Transmission characteristics of modulation modulation system with variable modulation level", IEICE Transactions, June 1995, B-II Vol.J78-B-II No.6 pp.435-444 Yoshiaki Tomoaki et al., `` OFDM adaptive modulation scheme using multilevel transmission power control for high-speed data communication '', IEICE Transactions, July 2001, B-II Vol.J84-B-II No. 7 pp.1141-1150

  When switching the modulation method according to the propagation path variation by the conventional adaptive modulation technique described above, in order for the receiving station to perform demodulation correctly, the transmitting station and the receiving station need to share information on the modulation method used. . If the modulation method is different between the transmitting station and the receiving station, the data position will shift and errors will be chained. For example, in the method of notifying the modulation method from the transmitting station to the receiving station, this notification signal is very It is necessary to communicate with high accuracy, and for example, even when the receiving station estimates the modulation scheme from the received signal, a training signal for estimating with high accuracy is required. For this reason, for example, in order to control the modulation scheme for each OFDM subcarrier, there is an increase in the number of modulation scheme control signals such as modulation notification signals and training signals. If the modulation control signal such as the modulation notification signal and training signal is reduced so as not to reduce the data signal throughput, the degree of freedom in modulation control is reduced and fine control can be performed. Therefore, there is a problem that communication cannot be performed by fully utilizing the propagation path.

  The present invention has been made to solve the above-described problem. For example, even when the modulation scheme is controlled for each subcarrier of OFDM, the matching of the modulation scheme between the transmitting station and the receiving station is not always accurate. Therefore, it is possible to switch the modulation method for each subcarrier while reducing the control signal for controlling the modulation method, and to control the overall communication throughput according to the overall quality of the propagation path. An object of the present invention is to provide a simple wireless communication system.

As means for solving the above problems, in the adaptive modulation and coding system according to the present invention, first, the transmitting station and the receiving station have the maximum number of transmission bits per symbol in each subcarrier, and a coding system that can be selected. Share information with your list.
The transmitting station determines the modulation scheme for each subcarrier from the propagation path quality of each subcarrier, selects the encoding scheme from the list based on information on the number of bits that can be communicated with the determined modulation scheme, and performs encoding. The code is divided and distributed to each subcarrier by the maximum number of transmission bits per symbol, and each subcarrier is modulated by the number of bits that can be transmitted by the previously determined modulation scheme and transmitted. I do.

The receiving station determines the modulation method used for demodulation in the subcarrier from the channel quality of each subcarrier and performs demodulation, and the number of bits obtained as a result of demodulation per symbol is the maximum number of bits transmitted per symbol. If it is less than, a signal with a likelihood of 0 is added and the demodulation results are collected, and the demodulation results are tried with the encoding methods in the encoding method list, and the decoding is successful. In this case, it is assumed that information obtained as a result of decoding is transmitted.
With this method, it is possible to switch the modulation method for each subcarrier according to the propagation path without matching the exact modulation system between the transmitting station and the receiving station, and to improve the average propagation path quality. Accordingly, the throughput can be controlled.

  According to the present invention, it is possible to switch the number of bits communicated per symbol in accordance with a change in the propagation path, without needing to notify modulation scheme information between the transmitting station and the receiving station. Provided is a system capable of communicating with an optimum throughput according to a change in a road.

The example of the adaptive modulation and the encoding system in the transmitting station in this invention. 6 shows an example of adaptive demodulation and decoding schemes at a receiving station according to the present invention. The example of the relationship between the bit number and the coding rate which can communicate by adaptive modulation in this invention. The example of the relationship between the number of bits which can communicate by adaptive modulation in this invention, and transmission power. 1 is a first example of a transmitting station according to the present invention. 6 shows a second example of the transmitting station in the present invention. 1 is a first example of a receiving station according to the present invention. 6 shows a second embodiment of a receiving station in the present invention. An example of implementation of a transmitting station adaptive modulation unit when the present invention is applied to a system in which information is divided into a plurality of codes and transmitted. An example of implementation of a transmitting station adaptive modulation unit when the present invention is applied to a system in which information is divided and transmitted to a plurality of antennas. An example of implementation of a transmitting station adaptive modulation unit when the present invention is applied to a system that divides and transmits information into a plurality of beam patterns. The example of the flow of a process of the transmitting station in this invention. The example of the flow of a process of the receiving station in this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, in the following, as an example, the maximum number of transmission bits per symbol in each subcarrier is set to 6 bits, and an adaptive modulation method using 64QAM, 16QAM, or QPSK as a modulation method will be described. It is not limited to the number of transmission bits and modulation method, but more generally, when the maximum number of transmission bits per symbol is 2 m bits, and the modulation method is ²² kQAM (k is a natural number of m or less). Is equally applicable. In the above, 4QAM corresponding to k = 1 represents the same modulation scheme as QPSK.

First, the configuration of the transmitting station and the receiving station and the signal flow will be described based on the configuration diagram of the transmitting station and the receiving station that perform communication using the adaptive modulation and coding method of the present invention shown in FIG.
However, in the following description, only the configuration in which the modulation / demodulation method of the present invention is applied only to communication from the transmitting station to the receiving station will be described. However, in the implementation, both functions of the receiving station and the transmitting station are provided in one communication device. In addition, the present invention can be applied to bidirectional communication. The terms transmitting station and receiving station in the present invention are used to mean a radio station that modulates a data signal to be transmitted and a radio station that performs demodulation, and any of these may be a base station or a mobile terminal, When terminals are connected to each other, any terminal may be a transmitting station / receiving station.

FIG. 5 shows a first configuration example of the transmission station in the present invention, FIG. 6 shows a second configuration example of the transmission station in the present invention, FIG. 7 shows a first configuration example of the reception station in the present invention, 2 shows a second configuration example of the receiving station in the present invention.
When performing communication using the transmitting station of FIG. 5 or FIG. 6 and the receiving station of FIG. 7 or FIG. 8, the transmitting station and the receiving station first determine the maximum number of transmission bits per symbol in each subcarrier. The information is shared with a list of selectable encoding methods, and stored in the storage unit prior to encoding transmission information and decoding received signals.

  As a method of sharing information between the transmitting station and the receiving station, it may be determined in advance as a system, or may be notified from the transmitting station or the receiving station at the start of communication. In addition, when one of the transmission station and the reception station is a base station and the other is a terminal, the base station notifies the terminal when performing location registration or handover, or broadcasts from the base station. It is also possible to use a method such as transmitting a signal including shared information. In addition, the maximum number of transmission bits per symbol is determined by propagation path conditions, communication request amounts, transmitter / receiver performance, and the like.

In the transmission station of FIG. 5, adaptive modulation control section 410 converts the signal received by radio section 400 into a frequency domain signal by FFT (Fast Fourier Transform), and determines the modulation scheme based on the propagation path quality for each subcarrier. Then, information on each modulation scheme for each subcarrier is notified to adaptive modulation section 430, and the sum of the number of bits per symbol of the modulation scheme selected for each subcarrier is notified to encoding section 420.
The encoding unit 420 selects an encoding method from the encoding method list based on the information obtained from the adaptive modulation control unit 410, performs an encoding process based on the selected encoding method, and performs the encoding process. The result is passed to adaptive modulation section 430. In the encoding process, error detection information is added to the information to be transmitted by a method such as parity or CRC, for example, encoded by a channel code such as a convolutional code or a Turbo code, and the bit position in the created codeword is changed by interleaving. If there is a surplus in the number of bits when distributed to each subcarrier, some bits are deleted by puncturing.

Adaptive modulation section 430 divides the data passed from coding section 420 into subcarriers, and each subcarrier performs modulation using the modulation scheme determined by adaptive modulation control section 410, and performs IFFT (Inverse Fast Fourier Transform). Each subcarrier signal is multiplexed with a time domain signal and transmitted through radio section 400.
The signal transmitted from the transmitting station in FIG. 5 is received by the receiving station configured as shown in FIG. 7, for example. In the receiving station of FIG. 7, the adaptive demodulation control unit 510 converts the signal received by the radio unit 500 into a frequency domain signal by FFT, determines the modulation method used for demodulation based on the propagation path quality for each subcarrier, Information on each modulation scheme used for demodulation for each subcarrier is notified to adaptive demodulation section 530, and the sum of the number of bits per symbol of the modulation scheme used for demodulation selected for each subcarrier is notified to decoding section 520.

  Adaptive demodulation section 530 converts the signal received by radio section 500 into a frequency domain signal by FFT, performs demodulation using the modulation scheme notified from adaptive demodulation control section for each subcarrier, and uses the modulation used for demodulation If the number of bits per symbol of the system is less than the maximum number of bits per symbol previously determined with the transmitting station, it is assumed that a signal with a likelihood of 0 is received for the shortage, and each sub The demodulation result of the maximum number of bits per symbol is output for each symbol from the carrier, and all the carriers are multiplexed and passed to the decoding unit.

The decoding unit 520 selects an encoding method from the encoding method list, performs depuncturing, deinterleaving, and channel code decoding processing on the data passed from the adaptive demodulation unit 530 according to the selected encoding method, and transmits It is determined whether or not the decoding result is incorrect by using the error detection information added sometimes.
When it is determined that the decoding result is not incorrect, the decoding unit 520 outputs the determined decoding result as reception information. If it is determined that the decoding result is incorrect, another encoding method is selected from the previous list of encoding methods, and the same decoding process is retried. When it is determined that the decoding result is incorrect for all the encoding methods in the list, a decoding failure is output.

  In the trial in the decoding unit 520, as an order determination method for selecting an encoding method to be used for decoding from a list, it is possible to easily select an order before communication and always select in a predetermined order. . As another determination method, a notification of reception quality is received from adaptive demodulation control section 510. If reception quality is high, a coding method with a high coding rate is preferentially tried. If reception quality is low, a code with a low coding rate is used. It is possible to preferentially select the conversion method. As another determination method, it is also possible to preferentially select and try an encoding method that has been successfully decoded in the previous decoding, and this method is particularly suitable when the quality variation of the propagation path is relatively moderate. Suitable for. As yet another determination method, the transmitting station notifies the receiving station of the encoding method selected by the encoding unit 420, and the receiving station preferentially selects the method notified from the transmitting station and tries it. It is also possible to do.

  The receiving station of the present invention can also be realized with the configuration shown in FIG. 8 instead of the configuration shown in FIG. In the receiving station of FIG. 7, adaptive demodulation control section 510 and adaptive demodulation section 530 perform the same processing as adaptive demodulation control section 510 and adaptive demodulation section 530 in the receiving station in the configuration example of FIG. The decoding unit 520 of the receiving station in FIG. 8 prepares a depuncture, a deinterleave, a channel decoding and an error detection unit for each encoding method list, and outputs an output of the decoding unit which is determined to be error-free as a result of the error detection process. It is also possible to output it as reception information.

The transmitting station of the present invention can be realized by a configuration such as that shown in FIG. 6 instead of the configuration shown in FIG. In the transmitting station configured as shown in FIG. 6, adaptive modulation control section 410 determines the overall quality of the propagation path based on the signal received by radio section 400, and notifies encoding section 420 of the result.
The encoding unit 420 selects an encoding method from the encoding method list based on the information obtained from the adaptive modulation control unit 410, performs code processing based on the selected encoding method, and outputs the result to the adaptive modulation unit. Pass to 430. In code or processing, error detection information is added to information to be transmitted, for example, using a method such as parity or CRC, encoded using a channel code such as a convolutional code or a Turbo code, and the bit position in the created codeword is changed by interleaving. If there is a surplus in the number of bits when distributed to each subcarrier, some bits are deleted by puncturing.

Adaptive modulation section 430 divides the data passed from encoding section 420 into subcarriers, and modulates the maximum number of transmission bits per symbol determined with the receiving station in advance on all subcarriers Is modulated using IFFT, and the signal of each subcarrier is multiplexed with the signal in the time domain by IFFT (Inverse Fast Fourier Transform) and transmitted through the radio section 400.
6 does not switch the modulation scheme according to the propagation path quality for each subcarrier as compared with the transmission station configured in FIG. 5, but the receiving station in FIG. 7 or FIG. Since the modulation scheme used for demodulation is switched in accordance with the propagation path quality for each channel, there is an advantage that the configuration of the transmission station can be simplified while communicating using the difference in quality for each subcarrier.

In addition, by using the transmission station having the configuration of FIG. 6, for example, when different frequencies are used in communication from the transmission station to the reception station and communication from the reception station to the transmission station, the transmission path for each subcarrier in the transmission station. The present invention can be applied even when it is difficult to measure the quality difference. In this case, it is desirable to receive the reception quality from the receiving station as feedback information.
Next, a detailed description will be given based on schematic diagrams for explaining the modulation scheme and the coding scheme of the present invention in each of the transmitting station and the receiving station shown in FIG. 1 and FIG. First, the transmitting station and the receiving station share information on the maximum number of transmission bits Nc per symbol in each subcarrier and a list of selectable coding schemes. In the following description and drawings, the value represented as Nc represents the maximum number of transmission bits per symbol in each subcarrier.

  The processes in the adaptive modulation control unit, coding unit, and adaptive modulation unit of the transmitting station will be described in detail with reference to FIG. In the transmitting station of FIG. 1, adaptive modulation control section 110 first determines modulation scheme 114 for each subcarrier based on channel quality 111 for each subcarrier, and bits that can be communicated per symbol of the determined modulation scheme. The number Nb115 is obtained. It should be noted that the value described as Nb in the following description and drawings represents the number of bits 115 that can be communicated per symbol, which is determined on the transmitting station side. Here, in determining the modulation scheme for each subcarrier, for example, signal power intensity, interference power intensity, signal-to-interference and noise power ratio, etc. can be used as the quality of the propagation path. In addition, the threshold value is determined simply by, for example, if the channel capacity of the subcarrier predicted from the channel quality 111 for each subcarrier is larger than 2, which is the number of bits that can be communicated per symbol of QPSK, than QPSK. Select threshold 112 to select a modulation scheme with a large modulation multi-level number, and select a modulation scheme with a larger modulation multi-level number than 16QAM if it is greater than 4 bits that can be communicated per symbol of 16QAM. Thus, a determination method for selecting the threshold value 113 is possible, and in order to further improve the communication quality, the threshold value can be determined according to the code to be used, the modulation method, and the characteristics of the propagation path.

  The encoding unit 120 performs encoding by selecting one code from a list of encoding methods shared by the transmitting station and the receiving station. Here, an example of a criterion for selecting a code is a relationship 301 shown in the graph of FIG. In the relationship 301, the sum of the number of bits Nb that can be communicated per symbol of the modulation scheme selected by each subcarrier in the section in which one codeword is transmitted is represented by the sum of the maximum number of transmission bits Nc per symbol of each subcarrier. A coding method having a coding rate smaller than the divided value is selected.

  For example, in the example of FIG. 1, since one code is transmitted at a time using six subcarriers, the code length 122 is a value obtained by adding the maximum number of transmission bits Nc per symbol of each subcarrier for six subcarriers. In other words, a coding scheme is selected such that the information bit length 121 is smaller than the value obtained by adding the number of bits Nb that can be communicated per symbol of the modulation scheme selected by each subcarrier for six subcarriers. Here, the selected coding method only needs to satisfy the condition that the coding rate is smaller than the quotient of the sum of Nb and the sum of Nc. In addition to this, for example, the code is divided into n times in terms of time. The code length is equal to the product of the sum of Nc and n for all carriers used for transmission of this code, and the information bit length of this code is for all carriers used for transmission of this code. A coding method is selected that is smaller than the product of the sum of Nb and n.

By selecting the coding method in this way, the higher the channel quality, the higher the coding rate is selected and the data rate is improved. The lower the channel quality, the lower the coding rate code. The error correction capability is improved by selecting the encoding method, and the encoding method corresponding to the quality of the propagation path is selected.
In addition, in the relationship 301 in FIG. 3, for example, a constant coding rate is selected in the range of 302, but, for example, as in the relationship diagram between the quotient of the sum of Nb and the sum of Nc and the transmission power shown in FIG. In the section 312 for selecting the same coding rate, the energy used per transmission information bit can be stabilized by controlling the power so that the transmission power increases as the quotient of the sum of Nb and the sum of Nc decreases. Communication quality can be further improved.

  In the code selection policy shown above, the coding rate is selected based on the quotient of the sum of Nb and the sum of Nc, but the quality of the channel can also be used as the selection criterion for the coding rate. . For example, the value obtained by multiplying the sum of the channel capacity of the propagation path in the section for transmitting one codeword by the sum of Nc multiplied by a coefficient having a positive correlation with the error correction capability of the channel code is used as a reference value. Select the encoding method list that has the closest encoding rate to the reference value, or select the largest encoding method within the encoding method list that does not exceed the reference value, or encode. A similar effect can be obtained even by a code selection method that selects the smallest method within a range where the coding rate does not fall below the reference value in the method list.

  Modulation section 130 divides the codeword created by encoding section 120 into subcarriers by the maximum number of transmission bits Nc bits per symbol of each subcarrier, and out of the Nc bits distributed to each subcarrier The number of bits that can be communicated per symbol of the subcarrier modulation scheme determined by adaptive modulation control section 110 is modulated using the subcarrier modulation scheme to generate a transmission signal. At this time, a bit that is not used for transmission is generated by the difference between the Nc bit and the Nb bit, but this is discarded without being used for transmission.

  Next, processing in the adaptive demodulation control unit, decoding unit, and demodulation unit of the receiving station will be described in detail with reference to FIG. 2, the adaptive demodulation control unit 210 first determines the modulation scheme 214 used for demodulation for each subcarrier based on the propagation path quality 211 for each subcarrier, and communicates per symbol of the determined modulation scheme. The number of possible bits Nd215 is obtained. It should be noted that the value described as Nd in the following description and drawings represents the number of bits that can be communicated per symbol, as determined by the transmitting station. Here, in determining the modulation scheme for each subcarrier, it is possible to use signal power intensity, interference power intensity, signal-to-interference, noise power ratio, and the like as the quality of the propagation path as in the transmission station.

  In addition, the threshold value is determined by, for example, modulation multilevel than QPSK if the channel capacity of the subcarrier predicted from the channel quality 211 for each subcarrier is larger than 2, which is the number of bits that can be communicated per symbol of QPSK. Select the threshold 212 to select a modulation scheme with a large number, and select a modulation scheme with a larger modulation multi-level number than 16QAM if it is larger than 4 which is the number of bits that can be communicated per symbol of 16QAM A determination method for selecting the threshold value 213 is possible, and the threshold value can be determined in accordance with the code to be used, the modulation method, and the characteristics of the propagation path in order to further improve the communication quality. Furthermore, communication quality can be improved by selecting threshold values 212 and 213 at the receiving station that are smaller than threshold values 112 and 113 at the transmitting station.

  The channel quality 211 measured at the receiving station is most preferably the same as the channel quality 111 measured at the transmitting station indicated by the dotted line in the figure. They do not always match because of differences in timing and the like. As a result, in the adaptive modulation and coding scheme of the present invention, the modulation scheme 214 determined at the receiving station does not necessarily match the modulation scheme 114 used for transmission at the transmitting station. However, in the present invention, the modulation scheme selection error is chained to the modulation result error of other subcarriers in order to fix the maximum transmission bit number Nc per symbol of each subcarrier regardless of the modulation schemes 214 and 114. In addition, by utilizing the error correction capability of the code, even when different modulation schemes are selected between the transmitting station and the receiving station, the characteristics are not greatly deteriorated. For this reason, if a code having sufficient error correction capability is used, a mechanism for accurately matching the modulation scheme between the transmitting station and the receiving station is not required unlike the conventional technique.

  The demodulator 230 performs demodulation processing according to the modulation scheme used for demodulation for each subcarrier determined by the adaptive demodulation controller 210 to obtain an Nd bit signal, and has a likelihood of 0 corresponding to the difference between the Nc bit and the Nd bit. A signal is added on the assumption that the signal has been received, and a signal of a total of Nc bits is output to decoding section 220 for each subcarrier.

  The decoding unit 220 selects one or a plurality of encoding methods from the list of encoding methods shared with the transmitting station, attempts decoding, and considers that the decoding is successful at the transmitting station. Complete the decoding of the transmission information. For example, the decoding success can be determined by adding an error detection signal such as parity or CRC at the time of transmission, and determining that the decoding has been successful when no error is detected by the determination at the time of decoding.

In the case where the decoding unit 220 sequentially tries decoding by a plurality of encoding methods, for example, the encoding method is estimated from Nd and Nc in the same manner as the method of determining the encoding method at the transmitting station, and the estimated method is It is possible to reduce the amount of calculation by using a method of preferentially trying or a method of preferentially trying the method that succeeded in decoding immediately before.
As a result of the above decoding process, the decoding unit 220 notifies the decoding result and the error detection signal to the upper communication layer as the reception result at the receiving station of the present invention.
FIG. 12 shows the flow of processing at the transmitting station and FIG. 13 shows the flow of processing at the receiving station for the adaptive modulation / coding processing according to the present invention.
In the processing flow of FIG. 12, the transmitting station first determines the maximum transmission bit number Nc per symbol of each subcarrier in processing 600. The process 600 is a process that can be performed for each series of communication units, and is performed at a frequency that is set once at the start of communication.

Next, the transmitting station measures the channel quality in process 601, determines the modulation scheme of each subcarrier in process 602 based on the measurement result, and determines the encoding scheme in process 603. These processes are performed at a frequency that follows the fluctuation speed of the propagation path. If the fluctuation speed of the propagation path is approximately the same as the code length, the frequency is about every code transmission based on the measurement result in the process 601. This is a process that is performed less frequently if the method of the process 602 and the process 603 is determined and if the propagation path variation is gentler than the code length. Next, the transmission station encodes the transmission information for each code in processing 604, modulates the encoded information for each symbol in processing 605, and transmits the signal.
In the processing flow of FIG. 13, the receiving station first determines the maximum transmission bit number Nc per symbol of each subcarrier in processing 610. The process 610 is a process that can be performed for each series of communication units in the same manner as the process 600 in the transmitting station, and is performed at a frequency that is set once at the start of communication, and is processed at the same timing as the process 600 in the transmitting station. Need to do.

  Next, the receiving station measures the channel quality in processing 611, and determines the modulation method used for demodulation of each subcarrier in processing 612 based on the measurement result. These processes are performed with a frequency that follows the fluctuation speed of the propagation path. If the fluctuation speed of the propagation path is approximately the same as the code length, the measurement in process 611 is performed with the same frequency as the code length of the received signal. Based on the result, the system is determined in the process 612, and the process is performed less frequently if the propagation path variation is gentler than the code length. The frequency of this processing is preferably about the same as the processing frequency of processing 601, processing 602, and processing 603 at the transmitting station, but does not necessarily need to match.

  Next, the receiving station demodulates the received signal based on the modulation scheme determined in process 612, estimates the encoding scheme in process 613 each time the demodulation process for the coding length is completed, and performs decoding processing in process 614. . If the receiving station has a plurality of decoding units like the receiving station in FIG. 8, the processing 613 and the processing 614 are performed only once every time the demodulation processing for the code length is completed. On the other hand, if the receiving station such as the receiving station of FIG. 7 is to repeatedly use one decoding unit by switching the method, the decoding is attempted with a candidate method every time the demodulation process for the code length is completed. If unsuccessful, the decryption is tried again using a different method, and if successful, the process is terminated.

In the above, the modulation scheme has been described for 2 ^2m QAM, but the application of the present invention is not limited to 22 ^2m QAM. For example, the signal point arrangement is recursively expanded using a gray code, and the bit to the signal point is Any modulation scheme can be applied, and the same control can be applied to 2 ^m PSK and 2 ^m ASK, where the maximum number of transmission bits per symbol is m bits.
Further, the code and encoding used in the above description does not only refer to encoding by an error correction code such as a simple convolutional code or a Turbo code, but more generally a bit for modulating from information to be communicated. This refers to mapping to a column. For example, processing including signal processing such as addition of error detection codes, interleaving, repetition, and puncturing is collectively referred to as encoding.

Further, in the above description, the number of bits when referred to as the number of bits per symbol or the maximum number of bits per symbol corresponds to the number of bits of the encoded code word, and in order to correspond to the number of transmitted information bits Need to be multiplied by the coding rate.
In the above description, a case has been described in which information is divided into a plurality of subcarriers using IFFT and FFT operations in a propagation path having different qualities for each frequency. The present invention is generally applicable to a system that communicates by dividing information into units.

For example, the adaptive modulation unit may be configured as shown in FIG. In adaptive modulation section 430 in FIG. 9, instead of performing IFFT, spreading is performed using a code such as a Walsh code, and in adaptive demodulation section 530, despreading is performed instead of performing FFT, so that a codeword is converted into a plurality of codes. The present invention can be applied in the same manner.
Further, instead of performing IFFT in adaptive modulation section 430, for example, as shown in FIG. 10, signals that are divided and modulated are transmitted from different antennas, and signals received by multiple antennas instead of performing FFT in adaptive demodulation section 530 By performing an interference removal process that separates each of the transmission source antennas, the codeword is divided into a plurality of antennas, and the present invention can be similarly applied.

  Instead of performing IFFT in adaptive modulation section 430, for example, as shown in FIG. 11, instead of performing primary conversion by multiplying a modulated signal by a complex coefficient and then transmitting from a different antenna, adaptive demodulation section 530 performs FFT In addition, the present invention is similarly applied to a codeword divided into a plurality of beam patterns by performing interference removal processing that separates signals received by a plurality of antennas for each signal before the primary conversion of the transmission source. be able to.

  110 Adaptive modulation control unit, 111 Example of channel quality for each subcarrier in the transmitting station, 112,113 Example of threshold for selecting modulation method, 114 Modulation method for each subcarrier, 115,132 Per symbol of the modulation method for each subcarrier Number of bits, 120 encoding unit, 121 information bits before encoding, 122 codeword, 130 adaptive modulation unit, 131,231 maximum number of bits per symbol per subcarrier, 210 adaptive demodulation control unit, 211 sub at receiving station Examples of channel quality for each carrier, 212, 213 Example of threshold for selecting modulation method used for demodulation, 214 Modulation method used for demodulation per subcarrier, 115,232 Bits per symbol of modulation method used for demodulation per subcarrier Number, 220 decoding unit, 221 information bits after decoding, 222 codeword, 230 adaptive demodulation unit, 301 coding rate example, 302,312 range where constant coding rate is selected Example, 311 Transmission power, 400 Transmitting station radio unit, 410 Adaptive modulation control unit, 420 Coding unit, 430 Adaptive modulation unit, 500 Receiving station radio unit, 510 Adaptive demodulation control unit, 520 Decoding unit, 530 Adaptive demodulation Maximum number of bits per 600 symbols determination processing, 601 propagation path quality estimation processing, 602 modulation scheme determination processing, 603 encoding scheme determination processing, 604 encoding processing, 605 modulation processing, 610 maximum number of bits determination processing per symbol, 611 propagation Channel quality estimation processing, 612 demodulation modulation method determination processing, 613 encoding method determination processing, 614 decoding processing, and 615 demodulation processing.

Claims (5)

A transmitting station that transmits transmission information to a receiving station in a wireless communication system,
Send transmission information divided into multiple communication units,
Sharing the information about the first number of bits, which is the maximum number of bits per communication unit, and a list of encoding schemes that can be used to encode transmission information with the receiving station,
Select a coding method from the list of coding methods based on the quality of the propagation path, generate transmission code using the selected coding method to generate a code word,
Notifying the second wireless station of the selected encoding method,
Select a part of the code word of the first number of bits for each communication unit from the code word,
The number of information bits required to select a modulation scheme for each communication unit based on the propagation path condition and create a modulation signal for the communication unit using the selected modulation scheme from a portion of the codeword. 2. A transmission station that extracts information of the number of bits of 2 and creates and transmits a modulated signal. The transmitting station according to claim 1, wherein communication is performed using a different center frequency for each communication unit. 2. The transmission station according to claim 1, wherein communication is performed by spreading using a different spreading code for each communication unit. The wireless communication system according to claim 1, wherein a plurality of antennas are used for transmission, and communication is performed using different antennas for each communication unit. The transmitting station according to claim 1, wherein a plurality of antennas are used for transmission, and communication is performed using different antennas for each result of linear conversion of the codeword divided into the communication units.

Images