JP2010109610A - Adaptive modulation communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adaptive modulation communication device, capable of detecting the time variations in the noise existing in a transmission path and accurately performing channel setting which is suitable for the transmission environment of the transmission path. <P>SOLUTION: The adaptive modulation communication device with an adaptive modulation function of performing communication via the transmission path, through which communication signals using a single carrier or a plurality of subcarriers are transmitted and setting a communication mode, according to the transmission environment includes: a channel-estimating part 17a for repeating the processing of measuring a noise level by a subcarrier for two or more number of times and performing channel estimation processing of selecting a usable communication mode for two or more number of times, on the basis of the respective measured results of the noise level; and a channel setting part 17b for setting the communication mode to be used, on the basis of the results of two or more number of times of estimations by the channel estimating part 17a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an adaptive modulation communication apparatus having an adaptive modulation function for performing communication via a transmission path through which a communication signal using a single carrier or a plurality of subcarriers is transmitted.

  An adaptive modulation communication apparatus having an adaptive modulation function is based on the result of measuring the noise level for each single carrier or subcarrier (hereinafter, single carrier and subcarrier are collectively referred to as a carrier). Select and set the communication mode such as coding rate and carrier to be used. This adaptive modulation is a method of channel setting that adapts (changes) the communication mode in accordance with changes in the transmission environment, and is used for multicarrier communication using a plurality of subcarriers and single carrier communication using one carrier. It is done.

  For example, in recent years, with the increase in speed of digital communication, orthogonal frequency multiplexing (OFDM), which is multicarrier communication, is used as the communication method. This OFDM scheme allocates data to a plurality of subcarriers and performs highly efficient transmission. As the data to be allocated to the subcarrier, so-called multi-level modulated data in which 1/0 bits are mapped to multi-level symbols is used, which is referred to as a modulation scheme (hereinafter referred to as a primary modulation scheme. The degree of multilevel varies depending on the next modulation method.

  And by increasing the number of subcarriers used for multicarrier communication and using a primary modulation method with high data multilevel, the communication speed becomes faster (the transmission efficiency becomes higher), but the bit error rate (Bit Error Rate) : BER) also increases.

Therefore, in order to perform the most efficient communication for each transmission path, the noise level of each subcarrier is measured, and the subcarrier used for multicarrier communication and the primary modulation method (multilevel) are set based on the measurement result. Channel estimation is performed (for example, see Patent Document 1).
JP 2006-319900 A

  In the conventional adaptive modulation communication apparatus, the process of measuring the noise level of the subcarrier is performed only once before or during communication, and channel estimation is performed based on the measurement result of this one time. For example, as shown in FIG. 13, in a multicarrier communication apparatus that performs communication using subcarriers C1 to C6 having different frequencies, when the noise G of the transmission path increases at the frequencies of subcarriers C5 and C6, Carriers C5 and C6 are not used for communication, and communication is performed using subcarriers C1 to C4.

  However, when the noise in the transmission path varies with time, the noise measurement result varies depending on the timing at which the noise level of each subcarrier is measured. For example, as shown in FIG. 14, when the noise level is measured at the timing t1 at which the noise G is minimized, the number of subcarriers used for communication increases, and the primary modulation scheme is also set to a scheme with a high multilevel. Is done. On the other hand, when the noise level is measured at the timing t2 at which the noise G is maximized, the number of subcarriers used for communication is reduced, and the primary modulation scheme is set to a scheme with a low multilevel.

  Therefore, when channel estimation is performed based on the result of measuring the noise level at the timing t1 at which the noise G is minimized, there is a possibility that a communication error may occur if the noise G increases due to time variation.

  In addition, there is a method in which the process of measuring the noise level of each subcarrier is performed a plurality of times before or during communication, and channel estimation is performed based on the average value (average value of noise levels) of the measurement results of the plurality of times. In order to perform channel estimation based on the average value of the noise level, the number of times of channel estimation is only one, and the estimation accuracy with respect to the temporal variation of noise is not good.

  The present invention has been made in view of the above-described reasons, and an object of the present invention is to detect a time variation of noise existing in a transmission line and accurately perform channel setting suitable for the transmission environment of the transmission line. An object is to provide an adaptive modulation communication apparatus.

  According to the first aspect of the present invention, an adaptive modulation having an adaptive modulation function for performing communication via a transmission path through which a communication signal using a single carrier or a plurality of subcarriers is transmitted and setting a communication mode according to the transmission environment. A channel estimation unit that repeats a process of measuring a noise level for each carrier a plurality of times and performs a channel estimation process for selecting a usable communication mode a plurality of times based on each measurement result of the noise level, and a channel Channel setting means for setting a communication mode to be used based on a plurality of estimation results by the estimation means.

  According to the present invention, it is possible to detect a time variation of noise existing in a transmission line and to perform channel setting suitable for the transmission environment of the transmission line with high accuracy.

  The invention of claim 2 is characterized in that, in claim 1, the channel estimation means varies the interval of each measurement process when the process of measuring the noise level for each carrier is repeated a plurality of times.

  According to the present invention, it is possible to detect a change in the transmission environment even when the noise on the transmission line fluctuates at a constant period.

  The invention of claim 3 is characterized in that, in claim 2, the channel estimation means randomly varies the interval of each measurement process when the process of measuring the noise level for each carrier is repeated a plurality of times.

  According to the present invention, it is possible to detect a temporal variation in noise of a transmission line at random timing.

  The invention of claim 4 is characterized in that, in claim 2, the channel estimation means regularly changes the interval of each measurement process when the process of measuring the noise level for each carrier is repeated a plurality of times. .

  According to the present invention, the circuit configuration for changing the measurement interval can be simplified as compared with the case where the measurement interval is changed randomly.

  The invention of claim 5 is characterized in that, in claim 4, the channel estimation means shortens the measurement interval as the number of measurements increases when the process of measuring the noise level for each carrier is repeated a plurality of times. .

  According to the present invention, it is possible to detect a change in the transmission environment even when the noise on the transmission line fluctuates at a constant period.

  The invention of claim 6 is characterized in that, in claim 4, the channel estimation means lengthens the measurement interval as the number of measurements increases when the process of measuring the noise level for each carrier is repeated a plurality of times. .

  According to the present invention, it is possible to detect a change in the transmission environment even when the noise on the transmission line fluctuates at a constant period.

  According to a seventh aspect of the present invention, in the fourth aspect, the channel estimation means sequentially selects a plurality of measurement interval patterns having different measurement intervals when repeating the process of measuring the noise level for each carrier a plurality of times, The measurement interval is varied based on the selected measurement interval pattern.

  According to the present invention, it is possible to detect a change in the transmission environment even when the noise on the transmission line fluctuates at a constant period.

  The invention of claim 8 is characterized in that, in claim 1, the channel estimation means changes a method of repeating a process of measuring a noise level for each carrier a plurality of times based on a history of estimation results.

  According to this invention, it is possible to achieve both improvement in transmission efficiency and improvement in estimation accuracy in accordance with changes in the transmission environment of the transmission path.

  The invention of claim 9 provides the channel estimation means according to claim 8, wherein when the same estimation result continues for a predetermined number of times, the channel estimation means sets the number of measurements when the next process of measuring the noise level for each carrier is repeated a plurality of times. It is characterized by decreasing.

  According to the present invention, if the transmission environment of the transmission path does not change, the number of estimations can be reduced and the transmission efficiency can be improved.

  A tenth aspect of the invention is characterized in that, in the ninth aspect, the channel estimation means reduces the number of measurements to one.

  According to the present invention, if the transmission environment of the transmission path does not change, a configuration for reducing the number of estimations and improving the transmission efficiency can be realized with a relatively simple algorithm.

  The invention of claim 11 is characterized in that, in claim 9, the channel estimation means gradually decreases the number of measurements.

  According to this invention, it is possible to suppress a significant deterioration in estimation accuracy while reducing the number of estimations based on the history of estimation results.

  A twelfth aspect of the invention is characterized in that, in any of the ninth to eleventh aspects, the channel estimation means increases the number of measurements when a communication error occurs after reducing the number of measurements.

  According to this invention, it is possible to suppress a decrease in estimation accuracy.

  According to a thirteenth aspect of the present invention, in the eighth aspect, the channel estimation unit sets a measurement interval when the same estimation result continues for a predetermined number of times or more and then repeats the process of measuring the noise level for each carrier a plurality of times. It is characterized by shortening.

  According to the present invention, if the transmission environment of the transmission path does not change, the estimation interval can be shortened to improve the transmission efficiency.

  The invention of claim 14 is characterized in that, in claim 8, the channel estimation means increases the number of measurements when a communication error occurs.

  According to this invention, it is possible to suppress a decrease in estimation accuracy.

  The invention of claim 15 is characterized in that, in claim 8, the channel estimation means varies the measurement interval when a communication error occurs.

  According to this invention, it is possible to suppress a decrease in estimation accuracy.

  According to a sixteenth aspect of the present invention, in the eighth aspect, the channel estimation means prepares a plurality of types of methods for repeating the process of measuring the noise level for each carrier a plurality of times, and determines the noise level for each carrier using each measurement method. After the measurement, a method having the highest noise level detection accuracy is used.

  According to this invention, it is possible to improve the estimation accuracy.

  A seventeenth aspect of the present invention provides the multicarrier communication using a plurality of subcarriers according to any one of the first to sixteenth aspects, wherein the channel setting means communicates most of a plurality of estimation results by the channel estimation means. A low-speed estimation result is set to a communication mode used for multicarrier communication.

  According to the present invention, it is possible to perform channel setting that enables communication even when the amplitude of noise is large with respect to noise fluctuation in the transmission path.

  According to an eighteenth aspect of the present invention, in the seventeenth aspect, the channel estimation means performs a channel estimation process for selecting at least a subcarrier usable for multicarrier communication a plurality of times based on each measurement result of noise level, and the channel The setting means sets subcarriers to be used for multicarrier communication based on a plurality of estimation results by the channel estimation means, and when there are a plurality of estimation results with the slowest communication speed among the plurality of estimation results, Only subcarriers common to all estimation results with low communication speeds are selected as settings used for multicarrier communication.

  According to the present invention, it is possible to perform channel setting that enables communication even when the amplitude of noise is large with respect to noise fluctuation of the transmission path, and channel setting that enables communication even when the noise frequency varies. It can be carried out.

  A nineteenth aspect of the present invention provides the multicarrier communication using a plurality of subcarriers according to any one of the first to sixteenth aspects, wherein the channel estimation means selects a subcarrier and a modulation scheme that can be used for the multicarrier communication. Channel estimation processing is performed a plurality of times based on each measurement result of the noise level, and the channel setting means sets subcarriers and modulation schemes used for multicarrier communication based on the estimation results obtained a plurality of times by the channel estimation means. Of the multiple estimation results by the channel estimation means, only the subcarriers that are common in all estimation results using the modulation scheme with the smallest multilevel value are selected as settings for use in multicarrier communication.

  According to the present invention, it is possible to perform channel setting that allows communication even when the noise frequency fluctuates with respect to noise fluctuation in the transmission path.

  According to a twentieth aspect of the present invention, in any one of the first to sixteenth aspects, multicarrier communication using a plurality of subcarriers is performed, and the channel estimation means selects subcarriers and modulation schemes usable for multicarrier communication. The channel estimation process is performed a plurality of times based on each measurement result of the noise level, and the channel setting means is independent of subcarriers and modulation schemes used for multicarrier communication based on the estimation results obtained a plurality of times by the channel estimation means. It is characterized by setting.

  According to the present invention, it is effective when it is desired to reduce the occurrence of communication errors with respect to noise fluctuations in the transmission path.

  A twenty-first aspect of the present invention provides the multi-carrier communication using a plurality of subcarriers according to any one of the first to sixteenth aspects, wherein the channel setting means is a communication speed among a plurality of estimation results by the channel estimation means. Is not selected as a setting used for multicarrier communication.

  According to the present invention, it is effective when it is desired to prioritize the communication speed with respect to noise fluctuations in the transmission path.

  As described above, according to the present invention, there is an effect that it is possible to detect a time variation of noise existing in a transmission path and to perform channel setting suitable for the transmission environment of the transmission path with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment)
In this embodiment, an adaptive modulation communication apparatus that performs multicarrier communication will be described. FIG. 1 is a block diagram showing a configuration of a multicarrier communication apparatus 100 according to an embodiment of the present invention, and includes a reception apparatus 1 and a transmission apparatus 2.

  In FIG. 1, a receiving apparatus 1 includes an A / D converter 11, a multicarrier demodulator 12 for performing a desired time-frequency conversion, such as a Fourier transformer (FFT) or a wavelet transformer (DWT), and a transmission. An equalizer 13 that corrects the received signal so as to cancel the influence of the path, a P / S converter 14 that converts parallel data into serial data, and converts the mapped symbol data into bit data that is a received signal. A demapper 15, an error correction decoder 16 that performs error correction decoding on bit data, and a transmission path estimator 17 that determines usable subcarriers from the noise level of the received signal and the primary modulation scheme used in each subcarrier. With.

  The transmission apparatus 2 includes an error correction encoder 21 that performs error correction coding on bit data that is a transmission signal, a symbol mapper 22 that converts the bit data subjected to error correction coding into symbol data, and performs symbol mapping, and An S / P converter 23 for converting serial data into parallel data, a multicarrier modulator 24 for performing desired frequency-time conversion, such as an inverse Fourier transformer (IFFT) and an inverse wavelet transformer (IWFT), and D / A converter 25.

  The operation of the communication apparatus 100 will be described below.

  First, in the transmission apparatus 2, after error correction coding is performed on bit data (transmission data) transmitted by the error correction encoder 21, the transmission data is converted into symbol data by a symbol mapper 22, and complex coordinates are converted according to each symbol data. Symbol mapping (PAM, QAM, etc. modulation) is performed on the surface. The S / P converter 23 gives a real value for each subcarrier, and the multicarrier modulator 24 converts it into a discrete multicarrier signal. As a result, sample values of the time axis waveform are generated, and a sample value series representing a transmission symbol is generated. Next, after serial conversion by a P / S converter (not shown), a D / A converter 25 generates a complex baseband OFDM signal having a temporally continuous analog signal waveform, and then a real part of the complex baseband OFDM signal. Is multiplied by a carrier wave to generate a carrier band OFDM signal and transmit it to the transmission path.

  In the receiving apparatus 1, after down-converting an analog signal (received signal) received via a transmission line such as a communication line or a power line, the A / D converter 11 samples the signal at the same sample rate as the transmitting apparatus 2 and performs complex processing. The signal is converted into a baseband OFDM signal and converted into a parallel sample value series by an S / P converter (not shown). Then, this sample value series is input to the multicarrier demodulator 12 and subjected to discrete multicarrier conversion on the frequency axis while being synchronized with the received signal by a synchronization circuit (not shown). The amount of equalization is obtained by comparison and equalized. Thereafter, the signal is converted into a serial signal by the P / S converter 14, and the demapper 15 performs processing (demodulation) reverse to that of the symbol mapper, and then the error correction decoder 16 performs error correction decoding to obtain received data.

  Here, in the multicarrier communication of the present embodiment, as shown in FIG. 2, the transmission path estimator 17 performs channel estimation N times (N ≧ 2) before communication between communication devices, and this 1 to N times of channel estimation is performed. A channel suitable for the transmission environment of the transmission path by detecting the time fluctuation of noise existing in the transmission path by setting the subcarrier and primary modulation method (multilevel) used for multicarrier communication based on the estimation result Setting can be performed with high accuracy.

  The transmission path estimator 17 includes a channel estimation section 17a (channel estimation means) and a channel setting section 17b (channel setting means). The operation of the transmission path estimator 17 will be described below.

  First, in multicarrier communication, the higher the S / N ratio (hereinafter referred to as SNR) of each subcarrier, the lower the bit error rate (hereinafter referred to as BER) (that is, the lower the noise level, the better communication). However, subcarriers having an SNR equal to or lower than a preset threshold value are determined to be in a poor transmission path state and are not used. Therefore, the channel estimation unit 17a measures SNR as the noise level of each subcarrier based on the output of the P / S converter 14, and only subcarriers whose SNR exceeds the threshold can be used for multicarrier communication. Select as.

  Furthermore, the channel estimation unit 17a selects a primary modulation scheme (multilevel) that can be used for multicarrier communication based on the SNRs of all subcarriers. In this embodiment, either 16QAM or 64QAM is used as the primary modulation scheme, and if it is determined that the transmission path state is good based on the SNRs of all subcarriers, 64QAM is selected as the usable primary modulation scheme. If it is determined that the transmission path condition is poor based on the SNRs of all subcarriers, 16QAM is selected as the usable primary modulation scheme. Whether the transmission path state is good or bad is determined by comparing the average value of SNRs of all subcarriers and the maximum and minimum values of SNR with a threshold value.

  That is, channel estimation refers to selecting a subcarrier and a primary modulation scheme that can be used for multicarrier communication based on the measurement result every time the SNR of all subcarriers is measured.

  Then, the channel estimation unit 17a performs selection (channel estimation) of subcarriers and primary modulation schemes that can be used for multicarrier communication N times (N ≧ 2) before communication between communication apparatuses, as shown in FIG. Each estimation content in the first to N estimation times is delivered to the channel setting unit 17b. In this estimation content, the usable primary modulation scheme is selectively set from “16QAM” and “64QAM”, and “1” corresponding to a usable subcarrier (subcarrier number), an unusable subcarrier. “0” is set corresponding to the carrier.

  The channel setting unit 17b sets subcarriers and primary modulation schemes used for multicarrier communication based on 1 to N estimation results performed by the channel estimation unit 17a, and the transmission apparatus 2 uses the channel setting unit 17b. The multicarrier signal is transmitted using the subcarrier and the primary modulation scheme set by.

There are various channel estimation methods of the channel estimation unit 17a, and each channel estimation method will be described below. First, as shown in FIG. 4A, when the SNRs of all subcarriers are measured N times, the SNR measurement intervals T _{1 to} T _N-1 are set to the same interval (T ₁ = T ₂ =. = T _N-1 ), there is a method of performing N channel estimations at the same interval. However, if the channel estimation is performed N times at the same interval, and the noise (transmission environment) of the transmission path fluctuates at a constant period, the channel estimation timing is synchronized with the fluctuation period of the noise and the fluctuation of the transmission environment is There is a possibility that it cannot be detected.

Therefore, when the SNRs of all subcarriers are measured N times, by changing the intervals T _{1 to} T _N-1 of the SNR measurement as shown in FIGS. Even when the frequency fluctuates at a constant period, it is possible to detect a change in the transmission environment. First, in the method of FIG. 4B, when the SNRs of all subcarriers are measured N times, the intervals T _{1 to} T _N-1 of the SNR measurement are randomly varied. Perform at random intervals. This method has an advantage that it is possible to detect temporal fluctuations of transmission path noise at random timing.

Further, the method of FIG. 4 (c) ~ (e) is the SNR of all the subcarriers when measuring N times, which vary each interval _T 1 _{through T N-1} of the SNR measurement regularly There is an advantage that the circuit configuration for changing the measurement interval in the channel estimation unit 17a can be simplified as compared with the case where the measurement interval is changed randomly.

First, in the method of FIG. 4C, the intervals T _{1 to} T _N-1 of the SNR measurement are gradually shortened (T ₁ > T ₂ >...> T _N-1 ), and FIG. In this method, the intervals T _{1 to} T _N-1 of the SNR measurement are gradually increased (T ₁ <T ₂ <... <T _N-1 ), and the N channel estimation intervals are set once. It is fluctuated regularly. Further, in the method of FIG. 4 (e), each of the SNR measurement intervals T _{1 to} T _N-1 is constituted by three patterns of measurement patterns Pa to Pc, and in the measurement pattern Pa, the SNR measurement interval is set to be constant Ta. In the pattern Pb, the SNR measurement interval is constant Tb, and in the measurement pattern Pc, the SNR measurement interval is constant Tc (Ta>Tb> Tc), and the measurement pattern Pa → Pb → Pc is changed every predetermined time. The channel estimation interval is regularly changed for each pattern. Thus, by regularly changing the intervals T _{1 to} T _N-1 of the SNR measurement, there is an advantage that even if the noise of the transmission path fluctuates at a constant period, a change in the transmission environment can be detected. .

  Next, a configuration in which the channel estimation unit 17a changes the estimation method based on the estimation result history will be described. First, as shown in FIG. 5 (a), the channel estimation unit 17a first performs channel estimation by setting the number of SNR measurements to N times, and performs 1 to N estimation results (usable primary modulations) in this channel estimation process. If the results are all the same for both the system and the usable subcarriers, in the next channel estimation process, as shown in FIG. Therefore, if the transmission environment of the transmission path does not change, the number of estimations is reduced, so that transmission efficiency can be improved. Thereafter, the channel estimation unit 17a continues the channel estimation process by setting the number of estimations to 1, but when a communication error occurs, the number of SNR measurements is again increased to N times as shown in FIG. Reduces estimation accuracy. In this way, the process of switching the number of estimations to either N times or once based on the history of estimation results can be realized by a relatively simple algorithm in the channel estimation unit 17a, but the number of estimations is changed to one. After that, the estimation accuracy is significantly reduced.

  Therefore, as shown in FIG. 6 (a), the channel estimation unit 17a initially performs channel estimation by setting the number of SNR measurements to N, and the estimation results (usable primarys) in this channel estimation process. If the results are the same for both the modulation scheme and the usable subcarriers), in the next channel estimation process, the number of SNR measurements is set to N-1, and the number of estimations is decreased by one. Thereafter, every time the estimation results coincide with each other in the total number of estimations, the number of SNR measurements is decreased by one (minimum number of measurements = 1) as shown in FIG. 6B, and every time a communication error occurs, FIG. As shown in (c), the number of SNR measurements is increased by one (maximum number of measurements = N). Therefore, while reducing the number of estimations based on the history of estimation results, it is possible to suppress a significant deterioration in estimation accuracy, and to increase the number of estimations when a communication error occurs, so it is possible to suppress a decrease in estimation accuracy. Note that n in FIG. 6 is the number of times that the estimation results match in the total number of estimations, m in FIG. 6 indicates the number of times that the SNR measurement has failed and an error has occurred in the estimation process, and N−n + m is Current estimated number of times.

  In the above estimation method, the channel estimation unit 17a changes the number of estimations based on the estimation result history. However, a method of changing the estimation interval based on the estimation result history may be used. In this case, as shown in FIG. 7A, the channel estimation unit 17a initially performs N channel estimations with N SNR measurement times, and 1 to N estimation results (in this channel estimation process) If all of the usable primary modulation schemes and usable subcarriers are the same, in the next channel estimation process, the SNR measurement interval Td is shortened. Thereafter, every time the estimation results coincide with each other in the total number of estimations, the SNR measurement interval Td is further shortened as shown in FIG. 7B, and whenever a communication error occurs, as shown in FIG. 7C. The SNR measurement interval Td is gradually increased. Therefore, if the transmission environment of the transmission path does not change, the estimation interval is shortened, so that transmission efficiency can be improved. Furthermore, since the estimation interval is lengthened when a communication error occurs, a decrease in estimation accuracy can be suppressed.

The channel estimation unit 17a may execute a plurality of channel estimation methods different from each other, and may perform channel estimation processing by adopting a method with the highest noise detection accuracy among the executed channel estimation methods. For example, as shown in FIG. 4C, a method of gradually shortening the intervals T _{1 to} T _N-1 of the SNR measurement (T ₁ > T ₂ >...> T _N-1 ) and FIG. As shown in e), each of the intervals T _{1 to} T _N-1 of the SNR measurement is composed of three patterns of measurement patterns Pa to Pc, and the measurement pattern Pa → Pb → Pc is changed in order in a predetermined time. Two types of methods are executed in advance before communication between communication devices, and a method with higher noise detection accuracy is employed.

  Then, the channel estimation unit 17a uses the channel estimation method alone or a combination of a plurality of the channel estimation methods in consideration of estimation accuracy, transmission efficiency, simplification of algorithm, simplification of circuit configuration, and the like.

  Next, the operation of the channel setting unit 17b will be described. First, the channel setting unit 17b sets the estimation result with the slowest communication speed among N estimation results in the channel estimation unit 17a to the subcarrier and primary modulation scheme used for multicarrier communication. The communication speed is determined by the multilevel value of the primary modulation method and the number of subcarriers to be used. The higher the multilevel value of the primary modulation method and the more subcarriers to be used, the faster the communication speed. Become. For example, as shown in FIG. 8, assuming that the number of estimations is N = 3, the first estimation result [primary modulation scheme “64QAM”, subcarrier availability “11100”], the second estimation result [primary modulation scheme “16QAM” In the case of the third estimation result [primary modulation scheme “16QAM”, subcarrier availability “11110”], the communication speed is the slowest in the primary modulation scheme of 16QAM. This is the third estimation result used for the four subcarriers, and the channel setting unit 17b sets the third estimation result to the subcarrier and primary modulation scheme used for multicarrier communication. This method has an advantage that communication can be performed even when the amplitude of noise is large with respect to noise fluctuations in the transmission path.

  Also, as shown in FIG. 9 (a), the number of estimations N = 3, the first estimation result [primary modulation scheme “64QAM”, subcarrier availability “11000”], the second estimation result [primary modulation In the case of scheme “16QAM”, subcarrier availability “11101”] and third estimation result [primary modulation scheme “16QAM”, subcarrier availability “11110”], the communication speed is the slowest in 16QAM. It is each estimation result of the 2nd time and the 3rd time which use a primary modulation system for four subcarriers. As described above, when the second and third estimation results are the slowest communication speeds, the channel setting unit 17b determines whether the second and third estimation results are as shown in FIG. 9B. Also select the subcarrier to be used. That is, the channel setting unit 17b sets “11100” as the subcarrier used for multicarrier communication, and sets “16QAM” as the primary modulation scheme. In this method, it is possible to set a channel capable of communication even when the amplitude of the noise is large, and to set a channel capable of communication even when the noise frequency fluctuates with respect to noise fluctuation of the transmission path. There is an advantage that can be.

  In addition, the channel setting unit 17b extracts one or a plurality of estimation results in which the primary modulation scheme having the smallest multi-level is selected from the N estimation results in the channel estimation unit 17a, and the extracted one to a plurality of estimation results A subcarrier to be used may be selected in any of the estimation results. For example, as shown in FIG. 10A, assuming that the number of estimations is N = 3, the first estimation result [primary modulation scheme “64QAM”, subcarrier availability “10000”], and the second estimation result [primary modulation scheme] In the case of “16QAM”, subcarrier availability “11001”] and the third estimation result [primary modulation scheme “16QAM”, subcarrier availability “11110”], the primary modulation scheme with the smallest multi-level is “ 16QAM ”, the channel setting unit 17b extracts the second and third estimation results and, as shown in FIG. 10 (b), further uses the second and third subcarriers. Select. That is, the channel setting unit 17b sets “11000” as the subcarrier used for multicarrier communication, and sets “16QAM” as the primary modulation scheme. In this method, it is possible to set a communicable channel even when the noise frequency fluctuates with respect to noise fluctuations in the transmission path, which is more effective than the methods shown in FIGS. 9 (a) and 9 (b). There is an advantage.

  Further, the channel setting unit 17b may set the primary modulation scheme and the subcarrier to be used independently of each other based on the N estimation results in the channel estimation unit 17a. For example, as shown in FIG. 11A, assuming that the number of estimations is N = 3, the first estimation result [primary modulation scheme “64QAM”, subcarrier availability “11100”], the second estimation result [primary modulation scheme In the case of “16QAM”, subcarrier availability “11110”] and the third estimation result [primary modulation scheme “16QAM”, subcarrier availability “11110”], the primary modulation scheme with the smallest multi-level is: In the second and third “16QAM”, since the number of usable subcarriers is the smallest “11100”, the channel setting unit 17b is shown in FIG. As shown, “11100” is set as the subcarrier used for multicarrier communication, and “16QAM” is set as the primary modulation scheme. This method has an advantage that it is effective when it is desired to reduce the occurrence of communication errors against noise fluctuations in the transmission path.

  The channel setting unit 17b does not use a measurement result whose communication speed is equal to or lower than a preset threshold among the N estimation results in the channel estimation unit 17a, and a measurement result where the communication speed exceeds a preset threshold. You may use only. For example, as shown in FIG. 12 (a), assuming that the number of estimations is N = 3, the first estimation result [primary modulation scheme “64QAM”, subcarrier availability “11100”], the second estimation result [primary modulation scheme In the case of “16QAM”, subcarrier availability “11110”] and the third estimation result [primary modulation scheme “16QAM”, subcarrier availability “11100”], the third communication speed is equal to or less than the threshold. To do. Thus, the channel setting unit 17b uses the second estimation result with the slowest communication speed among the first and second estimation results when the communication speed exceeds the preset threshold. That is, the channel setting unit 17b sets “11100” as the subcarrier used for multicarrier communication and “16QAM” as the primary modulation scheme, as shown in FIG. This method has an advantage that it is effective when priority is given to the communication speed with respect to noise fluctuations in the transmission path.

  As described above, in the present embodiment, N times (N ≧ 2) channel estimation is performed before communication between communication apparatuses, and subcarriers and primary modulation used for multicarrier communication are performed based on the estimation results of 1 to N times. By setting the communication mode (including the multi-level) (including the error correction coding rate if necessary), it detects the temporal fluctuations of noise existing in the transmission line, and the transmission environment of the transmission line Can be set with high accuracy. Therefore, even when the transmission environment fluctuates in a worsening direction, good multicarrier communication can be performed.

  In this embodiment, subcarriers and primary modulation schemes (multilevel) used for multicarrier communication are estimated and set. However, subcarriers used for multicarrier communication, primary modulation schemes, and error correction coding rates. Any one or more of these may be estimated and set as the communication mode.

  Further, also in the adaptive modulation communication apparatus that performs single carrier communication, channel estimation is performed N times (N ≧ 2) before communication between the communication apparatuses as in the present embodiment, and each estimation result of 1 to N times is obtained. Based on the communication mode such as carrier used for single carrier communication, modulation method used, coding rate for error correction, etc., it detects the time fluctuation of noise existing in the transmission line and makes it suitable for the transmission environment of the transmission line. Appropriate channel setting can be performed with high accuracy. Therefore, even when the transmission environment fluctuates in a worsening direction, good single carrier communication can be performed.

It is a figure which shows the block configuration of embodiment. It is a figure which shows the outline of a channel estimation timing same as the above. It is a figure which shows a channel estimation result same as the above. (A)-(e) It is a figure which shows each example of the channel estimation timing same as the above. (A) (b) It is a figure which shows the example of a fluctuation | variation of the frequency | count of the channel estimation timing same as the above. (A)-(c) It is a figure which shows the example of a fluctuation | variation of the frequency | count of the channel estimation timing same as the above. (A)-(c) It is a figure which shows the example of a fluctuation | variation of the space | interval of the channel estimation timing same as the above. It is a figure which shows the example of a channel setting same as the above. (A) (b) It is a figure which shows the example of a channel setting same as the above. (A) (b) It is a figure which shows the example of a channel setting same as the above. (A) (b) It is a figure which shows the example of a channel setting same as the above. (A) (b) It is a figure which shows the example of a channel setting same as the above. It is a figure which shows the example of the conventional carrier setting. It is a figure which shows the outline of the conventional channel estimation timing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reception apparatus 11 A / D converter 12 Multicarrier demodulator 13 Equalizer 14 P / S converter 15 Demapper 16 Error correction decoder 17 Transmission path estimator 17a Channel estimation part 17b Channel setting part 2 Transmission apparatus

Claims (21)

An adaptive modulation communication apparatus having an adaptive modulation function of performing communication via a transmission path through which a communication signal using a single carrier or a plurality of subcarriers is transmitted and setting a communication mode according to a transmission environment,
Channel estimation means for repeating the process of measuring the noise level for each carrier a plurality of times and performing channel estimation processing for selecting a usable communication mode a plurality of times based on each measurement result of the noise level;
Channel setting means for setting a communication mode to be used, based on a plurality of estimation results by the channel estimation means;
An adaptive modulation communication apparatus comprising:   The adaptive modulation communication apparatus according to claim 1, wherein the channel estimation unit varies the interval of each measurement process when the process of measuring the noise level for each carrier is repeated a plurality of times.   3. The adaptive modulation communication apparatus according to claim 2, wherein the channel estimation unit randomly varies the interval of each measurement process when the process of measuring the noise level for each carrier is repeated a plurality of times.   3. The adaptive modulation communication apparatus according to claim 2, wherein the channel estimation unit regularly varies the interval of each measurement process when the process of measuring the noise level for each carrier is repeated a plurality of times.   The adaptive modulation communication apparatus according to claim 4, wherein the channel estimation means shortens the measurement interval as the number of measurements increases when the process of measuring the noise level for each carrier is repeated a plurality of times.   5. The adaptive modulation communication apparatus according to claim 4, wherein the channel estimation means lengthens the measurement interval as the number of measurements increases when the process of measuring the noise level for each carrier is repeated a plurality of times.   The channel estimation means sequentially selects a plurality of measurement interval patterns having different measurement intervals when repeating the process of measuring the noise level for each carrier a plurality of times, and varies the measurement intervals based on the selected measurement interval patterns. The adaptive modulation communication apparatus according to claim 4, wherein:   2. The adaptive modulation communication apparatus according to claim 1, wherein the channel estimation unit changes a method of repeating a process of measuring a noise level for each carrier a plurality of times based on a history of estimation results.   9. The channel estimation unit according to claim 8, wherein when the same estimation result continues for a predetermined number of times or more, the channel estimation unit reduces the number of measurement when the process of measuring the noise level for each carrier is repeated a plurality of times. Adaptive modulation communication device.   The adaptive modulation communication apparatus according to claim 9, wherein the channel estimation unit reduces the number of measurements to one.   The adaptive modulation communication apparatus according to claim 9, wherein the channel estimation unit gradually decreases the number of measurements.   The adaptive modulation communication apparatus according to claim 9, wherein the channel estimation unit increases the number of measurements when a communication error occurs after reducing the number of measurements.   The said channel estimation means shortens a measurement space | interval when repeating the process which measures the noise level for every next carrier several times, when the same estimation result continues more than predetermined times. Adaptive modulation communication device.   9. The adaptive modulation communication apparatus according to claim 8, wherein the channel estimation means increases the number of measurements when a communication error occurs.   9. The adaptive modulation communication apparatus according to claim 8, wherein the channel estimation unit varies the measurement interval when a communication error occurs.   The channel estimation means prepares a plurality of methods for repeating the process of measuring the noise level for each carrier a plurality of times, and after measuring the noise level for each carrier using each measurement method, the highest noise level detection accuracy is obtained. 9. The adaptive modulation communication apparatus according to claim 8, wherein the method is used.   Multi-carrier communication using a plurality of subcarriers is performed, and the channel setting unit sets the estimation result with the slowest communication speed among the estimation results obtained by the channel estimation unit to the communication mode used for multi-carrier communication. The adaptive modulation communication apparatus according to any one of claims 1 to 16.   The channel estimation means performs a channel estimation process for selecting at least a subcarrier usable for multicarrier communication based on each measurement result of noise level, and the channel setting means performs a plurality of times by the channel estimation means. Based on the estimation results, subcarriers used for multicarrier communication are set, and if there are multiple estimation results with the slowest communication speed among multiple estimation results, the subcarriers common to all the estimation results with the slowest communication speed 18. The adaptive modulation communication apparatus according to claim 17, wherein only a carrier is selected as a setting used for multicarrier communication.   Multi-carrier communication using a plurality of subcarriers is performed, and the channel estimation means performs channel estimation processing for selecting subcarriers and modulation schemes usable for multicarrier communication a plurality of times based on each measurement result of noise level. The channel setting means sets subcarriers and modulation schemes used for multicarrier communication based on a plurality of estimation results by the channel estimation means, and among the plurality of estimation results by the channel estimation means, The adaptive modulation communication apparatus according to any one of claims 1 to 16, wherein only a subcarrier common to all estimation results using the modulation scheme with the smallest is selected as a setting used for multicarrier communication.   Multi-carrier communication using a plurality of subcarriers is performed, and the channel estimation means performs channel estimation processing for selecting subcarriers and modulation schemes usable for multicarrier communication a plurality of times based on each measurement result of noise level. The channel setting means sets a subcarrier and a modulation scheme used for multicarrier communication independently from each other based on a plurality of estimation results by the channel estimation means. The adaptive modulation communication device described.   The multi-carrier communication using a plurality of subcarriers is performed, and the channel setting unit is configured to use an estimation result having a communication speed equal to or lower than a predetermined threshold among multi-time estimation results by the channel estimation unit as a setting used for multi-carrier communication The adaptive modulation communication apparatus according to claim 1, wherein the adaptive modulation communication apparatus is not selected.

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