JP2010035060A - Channel prediction system, wireless communication apparatus and channel prediction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a channel prediction system with a further improved channel prediction accuracy while reducing an increase of processing load for obtaining predicted channel information when performing channel prediction in a wireless communication system using the OFDM method. <P>SOLUTION: A channel prediction system 100 includes an estimated channel information correction part 103. The estimated channel information correction part 103 performs reduction processing for reducing the number of pieces of estimated channel information to be used for channel estimation by thinning out the estimated channel information calculated by a channel estimation part 102 at a given time interval, and corrects the estimated channel information after reduction processing according to a time difference between a setup position of an FFT window and a reference position of the setup position. A channel prediction part 104 uses the estimated channel information corrected by the estimated channel information correction part 103 to perform channel prediction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a channel prediction system, a wireless communication apparatus, and a channel prediction method used in a wireless communication system employing an orthogonal frequency division scheme.

  In a wireless communication system that employs an orthogonal frequency division (OFDM) scheme, the receiving side performs a fast Fourier transform (FFT) on a radio signal received from the transmitting side to generate a frequency domain signal (hereinafter, “frequency domain signal”). Convert. At that time, the receiving side establishes synchronization based on the received radio signal, and sets a time window (FFT window) for extracting a signal section (effective symbol section) to be subjected to FFT according to the result of establishing the synchronization. To do.

  In addition, the state (amplitude, phase, etc.) of the radio signal transmitted and received in the radio communication system changes according to the characteristics of the radio propagation path (hereinafter, “propagation path characteristic”). In order to realize communication control adapted to such changes in propagation path characteristics (hereinafter referred to as “adaptive communication control”), estimated channel information indicating propagation path characteristics between the transmitting side and the receiving side is periodically updated. The channel estimation calculated in (2) is widely used (see Patent Document 1).

In recent years, the provision of channel prediction, which is a technology developed from channel estimation, has been studied. In channel prediction, predicted channel information that is a predicted value of estimated channel information in the future, specifically, a timing at which the transmission side next transmits a radio signal is calculated using estimated channel information obtained by channel estimation. In the channel prediction, by using the past estimated channel information, it becomes possible to accurately grasp the fluctuation tendency of the propagation path characteristics, and the channel prediction accuracy is further improved.
JP 2004-320677 A

  In a wireless communication system that employs the OFDM scheme, the receiving side calculates estimated channel information from frequency domain signals obtained by FFT. However, when an error occurs between the FFT window and the effective symbol period, phase rotation occurs in the frequency domain signal, and accurate estimated channel information cannot be obtained. For this reason, a method for correcting the estimated channel information according to the setting position of the FFT window has been proposed (eg, [Summary] in Patent Document 1).

  However, when more estimated channel information is used, more estimated channel information is used for channel prediction. Therefore, the processing load for obtaining predicted channel information, specifically, both correction processing and channel prediction There is a problem that the processing load required for the process increases.

  Therefore, the present invention provides a channel prediction system that further improves the channel prediction accuracy while suppressing an increase in processing load for obtaining predicted channel information when performing channel prediction in a wireless communication system employing the OFDM scheme, An object of the present invention is to provide a wireless communication apparatus and a channel prediction method.

  In order to solve the above-described problems, the present invention has the following features. First, the first feature of the present invention is that a transmission side (transmitter 10) that transmits a radio signal (OFDM signal) according to an orthogonal frequency division method, and the radio signal received from the transmission side is converted into a frequency domain signal. A calculation unit (channel estimation unit 102) that calculates estimated channel information indicating propagation path characteristics with the receiving side (receiver 20) to be converted at a predetermined time interval based on the frequency domain signal; and the estimated channel information A channel prediction system (channel prediction system 100) having a prediction unit (channel prediction unit 104) that performs channel prediction to calculate prediction channel information that is a prediction value of the estimated channel information in the future using a plurality of Then, the estimation unit used for the channel prediction is obtained by thinning out the estimated channel information calculated by the calculation unit at the predetermined time interval. A reduction processing unit (estimated channel information correction unit 103) that performs a reduction process for reducing the number of channel information, and a time for extracting a signal section to be converted into the frequency domain signal from the radio signal received by the receiving side A correction unit (estimated channel information correction unit 103) that corrects the estimated channel information after the reduction process according to a time difference between a set position of a window and a reference position of the set position, and the prediction unit includes: The gist is to execute the channel prediction using the estimated channel information corrected by the correction unit.

  According to such a feature, the reduction processing unit executes a reduction process for reducing the number of estimated channel information used for channel prediction. The correction unit corrects the estimated channel information after the reduction process. Then, the prediction unit performs channel prediction using the estimated channel information corrected by the correction unit. Therefore, it is possible to improve channel prediction accuracy while suppressing an increase in processing load for obtaining predicted channel information.

  The reduction processing unit executes the above-described reduction processing by thinning out the estimated channel information calculated at a predetermined time interval by the calculation unit. Therefore, the reduction processing unit is used for channel prediction while using more past estimated channel information. The number of estimated channel information can be reduced. For this reason, it is possible to further improve the channel prediction accuracy while suppressing an increase in processing load for obtaining the prediction channel information.

  A second feature of the present invention relates to the first feature of the present invention, wherein the prediction unit is provided on the reception side, and the correction unit includes a plurality of antennas (transmission antennas T # 1 to T # 1) on the transmission side. When multi-antenna transmission for transmitting the radio signal using T # n) is performed and feedback of a value based on the predicted channel information is performed from the receiving side to the transmitting side, the estimated channel The gist is to correct the information.

  A third feature of the present invention relates to the first feature of the present invention, wherein the prediction unit is provided on the transmission side, and the correction unit is configured to output the radio signal using a plurality of antennas on the transmission side. When multi-antenna transmission is performed and feedback of a value based on the estimated channel information is performed from the receiving side to the transmitting side, the estimated channel information is corrected and corrected by the correcting unit. Further, the gist is that the feedback is executed on the estimated channel information.

  A fourth feature of the present invention relates to the second or third feature of the present invention, wherein the correction unit performs the multi-antenna transmission and restarts the feedback after the feedback is stopped. (For example, when calculation of a prediction filter coefficient used for calculation of the prediction channel information is started in the prediction unit in preparation for resumption of the feedback after the feedback is stopped), the estimation channel information is corrected. This is the gist.

  A fifth feature of the present invention relates to any one of the first to fourth features of the present invention, wherein the prediction unit is a prediction filter coefficient used for calculation of the prediction channel information based on the estimation channel information. And the channel prediction system using the prediction filter coefficient, the channel prediction system determines whether the time difference exceeds a threshold, and determines that the time difference exceeds the threshold , Further comprising a prediction control unit (prediction control unit 105) that initializes the estimated channel information and a value calculated by the prediction unit based on the estimated channel information. When the calculation is performed, the prediction filter coefficient is calculated again based on the estimated channel information newly calculated by the calculation unit, and the calculated prediction coefficient is calculated again. And gist performing said channel prediction using filter coefficients.

  A sixth feature of the present invention is that a transmitting side (transmitter 10) that transmits a radio signal (OFDM signal) according to an orthogonal frequency division method, and that the radio signal received from the transmitting side is converted into a frequency domain signal. A calculation unit for calculating estimated channel information indicating a propagation path characteristic with the receiving side (receiver 20) at a predetermined time interval based on the frequency domain signal, and using a plurality of the estimated channel information, A wireless communication device (receiver 20) having a prediction unit that executes channel prediction for calculating prediction channel information that is a prediction value of the estimated channel information, wherein the calculation unit calculates the predetermined time interval. By reducing the estimated channel information, a reduction processing unit (estimated channel information supplement) that executes a reduction process for reducing the number of the estimated channel information used for the channel prediction. Part 103) and a time interval between a set position of a time window for extracting a signal section to be converted into the frequency domain signal from the radio signal received by the receiving side and a reference position of the set position, A correction unit (estimated channel information correction unit 103) that corrects the estimated channel information after the reduction process, and the prediction unit performs the channel prediction using the estimated channel information corrected by the correction unit. The gist is to do it.

  A seventh feature of the present invention is between a transmitting side that transmits a radio signal (OFDM signal) according to an orthogonal frequency division method and a receiving side that converts the radio signal received from the transmitting side into a frequency domain signal. A step (step S102) of calculating estimated channel information indicating a propagation path characteristic at predetermined time intervals based on the frequency domain signal, and using a plurality of the estimated channel information, a predicted value of the estimated channel information in the future A channel prediction method for calculating prediction channel information that is calculated (step S106) by thinning out the estimated channel information calculated at the predetermined time interval in the calculation step. A step of performing a reduction process for reducing the number of the estimated channel information used for the channel prediction. (Step S103), and according to the time difference between the set position of the time window for extracting the signal section to be converted into the frequency domain signal from the radio signal received by the receiving side and the reference position of the set position, Correcting the estimated channel information after the reduction process (step S104), and in the step of executing the channel prediction, the channel prediction is performed using the estimated channel information corrected by the correcting step. The main point is to execute.

  According to the present invention, when performing channel prediction in a wireless communication system employing the OFDM scheme, a channel prediction system that further improves channel prediction accuracy while suppressing an increase in processing load for obtaining predicted channel information, A wireless communication apparatus and a channel prediction method can be provided.

  Next, a first embodiment and a second embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings in the first embodiment and the second embodiment, the same or similar parts are denoted by the same or similar reference numerals.

[First Embodiment]
In the first embodiment, (1) the configuration of a wireless communication system, (2) an example of feedback information, (3) details of correction processing, (4) operation of a channel prediction system, and (5) actions and effects will be described.

(1) Configuration of Radio Communication System FIG. 1 is a block diagram showing the configuration of the radio communication system 1 according to the first embodiment. The wireless communication system 1 includes a transmitter 10 and a receiver 20 that perform wireless communication according to the OFDM system via the wireless propagation path 3.

  The transmitter 10 is provided in one of the radio base station and the radio terminal, and the receiver 20 is provided in the remaining one. In the first embodiment, it is assumed that the transmitter 10 is provided in a radio base station and the receiver 20 is provided in a radio terminal. In addition, when the characteristics of the wireless propagation path 3 (propagation path characteristics) fluctuate due to movement of the receiver 20 (wireless terminal) or movement of a scatterer existing between the transmitter 10 and the receiver 20. Is assumed.

  The transmitter 10 has a plurality of transmission antennas T # 1 to T # n, and the receiver 20 has a plurality of reception antennas R # 1 to R # m (n ≧ 2, m ≧ 2). That is, the wireless communication system 1 is a multiple-input multiple-output (MIMO) wireless communication system.

  The transmitter 10 can simultaneously transmit a plurality of communication streams using the same frequency band via the transmission antennas T # 1 to T # n. The receiver 20 can receive a plurality of communication streams via the receiving antennas R # 1 to R # m and can separate the communication streams.

  The receiver 20 analyzes the communication stream from the transmitter 10 and feeds back feedback information for adaptively controlling multi-antenna transmission and the like in the transmitter 10 to the transmitter 10. A MIMO communication system that feeds back feedback information from the receiver 20 to the transmitter 10 is called a “closed loop” MIMO communication system.

  The transmitter 10 includes an adaptive transmission processing unit 11 in addition to the transmission antennas T # 1 to T # n. The adaptive transmission processing unit 11 executes adaptive communication control (for example, adaptive modulation, transmission power control, or transmission weight control) for improving frequency use efficiency based on feedback information fed back from the receiver 20.

  The adaptive transmission processing unit 11 generates an OFDM signal by performing inverse fast Fourier transform (IFFT) on the transmission data and generating a guard interval obtained by copying a part of the transmission symbol. The OFDM signal is configured using a guard interval and an effective symbol period (transmission symbol).

  The transmitter 10 transmits the generated OFDM signal to the receiver 20 via the wireless propagation path 3. The receiver 20 receives the OFDM signal transmitted by the transmitter 10 via the wireless propagation path 3. Note that the OFDM signal transmitted by the transmitter 10 includes a preamble signal for timing synchronization, a known signal for channel estimation, and the like.

  The receiver 20 includes a reception processing unit 21 and a channel prediction system 100 in addition to the reception antennas R # 1 to R # m. The reception processing unit 21 performs reception processing (specifically, FFT, communication stream separation, equalization processing, etc.) on the OFDM signals received by the reception antennas R # 1 to R # m. By such reception processing, the receiver 20 generates reception data from the received OFDM signal.

  The channel prediction system 100 performs the above-described channel estimation and channel prediction. Specifically, the channel prediction system 100 calculates predicted channel information that is a predicted value of estimated channel information in the processing delay time ahead (that is, the timing at which the transmitter 10 next transmits an OFDM signal), and calculates the calculated prediction A value based on the channel information is generated as feedback information.

  There is a processing delay due to feedback or the like between the timing of the estimated channel information obtained by channel estimation and the timing at which the transmitter 10 actually transmits the OFDM signal. Adaptive communication control functions appropriately by feeding back feedback information based on prediction channel information ahead of the processing delay time by channel prediction. Details of the feedback information will be described later.

  The channel prediction system 100 includes a timing synchronization unit 101, a channel estimation unit 102, an estimated channel information correction unit 103, and a channel prediction unit 104.

  The timing synchronization unit 101 performs timing synchronization for each communication frame based on the preamble included in the OFDM signal, and determines the setting position of the FFT window on the time axis. Basically, the timing synchronization unit 101 performs timing synchronization in units of preceding-wave communication frames, but may also perform timing synchronization in units of delayed-wave communication frames. Note that the preamble is a symbol that is arranged at the beginning of a communication frame, for example, and is known by the receiver 20.

  The timing synchronization unit 101 supplies a synchronization signal to the reception processing unit 21 in communication frame units. Accordingly, the reception processing unit 21 can adjust the FFT window to the effective symbol period. The synchronization signal generated by the timing synchronization unit 101 is also supplied to the estimated channel information correction unit 103.

  The channel estimation unit 102 performs channel estimation. Specifically, the channel estimation unit 102 compares a known signal included in the OFDM signal with a reference signal stored in advance, and periodically calculates estimated channel information indicating channel characteristics based on the comparison result. calculate. That is, in the first embodiment, the channel estimation unit 102 constitutes a calculation unit that calculates estimated channel information at a predetermined time interval.

  The known signals are distributed and arranged in, for example, the frequency domain and the time domain. The reference signal is a signal sequence equivalent to the known signal. The estimated channel information generated by the channel estimation unit 102 is supplied to the estimated channel information correction unit 103. The estimated channel information is also supplied to the reception processing unit 21 and used for reception processing (equalization processing or the like) in the reception processing unit 21. Here, the estimated channel information supplied to the reception processing unit 21 does not pass through the estimated channel information correction unit 103.

  The estimated channel information correcting unit 103 thins out the estimated channel information calculated by the channel estimating unit 102 at predetermined time intervals, and reduces the number of estimated channel information used for channel prediction. For example, the estimated channel information correction unit 103 sets the rate (sampling rate) of the estimated channel information to 1 / n. Hereinafter, such processing is referred to as “decrease processing”. In the first embodiment, the estimated channel information correction unit 103 constitutes a reduction processing unit that executes a reduction process.

  Further, the estimated channel information correction unit 103 corrects the estimated channel information based on the synchronization signal from the timing synchronization unit 101. That is, in the first embodiment, the estimated channel information correction unit 103 corrects the estimated channel information after the reduction process according to the time difference between the set position of the FFT window and the reference position of the set position. In the first embodiment, the estimated channel information correction unit 103 constitutes a correction unit that corrects the estimated channel information after the reduction process. Details of such correction processing will be described later.

  The channel prediction unit 104 performs channel prediction. Specifically, channel prediction section 104 uses a plurality of estimated channel information corrected by estimated channel information correction section 103 to calculate predicted channel information that is a predicted value of estimated channel information in the future. In the first embodiment, the channel prediction unit 104 linearly predicts predicted channel information from a plurality of past estimated channel information. That is, the channel prediction unit 104 calculates predicted channel information according to the variation tendency of the propagation path characteristics (or estimated channel information).

  The channel prediction unit 104 minimizes a prediction error (square error) indicating a difference between new estimated channel information and predicted channel information calculated for the same timing as the new estimated channel information based on, for example, the MMSE norm. Calculate prediction filter coefficients. And the channel estimation part 104 calculates | requires new prediction channel information from the said new estimated channel information using the calculated prediction filter coefficient. Further, the channel prediction unit 104 generates feedback information based on the calculated prediction channel information, and feeds back the generated feedback information to the transmitter 10 via the wireless propagation path 3.

(2) Example of Feedback Information Next, an example of feedback information generated by the channel prediction unit 104 will be described.

  The feedback information includes, for example, “PMI (Precoding Matrix Indicator)” and “CQI (Channel Quality Indicator)”. The PMI is control information for controlling the transmission antenna weight in the transmitter 10. CQI is reception quality information for controlling transmission power, modulation scheme, coding rate, and the like in transmitter 10.

  Here, the CQI will be described in detail. In order to improve the frequency utilization efficiency in the OFDM system, it has been studied to perform adaptive modulation and transmission power control according to the propagation path characteristics for each subcarrier. In the case of a frequency selective fading environment, as shown in FIG. 2, a drop in received power occurs in some subcarriers. Thus, frequency utilization efficiency is improved by reducing the allocation of transmission bits to subcarriers where reception power is reduced and assigning more to subcarriers with large reception power.

  In order to realize such adaptive communication control, channel prediction system 100 calculates CQI from predicted channel information for a subband set including a plurality of consecutive subcarriers and a plurality of OFDM symbols, and transmits the calculated CQI to a transmitter. Feedback to 10. As a result, the transmitter 10 applies a high modulation scheme and coding rate when the channel characteristics are good, and applies a low modulation scheme and coding rate when the channel characteristics are poor.

(3) Details of Correction Processing Next, details of the correction processing executed by the estimated channel information correction unit 103 will be described with reference to FIG.

  In the channel prediction performed by the channel prediction unit 104, the prediction channel information is calculated from a plurality of pieces of estimated channel information. Therefore, it is necessary to maintain continuity between the plurality of pieces of estimated channel information.

  On the other hand, the timing synchronization unit 101 periodically performs timing synchronization such that an FFT window is set in the effective symbol period of the preceding wave. However, for example, if the reception level of the preceding wave drops due to the movement of the receiver 20 side (wireless terminal), the timing synchronization unit 101 may fit the FFT window to the delayed wave.

  When the setting position of the FFT window is changed by the timing synchronization unit 101, linear phase rotation occurs in the estimated channel information on the frequency axis. That is, when the setting position of the FFT window is changed from the reference position, a linear phase component having a slope corresponding to the time difference is added to the estimated channel information, and phase rotation corresponding to the subcarrier frequency occurs. If the subcarrier has a small frequency difference with respect to the DC subcarrier, the amount of phase rotation is small, but in the case of a wideband OFDM system, a large phase rotation occurs in a subcarrier having a large frequency difference. In the estimated channel information calculated from such received symbols, phase discontinuity occurs with the past estimated channel information, and the accuracy of channel prediction based on a plurality of past estimated channel information deteriorates.

  Such a phase rotation amount is determined by an adjustment amount (time difference) between the subcarrier interval and the FFT window setting position. Therefore, the estimated channel information correcting unit 103 corrects the estimated channel information according to the subcarrier interval and the time difference, thereby maintaining continuity between the past estimated channel information.

  Specifically, propagation at time t with reference to the FFT window setting position when communication is started or when channel estimation for channel prediction is started (ideally, set to the effective symbol portion of the preceding wave) Road characteristics (estimated channel information)

It is expressed. Here, ω is a frequency difference from the DC subcarrier. When the FFT window setting position deviates by τ from the reference position, a phase rotation component of e ^−jωτ is added,

It is expressed. The estimated channel information correction unit 103 corrects the estimated channel information by multiplying the estimated channel information by the inverse component e ^jωτ of the phase rotation component according to the time difference τ of the FFT window setting position with respect to the reference position.

(4) Operation of Channel Prediction System FIG. 4 is a flowchart showing the operation of the channel prediction system 100 according to the first embodiment.

  In step S101, the timing synchronization unit 101 performs timing synchronization for each communication frame based on the preamble included in the OFDM signal, and determines the setting position of the FFT window on the time axis.

  The reception processing unit 21 sets an FFT window according to the result of timing synchronization by the timing synchronization unit 101. Further, the reception processing unit 21 performs FFT on the effective symbol section extracted by the FFT window, and converts it to a frequency domain signal.

  In step S102, the channel estimation unit 102 performs channel estimation of each subcarrier symbol on the frequency domain signal converted into subcarrier symbols by FFT. As a result, a plurality of estimated channel information is obtained.

  In step S103, the estimated channel information correction unit 103 executes a reduction processing unit. That is, the estimated channel information correcting unit 103 reduces the number of estimated channel information used for channel prediction by thinning out a plurality of estimated channel information calculated by the channel estimating unit 102.

  In step S <b> 104, the estimated channel information correction unit 103 corrects the estimated channel information based on the synchronization signal from the timing synchronization unit 101. Specifically, the estimated channel information correction unit 103 corrects the estimated channel information by the procedure described in the details of the above (3) correction processing.

  In step S <b> 105, the channel prediction unit 104 uses a plurality of estimated channel information corrected by the estimated channel information correction unit 103 to calculate prediction filter coefficients for obtaining predicted channel information. As described above, the prediction filter coefficient is calculated based on the MMSE standard using the past estimated channel information as training information. In step S106, the channel prediction unit 104 obtains prediction channel information using the prediction filter coefficient obtained in step S105.

  For example, the channel prediction unit 104 predicts channel information at time t as shown in the following equation when performing channel prediction from the past P pieces of estimated channel information in the subcarrier number k.

ω _k is the frequency of subcarrier number k, d _j is the prediction filter coefficient, and T is the channel estimation period (channel estimation interval).

  Further, the channel prediction unit 104 generates feedback information from the prediction channel information obtained in step S106, and feeds back the generated feedback information to the transmitter 10.

  The adaptive transmission processing unit 11 of the transmitter 10 performs modulation scheme, coding rate, transmission weight control, and the like based on feedback information. For example, the adaptive transmission processing unit 11 holds a table defining a modulation scheme and a coding rate that maximize the frequency use efficiency with respect to the SNR, and the receiver 20 side calculates the square of the absolute value of the estimated channel information. And the corresponding modulation scheme and coding rate corresponding to the calculated SNR are selected.

(5) Operation / Effect As described above, according to the first embodiment, the estimated channel information correction unit 103 performs a reduction process for reducing the number of estimated channel information used for channel prediction, and performs the reduction process. Later estimated channel information is corrected. The channel prediction unit 104 performs channel prediction using the estimated channel information corrected by the estimated channel information correction unit 103. Therefore, it is possible to improve channel prediction accuracy while suppressing an increase in processing load for obtaining predicted channel information.

  Further, the estimated channel information correcting unit 103 performs the above reduction process by thinning out the estimated channel information calculated at a predetermined time interval by the channel estimating unit 102. The number of estimated channel information used for prediction can be reduced. For this reason, it is possible to further improve the channel prediction accuracy while suppressing an increase in processing load for obtaining the prediction channel information.

  Therefore, according to the first embodiment, even in an environment where the setting position of the FFT window is changed by movement of the receiver 20 (wireless terminal), by correcting the estimated channel information based on the change amount, Highly accurate channel prediction is realized.

  Further, according to the first embodiment, the estimation channel information correction unit 103 corrects only the estimation channel information used for channel prediction and does not correct the estimation channel information used for reception processing. The unit 21 can start the reception process without waiting for the correction process of the estimated channel information.

[Second Embodiment]
The linear prediction method in the channel prediction described above is based on the actual radio propagation path, such as the radiation / arrival direction of the reflected / scattered wave, the moving speed on the receiver 20 side (wireless terminal), and the autocorrelation characteristic of the propagation path characteristic variation. Compared to the change in 3, it is considered to change very slowly.

  However, in an actual wireless communication environment, for example, when a wireless base station and a wireless terminal are in a line-of-sight environment, when entering the shadow of a building by making a turn on the road, the radiation / arrival direction of reflected / scattered waves is large. Change. In this case, the prediction filter coefficient calculated in the line-of-sight environment becomes inappropriate, and the prediction performance is significantly deteriorated.

  Furthermore, in the RLS (Recursive Least Square) algorithm and the like, the prediction filter coefficient is calculated while weighting the value obtained from the past estimated channel information, so when a sudden change in the wireless communication environment occurs, the past Therefore, it takes a long time to optimize a new prediction filter coefficient.

  When the prediction filter coefficient is calculated based on the RLS algorithm, the following expression is obtained.

Is estimated channel information, and P is the number of taps of the prediction filter.

Is a prediction filter coefficient, and α is a weighting coefficient (forgetting coefficient). Note that if the weighting coefficient is set to an appropriate value smaller than 1, new estimated channel information will be emphasized over time, and prediction filter coefficients that follow changes in the wireless communication environment can be calculated.

Is the inverse of the correlation matrix.

  In the second embodiment, when a sudden change in the wireless communication environment occurs, a correlation matrix obtained from estimated channel information that has lost the past relationship is initialized, and is optimized to a new wireless communication environment sooner. It is possible to obtain a predictive filter coefficient.

  In the second embodiment, (1) the configuration of the channel prediction system, (2) the operation of the channel prediction system, and (3) the action / effect will be described. However, the overlapping description is abbreviate | omitted about the structure and operation | movement similar to 1st Embodiment.

(1) Configuration of Channel Prediction System FIG. 5 is a block diagram showing a configuration of a wireless communication system 1 including a channel prediction system 100 according to the second embodiment. As shown in FIG. 5, the channel prediction system 100 according to the second embodiment is different from the first embodiment in that it includes a prediction control unit 105.

  When the FFT window setting position is changed from the reference position by a certain threshold value or more, the prediction control unit 105 determines the past estimated channel information and the value calculated by the channel prediction unit 104 using the past estimated channel information (correlation matrix Initialize the inverse matrix and prediction filter coefficients).

  Specifically, the prediction control unit 105 determines whether or not the time difference τ (timing change) exceeds a threshold value, and executes the initialization when it is determined that the time difference τ exceeds the threshold value. Or the prediction control part 105 may compare the time difference of the said reference position and this FFT window setting position with a threshold value by making the last FFT window setting position into a reference position.

  When the initialization by the prediction control unit 105 is executed, the channel prediction unit 104 recalculates the prediction filter coefficient based on the estimated channel information newly calculated by the channel estimation unit 102, and calculates the newly calculated prediction filter coefficient. Perform the used channel prediction.

  As a result, the calculation can be advanced toward the prediction filter coefficient optimized for the wireless communication environment after the change without being affected by the estimated channel information and the prediction filter coefficient before the wireless communication environment rapidly changes. it can.

(2) Operation of Channel Prediction System FIG. 6 is a flowchart showing the operation of the channel prediction system 100 according to the second embodiment. In addition, since processes other than step S201 and step S202 are the same as that of 1st Embodiment, the process of step S201 and step S202 is demonstrated here.

  In step S201, the prediction control unit 105 determines whether or not the time difference (timing change) exceeds a threshold value. If the time difference (timing change) exceeds the threshold value, the process proceeds to step S202. If the time difference does not exceed the threshold value, the process proceeds to step S102.

  In step S202, the prediction control unit 105 initializes past estimated channel information and a value calculated by the channel prediction unit 104 using past estimated channel information.

(3) Operation / Effect According to the second embodiment, since the prediction control unit 105 performs initialization, only a low-precision prediction filter coefficient is calculated until a certain number of pieces of estimated channel information are obtained. Since it cannot be dragged by past information, it can be converged to the optimum prediction filter coefficient earlier. As a result, even when a sudden change in the wireless communication environment occurs, the time during which the channel prediction accuracy is degraded can be shortened.

[Other Embodiments]
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in the above-described embodiment, it has been described that the transmitter 10 is provided in the radio base station and the receiver 20 is provided in the radio terminal. However, the transmitter 10 is provided in the radio terminal and the receiver 20 is the radio base station. May be provided. Further, although the channel prediction system 100 is provided in the receiver 20, at least a part of the channel prediction system 100 (for example, the channel prediction unit 104) may be provided in the transmitter 10.

  In the above-described embodiment, the MIMO communication system using the closed-loop scheme has been described. However, channel estimation and channel prediction are performed on the transmission side using the reversibility of the propagation path when the time division multiplexing (TDD) scheme is adopted. it can. Therefore, the present invention can be applied to a MIMO communication system based on an open loop system that does not use feedback.

  However, in the MIMO communication system using the closed loop method, the processing delay time becomes long due to feedback, and therefore the function of the estimated channel information correction unit 103 is particularly effective. Therefore, the estimated channel information correction unit 103 may be operated only for the closed loop method, and the estimated channel information correction unit 103 may not be operated for the open loop method. Thereby, the processing load can be reduced.

  Furthermore, when sufficient performance cannot be obtained in the closed loop system and switching to the open loop system is performed, the operation of the estimated channel information correction unit 103 may be stopped. Then, the operation of the estimated channel information correction unit 103 may be resumed when returning from the open loop method to the closed loop method, or before a certain time before returning from the open loop method to the closed loop method. By such control, the estimated channel information correction unit 103 can be operated when it is particularly necessary to improve the channel prediction accuracy while reducing the processing load.

  In the above-described embodiment, the MIMO communication system in which both the transmitter 10 and the receiver 20 have a plurality of antennas has been described. However, the receiver 20 has a single-antenna (MISO) communication system having only one antenna. However, the present invention is applicable.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters in the scope of claims reasonable from this disclosure.

It is a block diagram which shows the structure of the radio | wireless communications system which concerns on 1st Embodiment. It is a figure for demonstrating a frequency selective fading environment. It is a figure for demonstrating the correction process performed by the estimation channel information correction | amendment part which concerns on 1st Embodiment. It is a flowchart which shows operation | movement of the channel prediction system which concerns on 1st Embodiment. It is a block diagram which shows the structure of the radio | wireless communications system which concerns on 2nd Embodiment. It is a flowchart which shows operation | movement of the channel prediction system which concerns on 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Wireless communication system, 3 ... Wireless propagation path, 10 ... Transmitter, 11 ... Adaptive transmission process part, 20 ... Receiver, 21 ... Reception process part, 100 ... Channel prediction system, 101 ... Timing synchronization part, 102 ... Channel Estimating unit 103 ... Estimated channel information correcting unit 104 ... Channel predicting unit 105 ... Prediction control unit

Claims (7)

Estimated channel information indicating channel characteristics between a transmitting side that transmits a radio signal according to an orthogonal frequency division scheme and a receiving side that converts the radio signal received from the transmitting side into a frequency domain signal, A calculation unit for calculating at predetermined time intervals based on the region signal;
A channel prediction system including a prediction unit that performs channel prediction to calculate prediction channel information that is a prediction value of the estimation channel information in the future using a plurality of the estimation channel information,
A reduction processing unit that performs a reduction process for reducing the number of the estimated channel information used for the channel prediction by thinning out the estimated channel information calculated by the calculation unit at the predetermined time interval;
According to the time difference between the set position of the time window for extracting the signal section to be converted into the frequency domain signal from the radio signal received by the receiving side and the reference position of the set position, the post-decreasing process A correction unit for correcting the estimated channel information,
The prediction unit is a channel prediction system that performs the channel prediction using the estimated channel information corrected by the correction unit. The prediction unit is provided on the receiving side,
The correction unit performs multi-antenna transmission in which the wireless signal is transmitted using a plurality of antennas on the transmission side, and feedback of a value based on the prediction channel information is performed from the reception side to the transmission side. The channel prediction system according to claim 1, wherein when executed, the estimated channel information is corrected. The prediction unit is provided on the transmission side,
The correction unit performs multi-antenna transmission in which the radio signal is transmitted using a plurality of antennas on the transmission side, and feedback of a value based on the estimated channel information is performed from the reception side to the transmission side. If executed, correct the estimated channel information,
The channel prediction system according to claim 1, wherein the feedback is performed on the estimated channel information corrected by the correction unit.   The channel prediction system according to claim 2 or 3, wherein the correction unit corrects the estimated channel information when the feedback is resumed after the multi-antenna transmission is performed and the feedback is stopped. The prediction unit calculates a prediction filter coefficient used for calculation of the prediction channel information based on the estimated channel information, and executes the channel prediction using the prediction filter coefficient,
The channel prediction system determines whether or not the time difference exceeds a threshold, and determines that the time difference exceeds the threshold, and the prediction unit calculates based on the estimated channel information and the estimation channel information. A prediction control unit that initializes
When the initialization by the prediction control unit is executed, the prediction unit recalculates the prediction filter coefficient based on the estimated channel information newly calculated by the calculation unit, and the prediction filter coefficient newly calculated The channel prediction system according to any one of claims 1 to 4, wherein the channel prediction using a channel is executed. Estimated channel information indicating channel characteristics between a transmitting side that transmits a radio signal according to an orthogonal frequency division scheme and a receiving side that converts the radio signal received from the transmitting side into a frequency domain signal, A calculation unit for calculating at predetermined time intervals based on the region signal;
A wireless communication device having a prediction unit that performs channel prediction to calculate predicted channel information that is a predicted value of the estimated channel information in the future using a plurality of the estimated channel information,
A reduction processing unit that performs a reduction process for reducing the number of the estimated channel information used for the channel prediction by thinning out the estimated channel information calculated by the calculation unit at the predetermined time interval;
According to the time difference between the set position of the time window for extracting the signal section to be converted into the frequency domain signal from the radio signal received by the receiving side and the reference position of the set position, the post-decreasing process A correction unit for correcting the estimated channel information,
The said prediction part is a radio | wireless communication apparatus which performs the said channel prediction using the said estimation channel information correct | amended by the said correction | amendment part. Estimated channel information indicating channel characteristics between a transmitting side that transmits a radio signal according to an orthogonal frequency division scheme and a receiving side that converts the radio signal received from the transmitting side into a frequency domain signal, Calculating at predetermined time intervals based on the region signal;
Using a plurality of the estimated channel information, and performing channel prediction to calculate predicted channel information that is a predicted value of the estimated channel information in the future,
Performing a reduction process for reducing the number of estimated channel information used for the channel prediction by thinning out the estimated channel information calculated at the predetermined time interval in the calculating step;
According to the time difference between the set position of the time window for extracting the signal section to be converted into the frequency domain signal from the radio signal received by the receiving side and the reference position of the set position, the post-decreasing process Correcting the estimated channel information,
In the step of executing the channel prediction, a channel prediction method of executing the channel prediction using the estimated channel information corrected in the correcting step.

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