JP4858199B2 - Radio communication receiving apparatus and receiving method - Google Patents

Description

  The present invention relates to a radio communication receiver using OFDM (Orthogonal Frequency Division Multiplexing) modulation.

  OFDM is adopted as a communication method for reducing the influence of multipath interference in a high-speed wireless LAN standard for performing broadband communication in a multipath environment with many reflected waves and WiMAX, which is one of the next generation wireless communication standards. In addition, WiMAX supports multi-antenna technology as an option to achieve better communication quality and faster communication speed, such as AAS (Adaptive Antenna System) and MIMO (Multi-antenna) using multiple antennas. Functions such as -Input Multi-Output: are provided (see Non-Patent Documents 1 and 2).

IEEE standard, 802.16 Revised wireless broadband textbook, high-speed IP wireless edition, issued on June 21, 2006, Impress R & D Co., Ltd.

However, the radio propagation environment (channel) is greatly affected by buildings around the installed base station, and in the case of mobile communication, it varies instantaneously depending on the speed of the mobile station and the environment surrounding the mobile station. . Therefore, even if a base station prepares a receiving apparatus that performs, for example, AAS array processing on an array antenna reception signal composed of a plurality of antenna elements, communication quality can be improved if the radio propagation environment changes. This will cause deterioration and a decrease in communication speed.
In view of such a problem, an object of the present invention is to suppress deterioration in communication quality and communication speed due to a change in a radio propagation environment in OFDM modulation wireless communication.

The present invention is a radio communication receiver using OFDM modulation, and based on a received signal received by an array antenna, channel estimation means for obtaining a channel estimated value using a pilot signal in a frequency domain, and the channel estimated value An inverse discrete Fourier transform unit for obtaining an impulse response, an array processing selection unit for selecting an array processing method based on the waveform of the impulse response, an array processing unit for performing the selected array processing on the received signal, A demodulator that demodulates the signal subjected to the array processing, and the array processing selector selects a magnitude of an impulse response in a time domain exceeding a time corresponding to a cyclic prefix of the received signal, and an impulse response By comparing the magnitude of the response excluding the maximum response with a predetermined threshold value, Law to select, is that.
In the wireless communication receiving apparatus as described above, the waveform of the impulse response obtained from the channel estimation value includes the presence / absence of an interference wave and the presence of multipath. Therefore, if an array processing method corresponding to the waveform of the impulse response is selected, optimal array processing corresponding to the channel at that moment can be performed.

Further, example embodiment, to select the AAS in the process of the array processing as the arrival of the interference wave as long as the magnitude of the impulse response in the time domain exceeding the time corresponding to the cyclic prefix is equal to or larger than the threshold, otherwise separately When the magnitude of the response excluding the maximum response in the impulse response is equal to or greater than the threshold, MIMO is selected as the presence of multipath, and MRC (Maximum Ratio Combining) is selected otherwise. be able to.

Further, in the above wireless communication receiving apparatus, the channel estimation means includes a CP removing unit for obtaining a reception signal having an effective symbol length obtained by removing a cyclic prefix from the reception signal in the time domain, and a reception signal having the effective symbol length. Is converted into a received signal in the frequency domain, a pilot signal generating unit that generates a pilot signal in the frequency domain, and a specific signal in which the pilot signal is inserted among the received signals in the frequency domain. A channel estimation unit may be provided that compares the subcarrier signal with the pilot signal generated by the pilot signal generation unit and applies interpolation to obtain a channel estimation value.
In this case, channel estimation can be performed quickly and accurately by comparing a signal of a specific subcarrier with a known pilot signal and obtaining a channel estimation value by applying interpolation.

On the other hand, the present invention is a wireless communication reception method using OFDM modulation, which acquires a reception signal received by an array antenna, obtains a channel estimation value using a pilot signal in a frequency domain based on the reception signal, The impulse response is obtained from the channel estimation value , and the magnitude of the impulse response in the time domain exceeding the time corresponding to the cyclic prefix of the received signal and the maximum response in the impulse response are excluded based on the waveform of the impulse response. A method of array processing is selected by comparing the magnitude of response with a predetermined threshold value , the selected array processing is performed on the received signal, and the signal subjected to the array processing is demodulated. It is what.
In the wireless communication reception method described above, the waveform of the impulse response obtained from the channel estimation value includes the presence / absence of an interference wave and the presence of multipath. Therefore, if an array processing method corresponding to the waveform of the impulse response is selected, optimal array processing corresponding to the channel at that moment can be performed.
Also, for example, if the magnitude of the impulse response in the time domain exceeding the time corresponding to the cyclic prefix is equal to or greater than the threshold, AAS is selected as the array processing method as the arrival of the interference wave, and otherwise, separately. When the magnitude of the response excluding the maximum response in the impulse response is equal to or greater than the threshold value, MIMO is selected as the presence of multipath, and MRC (Maximum Ratio Combining) is selected otherwise. Can do.

  According to the wireless communication receiver / reception method of the present invention, by selecting the array processing method according to the waveform of the impulse response, it is possible to perform the optimal array processing according to the channel at the moment. It is possible to suppress deterioration in communication quality and decrease in communication speed due to changes in the propagation environment.

  FIG. 1 is a block diagram showing a configuration of a wireless communication receiving apparatus according to an embodiment of the present invention. The receiving apparatus performs wireless communication by OFDM modulation with a mobile station terminal (not shown). In the figure, a receiving apparatus 100 includes, in addition to a conversion / synchronization unit 3 that performs a predetermined process on a signal received by an array antenna 2 that combines a plurality of antenna elements 1, a processing method determination unit 4 and an array process. Part 5, demodulator 6 and higher layer 7. The conversion / synchronization unit 3 and the demodulation unit 6 are provided with a plurality of systems (two systems are shown in the figure) corresponding to the number of antenna elements 1.

  The conversion / synchronization unit 3 converts a signal received by the antenna element 1 to a baseband frequency, performs various synchronizations necessary for OFDM, and then converts the signal from analog to digital (part of synchronization processing). May be performed after AD conversion.) In the following description, it is assumed that carrier frequency synchronization, clock synchronization, symbol synchronization, and the like have been established.

  The processing method determination unit 4 can select a method of array processing in response to a control signal from the upper layer 7, select an appropriate array processing method by itself, and instruct the array processing unit 5. It has a function of notifying the upper layer 7. The array processing unit 5 includes a processing method switching unit 50, a plurality of array processing function units (51 to 53), and an output selection unit 54 after array processing. Here, AAS 51, MIMO 52, and MRC 53 are shown as examples of the array processing function unit.

  The processing method switching unit 50 receives an instruction from the processing method determination unit 4, and passes the signal that has passed through the processing method determination unit 4 (that is, the output signal of the conversion / synchronization unit 3) to any one of AAS 51, MIMO 52, and MRC 53. Send to one. Moreover, the output selection part 54 returns the signal after an array process to the original system | strain.

  FIG. 2 is a block diagram showing an internal configuration of the processing method determination unit 4. The processing method determination unit 4 sends the received signal after AD conversion sent from the conversion / synchronization unit 3 to the processing method switching unit 50 as it is and also to the channel estimation means 40 for estimating the channel (wireless propagation environment). Is also sent. The channel estimation means 40 includes a CP removal unit 41, a DFT unit (discrete Fourier transform unit) 42, a pilot signal generation unit 43, and a channel estimation unit 44. In addition to the channel estimation means 40, an IDFT unit (inverse discrete Fourier transform unit) 45 and an array processing selection unit 46 are provided as shown in the figure.

  The CP removing unit 41 obtains a received signal having an effective symbol length obtained by removing a cyclic prefix (guard interval) from the received signal in the time domain. The DFT unit 42 converts the reception signal having an effective symbol length into a reception signal in the frequency domain. The pilot signal generation unit 43 generates a pilot signal in the frequency domain. The channel estimation unit 44 compares a signal of a specific subcarrier into which a pilot signal is inserted among received signals in the frequency domain with a known pilot signal, and applies interpolation to obtain a channel estimation value.

FIG. 4A is a diagram conceptually showing a state where a pilot signal (black circle) is inserted into a data signal (white circle) in the frequency domain. In OFDM, generally, pilot signals are inserted at regular subcarrier intervals. Therefore, from the known pilot signal that is generated by the pilot signal generation unit 43 and serves as a reference, and the received signal on the subcarrier in which the pilot signal is inserted, the channel estimation unit 44
A channel estimation value is obtained by calculating channel estimation value = received signal / pilot signal. FIG. 4B is a diagram showing a plurality of channel estimation values obtained in this way. Further, the channel estimation unit 44 obtains channel estimation values in subcarriers other than these channel estimation values by interpolation as shown in FIG.

  If the channel estimation value obtained as described above is, for example, the waveform shown in FIG. 5A, the IDFT unit 45 (FIG. 2) performs inverse discrete Fourier transform on this, and the result is shown in FIG. Find the impulse response. The first waveform A in the impulse response is a direct wave without delay, the next waveform B is a delayed wave slightly delayed by multipath or a radio wave (interference wave) other than the desired wave to be originally received, and the subsequent waveform C is interference. It is understood to be a wave. That is, the waveform of the impulse response (mainly the reduction in size) includes information on the presence of interference waves and multipaths. Therefore, the array processing selection unit 46 performs the processing of the flowchart shown in FIG. 3 based on the waveform of the impulse response.

  In FIG. 3, first, the array processing selection unit 46 (FIG. 2) acquires an impulse response (step S1). The acquisition of the impulse response referred to here includes an averaging process. The averaging process includes, for example, (a) averaging impulse responses for several symbols for one antenna element, or (b) averaging impulse responses from all antenna elements. In the case of (a), there is an advantage that the calculation amount can be reduced, and in the case of (b), there is an advantage that the reliability can be improved.

  Next, the array processing selection unit 46 calculates the magnitude Y1 of the impulse response in the time domain exceeding the time corresponding to CP (cyclic prefix) (step S2). Then, the array process selection unit 46 compares Y1 with the threshold value T1 (step S3), and when Y1 is equal to or greater than the threshold value T1, selects the AAS as the array process (step S4). Here, it is assumed that the threshold value T1 is given from the upper layer 7 in advance.

  6 to 8 are graphs showing three examples of impulse response waveforms. For the impulse response of FIG. 6, AAS is selected as the array processing when the magnitude (for example, average value) Y1 of the impulse response in the time domain exceeding the CP equivalent time (maximum delay) is equal to or greater than the threshold T1. . That is, in the case of this impulse response, the level does not decrease even when the CP equivalent time is exceeded, and AAS is suitable because it is a propagation environment in which interference waves exist. However, in the case of the impulse responses of FIGS. 7 and 8, as shown in the figure, Y1 is less than the threshold value T1, and AAS is not selected.

  On the other hand, if Y1 is less than the threshold value T1 in step S3, the array processing selection unit 46 calculates the response magnitude Y2 excluding the maximum response among the impulse responses within the CP equivalent time (step S5). Then, the array process selection unit 46 compares Y2 with the threshold value T2 (step S6), and when Y2 is equal to or greater than the threshold value T2, selects MIMO as the array process (step S7). Here, the threshold value T2 is assumed to be given in advance from the upper layer 7. Moreover, the array process selection part 46 selects MRC as an array process, when Y2 is less than a threshold value (step S8).

For example, in the case of the impulse response in FIG. 7, MIMO is selected as the array processing when the magnitude (for example, peak value) Y2 of the response excluding the maximum response among the impulse responses within the CP equivalent time is equal to or greater than the threshold T2. . That is, in the case of this impulse response, MIMO is suitable because it is a multipath propagation environment in which a delayed wave arrives with a slight delay.
On the other hand, in the case of the impulse response of FIG. 8, as shown in the figure, Y2 is less than the threshold value T2, and MRC is selected. That is, in the case of this impulse response, since the propagation environment has a small influence other than the desired wave, MRC is suitable for the array processing. In MRC, the received signals from each antenna element 1 are weighted according to their levels and combined so as to maximize the SN ratio.

  As described above, an impulse response is obtained from the channel estimation value, and the presence / absence of an interference wave and the presence / absence of a multipath can be detected based on the waveform of the impulse response. Therefore, if an array processing method corresponding to the waveform of the impulse response is selected, the optimum array processing corresponding to the channel at that moment can be performed, and communication quality deteriorates and communication speed decreases due to changes in the radio propagation environment. Can be suppressed.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined not by the above-mentioned meaning but by the scope of claims for patent, and is intended to include all modifications within the scope and meaning equivalent to the scope of claims for patent.

It is a block diagram which shows the structure of the receiver of radio | wireless communication by one Embodiment of this invention. It is a block diagram which shows the internal structure of the processing method determination part in FIG. It is a flowchart which shows operation | movement of the array process selection part in FIG. (A) is a diagram conceptually showing a state where a pilot signal (black circle) is inserted into a data signal (white circle) in the frequency domain, (b) is a diagram showing a channel estimation value, and (c) is a diagram of (b). It is the figure which applied the interpolation to the channel estimated value. (A) is a graph which shows an example of the waveform of a channel estimated value, (b) is a graph which shows the outline | summary of the waveform of the impulse response. It is a graph which shows an example of the waveform of the impulse response suitable for AAS as an array process. It is a graph which shows an example of the waveform of the impulse response suitable for MIMO as an array process. It is a graph which shows an example of the waveform of the impulse response suitable for MRC as an array process.

Explanation of symbols

2 array antenna 5 array processing unit 6 demodulating unit 40 channel estimation means 41 CP removing unit 42 DFT unit (discrete Fourier transform unit)
43 Pilot Signal Generation Unit 44 Channel Estimation Unit 45 IDFT Unit (Inverse Discrete Fourier Transform Unit)
46 Array Processing Selection Unit 100 Receiver

Claims (3)

A wireless communication receiver using OFDM modulation,
Channel estimation means for obtaining a channel estimation value using a pilot signal in the frequency domain based on a reception signal received by the array antenna;
An inverse discrete Fourier transform unit for obtaining an impulse response from the channel estimation value;
An array processing selection unit that selects an array processing method based on the waveform of the impulse response;
An array processing unit for performing the selected array processing on the received signal;
A demodulator that demodulates the arrayed signal ,
The array processing selection unit sets a magnitude of an impulse response in a time domain exceeding a time corresponding to a cyclic prefix of the received signal and a magnitude of a response excluding a maximum response in the impulse response as a predetermined threshold value, respectively. An apparatus for wireless communication, wherein an array processing method is selected by comparison . The channel estimation means includes
A CP removing unit for obtaining a received signal having an effective symbol length obtained by removing a cyclic prefix from the received signal in the time domain;
A discrete Fourier transform unit that converts the received signal of the effective symbol length into a received signal in a frequency domain;
A pilot signal generator for generating a pilot signal in the frequency domain;
Of the received signal in the frequency domain, the signal of a specific subcarrier in which a pilot signal is inserted is compared with the pilot signal generated by the pilot signal generation unit, and interpolation is applied to obtain a channel estimation value. The channel estimator
The wireless communication receiving device according to claim 1. A method of receiving wireless communication by OFDM modulation,
Obtain the received signal received by the array antenna,
Obtain a channel estimate using a pilot signal in the frequency domain based on the received signal,
Obtaining an impulse response from the channel estimate;
Based on the waveform of the impulse response, the magnitude of the impulse response in the time domain exceeding the time corresponding to the cyclic prefix of the received signal, and the magnitude of the response excluding the maximum response in the impulse response are respectively set to predetermined values. Select the method of array processing by comparing with the threshold,
Apply the selected array processing to the received signal,
Demodulate the arrayed signal
A wireless communication reception method .

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