JP2006115094A - Radio communication equipment, signal processing method, program, and storage medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication technique which realizes excellent communication quality by variably setting sampling sections according to a delay wave propagation environment. <P>SOLUTION: A radio communication device which processes a received signal having a data portion of an orthogonal frequency-division multiplex signal and a signal-less portion whose no signal is present is characterized by having: a reception unit which receives a plurality of incoming waves; a decision unit which decides delay propagation characteristics of the plurality of incoming waves; and a setting unit which sets sampling sections of the received signals based upon the delay propagation characteristics decided by the decision unit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless communication apparatus, a signal processing method, a program, and a storage medium.

  Currently, it is proposed to use the UWB (Ultra Wide Band) communication method as a physical layer method capable of realizing higher-speed communication than the conventional WPAN (Wireless Personal Area Network) system such as the Bluetooth system, and it is standard as the IEEE802.15 standard group. Standards are being developed. UWB is a method to spatially improve frequency utilization efficiency by suppressing the radiated power to the level of radiation noise generated by ordinary equipment instead of occupying a very wide band and communicating. Since the transmission level is low because the transmission level is low, it is considered that a relatively high-speed data communication can be realized because a communication path with a clear line of sight can be assumed. Therefore, it can be said that the UWB system is very suitable for communicating large-capacity data such as multimedia data at a very short distance such as WPAN.

  In indoor wireless communication systems such as wireless LAN and WPAN, wireless signals transmitted from transmitters are reflected by walls and ceilings, furniture and fixtures placed indoors, and direct and delayed arrival waves at receivers. Are received as a combined signal. Such a wireless communication environment is called a delay propagation environment or a multiple propagation environment. In such a multiple propagation path, in order to correctly demodulate transmission data at the receiver, it is necessary to correct the waveform distortion caused by the delayed wave by some method. As a method for correcting such waveform distortion, there is a method of correcting by an adaptive equalizer on the time axis, and there is also a method of giving the modulation method itself resistance to delayed waves.

  An OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme (orthogonal frequency division multiplexing modulation scheme) is one of communication schemes that can eliminate the effects of delayed wave interference.

  The OFDM method is already used in digital television broadcasting and wireless LAN systems, and is a modulation method in which a plurality of orthogonal narrowband signals are arranged on the frequency axis of the occupied band. Here, these multiple narrowband signals are called subcarriers. Since each subcarrier is a signal having a low transmission rate, it has a relatively strong characteristic against delayed wave interference due to multipath. Furthermore, by providing an area called a guard interval between data symbols on the time axis, interference between data symbols due to delayed waves is further reduced. For the modulation and demodulation processing of the OFDM signal, fast Fourier transform (FFT) processing by digital calculation is used.

  FIG. 5 is a diagram illustrating a configuration of data symbols (also referred to as “frames”, hereinafter the same) of an OFDM packet used in a wireless LAN standard such as IEEE802.11g or IEEE802.11a. These data symbols (N-1, N, N + 1) have an effective FFT in the guard interval section in front of the effective data symbol with respect to the effective FFT section length (effective data symbol) corresponding to one period of the OFDM signal. It is formed by copying the same waveform as the rear part of the section length. The guard interval format for copying a part of the data symbol in this way is called a cyclic prefix format. In OFDM communication, the data symbols formed in this way are continuously transmitted on the time axis.

  FIG. 6 is a diagram for explaining a process of demodulating an OFDM symbol in the cyclic prefix format, and exemplifies a two-wave model in which a direct wave and one delayed wave are synthesized. Since OFDM symbols including cyclic prefixes are longer in time than the effective FFT interval length, the receiver determines an appropriate sampling start point from within the symbol for the received signal and samples the effective FFT interval length from there. Sample data as intervals. For example, if the received signal is only one wave, such as a direct wave, it can be demodulated correctly by FFT processing using any sampling data at any position within the FFT valid section included in one symbol. When a signal shifted in time due to a delayed wave is superimposed, data between adjacent symbols overlaps in the vicinity of the symbol change point in the received signal, causing intersymbol interference.

  When a signal portion that has received such intersymbol interference in FFT processing is used for data demodulation, the demodulation quality deteriorates due to intersymbol interference. Therefore, the receiver can perform intersymbol interference within one symbol as shown in FIG. It is necessary to perform data sampling using the unaffected part as a sampling interval. Since it is possible to perform demodulation correctly by setting the FFT interval except for the guard interval interval that is receiving interference in this way, it is considered that the OFDM method is resistant to delayed wave interference, and generally delay multiplexing up to the guard interval length is performed. It becomes possible to prevent the influence of interference on the waves.

  On the other hand, a multiband OFDM system is currently proposed as a communication system related to UWB adopted as a physical layer of WPAN. The multiband OFDM scheme is a scheme in which radio signals multiplexed by the OFDM modulation scheme are communicated by switching different frequency bands for each symbol.

  FIG. 7 is a diagram for explaining the operation principle of the multiband OFDM method using three different frequency bands. The multiband OFDM transmitter transmits an OFDM signal while sequentially switching the three frequency bands f1, f2, and f3 on the time axis as shown in FIG. In such a multiband OFDM system, it is the same that the influence of delayed multiplexed waves can be removed by using a guard interval. However, in this system, the guard of zero prefix format is used instead of the cyclic prefix format described above. An interval is used.

  Similarly to the cyclic prefix format, the zero prefix format inserts a guard interval between adjacent symbols for a symbol that is an effective FFT interval, but in the zero prefix format, a null interval where no signal exists as a guard interval. Insert. FIG. 8 shows the structure of an OFDM symbol (also referred to as “frame”, hereinafter the same) using the zero prefix format.

  In the case of the zero prefix format, the manner in which the delayed multiplexed wave is superimposed shows a behavior different from that in the case of the cyclic prefix.

  FIG. 9 is a diagram for explaining the state of delayed multiple waves in the zero prefix format and the principles of sampling and signal synthesis. In the cyclic prefix format, intersymbol interference (FIG. 6) occurs due to the addition of adjacent symbols in the vicinity of the symbol switching point due to the delayed multiplexed wave, but in the zero prefix format, the symbol as shown in FIG. Since there is a null interval between them, there is no interference from adjacent symbols, and a single delayed wave is shifted on the time axis over the entire symbol period, resulting in a superimposed waveform (received signal) added to the direct wave.

  As a result, both ends of the symbol have only one of these two waves, so that waveform discontinuity occurs, resulting in waveform distortion. However, as shown in the figure, the zero-prefixed OFDM receiver samples the received signal continuously in both the effective FFT interval and the guard interval, and obtains the sampling data in the obtained guard interval. Add to the beginning of the effective FFT interval. The signal obtained by this processing is obtained by adding two continuous signal waveforms within the symbol period, and therefore correct demodulation by FFT processing is possible.

  FIG. 4 shows a configuration example of an OFDM receiver that demodulates such a zero prefix OFDM signal. The OFDM receiver includes an antenna 11, an RF processing unit 12, an AD converter 13 that converts an analog signal into a digital signal, and a digital demodulator 14 that performs demodulation by digital computation.

  Next, FIG. 10 shows a configuration of a conventional digital demodulator 14 provided in such an OFDM receiver. The digital demodulator 14 according to the prior art includes a synchronization unit 101, a sampling unit 102, a sampling synthesis unit 103, an FFT unit 104, an equalizer 105, a channel decoder 106, and the like.

  For the received signal received by the antenna 11, the receiver converts the received signal into a low frequency band received signal in the RF processing unit 12. The converted signal is converted into digital data by the AD converter 13 and transmitted to the digital demodulator 14.

  In the digital demodulator 14, the synchronization unit 101 captures the frame synchronization from the obtained digital data from a correlation calculation with a training waveform such as a preamble. After the frame synchronization is acquired, the sampling start point of the reception data is determined from the synchronization point, and the reception data is sampled in the sampling unit 102 in the effective FFT length and the guard interval period. The sampling data obtained in this way is sent to the sampling synthesis unit 103, and the sampling data in the guard interval period is added to the head portion of the sampling data in the effective FFT period as in the process shown in FIG.

  The combined sampling data obtained in this way is sent to the FFT processing unit and converted from a signal on the time axis to a demodulated signal on the frequency axis. Since a delay wave is superimposed on the received signal, the phase and amplitude for each subcarrier of this demodulated signal change compared to the transmission waveform, but each subcarrier is a continuous signal and a symbol Not affected by interference. Therefore, the received signal is correctly FFT processed in the FFT unit 104, and the phase and amplitude are corrected for each subcarrier on the frequency axis in the equalizer 105, and the correct received data is demodulated. The demodulated received data is then transmitted to the channel decoder 106, subjected to decoding processing, and then sent to an upper layer such as an application.

  As mentioned above, the configuration example of the conventional OFDM receiver of the zero prefix format is given and it is shown that the OFDM signal can correctly demodulate the received data even in the multiwave propagation environment. However, in the conventional demodulator 14, since the sampling interval length is determined in advance, even if the desired delay wave does not exist in the guard interval, or the delay time is short and no signal is present in the rear part of the guard interval, Demodulation was performed using these sampling data. Therefore, when an interference component other than a desired delayed wave exists in the guard interval period, there is a problem that the communication quality deteriorates because this component affects the demodulation characteristics.

  In particular, in the multi-band OFDM method, it is assumed that multiple systems having different frequency hopping patterns share the bandwidth in a time-sharing manner. In such a case, synchronization with other hopping patterns due to hopping timing shifts. There is a risk of receiving a signal from a wireless station during this guard interval period, and when demodulating using the sampling value of this non-signal section, it is greatly affected. In order to solve such a problem, a method is required in which the sampling interval length is adaptively varied according to the surrounding radio propagation environment characteristics, and the sampling values of unnecessary sampling intervals are not employed in the demodulation process.

  As a conventional technique for controlling the sampling interval in the OFDM communication system as described above, Patent Document 1 is cited. In Patent Document 1, the start of the sampling interval is set with reference to the peak time point that is the earliest timing for a plurality of peak detection timings detected by the influence of the delayed multiplexed wave. In Patent Document 1, sampling for an OFDM frame using a cyclic prefix format is effective for adaptively selecting a sampling start point, but for an OFDM symbol of a zero prefix format, a constant sampling is used. Since the sampling is performed with the section length, the effect of removing the delayed wave cannot be obtained.

Further, Patent Document 2 is another conventional technique for controlling the sampling interval in the OFDM communication system. In Patent Document 2, an FFT operation is performed on a plurality of sampling data obtained from a plurality of sampling point candidates, and the above-described plurality of sampling point candidates are obtained from pilot subcarrier phase and amplitude information obtained from the FFT operation result. The most probable synchronization start point is selected. In Patent Document 2, since FFT calculation is performed on sampling data corresponding to a plurality of synchronization point candidates, there is a disadvantage that a processing delay is large and a circuit configuration and a calculation amount are also increased. Further, as in the above-described prior art, only the synchronization point at which the FFT operation is started is determined, and it cannot be applied to an OFDM modulation scheme using a guard interval of the zero prefix format.
JP 2000-224132 A JP2003-134083

  As described above, in the OFDM communication system using the zero-prefix format, sampling is continuously performed even during the guard interval period, thereby suppressing the occurrence of waveform distortion due to delayed wave interference. Since a sampling value in a non-existing section is also used for demodulation, there is a problem in that communication quality deteriorates due to unnecessarily capturing noise and interference waves.

  In view of such a problem, an object of the present invention is to provide a wireless communication technique that realizes good communication quality according to a delayed wave propagation environment.

In order to achieve the above object, a wireless communication apparatus according to the present invention is a wireless communication apparatus that processes a received signal having a data part of an orthogonal frequency division multiplexed signal and a no-signal part in which no signal exists, Receiving means for receiving an incoming wave; discriminating means for discriminating delay propagation characteristics of the plurality of incoming waves; setting means for setting a sampling interval of a received signal based on the delay propagation characteristics discriminated by the discriminating means; It is characterized by having.
Further, the signal processing method according to the present invention is a signal processing method for processing a received data symbol in a zero-prefix format, wherein a determination step for determining delay propagation characteristics of a plurality of received incoming waves, and the determination step And a setting step for setting a sampling interval of the received signal based on the delay propagation characteristic determined in step (1).

  According to the present invention, since the sampling interval is variably set according to the delay wave propagation environment, it is possible to demodulate by removing interference components other than the desired delay wave, and to provide a radio communication technique with good communication quality It becomes possible to do.

  An embodiment of a receiving apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1B is a block diagram showing the configuration of the receiving apparatus, and the same reference numerals are used for portions that overlap with FIG. 4 showing the configuration of the conventional receiving apparatus. The receiving device includes an antenna 11, an RF processing unit 12, an AD converter 13 for converting an analog signal into a digital signal, and a digital demodulator 140 that performs demodulation by digital computation. It differs from the configuration of FIG. 4 in that there is a feature.

  A communication system using an OFDM modulation scheme having a symbol structure of the zero prefix format can be applied to various antenna configurations, frequency bands to be used, configurations of high frequency processing units, and the like. As for the sampling of the analog signal, FIG. 1B assumes that sampling is performed in the passband band, so that one AD converter is provided, but sampling of the in-phase channel and the quadrature channel is performed in the baseband band. In some cases, two AD converters can be used.

  FIG. 1A is a diagram showing a configuration of a digital demodulator 140 in the receiving apparatus according to the embodiment of the present invention. The digital demodulator 140 includes a synchronization unit 201, a sampling interval setting unit 202, a sampling unit 203, a sampling synthesis unit 204, an FFT unit 205, an equalizer 206, a communication path decoder 207, and the like.

  A transmission apparatus constituting a wireless communication system using the OFDM communication system transmits an OFDM-modulated transmission signal, and this transmission signal is composed of a data symbol having an effective FFT interval (time) length and a null interval in which no signal exists. The null section has a data structure inserted between consecutive data symbols.

  In a receiving apparatus that constitutes a radio communication system, first, a transmission signal transmitted from a transmitting apparatus is received by an antenna 11 of the receiving apparatus (OFDM received signal). The processing unit 12 performs conversion to a low signal band that can be AD converted. The converted reception signal is converted into digital reception data by the AD converter 13. In wireless LAN and WPAN, packet-type communication is generally performed. However, in the receiving apparatus, the synchronization unit 201 first acquires frame synchronization for an incoming packet. In packet-type communication, a synchronization point is determined mainly by performing a correlation operation on a preamble added to the head of a packet (see FIG. 2). For the preamble, a signal pattern having a good autocorrelation characteristic, that is, a periodic autocorrelation characteristic having a sharp peak only at a synchronization point and having zero or an extremely low correlation value at a portion other than the synchronization point is used. The synchronization unit 201 includes a matched filter having a replica pattern having the same waveform as such a preamble signal pattern (this replica pattern is data prepared in advance, hereinafter also referred to as “normative data”). As a result of the correlation calculation with the received signal, a correlation peak is calculated as a matched filter output in accordance with the correlation level at which the waveform patterns match.

  In the delayed multiwave propagation environment, since the received signal includes a plurality of incoming waves, the actual matched filter output has a strength corresponding to the signal level depending on the delay time of each incoming wave as shown in FIG. A plurality of correlation peaks appear. A waveform as shown in FIG. 2 indicates an impulse response of a communication path from the transmission device to the reception device, and is generally called a delay profile. The synchronization unit 201 measures such a delay profile by performing a correlation operation on the received signal, and transmits the measurement result to the sampling interval setting unit 202.

  The sampling interval setting unit 202 determines the maximum delay time that the delay wave arrives from this delay profile. Here, when a signal having a low signal level among a plurality of delayed waves can be ignored as it does not affect demodulation, for example, a certain threshold value is set for determining the maximum delay time as shown in FIG. Only the correlation peak having the correlation level equal to or higher than the threshold is extracted, and the arrival time difference between the earliest wave and the earliest wave among them can be determined as the maximum delay time. The sampling interval setting unit 202 determines the timing of the correlation peak A (synchronization point A) in this delay profile as the sampling start time, and the timing of the correlation peak A and the correlation peak B (synchronization point B) with respect to the effective FFT interval length. ) To set the sampling interval (time).

  FIG. 3 is a diagram for explaining a delay profile when the maximum delay time of an incoming delay wave is large (a) and small (b), and a sampling interval setting method (c) for a received signal.

  Here, T is the effective FFT section (time) length of one symbol length of the received signal received by the receiving apparatus. In the receiving apparatus, when the maximum delay time of the delayed multiplexed wave is large (a), the sampling interval setting unit 202 adds the time t1 between the correlation peak A1 and the correlation peak B1 to T, and the sampling interval ( Time) is set as T + t1 (see (c)).

  On the other hand, when the maximum delay time of the delayed multiplexed wave is small (b), the sampling interval setting unit 202 adds the time t2 between the correlation peak A2 and the correlation peak B2 to T, and the sampling interval (time) for the received signal. ) Is set as T + t2 (see (c)). By setting the sampling period in this way, it is possible to adaptively (variably) set the optimal sampling time length according to the delay propagation environment characteristics.

  Even when a delayed interference signal is present in the received signal, such an interference signal component does not appear in the matched filter because the interference signal is uncorrelated with the waveform pattern of the preamble. Therefore, only the delayed wave component is extracted by using the matched filter output, and the minimum sampling interval necessary for demodulation can be correctly determined.

  Further, the sampling start point and the sampling interval (time) length determined in this way are transmitted to the sampling unit 203, and the sampling unit 203 takes in the data at the timing designated by the sampling interval setting unit 202 from the received digital data. . The sampling unit 203 samples the fetched data and outputs the obtained sampling data to the sampling synthesis unit 204. The sampling synthesis unit 204 adds the data after the effective FFT interval length of the received sampling data (the data of the time interval added to the effective FFT interval based on the maximum delay time) to the data of the head portion of the effective FFT interval, The data is output to the FFT unit 205, and demodulated data on the frequency axis is obtained by the FFT unit 205. By adaptively setting the required sampling interval length variably from the delay propagation characteristics obtained by the synchronization unit 201, it is possible to perform FFT computation using sampling data from which unnecessary interference components have been removed. .

  After the FFT operation, the phase and amplitude are corrected for each subcarrier by the equalizer 206 on the frequency axis in the same manner as a general OFDM demodulator, and correct received data is demodulated. The demodulated received data is then transmitted to the channel decoder 207, subjected to decoding processing, and then sent to an upper layer such as an application.

  According to this embodiment, in order to set an adaptive (variable) optimum sampling section (time) according to the delay wave propagation environment, it is possible to demodulate by removing interference components other than the desired delay wave, It becomes possible to provide a wireless communication technology with good communication quality.

  Also, in this description, the system of zero prefix format that does not switch the frequency band as an example of communication is taken as an example. However, since the present invention focuses on a single OFDM data symbol, not only the normal OFDM method. The present invention can also be applied to a communication system using frequency hopping, such as a multiband OFDM system in which a plurality of frequency bands are switched for communication.

[Other embodiments]
As described above, an object of the present invention is to process a received signal having an effective data portion corresponding to one period of the orthogonal frequency division multiplexed signal transmitted according to the above-described embodiment and a no-signal portion in which no signal exists. Providing a storage medium storing a program code of a signal processing program for realizing the function of the wireless communication apparatus to be executed, and reading and executing the program code stored in the storage medium by a computer (or CPU or MPU) of the apparatus Is also achieved.

  In this case, the signal processing method executed in the above-described wireless communication apparatus is a signal processing method for processing a received data symbol in the zero prefix format, and determining the delay propagation characteristics of a plurality of received waves received And a setting step of setting a sampling interval of the received signal based on the delay propagation characteristic determined in the determination step.

  The signal processing program causes the computer to function as the processing operation of the computer, and the code of the program is stored in a computer-readable storage medium.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. As a storage medium for supplying such a program code, for example, a floppy disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a CD-R, a magnetic tape, a nonvolatile memory card, a ROM, or the like is used. Can do.

  Further, by executing the program code read by the computer, not only the functions of the above-described embodiments are realized, but also an OS (operating system) running on the computer based on the instruction of the program code Includes a case where the function of the above-described embodiment is realized by performing part or all of the actual processing.

  Furthermore, after the program code read from the storage medium is written in the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, the function is determined based on the instruction of the program code. This includes the case where the CPU of the expansion board or function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing.

  According to the present embodiment, since an optimal sampling interval is adaptively set according to the delay wave propagation environment, it is possible to demodulate by removing interference components other than the desired delay wave, and a signal with good communication quality. It is possible to provide a processing program and a computer-readable storage medium storing the program.

It is a figure which shows the structure of the digital demodulator in the receiver which concerns on embodiment of this invention. It is a figure which shows the structure of the receiver which concerns on embodiment of this invention. It is a figure explaining a delay profile. It is a figure explaining the setting method (c) of the delay profile of the case where the maximum delay time of the incoming delay wave is large (a) and the case where it is small (b), and the sampling interval with respect to a received signal. It is a figure which shows the structural example of the receiver which demodulates the OFDM signal of a zero prefix format. It is a block diagram of OFDM data symbols in a cyclic prefix format. It is a figure explaining the process which demodulates the OFDM signal of a cyclic prefix format. It is a figure explaining the principle of a multiband OFDM communication system. It is a figure explaining the structure of the OFDM data symbol of a zero prefix format. It is a figure explaining the demodulation principle of the OFDM signal of a zero prefix format. It is a figure explaining the structure of the digital demodulator in the conventional OFDM receiver.

Claims (9)

A wireless communication device for processing a received signal having a data part of an orthogonal frequency division multiplexed signal and a non-signal part where no signal exists,
Receiving means for receiving a plurality of incoming waves;
Discrimination means for discriminating delayed propagation characteristics of the plurality of incoming waves;
Setting means for setting a sampling interval of the received signal based on the delay propagation characteristic determined by the determining means;
A wireless communication apparatus comprising: Sampling means for sampling the data of the sampling interval set by the setting means and outputting a sampling value;
The addition means for adding the data after the effective FFT section of the sampling value sampled by the sampling means to the head portion of the data of the effective FFT section;
Conversion means for converting the data added by the addition means into data on the frequency axis;
The wireless communication apparatus according to claim 1, further comprising: The discriminating unit discriminates a delay time between the earliest incoming wave and the latest incoming wave based on a correlation level between a plurality of incoming waves received by the receiving unit and preliminarily prepared reference data. The wireless communication apparatus according to claim 1, wherein the wireless communication apparatus is a wireless communication apparatus. The wireless communication apparatus according to claim 1, wherein the setting unit sets a time obtained by adding the delay time to the time of the effective FFT interval as the sampling interval. The wireless communication apparatus according to claim 1, wherein the reception unit receives a signal transmitted by switching a plurality of frequency bands. A signal processing method for processing a received data symbol in a zero prefix format,
A discriminating step for discriminating delay propagation characteristics of a plurality of incoming waves received;
Based on the delay propagation characteristics determined in the determination step, a setting step for setting a sampling interval of the received signal;
A signal processing method characterized by comprising: 7. The signal processing method according to claim 6, further comprising an addition step of adding data of a delay portion of sampling data in the sampling interval to a head portion of the sampling data based on the determination in the determination step. A program causing a computer to execute the signal processing method according to claim 6. A computer-readable storage medium storing the program according to claim 8.

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