JP2015084494A - Receiver, symbol timing synchronization device, and symbol timing synchronization method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce erroneous symbol timing synchronization (false synchronization, or no detection of synchronization), even under a poor radio wave condition.SOLUTION: A receiver, having a plurality of diversity branches, provides a plurality of symbol timing synchronization means for synchronizing symbol timings of orthogonal frequency division multiplex signals received by different antenna parts, respectively. Each of the symbol timing synchronization means informs other symbol timing synchronization means of a boundary timing between a short preamble and a long preamble, and performs symbol timing synchronization of the received orthogonal frequency division multiplex signals on the basis of a boundary timing detected by own means and a boundary timing detected by other symbol timing synchronization means.

Description

  The present invention relates to a receiver, and can be applied to, for example, a receiver that performs a symbol timing synchronization method using an Orthogonal Frequency Division Multiplexing (OFDM) modulation system having a spatial diversity function.

  Conventionally, radio waves are reflected at a building or the like, and a plurality of reflected radio waves are overlapped, so that instantaneous amplitude and phase fluctuations of the radio waves occur and multipath fading occurs. Such multipath fading occurs as the terminal moves. Therefore, if the terminal antenna moves along a different route, it undergoes completely different fading fluctuations. The diversity technique is a technique for improving reception characteristics by utilizing such characteristics. For example, two antennas are arranged at an appropriate interval in a terminal, and the signals received by the respective antennas are moved as the terminal moves. Fading fluctuations are independent fluctuations.

  One type of diversity is spatial diversity. In spatial diversity, signals that have undergone multiple independent fading are obtained by spatially separated antennas. In the case of spatial diversity, the configuration is relatively simple, and the number of diversity branches (that is, the number of antennas) can be set to an arbitrary number, and there is no need to increase the bandwidth and transmission power. This is a practical technology adopted in the system.

  Conventionally, in the case of a communication scheme using an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme, an OFDM signal (packet signal) transmitted from a transmitter is composed of a preamble signal and a data signal. Among these, the preamble signal is used for channel estimation and a short preamble configured by repeating a plurality of known synchronization patterns (hereinafter also referred to as short symbols) for each basic period in order to establish symbol timing synchronization. It consists of a long preamble configured by repeating a known synchronization pattern (hereinafter also referred to as a long symbol), and the long preamble follows the short preamble.

  In the symbol timing synchronization establishment method using a short preamble, first, a complex correlation operation is performed using a received signal and a known specific pattern. Then, the obtained correlation value is compared with a threshold value, and when the correlation value exceeds the threshold value, the peak of the correlation value (correlation peak) is detected. If the correlation peak is detected continuously and no short symbol is detected at the timing when a predetermined time has elapsed, it can be determined that the short preamble has shifted to the long preamble at that time. By detecting the boundary between the short preamble and the long preamble, it can be determined that synchronization is established. Note that the above-described predetermined time can be, for example, the time of one short preamble.

JP 2009-239548 A

Seiichi Sampei, "Digital Wireless Transmission Technology-From Basics to System Design", Pearson Education, September 2002, pp. 146-154

  However, the symbol timing synchronization establishment method using the conventional OFDM modulation method has the following two problems.

  First, it is necessary for the receiver to detect all the short symbols without omission when receiving the short preamble. However, for example, when a short symbol cannot be detected even once in the middle due to fluctuations in the received radio signal due to the external environment where the terminal is placed or an AGC (Automatic Gain Control) operation, the short symbol is detected even during the short preamble detection. It is erroneously determined that the preamble has shifted to the long preamble, and the boundary between the short preamble and the long preamble cannot be detected correctly. In this case, there is a problem in that the subsequent data signal cannot be correctly interpreted, and there is a possibility of erroneous synchronization in which a reception error occurs.

  Secondly, when the short symbol cannot be detected even once in the receiver, the start position of the data signal cannot be interpreted, and there is a problem that synchronization non-detection that a reception error occurs may occur.

  The present invention has been made in view of the above problems. A receiver, a symbol timing synchronization device, and a symbol timing capable of reducing symbol timing synchronization errors (mis-synchronization, synchronization non-detection) even when the radio wave condition is bad. It is intended to provide a synchronization method.

  In order to solve this problem, a first aspect of the present invention provides a plurality of symbol timing synchronization means for performing symbol timing synchronization of orthogonal frequency division multiplexed signals received by different antenna units in a receiver having a plurality of diversity branches. Each of the plurality of symbol timing synchronization means notifies the boundary timing between the short preamble and the long preamble mutually with the other symbol timing synchronization means, and the boundary timing detected by itself and other symbol timings The symbol timing synchronization of the received orthogonal frequency division multiplex signal is performed based on the boundary timing detected by the synchronization means.

  A symbol timing synchronization apparatus according to a second aspect of the present invention is a symbol timing synchronization apparatus that performs symbol timing synchronization of orthogonal frequency division multiplexed signals received by different antenna units in a receiver having a plurality of diversity branches. The timing synchronization means mutually notifies the boundary timing between the short preamble and the long preamble, and the received timing is based on the boundary timing detected by itself and the boundary timing detected by other symbol timing synchronization means. Symbol timing synchronization means for performing symbol timing synchronization of the orthogonal frequency division multiplexed signal is provided.

  According to a third aspect of the present invention, there is provided a symbol timing synchronization method for performing symbol timing synchronization of orthogonal frequency division multiplexed signals received by different antenna units in a receiver having a plurality of diversity branches. However, it notifies the boundary timing between the short preamble and the long preamble mutually with other symbol timing synchronization means, and based on the boundary timing detected by itself and the boundary timing detected by other symbol timing synchronization means Thus, symbol timing synchronization of the received orthogonal frequency division multiplex signal is performed.

  According to the present invention, it is possible to reduce symbol timing synchronization errors (mis-synchronization, synchronization non-detection) even when the radio wave condition is poor.

It is a block diagram which shows the structure of the receiver which concerns on embodiment. It is an internal block diagram which shows the internal structure of the demodulation part of the receiver which concerns on embodiment. It is a block diagram which shows the internal structure of the symbol timing synchronization part of the receiver which concerns on embodiment. It is a flowchart which shows the processing operation of the symbol timing synchronization part in the receiver which concerns on embodiment. It is a flowchart which shows the processing operation of the symbol timing synchronization part in the receiver which concerns on embodiment. It is a flowchart which shows the processing operation of the symbol timing synchronization part in case the receiver which concerns on embodiment is provided with the number of branches of 3 or more. It is explanatory drawing explaining the operation | movement in the counter part which concerns on embodiment (the 1). It is explanatory drawing explaining the operation | movement in the counter part which concerns on embodiment (the 2). It is explanatory drawing explaining the operation | movement in the counter part which concerns on embodiment (the 3). It is explanatory drawing explaining the operation example of the symbol timing synchronization by the symbol timing synchronization part which concerns on embodiment (the 1). It is explanatory drawing explaining the operation example of the symbol timing synchronization by the symbol timing synchronization part which concerns on embodiment (the 2).

(A) Main Embodiments Hereinafter, embodiments of a receiver, a symbol timing synchronization apparatus, and a symbol timing synchronization method of the present invention will be described in detail with reference to the drawings.

  This embodiment corresponds to a communication system that employs an OFDM modulation system, and illustrates a case where the present invention is applied to a receiver having a spatial diversity function.

(A-1) Configuration of Embodiment (A-1-1) Configuration of Receiver FIG. 1 is a configuration diagram illustrating a configuration of a receiver 1 according to the embodiment. In FIG. 1, a receiver 1 according to this embodiment includes an antenna unit 10, a demodulation unit 11, a symbol timing synchronization unit 15, a guard interval (GI) removal unit 14, a serial-parallel (S / P) conversion unit 12, a discrete unit. Fourier transform (DFT) unit 13, antenna unit 20, demodulation unit 21, symbol timing synchronization unit 25, guard interval (GI) removal unit 24, serial-parallel (S / P) conversion unit 22, discrete Fourier transform (DFT) unit 23, diversity combining units 30-1 to 30-L, a parallel-series (P / S) conversion unit 33, and a determination unit 34.

  The receiver 1 according to this embodiment is an OFDM receiver having a spatial diversity function, and illustrates the case where the number of diversity branches (hereinafter also simply referred to as branches) is two. In this embodiment, the diversity branch is expressed as a diversity branch (branch) 51 and a diversity branch (branch) 52 as necessary.

  In addition, the number of carriers (number of subcarriers) for dispersing the carriers used in the OFDM modulation scheme is set to “L”.

  A transmitter (not shown) encodes an information bit string in a baseband (baseband) and converts it into a carrier frequency (high frequency) band. The modulated signal is radiated to the space by the antenna unit of the transmitter, and is captured (received) by the antenna unit 10 and the antenna unit 20 of the receiver 1.

  The antenna unit 10 converts captured (received) radio waves into electrical signals and supplies them to the demodulation unit 11.

  The demodulator 11 extracts a signal component in the carrier frequency band from the signal from the antenna unit 10, demodulates the signal in the carrier frequency band, and reproduces a baseband digital signal. The digital signal is supplied to the GI removal unit 14 and the symbol timing synchronization unit 15.

  The symbol timing synchronization unit 15 acquires a baseband digital signal from the demodulation unit 11 and specifies the boundary of each OFDM symbol in the baseband digital signal (that is, the timing at which the guard interval unit is removed). That is, the symbol timing synchronization unit 15 performs a complex correlation operation using the baseband digital signal and a known specific pattern, compares the correlation value with the threshold value, and if the correlation value exceeds the threshold value, the correlation peak Is detected. Then, when the correlation peak is detected continuously and no short symbol is detected at a timing when a predetermined time has elapsed, it is determined that the short preamble has shifted to the long preamble at that time. The symbol timing synchronization unit 15 notifies the GI removal unit 14 of the boundary of each identified OFDM symbol.

  The symbol timing synchronization unit 15 counts the elapsed time from the end of the short symbol and notifies the count value (that is, the elapsed time from the end of the short symbol) to the symbol timing synchronization unit 25 of the other branch. is there.

  In order to reduce intersymbol interference, the GI removal unit 14 is configured to generate a baseband digital signal from the demodulation unit 11 based on information (timing to remove the guard interval) indicating the boundary of each OFDM symbol from the symbol timing synchronization unit 15. Is used to remove the guard interval portion. The GI removal unit 14 gives the digital signal after removal of the guard interval to the S / P conversion unit 12 in units of OFDM symbols.

  The S / P converter 12 obtains the baseband digital signal in units of OFDM symbols after the guard interval is removed from the GI remover 14, performs serial-parallel conversion on the baseband digital signal in units of OFDM symbols, and The sample values for L (L indicates the number of carrier waves) are accumulated and collectively supplied to the DFT unit 13. That is, the S / P converter 12 distributes serial digital signals transmitted in time series to L parallel circuits, and supplies sample values of L baseband digital signals to the DFT unit 13.

  The DFT unit 13 converts the L baseband digital signals from the S / P conversion unit 12 into a signal component on the frequency axis from a signal waveform on the time axis by discrete Fourier transform, and outputs each of the L carrier waves ( The baseband signal modulated by the subcarrier) is separated. The DFT unit 13 supplies L baseband signals obtained by discrete Fourier transform to the diversity combining units 30-1 to 3-L, respectively.

  The antenna unit 20 converts the captured (received) radio wave into an electrical signal and supplies it to the demodulation unit 21.

  The demodulator 21 extracts a signal component in the carrier frequency band from the signal from the antenna unit 20, demodulates the signal in the carrier frequency band, and reproduces a baseband digital signal. The digital signal is supplied to the GI removal unit 24 and the symbol timing synchronization unit 25.

  The symbol timing synchronization unit 25 acquires a baseband digital signal from the demodulation unit 21 and specifies the boundary of each OFDM symbol in the baseband digital signal. That is, the symbol timing synchronization unit 25 performs a complex correlation operation using the baseband digital signal and a known specific pattern, compares the correlation value with the threshold value, and if the correlation value exceeds the threshold value, the correlation peak Is detected. Then, when the correlation peak is detected continuously and no short symbol is detected at a timing when a predetermined time has elapsed, it is determined that the short preamble has shifted to the long preamble at that time. The symbol timing synchronization unit 25 notifies the GI removal unit 24 of the boundary of each identified OFDM symbol.

  The symbol timing synchronization unit 25 counts the elapsed time from the end of the short symbol and notifies the count value (that is, the elapsed time from the end of the short symbol) to the symbol timing synchronization unit 15 of another branch. is there.

  The GI removal unit 24 removes the guard interval unit from the baseband digital signal from the demodulation unit 21 based on the information indicating the boundary of each OFDM symbol from the symbol timing synchronization unit 25 in order to reduce intersymbol interference. Is. The GI removal unit 24 gives the digital signal after removal of the guard interval to the S / P conversion unit 22 in units of OFDM symbols.

  The S / P converter 22 acquires the baseband digital signal in units of OFDM symbols after the guard interval is removed from the GI remover 14, and performs serial-parallel conversion on the baseband digital signal in units of OFDM symbols to obtain a time direction. Thus, L sample values are accumulated and given to the DFT unit 23 at once. That is, the S / P converter 22 distributes serial digital signals transmitted in time series to L parallel circuits, and supplies sample values of the L baseband digital signals to the DFT unit 23.

  The DFT unit 23 converts the L baseband digital signals from the S / P conversion unit 22 into a signal component on the frequency axis from a signal waveform on the time axis by discrete Fourier transform, and outputs each of the L carrier waves ( The baseband signal modulated by the subcarrier) is separated. The DFT unit 23 supplies L baseband signals obtained by the discrete Fourier transform to the diversity combining units 30-1 to 3-L, respectively.

  Diversity combining sections 30-1 to 30-L obtain L baseband signals subjected to discrete Fourier transform from DFT sections 13 and DFT sections 23 of two branches, and have the same carrier frequency (that is, the same subcarrier). Number) is synthesized by a predetermined method and given to the P / S converter 33 as one received signal. Here, various existing techniques such as a selective synthesis method or a maximum ratio synthesis method can be widely applied as a synthesis method by the diversity synthesis units 30-1 to 30-L. Detailed description of the processing in diversity combining sections 30-1 to 30-L will be omitted.

  The P / S conversion unit 33 performs parallel-to-serial conversion on baseband signals relating to L carriers from the diversity combining units 30-1 to 30-L, and supplies the result to the determination unit 34 as L sample values in the time direction. It is.

  The determination unit 34 performs a decoding process on the baseband signal from the P / S conversion unit 33 and reproduces the original information bit string.

  In this embodiment, the case where the receiver 1 has two branches is illustrated, but the number of branches may be three or more. Even in that case, the configuration of each branch may be the same as or corresponding to the configuration illustrated in FIG. That is, each branch includes an antenna unit, a demodulation unit, a symbol timing synchronization unit, a GI removal unit, an S / P conversion unit 12, and a DFT conversion unit 13. Also, diversity combining sections 30-1 to 30-L are input with received signals from the DFT sections of all branches.

  When the number of branches is three or more, the elapsed time from the end of the short symbol is notified from the symbol timing synchronization unit of each branch to the symbol timing synchronization units of all other branches.

(A-1-2) Detailed Configuration of Demodulation Unit FIG. 2 is an internal configuration diagram showing an internal configuration of the demodulation units 11 and 21 of the receiver 1 according to the embodiment. The demodulating units 11 and 21 have the same configuration.

  In FIG. 2, the demodulation units 11 and 21 according to the embodiment include a band pass filter (BPF) 101, an AGC amplifier 102, a down converter 103, a local oscillator 104, a low pass filter (LPF) 107, and analog-digital (A / D). A conversion unit 108, a low-pass filter (LPF) 105, and an AGC control unit 106 are included.

  The bandpass filter (BPF) 101 passes a signal component in a predetermined band centered on a desired carrier frequency through the signal from the antenna unit 10 or 20 in order to extract the modulation frequency of the carrier frequency. The carrier frequency band modulation signal is extracted, and the carrier frequency band modulation signal is supplied to the AGC amplifier 102.

  The AGC amplifier 102 applies a predetermined gain to the modulated signal in the carrier frequency band from the bandpass filter 101 in order to adjust the reception gain according to the input level, and the signal after the gain is applied to the down converter 103. It is something to give to. The AGC amplifier 102 determines the gain to be given to the modulated signal in the carrier frequency band under the control of the AGC control unit 106.

  In this embodiment, a case where only one AGC amplifier 102 is provided between the output of the BFP 101 and the input to the down converter 103 is illustrated. However, if the reception gain can be adjusted, the AGC amplifier 102 may be arranged at a different position or a plurality of positions. For example, in addition to the AGC amplifier 102 illustrated in FIG. 2, another output is provided between the output of the down converter 103 and the input to the LPF 107, or between the output of the LPF 107 and the input to the A / D conversion unit 108. A plurality of AGC amplifiers may be arranged by adding an AGC amplifier. In any case, the generality of the present invention is not impaired. Therefore, in this embodiment, only the case where the AGC amplifier 102 is only one between the output of the BFP 101 and the input to the down converter 103 is illustrated.

  The down converter 103 multiplies the modulated signal in the carrier frequency band from the AGC amplifier 102 and the reference signal from the local oscillator 104 to reproduce the baseband signal, and provides the baseband signal to the LPF 105.

  In this embodiment, the case where the down converter 103 assumes direct conversion and the frequency of the reference signal is the same as the carrier frequency to reproduce the baseband signal directly is exemplified. However, the down-converter 103 may apply a method of converting the signal into a signal in a frequency band that is intermediate between the carrier frequency band and the base band and then converting the signal into a base band signal. In any method, since the down converter does not impair the generality of the present invention, the description will be made here assuming that the down converter 103 performs direct conversion.

  A low-pass filter (LPF) 107 passes the baseband signal from the down-converter 103 through only a signal component in a band equal to or lower than a predetermined frequency, so that a signal from which unnecessary signal components are removed is sent to the A / D converter 108. Give. That is, the LPF 107 passes a signal component below the frequency band for extracting a desired signal obtained by removing the additional noise component from the received signal. Since the LPF 107 can apply an analog filter, it may be difficult to achieve the same and steep characteristics as the bandwidth of the desired signal because of its ease of implementation. However, it is desirable that the pass bandwidth is a little wider.

  The A / D converter 108 samples the analog signal from the LPF 107 at a predetermined frequency, converts the sampled signal into a quantized digital signal, and outputs the digital signal to the LPF 105.

  The low-pass filter (LPF) 105 passes the digital signal from the A / D converter 108 only through a band equal to or lower than a predetermined frequency, thereby removing a signal from which unnecessary components are removed as a GI remover (GI in FIG. 1). To the removal unit 14 or 24), the symbol timing synchronization unit (symbol timing synchronization unit 15 or 25 in FIG. 1), and the AGC control unit 106. For example, a digital filter based on FIR (finite impulse response) or the like can be used as the LPF 105, and a signal having a wider bandwidth than the desired signal that has passed through the LPF 107 can be limited to the bandwidth of the desired signal.

  The AGC control unit 106 determines the gain of the AGC amplifier 102 so that the level value (power value) of the input / output signal of each component in the receiver 1 is maintained within a predetermined range, and the gain is set to the AGC amplifier. 102. That is, the AGC control unit 106 holds the upper limit value and the lower limit value of the voltage value that can be output by each component (each circuit element), and the signal level value becomes larger than the upper limit value or lower than the lower limit value. If it becomes smaller, the amplitude of the signal is not proportional to the voltage value of each component (each circuit element), and the signal waveform cannot be reproduced correctly. Therefore, the AGC control unit 106 determines the gain of the AGC amplifier 102 in order to maintain the signal level value at an appropriate value between the upper limit value and the lower limit value. Specifically, the AGC control unit 106 observes the level value (power value) of the baseband signal from the A / D conversion unit 108, and smoothes the level of the baseband signal. Calculate Then, the AGC control unit 106 determines the gain of the AGC amplifier 102 so that the integrated value converges to a predetermined target value.

  In this embodiment, an example in which the AGC control unit 106 inputs an output signal from the LPF 105 and calculates an integral value of the power value of the signal is illustrated. However, the AGC control unit 106 inputs any of the output signal of the BPF 101, the output signal of the AGC amplifier 102, the output signal of the down converter 103, the output signal of the LPF 107, or the output signal of the A / D conversion unit 108, An integral value of the power value of the signal may be calculated. As described above, regardless of which output signal is input to the AGC control unit 106, the AGC control unit 106 does not impair the generality of the present invention. The case where (the input signal to the AGC control unit 106) is the output signal of the LPF 105 is illustrated.

(A-1-3) Detailed Configuration of Symbol Timing Synchronization Unit FIG. 3 is a configuration diagram illustrating an internal configuration of the symbol timing synchronization unit 15 or 25 of the receiver 1 according to the embodiment. Each of the symbol timing synchronization units 15 or 25 has the same configuration.

  In FIG. 3, the symbol timing synchronization unit 15 or 25 according to the embodiment includes a correlation unit 201, a peak detection unit 202, a counter unit 203, and a timing control unit 204.

  The correlation unit 201 calculates a correlation value between the received signal from the demodulation unit 11 or 21 and the short preamble signal (specific pattern signal) provided in the correlation unit 201, and gives the correlation value to the peak detection unit 202. As the symbol timing synchronization method by the correlator 201, an autocorrelation type, a cross-correlation type, or the like can be applied. However, since neither method impairs the generality of the present invention, a cross-correlation type is assumed here. The case where it did is illustrated.

  The peak detection unit 202 compares the correlation value calculated by the correlation unit 201 with a predetermined threshold, and determines that a peak (also referred to as a correlation peak) is detected when the correlation value is larger than the threshold. It is.

  The counter unit 203 observes the elapsed time from the peak detection position (short symbol end). The counter unit 203 gives the elapsed time (that is, the count value) from the peak detection position to the timing control unit 204 and the symbol timing synchronization unit of another branch. The detailed processing operation of the counter unit 203 will be described in detail in the section on operation description.

  The timing control unit 204 detects the elapsed time from the peak detection position observed by the counter unit 203 (that is, the count value of the counter unit 203 of its own branch) and the peak detection observed by the symbol timing synchronization unit of another branch. And the elapsed time from the position (that is, the count value of the counter unit 203 of the symbol timing synchronization unit of the other branch), and based on these count values, the boundary between the short preamble and the long preamble in the preamble of the received signal is obtained. The determination is made and the boundary of each OFDM symbol is notified to the GI removal unit 14. The detailed processing operation of the timing control unit 204 will be described in detail in the section on operation description.

(A-2) Operation of Embodiment (A-2-1) Overall Operation First, in a transmitter facing the receiver 1 according to this embodiment, an information bit string is encoded in a baseband (baseband), and a carrier wave Modulated to frequency (high frequency) band. The modulated signal is radiated into the space from the antenna unit of the transmitter and captured by the antenna unit 10 and the antenna unit 20 of the receiver 1.

  In the receiver 1, radio waves captured by the antenna unit 10 and the antenna unit 20 of each branch are converted into electric signals and supplied to the demodulation unit 11 and the demodulation unit 21. The demodulator 11 and the demodulator 21 of each branch extract the modulated signal in the carrier frequency band and reproduce the baseband digital signal. The baseband signal is converted into the GI removers 14 and 24 and the symbol timing synchronizer 15. And 25.

  In the symbol timing synchronization units 15 and 25 of each branch, the boundaries of individual OFDM symbols in the baseband digital signals from the demodulation units 11 and 21 are specified and notified to the GI removal units 14 and 24.

  On the other hand, the GI removal units 14 and 25 of each branch remove the guard interval unit from the symbol timing synchronization units 15 and 25 of each branch based on the information indicating the boundary of the OFDM symbol, and the baseband from which the guard interval is removed A signal is given to S / P converters 12 and 22 in units of OFDM symbols.

  In the S / P converters 12 and 22 of each branch, the baseband digital signal in OFDM symbol units from which the guard interval part is removed accumulates L sample values in the time direction by serial-parallel conversion, The data is input to the DFT units 13 and 23 all at once.

  The L baseband signals input to the DFT units 13 and 23 are separated into baseband signals that have been modulated by the L carrier frequencies (subcarriers) by discrete Fourier transform, and are each provided with different diversity combining units 30. -1 to 30-L.

  Diversity combining sections 30-1 to 30-L combine received signals from two branches having the same carrier frequency (the same subcarrier number) by a predetermined method, and provide P / S conversion section 33 as one received signal. Output.

  The baseband signals relating to each of the L carrier waves input to the parallel-serial converter 33 are parallel-serial converted and input to the determination unit 34 as L sample values in the time direction.

  The baseband signal input to the determination unit 34 is reproduced as an original information bit string by performing processing such as decoding.

(A-2-2) Operation of symbol timing synchronization unit 15 or 25 when there is no time difference between branches Next, the timing control unit 204 detects the boundary between the short preamble and the long preamble in the received signal of its own branch. A process for determining the latest time among the short preambles and long preamble boundaries of all the branches from the time when each branch detected the boundary between the short preamble and the long preamble will be described.

  First, here, a case will be described where it is assumed that there is no time difference between signals input to the antenna unit 10 and the antenna unit 20 of each diversity branch.

  FIG. 4 is a flowchart showing the processing operation of the symbol timing synchronization unit 15 or 25 in the receiver 1 according to this embodiment.

In the following description, it is assumed that time is normalized by the sampling period. That is, when the real time is t, the normalized time is t / (sampling period). In addition, the short symbol length and the GI length of the long preamble are T _p and T _GI2 , respectively. At this time, the GI length _{T GI2} short symbol length _{T p} and the long preamble _is a relation of _T GI2> _{T p,} for example, in the case of IEEE802.11a / g _standard, the relationship between _T GI2 = 2T _p.

  When the baseband digital signal from demodulator 11 is input to correlator 201 (S1), correlator 201 identifies the baseband digital signal and the specific pattern of the short preamble signal provided in correlator 201. A correlation value with (for example, a repeated pattern of short symbols) is obtained (S2).

  The peak detection unit 202 determines whether the correlation value calculated by the correlation unit 201 is larger than a predetermined threshold (S3). When it is determined that the correlation value is greater than the threshold value, the peak detection unit 202 determines that a peak has been detected, and outputs a peak detection signal to the counter unit 203 (S4). If the correlation value is determined to be equal to or less than the threshold value, the start position and end position of the correlation value calculation range of the received signal are advanced by one clock (one sampling period), respectively, and the received signal and the correlation unit 201 are again transmitted. The correlation value with the short preamble signal provided in is calculated (S2).

  When the peak detection signal is input from the peak detection unit 202 (S4), the counter unit 203 initializes the counter value and sets the value to “1” (S5).

Subsequently, the counter unit 203 counts the counter value until the short symbol length T _p elapses. That is, by increasing by "1" in one clock (= sampling period) for each, the counter value of the short symbol length _{T p} has elapsed after the counter 203 becomes _{T p} (S6). At this time, the counter unit 203 determines whether or not the peak detection signal from the peak detection unit 202 has been input again (S7).

  FIG. 7 is an explanatory diagram for explaining the operation of the counter unit 203. As shown in FIG. 7, when the peak detection signal is notified to the peak detection circuit unit 203 (S301), the counter unit 203 initializes the counter value to “1” (S302).

In S7, when the peak detection signal from the peak detection unit 202 is input again to the counter unit 203, it is determined that the short symbol has been received twice consecutively during the past “2T _p ”.

That is, as shown in FIG. 7, when the peak detection signal is input to the counter unit 203 (S304), when the current time is “0”, the received signal of “−2T _{p to} T _p ” is a short symbol. It is determined (S304), and the received signal of “−T _p ˜0” is also determined to be a short symbol (S305). In this case, in order to determine whether or not to continue receiving the short symbol (that is, during the subsequent T _p (for example, when the current time is “0”, a period of “0 to T _p ”)) In order to determine whether or not it is a short symbol, the counter unit 203 initializes the counter and sets the counter value to “1” (S5).

  On the other hand, when the peak detection signal is not input from the peak detection unit 202 to the counter unit 203 in S7, the following operation is performed.

  8 and 9 are explanatory diagrams for explaining the operation in the counter unit 203. FIG. The operation of the counter unit 203 after S7 will be described with reference to the explanatory diagrams of FIGS.

In S7, when the peak detection signal from the peak detection unit 202 is not input to the counter unit 203 (S401), during the past “T _p ” (when the current time is “0”, “−T _p ˜0”) the received signal of the period) is determined not to be a short symbol (S402), between the T _p even before than this (and the current time is set to "0", - the "2T _{p ~-T} p" period of) It is determined that the received signal is the last short symbol among consecutive short symbols (S403). In other words, the boundary between the short preamble and long preamble, (when the current time is set to "0", - the time of the "T _p") T _p back time from the current is determined to be a (S404).
In this case, the counter unit 203 continues counting the counter value, and counts the counter value until the GI length T _GI2 of the long preamble elapses when the timing at which the counter value is initialized is used as a base point (S405). That is, the counter unit 203 counts the counter value until “T _GI2 −T _p ” elapses when the current point is the base point. Specifically, by incrementing “1” every clock, the counter value of the counter unit 203 becomes “T _GI2 ” after T _{GI2 has} elapsed (S8).

  Here, as described above, the timing control unit 204 is given the counter value of the counter unit 203 in the symbol timing synchronization unit of the other branch.

The timing control unit 204 determines whether or not the counter value of the counter unit 203 of the symbol timing synchronization unit of the other branch is “T _GI2 ” (S100).

For example, if it is the symbol timing synchronization unit 15, it is determined whether the counter value of the counter unit 203 in the symbol timing synchronization unit 25 of the other branch is “T _GI2 ”. Further, for example, when the symbol timing synchronization unit 25 itself is, it is determined whether the counter value of the counter unit 203 in the symbol timing synchronization unit 15 of the other branch is “T _GI2 ”. This is to determine whether there is another branch that will detect the boundary between the short preamble and the long preamble later than the own branch.

In S100, when it is determined that the count value in the symbol timing synchronization unit of the other branch is “T _GI2 ” (S406 in FIG. 8), the GI length of the long preamble is detected after detecting the boundary between the long preamble and the short preamble in the other branch. That is, “T _GI2 ” or more has elapsed, and specifically, it is determined that the following [1] or [2].

[1] Similarly to the local branch, the received signal in the past T _GI2 (a period of “−T _GI2 ˜0” when the current time is “0”) is not a short symbol and the other branch is earlier than this. (If the current time is set to "0", "- T _GI2 -T _p" - the period of "-T _GI2") between the T _p and is the last of the short symbol of the short symbol of the received signal is a series of to decide. That is, the boundary between the short preamble and the long preamble is a time that goes back from _TGI2 from the present time (when the current time is “0”, the time point is “ _−TGI2 ”) (S407 in FIG. 8).

[2] In other branches, it is determined that no peak has been detected once reception of the previous frame is completed. In this case, since the transition is repeatedly made between S2 and S3, the counter value is not initialized in S5, and it is determined that the counter value “T _GI2 ” last set in S8 is maintained when the previous frame is received. To do. Note that the counter value of the counter unit 203 is set to “T _GI2 ” when the receiver is activated (that is, before the first frame is received). Accordingly, the boundary between the short preamble and the long preamble detected by the own branch is regarded as correct, and the process proceeds to S9.

On the other hand, when it is determined in S100 that the count value in the symbol timing synchronization unit of the other branch is not “T _GI2 ” (S407 in FIG. 9), in the other branch, the elapsed time after detecting the boundary between the long preamble and the short preamble is , Less than _TGI2 . That is, it is determined that the received signal in the period from “2T _p ” back to T _p (when the current time is “0”, “−2T _p to −T _p ”) is a short symbol. (S408 in FIG. 9). At this time, the counter value of the counter unit 203 in the symbol timing synchronization unit of the other branch is “T _p (≠ T _GI2 )”. That is, it is determined that the boundary between the short preamble and the long preamble is after the past T _p (or “−T _p ” when the current time is “0”).

This is at least T _p later than the time when the branch is determined to be the boundary between the short preamble and the long preamble (when the current time is “0”, “−2T _p ”), Assume that the boundary between the detected short preamble and long preamble is more correct (that is, the own branch has not been able to detect the short symbol due to fluctuations in the received radio signal due to the external environment and AGC operation), and at least T _p more than the own branch The boundary between the short preamble and the long preamble detected by the late other branch is set as the boundary between the short preamble and the long preamble of the local branch. Therefore, the counter value of the counter unit 203 of its own branch is decreased by T _p and the counter value is set to “T _GI2 −T _p ” (S101).

Subsequently, the process proceeds to S8. In S8, the counter unit 203 counts again during the period “T _p ” from the counter value “T _GI2 −T _p ” to the counter value “T _GI2 ”, so that the boundary between the short preamble and the long preamble of its own branch Is delayed by T _p .

  In S9, the timing control unit 204 notifies the GI removal units 14 and 24 that the current position of the received signal is the boundary between the GI and the long symbol in the long preamble, and the GI removal unit 14 The sampling value of the received signal from the demodulator 11 until the long symbol length elapses is acquired as the sampling value of the first long symbol and output to the S / P converter 12 (S9).

  Thereafter, the second long symbol, the first data part (in the case of the IEEE 802.11a / g standard, the first data part is the SIGNAL part), the second data part,..., The last data part Are output to the S / P converter 12 in units of OFDM symbols excluding the guard interval. After completion of frame reception (after reception of the last data portion), the process proceeds to S1 and the process is repeated again.

(A-2-3) Operation of Symbol Timing Synchronization Unit 15 or 25 in Case of Time Difference Between Branches FIG. 5 is a flowchart showing the processing operation of the symbol timing synchronization unit 15 or 25 in the receiver 1 according to the embodiment. is there.

Here, a difference in position of each antenna unit 10 and 20 in the diversity branch of the receiver 1 causes a difference in radio wave arrival time, and therefore a time difference T _{diff of} signals input to the antenna unit 10 and the antenna unit 20 occurs. Think about the case.

That is, when | T _diff | ≦ T _{diff, max} (0 ≦ T _{diff, max} <(T _GI2 −T _p ) / 2), and T _diff > 0, the signal input to the antenna unit 10 is the antenna. Assume that the signal is slower than the signal input to the unit 20. On the other hand, when T _diff <0, it is assumed that the signal input to the antenna unit 10 is earlier than the signal input to the antenna unit 20.

When T _diff = 0, it means that there is no time difference between signals input to the antenna unit 10 and the antenna unit 20, and as a result, the processing is the same as the flow shown in FIG.

  In FIG. 5, operations from processing S1 to S8 are the same as or correspond to operations from processing S1 to S8 in FIG. 4, and thus detailed description thereof is omitted here.

In S102, the timing control unit 204 determines whether or not the counter value of the counter unit 203 in the symbol timing synchronization unit of the other branch is equal to or greater than “T _GI2 −T _{diff, max} ” (S102).

For example, if it is the symbol timing synchronization unit 15, it is determined whether or not the counter value of the counter 203 in the symbol timing synchronization unit 25 of another branch is equal to or greater than “T _GI2 −T _{diff, max} ”. If the symbol timing synchronization unit 25 is itself, it determines whether or not the counter value of the counter 203 in the symbol timing synchronization unit 15 of the other branch is equal to or greater than “T _GI2 −T _{diff, max} ”.

This is because the other branch that detects the boundary between the short preamble and the long preamble later than the own branch in consideration of the time difference T _diff that may occur between the signal of the own branch and the signal of the other branch. Determine if it exists.

If it is determined in S102 that the counter value in the symbol timing synchronization unit of the other branch is equal to or greater than “T _GI2 −T _{diff, max} ”, the boundary between the long preamble and the short preamble is detected in the other branch, and then “T _GI2 −T _{diff, max} "or more has elapsed, and specifically, it is determined that the following [1] or [2].

[1] For example, the local branch is the branch 51 and the other branch is the branch 52. In this case, the other branch 52 does not receive the received signal during the past “T _GI2 + T _diff ” (the period of “−T _GI2 −T _diff ˜0” when the current time is “0”), A short circuit in which the received signal is continuously short during “T _p ” before this (when the current time is “0”, a period of “−T _GI2 −T _diff −T _p ˜−T _GI2 −T _diff ”). This is the last short symbol among the symbols. That is, the boundary between the short preamble and the long preamble is a time that is “T _GI2 + T _diff (≧ T _GI2 −T _{diff, max} )” from the present (when the current time is “0”, “−T _GI2 −T _diff ").

Also, for example, the local branch is the branch 52 and the other branch is the branch 51. In this case, the other branch 51 does not receive the received signal during the past “T _GI2 −T _diff ” (period “−T _{GI 2} + T _diff ˜0” when the current time is “0”), Prior to this, the received signal during a period of “T _p ” (a period of “−T _GI2 + T _diff −T _p ˜−T _{GI 2} + T _diff ”, _assuming that the current time is “0”) is a continuous short symbol. It is the last short symbol. That is, the boundary between the short preamble and the long preamble is a time that is “T _GI2 −T _diff (≧ T _GI2 −T _{diff, max} )” from the present (when the current time is “0”, “−T _GI2 + T _diff ").

In any case, there is no time difference T _diff between the signals input to the antenna unit 10 and the antenna unit 20 (that is, T _diff = 0), and the other branch is also in the past _TGI2 (current When the time is “0”, the received signal in the period “−T _GI2 ˜0” is not a short symbol, but during the previous T _p (when the current time is “0”, “−T _GI ”). the received signal of _GI2 -T _{p ~-T GI2} period ") is the last of the short symbol of the continuous short symbol. In other words, the boundary between the short preamble and long preamble, "T _GI2" going back time from the current (and the current time is set to "0", "- T _GI2") is.

[2] In other branches, it is determined that no peak has been detected once reception of the previous frame is completed. In this case, since the transition is repeatedly made between S2 and S3, the counter is not initialized in S5, and the value _TGI2 last set in S8 is maintained when the previous frame is received. Note that the value of the counter 203 is set to _TGI2 when the receiver is activated (before receiving the first frame).

  Accordingly, the boundary between the short preamble and the long preamble detected by the own branch is regarded as correct, and the process proceeds to S9.

In S102, when it is determined that the counter value in the symbol timing synchronization unit of the other branch is not equal to or greater than T _GI2 −T _{diff, max} , the elapsed time after detecting the boundary between the long preamble and the short preamble is “T _GI2− T _diff, less than _max ”, specifically, as follows.

For example, the local branch is the branch 51 and the other branch is the branch 52. In this case, the other branch 52 has a time interval “T _p ” from the time “2T _p + T _diff ” that has _gone back in the past (if the current time is “0”, “−2T _p −T _diff ˜−T _p −T _diff The received signal during the period “” is a short symbol. At this time, the counter value of the counter unit 203 in the symbol timing synchronization unit of the other branch is “T _p + T _diff (<T _GI2 −T _{diff, max} )”. That is, the boundary between the short preamble and the long preamble is determined to be after the past “T _p + T _diff ” (“−T _p −T _diff ” when the current time is “0”).

This is at least “T _p −T _diff ” after the time when the branch 51 determines that it is the boundary between the short preamble and the long preamble (when the current time is “0”, “−2T _p” ). It becomes. Therefore, it can be considered that the boundary between the short preamble and the long preamble detected by the other branch 52 is correct, and it is considered that the own branch 51 has not been able to detect the short symbol due to, for example, fluctuation of the received radio signal due to the external environment and the AGC operation. It is done. Therefore, the time difference τ = T _diff between the signal of the own branch and the signal of the other branch is added to the boundary between the short preamble and the long preamble detected by the other branch 52 that is at least “T _p −T _diff ” later than the own branch 51. A boundary between the short preamble and the long preamble of the position own branch 51 can be formed.

At this time, when the time difference τ> 0, the signal of the own branch 51 is slower than the signal of the other branch 52, and when the time difference τ <0, the signal of the own branch 51 is the signal of the other branch 52. Faster than that. When τ = 0, there is no time difference between the signals of both branches. Accordingly, the counter value of the short counter 203 of the own branch 51 is decreased by “T _p ”, and the counter value is set to “T _GI2 −T _p ” (S101).

Subsequently, the process proceeds to S8, and the counter unit 203 counts again during the period “T _p ” from the counter value “T _GI2 −T _p ” to “T _GI2 ”, thereby reducing the short preamble of the branch 51 itself. it is possible to delay the boundary of the long preamble only T _p.

Also, for example, the local branch is the branch 52 and the other branch is the branch 51. In this case, the other branch 51 has a time interval “T _p ” from the time “2T _p −T _diff ” that has _gone back in the past (if the current time is “0”, “−2T _p + T _diff ˜−T _p + T _diff In this case, the counter value of the counter unit 203 in the symbol timing synchronization unit of the other branch 51 is “T _p −T _diff (<T _GI2 −T _{diff, max} )”. . That is, the boundary between the short preamble and the long preamble is determined to be after the past “T _p −T _diff ” (“−T _p + T _diff ” when the current time is “0”). This is at least “T _p + T _diff ” after the time when the branch 52 determines that it is the boundary between the short preamble and the long preamble (when the current time is “0”, “−2T _p ”). Therefore, the boundary between the short preamble and the long preamble detected by the other branch 51 is considered to be correct. It is considered that the local branch 52 could not detect the short symbol due to, for example, fluctuations in the received radio signal due to the external environment and AGC operation. A position obtained by adding a time difference τ = −T _diff between the signal of the own branch 52 and the signal of the other branch to the boundary between the short preamble and the long preamble detected by the other branch at least by “T _p + T _diff ” later than the own branch 52 To do. Since the definition of the sign of the time difference τ is as described above, the sign is reversed from the previous example when the own branch 52 and the other branch 51 are switched. That is, the position delayed by T _p (= (T _p + T _diff ) + τ) from the boundary between the short preamble and the long preamble detected by the own branch 52 is set as the boundary between the short preamble and the long preamble of the own branch 52. Therefore, the counter value of the counter unit 203 of the own branch 52 is decreased by “T _p ”, and the counter value is set to “T _GI2 −T _p ” (S101).

Subsequently, the process proceeds to S8, and the counter unit 203 counts again during the period “T _p ” from the counter value “T _GI2 −T _p ” to “T _GI2 ”, thereby reducing the short preamble of the branch 51 itself. it is possible to delay the boundary of the long preamble only T _p.

Therefore, in any branch, regardless of the time difference between the signals input to the antenna unit 10 and the antenna unit 20 (that is, regardless of the value of the time difference T _diff ), the short preamble and the long preamble detected by the own branch A position delayed by T _p from the boundary can be used as a boundary between the short preamble and the long preamble of the own branch.

  As described above, the time difference between the received signal of the own branch and the received signal of the other branch is added to the position of the boundary between the short preamble and the long preamble detected by the other branch with a short symbol period slower than that of the own branch. It is possible to set the position of the boundary between the short preamble and the long preamble of the own branch.

  In addition, since the time difference between the reception signal of the own branch and the reception signal of the other branch is estimated by the counter value of the counter 203, the time difference between the reception signal of the own branch and the reception signal of the other branch is determined from the termination time of the short symbol. It can be said that is estimated.

(A-2-4) Operation of the symbol timing synchronization unit 15 or 25 when the receiver 1 has three or more branches The operation of the symbol timing synchronization unit when the number of branches is two has been described. The same operation is performed when the number of branches is three or more.

  FIG. 6 is a flowchart illustrating the processing operation of the symbol timing synchronization unit when the receiver 1 according to the embodiment includes three or more branches.

  In FIG. 6, the operations from processing S1 to S8 are the same as or correspond to the operations from processing S1 to S8 in FIGS. 4 and 5, and thus detailed description thereof is omitted here.

In S102, the timing control unit 204 determines whether or not the counter value of the counter unit 203 in the symbol timing synchronization unit of all other branches is equal to or greater than “T _GI2 −T _{diff, max} ” (S103). In this way, the own branch determines the counter value of the counter unit 203 of the symbol timing synchronization unit of all other branches, and the subsequent operations are the same as in FIG. Even in the case of, it becomes applicable.

(A-2-5) Symbol Timing Synchronization Operation Example FIG. 10 is an explanatory diagram for explaining a symbol timing synchronization operation example by the symbol timing synchronization units 15 and 25 according to this embodiment.

  10A shows the correspondence between the received signal and the correlation value in the branch 51 of the receiver 1, and FIG. 10B shows the correspondence between the received signal and the correlation value in the branch 52 of the receiver 1. Showing the relationship.

FIG. 10A-1 shows the configuration of the received signal received at the branch 51. The received signal has a short preamble, a long preamble, and an OFDM symbol. The short preamble is composed of short symbols “p1” to “p10”, and the symbol length of each short symbol is “T _p ”. The long preamble has “GI2” which is a guard interval of the long preamble and “P1” and “P2” which are long symbols. The length of the guard interval “GI2” of the long preamble is “T _GI2 ”. The OFDM symbol has a guard interval “GI” and a data part “D”. For example, in the case of the IEEE802.11a / g standard, the first “D” is a SIGNAL part. The OFDM symbol is then followed by an OFDM symbol of the same length. Note that the structure illustrated in FIG. 10B-1 is similar to the structure illustrated in FIG.

FIG. 10A-2 shows a correlation value corresponding to the received signal of the branch 51 in FIG. In FIG. 10A-2, the horizontal axis indicates time, and the vertical axis indicates a correlation value. Further, a dotted line illustrated in FIG. 10A-2 is a threshold value _Cth for detecting a peak. Note that FIG. 10B-2 shows a correlation value corresponding to the received signal of the branch 52 of FIG.

  FIG. 10 illustrates a case where there is no time difference between signals input to the antenna unit 10 and the antenna unit 20 of each branch of the receiver 1.

First, the operation in the branch 51 will be described. In FIG. 10A, the time at the input start position of the short symbol “p1” in the branch 51 is “0”. After the signal of the short symbol “p1” is input, the counter unit 203 starts counting, and after the time “Tp” has elapsed, the correlation value of the short symbol “p1” exceeds the threshold value C _th and a peak is detected. . Thereafter, peaks are also detected for the short symbols “p2”, “p3”,..., “P7” in the same manner as the short symbol “p1”. That is, when the time at the start position of p1 is “0”, a peak is detected at times “2T _p ”, “3T _p ”,..., “7T _p (= t _{end, 1} )”.

In the branch 51, no peak is detected at the time “8T _p (= t _{end, 1} + T _p )” when the time of the input start position of the short symbol “p1” is “0”. Therefore, the counter unit 203 of the branch 51 counts up to the counter value “T _GI2 ”. That is, the counter unit 203 counts up to time “9T _p (= t _{end, 1} + T _GI2 )”.

At this time, when the timing control unit 204 of the branch 51 determines whether or not the counter value from the counter unit 203 of the branch 52 is “T _GI2 ”, in the branch 52, the peak of the correlation value of the short symbol “p9”. Is detected. Therefore, the counter value of the counter unit 203 of the branch 52 is “T _p ”, not “T _GI2 ”. Therefore, the branch 51 determines that the signal in the section of time “8T _p ” is the short symbol “p8”.

Next, in the branch 51, even at the time “10T _p (= t _{end, 1} + T _p + T _GI2 )”, the timing control unit 204 has the counter value from the counter unit 203 of the branch 52 “T _GI2 ”. It is determined whether or not. Also in this case, the branch 52 detects the peak of the correlation value of the short symbol “p10”. Therefore, the counter value of the counter unit 203 of the branch 52 is “T _p ”, not “T _GI2 ”. Accordingly, the branch 51 determines that the signal in the section of time “9T _p ” is the short symbol “p9”.

After that, in the branch 51, even at the time “11T _p (= t _{end, 1} + 2T _p + T _GI2 )”, the timing control unit 204 determines whether the counter value from the counter unit 203 of the branch 52 is “T _GI2 ”. Determine whether or not. In this case, in the branch 52, the peak of the correlation value is not detected, but the counter value of the counter unit 203 of the branch 52 is “T _p ” and not “T _GI2 ”.

Furthermore, in the branch 51, at the time “12 Tp (= t _{end, 1} + 3T _p + T _GI2 )”, the timing control unit 204 determines whether the counter value from the counter unit 203 of the branch 52 is “T _GI2 ”. Determine whether. At this time, the count value of the other branch 52 is “T _GI2 ”. Therefore, it is determined that the boundary between the short preamble and the long preamble is the time “10T _p ”. Thereafter, synchronization using the long preamble is performed, the GI removal unit 14 removes the guard interval, and the OFDM symbol is provided to the S / P conversion unit 12 in units of OFDM symbols.

  Next, the operation in the branch 52 will be described. Also here, for the sake of convenience of explanation, the time at the input start position of the short symbol “p1” in the branch 51 is described as “0” for convenience.

In the branch 52, when the signal of the short symbol “p5” is input at the time “5T _p ”, the counter unit 203 starts counting, and after the time “Tp” has elapsed, the correlation value of the short symbol “p5”. Exceeds the threshold _Cth, and a peak is detected. Thereafter, peaks are also detected for the short symbols “p6”, “p7”,..., “P10” in the same manner as the short symbol “p5”. That is, when the time of the input start position of “p1” of the branch 51 is set to “0”, a peak is detected at times “5T _p ”, “6T _p ”,..., “10T _p (= t _{end, 2} )”. Has been.

In the branch 52, no peak is detected at the time “11T _p (= t _{end, 2} + T _p )” when the time of the input start position of the short symbol “p1” is “0”. Therefore, the counter unit 203 of the branch 51 counts up to the counter value “T _GI2 ”. That is, the counter unit 203 counts up to time “12T _p (= t _{end, 2} + T _GI2 )”.

Furthermore, in the branch 52, at the time “12 Tp (= t _{end, 2} + T _GI2 )”, the timing control unit 204 determines whether or not the counter value from the counter unit 203 of the branch 51 is “T _GI2 ”. judge. At this time, the count value of the other branch 51 is “T _GI2 ”. Therefore, it is determined that the boundary between the short preamble and the long preamble is a time point of time “10T _p (= t _{end, 1} + T _p + T _GI2 )”. Thereafter, synchronization using the long preamble is performed, the GI removal unit 14 removes the guard interval, and the OFDM symbol is provided to the S / P conversion unit 12 in units of OFDM symbols.

FIG. 11 is an explanatory diagram for explaining an operation example of symbol timing synchronization by the symbol timing synchronization units 15 and 25 according to this embodiment. In FIG. 11, there is a time difference between signals input to the antenna unit 10 and the antenna unit 20, and the value is assumed to be T _delay (0 <T _delay <T _{diff, max} ).

  FIG. 11A shows the correspondence between the received signal and the correlation value in the branch 51 of the receiver 1, and FIG. 11B shows the correspondence between the received signal and the correlation value in the branch 52 of the receiver 1. Showing the relationship.

First, the operation in the branch 51 will be described. In FIG. 10A, the time at the input start position of the short symbol “p1” in the branch 52 is “0”. After the signal of the short symbol “p1” is input, the counter unit 203 starts counting, and after the time “Tp” has elapsed, the correlation value of the short symbol “p1” exceeds the threshold value C _th and a peak is detected. . Thereafter, peaks are also detected for the short symbols “p2”, “p3”,..., “P7” in the same manner as the short symbol “p1”. That is, when the time of the start position of p1 is “T _delay ”, the peak is at time “T _delay + 2T _p ”, “T _delay + 3T _p ”,..., “T _delay + 7T _p (= t _{end, 1} )”. Has been detected.

In the branch 51, no peak is detected at the time “T _delay + 8T _p (= t _{end, 1} + T _p )” when the time of the input start position of the short symbol “p 1” is “T _delay ”. Therefore, the counter unit 203 of the branch 51 counts up to the counter value “T _GI2 ”. That is, the counter unit 203 counts up to the time “T _delay + 9T _p (= t _{end, 1} + T _GI2 )”.

At this time, when the timing control unit 204 of the branch 51 determines whether or not the counter value from the counter unit 203 of the branch 52 is equal to or greater than “T _GI2 −T _diff.max ”, the short symbol “ _p9 ” is determined in the branch 52. ”Correlation value peak is detected. Therefore, the counter value of the counter unit 203 of the branch 52 is “T _delay ”, and is not _{equal to} or greater than “T _GI2 −T _diff.max ”. Accordingly, the branch 51, the signal interval time _{"T delay} + 8T _p" is determined to be short symbols "p8".

Next, in the branch 51, even at the time “T _delay + 10T _p (= t _{end, 1} + T _p + T _GI2 )”, the timing control unit 204 determines that the counter value from the counter unit 203 of the branch 52 is “T _GI2 − It is determined whether or not “T _diff.max ” or more. Also in this case, the branch 52 detects the peak of the correlation value of the short symbol “p10”. Therefore, the counter value of the counter unit 203 of the branch 52 is “T _delay ”, and is not _{equal to} or greater than “T _GI2 −T _diff.max ”. Therefore, in the branch 51, it is determined that the signal in the section of time “T _delay + 9T _p ” is the short symbol “p9”.

Thereafter, in the branch 51, the timing control unit 204 also _sets the counter value from the counter unit 203 of the branch 52 to “T _GI2 −T” even at the time “T _delay + 11T _p (= t _{end, 1} + 2T _p + T _GI2 )”. It is determined whether or not “ _diff.max ” or more. In this case, the peak of the correlation value is not detected in the branch 52, but the counter value of the counter unit 203 of the branch 52 is “T _p + T _delay ”, which is not _{equal to} or greater than “T _GI2 −T _diff.max ”. Therefore, in the branch 51, it is determined that the signal in the section of the time “T _delay + 10T _p ” is the short symbol “p10”.

Furthermore, in the branch 51, at the time “T _delay + 12Tp (= t _{end, 1} + 3T _p + T _GI2 )”, the timing control unit 204 sets the counter value from the counter unit 203 of the branch 52 to “T _GI2 −T _{diff. .Max} "or more. At this time, the count value of the other branch 52 is “T _GI2 ”, which is _{equal to} or greater than “T _GI2 −T _diff.max ”. Therefore, it is determined that the boundary between the short preamble and the long preamble is the time “T _delay + 10T _p (= t _{end, 1} + T _p + T _GI2 )”. Thereafter, synchronization using the long preamble is performed, the GI removal unit 14 removes the guard interval, and the OFDM symbol is provided to the S / P conversion unit 12 in units of OFDM symbols.

  Next, the operation in the branch 52 will be described. Here too, for the sake of convenience, the time at the input start position of the short symbol “p1” in the branch 52 will be described as “0” for convenience.

In the branch 52, when the signal of the short symbol “p5” is input at the time “5T _p ”, the counter unit 203 starts counting, and after the time “Tp” has elapsed, the correlation value of the short symbol “p5”. Exceeds the threshold _Cth, and a peak is detected. Thereafter, peaks are also detected for the short symbols “p6”, “p7”,..., “P10” in the same manner as the short symbol “p5”. That is, when the time of the input start position of “p1” of the branch 51 is set to “0”, a peak is detected at times “5T _p ”, “6T _p ”,..., “10T _p (= t _{end, 2} )”. Has been.

In the branch 52, no peak is detected at the time “11T _p (= t _{end, 2} + T _p )” when the time of the input start position of the short symbol “p1” is “0”. Therefore, the counter unit 203 of the branch 51 counts up to the counter value “T _GI2 ”. That is, the counter unit 203 counts up to time “12T _p (= t _{end, 2} + T _GI2 )”.

Further, in the branch 52, at the time “12Tp (= t _{end, 2} + T _GI2 )”, the timing control unit 204 has the counter value from the counter unit 203 of the branch 51 equal to or greater than “T _GI2 −T _diff.max ”. It is determined whether or not. At this time, the count value of the other branch 51 is “T _GI2 ”. Therefore, it is determined that the boundary between the short preamble and the long preamble is the time “10T _p ”. Thereafter, synchronization using the long preamble is performed, the GI removal unit 14 removes the guard interval, and the OFDM symbol is provided to the S / P conversion unit 12 in units of OFDM symbols.

(A-3) Effect of Embodiment As described above, according to this embodiment, it is possible to reduce the symbol timing synchronization error (mis-synchronization, synchronization non-detection) even when the radio wave condition is bad. It is done.

(B) Other Embodiments Although various modified embodiments have been mentioned in the above-described embodiments, the present invention can also be applied to the following modified embodiments.

(B-1) In the embodiment described above, the flowcharts of FIGS. 4 and 5 are provided with the following three restrictions on the symbol timing synchronization conditions in order to clarify the characteristic operation of the present invention. explained.

[A] If a peak is detected even once, it is considered that symbol timing synchronization has been established.

[B] When a peak cannot be detected after T _{p has} elapsed since the peak detection (when short symbols are not continuously detected), it is considered that a transition has been made to a long symbol.

[C] The determination timing of peak detection is only when T _{p has} elapsed since the previous peak detection (even if a peak is detected at other timings, it is ignored).

  However, the present invention may set detailed conditions regarding symbol timing synchronization.

  In [a], for example, in order to set the number of peak detections regarded as having established symbol timing synchronization to n times continuously (an integer of n ≧ 2), between S7 and S8, “the number of peak detections is n times or more. Is entered, if Yes, the process proceeds to S8, and if No, the process proceeds to S2.

  In [b], for example, in order to be able to skip the detection of the short symbol once, a step of “count to 2 Tp” is inserted between S7 and S8, and then the “peak detection signal is changed. The determination condition “input?” Is entered. If Yes, the process proceeds to S5. If No, the process proceeds to S8.

In [c], for example, when the detection timing of peak detection includes from the previous peak detection to before and after δt when T _{p has} elapsed (a window having a width of 2δt is provided), the time when the peak detection signal is generated record the, change to S6 "counts to T _p" to "count up T _{p +} .DELTA.t", "peak detection time the S7 from the" input peak detection signal? 'is, T _p -.DELTA.t least T _p Change to “+ δt or less?” And change S100 from “the count value of other branch is T _GI2 ?” To “the count value of other branch is more than T _GI2 −δt?” (S100 is changed to “the count value of other branch is T _GI2? If “−T _{diff, max} or more?”, “The count value of the other branch is changed to T _GI2 −T _{diff, max} −δt or more?”).

DESCRIPTION OF SYMBOLS 1 ... Receiver, 10 and 20 ... Antenna part, 11 and 21 ... Demodulation part, 12 and 22 ... S / P conversion part, 13 and 23 ... DFT part, 14 and 24 ... GI removal part, 15 and 25 ... Symbol timing Synchronizing unit, 30-1 to 30-L ... diversity combining unit, 33 ... P / S converting unit, 34 ... determining unit,
201 ... correlation unit, 202 ... peak detection unit, 203 ... counter unit, 204 ... timing control unit.

Claims (10)

In a receiver with multiple diversity branches,
A plurality of symbol timing synchronization means for performing symbol timing synchronization of orthogonal frequency division multiplexed signals received by different antenna units,
Each of the plurality of symbol timing synchronization means notifies the boundary timing between the short preamble and the long preamble mutually with the other symbol timing synchronization means, and the boundary timing detected by itself and other symbol timing synchronization A receiver which performs symbol timing synchronization of the received orthogonal frequency division multiplex signal based on the boundary timing detected by the means.   The plurality of symbol timing synchronization means is characterized in that the latest detected timing among the boundary timings detected by the symbol timing synchronization means is used as the boundary timing between the short preamble and the long preamble. The receiver according to claim 1. Each symbol timing synchronization means is
A detection unit for detecting a symbol included in the preamble of the received orthogonal frequency division multiplexing signal;
While measuring the signal interval length based on the detection result by the detection unit, a time timing unit for notifying the signal interval length measured to the other symbol timing synchronization means,
It determines the symbol timing of its own branch based on the signal interval length from the time measuring unit, and when the signal interval length from the end point of the last detected short symbol is a predetermined length, A timing control unit that determines a boundary timing between the short preamble and the long preamble according to whether or not the signal interval length of the corresponding other branch acquired from the symbol timing synchronization unit is equal to or longer than a predetermined length. The receiver according to claim 1 or 2. The timing controller is
When the signal interval length from the end point of the last detected short symbol is a predetermined length, and when the signal interval length of the corresponding other branch is less than a predetermined length, from the end point of the last detected short symbol Judge that the signal in the section up to a predetermined time length is a short symbol,
4. The receiver according to claim 3, wherein a value obtained by subtracting a predetermined time length from the signal interval length measured by the time measuring unit is set as a new signal interval length.   5. The receiver according to claim 4, wherein the predetermined time length subtracted from the signal section length timed by the timing controller is a short symbol length. The timing controller is
When the signal interval length from the end point of the last detected short symbol is a predetermined length and the signal interval length of the corresponding other branch is equal to or longer than the predetermined length, the end point of the last detected short symbol The receiver according to claim 3, wherein the receiver is determined as the boundary timing.   The receiver according to claim 3, wherein the predetermined length is a guard interval length of a long preamble.   7. The receiver according to claim 3, wherein the predetermined length has a guard interval length of a long preamble and a delay time between diversity branches. In a symbol timing synchronization apparatus that performs symbol timing synchronization of orthogonal frequency division multiplexed signals received by different antenna units in a receiver having a plurality of diversity branches,
Communicates with the other symbol timing synchronization means the boundary timing between the short preamble and the long preamble, based on the boundary timing detected by itself and the boundary timing detected by the other symbol timing synchronization means A symbol timing synchronization apparatus comprising symbol timing synchronization means for performing symbol timing synchronization of the received orthogonal frequency division multiplexed signal. In a symbol timing synchronization method for performing symbol timing synchronization of orthogonal frequency division multiplexed signals received by different antenna units in a receiver having a plurality of diversity branches,
Each of the plurality of symbol timing synchronization means notifies the boundary timing between the short preamble and the long preamble mutually with the other symbol timing synchronization means, and the above-described boundary timing detected by itself and other symbol timing synchronization A symbol timing synchronization method comprising: performing symbol timing synchronization of the received orthogonal frequency division multiplexing signal based on the boundary timing detected by the means.

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