JP4867768B2 - Synchronization establishment method, orthogonal frequency division multiplex modulation method, and communication apparatus - Google Patents

Description

  The present invention relates to a method for establishing synchronization of a communication apparatus including a transmitter and a receiver, an orthogonal frequency division multiplexing modulation method, and a communication apparatus.

  A conventional synchronization establishment method is described in Patent Document 1.

The synchronization establishment method described in Patent Document 1 is for establishing symbol timing synchronization in a receiver using an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme. A signal (packet signal) transmitted from a transmitter is used for packet control in which information for a packet modulated by a predetermined modulation method is stored for a synchronization area (synchronization block) composed of a known pattern. Area (control block) and an area (data block) for data transmission in which information bits modulated by the modulation scheme described in the control block are stored. The synchronization block includes a preamble for detecting a packet and establishing symbol timing synchronization. In the preamble, a plurality of synchronization patterns known by both the transmitter and the receiver are present at a certain basic period. The symbol timing synchronization detection circuit provided in the receiver calculates a correlation value between the head portion of the received signal and the synchronization pattern by the correlation value calculation circuit, and compares the correlation value with a predetermined threshold value by the peak detection circuit. If a peak is detected, a detection signal is input to the symbol synchronization processing circuit, and one threshold value used for a predetermined prediction period and other periods after the peak is first detected is different. The threshold value of the peak detection circuit is set so that the first peak is detected with a strict threshold value outside the predetermined prediction period, the next peak detection timing is predicted according to this detection, and the correlation value is calculated at the prediction timing. If no peak is detected, it is determined that synchronization is established.
JP 2005-303691 A

  By the way, in the above conventional example, in order to improve the detection accuracy of the plurality of synchronization patterns constituting the preamble, the threshold value set in the peak detection circuit is set to a threshold value in the prediction period (a period equal to the basic period of the synchronization pattern) other than the prediction feedback. However, if the periodicity of the synchronization pattern is disrupted by an interference wave, for example, the correlation value peak cannot be detected within the prediction period equal to the basic period. There was a problem that it could not be established.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a synchronization establishment method, an orthogonal frequency division multiplexing modulation method, and a communication apparatus that can establish synchronization even when the periodicity of the synchronization pattern is lost. There is to do.

In order to achieve the above object, the invention according to claim 1 is a synchronization establishment method for a communication apparatus comprising a transmitter and a receiver, wherein a synchronization establishment preamble is included at the head of a signal transmitted from the transmitter, In the preamble, a plurality of synchronization patterns that are known by both the transmitter and the receiver exist in a certain basic period, and a correlation value between the head portion of the signal received by the receiver and the synchronization pattern is obtained. In addition, the correlation value is compared with a predetermined threshold value, and time measurement is started each time the correlation value exceeds the threshold value, and a plurality of timings substantially equal to the timing at which a time equal to the basic period or an integral multiple of the basic period is measured determines that the synchronization if the correlation value exceeds the threshold value at the timing is established, the correlation at a plurality of timings that time equal to an integer multiple is substantially coincident with the timing clocked fundamental period There deciding whether exceeds a threshold value, and changing to a longer time in order the timing starting from the same time as the basic period.

The invention of claim 2 is the first correlation value exceeding the threshold value in the invention of claim 1 , and the basic period or the basic period after starting the time measurement when the first correlation value exceeds the threshold value. When a second correlation value exceeding the first correlation value appears at a timing when a time not equal to an integral multiple is timed, timing is started at a timing when the second correlation value exceeds the first correlation value. It is characterized by that.

According to a third aspect of the present invention, in order to achieve the above object, synchronization is established by the synchronization establishment method according to the first or second aspect.

In order to achieve the above object, a fourth aspect of the present invention is a communication apparatus configured by a transmitter and a receiver and performing packet communication using a signal subjected to orthogonal frequency division multiplexing modulation. A preamble for establishing synchronization is included at the beginning, and the preamble includes a plurality of synchronization patterns that are known by both the transmitter and the receiver in a certain basic period. Alternatively, a symbol timing synchronization detection circuit for establishing synchronization by the synchronization establishment method described in 2 is provided .

According to the first, third , and fourth aspects of the invention, for example, even when the periodicity of the synchronization pattern included in the head portion of the received signal is disrupted due to the influence of an interference wave, the time equal to an integral multiple of the basic period is counted. The synchronization can be established by determining that the synchronization is established when the correlation value exceeds the threshold at a plurality of timings substantially coincident with the timing to be performed, and the time until the synchronization is established can be shortened. .

According to the invention of claim 2 , even when noise other than the synchronization pattern is detected as the first correlation value, synchronization can be established by detecting the subsequent synchronization pattern as the second correlation value.

  Hereinafter, embodiments of a synchronization establishment method, an orthogonal frequency division multiplexing modulation method, and a communication apparatus according to the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
First, the configuration of the communication apparatus in the present embodiment will be described with reference to FIG. The communication apparatus according to the present embodiment includes a transmitter Tx and a receiver Rx, and performs packet communication using an orthogonal frequency division multiplexing (hereinafter referred to as “OFDM”) modulated signal (hereinafter referred to as “OFDM signal”). Is going. However, the transmission path for transmitting a signal from the transmitter Tx to the receiver Rx may be either wired or wireless.

  In the transmitter Tx, the input transmission data (information bit string) is scrambled (randomized) by the scrambler 10 so that the same bit value does not continue, error-correction-coded by the convolutional encoder 11, and the bit interleaver 12 Are interleaved (randomized) by the mapper 13 on the complex plane, and the mapper 13 symbolizes the bits as complex numbers (digital modulation), and each symbol is sequentially sent to an inverse discrete Fourier transform (IFFT) 14. Then, the inverse discrete Fourier transform is performed, and the latter half of the time signal (hereinafter referred to as “complex baseband OFDM signal”) output from the IFFT 14 by the GI addition / framing unit 15 is copied and added to the complex baseband OFDM signal. By doing so, an OFDM symbol is generated. Further, the oversampling unit 16 performs oversampling at a sampling period in a subsequent DAC (digital / analog codec) unit 17, then performs digital / analog conversion in the DAC unit 17, and the analog circuit 18 performs frequency conversion of the baseband OFDM signal. To transmit the OFDM signal shifted to the necessary frequency band to the transmission line. When the GI addition / framing unit 15 generates an OFDM symbol, the synchronization pattern held by the synchronization block unit 19 is stored in the synchronization block.

  On the other hand, in the receiver Rx, the OFDM signal transmitted through the transmission path is frequency-converted by the analog circuit 20 and analog / digital converted by the ADC (Analog / Digital Codec) unit 21, and is described later by the downsampling unit 22. After down-sampling to the number of samples of the discrete Fourier transform to be performed, the GI removal unit 23 removes the guard interval. However, in order for the GI removal unit 23 to remove the guard interval, it is a necessary condition that the symbol timing synchronization is established by the symbol timing synchronization detection unit 1. The complex baseband OFDM signal from which the guard interval is removed is subjected to discrete Fourier transform by a discrete Fourier transformer (FFT) 24 to generate a complex symbol example from the complex baseband OFDM signal. The generated complex symbol sequence is converted into a soft decision metric value by the demapper 25 and deinterleaved in units of data bits by the deinterleaver 26. Then, the deinterleaved soft decision metric value is decoded by the Viterbi decoder 27 and descrambled by the descrambler 28 to reproduce the transmission data (information bit string).

  The symbol timing synchronization detection unit 1 provided in the receiver Rx includes a correlator 2, a peak detector 3, a counter 4, and a timing detector 5, as shown in FIG. The correlator 2 uses a symbol waveform (see FIG. 3 (a)) stored in the synchronization block of the OFDM symbol after downsampling, and a synchronization pattern waveform (see FIG. 3 (b)) stored in advance. A cross-correlation value (hereinafter abbreviated as a correlation value) is calculated and can be realized using a cross-correlation type matched filter. Then, the correlator 2 outputs the correlation value obtained by the calculation to the peak detector 3.

  The peak detector 3 compares the correlation value output from the correlator 2 with a threshold value stored in advance, and outputs a peak detection signal to the counter 4 when a correlation value (peak value) exceeding the threshold value is detected. The counter 4 counts up the count value at the rising edge of a fixed period clock input from an oscillator (not shown). When the peak detection signal is input, the counter 4 initializes the count value to zero and starts counting again.

  The timing detector 5 determines whether or not symbol timing synchronization is established based on the count value input from the counter 4 and the peak detection signal input from the peak detector 3, and when it is determined that synchronization is established. Output synchronization detection signal. A method for determining synchronization establishment in the timing detector 5, that is, a synchronization establishment method according to the present invention will be described in detail below.

For example, when 54 subcarriers are used for multicarrier modulation (OFDM modulation) in the transmitter Tx, a synchronization pattern for symbol timing synchronization (hereinafter referred to as a preamble symbol) is used using all 54 subcarriers. When pas (n) is generated, it can be obtained by the following equation (1). Here, k is a subcarrier index, Sk is symbol data (complex symbol sequence) for each subcarrier, f _s is a sampling frequency in inverse discrete Fourier transform, n is a time index, T is a sampling period, and “64” is inverse discrete. This is the number of samples in the Fourier transform.

  When the preamble symbol pas (n) is used every four carriers and the carrier interval is increased to four times the normal, the preamble symbol pas (n) in the above equation (1) is expressed by the following equation (2). .

That is, as is clear from the above equation (2), the preamble symbol pas (n) has a cyclic property for every 16 samples of the inverse discrete Fourier transform, and the period of the preamble symbol pas (n) (synchronization pattern) is reversed. This is a quarter of the number of discrete Fourier transform samples (= 64).

In the receiver Rx, stored in the synchronous block of the symbol timings for the correlators second synchronous detection circuit 1 are stored in a memory (not shown) preamble symbols pas of 16 samples (one cycle), the received packet signal The correlation value with the preamble symbol pas is calculated. Here, in order to simplify the explanation, assuming that the transfer function between the transmitter Tx and the receiver Rx is 1, the correlation value C (k) is obtained as follows. However, p shows a frequency index.

The maximum value of the correlation value C (k) is obtained when m = p and k is an integer multiple of 16.

  Next, a case where the periodicity of the preamble symbol pas is hindered due to the influence of noise or the like will be described.

  For example, assuming that an interference wave having an amplitude INT is mixed in the preamble symbol pas, the preamble symbol pas including the interference wave is expressed by the following expression. Here, l (el) is a frequency index of an interference wave in a baseband (complex number region) in which 0 is a direct current.

Further, the correlation value C (k) at this time is expressed by the following equation.

The first term on the right side is the same as when no interfering wave is mixed, and the maximum value is output every 16 sample periods, while the second term on the right side is output by l value (interference wave frequency index). The maximum value (peak value) period changes. That is, when the l value is an odd number, the period in which the peak value appears is 64 sample periods (see FIG. 4A), and when the l value is a multiple of 2, the period in which the peak value appears is 32 sample periods (FIG. 4). (See (b)), when the l value is a multiple of 4, the period in which the peak value appears is 16 sample periods (see FIG. 4C).

Here, the l value is a frequency index of an interference wave in a baseband (complex number region) in which 0 is a direct current, and f _s / 64 represents a subcarrier frequency interval. For example, if f _s is 20 MHz, the subcarrier frequency interval is 312.5 kHz, and if the basic (lowest) subcarrier frequency is f _c , the l value is an odd number. This means that the frequency is one of the frequencies represented by the following expression in the passband (real number region) (see FIG. 4A).

f _c + (2q−1) × 312.5 kHz (where q = −13: 14)
Further, when l = 2q (q = −13: 13, where q is an odd number), as shown in FIG. 4B, the correlation value has a peak every 32 sample periods. When the frequency of the interference wave is expressed by the following equation in the passband, the correlation value has a peak in such a period.

f _c + 2q × 312.5 kh
Further, in the case of l = 4q (q = −6: 6), as shown in FIG. 4C, the correlation value has a peak every 16 sample periods. When the frequency of the interference wave is expressed by the following equation in the passband, the correlation value has a peak in such a period.

f _c + 4q × 312.5 kHz
Thus, if no interference wave is mixed in the preamble symbol pas, the correlation value has a peak every 16 sample periods according to the periodicity of the preamble symbol pas (see FIG. 3C). It can be predicted that the peak value is detected every 16 sample periods after the peak is detected, and it is determined that the synchronization of the symbol timing is established by detecting the peak value multiple times every 16 sample periods. There is no problem. However, as described above, if the periodicity of the preamble symbol pas is disrupted due to the interference wave, the peak of the correlation value appears every period that is an integral multiple of the 16-sample period originally predicted. There is a possibility that synchronization cannot be established.

  Therefore, in this embodiment, considering the case where the interference wave is mixed in the preamble symbol pas as described above, the symbol timing synchronization is established by the procedure shown in the flowchart of FIG.

  The received OFDM symbol is input to the symbol timing synchronization detection circuit 1 (S1), and is stored in advance by the correlator 2 in the symbol waveform (see FIG. 3A) stored in the OFDM symbol synchronization block. A correlation value with the waveform of the preamble symbol pas (see FIG. 3B) is calculated (S2). The correlation value obtained by the correlator 2 is input to the peak detector 3, and the peak detector 3 compares the correlation value with the threshold value (S3). The peak detector 3 does not output a peak detection signal if the correlation value does not exceed the threshold value, and outputs a peak detection signal if the correlation value exceeds the threshold value (S4). The counter 4 counts up at the rising edge of the clock synchronized with the sample frequency of the discrete Fourier transform in the discrete Fourier transformer 24 from the time when the peak detection signal is first output from the peak detector 3 and detects the timing of the count value. When the peak detection signal is input, the count value (= the number of samples of the discrete Fourier transform) is initialized to zero and the count up is started again (S5).

  The timing detector 5 counts up to the count value of the counter 4 without outputting the peak detection signal, that is, the value (= 16) in which the number of samples of the discrete Fourier transform is equal to the basic period (= 16 sample periods) of the preamble symbol pas. If the peak detection signal is input (S6), it is determined whether or not the peak detection signal is input from the peak detector 3 at the counted up timing (S7). If the peak detection signal is input, the symbol timing is synchronized. It determines with having established, and outputs a synchronous detection signal (S8). However, if the periodicity of the preamble symbol pas is broken due to the interference wave, the peak value of the correlation value is not detected in the basic period (16 sample periods). Therefore, in this embodiment, when the peak detection signal is not input from the peak detector 3 at the timing counted up to a value (= 16) equal to the basic period (= 16 sample periods), the timing detector 5 When the count value of 4 is counted up to a value (= 32) equal to twice the basic period of the preamble symbol pas (= 32 sample periods) (= 32) (S9), the peak detection signal is input again from the peak detector 3 If the peak detection signal is input, it is determined that the synchronization of the symbol timing has been established, and the synchronization detection signal is output (S11).

  Further, when no peak detection signal is input from the peak detector 3 at a timing counted up to a value (= 32) equal to twice the basic period (= 32 sample periods), the timing detector 5 uses the counter 4 Is counted up to a value (= 64) equal to four times the basic period of the preamble symbol pas (= 64 sample periods) (S12), and the peak detection signal is input again from the peak detector 3 If a peak detection signal is input, it is determined that symbol timing synchronization has been established, and a synchronization detection signal is output (S14).

  On the other hand, if the peak detection signal is not input from the peak detector 3 even at a timing counted up to a value (= 64) equal to four times the basic period (= 64 sample periods), the timing detector 5 is no longer a symbol. It is determined that timing synchronization cannot be established, and a synchronization error signal is output (S15).

  As described above, according to the synchronization establishment method of the present embodiment, the correlation value between the head portion (synchronization block) of the signal received by the receiver Rx and the synchronization pattern (preamble symbol pas) is obtained, and the correlation value is determined as a predetermined value. A plurality of times substantially equal to the timing at which a time equal to the basic period of the preamble symbol pas or an integer multiple of the basic period is started by counting time (counting of the counter 4) each time the correlation value exceeds the threshold value compared with the threshold value When the correlation value exceeds the threshold value at the timing of, it is determined that synchronization has been established, so even if the periodicity of the synchronization pattern included in the head part of the received signal is disrupted due to the influence of jamming waves, the symbol timing is synchronized. Can be established.

(Embodiment 2)
By the way, when the interference wave is mixed in the preamble symbol pas, the peak of the correlation value detected first may be a peak due to the interference wave. For example, when counting up of the counter 4 is started from the point in time when an incorrect peak position is detected, the peak is not detected at the timing of the basic period or an integral multiple of the basic period in the first embodiment. Symbol timing synchronization cannot be established until the count value is initialized.

  Therefore, in the present embodiment, symbol timing synchronization is established by the procedure shown in the flowchart of FIG.

  The received OFDM symbol is input to the symbol timing synchronization detection circuit 1 (S1), and the peak detector 3 initializes the peak maximum value stored in the memory (S2) and also initializes the count value of the counter 4 (S3). ). It is determined whether or not the count value of the counter 4 has been counted up to a value (= 16) equal to the basic period (= 16 sample period) of the preamble symbol pas, that is, the number of samples of the discrete Fourier transform (S4). If not, the correlator 2 calculates the correlation value between the symbol waveform stored in the synchronization block of the OFDM symbol and the waveform of the preamble symbol pas stored in advance (S5). The correlation value obtained by the correlator 2 is input to the peak detector 3, and the peak detector 3 compares the correlation value with the threshold value (S6). The peak detector 3 does not output a peak detection signal unless the correlation value exceeds the threshold value, and compares the correlation value (peak value) with the maximum peak value stored in the memory if the correlation value exceeds the threshold value. (S7) If the correlation value (second correlation value) exceeds the maximum peak value (first correlation value) stored in the memory, the count value of the counter 4 is obtained by outputting a peak detection signal. At the same time as initialization (S8), the second correlation value is stored in the memory as the maximum peak value instead of the first correlation value (S9).

  Until the count value of the counter 4 is counted up to 16, the processes of S5 to S9 are repeated. When the count value of the counter 4 is counted up to 16, the timing detector 5 is counted up. Whether or not a peak detection signal is input from the peak detector 3 is determined (S10), and if a peak detection signal is input, it is determined that symbol timing synchronization has been established and a synchronization detection signal is output. (S11). On the other hand, when the peak detection signal is not input from the peak detector 3 at the timing counted up to 16, the timing detector 5 has a count value of the counter 4 that is twice the basic period of the preamble symbol pas (= 32 samples). (S12), it is determined again whether the peak detection signal is input from the peak detector 3 (S13), and the peak detection signal is input. If so, it is determined that symbol timing synchronization has been established, and a synchronization detection signal is output (S14).

  When no peak detection signal is input from the peak detector 3 at the timing when the count value of the counter 4 is counted up to 32, the timing detector 5 indicates that the count value of the counter 4 is equal to the basic period of the preamble symbol pas. At the timing of counting up to a value (= 64) equal to four times (= 64 sample periods) (S15), it is determined again whether a peak detection signal is input from the peak detector 3 (S16), If a peak detection signal has been input, it is determined that symbol timing synchronization has been established, and a synchronization detection signal is output (S17). However, if the peak detection signal is not input from the peak detector 3 even when the count value of the counter 4 is counted up to 64, the timing detector 5 determines that synchronization of symbol timing can no longer be established and synchronizes. An error signal is output (S18).

  Here, although not described in the flowchart of FIG. 6, the timing detector 5 always executes the update processing (S5 to S9) of the maximum peak value stored in the memory, and detects the peak value by mistake. Prevents malfunctions.

  As described above, according to the synchronization establishment method of the present embodiment, even if the counter 4 starts counting up from the time when an incorrect peak position is detected, the correct peak position is detected again to establish symbol timing synchronization. Can do.

  In the first and second embodiments, it is determined whether or not a peak detection signal is input from the peak detector 3 at the timing when the count value of the counter 4 is counted up to a basic period or an integer multiple of the basic period. Although it is determined by the timing detector 5, in consideration of the occurrence of a time difference of about ± 1 sample period due to the influence of the interference wave, the timing one sample period before or one sample period after the counted up timing Whether or not a peak detection signal is input from the peak detector 3 may be determined.

It is a block diagram of a symbol timing synchronization detection circuit in an embodiment of the present invention. It is a block diagram of the communication apparatus (a transmitter and a receiver) in the same as the above. (A) is a symbol waveform diagram stored in a synchronization block of an OFDM symbol, (b) is a waveform diagram of a synchronization pattern (preamble symbol) stored in a correlator, and (c) is a waveform indicating a peak of a correlation value. FIG. (A)-(c) is a wave form diagram which shows the peak of a correlation value when an interference wave mixes in a preamble symbol. It is a flowchart for demonstrating the synchronization establishment method in the same as the above. 10 is a flowchart for explaining a synchronization establishment method according to the second embodiment.

Explanation of symbols

1 Symbol Timing Synchronization Detection Circuit 2 Correlator 3 Peak Detector 4 Counter 5 Timing Detector

Claims (4)

In a synchronization establishment method for a communication apparatus including a transmitter and a receiver, a preamble for synchronization establishment is included at the head of a signal transmitted from the transmitter, and the preamble is known by both the transmitter and the receiver. Are present in a certain basic period,
The correlation value between the head portion of the signal received by the receiver and the synchronization pattern is obtained, and the correlation value is compared with a predetermined threshold value to start counting each time the correlation value exceeds the threshold value. When the correlation value exceeds the threshold at multiple timings that approximately match the time that is equal to an integer multiple of the basic period, it is determined that synchronization has been established, and the time equal to an integral multiple of the basic period is counted. A synchronization establishment method, characterized in that, when determining whether or not the correlation value exceeds a threshold at a plurality of timings substantially coincident with timings, the timing is changed from a time starting with the same time as a basic cycle to a longer time in order. . The first correlation value exceeding the threshold value and the first timing at which the basic period or a time not equal to an integral multiple of the basic period is measured after the time measurement starts when the first correlation value exceeds the threshold value 2. The synchronization establishment method according to claim 1 , wherein when a second correlation value exceeding the first correlation value appears, timing is started at a timing when the second correlation value exceeds the first correlation value . 3. An orthogonal frequency division multiplexing modulation method, wherein synchronization is established by the synchronization establishment method according to claim 1 . A communication device configured by a transmitter and a receiver and performing packet communication using a signal subjected to orthogonal frequency division multiplexing modulation, wherein the transmitter includes a preamble for establishing synchronization at the head of the signal, and the preamble is A plurality of synchronization patterns known at both the transmitter and the receiver exist in a certain basic period,
A communication apparatus comprising a symbol timing synchronization detection circuit for establishing synchronization by the synchronization establishment method according to claim 1 or 2 .

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