CN104717168B - Orthogonal frequency division multiplexing (OFDM) ultra wide band system anti-multipath regular synchronization scheme - Google Patents

Abstract

Aiming at the orthogonal frequency division multiplexing ultra-wideband system, the invention researches and designs a timing synchronization scheme capable of resisting channel multipath interference based on the complementary correlation characteristic of the preamble Gray complementary sequence. First, the normalized sliding autocorrelation values of two consecutive windows are calculated using the leading repeated training sequence, and the frame detection is performed based on the falling edge of the correlation peak and the coarse timing position is determined. Furthermore, using the Gray complementary sequence structure inside the training sequence, a unique normalized separation maximum correlation calculation method is designed, and the fine timing position is determined by taking the average of multiple correlation peaks obtained. The simulation shows that under the CM1 multipath channel model with low signal-to-noise ratio, the root mean square error of the residual timing deviation after fine timing can reach the order of 10 ^‑3 , the algorithm has high precision, and can effectively resist multipath interference. At the same time, the algorithm have lower complexity.

Description

Anti-Multipath Timing Synchronization Scheme for Orthogonal Frequency Division Multiplexing UWB System

technical field

The invention relates to a timing synchronization scheme for an Orthogonal Frequency Division Multiplexing (OFDM) ultra-wideband (Ultra Wide Band, UWB) system that can resist multipath interference. For the 60GHz OFDM ultra-wideband system specified in the IEEE802.15.3c standard, the frame detection, coarse timing and fine timing schemes suitable for the system are designed by using the complementary correlation characteristics of the preamble Gray complementary sequence, so that it can be used in multipath fading channels. The symbol start position is detected with high precision for correct OFDM demodulation.

Background technique

Ultra-wideband wireless communication technology has the characteristics of low power spectral density, high transmission rate, and strong anti-multipath interference ability. It is mainly used in short-distance high-speed wireless communication, penetrating imaging, and measurement. The IEEE802.15.3c standard proposed in 2009 can be used for wireless personal area network (WPAN), mainly working in the 60GHz radio frequency band. The frequency band that countries can use for free without a license is in the range of 56GHz-66GHz, and the supported data transmission rate exceeds Gbit /s. Orthogonal Frequency Division Multiplexing (OFDM) technology is one of the physical layer modulation schemes with its advantages of high spectrum utilization, strong anti-symbol crosstalk ability, and strong anti-frequency selective fading ability. The standard stipulates the main parameters of the system: the total number of subcarriers is 512, including 336 information subcarriers, 16 pilot subcarriers, 16 protection subcarriers, 3 DC subcarriers and 141 empty subcarriers. A cyclic prefix with a length of 64 is added after IFFT at the sending end as a guard interval to form an OFDM symbol with a length of 576. Each frame begins with a preamble sequence, including a frame synchronization sequence (SYNC), a frame delimiter (SFD) and a channel estimation sequence (CES), and they are composed of Golay complementary sequences, as shown in FIG. 1 .

For high-speed ultra-wideband systems, the OFDM scheme has higher requirements for the orthogonality of subcarriers and higher requirements for timing synchronization. If the timing of the system is advanced and does not exceed the length of the cyclic prefix, it will cause the phase rotation of the frequency data, resulting in subcarrier interference (ICI), which needs to be compensated by channel estimation; if the timing lags, it will cause subcarrier interference and more serious The inter-symbol interference (ISI) seriously affects the system performance.

Multipath fading channel is another key technical problem faced by OFDM wireless communication system. Multipath interference not only affects signal transmission quality, but also directly affects timing synchronization performance. In a Gaussian white noise channel, conventional timing synchronization algorithms can achieve good timing accuracy. However, in a channel with multipath delay, since the timing location has the strongest energy instead of the first path, the timing location often lags behind and the uncertainty of the location increases, which deteriorates the timing synchronization performance sharply.

The channel impulse response proposed in IEEE802.15.3c is a modified model based on the S-V model, as shown in the following formula,

Among them, δ(.) is the Dirac impulse function, βδ(τ, φ) is the direct path component, L is the number of clusters, K _l is the number of multipath components arriving in the Lth cluster, α _{k, l} , τ _{k, l} and ω _{k, l} are the complex amplitude, time delay and azimuth of arrival of each multipath component, respectively, and T _l and θ _l are the time delay and average azimuth of arrival of each cluster. IEEE802.15.3c gives the channel model parameters in each channel environment, and divides 9 channel models CM1-CM9 according to different parameters, among which CM1 and CM2 channel models correspond to office scenarios.

Gray complementary sequences have complementary autocorrelation properties, and only when they are completely correlated, there is a non-zero value output, which is the channel response. This property of Gray's complementary sequence determines its advantage of insensitivity to multipath channels. The Gray complementary sequence has a simple structure and has no requirement on the length, so there is no limit to the length of the delay spread of the channel, and it can resist longer multipath delay spread.

Contents of the invention

Aiming at the OFDM ultra-wideband system adopted by the IEEE802.15.3c standard, the present invention designs a multipath-resistant timing synchronization scheme suitable for the system by utilizing the complementary correlation characteristics of Gray complementary sequences, and realizes precise timing under multipath fading channels .

Technical scheme of the present invention

The normalized sliding autocorrelation value is calculated using the leading repeated Gray sequence, and the frame detection and coarse timing are performed based on the falling edge of the correlation plateau. In fine timing, the complementary autocorrelation property of the leading Golay complementary sequence is used to calculate multiple autocorrelation peaks that are resistant to multipath, and then the positions of multiple correlation peaks are averaged. The invention can realize high-precision timing of the system, and at the same time, the scheme has relatively low complexity.

Beneficial effects of the present invention

The invention designs a multipath-resistant timing synchronization scheme for an OFDM ultra-wideband system. This scheme takes into account both timing synchronization performance and system implementation complexity, and can realize high-precision timing under multipath fading channels, and control the residual timing deviation in a very small range, which ensures the demodulation performance of the receiver and makes the system correct Restoring the original data reduces the implementation cost and has practical guiding significance for the hardware implementation of the UWB communication receiver.

Description of drawings

Figure 1 is a structural diagram of the preamble synchronization sequence

Figure 2(a) calculates the aperiodic autocorrelation result R _b for Gray sequence b128

Figure 2(b) calculates the aperiodic autocorrelation result R _a for Gray sequence a128

Figure 2(c) is the sum of R _a and R _b

Figure 3(a) is the normalized sliding autocorrelation value C _i calculated in the frame detection stage with a correlation window length of 128

Figure 3(b) shows the normalized separation correlation value D _i calculated in the fine timing stage with a correlation window length of 32

Figure 4 shows the false alarm and missing alarm probability of frame detection under different thresholds

Figure 5 shows the rough timing root mean square error (MSRE) under different multipath channel models

Figure 6 shows the detailed timing root mean square error (MSRE) under different multipath channel models

detailed description

Below in conjunction with accompanying drawing and by embodiment the specific embodiment of the present invention will be further described:

The present invention has designed the anti-multipath timing synchronization scheme of the OFDM ultra-wideband system, which is characterized in that: the scheme includes the following steps:

a. Calculate the normalized sliding autocorrelation value C _i based on the repeated preamble synchronization sequence, and use it as the judgment quantity, set a threshold value G, when C _i is less than G, it is confirmed that the frame is detected, let Corresponding to i ₌ it , where _i is the sample number, and it is the position of the detected frame;

b. Find the maximum value of _{C i} in the range where i is greater than it and less than it + M, and record the sample number corresponding to this maximum value as i = μ, then the rough timing position is P _c = L- _μ , where M is the length of a symbol, and L is the length of the preamble synchronization sequence;

c. Calculate the normalized separation correlation value D _i based on the reconstructed preamble synchronization sequence, record the sample number i _m corresponding to all M peaks in the calculation result, m=1, 2, ..., M, and put The first M-1 peak positions are averaged to the last peak position as the fine timing position P _f .

The repeated preamble synchronization sequence in step a is Gray sequence b128 specified in the IEEE802.15.3c standard.

The calculation formula of the normalized sliding autocorrelation value _Ci described in step a is

Among them, p _i is the i-th sample value received, and the length N of the autocorrelation window is 128 of the length of a Gray sequence.

The reconstructed preamble synchronization sequence described in step c is a low-order Golay complementary sequence separated from a high-order Golay sequence, and its structure is

Among them, b128 is a Golay sequence with a length of 128, and a32 and b32 are Golay complementary sequences with a length of 32.

The calculation formula of the normalized separation correlation value described in step c is

Among them, p _i is the i-th sample value received, and the autocorrelation window length N is 32.

The determination method of fine timing position P _f described in the step c is

Among them, M is the number of correlation peaks, and i _m is the sample number corresponding to the peak position.

Example

The invention is applied in the OFDM ultra-wideband system of the IEEE802.15.3c standard, and the system is simulated based on Matlab/Simulink.

As shown in Figure 2(a)(b)(c), the autocorrelation sidelobe of a single Golay sequence is larger, while the non-periodic autocorrelation of Golay complementary sequence has all sidelobe zero due to complementary cancellation. This ideal complementary autocorrelation property of Gray's complementary sequence is very suitable for high-precision timing synchronization.

Figure 3(a) shows the waveforms of the normalized sliding autocorrelation values calculated in the frame detection and coarse timing phases. It can be seen that when the correlation window length is 128, there is an obvious falling edge between the first part of the leading frame synchronization sequence (SYNC) and the second part of the frame delimiter (SFD). Figure 3(b) shows the waveform diagram of the separated autocorrelation value calculated in the fine timing stage. It can be seen that when the correlation window length is 32, a sharp correlation peak is generated every 64 samples, and a total of multiple related peaks.

Figure 4 shows the false alarm and missing alarm probabilities of frame detection corresponding to different thresholds G when the signal-to-noise ratio is 0dB, the CM2 channel, and the correlation window length is 128. It can be seen that the false detection rate is the lowest when the threshold G is 0.14 to 0.16 .

Figure 5 shows the coarse timing root mean square error (MSRE) curves for different channel models. It can be seen that under the Gaussian channel and the multipath channel CM1, the MSRE performance of the coarse timing is similar, but under the CM2 channel, the MSRE of the coarse timing is larger, and with the increase of the signal-to-noise ratio, the MSRE gradually stabilizes at 5 samples within.

Figure 6 shows the coarse timing root mean square error (MSRE) curves for different channel models. It can be seen that under the 14dB Gaussian channel and the CM1 channel, the MSRE can reach the order of 10 ^-3 , and the MSRE under the CM2 channel can also reach the order of 10 ^-2 .

This embodiment shows that through the above simulation, the timing synchronization scheme proposed by the present invention can effectively resist multipath interference, and can realize high-precision timing of received symbols.

Claims (4)

1. The anti-multipath timing synchronization method of OFDM UWB system is characterized in that: the method comprises the following steps: a. Calculate the normalized sliding autocorrelation value C _i based on the repeated preamble synchronization sequence, and use it as the judgment quantity, set a threshold value G, when C _i is less than G, it is confirmed that the frame is detected, let Corresponding to i ₌ it , where _i is the sample number, and it is the position of the detected frame; b. Find the maximum value of _{C i} within the range where i is _greater than it and less than it + M, and record the sample number corresponding to this maximum value as i=μ, then the rough timing position is P _c =L-μ, Where M is the length of a symbol, and L is the length of the preamble synchronization sequence; c. Calculate the normalized separation correlation value D _i based on the reconstructed preamble synchronization sequence, record the sample number i _m corresponding to all M peaks in the calculation result, m=1, 2, ..., M, and put the first M - 1 peak position is averaged to the last peak position as the fine timing position P _f ; d. The reconstructed preamble synchronization sequence is a low-order Golay complementary sequence separated from a high-order Golay sequence, and its structure is <mrow><mi>b</mi><mn>128</mn><mo>=</mo><mo>&amp;lsqb;</mo><mtable><mtr><mtd><mrow><mi>a</mi><mn>32</mn></mrow></mtd><mtd><mrow><mi>b</mi><mn>32</mn></mrow></mtd><mtd><mrow><mover><mi>a</mi><mo>&amp;OverBar;</mo></mover><mn>32</mn></mrow></mover>mtd><mtd><mrow><mi>b</mi><mn>32</mn></mrow></mtd></mtr></mtable><mo>&amp;rsqb;</mo></mrow> Among them, b128 is a Golay sequence with a length of 128, and a32 and b32 are Golay complementary sequences with a length of 32; e. The calculation formula of the normalized separation correlation value is <mrow><msub><mi>D</mi><mi>i</mi></msub><mo>=</mo><mfrac><mrow><mo>|</mo><munderover><mo>&amp;Sigma;</mo><mrow><mi>n</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></munderover><mrow><msub><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi></mrow></msub><mo>&amp;times;</mo><msubsup><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi><mo>+</mo><mn>64</mn></mrow><mo>*</mo></msubsup></mrow><mo>+</mo><munderover><mo>&amp;Sigma;</mo><mrow><mi>n</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></munderover><mrow><msub><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi></mrow></msub><mo>&amp;times;</mo><msubsup><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi><mo>+</mo><mn>128</mn></mrow><mo>*</mo></msubsup><mo>|</mo></mrow></mrow><mrow><mo>|</mo><munderover><mo>&amp;Sigma;</mo><mrow><mi>n</mi><mo>=</mo><mn>0</mn></mo>mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></muunderover><mrow><msubsup><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi></mrow><mo>*</mo></msubsup><mo>&amp;times;</mo><msub><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi></mrow></msub><mo>|</mo></mrow></mrow></mfrac></mrow> Among them, p _i is the i-th sample value received, and the autocorrelation window length N is 32. 2. the OFDM ultra-wideband system anti-multipath timing synchronization method according to claim 1 is characterized in that: the repeated preamble synchronization sequence described in the step a is the gray sequence b128 of the IEEE 802.15.3c standard . 3. OFDM UWB system anti-multipath timing synchronization method according to claim 1, is characterized in that: the calculation formula of normalized sliding autocorrelation value _Ci described in the step a is: <mrow><msub><mi>C</mi><mi>i</mi></msub><mo>=</mo><mo>|</mo><mfrac><mrow><munderover><mo>&amp;Sigma;</mo><mrow><mi>n</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></munderover><msubsup><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi></mrow><mo>*</mo></msubsup><mo>&amp;times;</mo><msub><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi><mo>+</mo><mi>N</mi></mrow></msub></mrow><mrow><munderover><mo>&amp;Sigma;</mo><mrow><mi>n</mi><mo>=</mo><mn>0</mn></mrow><mrow><mi>N</mi><mo>-</mo><mn>1</mn></mrow></munderover><msubsup><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi></mrow><mo>*</mo></msubsup><mo>&amp;times;</mo><msub><mi>p</mi><mrow><mi>i</mi><mo>+</mo><mi>n</mi></mrow></msub></mrow></mfrac><mo>|</mo></mrow> Among them, p _i is the i-th sample value received, and the length N of the autocorrelation window is 128 of the length of a Gray sequence. 4. OFDM UWB system anti-multipath timing synchronization method according to claim 1, is characterized in that: the determination method of fine timing position Pf described in the step _c is <mrow><msub><mi>P</mi><mi>f</mi></msub><mo>=</mo><mfrac><mn>1</mn><mi>M</mi></mfrac><munderover><mo>&amp;Sigma;</mo><mrow><mi>m</mi><mo>=</mo><mn>1</mn></mrow><mi>M</mi></munderover><mo>&amp;lsqb;</mo><msub><mi>i</mi><mi>m</mi></msub><mo>+</mo><mn>64</mn><mrow><mo>(</mo><mi>M</mi><mo>-</mo><mi>m</mi><mo>)</mo></mrow><mo>&amp;rsqb;</mo></mrow> Among them, M is the number of correlation peaks, and i _m is the sample number corresponding to the peak position.