Low-complexity anti-frequency offset synchronization method based on CAZAC sequence

Abstract

The invention discloses a low-complexity anti-frequency offset synchronization method based on a CAZAC sequence in a multi-carrier OFDM system, which mainly solves the problems of poor synchronizationperformance and high complexity of the existing algorithm, and adopts the implementation scheme by comprising the following steps of creating a training sequence based on the CAZAC sequence at a sending end; constructing a timing metric function at a receiving end, searching the maximum value of the timing metric function, and finishing timing synchronization; and estimating rough decimal frequency offset, then estimating fine decimal frequency offset and finally estimating integral multiple frequency offset by utilizing a timing synchronization result to finish frequency synchronization. Thesynchronization performance of the OFDM system is improved, the timing metric function is simplified, the calculation complexity is reduced, and the method can be applied to a wireless communicationscene of burst transmission or continuous transmission.

Description

technical field [0001] The invention belongs to the technical field of communication, and in particular relates to a multi-carrier OFDM system-oriented synchronization method, which can be used in wireless communication scenarios of burst transmission or continuous transmission. Background technique [0002] Orthogonal Frequency Division Multiplexing (OFDM), as a multi-carrier modulation method, has the advantages of high spectral efficiency, resistance to frequency selective fading, and easy modulation and demodulation. It has been widely used in many wireless communication scenarios, such as long-term evolution LTE, Digital video broadcasting DVB, wireless local area network WLAN and so on. Although OFDM has the above advantages, its signal modulation mechanism also has some disadvantages in the transmission process of OFDM signals, for example, it is very sensitive to timing deviation and frequency deviation caused by Doppler frequency shift or oscillator instability. Se...

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Problems solved by technology

Among them, the representative algorithms for synchronization based on PN sequences are: SC proposed to use two identical sequences in his paper "Robust Frequency and Timing Synchronization for OFDM" (IEEE Transactions on Communications, 1997, 45:1613-1621) Timing synchronization scheme, but due to the existence of cyclic prefix, its timing measurement has a flat-top effect; Minn published a paper "On Timing Offset Estimation for OFDM Systems" (IEEE Communications Letters, 2000, 4:242-244) in the SC algorithm Based on the improvement, the four-part sequence is used for timing synchronization. Although this method eliminates the flat top effect, there are still high side lobes; Park published the paper "A Novel TimingEstimation Method for OFDM Systems" (IEEE Communications Letters ,2003,7:53-55) designed a training sequence structure with conjugate symmetry properties. Compared with SC algorithm and Minn algorithm, this algorithm has a larger peak at the correct starting point position, which improves the Accuracy of the timing measurement, but there are still small sidelobes; Yang proposed a A coarse symbol timing algorithm based on optimal correlation cyclic shift preamble sequence CSP, the algorithm has good performance in multipath fading channel, but its computational complexity is high

[0006] The peak flat-top effect or the large side lobe of these algorithms have a certain impact on timing synchronization, and when using PN sequences for symbol timing synchronization, there will be problems with peak-to-average ratios, while CAZAC sequences have good correlation characteristics and low peak-to-average ratio characteristics can just solve these problems, so the use of CAZAC sequences for synchronization has been widely used in OFDM systems

[0007] The existing representative algorithms for synchronization based on CAZAC sequences are: Fang used random The exponential sequence weights the CAZAC sequence to complete timing synchronization. Shao published the paper "Robust Timing and Frequency Synchronization Based on Constant Amplitude Zero Autocorrelation Sequence for OFDM Systems" (IEEE International Conference on Communication Problem-solving, 2014:14–17) A training sequence structure similar to the Park algorithm is adopted in the method, and a new weighting factor is used to weight the CAZAC sequence at the receiving end to complete timing synchronization. The Fang algorithm and the Shao algorithm perform well in multipath fading channels, but at the receiving end Additional weighted sequences need to be used for synchronization, which wastes some storage space and increases its computational complexity; Jian published in his paper "ANovel Timing Synchronization Method Based on CAZAC Sequence for OFDM Systems" (IEEE International Conference on Signal Processing, Communications and Computing, 2018:10-15) designed a new training sequence structure, which can reduce the computational complexity when using this structure for timing synchronization, but when there is a frequency offset, its timing Significantly lower sync performance

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