Study On Timing Recovery Technology For All-digital QAM Receivers

With the development of digital communication technique and the requirement of high capacity of transmission, the degree of digital integrated and the transmission rate of signal has increased constantly. The all-digital receiver with QAM modulation mode, with its all-digital processing and high bandwidth efficiency and other advantages, was widely used. Timing recovery technology in digital receiver as one of the key technology is to safeguard the system comprehensive performance of premise. Therefore, it has theory and practical application significance to study the timing recovery technology in digital receiver in different channel.In this paper, we mainly studies timing recovery technique for all-digital QAM receivers under the influence of different channel. The main aspects are as followed:①We has studied the common method of timing recovery, then analyzed and compared two aspects of timing recovery as the structure of timing recovery , the method of timing-error correction and timing-error timing-error extraction. We have designed the feedforward structure of timing recovery, it estimates timing-error using the digital-square-filtering algorithm, and corrects timing-error by the interpolation filter.②The study was done on the interpolation filter with FARROW structure in the loop of timing recovery. In order to make the impulse response of filter equalized with ideal low-pass in sample optimal plots In the time domain, and inhibitory second-channel frequency as much as possible in the frequency domain, we approximate performance of interpolation filter by using partitioned imitation polynomial, we worked out polynomial coefficient utilizing minimum mean-square-error method. Analysis and simulation results show that, optimized coefficient could satisfy impulse response requirements, while it has greater inhibition before second-channel frequency optimized.③The analysis was done on the performance of digital-square-filtering algorithm at Gaussian white noise channel. Aimed at the problem of the jitter of the timing-error estimates, we further studied the rearmounted Kalman filter reduces timing jitter, and the prepositive band-pass filter filters out-of-band interference optimization method in this paper. Simulation results show that, the velocity of convergence of optimized estimate error is fast, estimated value is stabled around exact value with small jitter. ④The research was done on the timing recovery technology in digital receiver at multi-path channel. The signal frequency offset, fading and delay are not the same, its efforts cannot be estimated before timing recovery at multi-path channel. In this paper, we studied the second-order cyclostationarity estimated algorithm under the assumptions that channel fading is constant, frequency offset can be ignored and other in the flat fading channel, then we optimize this estimated algorithm for the fast fading channel. Simulation and experimental results indicated that, the error estimation performance of optimized estimated algorithm was greater degree improvement.