16QAM symbol timing recovery in the upstream transmission of DOCSIS standard

This paper investigates the performance of the digital symbol timing recovery schemes for 16QAM upstream transmission of the DOCSIS standard. Two forms of nonlinearity are considered: the magnitude square operation and the delay multiplication operation, both of which generate the output signal that contains the symbol timing information. The detailed analysis for the magnitude square timing recovery is given in the digital domain, and consequently the symbol timing estimate can be directly obtained by the discrete Fourier transform. The simulation results show that the magnitude square timing recovery and delay multiplication timing recovery algorithms suffer from the same problem that the estimation error is reduced slowly at high signal-to-noise ratios due to the effect of self-noise. To this end, the third scheme, which is the magnitude square timing recovery with prefilter, is examined. This scheme shows a superior performance and a comparison with the results of the other two schemes is made.