Synchronization Problems in PAM Systems

In a PAM system with unknown carrier phase and timing phase the receiver has to estimate these parameters. The "dataaided" approach involves the joint estimation of the data symbols and the unknown parameters. This is in contrast with the "nondataaided" approach, where the carrier phase and timing phase are estimated independently of the data symbols. We first establish the equivalence of these two strategies for high signal-to-noise ratios. Then we demonstrate that several PAM systems (baseband, VSB, QAM) perform better when the data symbols are independent equiprobable bits, instead of independent identically distributed Gaussian random variables (a high signal-to-noise ratio is assumed). Finally, some generalizations of the previous conclusions are treated.