On fractionally-spaced blind adaptive equalization under symbol timing offsets using Godard and related equalizers

The problem of fractionally-spaced (FS) blind adaptive equalization under symbol-timing-phase offsets is considered. It is well-known that in the case of trained (non-blind) equalizers, the performance of FS equalizers is independent of the timing-phase unlike that of baud-rate equalizers. Moreover, trained FS equalizers synthesize optimal filters in the MMSE sense, and hence are superior to baud-rate trained equalizers. These advantages of trained FS equalizers have not been shown to be true for blind equalizers, rather they have been simply assumed. The authors present a simulation example where such advantages do not materialize. Then they present a solution based upon a parallel, multimodel Godard adaptive filter bank approach which yields a performance almost invariant w.r.t. symbol-timing-phase. An illustrative simulation example 16-QAM (V22 source) signal is presented where the effect of symbol-timing-phase offset is studied via computer simulations.