Conjugate gradient based multichannel decision feedback equalization for digital television

We examine the performance of a multichannel decision feedback equalizer (DFE) employing conjugate gradients (CG) based adaptive filtering in the context of digital television based on the 8-VSB standard. The 8-VSB modulation scheme employs real-valued 8-PAM symbols but complex root-raised cosine (spectral) pulse shaping for bandwidth efficiency. Thus, even in the case of a single receive antenna, two virtual channels may be realized via the real and imaginary parts of the received signal. A dual virtual channel minimum mean-square error (MMSE) DFE is derived. Given multiple channels, the high symbol rate of 8-VSB based TV, 10.76 MHz, and the rather large delay spreads one has to contend with in the UHF and VHF bands, the composite DFE weight lies in a space of high dimensionality. We thus implement the MMSE-DFE adaptively using the conjugate gradient (CG) algorithm since it has been shown to effect reduced-rank adaptive filtering, for improved performance with insufficient training, and is also amenable to "smart" initialization.