Timing recovery using soft information feedback and efficiency of array codes

The main contribution of the thesis provides techniques for symbol frequency and phase tracking in a pilotless Low-Density Parity-Check (LDPC) coded transmission over an AWGN channel. In traditional receiver architectures, symbol acquisition and tracking are performed using phase-lock techniques that are independent of the channel-code decoding process. In burst reception scenarios, bandwidth inefficient piloting must often be embedded in a transmission in order to accelerate acquisition to aid symbol time tracking at low signal-to-noise ratios (SNRs). In this thesis we show that outputs from the constraint node side of a bi-partite decoding graph can be used to improve the estimation of symbol frequency and phase. We focus on the problem of a symbol frequency and/or timing offset between transmitter and receiver and describe a method capable of handling very large offsets with complexity that grows linearly with the maximum offset size. Combining information from the set of parity-check equations of a LDPC code observations with a properly calibrated phase locked loop allows successful tracking of a constant time delay, a frequency offset and a random phase walk.; The problem of carrier-phase estimation in a coded environment is also addressed. Once again we assume a pilotless scenario where, by feeding back soft information from an iterative LDPC decoder, the phase information of the carrier is estimated. The joint problem of symbol-timing estimation in a digital transmission affected by carrier phase offsets is also analyzed.; We conclude this dissertation by examining the rate efficiency of array codes. By allowing a slight increase in encoding and decoding complexity, we observed that the same error correcting properties of these codes can be achieved by Hamming and Reed-Solomon (RS) codes over GF( q). For single phased burst correction, non-binary Hamming codes maximize the possible code rate and can be decoded with similar complexity as array codes. For multiple burst correction, RS codes offer the same error correcting capability as array codes with a higher code rate.