LDPC Code Construction and Iterative Receiver Techniques for Channels with Phase Noise

We present a novel LDPC code construction technique and an algorithm that assists phase estimation on sub- blocks to provide a near-coherent performance on channels with a large phase noise. Sub-blocks are very small observation intervals on the received vector over which phase estimation techniques are applied to provide ambiguous phase estimates. Iterative decoding on LDPC codes are affected by these phase ambiguities on sub- blocks. In our earlier work, we resolved this sub-block phase ambiguity at the start of the decoding based on a set of check nodes called 'local check nodes (LCN)' that are connected locally within the sub-blocks. Due to the poor signal-to-noise ratio at the start of decoding, a large number of LCNs were required to provide a reliable phase ambiguity. In this paper, we show that random LDPC codes can be constructed such that their decoding is not affected by the presence of sub-block phase ambiguities. Because of this, the signal quality is improved due to the code convergence and hence requires significantly less local check nodes to resolve phase ambiguity. We present performance results for a binary LDPC code with BPSK modulation. They show that with little loss, the receiver could tolerate a Wiener phase noise of up to 3deg standard deviation per symbol.