  The non-binary low-density parity-check (NB-LDPC) codes can offer promising
performance advantages but suffer from high decoding complexity. To tackle this
challenge, in this paper, we consider NB-LDPC codes over finite fields as codes
over \textit{subfields} as a means of reducing decoding complexity. In
particular, our approach is based on a novel method of expanding a non-binary
Tanner graph over a finite field into a graph over a subfield. This approach
offers several decoding strategies for a single NB-LDPC code, with varying
levels of performance-complexity trade-offs. Simulation results demonstrate
that in a majority of cases, performance loss is minimal when compared with the
complexity gains.
