  We present a novel decoding algorithm for q-ary low-density parity-check
codes, termed symbol message passing. The proposed algorithm can be seen as a
generalization of Gallager B and the binary message passing algorithm by
Lechner et al. to q-ary codes. We derive density evolution equations for the
q-ary symmetric channel, compute thresholds for a number of regular low-density
parity-check code ensembles, and verify those by Monte Carlo simulations of
long channel codes. The proposed algorithm shows performance advantages with
respect to an algorithm of comparable complexity from the literature.
