We analyze the asymptotic performance of nonbinary spatially-coupled low-density
parity-check (SC-LDPC) codes built on the general linear group, when the
transmission takes place over the binary erasure channel. We propose an
efficient method to derive an upper bound to the maximum a posteriori
probability (MAP) threshold for nonbinary LDPC codes, and observe that the MAP
performance of regular LDPC codes improves with the alphabet size. We then
consider nonbinary SC-LDPC codes, and show that, contrary to regular and
irregular LDPC codes, the BP threshold of nonbinary SC-LDPC codes with large
termination length improves with the number of bits per symbol and tends to the
Shannon limit. We finally show that threshold saturation also occurs for
nonbinary SC-LDPC codes.