  The typical behaviour of the relay-without-delay channel and its many-units
generalisation, termed the relay array, under LDPC coding, is studied using
methods of statistical mechanics. A demodulate-and-forward strategy is
analytically solved using the replica symmetric ansatz which is exact in the
studied system at the Nishimori's temperature. In particular, the typical level
of improvement in communication performance by relaying messages is shown in
the case of small and large number of relay units.
