  Distributed space time coding for wireless relay networks when the source,
the destination and the relays have multiple antennas have been studied by Jing
and Hassibi. In this set-up, the transmit and the receive signals at different
antennas of the same relay are processed and designed independently, even
though the antennas are colocated. In this paper, a wireless relay network with
single antenna at the source and the destination and two antennas at each of
the R relays is considered. A new class of distributed space time block codes
called Co-ordinate Interleaved Distributed Space-Time Codes (CIDSTC) are
introduced where, in the first phase, the source transmits a T-length complex
vector to all the relays and in the second phase, at each relay, the in-phase
and quadrature component vectors of the received complex vectors at the two
antennas are interleaved and processed before forwarding them to the
destination. Compared to the scheme proposed by Jing-Hassibi, for $T \geq 4R$,
while providing the same asymptotic diversity order of 2R, CIDSTC scheme is
shown to provide asymptotic coding gain with the cost of negligible increase in
the processing complexity at the relays. However, for moderate and large values
of P, CIDSTC scheme is shown to provide more diversity than that of the scheme
proposed by Jing-Hassibi. CIDSTCs are shown to be fully diverse provided the
information symbols take value from an appropriate multi-dimensional signal
set.
