In this paper we propose and assess the
performance of relay-assisted schemes designed for both the
uplink and downlink OFDM based systems, using efficient
distributed space-frequency block coding protocols. We
consider the use of an antenna array at the base station and a
single antenna at the user terminal. At the relay node we
consider either single antenna or an antenna array. We assume
that some of the user terminals deployed in a certain area
could act as relaying-able terminals for the communication of
other users. Two types of relay-assisted protocols are
considered: equalize-and-forward and decode-and-forward.
The optimal maximum ratio combining coefficients are derived
for the proposed relay-assisted schemes. The performance of
these cooperative schemes is evaluated under realistic
scenarios, considering typical pedestrian scenarios based on
WiMAX specifications and using channel convolutional turbo
code. The proposed schemes are also compared against the
non-cooperative OFDM based systems. +umerical results show
that the availability of antenna arrays at the relays
significantly improves the cooperative systems performance,
which outperform the non-cooperative ones in most studied
scenarios
