The design and analysis of various distributed space time block coding
schemes for asynchronous cooperative relay networks is considered
in this thesis. Rayleigh frequency flat fading channels are assumed to
model the links in the networks, and interference suppression techniques
together with an orthogonal frequency division multiplexing type transmission
approach are employed to mitigate the synchronization errors
at the destination node induced by the different delays through the
relay nodes.
Closed-loop space time block coding is first considered in the context
of decode-and-forward (regenerative) networks. In particular, quasi orthogonal
and extended orthogonal coding techniques are employed for
transmission from four relay nodes and parallel interference cancellation
detection is exploited to mitigate synchronization errors. Availability
of a direct link between the source and destination nodes is studied,
and a new Alamouti space time block coding technique with parallel
interference cancellation detection which does not require such a direct
link connection and employs two relay nodes is proposed. Outer
coding is then added to gain further improvement in end-to-end performance
and amplify-and-forward (non regenerative) type networks
together with distributed space time coding are considered to reduce
relay node complexity.
Novel detection schemes are then proposed for decode-and-forward
networks with closed-loop extended orthogonal coding which reduce
the computational complexity of the parallel interference cancellation.
Both sub-optimum and near-optimum detectors are presented for relay
nodes with single or dual antennas. End-to-end bit error rate simulations
confirm the potential of the approaches and their ability to
mitigate synchronization errors. A relay selection approach is also formulated
which maximizes spatial diversity gain and attains robustness
to timing errors.
Finally, a new closed-loop distributed extended orthogonal space
time block coding solution for amplify-and-forward type networks which
minimizes the number of feedback bits by using a cyclic rotation phase
is presented. This approach utilizes an orthogonal frequency division
multiplexing type transmission structure with a cyclic prefix to mitigate
synchronization errors. End-to-end bit error performance evaluations
verify the efficacy of the scheme and its success in overcoming synchronization
errors
