| dc.description.abstract | In this thesis, space-time block codes originally developed for multiple antenna systems are
extended to cooperative multi-hop networks. The designs are applicable to any wireless
network setting especially cellular, adhoc and sensor networks where space limitations
preclude the use of multiple antennas. The thesis first investigates the design of distributed
orthogonal and quasi-orthogonal space time block codes in cooperative networks with single
and multiple antennas at the destination. Numerical and simulation results show that by
employing multiple receive antennas the diversity performance of the network is further
improved at the expense of slight modification of the detection scheme. The thesis then
focuses on designing distributed space time block codes for cooperative networks in which
the source node participates in cooperation. Based on this, a source-assisting strategy is
proposed for distributed orthogonal and quasi-orthogonal space time block codes. Numerical
and simulation results show that the source-assisting strategy exhibits improved diversity
performance compared to the conventional distributed orthogonal and quasi-orthogonal
designs.Motivated by the problem of channel state information acquisition in practical wireless
network environments, the design of differential distributed space time block codes is
investigated. Specifically, a co-efficient vector-based differential encoding and decoding
scheme is proposed for cooperative networks. The thesis then explores the concatenation of
differential strategies with several distributed space time block coding schemes namely; the
Alamouti code, square-real orthogonal codes, complex-orthogonal codes, and quasiorthogonal
codes, using cooperative networks with different number of relay nodes. In order
to cater for high data rate transmission in non-coherent cooperative networks, differential distributed quasi-orthogonal space-time block codes which are capable of achieving full
code-rate and full diversity are proposed. Simulation results demonstrate that the differential
distributed quasi-orthogonal space-time block codes outperform existing distributed space
time block coding schemes in terms of code rate and bit-error-rate performance. A multidifferential
distributed quasi-orthogonal space-time block coding scheme is also proposed to
exploit the additional diversity path provided by the source-destination link.A major challenge is how to construct full rate codes for non-coherent cooperative broadband
networks with more than two relay nodes while exploiting the achievable spatial and
frequency diversity. In this thesis, full rate quasi-orthogonal codes are designed for noncoherent
cooperative broadband networks where channel state information is unavailable.
From this, a generalized differential distributed quasi-orthogonal space-frequency coding
scheme is proposed for cooperative broadband networks. The proposed scheme is able to
achieve full rate and full spatial and frequency diversity in cooperative networks with any
number of relays. Through pairwise error probability analysis we show that the diversity gain
of the proposed scheme can be improved by appropriate code construction and sub-carrier
allocation. Based on this, sufficient conditions are derived for the proposed code structure at
the source node and relay nodes to achieve full spatial and frequency diversity. In order to
exploit the additional diversity paths provided by the source-destination link, a novel multidifferential
distributed quasi-orthogonal space-frequency coding scheme is proposed. The
overall objective of the new scheme is to improve the quality of the detected signal at the
destination with negligible increase in the computational complexity of the detector.Finally, a differential distributed quasi-orthogonal space-time-frequency coding scheme is
proposed to cater for high data rate transmission and improve the performance of noncoherent
cooperative broadband networks operating in highly mobile environments. The approach is to integrate the concept of distributed space-time-frequency coding with
differential modulation, and employ rotated constellation quasi-orthogonal codes. From this,
we design a scheme which is able to address the problem of performance degradation in
highly selective fading environments while guaranteeing non-coherent signal recovery and
full code rate in cooperative broadband networks. The coding scheme employed in this thesis
relaxes the assumption of constant channel variation in the temporal and frequency
dimensions over long symbol periods, thus performance degradation is reduced in frequencyselective
and time-selective fading environments. Simulation results illustrate the
performance of the proposed differential distributed quasi-orthogonal space-time-frequency
coding scheme under different channel conditions. | en_US |
