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Toward realistic wireless cooperative communications networks

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El Astal, MTO (2015) Toward realistic wireless cooperative communications networks. PhD thesis, University of Tasmania.

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Abstract

Recently, the space-time block codes (STBCs) were suggested to use in wireless relaying
networks (WRNs), denoted as distributed-STBCs (D-STBCs). This is to exploit effectively the
spatial diversity and hence improve the link reliability. In addition, this usage may increase
the network’s spectrum efficiency as it allows concurrent transmission from the relaying
nodes. However, these networks encounter numerous issues that limit their wide practical
use. This thesis addresses three critical issues of WRNs, and proposes solutions for each part
individually.
In Part I, WRNs are considered under imperfect synchronization. In the literature, most research
tends to assume perfect synchronization among the cooperative relays. Unfortunately,
this level of synchronization is almost impossible to achieve in real communication networks,
and this introduces a significant performance degradation if imperfect synchronization is
present in the network. This part includes mathematical models that are derived for WRNs,
either one-way or two-way, under imperfect synchronisation conditions. Unlike existing
models, this model provides a simple method of evaluating the problem for variant network
configurations. In addition, this model considers the WRNs with N relays, each is equipped
with Ra antennas, where N, Ra ∈ N+. With respect to current literature, the contributions of
this part are : (1) both the existing PIC and SIC based detectors, which were proposed for
specific network configurations instances, are extended here to work with the general model.
(2) an enhanced interference cancellation based detector (EIC) is proposed. These proposed
detectors shows significant performance improvement compared to the conventional detector
under imperfect synchronisation conditions. In addition, the proposed EIC detector provides
better improvement due to the designed interference cancellation process. It reduces
the reliance on low-performance symbols and it benefits from interference components of
currently-detected symbols using a modified maximum likelihood (ML) scheme. Accordingly,
an extra performance improvement is achieved, particularly in the first iteration.
Part II considers the issue of designing D-STBCs for WRNs with an arbitrary number of
relays. It has been shown that the reliability of WRNs increases by adding more relays as a result of more communication paths becoming available. Unlike most existing D-STBCs, this part proposes two high rate coding schemes to accommodate an arbitrary number of
relays, while retaining low decoding complexity at the destination. The first scheme, full-rate
distributed space-time block coded-joint transmit/receive antenna diversity (D-STBC-JTRD),
is proposed for AF WRNs. Its code rate is independent of the number of relays and hence no
code rate loss is incurred as the relays number increases. In addition, this scheme deploys
the same encoding matrices at every relay; this eliminates the need for additional network
overhead to coordinate the code generation by the relays. In other words, there is no need
to interrupt the transmission if a relay has been up/down. The second scheme aims to find
a flexible trade-off between reliability and code-rate that can be offered by DF networks.
Towards this end, a method to construct a D-STBC that is combined with spatial modulation
(SM), denoted as D-STBC-SM, is proposed. This method is not restricted to a specific number
of relays and can be constructed as necessary. In addition, a novel adaptive transmission
protocol that uses the constructed codes, is proposed to achieve higher space diversity gain,
even with relays equipped with a single antenna. Unlike most existing schemes, this protocol
offers a throughput that increases as the number of relays increases. Moreover, the offered
throughput is achieved using the same total average transmit energy, as only N0 of the N
available participating relays are active at any given time.
In Part III, the multi-user interference of WRNs is considered. Two transmission protocols
with an interference cancellation scheme are proposed: the concurrentS−R−D-PICR,D protocol
for DF WRNs and the concurrentS−R−D-PICD protocol for AF WRNs. Unlike existing
protocols, these protocols allow the concurrent transmission in both phases of the transmission.
Thus, high spectral efficiency is offered while maintaining low decoding complexity.
This low decoding complexity is maintained due to the adaptation of the partial interference
cancellation group decoding (PICGD) approach for WRNs, which was initially proposed by
Guo, et al., for point-to-point (P2P) communication link. For a WRN consisting of J users
equipped each with Ja-antenna, a single half duplex (HD) Ra-antenna relay, and M-antenna
destination, the concurrentS−R−D-PICR,D protocol achieves the interference-free diversity
gain (i.e., Ra × min {Ja,M}) without imposing any conditions on a node’s antenna number.
The interference-free is the diversity gain achieved, assuming that each user in the network
is transmitting solely without experiencing any interference from other users, hence it is
considered as the natural upper bound of the diversity gain in multi-user WRNs. Similar to
most exiting protocols, this protocol requires the CSI of the users-relay links at the relay. In
contrast, the concurrentS−R−D-PICR,D protocol achieves a diversity gain of Ja ×M, given that Ra > 8, while the CSI is required only at the destination. Although the diversity’s upper bound is not achieved, this protocol uses a simple relay as no CSI or encoding is required
at the relay. In addition, and unlike the existing protocols, the achievable diversity gain is
determined by both Ja and M and it is not sacrificed while J is increased. This part also
establishes sufficient conditions for an STBC to achieve the prior mentioned diversity gains,
when the PICGD approach is employed by multi-users WRNs.

Item Type: Thesis (PhD)
Keywords: wireless relaying networks, Space-time codes, imperfect-synchronization, scalable code, scalable networks, multi-user interference
Copyright Holders: The Author
Copyright Information:

Copyright 2015 the author

Date Deposited: 27 Jul 2016 02:23
Last Modified: 27 Jul 2016 02:23
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