170 research outputs found
Eigen-Based Transceivers for the MIMO Broadcast Channel with Semi-Orthogonal User Selection
This paper studies the sum rate performance of two low complexity
eigenmode-based transmission techniques for the MIMO broadcast channel,
employing greedy semi-orthogonal user selection (SUS). The first approach,
termed ZFDPC-SUS, is based on zero-forcing dirty paper coding; the second
approach, termed ZFBF-SUS, is based on zero-forcing beamforming. We first
employ new analytical methods to prove that as the number of users K grows
large, the ZFDPC-SUS approach can achieve the optimal sum rate scaling of the
MIMO broadcast channel. We also prove that the average sum rates of both
techniques converge to the average sum capacity of the MIMO broadcast channel
for large K. In addition to the asymptotic analysis, we investigate the sum
rates achieved by ZFDPC-SUS and ZFBF-SUS for finite K, and show that ZFDPC-SUS
has significant performance advantages. Our results also provide key insights
into the benefit of multiple receive antennas, and the effect of the SUS
algorithm. In particular, we show that whilst multiple receive antennas only
improves the asymptotic sum rate scaling via the second-order behavior of the
multi-user diversity gain; for finite K, the benefit can be very significant.
We also show the interesting result that the semi-orthogonality constraint
imposed by SUS, whilst facilitating a very low complexity user selection
procedure, asymptotically does not reduce the multi-user diversity gain in
either first (log K) or second-order (loglog K) terms.Comment: 35 pages, 3 figures, to appear in IEEE transactions on signal
processin
Wireless transmission protocols using relays for broadcast and information exchange channels
Relays have been used to overcome existing network performance bottlenecks in meeting the growing
demand for large bandwidth and high quality of service (QoS) in wireless networks. This thesis
proposes several wireless transmission protocols using relays in practical multi-user broadcast and
information exchange channels. The main theme is to demonstrate that efficient use of relays provides
an additional dimension to improve reliability, throughput, power efficiency and secrecy. First,
a spectrally efficient cooperative transmission protocol is proposed for the multiple-input and singleoutput
(MISO) broadcast channel to improve the reliability of wireless transmission. The proposed
protocol mitigates co-channel interference and provides another dimension to improve the diversity
gain. Analytical and simulation results show that outage probability and the diversity and multiplexing
tradeoff of the proposed cooperative protocol outperforms the non-cooperative scheme. Second,
a two-way relaying protocol is proposed for the multi-pair, two-way relaying channel to improve the
throughput and reliability. The proposed protocol enables both the users and the relay to participate
in interference cancellation. Several beamforming schemes are proposed for the multi-antenna
relay. Analytical and simulation results reveal that the proposed protocol delivers significant improvements
in ergodic capacity, outage probability and the diversity and multiplexing tradeoff if compared
to existing schemes. Third, a joint beamforming and power management scheme is proposed for
multiple-input and multiple-output (MIMO) two-way relaying channel to improve the sum-rate. Network
power allocation and power control optimisation problems are formulated and solved using
convex optimisation techniques. Simulation results verify that the proposed scheme delivers better
sum-rate or consumes lower power when compared to existing schemes. Fourth, two-way secrecy
schemes which combine one-time pad and wiretap coding are proposed for the scalar broadcast channel
to improve secrecy rate. The proposed schemes utilise the channel reciprocity and employ relays
to forward secret messages. Analytical and simulation results reveal that the proposed schemes are
able to achieve positive secrecy rates even when the number of users is large. All of these new wireless
transmission protocols help to realise better throughput, reliability, power efficiency and secrecy
for wireless broadcast and information exchange channels through the efficient use of relays
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