5,723 research outputs found
Distributed Space Time Coding for Wireless Two-way Relaying
We consider the wireless two-way relay channel, in which two-way data
transfer takes place between the end nodes with the help of a relay. For the
Denoise-And-Forward (DNF) protocol, it was shown by Koike-Akino et. al. that
adaptively changing the network coding map used at the relay greatly reduces
the impact of Multiple Access interference at the relay. The harmful effect of
the deep channel fade conditions can be effectively mitigated by proper choice
of these network coding maps at the relay. Alternatively, in this paper we
propose a Distributed Space Time Coding (DSTC) scheme, which effectively
removes most of the deep fade channel conditions at the transmitting nodes
itself without any CSIT and without any need to adaptively change the network
coding map used at the relay. It is shown that the deep fades occur when the
channel fade coefficient vector falls in a finite number of vector subspaces of
, which are referred to as the singular fade subspaces. DSTC
design criterion referred to as the \textit{singularity minimization criterion}
under which the number of such vector subspaces are minimized is obtained.
Also, a criterion to maximize the coding gain of the DSTC is obtained. Explicit
low decoding complexity DSTC designs which satisfy the singularity minimization
criterion and maximize the coding gain for QAM and PSK signal sets are
provided. Simulation results show that at high Signal to Noise Ratio, the DSTC
scheme provides large gains when compared to the conventional Exclusive OR
network code and performs slightly better than the adaptive network coding
scheme proposed by Koike-Akino et. al.Comment: 27 pages, 4 figures, A mistake in the proof of Proposition 3 given in
Appendix B correcte
Multi-Source Cooperative Communication with Opportunistic Interference Cancelling Relays
In this paper we present a multi-user cooperative protocol for wireless
networks. Two sources transmit simultaneously their information blocks and
relays employ opportunistically successive interference cancellation (SIC) in
an effort to decode them. An adaptive decode/amplify-and-forward scheme is
applied at the relays to the decoded blocks or their sufficient statistic if
decoding fails. The main feature of the protocol is that SIC is exploited in a
network since more opportunities arise for each block to be decoded as the
number of used relays NRU is increased. This feature leads to benefits in terms
of diversity and multiplexing gains that are proven with the help of an
analytical outage model and a diversity-multiplexing tradeoff (DMT) analysis.
The performance improvements are achieved without any network synchronization
and coordination. In the final part of this work the closed-form outage
probability model is used by a novel approach for offline pre-selection of the
NRU relays, that have the best SIC performance, from a larger number of NR
nodes. The analytical results are corroborated with extensive simulations,
while the protocol is compared with orthogonal and multi-user protocols
reported in the literature.Comment: in IEEE Transactions on Communications, 201
Dispensing with channel estimation: differentially modulated cooperative wireless communications
As a benefit of bypassing the potentially excessive complexity and yet inaccurate channel estimation, differentially encoded modulation in conjunction with low-complexity noncoherent detection constitutes a viable candidate for user-cooperative systems, where estimating all the links by the relays is unrealistic. In order to stimulate further research on differentially modulated cooperative systems, a number of fundamental challenges encountered in their practical implementations are addressed, including the time-variant-channel-induced performance erosion, flexible cooperative protocol designs, resource allocation as well as its high-spectral-efficiency transceiver design. Our investigations demonstrate the quantitative benefits of cooperative wireless networks both from a pure capacity perspective as well as from a practical system design perspective
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