8,450 research outputs found
Performance Analysis of Adaptive Physical Layer Network Coding for Wireless Two-way Relaying
The analysis of modulation schemes for the physical layer network-coded two
way relaying scenario is presented which employs two phases: Multiple access
(MA) phase and Broadcast (BC) phase. It was shown by Koike-Akino et. al. that
adaptively changing the network coding map used at the relay according to the
channel conditions greatly reduces the impact of multiple access interference
which occurs at the relay during the MA phase. Depending on the signal set used
at the end nodes, deep fades occur for a finite number of channel fade states
referred as the singular fade states. The singular fade states fall into the
following two classes: The ones which are caused due to channel outage and
whose harmful effect cannot be mitigated by adaptive network coding are
referred as the \textit{non-removable singular fade states}. The ones which
occur due to the choice of the signal set and whose harmful effects can be
removed by a proper choice of the adaptive network coding map are referred as
the \textit{removable} singular fade states. In this paper, we derive an upper
bound on the average end-to-end Symbol Error Rate (SER), with and without
adaptive network coding at the relay, for a Rician fading scenario. It is shown
that without adaptive network coding, at high Signal to Noise Ratio (SNR), the
contribution to the end-to-end SER comes from the following error events which
fall as : the error events associated with the removable
singular fade states, the error events associated with the non-removable
singular fade states and the error event during the BC phase. In contrast, for
the adaptive network coding scheme, the error events associated with the
removable singular fade states contributing to the average end-to-end SER fall
as and as a result the adaptive network coding scheme
provides a coding gain over the case when adaptive network coding is not used.Comment: 10 pages, 5 figure
Wireless Network-Coded Three-Way Relaying Using Latin Cubes
The design of modulation schemes for the physical layer network-coded
three-way wireless relaying scenario is considered. The protocol employs two
phases: Multiple Access (MA) phase and Broadcast (BC) phase with each phase
utilizing one channel use. For the two-way relaying scenario, it was observed
by Koike-Akino et al. \cite{KPT}, that adaptively changing the network coding
map used at the relay according to the channel conditions greatly reduces the
impact of multiple access interference which occurs at the relay during the MA
phase and all these network coding maps should satisfy a requirement called
\textit{exclusive law}. This paper does the equivalent for the three-way
relaying scenario. We show that when the three users transmit points from the
same 4-PSK constellation, every such network coding map that satisfies the
exclusive law can be represented by a Latin Cube of Second Order. The network
code map used by the relay for the BC phase is explicitly obtained and is aimed
at reducing the effect of interference at the MA stage.Comment: 13 Pages, 16 Figures. Some mistakes in the previous version have been
fixe
Linear physical-layer network coding and information combining for the K-user fading multiple-access relay network
© 2002-2012 IEEE. We propose a new linear physical-layer network coding (LPNC) and information combining scheme for the K -user fading multiple-access relay network (MARN), which consists of K users, one relay, and one destination. The relay and the destination are connected by a rate-constraint wired or wireless backhaul. In the proposed scheme, the K users transmit signals simultaneously. The relay and the destination receive the superimposed signals distorted by fading and noise. The relay reconstructs L linear combinations of the K users' messages, referred to as network-coded (NC) messages, and forwards them to the destination. The destination then attempts to recover all K users' messages by combining its received signals and the NC messages obtained from the relay. We develop an explicit expression on the selection of the coefficients of the NC messages at the relay that minimizes the end-to-end error probability at a high signal-to-noise ratio. We develop a channel-coded LPNC scheme by using an irregular repeat-accumulate modulation code over GF( q ). An iterative belief-propagation algorithm is employed to compute the NC messages at the relay, while a new algorithm is proposed for the information combining decoding at the destination. We demonstrate that our proposed scheme outperforms benchmark schemes significantly in both un-channel-coded and channel-coded MARNs
Lossy Compression for Compute-and-Forward in Limited Backhaul Uplink Multicell Processing
We study the transmission over a cloud radio access network in which multiple
base stations (BS) are connected to a central processor (CP) via
finite-capacity backhaul links. We propose two lattice-based coding schemes. In
the first scheme, the base stations decode linear combinations of the
transmitted messages, in the spirit of compute-and-forward (CoF), but differs
from it essentially in that the decoded equations are remapped to linear
combinations of the channel input symbols, sent compressed in a lossy manner to
the central processor, and are not required to be linearly independent. Also,
by opposition to the standard CoF, an appropriate multi-user decoder is
utilized to recover the sent messages. The second coding scheme generalizes the
first one by also allowing, at each relay node, a joint compression of the
decoded equation and the received signal. Both schemes apply in general, but
are more suited for situations in which there are more users than base
stations. We show that both schemes can outperform standard CoF and successive
Wyner-Ziv schemes in certain regimes, and illustrate the gains through some
numerical examples.Comment: Submitted to IEEE Transactions on Communication
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