332 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
Physical Layer Network Coding for the Multiple Access Relay Channel
We consider the two user wireless Multiple Access Relay Channel (MARC), in
which nodes and want to transmit messages to a destination node
with the help of a relay node . For the MARC, Wang and Giannakis proposed a
Complex Field Network Coding (CFNC) scheme. As an alternative, we propose a
scheme based on Physical layer Network Coding (PNC), which has so far been
studied widely only in the context of two-way relaying. For the proposed PNC
scheme, transmission takes place in two phases: (i) Phase 1 during which
and simultaneously transmit and, and receive, (ii) Phase 2 during
which , and simultaneously transmit to . At the end of Phase 1,
decodes the messages of and of and during Phase 2
transmits where is many-to-one. Communication protocols in
which the relay node decodes are prone to loss of diversity order, due to error
propagation from the relay node. To counter this, we propose a novel decoder
which takes into account the possibility of an error event at , without
having any knowledge about the links from to and to . It is
shown that if certain parameters are chosen properly and if the map
satisfies a condition called exclusive law, the proposed decoder offers the
maximum diversity order of two. Also, it is shown that for a proper choice of
the parameters, the proposed decoder admits fast decoding, with the same
decoding complexity order as that of the CFNC scheme. Simulation results
indicate that the proposed PNC scheme performs better than the CFNC scheme.Comment: 10 pages, 5 figure
Physical Layer Network Coding for the K-user Multiple Access Relay Channel
A Physical layer Network Coding (PNC) scheme is proposed for the -user
wireless Multiple Access Relay Channel (MARC), in which source nodes
transmit their messages to the destination node with the help of a relay
node The proposed PNC scheme involves two transmission phases: (i) Phase 1
during which the source nodes transmit, the relay node and the destination node
receive and (ii) Phase 2 during which the source nodes and the relay node
transmit, and the destination node receives. At the end of Phase 1, the relay
node decodes the messages of the source nodes and during Phase 2 transmits a
many-to-one function of the decoded messages. Wireless networks in which the
relay node decodes, suffer from loss of diversity order if the decoder at the
destination is not chosen properly. A novel decoder is proposed for the PNC
scheme, which offers the maximum possible diversity order of for a proper
choice of certain parameters and the network coding map. Specifically, the
network coding map used at the relay is chosen to be a -dimensional Latin
Hypercube, in order to ensure the maximum diversity order of Also, it is
shown that the proposed decoder can be implemented by a fast decoding
algorithm. Simulation results presented for the 3-user MARC show that the
proposed scheme offers a large gain over the existing scheme for the -user
MARC.Comment: More Simulation results added, 12 pages, 10 figures. arXiv admin
note: substantial text overlap with arXiv:1210.049
Broadcast Channels with Cooperating Decoders
We consider the problem of communicating over the general discrete memoryless
broadcast channel (BC) with partially cooperating receivers. In our setup,
receivers are able to exchange messages over noiseless conference links of
finite capacities, prior to decoding the messages sent from the transmitter. In
this paper we formulate the general problem of broadcast with cooperation. We
first find the capacity region for the case where the BC is physically
degraded. Then, we give achievability results for the general broadcast
channel, for both the two independent messages case and the single common
message case.Comment: Final version, to appear in the IEEE Transactions on Information
Theory -- contains (very) minor changes based on the last round of review
Multilevel Coding Schemes for Compute-and-Forward with Flexible Decoding
We consider the design of coding schemes for the wireless two-way relaying
channel when there is no channel state information at the transmitter. In the
spirit of the compute and forward paradigm, we present a multilevel coding
scheme that permits computation (or, decoding) of a class of functions at the
relay. The function to be computed (or, decoded) is then chosen depending on
the channel realization. We define such a class of functions which can be
decoded at the relay using the proposed coding scheme and derive rates that are
universally achievable over a set of channel gains when this class of functions
is used at the relay. We develop our framework with general modulation formats
in mind, but numerical results are presented for the case where each node
transmits using the QPSK constellation. Numerical results with QPSK show that
the flexibility afforded by our proposed scheme results in substantially higher
rates than those achievable by always using a fixed function or by adapting the
function at the relay but coding over GF(4).Comment: This paper was submitted to IEEE Transactions on Information Theory
in July 2011. A shorter version also appeared in the proceedings of the
International Symposium on Information Theory in August 2011 without the
proof of the main theore
Capacity Bounds for a Class of Interference Relay Channels
The capacity of a class of Interference Relay Channels (IRC) -the Injective
Semideterministic IRC where the relay can only observe one of the sources- is
investigated. We first derive a novel outer bound and two inner bounds which
are based on a careful use of each of the available cooperative strategies
together with the adequate interference decoding technique. The outer bound
extends Telatar and Tse's work while the inner bounds contain several known
results in the literature as special cases. Our main result is the
characterization of the capacity region of the Gaussian class of IRCs studied
within a fixed number of bits per dimension -constant gap. The proof relies on
the use of the different cooperative strategies in specific SNR regimes due to
the complexity of the schemes. As a matter of fact, this issue reveals the
complex nature of the Gaussian IRC where the combination of a single coding
scheme for the Gaussian relay and interference channel may not lead to a good
coding scheme for this problem, even when the focus is only on capacity to
within a constant gap over all possible fading statistics.Comment: 23 pages, 6 figures. Submitted to IEEE Transactions on Information
Theory (revised version
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