168,919 research outputs found
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
Network Coding Tree Algorithm for Multiple Access System
Network coding is famous for significantly improving the throughput of
networks. The successful decoding of the network coded data relies on some side
information of the original data. In that framework, independent data flows are
usually first decoded and then network coded by relay nodes. If appropriate
signal design is adopted, physical layer network coding is a natural way in
wireless networks. In this work, a network coding tree algorithm which enhances
the efficiency of the multiple access system (MAS) is presented. For MAS,
existing works tried to avoid the collisions while collisions happen frequently
under heavy load. By introducing network coding to MAS, our proposed algorithm
achieves a better performance of throughput and delay. When multiple users
transmit signal in a time slot, the mexed signals are saved and used to jointly
decode the collided frames after some component frames of the network coded
frame are received. Splitting tree structure is extended to the new algorithm
for collision solving. The throughput of the system and average delay of frames
are presented in a recursive way. Besides, extensive simulations show that
network coding tree algorithm enhances the system throughput and decreases the
average frame delay compared with other algorithms. Hence, it improves the
system performance
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Enabling decentralized wireless index coding in practice
Index coding is a problem in theoretical computer science and network information theory that studies the optimal coding scheme for transmitting multiple messages across a network to receivers with different side information. The ultimate goal of index coding is to reduce transmission time in a communication network by minimizing the number of messages based on shared information. Index coding theory extends to several key engineering problems in network communication including peer to peer communication, distributed broadcast networks, and interference alignment. Although the theoretical connection between index coding and wireless networks is valuable, we focus on finding index coding strategies for a realistic wireless network. More specifically, we investigate how index coding can be applied to an OFDMA downlink network during the retransmission phase. An orthogonal frequency-division multiple access (OFDMA) downlink network is a network where data is sent downward from a designated higher-level transmitter to a group of receiving nodes. In addition, receivers can often decode the other receivers' physical layer signals on the other sub-channels that can be exploited as side information. If this side information is sent back to the transmitter, it can then be coded to cancel the interference in subsequent retransmission phases resulting in fewer retransmission messages. In this report, we explain the coding model and characterize the benefits of index coding for retransmissions within an OFDMA downlink network. In addition, we demonstrate the results of applying this index coding scheme in such network in both simulation and in an active wireless mesh network.Electrical and Computer Engineerin
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
Achievable Rate and Optimal Physical Layer Rate Allocation in Interference-Free Wireless Networks
We analyze the achievable rate in interference-free wireless networks with
physical layer fading channels and orthogonal multiple access. As a starting
point, the point-to-point channel is considered. We find the optimal physical
and network layer rate trade-off which maximizes the achievable overall rate
for both a fixed rate transmission scheme and an improved scheme based on
multiple virtual users and superposition coding. These initial results are
extended to the network setting, where, based on a cut-set formulation, the
achievable rate at each node and its upper bound are derived. We propose a
distributed optimization algorithm which allows to jointly determine the
maximum achievable rate, the optimal physical layer rates on each network link,
and an opportunistic back-pressure-type routing strategy on the network layer.
This inherently justifies the layered architecture in existing wireless
networks. Finally, we show that the proposed layered optimization approach can
achieve almost all of the ergodic network capacity in high SNR.Comment: 5 pages, to appear in Proc. IEEE ISIT, July 200
Wireless Network-Coded Four-Way Relaying Using Latin Hyper-Cubes
This paper deals with physical layer network-coding for the four-way wireless
relaying scenario where four nodes A, B, C and D wish to communicate their
messages to all the other nodes with the help of the relay node R. The scheme
given in the paper is based on the denoise-and-forward scheme proposed first by
Popovski et al. Intending to minimize the number of channel uses, the protocol
employs two phases: Multiple Access (MA) phase and Broadcast (BC) phase with
each phase utilizing one channel use. This paper does the equivalent for the
four-way relaying scenario as was done for the two-way relaying scenario by
Koike-Akino et al., and for three-way relaying scenario in [3]. It is observed
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. These network
coding maps are so chosen so that they satisfy a requirement called exclusive
law. We show that when the four users transmit points from the same M-PSK
constellation, every such network coding map that satisfies the exclusive law
can be represented by a 4-fold Latin Hyper-Cube of side M. 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: 14 pages, 6 figures, 2 tables. arXiv admin note: substantial text
overlap with arXiv:1112.158
Wireless Bidirectional Relaying using Physical Layer Network Coding with Heterogeneous PSK Modulation
In bidirectional relaying using Physical Layer Network Coding (PLNC), it is
generally assumed that users employ same modulation schemes in the Multiple
Access phase. However, as observed by Zhang et al., it may not be desirable for
the users to always use the same modulation schemes, particularly when
user-relay channels are not equally strong. Such a scheme is called
Heterogeneous PLNC. However, the approach in [1] uses the computationally
intensive Closest Neighbour Clustering (CNC) algorithm to find the network
coding maps to be applied at the relay. Also, the treatment is specific to
certain cases of heterogeneous modulations. In this paper, we show that, when
users employ heterogeneous but symmetric PSK modulations, the network coding
maps and the mapping regions in the fade state plane can be obtained
analytically. Performance results are provided in terms of Relay Error Rate
(RER) and Bit Error Rate (BER).Comment: 10 pages, 10 figures and 3 table
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