2,348 research outputs found
Performance Bounds for Bi-Directional Coded Cooperation Protocols
In coded bi-directional cooperation, two nodes wish to exchange messages over
a shared half-duplex channel with the help of a relay. In this paper, we derive
performance bounds for this problem for each of three protocols.
The first protocol is a two phase protocol were both users simultaneously
transmit during the first phase and the relay alone transmits during the
second. In this protocol, our bounds are tight and a multiple-access channel
transmission from the two users to the relay followed by a coded broadcast-type
transmission from the relay to the users achieves all points in the two-phase
capacity region.
The second protocol considers sequential transmissions from the two users
followed by a transmission from the relay while the third protocol is a hybrid
of the first two protocols and has four phases. In the latter two protocols the
inner and outer bounds are not identical, and differ in a manner similar to the
inner and outer bounds of Cover's relay channel. Numerical evaluation shows
that at least in some cases of interest our bounds do not differ significantly.
Finally, in the Gaussian case with path loss, we derive achievable rates and
compare the relative merits of each protocol in various regimes. This case is
of interest in cellular systems. Surprisingly, we find that in some cases, the
achievable rate region of the four phase protocol sometimes contains points
that are outside the outer bounds of the other protocols.Comment: 15 page
Superposition Coding Aided Bi-directional Relay Transmission Employing Iteratively Decoded Self-Concatenated Convolutional Codes
In this paper, we consider coding schemes designed for two nodes communicating with each other with the aid of a relay node, which receives information from the two nodes in the first time slot. At the relay node we combine a powerful Superposition Coding (SPC) scheme with Iteratively Decoded Self-Concatenated Convolutional Codes (SECCC-ID), which exchange mutual information between each other. It is assumed that decoding errors may be encountered at the relay node. The relay node then broadcasts this information in the second time slot after re-encoding it, again, using a SECCC encoder. At the destination, an amalgamated SPC-SECCC block then detects and decodes the signal either with or without the aid of a priori information. Our simulation results demonstrate that the proposed scheme is capable of reliably operating at a low BER for transmission over both AWGN and uncorrelated Rayleigh fading channels. We compare the proposed scheme’s performance to a direct transmission link between the two sources having the same throughput. Additionally, the SPC-SECCC system achieves a low BER even for realistic error-infested relaying
Cooperative network-coding system for wireless sensor networks
Describes a cooperative network coding system for wireless sensor networks. In this paper, we propose two practical power) and bandwidth)efficient systems based on amplify)and)forward (AF) and decode)and)forward (DF) schemes to address the problem of information exchange via a relay. The key idea is to channel encode each source’s message by using a high)performance non)binary turbo code based on Partial Unit Memory (PUM) codes to enhance the bit)error)rate performance, then reduce the energy consumption and increase spectrum efficiency by using network coding (NC) to combine individual nodes’ messages at the relay before forwarding to the destination. Two simple and low complexity physical layer NC schemes are proposed based on combinations of received source messages at the relay. We also present the theoretical limits and numerical analysis of the proposed schemes. Simulation results under Additive White Gaussian Noise, confirm that the proposed schemes achieve significant bandwidth savings and fewer transmissions over the benchmark systems which do not resort to NC. Theoretical limits for capacity and Signal to Noise Ratio behaviour for the proposed schemes are derived. The paper also proposes a cooperative strategy that is useful when insufficient combined messages are received at a node to recover the desired source messages, thus enabling the system to retrieve all packets with significantly fewer retransmission request messages
Pairwise Check Decoding for LDPC Coded Two-Way Relay Block Fading Channels
Partial decoding has the potential to achieve a larger capacity region than
full decoding in two-way relay (TWR) channels. Existing partial decoding
realizations are however designed for Gaussian channels and with a static
physical layer network coding (PLNC). In this paper, we propose a new solution
for joint network coding and channel decoding at the relay, called pairwise
check decoding (PCD), for low-density parity-check (LDPC) coded TWR system over
block fading channels. The main idea is to form a check relationship table
(check-relation-tab) for the superimposed LDPC coded packet pair in the
multiple access (MA) phase in conjunction with an adaptive PLNC mapping in the
broadcast (BC) phase. Using PCD, we then present a partial decoding method,
two-stage closest-neighbor clustering with PCD (TS-CNC-PCD), with the aim of
minimizing the worst pairwise error probability. Moreover, we propose the
minimum correlation optimization (MCO) for selecting the better
check-relation-tabs. Simulation results confirm that the proposed TS-CNC-PCD
offers a sizable gain over the conventional XOR with belief propagation (BP) in
fading channels.Comment: to appear in IEEE Trans. on Communications, 201
Alternative Awaiting and Broadcast for Two-Way Relay Fading Channels
We investigate a two-way relay (TWR) fading channel where two source nodes
wish to exchange information with the help of a relay node. Given traditional
TWR protocols, transmission rates in both directions are known to be limited by
the hop with lower capacity, i.e., the min operations between uplink and
downlink. In this paper, we propose a new transmission protocol, named as
alternative awaiting and broadcast (AAB), to cancel the min operations in the
TWR fading channels. The operational principles, new upper bound on ergodic
sum-capacity (ESC) and convergence behavior of average delay of signal
transmission (ST) (in relay buffer) for the proposed AAB protocol are analyzed.
Moreover, we propose a suboptimal encoding/decoding solution for the AAB
protocol and derive an achievable ergodic sum-rate (ESR) with corresponding
average delay of ST. Numerical results show that 1) the proposed AAB protocol
significantly improves the achievable ESR compared to the traditional TWR
protocols, 2) considering the average delay of system service (SS) (in source
buffer), the average delay of ST induced by the proposed AAB protocol is very
small and negligible.Comment: to appear in IEEE Transactions on Vehicular Technology, 201
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