1,406 research outputs found
Asymptotic Analysis on Spatial Coupling Coding for Two-Way Relay Channels
Compute-and-forward relaying is effective to increase bandwidth efficiency of
wireless two-way relay channels. In a compute-and-forward scheme, a relay tries
to decode a linear combination composed of transmitted messages from other
terminals or relays. Design for error correcting codes and its decoding
algorithms suitable for compute-and-forward relaying schemes are still
important issue to be studied. In this paper, we will present an asymptotic
performance analysis on LDPC codes over two-way relay channels based on density
evolution (DE). Because of the asymmetric nature of the channel, we employ the
population dynamics DE combined with DE formulas for asymmetric channels to
obtain BP thresholds. In addition, we also evaluate the asymptotic performance
of spatially coupled LDPC codes for two-way relay channels. The results
indicate that the spatial coupling codes yield improvements in the BP threshold
compared with corresponding uncoupled codes for two-way relay channels.Comment: 5 page
On the Performance of SR and FR Protocols for OSTBC based AF-MIMO Relay System with Channel and Noise Correlations
This paper proposes selection relaying (SR) protocol for a cooperative multiple-input multiple-output (MIMO) relay system that consists of a direct link between a source and a destination. The system has only receive-side channel state information (CSI), spatially correlated MIMO channels, and the receiver nodes observe spatially correlated noise. The transmit nodes employ orthogonal space-time block codes (OSTBC), whereas the receiver nodes employ optimum minimum mean-square-error (MMSE) detection. The SR protocol, which transmits via the relay only when the direct link between the source and destination is in outage, is compared with the fixed relaying (FR) protocol which always uses the relay. By deriving novel asymptotic expressions of the outage probabilities, it is analytically shown that both protocols provide the same diversity gain. However, the coding gain (CG) of the SR protocol can be much better than that of the FR protocol. In particular, when all MIMO links have the same effective rank, irrespective of its value, the SR protocol provides better CG than the FR scheme if the target information rate is greater than ln2(3) bits per channel use. Simulation results support theoretical analysis and show that the SR scheme can significantly outperform FR method, which may justify the increased complexity due to one-bit feedback requirement in the SR protocol
On the Performance of SR and FR Protocols for OSTBC based AF-MIMO Relay System with Channel and Noise Correlations
This paper proposes selection relaying (SR) protocol for a cooperative multiple-input multiple-output (MIMO) relay system that consists of a direct link between a source and a destination. The system has only receive-side channel state information (CSI), spatially correlated MIMO channels, and the receiver nodes observe spatially correlated noise. The transmit nodes employ orthogonal space-time block codes (OSTBC), whereas the receiver nodes employ optimum minimum mean-square-error (MMSE) detection. The SR protocol, which transmits via the relay only when the direct link between the source and destination is in outage, is compared with the fixed relaying (FR) protocol which always uses the relay. By deriving novel asymptotic expressions of the outage probabilities, it is analytically shown that both protocols provide the same diversity gain. However, the coding gain (CG) of the SR protocol can be much better than that of the FR protocol. In particular, when all MIMO links have the same effective rank, irrespective of its value, the SR protocol provides better CG than the FR scheme if the target information rate is greater than ln2(3) bits per channel use. Simulation results support theoretical analysis and show that the SR scheme can significantly outperform FR method, which may justify the increased complexity due to one-bit feedback requirement in the SR protocol
Spatially Coupled LDPC Codes Constructed from Protographs
In this paper, we construct protograph-based spatially coupled low-density
parity-check (SC-LDPC) codes by coupling together a series of L disjoint, or
uncoupled, LDPC code Tanner graphs into a single coupled chain. By varying L,
we obtain a flexible family of code ensembles with varying rates and frame
lengths that can share the same encoding and decoding architecture for
arbitrary L. We demonstrate that the resulting codes combine the best features
of optimized irregular and regular codes in one design: capacity approaching
iterative belief propagation (BP) decoding thresholds and linear growth of
minimum distance with block length. In particular, we show that, for
sufficiently large L, the BP thresholds on both the binary erasure channel
(BEC) and the binary-input additive white Gaussian noise channel (AWGNC)
saturate to a particular value significantly better than the BP decoding
threshold and numerically indistinguishable from the optimal maximum
a-posteriori (MAP) decoding threshold of the uncoupled LDPC code. When all
variable nodes in the coupled chain have degree greater than two,
asymptotically the error probability converges at least doubly exponentially
with decoding iterations and we obtain sequences of asymptotically good LDPC
codes with fast convergence rates and BP thresholds close to the Shannon limit.
Further, the gap to capacity decreases as the density of the graph increases,
opening up a new way to construct capacity achieving codes on memoryless
binary-input symmetric-output (MBS) channels with low-complexity BP decoding.Comment: Submitted to the IEEE Transactions on Information Theor
Spatially-Coupled LDPC Codes for Decode-and-Forward Relaying of Two Correlated Sources over the BEC
We present a decode-and-forward transmission scheme based on
spatially-coupled low-density parity-check (SC-LDPC) codes for a network
consisting of two (possibly correlated) sources, one relay, and one
destination. The links between the nodes are modeled as binary erasure
channels. Joint source-channel coding with joint channel decoding is used to
exploit the correlation. The relay performs network coding. We derive
analytical bounds on the achievable rates for the binary erasure time-division
multiple-access relay channel with correlated sources. We then design bilayer
SC-LDPC codes and analyze their asymptotic performance for this scenario. We
prove analytically that the proposed coding scheme achieves the theoretical
limit for symmetric channel conditions and uncorrelated sources. Using density
evolution, we furthermore demonstrate that our scheme approaches the
theoretical limit also for non-symmetric channel conditions and when the
sources are correlated, and we observe the threshold saturation effect that is
typical for spatially-coupled systems. Finally, we give simulation results for
large block lengths, which validate the DE analysis.Comment: IEEE Transactions on Communications, to appea
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