345 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
Joint Compute and Forward for the Two Way Relay Channel with Spatially Coupled LDPC Codes
We consider the design and analysis of coding schemes for the binary input
two way relay channel with erasure noise. We are particularly interested in
reliable physical layer network coding in which the relay performs perfect
error correction prior to forwarding messages. The best known achievable rates
for this problem can be achieved through either decode and forward or compute
and forward relaying. We consider a decoding paradigm called joint compute and
forward which we numerically show can achieve the best of these rates with a
single encoder and decoder. This is accomplished by deriving the exact
performance of a message passing decoder based on joint compute and forward for
spatially coupled LDPC ensembles.Comment: This paper was submitted to IEEE Global Communications Conference
201
Performance Analysis of Optimal Single Stream Beamforming in MIMO Dual-Hop AF Systems
This paper investigates the performance of optimal single stream beamforming
schemes in multiple-input multiple-output (MIMO) dual-hop amplify-and-forward
(AF) systems. Assuming channel state information is not available at the source
and relay, the optimal transmit and receive beamforming vectors are computed at
the destination, and the transmit beamforming vector is sent to the transmitter
via a dedicated feedback link. Then, a set of new closed-form expressions for
the statistical properties of the maximum eigenvalue of the resultant channel
is derived, i.e., the cumulative density function (cdf), probability density
function (pdf) and general moments, as well as the first order asymptotic
expansion and asymptotic large dimension approximations. These analytical
expressions are then applied to study three important performance metrics of
the system, i.e., outage probability, average symbol error rate and ergodic
capacity. In addition, more detailed treatments are provided for some important
special cases, e.g., when the number of antennas at one of the nodes is one or
large, simple and insightful expressions for the key parameters such as
diversity order and array gain of the system are derived. With the analytical
results, the joint impact of source, relay and destination antenna numbers on
the system performance is addressed, and the performance of optimal beamforming
schemes and orthogonal space-time block-coding (OSTBC) schemes are compared.
Results reveal that the number of antennas at the relay has a great impact on
how the numbers of antennas at the source and destination contribute to the
system performance, and optimal beamforming not only achieves the same maximum
diversity order as OSTBC, but also provides significant power gains over OSTBC.Comment: to appear in IEEE Journal on Selected Areas in Communications special
issue on Theories and Methods for Advanced Wireless Relay
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
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