89 research outputs found
A Partial Compress-and-Forward Strategy for Relay-assisted Wireless Networks Based on Rateless Coding
In this work, we propose a novel partial compress-and-forward (PCF) scheme
for improving the maximum achievable transmission rate of a diamond relay
network with two noisy relays. PCF combines conventional compress-and-forward
(CF) and amplify-and-forward (AF) protocols, enabling one relay to operate
alternately in the CF or the AF mode, while the other relay works purely in the
CF mode. As the direct link from the source to the destination is unavailable,
and there is no noiseless relay in the diamond network, messages received from
both relays must act as side information for each other and must be decoded
jointly. We propose a joint decoder to decode two Luby transform (LT) codes
received from both relays corresponding to the same original message. Numerical
results show that PCF can achieve significant performance improvements compared
to decode-and-forward (DF) and pure CF protocols when at least the channels
connected to one of the relays are of high quality
Bilayer Low-Density Parity-Check Codes for Decode-and-Forward in Relay Channels
This paper describes an efficient implementation of binning for the relay
channel using low-density parity-check (LDPC) codes. We devise bilayer LDPC
codes to approach the theoretically promised rate of the decode-and-forward
relaying strategy by incorporating relay-generated information bits in
specially designed bilayer graphical code structures. While conventional LDPC
codes are sensitively tuned to operate efficiently at a certain channel
parameter, the proposed bilayer LDPC codes are capable of working at two
different channel parameters and two different rates: that at the relay and at
the destination. To analyze the performance of bilayer LDPC codes, bilayer
density evolution is devised as an extension of the standard density evolution
algorithm. Based on bilayer density evolution, a design methodology is
developed for the bilayer codes in which the degree distribution is iteratively
improved using linear programming. Further, in order to approach the
theoretical decode-and-forward rate for a wide range of channel parameters,
this paper proposes two different forms bilayer codes, the bilayer-expurgated
and bilayer-lengthened codes. It is demonstrated that a properly designed
bilayer LDPC code can achieve an asymptotic infinite-length threshold within
0.24 dB gap to the Shannon limits of two different channels simultaneously for
a wide range of channel parameters. By practical code construction,
finite-length bilayer codes are shown to be able to approach within a 0.6 dB
gap to the theoretical decode-and-forward rate of the relay channel at a block
length of and a bit-error probability (BER) of . Finally, it is
demonstrated that a generalized version of the proposed bilayer code
construction is applicable to relay networks with multiple relays.Comment: Submitted to IEEE Trans. Info. Theor
Coding for Cooperative Communications
The area of cooperative communications has received tremendous research interest
in recent years. This interest is not unwarranted, since cooperative communications
promises the ever-so-sought after diversity and multiplexing gains typically
associated with multiple-input multiple-output (MIMO) communications, without
actually employing multiple antennas. In this dissertation, we consider several cooperative
communication channels, and for each one of them, we develop information
theoretic coding schemes and derive their corresponding performance limits. We next
develop and design practical coding strategies which perform very close to the information
theoretic limits.
The cooperative communication channels we consider are: (a) The Gaussian relay
channel, (b) the quasi-static fading relay channel, (c) cooperative multiple-access
channel (MAC), and (d) the cognitive radio channel (CRC). For the Gaussian relay
channel, we propose a compress-forward (CF) coding strategy based on Wyner-Ziv
coding, and derive the achievable rates specifically with BPSK modulation. The CF
strategy is implemented with low-density parity-check (LDPC) and irregular repeataccumulate
codes and is found to operate within 0.34 dB of the theoretical limit. For
the quasi-static fading relay channel, we assume that no channel state information
(CSI) is available at the transmitters and propose a rateless coded protocol which
uses rateless coded versions of the CF and the decode-forward (DF) strategy. We
implement the protocol with carefully designed Raptor codes and show that the implementation suffers a loss of less than 10 percent from the information theoretical limit. For
the MAC, we assume quasi-static fading, and consider cooperation in the low-power
regime with the assumption that no CSI is available at the transmitters. We develop
cooperation methods based on multiplexed coding in conjunction with rateless
codes and find the achievable rates and in particular the minimum energy per bit to
achieve a certain outage probability. We then develop practical coding methods using
Raptor codes, which performs within 1.1 dB of the performance limit. Finally, we
consider a CRC and develop a practical multi-level dirty-paper coding strategy using
LDPC codes for channel coding and trellis-coded quantization for source coding. The
designed scheme is found to operate within 0.78 dB of the theoretical limit.
By developing practical coding strategies for several cooperative communication
channels which exhibit performance close to the information theoretic limits, we show
that cooperative communications not only provide great benefits in theory, but can
possibly promise the same benefits when put into practice. Thus, our work can be
considered a useful and necessary step towards the commercial realization of cooperative
communications
Dynamic block-cycling over a linear network in underwater acoustic channels
ABSTRACT The underwater acoustic (UWA) environment is known to have large spatial and temporal variations. In this paper, we propose a dynamic cooperative relaying protocol, termed dynamic block-cycling (DBC) protocol, for a UWA linear network. Considering large channel variations, we assume one node can hear from not only its direct but also several remote neighbors. A transmission package with multiple blocks is taken as one relay unit, where an erasure-correction code and an error-correction code are used for inter-block encoding and intra-block encoding, respectively. During the relaying process, each node in the proposed protocol starts relaying immediately after it decodes the relayed message, hence a reduced end-to-end transmission latency can be achieved. Meanwhile, to avoid the overhead for relay cooperation, the relays' transmissions are cyclically synchronized, such that in each time slot, the blocks arriving at the downstream receiving nodes from all the upstream transmitting nodes have the same block index. Numerical results show that for a one-shot transmission, the proposed protocol achieves a reduced end-to-end delay relative to existing protocols while maintaining a decent outage performance
Random Linear Network Coding For Time Division Duplexing: When To Stop Talking And Start Listening
A new random linear network coding scheme for reliable communications for
time division duplexing channels is proposed. The setup assumes a packet
erasure channel and that nodes cannot transmit and receive information
simultaneously. The sender transmits coded data packets back-to-back before
stopping to wait for the receiver to acknowledge (ACK) the number of degrees of
freedom, if any, that are required to decode correctly the information. We
provide an analysis of this problem to show that there is an optimal number of
coded data packets, in terms of mean completion time, to be sent before
stopping to listen. This number depends on the latency, probabilities of packet
erasure and ACK erasure, and the number of degrees of freedom that the receiver
requires to decode the data. This scheme is optimal in terms of the mean time
to complete the transmission of a fixed number of data packets. We show that
its performance is very close to that of a full duplex system, while
transmitting a different number of coded packets can cause large degradation in
performance, especially if latency is high. Also, we study the throughput
performance of our scheme and compare it to existing half-duplex Go-back-N and
Selective Repeat ARQ schemes. Numerical results, obtained for different
latencies, show that our scheme has similar performance to the Selective Repeat
in most cases and considerable performance gain when latency and packet error
probability is high.Comment: 9 pages, 9 figures, Submitted to INFOCOM'0
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