1,683 research outputs found
Cross Layer Coding Schemes for Broadcasting and Relaying
This dissertation is divided into two main topics. In the first topic, we study the
joint source-channel coding problem of transmitting an analog source over a Gaussian
channel in two cases - (i) the presence of interference known only to the transmitter and (ii) in the presence of side information about the source known only to the
receiver. We introduce hybrid digital analog forms of the Costa and Wyner-Ziv coding schemes. We present random coding based schemes in contrast to lattice based
schemes proposed by Kochman and Zamir. We also discuss superimposed digital and
analog schemes for the above problems which show that there are infinitely many
schemes for achieving the optimal distortion for these problems. This provides an
extension of the schemes proposed by Bross and others to the interference/source
side information case. The result of this study shows that the proposed hybrid digital analog schemes are more robust to a mismatch in channel signal-to-noise ratio
(SNR), than pure separate source coding followed by channel coding solutions. We
then discuss applications of the hybrid digital analog schemes for transmitting under
a channel SNR mismatch and for broadcasting a Gaussian source with bandwidth
compression. We also study applications of joint source-channel coding schemes for
a cognitive setup and also for the setup of transmitting an analog Gaussian source
over a Gaussian channel, in the presence of an eavesdropper.
In the next topic, we consider joint physical layer coding and network coding
solutions for bi-directional relaying. We consider a communication system where two transmitters wish to exchange information through a central relay. The transmitter
and relay nodes exchange data over synchronized, average power constrained additive
white Gaussian noise channels. We propose structured coding schemes using lattices
for this problem. We study two decoding approaches, namely lattice decoding and
minimum angle decoding. Both the decoding schemes can be shown to achieve the
upper bound at high SNRs. The proposed scheme can be thought of as a joint physical
layer, network layer code which outperforms other recently proposed analog network
coding schemes. We also study extensions of the bi-directional relay for the case with
asymmetric channel links and also for the multi-hop case. The result of this study
shows that structured coding schemes using lattices perform close to the upper bound
for the above communication system models
Network coded modulation for two-way relaying
Network coding compresses multiple traffic flows with the aid low-complexity algebraic operations, hence holds the potential of significantly improving both the power and bandwidth efficiency of wireless networks. In this contribution, the novel concept of Network Coded Modulation (NCM) is proposed for jointly performing network coding and modulation in bi-directional/duplex relaying. Each receiver is colocated with a transmitter and hence has prior knowledge of the message intended for the distant receiver. As in classic coded modulation, the Euclidian distance between the symbols is maximized, hence the Symbol Error Ratio (SER) is minimized. Specifically, we conceive NCM methods for PSK, PAM and QAM based on modulo addition of the normalized phase or amplitude. Furthermore, we propose low complexity decoding algorithms based on the corresponding conditional minimum distance criteria. Our performance analysis and simulations demonstrate that NCM relying on PSK is capable of achieving a SER at both receivers of the NCM scheme as if the relay transmitted exclusively to a single receiver only. By contrast, when our NCM concept is combined with PAM/QAM, an SNR loss (<1.25dB) is imposed at one of the receivers, usually at the one having a lower data rate in a realistic different rate scenario. Finally, we will demonstrate that the proposed NCM is compatible with existing physical layer designs
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
Maximum Euclidean distance network coded modulation for asymmetric decode-and-forward two-way relaying
Network coding (NC) compresses two traffic flows with the aid of low-complexity algebraic operations, hence holds the potential of significantly improving both the efficiency of wireless two-way relaying, where each receiver is collocated with a transmitter and hence has prior knowledge of the message intended for the distant receiver. In this contribution, network coded modulation (NCM) is proposed for jointly performing NC and modulation. As in classic coded modulation, the Euclidean distance between the symbols is maximised, hence the symbol error probability is minimised. Specifically, the authors first propose set-partitioning-based NCM as an universal concept which can be combined with arbitrary constellations. Then the authors conceive practical phase-shift keying/quadrature amplitude modulation (PSK/QAM) NCM schemes, referred to as network coded PSK/QAM, based on modulo addition of the normalised phase/amplitude. To achieve a spatial diversity gain at a low complexity, a NC oriented maximum ratio combining scheme is proposed for combining the network coded signal and the original signal of the source. An adaptive NCM is also proposed to maximise the throughput while guaranteeing a target bit error probability (BEP). Both theoretical performance analysis and simulations demonstrate that the proposed NCM can achieve at least 3 dB signal-to-noise ratio gain and two times diversity gain
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