1,447 research outputs found
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
Wireless Bidirectional Relaying using Physical Layer Network Coding with Heterogeneous PSK Modulation
In bidirectional relaying using Physical Layer Network Coding (PLNC), it is
generally assumed that users employ same modulation schemes in the Multiple
Access phase. However, as observed by Zhang et al., it may not be desirable for
the users to always use the same modulation schemes, particularly when
user-relay channels are not equally strong. Such a scheme is called
Heterogeneous PLNC. However, the approach in [1] uses the computationally
intensive Closest Neighbour Clustering (CNC) algorithm to find the network
coding maps to be applied at the relay. Also, the treatment is specific to
certain cases of heterogeneous modulations. In this paper, we show that, when
users employ heterogeneous but symmetric PSK modulations, the network coding
maps and the mapping regions in the fade state plane can be obtained
analytically. Performance results are provided in terms of Relay Error Rate
(RER) and Bit Error Rate (BER).Comment: 10 pages, 10 figures and 3 table
Physical Layer Network Coding for Two-Way Relaying with QAM
The design of modulation schemes for the physical layer network-coded two way
relaying scenario was studied in [1], [3], [4] and [5]. In [7] it was shown
that every network coding map that satisfies the exclusive law is representable
by a Latin Square and conversely, and this relationship can be used to get the
network coding maps satisfying the exclusive law. But, only the scenario in
which the end nodes use -PSK signal sets is addressed in [7] and [8]. In
this paper, we address the case in which the end nodes use -QAM signal sets.
In a fading scenario, for certain channel conditions ,
termed singular fade states, the MA phase performance is greatly reduced. By
formulating a procedure for finding the exact number of singular fade states
for QAM, we show that square QAM signal sets give lesser number of singular
fade states compared to PSK signal sets. This results in superior performance
of -QAM over -PSK. It is shown that the criterion for partitioning the
complex plane, for the purpose of using a particular network code for a
particular fade state, is different from that used for -PSK. Using a
modified criterion, we describe a procedure to analytically partition the
complex plane representing the channel condition. We show that when -QAM () signal set is used, the conventional XOR network mapping fails to remove
the ill effects of , which is a singular fade state for
all signal sets of arbitrary size. We show that a doubly block circulant Latin
Square removes this singular fade state for -QAM.Comment: 13 pages, 14 figures, submitted to IEEE Trans. Wireless
Communications. arXiv admin note: substantial text overlap with
arXiv:1203.326
User-Antenna Selection for Physical-Layer Network Coding based on Euclidean Distance
In this paper, we present the error performance analysis of a multiple-input
multiple-output (MIMO) physical-layer network coding (PNC) system with two
different user-antenna selection (AS) schemes in asymmetric channel conditions.
For the first antenna selection scheme (AS1), where the user-antenna is
selected in order to maximize the overall channel gain between the user and the
relay, we give an explicit analytical proof that for binary modulations, the
system achieves full diversity order of in the
multiple-access (MA) phase, where , and denote the number of
antennas at user , user and relay respectively. We present a
detailed investigation of the diversity order for the MIMO-PNC system with AS1
in the MA phase for any modulation order. A tight closed-form upper bound on
the average SER is also derived for the special case when , which is
valid for any modulation order. We show that in this case the system fails to
achieve transmit diversity in the MA phase, as the system diversity order drops
to irrespective of the number of transmit antennas at the user nodes.
Additionally, we propose a Euclidean distance (ED) based user-antenna selection
scheme (AS2) which outperforms the first scheme in terms of error performance.
Moreover, by deriving upper and lower bounds on the diversity order for the
MIMO-PNC system with AS2, we show that this system enjoys both transmit and
receive diversity, achieving full diversity order of in the MA phase for any modulation order. Monte Carlo simulations are
provided which confirm the correctness of the derived analytical results.Comment: IEEE Transactions on Communications. arXiv admin note: text overlap
with arXiv:1709.0445
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