12 research outputs found
Performance Analysis of Adaptive Physical Layer Network Coding for Wireless Two-way Relaying
The analysis of modulation schemes for the physical layer network-coded two
way relaying scenario is presented which employs two phases: Multiple access
(MA) phase and Broadcast (BC) phase. It was shown by Koike-Akino et. al. that
adaptively changing the network coding map used at the relay according to the
channel conditions greatly reduces the impact of multiple access interference
which occurs at the relay during the MA phase. Depending on the signal set used
at the end nodes, deep fades occur for a finite number of channel fade states
referred as the singular fade states. The singular fade states fall into the
following two classes: The ones which are caused due to channel outage and
whose harmful effect cannot be mitigated by adaptive network coding are
referred as the \textit{non-removable singular fade states}. The ones which
occur due to the choice of the signal set and whose harmful effects can be
removed by a proper choice of the adaptive network coding map are referred as
the \textit{removable} singular fade states. In this paper, we derive an upper
bound on the average end-to-end Symbol Error Rate (SER), with and without
adaptive network coding at the relay, for a Rician fading scenario. It is shown
that without adaptive network coding, at high Signal to Noise Ratio (SNR), the
contribution to the end-to-end SER comes from the following error events which
fall as : the error events associated with the removable
singular fade states, the error events associated with the non-removable
singular fade states and the error event during the BC phase. In contrast, for
the adaptive network coding scheme, the error events associated with the
removable singular fade states contributing to the average end-to-end SER fall
as and as a result the adaptive network coding scheme
provides a coding gain over the case when adaptive network coding is not used.Comment: 10 pages, 5 figure
Transmit Antenna Selection for Physical-Layer Network Coding Based on Euclidean Distance
Physical-layer network coding (PNC) is now well-known as a potential
candidate for delay-sensitive and spectrally efficient communication
applications, especially in two-way relay channels (TWRCs). In this paper, we
present the error performance analysis of a multiple-input single-output (MISO)
fixed network coding (FNC) system with two different transmit antenna selection
(TAS) schemes. For the first scheme, where the antenna selection is performed
based on the strongest channel, we derive a tight closed-form upper bound on
the average symbol error rate (SER) with -ary modulation and show that the
system achieves a diversity order of 1 for . Next, we propose a
Euclidean distance (ED) based antenna selection scheme which outperforms the
first scheme in terms of error performance and is shown to achieve a diversity
order lower bounded by the minimum of the number of antennas at the two users.Comment: 15 pages, 4 figures, Globecom 2017 (Wireless Communications
Symposium
Space-Time Coded Spatial Modulated Physical Layer Network Coding for Two-Way Relaying
Using the spatial modulation approach, where only one transmit antenna is
active at a time, we propose two transmission schemes for two-way relay channel
using physical layer network coding with space time coding using Coordinate
Interleaved Orthogonal Designs (CIOD's). It is shown that using two
uncorrelated transmit antennas at the nodes, but using only one RF transmit
chain and space-time coding across these antennas can give a better performance
without using any extra resources and without increasing the hardware
implementation cost and complexity. In the first transmission scheme, two
antennas are used only at the relay, Adaptive Network Coding (ANC) is employed
at the relay and the relay transmits a CIOD Space Time Block Code (STBC). This
gives a better performance compared to an existing ANC scheme for two-way relay
channel which uses one antenna each at all the three nodes. It is shown that
for this scheme at high SNR the average end-to-end symbol error probability
(SEP) is upper bounded by twice the SEP of a point-to-point fading channel. In
the second transmission scheme, two transmit antennas are used at all the three
nodes, CIOD STBC's are transmitted in multiple access and broadcast phases.
This scheme provides a diversity order of two for the average end-to-end SEP
with an increased decoding complexity of for an arbitrary
signal set and for square QAM signal set.Comment: 9 pages, 7 figure
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
Low-complexity energy-efficient resource allocation for delay-tolerant two-way orthogonal frequency-division multiplexing relays
Energy-efficient wireless communication is important for wireless devices with a limited battery life and cannot be recharged. In this study, a bit allocation algorithm to minimise the total energy consumption for transmitting a bit successfully is proposed for a two-way orthogonal frequency-division multiplexing relay system, whilst considering the constraints of quality-of-service and total transmit power. Unlike existing bit allocation schemes, which maximise the energy efficiency (EE) by measuring ‘bits-per-Joule’ with fixed bidirectional total bit rates constraint and no power limitation, their scheme adapts the bidirectional total bit rates and their allocation on each subcarrier with a total transmit power constraint. To do so, they propose an idea to decompose the optimisation problem. The problem is solved in two general steps. The first step allocates the bit rates on each subcarrier when the total bit rate of each user is fixed. In the second step, the Lagrangian multipliers are used as the optimisation variants, and the dimension of the variant optimisation is reduced from 2N to 2, where N is the number of subcarriers. They also prove that the optimal point is on the bounds of the feasible region, thus the optimal solution could be searched through the bounds
Two–Way Relaying Communications with OFDM and BICM/BICM-ID
Relay-aided communication methods have gained strong interests in academic community
and been applied in various wireless communication scenarios. Among different techniques
in relay-aided communication system, two-way relaying communication (TWRC) achieves
the highest spectral efficiency due to its bi-directional transmission capability. Nevertheless,
different from the conventional point-to-point communication system, TWRC suffers from
detection quality degradation caused by the multiple-access interference (MAI). In addition,
because of the propagation characteristics of wireless channels, fading and multipath
dispersion also contribute strongly to detection errors. Therefore, this thesis is mainly concerned
with designing transmission and detection schemes to provide good detection quality
of TWRC while taking into account the negative impacts of fading, multipath dispersion
and multiple-access interference.
First, a TWRC system operating over multipath fading channels is considered and orthogonal
frequency-division multiplexing (OFDM) is adopted to handle the inter-symbol
interference (ISI) caused by the multipath dispersion. In particular, adaptive physical-layer
network coding (PNC) is employed to address the MAI issue. By analyzing the detection
error probability, various adaptive PNC schemes are discussed for using with OFDM and
the scheme achieving the best trade-off among performance, overhead and complexity is
suggested.
In the second part of the thesis, the design of distributed precoding in TWRC using
OFDM under multipath fading channels is studied. The objective is to design a distributed
precoding scheme which can alleviate MAI and achieve multipath diversity to combat fading.
Specifically, three types of errors are introduced when analyzing the error probability in the
multiple access (MA) phase. Through analysis and simulation, the scheme that performs
precoding in both time and frequency domains is demonstrated to achieve the maximum
diversity gains under all types of errors.
Finally, the last part of the thesis examines a communication system incorporating forward
error correction (FEC) codes. Specifically, bit-interleaved code modulation (BICM)
without and with iterative decoding (BICM-ID) are investigated in a TWRC system. Distributed
linear constellation precoding (DLCP) is applied to handle MAI and the design
of DLCP in a TWRC system using BICM/BICM-ID is discussed. Taking into account the
multiple access channel from the terminal nodes to the relay node, decoding based on the
quaternary code representation is introduced. Several error probability bounds are derived
to aid in the design of DLCP. Based on these bounds, optimal parameters of DLCP are
obtained through analysis and computer search. It is also found that, by combining XORbased
network coding with successful iterative decoding, the MAI is eliminated and thus
DLCP is not required in a BICM-ID system