573 research outputs found
Iterative Transceiver Beamformer Design for Multi-Pair Two-Way Distributed Relay Networks
In this paper the transceiver beamforming design
problem for multipair two-way distributed relay networks is
studied, where each multi-antenna user in one user group communicate
with its partner in the other user group via distributed
single-antenna relay nodes. To achieve a satisfactory performance
while relieving relay nodes of the usual computation task, two
iteration-based transceiver beamforming schemes are proposed
to coordinate the operation of the users from the two user groups,
where the beamforming vectors are determined at the user nodes
through an iterative process. Simulation results indicate that both
schemes can achieve considerable SINR improvement after only
a few iterations compared to the existing zero-forcing scheme
Linear Precoding Designs for Amplify-and-Forward Multiuser Two-Way Relay Systems
Two-way relaying can improve spectral efficiency in two-user cooperative
communications. It also has great potential in multiuser systems. A major
problem of designing a multiuser two-way relay system (MU-TWRS) is transceiver
or precoding design to suppress co-channel interference. This paper aims to
study linear precoding designs for a cellular MU-TWRS where a multi-antenna
base station (BS) conducts bi-directional communications with multiple mobile
stations (MSs) via a multi-antenna relay station (RS) with amplify-and-forward
relay strategy. The design goal is to optimize uplink performance, including
total mean-square error (Total-MSE) and sum rate, while maintaining individual
signal-to-interference-plus-noise ratio (SINR) requirement for downlink
signals. We show that the BS precoding design with the RS precoder fixed can be
converted to a standard second order cone programming (SOCP) and the optimal
solution is obtained efficiently. The RS precoding design with the BS precoder
fixed, on the other hand, is non-convex and we present an iterative algorithm
to find a local optimal solution. Then, the joint BS-RS precoding is obtained
by solving the BS precoding and the RS precoding alternately. Comprehensive
simulation is conducted to demonstrate the effectiveness of the proposed
precoding designs.Comment: 13 pages, 12 figures, Accepted by IEEE TW
Robust Iterative Transceiver Beamforming For Multipair Two-Way Distributed Relay Networks
OAPA In this paper, the transceiver beamforming problem is studied for multipair two-way distributed relay networks, particularly with multi-antenna user nodes and in the presence of channel state errors. With multi-antenna setting on the user nodes, some of the usual signal processing tasks are shifted from the relay nodes to the user nodes with the proposed transceiver beamforming designs. The transmit beamforming vectors, distributed relay coefficients and the receive beamforming vectors are obtained by iteratively solving three sub-problems, each having a closed-form solution. The tasks of maximizing desired signal power, and reducing inter-pair interference (IPI) and noise are thus allocated to different iteration steps. By this arrangement, the transmit and receive beamformers of each user are responsible for improving its own performance and the distributed relay nodes with simple amplify-and-forward protocol aim at creating a comfortable communication environment for all user pairs. With respect to the channel uncertainty, two relay strategies are proposed considering two different requirements from the communication network: sum relay output power and individual relay output power. Our simulation demonstrates that the performance improvement can be very significant through cooperation of the three components, especially when the number of relay nodes is large
Optimal Beamforming for Two-Way Multi-Antenna Relay Channel with Analogue Network Coding
This paper studies the wireless two-way relay channel (TWRC), where two
source nodes, S1 and S2, exchange information through an assisting relay node,
R. It is assumed that R receives the sum signal from S1 and S2 in one
time-slot, and then amplifies and forwards the received signal to both S1 and
S2 in the next time-slot. By applying the principle of analogue network (ANC),
each of S1 and S2 cancels the so-called "self-interference" in the received
signal from R and then decodes the desired message. Assuming that S1 and S2 are
each equipped with a single antenna and R with multi-antennas, this paper
analyzes the capacity region of an ANC-based TWRC with linear processing
(beamforming) at R. The capacity region contains all the achievable
bidirectional rate-pairs of S1 and S2 under the given transmit power
constraints at S1, S2, and R. We present the optimal relay beamforming
structure as well as an efficient algorithm to compute the optimal beamforming
matrix based on convex optimization techniques. Low-complexity suboptimal relay
beamforming schemes are also presented, and their achievable rates are compared
against the capacity with the optimal scheme.Comment: to appear in JSAC, 200
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
Cellular Multi-User Two-Way MIMO AF Relaying via Signal Space Alignment: Minimum Weighted SINR Maximization
In this paper, we consider linear MIMO transceiver design for a cellular
two-way amplify-and-forward relaying system consisting of a single
multi-antenna base station, a single multi-antenna relay station, and multiple
multi-antenna mobile stations (MSs). Due to the two-way transmission, the MSs
could suffer from tremendous multi-user interference. We apply an interference
management model exploiting signal space alignment and propose a transceiver
design algorithm, which allows for alleviating the loss in spectral efficiency
due to half-duplex operation and providing flexible performance optimization
accounting for each user's quality of service priorities. Numerical comparisons
to conventional two-way relaying schemes based on bidirectional channel
inversion and spatial division multiple access-only processing show that the
proposed scheme achieves superior error rate and average data rate performance
Linear Precoders for Non-Regenerative Asymmetric Two-way Relaying in Cellular Systems
Two-way relaying (TWR) reduces the spectral-efficiency loss caused in
conventional half-duplex relaying. TWR is possible when two nodes exchange data
simultaneously through a relay. In cellular systems, data exchange between base
station (BS) and users is usually not simultaneous e.g., a user (TUE) has
uplink data to transmit during multiple access (MAC) phase, but does not have
downlink data to receive during broadcast (BC) phase. This non-simultaneous
data exchange will reduce TWR to spectrally-inefficient conventional
half-duplex relaying. With infrastructure relays, where multiple users
communicate through a relay, a new transmission protocol is proposed to recover
the spectral loss. The BC phase following the MAC phase of TUE is now used by
the relay to transmit downlink data to another user (RUE). RUE will not be able
to cancel the back-propagating interference. A structured precoder is designed
at the multi-antenna relay to cancel this interference. With multiple-input
multiple-output (MIMO) nodes, the proposed precoder also triangulates the
compound MAC and BC phase MIMO channels. The channel triangulation reduces the
weighted sum-rate optimization to power allocation problem, which is then cast
as a geometric program. Simulation results illustrate the effectiveness of the
proposed protocol over conventional solutions.Comment: 30 pages, 7 figures, submitted to IEEE Transactions on Wireless
Communication
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