68 research outputs found
A Low-Complexity Precoding Scheme for the Downlink of Multi-Cell Multi-User MIMO AF System
Because of its simplicity, amplify-and-forward (AF) is one of the most popular cooperative relaying technique. Relays are used in cooperative communication to improve reliability, coverage or spectral efficiency of cell-edge users. However, relays tend to increase the interferences seen by users of adjacent cells, particularly by the cell-edge users, when used in multi-cell systems. In this paper, we propose a low-complexity precoding scheme to mitigate the effect of other-cell interference (OCI) in cooperative communication. The scheme is designed by taking into account the interference plus noise covariance matrix of each user for mitigating the interference at each receiver by means of precoding at the relay node. Simulation results show the effectiveness of the proposed scheme, both in terms of sum-rate and computational complexity, when compared to other existing OCI-aware precoding algorithms for AF
Low-Complexity Power Allocation Schemes for the Downlink of Nonregenerative Cooperative Multi-User MIMO Communication System
Abstract: Amplify-and-forward (AF) is one of the most popular and simple approaches to transmit information over a cooperative multi-input multi-output (MIMO) relay channel. In this paper, we propose two novel power allocation methods for the downlink of multi-user multi-input multi-output AF cooperative system, which are designed to optimise the sum-rate of the cooperative system according to the weighted sum-rate criterion. The main optimisation problem is not concave and our two methods aim at simplifying it in order to turn it into a concave problem, which can then be easily solved
Near-Optimal Energy-Efficient Joint Resource Allocation for Multi-Hop MIMO-AF Systems
Energy efficiency (EE) is becoming an important performance indicator for ensuring both the economical and environmental sustainability of the next generation of communication networks. Equally, cooperative communication is an effective way of improving communication system performances. In this paper, we propose a near-optimal energy-efficient joint resource allocation algorithm for multi-hop multiple-input-multiple-output (MIMO) amplify-and-forward (AF) systems. We first show how to simplify the multivariate unconstrained EE-based problem, based on the fact that this problem has a unique optimal solution, and then solve it by means of a low-complexity algorithm. We compare our approach with classic optimization tools in terms of energy efficiency as well as complexity, and results indicate the near-optimality and low-complexity of our approach. As an application, we use our approach to compare the EE of multi-hop MIMO-AF with MIMO systems and our results show that the former outperforms the latter mainly when the direct link quality is poor
Resource Allocation for Outdoor-to-Indoor Multicarrier Transmission with Shared UE-side Distributed Antenna Systems
In this paper, we study the resource allocation algorithm design for downlink
multicarrier transmission with a shared user equipment (UE)-side distributed
antenna system (SUDAS) which utilizes both licensed and unlicensed frequency
bands for improving the system throughput. The joint UE selection and
transceiver processing matrix design is formulated as a non-convex optimization
problem for the maximization of the end-to-end system throughput (bits/s). In
order to obtain a tractable resource allocation algorithm, we first show that
the optimal transmitter precoding and receiver post-processing matrices jointly
diagonalize the end-to-end communication channel. Subsequently, the
optimization problem is converted to a scalar optimization problem for multiple
parallel channels, which is solved by using an asymptotically optimal iterative
algorithm. Simulation results illustrate that the proposed resource allocation
algorithm for the SUDAS achieves an excellent system performance and provides a
spatial multiplexing gain for single-antenna UEs.Comment: accepted for publication at the IEEE Vehicular Technology Conference
(VTC) Spring, Glasgow, Scotland, UK, May 201
Robust MMSE beamforming for multiantenna relay networks
In this paper, we propose a robust minimum mean square error (MMSE) based beamforming
technique for multiantenna relay broadcast channels, where a multi-antenna base station transmits signal to single antenna users with the help of a multiantenna relay. The signal transmission from the base station to the single antenna users is completed in two time slots, where the relay receives the signal from the base station in the first time slot and it then forwards the received signal to different users based on amplify and forward protocol. We propose a robust beamforming technique for sum-power
minimization problem with imperfect channel state information (CSI) between the relay and the users. This robust scheme is developed based on the worst-case optimization framework and Nemirovski
Lemma by incorporating uncertainties in the CSI. The original optimization problem is divided into three subproblems due to joint non-convexity in terms of beamforming vectors at the base station, the relay amplification matrix, and receiver coefficients. These subproblems are formulated into a convex optimization framework by exploiting Nemirovski Lemma, and an iterative algorithm is developed by
alternatively optimizing each of them with channel uncertainties. In addition, we provide an optimization framework to evaluate the achievable worst-case mean square error (MSE) of each user for a given set of design parameters. Simulation results have been provided to validate the convergence of the proposed algorithm
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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