470 research outputs found
Hardware Impairments Aware Transceiver Design for Full-Duplex Amplify-and-Forward MIMO Relaying
In this work we study the behavior of a full-duplex (FD) and
amplify-and-forward (AF) relay with multiple antennas, where hardware
impairments of the FD relay transceiver is taken into account. Due to the
inter-dependency of the transmit relay power on each antenna and the residual
self-interference in an FD-AF relay, we observe a distortion loop that degrades
the system performance when the relay dynamic range is not high. In this
regard, we analyze the relay function in presence of the hardware inaccuracies
and an optimization problem is formulated to maximize the signal to
distortion-plus-noise ratio (SDNR), under relay and source transmit power
constraints. Due to the problem complexity, we propose a
gradient-projection-based (GP) algorithm to obtain an optimal solution.
Moreover, a nonalternating sub-optimal solution is proposed by assuming a
rank-1 relay amplification matrix, and separating the design of the relay
process into multiple stages (MuStR1). The proposed MuStR1 method is then
enhanced by introducing an alternating update over the optimization variables,
denoted as AltMuStR1 algorithm. It is observed that compared to GP, (Alt)MuStR1
algorithms significantly reduce the required computational complexity at the
expense of a slight performance degradation. Finally, the proposed methods are
evaluated under various system conditions, and compared with the methods
available in the current literature. In particular, it is observed that as the
hardware impairments increase, or for a system with a high transmit power, the
impact of applying a distortion-aware design is significant.Comment: Submitted to IEEE Transactions on Wireless Communication
Securing Downlink Non-Orthogonal Multiple Access Systems by Trusted Relays
A downlink single-input single-output non-orthogonal multiple access system
is considered in which a base station (BS) is communicating with two legitimate
users in the presence of an external eavesdropper. A group of trusted
cooperative half-duplex relay nodes, powered by the BS, is employed to assist
the BS's transmission. The goal is to design relaying schemes such that the
legitimate users' secrecy rate region is maximized subject to a total power
constraint on the BS and the relays' transmissions. Three relaying schemes are
investigated: cooperative jamming, decode-and-forward, and amplify-and-forward.
Depending on the scheme, secure beamforming signals are carefully designed for
the relay nodes that either diminish the eavesdropper's rate without affecting
that of the legitimate users, or increase the legitimate users' rates without
increasing that of the eavesdropper. The results show that there is no relaying
scheme that fits all conditions; the best relaying scheme depends on the system
parameters, namely, the relays' and eavesdropper's distances from the BS, and
the number of relays. They also show that the relatively simple cooperative
jamming scheme outperforms other schemes when the relays are far from the BS
and/or close to the eavesdropper.Comment: To appear in IEEE Globecom 201
Energy-efficiency for MISO-OFDMA based user-relay assisted cellular networks
The concept of improving energy-efficiency (EE) without sacrificing the service quality has become important nowadays. The combination of orthogonal frequency-division multiple-access (OFDMA) multi-antenna transmission technology and relaying is one of the key technologies to deliver the promise of reliable and high-data-rate coverage in the most cost-effective manner. In this paper, EE is studied for the downlink multiple-input single-output (MISO)-OFDMA based user-relay assisted cellular networks. EE maximization is formulated for decode and forward (DF) relaying scheme with the consideration of both transmit and circuit power consumption as well as the data rate requirements for the mobile users. The quality of-service (QoS)-constrained EE maximization, which is defined for multi-carrier, multi-user, multi-relay and multi-antenna networks, is a non-convex and combinatorial problem so it is hard to tackle. To solve this difficult problem, a radio resource management (RRM) algorithm that solves the subcarrier allocation, mode selection and power allocation separately is proposed. The efficiency of the proposed algorithm is demonstrated by numerical results for different system parameter
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