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Cooperative Beamforming for Dual-Hop Amplify-and-Forward Multi-Antenna Relaying Cellular Networks  [PDF]
Chengwen Xing,Minghua Xia,shaodan Ma,Yik-Chung Wu
Mathematics , 2011,
Abstract: In this paper, linear beamforming design for amplify-and-forward relaying cellular networks is considered, in which base station, relay station and mobile terminals are all equipped with multiple antennas. The design is based on minimum mean-square-error criterion, and both uplink and downlink scenarios are considered. It is found that the downlink and uplink beamforming design problems are in the same form, and iterative algorithms with the same structure can be used to solve the design problems. For the specific cases of fully loaded or overloaded uplink systems, a novel algorithm is derived and its relationships with several existing beamforming design algorithms for conventional MIMO or multiuser systems are revealed. Simulation results are presented to demonstrate the performance advantage of the proposed design algorithms.
Outage Capacity of Bursty Amplify-and-Forward with Incremental Relaying  [PDF]
Tobias Renk,Holger Jaekel,Friedrich Jondral,Deniz Gunduz,Andrea Goldsmith
Mathematics , 2010,
Abstract: We derive the outage capacity of a bursty version of the amplify-and-forward (BAF) protocol for small signal-to-noise ratios when incremental relaying is used. We show that the ratio between the outage capacities of BAF and the cut-set bound is independent of the relay position and that BAF is outage optimal for certain conditions on the target rate R. This is in contrast to decode-and-forward with incremental relaying, where the relay location strongly determines the performance of the cooperative protocol. We further derive the outage capacity for a network consisting of an arbitrary number of relay nodes. In this case the relays transmit in subsequent partitions of the overall transmission block and the destination accumulates signal-to-noise ratio until it is able to decode.
Outage Probability of Overhearing Amplify-and-Forward Cooperative Relaying  [PDF]
Yu Zhang,Ke Xiong
Mathematics , 2015,
Abstract: This paper investigates the outage performance of overhearing amplify-and-forward (AF) cooperative relaying, where a source transmits information to its destination through multiple helping overhearing AF relays with space-time network coding (STNC) employed. Firstly, the transmission protocol of such a relaying system, i.e., cooperative relaying with overhearing AF relays based on STNC (STNC-OHAF) is presented. Then, the instantaneous end-to-end SNR expression of STNC-OHAF is analysed. Based on this, an explicit expression of the outage probability for STNC-OHAF over independent but not necessarily identically distributed (i.n.i.d) Rayleigh fading channels is theoretically derived. Numerical results validate our theoretical analysis and show that by introducing overhearing among relays, the outage performance of the system can be greatly improved. It also shows that there is a trade-off between system sum outage capacity and the transmitted number of symbols.
Opportunistic Multiuser Two-Way Amplify-and-Forward Relaying with a Multi Antenna Relay  [PDF]
Duckdong Hwang,Bruno Clerckx,Sung Sik Nam,Tae-Jin Lee
Computer Science , 2013,
Abstract: We consider the opportunistic multiuser diversity in the multiuser two-way amplify-and-forward (AF) relay channel. The relay, equipped with multiple antennas and a simple zero-forcing beam-forming scheme, selects a set of two way relaying user pairs to enhance the degree of freedom (DoF) and consequently the sum throughput of the system. The proposed channel aligned pair scheduling (CAPS) algorithm reduces the inter-pair interference and keeps the signal to interference plus noise power ratio (SINR) of user pairs relatively interference free in average sense when the number of user pairs become very large. For ideal situations, where the number of user pairs grows faster than the system signal to noise ratio (SNR), the DoF of $M$ per channel use can be achieved when $M$ is the relay antenna size. With a limited number of pairs, the system is overloaded and the sum rates saturate at high signal to noise ratio (SNR) though modifications of CAPS can improve the performance to a certain amount. The performance of CAPS can be further enhanced by semi-orthogonal channel aligned pair scheduling (SCAPS) algorithm, which not only aligns the pair channels but also forms semi-orthogonal inter-pair channels. Simulation results show that we provide a set of approaches based on (S)CAPS and modified (S)CAPS, which provides system performance benefit depending on the SNR and the number of user pairs in the network.
A Simple Amplify-and-Forward Relaying Scheme Based on Clipping and Forwarding for Dual-Hop Transmissions  [cached]
Xiao Juan Zhang,Yi Gong
Journal of Communications , 2010, DOI: 10.4304/jcm.5.4.348-353
Abstract: In this paper, we propose a simple relaying protocol, namely clip-amplify-forward (CAF), for dual-hop transmissions. In the CAF relaying protocol, the received signal at the relay node is clipped firstly and then amplified with a fixed amplification gain before retransmission. Only a hard clipper and a linear amplifier are needed at the relay node, where no channel estimation is needed. Simulation results show that with a relatively small amplification gain, the CAF relaying protocol has very close performance to the AF relaying protocol while enjoying the simplicity of implementation. A simple design criterion for the amplification gain is also presented.
Amplify-and-Forward Relaying in Two-Hop Diffusion-Based Molecular Communication Networks  [PDF]
Arman Ahmadzadeh,Adam Noel,Andreas Burkovski,Robert Schober
Mathematics , 2015,
Abstract: This paper studies a three-node network in which an intermediate nano-transceiver, acting as a relay, is placed between a nano-transmitter and a nano-receiver to improve the range of diffusion-based molecular communication. Motivated by the relaying protocols used in traditional wireless communication systems, we study amplify-and-forward (AF) relaying with fixed and variable amplification factor for use in molecular communication systems. To this end, we derive a closed-form expression for the expected end-to-end error probability. Furthermore, we derive a closed-form expression for the optimal amplification factor at the relay node for minimization of an approximation of the expected error probability of the network. Our analytical and simulation results show the potential of AF relaying to improve the overall performance of nano-networks.
Non-combining Incremental Relaying Protocol for Amplify-and-forward Cooperative Systems  [PDF]
Tang Jun,Wang Liejun
Information Technology Journal , 2013,
Abstract: In this study, a two-hop amplify-and-forward cooperative system is considered. By exploiting the limited feedback from the destination, this study has proposed a Non-combining Incremental Relaying (NCIR) protocol. The asymptotic behavior of the symbol error probability is analyzed and its spectral efficiency issue is addressed. The study also utilizes the relay selection technique to further improve the system performance. Simulation results demonstrate that the proposed scheme outperforms the conventional alternatives in terms of both error performance and bandwidth efficiency.
Differential Amplify-and-Forward Relaying Using Linear Combining in Time-Varying Channels  [PDF]
M. R. Avendi,Ha H. Nguyen,Dac-Binh Ha
Mathematics , 2015,
Abstract: Differential encoding and decoding can be employed to circumvent channel estimation in wireless relay networks. This article studies differential amplify-and-forward relaying using linear combining with arbitrary fixed combining weights in time-varying channels. An exact bit error rate (BER) analysis is obtained for this system using DBPSK modulation and over time-varying Rayleigh fading channels. The analysis is verified with simulation results for several sets of combining weights and in various fading scenarios.
Grassmannian Beamforming for MIMO Amplify-and-Forward Relaying  [PDF]
Behrouz Khoshnevis,Wei Yu,Raviraj Adve
Mathematics , 2007,
Abstract: In this paper, we derive the optimal transmitter/ receiver beamforming vectors and relay weighting matrix for the multiple-input multiple-output amplify-and-forward relay channel. The analysis is accomplished in two steps. In the first step, the direct link between the transmitter (Tx) and receiver (Rx) is ignored and we show that the transmitter and the relay should map their signals to the strongest right singular vectors of the Tx-relay and relay-Rx channels. Based on the distributions of these vectors for independent identically distributed (i.i.d.) Rayleigh channels, the Grassmannian codebooks are used for quantizing and sending back the channel information to the transmitter and the relay. The simulation results show that even a few number of bits can considerably increase the link reliability in terms of bit error rate. For the second step, the direct link is considered in the problem model and we derive the optimization problem that identifies the optimal Tx beamforming vector. For the i.i.d Rayleigh channels, we show that the solution to this problem is uniformly distributed on the unit sphere and we justify the appropriateness of the Grassmannian codebook (for determining the optimal beamforming vector), both analytically and by simulation. Finally, a modified quantizing scheme is presented which introduces a negligible degradation in the system performance but significantly reduces the required number of feedback bits.
Multiplexing Gain of Amplify-Forward Relaying in Wireless Multi-Antenna Relay Networks  [PDF]
Shahab Oveis Gharan,Amir K. Khandani
Mathematics , 2009,
Abstract: This paper studies the general multi-antenna multiple-relay network. Every two nodes of the network are either connected together through a Rayleigh fading channel or disconnected. We study the ergodic capacity of the network in the high SNR regime. We prove that the traditional amplify-forward relaying achieves the maximum multiplexing gain of the network. Furthermore, we show that the maximum multiplexing gain of the network is equal to the minimum vertex cut-set of the underlying graph of the network, which can be computed in polynomial time in terms of the number of network nodes. Finally, the argument is extended to the multicast and multi-access scenarios.
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