Optimal Relay Placement Research Articles

On the mobile relay placement in hybrid MANETs with secure network coding

In mobile ad hoc networks MANET, deploying a small number of mobile relays can greatly improve the throughput, delay, and security performance. However, in such a hybrid MANET, it is challenging to determine the optimal locations of mobile relays. In this paper, we study a mobile relay placement problem to maximize the network throughput of hybrid MANET with secure network coding capability. Specifically, we first study the maximal throughput of a hybrid MANET, in which the position of each mobile relay is known. For such a special case, we model the maximal throughput problem as a linear programming problem. On the basis of the understanding of this problem, we then formulate the optimal relay placement problem as an integer linear programming problem. Because integer linear programming is too complex to solve for a large MANET, we propose an efficient near-optimal approximation algorithm based on linear programming-relaxation. Finally, we conduct extensive simulation experiments, which demonstrate the effectiveness of the proposed algorithms. Copyright © 2013 John Wiley & Sons, Ltd.

Relay Placement for Amplify-and-Forward Relay Channels with Correlated Shadowing

In this letter, we investigate the optimal relay placement problem for the amplify-and-forward relay channels. Considering the joint effects of path loss, correlated shadowing, and flat Rayleigh fading, we first derive the approximate outage probability in the high signal-to-noise ratio (SNR) regime. Then, the optimal relay placement problem is formulated to minimize the derived approximate outage probability. It is shown by the analytical results that the correlation coefficients and the standard deviations of shadowing have significant impacts on the optimal relay placement. Somewhat surprisingly, we show that the optimal relay position may not be on the line connecting the source and the destination for certain scenarios.

Optimal Relay Placement and Diversity Analysis of Relay-Assisted Free-Space Optical Communication Systems

Relay-assisted free-space optical (FSO) transmission exploits the fact that atmospheric turbulence fading variance is distance dependent and yields significant performance gains by taking advantage of the resulting shorter hops. In this paper, we investigate how to determine optimal relay locations in serial and parallel FSO relaying so as to minimize the outage probability and quantify performance improvements obtained through optimal relay placement. We further present a diversity gain analysis for serial and parallel FSO relaying schemes and quantify their diversity advantages in terms of the number of relays and channel parameters.

Generalizing the Amplify-and-Forward Relay Gain Model: An Optimal SEP Perspective

Two models for AF relaying, namely, fixed gain and fixed power relaying, have been extensively studied in the literature given their ability to harness spatial diversity. In fixed gain relaying, the relay gain is fixed but its transmit power varies as a function of the source-relay channel gain. In fixed power relaying, the relay transmit power is fixed, but its gain varies. We revisit and generalize the fundamental two-hop AF relaying model. We present an optimal scheme in which an average power constrained AF relay adapts its gain and transmit power to minimize the symbol error probability (SEP) at the destination. Also derived are insightful and practically amenable closed-form bounds for the optimal relay gain. We then analyze the SEP of MPSK, derive tight bounds for it, and characterize the diversity order for Rayleigh fading. Also derived is an SEP approximation that is accurate to within 0.1 dB. Extensive results show that the scheme yields significant energy savings of 2.0-7.7 dB at the source and relay. Optimal relay placement for the proposed scheme is also characterized, and is different from fixed gain or power relaying. Generalizations to MQAM and other fading distributions are also discussed.

Network Coded Multi-Source Cooperative Communication in BICM-OFDM Networks

In this paper, we study a cooperative diversity scheme for wireless systems employing network coding and the combination of bit-interleaved coded modulation (BICM) and orthogonal frequency division multiplexing (OFDM). The considered system comprises multiple sources, one relay, and one destination. The relay decodes the signal received from all sources and performs network coding before forwarding the signal to the destination. We propose a simple cooperative maximum-ratio combining scheme for the destination which can successfully exploit the full spatial and frequency diversity offered by the channel for arbitrary numbers of sources and arbitrary linear modulation schemes. Furthermore, we propose techniques to reduce the signaling overhead and the decoding complexity at the destination. To gain insight for system design, we derive a closed-form upper bound for the asymptotic worst-case pairwise error probability and the diversity gain of the considered network coded cooperative BICM-OFDM system. These analytical results reveal the influence of various system parameters, including the number of sources, the free distance of the code, and the frequency diversity of the involved links, on performance. Based on the derived analytical results, we develop schemes for optimal relay placement and power allocation. Simulation results corroborate the derived analytical results and confirm the effectiveness of the developed optimization framework.

A new adaptive model for throughput enhancement and optimal relay selection in IEEE 802.16j MMR networks

Network deployment problem is one of the major issues when base stations and relay stations are jointly deployed. Deploying relay station at suitable position covers throughput enhancement and coverage extension problem in IEEE 802.16j MMR networks. In this paper we have proposed a new adaptive model for throughput enhancement and optimal relay selection in IEEE 802.16j MMR networks and studied about the average output/input throughput. A group of mobile stations are connected to base stations which are moving at a speed of 20 m/s. The Mobile Station is initially placed near to Base station and is moving away from Base station. The average throughput achieved without a relay station is 6.193 Mbits/s and the average throughput achieved with Relay Station is 9.867 Mbits/s. There is 37.2318% increase in the throughput by placing a transparent mode relay Station at suitable position. This paper also discusses optimal relay selection when a group of relay stations are deployed, the user is allowed to select an appropriate relay transmission that provides her required bandwidth and less cost. The mobile station selects a suitable relay station from the group of relay station. Key words: NCTUns, Institute of Electrical and Electronics Engineers 802.16j, relay modes, optimal relay placement, worldwide interoperability for microwave access.

Achievable Rates in Low-Power Relay Links Over Fading Channels

Relayed transmissions enable low-power communications among nodes (possibly separated by a large distance) in wireless networks. Since the capacity of general relay channels is unknown, we investigate the achievable rates of relayed transmissions over fading channels for two transmission schemes: the block Markov coded and the time-division multiplexed (TDM) transmissions. The normalized achievable minimum energy per bit required for reliable communications is derived, which also enables optimal power allocation between the source and the relay. The time-sharing factor in TDM transmissions is optimized to improve achievable rates. The region where relayed transmission can provide a lower minimum energy per bit than direct transmission, as well as the optimal relay placement for these two transmission schemes, are also investigated. Numerical results delineate the advantages of relayed, relative to direct, transmissions.