Optimal Cooperative MAC Protocol with Efficient Selection of Relay Terminals

A new cooperative protocol is proposed in the context of wireless mesh networks. The protocol implements ondemand cooperation, i.e. cooperation between a source terminal and a destination terminal is activated only when needed. In that case, only the best relay among a set of available terminals is re-transmitting the source message to the destination terminal. This typical approach is improved using three additional features. First, a splitting algorithm is implemented to select the best relay. This ensures a fast selection process. Moreover, the duration of the selection process is now completely characterized. Second, only terminals that improve the outage probability of the direct link are allowed to participate to the relay selection. By this means, inefficient cooperation is now avoided. Finally, the destination terminal discards the source message when it fails to decode it. This saves processing time since the destination terminal does not need to combine the replicas of the source message: the one from the source terminal and the one from the best relay. We prove that the proposed protocol achieves an optimal performance in terms of Diversity-Multiplexing Tradeoff (DMT)

DMT Optimal Cooperative Protocols with Destination-Based Selection of the Best Relay

We design a cooperative protocol in the context of wireless mesh networks in order to increase the reliability of wireless links. Destination terminals ask for cooperation when they fail in decoding data frames transmitted by source terminals. In that case, each destination terminal D calls a specific relay terminal B with a signaling frame to help its transmission with source terminal S. To select appropriate relays, destination terminals maintain tables of relay terminals, one for each possible source address. These tables are constituted by passively overhearing ongoing transmissions. Hence, when cooperation is needed between S and D, and when a relay B is found by terminal D in the relay table associated with terminal S, the destination terminal sends a negative acknowledgment frame that contains the address of B. When the best relay B has successfully decoded the source message, it sends a copy of the data frame to D using a selective decode-andforward transmission scheme. The on-demand approach allows maximization of the spatial multiplexing gain and the cooperation of the best relay allows maximization of the spatial diversity order. Hence, the proposed protocol achieves optimal diversitymultiplexing trade-off performance. Moreover, this performance is achieved through a collision-free selection process

Splitting algorithm for DMT optimal cooperative MAC protocols in wireless mesh networks

A cooperative protocol for wireless mesh networks is proposed in this paper. The protocol implements both on-demand relaying and a selection of the best relay terminal so only one terminal is relaying the source message when cooperation is needed. Two additional features are also proposed. The best relay is selected with a splitting algorithm. This approach allows fast relay selection within less than three time-slots, on average. Moreover, a pre-selection of relay candidates is performed prior to the splitting algorithm. Only terminals that are able to improve the direct path are pre-selected. So efficient cooperation is now guaranteed. We prove that this approach is optimal in terms of diversity-multiplexing trade-off. The protocol has been designed in the context of Nakagami-mfading channels. Simulation results show that the performance of the splitting algorithm does not depend on channel statistics

DMT Optimal On-Demand Relaying for Mesh Networks

This paper presents a new cooperative MAC (Medium Access Control) protocol called BRIAF (Best Relay based Incremental Amplify-and-Forward). The proposed protocol presents two features: on-demand relaying and selection of the best relay terminal. “On-demand relaying” means that a cooperative transmission is implemented between a source terminal and a destination terminal only when the destination terminal fails in decoding the data transmitted by the source terminal. This feature maximizes the spatial multiplexing gain r of the transmission. “Selection of the best relay terminal” means that a selection of the best relay among a set of (m-1) relay candidates is implemented when a cooperative transmission is needed. This feature maximizes the diversity order d(r) of the transmission. Hence, an optimal DMT (Diversity Multiplexing Tradeoff) curve is achieved with a diversity order d(r) = m(1-r) for 0 ≤ r ≤ 1

On-Demand Cooperation MAC Protocols with Optimal Diversity-Multiplexing Tradeoff

This paper presents access protocols with optimal Diversity-Multiplexing Tradeoff (DMT) performance in the context of IEEE 802.11-based mesh networks. The protocols are characterized by two main features: on-demand cooperation and selection of the best relay terminal. The on-demand characteristic refers to the ability of a destination terminal to ask for cooperation when it fails in decoding the message transmitted by a source terminal. This approach allows maximization of the spatial multiplexing gain. The selection of the best relay terminal allows maximization of the diversity order. Hence, the optimal DMT curve is achieved with these protocols

Green Cellular Networks: A Survey, Some Research Issues and Challenges

Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogeneous network deployment based on micro, pico and femto-cells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technologyComment: 16 pages, 5 figures, 2 table

A Simple Cooperative Diversity Method Based on Network Path Selection

Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However most of the proposed solutions require distributed space-time coding algorithms, the careful design of which is left for future investigation if there is more than one cooperative relay. We propose a novel scheme, that alleviates these problems and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this best relay for cooperation between the source and the destination. We develop and analyze a distributed method to select the best relay that requires no topology information and is based on local measurements of the instantaneous channel conditions. This method also requires no explicit communication among the relays. The success (or failure) to select the best available path depends on the statistics of the wireless channel, and a methodology to evaluate performance for any kind of wireless channel statistics, is provided. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M nodes is required, such as those proposed in [7]. The simplicity of the technique, allows for immediate implementation in existing radio hardware and its adoption could provide for improved flexibility, reliability and efficiency in future 4G wireless systems.Comment: To appear, IEEE JSAC, special issue on 4

Outage probability of an optimal cooperative MAC protocol in Nakagami-m channels

A new cooperative access protocol is presented in the context of IEEE 802.11-based fixed ad hoc networks. The protocol achieves optimal diversity-multiplexing tradeoff thanks to two known functionalities: on-demand cooperation and selection of the best relay. The on-demand approach allows maximization of the spatial multiplexing gain. The selection of the best relay allows maximization of the spatial diversity order. The main contribution of this paper consists in the design of a proactive mechanism in order to select the best relay. The mechanism is centralized at the destination terminal. Destination terminals maintain lists of relays for all possible source terminals by overhearing ongoing transmissions. So when cooperation is needed, a destination terminal just picks the best relay for a specific source terminal in the corresponding table. Hence, collision among relay candidates is now avoided. Moreover, only terminals that can improve the direct transmission are selected. This guarantees the usefulness of relaying. This study focusses on Nakagami-m wireless channel models in order to encompass a wide variety of fading models