Opportunistic Cooperative Transmission Research Articles

Opportunistic Cooperative Transmission for Underwater Communication Based on the Water’s Key Physical Variables

Underwater is a harsh and dynamic environment. Its physical properties are unsteady in the space-time domain and that complicates the communication process inside the water. Moreover, underwater transmissions suffer from many attenuations and scattering sources due to several environmental noises such as shipping, turbulence, wave dynamics, and the background life of the marine organisms. Therefore, opportunistic and cooperative communications are necessary to compensate for the prompt changes in underwater environments. In this paper, we propose a new opportunistic cooperative transmission scheme for underwater networks that is adaptable for various environmental conditions. The proposed scheme employs the key physical variables of the seawater, e.g. temperature, salinity, density, and waves speed, to indicate the proper relaying scheme jointly with the appropriate modulation method and the transmitting power level that suit the current transmission situations. The paper also proposes a study that demonstrates the effects of these variables on the underwater speed of sound which is the most commonly used carrier for underwater communication and hence affect the transmitted signal intensity. The results show that the proposed opportunistic cooperative transmission scheme provides an efficient compromise between the overall network performance and the energy efficiency at the nodes.

Analysis and Enhancement of Joint Security and Reliability in Cooperative Networks

In this study, we deal with a cooperative wireless communications system of security constraints in which there is no knowledge about channel state information (CSI) of the eavesdropper. In order to improve the tradeoff between security and reliability, we opportunistically employ relays via an incremental and selective cooperation with respect to the CSI of the main link. In this cooperation, named as opportunistic cooperative transmission (OCT), the first priority is communication through the direct link as far as possible. However, a relay that has the best link to the main destination is employed for retransmitting the source information when the direct link is so weak which cannot provide a specific quality. In fact, since improving the reliability of the favorable communications by use of the relays increases the risk of successful interception by the eavesdropper at the same time, the OCT scheme tries to avoid excess of rebroadcasting the secret information by the relays whenever the direct link is strong enough; otherwise it employs an opportunistically selected relayed link. Hence, it can improve the security for a specific level of reliability and vice versa. We derive closed-form expressions for the security-reliability tradeoff (SRT) and secrecy outage probability (SOP) of the OCT scheme. Moreover, we provide asymptotic analyses which are illustrative on the security behavior of the proposed scheme. Finally, simulation results are presented which confirm validity of the analysis and reveal the desired performance of OCT in terms of both SRT and SOP.

A Novel Opportunistic Relay and Energy Efficient Power Allocation Algorithm in Cooperative Wireless Sensor Networks

A series of challenges exist in the process of sensor network research which can not be solved by one sensor node. Cooperative communication, based on the idea of spatial diversity, which makes different users or nodes in wireless network share their antennas or other network resources, is a promising technique toward improving performance of wireless sensor network significantly. This article adopts cooperation between nodes and opportunistic collaboration transmission strategy is proposed. Energy efficient power allocation algorithm in wireless sensor network is put forward to optimize performance of opportunistic cooperative transmission. Through the simulation, regardless of statistical feature of channel state of opportunistic node, opportunistic cooperation can effectively improve the performance of the system. Using energy efficient power allocation algorithm can effectively reduce energy consumption of the network and improve the network performance

Energy efficient opportunistic cooperative transmission with different ratio combinings: from a new perspective

In cooperative communication, different ratio combining approaches can be utilized at the receiver based on the channel state information (CSI) available to the destination. In this paper, we focus on optimal energy allocation under amplify-and-forward (AF) cooperative communications when various ratio combining methods are utilized. More specifically, we consider a suite of important and fundamental problems, including signal-to-noise ratio (SNR) maximization under a weighted total energy constraint, weighted total energy minimization under an SNR constraint, weighted total energy minimization under an outage probability constraint and outage probability minimization under instantaneous weighted total energy constraint, and analyze the relationship among these problems. We first consider maximal ratio combining (MRC) and derive exact analytical solutions. To reveal the key factors in the resource allocation problem, we further transform the exact results with multiple parameters into more intuitive results with only two quantities. The resulting solutions provide a new perspective to understand optimal energy-efficient opportunistic cooperative transmissions. We then consider fixed ratio combining (FRC) and show that an explicit analytical solution does not exist to the original problem. To this end, based on the convexity proofs for the objective functions, we utilize numerical convex optimizations to obtain the unique solution. Both numerical and simulation studies are conducted to validate our theoretical analysis.