With the popularity of wireless devices and the increase of computing and storage resources, there are increasing interests in supporting mobile computing techniques. Particularly, ad hoc networks can potentially connect different wireless devices to enable more powerful wireless applications and mobile computing capabilities. To meet the ever increasing communication need, it is important to improve the network throughput while guaranteeing transmission reliability. Multiple-input multiple-output (MIMO) technology can provide significantly higher data rate in ad hoc networks where nodes are equipped with multi-antenna arrays. Although MIMO technique itself can support diversity transmission when channel condition degrades, the use of diversity transmission often compromises the multiplexing gain and is also not enough to deal with extremely weak channel.
In this work, we exploit the use of cooperative relay transmission (which is often used in a single antenna environment to improve reliability) in a MIMO-based ad hoc network to cope with harsh channel condition. We design both centralized and distributed scheduling algorithms to support adaptive use of cooperative relay transmission when the direct transmission cannot be successfully performed. Our algorithm effectively exploits the cooperative multiplexing gain and cooperative diversity gain to achieve higher data rate and higher reliability under various channel conditions.
Our scheduling scheme can efficiently invoke relay transmission without introducing significant signaling overhead as conventional relay schemes, and seamlessly integrate relay transmission with multiplexed MIMO transmission. We also design a MAC protocol to implement the distributed algorithm. Our performance results demonstrate that the use of cooperative relay in a MIMO framework could bring in a significantly throughput improvement in all the scenarios studied, with the variation of node density, link failure ratio, packet arrival rate and retransmission threshold. Exploiting Cooperative Relay for High Performance Communications in MIMO Ad Hoc Networks
In this Existing System, a various MAC schemes have been designed to exploit the intrinsic features of MIMO to improve the throughput and reliability; they may not be able to handle consecutive packet loss due to severe path loss, continuous deep fading or temporary topology changes and link breakages. Continuous packet retransmissions would lead to significantly throughout reduction. The severe transmission conditions pose a big threat to the growth of wireless applications. Although beamforming can help improve the transmission reliability, it compromises the potential multiplexing gain and hence reduces the transmission rate.
In addition, when the channel condition is extremely weak or the distance between the transmitter and receiver is temporarily very long, even beaming-forming may not be able to ensure the transmission reliability for the direct link. Moreover, the design of MAC scheme to coordinate beamforming transmissions in a multi-hop network is very difficult.
In this Proposed System, an alternative to MIMO technique, recent efforts have been made to enable cooperative relay transmission to cope with channel degradation, with the assumption that network nodes have single antenna.
Our proposed strategy is named as Cooperative Relayed Spatial Multiplexing (CRSM). The main contributions of this paper are as follows.