Interference Alignment Based Multiuser Mixed RF/FSO MIMO Networks

With the drastically increasing demands of wireless networks users for high data-rates and high quality-of-service (QoS) requirements, the need for proposing new efficient techniques, schemes, protocols and algorithms that can provide high data-rates and enhance the spectral-efficiency in wireless networks becomes imperative. Improving the spectral-efficiency through network densification and interference management is the key goal for the future wireless communication systems. Several techniques have been proposed in literature to enhance the spectral efficiency of wireless systems and increase their data rates. Among these techniques are the multiple-input multiple-output (MIMO), cooperative relay networks, and interference alignment (IA). The radio resources and interference management in the networks are the most challenging phenomena that limit the spectral-efficiency of wireless networks. Hence, there is a tremendous potential for efficient resources and interference management to minimize the interference effect and greatly improve the capacity of wireless networks. It is claimed that the existing resource allocation and interference management schemes may not be efficient for the future wireless networks. The IA makes a clean break with the current practice through minimizing the dimensionality of the interference subspace, where the desired signal can occupy half of the available subspaces leading to the optimal spectral-efficiency. Beside the relay networks, the free space optical (FSO) communication has recently attracted the attention as a vital means of transferring data at high rates over short distances, especially in last mile problem in wireless networks. FSO operates in the unlicensed optical beam offering high bandwidth, in which it provides an effective and efficient point-to-point wireless communications. They present a cost-effective alternative and/or a complement to radio frequency (RF) counterparts In this project, we propose an opportunistic and cooperative communication solution that is IA based RF/FSO network. We will consider a practical scenario for multiuser mixed RF/FSO relay networks and develop new approaches on the base of IA to assist dual-hop RF/FSO and FSO/RF relaying in order to improve their spectral efficiency. Multiple users are enabled to communicate via an FSO link. The users are connected to two relaying nodes, while the two relays are connected via an FSO link. IA technique is employed to enable the users to share the concurrent time slot simultaneously and hence, increase the degree of freedom (DoF) of the system. Under the assumption of amplify-and-froward (AF) relaying, we derive closed-form expressions for the precoding, relay filter and zero-forcing matrices of mixed RF/FSO system. Moreover, we propose an adaptive relay selection algorithm, which offers better performance than the fixed relay approach. Furthermore, we will develop new general analytical frameworks for understanding the achieved performance limits of the proposed scenarios. Among the main targets of this objective are: to investigate the effect of the number of users, the multiuser scheduling algorithms, the relaying protocols, and fading parameters on the system performance. Understanding exactly how the scenarios work and how they respond to real life operating conditions is vital in assessing their feasibility for use in actual networks. The proposed research work is expected to result in several journal and conference papers, in addition to one or two patents.