Collaborative Techniques for Enhancing Spatial Diversity

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Convergence of mobile communications and computing has resulted in a massive migration from legacy (2G) mobile phones to so called Smart Phones that support new broadband data and multimedia applications. These new applications require a large amount of power not always compatible with the size of the mobile devices since the increase in power consumption for new services has outpaced the advances in battery technology. Multiple Input Multiple Output (MIMO) is an efficient technique for increasing the network capacity through utilization of spatial diversity. It has been shown that in many networks, spatial diversity gains typical of MIMO can be achieved through cooperation, without the need for multiple antennas. Our team, under previous grants, has developed several collaborative communication strategies and code design guidelines for relay networks. We have also shown that in multiple access channels the use of non-orthogonal transmission together with interference cancellation aided by rateless codes such as Raptor codes can result in sum rates close to information theoretic bounds. Using rateless codes also results in schemes that adapt to the channel condition without prior knowledge of the channel state information. We intend to expand our research by considering more elaborate network scenarios including relay networks with multiple sources, relays and destinations. On the theoretical side, we will aim at finding information theoretic bounds on the achievable rates for various network configurations. On the practical side, we will develop coding schemes for particular network configurations under different channel realizations and to gauge the performance of the developed techniques against the theoretical bounds. The main tasks under this research project include: 1) Derivation of theoretical bounds on the achievable rate of several networks of interest including compound multiple access channels and relay channels. 2) Development of collaboration techniques utilizing network coding, nested codes and Raptor codes. 3) Assessment of adaptability of the developed schemes for wireless communication standards such as 3GPP's LTE-Advanced (Long Term Evolution-Advanced) and IEEE's 802.16 (WiMax).