CORDIS - EU research results

Cooperation in Hybrid Wireless Networks

Final Activity Report Summary - COPHiWi (Cooperation in Hybrid Wireless Networks)

Wireless communications systems in general and hybrid networks (such as cellular systems) in particular are of major interest as they allow the provision of continuous services to mobile users. In recent years, a considerable research effort has been devoted to the development of new technologies for providing better services and extending system coverage. In this context, the use of multi-cell processing (MCP) has been identified as a key tool for enhancing system performance. Unlike the conventional approach, in which each infrastructure node (or base-station) processes its user nodes' signals treating other signals as noise, in MCP a subset of the system infrastructure nodes jointly process their user nodes' signals to reduce the inter-system interference and increase the overall system performance. This project explores various aspects of infrastructure nodes and user nodes cooperation in hybrid wireless networks.

In particular, suboptimal MCP schemes such as joint zero forcing beam forming were proposed and shown to provide near optimal performance. Another aspect investigated here is the impact of real life impairments of the backhaul network connecting the base-stations. In this context both limited connectivity, and limited capacity link backhaul networks were considered. In yet another part of the work the benefits of combining relaying and MCP were studied for various relaying schemes such as decode-and-forward, amplify-and-forward, and compress-and-forward. The dynamic nature of such systems was also addressed, where the interplay between random number of users and MCP technique was investigated.

The various schemes involving MCP were shown to provide dramatic improvement on the achievable throughputs when compared to those achieved by the traditional approaches. It is noted that several system models (involving relaying and limited backhaul networks in cellular systems) presented in the project papers were widely adopted by the relevant research community. The analyses carried out involve advanced techniques from the fields of information theory, probability theory, and random matrix theory.

The results of this project were published in 11 peer-reviewed journal papers and were presented in 24 oral presentations of peer-reviewed conferences papers. Some of the results were summarised in a book chapter dealing with distributed antenna systems. Furthermore, a paper considering the impact of limited backhaul networks on the performance of MCP, won the first best student paper award of the IEEE international symposium on information theory (ISIT'07).