Wireless Networks

By the topic wireless networks, we refer to protocols which are ‘above’ the physical layer, i.e. problems in architecture, scheduling, resource allocation and transport. The focus therefore is on multiuser wireless communication, where nodes could cooperate to disseminate information. Our work on such topics is listed below.

Role of diversity in network communication

In this work, the effect of spatial diversity on the throughput and reliability of wireless networks is examined. Spatial diversity is realized through multiple independently fading transmit/receive antenna paths in single-user communications and through independently fading links in multi-user communications. Adopting spatial diversity as a central theme, we study its information-theoretic foundations, then we examine its benefits across the physical (signal transmission/coding and receiver signal processing) and networking (resource allocation, routing, and applications) layers. The work is focussed around a discussion of engineering intuition and tradeoffs, with an emphasis on the strong interactions between the various network functionalities.

Reliable transport over hybrid networks

The next generation wireless networks are posited to support largescale data applications. Implementing end-to-end TCP in such networks faces two problems. First, it is well known that TCP can not distinguish packet losses due to wireless link failures and that due to network congestion (see Balakrishnan et al, IEEE/ACM Trans. on Networking, Dec. 1997, and references therein). There it was shown that a loss notification scheme is important for efficient and reliable transport mechanisms. Second, the TCP congestion control mechanism does not deal effectively with large amounts of out-of-order packet retransmissions; this problem has not been studied thoroughly before. In this work, we present solutions to both these problems. In particular, we present a Link Layer Protection (LHP) protocol which implements Explicit Loss Notification (ELN) in a simple, scalable manner, addressing the first problem. We also modify the congestion control mechanism to incorporate knowledge of ELN and packet loss pattern into retransmission decisions, solving the second problem. We combine both these solutions with TCP to present a scalable, reliable end-to-end wireless transport protocol.