Kiran M. Rege

Fade margins for soft and hard handoffs

A particularly attractive feature of CDMA wireless systems proposed in the Telecommunication Industry Associations standard IS-95 [1] is their ability to get into what is known as “soft handoff”. A mobile in soft handoff maintains simultaneous radio links with multiple base-stations which enables it to make use of the best quality leg most of the time. This is believed to result in a reduction of the fade margin that is needed to provide the desired coverage in a given geographical area in the presence of log-normal shadow fading. This paper presents an analysis of fade margins for systems allowing soft handoffs (e.g. CDMA) and those where only hard handoffs are possible (e.g. FDMA, TDMA). The analysis is based on a model for hard handoffs with hysteresis and connection delay and confirms the belief that soft handoffs result in smaller fade margins.

Clearmedia: A Proxy-based Architecture for Streaming Media Services over Wireless Networks

Streaming media over wireless networks typically rely on end-to-end feedback from client devices to help media servers adjust to changing channel conditions. In rapidly fluctuating channel conditions, the client device may not be able to effectively track changes and report them to the server. Furthermore, bandwidth constraints often limit the frequency of end-to-end feedback. In order to overcome these constraints, we propose Clearmedia, a signaling proxy-based architecture for streaming media services over wireless networks. This architecture enables media servers to receive frequent and reliable feedback on network conditions, which leads to enhanced service quality. Our performance studies show that the Clearmedia architecture achieves improvement in several key performance metrics that are representative of end-user perceived video quality.