Browsing by Subject "Wireless communication systems--United States"

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Energy conserving protocols for wireless data networks
(2001-08) Stine, John Andrew, 1959-; De Veciana, Gustavo
In this thesis we study how wireless medium access control (MAC) protocols can be used to conserve energy in wireless portable communication systems. We start by evaluating protocols for centrally controlled networks separately evaluating the protocols used in the management of the exchange of data from those used by nodes to announce to the central controller that they have data to exchange. In the former, we compare different methods of scheduling, methods to announce schedules, and methods to recover from errors. In the latter, we compare various random access and polling techniques. We conclude that there are two significant energy conserving objectives. First, the primary goal of MAC protocols should be to put nodes not participating in data exchanges into a low energy state. Second, information that enables these nodes to enter these states must be made available to them as soon as they can use it. We then consider energy consumption in ad hoc networks. The objectives identified for centrally controlled networks are applicable but are not easily applied because most ad hoc MAC protocols rely on temporally random access techniques. vii As a result, we created a new MAC protocol called Synchronous Collision Resolution (SCR). SCR assumes nodes are synchronized and thus can contend simultaneously. A collision resolution signaling mechanism is used to resolve contentions and request-to-send and clear-to-send exchanges are used to guard against hidden nodes. SCR has many other enhanced capabilities. In particular, the protocol includes a novel priority access scheme and a cooperative signaling approach to robustly support mutlihop stream based services. The proposed mechanisms for resolving contention are especially effective at identifying a spatially distributed set of transmitting nodes that can exchange data simultaneously. We show through analysis and simulation that the protocol is stable to spatial loads exceeding 40%, avoids congestion collapse, and has spatial capacity exceeding 60%. Moreover, we show that next hop routing strategies and the use of spread spectrum coding can more than double these performance measures. We conclude by arguing that the network can easily adapt to congestion (high load and/or node density) by varying the transmission power used during the contention process. Overall, SCR achieves performance levels in ad hoc networks that have heretofore only been possible for centrally controlled networks