Scanning the literature

Abstract

This paper develops a model using a combination of empirical data and theoretical models, to capture the user behavior in a PCS environment. Mobility management is in terms of keeping track of and locating users so that calls arriving for the particular users can be delivered to their current locations, which usually consists of two parts: users notifying the system of the location once moved (updating), and system notifying the users that calls arriving for them (paging). PCS network differs from conventional cellular network in several aspects. For example more stringent QoS requirements from users are expected, and smaller cells to support more users and greater traffic density. As a result the updating and paging traffic have to be carefully managed. To handle the updates, the model presented in this paper combines automatic updated by the users whenever they make significant moves or when they lose network interaction for extended period of time. And a focused paging mechanism is introduced to minimize the number of pages under the constraint of the amount of time allowed to a page. The model shows that over a range of systems and user parameters, the total paging and updating traffic can be kept under 1 per 2000 user seconds, and the impact on the user is less than 10 updates per day. To satisfy the needs of wireless data networking, study group 802.11 was formed under IEEE project 802 to recommend an international standard for Wireless Local Area Networks (WLANs). A key part of standard are the Medium Access Control (MAC) protocol needed to support asynchronous and time bounded delivery of data frames. It has been proposed that unslotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) be the basis for the IEEE 802.11 WLAN MAC protocols. This paper conducts performance evaluation of the asynchronous data transfer protocols that are a part of the proposed IEEE 802.11 standard taking into account the decentralized nature of communication between stations, the possibility of "capture", and presence of "hidden" stations. System throughput is obtained, and fairness properties of the proposed MAC protocols are evaluated. Further, the impact of spatial characteristics on the performance of the system and that observed by individual stations is determined. A comprehensive comparison of the access methods provided by the 802.11 MAC protocol is done and observations are made as to when each should be employed. Extensive numerical and simulation results are presented to help understand the issues involved.