Network Deployment

Abstract

The concept of cellular communication systems is based on the assumption that a mobile user is served by the base station that provides the best link quality [1,2]. Spectrum allocation strategies, discussed in Chapter 12, are based on this assumption. In many cases, however, a mobile user can establish a communication link of acceptable quality with more than one base. Therefore, at many locations there is overlapping coverage, usually by nearby base stations [3].The coverage overlap can be used to improve the system performance. Several schemes that consider this have been suggested [4][5][6][7][8]. Generalized fixed channel assignment (GFCA), a scheme that allows a call to be served by any of several nearby base stations, was considered in Choudhury and Rappaport [4]. Directed retry, discussed in References [5, 6], allows a new call that cannot be served at one base to attempt access via a nearby alternative base. Load sharing is an enhancement of directed retry that allows calls in congested cells to be served by neighboring base stations. In Chu and Rappaport [7] overlapping coverage for highway microcells was considered. The use of overlapping coverage with channel rearrangement was discussed in Chu and Rappaport [8].Reuse partitioning [9][10][11] can also improve traffic performance of fixed channel assignment (FCA). The method divides the channels into several disjoint partitions. These partitions are associated with different cluster sizes (or reuse factors). Channels are allocated to base stations according to these cluster sizes. To meet the same signal quality requirement, channels corresponding to smaller cluster sizes are used within a smaller area than that for channels associated with larger cluster sizes [9]. Since channels are reused more often for a smaller cluster size, there may be more channels available at a base in reuse partitioning than in FCA. Therefore, improved traffic performance can be obtained. Because there is a fixed relationship between channels and base stations, reuse partitioning is a fixed channel assignment scheme. In this section the acronym FCA is used only to refer fixed channel assignment without utilizing overlapping coverage or reuse partitioning. That is, in FCA all channels are allocated using a single cluster size and overlapping coverage is not exploited.When overlapping coverage exists in a system and is being used to provide enhanced access, users in overlapping areas may benefit. However, this may be at the expense of users in nonoverlapping areas who may encounter increased blocking or handoff failure because of the higher Advanced Wireless Networks: Cognitive, Cooperative and Opportunistic 4G Technology Second Edition Savo Glisic and Beatriz Lorenzo