Location Management in Personal Communication Systems

Cellular communication allows subscribers to make and receive calls from anywhere. In the USA, cellular communication was fi rst deployed at the 800MHz band. In order to accommodate more subscribers, the FCC (Federal Communications Commission) allocated the 1900MHz band for PCSs. PCS uses a cellular network as its infrastructure. In a cellular network, a service coverage area is divided into smaller areas called cells, each of which is served by a base station (Black 1996 , Rappaport 2002 ). Mobile terminals (also known as mobile stations) such as cell phones within a cell can be reached wirelessly through the corresponding base station. In order to reach a mobile terminal, the cellular network needs to know the cell in which the mobile terminal is located. Location management deals with how to fi nd the cell location of a mobile terminal that is not in a call. There are two operations in location management: location update and paging. The cellular network performs the paging operation. The goal of this operation is to fi nd the cell in which the mobile terminal is located when an incoming call arrives for it. Once the mobile terminal is located, the incoming call can be routed to the corresponding base station. The location update operation is performed by the mobile terminal. When performing the location update operation, the mobile station sends to the network its current cell location and other related information depending on the specifi c location management scheme. The number of cells to be paged in the paging operation usually depends on how frequently the location update operation is performed. The current cellular network uses the location areas’ location management scheme (Rahnema 1993 ). In this scheme, the service coverage area is divided into location areas, each of which consists of contiguous cells. When a mobile terminal enters a new location area, it needs to update its location (i.e. the new location area) with the network. When an incoming call arrives for the mobile terminal, the network pages all the cells within the location area last reported by the mobile terminal. The location areas scheme is global in the sense that all mobile terminals update their locations in the same set of cells, and it is static in the sense that the location areas in the network are fi xed (Bar-Noy, Kessler and Sidi 1995 ; Ramanathan and Streenstrup 1996 ). In contrast, a location management scheme is individualized if each individual terminal can decide when and where to update its location, and it is dynamic if a mobile terminal can update its location in any cell instead of in a pre-defi ned set of cells. In this chapter, individualized and dynamic schemes as well as global and static schemes will be described. The call arrival rate and the mobility of mobile terminals can greatly affect the design of a location management scheme. If the call arrival time to a mobile terminal is known beforehand, the mobile terminal can update its location just before the call arrives. In this way, the number of location updates and the scale of paging (i.e., the number of cells to be paged) will be minimized. Similarly, if the mobility of a mobile terminal is known or can be predicted, only the cells on the predicted or known mobility path need to be paged. This will also reduce the number of locate updates and the scale of paging. In this chapter, the location management schemes that take advantage of the call arrival rate and the mobility of mobile terminals will be discussed. In the location areas scheme, no matter how well the location areas are designed, there is a ping-pong location update effect when a mobile terminal moves back and forth between two neighboring location areas. This chapter presents several location management schemes proposed to reduce or eliminate the ping-pong effect, thereby effectively reducing the number of location updates. In the location areas scheme, all the cells in the last-reported location area are paged simultaneously. If a paging delay is allowed, the paging task can be divided into multiple rounds and the most probable set of cells will be paged fi rst. This will greatly reduce the number of cells to be paged to locate the mobile terminal. In this chapter, we will also discuss selective paging schemes that minimize the number of cells to be paged within a constrained paging delay. This chapter introduces location management in PCS networks. It does not offer an exhaustive description of