H Handoff in Cellular Systems

a process of transferring a mobile station (MS) from one base station (BS) or channel to another. The channel change due to handoff may be through a time slot, frequency band, codeword, or combination of these for time-division multiple access (TDMA), frequency division multiple access (FDMA), code-division multiple access (CDMA), or a hybrid scheme, respectively [1]. This article includes four major topics. Topic 1: Deployment Scenarios and Handoff — Topic 1 describes different system deployment scenarios and their constraints on the handoff procedure. Handoff algorithms with a specific set of parameters cannot perform uniformly well in different communication system deployment scenarios since these scenarios are characterized by specific environments. Examples of different system structures include macro-cells, microcells, overlays, integrated cellular systems, integrated cordless and cellular systems, and integrated terrestrial and satellite systems. Note that these system structures are expected to coexist in future wireless communication systems and warrant closer study. Topic 2 views handoff and other resource management tasks and details handoff-related system performance improvement. Prioritizing handoff is one way to improve handoff-related system performance. Several handoff prioritization schemes (e.g., guard channels and queuing) are discussed. Handoff represents one of the radio resource management tasks carried out by cellular systems. Some other resource management functions include admission control, channel assignment, and power control. If some of the resource management tasks are treated in an integral manner, better overall performance can be obtained in a global sense by making appropriate trade-offs. Topic 3: Implementation of Handoff — Topic 3 describes how handoff procedure is implemented. The decision making process of handoff may be centralized or decentralized (i.e., the handoff decision may be made at the MS, BS, or mobile switching center, MSC). Different systems use different approaches to execute the process of handoff, and handoff protocols characterize these approaches. Topic 4: Analysis of Handoff Algorithms — Three basic mechanisms have been used to evaluate the performance of handoff algorithms, and these mechanisms — the analytical approach, simulation approach, and emulation approach — are described in topic 4. The radio propagation environment and related handoff challenges are different in different cellular structures. A handoff algorithm with fixed parameters cannot perform well in different system environments. Specific characteristics of the communication systems should be taken into account while designing handoff algorithms. Several basic cellular structures (e.g., macrocells, microcells, and overlay systems) and special architectures (e.g., underlays, multichannel bandwidth systems , and evolutionary architectures) …