Handoff in cellular systems

Abstract

andoff is 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 macrocells, 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: Resource Management in Cellular Systems-Topic 2 views handoff and other resource management tasks and details handoff-related system performance improvement. Prioritizing handoff is one way to improve handoffrelated 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 approachare described in topic 4.

Soft handoff analysis for hierarchical CDMA cellular systems

“…In dynamic parameter assignment is not fixed, but is dynamically updated as a function of the to improve the handoff performance. The concept is similar to that of "cell breathing" [16], [17], where a heavily loaded cell shrinks its size to force handoffs and reduce interference. In our case the objective is to control the microcell handoff region according to given interference imbalance condition (as defined by the ) to limit unnecessary overhead.…”

Dynamic guard bandwidth scheme for wireless broadband networks

“…While the MTs could change direction and speed as it approaches the cell boundary, the target handoff cell prediction is erroneous only if the trajectory of the MT changes so much that it enters a different cell from the one predicted. In addition, we do not require precise knowledge of the exact time at which a handoff-request is made, which is an intractable task since a handoff could occur anywhere within the handoff region [6], and a MT's speed and direction could change randomly. Our scheme would be effective so long as the system has sufficient time to set aside the required bandwidth for the handoff.…”

“…An important point to emphasize here is that the location information obtained from the GPS receivers are only used to estimate T remain and C target , so as to make dynamic adjustment of guard bandwidth; actual handoff-requests are still initiated based on received signal strength measurements, error rates, interference, as well as handoff protocols used [6].…”

“…We assume that a MT's initial position within the cell during call establishment is uniformly distributed. Its initial speed follows a truncated Gaussian distribution [6], [23], with mean S mean and standard deviation σ speed , limited to the range [0, S max ]. We also assume that each MT will travel towards a random virtual destination cell (VDC) chosen from the 268 cells in the network with equal probability.…”

“…E-mail: wsoh@ece.cmu.edu and kim@ece.cmu.edu. traffic conditions [5], and risk under-utilizing the spectrum [6]. In addition, they only utilize local information (e.g.…”