Unnecessary Handoffs Research Articles

A Seamless and Proactive End-to-End Mobility Solution for Roaming Across Heterogeneous Wireless Networks

Roaming across heterogeneous wireless networks such as wireless wide area network (WWAN) and wireless local area network (WLAN) poses considerable challenges, as it is usually difficult to maintain the existing connections and guarantee the necessary quality-of-service. This paper proposes a novel seamless and proactive end-to-end mobility management system, which can maintain the connections based on the end-to-end principle by incorporating an intelligent network status detection mechanism. The proposed system consists of two components, connection manager (CM) and virtual connectivity (VC). The CM, by using novel media access control-layer and physical-layer sensing techniques, can obtain accurate network condition, while at the same time reducing the unnecessary handoff and ping-pong effect. The VC can make mobility transparent to applications without additional network-layer infrastructure support using a local connection translation, and can handle mobility well in the network address translator and simultaneous movement cases using a subscription/notification service. The proposed system enjoys several unique advantages: 1) capable of reacting to roaming events proactively and accurately; 2) maintaining the connection's continuity with small handoff delay; and 3) being a unified end-to-end approach for both IPv4 and IPv6 networks. We have built a prototype system and performed experiments to demonstrate the advantages of the proposed system.

Two-state pattern-recognition handoffs for corner-turning situations

Handoff algorithms are used in wireless cellular systems to decide when and to which base station to handoff. Traditional handoff algorithms generally cannot keep both the average number of unnecessary handoffs and the handoff decision delay low. They do not exploit the relative constancy of path loss and shadow fading effects at any given location around a base station. However, handoff algorithms with both a negligible number of unnecessary handoffs and a negligible decision delay can be realized by exploiting this information. One example is the set of handoff algorithms using pattern-recognition introduced in previous work. In this paper, we describe how pattern-recognition handoff algorithms can be applied to the problem of turning a corner. This can be used as part of an integrated pattern-recognition handoff algorithm or together with a traditional handoff algorithm, in which case the pattern-recognition handles only the special cases like turning a corner.

A pattern recognition system for handoff algorithms

In wireless cellular systems, handoff algorithms decide when and to which base station to handoff. Traditional handoff algorithms generally cannot keep both the average number of unnecessary handoffs and the handoff decision delay low. They do not exploit the relative constancy of path loss and shadow fading effects at any given location around a base station. This information can in fact be used to improve the efficiency of handoff algorithms, as we do in our new handoff algorithms using statistical pattern recognition. Handoff algorithms with both a negligible number of unnecessary handoffs and a negligible decision delay can therefore be realized.

A movable safety zone scheme in urban fiber-optic microcellular systems

We consider an urban fiber-optic microcellular system in which a cigar-shaped cell consists of several microzones with their own antenna sites connected to a central station through optical fibers. To increase the efficiency of radio resources and reduce unnecessary handoffs between microzones, we propose a movable safety zone scheme. A safety zone is a virtually guarded area that does not permit cochannel interference. Outside the safety zone, cochannels can be reused. The safety zone can move under the condition that its user does not meet cochannel interference as he moves to an adjacent microzone. Considering user mobility characteristics in the cigar-shaped cell, we analyze and evaluate the proposed system in terms of intracell and intercell handoff rates, blocking probability, intracell call-dropping probability, and channel reuse parameter. The proposed system can handle a traffic capacity of about 12 Erlangs for seven traffic channels under a call blocking probability of 1% and generates a negligible number of intracell handoffs compared with those of intercell handoffs.

Improving idle handoff in CDMA mobile systems

In this letter, we have developed an efficient idle handoff technique, starting from field-test results obtained with the method used in present CDMA mobile phones, where the handoff is performed when a new pilot rises over the current one by a predefined constant. Unlike the conventional method, the proposed method decides the handoff based on a variable threshold, the value of which is automatically determined depending on the pilot strength received from the home base. It is shown that the proposed method reduces unnecessary idle handoffs and keeps the mobile tracking the pilot received with sufficient strength.

A model for analyzing handoff algorithms (cellular radio)

A model for analyzing the performance of handoff algorithms based on signal strength measurements made by mobile stations in a lognormal fading environment is presented. This model enables one to evaluate the effect of averaging the hysteresis on the handoff process. Handoffs are related to level crossings of the difference between the received signal strengths from two base stations. The algorithm performance is derived by modeling the level crossings as Poisson processes with time-varying rate functions. The model is seen to yield results that agree with simulations over the range of algorithm parameters of practical interest. These results can be used to determine the averaging interval and hysteresis level that achieve the optimum tradeoff between the number of unnecessary handoffs and the delay in handing off.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Cell Boundary Detection in the German Cellular Mobile Radio: System C

The efficiency of frequency utilization in mobile radio strongly depends on the performance of handoffs. Criteria for handoffs are usually derived from measured carrier-to-interference ratios (C/I). However, in mobile radio signal levels vary so rapidly that channel allocation cannot be performed in real time for optimum C/I. On the other hand, too many handoffs reduce frequency efficiency. The determination of cell boundaries, which are not only governed by C/I, but allocated to geographical lines in the terrain avoid unnecessary handoffs. In addition to C/I auxilary data are measured in the German system C and processed to detect the cell boundaries. The improvements gained from this procedure are demonstrated by measured results.