Abstract
For cellular communication systems, mobility and limited radio coverage of a cell require calls to be handed over from one Base Station System (BSS) to another. Due to the limited band width available in various cells, there is a finite probability that an ongoing call, while being handed off, may get dropped. Minimizing the dropping of ongoing calls during hand off is an important design criterion. Some digital cellular systems, e.g., the Global System for Mobile Communications and the IS-136, use Mobile-Assisted Hand off (MAHO), in which a Mobile Terminal (MT) assists, it's BSS and a mobiles witching center in making hand off decisions. MAHO requires an MT to regularly report, back to its serving BSS, its current radio-link state (defined in terms of the Received Signal Strength Indicator (RSSI) and the Bit Error Rate (BER)) of transmissions received from neighboring BSSs. In the proposed technique, the MT reports back not only the RSSI and the BER but the number of free channels that are available for the hand off traffic as well. This will ensure that a handed-off call has acceptable signal quality as well as a free available channel. The performance of this hand off technique is analyzed using an analytical model whose solution gives the desired performance measures in terms of blocking and dropping probabilities.
Highlights
Handoff is an important aspect of cellular and mobile communication
Pilot SINR measurements of all the pilots in the neighbor list of an IS-95 CDMA system were obtained using standard drive test techniques for a suburban morphology
We presented a semi analytical model to study the performance degradation of soft and hard handoff schemes in a downlink CDMA system due to delay in the completion of handoff decisions
Summary
A Mobile Terminal (MT) has a radio link to a Base Station System (BSS) that provides “best service” to the MTs that are currently located within a cell. A cell’s BSS provides a radio link to each MT that is active in this cell. One or more BSSs are, Interns, under the control of a Mobiles witching Center (MSC). Aside from other functions, an MSC has the primary responsibility of managing mobility. If and when an MT moves, it is quite possible that the currently serving BSS may no longer be able to provide reasonable quality of service as compared to some other BSS. Rather than dropping the service to this MT, the currently serving MSC may decide to hand over this service to some other better serving BSS or, in some cases, to another MSC. Several different hand-off techniques have been proposed and implemented
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