Performance Study of the Dynamic Threshold-Based Soft-Handoff Algorithms in CDMA System

Kang Won LEE
Kwang Ho KOOK

Publication
IEICE TRANSACTIONS on Communications   Vol.E86-B    No.1    pp.388-396
Publication Date: 2003/01/01
Online ISSN: 
DOI: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technology
Keyword: 
soft-handoff,  dynamic threshold,  CDMA system,  

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Summary: 
Traditional soft-handoff algorithms are based on the static threshold handoff algorithm recommended in the IS-95 standard. They are characterized by two parameters, an add threshold Tadd and a drop threshold Tdrop. These two parameters are assumed to have some constant values irrespective of the received signal strength of the pilot in the active set. To improve the performance of the soft-handoff, a dynamic threshold concept was proposed in previous work, where Tadd and Tdrop are dynamically determined according to the received signal strength of the pilot channel in the active set. In this study, previous work of the dynamic threshold algorithm is extended by including additional handoff criteria based on absolute signal strength and/or drop timer. Some functional forms with two new parameters, called boundary thresholds, and slope constant are proposed to dynamically determine Tadd and Tdrop. The dynamic threshold algorithms are compared with static ones in four different cases. Computer simulations show that the dynamic threshold algorithms outperform the static algorithms. We can see that the performance improvements differ from case to case. For example, when a pure dynamic threshold algorithm is compared with a pure static one (case 1), the decrease in the number of active set is about 13.7%. When the absolute threshold and the drop timer are also included in the handoff decision criteria (case 4), however, the decrease is only about 6.2%.