Coverage expansion and capacity improvement from soft handoff for CDMA cellular systems

Abstract

Previous research examining coverage expansion due to soft handoff in code division multiple access (CDMA) cellular networks did not address the relationship between the coverage expansion and the amount of carried traffic in the cell. In this paper, we first present a method to estimate reverse-link multicell coverage using a duration-outage approach. Using this, we then proceed to quantitatively analyze reverse-link coverage expansion from soft handoff as a function of the carried traffic in the cell under different propagation environments. Our results show that for modest values of carried traffic, the coverage expansion is almost constant. However, when the amount of carried traffic is large, the coverage expansion can increase dramatically. Next, we examine the dependence of the soft-handoff coverage expansion on key characteristics of the large-scale shadowing environment. Results are presented that quantify the coverage-expansion dependence on the large-scale shadowing's correlation distance (d/sub c/), variability (/spl sigma//sub Z/), path-loss exponent (K/sub 2/), and the correlation between the two-cell large-scale shadowing environments (C/sub Z/). The results indicate that realistic variations in these propagation conditions have a significant, and sometimes dramatic, effect on the coverage expansion provided by soft handoff. Finally, we analyze the capacity improvement from soft handoff and the tradeoff between capacity improvement versus coverage expansion. Understanding and managing the capacity improvement versus coverage expansion tradeoff is critical for achieving optimal CDMA cell-network performance.