Soft
Handoff (SHO) is used in cellular Code Division Multiple
Access (CDMA) systems. One possible method for improving
the performance of conventional soft handoff is to adapt
the soft handoff thresholds. In this paper, the performance
of the soft handoff algorithm in CDMA systems using
fuzzy logic is analyzed, and a new procedure is proposed.
The proposed algorithm is compared with IS-95A and IS-95B
SHOs. The proposed algorithm has two aims: to decrease
the thresholds at low traffic loads so that high quality
of traffic channel can be assured, and to increase the
thresholds at high traffic loads so as to release the
traffic channel for supporting more carried traffic.
Analysis of the results shows that the proposed algorithm
has better performance in terms of outage probability,
blocking probability and Eb/I0 ratio,
when compared to IS-95A and IS-95B SHO algorithms.
Soft
Handoff (SHO) is used in cellular Code Division Multiple
Access (CDMA) whereby Mobile Stations (MSs) near the
cell boundary communicate the same transmitted signals
to more than one Base Station (BS) within their vicinity.
The handoff process in SHO algorithms starts at the
threshold value of the parameters. These SHO threshold
parameters can be fixed or adjusted dynamically (Hwang
et al., 1997; and Wong and Lim, 1997). The fixed
thresholds perform poorly compared to the dynamically
adjusted threshold handoff algorithm. At increased thresholds
and high traffic loads, the performance of the SHO algorithm
increases in order to release the traffic channel so
that it can support more carried traffic. On the other
hand, at decreased thresholds and low traffic loads,
the performance of SHO decreases in order to provide
high quality of traffic channel (Chheda, 1999).
The
performance of the SHO algorithm also depends upon a
number of input parameters such as the number of remaining
channels at each BS, and the number of active pilots
in the active set of each mobile. The output of the
SHO algorithm is the adjusted threshold value. Chheda
(1999) analyzed the performance of IS-95A and IS-95B/cdma2000
SHO algorithm, based on this adjusted value of the threshold
parameter. The performance of IS-95A and IS-95B/cdma2000
SHO at high traffic loads and lower SHO threshold for
an acceptable quality traffic channel was also reported
for a wider SHO threshold value of algorithm. |
