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This paper presents a new approach of power control in
downlink direction of WCDMA system during soft handoff.
It also discusses and compares the shadowing and non-shadowing
cases. CDMA systems are interference limited systems, i.e.,
performance of CDMA system depends mainly on interference
reduction and this new approach, when compared to the earlier
approach, shows a significant reduction in interference.
The downlink capacity is increased to a good extent, and
hence improves the system performance in general.
Cellular radio system is designed in order to increase
the tele-traffic capacity in the service area. The demand
for the service is growing rapidly, and in heavily populated
areas, the service is reaching its limit. The trend is further
enhanced by the increasing penetration of hand-held portable
units into service. Code Division Multiple Access (CDMA)
is known for its high capacity in cellular (macro and micro)
radio systems. Especially, combining CDMA with macro-cells
may provide high capacity radio access to cellular systems.
CDMA system is an interference limited system in the sense
that the system capacity is determined by the amount of
interference it can tolerate. To reduce the interference
and achieve high capacity, the CDMA mobile cellular system
employs power control techniques (Viterbi et al., 1994;
and Jansen and Prasad, 1995). An important feature of CDMA
system is Soft Handoff (SHO). In SHO, the Mobile Station
(MS) starts communication with a new Base Station (BS) without
disconnecting from the old BS. The voice quality is improved
due to diversity provided by extra channel path at the cell
edge if compared with hard handoff. From the network point
of view, however, more resources are required to support
this procedure. As a crucial technology for seamless communication,
SHO has been investigated in literature since the emergence
of CDMA. Compared with conventional hard handoff (Zhang
and Holtzman, 1998; and Hong and Lu, 2001), it provides
a smoother transition and enhanced communication quality
by getting benefit from macro-diversity (Chedda, 1999).
Wideband Code Division Multiple Access (WCDMA) radio access
technology for 3G mobile communication systems is now offering
the transfer of high bit rate packet data needed for wireless
Internet access and video services. As mobility of mobile
terminal is handled by SHO procedure and interference can
be reduced by power control strategy, hence, spectral efficiency
in the CDMA based systems can be increased to a good extent
with the help of SHO and power control techniques (Holma
and Toskala, 2004). In the mobile cellular networks, power
control compensates the near-far problem so that an MS which
is near to the BS should not overshadow the signals coming
from an MS which is far away from BS. Power balancing is
needed extremely, so that the MS located nearer to BS should
not block the signal from a far away MS (William and Lee,
1989). In the uplink (UL) direction, SHO increases the capacity
and coverage, and reduces the call drop rate. In the downlink
(DL) direction, SHO gives some adverse effects. Diversity
gain obtained by MS in SHO increases the other-cell interference
(Viterbi et al., 1994; and Viterbi, 1995).
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