1.2.3.2 Adaptive Array
From [11], it is reported that it is possible to achieve
greater performance improvements than that obtained using the SBA system. This
can be accomplished by increasing the complexity of the array signal processing
to form the Adaptive Antenna Systems, which is considered to be the most
advance smart antenna approach to date.
The adaptive antenna systems approach communication between a
user and the base station in a different way, in effect adding a dimension in
space. By adapting to the RF
environment as it changes, adaptive antenna technology can
dynamically modify the signal patterns to near infinity to optimize the
performance of the wireless system.
Adaptive arrays continuously differentiate between the desired
signals, multipath, and interfering signals as well as calculate their
directions of arrival by utilizing sophisticated signal-processing algorithms.
The technique constantly updates its transmitting approach based on changes in
both the desired and interfering signal locations. It ensures that signal links
are maximized by tracking and providing users with main lobes and interferers
with nulls, because there are neither micro sectors nor predefined patterns
[12].
Although both systems seek to increase gain with respect to
the location of the users, however, only the adaptive system is able to
contribute optimal gain while simultaneously identifying, tracking, and
minimizing interfering signals. This can be seen from Fig 1.6 that only the
main lobe is directed towards the user while a null being directed at a co
channel interferer. Illustrated in Fig (1.7) is the network structure of an
adaptive array.
Fig
1.6: An adaptive antenna [11].
Fig
1.7: Network structure of an adaptive array [11].
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