Intelligent Antennas

Intelligent antenna systems are being introduced to commercial wireless
communication systems. The concepts and implementation for intelligent
antenna systems have been utilized in other industries for some time, primarily
the military.
Intelligent antenna systems can be configured for either receive only or
full duplex operations. The configuration of the intelligent antenna systems
can be arranged as either in an omni or sector cell site depending on the
application at hand.
With CDMA2000 and WCDMA the use of intelligent antenna systems
are supported directly, unlike 1G and 2G systems, with the use of auxiliary
and dedicated pilot channels.
Intelligent antennas were initially promoted as providing an increase to
the S/N of a sector by reducing the amount of N, noise and interference, and
possibly increasing the S, serving signal, in the same process. All the technologies
referenced are based on the principle that narrower radiation
beam patterns will provide increased gain and can be directed toward the
subscriber and at the same time offer less gain to interfering signals that
will arrive at an off axis angle due to the reduced beam width size.
Intelligent antennas are now promoted as not only being able to improve
the S/N of a sector or system but also more uniformly balance traffic
between sectors and cells and improve on the system performance through
reducing softhandoffs for IS-95 systems.

Figure 11-11 illustrates three types of intelligent antenna systems, each
has positive and negative attributes.
All the illustrations shown can be either receive only or full duplex. The
difference between the receive only and the full duplex systems involves
the amount of antennas and potential number of transmitting elements in
the cell site itself.
The beam switching antenna arrangement shown is the simplest to
implement. It normally involves four standard antennas of narrow azimuth
beam width, 30 degrees for a 120 degree sector, and based on the receive signal
received, the appropriate antenna will be selected by the base station
controller for use in the receive path.
The multiple beam array shown involves utilizing an antenna matrix to
accomplish the beam switching.
The beam steering array, however, utilizes phase shifting to direct the
beam toward the subscriber unit. However, the direction that is chosen by
the system for directing the beam will affect the entire sector. Normally
amplifiers for transmit and receive are located in conjunction with the
antenna itself. In addition the phase shifters are located directly behind
each antenna element. The objective of placing the electronics in the mast
head is to maximize the receive sensitivity and exploit the maximum transmit
power for the site. 452