Page 158 - Antennas for Base Stations in Wireless Communications

Advanced Antennas for Radio Base Stations 131

spatial filtering allows for tighter frequency reuse giving more channels
and higher capacity per sector. In a third-generation system, like
WCDMA, the improved spatial filtering allows more traffic per sector
and frequency.
Coverage solutions exist for uplink only, downlink only, as well as
for both up- and downlink. Extended downlink or transmit coverage is
obtained either by increased antenna gain or higher power amplifica-
tion or a combination thereof. The transmit coverage is characterized by
the Effective Isotropically Radiated Power (EIRP) of an antenna, deter-
mined by the relationship, EIRP = P · G, where G is the antenna gain
and P is the net power accepted by the antenna. The link budget is bal-
anced with low-noise amplifiers in the receive (uplink) chain. Examples
of coverage solutions are transmit diversity, high-gain antennas, higher
order receive diversity, remote radio units, amplifier integrated anten-
nas, and relays/repeaters. On downlink, increased EIRP, as provided by
transmit diversity, high-gain antennas, amplifier integrated antennas,
and relays/repeaters, gives increased signal strength at the user device.
On uplink, higher order receive diversity, tower-mounted amplifiers, and
high-gain antennas provide an increase in effective radio base station
receiver sensitivity by extracting additional signal energy using statisti-
cal diversity gains and effectively larger antenna apertures.

4.2 Advanced Antenna Technologies
The main principles and concepts of advanced antenna systems are
presented in terms of block diagrams and basic properties. Performance
figures given are based on first order models and assume mostly that all
base stations in the network are equal. The following advanced antenna
concepts for radio base stations, in addition to a three-sector reference
system, are described:

■ Three-sector omnidirectional antenna
■ Higher order receive diversity
■ Transmit diversity
■ Antenna beamtilt
■ Modular high-gain antenna
■ Higher order sectorization
■ Fixed multibeam array antenna
■ Steered beam array antenna
■ Amplifier integrated sector antenna
■ Amplifier integrated multibeam array antenna