29-12-2012, 05:27 PM
Smart Antennas for Mobile Communications
Smart Antennas for Mobile Communications.pdf (Size: 243.36 KB / Downloads: 67)
I. Introduction
Wireless cellular networks are growing rapidly around
the world and this trend is likely to continue for several
years. The progress in radio technology enables new and
improved services. Current wireless services include transmission
of voice, fax and low-speed data. More bandwidthconsuming
interactive multimedia services like video-ondemand
and internet access will be supported in the future.
Wireless networks must provide these services in a
wide range of environments, spanning dense urban, suburban,
and rural areas. Varying mobility needs must also be
addressed. Wireless local loop networks serve xed subscribers.
micro-cellular networks serve pedestrians or slow
moving users, and macro-cellular networks serve high speed
vehicle-borne users. Several competing standards have
been developed for terrestrial networks. AMPS (advanced
mobile phone system) is an example of rst-generation frequency
division multiple access analog cellular system. Second
generation standards include GSM (Global System for
Mobile) and IS-136, using Time division multiple access
(TDMA), and IS-95 using code division multiple access
(CDMA). IMT-2000 is proposed to be the third generation
standard and will use either a wide-band CDMA or
TDMA technology.
Selection diversity
Selection diversity is one of the simplest form of diversity
combining. Given several branches with varying carrier-tonoise
ratios (C=N), selection diversity consists in choosing
the branch having the highest instantaneous C=N. The
performance improvement from selection diversity is evaluated
as follows: Let us suppose that M branches experience
independent fading but have the same mean C=N,
denoted by