Video services are becoming an integral part of future
communication systems. Especially for the upcoming 3G-CDMA system wireless
networks such as UMTS, video may very well turn out to be the key value
addition that achieves the required return of investment. While previous
generations of wireless communication systems were primarily designed and used
for voice services, next generation systems have to support a broad range of
applications in a wide variety of settings. The early market stages were characterized
by the needs of early adopters, mostly for professional use. As the market
matures from the early adopters to normal users, new services will be demanded.
These demands will likely converge toward the demands that exist for wired
telecommunications services.
Market research finds that mobile commerce for 3G wireless
systems and beyond will be dominated by basic human communication such as
messaging, voice, and video communication. Because of its typically large
bandwidth requirements, video communication (as opposed to the lower rate voice
and the elastic e-mail) is expected to emerge as the dominant type of service
in 3G/4G wireless systems. Video services obth real-time services and streaming
services are gaining a lot of importance and applications in CDMA systems.
Introduction to CDMA:
CDMA is a form of
Direct Sequence Spread Spectrum communications. In general, Spread Spectrum
communications is distinguished by three key elements:
1. The signal
occupies a bandwidth much greater than that which is necessary to send the
information. This results in many benefits, such as immunity to interference
and jamming and multi-user access, which we’ll discuss later on.
2. The bandwidth is
spread by means of a code which is independent of the data. The independence of the code distinguishes
this from standard modulation schemes in which the data modulation will always
spread the spectrum somewhat.
3.The receiver
synchronizes to the code to recover the data. The use of an independent code
and synchronous reception allows multiple users to access the same frequency
band at the same time.
In order to protect
the signal, the code used is pseudo-random. It appears random, but is actually
deterministic, so that the receiver can reconstruct the code for synchronous detection.
This pseudo-random code is also called pseudo-noise (PN).
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