Page 128 - DCAP307_PLANNING_AND_MANAGING_IT_INFRASTRUCTURE

Planning and Managing IT Infrastructure

Notes 2G systems: These second-generation systems are digital, and use either TDMA (Time
Division Multiple Access) or CDMA (Code Division Multiple Access) access methods. The
European GSM (Global System for Mobile communications) is a 2G digital system with its
own TDMA access methods. The 2G digital services began appearing in the late 1980s,
providing expanded capacity and unique services such as caller ID, call forwarding, and
short messaging. A critical feature was seamless roaming, which lets subscribers move
across provider boundaries.
3G systems: 3G has become an umbrella term to describe cellular data communications
with a target data rate of 2 Mbits/sec. The ITU originally attempted to define 3G in its IMT-
2000 (International Mobile Communications-2000) specification, which specified global
wireless frequency ranges, data rates, and availability dates. However, a global standard
was difficult to implement due to different frequency allocations around the world and
conflicting input. So, three operating modes were specified. According to Nokia, a 3G
device will be a personal, mobile, multimedia communications device that supports speech,
colour pictures, and video, and various kinds of information content. There is some doubt
that 3G systems will ever be able to deliver the bandwidth to support these features
because bandwidth is shared. However, 3G systems will certainly support more phone
calls per cell.
4G Systems: On the horizon are 4G systems that may become available even before 3G
matures (3G is a confusing mix of standards). While 3G is important in boosting the
number of wireless calls, 4G will offer true high-speed data services. 4G data rates will be
in the 2-Mbit/sec to 156-Mbit/sec range, and possibly higher. 4G will also fully support
IP. High data rates are due to advances in signal processors, new modulation techniques,
and smart antennas that can focus signals directly at users. OFDM (orthogonal frequency
division multiplexing) is one scheme that can provide very high wireless data rates.
The move to digital technologies opened up the wireless world. It improved capacity, reduced
equipment costs, and allowed for the addition of new features. Reduced handset costs meant
more people were vying for services and taxing systems.

Did u know? 3G systems add more capacity. In addition, packet technologies were
developed that use bandwidth more efficiently.
When digital cellular services were being designed in the early 1980s, the choice was to design
a system that was backward compatible with existing analog systems (and used the same
frequency allocation) or to design a whole new system. The European community had about
seven incompatible analog services, so it created the GSM system from scratch to operate in the
900-MHz range (and later in the 1,800 MHz range).

Self Assessment

Fill in the blanks:

4. ..................................... were initially designed for mobile terminals inside vehicles with
antennas mounted on the vehicle roof.
5. “Mobile” wireless technologies provide voice and data ..................................... services to
mobile users who use cell phones, PDAs, etc.
6. The ..................................... system is a circuit-oriented communication system that operates
in the 824 MHz to 894 MHz frequency range.

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