The challenge for wireless communications
As the demand grows for communication services,
wireless solutions are becoming increasingly important.
Wireless can offer high-bandwidth service provision
without reliance on fixed infrastructure and represents a
solution to the ‘last mile’ problem, i.e. delivery directly to
a customer’s premises, while in many scenarios wireless
may represent the only viable delivery mechanism.
Wireless is also essential for mobile services, and cellular
networks (e.g. 2nd generation mobile) are now
operational worldwide. Fixed wireless access (FWA)
schemes are also becoming established to provide
telephony and data services to both business and home
users.
The emerging market is for broadband data provision
for multimedia, which represents a convergence of highspeed
Internet (and e-mail), telephony, TV, video-ondemand,
sound broadcasting etc. Broadband fixed
wireless access (B-FWA) schemes aim to deliver a range
of multimedia services to the customer at data rates of
typically at least 2 Mbit/s. B-FWA should offer greater
capacity to the user than services based on existing
wirelines, such as ISDN or xDSL, which are in any event
unlikely to be available to all customers. The alternative
would be cable or fibre delivery, but such installation may
be prohibitively expensive in many scenarios, and this
may represent a barrier to new service providers. B-FWA
is likely to be targeted initially at business, including SME
(small–medium enterprise) and SOHO (small office/
home office) users, although the market is anticipated to
extend rapidly to domestic customers.
However delivering high-capacity services by wireless
also presents a challenge, especially as the radio
spectrum is a limited resource subject to increasing
pressure as demand grows. To provide bandwidth to a
large number of users, some form of frequency reuse
strategy must be adopted, usually based around a fixed
cellular structure. Fig. 1a illustrates the cellular concept,
where each hexagon represents a cell having a basestation
near its centre and employing a different
frequency or group of frequencies represented by the
colour. These frequencies are reused only at a distance,
the reuse distance being a function of many factors,
including the local propagation environment and the
acceptable signal-to-interference-plus-noise ratio.
To provide increased capacity, the cell sizes may be
reduced, thus allowing the spectrum to be reused more
often within a given geographical area, as illustrated in
Fig. 1b. This philosophy leads to the concept of microcells
for areas of high user density, with a base-station on
perhaps every street corner. Indeed, taking the concept to
its extreme limit, one might envisage one cell per user, the
evident price in either case being the cost and
environmental impact of a plethora of base-station
antennas, together with the task of providing the backhaul
links to serve them, by fibre or other wireless means, and
the cost of installation.
Pressure on the radio spectrum also leads to a move
towards higher frequency bands, which are less heavily
congested and can provide significant bandwidth. The
main allocations for broadband are in the 28GHz band
(26GHz in some regions), as well as at 38GHz1. Existing
broadband schemes may be variously described as LMDS
(Local Multipoint Distribution Services) or MVDS
(Multipoint Video Distribution Services)2,3


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