Install Manual

BRITECELL System Manual MN010-04 June 2003 Page 72 of 78
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reserve the right to vary any information quoted without prior notice.
65. APPENDIX A - Britecell system design basics
65.1. Indoor propagation
Radio signals from wireless mobile telephone systems are located in the high UHF
spectrum, between 800MHz and 2,2GHz, according to the common standards such
as ETACS, AMPS, GSM, DCS, PCS, UMTS, etc.. At such high frequencies
electromagnetic waves are subjected to phenomena like diffraction and reflection;
these effects become dominant in cellular systems where propagation rarely occurs
in free space.
In a cellular system a single radiation point is normally provided for each cell or
sector, located at the BTS site. This may not have line of sight to every user in the
coverage area.
The simultaneous occurrence of diffraction and multiple reflections (multipaths) in
the indoor environment makes this the most critical, as far as signal propagation
and coverage is concerned. The presence of natural or artificial openings and
obstructions (such as walls) leads to a mean loss term, which is normally higher
than the free space loss.
The point is easily reached in indoor environments where the radio link loss
exceeds the maximum loss, determined by the transmitter power and receiver
sensitivity, for acceptable communication quality. This can happen in a few spots
of a room, affecting uniform coverage, or in entire sections of the building.
A common issue is the need to provide sufficient signal level in all parts of a
structure to dominate the signal from a local external cell, ensuring that calls
originating within the building are set-up on the internal system. This can add a
considerable challenge to the in-building coverage design as very high signal levels
may be required close to external openings, such as doors and windows.
When supplying cellular coverage to indoor environments, in order to reach full
network performances, receive levels at both the BTS and mobile handset must be
kept uniformly high by keeping link loss as low as possible. This can be obtained
using Britecell.
When supplying coverage to indoor composite areas, the radiation points should
be planned to be in line of sight with the mobile so that the radio link loss can be
kept consistently low.
The location of the BTS is no longer determined by the required radiation point;
more practical BTS locations are thus feasible and the radiation point locations can
be optimised to suit the coverage area.
Deploying a Britecell system fulfils these criteria. By using fibre optic guided
propagation very low link losses can be achieved, allowing signals to be carried
long distances in the building without appreciable degradation. Specific areas can
be targeted to fit traffic distribution, regardless of obstructions or location; cell
planning is simplified with minimum or no changes in network parameters setting.
In addition, the use of Britecell can avoid the introduction of further BTS's, where
coverage is required but there are no requirements for more traffic channels. This
can achieve considerable savings in the cellular system rollout.