Product Description

Product Description
22 (98) © Nokia Corporation Draft DN991444
Nokia Proprietary and Confidential Issue 3-0 en Draft
Multipath propagation of the radio signal may cause local variations of signal
strength. Deep fades, particularly when the mobile station is near a cell border,
reduce the quality of the received signal. To minimise this effect, a spatial or
polarisation receiver diversity can be used, which means that two different paths
are used for the received signals.
Antennas are placed physically apart or they employ different polarisation so that
correlation between received signals is minimised. It is probable that even if one
of the receiver branches suffers from a deep fading drop, the other receives a
signal of sufficient quality. The two separate paths are processed in the baseband
section of the BTS transceiver, and the pre-detection weighted summing method
is used to combine the signals of the two branches.
Diversity can be enabled or disabled from the BSC. When diversity is employed,
the BTS must be physically equipped according to the logical sector
configuration at the BSC.
3.2.2 Frequency hopping
The Nokia MetroSite EDGE Base Station supports synthesised (RF) frequency
hopping when there are at least two TRXs in the same sector.
The most significant property of frequency hopping is that it enables averaging of
the interference to RF signal between network users. Frequency hopping can be
used to minimise signal quality degradation caused by frequency selective fading,
especially for slow moving MSs and narrow band interfering signals.
Synthesised frequency hopping enables each TRX to change frequency on
successive time slots, so that a given carrier can hop at several frequencies in
quick succession.
It is possible to use either a cyclic or random frequency hopping scheme as
defined in GSM 05.02, 05.08 recommendations.
3.2.3 Antenna solution
The MetroSite antenna is a small and unobtrusive dual band antenna designed for
microcellular, building infill and roadside coverage. It is a directional two-port
antenna with two antenna elements in one casing. This means that two TRXs can
be connected to one antenna. The gain of the antenna is 6 dBi and it provides 130°
coverage.
Other directional, omnidirectional and cross-polarised antennas can also be used
with the Nokia MetroSite EDGE Base Station. Furthermore, distributed antenna
systems (DAS), which are primarily used for building fill-in coverage, can be
employed.