English - Rohde & Schwarz

MOBILE RADIO
Coverage measurement systems
for UMTS connections (FIG 3). In these
cases, too, the incoming RF power at the
mobile phone is at first sufficient. It is,
however, partitioned into different paths
which, depending on the quality of the
mobile phone, provide a greater or lesser
number of signal components for transmission.
In the case of different signal
delays, the orthogonality of all codes
transmitted by a base station fades. This
causes all signals sent by the server station,
and in particular the signals of
other subscribers, to strongly interfere
with mobiles that have multipath reception.
This CDMA-specific effect, which
is not present in the case of FDMA and
TDMA, calls for careful analysis of the
multipath propagation when setting up
and optimizing UMTS networks.
PN scanners are superior
to UMTS test mobiles
Network operators face the challenge
of making full use of the improved features
of mobile radio coverage provided
by UMTS technology. As with GSM networks,
test mobiles are utilized with
UMTS to determine the coverage quality.
However, they cannot adequately
determine the causes for poor quality.
PN scanners are far better suited for
these tasks, because they have superior
characteristics compared to a terminal
and can keep track of the overall situation,
especially in difficult areas.
In contrast to UMTS mobile phones
that process only a few signals from
the strongest paths of one or two base
stations simultaneously, PN scanners
must be able to measure the pilot carriers
of any number of base stations in as
many paths as possible so that interference
such as pilot pollution, multipath
propagation and fading can be reliably
detected. This capability is provided in
FIG 2 The pilot pollution map shows how many base station pilot signals
within a channel exceed a power threshold value that is within a configurable
spacing below the pilot power of the best server.
FIG 3 Birth death fading, 3GPP-specified for mobile conformance tests,
generated by the Signal Generator R&S SMIQ and measured with the
R&S PN scanner. Two pseudo-randomly selected paths out of a total of 11
are active with the same signal power on an alternating basis.
News from Rohde&Schwarz
5
Number 176 (2002/IV)