Behavior of different protocol signals in a single system - RF Cafe
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Post subject: Behavior of different protocol signals in a single system
Posted: Sun Apr 15, 2007 12:48 pm
Joined: Sat Sep 18, 2004
I have a in-building antenna system where I have
threee different Wireless Providers. Two of the
providers are GSM based and the third is a CDMA
provider. The system is designed to provide a ubiquitous
-85 dBm or better coverage in the coverage area.
The power per carrier levels for each of the three
providers is +4 dBm for each RF carrier. When the
two GSM Providers came on the system at the said
power levels for eac of their RF carriers, the RSSI
measurements matched the design predictions. However,
for the CDMA Provider the RSSI levels in the coverage
area are atleast 10 dB or more lower than the GSM
levels. And note that all are coming into my antenna
system at the same power level per RF carrier. Also,
all operate in the same vicinity of the spectrum
(1900 MHz). With this strange behavior, while the
two GSM Providers are satisfied with the coverage
provided, I am unable to provide the same level
of coverage to the third provider.
Posted: Mon Apr 16, 2007 5:33 am
Joined: Fri Feb 17, 2006
Location: London UK
I guess you have done all the obvious things to
eliminate strange component behaviour, like frequency
sweep the combining/splitting system, the feeders
and the antenna with a VNA for S11 and S21 over
the entire band?
Also you need to check the vertical
pattern of the antenna and see if, at the CDMA frequency,
there is an excess up-tilt or down-tilt due to element
phasing. On the other hand, perhaps you are using
multiple distributed antennas around the building?
If nothing unusual comes from those investigations,
then my first thought is this problem is due to
unfortunate vector cancellation. If the average
level across many parts of the building is consistently
10dB below expectation, however, this is unlikely
to be the explanation. It would only present itself
in certain areas but not in others.
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