Subject: [NEXTEL-1] TM A Smiths Group Company On 800Mhz Interference-

From: [email-masked]
Date: Thu, 17 Jul 2003 15:33:14 -0400

A Smiths Group Company

12503 E. Euclid Drive, Suite 10
Englewood, CO 80111 USA
Phone: (303) 768-8080; FAX: (303) 768-8181

TM A Smiths Group Company

Referring to Docket 02-55,

It is well known that there is interference in the 800 MHz public safety bands
resulting from ESMR (mainly Nextel) and other CMRS providers. Summitek has a product that
can provide an objective evaluation of the level of threat at a location. This is
achieved by first characterizing the local RF environment using the Summitek OASIS II product,
and then evaluating the impact on the public safety radio by using a mathematical
model of the receiver.  The ITU-R SM.1009-1 model looks promising for this purpose, but
would have to be adapted to model public safety receivers. Assuming the availability of
a mathematical model for the public safety receivers of interest, Summitek is
prepared to modify their existing solution to incorporate this model.  The end result is a
test instrument that can be taken to a spot, measure the RF emissions present at that
spot and then, using the mathematical receiver model, quantify the potential for
harmful interference.

There are three primary interference threats to public safety radio:

1.  Out-of-band-emissions. These are emissions from nearby active channels that
exceed the FCC mandated limits.

2.  ESMR to ESMR IM Interference generated in the front end of the receiver.

3.  ESMR to A-Block Cellular IM Interference generated in the front end of the
receiver.

The Summitek solution addresses all three threats.

To evaluate the potential for IM related interference, the basic analysis proceeds
as
follows.

1.  Using a calibrated antenna and a spectrum analyzer, measure the level of RF
emissions at the site over an operator selected frequency range, but typically 851

to 894 MHz. This would be done over an operator specified period of time and the
data (amplitude vs. frequency vs. time vs. location) would be stored. In cases
where the ESMR downlink is on all of the time, it can be characterized very
quickly. Since the data is archived, a history of the emissions can be replayed at

any later time to observe events of interest. There are a variety of ways this
data
can be evaluated and/or plotted depending upon the need.

2.  This data is then entered into the model of the radio to determine what
channels
might experience interference. This channel set is determined on the basis of
frequency and power. That is, if a combination of 2 or 3 active channels can
create an IM product on a channel of interest, it will be considered a possible
threat. The output is a list of IM Power vs. Frequency for all possible 2 and 3
carrier combinations that can impact a channel(s) of interest.

3.  In order to calculate a C/I for a given channel of concern, at some point
during the
measurement, the public safety channel(s) of concern will have to be keyed up to
produce a reference signal at the spot being evaluated. Since the data can be
filtered for maximum power received during the data-logging period, this level
can be rapidly identified. It is even possible to compare signal levels at
different
times to identify fluctuations caused by fading and other propagation affects, if
the data is monitored for a longer period of time then the minimum time necessary
to characterize the ESMR signal levels.

4.  Knowing the IM levels that can be generated on a channel of concern and the RF

levels received when these channels are active, the Summitek solution can
calculate the C/I that can be expected at that spot and highlight channels where
public safety communication is likely to fail.

5.  With the ESMR signal levels and frequencies known from measurement, it is then

possible to determine and report what frequencies and power levels generated by
an A-Block cellular provider could also generate channel blocking interference in
the public safety receiver ? even if the A-Block power level was not characterized

during the monitoring process.

Evaluating the potential threat of Out of Band Emissions (OOBE) proceeds as
follows.

1.  The same data measured and archived for the IM analysis is used for OOBE
analysis, so it is not necessary to take two different acquisitions.

2.  This data is then used to build an emission mask for that location. The mask
creates an emission envelope based on mandated emission levels intended to
prevent adjacent channel interference.

3.  The measured data is then checked for compliance to the standard.
Non-compliant
conditions are flagged. Since the data is logged, it can be readily replayed to
observe the offending emissions as if you were there during the event.

4.  Using the reference signal level generated in step 3 above, it is also
possible to
calculate C/I for this OOBE condition and determine if it will have an
unacceptable impact on the public safety communication channel.
All of the measurement and logging of data necessary for this analysis already
exists in
the Summitek product. Therefore, by incorporating a mathematical model of the
public
safety receivers, Summitek is prepared to provide the integrated solution to
evaluate the
magnitude of the problem in an objective way using real world measurements.

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