Subject: [NEXTEL-1] Rapp-A-Who? No, Rappaport- Now You Know-

From: [email-masked]
Date: Sun, 09 May 2004 10:47:16 -0400

Rapp-A-Who? No, Rappaport- Now You Know-

Getting In

 Robert K. Morrow Jr. & Theodore S. Rappaport
 Wireless Review, Mar 1, 2000

As cells become smaller and indoor wireless use increases, RF
penetration into buildings from outside sources has become
one of today's hottest issues. Will a nearby cell provide reliable
service throughout the entire office, or will the conference
room be a "dead zone?" On the other hand, will your indoor wireless PBX
be blown away by the co-channel user in the
building next door? The cost of in-building and microcell devices is
decreasing, and the workload for RF engineers and
technicians to install these on-premises systems soon will skyrocket.
Rapid engineering design and deployment will be vital for
cost-efficient build-out.

Thanks to new wireless engineering software, service providers can model
co-channel interference's effects on indoor systems
and find dead zones within the building that the outdoor macrocellular
system serves. Even before setting foot into the building,
you can assess the RF environment in a systematic, organized fashion by
plotting either signal strength or interference levels.
New programs use 3-D computer-aided design (CAD) renditions of buildings
or collections of buildings. These renditions show partitions and are
assigned appropriate RF attenuation values. For example, outside walls
may be assigned a 10dB loss.  Signals passing through thinner and more
RF-friendly interior walls may drop by 3dB, and windows may show a 2dB
RF penetration loss.

You can extract estimated partition loss values from extensive
in-building measurements. You can deduce these measurements
from field experience or you can measure the partition losses in the
actual building directly and optimize them with a software
program. Once the appropriate partition values are specified, you can
place any RF sources, either within or outside the
building, in a 3-D building database, and plot received-signal-strength
identification (RSSI) or C/I ratios directly onto the CAD
drawing. With the right software, you also can carry out
traffic-capacity analysis, frequency planning and
co-channel-interference analysis simultaneously within the propagation
model.

SIGNAL STRENGTH Will the macrocell located several miles north of the
office building provide sufficient signal strength for
indoor use in your customer's sixth-floor office? If you scale the CAD
drawing to include the macrocell at its actual distance,
the building itself will appear too small in the drawing to be useful.
Although site-planning programs offer a scaleable zoom-in
capability where actual macrocell maps may be represented in the 3-D
world, it is often more convenient to model the external
macrocell in a virtual location closer to the building. To do this, you
should use a standard path-loss propagation formula to calculate that
cell's lower transmitted power as if it were located just outside the
building's wall.

WHAT ABOUT INTERFERENCE? With wireless systems springing up almost
everywhere, interference, instead of simple signal strength, is the
dominant performance-limiting factor in many locations. Modeling
macrocell interference to an established or contemplated indoor wireless
system also is relatively straightforward.

Suppose, for example, that an indoor base station is assigned a
frequency set identical to an outdoor macrocell. Although the indoor
node may provide sufficient RSSI throughout its coverage area,
interference from the outside cell may render the indoor wireless system
unavailable in certain parts of the building.

Be careful, however, when modeling and analyzing interference, because
its detrimental effect also may depend on signal processing at the
receiver, not just raw signal levels. For example, a geographic area
could have similar AMPS and CDMA signal-strength levels in the 800MHz
band, but phones using either method may co-exist because their
respective demodulation processes reject interference that the undesired
cell provides. A proper C/I model in this situation examines AMPS
interference to the CDMA network by reducing the effective narrowband
signal strength by a factor related to the CDMA processing gain.

ANALYZING IN-BUILDING SIGNALS Analyzing in-building signal penetration
is critical. Will the existing outdoor
macrocell adequately supplement its coverage throughout the building? If
not, will other existing macrocells adequately
supplement its coverage, or must you add indoor picocells? Where should
you place these cells? If you are planning an indoor
wireless system that competes with signals from an outside macrocell,
how much interference can you expect, and where will it
occur within the building? As in-building wireless systems proliferate,
you must answer questions quickly and inexpensively in a
systematic and repeatable manner. You can address these issues by
modeling the situation with today's latest engineering programs and
examining the resulting RSSI or C/I contours.

http://industryclick.com/magazinearticle.asp?releaseid=2916&magazinearticleid=17473&siteid=3&magazineid=9

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