Page 201 - Integrated Wireless Propagation Models

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M a c r o c e I P r e d i c t i o n M o d e I s - P a r t 2 : P o i n t - t o - P o i n t M o d e I s 179

been used internally in Pactel and AirTouch markets. Some new algorithms and
enhancements for the Lee macrocell prediction model are discussed in this chapter.
The results are based on measurement data collected from all over the world to
prove that the Lee model is one of the most efficient and accurate macrocell predic­
tion models.
The Carey (Part 22) propagation modeP4 started in Chap. 2 is based on the perti­
nent sections of the U.S. FCC Rules and Regulations. This method is essentially a
simplified statistical method of estimating field strength and coverage based only on
a station's effective radiated power and height above average terrain. Many details
of terrain information have been ignored. Therefore, it can be used only for a gener­
ally for designing cellular systems. It cannot be used to design a realistic cellular
system in a specified area. The main use of this model is for license applications or
other submissions to the FCC that specifically require the use of the methods
described in Part 22 of the FCC Rules. The Carey model is also used for other admin­
istrative requirements, such as certain frequency coordination procedures.
The Bullington,35 Okumura,36 Lee/ and Longley-Rice32 models described both in
Chaps. 2 and 3 are more analytical and consider a number of other factors, such as indi­
vidual obstructions (either terrain or human-made), and terrain roughness. Okumura is
often used in urban environments and includes correction factors for various area
types, such as urban and suburban. Bullington considers individual obstructions and
computes losses, such as for terrain obstructions, and ridges. The Longley-Rice model
is a general model that considers radio horizons and various environmental condi­
tions. The Lee model has been enhanced with much drive test data and can deal
with more situations with more accuracy and is a better point-to-point prediction
model. In the past, the first author and his colleagues had used their hand calculation
on the 5 x 8 mile terrain contour maps from the Defense Map Agency to get the pre­
dicted signal strengths along mobile routes. Therefore, the basic Lee model is very simple
to use and has developed the ability to integrate measured data back to the model to
continue to improve its accuracy. The Lee model also can evolve from macrocell to
microcell, covering dense urban and in-buildings with an integrated solution.
To sum up, we can see that all the propagation models were developed based on
the requirement of deployed information, the available data, and the technology.
When the cellular network first started, the goal was to provide a large coverage,
and the focus was only on terrain contour. As capacity demand rises, especially in
urban areas, the human-made environment becomes more important. Once wireless
services become more popular, the dense urban microcell prediction models take
center stage. These models will be introduced in Chap. 4. Many old existing theories
that were prohibited before have now reinvented themselves; such as FDTD and ray
tracing. Then in-building coverage, such as intrabuilding and interbuilding pene­
tration from outdoor cells, becomes necessary. In-building models will be intro­
duced in Chap. 5. The macrocell models were developed very early, then microcell
and in-building (or picocell) models came out later. Table 3.5.1 shows a timetable of
the different models.
Although there are many different ways to implement these different models, the
basic principles do not change, and the fundamental challenges among them are still
the same. We need to collect measured data to fine-tune the models.