Page 283 - Integrated Wireless Propagation Models

CHAPTER 5

In-Building P icocell)
(

Prediction Models

5.1 I n troduction

5.1 . 1 Differences from Other Models
The principal characteristics of an indoor RF propagation environment that distinguish
it from an outdoor environment are that the multipath is usually severe, a line-of-sight
(LOS) path may not exist, and the characteristics of the environment can change drasti­
1
cally over a very short time or distance. The ranges involved tend to be rather short, on
the order of 100 m or less. Walls, doors, furniture, and people can cause significant
signal loss. Indoor path loss can change dramatically with either time or position
because of the amount of multipath present and the movement of people, equipment,
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and/ or doors. As discussed in the previous chapter, multiple reflections can produce
signal smearing (delay spread) and may cause signal fading.
Propagation prediction for indoor radio systems has some unique considerations,
requirements, and challenges. As we have mentioned earlier, the in-building prediction
has become more and more crucial to the performance of many wireless systems, espe­
cially as WLAN, WiMax, 3G, and 4G become more and more popular. There are several
ways of implementing an in-building prediction model. From the empirical model
based on the earlier measurement data, we include building layout to characterize
the radio behavior in a specific building. With more building data available and the
improvement of computer speed, site-specific propagation models can be created,
including building materials of walls, ceilings, and partitions into its calculation. Some
radio propagation theories can now be applied to calculate the propagation for inside
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and outside buildings.3- 6 For example, ray tracing combined with GTD/UTD, FDTD,
and TLM models can all be used to predict the coverage of in-building systems. The
ray-tracing technique will be described in Sec. 5.6 1 . Once the required coverage is
.
defined, all-critical parameters can be used to make a suitable prediction for the signal
coverage. Furthermore, taking some specific parameters due to a particular area under
test into the model so that the deduction of interference, the capacity, the system perfor­
mance, and handoffs can be optimized.
The ultimate purposes, just as when dealing with outdoor systems, are to ensure suf­
ficient signal coverage in a required area (or to ensure a reliable path in the point-to-point
systems) and to avoid interference both within its own system and to other systems.

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