Lecture 4 (Part C) – Radio Channel Characteristics-Empirical Models

Prof. Zhanyang Zhang

Remarks:

• The Radio Link Range equations so far we studied is to provide a means for prediction path loss for a particular application environment (such as Free Space or Two Ray models). It is useful to start a system design for initial system layout. But is very limited in its applications in real world environments (such as, urban and complex landscapes).

• In most cases, the complexity of the environments and the numbers of signal paths make it extreme difficult if not impossible to relay on solely on these analytical models to predict or approximate the signal propagation patterns. In the wireless industry, the most widely used propagation models are derived from measured data which include the effects of terrain profile and some general characteristics of land use (builds and constructions).

4.1 The Okumura Model

One of the most successful early models for the urban land mobile propagation environment was proposed by Okumura which provides a extensive measurement taken in Tokyo. This model has provides better measurement for these conditions:

• Range span: 1 to 100 km

• Frequency range: 100 to 1920 MHz

• Accurate to around: 10 dB to 14 dB

Okumura model is a pure statistical measurement model. It is difficult to incorporate into computer based design tools as a set of algorithms. Hata model is an analytical model that gives formulas as approximations to Okumura’s curves, so that it can be suited for computer implementation.

The Hata model is application over the following range of parameters:

• f0: 1.50 to 1500 mHz • ht: 30 to 200 m • hr: 1 to 10 m

• d: 1 to 20 km

Eg. 4.4

A base station in a mid-size city transmits from an antenna height of 30 m to a receiver 10 km away. The receiver antenna height is 2m, and the carrier frequency is 850 mHz . Given a(hr)=1.27 dB, using the Hata model to determine the median path loss. Then compare it to the to the path loss obtained by the two-ray model.

4.2 The Lee Model

The Lee model is based upon extensive measurements made on the Philadelphia, Camden, Newark, Denville and Whippany areas by members of Bell Labs in 1970’s. This model provides a method for calculation path loss for a specified set of “standard” conditions:

• Transmitter power: 40 dBm • Base station antenna heights: 100 ft • Transmitting antenna gain: 6 dB

• Receiving antenna gain: 0 dB • Receiving antenna height: 10 ft

• Carrier frequency: 850 mHz