TEAM FLY WIRELESS NETWORK DEPLOYMENTS phần 9 potx

General Packet Radio Service (GPRS) 205

Here, k is the propagation constant and is the total distance traveled

by the first and second rays from the diffraction point to the terminal. The

distance can be calculated in terms of the given geometry as follows

The diffraction angles is

The second diffraction ray, with angle gives the reflected path excess

path loss given by

Here is the reflection coefficient of the car rooftop surface. The total

distance from the diffraction point to the terminal is given by the

following equation

The diffraction angle for the second ray is

Representing the ratio of the received power levels of the two rays with

one can calculate the maximum fade depth in dB as

206 Chapter 10

The variation of the power level ratio and the maximum fade depth

is given in Figure 4 as a function of the receiver terminal height.

The time variation of the received signal level measured at the

intersection of Nevada / Platte Avenue, in Colorado Springs / Colorado, is

depicted in Figure 5. In this measurement, the transmitter antenna height

was 57 meters, and receiver antenna height was 3 meters. The maximum

fade depth within a 60 second test duration, was measured as 8 dB, yielding

perfect agreement with the analysis results.

General Packet Radio Service (GPRS) 207

4. GPRS DEPLOYMENT CONSIDERATIONS

Introduction

At the radio interface, GPRS must co-exist in a radio environment that is

polluted by other systems using the same or nearby radio frequency

resources. In particular, for the United States PCS band, these other radio

resources include both co-located and non co-located GPRS/GSM, TDMA

(IS-54), and CDMA (IS-95) base stations and mobiles. Interference from

these sources can result in performance degradation of the GPRS radio

receiver through such mechanisms as co-channel wideband phase noise and

modulated carrier power, reciprocal mixing, in-band intermodulation and

spurious products, and high level blocking of the receiver front end.

The GPRS system requirements specify the radio receiver performance,

given a maximum input interference power level, for co-channel, adjacent

channel, and intermodulation, and spurious products. This document is used

for the design of the radio receiver, but it is a practical matter to design the