Ở đây, k là công tác tuyên truyền liên tục và tổng khoảng cách đi du lịch bởi những tia nắng đầu tiên và thứ hai từ quan điểm nhiễu xạ thiết bị đầu cuối. Khoảng cách này có thể được tính toán về hình học nhất định như sau | 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 r d2 hb-h 2 2 The diffraction angles 0l is e tan -A - I d 3 The second diffraction 1 ay. with angle ớ2 gives the reflected path excess path loss siven by Here r is the reflection coefficient of the car rooftop surface. The total distance from the diffraction point to the terminal r2 is given by the following equation Tile diffraction ongle e 6 2 for the second ray is . -11 hh h 02 tan c I rtP 6 Representing the ratio of the received power levels of dhe two rays with A one can calculate the maximum fade depth in dB as 206 Chapter 10 max 10Log10 -Ỉ 11-A 7 The variation of the power level ratio A and the mranum fade depth is given in Fi re 4 as a function of the receiver terminal height. Till. 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 51 meters and receiver Mtenna 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 xesults. General Packet Radio Service GPRS 207 Figure 5. Colorado Springs Static Channel Time Variation Measurement 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 sa-tions and mobiles. Interference from these eotirces can result in peribrninnce degradation of the GPRS radio receiver through such mechanisms as co-channel wideband phase noise and modulated .
