第三章 无线电波传播--大尺度衰落(2)

重庆交通大学计算机与信息学院通信工Baidu Nhomakorabea系
Log-normal Shadowing Models (3)

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Log-normal shadowing: The log-normal distribution describes the random shadowing effects which occur over a large number of measurement locations which have the same T-R separations,but have different levels of clutter on the propagation path(对数正态阴影:正态对数分布描述了一 种随机阴影效应,不同的地点,即使T-R距离一样,其路径损耗不 同). Log-normal shadowing implies that measured signal levels at a specific T-R separation have a Gaussian (normal) distribution about the distance-dependent mean of (对数正 态阴影模型表明具有相同T-R距离的测量信号水平是一种与 距离有关的对数正态分布,其均值为:)
Log-normal Shadowing Models (4)

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Practice Parameter n and can obtained from measured data, for example using linear recursive such that the difference between the measured and estimated path losses is minimized in a mean square error (MMSE) sense over a wide range of measurement locations and T-R separations.(参数n和标准差可以从测量数据中来,如使用线 性递归使测量值和估计值具有最小的均方误差得到.) PL(d0 ) is based on either close-in measurements or on a free space assumption from the transmitter to d0.

重庆交通大学计算机与信息学院通信工程系
Four
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received power measurements were taken at distances of 100m, 200m, 1000m, and 2 km from a transmitter. These measured values are given in the following table. It is assumed that the path loss for these measurements follows the model in the following equation:
重庆交通大学计算机与信息学院通信工程系
Distance 100m
200m
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1000m 2000m
from transmitter Received power 0dBm -20dBm -30dBm -60dBm
重庆交通大学计算机与信息学院通信工程系
d PL( d ) d0
n
重庆交通大学计算机与信息学院通信工程系
Log-distance Path Loss Model(2)
d PL(d ) ＝ PL(d0 ) 10n log d0
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Where n is the path loss exponent which indicates the rate at which the path loss increase with distance. n是路径损耗 指数,表明路径损耗随距离增长的速率. d is the T-R separation distance. d0 is the close-in reference distance , in reference distance which is determined from measurement close to the transmitter. D0是自由空间参考距离,在大覆盖蜂窝系统中,经 常使用1km的参考距离,而在微蜂窝中使用较小的距离(如 100m或1m,参考距离应永远在天线的远场处,以避免远近效应 对参考路径损耗的影响.
d PL(d )[ dB] P L (d 0 ) 10 n log d 0
重庆交通大学计算机与信息学院通信工程系
X
Where
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d0=100m: Find the minimum mean square error (MMSE) estimate for the path loss exponent, n; Calculate the standard deviation about the mean value; Estimate the received power at d=10km using the model presented above.
Outdoor Propagation Models (1)
Link
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重庆交通大学计算机与信息学院通信工程系
Link Budget Design using path loss models(运用路
径损耗模型进行实际链路预算设计)
Log-distance
Path Loss Model(对数距离路径损耗
模型) Log-normal Shadowing Model(对数正态阴影模型)
重庆交通大学计算机与信息学院通信工程系
Log-distance Path Loss Model(3)

Practice
d PL(d ) ＝ PL(d0 ) 10n log d0 n depends on the specific propagation environment, for example, in free space n=2, in urban area cellular radio, value n from 2.7 to 3.5. d0 =1km for large coverage cellular system d0 =100m or 1m for microcellular system
d Pt [dBm] -( PL(d 0 ) 10n log ＋X ) d0
Where
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random variable (in dB) with standard deviation
X is zero-mean Gaussian distributed
d PL(d ) ＝ PL(d0 ) 10n log d0

Measurement have shown that at any value of d, the path loss PL(d) at a particular location is random and distributed log-normally (normal in dB) about the mean distancedependent value.(测量表明,对任意一个d值,路径损耗是随机 的并呈正态分布.)
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d0 : close-in reference distance n : path loss exponent : standard deviation Computer modeling and simulation

重庆交通大学计算机与信息学院通信工程系

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Log-distance Path Loss Model does not consider fact that the surrounding environmental clutter may be vastly different at two different locations having the same T-R separations. This leads to measured signals which are vastly different than the average value predicated by (对数 路径损耗模型没有考虑到事实上的无线环境当T-R相距相同 的任意两个方向其测量信号强度并不一样.)
d PL(d ) ＝ PL(d 0 ) 10n log d0
重庆交通大学计算机与信息学院通信工程系
Log-normal Shadowing Models (4)
Pr (d )[dBm] ＝Pt [dBm] -PL (d )[dB] d Pt [dBm] -( PL(d 0 ) 10n log ＋X ) d0 d (Pt [dBm] - PL(d 0 )-10n log )-X d0
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重庆交通大学计算机与信息学院通信工程系
Log-distance Path Loss Model (1)
Average
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received signal power decreases logarithmically with distance,whether in indoor or outdoor radio channel. (接收信号平均功率随距离 的增加而呈对数下降趋势,不管是在室内还是室外无 线环境) The average large-scale path loss for an arbitrary T-R separation is expressed as a function of distance d by using a path loss exponent n. (T-R之 间的平均大尺度损耗与距离的n次冥成正比.)
Chapter 3 Mobile Radio Propagation: Large-Scale Path Loss (2)
Content
Budget Design (1) using path loss models(运 用路径损耗模型进行实际链路预算设计) Outdoor Propagation Models(户外传播模型) Indoor Propagation Models(室内传播模型) Link Budget Design Examples
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d0 d f
2D2

重庆交通大学计算机与信息学院通信工程系
Typical large-scale path loss
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重庆交通大学计算机与信息学院通信工程系
Log-normal Shadowing Models 对数正态阴影模型
重庆交通大学计算机与信息学院通信工程系
Log-normal Shadowing Models (2)
PL(d )[dB] ＝ PL(d )＋X d PL(d 0 ) 10n log ＋X d0 Pr (d )[dBm] ＝Pt [dBm] -PL (d )[dB]