Large Scale Fading Essays

2010 Words Aug 9th, 2012 9 Pages
Large Scale Fading and
Channel modeling
Using Matlab

March 2012

Large scale fading and channel modeling

Using Matlab

The fading phenomenon can be broadly classified into two different types: large-scale fading and small-scale fading. Large-scale fading occurs as the mobile moves through a large distance, for example, a distance of the order of cell size . It is caused by path loss of signal as a function of distance and shadowing by large objects such as buildings, intervening terrains, and vegetation. Shadowing is a slow fading process characterized by variation of median path loss between the transmitter and receiver in fixed locations. In other words, large-scale fading is characterized by
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As illustrated in Figure 1.3, large-scale and small-scale margins must be set so as to maintain the outage rate within 1 2%, which means that the received signal power must be below the target design level with the probability of 0.02 or less . In this analysis, therefore, it is essential to characterize the probabilistic nature of shadowing as well as the path loss.

Large-Scale Fading

General Path Loss Models

The free-space propagation model is used for predicting the received signal strength in the line-of-sight (LOS) environment where there is no obstacle between the transmitter and receiver. It is often adopted for the satellite communication systems. Let d denote the distance in meters between the transmitter and receiver. When non-isotropic antennas are used with a transmit gain of Gt and a receive gain of Gr, the received power at distance d, Pr(d), is expressed by the well-known Friis equation, given as Pr(d) = PtGtGrλ2d2 L(4π)2 ………………………………(1.1) where Pt represents the transmit power (watts), is the wavelength of radiation (m), and L is the system loss factor which is independent of propagation environment. The system loss factor represents overall attenuation or loss in the actual system hardware, including transmission line, filter, and antennas. In general, L > 1, but L = 1 if we assume that there

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