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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer - page 46 / 107





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signal component is present, such as a line­of­sight propagation path, the small­scale fading envelope is described by a Rician pdf [14]. In other words, the small­scale fading statistics are said to be Rayleigh whenever the line­of­sight path is blocked, and Rician otherwise.

In our channel model we will consider Rician fading distribution. The key parameter of this distribution is the K­factor, defined as the ratio of the direct component power and the scatter component power.

Doppler Spread:

In fixed wireless access, a doppler frequency shift is induced on the signal due to movement of the objects in the environment. Doppler spectrum of fixed wireless channel differs from that of mobile channel [12]. It is found that the doppler is in the 0.1­2 Hz frequency range for ixed wireless channel. The shape of the spectrum is also different than the classical Jake's spectrum for mobile channel.

Along with the above channel parameters, coherence distance, co­channel interference, antenna gain reduction factor should be addressed for channel modeling.

Having the primary requirements for our channel model, we have two options to go with. Either we can use mathematical model for each of them or we can choose an empirical model that care of the above requirements. We opted for the later one and chose the Stanford University Interim (SUI) channel model for our simulation.

4.3.1 Stanford University Interim (SUI) Channel Models

SUI channel models are an extension of the earlier work by AT&T Wireless and Erceg et al [14]. In this model a set of six channels was selected to address three different terrain types that are typical of the continental US [13]. This model can be used for simulations,


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