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Simulation of NLOS WiMAX-IEEE 802.16e Physical Layer Using MIMO Doppler Channel Model with Imposed Comb Pilots

WiMAX being the first standard based on OFDM/OFDMA and MIMO technologies with extensive IP capabilities. Here in this paper we have attempted to simulate the physical layer that takes into consideration vehicular mobility associated and time based changing effects for a typical WiMAX IEEE 802.16e-2005 channel-environment. In the first phase, we have mainly considered the NLOS WiMAX link and then developed a channel model that incorporates Doppler effect and simulated the whole link. The results of the simulations depicts that effects of doppler being not very serious for single carrier transmissions, however, during multi-carrier transmissions the effect are serious and requires more rigorous modeling especially with MIMO and study to estimate the channel response. The mentioned channel effects, perturb the orthogonality (amongst the carriers) as the sub-carriers being very close to each other. While, in the second phase of our study, issues related to estimation at the receiver end (processing) have been dealt with vis-à-vis, fast fading and frequency selective effects (due to vehicular mobility) in frequency domain, frequency domain power spectrum estimation methods (most changes are observed in frequency domain). To estimate a time varying, MIMO Doppler channel using spectrum estimation methods, a imposed pilot pattern is used as this consumes minimum spectrum and lesser power though it differs from the standard. Through this simulation study, channel estimation issues are investigated, discussed and presented.