Aeronautical channel modeling
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The main purpose of this study was to develop a Matlab-based aeronautical channel simulator and subsequently test the performance of SISO, MIMO and MIMO-OFDM transceiver techniques on the developed simulator for various weather conditions. In many publications 'Aeronautical Channel' is usually a term that includes air-ground and air-air links, however, in this thesis we have assumed that, the 'Aeronautical Channel' refers to air-to-air links and we restrict ourselves to building a simulator for communication between two air-borne vehicles only. Thus we can define the aeronautical channel as the communication channel between two air-borne objects which are affected by environmental factors such as rain, clouds, temperature etc. and also by the effects of flying like Doppler shifts and height. This thesis is based on three core contributions. First, we surveyed and compared published aeronautical channel measurement results and theoretical analysis for various aeronautical channels, including air-ground channels, air-air channels, space-ground channels, and under various weather conditions. After weighing all the criteria for developing a mathematical model for an aeronautical channel, we concluded that the channel is Rician in nature due to a distinct and variable Line of Sight component and hence modeled it as a combination of a Rayleigh and a lognormal fading channel. While the Rayleigh component accounts for the multipath fading due to ground reflections and atmospheric scattering in the aeronautical channel and Doppler effects due to high velocities in air-planes, the lognormal fading takes into account the Line-of-Sight(LOS) component and the fluctuations due to weather conditions i.e. the long-term gradual variations in the mean level. Variables have been introduced to take into account various weather conditions like rain and clouds. We suggested parameters for this channel based on published measurement results and empirical data. Second, we developed a Matlab simulator to generate aeronautical channels for air-borne networks. An effort has been made to provide a standard independent aeronautical channel simulator that takes into account Doppler effects, multipath fading and slow-fading in the LOS component. This model can be used easily to simulate performance comparison in both discrete-time and discrete-frequency systems. Finally, we tested SISO (Single Input Single Output), MIMO (Multiple Input Multiple Output), MIMO-OFDM (Orthogonal frequency division multiplexing) transceiver techniques over the airborne channel simulator. We have used bit error rate(BER) curves over varying signal-to-noise ratios (SNR) as a performance metric to compare the three different techniques and have found that MIMO-OFDM performs better than both SISO and MIMO. Especially for high Rice factors and good weather conditions, MIMO-OFDM behaves almost like a Gaussian channel. The future scope of this study is immense since it can be extended to test the performance of many upcoming transceiver techniques and new STF (Space-Time-Frequency) coding methods for MIMO-OFDM, and the simulator can be easily modified to include more parameters from new aeronautical channel measurements that are published.