Multicarrier OFDM with Application to Adaptive Spectrum Utilization: A Design Study

As the demand for wireless spectrum exceeds regulatory allocation, there is a need to look at new ways to manage and utilize unused spectrum. One method is to use smart, or cognitive radios that are able to sense and utilize unused spectrum. As the bandwidth requirements for these adaptive radios increase, there is a need to aggregate the data over non-contiguous channels over a wide bandwidth. This requirement of both being adaptive and flexible proposes challenges to the design of the transmitter and receiver. These challenges are increased when the radios are used in a multi-user scenario where users are asynchronous to one another.

In this thesis we will propose solutions relating to the physical layer requirements of a wideband Adaptive Spectrum Aggregation & Management (ASAM) system for asynchronous users. Specifically an application using multiple-user OFDM between possibly supersonic aircraft and a ground terminal will be studied. The challenges of timing estimation, frequency offset correction, and channel equalization will be evaluated and solutions explored. The performance of various channelizing transmitting and receiving architectures will be evaluated and compared. Often the performance of a channelizer is limited to its prototype FIR filter, so optimization of efficient root-Nyquist and compensated FIR filters will be presented. At the conclusion, an end-to-end simulation will be presented to measure the performance of the multiple-user OFDM system.