UC San Diego

The use of wireless communications is increasing and will continue growing, not only for personal communications but also for machine-to-machine applications. Therefore, the use of physical resources for wireless communications, i.e., time and frequency, need to be optimized to maximize the communication link efficiency and to reduce the "cost" of moving bits over the air. The joint use of ultra wideband (UWB) and cognitive radio (CR) has been identified as a solution to maximize the use of physical resources for wireless communications and to minimize the cost associated with its transfer. UWB and CR, in conjunction with software defined radio receivers, open up a whole new spectrum of possibilities to re-think the design and implementation of wireless communications. In that sense, the setting of the system parameters can become less rigid and can attempt to adapt to different scenarios with the goal to maximize the communication link efficiency. This dissertation presents a study on how to realize a cognitive Orthogonal Frequency Division Multiplexing (OFDM) wireless system with the goal of maximizing the utilization of physical resources. We first parameterize the OFDM system to a limited set of degrees of freedom, and then we identify the performance of a non- ideal OFDM system. The non-idealities that we consider are imperfections at the receiver, such as timing errors, residual frequency error and imperfect channel estimation, as well as channel perturbations such as inter-symbol interference (ISI) from a channel delay spread larger than the cyclic prefix (CP) or Doppler stemming from the motion of the transmitter and/or receiver. th the parameterization of the OFDM system and the performance characterization as a function of different parameters, we present how the cognitive OFDM receiver will select the set of parameters that maximize the communication link efficiency. These parameters are the position, at the receiver, of the DFT window, the pilot structure, the CP duration, and the OFDM symbol duration.