On Synchronization of Opportunistic Radio OFDM Systems

In this paper we present a study on pilot aided time and frequency synchronization for opportunistic radio (OR) OFDM systems which apply adaptive subcarrier allocation techniques to either avoid narrow band interference or to prevent licensed spectrum owners (so called primary users) from harmful disturbance. The variable subcarrier allocation of OR OFDM requires adaptive preamble designs to use state-of-the-art OFDM synchronization methods. Since these synchronization algorithms mainly require repetitive time-domain pilot structures, the novel task of providing repetitive pilot signals under arbitrary sub-carrier allocations is addressed in the paper. Furthermore we analyze the stochastic characteristics of the OR-OFDM carrier frequency offset synchronization procedure.