Spectrum Shaping to Avoid OFDM Interference to In-Band Radars in the U-NII Bands

Interference avoidance will be an essential feature of wireless communication systems in the future. Interference avoidance to narrowband users is particularly difficult with Orthogonal Frequency Division Multiplexing (OFDM) due to the side lobes of the subcarriers. Spectrum-nulling algorithms based on cancellation signals have been studied in the literature. In this letter, we describe a general technique to design spectrum nulls for arbitrary signal and canceler bases. Appropriately chosen nonorthogonal canceler bases can result in data rate- and energy-efficient design of spectrum nulls. We also describe an iterative algorithm to cancel the resulting inter-carrier interference at the receiver. Spectrum nulls that meet requirements for avoiding interference to weather radars in the 5 GHz band can be designed using this technique. Bit error rates have been evaluated using simulations.