Directional spectrum sensing using tunable multi-D space-time discrete filters

The potential use of multi-dimensional (MD) signal processing concepts and 1-D tunable bandpass filtering (BPF) for 2-D space-time (ST) spectrum sensing in a cognitive radio environment is proposed. The 2-D ST spectrum sensing allows the secondary users to search and detect white spaces along different spatial directions at a given time instance. This 2-D ST interrogation of the radio environment enables efficient sharing of primary frequency bands over multiple spatial directions in different instances of time. The use of frequency agile antennas is highlighted to mitigate interferences at known frequencies. Broadband/intermediate-frequency (IF) and analog/digital realizations of 2-D ST filters are proposed to perform the directional enhancement of signals. A low complexity highly-selective tunable 1-D digital BPF is proposed to be used with energy detection to perform spectral sensing along the required direction in space. The tunable BPF eliminates the need of computationally intensive high resolution FFT for frequency scanning. A prototype FPGA implementation of the BPF operating at 66 MHz is used to study the effect of finite precision arithmetic with a word length of 8 bits.