An FPGA-Based Implementation of a Multifunction Environment Sensing Device for Shared Access With Rotating Radars

To protect radar receivers and to facilitate shared access in radar bands, regulatory bodies have recommended the use of spectrum monitoring devices called environmental sensing capability (ESC). High-speed and low-cost ESC devices are required to process in real time the large amount of data (in-phase and quadrature samples) for the detection of radar signals and to differentiate them from secondary users (SUs) signals. In this paper, we present a field-programmable gate array (FPGA)-based design and implementation of a multifunction ESC device that can detect radar pulses and can also differentiate them from SU signals in microsecond time scales. The proposed ESC device performs the following tasks in parallel: 1) it detects and differentiates between radar and SU signals; 2) it measures received signal strength from SUs for radar protection; and 3) it also measures SUs' airtime utilization (ATU) in a channel, which can be used to perform load balancing (based on ATU) of SUs on different channels for efficient access. Detection of signals requires threshold setting. We present a novel minimum-based threshold setting technique, which is suitable for real-time operation of energy detectors. We implement a prototype of the proposed ESC device design on a Wireless Open-Access Research Platform node, which is equipped with a Xilinx FPGA. We evaluate the performance of the implemented device and show that with very high probability (close to 100%), it detects and differentiates between radar and SU signals. Moreover, it also accurately measures the ATU of SUs.