A communications method is presented based on the backscatter modulation of incident radio frequency signals using low-complexity tags. The incident signals arise from digital television stations used as illuminators of opportunity. A receiver detects the tag using coherent processing algorithms similar to those used in passive radar, extending the detection range over published noncoherent techniques. This method enables shared use of the UHF television band for low-data-rate applications. While analyses suggest that rates exceeding 1 kbps might be achievable at 1 km range, experimental results demonstrate the challenges in designing and implementing such a system.
Dual port mach-zehnder modulator in fiber-optic transmission lines of radio frequency signals