Digi-FH-OFDM: An all-digital wideband frequency-hopped OFDM system

Frequency-hopped spread-spectrum systems (FHSS) traditionally employ a super-heterodyne receiver architecture to perform frequency hopping in the passband. Such an architecture consists of analog blocks such as the mixer and the local oscillator that contribute greatly to the overall cost and hardware complexity of the system. The recent development of direct radio-frequency (RF) data converters has led to the possibility of having an all-digital receiver architecture where an RF signal is digitized directly to baseband, without the need to translate it to an intermediate frequency. Motivated by this, we propose an all-digital wideband frequency-hopped orthogonal frequency division multiplexing system which is abbreviated as Digi-FH-OFDM in this paper. The system performs two-stage frequency hopping — one in the wideband and the other in the baseband. The system architecture and the implementation details are presented. Real-time power spectra of the hopped signals in the wideband are obtained after transmitting them over the air via the RF data converters of the reconfigurable Xilinx Ultrascale ZCU111 RFSoC board and the Qorvo RF front end card. The bit error rate performance of the system is studied against eavesdropping and jamming attacks under a slow-fading channel and pilot-based channel estimation. The proposed Digi-FH-OFDM system outperforms the existing analog and partially digital FH-OFDM systems in terms of hardware complexity, robustness to eavesdropping and jamming, and the overall latency.