SDR System Design and Implementation on Delay-Doppler Communications and Sensing

Orthogonal time frequency space (OTFS) modulation has shown promising application perspectives, thanks to its strong delay and Doppler resilience. Furthermore, the delay-Doppler domain channel response directly reflects the physical attributes of channel scatterers, which provides fundamentally new perspectives for channel estimation (CE) and radar sensing. The success of OTFS has stimulated various CE and equalization algorithms with promising performance. However, only few of them were validated by hardware experiments. In this paper, we develop an OTFS communication and sensing (C&S) system using software defined radio (SDR), which invokes the off-grid target sensing and minimum mean square error (MMSE) channel equalization. In particular, we design and emulate the high-mobility wireless channel with multiple scatterers (sensing targets) and conduct the channel equalization with MMSE for data detection. Moreover, we study the influence of transceiver impairments, such as in-phase and quadrature (IQ) imbalance, DC offset, and carrier frequency offsets (CFO). With real-time experiments, the results show that the addition of scatterers engenders the distortion of the DD domain signals which curtail the BER performance of the communication system and further trims the MSE of sensing parameters with the increasing number of scatterers.