A Simplified OTFS Technique to Enhance the Radcom V2X System in the High Doppler Channel Scenario

This paper addresses the vehicle-to-everything (V2X) Radar-Communication (Radcom) issue in a high-mobility channel, a phenomenon which is commonly referred to as high-Doppler channel estimation. In higher Doppler channels, the characteristics of the channel change with great rapidity, resulting in a reduction in the coherence time of the channel. The coherence time is inversely proportional to the variability of the channel coefficient. In the context of V2X detection and communications, the transmitter radar transmits a signal to the receiver, which is reflected multiple times before reaching the receiver. The high-Doppler multi-path shift phenomenon is a consequence of the vehicle's movements in relation to the receiver. This subsequently results in the inability to cancel the Inter-Symbol Interference (ISI), which in turn leads to the Inter-Carrier Interference (ICI). Contrary to the majority of contemporary Radcom systems, which utilize the Orthogonal Frequency Division Multiplexing (OFDM), these systems are susceptible to encountering challenges in high Doppler channels due to their inability to effectively cancel the Inter-Carrier Interference (ICI) phenomenon. This paper introduces an enhanced Simplified Orthogonal Time-Frequency Space (S-OTFS) Modulation based on a discrete Zak-transform coupled with a Linear Minimum Mean Square Error Equalizer (LMMSEE). The S-OTFS based-DZT-LMMSEE approach is proposed as a solution to the challenges posed by V2X communications in a Radcom system. The enhanced S-OTFS modulation-demodulation technique based on the new approach exhibits superior inter-carrier interference (ICI) cancellation capabilities in the delay-Doppler (DD) domain in high mobility channels in the presence of multi-path scenarios. Consequently, it demonstrates a reduced Bit-Error-Rate (BER) and Error vector magnitude - Root Mean Square (EVM RMS) values in comparison to the conventional Orthogonal Frequency Division Multiplexing (OFDM) technique. The MATLAB software development framework was employed to validate the compelling evidence that the novel approach, S-OTFS based on Discrete Zak-LMMSEE, is an effective solution for high-speed vehicle detection and communication, even in the presence of high Doppler channels. The performance of the new Radcom V2X system simulator was then validated by referring to an experimental test involving different velocities for three vehicles.