OTFS Modem SDR Implementation and Experimental Study of Receiver Impairment Effects

This paper presents a software defined radio (SDR) Design and Implementation of an orthogonal time frequency space (OTFS) modem. OTFS is a novel modulation scheme based on multiplexing information symbols over localized pulses in the delay-Doppler signal representation. Traditional OFDM modulation operates in the frequency-time domains. In contrast, OTFS modulation operates in the delay spread-Doppler plane domains, which are related to frequency and time by the symplectic Fourier transform (similar to a two-dimensional discrete Fourier transform). OTFS is shown to perform very well under the 5G usage scenarios such as high speed vehicle to vehicle communication with wide Doppler spreads, where the traditional OFDM system performance degrades. Like any other communications system, the OTFS modem is not free from receiver impairments such as DC offset and carrier frequency offset, which affects the channel estimation and hence the decoding process. We study the effects of these receiver impairments on the receiver performance from real time experiments conducted on the implemented OTFS modem in a real indoor wireless channel. We also compare the performance of OTFS modulation and OFDM modulation using the same hardware setup and environment for the real frequency selective and partially emulated doubly selective channel.