Zeros Insertion: An OTFS Scheme for a Sparse Equivalent Channel Matrix

Orthogonal time frequency space (OTFS) modulation is a new 2-dimensional technique that encodes information in the delay and Doppler domains. It can outperform orthog-onal frequency division multiplexing (OFDM) in high-mobility wireless communication scenarios. The advantage of the OTFS technique is it exploits full diversity over both time and frequency [2]. However, an ideal OTFS rectangular waveform that satisfies the bi-orthogonality conditions is unrealistic for implementation. Therefore, in order to suppress inter-symbol interference (ISI), techniques such as a guard intervals (GI) should be considered in signal generation. In this paper, we present an overview of different OTFS GI schemes, including the cyclic prefix (CP) as well as the zero suffix (ZS). We also propose a new scheme by inserting zeros into the information stream randomly. This simple approach can reduce the eigen-value ratio (EVR) of the channel matrix thus providing more robust performance. Finally, the simulation results demonstrate the proposed zero insertion technique can help to improve the transmission performance compared to other OTFS schemes.