Interference-Aware Frequency Domain Equalizer for Orthogonal Chirp Division Multiplexing with Insufficient Guard Interval

Orthogonal Chirp Division Multiplexing (OCDM) is a multi-carrier scheme based on the chirp spread spectrum (CSS) that has been introduced to overcome the limitations of conventional multiplexing techniques. In this paper, we derive the input-output relationship (IOR) for the OCDM scheme over frequency-selective fading channels. We consider two cases: when the guard interval (GI) between successive OCDM symbols is longer than the channel delay spread (sufficient) or not (insufficient). First, we demonstrate that the IOR of OCDM is equivalent to that of the single-carrier (SC) scheme with a sufficient GI. Next, we show that for OCDM with an insufficient GI, the intersymbol interference (ISI) at the receiver follows a Gaussian distribution. We then derive the signal-to-interference-plus-noise ratio (SINR) of the OCDM scheme at the receiver. By leveraging this SINR analysis, we present a novel single-tap linear minimum mean square error (MMSE) based frequency domain equalizer (FDE). Our simulation results, which highlight the significant performance improvement of the proposed MMSE one-tap equalizer, demonstrate that by exploiting derived SINR, its effectiveness in enhancing the performance of OCDM compared with the conventional MMSE receiver. We also evaluate the bit error rate (BER) performance and validate our analysis. Our results provide novel insights into the achievable gains by our interference-aware FDE for OCDM over the existing benchmarks for different values of key system parameters.