Interference Cancellation and Iterative Detection for Orthogonal Time Frequency Space Modulation

Abstract

The recently proposed orthogonal time frequency space (OTFS) modulation technique was shown to provide significant error performance advantages over orthogonal frequency division multiplexing (OFDM) in Doppler channels. In this paper, we first derive the explicit input-output relation describing OTFS modulation and demodulation (mod/demod) for delay-Doppler channels. We then analyze the cases of (i) ideal pulse-shaping waveforms that satisfy the bi-orthogonality conditions, and (ii) rectangular waveforms which do not. We show that while only inter-Doppler interference (IDI) is present in the first case, additional inter-carrier interference (ICI) and inter-symbol interference (ISI) occur in the second case. We next analyze the interferences and develop a novel low-complexity yet efficient message passing (MP) algorithm for joint interference cancellation (IC) and symbol detection. While ICI and ISI are eliminated through appropriate phase shifting, IDI can be mitigated by adapting the MP algorithm to account for only the largest interference terms. The proposed MP algorithm can effectively compensate for a wide range of channel Doppler spreads. Our results indicate that OTFS using practical rectangular waveforms can achieve the performance of OTFS using ideal but non-realizable pulseshaping waveforms. Finally, simulations results demonstrate the superior error performance gains of the proposed uncoded OTFS schemes over OFDM under various channel conditions.

OTFS-NOMA: An Efficient Approach for Exploiting Heterogenous User Mobility Profiles

“…where perfect decision-making is assumed, i.e.,x = x, and there is no error propagation [29]- [31]. We note that (22) yields an upper bound on the reception reliability of FD-DFE when error propagation cannot be completely avoided.…”

“…Similar to [20]- [22], we first define the delay-Doppler profile for U 0 's channel as shown in Table I, where P 0 = 3 and the subchannel spacing is ∆f = 7.5 kHz. Therefore, the maximal speed corresponding to the largest Doppler shift ν 0,3 = 468.8 Hz is 126.6 km/h if the carrier frequency is f c = 4 GHz.…”

Robust Beamforming Design for OTFS-NOMA

“…Therefore, the design of beamforming is focused in this paper, where the joint design of beamforming and power allocation is a promising direction for future research but beyond the scope of this paper. Following steps similar to those in [3]- [6], the received signal at U i in the time-frequency plane can be modelled as follows:…”

OTFS: Interleaved OFDM with Block CP

“…The delay and Doppler values for pth path is given as τ p = lp M∆f and ν p = kp N T where l p ∈ N[0 M − 1] and k p ∈ N[0 N − 1] are delay and Doppler bin number on De-Do lattice Λ for p th path. In this work, we assume that N and M are sufficiently large so that there is no effect of fractional delay and Doppler on the performance [7]. We also define time varying frequency response of channel as,…”