A Comparison among Single Carrier, OFDM, and OTFS in mmWave Multi-Connectivity Downlink Transmissions

TL;DR

The paper addresses robust downlink transmission in mmWave multi-connectivity with imperfect synchronization by comparing SC, OFDM, and OTFS under a fair, reduced-complexity detection framework. It introduces a novel cross-domain iterative detector for OTFS that exchanges extrinsic information between time and delay-Doppler domains via a time-to-frequency and frequency-to-time transformation with SIC, integrated into a pragmatic-capacity evaluation. The key contribution is showing that OTFS achieves significantly higher pragmatic capacity than SC and OFDM, thanks to its DD-domain symbol placement and the proposed cross-domain detector, with only a moderate increase in detection complexity. This finding suggests OTFS as a promising modulation for ultra-dense mmWave networks with multi-connectivity where synchronization imperfectness is present, potentially enabling higher data rates and more reliable links in practice.

Abstract

In this paper, we perform a comparative study of common wireless communication waveforms, namely the single carrier (SC), orthogonal frequency-division multiplexing (OFDM), and orthogonal time-frequency-space (OTFS) modulation in a millimeter wave (mmWave) downlink multi-connectivity scenario, where multiple access points (APs) jointly serve a given user under imperfect time and frequency synchronization errors. For a fair comparison, all the three waveforms are evaluated using variants of common frequency domain equalization (FDE). To this end, a novel cross domain iterative detection for OTFS is proposed. The performance of the different waveforms is evaluated numerically in terms of pragmatic capacity. The numerical results show that OTFS significantly outperforms SC and OFDM at cost of reasonably increased complexity, because of the low cyclic-prefix (CP) overhead and the effectiveness of the proposed detection.

Figures (6)

• Figure 1: Considered system model for downlink transmission with multi-connectivity.
• Figure 2: Considered frame structures for SC, OFDM, and OTFS.
• Figure 3: Transceiver diagrams for SC, OFDM, and OTFS.
• Figure 4: The block diagram for the considered FDE-based CDID for OTFS.
• Figure 5: The comparison among three waveforms in terms of the pragmatic capacity, where the blocking rate is $q=0.2$.