Outage Probability Analysis for OTFS with Finite Blocklength

TL;DR

The paper addresses outage probability for OTFS modulation under finite blocklength, reframing the problem as outage over $L$ parallel AWGN channels using an equivalent-noise approach. It derives theoretical lower bounds on outage probability under average and water-filling power allocations, expressed via $P_{out}^{theo}$ and the parallel-channel metrics $C_L(\alpha)$ and $V_L(\alpha)$ with per-path SNRs $\alpha_i$. By modeling the DD-domain channel as a sparse $L$-path system and validating with Monte-Carlo simulations, the work illuminates how the number of resolvable paths and coding rates shape outage performance and provides guidance for blocklength, power control, and rate selection in high-mobility 6G-like contexts. The results demonstrate that water-filling offers gains over equal power allocation, particularly at higher SNRs, and that increased path diversity yields a nuanced trade-off across operating regimes. Overall, the study offers a tractable framework for designing OTFS systems under finite-blocklength constraints.

Abstract

Orthogonal time frequency space (OTFS) modulation is widely acknowledged as a prospective waveform for future wireless communication networks.To provide insights for the practical system design, this paper analyzes the outage probability of OTFS modulation with finite blocklength.To begin with, we present the system model and formulate the analysis of outage probability for OTFS with finite blocklength as an equivalent problem of calculating the outage probability with finite blocklength over parallel additive white Gaussian noise (AWGN) channels.Subsequently, we apply the equivalent noise approach to derive a lower bound on the outage probability of OTFS with finite blocklength under both average power allocation and water-filling power allocation strategies, respectively.Finally, the lower bounds of the outage probability are determined using the Monte-Carlo method for the two power allocation strategies.The impact of the number of resolvable paths and coding rates on the outage probability is analyzed, and the simulation results are compared with the theoretical lower bounds.

Figures (6)

• Figure 1: The system model of OTFS with finite channel coding length.
• Figure 2: Power allocation and SNR calculation for $L$-parallel AWGN paths in OTFS with finite blocklength.
• Figure 3: Outage probability lower bounds for different number of resolvable paths under average and water-filling power allocation, where $R_c=0.8$.
• Figure 4: Outage probability lower bounds for different coding rate under average and water-filling power allocation, where $P=5$.
• Figure 5: Comparison of simulation and lower bound of outage probability with average power allocation, where $L=3$.