PHY8 – Waveforms and modulation
Friday, 5 June 2026, 9:00-10:30, room Sala 3 (1st floor)
Session Chair: Ana Garcia Armada (Univ. Carlos III de Madrid, ES)
Block Turbo Equalization for ZP-OTFS in Fractional Delay-Doppler Channels
Antony Pottier (CEA-Leti, France); Valérian Mannoni (CEA, France); Jean-Baptiste Doré (CEA-Leti, France)
This paper presents a block turbo equalizer for \ac-\ac modulation, combining the \ac criterion with soft processing of \emph information. Mobile channels are considered under general assumptions, without constraining delays and/or Doppler shifts to be interger multiple of the \ac grid resolution – an hypothesis on which many works on the topic rely. Our algorithm is designed so as to remove the inter-Doppler interference coming from the most significant channel taps, assumed to be contained within the guard interval. For a 16-QAM modulation with small delay-Doppler grid size, FER results shows performance within 1 dB of the genie-aided equalizer.
Interference-Limited Zero-Crossing Modulation MIMO System for Energy-Efficient Tbps Links
Daniel Swist (TU Dresden, Germany); Huasheng Zhang (Delft University of Technology, The Netherlands); Stephan Zeitz (TU Dresden, Germany); Nuria LLombart (Delft University of Technology, The Netherlands); Meik Dörpinghaus (TU Dresden, Germany); Gerhard P. Fettweis (Technische Universität Dresden, Germany)
Sub-THz wireless links targeting Tbps throughput face a fundamental tension between bandwidth and energy efficiency. Zero-Crossing Modulation (ZXM) is a promising approach to reduce receiver power consumption by combining 1-bit quantization with temporal oversampling. However, the resulting 1-bit receive chain introduces a strong nonlinearity, which limits the applicability of conventional linear MIMO spatial equalization techniques and makes the impact of coupling and crosstalk a primary system design constraint. This motivates the use of ZXM in combination with 1-bit quantization for a quasi-optical (QO) MIMO system, where the spatial inter-stream interference is very small. Hence, we present a system-level link-budget analysis for an 8×8 QO MIMO architecture at sub-THz, based on an SINR analysis that treats inter-stream interference as additional noise after 1-bit quantization. The end-to-end coupling matrix is modeled as the cascade of antenna coupling and RF front-end crosstalk contributions. Using this framework, we quantify when the link transitions from noise-limited to interference-limited operation, show SINR saturation with increasing transmit power, and derive feasible operating regions over distance and spectral-efficiency targets for wideband 50 GHz operation. The results substantiate the feasibility of energy-efficient Tbps-class wireless connectivity.
LoCDM: A New Chirp Division Multiplexing Waveform Using LoRa-Based Chirp Bank
Omar El marzougui (Institut de Recherche En Informatique de Toulouse (IRIT), France); Nathalie Thomas (University of Toulouse, France); Charly Poulliat (Toulouse INP, France)
The integration of Non-Terrestrial Networks (NTN), particularly Low Earth Orbit (LEO) satellites, is a defining feature of Beyond 5G and 6G systems. However, the severe Doppler shifts inherent to LEO mobility compromise the performance of current systems based on OFDM. In this paper, we introduce LoRa-based Chirp Division Multiplexing (LoCDM) waveform, a chirp-based multicarrier modulation that reuses the chirp bank of Long Range (LoRa) in a Chirp Division Multiplexing mode. Furthermore, we introduce DFT-Precoded LoCDM (DFT-P-LoCDM), a low PAPR variant better suited for uplink transmissions, effectively proposing a chirp-based alternative to the OFDM/SC-FDMA waveforms. We provide a comprehensive continuous and discrete time signal model and derive a Low Complexity Linear Minimum Mean Square Error (LMMSE) equalizer based on LDL factorization. Simulation results demonstrate the pertinence of LoCDM and DFT-P-LoCDM in terms of PAPR characteristics and BER performance in high mobility NTN transmissions.
Low-Complexity Detection of CIM-SSK over Rayleigh MIMO Channels: A Deep Learning Approach
Fatih Cogen and Zehra Yigit (Turkcell, Turkey); Mehmet Basaran (Turkcell, Turkey & Istanbul Technical University, Turkey); Semiha Koşu and Gokhan Kalem (Turkcell Technology, Turkey); Burak Ahmet Ozden (Yildiz Technical University, Turkey); Erdogan Aydin (Istanbul Medeniyet University, Turkey); Ertugrul Basar (Tampere University, Finland & Koc University, Turkey)
Code index modulation (CIM) combined with space shift keying (SSK), referred to as CIM–SSK, increases spectral efficiency by embedding information jointly into the active transmit-antenna index and the spreading-code indices assigned to the in-phase and quadrature components. However, conventional exhaustive joint maximum-likelihood (ML) detection becomes increasingly burdensome as the antenna and codebook sizes grow. In this study, a deep-learning (DL)-assisted receiver is presented for CIM–SSK over Rayleigh block-fading multiple-input multiple-output (MIMO) channels with additive white Gaussian noise (AWGN). Receiver-side inputs are formed from channel state information, correlator-bank statistics, raw chip-rate observations, and explicit noise/signal-to-noise ratio (SNR) side information, which are organized into a structured three-channel tensor that preserves the antenna/code/chip ordering. A compact residual CNN2D is then used to produce a probabilistic ranking of the joint hypotheses, and a short Top-$K$ candidate list is generated. The final decision is then obtained by applying the chip-domain Euclidean refinement only to the Top-$K$ candidates. Bit error rate (BER) results indicate gains relative to the considered CIM–SSK joint-ML baseline as well as equal-rate SSK and SM benchmarks, while the CNN ranking stage achieves 95.92% Top-1 and 98.99% Top-4 accuracy for 64 hypotheses, supporting reliable shortlist-based detection with reduced online search.
Weyl-Heisenberg Framework-Based Orthogonal Waveform Design for Doubly Selective Channels
Zhuangzhuang Liao (Harbin Institute of Technology, China & Eurecom, France); Xiaojie Fang (Harbin Institute of Technology, China); Lizhe Liu (54th Research Institute of China Electronics Technology Group Corporation, China); Xuejun Sha (Communication Research Center, Harbin Institute of Technology, China); Dirk Slock (EURECOM, France)
This paper proposes a unified waveform design framework for doubly selective channels based on the Weyl-Heisenberg (WH) group. By linking waveform orthogonality to the ambiguity function and its zero set under unitary time-frequency shift operators, the proposed framework unifies SC-FDE, OFDM, OTFS, and AFDM as different operator paths on the delay-frequency-shift grid. Within this framework, we further design a novel WH-based waveform with a constant-modulus prototype in both the time and frequency domains, yielding orthogonal basis signals with near-uniform time-frequency energy spreading. This structure provides a time-frequency averaging effect and yields bit-error-rate (BER) performance close to the theoretical minimum mean-square error (MMSE) lower bound in doubly selective channels.
