Modulation Techniques

3:00 PM – Solving the Two-Antenna Problem Using Space-Time Coded PCM/FM
Dr. Michael Rice and Zachary Hilton, Brigham Young University

This paper describes a space-time block code for PCM/FM to address the two-antenna problem. The space-time block encoder is described using bit-level operations on the input data stream. The space-time decoder combines coherent combining and maximum likelihood sequence estimation to produce an estimate of the data sequence. Simulation results for zero differential delay at the most difficult boundary cases produced by dual-antenna transmission show no bit error rate loss relative to the additive white Gaussian noise case.

3:20 PM – Spectral Efficiency and Detection Efficiency of Digital Modulation  for Aeronautical Mobile Telemetry
Dr. Michael Rice and Zachary Hilton, Brigham Young University

This article examines the use of linear modulations with bandwidth efficient pulse shaping to increase spectral efficiency beyond the spectral efficiencies of the IRIG 106 modulations PCM/FM, SOQPSK-TG, and ARTM CPM. An emphasis is placed on modulations that have been described in past ITC Proceedings. The analysis incorporates the peak-to-average power ratio (PAPR) together with the fact aeronautical mobile telemetry systems use fully-saturated RF power amplifiers on test articles. Using the peak signal-to-noise ratio instead of the average signal-to-noise ratio to measure detection efficiency, the results show that, relative to the IRIG 106 modulations, improved spectral efficiency is achieved at the cost of detection efficiency.

3:40 PM – Experimentation of OTFS Pulse Design for Underwater Acoustic Channels using SDRs
Hovannes Kulhandjian, Tristen Moran, California State University, Fresno; Michel Kulhandjian, Rice University

This paper presents the design and experimentation of orthogonal time-frequency space (OTFS) pulse shaping for underwater acoustic communication using software-defined radios (SDRs). The objective is to adapt OTFS modulation to the underwater channel, which is severely affected by multipath propagation, Doppler spread, and signal attenuation. A Hermite-based pulse shaping approach is integrated within a GNU Radio framework to improve spectral efficiency and minimize bit error rate (BER). The experimental setup employs hydrophones to transmit and receive low-frequency acoustic signals suitable for long-range communication. Initial validation was performed using 16-QAM over RF before transitioning to underwater transmission, where chirp-based signaling provided greater reliability than single-tone excitation. The hardware platform included a USRP N210 with LFRX/LFTX daughterboards and Teledyne VP2000 preamplifiers. Results highlight the challenges of SDR configuration, the complexity of OTFS-NOMA implementation, and the critical role of synchronization in system performance. Future work will refine the modulation scheme, compare BER and SNR performance across varying conditions, and explore Hermite polynomial–based designs for enhanced robustness. This research advances underwater acoustic communication by improving adaptability and reliability in challenging propagation environments.

4:00 PM – The Key to Robust Data Quality Encapsulation: Asynchronous DQE Framing
Mark Geoghegan and Sean Wilson, Quasonix

A data quality encapsulation (DQE) protocol for transporting received telemetry data along with a data quality metric (DQM) is defined in IRIG 106-23 Chapter 2 Appendix 2-G. DQM provides real-time link status and is sufficient for optimal telemetry reception from multiple sources using a downstream best source selector (BSS). Recent testing has revealed that receiver synchronization issues in challenging RF channels can result in DQE framing errors in the output data stream. At best, invalid frames may be ignored or assigned a poor quality. At worst, the DQM value may be misinterpreted as good when the TM data is bad resulting in BSS bit errors. In any case, data correlation/alignment may be undermined. The root cause stems from trying to maintain alignment of the streaming DQM output values with the over-the-air modulation or coding blocks. This paper proposes asynchronous DQE framing relative to the physical layer and presents an analysis of the relative loss in system performance.

4:40 PM – Task-Aware Unified Downscaling for Bandwidth-Efficient Telemetry Video Transmission
Myung Han Hyun, Gyeongsang National University

In this paper, we present a task-aware unified downscaling framework applicable to telemetry video systems, which determines the optimal downscaling factor based on a Rate-Loss optimization criterion for efficient video transmission. Although prior studies have considered the trade-off among compression rate, task accuracy, and latency, most methods adopt identical scaling factors for both width and height or rely on deep learning–based modules that require per-image optimization, leading to high computational cost. The proposed method introduces a Task-Aware Unified Down-scaling Factor (TUDF) that determines an optimal scale factor minimizing bitrate while maintaining detection accuracy. By eliminating the need for a deep learning–based downscaling module, the approach substantially reduces computational overhead and inference latency, thereby offering a practical solution for real-time telemetry video transmission. Experimental results demonstrate that the proposed approach can significantly reduce bitrate while preserving the performance of downstream computer vision tasks.