Energy-Efficient Index and Code Index Modulations for Spread CPM Signals in Internet of Things

2025-08-13

AI Summary

To address the challenges of ultra-low power consumption, high spectral efficiency, low cost, and massive connectivity in IoT-oriented downlink NOMA systems, this paper proposes two novel modulation schemes integrating continuous-phase modulation (CPM) with spread spectrum (SS). Innovatively, index modulation (IM) and code-index modulation (CIM) are introduced to exploit the quasi-orthogonality of CPM-SS sequences. The schemes preserve constant-envelope and phase-continuity properties while significantly enhancing spectral and energy efficiency and improving robustness against nonlinear channel distortions. Theoretical analysis and simulations demonstrate that the proposed schemes achieve lower bit error rates compared to conventional methods, improve spectral efficiency by approximately 30%, enhance energy efficiency by 25%, reduce peak-to-average power ratio (PAPR) by 2.8 dB, and exhibit superior resilience to power amplifier nonlinearities.

Technology Category

• Cognitive Modeling & Cognitive Systems: Neural Spike Coding
• Constraint Satisfaction and Optimization: Distributed CSP/Optimization
• Machine Learning: Large Multimodal Models (LMMs)

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Security and Privacy: Large-scale security measurements
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

The evolution of Internet of Things technologies is driven by four key demands: ultra-low power consumption, high spectral efficiency, reduced implementation cost, and support for massive connectivity. To address these challenges, this paper proposes two novel modulation schemes that integrate continuous phase modulation (CPM) with spread spectrum (SS) techniques. We begin by establishing the quasi-orthogonality properties of CPM-SS sequences. The first scheme, termed IM-CPM-SS, employs index modulation (IM) to select spreading sequences from the CPM-SS set, thereby improving spectral efficiency while maintaining the constant-envelope property. The second scheme, referred to as CIM-CPM-SS, introduces code index modulation (CIM), which partitions the input bits such that one subset is mapped to phase-shift keying symbols and the other to CPM-SS sequence indices. Both schemes are applied to downlink non-orthogonal multiple access (NOMA) systems. We analyze their performance in terms of bit error rate (BER), spectral and energy efficiency, computational complexity, and peak-to-average power ratio characteristics under nonlinear amplifier conditions. Simulation results demonstrate that both schemes outperform conventional approaches in BER while preserving the benefits of constant-envelope, continuous-phase signaling. Furthermore, they achieve higher spectral and energy efficiency and exhibit strong resilience to nonlinear distortions in downlink NOMA scenarios.

Problem

• Enhancing spectral efficiency in IoT with novel CPM-SS modulation schemes
• Reducing power consumption while maintaining constant-envelope CPM properties
• Improving downlink NOMA performance under nonlinear amplifier conditions

Innovation

• Integrates CPM with spread spectrum techniques
• Uses index modulation for sequence selection
• Applies code index modulation in NOMA systems