Generalized Two-Dimensional Index Modulation in the Code-Spatial Domain for LPWAN

TL;DR

This paper proposes a novel 2D code-index modulation transceiver for LPWANs that combines spatial modulation, space-time coding, and spreading sequences to enhance data rate and energy efficiency.

Contribution

It introduces a unified 2D coding structure integrating multiple modulation techniques and proposes three schemes with analytical performance evaluation.

Findings

Proposed schemes outperform benchmark methods in simulations.

Closed-form bit error probability expressions are derived.

The designs improve data rate and energy efficiency in LPWANs.

Abstract

Low-power wide-area networks (LPWANs) are crucial for large-scale Internet of Things (IoT) applications, yet they face increasing demands for higher data rates, improved reliability, and enhanced energy efficiency under stringent hardware constraints. To address these challenges, this paper introduces a generalized code-index modulation (CIM) transceiver that employs multiple-antenna index modulation (IM). The transmitter integrates spatial modulation (SM), space-time block coding (STBC), and CIM into a unified two-dimensional (2D) coding structure, where the spreading sequences -- realized via continuous phase modulation with spread spectrum (CPM-SS), chirp spread spectrum, or Zadoff-Chu sequences -- serve as spreading codes. Three specific schemes are proposed: SM-CIM, STBC-SM-CIM, and an enhanced STBC-SM-CIM (ESTBC-SM-CIM), designed to jointly improve data rate and energy efficiency. Closed-form expressions for the average bit error probability are derived, and system performance is analyzed in terms of data rate, energy efficiency, and computational complexity. Simulation results show that the proposed designs consistently outperform benchmark schemes, demonstrating their potential for enabling high-data-rate, energy-efficient LPWAN and IoT communications.