Performance Analysis of Time-Hopping Multiple Access Using Multilevel PPM for Terahertz Nanocommunications

Abstract

Terahertz (THz)-band nanocommunication is envisioned to revolutionize the future of wireless communications by enabling applications in nanoscale domains such as the Internet of Nanothings, wireless on-chip communications, and advanced health monitoring. However, communication between nanodevices is hindered by the highly frequency-selective and distance-dependent nature of the THz channel, which ultimately restricts nanocommunication distances to a few millimeters. Moreover, attempts by multiple nanodevices to access the channel simultaneously increase the interference in the overall communication system. In this study, a new pulse-based modulation scheme for nanonetworks called <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">time-hopping multilevel pulse position modulation (TH ML-PPM)</i> is proposed and its performance in a multiuser nanocommunication scenario is analyzed. In ML-PPM, each nanomachine in the nanonetwork first transforms the transmitted bits into multilevels by using several orthogonal codes and then modulates each multilevel code into a pulse position. The generated ML-PPM signal is subsequently time-hopped to achieve multiple access. Employing orthogonal coding results in spreading gain at the nanoreceiver, which improves the performance of the proposed scheme. The bit error rate and link capacity of the time-hopped multilevel PPM scheme are evaluated for different THz propagation conditions and system design parameters. The results show that for a THz channel with 10% water vapor concentration, a link capacity of more than 100 gigabits per second is achieved across a transmission distance of 0.5 mm.