Performance Analysis of Time-Hopping Multiple Access Using Multi-Level PPM for Terahertz Nanocommunication

Abstract

<p>Terahertz (THz) band nanocommunication is envisioned to revolutionize the future of wireless communications enabling applications in the nanoscale domains including the internet of nanothings, wireless on-chip communications, and advanced health monitoring. The communication among nanodevices, however, is hindered by the THz channel, which is highly frequency-selective and distance-dependent in nature, ultimately restricting the nanocommunication distances to a few millimeters. Moreover, multiple nano-devices trying to access the channel simultaneously increase interference in the overall communication system. This paper proposes a new pulse-based modulation for nanonetworks called multi-level pulse position modulation (ML-PPM) and analyzes its performance in the multiuser nanocommunication scenario. In ML-PPM, each nanomachine in the nanonetwork first transforms the transmitting bits into multi-levels by using several orthogonal codes, and then, each multi-level is modulated as a pulse position. The ML-PPM signal thus generated is subsequently time-hopped to achieve multiple access. As a consequence of employing orthogonal coding, the spreading gain is achieved at the nanoreceiver, which improves the performance of the proposed scheme. The time-hopped multilevel PPM scheme is evaluated in terms of bit error rate (BER) and link capacity, for different THz propagation conditions and different system design parameters. The results show that for a THz channel concentrated with 10% water vapor, a link capacity of approximately 1 Gigabits-per-second is achieved for a transmission distance of 0.5mm.</p>

Multilevel Pulse Position Modulation With Level Trimming for Electromagnetic Nanocommunications in the Terahertz Band

“…For simplicity, we omit the multiple-access scheme [32] and assume a single user case. After passing through the THz pulse shaping filter, the transmitted THz signal in ML-PPM has the form…”

“…As values of L becomes large, the multilevels become smaller. In the conventional ML-PPM (see Section II) [32], after generating the transmitted signal, as shown in (7), we transmit all the generated positions regardless of their different occurrence probabilities. As a consequence, the overall spectral efficiency of the conventional ML-PPM is low, which also increases the computation complexity at the nanoreceiver, which requires each level to process.…”

“…Along the same lines, in our previous study, we developed a modulation scheme for THz band-based nanocommunication called multilevel pulse position modulation (ML-PPM) [32]. A multilevel scheme uses several orthogonal codes simultaneously and is combined with a PPM scheme to achieve not only variable and high data rates but also processing gain at the nanoreceiver end, thereby guaranteeing the benefits of PPM.…”