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

Nanomachines are submicrometer-scale devices led by nanotechnology that can perform simple sensing, local actuation, limited data processing, storage, and communication tasks in the terahertz (THz) band, that is, from
$\mathrm {0.1~}$
-
$\mathrm {10~ \text {T} \text {Hz} }$
. Electromagnetic nanocommunication among nanomachines results in a nanonetwork which could breakthrough promising applications in multiple domains such as software-defined metamaterials, in-body communication, and on-chip communication. This study adopts a modulation scheme for nanomachine communication based on
multilevel
pulse position modulation (ML-PPM). The multilevel scheme uses several orthogonal codes and is combined with PPM to generate the final transmit signal consisting of several multilevels. In this paper, we propose a more advanced scheme called
level trimming
to further boost the data rates of the ML-PPM scheme. Employing level-trimming, we transmit a fewer number of levels than required in ML-PPM, which will result in an spectral efficiency gain at the nanoreceiver. The simulation results reveal that the link capacity of the proposed scheme can be increased more than twofold using the level-trimming approach while the error rate performance remains better than the conventional ML-PPM. For instance, ML-PPM with level trimming achieves a data rate of approximately 4.5 terabits per second (Tbps) when trimming the levels from seven to one compared to ML-PPM that achieves around
$\mathrm {1~Tbps}$
under the same network conditions. At the same time, a
$\mathrm {2~dB}$
gain in BER performance is achieved with level trimming. Moreover, the computational complexity of nanotransceivers is reduced with the transmission of fewer levels. Furthermore, although level-trimming causes artificial errors, it improves the decoding performance by reducing the number of levels. We believe that the potential impact of this study will open doors for further investigations on various possible modulation formats for THz nanocommunication.