Enhanced Spread in Time On-Off Keying Technique for Dense Terahertz Nanonetworks

Nanotechnology becomes reality paving the way for many new applications. In nanonetwork system, each nanosized device is equipped with limited capabilities and is dedicated to a basic task but the combination of the numerous devices actions results in high-level functions. In this context, large number of devices concentrated in a limited area must exchange data using wireless links. Spread in Time On-Off Keying (TS-OOK) protocol was proposed as a technique to share the radio channel over the different terahertz nano-devices. TS-OOK is based on a Femtosecond-Long pulse modulation where communication data are sent using a sequence of pulses interleaved by a constant duration randomly selected. In this paper we provide a critical analysis of the TS-OOK approach. We prove that the TS-OOK is not adaptive against the traffic load variation and induces an imbalance between the active nodes. This inequity is due to the dependency of a communication quality on the randomly chosen symbol rate. We propose a dynamic TS-OOK modulation approach, called SRH-TSOOK (Symbol rate Hopping TSOOK), where the duration between two consecutive pulses of the same transmission follows a pseudo-random sequence. We show that this approach performs better than the standard protocol when the number of active nodes increases and guarantees a better distribution of the channel capacity over the active communications. For instance, while the throughput of a communication within a TS-OOK protocol may falls bellow 10(5) frames/s with 300 active nodes, the throughput in the SRH-TSOOK protocol stabilizes around 20(7) frames/s for all the active communications. The comparison is made on the basis of probabilistic analysis allowing a numerical and accurate evaluation of the protocols performance.