Terahertz (THz) band (0.1-10 THz) communication is envisioned as a key wireless technology to support faster and denser wireless networks. However, absorption by water vapor molecules splits the THz band into multiple transmission windows, each tens to hundreds of Gigahertz (GHz) wide. Because of the broadening of the absorption lines, the available bandwidth within each transmission window changes drastically with distance. As a result, a large portion of the bandwidth close to the absorption lines is considered not practical for communications or, in the best case, practical only for short-range applications. In this paper, chirp spread spectrum communication is proposed as a way to enable ultra-broadband communication links spanning across absorption lines in the THz band. More specifically, first, the performance of Chirp-Spread Binary Phase Shift Keying (CS-BPSK) is analytically derived and compared to that of Binary Chirp Spread Spectrum (BCSS) as well as non-spread Binary Phase Shift Keying (BPSK). Extensive numerical results based on an analytical channel model of the THz band are provided to illustrate the performance of the proposed scheme. Finally, experimental results above conducted in the first absorption-defined window above 1 THz are provided, validating the original hypothesis and highlighting the opportunities and challenges in communication across absorption lines at THz frequencies.
Major advancements in the fields of electronics, photonics and wireless communication have enabled the development of compact wearable devices, with applications in diverse domains such as fitness, wellness and medicine. In parallel, nanotechnology is enabling the development of miniature sensors that can detect events at the nanoscale with unprecedented accuracy. On this matter, in vivo implantable Surface Plasmon Resonance (SPR) nanosensors have been proposed to analyze circulating biomarkers in body fluids for the early diagnosis of a myriad of diseases, ranging from cardiovascular disorders to different types of cancer. In light of these results, in this paper, an architecture is proposed to bridge the gap between these two apparently disjoint paradigms, namely, the commercial wearable devices and the advanced nano-biosensing technologies. More specifically, this paper thoroughly assesses the feasibility of the wireless optical intercommunications of an SPR-based nanoplasmonic biochip -implanted subcutaneously in the wrist-, with a nanophotonic wearable smart band which is integrated by an array of nano-lasers and photon-detectors for distributed excitation and measurement of the nanoplasmonic biochip. This is done through a link budget analysis which captures the peculiarities of the intra-body optical channel at (sub) cellular level, the strength of the SPR nanosensor reflection, as well as the capabilities of the nanolasers (emission power, spectrum) and the nano photon-detectors (sensitivity and noise equivalent power). The proposed analysis guides the development of practical communication designs between the wearable devices and nano-biosensing implants, which paves the way through early-stage diagnosis of severe diseases.
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