Low-Complex Synchronization Method for Intra-Body Links in the Terahertz Band

Precision medicine applications supported by nanotechnologies enforce designing a communication interface between in-body nanosensors and external gateways. Such a communication interface will enable both a data and a control channel between nanodevices operating within the human body and external control units. In this direction, recent literature focuses on deriving analytic channel models for intra-body links through the human tissues, including the analysis of achievable communication capacities in the terahertz band. A yet missing component, however, is a synchronization module to implement communication schemes in the intra-body link. Such synchronization module will ultimately bound the communication performance regarding the perceived signal to noise ratio (SNR) and bit error rate (BER), for instance. This paper contributes to the state of the art in two directions: (a) evaluating the bounds on the communication performance with the Cramer-Rao lower bound (CRLB) for the synchronization symbol timing offset (STO) and (b) designing a low-complex mechanism to synchronize communication. This analysis considers a communication link between external gateways located on the skin and nanosensor devices flowing in the human vessels. Using envelope and slope detectors, we devise a low-complex solution that relies on the received signal strength (RSS) metric to trigger data emissions. The method estimates the peak of the received RSS metric to ignite communication in the most favorable location, i.e., when the nanosensor is located at the shortest distance in the communication range with external gateways. Our findings illustrate the feasibility of such a low-complex synchronization method. Performance illustrates a BER less than $1\times 10^{-5}$ for those nanosensors traveling close to the upper vessel wall.

I. Introduction

Advances in nanotechnologies progressively bridge the boundaries between the human body and the digital world. Battery-free electronics smoothly integrate with the skin as unnoticeable patches [1], integrating processing units running artificial intelligence (AI) modules, sensors [2], and radio frequency (RF) interfaces [3]. Inside the human body, nanotechnologies also allow radiating information from sensors to the outside through plasmonic antennas in the THz band [4]. Measurements with human-phantoms demonstrate the communication capabilities through the human tissues [5]. Such promising technologies advocate the paradigm of cell-connected-to-internet, where specific body regions are monitored and treated from remote locations, with impactful applications in precision medicine [6]. Making use of gateway systems, very powerful communication and control applications become possible [7], [8].