TeraHertz band communications have been proposed as a notable candidate for the deployment of high data rate networks in 6G and beyond scenarios. While research activity on TeraHertz mostly focused so far on channel measurements and modeling, recently Multi User Interference (MUI) in TeraHertz networks received an increasing attention, as MAC and network algorithms and protocols for TeraHertz networks are being designed.
Existing Impulse Radio TeraHertz MUI models mostly rely on stochastic geometry to determine the MUI power as a function of the positions of the devices generated according to a point process, but either rely on simplified propagation models, or fail to take into account the impact of receiver structure, pulse waveform and modulation options.
The goal of this project is to define an innovative MUI model that takes into account the specific propagation characteristics of the TeraHertz channel, as well as the configuration of the transmitter and receiver. The definition of the model will move from the existing research on MUI for Impulse Radio Ultra Wide Band (IR-UWB) networks in the 3-10 GHz band, leveraging the common characteristics of MUI due to the impulsive nature of the signals shared by IR-THz and IR-UWB, and extend and complement such research so to account for waveforms and propagation characteristics typical of TeraHertz communications.
The model will be evaluated by comparing its predicted MUI contribution at the output of the receiver with the results of system level simulations carried out within a THz communications software package appositely developed within the project as a Matlab app. The package will be equipped with a GUI for maximum usability and released under an open source license to the research community; it will constitute thus by itself a valuable outcome of the project.
The achievement of the goals of the project defined in the previous section will lead to the following innovative contributions in the field of MUI modeling for TeraHertz communications.
1) the MUI model to be developed within the project will go beyond current state of the art in TeraHertz communications by taking into account specific characteristics of impulsive communications, building on the research work carried out in the last 15 years by the research group the proposer is part of, focusing on Impulse Radio Ultra Wide Band (IR-UWB) communications in the 3-10 GHz frequency band. MUI in IR-UWB is in fact characterized by specific properties [19]:
a) IR-UWB signals are characterized by a duty cycle D
b) the presence of peaks in the PDF of the MUI corresponding to nulls in the autocorrelation of the transmitted waveform
c) the presence of "heavy tails" in the PDF of MUI, with values of the PDF at large values od MUI larger than in non-impulsive signals.
The above properties of IR-UWB networks emerge from the impulsive nature of the transmitted signals, and since they are not related to the frequency range of operation, they remain valid for IR-THz networks. The typical duration of TeraHertz pulses is in the order of 0.1 picoseconds [05] leading to extremely low duty cycles even for transmission bit rates in the order of tens of Gb/s, which implies the above properties a) and c). In addition, typical adopted waveforms in THz communications are the derivatives of the Gaussian pulse, in particular the first [05], [21], [18] and the second [03], characterized by the presence of nulls in the autocorrelation, corresponding to peaks in the PDF of the MUI, as predicted by property b). Such properties are currently not captured by existing models for MUI in TeraHertz networks, and including them will be a clear advancement with respect to the current state of the art in interference modeling in IR-THz networks.
2) The proposed model will take into account the structure of the receiver, and include both OOK and Pulse Position Modulation (PPM) modulation schemes, which are the most common schemes considered in IR communications; current models for IR-THz networks only consider OOK modulation, and furthermore do not take into account the impact of the receiver, as discussed in the previous section.
3) The proposed model will focus on networks without power control, building on existing approaches proposed for UWB networks [22], and adapting and extending them so to take into account the propagation characteristics of TeraHertz channels.
4) The Matlab software package to be released as part of project outcomes will include all key aspects of TeraHertz propagation, and integrate them in a full-fledged transmission and communication chain, providing a comprehensive tool for system simulations not currently available to the research community, as current tools mostly focus on propagation and channel simulation, rather than on system-level modeling of a communication network. The package will be released as an open-source contribution to the research community
[19] N. C. Beaulieu and D. J. Young, "Designing time-hopping ultrawide bandwidth receivers for multiuser interference environments," Proceedings of the IEEE, vol. 97, no. 2, pp. 255-284, Feb 2009.
[20] A. R. Forouzan, M. Nasiri-Kenari, and J. A. Salehi, "Performance analysis of time-hopping spread-spectrum multiple-access systems: uncoded and coded schemes," IEEE Transactions on Wireless Communications, vol. 1, no. 4, pp. 671-681, Oct 2002.
[21] P. Singh, B.-W. Kim, and S.-Y. Jung, "Compressed Detection for Pulse- Based Communications in the Terahertz Band," Wireless Communications and Mobile Computing, vol. 2018, no. Article ID 2408496, pp. 1-10, September 2018.
[22] J. Mitra and L. Lampe, "Robust detectors for TH-IR-UWB systems with multiuser interference," in 2007 IEEE International Conference on Ultra-Wideband, Sep. 2007, pp. 745-750.