Frequency and Bandwidth Tunable Pulse Waveform Design for Carrier-Free THz Communications

Abstract

Carrier-free pulse-based waveforms are desired in terahertz (THz) communications, since pulse-based systems have simpler transceiver architectures than carrier-based systems. Nowadays, Gaussian pulses and higher time order derivative (HTOD) Gaussian pulses are commonly used in pulse-based communications. However, existing Gaussian pulses span a large consecutive spectrum, so the communication distance is constrained by those frequencies with high molecular absorption loss. HTOD Gaussian pulses can avoid the frequency band of molecular absorption peak by tuning its center frequency, but the center frequency cannot be adjusted continuously. To resolve these issues, a pulse-based waveform with continuously tunable center frequencies and bandwidths is designed for carrier-free THz communications. More specifically, a Gaussian pulse is utilized as the basic pulse, and then the weighted sum of its high-order derivatives is used to generate waveforms with tunable frequencies and bandwidths according to the probability density function of Rice distribution. In this paper, such a pulse-based waveform is called frequency and bandwidth continuously tunable (FBCT) pulse. Moreover, with frequency and bandwidth tunability, FBCT pulse can support pulse division multiple access (PDMA) with tunable bandwidth, through which frequencies with high molecular absorption loss can be avoided. The basic mechanisms of multiple access based on FBCT pulse are analyzed. Numerical results demonstrate that FBCT pulse is significantly effective and flexible in supporting carrier-free THz communications.