Pulse-based communication systems are essential for terahertz (THz) communications, offering exceptional performance in diverse application scenarios, such as nanonetworks, THz integrated sensing and communications, and short-range ultra-high-speed communications. However, classical pulse-based modulations, such as time spread on-off keying (TS-OOK), pulse amplitude modulation (PAM), and pulse position modulation (PPM), suffer from limited capacity, mainly due to the absence of effective high-order modulation schemes and the long duration of consecutive transmission between adjacent pulses. Although these modulations have low energy consumption, they are difficult to balance the relationship between capacity and energy consumption. Recently, the generation of THz frequency and bandwidth continuously tunable (FBCT) pulses has enabled pulse-based M-ary QAM (PMQAM) to improve capacity, but it increases energy consumption compared with the classical modulations. To address these issues, an efficient high-order modulation method called position interleaved pulse modulation (PIPM) is proposed in this paper. More specifically, PIPM increases the dimension of modulation by using multiple pulse positions and interleaves the odd and even components of FBCT orthogonal pulses at these positions. In this design, PIPM utilizes the information from the odd component, even component, and pulse position to achieve high-order modulation. Furthermore, PIPM can balance the capacity and energy consumption by flexibly adjusting the relationship between the three-dimensional information. Detailed analysis of PIPM and its performance under multiple access scenarios is performed in this paper. Numerical results show that PIMP achieves a much better balance between energy efficiency and spectrum efficiency, as compared to existing schemes.

Carrier-free pulse-based waveforms are desired in terahertz (THz) communications since pulse-based systems have simpler transceiver architectures than carrier-based systems. For such a pulse-based THz communication system, there still lacks pulse waveforms that can support high-order modulation and flexible multiple access. In this paper, 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. Such a pulse-based waveform is called frequency and bandwidth continuously tunable (FBCT) pulse. By making the derivative orders of all weighted terms odd or even, a pair of orthogonal FBCT pulses can be generated. Based on the pair of orthogonal FBCT pulses, a basic pulse-based$M$-ary quadrature amplitude modulation ($\text{P}M$QAM) scheme can be readily achieved. 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. Numerical results demonstrate that FBCT pulse is significantly effective and flexible in supporting carrier-free THz communications.

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.

In a 5G integrated backhaul and access (IAB) network, an IAB-donor and multiple IAB-nodes form a multi-hop wireless backhaul network. When a terminal is connected to an IAB-node, the traffic flows generated by the terminal can be backhauled to the IAB-donor. Due to the mobility of terminals, access links are error-prone and cause difficulty in ensuring end-to-end quality of service (QoS) of traffic flows. To improve access link reliability, multi-connectivity is considered in IAB, i.e., a terminal is connected to multiple IAB-nodes. However, to ensure end-to-end QoS, multi-connectivity must be considered together with multi-hop backhauling. Thus, an effective-capacity based resource allocation (eReal) scheme is developed to establish end-to-end multi-connectivity. The objective of the scheme is to guarantee end-to-end QoS and ensure outage probability is below the given threshold. Since traffic flows are classified into the guaranteed bit rate (GBR) and the non-GBR types, the scheme is formulated as two joint route selection and resource allocation problems to provide differentiated services with minimum resource consumption. Since both problems are NP-hard, they are solved using column generation. Performance results show that eReal serves various traffic flows with over 95% QoS guarantees and also significantly outperforms existing schemes.