Integrated sensing and communications (ISAC) has emerged as a promising technology for future wireless networks, particularly for aerial platforms where efficient waveform designs are indispensable for joint communication and sensing. In this paper, we investigate the waveform characteristics of orthogonal time frequency space (OTFS) and orthogonal frequency division multiplexing (OFDM) signals modulated with Zadoff–Chu (ZC) sequences. We construct two-dimensional (2D) ZC sequence codewords for OTFS modulation and a truncated ZC sequence for OFDM, and analyze their delay–Doppler (DD) domain behavior using the ambiguity function. The analytical results show that both waveforms exhibit symmetric resolution properties in the delay and Doppler dimensions, while numerical evaluations demonstrate that ZC-modulated OTFS (ZC-OTFS) achieves a narrower mainlobe, a higher peak-to-sidelobe ratio (PSLR), and more stable sidelobes compared to ZC-modulated OFDM (ZC-OFDM), and simultaneously maintains a low peak-to-average power ratio (PAPR). In addition, the simulation results further confirm the DD symmetry of both waveforms.

This paper proposes an integrated sensing and communication (ISAC) waveform design using the Zadoff-Chu (ZC) sequence based on orthogonal frequency division multiplexing (OFDM). The correlation property of the ZC sequence is utilized to achieve the target range (root mean square error (RMSE) can reach approximately 0.3m) and velocity (RMSE can reach approximately 0.2m/s) detection. This proposal also implements a fixed-angle beam-scanning method to obtain the targets' 3D positions. This scheme is simulated with different bands and numerologies to verify its versatility.

This paper investigates a spatial division multiple access (SDMA) enabled non-orthogonal multiple access (NOMA) integrated sensing and communications (ISAC) framework. A dual-functional base station serves multiple communication users via SDMA and transmits a superimposed NOMA-ISAC signal for radar sensing. A transmit beamforming optimization problem is formulated to maximize the sensing signal-to-interference-plus-noise ratio (SINR). To address the non-convexity, a two-level iterative algorithm based on the Dinkelbach method and semidefinite relaxation (SDR) is proposed. Numerical results show the performance gain of combining SDMA into the NOMA-ISAC system and the trade-off between sensing and communications.

In most Internet of Vehicles (IoV) scenarios, intelligent vehicle terminals are required to cope with a multitude of heterogeneous tasks, each of which is subject to increasingly strict constraints on delay and energy consumption. Task offloading is an efficient way to tackle this issue. However, due to performance constraints, a single or two-tier offloading strategy can not enable fine-grained task allocation and flexible service deployment. To address the above problems, we propose a collaborative cloud-edge-end task offloading scheme for IoV scenarios. Since traditional single-agent Deep Reinforcement Learning (DRL) makes it difficult to coordinate multiple objectives of dynamic services simultaneously, we propose a task offloading strategy based on multiagent Deep Deterministic Policy Gradient (DDPG), to jointly consider service delay and energy consumption. We further introduce attentive experience replay (AER) to mitigate the issue of insufficient experience sampling in the DDPG algorithm caused by the catastrophic forgetting problem. Through simulation of IoV scenarios, our proposed model significantly enhances task offloading effectiveness and concurrently reduces delay by 10.6% and energy consumption by 8.1% compared to other state-of-the-art baseline algorithms.

Orthogonal time frequency space (OTFS) has been identified as an effective approach for addressing delay and Doppler shifts inherent in the physical transmission character-istics of low earth orbit satellite (LEO-Sat) communications. In this paper, we investigated the performance of zero-forcing (ZF) and linear minimum mean square error (LMMSE) equalizers in OTFS LEO-Sat unmanned aircraft systems (UAS)-assisted multi-hop system. We analytically derived the signal-to-noise ratio (SNR) and signal-to-interference-plus-noise ratio (SINR) for these equalizers. Further, we developed the multi-hop ZF and LMMSE equalizers tailored for the multi-hop Amplify-and-Forward (AF) relay scheme. Utilizing the aforementioned expressions, we derived the SNR for multi-hop Decode-and-Forward (DF) relay and multi-hop AF relay schemes. Simulation results indicate that, with appropriate link combining selection, the use of multi-hop AF relay scheme is feasible. Moreover, in LEO-Sat multi-hop scenarios, strict adherence to the equalization sequence is crucial for optimal performance.

Application of Unmanned Aerial Vehicles (UAVs) as small airborne base stations is gradually becoming a research hotspot in the field of wireless communications. With the flexible deployment, wide coverage and low cost, UAV communications show great potential in the fields of emergency rescue, environmental monitoring and military operations. In particular, the easier availability of line-of-sight (LOS) links for UAVs makes its combination with millimetre wave (mmWave) technology significantly enhance the communication bandwidth and data transfer rate. However, the very limited coverage of mmWave communications greatly affects the actual data rates provided by small aerial base stations of mmWave UAVs, especially considering user movement on the ground. In this paper, we study the joint optimisation problem of UAV deployment, user association, spectrum resource allocation in millimetre-wave heterogeneous networks, and explore the impact of different user movement models on system performance. Given that this problem is NP-hard, our paper proposes an MCR-SAC method to maximize the network’s total throughput. Simulation results demonstrate an average 18% improvement in total transmission rate compared to the conventional.

Orbital Angular Momentum (OAM) has attracted significant attention in the field of wireless communications due to its potential for high-capacity data transmission through mode multiplexing. However, OAM experiences severe performance degradation due to inter-mode interference (IMI) caused by antenna misalignment. In this paper, we propose a novel method to suppress IMI caused by misalignment for uniform circular array (UCA)-based OAM multiplexing. We discovered that IMI can be minimized when the IQ data of each OAM mode are close to each other in the constellation, enhancing robustness to misalignment. Therefore, we propose a method, where the IQ data of one OAM mode (reference OAM mode) is selected from the entire constellation range, and the IQ data of the other OAM modes are selected from a range close to this reference OAM mode. The proposed method is shown to prevent system capacity degradation compared to traditional method when the antenna is tilted. Moreover, in the proposed method, the reference OAM mode stream shows minimal performance degradation when the antenna is tilted. Furthermore, our proposed method is well-suited for adaptive modulation, effectively adjusting to varying communication conditions to maintain optimal performance.

With the increasing demand for sensing functions in the 6-th generation (6G) wireless communication networks, waveform design has become critical. The waveform must ensure a high quality of service in communication and achieve high precision in sensing; thus, interference between these two functions should be minimized. This paper proposes a power division waveform design for integrated sensing and communication (ISAC) based on orthogonal frequency division modulation (OFDM). This waveform design utilizes the Zadoff-Chu (ZC) sequence as the symbol sequence for sensing. The probability of detection for this method can reach approximately 0.8. The properties of the ZC sequence make it easy to implement in LTE and NR base stations and allow it to be effectively eliminated through successive interference cancellation. Additionally, the potential of this waveform in channel estimation (CE) is also analyzed, demonstrating an accuracy of CE under 3.5 × 10−3.

The number of terminals connected to the satellite network is expected to increase, influenced by the recent increase in communication requirements. Since the delay time cannot be ignored in links between geostationary orbit satellites and ground stations, a multiple access scheme that can accommodate many stations while minimizing retransmissions is required. In this paper, we propose a protocol for mobile satellite communications that aims to achieve low latency and high reliability by applying Successive Interference Cancellation (SIC) to Power Level Division Multiple Access (PDMA) using power and time domains. As one of the use cases, an urban model with traffic signals and buses as relay stations was assumed. First, we conducted a theoretical evaluation of communication quality and confirmed that PDMA achieves higher spectrum efficiency than conventional schemes. Then, we conducted simulations assuming the actual urban environment based on the Line of Sight duration and other factors to compare the performance of the proposed method with that of other multiple access schemes. The results showed that the proposed method reduced the delay by about 70% and reached higher throughput compared to the conventional scheme, even when using a lower level primary modulation scheme.

The use of space elevators is being considered as a new possibility for satellite communications. However, there has been no research on communication using space elevators. In this study, we evaluated the communication performance using space elevators. In particular, we studied the installation altitude of the space elevator at low-altitude stations. As a use case of communication, wireless communication was assumed to be used in the downlink of communication from the space elevator to the ground. The communication performance in wireless communication is mainly determined by the received power. The received power is mainly affected by transmit power, distance attenuation, shadowing, and fading. Among them, fading affects the received power due to different communication models depending on whether direct waves are available for communication or not. Since space elevator-based communications can be regarded as low earth orbit satellite communications and fixed communications due to the nature of space elevators, fading models are an important factor in evaluating the communications performance of space elevators, assuming actual communications. In this study, a communication model for each city model was obtained from data of real cities. Using the communication model, the communication performance of the space elevator was evaluated for each city model.

Non-terrestrial network (NTN), especially HighAltitude Platform Station (HAPS), is a popular choice because of low latency, deployment flexibility, and disaster resilience. In order to increase the availability of HAPS, a new multiple access system that improves performance, such as throughput and user fairness, is required. Although Non-Orthogonal Multiple Access (NOMA) is a promising technology for improving spectral efficiency, there are significant differences in transmission rate according to power levels for NOMA. Since ground-HAPS links are the end part of NTN and the HAPS network is expected to be used for the mobile network, the user fairness of NOMA should be improved. Thus, to increase throughput guaranteeing user fairness and transmission accuracy for HAPS, we implement Power Level Division Multiple Access (PDMA) which power levels of users are randomly switched in each timeslot. In this paper, we propose a new system applying PDMA for ground-HAPS uplink network with hybrid Free Space Optics (FSO) / millimeter wave communication. In our system, it switches optical and millimeter waves according to the channel state of users. By simulation results, the throughput of PDMA is higher than that of Orthogonal Multiple Access (OMA), and its user fairness is significantly improved compared with NOMA.

GPS is known to be vulnerable to GPS spoofing. This can be divided into three stages based on technical aspects: Simplistic, Intermediate, and Sophisticated [1]. Intermediate spoofing is a feasible and threatening technology. However, most of the existing research on mobile device spoofing focuses only on the Simplistic spoofing, which is the least threatening, and there are few experimental-based studies specifically on Intermediate spoofing. In this article, we conduct an experiment of Simplistic and Intermediate spoofing on mobile terminals using an open-source GPS signal generation simulator and analyze the threats.

Terahertz (THz) band is a frequency range starting from 0.1 THz to 10 THz. It is considered a new frequency band resources for future communication systems. However, the high absorption attenuation of THz waves in the atmosphere makes utilizing this frequency range very difficult. Current research on THz has rarely focused on satellites, aircraft, or other long-distance communications. Moreover, due to the channel model’s limitations, some research cannot easily be applied to the entire THz band. So in this paper, we analyze the atmospheric attenuation on the propagation of THz waves in the long-distance scenario with a universal model. Then we propose a new non-orthogonal multiple access (NOMA) scheme (direct NOMA) according to the atmospheric attenuation. Through simulation, we analyzed the system capacity and the bit error rate of the three multiple access schemes (conventional NOMA, direct NOMA, and OMA) in this scenario. The simulation result verified the feasibility of THz in this scenario, and it points out that direct NOMA can increase the capacity and reliability of this system.

Non-Orthogonal Multiple Access (NOMA) is attracting attention as a key technology for 5G because of its high spectral efficiency and high throughput. In addition, satellite communication, especially Low Earth Orbit (LEO), is popular choice for global communication because of its high global connectivity. In this paper, we apply uplink and downlink NOMA for inter-satellite communication to achieve delay suppression and increased throughput. We analyze the BER and transmission rate of the proposed system by simulation.