This survey provides a comprehensive analysis of digital twin (DT) technology as a transformative tool for advancing connected and autonomous vehicles (CAVs) and intelligent transportation systems (ITSs), focusing on advancements in vehicle safety, traffic management, and autonomous driving capabilities. The paper begins by discussing the foundational concepts and enabling technologies behind DT systems, setting the stage for their application in transportation networks. We review DT applications in vehicle safety, highlighting their role in real-time monitoring, predictive maintenance, and risk mitigation. Next, we explore the role of DT technology in optimizing traffic flow, enhancing traffic management, and enabling adaptive responses to dynamic conditions. The paper then examines the integration of DTs in intelligent and autonomous vehicles, emphasizing advancements in simulation, testing, and the development of autonomous driving functionalities. Finally, we outline future research opportunities and challenges for DT applications, providing a roadmap for their continued evolution in CAVs and ITS.

In this paper, we propose Euclidean geometric schemes to construct the codebooks for the space-time block coded spatial modulation (STBC-SM) system. The new codebook constructing schemes are more efficient than the previous exhaustive searching scheme. The result system is referred to as Euclidean geometry based space-time block coded spatial modulation (EG-STBC-SM) system. To achieve transmit diversity, two different schemes are introduced to construct sub-codebooks for the EG-STBC-SM system. In the first scheme, active transmits are selected based on the points and μ-flats of $d$ -dimensional Euclidean geometry over the Galois field $GF(p^s)$ . Furthermore, the extended orthogonal space-time block codes (EO-STBCs) are used to support more than two active transmit antennas (TAs) in the EG-SM-STBC system. In the second scheme, the flats of a Euclidean geometry are grouped into cyclic structure, which makes the encoding of EG-STBC-SM scheme very easy. In addition, a simple maximum-likelihood (ML) decoder is derived in this paper. BER performance of the EG-SM-STBC system is evaluated via computer simulation and theoretical upper bound. It is shown that the proposed EG-SM-STBC system outperforms various existing multiple-input multiple-output (MIMO) transmission counterparts of the same or lower spectral efficiencies.

Delay/disruption tolerant networking (DTN) is considered one of the most suitable technologies for implementing a space system of systems (SoS) internetworking architecture. Aggregation of multiple DTN bundles within a data transport block, which was proposed to resist space channel asymmetry, has been a controversy for years. In this paper, an experimental investigation of whether or not the aggregation of multiple DTN bundles within a single data transport block has performance advantage is presented. The investigation focuses on a space SoS internetworking scenario characterized by an asymmetric data rate. A model is developed for the minimum number of data bundles that should be aggregated within a Licklider transmission protocol block to avoid delay of acknowledgment transmission caused by channel asymmetry in the space SoS internetworking system.

The main objective of a Cooperative Multiple-Input Multiple-Output (CMIMO) system is to improve network throughput and network coverage and save energy. By grouping wireless devices as virtual multi-antenna nodes, it can thus simulate the functions of multi-antenna systems. A Space-Time Block Code (STBC) was proposed to utilize the spatial diversity of MIMO systems to improve the diversity gain and coding gain. In this paper, we proposed a cooperative strategy based on STBC and CMIMO, which is referred to as Space-Time Block Coded Cooperative Multiple-Input Multiple-Output (STBC-CMIMO) to inherit the advantages from both STBC and CMIMO. The theoretical performance analysis for the proposed STBC-CMIMO is presented. The performance advantages of the STBC-CMIMO are also shown by simulations. In the simulations, it is demonstrated that STBC-CMIMO can obtain significant performance compared with the existing CMIMO system.

In order to improve the energy efficiency (EE) performance of cooperative networks, this study combines non-orthogonal multiple access (NOMA) with simultaneous wireless information and power transfer (SWIPT) technologies to construct a cooperative relay network composed of one base station (BS), multiple near users, and one far user. Based on the network characteristics, a time-division resource allocation rule is proposed, and EE formulas regarding direct-link mode and cooperative mode are derived. Considering user selection and decoding performance, to obtain the optimal EE, this study utilizes a DinkelBach iterative algorithm based on the golden section (GS-DinkelBach) to solve the EE optimization problem, which is affected by power transmitted from the BS, achievable rates under three communication links, and quality of service (QoS) constraints of users. The simulation results show that the GS-DinkelBach algorithm can obtain precise EE gains with low computational complexity. Compared with the traditional NOMA–SWIPT direct-link network model and the relay network model, the optimal EE of the established network model could be increased by 0.54 dB and 1.66 dB, respectively.