The convergence of intelligent transportation, digital twin (DT) ecosystems, and vehicular edge intelligence is reshaping smart cities. With the rise of autonomous and context-aware vehicles, ultra-reliable, low-latency, and energy-efficient task orchestration frameworks are crucial in Internet of Vehicles (IoV) networks. In mission-critical situations, such as emergency response routing, disaster relief, and high-priority health transport, semantic task offloading must account for trust, adapt to high vehicle mobility, edge node reliability, and energy limitations. This paper proposes a quantum-inspired meta Proximal Policy Optimization (Qi-mPPO) algorithm for trust-aware semantic offloading in DT-enabled IoV systems with wireless energy harvesting. The approach leverages variational quantum circuits integrated with meta-learning to address non-stationary environments. A multi-objective reward function is formulated to jointly optimize latency, energy efficiency, semantic accuracy, and trust preservation. To ensure semantic relevance under vehicular mobility and energy constraints, quantum-informed policy regularization is applied. Simulation results demonstrate that Qi-mPPO outperforms classical and meta-reinforcement learning baselines in convergence rate, task latency, trust robustness, and energy consumption under realistic vehicular conditions.

This paper focuses on the energy and spectral efficient design of an indoor communication system that leverages terahertz (THz) and visible light communication (VLC). We first optimize THz access points (APs) deployment in an indoor environment equipped with VLC APs such that uniform data rate can be guaranteed for all arbitrarily located users in the room. We discretize the placement problem and then apply fractional programming techniques and a Majorization-Minimization (MM) approach to solve it. Then, we develop a novel mobility-aware resource allocation framework to optimize user-AP assignment, subchannel allocation (SA), and power allocation (PA) to maximize the handoff (HO)-aware sum rate and energy efficiency (EE) of hybrid THz/VLC networks. The HO-aware sum rate and EE adapts according to the HOs experienced by users. The proposed framework constrains users’ quality-of-service demands, transmit power budgets, molecular absorption loss thresholds, illumination requirements, and minimum electromagnetic field exposure. This joint problem is a mixed integer nonlinear programming problem which is generally intractable and mostly solved by decomposing into multiple sub-problems via alternating optimization. Different from the traditional approach, we cast this problem as a multi-objective optimization problem and obtain a solution that jointly optimizes all variables using quadratic optimization and MM approach. Computational complexity analysis is presented for both solutions. The proposed placement solution is much faster than the optimal solution. Moreover, the time complexity does not increase with augmenting the number of THz APs. Also, the proposed mobility-aware joint resource allocation solution significantly outperforms the existing benchmarks.

This paper explores the evolution of wireless communication networks from utilizing the sub-6 GHz spectrum and the millimeter wave frequency band to incorporating extremely high frequencies like optical and terahertz for 6G and beyond. While these higher frequencies offer broader bandwidths and extreme data rate capabilities, the transition from single-band and heterogeneous networks to multi-band networks (MBNs), where various frequency bands coexist introduces novel challenges in channel modeling, transceiver and antenna design, programmable simulation platforms, standardization, and resource allocation. This paper provides a tutorial overview from the communication design perspective of the various frequency bands, elaborating on the above issues. Then, we introduce and examine typical MBN architectures for future networks and provide a detailed overview of state-of-the-art resource allocation problems for existing MBNs that typically operate on two frequency bands. The considered resource allocation optimization problems and solution techniques are discussed comprehensively. We then identify key performance metrics and constraint sets that should be considered for resource allocation optimization in future MBNs and provide numerical results to depict how various system parameters and user behaviors can influence their performance. Finally, we present several potential research issues as future work for the design and performance optimization of MBNs.

Visible light communication (VLC) is envisioned as a core component of future wireless communication networks due to, among other reasons, the very large unlicensed bandwidth it offers and the fact that it does not cause any interference to existing radio frequency (RF) communication systems. In order to take advantage of both RF and VLC, most research on their coexistence has focused on hybrid designs where data transmission to any user could originate from either an RF or a VLC access point (AP). However, hybrid RF/VLC systems fail to exploit the distinct transmission characteristics (e.g., susceptibility of VLC transmissions to blockages, limited field-of-view of VLC APs and receivers, more coverage and better reliability of RF systems, etc.) of RF and VLC systems to fully reap the benefits they can offer. Aggregated RF/VLC systems, in which any user can be served simultaneously by both RF and VLC APs, have recently emerged as a more promising and robust design for the coexistence of RF and VLC systems. To this end, this paper, for the first time, investigates AP assignment, subchannel allocation (SA), and transmit power allocation (PA) to optimize the energy efficiency (EE) of aggregated RF/VLC systems while considering the effects of interference and VLC line-of-sight link blockages. A novel and challenging EE optimization problem is formulated for which an efficient joint solution based on alternating optimization is developed. More particularly, an energy-efficient AP assignment algorithm based on matching theory is proposed. Then, a low-complexity SA scheme that allocates subchannels to users based on their channel conditions is developed. Finally, an effective PA algorithm is presented by utilizing the quadratic transform approach and a multi-objective optimization framework. Extensive simulation results reveal that: 1) the proposed joint AP assignment, SA, and PA solution obtains significant EE, sum-rate, and outage performance gains with low complexity, and 2) the aggregated RF/VLC system provides considerable performance improvement compared to hybrid RF/VLC systems.

In this paper, we study the secrecy performance of non-orthogonal multiple access (NOMA) enabled visible light communication (VLC) broadcast channels in the presence of an active eavesdropper (Eve). The considered VLC system consists of multiple separately distributed light-emitting diodes arrays and multiple randomly located users (UEs) in an indoor room. User clustering is conducted to reduce the implementation complexity of successive interference cancellations. Two cooperative precoding strategies based on zero-forcing (ZF) and maximum ratio transmission (MRT) are designed using the effective channel of each cluster. Based on each precoding strategy, a sum secrecy rate maximization problem is developed to obtain the near-optimal power allocation (PA) to strengthen UEs’ confidential transmission and degrade Eve’s reception under minimum secrecy rate requirement, peak amplitude, non-negativity, and power constraints. To tackle the challenging non-convex problem for each precoding strategy, equivalent transformations and arithmetic-geometric mean approximation are conducted to convert the original problem into a series of geometric programming (GP) problems. Based on the reformulated problems, iterative algorithms are proposed to obtain near-optimal solutions by solving the GP problems through successive convex approximations. The convergence and complexity analysis of the proposed algorithms are studied. Simulation results show that the sum security performance of the proposed PA approach outperforms the conventional PA approaches in both ZF-based and MRT-based precoder schemes. The effectiveness of applying NOMA compared with the orthogonal multiple access-based scheme is also validated for the proposed system.

Visible light communication (VLC) has attracted a significant amount of research interest due to its ability to support high data-rates. However, the issue of inter-cell interference (ICI) caused by resource sharing and the line-of-sight (LoS) blockage problem are significant challenges that need to be considered in the design and analysis of VLC systems. This paper investigates the resource allocation problem for the downlink of an orthogonal frequency-division multiple access-based multi-cell VLC system, while considering ICI and LoS blockage. This is carried out under various system configurations employing different transmission modes. Specifically, the joint problem of subchannel allocation (SA) and power allocation (PA) to maximize the sum-rate is formulated as a combinatorial and highly non-convex optimization problem due to the binary and continuous optimization variables. To obtain an efficient solution, the original problem is first separated into the SA problem and the PA problem. Two simple, yet efficient, procedures based on the quality of the channel conditions and matching theory are proposed for the SA problem, respectively. Then, the quadratic transform approach is exploited to develop an algorithm for the PA problem. Simulation results demonstrate the effectiveness of the proposed solutions in terms of their fast convergence and overall performance.

This paper investigates the joint problem of access point (AP) assignment and power allocation (PA) in a three-tier hybrid radio frequency/visible light communication (VLC) heterogeneous network (HetNet). The main goal is to maximize the HetNet’s sum-rate under practical constraints such as APs’ power budgets and users’ quality-of-service (QoS) requirements, while maintaining an acceptable level of illumination in the VLC system. When this design problem is formulated mathematically, it turns out to be a combinatorial decision problem that involves non-linear constraints, and hence is NP hard. To efficiently obtain good quality solutions for the formulated problem, a reformulation into thecollege admission modelis first performed. Then, a distributed and low-complexity algorithm based on matching theory and an efficient heuristic PA scheme are proposed to obtain a good quality suboptimal solution for the joint problem. Simulation results highlight the robustness of the proposed solution and its significant gain in network sum-rate as compared to different benchmark schemes. The effect of various system parameters such as the minimum QoS and maximum illumination requirements on the performance of the proposed solution is studied. Finally, the theoretical analysis of convergence, stability, and complexity of the proposed technique is performed.

This paper investigates the joint problem of access point (AP) assignment and power allocation in a three-tier hybrid radio frequency/visible light communication (VLC) heterogeneous network (HetNet). The target is to maximize the HetNet's sum-rate under practical constraints such as APs' power budgets and users' quality-of-service constraints, while maintaining an acceptable level of illumination in the VLC system. This is an NP-hard problem due to the binary and continuous optimization variables. To obtain an efficient solution, the original problem is first reformulated into the well-known college admissions model. Then, a distributed and low-complexity algorithm based on matching theory and convex optimization is proposed to solve the joint problem. Simulation results highlight the robustness of the proposed algorithm and its significant gain in network sum-rate as compared to the considered benchmarks. Finally, the theoretical analysis on convergence, stability, and complexity of the proposed algorithm is provided.

Energy efficiency (EE) and spectral efficiency (SE) have been identified as key performance indicators in the design of future cellular networks. However, the available radio frequency (RF) spectrum is becoming highly saturated, thus making it difficult for network operators to achieve significant throughput and SE enhancement without increasing their power consumption. To that end, exploiting the abundant unlicensed spectrum in the visible light band to complement RF communication has become an important research direction in the design of wireless systems. Visible light communication (VLC) combines illumination and communication while significantly reducing the power consumption and related carbon footprint of wireless systems. This paper investigates the introduction of a VLC system in a two-tier RF heterogeneous network (HetNet). The EE and SE performance of the resulting three-tier HetNet is investigated, and a novel energy efficient resource allocation scheme is proposed. More specifically, the joint problem of user association and power control to maximize the EE is formulated as a fractional programming problem under the transmit power and quality-of-service requirements constraints. To tackle the nonconvexity of the problem, the original EE problem is first transformed into a parametric subtractive form. Then, the joint problem is separated into a user association and power control sub-problems. An efficient iterative algorithm is proposed to solve these two sub-problems, alternately. The performance of the proposed algorithm in terms of total network throughput, EE, and SE for different user densities is verified using simulation results.

The study of spectral efficiency (SE) in cellular networks has attracted significant research interest in the wireless community. Heterogeneous networks (HetNets) have emerged as a new paradigm to meet the fast growing demands for higher capacity and coverage in cellular networks. Previous works have focused on investigating either the power and bandwidth allocation problem or the power allocation problem for SE maximization in HetNets. These works were carried out under the assumption that users have already been associated. This paper presents a simple and effective method to optimize the SE of two-tier HetNets. Specifically, the joint optimization of user association and power control is formulated as a mixed integer programming problem. To tackle the non-convexity of the optimization problem, the Lagrange duality theory is applied to decompose the original problem into a user association sub- problem and a power control sub-problem, which are solved alternatively. Simulation results are used to demonstrate the fast convergence rate and the noticeable performance gains of the proposed algorithm as compared with conventional user association schemes under the assumption of equal power allocation.

In this paper, we investigate the joint effect of optimizing power allocation and backhaul links flow assignment within the backhaul network on the energy efficiency (EE) of a millimeter wave backhaul heterogeneous network (HetNet). We consider enforcing a strict throughput demand on all user equipment(UEs), called joint EE, power, and flow control (JEEPF), versus allowing an acceptable range of demands for each, called joint EE, power, flow control, and throughput (JEEPFT). This little change causes a drastic difference in the formulations of both problems. JEEPF is convex while JEEPFT is quasiconvex, for which we propose a bisection method based approach. Our simulation results show the superiority of JEEPFT over JEEPF and other simple benchmark schemes.