The future of wireless network generations is revolving toward unlocking the opportunities offered by virtualization and digitization services in smart city applications, with the aim to realize improved quality-of-experience (QoE) and bring several advantages to modern cities. According to the rapid development in the field of network virtualization, we envision that future smart cities will run over ubiquitous deployment of virtualized components that are controlled by artificial intelligence (AI), i.e., the conceptualization of the Digital Twin (DT) paradigm. The key principle of the DT relies on creating a holistic representation of wireless network elements, in addition to decoupling the information pertaining to physical objects and dynamics, into a cyber twin. The cyber twin will then leverage this information for AI models training, and then reasoning and decision making operations, which will be then reflected to the physical environment, for improved sustainability. Motivated by this, in this article, we put a forward-looking vision to the integration of DT in smart city applications, and the intertwined role of wireless technologies as being enablers and enabled by the DT. Moreover, we sketch the roadmap toward identifying the limitations of the DT in 6G-enabled smart cities, and open new horizons for further developments in different design aspects.

The highly dynamic nature of cognitive radio (CR) systems and their stringent latency requirements pose a major challenge in the realization of efficient intelligent transport systems (ITS). In this paper, we investigate relay selection and opportunistic spectrum access in conjunction with blockchain technology in a secure manner. Specifically, we propose a cross-layer method for secure relay selection, where secondary relays (SRs) are granted access to available spectrum bands based on the balance of their respective virtual wallets. These virtual wallets, which are built based on the SRs’ secrecy capacity and their behavior in the network, are the predominant factors that allow SRs to participate in an auction model. To quantify the trustworthiness of the SRs, we formulate a mathematical framework to evaluate the trust value of each SR, which is then leveraged for rewarding or penalizing the SR. Furthermore, we develop an offline blockchain framework to store the information of participating relays and make it available for future operations, in order to detect reputable and non-reputable relays in the presence of multiple eavesdroppers. The stored reputations of the participating relays are used to develop a self-learning algorithm to exclude the non-reputable relays from the selection group. Finally, we present thorough numerical results to demonstrate the superiority of the proposed system in terms of security, credibility, and integrity.

The advancements of mixed reality services, with the evolution of network virtualization and native artificial intelligence (AI) paradigms, have conceptualized the vision of future wireless networks as a comprehensive entity operating in whole over a digital platform, with smart interaction with the physical domain, paving the way for the blooming of the Digital Twin (DT) concept. The recent interest in the DT networks is fueled by the emergence of novel wireless technologies and use-cases, that exacerbate the level of complexity to orchestrate the network and to manage its resources. Driven by the internet-of-sensing and AI, the key principle of the DT is to create a virtual twin for the physical entities and network dynamics, where the virtual twin will be leveraged to generate synthetic data, in addition to the received sensed data from the physical twin in an on-demand manner. The available data at the twin will be the foundation for AI models training and intelligent inference process. Despite the common understanding that AI is the seed for DT, we anticipate the DT and AI will be enablers for each other, in a way that overcome their limitations and complement each other benefits. In this article, we dig into the fundamentals of DT, where we reveal the role of DT in unifying model-driven and data-driven approaches, and explore the opportunities offered by DT in order to achieve the optimistic vision of 6G networks. We further unfold the essential role of the theoretical underpinnings in unlocking further opportunities by AI, and hence, we unveil their pivotal impact on the realization of reliable, efficient, and low-latency DT. Finally, we identify the limitations of AI-DT and overview potential future research directions, to open the floor for further exploration in AI for DT and DT for AI.

Jamming attacks significantly degrade the performance of wireless communication systems and can lead to significant overhead in terms of re-transmissions and increased power consumption. Although different jamming techniques are discussed in the literature, numerous open-source implementations have used expensive equipment in the range of thousands of dollars with the exception of a few. These implementations have also tended to be partial band, and do not cover the whole available bandwidth of the system under attack. In this work, we demonstrate that flexible, reliable, and low priced software-defined radio (SDR) jamming is feasible by designing and implementing different types of jammers against IEEE 802.11n networks. First, to demonstrate the optimal jamming waveform, we present an analytical bit error rate expression of the system under attack by employing two common jamming waveforms: Gaussian noise and digitally modulated. Then, we validate this analysis through simulations using the MATLAB WLAN toolbox. Afterwards, we implement JamRF, a toolkit that employs a low-cost SDR to implement numerous types of jammers to validate the analysis. Obtained results showed that, to jam the whole 2.4GHz spectrum, a stateful-reactive jammer employing random channel hopping jamming strategy, achieves a packet loss ratio above 90%.

Hybrid precoding has been envisaged as an attractive alternative to fully digital precoding in massive multiple-input-multiple-output (mMIMO) systems, where it can ultimately reduce the cost and the power consumption while maintaining an acceptable sum rate. Within this context, deep learning (DL) is proposed as an optimization tool to realize this. However, most of the existing DL based hybrid precoding solutions are based on the convolutional neural networks (CNNs), which have inductive bias that limits the learning capability of the highly stochastic massive MIMO channel. Conversely, the present contribution proposes a novel DL based hybrid precoder that can achieve an improved performance at a reduced computation time compared to the CNN based techniques. This is achieved through the design of a Perceiver Neural Network (PNN) architecture for hybrid precoding, where the PNN accepts a noisy channel matrix as an input and produces the analog precoder and combiners as an output. Also, the proposed architecture learns to reshape the input data in order to achieve the best accuracy through a novel trainable reshaping module. Our design involves an offline phase, in which we build our realistic ray tracing based massive MIMO dataset to train our Perceiver-based hybrid precoder (PBHP). In this context, we conduct extensive experiments to compare the PBHP with a CNN-based hybrid precoder (CNN-HP). It is extensively shown that the proposed PBHP outperforms the CNN-HP in terms of both accuracy and inference time. Moreover, the PBHP is more robust when the transmit power is low and the number of antennas is large. Finally, the offered results demonstrate that the PBHP exhibits a drastically less inference time (by nearly an order of magnitude) than the CNN-HP, especially for higher number of antennas, rendering it a promising candidate for the next-generation wireless networks.

Visible Light Communication (VLC) is a promising enabling technology for the next-generation wireless networks, as it complements radio-frequency (RF)-based communications by providing wider bandwidth, higher data rates, and immunity to interference from electromagnetic sources. However, due to its unique characteristics, VLC is highly sensitive to the line-of-sight (LoS) blockage. Recently, intelligent reflecting surface (IRS) has been proposed as an innovative solution that dynamically reconfigures the wireless environment. The present contribution proposes a two-stage resource management framework in an indoor VLC system: In the first stage, a maximum possible fairness (MPF) algorithm is presented in order to maximize the fairness amongst the users. In the second stage, deep Q-learning is exploited in order to maximize the overall spectral efficiency (SE). The corresponding numerical results have shown that the proposed DQL-MPF framework exhibits superior performance in terms of the overall SE, achieved at fast convergence rate. More specifically, when the noise power is high and the number of users is relatively large, the DQL-MPF algorithm achieves a more than tenfold overall SE compared to the Baseline scheme. Moreover, the synergy between the MPF and the DQL algorithms is investigated. To this end, we demonstrate that the MPF algorithm maximizes the fairness amongst the users while the DQL algorithm maximizes the overall SE and improves the robustness against the noise.

Visible light communication (VLC) has been introduced as a key enabler for high-data rate wireless services in future wireless communication networks. In addition to this, it was also demonstrated recently that non-orthogonal multiple access (NOMA) can further improve the spectral efficiency of multi-user VLC systems. In this context and owing to the significantly promising potential of artificial intelligence in wireless communications, the present contribution proposes a deep Q-learning (DQL) framework that aims to optimize the performance of an indoor NOMA-VLC downlink network. In particular, we formulate a joint power allocation and LED transmission angle tuning optimization problem, in order to maximize the average sum rate and the average energy efficiency. The obtained results demonstrate that our algorithm offers a noticeable performance enhancement into the NOMA-VLC systems in terms of average sum rate and average energy efficiency, while maintaining the minimum convergence time, particularly for higher number of users. Furthermore, considering a realistic downlink VLC network setup, the simulation results have shown that our algorithm outperforms the genetic algorithm (GA) and the differential evolution (DE) algorithm in terms of average sum rate, and offers considerably less run-time complexity.

The emergence of Internet-of-Things (IoT) has led to the development of new energy efficient and long-range wireless technologies, which are necessary for the successful realization of IoT applications. Within this context, long range (LoRa) has emerged as one of the prominent low power wide area network (LPWAN) technologies that is envisioned to accommodate the future IoT requirements. However, current LoRa frameworks suffer from limited network capacity, particularly in dense deployments. Consequently, power domain-superposition modulation (PD-SPM) is integrated with LoRa to alleviate the aforementioned problem. In this paper, the error rate performance of a LoRa-enabled PD-SPM system is investigated over Rayleigh fading channels. Specifically, symbol error rate (SER) expressions are derived to characterize the performance of an arbitrary number of users under extreme fading conditions. Furthermore, Monte Carlo simulations are presented to validate the analytical framework.

The unprecedented growth in the number of connected devices has given rise to the Internet-of-Things (IoT) and led to an increasing demand for additional computational and communication resources. Within this context, unmanned aerial vehicles (UAVs) have shown to provide extended coverage, flexibility, and reachability. Motivated by this, in this paper, we develop a UAV-assisted data dissemination framework for IoT networks.  To this end, we formulate a joint optimization problem that aims to minimize the total energy expenditure, i.e., the sum of the energy consumed by the UAV and all the spatially-distributed IoT devices. We propose a deep reinforcement learning approach to solve the joint device classification, device association, and path planning optimization problem. In particular, we aim to 1) train a double deep Q-network agent in order to classify devices into two classes, and then using this classification we 2) develop an association algorithm based on the nearest-neighbor heuristic for device association, and 3) develop a path planning algorithm based on the Lin-Kernighan heuristic. Simulation results show that the proposed approach efficiently reduces the energy consumption as compared with the benchmark approaches, i.e., brute force approach and baseline approach. Furthermore, obtained results show that our approach provides a near optimum solution with a fraction of the time required compared to the brute force approach.

Federated learning (FL) has recently emerged as a novel technique for training shared machine learning models in a distributed fashion while preserving data privacy. However, the application of FL in wireless networks poses a unique challenge on the mobile users (MUs)’ battery lifetime. In this paper, we aim to apply reconfigurable intelligent surface (RIS)-aided wireless power transfer to facilitate sustainable FL-based wireless networks. Our objective is to minimize the total transmit power of participating MUs by jointly optimizing the transmission time, power control, and the RIS’s phase shifts. Numerical results demonstrate that the total transmit power is minimized while satisfying the requirements of both minimum harvested energy and transmission data rate.

UAVs can be used as aerial relays to provide communication services in remote uncovered areas or dense environments with occasional high capacity demands. However, due to the low power of Internet-of-Things (IoT) devices, UAV-based IoT applications, such as precision agriculture and environment monitoring, may experience high shadowing or equipment failure, which degrades the communications’ quality between IoT devices and their gateways. To tackle this issue, we consider the long range (LoRa) communication technology. Specifically, we investigate the performance of LoRA-enabled aerial communications, where a LoRa gateway communicates with a distant IoT device through the assistance of an amplify-and-forward aerial relay. Under the assumption of shadowed Rician fading channels, we characterize at first the end-to-end LoRa communication link. Then, we derive an exact symbol error rate expression for the underlying system model. Finally, numerical results are presented to corroborate the efficacy of our derived expressions and provide valuable insights into the error performance of LoRa-enabled aerial networks.

In this letter, we investigate the performance of reconfigurable intelligent surface (RIS)-assisted communications, under the assumption of generalized Gaussian noise (GGN), over Rayleigh fading channels. Specifically, we consider an RIS, equipped with N reflecting elements, and derive a novel closed-form expression for the symbol error rate (SER) of arbitrary modulation schemes. The usefulness of the derived new expression is that it can be used to capture the SER performance in the presence of special additive noise distributions such as Gamma, Laplacian, and Gaussian noise. These special cases are also considered and their associated asymptotic SER expressions are derived, and then employed to quantify the achievable diversity order of the system. The theoretical framework is corroborated by numerical results, which reveal that the shaping parameter of the GGN (alpha) has a negligible effect on the diversity order of RIS-assisted systems, particularly for large (alpha) values. Accordingly, the maximum achievable diversity order is determined by N.