Research on Ultra‐Connectivity in 6G Wireless Networks at Informatics Institute

Information and Communications Research Group (ICRG) at Informatics Institute conducts academic and industrial research projects for beyond-5G and 6G next-generation communication networks. Along with that, ICRG publishes in the fields of green communications, NOMA, mobile edge computing, IRS, FSO, and vehicular communications in journals of high impact factors.

We are heading toward a future where everything is entirely automated and managed remotely. The fast development of new applications like artificial intelligence (AI), virtual reality, three-dimensional (3D) media, and the internet of things (IoT) has led to a vast amount of traffic. Autonomous systems are gaining popularity in a variety of fields, including industry, health, transportation, seas, and space. Millions of sensors will be implanted in cities, automobiles, houses, industries, toys, and other settings to give a smart life and automated systems. As a result, these apps will demand a high data throughput as well as reliable connectivity. Fifth-generation (5G) wireless networks have already been installed in several regions of the world. 5G networks will be unable to create a fully automated and intelligent network that offers everything as a service and a fully immersive experience.

To overcome the limitations of 5G for obstacles, a sixth-generation (6G) wireless technology with additional appealing characteristics will be required. The convergence of all previous aspects, such as network densification, high throughput, high dependability, low energy consumption, and huge connection, will be the major drivers of 6G. The 6G system would also carry on the previous generations’ tendencies, which included new services and the introduction of new technology. AI, smart wearables, implants, autonomous vehicles, computing reality gadgets, sensing, and 3D mapping are among the new offerings. The capacity to handle large amounts of data and very high-data-rate connection per device is the most crucial need for 6G wireless networks. In other words, massive connection, low latency, high data rates, extensive coverage, and great dependability are expected to be possible with 6G wireless networks shown in Figure 1.

ICRG Group
Our group in the informatics institute mainly focuses on the cutting-edge research field of 6G. Several topics on the 6G fields are given in Figure 1 such as battery lifetime, latency, energy efficiency. Along with that, green communication, NOMA, edge computing, IRS, FSO, non-terrestrial networks and vehicular communications are involved in the scope area of our research topics (hyper-link: https://icrg.itu.edu.tr/research/). Being a part of the Informatics Institute, ICRG has 10+ active researchers including post-doctoral research associates, Ph.D./MS students, and undergraduate students, as well as collaborators from several different universities. More information on our group is provided at https://icrg.itu.edu.tr. During this year, our group members have published several papers. The published papers in 2023 are listed in the following:

S. Koşu, M. Babaei, S. Ö. Ata, L. Durak-Ata and H. Yanikomeroglu, “Linear/Non-Linear Energy Harvesting Models via Multi-Antenna Relay Cooperation in V2V Communications”, IEEE Trans. Green Commun., 2023. M. Ardanuc, M. Basaran, Y. Hmamouche, L. Durak-Ata and H. Yanikomeroglu, “Energy Efficiency Analysis in Heterogeneous Networks: A Stochastic Geometry Perspective,” IEEE Open Journal of Vehicular Technology,vol. 4, pp. 438-443, 2023, doi: 10.1109/OJVT.2023.3269890. H. Maleki, M. Basaran, L. Durak-Ata, “Handover-enabled dynamic computation offloading for vehicular edge computing networks,” IEEE Transactions on Vehicular Technology, vol. 72, no. 7, pp. 9394-9405, July 2023, doi: 10.1109/TVT.2023.3247889. S. Koşu and S. Ö. Ata , “NOMA-enabled Cooperative V2V Communications with Fixed-Gain AF Relaying”, Balkan Journal of Electrical and Computer Engineering, vol. 11, no. 1, pp. 1-12, Jan. 2023, doi:10.17694/bajece.1090937 B. Atan, M. Basaran, N. Calik, S. T. Basaran, G. Akkuzu and L. Durak-Ata, “AI-Empowered Fast Task Execution Decision for Delay-Sensitive IoT Applications in Edge Computing Networks,” in IEEE Access, vol. 11, pp. 1324-1334, 2023, doi: 10.1109/ACCESS.2022.3232073. H. Alakoca, M. Namdar, S. Aldirmaz-Colak, M. Basaran, A. Basgumus, L. Durak-Ata, H. Yanikomeroglu, “Metasurface Manipulation Attacks: Potential Security Threats of RIS-Aided 6G Communications,” in IEEE Communications Magazine, vol. 61, no. 1, pp. 24-30, January 2023, doi: 10.1109/MCOM.005.2200162. S. Koşu, M. Babaei and L. Durak-Ata, “Integrated Satellite-Terrestrial Relay Network over Generalized-K Fading Channel”, IEEE Int. Black Sea Conf. Commun. and Networking (BLACKSEA’23), 4-7 July 2023, Istanbul, Turkey. S. Aldirmaz-Colak, M. Basaran, N.A. Bastug, N. Calik, E. Basar, L. Durak-Ata, “Estimation of Correlated Channels in Reconfigurable Intelligent Surfaces-Enabled 6G Networks,” IEEE Int. Black Sea Conf. Commun. and Networking (BLACKSEA’23), 4-7 July 2023, Istanbul, Turkey. M. Namdar, A. Basgumus, H. Alakoca, S.O. Ata, and L. Durak-Ata, “IRS-aided Communication Systems in the Presence of Multiple Eavesdroppers,” IEEE Signal Proc. Commun. Appl. Conf. (SIU’22), 5-8 Jul. 2023, Istanbul, Turkey.

Project:
The Scientific and Technological Research Council of Turkey (TUBITAK) in the context of the 1001 project, “Ultra-Connectivity for 6G Wireless Communications: UAV and Intelligent Reflective Surface Enabled Heterogeneous Network Design”.

In the context of 6G, networks are anticipated to include not just terrestrial but also flyable network pieces, and hence infrastructure functionality for both terrestrial and non-terrestrial networks would differ significantly. Non-terrestrial networks will be made up of a variety of vertical parts, including satellites and flying base stations equipped with unmanned aerial vehicle (UAV) BSs. In contrast to fixed-position terrestrial BSs, wireless networks utilizing UAVs can ensure communication continuity in unanticipated extreme conditions by working autonomously in hard-to-reach places. In heterogeneous networks (HetNets), intelligent reflecting surfaces (IRS), which are designed as next-generation transceivers, come into focus with low power consumption and secure communication characteristics. In the near future, these communication nodes, which may function as either BSs or users in a network connection, are expected to become increasingly widespread. Its goal is to use UAV and IRS to reveal the vertical HetNet’s (VhetNet) energy and communication efficiency, as well as physical layer security, in terms of trajectory, position, and altitude depicted in Figure 2. This project has been successfully completed.

Thesis:
Our ICRG group member, Beste Atan, defended his PhD thesis, entitled “New Edge Computing Offloading Methods for Next Generation Wireless Networks.”

The increasing number of mobile applications and massive deployment of connected IoT devices cause computation load due to intensive task requests coming from devices. Computing these tasks by fulfilling the latency requirements of the features or applications are one of the big argument in the next generation of networks. One of the promising methods to address the aforementioned problems is offloading the task computing process to edge servers that are in close proximity to the users. This solution is defined by The European Telecommunications Standards Institute (ETSI) and called multi-access edge computing (MEC). In recent years, the development of learning methods in artificial intelligence (AI) technology helps to create new methods for resolving these kinds of challenging problems. By integrating AI algorithms into edge network environments, it is possible to accelerate the task execution decision-making process and answer the latency-sensitive task execution demands of mobile and IoT devices.

Published journals:

S. Koşu, M. Babaei, S. Ö. Ata, L. Durak-Ata and H. Yanikomeroglu, “Linear/Non-Linear Energy Harvesting Models via Multi-Antenna Relay Cooperation in V2V Communications”, IEEE Trans. Green Commun., 2023.

Vehicle-to-vehicle (V2V) communications is a part of next-generation wireless networks to create smart cities with the connectivity of intelligent transportation systems. Besides, green communications is considered in V2V communication systems for energy sustainability and carbon neutrality. In this scope, radio-frequency (RF) energy harvesting (EH) provides a battery-free energy source as a solution for the future of V2V communications. Herein, the employment of RF-EH in V2V communications is considered, where the bit error probability (BEP) of a dual-hop decode-and-forward relaying system is obtained depending on the utilization of antennas at the relay. The multiple antenna power-constraint relay harvests its power by applying dedicated antenna (DA)/power splitting (PS) EH modes and linear (L)/nonlinear (NL) EH models. Moreover, the links between nodes are exposed to double-Rayleigh fading. Finally, the performance of different system parameters is compared using theoretical derivations of BEP. The results provide a comprehensive analysis of the proposed system considering PS/DA-EH modes and L/NL-EH models, as well as deterministic/uniformly distributed placement of nodes. It is observed that PS-EH outperforms DA-EH assuming a placement of an equal number of antennas and distances. Moreover, optimal performance of PS/DA-EH is achieved by allocating more power and increasing the number of antennas for EH, respectively.   M. Ardanuc, M. Basaran, Y. Hmamouche, L. Durak-Ata and H. Yanikomeroglu, “Energy Efficiency Analysis in Heterogeneous Networks: A Stochastic Geometry Perspective,” IEEE Open Journal of Vehicular Technology,vol. 4, pp. 438-443, 2023, doi: 10.1109/OJVT.2023.3269890. In this paper, we present the energy efficiency (EE) analysis of a multi-tier cellular network, where intra- and inter-tier dependence in the base station (BS) locations are captured via point processes, i.e., three variants of hard-core point processes (HCPPs) and the Poisson hole process (PHP). The analytical expression for EE is derived by approximating both the average power consumption of BSs and the coverage probability using an approximate signal-to-interference ratio analysis based on the Poisson point process (PPP). It is demonstrated that the proposed Matérn HCPP Type-I-PHP model provides better EE results compared to the other HCPP-PHP and PPP models.

H. Maleki, M. Basaran, L. Durak-Ata, “Handover-enabled dynamic computation offloading for vehicular edge computing networks,” IEEE Transactions on Vehicular Technology, vol. 72, no. 7, pp. 9394-9405, July 2023, doi: 10.1109/TVT.2023.3247889.

The computation offloading technique is a promising solution that empowers computationally limited resource devices to run delay-constrained applications efficiently. Vehicular edge computing incorporates the processing capabilities into the vehicles, and thus, provides computing services for other vehicles through computation offloading. In this paper, we consider an intelligent task offloading scenario for vehicular environments including smart vehicles and roadside units, which can cooperate to perform resource sharing. Intending to minimize the average offloading cost which takes into account energy consumption together with delay in transmission and processing phases, we formulate the task offloading problem as an optimization problem and implement an algorithm based on deep reinforcement learning with Double Q-learning which allows user equipments to learn the offloading cost performance by observing the environment and make steady sequences of offloading decisions despite the uncertainties of the environment. Simulation results demonstrate that the proposed scheme achieves low-cost performance compared to the existing offloading decision strategies in the literature.

B. Atan, M. Basaran, N. Calik, S. T. Basaran, G. Akkuzu and L. Durak-Ata, “AI-Empowered Fast Task Execution Decision for Delay-Sensitive IoT Applications in Edge Computing Networks,” in IEEE Access, vol. 11, pp. 1324-1334, 2023, doi: 10.1109/ACCESS.2022.3232073.

As the number of smart connected devices increases day by day, a massive amount of tasks are generated by various types of Internet of Things (IoT) devices. Intelligent edge computing is a promising enabler in next-generation wireless networks to execute these tasks on proximate edge servers instead of smart devices. Additionally, regarding the execution of tasks in edge servers, smart devices could provide a low-latency environment to the end users. In edge computing scenarios, the number of task requests, resource constraints of edge servers, mobility of connected devices, and energy consumption are the main performance considerations. In this paper, the AI-empowered fast task decision method is proposed to solve the multi-device edge computing task execution problem by formulating it as a multi-class classification problem. The extensive simulation results demonstrate that the proposed framework is extremely fast and precise in decision-making for offloading computation tasks compared to the conventional Lyapunov optimization-based algorithm results by ensuring the guaranteed quality of experience. H. Alakoca, M. Namdar, S. Aldirmaz-Colak, M. Basaran, A. Basgumus, L. Durak-Ata, H. Yanikomeroglu, “Metasurface Manipulation Attacks: Potential Security Threats of RIS-Aided 6G Communications,” in IEEE Communications Magazine, vol. 61, no. 1, pp. 24-30, January 2023, doi: 10.1109/MCOM.005.2200162. We propose novel reconfigurable-intelligent-surface (RIS)-based energy harvesting (EH) systems with linear EH (L-EH) and non-linear EH (NL-EH) models where channels are exposed to Nakagami- m fading. We also compare two RIS-based EH systems in terms of RIS locations, namely RIS-EH and RIS-information processing (RIS-IP). In the RIS-EH, RIS increases the amount of harvested energy, while in the RIS-IP, RIS is utilized to improve the information processing link. Closed-formed expressions of throughput, outage probability, and average harvested power are derived and confirmed via simulation. The L-EH model overestimates system performance, while the NL-EH model provides a realistic interpretation of EH system design.   S. Koşu and S. Ö. Ata , “NOMA-enabled Cooperative V2V Communications with Fixed-Gain AF Relaying”, Balkan Journal of Electrical and Computer Engineering, vol. 11, no. 1, pp. 1-12, Jan. 2023, doi:10.17694/bajece.1090937 By virtue of its improving bandwidth efficiency along with user fairness, non-orthogonal multiple access (NOMA) technique is considered a promising method for next-generation wireless communication systems. Since fading effect of wireless channels in vehicle-to-vehicle (V2V) communication systems are more severe than those in traditional systems, in this study, we employ the power-domain downlink NOMA technique in cooperative V2V communication systems to enhance data transmission capacity and network efficiency. In the proposed system, the base station communicates with two vehicular nodes, namely near and far users, through a relay vehicle employing the fixed-gain amplify-and-forward scheme. In real-life scenarios, the relay and the users move in high velocities; hence, the corresponding fading channels between these nodes are exposed as having double-Rayleigh fading characteristic in which the fading coefficient of a wireless channel is modeled as the product of two Rayleigh distributed random variables. To analyze the system performance, we first investigate the outage probability and derive its exact closed-form expressions for the near and far users. Then, we make the exact ergodic capacity analysis and obtain the closed-form solution for the near user. We also give analytic and numerical results to evaluate the performance of the proposed system and show the consistency of Monte-Carlo simulations with analytical derivations. It is observed that even with the small power allocation, both performances of the near user mostly outperform the far user.

Published conference papers:

S. Koşu, M. Babaei and L. Durak-Ata, “Integrated Satellite-Terrestrial Relay Network over Generalized-K Fading Channel”, IEEE Int. Black Sea Conf. Commun. and Networking (BLACKSEA’23), 4-7 July 2023, Istanbul, Turkey.

Current satellite communication solutions propose a network solution that is compatible with the existing network and 6G architecture in order to provide global coverage for rural areas and emergency applications worldwide. Therefore, integrated satellite-terrestrial technologies will enable ubiquitous connectivity for any type of end user. In this paper, we propose cooperative communication in which the satellite station transmits its information to the ground base station. The signal is then transmitted to the receiver using a decode-and-forward relaying protocol. The satellite link is presumed to be shadowed Rician, whereas the terrestrial link is referred to as Generalized-K fading since it is the generalized representation of conventional small-scale channel models in cellular communications. Alternatively, assuming a special case in which the end user is a vehicular node, the appropriate channel is selected as double Rayleigh fading on the terrestrial link. Due to the mobility of the ground user, it is assumed that the distance over the terrestrial link is uniformly distributed. In addition, several system parameters are considered when evaluating system performance, including outage probability and bit-error probability. In order to confirm the derived mathematical formulas, computer-based Monte Carlo simulations are conducted. The results indicate that the shadowing parameter of the satellite link and the distance of the terrestrial link has a significant impact on the proposed system performance.

S. Aldirmaz-Colak, M. Basaran, N.A. Bastug, N. Calik, E. Basar, L. Durak-Ata, “Estimation of Correlated Channels in Reconfigurable Intelligent Surfaces-Enabled 6G Networks,” IEEE Int. Black Sea Conf. Commun. and Networking (BLACKSEA’23), 4-7 July 2023, Istanbul, Turkey.

Reconfigurable intelligent surfaces (RIS) are one of the possible candidate technologies for 6th generation (6G) wireless communications owing to their robustness against weak channel conditions. They allow using of an additional reflecting surface to assist the information transmission between the base station (BS) and user equipments (UEs) to improve the communication system performance resulting in a more favorable communication environment. In this paper, an overall perspective for RIS-enabled channel estimation is presented where the channels are modeled as correlated (i.e., as the realistic case) due to the spatial deployment of transceiver antennas. Accordingly, two main channel estimation approaches are considered to determine the performance of the overall RIS-enabled wireless communication. These approaches include i) least squares-based conventional estimation for the effective channel consisting of a direct channel and RIS-assisted cascaded channel and ii) deep learning (DL)-aided estimation. Computer simulation results show that the channel estimation performance improves as the channel correlation coefficient increases and bit error rate performance enhances when the number of RIS elements increases. The presented framework is important in the overall evaluation of the channel estimation performance of RIS-enabled 6G communication systems.

M. Namdar, A. Basgumus, H. Alakoca, S.O. Ata, and L. Durak-Ata, “IRS-aided Communication Systems in the Presence of Multiple Eavesdroppers,” IEEE Signal Proc. Commun. Appl. Conf. (SIU’22), 5-8 Jul. 2023, Istanbul, Turkey.

In this study, the performance analysis of secrecy capacity and secrecy outage probability in the presence of multiple eavesdroppers that cooperate (colluding) and do not cooperate (non-colluding) with each other, respectively, is studied for the intelligent reflective surfaces (IRS) assisted communication system model in urban wireless networks. In both approaches, realistic security problems and solutions regarding the system model related to physical layer security for legitimate users, designed with the help of the IRS, are evaluated.