When RIS Meets GEO Satellite Communications: A New Sustainable Optimization Framework in 6G

Scientific Conference (2022, June 19)

Reflecting intelligent surfaces (RIS) is a low-cost and energy-efficient solution to achieve high spectral efficiency in sixth-generation (6G) networks. The basic idea of RIS is to smartly reconfigure the ... [more ▼]

Reflecting intelligent surfaces (RIS) is a low-cost and energy-efficient solution to achieve high spectral efficiency in sixth-generation (6G) networks. The basic idea of RIS is to smartly reconfigure the signal propagation by using passive reflecting elements. On the other side, the demand of high throughput geostationary (GEO) satellite communications (SatCom) is rapidly growing to deliver broadband services in inaccessible/insufficient covered areas of terrestrial networks. This paper proposes a GEO SatCom network, where a satellite transmits the signal to a ground mobile terminal using multicarrier communications. To enhance the effective gain, the signal delivery from satellite to the ground mobile terminal is also assisted by RIS which smartly shift the phase of the signal towards ground terminal. We consider that RIS is mounted on a high building and equipped with multiple re-configurable passive elements along with smart controller. We jointly optimize the power allocation and phase shift design to maximize the channel capacity of the system. The joint optimization problem is formulated as nonconvex due to coupled variables which is hard to solve through traditional convex optimization methods. Thus, we propose a new optimal algorithm which is based on Mesh Adaptive Direct Search to obtain an efficient solution. Simulation results unveil the benefits of RIS-assisted SatCom in terms of system channel capacity. [less ▲]

Mixed RIS-Relay NOMA-Based RF-UOWC systems

Poster (2022, June)

Reconfigurable intelligent surface (RIS), nonorthogonal multiple access (NOMA), and underwater optical wireless communication (UOWC) are paradigms of technologies that drive the development of ... [more ▼]

Reconfigurable intelligent surface (RIS), nonorthogonal multiple access (NOMA), and underwater optical wireless communication (UOWC) are paradigms of technologies that drive the development of communications nowadays. In this paper, we investigate the performance of a NOMA-based RISassisted hybrid radio frequency (RF)-UOWC system. Due to the interruption of the direct link between the base station and the ship floating on the surface of the water, communication will be carried out via an RIS fixed to an intermediate building. The ship works as a relay that redirects the received signal to two underwater destinations simultaneously. In this paper, we provide new analytical expressions for the outage probability (OP), asymptotic analyses of the OP, and diversity order (D) to gain insights into the system performance. The results showed that the diversity order depends on the UOWC receiver detection technique. In the end, we illustrated that the NOMA-based RISassisted system significantly improves the outage performance of hybrid RF-UWOC systems over a benchmark systems. [less ▲]

Traffic Steering for eMBB and uRLLC Coexistence in Open Radio Access Networks

in Traffic Steering for eMBB and uRLLC Coexistence in Open Radio Access Networks (2022, May 16)

Existing radio access network (RAN) architectures are lack of sufficient openness, flexibility, and intelligence to meet the diverse demands of emerging services in beyond 5G and 6G wireless networks ... [more ▼]

Existing radio access network (RAN) architectures are lack of sufficient openness, flexibility, and intelligence to meet the diverse demands of emerging services in beyond 5G and 6G wireless networks, including enhanced mobile broadband (eMBB) and ultra-reliable and low-latency (uRLLC). Open RAN (ORAN) is a promising paradigm that allows building a virtualized and intelligent architecture. In this paper, we focus on traffic steering (TS) scheme based on multi-connectivity (MC) and network slicing (NS) techniques to efficiently allocate heterogeneous network resources in “NextG” cellular networks. We formulate the RAN resource allocation problem to simultaneously maximize the weighted sum eMBB throughput and minimize the worst-user uRLLC latency subject to QoS requirements, and orthogonality, power, and limited fronthaul constraints. Since the formulated problem is categorized as a mixed integer … [less ▲]

Effective Rate of RIS-aided Networks with Location and Phase Estimation Uncertainty

in Proceedings of IEEE Wireless Communications and Networking Conference (WCNC) (2022, May)

THz-Empowered UAVs in 6G: Opportunities, Challenges, and Trade-Offs

in IEEE Communications Magazine (2022), 60(5), 24-30

Envisioned use cases of unmanned aerial vehicles (UAVs) impose new service requirements in terms of data rate, latency, and sensing accuracy, to name a few. If such requirements are satisfactorily met, it ... [more ▼]

Envisioned use cases of unmanned aerial vehicles (UAVs) impose new service requirements in terms of data rate, latency, and sensing accuracy, to name a few. If such requirements are satisfactorily met, it can create novel applications and enable highly reliable and harmonized integration of UAVs in the 6G network ecosystem. Towards this, terahertz (THz) bands are perceived as a prospective technological enabler for various improved functionalities such as ultra-high throughput and enhanced sensing capabilities. This paper focuses on THz-empowered UAVs with the following capabilities: communication, sensing, localization, imaging, and control. We review the potential opportunities and use cases of THz-empowered UAVs, corresponding novel design challenges, and resulting trade-offs. Furthermore, we overview recent advances in UAV deployments regulations, THz standardization, and health aspects related to THz bands. Finally, we take UAV to UAV (U2U) communication as a case-study to provide numerical insights into the impact of various system design parameters and environment factors. [less ▲]

Reconfigurable Intelligent Surface-Assisted Massive MIMO: Favorable propagation, channel hardening, and rank deficiency

in IEEE Signal Processing Magazine (2022), 39(3),

Massive multiple-input multiple-output (MIMO) and reconfigurable intelligent surface (RIS) are two promising technologies for 5G-and-beyond wireless networks, capable of providing large array gain and ... [more ▼]

Massive multiple-input multiple-output (MIMO) and reconfigurable intelligent surface (RIS) are two promising technologies for 5G-and-beyond wireless networks, capable of providing large array gain and multiuser spatial multiplexing. Without requiring additional frequency bands, those technologies offer significant improvements in both spectral and energy efficiency by simultaneously serving many users. The performance analysis of an RIS-assisted massive MIMO system as a function of channel statistics relies heavily on fundamental properties, including favorable propagation, channel hardening, and rank deficiency. The coexistence of both direct and indirect links results in aggregated channels, whose properties are the main concerns of this “Lecture Notes” article. For practical systems with a finite number of antennas and engineered scattering elements of the RIS, we evaluate the corresponding deterministic metrics, with Rayleigh fading channels as a typical example. [less ▲]

Architectures and Synchronization Techniques for Distributed Satellite Systems: A Survey

in IEEE Access (2022), 10

Cohesive Distributed Satellite Systems (CDSSs) is a key enabling technology for the future of remote sensing and communication missions. However, they have to meet strict synchronization requirements ... [more ▼]

Cohesive Distributed Satellite Systems (CDSSs) is a key enabling technology for the future of remote sensing and communication missions. However, they have to meet strict synchronization requirements before their use is generalized. When clock or local oscillator signals are generated locally at each of the distributed nodes, achieving exact synchronization in absolute phase, frequency, and time is a complex problem. In addition, satellite systems have significant resource constraints, especially for small satellites, which are envisioned to be part of the future CDSSs. Thus, the development of precise, robust, and resource-efficient synchronization techniques is essential for the advancement of future CDSSs. In this context, this survey aims to summarize and categorize the most relevant results on synchronization techniques for Distributed Satellite Systems (DSSs). First, some important architecture and system concepts are defined. Then, the synchronization methods reported in the literature are reviewed and categorized. This article also provides an extensive list of applications and examples of synchronization techniques for DSSs in addition to the most significant advances in other operations closely related to synchronization, such as inter-satellite ranging and relative position. The survey also provides a discussion on emerging data-driven synchronization techniques based on Machine Learning (ML). Finally, a compilation of current research activities and potential research topics is proposed, identifying problems and open challenges that can be useful for researchers in the field. [less ▲]

Joint resource allocation for full-duplex ambient backscatter communication: A difference convex algorithm

in IEEE Transactions on Wireless Communications (2022)

Nowadays, Ambient Backscatter Communication (AmBC) systems have emerged as a green communication technology to enable massive self-sustainable wireless networks by leveraging Radio Frequency (RF) Energy ... [more ▼]

Nowadays, Ambient Backscatter Communication (AmBC) systems have emerged as a green communication technology to enable massive self-sustainable wireless networks by leveraging Radio Frequency (RF) Energy Harvesting (EH) capability. A Full-duplex Ambient Backscatter Communication (FAmBC) network with a Full-duplex Access Point (AP), a dedicated Legacy User (LU), and several Backscatter Devices (BDs) is considered in this study. The AP with two antennas transfers downlink Orthogonal Frequency Division Multiplexing (OFDM) information and energy to the dedicated LU and several BDs, respectively, while receiving uplink backscattered information from BDs at the same time. One of the key aims in AmBC networks is to ensure fairness among BDs. To address this, we propose the Multi-objective Lexicographical Optimization Problem (MLOP), which aims to maximize the minimum BD’s … [less ▲]

Differential Phase Compensation in Over-the-air Precoding Test-bed for a Multi-beam Satellite

Scientific Conference (2022, April 10)

This article presents a closed-loop differential phase compensation system for a precoding-enabled multibeam satellite forward link and its validation by live experiments on a GEO satellite scenario. The ... [more ▼]

This article presents a closed-loop differential phase compensation system for a precoding-enabled multibeam satellite forward link and its validation by live experiments on a GEO satellite scenario. The precoding operation avoids inter-beam interference and maximizes the spectrum efficiency by full frequency reuse as an alternative to the traditional two-color or four-color reuse methods proposed in the DVB-S2 standard. However, the satellite payload introduces differential phase and frequency impairments, which can degrade the precoding performance. This work describes the implementation of the differential phase and frequency tracking and compensation loop in an end-to-end testbed over a multibeam satellite system with independent local oscillators. The developed system performs end-to-end real-time communication over the satellite link, including channel measurements and precompensation. Results are validated by an over-the-air demonstration using two beams of the SES-14 multibeam satellite. Each beam is transmitted by independent transponders, which results in differential frequency and phase offsets due to the transponder undisciplined local oscillators. This phase offset makes it impossible to use precoding without the phase compensation loop. We prove that the implemented system can successfully track and compensate the differential phase and frequency to improve precoding performance. [less ▲]

Satellite-assisted UAV Trajectory Control in HostileJamming Environments

in IEEE Transactions on Vehicular Technology (2022), 71(4), 3760-3775

Satellite and unmanned aerial vehicle (UAV) net-works have been introduced as enhanced approach to providedynamic control, massive connections and global coverage forfuture wireless communication systems ... [more ▼]

Satellite and unmanned aerial vehicle (UAV) net-works have been introduced as enhanced approach to providedynamic control, massive connections and global coverage forfuture wireless communication systems. This paper considersa coordinated satellite-UAV communication system, where theUAV performs the environmental reconnaissance task with theassistance of satellite in a hostile jamming environment. To fulfillthis task, the UAV needs to realize autonomous trajectory controland upload the collected data to the satellite. With the aid ofthe uploading data, the satellite builds the environment situationmap integrating the beam quality, jamming status, and trafficdistribution. Accordingly, we propose a closed-loop anti-jammingdynamic trajectory optimization approach, which is divided intothree stages. Firstly, a coarse trajectory planning is made accord-ing to the limited prior information and preset points. Secondly,the flight control between two adjacent preset points is formulatedas a Markov decision process, and reinforcement learning (RL)based automatic flying control algorithms are proposed to explorethe unknown hostile environment and realize autonomous andprecise trajectory control. Thirdly, based on the collected dataduring the UAV’s flight, the satellite utilizes an environmentsituation estimating algorithm to build an environment situationmap, which is used to reselect the preset points for the first stageand provide better initialization for the RL process in the secondstage. Simulation results verify the validity and superiority of theproposed approach. [less ▲]