With the rapid development of advanced electromagnetic manipulation technologies, researchers and engineers are starting to study smart surfaces that can achieve enhanced coverages, high ...reconfigurability, and are easy to deploy. Among these efforts, simultaneously transmitting and reflecting intelligent omni-surface (STAR-IOS) is one of the most promising categories. Although pioneering works have demonstrated the benefits of STAR-IOSs in terms of its wireless communication performance gain, several important issues remain unclear including practical hardware implementations and physics-compliant models for STAR-IOSs. In this paper, we answer these pressing questions of STAR-IOSs by discussing four practical hardware implementations of STAR-IOSs, as well as three hardware modelling methods and five channel modelling methods. These discussions not only categorize existing smart surface technologies but also serve as a physicscompliant pipeline for further investigating the STAR-IOSs.
Driven by great demands on low-latency services of the edge devices (EDs), mobile edge computing (MEC) has been proposed to enable the computing capacities at the edge of the radio access network. ...However, conventional MEC servers suffer disadvantages such as limited computing capacity, preventing the computation-intensive tasks to be processed in time. To relief this issue, we propose the heterogeneous MEC (HetMEC) where the data that cannot be timely processed at the edge are allowed be offloaded to the upper-layer MEC servers, and finally to the cloud center (CC) with more powerful computing capacity. We design the latency minimization algorithm by jointly coordinating the task assignment, computing and transmission resources among the EDs, multi-layer MEC servers, and the CC. Simulation results indicate that our proposed algorithm can achieve a lower latency and higher processing rate than the conventional MEC scheme.
The intelligent omni-surface (IOS) is a dynamic metasurface that has recently been proposed to achieve full-dimensional communications by realizing the dual function of anomalous reflection and ...anomalous refraction. Existing research works provide only simplified models for the reflection and refraction responses of the IOS, which do not explicitly depend on the physical structure of the IOS and the angle of incidence of the electromagnetic (EM) wave. Therefore, the available reflection-refraction models are insufficient to characterize the performance of full-dimensional communications. In this paper, we propose a complete and detailed circuit-based reflection-refraction model for the IOS, which is formulated in terms of the physical structure and equivalent circuits of the IOS elements, as well as we validate it against full-wave EM simulations. Based on the proposed circuit-based model for the IOS, we analyze the asymmetry between the reflection and transmission coefficients. Moreover, the proposed circuit-based model is utilized for optimizing the hybrid beamforming of IOS-assisted networks and hence improving the system performance. To verify the circuit-based model, the theoretical findings, and to evaluate the performance of full-dimensional beamforming, we implement a prototype of IOS and deploy an IOS-assisted wireless communication testbed to experimentally measure the beam patterns and to quantify the achievable rate. The obtained experimental results validate the theoretical findings and the accuracy of the proposed circuit-based reflection-refraction model for IOSs.
The downlink coordinated multiple points transmission (CoMP) has addressed a greet number of attentions in recent years. However, an open problem is still remaining that the QoS requirements from the ...edge users are not guaranteed to be fully achieved due to the low data rate and the high frequency handoff between cells. In this paper, we discuss the spectrum allocation in the downlink CoMP with incomplete QoS requirements. Based on a real world dataset, China Family Panel Studies (CFPS) dataset, we use a number of learning algorithms to anticipate the users' QoS requirements based on their profiles before the CoMP implementation. Based on the learning results, we further propose a learning embedded three-side matching to do the spectrum allocation. Simulation results show that the human behavior based learning framework can achieve a larger coverage ratio than other learning approaches. Simulation results also show that the learning embedded three-side matching can obtain a larger coverage ratio than the naive matching and random allocation.
Unmanned aerial vehicle (UAV) has greatly extended the scope of wireless broadband access by serving as a relay between the base station and user devices. In the paradigm of dynamic spectrum access ...(DSA), a UAV needs to traverse the flight area without interfering with incumbent users, and takes tune to serve the secondary users in the user area. It is important to minimize the service period by planning the UAV's trajectory. In this paper, we study the trajectory planning problem of optimizing the flight route of the UAV, given the incumbent protection zone where the UAV cannot enter, for DSA. We divide the user area and the flight area into multiple 2D grids. Then, we formulate the problem as finding the optimal trajectory in the flight area to cover the user area. We propose an algorithm that first finds the trajectory in each divided 2D grid by generating the minimum dominating path and selecting necessary critical flight locations within the path, and then concatenates the obtained trajectories to the trajectory in the flight area. Experimental results show that the UAV takes 32% less time to finish trajectory under proposed algorithm, and as the user area and the flight area become larger, the gap among algorithms increases.
Recently, reconfigurable intelligent surfaces (RIS) have attracted a lot of attention due to their capability of extending cell coverage by reflecting signals toward the receiver. In this letter, we ...analyze the coverage of a downlink RIS-assisted network with one base station (BS) and one user equipment (UE). Since the RIS orientation and the horizontal distance between the RIS and the BS have a significant influence on the cell coverage, we formulate an RIS placement optimization problem to maximize the cell coverage by optimizing the RIS orientation and horizontal distance. To solve the formulated problem, a coverage maximization algorithm (CMA) is proposed, where a closed-form optimal RIS orientation is obtained. Numerical results verify our analysis.
In this paper, we study an intelligent omni-surface (IOS)-assisted downlink communication system, where the link quality of a mobile user (MU) can be improved with a proper IOS phase shift design. ...Unlike the intelligent reflecting surface (IRS) in most existing works that only forwards the signals in a reflective way, the IOS is capable to forward the received signals to the MU in either a reflective or a transmissive manner, thereby enhancing the wireless coverage. We formulate an IOS phase shift optimization problem to maximize the downlink spectral efficiency (SE) of the MU. The optimal phase shift of the IOS is analysed, and a branch-and-bound based algorithm is proposed to design the IOS phase shift in a finite set. Simulation results show that the IOS-assisted system can extend the coverage significantly when compared to the IRS-assisted system with only reflective signals.
In this letter, we study a buffer-aided Internet of unmanned aerial vehicles (UAVs) in which a UAV performs data sensing, stores the data, and sends it to the base station (BS) in cellular networks. ...To minimize the overall completion time for all the sensing tasks, we formulate a joint trajectory, sensing location, and sensing time optimization problem. To solve this NP-hard problem efficiently, we propose an iterative trajectory, sensing location and sensing time optimization (ITLTO) algorithm, and discuss the trade-off between sensing time and flying time. Simulation results show that the proposed algorithm can effectively reduce the completion time for the sensing tasks.
In this paper, the optimum design of the downlink sparse code multiple access (SCMA) based user-centric ultra-dense networks (UUDNs) is studied, in which lots of access points (APs) are deployed to ...provide service to many user equipments (UEs). In UUDNs, the network architecture is shifted from traditional cell-centric to user-centric, where many APs can serve for one single UE, with the density of APs higher than that of UEs. One main challenge faced by UUDN design is the large interference due to the dense AP/UE deployments. The objective of this paper is to find the optimum SCMA codebooks allocation scheme to minimize the network interference that can maximize the system throughput, subject to the quality of service (QoS) constraints for each UE. The design is formulated as a mixed-integer nonlinear program (MINLP) problem by using different codebooks allocation among different APs serving the same UE, and it is a well known NP-hard problem. To tackle this problem, we use a weighted hypergraph model to transform it into a clustering problem, where machine learning (ML) algorithms are proposed to solve this MINLP problem efficiently. Simulation results show that the proposed hypergraph based ML algorithm outperforms the existing algorithm.
In this paper, we propose a linear probabilistic data association (PDA) based signal detector for V-BLAST. The main idea is to utilize the principle of a pre-whitening filter to realize single symbol ...detection, similar to virtual single input and single output (SISO) system, by removing the effects of past decisions. Simulation results show that our scheme can provide performance very close to ML decoding with extremely low computational complexity.
