Virtual Base Station Research Articles

Topological Interference Management for MIMO Interference Broadcast Channels

In this paper, we investigate the topological interference management (TIM) for MIMO interference broadcast channels (IBC) under the fixed topology, where only topology information is needed to cancel the inter-cell interference (ICI). For the single user case, where the MIMO IBC network is reduced to the MIMO interference channel (IC) networks, we propose one novel TIM scheme by exploiting the solution to the corresponding SISO IC TIM based on topology information. And also, we present one theorem to characterize the achievable degrees of freedom (DoFs). For the multiple user case, assuming that each BS not only knows topology information but also knows the channel state information at transmitters (CSIT) within its own cell, we propose two novel TIM schemes, i.e., the virtual user compression-based scheme and the virtual base station extension-based scheme. For each scheme, we design transceivers to cancel both the ICI only based on the topology information by exploiting the solution to the corresponding SISO IC TIM and the multiple user interference (MUI) within its own cell based on the CSIT. Furthermore, we present one theorem to characterize the achievable DoF, respectively. Moreover, we prove that the DoF achieved by the virtual base station extension-based scheme is higher than or equal to that achieved by the virtual user compression-based scheme. Hence, the achievable DoF of MIMO IBC TIM is lower bounded by the optimal DoF attainable for the base station extension scheme. Furthermore, the numerical results show that our schemes can achieve significant performance gain against the traditional interference avoidance scheme.

Exploiting User-Centric Joint Transmission – Coordinated Multipoint With a High Altitude Platform System Architecture

User-centric joint transmission coordinated multipoint (JT-CoMP) has been shown to enhance the capacity of terrestrial cellular systems, by overcoming cell-edge interference. This paper investigates how JT-CoMP can be extended to a new high altitude platform (HAP) system architecture by exploiting a phased array antenna, which generates multiple beams that form cells, each of which can map on to pooled virtual base-station equipment, thereby replacing multiple terrestrial cell sites. The strategy to implement CoMP is designed to best enhance the user experience at the edge of the HAP cells, including the overall performance of the system. Methods to overcome the known tradeoff for JT-CoMP between carrier-to-interference plus noise ratio (CINR) gain and loss of capacity accessible to the users are considered. Two different methods of identifying non-CoMP and CoMP users are introduced based upon the centralized CINR threshold and flexible CINR threshold approaches. For the bandwidth allocation technique, two approaches are used: full bandwidth (FBW) and half bandwidth (HBW). These four approaches are combined, delivering the FBW, HBW, Flex FBW, and Flex HBW schemes that are used to control the JT-CoMP. It is shown that 57% and 45% of users gain benefit from the use of HBW and FBW, respectively. Overall, the schemes based on the flexible CINR threshold approach provide the best balance between loss and gain of the user capacity, while the centralized CINR threshold-based schemes performed well, beneficiary up to 57% of the users, but with the drawbacks of a higher percentage of losing users.

Resource Allocation in NOMA Virtualized Wireless Networks Under Statistical Delay Constraints

For 5G wireless communication networks, low latency and high spectral efficiency are required to provide ubiquitous communication for emerging applications. In this letter, we propose a novel framework which considers these requirements simultaneously by integrating the notion of effective capacity (EC) and non-orthogonal multiple access (NOMA) into virtualized wireless networks (VWNs). At first, we consider a virtual base station architecture to achieve isolation between different service providers (slices). Then, a resource allocation design for maximization of the EC is formulated as a non-convex optimization problem which takes into account the average maximum power constraints and delay quality-of-service requirements. To strike a balance between computational complexity and system performance, we apply the successive convex approximation to the non-convex optimization problem. Subsequently, an iterative low-complexity suboptimal algorithm is proposed. Numerical results illustrate that there is a non-trivial fundamental tradeoff between delay and spectral efficiency in VWNs while NOMA provides a significant improvement in terms of EC compared to conventional orthogonal multiple access.

Cellular access multi-tenancy through small-cell virtualization and common RF front-end sharing

Mobile traffic demand is expected to grow as much as eight-fold in the coming next five years, putting strain in current wireless infrastructures. Meanwhile the diversity of traffic and standards may explode as well. One of the most common means for matching these mounting requirements is through network densification, essentially increasing the density of deployment of operators’ base stations in many small cells and handling timing critical traffic at the edge. In this paper we take a step in that direction by implementing a virtualized small cell base station consisting of multiple, isolated LTE PHY stacks running concurrently on top of a hypervisor deployed on a cheap, off-the-shelf x86 server and a shared radio head. In particular, we show that it is possible to run multiple virtualized base stations while achieving throughput equal or close to the theoretical maximum. In contrast to C-RAN (Cloud/Centralized Radio Access Network), our virtualized small cell base station has full stack at the edge so that a low latency high throughput front-haul, which is necessary in C-RAN architecture, is not needed. This approach brings all the flexibility and configurability (from network management point of view) that a software based implementation provides while the transparent architecture enables the possibility of multiple standards sharing the same radio infrastructure.

Joint mode selection, VBS association and resource allocation for WNV-enabled cellular D2D communication networks

Cellular device-to-device (D2D) communication networks are expected to improve user quality of service and network transmission performance significantly. In this paper, we apply the technology of wireless network virtualization to cellular D2D communication networks, and slice physical base stations into virtual base stations (VBSs). The problems of transmission mode selection, resource allocation and VBS association are jointly studied. Stressing the importance of the service delay of all the user equipments in the networks, we formulate the joint optimal design problem as a service delay minimization problem. As the formulated optimization problem is an NP-hard problem, which cannot be solved conveniently, we propose a heuristic algorithm, which iteratively solves three subproblems, i.e., transmission mode selection subproblem, resource allocation subproblem and VBS association subproblem. In particular, to solve the resource allocation and VBS association subproblems, we apply Lagrange dual method and modified Kuhn–Munkres algorithm, respectively. Simulation results demonstrate the effectiveness of the proposed algorithm.

Delineation of Agricultural Drainage Pipe Patterns Using Ground Penetrating Radar Integrated with a Real-Time Kinematic Global Navigation Satellite System

Better methods are needed for mapping agricultural drainage pipe systems. Prior research on small test plots indicates that ground penetrating radar (GPR) is oftentimes capable of detecting buried drainage pipes; however, the feasibility of employing this geophysical technique in larger field areas has not been adequately evaluated. Ground penetrating radar integrated with a Real-Time Kinematic (RTK) Global Navigation Satellite System (GNSS) may be an effective and efficient means of mapping drain lines within agricultural fields. Therefore, GPR-RTK/GNSS was tested in three agricultural settings; with Site 1 and Site 2 located in Beltsville, MD, USA and Site 3 near Columbus, OH, USA. Soils at the three sites ranged from silty clay loam to loamy sand. A GPR unit with 250 MHz antennas was used to detect drainage pipes, and at Sites 1 and 2, a physical GNSS base station was utilized, while a virtual base station was employed at Site 3. The GPR-RTK/GNSS configurations used in this study delineated a complex rectangular drainage pipe system at Site 1, with one set of drainage pipes oriented southwest-northeast and a second oriented southeast-northwest. At Site 2, a herringbone drain line pattern was outlined, and at Site 3, random drain lines were found. When integrated with RTK/GNSS, spiral or serpentine GPR transects (or spiral/serpentine segments of a GPR transects) were utilized to provide insight on drain line directional trends. Consequently, given suitable field conditions, GPR integrated with RTK/GNSS can be a valuable tool for farmers and drainage contractors needing to map subsurface drainage systems.

A Super Base Station Architecture for Future Ultra-Dense Cellular Networks: Toward Low Latency and High Energy Efficiency

To meet the explosive growth of mobile data traffic, ultra-dense networks have emerged to enhance spatial and spectral efficiency. Densely deployed small cell architecture faces several major challenges, including low infrastructure utilization ratio, severe inter-cell interference, and so on. In this article, we aim to develop a novel super base station (SupBS) network architecture to tackle these issues. The proposed SupBS architecture consists of two layers, namely, an infrastructure layer and a virtualized network layer. In the infrastructure layer, there are three key physical components: the hybrid heterogeneous radio unit pool, line interface switch unit, and computing resources pool. In the virtualized network layer, there are two logical modules designed on top of the three physical components, namely, the virtualized base station and virtualized software defined core network. The two logical modules are designed to facilitate the use of the underlying three physical components by reducing the energy consumption and processing delay. We present the functionalities of the two virtualized modules and explain how they are utilized to create virtual networks. Moreover, we demonstrate a recently developed SupBS prototype, and provide an application scenario for this prototype in an Internet information broadcast-storage system to show the advantages of our architecture.

Trajectory Design for Completion Time Minimization in UAV-Enabled Multicasting

This paper studies an unmanned aerial vehicle (UAV)-enabled multicasting system, where a UAV is dispatched to disseminate a common file to a set of ground terminals (GTs). We aim to design the UAV trajectory to minimize its mission completion time, while ensuring that each GT successfully recovers the file with a desired high probability. The formulated problem is nonconvex and difficult to be solved in its original form. Therefore, we first derive an effective lower bound for the success file recovery probability of each GT. The problem is then reformulated in a more tractable form, where the UAV trajectory only needs to be designed to ensure the minimum connection time constraint with each GT, during which their distance is below a certain threshold. We show that without loss of optimality, the UAV trajectory consists of connected line segments only, which can be obtained by determining the optimal set of waypoints as well as the UAV speed along the path connecting the waypoints. We propose efficient schemes for the waypoint design based on a novel concept of virtual base station placement and by applying convex optimization. Furthermore, for fixed waypoints, the optimal UAV speed is efficiently obtained by solving a linear programming problem. Numerical results show that the proposed UAV-enabled multicasting with optimized trajectory design achieves significant performance gains over other benchmark schemes.

An enhanced distributed evolved node-b architecture in 5G tele-communications network

To meet the regularly expanding versatile information movement request, the portable administrators are conveying a heterogeneous system with numerous entrance innovations and an ever-increasing number of base stations to build the system scope and limit. Be that as it may, the base stations are disconnected from each other, so unique sorts of radio assets and equipment assets can't be shared and dispensed inside the general system agreeably. The versatile administrators are in this manner confronting expanding system operational costs and a high framework control utilization. In this paper, a brought together radio access organize design, alluded to as the super base station (super BS), is proposed, as a conceivable answer for a vitality productive fifth-age (5G) versatile framework. The super base station decouples the coherent capacities and physical elements of conventional base stations, so unique sorts of framework assets can be on a level plane shared and factually multiplexed among all the virtual base stations all through the whole framework. The framework structure and principle functionalities of the super BS are portrayed. Some key advances for framework usage, i.e., the asset pooling, continuous virtualization, versatile equipment asset assignment are likewise featured.

Joint virtual edge-clustering and spectrum allocation scheme for uplink interference mitigation in C-RAN

Fractional Frequency Reuse (FFR) and Coordinated MultiPoint (CoMP) processing are two of the conventional methods to mitigate the Inter-Cell Interference (ICI) and to improve the average Signal-to-Interference-plus-Noise Ratio (SINR). However, FFR is associated with low system spectral efficiency and CoMP does not take any action to mitigate the inter-cluster interference. In this article, we study the challenges and problems of the current interference management techniques and explain why the clustering and spectrum allocation must be studied jointly. Then, in the context of Cloud Radio Access Network (C-RAN), we propose a joint virtual clustering and spectrum allocation scheme, called Cloud-CFFR, to address such problems. With respect to both FFR and CoMP, Cloud-CFFR decreases the complexity, delay, and ICI while increasing the system spectral efficiency. Since the system performance in cell-edge regions relies on the cooperation of different Virtual Base Stations (VBSs), there is no service interruption in handling handovers; moreover, in order to address the unanticipated change in capacity demand, a flexible spectrum management technique is proposed which dynamically changes the subband boundaries based on the number of active users in the clusters. Simulation results confirm the validity of our analysis and show the benefits of this novel uplink solution compared to the traditional schemes.

Trusted Cooperation Among Virtual Base Stations in C-RAN

Cloud radio access network (C-RAN) has become one of the hot-spot research directions in both industry and academia to facilitate 5G development. Its architecture is mainly divided into three parts: 1) Virtual base station (VBS) pool including a number of base band units that apply for real-time cloud computing technology to carry out digital processing tasks; 2) Remote radio heads (RRH) that are used to collect the wireless signals from all wireless devices; 3) Front-haul network connecting the RRH to the VBS pool. The information of base stations (BS) resides in a centralized VBS pool, multiple operators can allow their VBS pools to exchange control data and cooperate with each other to provide high-quality 5G services. In this process, trustworthy cooperation and platform-trust authentication among multiple mobile operators are required to realize high networking performance and secure 5G environment. However, this topic has been scarcely studies and is still in its infancy. In this paper, we first propose a C-RAN inter-operator cooperation scheme (IOCS) to support the cooperation of multiple operators in C-RAN and allow them to share resources in a trustworthy and secure way based on trusted computing platform. An access trust management pool including VBS trust managers is set up in IOCS to administrate an operator’s VBS pool. It allows an end user to consume other operators’ network resources in a trustworthy manner when its own operator’s network cannot satisfy the quality of service requirements. Furthermore, we design a trusted cooperative platform based on OpenStack to implement IOCS. Performance evaluation and simulation results illustrate the high operation efficiency in IOCS comparing with other schemes. Game theoretical analysis shows the condition of inter-operator cooperation by taking operator trust into concern.

Evaluation Methodology for Virtual Base Station Platforms in Radio Access Networks

Virtual base stations (BS) with scalable resources and flexible functions are necessary for the fifth-generation and future mobile systems. The virtualization platform is the fundamental component of virtual BSs and plays a very important role in determining BS performance. As BS virtualization platforms can be provided by both conventional BS manufactures and third-party software vendors, it is crucial to define unified methodology to evaluate the performance of different virtualization platforms. In this paper, for the first time in literature, we design a set of comprehensive performance metrics and propose evaluation methods for BS virtualization platforms. More specifically, there are two types of metrics, i.e., micro level and macro level metrics. Micro level metrics quantify the virtualization platforms’ basic performances including real-time performance and virtualization overhead. Macro level metrics quantify the platforms ability to support BS resource and function virtualization while satisfying the radio access network requirements. Correspondingly, two-level evaluation methodology is designed to collect micro and macro level metrics from different parts of a virtual BS by running proper workloads. Finally, using the proposed methodology, two representative virtualization platforms, i.e., KVM hypervisor and Super BS virtualization platform are evaluated. These experiments verify that the proposed methodology can effectively evaluate the performance of different platforms to provide a valuable reference for the selection of virtual BS platforms. Moreover, the proposed evaluation methodology is a significant step toward constructing an open ecosystem for radio access networks.

Precise GNSS Positioning Using Smart Devices.

The recent access to GNSS (Global Navigation Satellite System) phase observations on smart devices, enabled by Google through its Android operating system, opens the possibility to apply precise positioning techniques using off-the-shelf, mass-market devices. The target of this work is to evaluate whether this is feasible, and which positioning accuracy can be achieved by relative positioning of the smart device with respect to a base station. Positioning of a Google/HTC Nexus 9 tablet was performed by means of batch least-squares adjustment of L1 phase double-differenced observations, using the open source goGPS software, over baselines ranging from approximately 10 m to 8 km, with respect to both physical (geodetic or low-cost) and virtual base stations. The same positioning procedure was applied also to a co-located u-blox low-cost receiver, to compare the performance between the receiver and antenna embedded in the Nexus 9 and a standard low-cost single-frequency receiver with external patch antenna. The results demonstrate that with a smart device providing raw GNSS phase observations, like the Nexus 9, it is possible to reach decimeter-level accuracy through rapid-static surveys, without phase ambiguity resolution. It is expected that sub-centimeter accuracy could be achieved, as demonstrated for the u-blox case, if integer phase ambiguities were correctly resolved.

Synergetic communication-and-computation optimization in software-defined hyper-cellular networks

Recently, the cloud radio access network (C-RAN) architecture has been proposed to enhance the cost effectiveness and flexibility of traditional cell-centric radio access networks. However, the massive fronthaul bandwidth required to centralize baseband computations in C-RAN results in extremely high costs. This paper summarizes our previous efforts toward solving this problem. We proposed the software-defined hyper-cellular network (SDHCN) based on the control/data separation principle. Under the proposed SDHCN framework, we studied two mechanisms that can greatly reduce fronthaul costs through the joint deployment of communicational and computational resources. First, we quantitatively characterized the relationship between the size of virtual base station (VBS) pools and the gains from computational statistical multiplexing by using queueing theory. We then showed that the marginal gain diminishes quickly with a growing pool size. Therefore, it is most economical to deploy mid-sized VBS pools. Finally, we proposed a genetic algorithm for baseband function splitting within a graph-clustering framework. This algorithm provides splitting schemes that can flexibly achieve different tradeoffs between fronthaul and computational costs based on different design preferences.

Scheduling for Cloud-Based Computing Systems to Support Soft Real-Time Applications

Cloud-based computing infrastructure provides an efficient means to support real-time processing workloads, for example, virtualized base station processing, and collaborative video conferencing. This article addresses resource allocation for a computing system with multiple resources supporting heterogeneous soft real-time applications subject to Quality of Service (QoS) constraints on failures to meet processing deadlines. We develop a general outer bound on the feasible QoS region for non-clairvoyant resource allocation policies and an inner bound for a natural class of policies based on dynamically prioritizing applications’ tasks by favoring those with the largest (QoS) deficits. This provides an avenue to study the efficiency of two natural resource allocation policies: (1) priority-based greedy task scheduling for applications with variable workloads and (2) priority-based task selection and optimal scheduling for applications with deterministic workloads. The near-optimality of these simple policies emerges when task processing deadlines are relatively large and/or when the number of compute resources is large. Analysis and simulations show substantial resource savings for such policies over reservation-based designs.

Dynamic Radio Cooperation for User-Centric Cloud-RAN With Computing Resource Sharing

A novel dynamic radio-cooperation strategy is proposed for a Cloud Radio Access Network (Cloud-RAN) consisting of multiple Remote Radio Heads connected to a central Virtual Base Station (VBS) pool. In particular, the key capabilities of Cloud-RAN in computing-resource sharing and real-time communication among the VBSs are leveraged to design a joint dynamic radio clustering and cooperative beamforming scheme that maximizes the downlink Weighted Sum-Rate System Utility (WSRSU). Due to the combinatorial nature of the radio clustering process and to the non-convexity of the cooperative beamforming design, the underlying optimization problem is NP-hard, and is extremely difficult to solve for a large network. The proposed approach aims for a suboptimal solution by transforming the original problem into a Mixed-Integer Second-Order Cone Program (MI-SOCP) and applying Sequential Convex Approximation (SCA) to derive a novel iterative algorithm. Numerical simulation results show that our low-complexity algorithm provides near-optimal performance in terms of WSRSU while significantly outperforming conventional radio clustering and beamforming schemes. Additionally, the results also demonstrate the significant improvement in computing-resource utilization of Cloud-RAN over a traditional RAN with distributed computing resources.

Virtualized Resource Sharing in Cloud Radio Access Networks Through Truthful Mechanisms

In the recent paradigm of cloud radio access networks (C-RAN), signal processing functions at the base stations (BSs) are virtualized and migrated into a mobile cloud that maintains a pool of virtual BS (VBS) instances. Remote radio heads and antennae at the BSs are connected to the VBS pool by fronthaul fiber links. Mobile operators may lease resources from the tower company who owns the C-RAN infrastructure. We study auction mechanisms for efficiently sharing C-RAN resources among mobile operators. Leveraging randomized rounding, we design an offline C-RAN auction mechanism that can achieve truthfulness and near-optimal social welfare. For the more realistic setting of online bid arrival, we design an online algorithm that executes in polynomial time and achieves a competitive ratio of $(1-\epsilon )$ . A tailored fractional Vickrey–Clarke–Groves mechanism works in concert with the online algorithm to elicit truthful bids. Extensive simulation studies verify the efficacy of our C-RAN auction mechanisms.

Development of a GNSS Buoy for Monitoring Water Surface Elevations in Estuaries and Coastal Areas.

In this work, a Global Navigation Satellite System (GNSS) buoy that utilizes a Virtual Base Station (VBS) combined with the Real-Time Kinematic (RTK) positioning technology was developed to monitor water surface elevations in estuaries and coastal areas. The GNSS buoy includes a buoy hull, a RTK GNSS receiver, data-transmission devices, a data logger, and General Purpose Radio Service (GPRS) modems for transmitting data to the desired land locations. Laboratory and field tests were conducted to test the capability of the buoy and verify the accuracy of the monitored water surface elevations. For the field tests, the GNSS buoy was deployed in the waters of Suao (northeastern part of Taiwan). Tide data obtained from the GNSS buoy were consistent with those obtained from the neighboring tide station. Significant wave heights, zero-crossing periods, and peak wave directions obtained from the GNSS buoy were generally consistent with those obtained from an accelerometer-tilt-compass (ATC) sensor. The field tests demonstrate that the developed GNSS buoy can be used to obtain accurate real-time tide and wave data in estuaries and coastal areas.

Virtualized Cloud Radio Access Network for 5G Transport

Current radio access networks (RANs) need to evolve to handle diverse service requirements coming from the growing number of connected devices and increasing data rates for the upcoming 5G era. Incremental improvements on traditional distributed RANs cannot satisfy these requirements, so the novel and disruptive concept of a cloud RAN (CRAN) has been proposed to decouple digital units (DUs) and radio units (RUs) of base stations (BSs), and centralize DUs into a central office, where virtualization and cloud computing technologies are leveraged to move DUs into the cloud. However, separating RUs and DUs requires low-latency and high-bandwidth connectivity links, called fronthaul, as opposed to traditional backhaul links. Hence, design of the 5G transport network, that is, the part of the network that carries mobile data traffic between BSs and the core network and data centers, is key to meet the new 5G mobile service requirements and effectively transport the fronthaul traffic. Today, consensus is yet to be achieved on how the fronthaul traffic will be transported between RUs and DUs, and how virtualization of network resources will occur from a radio network segment to the centralized baseband processing units. In this article, we present a new 5G architecture, called virtualized cloud radio access network (V-CRAN), moving toward a cell-less 5G network architecture. We leverage the concept of a virtualized BS (V-BS) that can be optimally formed by exploiting several enabling technologies such as software defined radio (SDR) and coordinated multipoint (CoMP) transmission/reception. A V-BS can be formed on a per-cell basis or per-user basis by allocating virtualized resources on demand. For the fronthaul solution, our approach exploits the passive optical network (PON), where a wavelength can be dynamically assigned and shared to form a virtualized passive optical network (VPON). Several use cases of the V-CRAN are presented to show how network architecture evolution can enhance system throughput, energy efficiency, and mobility management.

VBS RTK GPS-ASSISTED SELF-CALIBRATION BUNDLE ADJUSTMENT FOR AERIAL TRIANGULATION OF FIXED-WING UAS IMAGES FOR UPDATING TOPOGRAPHIC MAPS

Unmanned Aircraft Systems (UASs) can collect high resolution and high quality images for local mapping. If the highly accurate GPS flying trajectory of a UAS is collected, it can support bundle adjustment aerial triangulation (AT) of UAS images and reduce the demands on ground control points (GCPs). This study installs a Trimble BD970 GNSS OEM on a fixed-wing UAS for capturing highly accurate GPS data by using a Virtual Base Station (VBS) RTK GPS technique for AT. Meanwhile, the GPS antenna-camera offset is resolved by stripwise linear drift parameters introduced in GPS observation equations, while performing bundle adjustment for AT. Additionally, self-calibration bundle adjustment is used in VBS RTK GPS-assisted AT to solve incomplete camera parameters calibrated by a close-range photogrammetric approach. The results show that the AT accuracy of fixed-wing UAS images collected with a 24 mm focal-length Canon EOS 5D Mark II camera at a flying height of 550 m above ground level is 0.21 m in planimetry and 0.22 m in height using two cross strips with two full GCPs at each corner of the block. The RMSE of check points from stereoscopic viewing can reach 0.27 m in planimetry and 0.24 m in height. The test results show that the accuracy of VBS RTK GPS-assisted bundle adjustment with self-calibration for the AT of fixed-wing UAS image can be used for updating local 1/5000 topographic maps in Taiwan.