Outdoor Base Station Research Articles

Study on an energy-saving thermal management system in outdoor base stations

In order to solve the poor heat dissipation in the outdoor mobile communication base station, especially in summer, high temperature alarm phenomenon occurs frequently, affecting the normal operation of building base band unite, this paper designs an energy-saving and efficient integrated thermal management system, which has achieved good results by applying the combined operation of heat pipe cooling and air conditioning system using the outdoor temperature switching mode. A mobile communication base station in Zhengzhou City was chosen for a pilot application. The measured results showed that the system ran stably, the temperature inside the cabinet was controlled between 12?C and 39?C with no high temperature alarm, the compressor running time was significantly reduced, the power consumption of the air conditioner was significantly reduced, and the annual power saving rate was as high as 58.63%.

Joint Precoding for Active Intelligent Transmitting Surface Empowered Outdoor-to-Indoor Communication in mmWave Cellular Networks

Outdoor-to-indoor communications in millimeter-wave (mmWave) cellular networks have been one challenging research problem due to the severe attenuation and the high penetration loss caused by propagation characteristics of mmWave signals. We propose a viable solution to implement the outdoor-to-indoor mmWave communication with the aid of an active intelligent transmitting surface (active-ITS), where the active-ITS allows the incoming signal from an outdoor base station (BS) to pass through the surface and be received by indoor users (UEs) after shifting its phase and magnifying its amplitude. Then, the problem of joint precoding of the BS and active-ITS is investigated to maximize the weighted sum-rate (WSR) of the system. An efficient block coordinate descent (BCD) based algorithm is developed to solve it with the suboptimal solutions in nearly closed-forms. In addition, to reduce the size and hardware cost of active-ITSs, we provide a block-amplifying architecture to partially remove the circuit components for power-amplifying, where multiple transmissive-type elements (TEs) in each block share the same power amplifier. Simulations indicate that active-ITS has the potential of achieving a given performance with much fewer TEs compared to the passive-ITS under the same total system power consumption, which makes it suitable for application to the space-limited and aesthetic-needed scenario, and the performance degradation caused by the block-amplifying architecture is negligible.

An Energy Efficient Dual IRS-Aided Outdoor-to-Indoor Communication System

Intelligent reflecting surfaces (IRSs) have emerged as a promising technology to realize energy- and spectrally efficient low-cost wireless communication systems. In this work, we propose a dual IRS-aided communication model for outdoor-to-indoor wireless communication. The scenario comprises an outdoor base station that communicates with the indoor users with the aid of two distinct IRSs. Specifically, we derived the closed-form expressions of the spectral efficiency (SE), energy efficiency (EE), and outage probability (OP) for the dual IRS-aided communication system. The results show that utilizing distributed IRSs, i.e., by dividing the large IRS into two smaller IRSs, significant performance gains in the SE and EE can be achieved over the single IRS scenario. Although the multiplicative pathloss effect impacts performance, it can be mitigated by increasing the number of reflecting elements. Initially, we evaluated the performance of a single-user scenario; later on, we generalized it to the multiuser scenario with nonorthogonal multiple access. Further, the performance is also compared with the baseline direct cellular transmission. The analytical derivations of the SE, EE, and OP are corroborated through simulations.

Radiative cooling gray paint with high solar reflectance for thermal management of electronic equipment

Colored appearance is an ongoing pursue for the devising of radiative cooling paint (RCP), while the inevitable absorption of solar radiation remains a huge hurdle to meet the threshold of RCP under intense sunlight. Gray is one of the most common color for the equipment appearance in the industrial design, but rarely works have been made to explore the potential of gray radiative cooling paint integrated on the engineering equipment. Herein, we utilize the poly (vinylidene fluoridehexafluoropropylene)-acrylic (PVDF-HFP-PMMA) containing yttria particle and commercial dye to fabricate radiative cooling gray paint (RCGP). The porous structure in paint endows an effective light scattering of sunlight, and the high refractive index and wide bandgap of yttria further promote the reflection of visible light. As a result, the RCGP with a grayscale value of 237 exhibits a high reflectance beyond 0.89 in solar waveband and a high emittance over 0.96 in the atmospheric transparence window (ATW, 8–13 μm). We theoretically and experimentally explore the cooling potential of RCGP on a heat sink module of outdoor base station, yielding a distinctive temperature drop beyond 10 ℃. Our work provides a feasible strategy for minimizing the adverse effect from the color on the reflective property, and makes tentative and significant exploration of radiative cooling in engineering thermal management.

An Efficient Method for Complex Antenna Design Based on a Self Adaptive Surrogate Model-Assisted Optimization Technique

Surrogate models are widely used in antenna design for optimization efficiency improvement. Currently, the targeted antennas often have a small number of design variables and specifications, and the surrogate model training time is short. However, modern antennas become increasingly complex, which needs much more design variables and specifications, making the training time become a new bottleneck, i.e., in some cases, even longer than electromagnetic (EM) simulation time. Therefore, a new method, called training cost reduced surrogate model-assisted hybrid differential evolution for complex antenna optimization (TR-SADEA), is presented in this article. The key innovations include: 1) a self-adaptive Gaussian process surrogate modeling method with a significantly reduced training time while mostly maintaining the antenna performance prediction accuracy and 2) a new hybrid surrogate model-assisted antenna optimization framework that reduces the training time and increases the convergence speed. An indoor base station antenna with 2G to 5G cellular bands (45 design variables and 12 specifications) and a 5G outdoor base station antenna (23 design variables and 18 specifications) are used to demonstrate TR-SADEA. Experimental results show that more than 90% of the training time and about 20% iterations (simulations and surrogate modeling) are reduced compared to a state-of-the-art method while obtaining high antenna performance.

High-fidelity indoor MIMO radio access for 5G and beyond based on legacy multimode fiber and real-time analog-to-digital-compression.

Dedicated indoor radio access network (RAN, such as C-RAN with fronthaul) will be in urgent demand for 5G and beyond ((B)5G), as it becomes more difficult for outdoor base stations to serve indoor mobile/IoT terminals due to the loss issue induced by higher carrier frequency. One cost-effective and time-saving strategy for indoor (B)5G RAN is to reuse the legacy multimode fibers (MMF) deployed in buildings and premises worldwide. In this work, we introduce the concept of indoor (B)5G fronthaul over legacy MMF based on analog-to-digital-compression (ADX), termed as ADX-RoMMF. Enabled by ADX for MIMO data compression, both high radio signal fidelity and fronthaul bandwidth efficiency can be achieved, which alleviates the limitation of low MMF bandwidth-distance product and supports decent indoor coverage. Meanwhile, its digital nature is highly compatible with low-cost optical transceivers (with nonlinearity and/or imperfection) and packet-based fronthaul networking such as time-sensitive networking. Furthermore, the ultralow latency of ADX processing meets the requirement of low-delay (B)5G fronthauling. We experimentally demonstrate an ADX-RoMMF link serving 16-channel MIMO signals with NR-class bandwidth and 1024QAM, leveraging a real-time ADX prototyped on a single-chip field-programmable radio platform. Results show that this 32Gb/s CPRI-equivalent rate can be transported over MMF distance of 850m within 1024QAM EVM requirement, which is 4-fold larger than that of conventional fronthaul compression scheme. Moreover, 500ns ADX latency overhead is also verified.

Comparison of Average Total EMF Exposure for Microcell/Macrocell Topologies Using Novel Methodology Based on Operational Network Measurements

Two outdoor base station macrocell/microcell topologies in operational Global System for Mobile communications (GSM) and Universal Mobile Telecommunications Service (UMTS) networks are compared with respect to average Electromagnetic Field (EMF) exposure over population in an area. A novel joint metric is used, accounting for exposure from both base stations and user equipment. The demonstrated method tends to use as much data as possible that can be extracted from various network systems, for the exact time of measurements or on long-term basis, with the aim of identifying the potential for EMF-awareness of future networks. The reduction of total exposure with the introduction of the microcell layer is shown using the proposed method with experimental measurements and compared by mobile network technologies. The introduction of the micro layer brought reduction to total population exposure of 84.6%, in the micro base station coverage area, mostly due to user device exposure reduction in GSM. UMTS user device exposure reduction was even more pronounced, 97.8%, but having less impact on overall exposure, contributing only 1%. Even with the increase in exposure originating from base stations, the reduction of total exposure was visible over the macro area as well, measuring 2.22%. The uncertainties of the evaluation method are identified and usage of advanced tools and methods is proposed to mitigate them.

Small Cell Planning: Resource Management and Interference Mitigation Mechanisms in LTE HetNets

In an attempt to address the huge data demand of indoor mobile users and poor signal strength from outdoor base stations to indoor environments, opertaors have started deploying variety of small cells likes Femtos, picos and micro cells. In this work, we used Femtos as small cells. Femto cells are low-cost, low-power consuming cellular base stations which operate only in licensed spectrum and are designed for both outdoor and indoor communication. Although small cells can be used for enhancing network capacity and coverage, arbitrary deployment of large number of small cells can lead to increase in operators expenditure and may create severe interference issues for cell edge users. In this paper, we look into optimal placement of small cell solutions to improve data rates of users in LTE HetNets using Femtos. Besides, these solutions address the main concerns of interference and resource management by proposing mechanisms for optimal placement of Femtos (OptFP, MinNF), dynamic power control and bandwidth allocation in Femtos (SOPC) and dynamic offloading. We provide a comparison of placement solutions and the applicability of each proposal keeping the operators’ revenue in mind.

Resource allocation and location decision of a UAV-relay for reliable emergency indoor communication

In this article, unmanned aerial vehicle (UAV) as a half-duplex decode-and-forward (DF) relay constructs a reliable link between the indoor user and the outdoor base station (BS) in an emergency scenario. During the outdoor–indoor signal propagation, the signal passing through the wall accelerates signal fading makes the signal fading model for outdoor communication not applicable to outdoor–indoor communication and increases the outage probability of the link. We propose an outdoor–indoor signal fading model and derive a closed expression of the outage probability. In order to minimize the outage probability and ensure that each link has the same outage probability, we made a decision-making scheme and designed a location optimization-power allocation-bandwidth allocation fairness (LPB-fairness) algorithm. The decision-making scheme iteratively optimizes two sub-problems: location optimization and power-bandwidth allocation. The simulation results show that reasonable location optimization, power allocation and bandwidth allocation can ensure the minimum outage probability, and the gaps of outage probability between relay links are within 1%.

A Low-Profile Dual-Band Dual-Polarized Antenna With an AMC Reflector for 5G Communications

A low-profile dual-band dual-polarized antenna with an artificial magnetic conductor (AMC) reflector is proposed for 5G communications. The antenna consists of a pair of crossed dual-polarized dual-band bowtie dipoles and a dual-band AMC reflector. By introducing trapezoidal slots and U-shaped slots on the bowtie dipoles, miniaturization and dual-band characteristics are achieved. Moreover, T-shaped feeding structures are utilized to broaden the bandwidth of the bowtie dipoles. By adopting a dual-band AMC reflector instead of a conventional perfect electric conductor (PEC) reflector, the distance between the radiator and the reflector can be reduced from $0.25\lambda _{0}$ to $0.08\lambda _{0}$ (where $\lambda _{0}$ is the free-space wavelength at 3.5 GHz). The radiator can maintain the impedance bandwidth and a high gain can also be achieved, even if it is close to the AMC reflector. A geometrical optics model is used to explain the mechanism of the AMC. The optimal parameters of the AMC depend on the antenna operating frequency and the distance between the radiator and the reflector. Measurements show that the proposed dual-band antenna has an impedance bandwidth of 19.8% (3.14-3.83 GHz) and 13.2% (4.40-5.02 GHz), covering the sub-6 GHz frequency spectra of 5G mobile communications. The peak gain is 7.1 dBi in the lower band and 8.2 dBi in the upper band. Port isolation better than 20 dB is achieved. The proposed antenna can be used alone for 5G indoor base station, or as the element of an array for 5G outdoor base station.

Relay-Aided Outdoor-to-Indoor Communication in Millimeter-Wave Cellular Networks

In this article, we examine the feasibility of serving an indoor mobile terminal (MT) by an outdoor base station (BS) in urban millimeter-wave (mmWave) cellular networks. Toward this, we consider two scenarios: 1) the signal reaches the reference MT directly by penetrating the building where it is located and 2) the communication is assisted by a relay placed on the rooftop of the building that conveys through a waveguide the desired signal to an indoor transmit antenna located at the floor where the reference MT is located. By using a stochastic-geometry-based framework, we derive for both scenarios, analytical expressions for the coverage and average rate, which exhibit a good match with respect to the simulations. In addition, from these expressions, we gain important insights regarding the performance comparison of the two scenarios. In particular, it is analytically proved and validated by the simulations that relaying notably enhances the performance of the low-rate MTs even under substantial waveguide losses. However, for such losses, the average rate in the relaying case can become worse than the case without relays.

A Framework for Automated Cellular Network Tuning With Reinforcement Learning

Tuning cellular network performance against always occurring wireless impairments can dramatically improve reliability to end users. In this paper, we formulate cellular network performance tuning as a reinforcement learning (RL) problem and provide a solution to improve the performance for indoor and outdoor environments. By leveraging the ability of Q-learning to estimate future performance improvement rewards, we propose two algorithms: (1) closed loop power control (PC) for downlink voice over LTE (VoLTE) and (2) self-organizing network (SON) fault management. The VoLTE PC algorithm uses RL to adjust the indoor base station transmit power so that the signal to interference plus noise ratio (SINR) of a user equipment (UE) meets the target SINR. It does so without the UE having to send power control requests. The SON fault management algorithm uses RL to improve the performance of an outdoor base station cluster by resolving faults in the network through configuration management. Both algorithms exploit measurements from the connected users, wireless impairments, and relevant configuration parameters to solve a non-convex performance optimization problem using RL. Simulation results show that our proposed RL based algorithms outperform the industry standards today in realistic cellular communication environments.

Thermal management of 48 V standby battery for outdoor base station at cold environment

The standby battery for outdoor base station could not function properly at cold environment for a long time. In order to improve its performance and lengthen its life time, it was necessary to heat the battery and keep warm. This dissertation presented the heating and heat preservation method of 48 V Lead-acid battery pack for base station based on the heating plate and phase change materials at cold environment. Then, the thermal management performances of this battery pack were simulated. The results showed that the uniformity of battery temperature field was increased and the heat preservation process was lengthened effectively. And the pack kept good working condition after continuous heating and heat preservation progress. The method was simple and practicable, and it could be used on the thermal management of lithium ion battery because of its good applicability

Design of Shaped Reflector Antennas for the Applications of Outdoor Base Station Antennas in LTE Mobile Communications

AbstractThis paper examines the radiation characteristics of a shaped reflector antenna applied as an outdoor base station antenna for mobile communications. A simpler architecture in a reflector antenna can reduce the implementation cost and complexity of a base station antenna. The aim of this reflector antenna design is to resemble the required radiation characteristics of conventional base station antennas, which employ a single‐column phased array of antennas to radiate directional beam patterns for radio coverage in cell planning, while improving the existing drawback of overly large beam overlapping in adjacent sectors. It also discards the beam forming circuits of conventional base station antennas to reduce the level of passive intermodulation. This reflector antenna is fed by the elemental antenna of conventional base station antennas and is thus equipped with the functionalities of beam tilting and dual‐polarization radiation to fulfill the requirements of adaptive sectorized cell adjustment. Both numerical simulation and measurement results are presented to demonstrate the feasibility.

Energy Efficiency Optimization by Spectral Efficiency Maximization in 5G Networks

Energy and spectral efficiency are the main challenges in 5th generation of mobile cellular networks. In this paper, we propose an optimization algorithm to optimize the energy efficiency by maximizing the spectral efficiency. Our simulation results show a significant increase in terms of spectral efficiency as well as energy efficiency whenever the mobile user is connected to a low power indoor base station. By applying the proposed algorithm, we show the network performance improvements up to 9 bit/s/Hz in spectral efficiency and 20 Gbit/Joule increase in energy efficiency for the mobile user served by the indoor base station rather than by the outdoor base station.

A Broadband Dual-Polarized Antenna With Front-to-Back Ratio Enhancement Using Semicylindrical Sidewalls

A novel dual-polarized antenna, with a large bandwidth and a high front-to-back ratio, is proposed in this communication. The antenna is composed of printed dipoles and tapered baluns above a square ground plane to yield a wide bandwidth. Semicylindrical walls are loaded on the edge of the ground plane to suppress the back lobe and produce a stable gain. Backward radiation is suppressed by the diffraction effect of the semicylindrical sidewalls. Simulation shows that the back-lobe level can be reduced below −13 dB in a large frequency range without degrading the antenna bandwidth. The proposed antenna is fabricated and the measured results show that it has an impedance bandwidth of 69.6% (1.46–3.02 GHz) for voltage standing wave ratio <1.5. Within the bandwidth, the gain varies between 7.1 and 8.4 dBi, and the front-to-back ratio is above 20 dB. The proposed antenna is suitable for outdoor base station applications, and the back-lobe suppression technique can be applied easily to base station antennas.

Thermal management of standby battery for outdoor base station based on the semiconductor thermoelectric device and phase change materials

In order to extend the life span of standby battery for outdoor base station, a semiconductor thermoelectric device/phase change materials (PCMs) coupled battery thermal management system (BTMS), as well as the three-dimensional model of 48 V 80 Ah battery pack, was designed in this paper. The effect of various influencing factors, especially semiconductor thermoelectric device arrangement, temperature range of thermal management, cooling and heating power was investigated numerically. The results showed that the semiconductor thermoelectric devices were arranged at two flanks of minimum size direction could effectively improve the uniformity of battery module temperature field and prolong the heat preservation process. When the temperature difference between upper or lower limit of thermal management temperature range and the phase change temperature of PCMs (TPCM) was no more than 5 K, the maximum temperature difference (ΔTmax) of battery module during the cooling or heating process was lower than 5 K. Both the best choice of cooling and heating power was 200 W. What’s more, after 1 C discharging and 0.5 C charging process, the maximum temperature (Tmax) of battery module was restrained under the 312 K. During continuous cooling and heat preservation cycle, the cooling time and heat preservation time was about 14 h and 4.15 days, respectively, when the average ambient temperature was 323 K. The simulation results will be useful for the design of PCMs based battery thermal management system for outdoor base station battery.

A Mathematical Framework to Evaluate Flexible Outdoor User Association in Urban Two-Tier Cellular Networks

In this paper, we present a mathematical framework to evaluate the performance of a typical outdoor user in an urban two-tier mobile network under a biased user association. The urban environment is abstracted by a Boolean scheme of blockages, which affects the deployment of outdoor base stations (BSs) and indoor small cell BSs, and the signal propagation characteristics of the wireless channels. A building is served by an indoor small cell BS with a certain probability, which we denote as occupation probability. Employing tools from stochastic geometry, we derive mathematical expressions for the coverage probability and the average spectral efficiency of a typical outdoor user. Numerical evaluations are carried out with the third generation partnership project compliant outdoor BS scenarios. Our results show that the increasing blockage density has a negative impact on the spectral efficiency in sparse outdoor BSs scenarios, but it has a positive impact on the performance of the network in dense outdoor BSs scenarios. We build our analysis on several assumptions, which are verified by extensive Monte Carlo simulations.

Design of a Novel Wideband and Dual-Polarized MagnetoElectric Dipole Antenna

A wideband antenna with ±45° dual polarization is proposed. The antenna is mainly comprised of four printed trapezoidal metal walls standing on a ground plane that forms a 3-D open square aperture cavity structure with tapered cut on the four wall edges. The metal walls are fed by two orthogonally positioned (±45°) feeding networks, forming two pairs of dipole arms. Because of the excited magnetic-electric resonances, wide bandwidth can be achieved. The proposed antenna is fabricated, and the measured results show that it has an impedance bandwidth of 56% (1.62–2.87 GHz) for VSWR < 1.5. In addition, isolation of larger than 30 dB is also exhibited across the bandwidth between the two feeding ports. Because the proposed antenna has a hollow inside structure, it is a good candidate for multiband sharing aperture antenna element. Furthermore, it has a simplified fabrication process and is suitable for outdoor base station antennas that require VSWR < 1.5.

Mobile femtocell utilisation in LTE vehicular environment: Vehicular penetration loss elimination and performance enhancement

Mobile computing is fast becoming a vital part of everyday life in which User Equipment (UE) demand being reachable anywhere and at anytime, as they spend much time travelling from one place to another, often by trains or buses. The ultimate aim of passengers is the ability to be connected to the Internet while they are moving from one place to another with their mobile devices. Providing indoor coverage on trains and buses directly with outdoor Base Stations (BSs) may not be a good solution due to the high density of use and path losses in the LTE network. This limitation can result in poor signal quality inside the train, and offering broadband services is not always possible. Clearly improvement to broadband access on buses and trains could be achieved by installing more BSs close to railway and bus routes and terminals. However, this solution is not ideal for the Internet Service Providers (ISPs) due to the high investment needed to deploy many more BSs. In addition, such a solution will introduce additional complexity by increasing the number of Handovers (HOs). This issue has focused the research community effort on developing solutions that take advantage of the existing wireless infrastructure without increasing the number of BSs. One method being considered is the development of more efficient methods and technologies to manage the UE's mobility in seamless ways. In this paper we propose adoption of Mobile Femtocell (Mobile-Femto) technology as a solution to mitigate the Vehicular Penetration Loss (VPL) and Path Loss, with consequent improvement to the vehicular UE's performance in LTE networks. Our results, using a Matlab simulation model, showed a noticeable improvement in the achieved Ergodic capacity by 5% under a VPL of 40 dB while 90% of vehicular UEs spectral efficiency has improved by 1.3 b/cu under a VPL of 25 dB. In addition, 80% of vehicular UEs have improved their throughput and SINR by 300 kb/s and 4 dB respectively after implementing the Mobile-Femto into the Macrocell in LTE networks.