5G Indoor Research Articles

In Situ Wireless Channel Visualization Using Augmented Reality and Ray Tracing.

This article presents a novel methodology for predicting wireless signal propagation using ray-tracing algorithms, and visualizing signal variations in situ by leveraging Augmented Reality (AR) tools. The proposed system performs a special type of spatial mapping, capable of converting a scanned indoor environment to a vector facet model. A ray-tracing algorithm uses the facet model for wireless signal predictions. Finally, an AR application overlays the signal strength predictions on the physical space in the form of holograms. Although some indoor reconstruction models have already been developed, this paper proposes an image to a facet algorithm for indoor reconstruction and compares its performance with existing AR algorithms, such as spatial understanding that are modified to create the required facet models. In addition, the paper orchestrates AR and ray-tracing techniques to provide an in situ network visualization interface. It is shown that the accuracy of the derived facet models is acceptable, and the overall signal predictions are not significantly affected by any potential inaccuracies of the indoor reconstruction. With the expected increase of densely deployed indoor 5G networks, it is believed that these types of AR applications for network visualization will play a key role in the successful planning of 5G networks.

Test Results for 5G Indoor Pico Base Station

The fifth generation (5G) New Radio (NR) has attracted a large amount of interest with its improvement of user experience and capacity. But the anticipated use of the new technology brings serious challenges to existing solutions for its high spectrum and large bandwidth. Among them, indoor coverage is an important issue before commercial deployment. However, there are few evaluation targeting the pico base station. A new distributed antenna system (DAS) solution towards 5G indoor coverage is introduced. In this paper, the new indoor picocell with different RF configuration is introduced to build more flexible, efficient and evolving network. Besides, A series of trials are carried out to verify the RF performance of two types of radio frequency units (RRU).

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.

LTE-indoor: a novel PHY layer design for future 5G indoor femtocell networks

Small cell technology such as femtocell plays an important role in 5G heterogeneous network especially in the indoor environments. However, it is unreasonable that the design of the PHY layer in femtocell networks follows that of the macrocell since the channel model used in indoor environments is entirely different from that used in urban or rural areas. To boost the PHY throughput of femtocell network, LTE-indoor (LTE-I), a new PHY layer frame structure, is proposed to accommodate more symbols in a slot time as well as to adopt higher order modulations and narrower guard bands. Furthermore, through carrier aggregation (CA) techniques, the PHY layer throughput can be further booted as high as 18.2 Gbps. The proposed LTE-I frame structure also supports the ultra-reliable and low latency communications (URLLC) by making the subcarrier spacing wider to increase the symbol rate with almost no throughput loss.

LTE-indoor: a novel PHY layer design for future 5G indoor femtocell networks

Small cell technology such as femtocell plays an important role in 5G heterogeneous network especially in the indoor environments. However, it is unreasonable that the design of the PHY layer in femtocell networks follows that of the macrocell since the channel model used in indoor environments is entirely different from that used in urban or rural areas. To boost the PHY throughput of femtocell network, LTE-indoor (LTE-I), a new PHY layer frame structure, is proposed to accommodate more symbols in a slot time as well as to adopt higher order modulations and narrower guard bands. Furthermore, through carrier aggregation (CA) techniques, the PHY layer throughput can be further booted as high as 18.2 Gbps. The proposed LTE-I frame structure also supports the ultra-reliable and low latency communications (URLLC) by making the subcarrier spacing wider to increase the symbol rate with almost no throughput loss.

Coverage Extension of Indoor 5G Network Using RoF-Based Distributed Antenna System

We propose and demonstrate a cascaded distributed antenna system (DAS) for efficiently extending the coverage of the mmWave-based 5G indoor network. For this, we exploit the radio-over-fiber (RoF) system based on the intermediate-frequency-over-fiber (IFoF) transmission technique that is enabled to add/drop the specific wavelength to the designated remote antenna unit (RAU) with using optical splitters and coarse wavelength division multiplexing (CWDM) filters. Moreover, the IFoF transceivers (TRx) perform the subcarrier multiplexing (SCM) in order to transmit 2 × 8 frequency allocation (FA) 5G signals per a single optical carrier, where each FA has 100 MHz bandwidth, leading each RAU to support 2 × 2 MIMO operation. Consequently, the cascaded structure allows for the adaptive and flexible configuration of the order of MIMO in accordance of the required data throughput at the specific indoor area. We introduce the cascaded IFoF link structure that can support up-to 13.5 dB optical power budget with following errorvector-magnitude (EVM) performance characterizations. And then we experimentally demonstrate the RoFbased cascaded DAS network, showing that more than 1 Gb/s total throughput can be achieved per a single antenna. Furthermore, we examine the use of avalanche photodiode (APD) to further increase the optical power budget (i.e., the coverage) based on experiment as well as simulation.

A TDOA and PDR Fusion Method for 5G Indoor Localization Based on Virtual Base Stations in Unknown Areas

Indoor positioning and navigation is an essential field of location-based service. Non-line of sight (NLOS) error restricts the accuracy of indoor positioning. Many researchers have studied the localization problem in indoor NLOS environments, but there is still a problem that NLOS error cannot be mitigated in unknown areas. To solve the above problems, this paper proposes a method of constructing virtual base stations in unknown areas (UA-VBS), and presents the corresponding positioning algorithm to calculate the location of the user equipment. Firstly, the base stations are selected and the initial positioning is carried out. Then, multiple virtual base stations are constructed according to the user equipment positions in the first three steps. The LOS base stations and virtual base stations participate in the TDOA calculation together, and calculate the base stations’ combination with the minimum residual and the corresponding positioning result. Finally, the pedestrian dead reckoning fusion weight is updated by the residual value, and the accurate positioning result in NLOS environment is obtained. Simulation and experimental results show that the proposed algorithm has high positioning accuracy and stability in NLOS environment.

Performance Comparison of Alternative Indoor 5G Micro-Operator Deployments in 3.6-GHz and 26-GHz Bands

The fifth generation (5G) networks will provide local high-quality wireless services, especially within indoor areas. New local 5G network operator models, such as the recently introduced micro-operators, are increasingly important for vertical specific service delivery. The emergence of 5G micro-operator networks in spatially confined areas depends on local spectrum availability. In this paper, we investigate the performance of local 5G indoor micro-operator networks in the 3.6-GHz and 26-GHz bands. We consider two uncoordinated time-division duplex networks in adjacent buildings sharing the same channel with different base station antenna configurations and deployment densities. We evaluate the resulting performance of the victim network via system simulations. We have observed that the center frequency does not significantly impact the downlink performance unless the network is noise-limited. However, the uplink performance in 26-GHz band is affected by higher coupling losses between the base stations and mobile terminals. Our results indicate that beamforming and wider bandwidths help to improve the performance in 26-GHz band. More importantly, two indoor micro-operators can successfully coexist with a very small separation distance in the 26-GHz band, while in the 3.6-GHz band, a considerably larger isolation between the networks is required, for example, in the form of a much larger separation distance.

Radio-propagation measurements and modeling in indoor stairwells at millimeter-wave bands

A good understanding of signal wave attenuation along a stairwell is necessary for successful wireless network planning. In this study, the propagation characteristics in indoor multi-floor stairwell environments are examined under the millimeter frequency band. An extensive signal measurement is conducted in two stairwells. These measurements provide information important for ensuring consistent radio transmission of data in such environment, which then enables immediate response during emergency operations. In these measurements, directional horn antennas for co-polarization and cross-polarization in transmitters and receivers are used for different millimeter frequencies (26, 28, 32, and 38 GHz). The feasibility of using the millimeter wave, which is suitable for indoor 5G wireless networks, in two different indoor stairwell environments is investigated. Four different models are employed for path loss investigation. Under single frequencies, the close-in free-space reference distance and floating-intercept path loss models are adopted. For multiple frequencies, the close-in free space reference distance with frequency dependent path loss exponent and alpha-beta-gamma models are applied. The measurements provide data on the received power at multi-floor stairwells through the stair steps, which are useful for path loss study. Accordingly, the path loss exponent values, standard deviations, and other parameters are obtained.

Investigation of optical power budget for expanding indoor-mobile coverage in 5G indoor distributed antenna system (DAS) supporting 32 FAs transmission

We experimentally present the maximum optical power budget in the analog IFoF-based indoor distributed antenna system (DAS) link supporting 32 FAs transmission of 5G wireless signals. For maximum optical power budget, we derive the maximum launched optical power and the optimum optical modulation index (OMI)/frequency assignment (FA) based on laser over-modulation. To investigate the effect, we analyze the impacts of nonlinear distortion of the single-mode-fiber (SMF) on the Tx side, and influence of noise and distortions of the analog IFoF-based indoor DAS link. Also, we include the avalanche photodiode (APD) as an optical receiver and the erbium-doped fiber amplifier (EDFA) as an optical power booster in mmWave 5G based indoor DAS link to meet the transmission performance at low received optical power. It is experimentally observed that the optical power budget is improved with using the laser over-modulation by 23 dB in analog IFoF based 5G indoor DAS link for 32 FAs x 100 MHz 5G wireless signals.

Path loss compensated beam switchable antennas with spatially modulated zero‐index metamaterial loading for 5G base stations

To achieve a uniform illumination on the ground in the context of an indoor millimetre-wave 5G base station, path loss compensation is necessary. The gains of the antenna radiating at ±45° require an additional gain of 3 dB to compensate for the additional path loss to maintain the same link budget at those angles. Thus, to enhance the end-fire gain with minimal electrical footprint, spatially modulated zero-index metamaterial is proposed and integrated with a tapered slot antenna. The antenna post integration is analysed for the phase correction of the wavefront leading to a gain of 8.5 dBi and aperture efficiency of 77% at 28 GHz. A co-polarised vertical stacking topology is proposed to achieve path loss compensated beam switchable antennas with an angular coverage of ±65° and mutual coupling <30 dB throughout the band. Detailed simulated and measured results are presented and are in good agreement.

MIMO-Supporting Radio-Over-Fiber System and its Application in mmWave-Based Indoor 5G Mobile Network

We demonstrate 4 × 4 multiple-input and multiple-output (MIMO) supporting mmWave-based indoor 5G mobile network based on a distributed antenna system (DAS) that has over-the-air interface to receive the broadband wireless signal from, e.g., remote radio head (RRH) of mobile fronthaul. To realize the cost/bandwidth-efficient and low-latency-inducing indoor 5G DAS network, we exploit the radio-over-fiber (RoF) system that is based on the intermediate frequency-over-fiber (IFoF) technology. To be more specific, we make simultaneous use of wavelength- and frequency-division multiplexing in the IFoF link so as to transport 4 × 4 MIMO 5G signal of which the bandwidth is effectively 3.2 GHz (= 4 × 800 MHz, where each antenna deals with 800 MHz 5G signal). The 4 × 4 MIMO-supporting IFoF link has error vector magnitude (EVM) performance of <4.5% at all channels of downlink and uplink for up to 2 km. The whole RoF system, exploiting the IFoF link, mmWave frequency conversion module, and control /management plane, proves itself to meet the 3GPP-defined EVM requirement (i.e., 8%) at all channels. Based on the RoF system, we demonstrate the indoor 5G DAS network in conjunction with Korea Telecom 5G mobile network, i.e., 5G baseband unit and RRH, investigating the downlink and uplink throughputs. We achieve ∼4 Gb/s total throughput for end user, where the additional latency induced by the DAS network is only a few hundreds of nanoseconds other than the single mode fiber transmission delay.

Reinforcement learning algorithm for 5G indoor device‐to‐device communications

AbstractFifth generation (5G), the next generation telecommunications will be striking the markets in near future. Device‐to‐device (D2D) communication would be a part of 5G to serve communication needs for billions of connected devices to support high data rate ultrareliable low latency communications. Indoor 5G will be relying on distributed small cell solutions and D2D along with machine‐to‐machine connections. Machine learning is one of the most promising tools for providing the best set of solutions to learn the influential scenarios and certain parameters of the communication networks. This research proposes reinforcement‐learning‐based latency controlled D2D connectivity (RL‐LCDC) algorithm and its Q‐learning approach in an indoor D2D communication network for strong 5G connectivity with minimum latency. The proposed approach, RL‐LCDC efficiently discovers the neighbors, decides the D2D link, and adaptively controls the communication range for maximum network connectivity. The results show that RL‐LCDC optimizes the connectivity with lower end‐to‐end delay and better energy efficiency with efficient convergence time when compared with other conventional schemes.

Analog MIMO Radio-Over-Copper Downlink With Space-Frequency to Space-Frequency Multiplexing for Multi-User 5G Indoor Deployments

Radio access network (RAN) centralization is at the basis of current mobile networks, in which BaseBand Units (BBUs) and radio antenna units (RAUs) exchange over the FrontHaul (FH) digitized radio-frequency signals through protocols such as the common public radio interface. However, such architecture, as it stands, does not scale to the demands of multiple-antennas 5G systems, thus leading to drastic RAN paradigm changes. Differently from digital RAN architectures, we propose to overcome bandwidth/latency issues due to digitization by employing an all-analog FH for multiple-antenna RAUs based on the analog radio-over-copper (A-RoC) paradigm. The A-RoC is an alternative/complementary solution to FH for the last 200 m, such as for indoor, to reuse existing local area network (LAN) cables with remarkable economic benefits. Although LAN cables contain 4 twisted-pairs with up to 500 MHz bandwidth/ea., their usage is limited by cable attenuation and crosstalk among pairs. This paper demonstrates that a judicious mapping of each radio-frequency signal of each antenna onto a combination of cable pair-frequency allocations, referred to as space-frequency to space-frequency multiplexing, optimized together with the design of the digital precoding at the BBU, substantially mitigates the cable impairments. The LAN cables can be exploited for last 100–200 m analog transport FH to meet the requirements of 5G indoor networks.

Analog MIMO-RoC Downlink With SF2SF

Analog MIMO radio-over-copper is an alternative/complementary solution to conventional fiber-based mobile-fronthaul suitable for the last 200m with goal to reuse existing indoor LAN cables with remarkable economic benefits. Although LAN cables contain four twisted-pairs with up to 500MHz bandwidth/ea., their usage is limited by cable attenuation and crosstalk among pairs. In this letter, we demonstrate by numerical evaluations that a judicious mapping of each radio-frequency signal of each antenna onto a combination of cable pair-frequency allocations, referred to as space-frequency to space-frequency multiplexing, minimizes the cable impairments. LAN cables bandwidth capabilities are thus exploited to evaluate the radio access requirements of 5G indoor networks.

A new double‐sided substrate‐integrated waveguide slot array antenna for 5G applications

AbstractA double‐sided substrate‐integrated waveguide (SIW) slot antenna with stripline feed, as 4‐by‐4 SIW slot array antenna, operating in millimeter‐waves bands is proposed. The whole antenna and feeding system are fabricated on a single substrate with 2 dielectric layers and 3 copper layers, which takes some advantage, such as, small size, low profile, low cost, and 2 radiation direction propagations. The design process and experimental results are presented. The prototypes can be used in dual band frequency ranges, 25 and 28 GHz, with 8 dBi gain and 63° for half power beamwidth in both sides, front and back antenna sides, and 2 GHz bandwidth. Thus, this component can be applied for 5G indoor environments.

A Novel Distributed Antenna Access Architecture for 5G Indoor Service Provisioning

In order to overcome the non-line-of-sight nature of the indoor environment so as to achieve a cost-effective solution of 5G indoor service provisioning, distribution of antenna units in indoor chambers is the most straightforward solution. This paper investigates a novel distributed antenna access architecture that allows the antenna units to be distributed over a wide geographical area via multi-pair LAN cables. The proposed architecture supports simultaneous transmission of multiple intermediate frequency signals between the remote radio unit and each distributed antenna unit. To explore the capacity of the LAN cables, we introduce a real-time multi-pair air-to-cable (MP-A2C) scheduler that allows for a graceful mapping between the radio signal spectrum and sub-channels of the cable twisted pairs, as well as power shaping of each sub-channel signal. We will first provide the problem formulation of the optimal MP-A2C process, which is nonetheless non-convex and computationally intractable. To achieve real-time solution of the problem, we reformulate the problem into two sub-problems that can be solved in a divide-and-conquer manner. Extensive numerical results show that the formulated MP-A2C problem can easily lead to quasi-optimal schedules.

MmWave and VLC-Based Indoor Channel Models in 5G Wireless Networks

MmWave and VLC are two promising technologies for future 5G indoor communications to enable gigabit-per-second data transmission and to meet the ever increasing capacity requirements. Only with a solid understanding of the channels on mmWave and VLC can researchers and industry practitioners further explore the appropriate architectures and efficient communication schemes. In this article we focus on two recent indoor channels in future 5G networks based on mmWave and VLC. The article first discusses their operating frequency, room dimension, and transceiver configuration, which are among the key factors deciding the channel characteristics and impacting the communication performance. The detailed analysis on path loss and time dispersion for both mmWave and VLC channels are then elaborated. Finally, comparisons between mmWave and VLC channels and discussions on VLC and mmWave applications are presented. The study in this article shows that VLC and mmWave channels share some common characteristics while differing in others, which makes them appealing in different application scenarios.

An Indoor Path Loss Prediction Model Using Wall Correction Factors for Wireless Local Area Network and 5G Indoor Networks

AbstractA modified indoor path loss prediction model is presented, namely, effective wall loss model. The modified model is compared to other indoor path loss prediction models using simulation data and real‐time measurements. Different operating frequencies and antenna polarizations are considered to verify the observations. In the simulation part, effective wall loss model shows the best performance among other models as it outperforms 2 times the dual‐slope model, which is the second best performance. Similar observations were recorded from the experimental results. Linear attenuation and one‐slope models have similar behavior, the two models parameters show dependency on operating frequency and antenna polarization.

A performance comparison of in-band full duplex and dynamic TDD for 5G indoor wireless networks

In-band full duplex has emerged as a solution for high data rate and low access delay for 5G wireless networks after its feasibility has been demonstrated. However, the impact of the in-band full duplex on the system-level performance of multi-cell wireless networks has not been investigated thoroughly. In this paper, we conduct an extensive simulation study to investigate the performance of in-band full duplex for indoor 5G small cell wireless networks. Particularly, we compare the in-band full duplex with static and dynamic time division duplexing schemes which require much less hardware complexity. We examine the effects of beamforming and interference cancellation under various traffic demands and asymmetry situations in the performance comparison. Our objective is to identify under which condition and with which technology support the in-band full duplex becomes advantageous over the simpler duplexing schemes. Numerical results indicate that for highly utilized wireless networks, in-band full duplex should be combined with interference cancellation and beamforming in order to achieve a performance gain over traditional duplexing schemes. Only then in-band full duplex is considered to be advantageous at any number of active mobile stations in the network and any downlink to uplink traffic proportion. Our results also suggest that in order to achieve a performance gain with the in-band full duplex in both links, the transmit power of the access points and the mobile stations should be comparable.