As the world anticipates the arrival of 6G networks, the spotlight is increasingly turning toward innovative technologies that can push the boundaries of wireless connectivity even further. Among these transformative technologies, Reconfigurable Intelligent Surfaces (RIS) have emerged as a promising solution that holds immense potential to revolutionize wireless communication in the 6G era.
RIS, also known as intelligent surfaces or metasurfaces, are planar structures comprising a large number of tiny passive elements that can manipulate and control the propagation of electromagnetic waves. Unlike conventional wireless communication systems that heavily rely on transmitting and receiving antennas, RIS operates by intelligently reflecting, refracting, or scattering electromagnetic waves to achieve specific objectives. By deploying these surfaces in the environment, it becomes possible to enhance and shape the wireless signal in unprecedented ways.
So, why are RIS gaining such attention in the context of 6G networks? First and foremost, RIS technology offers the potential to address the challenges posed by the ever-increasing demand for higher data rates and network capacity. By carefully optimizing the reflections of wireless signals, RIS can help overcome the limitations of traditional wireless networks, such as signal fading, interference, and path loss. These surfaces act as virtual mirrors, steering and focusing signals to improve coverage, boost signal strength, and increase the overall network capacity.
RIS holds promise in significantly reducing latency, which is crucial for emerging applications like virtual reality, augmented reality (AR), autonomous vehicles, and industrial automation. By precisely manipulating the propagation of signals, RIS can introduce controlled delays, phase shifts, and beamforming effects, thereby enabling ultralow latency communication and enhancing the quality of real-time applications.
Additionally, RIS has the potential to improve energy efficiency in wireless networks. By enabling finer control over signal propagation, RIS can facilitate the more efficient use of radio resources, reducing the power consumption of both the base stations and user devices. This energy-saving capability aligns with the growing emphasis on sustainable and environmentally friendly communication systems, making RIS an attractive technology for the future. In this issue’s column, we report on a new white paper addressing relevant RIS use cases.
On 16 May 2023, the European Telecommunications Standards Institute (ETSI) announced the release of the first Group Report (GR) developed by its Reconfigurable Intelligent Surface Industry Specification Group. The ETSI Report ETSI GR RIS-001 [1] identifies and defines relevant RIS use cases, with corresponding general key performance indicators (KPIs). It also describes deployment scenarios as well as potential requirements for each identified use case to enable interoperability with existing and upcoming wireless technologies and networks.
The emergence of RIS has motivated a host of potential new use cases targeting the enhancement of various system KPIs and the support of new wireless technology applications and capabilities. These use cases include enhancements to the capacity, coverage, positioning, security, and sustainability as well as the support of further sensing, wireless power transfer, and ambient backscattering capabilities. The ETSI Report, ETSI GR RIS-001, specifies 11 concrete key use cases where RIS deployment may provide enhancements or new functionalities.
“In the future 5G-Advanced and 6G wireless networks, many new applications, such as in eHealth, strongly impose requirements on both the communication and sensing performance,” explains Arman Shojaeifard, chair of the ETSI RIS group. “As an example, a RIS can reconfigure the radio environment to sense human posture and detect someone falling, a useful application for elderly care,” he adds.
Providing coverage continues to be a challenge for operators commercializing 5G, and existing deployment solutions, such as Integrated Access and Backhaul (IAB) and Network Controller Repeater (NCR), may not be economically viable in all cases, e.g., indoor scenarios. RIS can serve as a new low-cost energy-efficient deployment solution for enhancing coverage performance in 5G-Advanced and future 6G systems by intently reflecting signals to and from the end users.
RIS corresponds to a planar surface composed of a certain arrangement of unit cells whose properties can be dynamically controlled to change the surface response in the electromagnetic domain. RIS can be controlled dynamically and/or semistatically through control signaling, such as to tune the incident wireless signals through reflection, refraction, focusing, collimation, modulation, absorption, or any combination of these.
RIS can be implemented using mostly passive components without requiring high-cost active components such as power amplifiers, resulting in low implementation cost and energy consumption. This allows the flexible deployment of RIS with the possibility of RIS taking any shape and being integrated onto objects (e.g., walls, buildings, lamp posts, etc.). RIS are supposed to run as nearly passive devices and hence are unlikely to increase exposure to electronic magnetic fields, and they can even potentially be used to reduce electromagnetic pollution in legacy deployments. These associated characteristics suggest that RIS may be considered as a sustainable environmentally friendly technology solution. RIS may have different structures with considerations of cost, form factor, design, and integration.
On 26 April 2023, Ericsson unveiled two new Open-Radio Access Network (O-RAN)-based automation applications (rApps) that will address energy efficiency, a top priority for communications service providers. The telecom industry’s commitment to sustainability drives the need for solutions that monitor and save energy while improving network performance.
With the introduction of 5G and an increased variety of network services with data-hungry applications, network operations are becoming increasingly complex. RAN will need to cope with the diverse use cases and devices while delivering the best user experience for each of them.
To manage this complexity profitably, service providers need to efficiently utilize limited resources. Faced with these challenges, rApps have emerged as a solution to provide the tools and applications needed to effectively manage complexity.
The announcement of Ericsson’s RAN Energy Control and RAN Energy Cockpit rApps supports service providers in their intelligent automation journey, with a focus on energy efficiency. The Ericsson RAN Energy Control rApp provides an autonomous mechanism using artificial intelligence (AI) and machine learning (ML) technologies with closed-loop automation. This mechanism autonomously determines which radio power-saving features per radio unit should be activated or deactivated every 15 min across the whole network on a radio unit level of granularity. It also takes traffic impact into consideration by using ML to ensure that network performance is protected. This reduces the daily radio network energy consumption by up to 25% without impacting user experience.
With a focus on improving the energy consumption and efficiency of the network at scale, the Ericsson RAN Energy Cockpit rApp monitors the energy performance of each radio unit and for the overall network. It does this by providing a visualization of the overall network energy efficiency with site granularity, automated identification and isolation of causes of inefficiencies, and resolution recommendations.
Ericsson’s new energy efficiency-focused rApps will be delivered initially on the Ericsson Intelligent Automation Platform. Both rApps are also platform agnostic and deliver functionality into Open RAN architectures by using the O-RAN Alliance’s R1 interface. This gives service providers the flexibility to choose their desired network evolution path while automating their network with greater energy efficiency.
Ericsson reported on 29 May 2023 that, together with MediaTek, they have set a new 5G upload speed record of 440 Mb/s in low-band and midband spectrum using uplink carrier aggregation. Fast uplink speed brings better and smoother experiences for the likes of video conference users, streamers, and their audiences with more frames per second and higher image resolution. Additionally, uplink speed is becoming more crucial with the expected uptake of gaming, extended reality, and video-based apps. For example, as AR devices gain popularity with larger augmentation objects, rendering becomes more demanding. This increases the demand on networks to deliver higher throughput and lower latency.
The record uplink speed was achieved in an interoperability development test at an Ericsson lab. The test was performed with a RAN Compute Baseband 6648 and a mobile device using a MediaTek Dimensity 9200 flagship 5G smartphone chipset. The uplink carrier aggregation combination involved a frequency division duplex (FDD) and time division duplex (TDD) channel in a frequency range widely deployed in today’s 5G networks.
More precisely, the combination used was 50-MHz FDD n1 and 100-MHz TDD n77. By aggregating these two bands, communications service providers can considerably increase their uplink speeds, resulting in better network performance and user experience.
Service providers are seeking innovative ways of boosting capacity while using the existing spectrum efficiently to meet growing demands for wireless data and applications. This is where carrier aggregation comes in, optimizing the service provider’s spectrum assets to bring better coverage, increased capacity, and higher data speeds to users.
In related news, on 9 May 2023, ZTE Corporation, in partnership with AIS, launched a new-generation ultralarge-bandwidth millimeter-wave active antenna unit (AAU). This milestone was celebrated at the joint innovation center in Bangkok. This millimeter-wave AAU is the world’s first to support 1.2-GHz bandwidth and above, with a maximum bandwidth of 1.6 GHz.
During the on-site live demonstration, the New Radio Dual Connectivity (NR-DC) mode was utilized along with the 1.2-GHz bandwidth millimeter-wave spectrum owned by AIS. The peak rate of single-sector units was measured to reach 22.01 Gbps in the downlink and 4.32 Gb/s in the uplink, which greatly exceeds the industry average. It is widely known that millimeter-wave offers rich spectrum resources, and many operators have access to millimeter-wave spectrum over 1 GHz. The ultralarge bandwidth and high capacity of this single AAU will help operators make full use of their millimeter-wave spectrum potential.
On 13 April 2023, Qualcomm Technologies and Xiaomi announced that they successfully verified meter-level positioning in a Xiaomi 12 T Pro powered by the Snapdragon 8+ Gen 1 Mobile Platform in Germany. Qualcomm meter-level positioning for mobile enables superior location capabilities and was first launched by Xiaomi via its Xiaomi 11 Pro and Xiaomi 11 Ultra in China.
Meter-level positioning accuracy can improve smartphone user experience in numerous scenarios, including mapping, driving, and other mobile applications. For instance, it enables greater accuracy when using:
This unprecedented level of accuracy in a commercial smartphone is enabled through Qualcomm meter-level positioning for mobile in combination with Trimble RTX (Real Time Extended) correction services. When integrated with Snapdragon mobile platforms, Trimble RTX supercharges premium phones’ positioning capabilities.
Accuracy verification tests, including driving tests, were conducted by Qualcomm Technologies, Xiaomi, and Trimble in various scenarios, such as open-sky rural roads and urban highways, and demonstrated meter-level positioning variance at a 95% confidence level—a rigorous threshold for mobile location technologies.
On 9 May 2023, Ericsson and Telia reported that they have joined forces to launch the Baltics’ first enterprise 5G private network at Ericsson’s supply site in Tallinn, Estonia. This milestone represents a significant step toward the region’s digital transformation, accelerating business operations and fostering innovation. The Tallinn supply site is a strategic player in Ericsson’s global supply chain footprint, accounting for nearly half of the new product introductions (NPIs).
The implementation of Ericsson Private 5G allows for dynamic new product development by enabling the agile layout and design of the manufacturing facility. Telia, a leader in 5G advancements in the Baltic states, is proud to be a part of this groundbreaking initiative.
Ericsson and Telia have set out to transform the manufacturing industry in the Baltics with the launch of the region’s first enterprise 5G private network, Ericsson Private 5G. The private cellular network went live on 2 May 2023 at Ericsson’s supply site in Tallinn, Estonia, with the goal of driving efficiencies in productivity, agility, and sustainability and being the platform for innovation at the smart factory.
Through its reliability, predictable latency, security, and speed, the 5G private network’s cutting-edge capabilities are enabling a variety of use cases, such as asset condition monitoring and management, computer vision, digital twins, and collaborative robotics, as well as new feature capabilities like 5G precise indoor positioning.
This latest development in the Ericsson and Telia collaboration is expected to have a significant impact, both locally and globally, on the Tallinn supply site and in the contribution to Estonia’s export market. The supply site in Tallinn plays a strategic role in Ericsson’s global supply chain footprint, accounting for nearly half of the company’s NPIs. These NPIs involve extensive R&D to ensure product relevance, competitiveness, and scalability, which are critical to the successful ramp-up of new products. The implementation of Ericsson Private 5G throughout the factory is reducing the dependency on wires dramatically to improve the agility of production layout and design while delivering greater mobility of impactful solutions like automated guided vehicles.
Ericsson Private 5G is Ericsson’s next-generation private network solution providing secure and reliable 4G and 5G connectivity through its single-server dual-mode core. Built for business operations, the solution comes preintegrated to ensure rapid time to use, enabling advanced and intelligent operations in any environment. The product serves as a platform for innovation and Industry 4.0, allowing facilities to modernize ways of working.
According to Andre Visse, the CTO of Telia Estonia, the close partnership between Telia and Ericsson has been working for decades, and in the process, different generations of mobile networks have emerged in Estonia. The new network has already started having an impact at the supply site, elevating business-critical operations through automation, safety, and agility. In particular, it is enabling the monitoring and management of numerous devices in a defined area, providing better coverage with less infrastructure and also ensuring seamless connectivity through a rapid increase in wireless sensors on the shop floor.
ZTE Corporation announced on 19 April 2023 that it has partnered with Multi PRO, part of Grupo Multi Company, to successfully deploy the ZTE Smart Cloud Platform (SCP) in Brazil. With its functions, including visual management, remote optimization, and proactive operation and maintenance (O&M) for home Wi-Fi networks, the ZTE SCP can significantly enhance the home broadband quality and user experience across the country.
The ZTE SCP enables intelligent O&M and visual management of home Wi-Fi devices. Common faults can be diagnosed with one click by operator engineers and remotely fixed by a call center or an O&M center to reduce engineer visits. Less common and more difficult faults can be quickly identified and resolved by performing an association analysis of the historical data of home network quality. Issues affecting the Wi-Fi quality of experience can be accurately positioned and addressed through tools such as those for multidimensional statistics and the analysis and health scoring of home networks.
Users can remotely manage their Wi-Fi networks, set parental and visitor controls, and perform other operations through a mobile app. The ZTE SCP can also manage Internet Protocol (IP) cameras and fiber-to-the-room devices, which saves operators from making additional investments to manage them.
The joint deployment of the SCP by ZTE and Grupo Multi marks an important milestone in the two parties’ transition from “building a better network” to “delivering a better experience.” It is expected to greatly improve the intelligent management of home Wi-Fi networks in Brazil.
GlobalData, a leading information services company, and Huawei jointly released a white paper—”The 5G Voice Transition: Managing the Complexity” [3]. It describes the current challenges facing operators who run voice networks over multiple generations and proposes building a convergent voice network that would solve network transition issues. It also points out that the high-value services supported by the IP Multimedia Subsystem (IMS) data channel are the new development direction for voice.
GlobalData surveyed 50 mobile operators around the world on their strategies for voice services and challenges. Andy Hicks, the lead author of the white paper and senior principal analyst at GlobalData, said that although Internet-based voice and video calls have been growing in popularity, operators’ voice services are still indispensable to people’s everyday life thanks to their high reliability and stability. As many as 82% of surveyed operators think that voice and short message service services are as important or almost as important as data services, even in the 5G era. In addition, the survey shows that following the disruptions caused by COVID-19, voice traffic on most networks has stabilized. In fact, on a few networks, it has even increased.
As networks evolve, operators may provide voice services over multiple network generations from 2G to 5G. This leads to problems such as increased operational expenditures, difficult Voice over LTE (VoLTE) roaming, and complex network transition. Thirty-two percent of surveyed operators indicated that they will not continue to invest in 2G and 3G networks after they enter the end phase of their lifecycle, up from 17% in 2020. These operators must therefore seek other ways to provide traditional services while they migrate their users to 4G and 5G. Some of them are considering using convergent voice solutions to improve performance while reducing operational expenditure. In addition, a convergent voice solution can greatly simplify VoLTE roaming, accelerate VoLTE adoption, maximize spectrum utilization, and promote the large-scale commercial use of 5G.
The white paper says that as 5G ramps up, operators need to leverage more innovative high-value services to open revenue streams on top of traditional voice services. It further notes that the latest 3rd Generation Partnership Project (3GPP) standards have defined a new way to do this: the IMS data channel. This innovation allows users to transmit data in parallel with voice, thereby enabling interactive communication and new services, such as 5G New Calling, which can bring enhanced experiences like visualized voice calling, real-time translation, and fun calling. Operators can use the IMS data channel to create more services, further improve the user experience, and rejuvenate voice services in 5G.
On 30 May 2023, ETSI published its new white paper, “Evolving NFV Toward the Next Decade,” [2] written by delegates of the ETSI Industry Specification Group on Network Function Virtualization (ISG NFV).
Network functions virtualization has been the catalyst of a radical change to the telecom industry, leading the transition from the traditional physical (hardware) network appliance into a new software-based virtualized network function era. Based on the use of general-purpose (commodity-off-the-shelf) servers and the deployment of network functions as software applications, NFV has broken through the technical challenges of software and hardware decoupling. The migration of network functions from dedicated physical appliances to distributed cloud infrastructure has revolutionized the way communications networks are developed, deployed, and operated nowadays.
In 2012, various international leading telecom service providers (network operators) jointly released an influential white paper about NFV’s concepts and vision and announced the beginning of a new era in the telecom industry. Since the creation of the ETSI ISG NFV the same year—the first standards organization of this kind in this domain—network operators, communications technology (CT) vendors, information technology vendors, small and medium-sized enterprises, and other core contributors (e.g., from open source, academia, and research communities) have been actively discussing and standardizing the NFV framework, which has become the telco cloud and virtualization network architecture of reference.
The mixture of IT and traditional telecom network viewpoints in NFV has also brought a challenging, yet important, network transformation environment. Traditionally, network operators and CT vendors have become accustomed to the consensus-based standard development process from which products are then developed and commercialized. However, the scenario of IT vendors and open source communities is different; these are based on a “code-first” process, whereby code is first developed and then contributed. These two ways of developing current telecom network technology need to be brought together as “sides of the same coin”; in this scenario, network operators, CT and IT vendors, and open source communities need to work together to bridge the gap between the two perspectives and facilitate broader support of ETSI NFV standards. For instance, while open source could further support and implement the standards as much as possible, standards could consider the “borrow-in philosophy” to take advantage of the core strength of open source in the specifications.
Ten years after the emergence of NFV (and after major investments and network deployments based on it), it is the right time to consider how the NFV framework can and will evolve. For this, it is important to understand and take action on the requirements that telecom service providers consider for their telco cloud.
Building on previous achievements, this white paper analyzes different challenges and technology trends and proposes several potential directions on how ETSI ISG NFV can evolve in the next decade. Aspects related to the development of application programming interfaces (APIs), open source, NFV multicloud, unified management, declarative intent-driven automation, and AI are considered as key drivers for the evolution.
On 17 May 2023, Nokia announced a contract with Belgian telecom operator Citymesh to supply its Nokia Drone Networks platform with 70 drone-in-a-box units. This is enough to blanket Belgium with a 5G automated drone grid that informs and speeds resource mobilization in emergency events.
Branded SENSE by Citymesh, the 70 drones are deployed in 35 emergency zones across the country and will gather information in the critical 15-min period immediately following a call. This ensures that first responder teams are fully apprised of and equipped to respond to each unique situation.
Belgium’s emergency services can receive more than 2 million calls a year, and typically, police and fire brigades are dispatched with incomplete data that can stymie the efficiency of their response. With Nokia Drone Networks, pilots will be able to operate 24/7 and dispatch drones from docking stations strategically located across the country.
Equipped with high definition and AI-enhanced thermal imaging, drones capture real-time aerial footage—such as smoke plumes, fire parameters, and the number/location of people—and transfer it to control centers even before emergency teams have had time to leave. These aerial images are essential to identifying a plan of action that can save lives and limit damage to affected assets and natural resources.
Nokia revealed a few weeks prior to this announcement that it is the first to offer a Conformité Européene (CE)-certified turnkey drone-in-a-box solution, designed to meet the growing demands of organizations, including public safety agencies, smart cities, construction, energy, and defense. CE-certified to meet the safety requirements of the European Union, the Nokia Drone Networks solution connects over public and private 4G/LTE and 5G networks to enhance situational awareness for first responders and other professionals.
The solution is manufactured in Europe and comprises Nokia drones, docking stations, dual gimbal cameras, and edge-cloud processing using the Nokia MX Industrial Edge (MXIE). By connecting over public and private 4G/LTE and 5G networks, customers will benefit from the highest reliability. Using cellular connectivity technologies also offers higher data rates and lower latency, enabling more data to be streamed than over Wi-Fi. Beyond-visual-line-of-sight operations with real-time kinetic positioning improve situational awareness. Dual modem connectivity allows Nokia drones to simultaneously connect to multiple networks, complying with system redundancy that is commonly required by aviation regulatory bodies.
The Nokia Drone Networks solution can be operated remotely for search and rescue activities and to assess damage in a hazardous environment. Nokia drones can also be programmed to manage autonomous scheduled flights for applications like additional security at large events or to manage regular remote equipment inspections. The docking station protects the drone and payload, such as the sensor devices or dual gimbal camera, from external hazards and harsh weather while it remotely charges the drone to prepare for the next flight.
When used in conjunction with the Nokia MXIE, data from Nokia drones can be collected and processed in real time at the edge cloud. An open API framework allows agencies and enterprises to on board preintegrated Nokia and third-party applications and systems and take advantage of a growing number of compelling public safety and Industry 4.0 use cases for drone automation, including object identification, tracking, and network measurements
Nokia and the New York Power Authority have already demonstrated the use of the Nokia Drone Networks solution, connected over private LTE, for transmission line inspection.
Today, most emergency services can receive only voice telephone calls. With all communication means that citizens now use in their daily life, they expect to use them as well to reach emergency services. To help achieve this goal, on 11 April 2023, ETSI released a revised version of the specification ETSI TS 103 479. Developed by the technical committee Emergency Telecommunications (EMTEL), this specification defines Next-Generation Core Services (NGCS).
These new services allow one to utilize multimedia emergency communication (i.e., voice, photos, video, or text) to contact the relevant emergency call center. Depending on the country, there may be one or more emergency control centers or public safety answering points. In case there are several control centers, they are networked via packet-switched infrastructure or, in standard terms, an Emergency Services IP Network (ESInet), to provide a reliable infrastructure for emergency communications and data sharing in real time. This will help to improve decision-making and response times during emergencies.
This revision also provides a technical basis for national packet-switched infrastructure, giving access to emergency services communications to all citizens. Indeed, it includes the requirement to support total conversation (i.e., voice, video, and real-time text combined in a single conversation) and real-time text, which can, for instance, help hearing-impaired people. In addition, to achieve a European harmonization of emergency communications, it is key to choose the right terminology, also included in this new specification. Interoperability at an international level is also very important, and the ETSI technical committee EMTEL, in coordination with the National Emergency Number Association (NENA) in the United States, has standardized the designation for namespaces to create the basis for a global standard.
Another main technical addition of ETSI TS 103 479 includes a mechanism to update location data directly from the terminal even during an active emergency communication. It allows the routing to the correct emergency control center based on the location information. This mechanism also makes it possible to manage roaming situations, for instance, when you are abroad but connected remotely to your originating service provider. The latter applies, in particular, to voice over IP or Accident Prevention Program service providers.
The ETSI specification enables a standard-compliant integration of different networks with the next-generation core services of an ESInet. As the use of mobile communications is constantly increasing, compatibility with 3GPP VoLTE is especially important and allows the use of the native communication functions of mobile devices in emergency situations.
In a report published on 25 May 2023, Surf Lifesaving New Zealand Search and Rescue (SLS NZSAR) detailed how it is increasing safety and efficiency for its interagency training exercises with rugged and reliable communications from Motorola Solutions. The volunteer agency depends on Motorola Solutions’ technologies to deliver rescue and emergency services throughout New Zealand every day. This includes the agency’s support for communities impacted by severe tropical cyclone Gabrielle in February 2023, one of the most damaging weather systems to strike New Zealand in decades.
To prepare for such events, SLS NZSAR conducts search and rescue exercises involving multiple public safety and emergency service personnel to test operational efficiency and response in the most challenging remote environments. In these dynamic conditions, reliable communication is essential to helping frontline teams collaborate seamlessly and coordinate successful operations.
On a recent training exercise amid towering peaks, waterfalls, and narrow fiordlands reaching as high as 1,000 m in New Zealand’s Milford Sound, Motorola Solutions’ MOTOTRBO SLR 1000 Repeater and rugged and dependable DP4000e and MOTOTRBO R7 two-way radios provided extended and interoperable coverage for all participating agencies. As a fully deployable communications solution, it can be mobilized wherever rescue missions take place.
“By placing the repeater on a mountaintop we remained connected while performing search and rescue training exercises in the lakes 1,000 metres below,” said Max Corboy, search and rescue volunteer. “Reliability is crucial to us. We’re deploying to remote locations and we need to make sure our team has the best possible equipment supporting them to get their job done,” he added.
Following the successful exercise, Motorola Solutions and SLS NZSAR are planning further enhancements to deployable mobile communications, including the introduction of live video streaming, body-worn video cameras, and software solutions. This will further enhance incident awareness and safety for field-based responders during rescue missions.
[1] “Reconfigurable intelligent surfaces (RIS); use cases, deployment scenarios and requirements,” ETSI, Sophia Antipolis, France, Apr. 2023. [Online] . Available: https://www.etsi.org/deliver/etsi_gr/RIS/001_099/001/01.01.01_60/gr_RIS001v010101p.pdf
[2] X. Cai et al., “Evolving NFV towards the next decade,” ETSI, Sophia Antipolis, France, May 2023. [Online] . Available: https://www.etsi.org/images/files/ETSIWhitePapers/ETSI-WP-54-Evolving_NFV_towards_the_next_decade.pdf
[3] “GlobalData and Huawei release a 5G voice transition white paper — Voice services are still critical to telcos,” Huawei, Apr. 2023. [Online] . Available: https://www.huawei.com/en/news/2023/4/5g-voice-transition-whitepaper
Digital Object Identifier 10.1109/MVT.2023.3284170