5.5G will fill in the gaps of 5G and enhance the key features of eMBB, URLLC, and mMTC. What features and benefits will 5.5G offer in practice?
By Wu Hequan, Academician, Chinese Academy of Engineering; Director, Advisory Committee of the Internet Society of China; Director, China Standardization Expert Committee
Global 5G deployment is now well underway, with more than 230 5G networks already in commercial use and more than 1 billion 5G users accounting for 12% of all mobile users worldwide. This number is remarkable, because it means that in just three years since the start of commercial deployment, 5G has as many users as 4G had after five years. Operators have deployed tens of thousands of private networks for the 5GtoB market and by the end of 2022, 2.312 million 5G base stations had been built in China. That is 21.3% of all base stations in the country and 60% of all 5G base stations worldwide.
China now has 561 million 5G users, accounting for 33.3% of all mobile users in the country and 56% of all 5G users worldwide. China is also home to more than half the world's 5G private networks.
The high download rates 5G enables have driven global mobile data traffic to double for two consecutive years. However, the increased speeds delivered by 5G are not really perceivable when using average consumer applications. They are also not adequate for industrial applications. In terms of user experience, 5G has not shown obvious advantages over 4G. Both 4G and 5G high-end handSet can support 2K screen resolution without any obvious differences in fluency. 5G's ability to support simultaneous access for more users is also an often-ignored factor in scenarios other than large venues, like stadiums. Likewise, its low latency is rarely noticed outside applications such as IoV and XR. XR services that require a headset need 5G's high bandwidth, but existing 5G networks can barely support XR video experiences. At the same time, although 5G has been successfully applied to applications like machine vision and remote control, it has not been effective in bringing the industrial Internet to the next level. In many industrial scenarios, massive MIMO, one of the most prominent features of 5G, rarely comes into play, because industrial applications need more: larger uplink, lower latency, more determinacy, higher security, higher reliability, more massive connectivity, higher-precision positioning, and lower power consumption. Lightweight and low cost is also required for ubiquitous connectivity.
To stimulate 5G's potential and keep pace with market growth, the industry is turning to 5G-Advanced (5.5G) as a stepping stone to 6G. 5.5G primarily enhances three of 5G's features: enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), and massive machine-type communications (mMTC). This improves the technology's capabilities in broadband, ubiquitousness, eco-friendliness, and intelligence.
From eMBB to eMBB+
The speed of 5.5G will be 10 times higher than that of 5G, meaning a peak uplink rate of 1 Gbit/s and a peak downlink rate of 10 Gbit/s. Massive MIMO is still the main focus here, as it significantly increases air interface bandwidth by using 64T or 128T radio frequency (RF) channels and by increasing antenna element counts from 192 to 1,000 or even 2,000. Extremely large aperture array (ELAA) technology also allows antenna units to be deployed on the wall of a building in a distributed manner, overcoming the limitations of centralized deployment such as antenna panel size, weight, and wind load. Innovative materials and structures alongside advanced technologies, like adaptive high-resolution beamforming algorithms (such as AHR Turbo), intelligent sounding reference signal (SRS) interference identification and suppression, and intelligent beam direction prediction, can enable ultra-high-resolution beams as well as their fast alignment and real-time tracking. This will, in turn, improve uplink and downlink coverage by 3 dB, increase user perceived rates by 30%, and reduce energy consumption by 30%. However, the specificity of the ELAA electromagnetic field must be considered during design. Innovative distributed baseband processing algorithms and architecture can be employed to achieve low complexity and low fronthaul overhead given the large number of antenna elements.
Spectrum resources will also be key to the high bandwidth delivered by 5.5G. A virtual large carrier frequency technology that shares synchronization signals and physical broadcast channel blocks (SSBs) can be used to utilize discrete frequency bands to address carrier bandwidth requirements for 400 MHz (sub-6 GHz band) or 800 MHz (millimeter wave band). This would improve traditional carrier aggregation methods, reducing common signaling overhead while supporting flexible scheduling across multiple cells. Unified division duplex (UDD) can also be used to enhance uplink by adding a pure uplink carrier or adding a carrier that adopts the TDD complementary frame structure through supplementary uplink (SUL). Furthermore, a 50-MHz SUL and 100-MHz TDD configuration can enable a peak uplink rate of over 1 Gbit/s per user.
Signals in high frequency bands have poor penetration performance and can easily be blocked, while repeaters lack flexible beamforming and interference management capabilities, which creates coverage weaknesses or blind areas on the network. 5.5G employs network-controlled repeaters (NCRs), which uses beam indication information to select and switch beams based on terminal conditions, improving both indoor and outdoor coverage capabilities.
In industrial applications, industrial licensed frequency bands can be set to provide large uplink services for large enterprises. This prevents interference due to inconsistent uplink and downlink TDD timeslot configurations when carriers are shared with consumers. Compared with LAN-based Wi-Fi networks, cellular-based NR in unlicensed spectrum (NR-U) can deliver better mobility, more accurate positioning and timing, and better support for QoS. However, NR-U will need AI to implement automatic frequency control (AFC) to avoid interference with other systems, satellites, and point-to-point microwave link. In terms of terminals, smart 5.5G terminals will shift from 2T4R to 3T8R and support aggregation of at least four carriers to enable a 10-gigabit experience.
From URLLC to URLLC+
The key indicators of 5G URLLC are 1 ms E2E latency and 99.999% reliability. According to 3GPP R17, 5.5G URLLC reliability must reach 99.9999% though underlying technologies like blind retransmission, URLLC-eMBB coordinated complementary TDD frame structure, and cross-layer optimization.
Blind retransmission means retransmission is performed before feedback is received. This improves reliability and reduces latency at the cost of spectral efficiency. The URLLC service has a high priority and can preempt the resources of other services like eMBB services. However, the packet scheduling algorithm must be optimized to reduce the impact on eMBB service performance. Additionally, the configuration of an uplink and downlink complementary TDD frame structure on non-overlapping frequency sub-bands can enable simultaneous uplink transmission and downlink reception in any timeslot, thereby improving reliability and reducing latency.
Cross-layer optimization and multi-stream coordination are also needed for XR services, which involve multiple types of data streams, such as audio, video, control information, and data collection information. These data streams are layered so that they are not transmitted in the same QoS flow. In terms of priority, the base layer is higher priority than enhanced layers, and I-frames have a higher priority than B-frames and P-frames in the same layer. Different macroblocks in the same frame also have different priorities. The network senses services and identifies frame priorities and integrity so that it can then selectively discard less important packets when there is congestion, ensuring reliable, low-latency transmission of high-priority data blocks.
5.5G's high bandwidth and low latency enable rendering to be moved from devices to the edge cloud, smoothly supporting XR services through collaboration between cloud, networks, edge, and devices.
From mMTC to mMTC+
5G expands the IoT from narrowband IoT (NB-IoT) to mMTC, which supports millions of connections per square kilometer, and broadband IoT, which features a channel rate of 100 Mbit/s. 5.5G will also expand IoT technologies and applications to make them more lightweight and ubiquitous. Reduced capability (RedCap) devices, for example, support medium-speed low-latency IoT. RedCap devices can realize 50 Mbit/s uplink and 100 Mbit/s downlink rates and 5- to 10-ms latency with a 20-MHz bandwidth by reducing the modulation order and the number of antennas and MIMO flows, as well as simplifying duplex mode, protocols, processes, and functions. RedCap channel bandwidth is 10 times that of LTE Cat 1. Compared with LTE Cat 4, RedCap devices can deliver doubled rates and 20% lower energy consumption at the same price. Their precision positioning and low latency features, as well as their low cost, make them well-suited for enterprise applications like monitoring cameras and large numbers of sensors. With 5.5G, lighter and lower-cost IoT devices that run at 5 MHz bandwidth will also become more common.
Ubiquitousness relies on passive IoT, which integrates cellular network and passive tag technologies, so that devices can gain power from 5G base stations and modulate the amplitude or phase of backscatter signals by adjusting antenna impedance. This enables a data transmission distance of 200 meters, which is ten times that of RFID technology and does not require a reader like RFID. Connection density with passive IoT can be a staggering 10 million connections per square kilometer.
This technology can be applied at very low cost to intensive and massive-amount applications, like fast moving consumer goods, logistics packages, product packaging, warehouse inventory, and smart meters.
5.5G has also triggered research into the standardization of harmonized communication and sensing (HCS). 5.5G base stations will adopt integrated air interface and hardware design; share software and hardware resources such as waveforms, frequency bands, antennas, and systems; and intelligently collaborate with each other, allowing them to function like radars.
Sensing-assisted communication enables more efficient beam management and more accurate beam tracking, while communication-assisted sensing enables functions like enhanced positioning, high-resolution imaging, environment reconstruction, and posture recognition. Actual test data shows that 5.5G can achieve a sensing distance of over 800 meters and sub-meter-level sensing precision. It outperforms traditional radar by three to five times in terms of coverage area, range resolution, and angle accuracy. HCS shows huge potential in applications that require both communication and sensing, such as the Internet of Vehicles, airports, high-speed rail perimeter detection, and hazardous chemicals transportation monitoring. 5.5G also marks the beginning of research into non-terrestrial networks (NTNs). Ubiquitous application of IoT can also expand to areas beyond the reach of terrestrial mobile communication signals, helping us achieve satellite-ground convergence.
Multi-dimensional energy saving for eco-friendliness
Eco-friendliness is another prominent feature of 5.5G. According to GSMA, the energy cost of mobile networks accounts for about 23% of total operations costs for operators, making air-interface energy saving especially critical. For example, Huawei's MetaAAU uses new materials, ultra-large-scale antenna arrays, ultra-wideband RF front-end technology, and an innovative wide-angle array scanning algorithm to achieve the precise and wide-amplitude sweeping of narrow beams, fast adaptive beam optimization, and high-resolution beam-domain noise reduction. Signal direct injection feeding (SDIF) technology is used to optimize cabling inside an antenna, greatly reducing the number of feeders and cables. This improves amplitude and phase precision and greatly reduces impedance loss, improving antenna efficiency by 15%. This technology can reduce the transmit power of base stations, reduce energy use by 30%, and ensure high energy efficiency even when the load is light, all without effecting coverage.
5.5G will fully utilize AI to save energy in the time, frequency, space, and power domains. In the time domain, network traffic shows an obvious tidal effect. When network loads are light, 5.5G can intelligently put some cells and channels to a dormant mode. In the frequency domain, 5.5G can dynamically and adaptively shut down some carriers or adjust transmit and receive bandwidths based on service traffic. In the space domain, 5.5G base stations can adaptively adjust the number of activated spatial elements to save energy, including the transmit unit, antenna panel, and logical antenna port. In the power domain, 5.5G base stations can adaptively optimize the TX/RX algorithm and process dynamics to adjust the power or power spectral density (PSD) of TX downlink channels, while ensuring uncompromised coverage areas and key performance indicators (KPIs) or key quality indicators (KQIs).
Simultaneously developing alongside 5.5G are F5.5G (F5G Advanced) for optical fiber transmission and Net5.5G, which is based on IPv6 Enhanced. Based on F5G's enhanced fixed broadband, all-optical connectivity, and reliable transport capabilities, F5.5G will enable real-time elasticity, green intelligence, and sensing capabilities. For radio access networks, fiber fronthaul will have to be based on 5.5G to deliver 10 times higher bandwidth than 5G. For optical access networks, C-WAN architecture enables ubiquitous 10 Gbit/s capabilities. For optical transport networks, the single-wavelength coherent polarization division multiplexing of 400 GHz will expand from 80 wavelengths to 120 wavelengths in C-band as well as further expand to L-band. This is expected to increase per-fiber capacity to 100 Tbit/s, which is adequate to support connections at million-server data centers. Pooled WDM supports the extension of optical-layer grooming to metro aggregation and access layers to realize all-optical connectivity.
In October 2022, the Ultra-Broadband Forum (UBBF) specified for the first time that Net5.5G aims to meet the predicted requirements of network data services in 2030. It is estimated that, by 2030, global computing power will increase 100-fold and storage latency will decrease 100-fold. Net5.5G will enable end-to-end IPv6 Enhanced/SRv6 (segment routing) networking capabilities and embed various end-to-end intelligent network management services on IP private lines to enable integrated sensing and scheduling of computing and network resources. Breakthroughs are expected in six areas: Green Ultra-Broadband, IPv6 Enhanced, High Resilience & Low Latency, Ubiquitous Trusted Network, Multi-domain Network AI, and Heterogeneous Massive IoT.
3GPP has also specified that the 5.5G period of mobile communications began with the R18 standardization released in 2022, as it defined new goals and capabilities for 5G development beyond 2025. This will enable 5G to generate greater social and economic value through comprehensive evolution and enhancement. In February 2023, GSMA led industry partners in establishing a 5.5G community at MWC Barcelona 2023, further accelerating the move towards 5.5G. According to the The Mobile Economy 2023 report published by GSMA Intelligence, the mobile industry's contribution to global GDP will amount to over US$6 trillion in 2030, up from US$5.2 trillion in 2022, and 5G will account for more than 15% of the mobile economy. This means that 5G will benefit the global economy by more than US$950 billion by 2030, and 5.5G will play an important role in this.
