Per a Global market Insight report, market size for 5G fixed wireless access (FWA) is set to be valued at more than $25 billion in 2022-2023 and is poised to depict a 30% CAGR through 2023-2032, on account of the growing demand for high-speed broadband in rural and suburban areas. A traditional FWA is a tall, fixed infrastructure of radio access network to provide wireless connectivity. At the same time, the growing adoption of CBRS-based spectrum sharing in GAA technology for 5G FWA is already offering growth opportunities for the market as depicted by recent report from NTIA.
GAA is the spectrum that will further grow in demand in both 5G and 6G. But there is a significant challenge with GAA that needs to be addressed. Without efficient spectrum sharing technique and improved uplink (UL) coverage in CBRS, the market for FWA may shrink. Main reason is that no service provider wants flexible bandwidth in n*10 MHz format because this impacts their SLA and guaranteed service commitment. Poor UL cost too dense network deployment which is very costly for new service providers.
Spectrum sharing is a technique where GAA licenses are shared among all CBRS GAA and PAL transmitters in a given cluster by keeping low interference and noise level. It also includes that co-existence mechanism of 5G-A/6G cells to continue radiating while Federal Incumbent user are also in operations. As of today, in LTE-CBRS, it is SAS server, which turn the cells off once ESC (federal radar sensors) detects the incumbent.
Other smart techniques what we have today are Licensed Shared Access (LSA), which uses a regulatory framework to share spectrum with incumbent users & Dynamic Spectrum Access (DSA), which enables to sense and adapt to the spectrum environment. But all above listed mechanism are very time consuming. 3GPP Release 19 version has proposed a new spectrum sharing with 5G-A/6G study item (3GPP TR 22.837 V19.0.0 (2023-06) – Feasibility Study on Integrated Sensing and Communication (Fs_Sensing) can enable variations of spectrum must vary in real time.
The prosed mechanism in 3GPP Release 19 relies on advanced capability of 5G-A/6G RAN. The challenges for 6G in spectrum sharing are:
- Predictability of available resources in CBRS-GAA at any instant of time,
- Interference detection and intelligent mitigation features
- Overall management of spectrum with same technology (3GPP-3GPP) and different technology (3GPP- non-3GPP).
A proposed RAN will be enabled with new continuously sensing signaling, a new UE capability to report 5G-A/6G RAN with the 3GPP sensing data, positioning information and UE ID for its surrounding environment. The proposed new RAN shall be able to sense a CBRS-GAA transmission from incumbent by obtaining 3GPP sensing data without active involvement of SAS/ESC/Incumbent radar. The 5G-A/6G RAN system shall be able to process the 3GPP sensing data in real time to produce the sensing results from a 5G sensing processing entity (through newly developed applications).
Based on operator’s policy and subject to regulatory requirements, the RAN system shall be able to adjust the cells parameters, and frequency allocations to avoid the conflict with incumbent users or PAL users. The new proposal also allows the 5G system to provide a mechanism for network operator to configure and adjust sensing operation (e.g. authorization, sensing area, sensing operation period and sensing operation time window etc.). ORAN RIC also has a new use case of Spectrum handling” through Reinforcement Learning (RL) algorithms for efficient spectrum allocation in real-time based on instant network conditions.
Efficient spectrum sharing also requires fast interference management and interference handling techniques. LTE-CBRS today has combined DU (distribution unit) & CU (centralized unit) and this makes fast interference coordination very tough among inter-cells. But a split design in 5G and shared DU with ORAN architecture makes most effective interference management for both intra-cell and inter-cell coordination. Advanced interference management algorithms with AI/ML technologies are designed in identifying interference patterns and dynamically optimizing spectrum resources in real-time among cells, different users or even incumbent like radars.
An ORAN disaggregated architecture is best suited for application of the spectrum sharing and interference management and handling because of greater flexibility in Software features tuning and openness for 3rd party applications through nRT-RIC/NRT-RIC (near real-time RAN Intelligent controller/Non-Realtime RAN intelligent controller).
Other issue is poor uplink coverage with CBRS spectrum. A report from Charter communications on CBRS FWA design (NCTA technical paper-2019) for coverage and capacity field study indicates the poor UL in outdoor with outdoor CPE. The report covers all possible field scenario and it was found that cell footprint with 12 Feet CPE with 4×4 MIMO is close to 2.6 mile. In this study, adjacent RF interference is not accounted for.
Despite the growth in both fixed and mobile broadband, there is a large under-served household market. This market can, to a very large extent, be served cost-efficiently with FWA. There are several methods for UL coverage enhancements like in IMT-2020, a concept of low-mobility- large-cell (LMLC) was introduced for rural coverage. This new configuration focuses on low- mobility users (a mix of the pedestrian with speeds less than 3 kmph and vehicles at 30 kmph) and an inter-site distance of 6 km which is valid until 21 kms.
3GPP release-15 based 5G has “Supplemental Uplink “based functionality for enhanced uplink when UE detects low uplink SINR then it can switch to co-located 2nd frequency band. Supplemental uplink extends NR-CBRS coverage by about 4-7 dB for semi-static power-sharing as claimed in some literature. In Release 17, 3GPP has added techniques to extend uplink coverage for the physical uplink shared channel (PUSCH) and physical uplink control channel (PUCCH).
In Release 18, 3GPP plans to enhance the coverage of physical random-access channel (PRACH) by enabling multiple transmissions for when UE is switched on. There is planned study techniques to increase UE power efficiency in the scenario of coverage-enhancing waveform and Quadrature Phase Shift Keying modulation. 5G-A/6G will optimize the uplink data rate within the given link budget by dynamically changing the uplink waveform. The new RAN will prioritize coverage-enhancing waveforms dynamically when the UE is close to the cell center or cell edge or indoor. FWA along with indoor/outdoor CPEs are planned for UL-MIMO enhancements like support for 8X8 MIMO (high receive/transmit diversity and high DL/UL data streams both), which can significantly improve the CBRS-GAA coverage for indoor as well at cell edge.
Conclusion
5G-A/6G network architecture will further evolve toward a cloud-native network design. R15 based split of RAN and Core could be replaced by a more scalable, self-intelligent and flexible architecture considering for coherent decision with joint design and protocols for further diverse services in 6G. CBRS-GAA 80 MHz most likely be the most valuable mid-band because of most tested and deployed 5G frequency (NAR/EU/Japan region) and its popularity is due to its common availability. FCC plans to further expand this for another 100 MHz extension.
Editor’s note: This article was submitted by Ayan Sharma, a senior at Plano West Senior High School that has recently developed an interest in telecommunication concepts, research developments, and future advancements.
