Fixed Mobile Convergence in F5G Era

Release Date:2021-07-26  Author:By Li Yufeng  Click:

Dual-Gigabit Network Drives Deep Integration of F5G and 5G
According to China’s Report on the Work of the Government 2021, China will step up the development of 5G and gigabit optical networks and extend their applications to more scenarios. The importance of gigabit optical networks has attracted unprecedented attention. A dual-gigabit network usually combines gigabit optical network and 5G network to provide users with the gigabit access capability of both the fixed and mobile networks. The dual-gigabit network features ultra high bandwidth, super low latency, and higher reliability, with the component networks complementing each other. Such a network is an important part of the new full-fiber infrastructure and serves as the base that carries services. To implement the service deployment requirements of the government work report, the Ministry of Industry and Information Technology (MIIT) of China released the Action Plan for Coordinated Development of Dual-Gigabit Networks (2021-2023) to make the fixed and mobile networks promote each other in construction and integrate each other in services.
The research of fixed-mobile convergence (FMC) based on fifth generation fixed networks (F5G) and 5G mainly focuses on two areas:
Integration of F5G and 5G networks: 5G macrocells or microcells are carried through the F5G infrastructure and undergo possible equipment integration. F5G continuously evolves to gain the capability to carry 5G base stations. China has basically achieved full fiber coverage. By the end of 2020, 880 million fiber-to-the-home/office (FTTH/O) ports had been deployed and 454 million optical access users had been signed up, accounting for 93.9% of China’s fixed broadband user base. Fibers and ducts are valuable fixed broadband (FBB) infrastructure resources that lay a foundation for the construction of integrated access areas. 5G microcells are the base station variant most likely to be used in fixed access deployments. The bulk of demand for 5G microcells, including the indoor distribution and home installation flavors, is expected to still come from operators. FMC provides a solution for operators to substantially reduce their total cost of ownership (TCO).
Management of fixed and mobile terminals, and integration of service process and 5G core (5GC): As dual-gigabit implementation advances, the public and campus networks both evolve towards a dual-gigabit architecture. While innovative services require significant changes in and are difficult to deploy on the public network, they are easier to trial and implement on the campus network where they can run on F5G and 5G. When used in the campus network, 5G has a number of advantages over Wi-Fi, including independent frequency bands, no interference, and low latency. Users demand the same superior experience whether they access the network via 5G or F5G. Therefore, a major area of FMC research is on access-independent technology. Before dual-gigabit technology emerged, the Wi-Fi/wireline terminals and 5G terminals in a campus used to be authenticated by two separate systems. With dual-gigabit integration, all the terminals can be controlled and authenticated in a unified fashion to simplify management.

Integration of F5G and 5G Networks 
Some operators that operate both fixed and mobile networks want to use the abundant fiber resources on their fiber-to-the-anything (FTTx) infrastructure to fronthaul or backhaul 5G macrocells. In some Chinese provinces or cities, radio access networks (RANs) have not been introduced but passive optical networks (PONs) have already been deployed. These markets present an opportunity for vendors to make breakthroughs and gain entry. In some European and American countries where installing new fibers is difficult, operators can use their existing FTTH resources to develop wireless services. They can utilize their market and technology advantages in both PON and RAN to raise the market access threshold and enhance customer stickiness.

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To address the needs of the backhaul and fronthaul markets, ZTE has launched the Combo PON Plus solution (Fig. 1) that overlays point-to-point wavelength division multiplexing (P2P WDM) wavelengths on the feeder fiber of the optical distribution network (ODN) and uses them to carry 5G backhaul or fronthaul services. Thanks to the characteristics of WDM transmission, the solution has the following advantages:
High reliability: Transmission goes through dedicated wavelengths and is not affected by what type of PON terminal is involved.
Low latency: Transmissions are conducted in P2P mode.
High bandwidth: Backhaul and fronthaul bandwidth is independent of PON bandwidth, leading to maximum single-wavelength rates of 10 Gbps currently and 25 Gbps in the future.
After rounds of discussion and revision conducted at end-2020 and in 2021, it was finally decided that Option 6 split microcells would target such scenarios as homes, small enterprises, and industrial parks. The microcells have strict latency requirements, so they must be carried using low-latency technology. Research shows that in the 4G era, around 4% of homes received poor wireless coverage because of weak signals. The problem is likely to get worse in the 5G age. In view of this, ZTE has collaborated with the Suzhou subsidiary of China Mobile to explore using the existing FTTx network to carry the services of 4G/5G home microcells. The result of the live validation indicates that low-latency PON technology can reduce the upstream delay from millisecond to nanosecond levels.
ZTE has also carried out research on improving the current PON standards. For example, ZTE's low-latency PON technology is based on the TDM-PON standard but upgrades its dynamic bandwidth allocation (DBA) mechanism. The main implementation principle of the technology is that a third dedicated wavelength channel is used for 10G PON registration and ranging. On the forwarding plane with upstream DBA, the 10G PON channel increases the burst density of ONU scheduling per superframe, thus cutting the waiting time for data. In January 2020, ZTE and China Mobile Suzhou validated the low-latency PON technology and achieved the expected results.

Management of Fixed and Mobile Terminals, and Integration of Service Process and 5GC
5G wireless wireline convergence (5WWC) is based on the public network and has existed as a study item of the 3rd Generation Partnership Project (3GPP) for many years. Implementing 5WWC would require major network upgrades and incur other costs, so its advancement has been slow and operators have not yet presented any demand for its implementation. By contrast, in a campus network, such as one built for an industrial park, a school, or a government compound, the 5GC is deployed to the campus. This makes the campus network cheaper to deploy and more likely to get implemented compared with the public network.
The FMC requirements of a campus network include high broadband, mobile office, secure and reliable industrial control, and flexible industrial protocol adaptation. Terminals connected to the campus network may or may not be 5G capable. 5G terminals include automated guided vehicles (AGVs) and mobile production devices, while non-5G terminals include Wi-Fi-enabled PCs, Wi-Fi terminals, and wired desktop PCs. These campus terminals need to be managed, controlled, and authenticated in a unified fashion. 
5G FMC offers a way to fulfil production and life needs in the campus. For example, unmanned goods transportation within a port, warehouse, or campus requires autonomous driving, which in turn calls for a high-bandwidth, high-reliability, and low-latency network to ensure that AGVs are automatically dispatched and controlled. The user plane function (UPF) is pushed closer to users, with the data plane terminated in the campus for classified processing or further AI analysis. The optical line terminal (OLT) contains multi-service edge computing (MEC)-capable blade servers, supports platform as a service (PaaS), and provides UPF services, thereby integrating the services and resources of fixed and mobile networks.

Outlook for FMC in F5G Era 
A converged infrastructure that allows 5G microcells to be carried over an FTTx network is still under research and will be the main application of the convergence of physical fixed and mobile networks. Low-latency PON and P2P wavelength overlaying technologies can fully reuse the FTTx and PON network infrastructure, making it possible to deploy 5G microcells rapidly and at low cost. The 3GPP working group responsible for 5WWC standardization is still studying how to perform unified management and authentication in a public network with fixed-mobile convergence. Because its implementation requires coordination among operators, 5WWC is not expected to see fast progress on standardization and rollout. A campus network is basically a private network, and its construction involves minor changes to the existing network. As the rollout of 5G networks and passive optical local area networks (POLs) progresses, implementing integrated management and authentication on the basis of FMC may be the direction of research and implementation in the future.

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