At Mobile World Congress Americas earlier this month vendors and operators pronounced that 5G is here and that has revitalized the mobile community and launched a new wave of optimism and enthusiasm. It is a given that there has been significant progress in the journey to 5G; however, in looking at the end-to-end mobile transport network, it appears there are a few technical and operational issues still open for consideration.

The most common technology choices for backhaul have been fiber and microwave, both of which are widely deployed in today’s LTE networks. However, given the ambitious expectations from 5G, which include a 20x increase in peak data rates and a 10x reduction in latency according to the latest GSMA 5G report, many operators are taking a closer look at alternative connectivity solutions such as WiFi and next-generation satellites to satisfy service expectations.

First the requirements: There is consensus that 5G will require increased capacity, near ubiquitous connectivity, and deliver flawless quality of service regardless of the stress placed on the network. In the 3G and LTE eras, backhaul was also critical, but solutions were focused primarily on providing connectivity between the macro base stations and the access/aggregation network. LTE has certainly increased capacity and availability in order to meet the demands of quality data services thus far. However, 5G is different thanks to the broad use case classifications — each with its own unique demands of the network.

[caption id="attachment_71974" align="aligncenter" width="365"] Source: Small Cell Forum.[/caption]

Clearly 5G must address a multitude of new requirements:

• Delivering 1 Gb/s or more mobile broadband services;
• Supporting new service types that require lower latency and ultra reliability;
• Supporting IoT and industrial applications with significantly varying connectivity and performance characteristics.

The net result: the issue is no longer just speeds and feeds, but is how to enable far greater manageability and flexibility.

Vendors — including Ciena, Ericsson, and Nokia — have launched end-to-end mobile transport solutions designed to apply network and application intelligence to efficiently handle the expected new mix of traffic types. SDN and network slicing technologies can be leveraged to deliver 5G and IoT services efficiently by creating virtual networks that are configured to meet application specific needs. While most mobile transport architectures are designed to accommodate multiple access technologies, so far most have focused on fiber and licensed wireless (microwave and millimeter wave) solutions.

To date, vendors have increased the capacity of their microwave solutions, and are now providing up to 10G per connection and have added SDN management with stringent quality-of-service. This, along with fiber, has enabled LTE networks to continue to grow and meet end-user expectations. These enhancements have so far forestalled the need to enlist other technologies. However, this could all change as 5G and IoT move into the mainstream.

The obvious question is whether traditional technologies will be enough to meet 5G demands. If not, then the natural follow-up question is whether unlicensed technologies like WiFi, shared access technologies such as fixed access, or the latest satellite innovations can be leveraged as a source of incremental bandwidth and connectivity. It is too early in the 5G deployment lifecycle to accurately determine the level of uptake, but there are moves by vendors to prepare solutions based on these solutions. In certain situations, their use may be the only alternative available to meet coverage or capacity shortfalls.

Next-Gen Fixed Access: SDN and NFV have evolved in fixed access networks, and we are beginning to see fixed access solutions that promise similar manageability, increased capacity, and traffic management characteristics as traditional Ethernet-based backhaul solutions. Prior fixed access solutions had two fundamental shortfalls when considered for backhaul: One, the media is shared by multiple users; and two, traffic management was weak, making them unacceptable for mobile backhaul. Although supported by mobile transport architectures, the use of fixed access may not materialize in the near term.

Next-Gen WiFi: WiFi has also evolved from its best-effort form and is well acquainted with the issues associated with providing high performance and broad connectivity. With the evolution to multi-access edge computing (MEC), it seems probable that WiFi, in its latest version (IEEE 802.11ax), could be used for connectivity between devices and the network edge — or most likely between a MEC location and the internet to support less latency sensitive applications. As with fixed access, the use of WiFi between the base station and the network will be limited, but supported conceptually in vendors’ mobile transport architectures.

High Performance Satellite: For remote or rural use cases, satellite technologies can be leveraged to provide connectivity from an underserved remote aggregation site to the network edge. As noted at the recent IEEE 5G World Forum conference (July 2018), satellite communications can play a significant role as a complementary solution to terrestrial networks due to its characteristics including coverage, broadcast, multicast, and emergency/disaster recovery.

Initiatives such as SaT5G will bring satcom into 5G by defining satellite-based backhaul and traffic offloading solutions. SaT5G’s standardization efforts, initiated in 3GPP and ETSI, will promote effective integration in to the 5G network.

However, SDN and NFV adoption is a necessary step in the evolution of satellite ground segment systems (e.g. satellite gateways and terminals). This market segment follows fixed access in adopting virtualizing the control structures. Adoption will most likely appear to provide connectivity to remote areas not well suited for fiber due to subscriber density, or microwave due to mountainous terrain.

In summary, operators appear to be somewhat reluctant to build a mobile transport network that relies on alternative solutions such as WiFi, fixed access, and next-gen satellite technologies; instead they keep to the tried and true fiber and microwave solutions commonly deployed in LTE networks, at least for the short term. Advances in microwave spectral efficiency and millimeter wave solutions have fulfilled the wireless backhaul needs, achieving speeds of over 10G.

However, as 5G and IoT emerge, and outdoor small cell deployments accelerate as expected, after their long hiatus, the situation could change. Small cell deployments may also leverage 5G self-backhaul (5G-SBH), further delaying the need to adopt alternative backhaul solutions. Fiber is likely to remain the first choice for connectivity, but there will a considerable level of deployment concerns as connectivity demands increase. Licensed microwave and millimeter wave will be the second choice, with high capacity point-to-point solutions being the obvious choice. Wi-Fi, fixed access, and satellite backhaul could be leveraged quite successfully to provide connectivity where fiber and microwave fall short.

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