Why 5G-Advanced Is the Unseen Backbone of AI Economy

Although mobile network download performance is now usually good enough on a 5G network, upload continues to be a problem for many activities. For upload, the challenge is that it is the user’s device that must transmit data, not the mobile base station. But mobile devices are much more restricted in their power output than base stations because they have small amounts of battery power available and there are tight limits on emissions for user safety, for example the allowed special absorption rate (SAR).

The new spectrum bands that have enabled the extremely fast 5G download speeds — typically around 3.5 GHz — are relatively high frequency and so are more difficult for constrained devices to transmit data across than the lower frequency bands that were used for 4G. Fortunately, the latest 5G standards include features to improve uplink performance and tackle this problem.

Why Upload Matters More Now for Consumers

There are many current users and devices that rely on upload, such as live-streamers, connected security cameras, remote virtual private network access for business, or simply sharing attachments on messaging or email. But these proven upload uses are increasingly being joined by new AI-powered consumer devices and business opportunities enabled by network slicing. As a result, operators that wish to differentiate on network quality in the years ahead must now focus on their network’s uplink performance.

The Ray-Ban Meta smart glasses illustrate the need for improved uplink performance. They already feature visual AI, in which a user can ask what they’re looking at, and the device takes a photo for upload to the cloud for analysis. That photo is typically 5 MB to 10 MB in size, so a fast connection is essential to minimize delay in the response. But more significantly, Meta also offers integration with the smartphone-powered service Be My Eyes, which connects users with limited eyesight in real time with human volunteers to help them understand and navigate the environment. Globally, Be My Eyes has about 800,000 users with low vision or who are blind and more than 8.5 million volunteers in over 150 countries.

Meta is also testing a feature called Live AI, which is designed to improve users’ experience of such visual AI. Once a user starts a Live AI session, the glasses continuously upload images to the cloud, so when the user asks a question about the world around them the response is swift, because the relevant images have already been uploaded. This generates much more upload data traffic than sending the occasional image on demand. Other smart glasses companies are likely to copy this approach.

The Role of Uplink in Marketing a New Football League

Some of the biggest 5G-Advanced networks globally are in China. Although professional football has had a few rocky years in the country, a new amateur super league has taken off in Jiangsu province. Tens of thousands of fans attend each match in the Jiangsu Football City League, which is dubbed the Suchao, and many more follow games remotely. One match had over 800,000 people tracking the sale of tickets. Suchao videos have racked up more than 820 million views on Douyin, China’s version of TikTok.

This means that attendees in the stadiums expect strong mobile network performance, especially for upload. 5G-Advanced supports a greater density of user devices than older cellular standards, as well as improved uplink performance. During league matches, uplink traffic accounted for more than 40% of total mobile network traffic. Of this, 80% were real-time interactions such as live match commentary, WeChat short videos or photos. The strong mobile network performance has boosted interest in the nascent league far beyond the stadiums.

China’s mobile operators have deployed multiple bands — the three-carrier approach — alongside supplemental uplink and the scheduling capabilities of 5G-Advanced to boost the network experience. This led to peak uplink speeds in excess of 240 Mbps during matches, which helped fans to share content easily.

Non-Consumer Applications Need Strong Uplink Performance

Network slicing also increases the importance of uplink performance, because many slices will have network quality guarantees for uploads, as well as latency and download performance. For example, first responders often share video footage of incidents to help control centres and other emergency teams to assess the situation and decide how to act.

Another example is where 5G is used as backhaul in public locations. Given this is a shared usage, for each end user to enjoy for example 10 Mbps or 20 Mbps upload performance, the overall backhaul link must support a multiple of that speed, because it will be shared by all devices simultaneously. This could be to connect a bus or a train, for which the combined uplink would need to be hundreds of megabits, perhaps even as high as 500 Mbps for an entire set of railway carriages, even if in some cases the devices may be connecting to Wi-Fi rather than directly to 5G.

Internet of things opportunities often have more-symmetric performance needs than other network applications. For example, to share sensor data, to control machinery remotely or for security applications. To manage drones, 25 Mbps is a typical target for uplink performance. Autonomous vehicles also have a high uplink requirement so that a remote human safety driver can quickly and reliably step in to take control if the local autonomous driving system has a problem, or in the event of severe weather during which the autonomous system is not rated to operate.

Newer 5G Standards Dramatically Improve Uplink Performance

One typical way to improve speeds with recent network generations has been to combine carriers, or spectrum bands, to boost throughput. For download, devices often support six or more carriers in aggregation. However, for upload, end-user devices typically have component constraints that limit uplink carrier aggregation to one or two carriers.

Another way to bolster speeds is to use multiple input multiple output (MIMO) for spatial multiplexing that adds additional data streams onto a single carrier, so boosting the effective capacity and speeds. This is typically used on time-division duplex (TDD) bands, which is the typical duplex mode used for higher frequencies such as the bands used to add large amounts of 5G capacity and enable very fast download speeds.

For TDD bands, operators can also increase the amount of time given to uplink, so boosting uplink capacity and upload speeds. This is a long-standing approach that also works with 4G networks on TDD bands. However, by increasing uplink capacity in this way, operators reduce downlink capacity, and so it’s not an ideal solution in many cases.

Another approach is to use a second carrier band in uplink carrier aggregation. However, although 5G uplink carrier aggregation has been supported since 2018’s 3GPP Release 15 standard, it’s been quite limited for 5G because of the ongoing usage of 4G bands for 5G non-standalone and because of technical problems combining TDD and frequency-division duplex (FDD) bands in uplink carrier aggregation. Typically, in 5G non-standalone, operators could use existing 4G bands alongside 5G. But with the increasing deployment of 5G standalone, operators need to combine two or more 5G bands for uplink.

One successful approach is to use a dedicated supplemental uplink (SUL) band alongside an existing band capable of both upload and download. Unlike altering the time allocation, using an additional uplink-only band adds capacity and improves upload speed without damaging the download experience. Although SUL is commonly used in China, the availability of this type of spectrum band is more limited globally.

To address the challenges with 5G uplink carrier aggregation, 3GPP Release 16 includes improvements. For example, uplink transmit switching combines both uplink carrier aggregation and additional spatial layers on a single band to further enhance uplink performance. In essence, the idea is to use a device’s uplink antenna in an FDD band during the time slots when the TDD band is using its capacity for downlink. Then, when the TDD schedule alters to enable upload, both antennas switch to the TDD band in MIMO mode to maximize upload performance.

Release 17 and Release 18 further enhance the support for uplink transmit switching. Release 17 adds the option of using the FDD band to transmit on both antennas. So, rather than having one band using just one antenna, both bands can use both antennas opportunistically to further improve performance. Release 18 adds the ability to enable switching across up to four frequency bands. If an operator has two contiguous carriers in the TDD band, the standard allows for switching between two uplink layers in FDD plus four layers by including uplink contiguous carrier aggregation with 2×2 MIMO in TDD.

The other key advantage in using an FDD band alongside the TDD band is to benefit from the improved coverage and signal reach of lower-frequency FDD bands. This helps mitigate the battery and power constraints that mobile devices have when transmitting on the higher-frequency TDD bands. FDD is used on coverage bands below 1 GHz and on most bands between 1 GHz and 2.2 GHz; TDD is used on most bands over those frequencies.

An alternative approach to uplink transmit switching in Release 18 is uplink transmission using three antennas (3Tx). This enables simultaneous transfers on both carriers. However, it is a more limited approach because it requires hardware modifications in devices and is typically only supported in fixed wireless access devices, which have three suitable antennas.

Newer 3GPP releases also add the capability for inter-band carrier aggregation. This is important for operators with large bandwidth allocations within a given spectrum band but where their spectrum allocation is not in one contiguous block.

Fast Latencies Even During Heavy Data Traffic with L4S

Another key feature of 5G-Advanced that helps with upload performance is Low Latency, Low Loss and Scalable Throughput (L4S). This technology has been deployed in fixed networks for some years, but is now coming to mobile as a part of 3GPP Release 18. It’s designed to deliver a responsive network experience all of the time, even when routers are busy.

Typically, network latency worsens dramatically if a network is under load. L4S is designed to improve responsiveness when routers become loaded and buffers fill. It’ll also improve downlink performance. There are already early deployments of L4S, for example by T-Mobile US. Like the other technologies listed here, L4S supports uplink performance but is also particularly important for real-time communication, gaming and extended reality applications.

5G Standalone Is the Foundation for Improving 5G Uplink Performance

Operators that have moved on from 5G non-standalone to a 5G network core are able to deploy these new 3GPP features to improve uplink performance. 5G-Advanced requires a network to be operating in standalone mode. Plus, with the shift to standalone, the lower-frequency FDD bands become usable for transmit switching to boost uplink speeds. Operators that are just starting on the standalone journey should plan their road map to support these new features and differentiate their network quality from that of rivals.