What Download Speed Do I Need for Good Smartphone User Experience?

Smartphone user experience is all about time-to-content

Time-to-content is what matters for smartphone users: after I click, how much longer do I have to wait before my video starts playing, or I can start scrolling on my news page? Like dropped voice calls I really don’t like that spinning wheel …

Figure 1: The damn spinning wheel

Time-to-content is the key metric that the content provider industry has been using for decades to assess user experience. Entire industry branches, such as content distribution networks, have emerged to minimize time-to-content, and thereby maximize user experience. A consistently low time-to-content is crucial for any online business since it can impact conversion rates, i.e., the probability that a customer stays on the online site and eventually clicks “Buy”.

How come the mobile industry has not adopted time-to-content as a way to measure user experience?

20Mbps at every click is what I need to have a great 5G user experience

At Ericsson we have conducted an in-depth study of smartphones requesting popular content (YouTube, Instagram, Amazon, ebay, Uber, IKEA, and many more) to derive the relationship between time-to-content and what we refer to as throughput “at click”. The throughput “at click” is the throughput that is available to the device during the time-to-content phase. The study was based on tools and guidelines provided by Google on web.dev. The relationship we derived is shown in Figure 2. The graph incorporates projections for the coming 5 years about the growth of the size of popular content, and improvements in device processing power.

Figure 2: Time-to-content depends largely on downlink throughput “at click”²

We have made a number of key findings:

1. A downlink throughput “at click” of 20Mbps and an uplink throughput “at click” of 1Mbps provides great smartphone user experience for the vast majority of popular content. Beyond these speeds, user experience improves only marginally.

1. User experience degrades sharply as the downlink throughput “at click” drops below 5Mbps or the uplink throughput “at click” drops below 300 kilobits per second (kbps).

1. Streaming video is less demanding. Even at High-Definition (1080p) YouTube videos start playing in less than 2 seconds given a downlink throughput “at click” of 10Mbps. Once the video has started playing, the downlink throughput may even drop to 5Mbps without impacting the video playout quality.

1. No matter how high the throughput “at click”, there is always the device processing delay that limits time-to-content. We project that in 2025 the device processing delay will be slightly less than 1 second for high-end smartphones.

Users expect a great experience everywhere and every time

Users not only expect great experience, but they also expect it everywhere and every time. Hence, 20Mbps in downlink and 1Mbps in uplink needs to be available to a user’s smartphone at every click, even in busy areas and during busy times when the network may be highly loaded. This is not always the case as shown in the chart below. It shows measurements of time-to-content collected from a smartphone in a live 4G network.

Figure 3: Congestion leads to poor user experience

The smartphone was stationary, in the business district of a major US city, measuring time-to-content for apple.com once per minute. As can be seen from the chart, time-to-content is consistently low in the middle of the night when the network load is low. But as the load increases during the day also the time-to-content increases. User experience also becomes increasingly inconsistent as the range between best- and worst-case time-to-content grows. In the middle of the day this 4G coverage area is completely congested.

Obviously, frequent samples over time are required to get the full picture of the situation.

High network load moves with the mass of people throughout the day. A typical scenario is that how high load first occurs in the morning at the central commuter station. Then high load moves to the business area, then to an event arena, and later in the evening to a residential area.

This article is an excerpt of Who cares about peak download speeds in 5G? from Ericsson.