One of the ‘generational’ shifts associated with 5G is the promise of near-zero latency. Now for most engineers, the reduction of latency is generally seen as a necessary good, which is why putting it at the heart of the 5G value proposition is so rarely questioned. But when it comes to making the business case for 5G, it’s important to start making judgements about how much value can be attributed to ultra-low latency and the use cases in which it is mission critical.
It also means making a call about when such applications are likely to achieve the critical mass necessary to deliver significant and sustainable returns that justify investment.
Latency has fallen across the cellular generations. It was around 500ms with 2G, perhaps 100ms with 3G and around 30-50ms with 4G. As surveys have noted, falling from 100ms in 3G to 50ms in 4G has improved user satisfaction. Further improvements may be both harder to deliver and have less impact and ROI associated with them.
Current LTE networks deliver a theoretical latency across the radio interface of 10ms, which translates in practice to around 40ms once delays in the core and external networks are taken into account. Improving this latency would not materially change the experience for most use cases.
For example, video streaming can accommodate very high latency using buffering. Web browsing does not improve materially with latencies below about 50ms. For any application with video it is worth remembering that the frame refresh rate on most devices is effectively 25Hz – which means a video frame is replaced by another every 40ms, generating the perception of a moving picture. Having a latency below 40ms does not help for such applications since the video will not refresh faster – and even if it did it would not be perceptible.
So where might significantly lower latency help? Possibly with ‘tactile’ communications, where a user is remotely controlling a robot using, for example, a special glove, which provides feedback on the touch sensation although there is some debate over whether latencies lower than 20-40ms are needed for this. But this is likely to be an indoor application where a wired or short-range wireless solution is more likely to be used.
Some claim low latency is needed for control of autonomous vehicles. However, it is likely there will be reluctance to depend upon low latency network connectivity for emergency situations such as harsh braking from a nearby car; direct car-to-car communications and advanced sensors are better suited to this situation.
Of course, the lower the latency the better, but it is hard to see any economically compelling cellular applications where reducing latency below that of LTE, the latency performance of which is still being improved by the standards, would make a material difference to the user experience.
At Real Wireless, whilst we are fully behind research towards future low latency communications technologies, we believe that there are still significant gains to be had from leveraging the full value of LTE investments and that delivering such capabilities to the sectors and communities that can most benefit from them must remain an urgent priority.