5. Power requirement
All this increase in processing on the device side goes hand in hand with the increase of power demand, yet such increase, as pointed out in previous posts, is not manageable because increased power means:
- increased dissipation in form of heat (second law of thermodynamics);
- increased drain on the battery
The answer to that goes through the creation of more efficient chips, decreasing the size of transistors (and thus the possibility of using lower voltage) is a way to approach it, the activation of those parts of a chip that are needed only when they are needed is another approach. Keeping the performance of silicon at a lower level (not increasing the clock rate) and using more silicon (multi core) is a further way that has made possible to balance increased performances with lower (stable) power consumption.
Clearly these are not specific issues for mobile devices, they apply to all chips. The problem, however, is more significant in mobile device since they have to rely on battery, ensure at least 18 hours between recharges, keep size and weight within reasonable limits (actually this is both an ergonomic and a marketing requirements since bulky and heavy phones would be difficult to sell) and cannot use active dissipation systems (like a fan).
A lot of research has gone into designing more efficient chips for smartphones and today a Snapdragon chip, or the Apple A14 Bionic (used in smartphones and tablets) delivers the same processing capacity with half power consumption of an equivalent chip used in a laptop, although at a higher cost). The signal processing part of these chips have adopted very sophisticated architectures and power saving tricks that have somehow balanced the increasing demand of the advanced signal processing required by new wireless systems (MIMO, multi frequency bands).
6G will require further sophistication in processing, something that today’s technology is not able to support (at price and performance point needed in the consumer market). Interestingly, the new chips are now embedding specific AI circuitry to support native AI processing. This will be crucial to support semantic based communications at the core of 6G. Also, the shift from silicon to graphene, or other single atom layer materials like molybdenum disulfide, would also help support the increased capacity requirements.
A last note on the device-side power consumption is how the power is needed and used by a device like a smartphone. Made 100 the power requirement to download data (figures refer to HSDPA, high speed 3G):
- 85 is the amount needed for WiFi data transmission
- 50 for managing SMS
- 48 for making a voice call
- 32 for playing an MP3 file (music)
- 18 to illuminate the smart phone screen
So, in absolute terms, data communications is by far the most power expensive activity on a smartphone. However, in terms total power consumption the situation changes significantly because data transmission is just a tiny fraction of the use of a smartphone: most of the time is spent on running apps, and some apps, like video games, are very power intensive.
In a 6G scenario we can expect that in relative terms the data transmission part will remain the most expensive one, however we will have to separate the very low range data communications (using the THz band) with the one using the GHz. This latter will compare with the power requirements of today’s 5G although the signal processing involving multi frequency bands will be more power hungry than today. The former will be using much less power in terms of transmission, because of the ultra small cells, but a bit more for signal processing (overall THz transmission will be cheaper in terms of power used than today’s 5G).
However, as it is now true for 4G and even more so with 5G, the variety of services supported will include a few that will require quite a bit of in-device processing and that will be increase the use of power. I will address this in a later post when discussing 6G services.