The Heat Death of 5G

Spend any time in wireless, or Technology in general, and the subject of 5G is almost certain to come up. We have written about it here (and here). The world is full of talk about fast 5G networks and all the incredible new things that 5G will unleash. A whole new Internet, they say.

Here at D2D, we like to think of ourselves as practical, nuts-and-bolts-and-antenna people. So for us, a lot of this 5G discussion strikes us a bit breathless. Yes, 5G is coming and data rates will improve, but we, the mobile industry, still have a lot of work to do. We could regale you with litanies of woe about roaming and hand-offs, or belabor the small cell backhaul density logjam. But perhaps the best example of roadblocks to 5G is much easier to grasp – Heat.

5G phones get hot. Really hot. Probably not hot enough to ignite your battery (probably), but enough to generate a definite burning sensation in your pants pockets. At Mobile World Congress in February, we spoke with an engineer from Sony who was demo’ing a phone (behind glass) that was clocking 1 Gbps speeds. Wow, fast. We asked the engineer why it was not going faster and he said “It overheats.” A good solid answer, from a nuts-and-bolts-and-antenna person. We will wager any amount that at next year’s show, no one on the floor will be as open about this problem.

The big improvement in data rates for 5G will only come with mmWave radios. This is a whole new spectrum band that allows for really high data rates (again, let’s set aside the whole densification issue for now). The trouble is that mmWave radios generate a lot of heat. To greatly oversimplify, mmWave frequencies are pretty close to microwave frequencies, as in the thing we use to reheat our lunches.

From some of our very recent industry conversations we know that the handset industry is using a tried-and-tested method for dealing with this problem – ignoring it and hoping it goes away. The whole issue strikes us as one of those issues where middle management really does not want to raise the subject with senior management who have wrapped themselves so tightly around the 5G flagpole. “Uh boss, your pants are literally on fire.”

There are other factors at play as well. We will spare you our Deep State conspiracy theories on this (Buy us a beer in Barcelona…), but there is a pretty clear disconnect in the supply chain on this topic right now.

Of course there are some solutions, but none of them are complete and they all have serious drawbacks. It turns out that the way we cool electronics has not advanced in 40 years. There are really two methods used currently to cool Things down- Fans and Dissipation.

Fans are what you think they are. Anyone who has ever opened up their desktop PC or overclocked their laptop knows what these look like. But fans have two problems: they are big and they have moving parts. Both of those require design decisions that go counter to every mobile design trend in the past 15 years.

Dissipation is just the idea of moving the heat around to hasten air cooling. In a PC, this is typified by those funny looking prong-things that sit on top of CPUs. Those things are too tall to fit inside a 10mm thick phone. So for mobiles, OEMs are looking at using ‘straws’, or copper pipes that span the length of the phone. These take up a lot of space and inserting a large conductive element (copper!) inside a phone wreaks havoc on mobile radios, (i.e. hurting data rates).

Before we can revel in the Fullness That Is 5G, the industry needs to find a solution to this problem. And that will likely mean a whole new approach to the problem.

28 responses to “The Heat Death of 5G

    • I think that’s the standard industry reply. But the problem is much worse than with 3G. Anyone at your conference mention any figures? I’m hearing a heat budget that’s 67% higher than current phones. That’s a lot of watts to shed.
      And anyone have any ideas how they’re going to solve the problem? Solving the issue in 3G broke a couple vendors.

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  2. What about the health hazards of the radiation from the towers which is present even if you dont own a 5G phone instrument? Was this discussed at the 5G conference?

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  7. Wikipedia says consumer microwave ovens operate at 2.45 GHz. Wouldn’t a mmWave microwave oven only cook the outside of the food?

    • It’s not literally the same as a microwave oven. Different frequency, very different power profile. My point is just that invisible radio waves can cause a lot of heat.

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  9. AFAICT, 5G is primarily a way to pause the costs of laying fiber while propping up the stock price. By the time the average investor realizes 5G is a no-go, and how dreadful the conditions of networks have fallen, all the “backers” will be cashed out or retired.

    If solutions are found in the meantime that will make it actually possible, hurray. But I don’t see any valid actions or real intent to actually overcome the myriad of issues 5G faces.

    • That’s too cynical a take for me. 5G has some real benefits. But it’s going to take while to deploy. There’s a lot of complexity involved and that level of detail gets obscured by marketing/social media/stock market discussion.

  10. It is not that the use of mm waves which is generating heat, it is the high clock speeds of the transistors in the chips. Probably also some effect of transmitting such a high frequency. I suppose it will get fixed eventually.

    The related problem is battery life. The phones are hot because of the circuits which are powered by the battery. A hot phone means the battery is draining quickly.

    • Both of those are correct. The bigger issue though is that the heat is very concentrated around a small subset of device electronics, and there is no easy way to remove that heat.
      I think the battery life will be an issue, as it is with every new air interface generation, but one that the industry has a standard playbook for addressing.

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  15. good article in overall but your comment on microwave oven is awfully wrong as it operates at 2.45 GHz which is not even close to mmwave 5G frequencies.

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  19. Hi, I love your blog and I learn a lot about the another face of the industry where I work. I hope you don’t mind some technical comments that seems to be are not very clear.

    The reason for this heating in the devices is because of the CMOS technology that microprocessors are made up by. Every cycle of clock your CPU will likely need to transit from a logic 0 to a logic 1, or vice-versa. Any of these transitions consumes a tiny amount of energy that has to be dissipated in a way of thermal energy. A tiny amount times millions of cycles of the clock (Gbps transmission speeds) brings you a non-negligible amount of energy to dissipate. This is common to all technology available today, and the only way to improve the thermal profile of your device is by improving its thermal management, or reducing the lithography of your CMOS circuitry.

    Regarding your comment about the similarity of mm-Waves to a microwave oven… Well, that’s not correct. By definition all electromagnetic waves transport an arbitrary amount of energy, so all RF signals will heat their surroundings depending on the output power, but no their frequency. The name of mm-Waves is because of the millimetric length of the wavelength of signals with frequency in the magnitude of hundred of GHz (100-300 GHz). Other frequency bands are VHF, UHF, S-band, Ka-band, etc.
    Something you will learn today is that right now, et this moment, 5G technology doesn’t work with mm-Waves. Not even close. For example 5 GHz or 10 GHz frequencies are not mm-Waves. The technology/industry is still not really to move to the mm-Waves spectrum massively. Not even cm-waves technology, as Ka-band, is ready to be in our phones tomorrow. 5G can work with mm-Waves in the lab, but not in your phone today. The industry is working hard to make it possible, but so far, we can say that marketing teams have done their job very well bringing this concept to the field.

    A microwave oven works in the ISM band of 2.45 GHz (S-band) and it works because of the dielectric heating of water diatomic molecules, and that’s the reason why a microwave oven only heats up the water inside your food. In order to do so efficiently, you need a stationary wave between the walls of the oven. In fact, your microwave oven works as a resonant cavity matched for this frequency. A phone will never create these stationary waves because you want to transmit information, and so you transmit stochastic signals, and so you will never have the conditions long enough to generate a dielectric heating, not even accidentally.

    • Wow, thanks for your thoughtful reply.
      A couple things:
      1) I agree with your analysis of the causes of the problem. And every ‘G’ has had to deal with these issues in the early days. However, most people I speak with say the problem for mmWave is much bigger than usual. Estimates I have heard is that the thermal budget for mmWave is more than twice that of sub 6GHz 5G/LTE. So there are real fears that optimizing the silicon is not sufficient. If you look at cooling tech, nothing has changed there in 40 years – we are still dealing with heat sinks and fans, neither of which work well in mobile form factors. So there a couple companies doing interesting work on some new technology.
      2) Yeah, the microwave oven example is wrong. I muddled that point. I should probably take it down.

      Thanks for your thoughts.

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