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Towards Battery-Free HD Video Streaming [video] (washington.edu)
701 points by InclinedPlane on April 20, 2018 | hide | past | favorite | 99 comments

The new batteryless wireless sensors coming out of uw are incredible. Dr. Smith is leading some great work. My interest started when I heard of the WISP [0]. The RF power harvesting design is so simple and elegant. It is amazing what can be done with uW of power!

[0] https://sensor.cs.washington.edu/WISP.html

Is this thing operating on the same principle as wireless charging? It can convert RF to power? And power consumption is so low that something like a wifi router can produce enough RF to satisfy it?

Same principle in that they both use electromagnetism, yes. But Qi and similar wireless charging using inductively couples coils. WISP power is generated from radio waves absorbed by the antenna generating a small current then boosted to a usable voltage for a low power microcontroller. The microcontroller can control the impedence of the antenna, changing the backscatter of the antenna, measure the change in backscatter you can get your 1s and 0s out of the sensor!

edit: wifi router could power these sensors, just a limited range.

Indeed, its _so amazing_ it has potential of replacing $.2 watch battery some day.

It is amazing. With this approach, you wouldn't have to change the battery every 10 minutes.

Although I don't recognise myself in the style of the comment you're responding to, I would like to point out a (watch) battery will not die in 10 minutes when drawing microwats only. I think we want to separate low energy usage, which is a cool feat by itself, and RF harvesting (which goes well with low energy usage, but so might a small, cheap, battery).

I'm not an RF engineer, but the video mentioned that the 'traditional' WiFi component would draw 1W. I assumed that, if you add a battery, it's to power this part.

No, backscatter is the only legit part of this writeup, everything else is made up.

"we simulate an ASIC, which achieves 60 fps 720p and 1080p HD video streaming for 321 µW and 806 µW, respectively" simulate, how convenient!

"Our inter and intra-frame compression algorithms reduces total bandwidth requirements by up to two orders of magnitude compared to raw video" so they also invented mpeg4 level of compression 1mW codec.

You might wonder how such an amazing compression codec works? its middle-out. They transmit "fullhd" by transmitting ~100x50 resolution intra frames ":). Everything is Simulated, Estimated, Planned, Theorized, Calculated and Faked. That cool 1080 YT clip of them walking around the corridor just after showing you face mounted camera models? Never happened, prototype is BW 112×112, "simulated" again. Their setup can do 1080@60 of a static picture, there is only enough bandwidth to sustain ~2fps without dropping data. They even conveniently kept all the calculations ignoring color (3x the data).

Reminds me of energy harvesting wristwatch crowdfunding HN was raving about few months back, conveniently ignoring particular design including battery able to power it for couple of years.

>10 minutes

try 10-20 days if you believe in their simulated 800uW ASIC with magic middle out compression. Assuming everything works according to their predictions and simulations (nothing was actually build to confirm that) you have to pump 1W from your cellphone to power 1mW wearable camera. Your cellphone will run out of battery after 4-6 hours.

Think about that for a second, they want you to recharge your phone every 6 hours to "save from inconvenience of recharging your wearable". This is they main proposed design, right there in YT presentation.

It really is. The bottom line is these sensors can scale to small sizes unlike watch batteries enabling remote sensing and integrated manufacturing. Think temperature sensors inside that watch battery. Strain sensors in existing and future infrastructure to monitor uninspectable areas for >50 years. There are a lot of novel applications.

In the video and paper, they don't actually explain what backscatter is in this context. The wifi signal is what's being "backscattered". Here's some of the leadup papers about it:

https://passivewifi.cs.washington.edu/files/passive_wifi.pdf https://homes.cs.washington.edu/~gshyam/Papers/wifibackscatt...

Here's a video explaining WiFi backscatter. It really is an amazing concept even without doing HD video with it. All kinds of devices - I'm imaging home automation sensors - could become batteryless.


> All kinds of devices - I'm imaging home automation sensors - could become batteryless.

That's terrifying.

You can still use jammers to prevent backscatter from being readable but your jamming signal will just power the sensor more. :)

That is an amazing concept, simple and effective, just reflecting backscattered wifi signal on and off to encode data.

Thanks, that second paper is helpful. The OP is really the proof that passive Wifi is actually useful. In my opinion, the real advance here is in that second paper you cite, the fact that they've built Wifi enabled devices that are powered by the Wifi signal itself.

This is the kind of submission that usually never gets anywhere on HN but it's very good.

Actually, there is a lot of great stuff that gets submitted that never gets anywhere.

It would be cool if somehow there was a manually edited "great but never got anywhere" stream for HN.

Edit: Now I've gone and said that, watch this get a 1000 points ;)

There have been lots of posts about new technologies that have not panned out so HN scepticism is to be expected (remember memristors)

I am still hoping for "yet" in the case of memristors.

It seems transmitting the raw sensor data would make it tricky to do this securely. Would it be possible to encrypt the signal with some sort of hardware cipher?

They address the security possibilities in the paper:

> Our current implementation does not account for security. However, to secure the wireless link between the camera and reader, we can leverage the fact that our digital core processes the PWM signal. Each wireless camera can be assigned a unique pseudo random security key. Based on this key, the camera’s digital core can modulate the width of the PWM-encoded pixel value using an XOR gate. The reader, which knows the security key, can map the received data to the desired pixel values by performing the analogous operation.

XOR encryption with a mostly static image doesn’t seem very secure to me.

It's XORed with a stream cipher, so it's totally secure (no part of the stream is reused).

The tricky bit might be deciding where to start the stream...

If the static image could be somehow "bankswitched", "shifted" or updated... I am thinking a huge one time pad. The problem is doing it power effeciently of course.

Thinking about, the main problem will be the penguin problem [1]. Which for a video is even worse as if a shape is moving, from seeing the pixels that are changing you can tell most of what is going on.

[1] https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation...

In my mind, strong encryption that can fend off the most serious attackers cannot apply to the analog part of the application.

However, analog scrambling techniques should still be effective in many cases.

The transmitter and the receiver are in close proximity. Whatever transmitted, the eavesdropper can observe nearby anyway.

How about through a wall? That would make security applications in an apartment a bit less attractive, and I’m sure there are others. I wonder if encryption would be possible without much extra power overhead.

Some sort of directional shielding? Isn't backscattering light directional? Someone knows more about backscattering can have a better answer.

Analog encryption might be possible if the sender and receiver measure some common optical signal (assuming optically local security is what you're after).

Maybe, but good luck doing encryption without a power source.

There is a power source: the radio signal, but there's only microwatts available. Nevertheless, it's not impossible that there might be some clever solution to the problem, however, since the signal is analog that makes things a bit more challenging.

Reading that instantly reminded me of the Great Seal bug the Soviets gifted to US Ambassador W. Averell Harriman in 1945 [0]

I'm not an engineer, but as I understand it the principles at work here are very similar?

[0] https://en.wikipedia.org/wiki/The_Thing_(listening_device)

Tangentially related to that: a Dutch radar company apparently was responsible for reverse engineering that for the CIA


My first thought too. :)

This reminds me of Theremin's Great Seal bug that was placed in the US embassy in Moscow:


Definitely, this project is basically the Great Seal Bug but for photodiodes. The authors even mention the Great Seal bug in their paper.

This is truly incredible. I've spent the last 4 years neck deep in live video broadcasting solutions for consumer, commercial, and government use cases, and this just blew my mind.

This is moving towards A Deepness in the Sky level surveillance tools.

My immediate thought is, even easier to install reversing cameras for older cars. Now my second thought is, spying devices, a wholly more troubling prospect.

Maybe I'm just too old-fashioned, but I generally dislike the idea of reversing cameras. I only reverse if I'm completely sure of my surroundings, based on turning back and using my eyes as well as the mirrors. Looking anywhere else tends to feel like a distraction.

Most people drive and reverse way too fast.

Worth noting that the pretty HD pictures came from a laptop hooked up to a DAC converter to simulate an analog HD video camera. The true analog camera shown on the page had nowhere near HD color resolution (though it could still recognize faces in a parking lot with 95% accuracy--impressive in itself.)

I saw the presentation for their paper at NSDI last week. I was (inwardly) giddy the whole time. They had a live demo. It doesn't even resemble something that could be turned into a real product in the near term. It is, despite that, comically amazingly cool tech.

Very cool project.

I wonder if compressed sensing would be useful here. In the paper they describe this custom (and seemingly ad-hoc) video compression algorithm that is suitable for the low-power device. Basically, the camera averages blocks of pixels into "super pixels" all in the analog domain, sends these super pixels over the wireless link, and then the receiver can request the individual pixels of any super pixel that seems like it might have changed since the last frame. But with compressed sensing, can't all of this be done by sending random linear combinations of all pixel values (like the single pixel camera)? It seems like then you can avoid the bi-directional link and also get rate adaptation for free.

Also, in the paper they say they used pulse-width modulation for the backscatter signal instead of just attaching the sensors directly to the antenna like the Great Seal Bug because the dynamic range of the photodiodes is much less than that of a microphone and they wanted to avoid using an amplifier (section 3.1 in the paper). But the PWM requires power as well. Would an amplifier that only has to map the range of a photodiode to the range of a microphone really require that much more power? And if so, are we talking like twice the power, 10x, 100x?

This is an incredible outcome and really shows how much work these UW grad students and Dr Smith have been working on low power passive tech. Great stuff, I wish more people in software were versed in physical tech so they could create hardware to enable their ideas.

Seems like this could be useful for AR. I'm sure adding two front-facing cameras to the Vive Pro cut into both power and bandwidth budgets. I'd love to hear from an AR expert on this!

What is AR?

Augmented Reality (e.g., Pokemon Go)

Incredible. Since it is analog and unencrypted, it’s wide open to attacks though, isn’t it?

what is there to attack? if someone is in range to get the backscattered signal they can just see what the camera is looking at...its 16ft LOS, for privacy concerns at such low powers any walls would attenuate the backscatter.

What about spoofing or jamming the signal?

I'm amazed they can get so much bandwidth out of backscatter. Their previous work [1] was more like RFID tag bandwidth.

[1] http://iotwifi.cs.washington.edu/files/wifiBackscatter.pdf

I'm really impressed with the bandwidth. Being analog and only having back-scatter for the modulation, I thought it'd be way worse than current digital or old analog schemes, but from the paper, they're saying 2.8Mhz worst case for 720p@10fps, 0.98Mhz on average.

Imagine everyone with google glasses broadcasting what they see unencrypted to people within ~20ft.

Super cool.

Surely everyone within 20ft of them can pretty much see what they see anyway?

It'd be useful for going around corners, visibility in parking lots, situational awareness for teams of military/SWAT in indoor environments, etc.

480p at 10fps at 16ft is really incredible. That's enough distance to put cameras all over cars to sense environments around it. My first immediate thought is to retrofit old cars with lane-changing assist camera with this in traffic.

The power requirements of a camera aren't even a tiny amount of the complication of retrofitting existing cars.

Perhaps it is, as cameras require looming and looming requires removing trim and finicking around which is expensive in man hours. Especially if literally every car that comes in is different.

Also fat looms the length of a car can still cost hundreds of dollars said and done.

Cost of installation is greatly reduced if all you need to do is line it up and rivet it on and there is no need to customise the power system to different cars (ie 12V, 24V) and loom layouts (ie old looms are crappy, hard to get apart for splicing, wires are old and might break during retrofit, some cars have +ive chassis)

Unless I'm mistaken, they actually achieved 720p at 10fps/16ft not 480p.

The solution to that problem is not battery-free video streaming.

This is pretty interesting and seems transferable to any application where you have a data source you don't mind pouring energy into as long as that data source doesn't need dedicated power.

You could apply this to other types of sensors, such as perhaps accelerometers or microphones. Device locations could be a smart wearable, a surgical implant, or some kind of hard to reach diagnostic sensor.

I suppose we already use something similar in rfids but I guess the novelty comes from updating sensor data instead of a ROM. Very cool stuff.

How does backscattering work in the presence of multiple networks?

The recived signal at 16 feet looks suprisingly good, you could probably fix it up with a bit of image processing and neural networks on the receiving end (eg. Smartphones)

Could this harvesting technique power battery-free AirPods?

For transmission of data yes, but you still need "lots" of energy to drive the loudspeakers.

AirPods no, but microphones yeah.

I just spent a lot of time researching energy harvesting (about a two week project) and I'm extremely impressed by this. To just power a simple sensor (temp, pressure) and sending out readings is a non-trivial thing to design in such a way that it works reliably. To do a lot of processing and to power a hungry sensor such a camera is orders of magnitude more complex.

They didnt. They simulated powering 112x112 black&white sensor, the rest is just props and 'recreations'.

It says:

"Finally, we design a proof-of-concept prototype with off-the-shelf hardware components that successfully backscatter 720p HD video at 10 fps up to 16 feet."

Which to me reads they have it working in principle the other design will be an optimization.

So even here it says 720p instead of fullhd :), and when you read the paper you learn they didnt even do that, they used 100x100 BW camera module in prototype. 720 transmission was done with a laptop.

Quick, someone put a blockchain on it. Battery-free blockchain Internet-of-Things sounds like a several million dollar ICO to me!

This is a very cool first effort. I don't think it's suitable as a security system yet, because it seems like it would be so easy to overwhelm the relevant spectrum. Eventually maybe.

Depends on the kind of security system. I manage over 150 IP cameras in our internal facility CCTV system and it is expensive to pull Ethernet cables to 10 different spots near the ceiling in a single production room just 20x30ft. I would buy these for $300/each if it meant I only need a couple of $500 hubs at desk level per room.

I'm not worried about sabotage/jamming etc. We are trying to monitor OSHA-violations, accidents, and quality control. If I didn't have to worry about power, I would put multiple cameras in every warehouse aisle, loading dock, and doorway. Local storage is embarrassingly cheap but dragging CAT5/6 all over, supporting ton of PoE switches, and coordinating with facility staff to maintain cameras 20ft up the wall is very expensive and time consuming.

I would also buy like 20 of these for my house and live-stream my mini zoo of prairie dogs, goats, tortoises, and birds.

This is quite an interesting concept in general, with cool results. Could there be extensions to other real-time imaging modalities (ultrasound for example)? Anyone have a hypothesis?

Somewhat related, a few days ago there was (is) a Kickstarter for a wireless 1080p surveillance camera that last a whole year with a single charge. Eufy

Edit: Added name

It does so by using (very low power) motion sensors before turning on the camera.

combine it with this and you get a 480p 10fps feed while no one’s moving, and a 1080p 60fps feed whenever motion is detected – the perfect combination.

"Any sufficiently advanced technology is indistinguishable from magic."—Arthur C. Clarke

It's crazy what you can do with such little power. Basically these cameras need no power at all.

This is amazing tech. Kudos for the theoretical foresight and the execution to make it come to life.

I like it. Throw a bunch of these around the city and you have some interesting applications.

Technically very interesting but also depressing that the panopticon continues to improve unabated.

Analog modulation? So interference will easily kill the signal?

this would be nice for a safety necklace cam.

This is pretty freaking cool.

I think your response to this will depend on whether or not you've read Dave Eggers' The Circle, in which battery-free wireless cameras play a central role. (Spoiler: it doesn't go well).

Imagine the current state of blanket surveillance, particularly in dense urban cities like London, but everywhere, invisibly. Cheap, battery-free, weatherproof cameras are a step towards this.

P.S.: The book isn't great, but it's miles better than the film.

The response needs to factor in that this is more or less inevitable. The solution to potential power abuse must be Sousveillance.

Or that video manipulation will become so easy and commonplace that video has zero value as evidence.

The underlying assumption behind sousveillance is people will make reasonable decisions in response to publicity if everything gets publicized.

But anyone paying attention to what goes viral on social networks should know how cruel and arbitrary people can be in practice.

Recording stuff and not sharing it unless there's good reason seems more humane?

Why wouldn't the average government just outlaw Sousveillance / Inverse surveillance?

Rules don't help as much in real life as we think. They are imaginary, and have influence on our behavior only because we let them. If violating a rule has no consequence or little chance of detection, we can expect large-scale violation.

Further, if an action satisfies some person ethic but violates a public rule, many folks will take that action anyway. Violating the speed limit to get a spouse to medical aid. Violating a confidence to stop injury. Things like that.

If a rule is counter to human nature (curiosity, personal safety) then it is likely to be useless.

They would. Enforcement is a separate issue

You aren't wrong, the film really was terrible.

What sort of security do these employ though? Could these end up being like police radio frequencies where anyone can tap in and watch? If anything that might be beneficial because you could then have independent sources verifying a feed's integrity? Then again could someone override those frequencies and broadcast whatever they want you to see?

In the book, the devices are all public, anyone can watch any feed.

Widespread open and mutlidirectional surveillance comes to a mostly good ending in David Brin's Earth. The doctrine gets a non-fiction (and IMO persuasive) treatment in The Transparent Society. I'm not so concerned about a panopticon open to all.

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