SEATTLE—Imagine equipping reporters, athletes, reality show participants and anyone else who has an interesting point-of-view perspective with an ultralight, 1080p HD camera that is battery-free. How would that change the way stations and producers tell certain stories?
A team of researchers from the University of Washington has hit upon an idea that may one day make possible small, lightweight, extremely power-efficient cameras capable of these types of shots. Their paper, “Towards Battery-Free HD Video Streaming,” describes a way to remove power-hungry components, such as analog-to-digital converters and codecs, from a camera assembly and employ an analog video backscatter technique to transmit pixels to a device, such as a cell phone, from which video can be streamed.
The approach eliminates the dual problems of overheating and weight that have made wearable cameras, particularly those that use a spectacle form factor, problematic. By dramatically reducing power consumption, the design may enable a new generation of wearable HD cameras.
“Existing approaches optimize the camera and communication modules individually to minimize power consumption. However, designing an efficient video streaming device requires power-consuming hardware components and video codec algorithms that interface to the camera and communications modules,” the paper says.
Optical lens and photo-diode arrays have been designed to use as little as 1.2 µW, and recent backscatter designs lower power consumption to a few microwatts with custom ICs. However, the ADCs and video codecs needed to interface the two “significantly add to power consumption,” it says.
To reduce power requirements, the researchers’ approach feeds “analog pixels from the photo-diodes directly to the backscatter antenna” and eliminates the camera head’s ADCs and codecs that gobble power. The research team evaluated its new design by simulating an ASIC and found it could achieve 720p 60fps with 321 µW and 1080p HD with 806 µW. “This translates to 1000x and 10,000x lower power than is used for existing digital video streaming approaches,” says the paper.
The researchers employed a backscatter design that leverages pulse width modulation (PWM). “Instead of using linear amplifiers to amplify the analog video stream, we use comparators to pulse width modulate the camera sensor’s analog output and convert into [the] digital domain…,” it says.
A smartphone equipped with an RFID reader that plugs into the headphone jack can be used as a backscatter reader. Future designs could see the backscatter readers built directly into smartphones, says the paper.
The research team built a prototype using off-the-shelf components on a custom-designed printed circuit board. The prototype was used to evaluate how the wireless camera performed. The researchers then used the ASIC design of the wireless camera to quantify how much power is consumed for various video resolutions and frame rates. Actually building the ASIC, however, was beyond the budget of the researchers, the paper says.
“Our empirical results also show that we can harvest sufficient energy to enable battery-free 30 fps 1080p video streaming at up to 8 feet,” the paper says. The researchers also demonstrated that with the prototype proof-of-concept camera they were able to backscatter 720p HD at 10 fps up to 16 feet.
The authors of the paper include Saman Naderiparizi, Mehrdad Hessar, Vamsi Talla, Shyamnath Gollakota and Joshua R. Smith.
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