Every VR demo on a PC I’ve seen begins with someone apologizing for the tether. At least with hosted demos, there is someone to manage the cord. Once you set up your own system, you’re left to trip over it shortly after you immerse yourself in your favorite VR game. Currently, the only way around having a tether is by using an expensive, special-purpose, backpack VR PC. Those aren’t all that much fun, either. Researchers at MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) aim to fix the problem by letting you cut the cord. By harnessing millimeter waves (mmWaves) along with a programmable reflector called MoVR, they expect to be able to provide enough two-way bandwidth to enable high-quality VR experiences without wires.
High-performance VR is hampered by the need for a tether
High-end VR headsets like the Vive and Oculus Rift feature two HD or better displays. That means they need to be fed data at nearly 6Gbps, with very-low latency. This has to happen while the user is moving around as they play a game or go through a VR experience. Today, that is almost always achieved by using a high-quality HDMI cable from the PC to the headset. In commercial settings it may be partially suspended from above, to stay off the floor. But for most consumers it’s snaked across the floor, where it can easily be run over by a chair, tripped on, or tangled up.
Improving on the promise of mmWaves
Millimeter waves are well understood as a way to transmit large amounts of data quickly over small distances. However, because they use very-high frequencies — from 30 to 300 GHz — they require line of sight between the transmitter and receiver. In the case of VR, that’s a problem because users are constantly turning their head, moving around, and gesturing. Any of those can quickly drop the signal. Unlike other kinds of data transmission, VR experiences can’t tolerate a momentary loss of signal, so mmWaves have been a non-starter for VR applications — until now.
The team at MIT has improved on typical mmWave system designs by adding a programmable signal reflector it calls MoVR (think repeater) that can quickly retarget, amplify, and retransmit a mmWave signal. The source AP (Access Point) and the MoVR use sophisticated real time signal processing to determine the correct angle of reflection for the programmable “mirror”, so that it will always be sending the signal directly to the headset-based receiver. Based on multiple simulations, having the signal come from both the AP and the MoVR is enough to insure that there is connectivity to the receiver under most conditions (short of the user completely blocking the receiver with their hand, for example). For more information, the authors have put their research paper online.
Other approaches to cutting the cord
In addition to using a VR backpack, there are other cordless solutions. Most common are smartphone-based devices, like Google Cardboard, Samsung Gear VR, and Google’s Daydream. However, by definition, these are much less powerful than those that harness a mainstream CPU and GPU. Microsoft HoloLens, and a few others, have taken the approach of stuffing an entire computer into their headsets. That’s an appealing option, but for now an expensive one that is still in the testing stages with developers.
More recently, HTC just announced a $ 220 wireless accessory for the Vive. By mounting it on top of the user’s head, it avoids some of the worst of the interference problems. But HTC and developer TPCAST have said little about the technology. If it is a traditional HDMI repeater, then it won’t solve the problem of gesturing, or even leaning over away from the transmitter. I look forward to MIT’s MoVR changing that.