Would a wireless goggle - one that does not require cables to connect to a PC - be desirable? I certainly think so. With a wireless goggle, you could:
- Use the goggle in the living room even if the computer is on your desk
- Have multiple people use multiple goggles in the same space - such as an arcade - without tripping over each other's wires
- Avoid the risk of wrapping the goggle's umbilical cord around you as you turn
- Have greater freedom of movement
For a wireless solution, one would need to consider three key components: video transmission (how you get the video to the goggles), wireless tracking (how the PC gets information about where the user is) and power.
- Low latency. Streaming a movie or a sports event to your TV does not require tight control over latency. If the movie is shown with a 1-second delay, that is perfectly acceptable. Streaming a game to a goggle with a 1-second delay is completely unacceptable. Sometimes, the need to control latency also dictates whether compression can be used. Compressed video saves on bandwidth but takes time to compress at the transmitter and decompress at the receiver.
- No line-of-sight requirement. Some wireless video solutions require there the transmitter can "see" the receiver, which is typically called 'line of sight'. Those solutions typically don't work for VR goggles because the whole premise of wireless goggles is to allow the user to move around as well as turn. Such turning will inadvertently result in breaking the line of sight from transmitter to receiver and thus dropping the connection. Other use cases, such as having the PC in one room and using the goggles in another probably don't even have line of sight to begin with. This requirement that the wireless signal can go through objects or walls also influences the wireless transmission frequency. Higher frequency transmission (e.g. 60 GHz) results in shorter wavelength which in turn results in greater difficulty in going through walls or humans. Lower frequency bands such as 5 GHz does a better job in penetrating through obstacles and is thus more suitable for wireless goggles.
- Support the right resolution. Wireless video solutions were originally designed with home entertainment in mind, and thus focus on supporting standard home video resolutions of 1080p (1920x1080) or 720p (1280x720). However, many consumer goggles use smartphone displays that have a native resolution of 1080x1920 - portrait mode - as opposed to the traditional 1920x1080 landscape mode. Many wireless video links do not support 1080x1920. One solution, that is now available as an option with the OSVR HDK is to use on-goggle FPGA to perform the video rotation, so that the wireless link still carries the standard 1920x1080 resolution but it is rotated in real-time to 1080x1920. This enables using wireless video links with such products (note: see the 'no free lunch' section below)
- Ability to support multiple independent video links. While this is not required if there is just one video link from the PC to the goggles, it might be required if 1) there are multiple goggles in the same space, and they each want to operate independently; 2) there is a need to carry video, such as from a video camera, from the goggles back to the PC (see this wireless camera) or 3) if the goggles require multiple HD1080p signals such as those goggles that have dual screens
There's no free lunch
- It costs more. One would need to factor in the price of the wireless video link, a potential price increase in the tracking costs, and the costs of a battery
- There may be a price to pay in video latency. If you use an on-board FPGA to rotate the image from 1920x1080 to 1080x1920, you add 1 frame's worth of latency, or 16mSec. This is because you have the store the entire image in memory before you can start outputting the rotated image.
- You are often limited to 60 FPS video. Because most wireless video solutions were designed for home entertainment, they provide 1080p @ 60 FPS. Newer solutions that aim to provide higher resolutions might be able to address this issue.
- You have to carry the battery and the receiver. This is can be done in a beltpack or small backpack.
- You have to recharge or change the battery from time to time.