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How To Extend HTC Vive Distance From PC

April 28, 2016 | vive htc pc distance extend hdmi usb repeater ethernet
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Introduction

You are likely faced with the problem that where you want to use your Vive is not right next to where your best or only computer for VR gaming is located. You may use your PC for other things that require a desk, monitors, or other peripherals that exist in a smaller space than is optimal for room-scale VR.

In this report, I'm going to lay out the challenges and solutions. Even if you are non-technical, don't fear. I'm going to show you a solution that worked with the actual products I used, but I want to impart basic technical understanding so that even if you don't have access to the same products or you have different needs, you can still figure out how to solve your particular challenge on your own. You owe it to yourself to have a basic technical understanding, so don't just skip to my solution!

What are we extending, exactly?

The Vive needs information from the computer to display images on the panels stuck to your eyeballs. Ok, they aren't literally stuck to your eyeballs, but they are pretty close. Regardless, they need data. The way the Vive gets this is via an HDMI cable (or a DisplayPort cable, but I'm going to stick to HDMI here because that's what the Vive uses from the link box to the headset itself).

Next, the Vive must send information to the computer so the computer knows where you are, where your head is pointed, and how you are holding the controllers. The computer can use this to draw the next frame it will send to the display panels from your new perspective. The Vive sends this information via USB.

So we are extending HDMI and USB cables. That's it.

Official Recommendations & Limitations

Let's first look at the official recommendations to determine if you even need to think about extension. The official recommendation is that you put your PC right at the edge of your play area, so we'll go with that. The Vive includes a 3' HDMI cable and a 3' USB cable to connect the link box to your computer. Think of the link box as just a VR power plus data strip - you plug power into it (which enables the headset to drive the panels), HDMI, and USB from the computer. Then the Vive headset also has a 3-in-1 cable (HDMI, USB, and power) that connects to the other side of the link box. The 3-in-1 cable from the link box to the headset is 16' long.

The USB and HDMI cables that come with the Vive. As you can see, they are short.

So, without using anything other than what comes in the box, you can theoretically move 19' feet away from the back of the computer. This seems pretty good. Some things to consider, however.

That's from the exact back of the computer. Usually you don't want to look at the back of the computer with all the cables hanging out. So you turn it around, which instantly uses about 1.5' of the cable just getting back to the front. If you turn it sideways, the loss is much less, but any orientation other than facing you is going to make it look like you have a square-shaped porcupine next to your play area.

Going back to that dismal word, theoretically, in theory we can do things like say the computer is positioned at exactly the height of your head from the floor, so you can really be 19' away with the cord stretched out between you and the computer, link box dangling in the air, looking like a chained cow desperately trying to break free of its stake to get that delicious piece of clover just out of tongue's reach. If you would rather not be thought of as a cow, you need to factor that the computer is probably on the floor, you don't want any part of the cable hanging in the air between your head and the computer for comfort and safety reasons, and you are a certain feet tall.

This means the cable needs to go from your head to the floor, across the floor, to the link box, to the computer, and up to the port on the computer. So, let's say you are 6' tall - that leaves 13' across the floor, subtract 1' to deal with the port on the computer not being at floor level, and you are down to 12'. This also means that the link box is in your play area and you might step on it when close to your PC, which is probably not a wise thing to do to the nerve center of your $800 VR system. If you place the link box outside the play area, you are working with only the 16' of the 3-in-1 cable, so only 10' after we subtract your height.

You could step on this and drag it across the floor with your head. The question is, do you really want to?

This is all predicated on the thought that your PC is exactly on the edge of your play area. If it's on the other side of your desk or anywhere other than exactly on the edge of your play area, you can see that your maximum wander distance is falling fast.

Basic Extension

In the next section, we're going to discuss how certain types of cables, including HDMI and USB, are only rated to carry data for a certain distance or length before the equipment on each end is no longer able to talk effectively through the cable. However, we don't have to do anything fancy if we stay within the known limitations of the cables. We just get longer basic cables.

In situations such as this, it's easy to simplify and see we are limited here by whichever cable has the shortest length limitation since both cables have to make the distance. The more limited cable is USB. It is rated to go only about 15' feet. So if we just bought a 15' USB cable and a 15' HDMI cable to go from our PC to the link box and used those instead of the included 3' USB and HDMI cables, we can theoretically get our tongues inches away from delicious clover 31' feet away from our PC. Well, I mean, if we were cows and really liked clover.

A basic USB extension cable. This one is only 5' long, though.

Extended Extension

Given the problems we've discussed already, and the fact that your PC may not even be in the same room as where you want to use the Vive, I'm guessing you'd like to roam further afield. So, to do that, we're going to have to bust through the official cable specs. Unfortunately, the official cable specs exist for a reason and all devices assume those specs are being honored, so we are going to have to turn to the cables themselves to play some tricks.

First, once you go over about 20', HDMI cables aren't rated to push through the amount of bandwidth we need to get display information from our computer to the headset, which is a lot even though the displays themselves are small (they have lots of pixels). Certain companies saw this as a problem for people in various media professions and created special in-line (in-cable) chips that would help extend this distance to 30', 50', or more. These are called "active HDMI" cables and they cost more, but run further. So those will help us with HDMI.

30' of active HDMI cable. Note there is a display end (connect to link box) and source end (connect to PC).

USB is different. The usual way to extend USB is to get a repeater cable that has its own power. You go 15' feet to the repeater and then plug another cable to go 15' feet from there. The problem is that the repeater is really a USB hub and it needs to wait and see a signal on one side, then recreate it on the other side. This adds delay and isn't really great for real time applications. It just so happens that VR is about as real time an application as you get.

One repeater probably isn't going to be too bad, but if you keep adding repeaters, well, that's just not good. Therefore, people have come up with another solution. Ditch the USB cable entirely and make the long run with something else that is designed for distance, like an Ethernet cable. Wait, you are probably thinking, how does USB run over an Ethernet cable? The answer is, it doesn't. But you can get a piece of equipment that will take USB on one side, turn it into data running over an Ethernet cable to a sister pair of equipment, and then convert that back into a USB port on the other side. Is this any better than a USB extender? No, not really, but it's better than multiple USB extenders.

Assembled USB-Ethernet repeater (short power transformer cable included and needed with remote box not shown).

There are also "active USB" cables that are similar to active HDMI cables where you do not need to have the additional gear like in the USB-Ethernet solution. However, these seem to vary in availability and quality by region. Therefore, you may be able to find an active USB solution that works, but I have not tested it personally.

The one other thing to note here is power. The link box needs to be powered by its transformer cable, which is also only about 3' long. Therefore, if you are going to put the link box somewhere far away from an electrical outlet in your Vive play space, you will need an extension cord for both that and the remote box of the USB-Ethernet extension system if you use one.

So this is how we can extend the range such we that can happily skip through the meadow on a clover tear. Distant fields beckon, but as we get closer to them, things start to... drift. It just doesn't seem that what we do and what we see is directly coupled!

... Lag

Unfortunately, at some point we learn physics always wins and our attempts to defy it come with serious consequences. You see, the further you extend the cabling, the more the problems of keeping data coherent while going the distance become acute and raise the probability that a frame or chunk of data will not be received on the other end. Also, just because of the physical distances, it's taking more time for the data to go from the headset to the PC and back, which gives rise to what is called input and output lag.

The easiest way to think about this is to take it to an extreme and imagine that you have galloped so far you are closing in on the tastiest piece of moon clover you have ever seen. The problem is, when you reach out for that clover with your big sticky tongue in all of its bovine glory, your tongue doesn't seem to start moving visually for almost 3 seconds, which is the time it's going to take for your intention to move your tongue to be communicated back along the USB cable leading to Earth, processed on the earthbound PC, and sent back along the HDMI cable leading back to the moon. And that's assuming fantastic cables that propagate electrical signals at the speed of light as well as numerous other sleights of fantasy physics and biology!

It... beckons.

So, with something as seriously real time as VR, where you've got to ideally do a full loop of input and output 90 times a second, every time you do anything that increases the distance between you and the PC, particularly when going outside cable specs and using active repeater equipment and cabling, you are driving the lag up. It's completely unavoidable. The real question is to what extent it is being driven up and whether this has a noticeable impact. There's not a lot of good data on it, but we should proceed with caution here, because VR is so finely tuned to deal with motion sickness and the like that even a very small amount of lag could interfere with the experience, even if we are not fully conscious of it.

A Working Solution

Now that you fully understand the challenges and the technology, at least to the level required for this discussion, I can simply post links to the items that enabled me to put 30' of distance between me and the link box, which gives me about 46' of play to roam my large tracking area with the cables coming from a PC located on the other side of my office in another room:

This seems to work. I'm not conscious of problems with input lag, although I am sure some additional lag exists (I have not found a good way to measure it with the tools I have - measuring lag scientifically is actually pretty challenging). At times I have a sense I may be becoming motion sick, but I don't ever actually get motion sick. I'm able to reliably hit marauders in the Longbow demo at extreme ranges. It feels like I'm interacting with the world, more or less, and the controllers move when I move them.

Live action recreation of Vive Longbow demo. I'm on the right.

Getting Another Computer

So far we've assumed that you don't want to get another computer. I'd prefer to have another computer right next to my tracking area, but having another computer for VR with a powerful GPU is expensive. However, if you can spring for one, that's a better solution than anything presented here.

Your Solution

I'm not recommending you go buy the same exact products I did, because your situation may be different. You may not need to go as far; you may need to go further. However, you now have what you need to know about the technical and distance fundamentals to figure out what your solution may be. My general hunch is 30' is not optimal, but doable. 50' is possible, but I haven't tried it. Beyond that, move your computer or get another one.

Note that there is also a lot of running back and forth to your keyboard and monitor from your VR space with this generation of VR, at least initially during setup, so at a certain point this is all becoming a tad ridiculous.

Especially for the clover.

I was this close right before my HDMI cable disconnected and life support failed.

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