[X4U] Does a wireless display exist

[Stroller]

* hands you a Gold Star (tm) *

Let's consider Airport Extreme to be typical of fast wireless  
solutions - it uses the 802.11g wireless protocol to achieve 54Mb  
connection speeds. The "Mb" in this case means that they can transmit  
54 million bits per second. That seems like quite a lot until you  
remember that a bit is only a singe "1" or "0" character, and alone  
is only any use for black & white displays with no greyscale.

In order to transmit colours to our hypothetical wireless display we  
need to use some of those bits to represent shades of colour. How do  
we do that? Well, we can represent black, white and two in-between  
shades by using 2 bits, that is with the four combinations of 00, 01,  
10 and 11. By the same reasoning we can represent 256 (2 x 2 x 2 x 2  
x 2 x 2 x 2 x 2) colours by using 8 bits but that's broken Windows 95  
territory so we'll probably accept that 16-bit colour depth (65,536  
colours) ought to be enough for anybody (your Mac probably uses 24- 
bit "millions of colours" but you probably wouldn't be able to see  
much difference if you changed the preference to 16-bit "thousands of  
colours").

So an Airport Extreme can usefully transmit (54 million bits divided  
by 16 bits) useful representations of a colour each second. That's  
3,375,000 representations, but we need to use each one of these for a  
pixel, of which you might have 1024 x 768. That's 768,432 pixels, so  
a full screen can be transmitted over the wireless link (3,375,000  
divided by 768,432) four times per second.

Now, if you go & look in "System Preferences" > "Displays" you'll  
probably see the current resolution is set to something like 1024 x  
768, 60Hz. That means that your display is being updated 60 times per  
second, which is generally considered a minimum to prevent headache- 
inducing flicker (75hz or 85hz is generally considered better). So in  
order to keep up with your current "refresh rate" (which is what the  
`Hz' bit refers to) you need a wireless connection that is  
approximately 15 times faster than an Airport Extreme. This is only  
considering a paltry small screen and ignoring the overhead of  
network protocols, of course, but wirless technologies 15 times  
faster than Airport Extreme just ain't being sold in the High Street.

There are ways around this; the VNC program displays screens across  
the network but it uses a computer at the "monitor" end to update the  
screen constantly (at 60Hz, or whatever) and only transmits across  
the network the parts of the screen that have changed. So in order to  
have a "wireless VNC monitor" you would need to have a computer built  
into the screen. This is known as "thin client" technology and hasn't  
been hugely successful outside industry; Microsoft came up with the  
idea for home media lifestyle use a couple of years ago but when  
faced with the prospect of buying a tablet with a 200mhz processor  
and leaving their PC switched on most consumers will buy a laptop  
instead (it only costs a couple of hundred extra to put a faster  
processor and a hard-drive in the wireless VNC monitor, you see, to  
make it a "real computer").

This is the kind of maths (please excuse me for being unable to  
resist mentioning it) that in my day was taught at school to  
teenagers; saying "does a wireless display exist" is a bit like  
saying "does a cardboard road-bridge exist", and specifying the 17"  
to 19" range is like expecting said cardboard road-bridge to support  
the weight of your hummer and span the Thames. I appreciate that not  
everyone finds the kind of approach I've laid out above as intuitive  
as I do so the short answer is: don't worry - with the current  
improvements of wireless technology a cardboard suitable for your  
wireless display will surely be developed within a decade or two!

Stroller.


On 8 Mar 2006, at 00:51, John Richardson wrote:
>
> Why not?
>
> Bandwidth of video exceeds that of wireless?
>
>> no
>>
>> On Mar 7, 2006, at 9:53 AM, John Richardson wrote:
>>
>>> Does a wireless display in the 17" to 19" range exist?