[SOCALWUG] Re: Reg WiF/WiMax questions

Mon, 27 Feb 2006 21:43:51 -0800

Thanks a lot Kevin and Mr.Thompson.

 
On 2/27/06, Jim Thompson <[EMAIL PROTECTED]> wrote:

kevincw01 wrote:

>I don't beleive it's this simple.  One problem is that the range for
> 802.11g is actually less than 802.11b at the maximum throughput.
>
The primary reason for this is that at the maximum modulation speed
(54Mbps .vs 11Mbps) a much higher Eb/No (SNR) is required for 11g than
for 11b.

At (nearly) equivalent bit rates (12Mbps 11g .vs 11Mbps 11b) the Eb/No
curves are almost identical.

If your environment has a high delay spread (lots of multipath), then
11g's 800ns guard interval may get a signal through a lot "farther" than
11b's nominal 110ns tollerance for delay spread.

>So you have to decide, do you want the range for the max throughput or at
>just the point before it stops working?  Another problem is that the
>power drain is largely dependent on the manufactuer's strength of the
>radio.  All radios are not the same strength.  Off the top of my head,
>I think many pcmcia 802.11b cards are 150mW but definiteily not all
>(don't quote me on that, it's just a number floating around in my head
>that seems right).  So you'd probably have to take the average here, or
>maybe different numbers for different strengths...  Then ofcourse the
>cost is going to be all over the map, good luck on that one.
>
>
The original questions are unaswerable without a lot more information.

However, the Eb/No (SNR) curves for the WiMax PHYs, operated in
unlicensed spectrum, at equivalent bit rates are approximately the same,
and anyone operating WiMax or WiFi in unlicensed spectrum must operate
under 47 CFR Part 15.247 (ISM) or 15.407 (U-NII), so there is *no*
inherent advantage of either WiMax or WiFi (compared to each other)
under these conditions.

If you don't believe me, I invite you to study the IEEE documents carefully.

*most* 802.11b cards operated with 16-17dBm (32mW - 50mW) of transmit
power.  There are specialty cards with 100mW or more of transmit power
available.  All other things being equal, building a high-power 11g card
is more expensive than building a high-power 11b card, due to
peak-to-average power ratio issues.   Since WiMax also uses OFDM, with
similar modulation envelopes, it will also face PAPR .vs linearity
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