The biggest problem which I have totally experienced is the current lack of adjacent channel rejection for OFDM of the current generation for adjacent yet non-overlapping channels (1, 6, 11). I was involved with a large roll out a will tons of 802.11b on 1 and 11, and the 802.11g on 6. The 802.11g was getting beat up performance wise so we looked into it. The numbers I was quoted were a 30db rejection for 802.11b (orinoco gear) and a < 6db rejection (I'm being nice here) for linksys and other G cards. Next time we will pick 1 or 11 for the 802.11g gear :/
What kind of adjacent channel rejection does your gear have? and have you adjusted your OFDM timings to handle multipath where the bit shift is larger than 802.11g? So far I've not been impressed with the stability of 802.11a or 802.11g gear, but I think the issues were not OFDM's fault, more implementation issues.
Cheers, Cliff
On Thursday, Jul 24, 2003, at 19:45 US/Pacific, Patrick Leary wrote:
Tim, your understanding of OFDM is way off. Extraordinarily stability is--
achieved with OFDM - far more than with our FHSS or our DSSS. We have
examples of links having only a single packet error over several weeks. I am
not basing these off theory, but off actual field results both beta and
commercial deployments. Here is a link to some such tests done using our
3.5GHz OFDM PMP which has been shipping for 18 months and is in use in major
carrier deployments around the world. This paper includes detailed photo
examples of the links.
http://www.alvarion-usa.com/RunTime/Materials/KnowledgePoolFiles/ alv_OFDM%20
wp.pdf
Keep in mind, this is 3.5GHz equipment
http://www.alvarion-usa.com/RunTime/ Products_2020.asp?tNodeParam=33working
off a very small channelization, so the max data rate is lower than our same
products using 20MHz 5GHz channels (BreezeACCESS VL and BreezeACCESS LB).
VL: http://www.alvarion-usa.com/RunTime/Products_2020.asp?tNodeParam=39
LB: http://www.alvarion-usa.com/RunTime/Products_2020.asp?tNodeParam=35
Patrick Alvarion
-----Original Message----- From: 'Tim Pozar' [mailto:[EMAIL PROTECTED] Sent: Thursday, July 24, 2003 8:43 PM To: Patrick Leary Cc: Ladjicke Diouf; [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: Re: [BAWUG] 802.11b Long Range non line of sight
On Thu, Jul 24, 2003 at 05:32:38PM -0700, Patrick Leary wrote:Tim, I am not sure if you are talking about OFDM or DSSS. With OFDM, you
DON'T need LOS. Of course its not going to connect forever with NLOS, but
for a few miles, it is a no brainer. We have ample empirical data that
proves it.
I haven't see your report but if you are basing it on using things like knife-edge diffraction or even multipath as your method of getting from point A to point B. I *would* be cautious about giving the link a high "up-time".
Looking forward to the report...
Tim
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