Hello Jack,
When testing the four port card with multiple radios, problems occur when the pigtail antennas are within some inches of each other. When you have real antennas that are separated by a meter or more (and on non-overlapping frequencies), you will not see big losses in the throughput.
Hmm.
2.4GHz LOS path loss:
1 meters is 41 dB 2 meters is 47 dB 3 meters is 51 dB 4 meters is 53 dB 5 meters is 55 dB 6 meters is 57 dB 7 meters is 58 dB 8 meters is 59 dB 9 meters is 60 dB 10 meters is 61.0 dB 20 meters is 67.0 dB 30 meters is 70.5 dB 40 meters is 73.0 dB 50 meters is 75.0 dB 60 meters is 76.6 dB 70 meters is 77.9 dB 80 meters is 79.1 dB 90 meters is 80.1 dB 100 meters is 81.0 dB
5.8GHz LOS path loss is basically the above + 7dB. Note that the IL of the u.fl connector is higher at 5GHz than it is at 2.4GHz. The combination of these two things explains why your customers (and ours, btw) "can't connect" without putting pigtails and antennas on the card(s). They're fighting at least another 9-10dB, perhaps more.
But back to the "hmm" part.
Lets assume a 26dBm EIRP output (from either), due to a good card, or operating at a low rate, or antenna gain, or whatever. I'm sure many of your customers are running higher EIRP than this.
Lets also assume that the card meets the IEEE minimums for ACR (16dB adjacent @ 6Mbps, 35dB @ 11Mbps CCK)
26dBm (EIRP) - 1m path loss (41 or 47dB depending on the band), plus the antenna gain (lets call it 6dBi) from the nearby antenna)
26 - 41 - 16 + 6 = -25dB, presented at the receiver input (possibly knocked down by another dB or 2 due to cable losses.) Thus, the "noise floor" of the adjacent receiver is -25dBm while one unit is transmitting.
Can you really assert that this doesn't impact range (or the modulation rate?)
Running the numbers for other separations, modulations, etc is left as an exercise for the reader. Your goal is to get the in-channel noise power as close as possible to the noise floor of the receiver(s), which is approximately -104dBm for most 2.4GHZ receivers, and something closer to -100dBm for a 5GHz receiver.
Incidentally, we have (mutual) competitors who like to brag about the "-104dBm" rx sensitivity (at 11Mbps!) of their cards. I challenge you to challenge them on their "story". (Which is also NFW, but I digress.)
As those that have tested with Atheros radios in the 5GHz band will probably know, if you don't put an antenna on the device, it sometimes won't connect even to other devices (also with no antenna) on the same table. We sometimes still get customers complaining that radios don't work in this form -- I think that is because we are all use to 2.4GHz radios that do happen to work with no antenna when on the same table. The point is, most Atheros mpci designs are better than others and have less RF leakage.
There is actually a lot of "RF leakage" if you're measuring in the right places, though this depends on what you call "a lot".
Will 2 (or more) cards work placed on the same board? Yes. We did a whole *BUNCH* of measurements (including things like conducted leakage across the PCI bus) on the Atheros designs at Vivato before we planted 6 (yes, 6) miniPCI cards into the 11g "switch" (oh wait, **basestation**) product. (That was my product.) I can state with some authority that 6 cards on the same board will work.
Note that all 6 run on the same channel, and there is a bunch of secret sauce that keeps any of them from transmitting while (any) one is receiving.
(One of the nice things about direct conversion is that its not as prone to injection locking as a super-het receiver.)
Your board lacks such logic (nor is it possible to completely perform the requisite functions from the PCI bus).
Therefore, if you have good pigtails and don't
mount/position the antennas close together, then you don't see a big enough problem to counter the benefits of the four or eight port setup.
There is no benefit to a 4 or 8 port setup (without a lot of additional work and materials).
Jim
John www.mikrotik.com
At 09:58 PM 9/29/2004, you wrote:
John,
I know you may disagree with what I'm about to say but using 8 radios that are physically spaced so close together is very likely going to lead to interference between the radios with consequent lost throughput.
If and only if the builder of an 8-radio system uses intelligent frequency planning (for example: Ch 1, 6, and 11 on 2.4 GHz and non-overlapping frequency selections on 5 GHz) will there be any chance of avoiding interference when the system is handling moderate-to-heavy traffic. Even then, it's going to take luck (and who can rely upon luck to secure their livelihood?) to keep the interference down and the throughput up.
My suggestion: Include advice and guidance on this topic in your documentation.
jack
John Tully wrote:
The eight port mpci to pci cards main use would be to easily use eight radios in you AP platform. This should be quite useful for multiradio APs with your choice of software.
John
www.mikrotik.com
RouterBOARD 18 -- 8 port mPCI to PCI board (Extreme)
http://www.routerboard.com/rb11.html#rboard18
(the back side has four ports also - tomorrow, both sides will be shown)
Price: $120 List
John www.routerboard.com www.mikrotik.com
-- Jack Unger - President, Ask-Wi.Com, Inc. Serving the License-Free Wireless Industry Since 1993 Author of the WISP Handbook - "Deploying License-Free Wireless WANs" True Vendor-Neutral WISP Consulting-Training-Troubleshooting Next 2-Day Hands-On WISP Workshop October 20-21 in Phoenix AZ [EMAIL PROTECTED] (818) 227-4220 http://www.ask-wi.com
