Do you know a way or additional configurations that can prevent or the above problem?

You can use ATPC feature available in Canopy/Alvarion to keep SMs below a maximum SNR value which allows the weakest SM on the opposite sector to operate with reasonable SNR.You can also manually reduce TX power output for strong signal SMs ... which are usually at close range and aim towards the center of the AP's sector antenna beam pattern. :)

P.S. The best technical solution requires implementing system-wide scheduling so that SMs transmitting in the same time slot provide similar rssi values at their APs by adjusting their transmit power per slot.]]>

"The only problem that can happen in TDMA systems is a very strong SM in one sector swamping a very weak SM beam in the directly opposite sector. Think about the short fat red arrow SM directly opposite one of the long thin red arrows on tower 2."

Do you know a way or additional configurations that can prevent or the above problem?]]>

Thanks Lutful... The green colors are facing to each other you think it will work that way? i am assuming that the green color are on the same polarity and same freq.

Yes, same color means same channel and polarity. SM antennas are usually more directional and there is no problem even if beams of same frequency and polarity cross each other while going to different APs.The only problem that can happen in TDMA systems is a very strong SM in one sector swamping a very weak SM beam in the directly opposite sector. Think about the short fat red arrow SM directly opposite one of the long thin red arrows on tower 2.

I drew some arrows to show how you could assign same SM to different APs in the various frequency zones. The general goal of frequency allocation and sector antenna orientation is to maximize SM-to-AP pairing options. You will notice that the green frequency zone is actually the largest and most flexible. :)]]>

The statements are based on throwing out the advantages of ATPC, GPS sync, and every benefit given by Motorola.

Ok, so you are saying that lutful was incorrect when he statedRegarding your current setup, even if you don't see any problems right now running same freq (5730) on 3 adjacent sectors of tower 3, eventually there would be issues with some SMs for exact same reason: strong/weak rssi SMs falling on same slot. Adding 5730 on the 4th sector would only increase the probability.

That entire statement is incorrect.

It would help if you were a little more definitive. Out of the three paragraphs could you quote the incorrect statement?]]>but i really want to cover the whole area using the 3 towers using 3 freq.

Here is a quick sketch using all 3 frequencies on each of your 3 towers. Of course Canopy setups use same frequency and polarity on opposite sectors all the time but I showed dotted red lines to indicate where using opposite polarity would eliminate potential problems with some SMs.The simple reason is that a very strong rssi SM on one side could swamp a very weak rssi SM on the other side. For example a -45dBm SM talking on one side while the opposite side is trying to detect a -70dBm SM.

Regarding your current setup, even if you don't see any problems right now running same freq (5730) on 3 adjacent sectors of tower 3, eventually there would be issues with some SMs for exact same reason: strong/weak rssi SMs falling on same slot. Adding 5730 on the 4th sector would only increase the probability.]]>

i dont have any problem with my PTP. i have a separate Freq. for that. ]]>

Tower 1 and 3 appear to have 3 APs only?]]>

above is my current setup and i dont have any problem with my setup. but i really want to cover the whole area using the 3 towers using 3 freq. ]]>

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Strange as it seems, no amount of learning can cure stupidity, and formal education positively fortifies it. -- Stephen Vizinczey]]>

3 towers in straight horizontal line that a triangle setup.... My plan is 2 channel per tower, A/B A/C B/C ...

If the towers are close together, both APs of the middle tower may see higher noise when communicating with SMs towards the edge. ]]>Using all three available frequencies at each tower to maximize his total wireless network capacity is just another option. :)

Until such time that the OP gives us more details, it is mostly conjecture.

--

Strange as it seems, no amount of learning can cure stupidity, and formal education positively fortifies it. -- Stephen Vizinczey]]>

he wants to run four sectors but he wants to run all four sectors on the same frequency.

Yes, he wanted to do that but obviously that won't work very well even with GPS sync and excellent front-to-back ratio sector antennas.There would be interference contribution from 3 SMs (belonging to the other 3 APs) in every time slot. When some or all of those SMs are located at shorter distance from the tower than the target SM, noise may rise above expected RSSI.

People already suggested using a single omni antenna or 2x 180 degree sectors or a 1:4 splitter at each tower to meet his original desire to run one frequency per tower.

Using all three available frequencies at each tower to maximize his total wireless network capacity is just another option. :)]]>

He really wants to run 4 sectors on each tower and he wants to use all 3 frequencies available to him.

Not quite. Yes, he wants to run four sectors but he wants to run all four sectors on the same frequency. He wants each tower to have its own frequency.As for the distances between the towers, they are not a factor under his current config since each tower has a unique frequency. It only becomes relevant if he decides to use the same frequency on more than one tower. Then the placement must take into consideration all factors.

There are so many permutations possible that it is senseless for me to post sketches based on conjecture. Maybe the towers are all on the periphery and no SMs would see two or more towers? J/K

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Strange as it seems, no amount of learning can cure stupidity, and formal education positively fortifies it. -- Stephen Vizinczey]]>

The multiple tower scenarios are all conjecture since the OP did not say where they are situated relative to each other.

The exact distances between towers (AB/BC/CA) will not make much of a difference since the 3 towers are located 1-2km from each other. He really wants to run 4 sectors on each tower and he wants to use all 3 frequencies available to him.My suggestion on previous page is a good setup considering all known factors. If you disagree, post a sketch showing what sector/frequency allocation may work better. :) ]]>

The multiple tower scenarios are all conjecture since the OP did not say where they are situated relative to each other.

I think the other SMs and other towers are not contributors to the problem. The SM sees two APs on the same tower, both with about the same signal strength, both on the same frequency and polarity.

Instead of trying to get four APs on a tower, all on the same frequency, he should try only using the same frequency on back-to-back APs, so two frequencies per tower. Of course then the two other towers come into play so he needs to plan his frequency reuse between towers as well.

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Strange as it seems, no amount of learning can cure stupidity, and formal education positively fortifies it. -- Stephen Vizinczey]]>

I stand behind your diagram being incorrect for the application.

You could draw a correct diagram for this application? If it uses same frequency in same direction, you will have to consider the scenario shown above.Its hard to remember who understands canopy and not with the flood of the UBNT noobs.

P.S. If you search my old posts for TDMA and FPGA, you will see references to a radio platform (my company) designed in 2004 before Canopy added FPGA and a Canopy clone with better spectrum sharing features in 2006. I disclosed recently that (my new company) has developed a TDMA system designed from scratch for HD IPTV delivery.]]>

That being said, I stand behind your diagram being incorrect for the application.]]>

Apples and oranges. We are dealing with Canopy in this application. Throw everything you know about 802.11 out - it doesn't apply.

I do understand how Canopy (gps) sync actually works and the gotchas. The sum of the received power from other sectors may swamp an AP because SMs also transmit at the same time. :)P.S. I recall you participated in this 2010 Canopy thread.

»Argh! What is doing this?!]]>

This is how we can run six 60 degree 900mhz sectors per tower with only three non-overlapping frequencies. It is also how channels can be used over and over and over again.

To the OP: The question still hasn't be answered if your towers are correctly GPS sync'ed. Based on your questions I would guess not so I would suggest a starting point of posting a simple diagram of your network along with your dl%, control slots, and range/distance settings per tower and exactly how you do GPS sync per tower.]]>

The diagram, while it is helpful on a non-canopy setup, really doesn't apply to the OP's situation.

The diagram, while it is helpful on a non-canopy setup, really doesn't apply to the OP's situation.]]>

we dont have enough freq. we are allowed to use only 3 frequencies but we have 3 Towers... 1 to 2 mile apart.

If you must have 4 sectors per tower, have a look at above sketch for some ideas on how to orient the sectors to minimize interference from same frequency AP on another tower.]]>

This way, you can use the other two towers for other freqs, if you want.]]>

Lets take a step back.

Why do you feel the need to use one frequency? Post some screen shots of your spectrum analysis.]]>

If you really really want to run 4 separate APs on a single tower ... there is only one reasonable solution to minimize the interference.

Change the polarization of 2 of the APs and their SMs. So opposite APs run same polarization while adjacent APs run opposite polarization. :)

Change the polarization of 2 of the APs and their SMs. So opposite APs run same polarization while adjacent APs run opposite polarization. :)]]>

im sorry what we want is a 360 coverage using 1 freq.

you can do it with a single AP and and omni antenna. ]]>

i hope that there is a way to solve my problem.]]>