question on 2x operation (900MHz)

i’ve been operating all of my sm’s (900MHz) at 1x since i thought that all of the sm’s accessing an ap had to be running at 1x or all be running at 2x…

(i have several customers that were not able to run at 2x because of distance and whatever else)

today i installed an sm for a photographer who wants higher upload speeds than i allocate to everyone (25% upload 75% download on the ap)

i don’t have bam/prizm because we are fairly small and can’t justify the cost…

so, i’ve been going back through the manuals to see how i can give this guy more upload bandwidth without changing the download rate (or upload rate) for the other customers…

i noticed something i didn’t see before (at least i think this is correct)… that i can set (leave) all of the other customers at 1x, and change the photographer’s sm to run at 2x (i’d also have to enable 2x on the ap)…

am i understanding this correctly?

i want to be sure because all of the sm’s that i have out there have 2x set to “enabled” and i just have it disabled on the ap… it will take a while to change all of the other customers to 1x…

will he notice much of a change in his upload speed?

i also read that if a connection can’t sustain 2x speed it will fall back to 1x… i guess that would mean that i wouldn’t have to change anything but enabling 2x on the ap, but, i would rather keep the ones running well at 1x to keep running well at 1x rather than have some out there that are fluctuating between 1x and 2x constantly…

that all said, is this the way to go, or is there a better option? (no, bam/prizm isn’t an option)

thanks for any input…

You are correct, if you enable 2x on the Ap he is connected to and enable 2x on his SM only, and leave everyone else at 1x, you will surely increase his upload and download rates, maybe double them. You could also enable high packet prioritization on your router for this client in the Vlan he is on and again increase his bandwidth.
If his link to the AP isn’t stable at 2x it will run at 2x/1x or vise versa.


One thing to keep in mind you’ll need to make sure that the client has very good signal at least 15-20db better then the noise floor. So If your noise floor is -90 then the client is probably gonna need a -75 or better to sustain the 2x rate and get maximum bandwidth.

We run everyone on 2X and switch to 1X if there is alot of re regs. It seems that for 2X you have to have LOS and at least -75db or better otherwise you will have packet loss.

agreed with WFN… moto has told us it is much better to run everyone who can in 2x mode.

Also agreed. You can actually reduce the radio traffic by enabling 2X. It sounds backwards, but here’s why:

From page 93 in the v8 manual:

Competition for Bandwidth
When multiple SMs vie for bandwidth, the AP divides its bandwidth among them, considering their effective CIR and MIR values. However, 2X operation uses bandwidth twice as efficiently as 1X, even where MIR values apply. This is because, in 2X operation, the modules transmit their data in 4-level frequency shift keying (FSK), not 2-level as they would in 1X operation. This moves twice the data per slot. Thus, for the sum of all bandwidth that 2X-eligible customers use, the bandwidth available to the remaining customers increases by half of that sum when these eligible customers are transmitting and receiving in 2X operation.

You have a limited amount of radio airtime to transmit data. Let’s say it looks like this:


Take any average activity; for example, viewing a big web page of about 100K. In 1X, the 100K download takes this much radio airtime |------|.

In 2X, the same 100K will only take this much |—|, leaving radio airtime open for others to use.

From page 92 in the v8 manual:

Although subscribers with Canopy SMs realize higher bursts, and subscribers with Advantage SMs realize both higher burst and higher sustained throughput, the network operator realizes higher sector throughput capacity in the AP.

The other main thing to remember, as mentioned above: you must have the extra fade margin available, as the 2x 4FSK modulation is less able to withstand interference than the 1x 2FSK is.

Make sure you take advantage of the manual, it really is an excellent resource!

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