What determines the speed of an USB dongle?

[marlboro]

What determines the speed of an USB dongle? E.g. Cell C have 2 different dongles, obviously both should work on 900MHz but one of them is advertised as maximum 7.2Mbps, the other 21Mbps. So what other specification on a particular modem one is to look for in order to determine the maximum speed?

[Lounger]

What determines the speed of an USB dongle? E.g. Cell C have 2 different dongles, obviously both should work on 900MHz but one of them is advertised as maximum 7.2Mbps, the other 21Mbps. So what other specification on a particular modem one is to look for in order to determine the maximum speed?

What about "receive diversity". That tells you the signal will be optimised. A lot of these dongles suffer from a bad signal, even on the biggest networks. The form change from a mouse-like device with a long USB cable to a dongle is primarily responsible.

[UnUnOctium]

What about "receive diversity". That tells you the signal will be optimised. A lot of these dongles suffer from a bad signal, even on the biggest networks. The form change from a mouse-like device with a long USB cable to a dongle is primarily responsible.

Receive diversity = multiple antennae at the receiver (aka dongle in this case). They usually use 2 since that's the optimal in terms of efficiency (Alamouti code). What you should look at is the HSDPA category of the device (http://en.wikipedia.org/wiki/Hsdpa#H....29_categories). The way these speeds are achieved is then dependent on whether they use receive diversity, different code rates, different constellation sizes, etc.

[RaeesD]

so let's say i have a 21.6Mbps dongle and i'm getting 7Mbps, will the 7.2Mbps dongle also get 7Mbps given the same signal strength? or is there a scaling factor involved?

[Cell_C]

What determines the speed of an USB dongle? E.g. Cell C have 2 different dongles, obviously both should work on 900MHz but one of them is advertised as maximum 7.2Mbps, the other 21Mbps. So what other specification on a particular modem one is to look for in order to determine the maximum speed?

Hi Marlboro

The dongles are physically different and have different chipsets in them. The specific chipset determines the features and speeds of the dongles. Our 7.2Mbps dongle (white) is capable of a maximum of 7.2Mbps DL and 5.76Mbps UL. The 21.6Mbps dongle (black) is capable of a maximum of 21.6Mbps DL and 5.76Mbps UL. Both are quad band and will work on all UMTS networks around the world.

[Cell_C]

so let's say i have a 21.6Mbps dongle and i'm getting 7Mbps, will the 7.2Mbps dongle also get 7Mbps given the same signal strength? or is there a scaling factor involved?

Hi RaeesD
Simple answer is yes - both will get 7Mbps. There is no scaling involved but the 21.6Mbps dongle is a little more efficient (better chipset) and also has an external antenna connector which can significantly improve data throughput.

[Jola]

...but the 21.6Mbps dongle is a little more efficient (better chipset) and also has an external antenna connector which can significantly improve data throughput.

Ah, thanks, then I can use this modem to replace my E272

[Jola]

Ah, thanks, then I can use this modem to replace my E272

I'm going to Durban this coming weekend, hope to pick it up there, assuming that Cell C launches there before the weekend.

[UnUnOctium]

Hi RaeesD
Simple answer is yes - both will get 7Mbps. There is no scaling involved but the 21.6Mbps dongle is a little more efficient (better chipset) and also has an external antenna connector which can significantly improve data throughput.

Damn, the rep got to it before me. As an added note on the replacement, by more efficient it means a few extra kbps, which can usually be thrown off by discrete component tolerances (analogue front-end) The only time you'll need the higher speed one is if your received signal strength (yes, improved by an external antenna) is high enough to warrant you getting anything higher than your current dongle's maximum HSDPA rate.