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breethon
EVDO Fledgling
Joined: 26 Sep 2006
Posts: 12
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 Posted: Sun Dec 10, 2006 6:46 pm Post subject: Signal vs. Speed question |
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I have an E815 Motorolla tethered to my pc and have an external amp/antenna hook up. I am receiving 67-73% signal and have consistent speeds of 450 kbps down and 90 kbps up. I am wondering if the extra 30% signal gain would help my speeds that much and/or improve latency? I know that there is normally high latency with EVDO, but curious if that gets better with a better signal?
Any thoughts are appreciated!
Thanks!  |
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n6gn
EVDO Junkie
Joined: 22 Aug 2006
Posts: 369
Location: Northern California
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| Posted: Sun Dec 10, 2006 11:14 pm Post subject: Re: Signal vs. Speed question |
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| breethon wrote: | I have an E815 Motorolla tethered to my pc and have an external amp/antenna hook up. I am receiving 67-73% signal and have consistent speeds of 450 kbps down and 90 kbps up. I am wondering if the extra 30% signal gain would help my speeds that much and/or improve latency? I know that there is normally high latency with EVDO, but curious if that gets better with a better signal?
Any thoughts are appreciated!
Thanks! |
MUCH more than signal strength goes into determing throughput. On top of that, the signal reading provided by the software may be questionable. Unless the person that implemented the software really knew what they were doing, it could be fairly misleading.
[see added note at bottom]
What truly matters to maximizing the potential speed of the lowest layer(s) is not signal strength but rather signal/noise ratio. While this *might* be reported by the software, it may also be that only the signal level at the detector is given. If adding an amplifier to your system causes your signal strength reading to increase dramatically, then almost certainly your software does not reveal signal/noise ratio.
This ratio is vital to supporting higher speed data transfer. As amplifier amplifies both signal and noise together. Unless it's noise figure is significantly lower than that of the un-aided handset or card, the ratio won't be particurlarly improved.
Even if there is plenty of signal/noise ratio a host of other things can impact speed. One important factor for EVDO is whether the tower/sector is being shared with another user. If that's the case, no improvement in signal will help.
There are also other factors like TCP/IP parameters and the application and device itself. It may be that data can't be 'digested' fast enough to keep up with the link with some applications and devices.
I see an almost 2:1 difference between my laptop/Noavatel card and my Treo 700P for maximum downlink speed... 1.2 Mbps vs about 700 kbps.
Latency is another complex issue. It has a relation to data rate, which can vary with signal strength, noise & interference. It may be affected by packet size. It can also be affected by sharing of the tower/sector as mentioned above.
You mileage will probably vary. Sorry if this wasn't the easy answer you hoped for.
n6gn
[edit]
In re-reading my answer I see I didn't address a significant part of your question --that of your particular signal strength indicator which gives per-cent rather than power level in dBm. This alone indicates to me a lack of understanding by the driver programmer. Since reveived power levels commonly span a range of more than one million to one, with everything but the bottom .001% or so giving the possibility of maximum link rate, levels are normally indicated with a logarithmic rather than a linear scale.
In the hardware, there is likely to be a logarithmic or semi-logarithmic RSSI detector which produces a voltage that is read by an internal ADC. This digital output is then reported by the software. Linearizing that logarithmic output, as evidenced by the per-cent display you have shows a lack of appreciation of thi fact. How it was interpereted and written and what it means is anybody's guess. I'd suggest that you poke around and see if there is a ##DEBUG# or other diagnostic available for your hardware that gives better information about the actual signal level. |
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chong67
EVDO Fledgling
Joined: 12 Jun 2006
Posts: 23
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| Posted: Wed Dec 13, 2006 10:51 pm Post subject: |
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I was at the Atlanta airport the other day and I get between 900kbp to 1100 kbps d/l tether with my Motorola Q. The bar show 3-4 signal strength. I can even see the same strength while inside the airport train.
At work and around any city, I get 300kbps-600kbps.
Hope that helps. |
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