help me understand some terms

Post new topic   Reply to topic    DD-WRT Forum Forum Index -> Broadcom SoC based Hardware
Author Message
Zachariah
DD-WRT Novice


Joined: 01 Aug 2006
Posts: 20
Location: Earth

PostPosted: Tue Aug 01, 2006 22:27    Post subject: help me understand some terms Reply with quote
What is good/bad for these:

(ie, do I want a high number or a low one
... and please say whether high means closer to zero
or higher ignoring the negative sign).

Signal
Noise
SNR
Signal Quality

(from http://192.168.1.1/Status_Wireless.asp)


(and, yes I looked in the wiki and did multiple searches, but didn't find the answer)


edit: ... forgot to say thanks, but don't feel like bumping the thread just for that

_________________
mozilla!


Last edited by Zachariah on Sun Sep 24, 2006 14:02; edited 1 time in total
Sponsor
CaScAdE
DD-WRT Guru


Joined: 18 Jun 2006
Posts: 1110
Location: Kiel (54.4247,10.1721)

PostPosted: Tue Aug 01, 2006 22:57    Post subject: Reply with quote
Signal -> Low is good (well -1 is good, -98 is bad, mathematically -1 is higher than -98 but you know what i mean because you asked for ignoring the minus)
Noise -> High is good (-98 is good, -1 is bad)
SNR -> High is good (should be the same as difference between noice and signal)
Signal Quality -> High is good (somehow like SNR but indexed to 100 with noise as base, percentage of the best theoretical available qualiry regarding to your local-noise, difficult to explain *g*)

Edit:
Regarding to one of my WRT's I will state an example, keep in mind that some numbers are rounded for output by the driver but internally kept with some more decimal places...
Examples would be:
Code:
Signal  Noise  SNR  Signal Quality
-82     -98    16   14%

Signal - Noise = SNR
-82    - -98   = 16

Signal/Noise * SNR = Signal Quality
-82   / -98  * 16  = 13.4% 

_________________
DD-WRT F.A.Q.

Webcam Kiel


Last edited by CaScAdE on Mon Aug 21, 2006 9:34; edited 2 times in total
AndyD
DD-WRT Novice


Joined: 08 Jun 2006
Posts: 29

PostPosted: Tue Aug 01, 2006 23:20    Post subject: Reply with quote
Good question...well answered.....thnx Smile
votetrev
DD-WRT Novice


Joined: 09 Jun 2006
Posts: 2

PostPosted: Mon Aug 21, 2006 19:33    Post subject: Reply with quote
Yeah, Great answer!
Sacrabolt
DD-WRT Novice


Joined: 06 Jul 2007
Posts: 22

PostPosted: Thu Nov 08, 2007 10:29    Post subject: Reply with quote
CaScAdE wrote:

Examples would be:
Code:
Signal  Noise  SNR  Signal Quality
-82     -98    16   14%

Signal - Noise = SNR
-82    - -98   = 16

Signal/Noise * SNR = Signal Quality
-82   / -98  * 16  = 13.4% 


I can't figure out how it works; say we have ...
S=-30 N=-98
SNR=68
Signal Quality = S/N *SNR = -30/-98 * 68 = 20.8

S=-20 N=-98
SNR=78
Signal Quality = S/N *SNR = -20/-98 * 78 = 15.9

where am I wrong?
dicksons
DD-WRT Guru


Joined: 07 Jun 2006
Posts: 980
Location: Coal Creek Canyon, Colorado

PostPosted: Thu Nov 08, 2007 20:09    Post subject: Reply with quote
negative numbers and logarithmic ratios leave a lot of people in the dust...

SNR is all you really care about (unless it's really low like below 10, in which case signal and noise need examined for optimization)

double-digit SNR will get you megabit thruput

I've seen a table somewhere detailing the SNR required to hit specific 802.11G link speeds (btw link speeds <> thruput)

the "percentage" isn't meaningful in practical terms - it only exists cause it's easy to graph. ignore it.

_________________
linksys GSv2, Gv4, Gv2, GLv1, G-TM, Buffalo wbr2, whr, whr-hp, whr-g125, wli-tx4-g54hp, Moto wr850gp, Alix.3C2
deneb
DD-WRT Novice


Joined: 06 Nov 2007
Posts: 5

PostPosted: Fri Nov 09, 2007 7:35    Post subject: Reply with quote
To elaborate a little, any number with dB after it means it is on a logarithmic scale. To get the SNR you would divide signal by noise, right? Well, yes, but remember that when working in a log scale you are basically dealing with an exponent, so where you would divide:

SNR = n^SIGNAL / n^NOISE

in regular, non-log world, you actually end up subtracting the exponents. Try it:

2^8 / 2^6 = 256/64 = 4 = 2^2 = 2^(8-6)

This is what you must do in log world to get your ratio, i.e. to get SNR from numbers in dB simply subract them:

SNR (dB) = SIGNAL (dBW) - NOISE (dBW)

Also, when a dB number is negative, that means it is less than 1:
0dB = 1
-1dB = a little less than 1
-99dB = almost 0

so you want your signal to be close to 0dB and your noise to be close to -99dB or lower

This brings me to my question, what does the noise reference setting do? Is this just used to calculate that useless percentage for signal strength?
Display posts from previous:    Page 1 of 1
Post new topic   Reply to topic    DD-WRT Forum Forum Index -> Broadcom SoC based Hardware All times are GMT

Navigation

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You can attach files in this forum
You can download files in this forum