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Some considerations for selecting the right WiFi device for your wireless network

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Old 06-02-2003, 12:11 AM   #1
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Some considerations for selecting the right WiFi device for your wireless network

1. brand, and of course price – depending on how deep is your pocket: there are the branded and upmarket (Cisco, 3Com, Proxim, Orinoco etc.), the good value, tried and tested (Linksys, Dlink, SMC etc.), the cheap and unexplored (Enzer, Mercury, Fulbond etc.)

2. overall quality – packaging, finishing, reliability etc.

3. supports –driver/utility software/firmware, user friendliness, ie. ease of installation/configuration, security features, customer supports.

4. forms, fits and functions – to meet networking requirements, usage profiles and system configurations.

5. hearsay – just post here in the forum, ask the forum’s opinion on brand xxx model yyy, and start to count the votes.

6. lastly, but in my opinion, the most importantly, the wireless link performance in meeting the needs of the networking environment.

Will discuss in the following postings about wireless link performance considerations, including free space radio wave propagation calculation for range/path loss, effects of building structure to indoor WiFi (IEEE 802.11B) link performance, eg. reduction of signal strength by walls, floors, doors, windows etc.
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Old 06-02-2003, 12:29 AM   #2
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tried and tested enzer's wireless router and pcmcia cards ... they sucked big time ... range was poor and i could neverf get it to work properly with my scv. when it did, browsing the web alone was heaps slower than dialup.

i've got them replaced with the linksys models ... the linksys wireless router and pcmcia cards were surprising. They flawlessly worked out of the box and with a firmware upgrade, the range improved somewhat ... i'm getting excellent (100%) signal strength and link quality even when the router is next door. directly one level down in the dining area, i'm still getting good reception (45~50%) and downloads are at full speed (180~200+ KB/s)

go for the wireless linksys routers and pcmcia cards (v.3) as they have been tried and tested.
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Old 06-02-2003, 02:16 AM   #3
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RF power measurement

basic unit for power measurement:
1. watt (w)
2. milliwatt (mw)
3. 1 watt = 1000 milliwatts

gain/loss of any analogue/RF system is best expressed by db = decibel, in log scale, to simplified computation.

Gain/loss (db) = 10log(base 10) P2/P1 where P1 = power input, P2 = power output

Eg. P2 = 10w, P1 = 5 w gain (db) = 10 log 10/5 = 10 log 2 = 10 x 0.3010 = 3 db
P2 = 100w, P1 = 1w gain (db) = 10 log 100 = 10 x 2 = 20 db

Most IEEE 802.11B WiFi equipment work in the milliwatts transmission power range
Using 1 mw as a base power unit in db scale:
10 log (1mw) = 0 dbm, or 0 db(mw)

all power values can be converted to dbm unit:

5 mw = 10 log 5mw/1mw = 10 log 5 = 10 x 0.69897 = 7dbm
10 mw = 10 log 10mw/1mw = 10 log 10 = 10 x 1 = 10 dbm
20 mw = 10 log 20 = 13 dbm
32 mw = 10 log 32 = 15 dbm
50 mw = 10 log 50 = 17 dbm
100 mw = 10 log 100 = 20dbm

to compute gain using dbm power level:

P2 = 20 mw (13 dbm) , P1 = 10 mw (10dbm)
Gain (db) = 13 dbm – 10 dbm = 3 db
Same as 10 log 20/10 = 3 db


........to be continued..........
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Old 06-02-2003, 02:45 PM   #4
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Computing wireless link gain/loss

It is easy to compute radio link gain (amplification) or loss (attenuation) using the db (logarithmic) scale.

0 db = unity gain (no change) => 10 log 1 = 10 X 0 = 0db
3 db = 2 times gain => 10 log 2 = 10 x 0.3010 = 3 db
6 db = 4 times gain => 10 log 4 = 10 x 0.6 = 6db
10 db = 10 times gain => 10 log 10 = 10 x 1 = 10 db
20 db = 100 times gain => 10 log 100 = 10 x 2 = 20 db
30 db = 1000 times gain => 10 log 1000 = 10 x 3 = 30 db
40 db = 10000 times gain => 10 log 10000 = 10 x 4 = 40 db

-3 db = ½ (signal reduced to ½) => 10 log (1/2) = 10 x (-0.301) = -3db
-6 db = ¼ (signal reduced by 4 times) => 10 log (1/4) = 10 x (-0.6) = -6 db
-10 db = 1/10 (10 times reduction) => 10 log (0.1) = 10 x (-1) = -10 db
-20 db = 1/100 (100 times reduction or attenuation, or loss in signal strength)

example 1: a signal of 10 dbm going through a 3 db amplifier

output signal = 10 dbm + 3 db = 13 dbm

example 2 : a signal of 20 dbm going though a wall with -6 db attenuation

signal received after the wall = 20 dbm – 6 db = 14 dbm

table below shows effect of various materials on radio wave attenuation for the 2.4 GHz signal use by IEEE 802.11B WiFi

Air (low) - will discuss later free air attenuation
Building Stones (moderate) - eg. wooden Partition (-2 db)
Gypsum (moderate) - eg. partition wall (-2 db)
Composite Material (moderate) - eg. Plywood Partition (-2 db)
Asbestos (moderate) - eg. Ceiling (-3db)
Glass (moderate) - eg. window pane, Wall (- 4 db)
Water (moderate) - eg. wet Wood (-5 db)
Brick (moderately high) - eg. brick wall (-6 db)
Marble (high) - eg. wall (-10 db)
Cement Concrete (high) -eg. floor, wall (-10 db)
Bulletproof Glass (high) - eg. sentinel cabin (-15 db)
Iron (very high) - eg. partition, reinforced concrete wall (-25 db)


.......to be continued.......

Last edited by wirelessdan2002; 06-02-2003 at 03:15 PM..
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Old 06-02-2003, 05:12 PM   #5
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Free space radio wave propagation

Path loss (PL) = attenuation of radio wave through free space (line of sight) as a result of range increase

PL (db) = 32.44 + 20 log (F) + 20 log (D)
F = radio frequency in GHz, D = distance in meter

Example: a WiFi link at 2.4 GHz over a range of 100 meter

PL (db) = 32.44 + 20 log 2.4 + 20 log 100 = 80 db

If an access point transmitting 20 dbm at point A, the power received at point B which is 100 meters away with no other obstruction

20 dbm – 80 db = -60 dbm

if there is a concrete wall in between, another 10 db attenuation

20 dbm – 80 db (PL) – 10 db (wall attenuation) = -70 dbm

........to be continued..........
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Old 06-02-2003, 08:00 PM   #6
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Receiver sensitivity and range computation

So far we only talk about transmitting power and how it is being attenuated through free space propagation + all other obstacles.

An equally important factor of how good a wireless link perform is the receiver sensitivity, or how low a signal the receiver can receive and still be able to clearly read the data sent, in more technical term, that the receiver still have 12 db signal to noise (S/N) ratio, or the signal is 16 times that of the noise being received.

Most Wifi products have receiver sensitivity in the region of -80dbm to -90dbm, ie. 0.00000001 mw to 0.000000001 mw, or 0.00001 microwatts to 0.000001 microwatts, or 0.01 nanowatts to 0.001 nanowatts ļ now you probably understand why dbm scale is used to work around RF power.

To compute how far can a wireless link go, lets take the Linksys WUSB11 USB adapter as transmitter, and WPC11 PCMCIA adapter as receiver. The WUSB11 has a transmitting power of 15 dbm, while the WPC11 sensitivity is -82 dbm.

the transmitter now has a 97 db margin over the receiver

15 dbm - (-82 dbm) = 97 db

in determining a robust wireless link, a fade margin of 20 db is usually introduced to cater for other environmental factors like weather, pressure, other transmission sources nearby and temporary obstacles introduced. Therefore in this case the usable margin is:

97 db - 20 db = 77 db = maximum allowable path loss.

Using the free space path loss formula:

PL (db) = 32.44 + 20 log (F) + 20 log (D)
77 = 32.44 + 20 log (2.4) + 20 log (D)
77 = 32.44 + 7.6 + 20 log (D)
20 log (D) = 37
log (D) = 1.85
D = 75 meters

Therefore in a free space transmission (line of sight), the Linksys pair of adapters has a range of 70 meters.

..........to be continued.........
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Old 07-02-2003, 01:42 AM   #7
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Indoor WiFi Link Budget consideration – a case study

Link budget = transmitter power – receiver sensitivity

Link budget must be enough to overcome:

Path loss (maximum range) + attenuation from all obstacles + fade margin (12db)

Example: a typical 3 bedroom apartment
Maximum distance from 2 corners : 15 meters
Maximum number of walls between any 2 points : 2 brick walls + 1 concrete wall

Path loss (20 meters free space)= 32.44 + 20 log 2.4 + 20 log 15 = 32.44 + 7.6 + 23.5 = 63.5 db
attenuation of 2 brick walls and 1 concrete walls = 12 db + 10 db = 22 db

minimum link budget required = 63.5 + 22 + 12 = 97.5 db

using Linksys BEFW11S4 as transmitter and WPC11 as receiver:

RF power of BEFW11S4 = 18 dbm
Sensitivity of WPC11 = -82 dbm

Link budget available = 18 dbm - (-82 dbm) = 100 db > 97.5 db

Conclusion: Linksys BEFW11S4 and WPC11 combination is able to meet a typical 3 bedroom apartment WiFi need.


.........to be continued...............
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Old 07-02-2003, 10:04 AM   #8
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Specifications of selected WiFi products

Access point

Linksys WAP11 power 18 dbm sensitivity -82 dbm
SMC 2655W power 20 dbm sensitivity -84 dbm
Dlink DWL-900AP+ power 15 dbm +/- 2 sensitivity -84 dbm
Cisco Aironet 340 power 15 dbm sensitivity -83 dbm
Cisco Aironet 350 power 20 dbm sensitivity -85 dbm
Enzer EWA122 power 16 to 18 dbm sensitivity -85 dbm
Enzer EWA311 power 16.5 dbm sensitivity -85 dbm
Fulbond XI-1250A power 20 dbm sensitivity -84 dbm

AP/router

Linksys BEFW11S4 power 18 dbm sensitivity -84 dbm
SMC 7004VWBR power 17 dbm sensitivity -80 dbm
Dlink DI-614+ power 15 dbm +/- 2 sensitivity -84 dbm
Fulbond XI-2300H power 20 dbm sensitivity -86 dbm
Enzer EWR884P power 16 dbm sensitivity -85 dbm
Senao SR2511SR+ power 23 dbm sensitivity -87 dbm

USB Client

Linksys WUSB11 power 15 dbm sensitivity -82 dbn
Orinoco USB Client power 15 dbm sensitivity -82 dbm
Netgear MA101 power 13 dbm sensitivity -84 dbm
Dlink DWL-120 power 19 dbm sensitivity -84 dbm
Enzer EWU311 power 17 dbm sensitivity -84 dbm
Fulbond XI-725USB power 15 dbm sensitivity -85 dbm
Senao SL2511UB power 15 dbm sensitivity -83 dbm

PCMCIA Client

Linksys WPC11 power 15 dbm sensitivity -82 dbm
Dlink DWL-650+ power 15 dbm sensitivity -84 dbm
Orinoco Silver power 15 dbm sensitivity -82 dbm
Cisco 342 power 17 dbm sensitivity -83 dbm
Cisco 352 power 20 dbm sensitivity -85 dbm
Enzer EWM311 power 16.5 dbm sensitivity -84 dbm
Fulbond XI-325H power 20 dbm sensitivity -85 dbm
Senao SL2511CD+ power 23 dbm sensitivity -87 dbm


………to be continued……..
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Old 12-02-2003, 04:06 AM   #9
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Some really good buys, and some not so good....

these are products that i have used without any problem, and real value for money, in my opinion.

Linksys BEFW11S4 4-port wireless router - $227, good quality finish, extremely user friendly, works out of the box most of the time. output 18 dbm (60 mw).

Linksys WAP11 access point - $250, 18 dbm output

Linksys WUSB11 USB adapter - $126, usual Linksys quality finish, user friendly, output 15 dbm (30 mw)

Linksys WPC11 PCMCIA adapter - $98, again good finishing close to the upmarket Cisco's client products, 15 dbm output.

Dlink DWL-120 USB adapter - $135, good finishing close to that of Linksys, but having the strongest output of 19 dbm (80 mw) among all USB adapter, mean almost 60% longer range than the Linksys WUSB11.

Enzer Skyroam Silver PCMCIA card - $79, cheapest PCMCIA WiFi adapter around, yet has commendable finishing, and higher power output than the Linksys WPC11, at 16.5 dbm (45 mw), translating to 20% more range.

Cisco Aironet AP352E2C access point - Rolls Royce of WiFi products, unparalleled finishing and quality, power output of 20 dbm (100 mw), used in most hot spots. at $1000, it is not real value for money, but for people who can afford it.

Cisco Aironet 342 PCMCIA card - possible to get it at $120, which will be a good value consider its brand name, quality, user friendliness as well as the 17 dbm (50 mw) output.

Cisco Aironet 352 PCMCIA card - $250, but some will pay for its quality and 20 dbm (100 mw) output, which means 70% longer range than the Linksys WPC11's 15 dbm output.

Orinoco Silver PCMCIA card - price has dropped to $129 from almost $200, if Cisco is the Rolls Royce of WiFi, and Linksys is the honda, then Orinoco is the Mercedes. a plus point is its ability to support also Linux and Mac OS. 15 dbm output.

Orinoco Silver USB client - price has dropped to around $160, support all OS, good quality and 15 dbm output.

Mercury KL-470 4-port wireless router - at $180, probably the cheapest 4-port wireless router in the market. can't compare its quality with that of the Linksys, but it does its job dutifully, easy setup, performs convincingly with output of 16 dbm.

some products which i am keen, and will be trying them out soon:

Fulbond XI-1250A - at $169, the cheapest access point with 20 dbm (100 mw) output, i.e. 25% longer range than the Linksys WAP11.

Senao SL2511SR plus 4-port wireless router - at $250, it is the highest output wireless router with 23 dbm (200 mw) output available locally, means 805 longer range than the Linksys BEFW11S4, good for multi-storey home.

Senao SL2511Cd plus PCMCIA adapter - $145, with 23 dbm (200 mw ) output, highest output of any PCMCIA WiFi adapter, 125% longer range than the Linksys WPC11, but guess it will reduce notebook battery life by quite a bit, still, worth a try to be how far it can go.

some products to avoid for now, until they are being improved"

Mercury USB adapter - cheap at $99, but the utility program causes USB device conflict under WinME.

Planex (PCI) USB adapter - $109, utility program cannot work properly in WinXP.

SMC USB adapter - $125, no utility program for WinXP, need to use WinXP built-in utility whch is not user friendly in its current version.

SMC PCMCIA adapter - $95, same as its USB adapter, no utility for WinXP.
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Old 12-02-2003, 11:21 AM   #10
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Originally posted by CCITT
Thanks for your great effort, enlightening, maybe we can use this thread to exchange our experience with wireless network setup.

To all the moderators: can we make this thread a sticky thread?
haha, guess no point, as most forumers are probably too busy to read all these heavy stuff.

thanks anyway.
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Old 12-02-2003, 12:42 PM   #11
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can anyone tell me, why is it that most people are using the 802.11B network routers or acess point, but no one is using the 802.11G based? i thought 802.11G is suppose to be better? pls correct me...i very green in these stuff.
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Old 12-02-2003, 02:20 PM   #12
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Originally posted by Theoden
can anyone tell me, why is it that most people are using the 802.11B network routers or acess point, but no one is using the 802.11G based? i thought 802.11G is suppose to be better? pls correct me...i very green in these stuff.
firstly 11G product is still in its infancy period, the cost is still very high, at 3 to 4 times the price of 11B's. you pay only $100 for a 11B PC card, but more than $300 for a 11G PC card,

next, 11B's data transfer rate of 11Mbps is more than enough for most of us, the DSL downstream is only 512 Mbps, so 11 Mbps is already more than 20 times of the DSL speed. even for files transfer, you can transfer a 4 MB MP3 files in 5 seconds, with the 11 Mbps speed.

so, unless you really have lots of extra money to spend, common folks like us don't need the 11G.

just an analogy: with our road speed limit of 90 KMPH, i am happy with my Toyota, it can bring me from Changi Airport to Raffles Country Club in 35 minutes. do i need a Ferrari, which may be able to do the same job within 30 minutes (not breaking the law), but it costs 6 times more?
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Old 12-02-2003, 05:47 PM   #13
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hehe, i get wat u mean...i thought if can get 11G for future expansion mah. well, u noe how technology advances really shock us.
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Old 12-02-2003, 11:10 PM   #14
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Originally posted by wirelessdan2002


firstly 11G product is still in its infancy period, the cost is still very high, at 3 to 4 times the price of 11B's. you pay only $100 for a 11B PC card, but more than $300 for a 11G PC card,

more?

the price of the pc card is only $126++ at www.buy.com

http://www.buy.com/retail/computers/....asp?loc=16749
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Old 13-02-2003, 12:45 AM   #15
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Originally posted by sharon



the price of the pc card is only $126++ at www.buy.com

http://www.buy.com/retail/computers/....asp?loc=16749
thanks for enlightening, guess we will see more downwards pressure for the 11B products.
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