View Full Version : wlan difficulty

02-22-2005, 01:12 PM
i am working on a proj to build wlan transceivers which is to be fullfilled in 45-50 days
the overview of the project is--- a pc is connected to onewlan transceiver through a rs232 port. this transceiver has to setup a wlan link with another wlan transceiver conected to other pc thru rs232.

:?: wat is the data rate i can achieve between rs232 and PIC microcontroller and pls tell me how in short
:?: wat is the data rate i can achieve between two transceivers(the rf module is to be build by me only)
:?: also tell me where can i get qpsk rf modules or is there some good and eay circuit using some specific chip

pls help me out

02-22-2005, 09:54 PM
Rs 232 can give you a max speed of 115200 baud between pic & the UART

You may include software that can set speeds of upto 56 Kbps...but its unlikely you'll get even close on a wireless link....try 9600 bps....for starters

you can used a combination of many logic chips or a second mcu + obiviously some VCXO ( for a carrier costs around Rs 100/- per pc), to genereate the QPSK

02-23-2005, 01:14 AM
:D vidur i got ur first point but i m a bit confused :!: on wat r u trying to tell in the next point ?
can u be a bit more clear on wat r u intending to xplain?

02-23-2005, 10:04 AM

YOu'll probably use some sort of modulation like PSK, QPSK , AM or FM for your radio link right.....many systems like commercial modems use circuits that can change between many modulation techniques depending on channel noise conditions.....
They use complex modulation like QAM-16, QPSK etc.etc

If you've used PSTN internet connections in India....you know what i mean...sometimes you get very low conn. speeds...sometimes very high....

so depending on the type of modulation u use , you get different speeds of actual communication....for eg in QPSK the actual speed is twice the baud rate

Alternatively you can adjust your speed ( Baud rate) by software written in the PIC, that can set specific bits in the UART to achieve this

If you want to keep things simple, use simple AM/FM link with a fixed baud rate....say a modest 9600 bps as i said earlier...its good enough for a bot

-> you can change communication speeds using QPSK,M-ary PSK etc...do this only if you've handled comm. projects before

->you can change comm. speeds ( Baud rate) by programming bits in te UART

->for starters dont try to hog up everything in one go...try a simple BPSK, AM,FM link , use a low baud rate....if sucessful, re-program the UART to higher speeds & so on

I hope this helps....do write in again for more detailed help...