Wifi based Radar?

[tobol.7uno]

I want to hack a wifi router somehow so that I can reprogram it to act as a radar. Emitting a signal for a microsecond and listening for returns and measuring their intensity. I dont know if the hardware in a router is fast enough for this or if it is possible to find an API or something to reprogram the router. I already posted this in another thread but I think this is a better match. Thanks ahead of time!

 

[Diver300]

I don't think that you have much chance of getting that to work.

The return signal will be extremely confused, as you will get bounces of everything.

If you have a very directional aerial, you might get something to work, but to get a 2 dimensional picture, you will need a rotating antenna, or very clever use of several antennas in something like a Netgear Rangemax.

Also, the power of a router is rather low for radar work. A 1 microsecond pulse is 300m long in free air, so if you emit a 1 microsecond pulse and look for returns on a 1 microsecond resolution, you are looking for objects around 150 m large, starting about 150m away from you. I doubt that Wifi can get that far and back as the return loss from a random object is huge.

I think that Wifi is limited to 1 W, so you won't get much more than that from a router. Marine radar starts at 4 kW. Typical resolution is 25 m, with a minimum range of 25 m, so I guess that they use pulses about 0.1 us long. The real problem is that the transmitted pulse will swamp any receiver, and you've got to get the receiver to recover from that before the return pulse arrives.

 

[tobol.7uno]

Thanks, that is what I was thinking, I could do the antenna (also the antenna would make the signal travel much farther because it would only be going one direction instead of every direction), but I have no idea how to reprogram a netgear router that is my problem, I can do the computer programming. Thanks for your help. Any other Ideas on some sort of radar? Preferably to detect precipitation.

 

[Torben]

Thanks, that is what I was thinking, I could do the antenna (also the antenna would make the signal travel much farther because it would only be going one direction instead of every direction), but I have no idea how to reprogram a netgear router that is my problem, I can do the computer programming. Thanks for your help. Any other Ideas on some sort of radar? Preferably to detect precipitation.

I have no idea how applicable it will be to your final project, but believe it or not you can buy a Hot Wheels radar gun for ~$50 US (google "Hot Wheels Radar Gun"). There is information on the net about hacking these things (i.e. Hacking the Hot Wheels Radar Gun ) for various purposes and if nothing else it would be a cheap and relatively easy way to get a little more familiar with radar.


Cheers,

Torben

 

[unclejed613]

the way a wifi radio works is this:
a DSP (or FPGA) chip takes data, forms it into packets, and creates two data streams. these data streams are fed to DAC's that give quadrature outputs. these analog signals (I and Q, for Inphase and Quadrature) are fed to a dual analog multiplier where they modulate a 2.4Ghz carrier, and the resulting 2.4Ghz I/Q signals are then mixed to produce a 2,4Ghz SSB signal with spread spectrum characteristics (all of the math and such was done back at the DSP chip while this was still a digital signal). the modulation scheme is OFDM, and is continuous while data is being sent. to change this to a pulsed CW (also known as OOK, for On-Off Keying) would require a major rewrite of the DSP code (or FPGA code, depending on what was used). this code rewrite would also need to change the receiver code as well. then you need some way of reading and interpreting the receiver data.

 

[tobol.7uno]

looks like something possibly worth a shot, will take a bit more studying. Thanks guys!

 

[tobol.7uno]

sorry wrong spot...

 

[tobol.7uno]

I have no idea how applicable it will be to your final project, but believe it or not you can buy a Hot Wheels radar gun for ~$50 US (google "Hot Wheels Radar Gun"). There is information on the net about hacking these things (i.e. Hacking the Hot Wheels Radar Gun ) for various purposes and if nothing else it would be a cheap and relatively easy way to get a little more familiar with radar.


Cheers,

Torben

No, that will not work for my application, I already investigated this possibility. 10 GHz does not bounce off of rain droplets (being my main focus) so it would be useless to radar down a car that is 50ft away anyway. I am looking for direction and range to produce an image on my computer. Thanks anyway though.

 

[tobol.7uno]

the way a wifi radio works is this:
a DSP (or FPGA) chip takes data, forms it into packets, and creates two data streams. these data streams are fed to DAC's that give quadrature outputs. these analog signals (I and Q, for Inphase and Quadrature) are fed to a dual analog multiplier where they modulate a 2.4Ghz carrier, and the resulting 2.4Ghz I/Q signals are then mixed to produce a 2,4Ghz SSB signal with spread spectrum characteristics (all of the math and such was done back at the DSP chip while this was still a digital signal). the modulation scheme is OFDM, and is continuous while data is being sent. to change this to a pulsed CW (also known as OOK, for On-Off Keying) would require a major rewrite of the DSP code (or FPGA code, depending on what was used). this code rewrite would also need to change the receiver code as well. then you need some way of reading and interpreting the receiver data.

Do you have any idea how I could go about reprogramming those chips (Netgear WGR614 v7)? Or would I have to build my own Transceiver?

 

[unclejed613]

to get at the actual DSP code requires proprietary software (usually) and a JTAG interface to the DSP chip itself. if the radio is a wifi SoC (system on a chip), it's not likely you would have that luxury. in fact, if it's an SoC made for high volume cheap production, the DSP code may be mask programmed on the die itself, and not alterable. some of the modulation and transmission functions may be adjustable in firmware code, but the basic function of the radio is truly "set in stone". you could however get some evaluation modules from TI, and they do have some 2.4Ghz and 900Mhz radio chips that can be programmed to do OOK. all you have to do is "talk" to the module through an SPI (Serial Peripheral Interface) and tell it what to transmit, and read what gets received... these modules are usually about $50 (i think for a pair of them) and they come with antennas.

you could have a microcontroller tell it "go into transmit mode, send an OOK pulse 1 clock cycle in length, sleep for 50 clock cycles, go into receive mode and read receive data for 500 clock cycles, sleep for 10 clock cycles, start over at the beginning..."

 

[tobol.7uno]

Thanks, sounds interesting. I am new to electronics so I will have to do some reading so that I can buy the right things, hopefully I can make something work. I do lots of programming software on the computer, but not any hardware/firmware.