then what do I. have to. do ?
what I need to. do for is this : I want to make a speed measurement on the car and send info and camera picture to the rc and from rc I am sending message for throtle and steering etc ... so?
Just use a 2.4ghz unit - perhaps an nrf24L01+ module or an a7105 module. Both of them are transceivers, so can transmit or receive.
If I understand right, you'd like to send control data from the Tx to the car. You would also like to send speed and a photo from the car to the Tx.
A basic telemetry setup. Well, the thing with standard rc transmitters is that they don't send a continuous data stream from the Tx to the car. They only send packets at regular intervals, meaning you have the remaining time to swap the mode of each radio and transmit data back the other way.
Turnigy 9x comes with a module that transmits every 1.496ms, other examples of modules transmit intervals are: Husban 12ms, FrSky 1 way 9ms, FrSky with telemtery 1.496ms. Assuming it takes 100us for a packet to be sent (should be quicker than that, but I'll err on the size of caution), you are spending 0.1ms every 1.496-12ms to actually receive the fwd/backwards left/right signal from the Tx. That would give you anywhere from 1.396/1.496 - 11.9/12 (93.32% - 99.2%) of the time to send data packets back from the car.
So, the nrf modules have a max on-air data rate of 2Mbps, which includes packet pre-amble and transmitter id, so you have a max effective data rate of about 1.5 mbps if using the largest size packets permitted by the radio. The a7105s on the other hand are about 1/4 of that speed. An uncompressed 24bit colour, 640x480 image is 921,600 bytes (7,372,800 bits) So, you'd need about 5 seconds 'flat-out' to transmit an image of that size using the nrf24L01 modules. You'd also have to make sure you've got a camera that can buffer the data. An ov670 with a fifo seems like it could work okay. You'd sure have your work cut-out receiving the radio signal, sending the control the the car electronics and at the same time handling the transmission of the camera data back to the Tx!
You might be able to realistically expect to transmit that 921,000 bytes from the car to the Tx in about 6 or 7 seconds or so, if you were able to shave off every cpu cycle possible.
Don't even consider less than 5.8ghz if you wish to transmit video!
There's a bunch of r/c Rx &/or Tx projects around in RcGroups. Here's a link: http://www.rcgroups.com/diy-electronics-199/