How RF transmission and reception is done?

we are designing a circuit for blind people where in we need some basic idea of how rf transmission and reception is done.the project is to attach an rf transceiver to a blind person which keeps intimating him about the obstacles that are present infront of him.we wish to know some facts about rf transmision in this regard as to whether we can get such transceivers worked for the above mentioned purpose of guiding the blind in the right direction and whether the cost of the circuits we prepare is low.all in all i want some basic knowledge about rf transmission and reception.thanks to all.

Basically, what you seem to be planning to do is create a radar system for the blind. RF is a poor choice for guiding the blind because of all the potential sources of interference, the size and complexity of the circuitry required to convert an RF signal to something a blind person could hear or feel, and the ultimate cost of such a system. Additionally, the power required to give extended range would present hazards to others - lower power would have no advantage over existing technology using ultrasound. Several existing systems touted as "radar for the blind" are actually ultrasonic.

A classic approach to accomplish the goal of guiding the blind is to use ultrasound. Such systems already exist in the form of ultrasound equipped canes, ultrasound equipped briefcases, handheld "flashlight" devices, etc. Ultrasound transducers are inexpensive, mechanically durable, and not prone to outside interferrence. They have a range of less than 10-15 feet; however, ranges greater have not been found to be of increased value to guiding the blind.

Another, newer, method involves bouncing laser diode pulses off of objects. It is similar to the method used in ultrasound; however, light frequencies are used instead of ultrasound. There are power (range) limitations with this method because of the potential hazard to the vision of nearby sighted bystanders from pulsed coherent light.

You should do a search on the internet to see what research and existing products are out there. A few places to get you started are:
http://www.batforblind.co.nz/
http://www.soundforesight.co.uk/freq..._questions.htm
http://www.tiresias.org/equipment/eb23.htm
http://www.acb.org/magazine/2005/bf052005-1.html

I always thought that a chirped radar system would be the way to go. You can send out a chirping waveform (linear ramp with frequency), receive the reflected signals, and downconvert them with the same chirping waveform. Since the waveform is ramping in frequency with time, the returns are downconverted at different beat notes, the frequency of which are related to distance away. You could then shift these tones into the audio range, and you would probably have a great "symphony of tones" that a blind person could see as distances to objects.

Modern DDS chips (Analog Devices) can easily program a very linear chirp over frequency, and you could up convert to some ISM band, like at 2.45 GHz for transmission.