Develop of a 2.4GHz RF transmitter and a RF receiver with 4 antennas to measure phase difference

The project objective is the development of a RF indoor localization system. This system is based on the deployment of transmitters at the ceiling of the room and a node that contains a receiver with four antennas. (The receiver is contained in the node whose localization must be determined) Due to the difference on the propagation delay of one signal generated at one transmitter and the four different antennas, receiver will observe that there is a phase difference between the signals captured at its antennas. Demodulating the received waves, if the same carrier signal is used at the four demodulators, the same phase difference captured at high frequency signals shall be observed at low frequency signals after the demodulator, allowing use an low cost ADCs to measure it. This phase difference depends on the node position respect the transmitter, so if the information extracted from multiple transmitters is processed, the node position could be extracted. This project is a prototype module, so its main objective is determine the precision of the phase difference measure. The requirements of the project are: The system should work correctly when the distance between transmitter and receiver is 10 meters. The system is oriented to wireless sensor networks, so low consumption is a constraint. The transmitter requirements are: - Modulate a low frequency cosine generated by a DAC (signal frequency is smaller than 10 MHz and amplitude is from 0V to 3.3V) up to the range of 2.4GHz – 2.5 GHz - It shall be possible to command the transmitter to low consumption mode (Disable RF devices) - The modulated signal frequency shall be variable (transmitter will transmit in a fixed frequency, but this frequency shall be possible to be configurable with a potentiometer, SPI command…) - The transmitter PCB size, after the components are soldered, shall be smaller than 1.0 cm x 2.0 cm x 0.4 cm (antenna is included in these measures) The receiver requirements are: - The system shall be able to demodulate the signal received at the 4 antennas simultaneously, from 2.4 GHz to 0 Hz and 2.5GHz to 100 MHz. - The antenna distribution is fixed. All antennas shall be placed in the same PCB face and must be place in the corners of an imaginary square whose side length is 4 cm. - The resultant of the demodulation process shall be the same signal generated at transmitter (maybe displaced in the frequency domain if carrier transmitter signal frequency is different from receiver carrier frequency) and an ADC shall be able to capture it (Signal amplitude shall be in the range of 0V to 3.3V) - A phase difference error between the demodulated signals (due to a difference of propagation delay on the paths from the antennas to the PCB outputs) is acceptable if this error could be estimated and discarded after calibrating the system. - The receiver PCB size, after the components are soldered, shall be smaller than 4.5 cm x 4.5 cm x 0.4 cm (antennas are included in these measures) These requirements could be modified/negotiated if there is a technical justification that simplifies the design.