RF Front-End Design And Implementation In Wireless Spread Spectrum Communication System

Telemetry technology is a measurement of remote parameters. In many cases, because of the distance, rugged environment or fast movement, the measured object is inaccessible and the testing data is difficult to obtain directly. Telemetry technology shows the advantages in these situations and has been widely used in the national economy, scientific research and the military.In the flight test data measurement system, carrier, target flight and telemetering missile are in high speed. Telemetry is necessary to enable the technician to obtain the timely flight test data. With telemetry technology, the test efficiency is improved and the test cycle is reduced.Based on the research on characteristics of the telemetry system, the carrier frequency band, application distance and modulation mode are analyzed and calculated. Because of small size, working in rugged environment and complex outside interference, the package, housing and layout are considered carefully. With the determination of system parameters, in view of the spread spectrum's characteristics of high code rate and low SNR, the transmitter and receiver is designed in detail. Direct up-conversion circuit topology, BPSK modulation and 3W power amplifier are adopted in transmitter. With the VHDL, setting carrier frequency by user between 2200 and 2300MHz is available. Superheterodyne circuit topology is used in receiver. The sensitivity is less than -90dBm without LNA. The dynamic range is greater than 60dB. The output is 70MHz IF modulation signal, with the constant power of 0dBm, for de-spread and demodulation in digital circuit.Then test the transmitter, receiver and VHDL program. Analyze and resolve the problems during debugging to improve the performance and stability of the system. With temperature, vibration and range experiment, the system performance meets the design requirements.