Research Of Adaptive FH/DSSS System Based On RAKE Receiving Technology

Impact of multipath propagation in wireless communication system may bring in signal phase shifting and fading. RAKE technique utilizes the correlation properties of pseudo-random codes for diversity reception of multipath signals, and interference is transformed into valid signal to be fully utilized, which further improves the performance of wireless communication system. Wireless frequency hopping spread spectrum communication system has the advantages of confidentiality and anti-interference, as well as the advantages of anti-multipath, anti-fading, and anti-noise, thus it’s widely used in military communication.In this paper, a RAKE based adaptive FH/DSSS communication system is designed. In digital baseband process, DQPSK modulation is adopted for being not sensitive to frequency offset and phase ambiguity. In order to process the modulated signal, DSSS is then used for its high processing gain. RAKE technique is employed at receiver to eliminate delay and phase offset, so that the processed multipath components can be used to improve the SNR of the received signal.Effects of spreading codes’ autocorrelation and the spreading factor on system performance are simulated, and a spreading factor selection algorithm based on BER detection is designed. As a result, the system is capable of adjusting the length of the spreading factor with the environmental change, so that it meets the requirements of reliable transmission for battlefield communication in complex electromagnetic environment.On the basis of theoretical design and simulation mentioned above, modules and algorithm of the proposed RAKE based adaptive FH/DSSS system are implemented with hardware description language, and systematic implementation is done on a hardware board with an FPGA core. Through the hardware test of final realization, feasibility of the design is verified.