Automatic identification of the digital modulation type of asignal has found applications in many areas, including software defined radio (SDR), surveillance and threat analysis.This paper describes theFPGA based implementation ofAutomatic Modulation Recognition (AMR) algorithm foradvanced communication payload.A wavelet transform based algorithm which involves multi-rate signal processing,is realizedto distinguish QAM, PSK and FSK digital modulation signal in noisy environment. The approach is to usewavelet transform to extract the transient characteristics ina digital modulation signal to identify the type of modulation. The optimum thresholds are derivedfrom rigorous simulation in MATLAB/Simulinkunder the condition that the input noise is Additive WhiteGaussian (AWGN). The performance of the identification schemeis investigated through simulations. The design is implemented and tested in Xilinx Virtex-4 FPGA based card.
In many low-noise applications, extracting information from the extremely noisy signal is required. This task can be accomplished by a lock-in amplifier if the frequency of the signal is known before detection. Error signal output from the physics package of the rubidium atomic clock (RbAC) is one of those noisy signals. A lock-in amplifier extracts the desired information from such a signal as the frequency of the error signal is known beforehand. The Space Applications Centre of the Indian Space Research Organisation is developing the Indian Rubidium Atomic Frequency Standard (IRAFS) for Navigation with Indian Constellation. We have developed a digital lock-in amplifier with a very high-resolution frequency control voltage for IRAFS. This paper demonstrates the digital lock-in amplifier with a novel method of combining two 12-bit digital-to-analog converters (DACs) to get higher resolution 20-bit output for precise frequency control and tuning. This design technique allows a digital lock-in amplifier to be used for high-performance RbAC for space applications as precision DACs with higher resolution are not available in space-qualified versions.
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