Simulation Of BPSK And 2FSK Hybrid Modulation And Demodulation Algorithm

In Wireless Sensor Networks, Low speed transmission service and high-speed transmission service are coexistence, Independent channels for the transmission are proposed new requirements. Therefore, the same band hybrid modulation transmission mode is always the focus of the industry. The same band hybrid modulation transmission mode mainly obtains TDD,FDD,and CSMA etc. However, the relevant theoretical research for the mixed transmission of PSK and FSK modulation is very rare.Therefore,this paper researchs modulation transmission mode based on PSK and FSK modulation, and proposed a new hybrid modulation transmission at the same band.In digital modulation, phase changes with the baseband data signal makes it be of limited value of discontinuous to realize data transmission method called digital phase modulation,also called phase shift keying, namely PSK. PSK digital modulation technique is flexible, suitable for high speed data transmission channel and fast fading channel, it becomes the main way of modulation of various wireless communication systems.Methods with the baseband data signal using two different frequency carrier modulation to realize the information transmission is called digital FM, called frequency shift keying, namely FSK. Frequency shift keying(FSK) is simple, easy to implement, and the demodulation is not required to restore the local carrier, can be asynchronous transmission, anti noise and anti fading performance is also strong. Therefore, the FSK modulation technique has been widely used in communication, and it mainly applied to for low, medium data.This paper mainly studied on BPSK and 2FSK hybrid transmission algorithm in same band,through orthogonality principle and filtering principle, implementation of mixed BPSK and 2FSK modulation and demodulation is achieved. In Hybrid transmission algorithm,BPSK and 2FSK are sent at the same time after superposition, and received at the same time.According to the spectral difference between BPSK and 2FSK they were separated by high pass filter. Because the spectrum of two kinds of modulation methods will produce aliasing in the superposition, and the BPSK signal and the signal modulation emission after filter have a big gap, it will have an influence on BER, So the traditional BPSK and 2FSK modulation method was improved in this paper. the traditional BPSK modulation has 180 degree phase mutation, the demodulated data occurred in carrier phase offset will be error, sothis paper use half cycle modulation of the BPSK,so that the carrier synchronization module is simplified; for the 2FSK modulation,it is also different with the traditional way.In the former 2FSK modulation is the carrier of two continuous based on frequency, in this paper, we use the partition to improve the demodulation precision of 2FS, the two kinds of demodulation mode improved the precision of the demodulation reduces the error rate of mixed transmission mode.Through computer simulation, in mixed mode. BER reached 1/1000 below, BPSK need the SNR is 7d B, 2FSK requires the SNR is 8d B.Based on the research of algorithm Simulation of the hybrid,modulation and demodulation process through MATLAB were given in frequency domain,and time domain.it gives various simulation signal waveform and the corresponding frequency spectrum. At the same time, the BER performance of demodulation algorithm is tested to verify the feasibility and practicality of the hybrid modulation and demodulation algorithm,also provides the theoretical basis for the mixed transmission of multi band PSK and FSK later.