The Research Of RS Error Correction Code Based On Visual Prosthesis Of Higher Order Modulation And Demodulation

Vision is the most important way that humans perceive the world.Ten thousands of people lost light perception or even blindness due to eye disease each year.Common diseases include Retinitis Pigmentosa(RP)and Age-Related Macular Degeneration(AMD),etc.Neuro-stimulator use the electrical signals to produce visual perception by stimulate the visual nerve cells.It is makes the blind to see again by using electronic devices supporting or replacing the defective tissue.High order difference amplitude phase shift keying(DAPSK)technology solves the contradiction between the quantity transfer efficiency and the transmission rate of the data based on visual prosthesis in a single coil.But the demodulation signal has error due to the influence of the noise.So,RS(15,9)soft decoding method is presented in this paper based on 16DAPSK soft demodulation to improve the reliability of communication,satisfying high accuracy and real-time requirements for visual prosthesis.Improved 16DAPSK soft demodulation algorithm:soft phase demodulation using the trigonometric values and using multiplication,addition and subtraction to instead of argument arithmetic and division operation of trigonometric.The complexity of improved 16DAPSK soft demodulation algorithm is low,which good for hardware implementation and not loss of the BER(bit error rate)performance.Secondly by comparing some methods of calculation for symbol reliability value,this paper come up with bit reliability multiplication method with more accuracy,using of the symbol reliability value to determine the test position.Finally to compromising decoding complexity and decoding performance,reduce the number of test sequences and the simulation of the bit error rate show that:On the one hand,bit error rate is improved under the same SNR(signal to noise ratio);On the other hand,under the same error rate(1*10-6)the Eb/No of soft decoding decrease 3dB than which without error correcting code circuit.The hardware implementation complexity is low of soft decoding algorithm and suitable for the application requirement of implantable visual prosthesis.