A soft decoding algorithm and hardware implementation for the visual prosthesis based on high order soft demodulation

BioMedical Engineering OnLine, Sep 2016

Background High order modulation and demodulation technology can solve the frequency requirement between the wireless energy transmission and data communication. In order to achieve reliable wireless data communication based on high order modulation technology for visual prosthesis, this work proposed a Reed–Solomon (RS) error correcting code (ECC) circuit on the basis of differential amplitude and phase shift keying (DAPSK) soft demodulation. Firstly, recognizing the weakness of the traditional DAPSK soft demodulation algorithm based on division that is complex for hardware implementation, an improved phase soft demodulation algorithm for visual prosthesis to reduce the hardware complexity is put forward. Based on this new algorithm, an improved RS soft decoding method is hence proposed. In this new decoding method, the combination of Chase algorithm and hard decoding algorithms is used to achieve soft decoding. In order to meet the requirements of implantable visual prosthesis, the method to calculate reliability of symbol-level based on multiplication of bit reliability is derived, which reduces the testing vectors number of Chase algorithm. The proposed algorithms are verified by MATLAB simulation and FPGA experimental results. During MATLAB simulation, the biological channel attenuation property model is added into the ECC circuit. Results The data rate is 8 Mbps in the MATLAB simulation and FPGA experiments. MATLAB simulation results show that the improved phase soft demodulation algorithm proposed in this paper saves hardware resources without losing bit error rate (BER) performance. Compared with the traditional demodulation circuit, the coding gain of the ECC circuit has been improved by about 3 dB under the same BER of 10 - 6 . The FPGA experimental results show that under the condition of data demodulation error with wireless coils 3 cm away, the system can correct it. The greater the distance, the higher the BER. Then we use a bit error rate analyzer to measure BER of the demodulation circuit and the RS ECC circuit with different distance of two coils. And the experimental results show that the RS ECC circuit has about an order of magnitude lower BER than the demodulation circuit when under the same coils distance. Therefore, the RS ECC circuit has more higher reliability of the communication in the system. Conclusions The improved phase soft demodulation algorithm and soft decoding algorithm proposed in this paper enables data communication that is more reliable than other demodulation system, which also provide a significant reference for further study to the visual prosthesis system.

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A soft decoding algorithm and hardware implementation for the visual prosthesis based on high order soft demodulation

Yang et al. BioMed Eng OnLine A soft decoding algorithm and hardware implementation for the visual prosthesis based on high order soft demodulation Yuan Yang Nannan Quan Jingjing Bu Xueping Li Ningmei Yu Background: High order modulation and demodulation technology can solve the frequency requirement between the wireless energy transmission and data communication. In order to achieve reliable wireless data communication based on high order modulation technology for visual prosthesis, this work proposed a Reed-Solomon (RS) error correcting code (ECC) circuit on the basis of differential amplitude and phase shift keying (DAPSK) soft demodulation. Firstly, recognizing the weakness of the traditional DAPSK soft demodulation algorithm based on division that is complex for hardware implementation, an improved phase soft demodulation algorithm for visual prosthesis to reduce the hardware complexity is put forward. Based on this new algorithm, an improved RS soft decoding method is hence proposed. In this new decoding method, the combination of Chase algorithm and hard decoding algorithms is used to achieve soft decoding. In order to meet the requirements of implantable visual prosthesis, the method to calculate reliability of symbol-level based on multiplication of bit reliability is derived, which reduces the testing vectors number of Chase algorithm. The proposed algorithms are verified by MATLAB simulation and FPGA experimental results. During MATLAB simulation, the biological channel attenuation property model is added into the ECC circuit. Results: The data rate is 8 Mbps in the MATLAB simulation and FPGA experiments. MATLAB simulation results show that the improved phase soft demodulation algorithm proposed in this paper saves hardware resources without losing bit error rate (BER) performance. Compared with the traditional demodulation circuit, the coding gain of the ECC circuit has been improved by about 3 dB under the same BER of 10−6. The FPGA experimental results show that under the condition of data demodulation error with wireless coils 3 cm away, the system can correct it. The greater the distance, the higher the BER. Then we use a bit error rate analyzer to measure BER of the demodulation circuit and the RS ECC circuit with different distance of two coils. And the experimental results show that the RS ECC circuit has about an order of magnitude lower BER than the demodulation circuit when under the same coils distance. Therefore, the RS ECC circuit has more higher reliability of the communication in the system. Conclusions: The improved phase soft demodulation algorithm and soft decoding algorithm proposed in this paper enables data communication that is more reliable than other demodulation system, which also provide a significant reference for further study to the visual prosthesis system. - Background Visual prosthesis is usually composed of external and internal parts, as illustrated in Fig. 1. Since we study the communication error performance in vitro and vivo, the modulation, biological channel and demodulation modules are the significant parts that we concentrate on in this paper. High-performance implantable biomedical microsystems mostly take advantage of a wireless interface to communication between the implanted modules to the external controller. Current-generation cortical (and retinal) visual prostheses are being researched to transfer energy and data with wireless way. The maximum carrier frequency for biomedical implants is limited to a few tens of megahertz due to the self-resonance frequency of the coupled coils, the energy loss in the transmission circuit, and energy dissipation in the tissue [1–4]. The significant consideration of the frequency limitation for wireless power transfer comes from the absorption of electromagnetic energy by tissues, which increases exponentially with frequency [5]. However, data transmission requires a data frequency high enough to stimulate electrodes so that the information can be received in real-time without distortion. So the trade-off of carrier frequency requirement is obvious between the power transmission and the data communication [6, 7]. Some scholars adopt two pairs of coils to transfer energy and data with their own frequency respectively, but this way will increase the area of the circuit [8]. In order to reduce the secondary implant volume, some researchers put forward two orthogonal coils assembly structure for energy and data transmission respectively, but there is the mutual interference between coils assembly [9]. Considering the safety of the implantable devices, we adopt a pair of coils to transfer date and energy with the same carrier frequency. Thus it is important to select an appropriate digital modulation and demodulation schemes and a suitable carrier frequency to meet the requirements of energy efficient and data rate. Since the energy transmission must adopt low carrier frequency, data transmission requires a high (...truncated)


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Yuan Yang, Nannan Quan, Jingjing Bu, Xueping Li, Ningmei Yu. A soft decoding algorithm and hardware implementation for the visual prosthesis based on high order soft demodulation, BioMedical Engineering OnLine, 2016, pp. 110, 15, DOI: 10.1186/s12938-016-0229-3