1. Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei, Anhui 230031, P. R. China
2. School of Computer Engineering, Shenzhen Polytechnic, Shenzhen, Guangdong 518055, P. R. China
3. Beijing Research Center of Intelligent Equipment for Agriculture, Beijing Academy of Agriculture and Forestry Science, Beijing 100097, P. R. China
4. School of Electronics and Communication Engineering, Anhui Xinhua University, Hefei, Anhui 230031, P. R. China