National Digital Switching System Engineering and Technological Research Center Zhengzhou 450001 China;
School of Electronics and Communication Engineering Sun Yat-Sen University Guangzhou 510000 China;
Anhui Institute of Quality and Standardization Hefei 230000 China;
National Digital Switching System Engineering and Technological Research Center Zhengzhou 450001 China;
National Digital Switching System Engineering and Technological Research Center Zhengzhou 450001 China;