School of Information Engineering Chang'an University Xi'an 710064 China;
Xi'an Aeronautical Polytechnic Institute Xi'an 710089 China;
School of Information Engineering Chang'an University Xi'an 710064 China;
Royal Institute of Technology Stockholm 10044 Sweden;
Royal Institute of Technology Stockholm 10044 Sweden;
Audible Inc. Newark NJ 07102 USA;
School of Computer Science and Engineering Xi'an University of Technology Xi'an 710048 China;