出处
《通讯和计算机（中英文版）》
2009年第6期20-25,共6页
Journal of Communication and Computer
基金
Aeknowledgements： This paper was supported by the National Natural Science Foundation of China （No. 60772082）, the Natural Science Foundation of Hebei Province. China （No. 08M010）, the Science Research Foundation of Ordnance Engineering
The author gratefully acknowledges DENG Gao-ming for discussions which inspired this research, LI Hua for his advice, and the （anonymous） referees for their suggestions.
