Affiliation: | 1. Department of Computer Science, Zhongshan University, Guangzhou 510275, China;2. Department of Computer Science, The University of Western Ontario, London, Ontario, N6A 5B7, Canada;3. SQIG–Instituto de Telecomunicações, IST, TULisbon, Av. Rovisco Pais 1049-001, Lisbon, Portugal |