1. Escuela de Ingeniería de Telecomunicación, Department of Signal Theory and Communications, University of Vigo, Vigo E-36310, Spain.
2. NTT Communication Science Laboratories, NTT Corporation, 3-1, Morinosato Wakamiya, Atsugi-Shi, Kanagawa 243-0198, Japan.
3. Mitsubishi Electric Corporation, Information Technology R&D Center, 5-1-1 Ofuna, Kamakura-shi, Kanagawa 247-8501 Japan.
4. Faculty of Engineering, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan.