[1] Univ Alcala de Henares, Dept Signal Theory & Commun, Madrid 28871, Spain
[2] Univ Calgary, Dept Elect & Comp Engn, iRadio Lab, Calgary, AB T2N 1N4, Canada
[3] Univ Aveiro, Inst Telecomunicacoes, P-3810193 Aveiro, Portugal
[4] Hong Kong Univ Sci & Technol, Dept Elect & Elect Engn, Analog Res Lab, Kowloon, Hong Kong, Peoples R China