上浒充通大￥ Background SHANGHAI JIAO TONG UNIVERSITY ▣Spectrum Scarcity >Growth of WLAN,Mobile Communications,etc. >Cisco:most mobile data are in unlicensed bands(ISM bands) Unlicensed bands are heavily-utilized Licensed bands are under-utilized Spectrum Utilization of Licensed Bands Heavy Use Heavy Use Sparse Use Medium Use Frequency (MHz) I.F.Akyildiz,W.Lee,M.Vuran,S.Mohanty,"NeXt generation/dynamic spectrum access/cognitive radio wireless networks:A survey",Computer Networks(Elsevier),2127-2159,2006 33 Background ❑ Spectrum Scarcity ➢ Growth of WLAN, Mobile Communications, etc. ➢ Cisco: most mobile data are in unlicensed bands (ISM bands) ➢ Unlicensed bands are heavily-utilized ➢ Licensed bands are under-utilized I. F. Akyildiz, W.Lee, M. Vuran, S. Mohanty, "NeXt generation/dynamic spectrum access/cognitive radio wireless networks: A survey", Computer Networks (Elsevier), 2127-2159, 2006. Spectrum Utilization of Licensed Bands