Ultra dense cloud small cell network (UDCSNet), which combines cloudcomputing and massive deployment of small cells, is a promising technology forthe fifth-generation (5G) LTE-U mobile communications because it canaccommodate the anticipated explosive growth of mobile users' data traffic. Asa result, fronthauling becomes a challenging problem in 5G LTE-U UDCSNet. Inthis article, we present an overview of the challenges and requirements of thefronthaul technology in 5G \mbox{LTE-U} UDCSNets. We survey the advantages andchallenges for various candidate fronthaul technologies such as optical fiber,millimeter-wave based unlicensed spectrum, Wi-Fi based unlicensed spectrum, sub6GHz based licensed spectrum, and free-space optical based unlicensed spectrum.
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