Cloud radio access network system and control method thereof

A cloud radio access network system includes remote signal sources, a baseband processing unit pool, an access management server, a software defined network controller and a network signal forwarder. Each remote signal source is configured to transmit an access signal. The baseband processing unit pool provides a baseband processing signal. The access management server provides an access state signal. Different maximum transmission rates are transmitted via the access state signal. When the baseband processing unit pool has authenticated one remote signal source, the baseband processing unit pool transmits an authentication notification signal to the access management server. Then, the access management server informs the software defined network controller according to the authentication notification signal to increase an upper limit of a signal transmission rate between the baseband processing unit pool and the authenticated remote signal source to a higher one of the maximum transmission rates.