Patent Publication Number: US-10785685-B2

Title: Cloud radio access network system and control method thereof

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to a cloud radio access network system and a control method of the system, and particularly to a cloud radio access network system using a software defined network controller and a control method of the system. 
     BACKGROUND OF THE INVENTION 
     A cloud radio access network (Cloud RAN) is a network which connects many distributed remote radio heads (RRH) to base stations of high density with only baseband function. The network load balancing is achieved by resource sharing. The cloud radio access network is an important development direction of next-generation networking. Recently, great research efforts are put on the system architecture and the control method for the cloud radio access network. 
     SUMMARY OF THE INVENTION 
     An aspect of the present disclosure provides a cloud radio access network (Cloud RAN) system. It includes a plurality of remote signal sources, a baseband processing unit pool, an access management server, a software defined network (SDN) controller and at least one 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 according to a request signal. The SDN controller is electrically connected to the access management server and the at least one network signal forwarder and configured to control the at least one network signal forwarder. The at least one network signal forwarder has at least two network connectors, each of which is configured to be connected to one of the baseband processing unit pool and the remote signal source. The SDN controller obtains connection relation between the at least two network connectors and the remote signal sources or the baseband processing unit pool, and generates and transmits network resource information to the at least one network signal forwarder according to the obtained connection relation. The at least one network signal forwarder establishes communication between one remote signal source and the baseband processing unit pool according to the network resource information. 
     Another aspect of the present disclosure provides a Cloud RAN system. It includes a plurality of remote signal sources, a baseband processing unit pool, an access management server, a SDN controller and at least one 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. The SDN controller is electrically connected to the access management server and the at least one network signal forwarder. The remote signal sources and the baseband processing unit pool are electrically connected to the at least one network signal forwarder so that the access signal and the baseband processing signal are transmitted through the at least one network signal forwarder. Signal transmission between the SDN controller and the access management server are independent of the at least one network signal forwarder. 
     Another aspect of the present disclosure provides a Cloud RAN system. It includes a plurality of remote signal sources, a baseband processing unit pool, an access management server, a SDN controller and at least one 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. The SDN controller is electrically connected to the access management server and the at least one network signal forwarder. The remote signal sources and the baseband processing unit pool are electrically connected to the at least one network signal forwarder. A plurality of different maximum transmission rates are transmitted via the access state signal. The maximum transmission rates includes at least a first maximum transmission rate and a second maximum transmission rate, and the first maximum transmission rate is lower than the second maximum transmission rate. 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 SDN controller according to the authentication notification signal to make SDN controller to increase an upper limit of a signal transmission rate between the baseband processing unit pool and the authenticated remote signal source from the first maximum transmission rate to the second maximum transmission rate. 
     Another aspect of the present disclosure provides a control of the Cloud RAN system. The control method includes the following steps. The at least one network signal forwarder receives an access signal from one remote signal source. The at least one network signal forwarder determines whether the access signal matches data in network resource information. When the access signal does not match the data in the network resource information, the at least one network signal forwarder transmits the access signal to the SDN controller; the SDN controller converts the access signal into a request signal and transmits the request signal to the access management server; the access management server transmits an access state signal to the SDN controller according to the request signal; and the SDN controller determines whether to update the network resource information stored in the at least one network signal forwarder according to the access state signal. When the access signal matches data in the network resource information, the at least one network signal forwarder establishes communication between the baseband processing unit pool and the remote signal source which transmits the access signal according to the network resource information. 
     Another aspect of the present disclosure provides a control of the Cloud RAN system. The control method includes the following steps. The at least one network signal forwarder determines whether an access signal from one of the remote signal sources conforms to a predetermined rule. When the access signal conforms to the predetermined rule, the at least one network signal forwarder generates a first notification signal corresponding to the access signal and transmits the first notification signal to the SDN controller, and the SDN controller generates a request signal according to the first notification signal and transmits the request signal to the access management server. Signal transmission between the SDN controller and the access management server is independent of the at least one network signal forwarder. 
     Another aspect of the present disclosure provides a control method of the Cloud RAN system. The control method includes the following steps. The access management server transmits an access state signal to the SDN controller wherein the access state signal contains a plurality of different maximum transmission rates includes at least a first maximum transmission rate and a second maximum transmission rate, and the first maximum transmission rate is lower than the second maximum transmission rate. The baseband processing unit pool performs authentication of one remote signal source at the first maximum transmission rate. After the baseband processing unit pool authenticates the remote signal source, the baseband processing unit pool transmits an authentication notification signal to the access management server. The access management server informs the SDN controller according to the authentication notification signal to make the SDN controller to increase an upper limit of a signal transmission rate between the baseband processing unit pool and the authenticated remote signal source from the first maximum transmission rate to the second maximum transmission rate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The advantages of the present disclosure will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
         FIG. 1  is a schematic diagram illustrating an architecture of a Cloud RAN system according to an embodiment of the present disclosure; 
         FIG. 2  is a flowchart illustrating a control method of the Cloud RAN system according to an embodiment of the present disclosure; 
         FIG. 3  is a flowchart illustrating a control method performed by the Cloud RAN system according to another embodiment of the present disclosure; and 
         FIG. 4  is a flowchart illustrating a control method performed by the Cloud RAN system according to a further embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present disclosure will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only. It is not intended to be exhaustive or to be limited to the precise form disclosed. 
     In the description, “electrically connect”, “communicate” and “communication” mean that an electrical signal path is provided for signal transmission. For example, if a first device is electrically connected to/communicated with a second device, it means that the first device can transmit/receive electrical signals to/from the second device via any known way such as wire, cable or wireless transmission in a direct or an indirect manner. 
     Please refer to  FIG. 1 , a schematic diagram illustrating a cloud radio access network (Cloud RAN) system according to an embodiment of the present disclosure. In the embodiment, the Cloud RAN system  10  includes a remote signal source set  100 , two network signal forwarders  110 ,  112 , a baseband processing unit pool  120 , an access management server  130  and a software defined network controller (SDN controller)  140 . The remote signal source set  100  includes at least one remote signal source, e.g. remote signal sources  100 ( 1 ),  100 ( 2 ), . . . ,  100 (N) in  FIG. 1 . The baseband processing unit pool  120  includes at least one baseband processing unit, e.g. baseband processing units  1202 ,  1204 , . . . ,  1206  in  FIG. 1 . Although the quantities of the remote signal sources, the network signal forwarders and the baseband processing units are specified in this embodiment and shown in  FIG. 1 , the quantities of these devices are not limited as those described in the embodiment and can be adjusted or arranged as desired without departing from the present invention. 
     In the embodiment, each remote signal source  100 ( 1 ),  100 ( 2 ), . . . ,  100 (N) may be an independent remote radio head (RRH), and its operation is not affected by any other RRH. The remote signal sources  100 ( 1 ),  100 ( 2 ), . . . ,  100 (N) can transmit and/or receive corresponding access signals AS 1 , AS 2 , . . . , ASN during activation and operation. In other words, each remote signal source can convert information into an access signal in a specific access signal format which is then sent to other devices of the Cloud RAN system  10  for further processing, or receive an access signal complying with a specific access signal format from other devices of the Cloud RAN system  10  to acquire information needed for individual operation. Each network signal forwarder  110 ,  112  forwards network signals based on specific rules. Each baseband processing unit  1202 ,  1204 ,  1206  is provided for performing specific function. Any known device which can work as required in the description is suitable for serving as the above described devices of the Cloud RAN system  10 . For example, a smart phone or a notebook computer may serve as the remote signal source; a network switch or a network router may serve as the network signal forwarder; or a notebook computer, a server or a personal computer may serve as the baseband processing unit. 
     As shown in  FIG. 1 , the remote signal sources  100 ( 1 ),  100 ( 2 ), . . . ,  100 (N) are in communication with the network signal forwarders  110 ,  112  via the access signals AS 1 , AS 2 , . . . , ASN. Specially, the remote signal source  100 ( 1 ) is electrically connected to the network connector  1101  of the network signal forwarder  110 , and communicated with the network connector  1101  via the access signal AS 1 ; the remote signal source  100 ( 2 ) is electrically connected to the network connector  1121  of the network signal forwarder  112 , and communicated with the network connector  1121  via the access signal AS 2 ; and the remote signal source  100 (N) is electrically connected to the network connector  1102  of the network signal forwarder  110 , and communicated with the network connector  1102  via the access signal ASN. 
     The network signal forwarder  110  has network connectors  1101 ˜ 4105  and the network signal forwarder  112  has network connectors  1121 ˜ 1125  for data transmission. As shown in  FIG. 1 , in addition to the network connectors electrically connected to the remote signal sources  100 ( 1 ),  100 ( 2 ), . . . ,  100 (N), the network signal forwarders  110 ,  112  have other network connectors to be electrically connected to other devices. For example, the network connector  1103  of the network signal forwarder  110  is electrically connected to the network connector  1123  of the network signal forwarder  112 ; the network connector  1104  of the network signal forwarder  110  is electrically connected to the SDN controller  140 ; the network connector  1105  of the network signal forwarder  110  is electrically connected to the baseband processing units  1202 ,  1204 ,  1206  in the baseband processing unit pool  120 ; the network connector  1124  of the network signal forwarder  112  is electrically connected to the baseband processing unit  1202  in the baseband processing unit pool  120 ; and the network connector  1125  of the network signal forwarder  112  is electrically connected to the baseband processing unit  1204  in the baseband processing unit pool  120 . It is to be noted that each network connector may be electrically connected to the remote signal source, the baseband processing unit pool or the SDN controller selectively to meet specific requirement, and real connections among devices are not limited to this embodiment. 
     As shown in  FIG. 1 , the access management server  130  is electrically connected to the baseband processing unit pool  120  and the SDN controller  140 . Specially, the access management server  130  is electrically connected to the baseband processing units  1202 ,  1204 ,  1206 , directly or indirectly. For example, the access management server  130  is electrically connected to each of the baseband processing units  1202 ,  1204 ,  1206 ; or the access management server  130  is electrically connected to at least one baseband processing unit in the baseband processing unit pool  120 , and the at least one baseband processing unit is further electrically connected to other baseband processing units. 
     The operation of the Cloud RAN system  10  is described as follows with reference to both  FIG. 1  and  FIG. 2 , a flowchart illustrating a control method of the Cloud RAN system according to an embodiment of the present disclosure. 
     Once the Cloud RAN system  10  starts operation, the SDN controller  140 , the remote signal sources  100 ( 1 )˜ 100 (N) and the baseband processing unit pool  120  start to be integrated under the architecture of the present Cloud RAN system  10 . Taking the remote signal source  100 ( 2 ) as an example, in the Cloud RAN system  10 , when the remote signal source  100 ( 2 ) is activated and connection is required, the remote signal source  100 ( 2 ) transmits the access signal AS 2  to the network signal forwarder  112  through the network connector  1121  (step S 200 ). After receiving the access signal AS 2 , the network signal forwarder  112  compares specific information contained in the access signal AS 2  with network resource information stored in the network signal forwarder  112  (step S 202 ), and then determines whether to forward the received access signal AS 2  according to a comparing result of the comparing step (step S 204 ). 
     The specific information contained in the access signal AS 2  may include at least one of an Internet Protocol address (IP address) of the remote signal source  100 ( 2 ), a media access control address (MAC address) of the remote signal source  100 ( 2 ) and a service type of the remote signal source  100 ( 2 ). The network resource information is broadly defined as any information related to the corresponding relation or connection relation between devices in the Cloud RAN system  10 . For example, the network resource information to be compared with the specific information contained in the access signal AS 2  may include at least one of IP addresses of permitted remote signal sources, MAC addresses of permitted remote signal sources, service types of permitted remote signal sources, input network connectors of network signal forwarders for access signals transmitted from permitted remote signal sources, and output network connectors of network signal forwarders for access signals transmitted from permitted remote signal sources. 
     If the specific information contained in the access signal AS 2  matches data in the network resource information, it is determined to forward the access signal AS 2  (steps S 202  and S 204 ). For example, the comparing result indicates that the IP address, the MAC address and the service type of the remote signal source  100 ( 2 ) are recorded in the network resource information, and the access signal AS 2  from the remote signal source  100 ( 2 ) selects the network connector  1121  of the network signal forwarder  112  as the input network connector. Then, it is determined that direct forwarding of the access signal AS 2 , which specifies the service type recorded in the network resource information, enters the network signal forwarder  112  through the network connector  1121 , and carries the recorded IP address and MAC address of the remote signal source  100 ( 2 ), is permitted. Entire or part of the permitted access signal AS 2  (e.g. only the information regarding service request) is forwarded to the baseband processing unit pool  120  through another network connector to be processed by a corresponding baseband processing unit in the baseband processing unit pool  120  (step S 206 ). 
     After the service request contained in the access signal AS 2  is transmitted to the corresponding baseband processing unit, the baseband processing unit will process the service request and transmit a corresponding baseband processing signal BSP to the network signal forwarder (step S 270 ). Upon receiving the baseband processing signal BSP, the network signal forwarder will determine whether the baseband processing signal BSP is recorded in the network resource information stored therein (step S 272 ). For example, the baseband processing signal BSP recorded in the network resource information may include at least one of an IP address of a specific baseband processing unit, a MAC address of the specific baseband processing unit, a serial number of a network signal forwarder corresponding to the specific baseband processing unit and a serial number of a network connector corresponding to the specific baseband processing unit. In an embodiment, to determine whether the received baseband processing signal BSP is recorded in the network resource information in step S 272 , corresponding information contained in the baseband processing signal BSP (e.g. the IP address and the MAC address of the baseband processing unit transmitting the baseband processing signal BSP, the serial numbers of the network signal forwarder and the network connector receiving the baseband processing signal BSP) is compared with the network resource information. If the IP address of the baseband processing unit transmitting the baseband processing signal BSP and the serial number of the network connector receiving the baseband processing signal BSP match the same entry of data in the network resource information, the network signal forwarder determines that the received baseband processing signal BSP is recorded in the network resource information. Otherwise, the network signal forwarder determines that the received baseband processing signal BSP is not recorded in the network resource information. In other embodiments, to determine whether the received baseband processing signal BSP is recorded in the network resource information, the comparison may be made based on other corresponding information, and is not limited to this embodiment. 
     After step S 272 , if it is determined that the network resource information has recorded the received baseband processing signal BSP, step S 274  directs the method to step S 276 . In step S 276 , the received baseband processing signal BSP is forwarded to the corresponding remote signal source (e.g. the original remote signal source transmitting the access signal at the start, i.e. the remote signal source  100 ( 2 ) in this embodiment). Otherwise, if it is determined that the received baseband processing signal BSP is not recorded in the network resource information (conforming to a predetermined rule to transmit data to the SDN controller  140 ), step S 274  directs the method to step S 278 . In step S 278 , the network signal forwarder generates a second notification signal NS 2  according to the baseband processing signal BSP, and transmits the second notification signal NS 2  to the SDN controller  140 . Subsequently, the SDN controller  140  updates the network resource information according to the received second notification signal NS 2  (step S 280 ), and thus generates new network resource information (step S 252 ). The network resource information is transmitted to the network signal forwarder via a control signal IF (step S 254 ). It is to be noted that while activating the SDN controller  140  (step S 250 ), the SDN controller  140  generally creates initial network resource information according to data previously stored therein (step S 252 ). The initial network resource information may include predefined information or empty information without contents. Furthermore, the step of generating the new network resource information in step S 252  and the step of transmitting the network resource information to the network signal forwarder in step S 254  may be performed for only updated portions of the network resource information rather than generating and transmitting complete network resource information. The updated network resource information is stored in the network signal forwarder for use in later steps (e.g. step S 202  or step S 272 ). 
     In the above description, the steps subsequent to step S 206  are performed when it is determined in step S 202  that the forwarding of the access signal is permitted. In another embodiment, it is determined in step S 202  that the forwarding of the access signal is not permitted, and the operation is described as follows. 
     Please refer to both  FIG. 1  and  FIG. 2 . If it is determined in step S 202  that the forwarding of the access signal is not permitted, step S 204  directs the method to step S 208 . In step S 208 , the network signal forwarder generates a first notification signal NS 1  according to the received access signal, and transmits the first notification signal to the SDN controller  140 . The SDN controller  140  generates a corresponding request signal REQ according to the first notification signal, and then transmits the request signal REQ to the access management server  130  (step S 210 ). After receiving the request signal REQ from the SDN controller  140 , the access management server  130  performs necessary operation (e.g. searching a corresponding database) according to the request signal REQ, generates an access state signal STAT corresponding to the request signal REQ according to the operation state, and respond to the SDN controller  140  with the access state signal STAT (step S 212 ). After receiving the access state signal STAT from the access management server  130 , the SDN controller  140  determines whether to update the network resource information according to the received access state signal STAT (step S 214 ). If it is determined that the network resource information need not be updated (e.g. the access state signal STAT indicates that the access does not conform to the requirement), step S 216  directs the method to step S 218 . In step S 218 , the network signal forwarder is controlled to deny the connection or access request from the remote signal source. Otherwise, if it is determined that the network resource information need be updated, step S 216  directs the method to step S 252 . In step S 252 , the SDN controller  140  generates new network resource information, and then transmits the new network resource information to the network signal forwarder (step S 254 ) for storage and use (e.g. for use in step S 202  or step S 272 ). Likewise, the step of generating the new network resource information in step S 252  and the step of transmitting the network resource information to the network signal forwarder in step S 254  may be performed for only updated portions of the network resource information rather than generating and transmitting complete network resource information. 
     The access signal AS 2  outputted from the remote signal source  100 ( 2 ) is taken for illustration. As described above, the access signal AS 2  is transmitted to the network signal forwarder  112  through the network connector  1121  (step S 200 ). If the specific information contained in the access signal AS 2  does not match data in the network resource information stored in the network signal forwarder  112  (for example, the service type is not recorded in the network resource information), the network signal forwarder  112  determines that the forwarding of the access signal AS 2  is not permitted (steps S 202 ˜S 204 ). In this situation, the network signal forwarder  112  will generate a first notification signal NS 1  correspondingly according to the specific information contained in the access signal AS 2 , especially the specific information which does not match data in the network resource information. The first notification signal NS 1  is transmitted to the network signal forwarder  110  through the network connectors  1123  and  1103 , and then transmitted to the SDN controller  140  through the network connector  1104  (step S 208 ). In this embodiment, the first notification signal NS 1  includes information indicating the receiving device (i.e. network signal forwarder  112  with network connector  1121 ) for the access signal AS 2 , information indicating the transmitting device (i.e. the remote signal source  100 ( 2 )) for the access signal AS 2 , information indicating the IP address of the remote signal source  100 ( 2 ), information indicating the MAC address of the remote signal source  100 ( 2 ), information indicating the service request from the remote signal source  100 ( 2 ) and other information needed for later determination step. It is to be noted that the contents of the first notification signal NS 1  are not limited to this embodiment, and may be adjusted or modified according to different environments without departing from the present disclosure. 
     After receiving the first notification signal NS 1 , the SDN controller  140  can determine whether the access signal AS 2  is permitted to be transmitted to the baseband processing unit pool  120  according to the information contained in the first notification signal NS 1 . For this purpose, the SDN controller  140  converts part or entire of the information contained in the first notification signal NS 1  into a request signal REQ suitable to be transmitted to the access management server  130  (step S 210 ). In this embodiment, the request signal REQ includes information indicating the IP address of the remote signal source  100 ( 2 ), information indicating the MAC address of the remote signal source  100 ( 2 ) and information indicating the service request in the access signal AS 2 . It is to be noted that the contents of the request signal REQ are not limited to this embodiment, and may be adjusted or modified according to different environments without departing from the present disclosure. 
     After receiving the request signal REQ, the access management server  130  searches a back-end database (not shown) to determine whether the source of the access signal AS 2  and the service request contained in the access signal AS 2  conform to the requirement (e.g. depending on whether the requester is a valid registered user, whether the service request corresponds to the terminal service provided by the remote signal source  100 ( 2 ), or whether the service request is within the service range of the Cloud RAN system  10 ). If the access management server  130  determines that the source of the access signal AS 2  and the service request conform to the requirement, the access management server  130  can select one baseband processing unit in the baseband processing unit pool  120  and transmit the access signal AS 2  to the selected baseband processing unit according to the data stored in the back-end database. Otherwise, the access management server  130  determines that the source of the access signal AS 2  or the service request does not conform to the requirement (e.g. the service request is not within the service range of the Cloud RAN system  10 ), the access management server  130  deny the service request contained in the access signal AS 2  via an access state signal STAT (step S 212 ). 
     The communication and signal transmission between the access management server  130  and the back-end database can be performed according to any known technology, and redundant description about the operation is not given here. 
     It is to be noted that no matter whether the signal transmission conforming to the same or different signal specifications, while the access management server  130  responding to the SDN controller  140 , the access state signal STAT permitting the service request contained in the access signal AS 2  is different from the access state signal STAT denying the service request contained in the access signal AS 2 . To simplify the description, the term “access state signal STAT” is used in both conditions without giving respective signal names. 
     After receiving the access state signal STAT, the SDN controller  140  decides how to control the network signal forwarders  110 ,  112  according to the access state signal STAT (steps S 214 ˜S 216 ). If the access state signal STAT indicates denial of the service request contained in the access signal AS 2 , the SDN controller  140  does not update the network resource information, and further transmits a control signal IF to control the network signal forwarder  112  to deny the connection of the remote signal source  110 ( 2 ) (step S 218 ). Otherwise, if the access state signal STAT indicates permission of the service request contained in the access signal AS 2 , the SDN controller  140  generates or updates the network resource information according to the access state signal STAT and the first notification signal NS 1  previously received from the network signal forwarder  112  (step S 252 ). Then, the SDN controller  140  outputs a control signal IF to transmit the network resource information to the network signal forwarder  112 , and the network signal forwarder  112  stores the received network resource information (step S 254 ). Thus, the network signal forwarder  112  can process the access signal AS 2  based on the updated network resource information as described above (step S 202 ). 
     It is to be noted that the network resource information generated by the SDN controller  140  need not be stored only in the network signal forwarder  112  which is designated to receive the access signal AS 2 . In fact, the network resource information generated by the SDN  140  controller can be stored in any network signal forwarder which is directly or indirectly controlled by the SDN controller  140 . Alternatively, each entry of data in the network resource information generated by the SDN controller  140  is stored into respective network signal forwarders. For example, the baseband processing unit  1206  is designated to process the access signal AS 2 , and the baseband processing unit  1206  is electrically connected to the network connector  1105  of the network signal forwarder  110 , but not the network signal forwarder  112 . The data in the network resource information in connection with the access signal AS 2  may be stored in both network signal forwarders  110 ,  112 . Thus, the access signal AS 2  can be transmitted from the network signal forwarder  112  to the baseband processing unit  1206  through the network signal forwarder  110  without repeating the steps of S 200 ˜S 254  for the network signal forwarder  110 . 
     The above description illustrates the operation about connecting a remote signal source to other devices of the Cloud RAN system  10  after the remote signal source is activated. It is to be noted that after the remote signal source is activated, if the state of the remote signal source changes (e.g. change in IP address due to moving the remote signal source, or change in service request from the remote signal source), the Cloud RAN system  10  can automatically and correspondingly adjust the network resource information according to the operation as described so as to achieve automatic setting the connection in the Cloud RAN system  10 . 
     The Cloud RAN system  10  can be automatically set to respond to the activation or state change of a remote signal source according to the present disclosure. Furthermore, the Cloud RAN system  10  can be also automatically set to respond to activation or state change of a baseband processing unit according to the present disclosure. Please refer to both  FIG. 1  and  FIG. 2 . When a baseband processing unit is activated, the baseband processing unit actively transmits a signal containing identifiable information to a corresponding network signal forwarder (step S 270 ). In the specification, all the signals generated by the baseband processing units are collectively called baseband processing signals BSP, including the signals containing the identifiable information and the signals generated in response to the access signals. The baseband processing signal BSP may be designed according to any protocol as required. Such variation will not affect the concept of operation of the present system and method, and further description need not be given here. 
     After the network signal forwarder receives the baseband processing signal BSP, steps S 272 ˜S 280  and steps S 252 ˜S 254  are performed as described in the above embodiments. The SDN controller  140  generates the network resource information according to the baseband processing signal BSP containing the identifiable information of the baseband processing unit, and then transmits the network resource information to the network signal forwarder via the control signal IF for storage and later use. In an embodiment, the identifiable information of the baseband processing unit contained in the baseband processing signal BSP may include at least one of an IP address and a MAC address corresponding to the specific baseband processing unit. 
     Similarly, if the state of the baseband processing unit changes (e.g. a new baseband processing unit appears or the IP address of the baseband processing unit changes), the Cloud RAN system  10  can automatically and correspondingly adjust the network resource information stored in the network signal forwarder according to the operation as described so as to achieve automatic maintenance of the architecture of the Cloud RAN system  10 . 
     According to the above-described technology, in response to the activation of the Cloud RAN system  10 , the corresponding relations between the remote signal source(s) and the baseband processing unit pool (or baseband processing unit(s)) is automatically detected, created and recorded without manual operation. Once there appears a new or changed remote signal source or baseband processing unit in the Cloud RAN system  10 , it can be recognized while it is requesting connection. The connection relation or corresponding relation of the new or changed device in the Cloud RAN system  10  is automatically established and stored so as to reduce manual operation. 
     It is to be noted that the signal transmission between the SDN controller  140  and the access management server  130  is independent of the network signal forwarders  110 ,  112  controlled by the SDN controller  140 . In other words, the signal transmitted between the SDN controller  140  and the access management server  130  does not pass through any network signal forwarder (e.g. network signal forwarder  110 ,  112 ) controlled by the SDN controller  140 . By this architecture, the access management server  130  can be hidden from the remote signal sources  100 ( 1 )˜ 100 (N) to prevent from network packet attack from the remote signal sources  100 ( 1 )˜ 100 (N) on the access management server  130 . 
     Please refer to both  FIG. 1  and  FIG. 3 .  FIG. 3  is a flowchart illustrating a control method wherein the signal transmission between the SDN controller and the access management server is independent of the network signal forwarder. 
     As shown in  FIG. 3 , after receiving the access signal, the network signal forwarder determines whether the access signal conforms to a predetermined rule (step S 300 ). In this embodiment, the determination is made by judging whether the access signal matches data in the network resource information. If the access signal does not match data in the network resource information, it is determined that the access signal conforms to the predetermined rule. In other words, when the specific information contained in the access signal matches data in the network resource information, the access signal can be transmitted to the baseband processing unit pool  120  without confirmation from the SDN controller  140  and the access management server  130 . Hence, this condition does not conform to the rule to transmit data to the SDN controller  140 . Otherwise, if the specific information contained in the access signal does not match data in the network resource information, transmission of the access signal to the baseband processing unit pool  120  should be upon confirmation from the SDN controller  140  and the access management server  130 . Hence, this condition conforms to the rule to transmit data to the SDN controller  140  and the access management server  130 . 
     After the determination is made in step S 300 , step S 302  directs the method to a corresponding step according to the determination result. If the access signal does not conform to the predetermined rule (i.e. no confirmation of forwarding the access signal is required), the method goes to step S 310 . In step S 310 , the access signal (the signal from the remote signal source) is forwarded to the corresponding baseband processing unit. Otherwise, if the access signal conforms to the predetermined rule (i.e. confirmation of forwarding the access signal is required), the access signal is not immediately forwarded to the access management server  130 . The access signal should be processed in advance. Hence, the network signal forwarder generates a first notification signal NS 1  according to the access signal, and then transmits the first notification signal NS 1  to the SDN controller  140  (step S 304 ). Subsequently, the SDN controller  140  generates a request signal REQ according to the first notification signal NS 1 , and then transmits the request signal REQ to the access management server  130  (step S 306 ). Lastly, the access management server  130  responds with an access state signal STAT, following a reverse path of the request signal REQ, to the SDN controller  140  (step S 308 ). The detailed operation is similar to steps S 202 ˜S 212  in  FIG. 2 , and is not given here again. 
     According to the architecture and control method, it significantly reduces possibility of network packet attack on the access management server from remote signal sources. Furthermore, since the steps of the control method are similar to some steps in  FIG. 2 , it is easy to integrate the control method with other steps in the above embodiments to provide control methods with various modifications. 
     The access state signal STAT may convey values of multiple maximum transmission rates, at least including a first maximum transmission rate and a second maximum transmission rate wherein the first maximum transmission rate is lower than the second maximum transmission rate. After the baseband processing unit pool  120  has authenticated one of the remote signal sources  100 ( 1 )˜ 100 (N), the baseband processing unit pool  120  transmits an authentication notification signal to the access management server  130  to inform the access management server  130  that a service is about to start. The network packet flow rate required for authentication is usually lower than that for network service. Therefore, the access management server  130  informs the SDN controller  140  according to the authentication notification signal to make the SDN controller  140  to increase the upper limit of the transmission rate between the baseband processing unit pool  120  and the authenticated remote signal source from the first maximum transmission rate to the second maximum transmission rate. 
     Please refer to both  FIG. 1  and  FIG. 4  for illustration of this control method, wherein  FIG. 4  is a flowchart illustrating a control method performed by the Cloud RAN system. Taking the remote signal source  100 ( 2 ) and the access signal AS 2  as an example again, after the SDN controller  140  generates the request signal REQ according to the first notification signal NS 1  and transmits the request signal REQ to the access management server  130  (step S 210  in  FIG. 2  or  FIG. 4 ), the access management server  130  determines whether the access signal AS 2  is valid according to the request signal REQ (step S 400 ). If the access signal AS 2  is invalid, the method goes to step S 410 . Otherwise, if the access signal AS 2  is valid, step S 402  directs the method to step S 404 , and the access management server  130  transmits the first maximum transmission rate to the SDN controller  140  via the access state signal STAT. Upon receiving the access state signal STAT containing the first maximum transmission rate, while updating the network resource information (step S 214 ), the SDN controller  140  limits the transmission rate between the remote signal source  100 ( 2 ) and the baseband processing unit (e.g. baseband processing unit  1206 ) designated to process the access signal AS 2  to be under the first maximum transmission rate. 
     After transmitting the first maximum transmission rate via the access state signal STAT (step S 404 ), the access management server  130  will transmit second maximum transmission rate to the SDN controller  140  via the access state signal STAT (step S 408 ) upon receiving the authentication notification signal (step S 406 ). After receiving the access state signal STAT containing the second maximum transmission rate, the SDN controller  140  increases the upper limit of the transmission rate between the remote signal source  100 ( 2 ) and the baseband processing unit designated to process the access signal AS 2  from the first maximum transmission rate to the second maximum transmission rate. 
     In this embodiment, authentication is performed when the remote signal source  100 ( 2 ) is initially connected to the baseband processing unit designated to process the access signal AS 2 . The authentication establishes preliminary communication between the remote signal source  100 ( 2 ) and the baseband processing unit, designated to process the access signal AS 2 , to create proper communication mechanism and confirm service request. Successful authentication represents that the communication between the remote signal source  100 ( 2 ) and the baseband processing unit designated to process the access signal AS 2  has been well established, and execution of the service request from the remote signal source  100 ( 2 ) can be started. Thus, after the authentication, the corresponding baseband processing unit or the baseband processing unit pool  120  can transmit the authentication notification signal to the access management server  130  to inform that the authentication has been finished successfully and service for the remote signal source starts. 
     In this embodiment, the limit of the transmission rate can be dynamically adjusted with different maximum transmission rates at different stages. Such adjustment can control and arrange the network bandwidth much effectively. Furthermore, the signal transmission between the access management server  130  and the baseband processing unit pool  120  is independent of the network signal forwarders  110 ,  112 . In other words, the signal transmitted between the access management server  130  and the baseband processing unit pool  120  does not pass through any network signal forwarder  110 ,  112 . By this architecture, the access management server  130  can be hidden from the remote signal sources  100 ( 1 )˜ 100 (N) to prevent from network packet attack on the access management server  130  from the remote signal sources  100 ( 1 )˜ 100 (N). 
     With the description of the above embodiments, the system architecture and control method of a Cloud RAN system are provided to reduce manual operation and achieve automatic connection between designated devices in the Cloud RAN system. 
     While the disclosure has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.