Abstract:
A baseband module for a base station is in a mobile communication network. The baseband module includes at least two baseband devices connected to each other by an internal interface, thereby forming a chain of baseband devices. The baseband module is connected to a radio frequency module by two external interfaces, each external interface being connected to a baseband device at the end of the chain of baseband devices.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a baseband module suitable to be used in a radio network element, such as a base station within a mobile network.  
       BACKGROUND OF THE INVENTION  
       [0002]     Increased demand and availability of mobile Internet services will create challenges for network operators and service providers due to the rising cost of the infrastructure. Large number of base transceiver stations (BTS) are needed to support the new technologies and to satisfy the capacity demand of the advanced services.  
         [0003]     The Open Base Station Architecture Initiative (OBSAI) is an organization that aims to create a set of open specifications for the base station architecture. OBSAI has defined a modular base station architecture and detailed specifications for the interfaces between the modules. This architecture is depicted in  FIG. 1 . The base station in  FIG. 1  includes a transport module  100  providing adaptation between external network interfaces and standard BTS internal interfaces. The processing module  102  provides baseband processing for the air interface and the radio module  104  provides radio frequency (RF) transceivers and conversion between digital baseband signals and analogue RF signals. Function module  106  includes functionality needed by the radio module. The control module  108  provides control processing of the base station. The open interfaces defined by OBSAI are shown in  FIG. 1  by reference points RP 1 , RP 2  and RP 3 . RP 1  interchanges control, such as status, alarm and synchronization data. RP 2  interchanges user data between the transport module and the processing module. RP 3  interchanges formatted air interface user data and fast control data between the base band module and the radio module.  
         [0004]      FIG. 2  illustrates one prior art base station topology, a star topology, for implementing the baseband module.  FIG. 2  also shows the external interface  214  between the baseband module  202  and the RF module  204 . The baseband module  202  includes a number of baseband devices  222 A to  222 D (indicated by F 1  to F 4 ) and a routing device  220  (indicated by O). The routing device is responsible for distributing/collecting all data to/from the baseband devices via the internal interfaces  224 A to  224 D.  
         [0005]     In  FIG. 2 , the interfaces can include at least one OBSAI RP 3  interfaces, for instance. As shown by  FIG. 2 , the data transfer capacity of the external interface and all the internal interfaces  224 A to  224 D is “N*RP 3 ” (only data rate of  224 A is shown in the figure), where N refers to the number of sub-interfaces and RP 3  to the type of interface. In the case of RP 3 , the smallest data rate is 768 Mbps. The star topology has the disadvantage that an expensive routing device is needed.  
         [0006]     Another prior art topology avoiding the use of a separate routing device is shown in  FIG. 3 . In this so-called daisy chain topology, the baseband devices  322 A to  322 D are arranged in a chain and the baseband device  322 A is directly connected to an external interface  314 . The number of interfaces (N) and the data rate of the baseband internal interfaces  324 A to  324 C is the same as in the external connections. In spite of the advantages over the star topology, the daisy-chain topology still suffers from a large number of interfaces per baseband device.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0007]     It is thus one object of the present invention to simplify the structure of the baseband module.  
         [0008]     In one aspect of the invention there is provided a baseband module for a base station in a mobile communication network, comprising at least two baseband devices connected to each other by an internal interface thereby forming a chain of baseband devices, the baseband module being connected to a radio frequency module by two external interfaces, each external interface being connected to a baseband device at the end of the chain of baseband devices.  
         [0009]     In one aspect of the invention, there is provided a data transmission method in a base station of a mobile communication network, comprising the step of transferring data in an external interface between a baseband module and a radio frequency module via both ends of a chain of baseband devices belonging to the baseband module.  
         [0010]     The preferred embodiments of the invention are disclosed in the dependent claims.  
         [0011]     The invention thus relates a base band module suitable to be used in base stations in a mobile network. A baseband module performs the baseband processing of a base station. The base station may contain several baseband modules, which each process some part of the baseband processing for the different carriers supported by the base station. An example implementation of a baseband module is a printed circuit board. The baseband module typically consists of several identical baseband processing devices. Each processing device performs some portion of the baseband processing done on the baseband module. A baseband processing device may be, for example, an integrated circuit or a cluster of integrated circuits. The baseband processing device may contain a programmable processor, acceleration hardware and interfacing hardware.  
         [0012]     The concept base station covers all various network elements suitable for implementing the air interface towards mobile terminals using the network. Thus the base station covers a base station according to the GSM (Global System for Mobile Communication) system and Node B of UMTS (Universal Mobile Telephony System) system, for instance. Other corresponding network elements in other mobile networks are considered covered by the inventive idea.  
         [0013]     In one embodiment, the inventive idea is applied to a base station complying with the architecture standardized by OBSAI. In that case, the interface between the baseband and RF modules is an RP 3  interface. The OBSAI structure as explained in accordance with the invention shall be considered to represent one advantageous embodiment, without restricting the invention thereto. The data rates of the interfaces and sub-interfaces presented have thus been given as examples, not in order to delimit the invention.  
         [0014]     The invention is characterised by the idea that both ends of the chain of baseband devices are connected to an RF module. In the context of the invention, the interface towards the RF module is called “external interface”. The baseband module has thus two external interfaces, one from each end of the chain. Each external interface includes one or more sub-interfaces, such as RP 3  interfaces. The interfaces between the baseband devices are called “internal interfaces”. Correspondingly, each internal interface includes one or more sub-interfaces. Each sub-interface has a minimum data transmission rate, referred to as “rate”. Sub-interfaces using a higher data rate than the minimum data rate are referred to as “double rate” or “triple rate”, for instance. In the baseband module internal interfaces it is possible to use even higher data rates than “triple rate”, which is here given only as an example.  
         [0015]     In one aspect of the invention, the baseband devices in the end of the chain comprise a larger number of external sub-interfaces than internal sub-interfaces. This reduction of internal sub-interfaces is achieved by using a higher data rate in the internal interfaces than in the external interfaces. The data rate in the internal interface can be equal or even exceed the sum of the data rates in the external interfaces.  
         [0016]     In the invention, data can be transferred in both directions along the chain, which is a daisy chain, for instance. That is, uplink data received from mobile terminals can be moved both ways along the chain of baseband devices. The baseband module is thus configured to transfer data received in either end of the chain to all the baseband devices belonging to the chain, if needed.  
         [0017]     The invention provides the significant advantage that the number of interfaces per device in the baseband module can be reduced, thereby resulting into a simplified baseband module structure and savings in the development costs of the module. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     In the following the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawings, in which  
         [0019]      FIG. 1  illustrates an already explained prior art modular base station structure;  
         [0020]      FIG. 2  illustrates an already explained prior art topology;  
         [0021]      FIG. 3  illustrates another already explained prior art topology;  
         [0022]      FIG. 4A  shows one embodiment of a topology according to the invention;  
         [0023]      FIG. 4B  illustrates another view of the embodiment of  FIG. 4A ;  
         [0024]      FIG. 5  shows still one embodiment of the invention;  
         [0025]      FIG. 6A  shows one embodiment of a topology according to the invention;  
         [0026]      FIG. 6B  illustrates another view of the embodiment of  FIG. 6A ;  
         [0027]      FIG. 7  shows one embodiment of the method according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]      FIG. 4A  shows one embodiment of a topology according to the invention. In  FIG. 4A , the baseband devices  422 A to  422 D within a baseband module  402  are arranged in a chain so that the baseband devices F 3  and F 4  in the middle of the chain have an interface with two other baseband devices. F 3 , for instance, has internal interfaces  424 B and  424 C to F 2  and F 4 . The baseband devices at the end of the chain, that is, devices F 1  and F 2  have one internal interface and one external interface. F 1 , for instance, has an internal interface  424 A with baseband device F 4  and an external interface  414 A with RF module  404 A.  
         [0029]     In  FIG. 4A , the baseband processing capacity of the baseband module is 2+2 meaning that there are two carrier waves and two sectors to be served. Each carrier wave is transmitted/received by two antennas whereby the baseband module  402  shall be capable of handling 8 duplex data streams. Therefore, the baseband module has two external RP 3  sub-interfaces, each of the sub-interfaces being capable of handling 4 data streams.  
         [0030]      FIG. 4A  shows how this need is satisfied in one embodiment of the invention. The baseband device  422 A has been illustrated to have one RP 3  interface with RF module  414 A and the other external interface  414 B is operated by the baseband device  422 D. The baseband module  402  shall be capable of transmitting all data to each baseband device  310 A to  310 D in the chain. That is, baseband device F 2   422 D shall have the possibility to transmit data via the external interface  414 A as well as via the external interface  414 B served by itself. Vice versa, data received via the interface  414 A shall be transmitted to device  422 D if need be, that is, if device  422 D is responsible for processing user data for a user that is in connection with the baseband module via the interface  414 A.  
         [0031]     In order to be able to support the described two-directional transmission in the internal interfaces, the internal interfaces in  FIG. 4A  are configured to be double rate interfaces compared to single rate interfaces at the external interfaces  414 A and  414 B. Reference is made to  FIG. 3 , where the total number of needed RP 3  interfaces is 8.  FIG. 4A  shows that in the disclosed embodiment, only 5 RP 3  interfaces are needed.  
         [0032]      FIG. 4B  specifies the embodiment of  FIG. 4A . External interfaces  414 A and  414 B have been illustrated to include one RP 3  sub-interface meaning that the interface supports duplex data stream at a predetermined rate.  FIG. 4B  also shows the internal double rate RP 3  sub-interfaces  424 A to  424 C. For instance, in the interface  424 A, the interface is capable of conveying also uplink data received via the interface  414 B in addition to uplink data received via the interface  414 A. The uplink and downlink functionalities can be separated, in the baseband device, as shown in  FIG. 4B . Additionally, baseband devices are configured to receive uplink and downlink data from either the neighbouring baseband device or the external interface. Correspondingly, a base band device comprises means for transmit downlink data towards both two internal, or one internal and one external, interfaces that the baseband device has.  
         [0033]      FIG. 5  illustrates another embodiment of the invention. The baseband module  502  arranged to support a 6-sector configuration, wherein one or two double rate carriers are served in each sector. The RF module  504 A supports four sectors and RF module  504 B serves two carrier waves in two sectors. Each double rate RP 3  can thus transfer data of 2 carriers transmitted in two sectors. The internal interfaces have a higher transmission capacity, that is, triple rate. The internal interfaces  524 A to  524 C are thereby capable of serving all the data transferred over both external interfaces  514 A and  514 B. From  FIG. 5  it can be seen that altogether 9 RP 3  interfaces are needed. If a baseband module supporting the similar amount of RF interfaces would be constituted using the prior art chain topology of  FIG. 3 , altogether 12 RP 3  interfaces would be needed, since both the external and internal interfaces would have the transmission capacity of 3*(double rate RP 3 ).  
         [0034]      FIG. 6A  shows still an embodiment of a topology according to the invention, that is, a configuration capable of supporting 4 carriers in three sectors (4+4+4). Both of the external interfaces are capable of handling one single rate RP 3  and one double rate RP 3 . The total processing capacity of the baseband module is thus 4+4+4, that is, four carrier waves in three sectors. The internal interfaces  624 A to  624 C have been depicted to have two triple rate interfaces.  
         [0035]     The embodiment of  FIG. 6A  is further specified in  FIG. 6B  illustrating the data rates in the various interfaces. The total number of RP 3  interfaces is shown to be 10, whereas the implementation of the same as a single-end daisy chain would require 16 RP 3  interfaces.  
         [0036]     In the example topologies presented above, it can be seen that part of the data flows in one direction and part to the other direction. To comply with the data streams coming from different directions, additional buffering can be provided in the baseband devices to re-align the data streams and to compensate for possible latency of the data streams. Furthermore, in order to support different data rates in the two interfaces of a baseband device, multiplexing/demultiplexing of data streams can be provided. This especially concerns baseband devices in the ends of the chain having one external interface and one internal interface. If, for instance, two external sub-interfaces shall be combined to one internal sub-interface, data has to be multiplexed between the interfaces.  
         [0037]     One embodiment of the method according to the invention is illustrated in  FIG. 7 . Step  700  shows a configuring step of the method, that is, manufacturing of a printed circuit board, where individual baseband devices are in the form of the chain. The both ends of the chain are according to step  702  connected to a radio frequency module. When the base station is in use, data is transferred in the chain at a higher data rate than towards the RF module. In one embodiment of the method when the base station is in use, uplink data can traverse in the chain in both directions. In one embodiment, the uplink and downlink data are multiplexed into the same internal interface. The baseband module shall be capable of transferring the received data through the whole chain until the device responsible for processing data has been reached. The same applies to downlink data, the baseband module is configured to transfer data to be transmitted through the whole chain, if need be.  
         [0038]     It will be obvious to a person skilled in the art that, as technology advances, the inventive idea can be implemented in various ways. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.