Patent Publication Number: US-9408108-B2

Title: Control unit and method for controlling the load in a mobile telecommunications network

Description:
This application is a divisional application of U.S. patent application Ser. No. 11/884,654 filed Aug. 20, 2007, which is the US national phase of international application PCT/SE2005/000224 filed Feb. 18, 2005, which designated the U.S., the entire content of which is hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The technology disclosed herein relates to a control node and a method for use in a telecommunications network. 
     BACKGROUND 
     Mobile telecommunications networks are generally divided into cells, each cell comprising a base station for communicating with mobile terminals within the cell. 
     Therefore, the base stations generally comprise functions for monitoring and controlling the quality of service and the load. 
     In WCDMA networks, the UTRAN comprises one or more base stations controlled by a radio network controller (RNC). According to the standard, the RNC is logically divided into two nodes: the Controlling RNC (CRNC) and the Serving RNC (SRNC). 
     The CRNC is concerned with resource control, that is, keeping the use of resources at a low level without compromising the quality. Resources include all hardware resources in the cell, and also, for example, capacity, interference and encoding. The SRNC monitors and controls the quality of service for each radio connection, including power control, Block Error Rate (BLER), Bit Error Rate (BER). It also keeps track of the type of communication going on in each connection, for example, speech, video or data communication. The SRNC comprises functions for instructing a mobile terminal to perform a handover if the performance becomes too poor. The handover can be performed either by switching to another channel in the WCDMA network or by changing to another network, for example, GSM. 
     If more than one RNC is used, the RNCs also comprise a third logical node, the Drift RNC (DRNC). 
     The load in each particular cell should be controlled so that it does not become too high. 
     It is an object of the technology disclosed herein to enable a method and apparatus for controlling the load in a particular cell. 
     SUMMARY 
     This object is achieved according to the technology disclosed herein by a logical control node for use in a mobile telecommunications network for controlling at least a first base station serving a first cell, said control node comprising functions for controlling resources in said cell and for communicating with a logical service node arranged for controlling quality of service, 
     said logical service node comprising context means for initiating actions needed for a handover, and terminal instruction means for instructing a mobile terminal communicating with said at least first base station to perform a handover, said logical control node being characterized in that it comprises
         determining means for determining if the load in the cell exceeds a first threshold,   selection means for selecting at least one mobile terminal communicating with the at least first base station, that should be moved to another carrier if the load in the cell exceeds the first threshold, and   control node instruction means for instructing the context means in the logical service node to instruct the at least one mobile terminal to perform a handover to the other carrier.       

     The object is also achieved by a logical service node for use in a mobile telecommunications network, said service node comprising functions for controlling the quality of service, and for communicating with a logical control node arranged to control at least a first base station serving a first cell, said logical service node further comprising terminal context means for initiating actions needed for a handover, and terminal instruction means for instructing a mobile terminal communicating in the network to perform a handover, said logical service node being characterized in that the terminal context means is arranged to
         receive from said control node instruction means, a handover instruction to order said terminal instruction means to instruct the at least one mobile terminal to perform a handover to another carrier,   instruct said terminal instruction means to instruct the at least one mobile terminal to perform a handover, when said handover instruction has been received from the control node instruction means.       

     The object is also achieved by a method for use in a mobile telecommunications network comprising at least a first base station serving a first cell, and at least one logical control node for controlling resources in said cell and at least one logical service node for controlling quality of service, wherein said logical service node comprises terminal instruction means for instructing a mobile terminal communicating with said at least first base station to perform a handover, 
     said method being characterized in that it comprises the steps of
         determining, in the logical control node, if the load in the cell exceeds a first threshold,   selecting, in the logical control node, at least one mobile terminal communicating with the at least first base station, that should be moved to another carrier if the load in the cell exceeds the first threshold, and   instructing, by the logical control node, said terminal instruction means in the logical service node to instruct the at least one mobile terminal to perform a handover to the other carrier, and   instructing, by said terminal instruction means, the at least one mobile terminal to perform a handover to the other carrier upon receiving said instruction from the control node instruction means.       

     Thus, the technology disclosed herein enables a handover to be performed in order to move one or more mobile terminals if the load in a particular cell becomes too high. Although the current standard comprises functions for initiating a handover if the service is poor, it does not specify functions for performing a handover based on the load in a cell. 
     According to the technology disclosed herein, the fact that the load is managed by the CRNC while handover functions are managed by the SRNC is overcome by letting the CRNC instruct the SRNC to initiate a handover when the CRNC determines that the load is too high. The CRNC also selects the terminals that are to be instructed to perform a handover. This ensures that the terminals that are selected are the ones that should actually be moved, involving a minimum of signalling between the SRNC and the CRNC. 
     Said control node instruction means may be arranged to instruct said context means by means of an RNSAP message over a Iur interface. In this case, the terminal context means is arranged to receive the handover instruction from the control node instruction means as an RNSAP message over an Iur interface. 
     This enables communication between a CRNC and an SRNC belonging to different RNCs, which is needed when a mobile terminal initiates communication while in one cell then moves to another cell that is controlled by another RNC. 
     In a preferred embodiment said at least one mobile terminal communicates with the at least first base station on a first frequency and said other carrier is a communication channel in the same network using a second frequency which is different from the first frequency. 
     The other carrier may alternatively be a communication channel in a different mobile telecommunications network. 
     In a preferred embodiment, for use in a WCDMA network, the logical service node comprises service indicator means for providing at least one service indicator for said at least one mobile terminal to said selection means in the logical control node. The selection means is arranged to receive at least one service indicator for said at least one mobile terminal from said service node and to base its selection on said service indicator. 
     The service indicator is reported by the exchange in the terrestrial network (MSC or SGSN) to the SRNC when a connection is established. Thus, for the CRNC to perform a selection in this case, the service indicator must be reported from the SRNC to the CRNC. In a preferred embodiment, the service indicator is reported from the SRNC to the CRNC at the establishment of each connection and stored in the CRNC. Alternatively, all service indicators can be reported from the SRNC to the CRNC at certain times, or the CRNC can request the service indicators from the SRNC. The important thing is that the service indicator is available to the CRNC when needed to make a decision about handover. 
     Preferably, the logical service node further comprises handover selection means for selecting the type of handover to be performed. 
     Preferably, the selection means is arranged to base its selection on the type of service between the at least one base station and the at least one mobile terminal. 
     The terminals that are to perform a handover may be selected on the basis of the type of communication going on between each terminal and the respective base station (speech, CS, multi or packet data). For example it will be suitable to select terminals involved in speech communication for handover to GSM since such communication will not suffer from this. 
     The terminals can also be selected on the basis of the service indicator. This is necessary if a handover to another network is to be performed. At present four service indicators are used: 
     Should: the terminal should always be handed over to another network if possible 
     Should not: the terminal may be handed over to another network if the quality of service is poor 
     Shall not: the terminal may never by handed over to another network Missing: no service indicator stated. 
     According to a preferred embodiment, mobile terminals having service indicator “should” or “missing” may be selected for handover if the load is too high. The step of selecting at least one mobile terminal may be based on the traffic class, for example, conversational, streaming, interactive or background, between the at least one base station and the at least one mobile terminal. 
     Alternatively, or in addition to this, the selection of at least one mobile terminal may be based on the rate and/or the use of resources in the connection between the at least one base station and the at least one mobile terminal 
     The technology disclosed herein also relates to a radio control node for use in a CDMA-based telecommunications network, characterized in that it comprises at least one logical control node as defined above. It may also comprise at least one logical service node as defined above, arranged to communicate with the logical control node. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The technology disclosed herein will be described in more detail in the following, with reference to the appended drawings, in which: 
         FIG. 1  is an overview of a mobile telecommunications network comprising one radio network controller controlling a number of base stations 
         FIG. 2  is an overview of a mobile telecommunications network comprising more than one radio network controller, each controlling a number of base stations. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is an overview of a mobile telecommunications network comprising one radio network controller (RNC)  1  controlling a number of base stations  3 , each capable of communicating, in at least one cell, with a number of mobile terminals  5 . As is common in the art, the RNC  1  comprises two logical nodes, a Control RNC (CRNC)  7  and a Service RNC (SRNC)  9 . The CRNC  7  is responsible for controlling the load in each of the cells covered by the base stations  3 . The CRNC comprises load determining means  11  for determining the load of each cell. If the load of a particular cell exceeds a first threshold, one or more mobile terminals  3  communicating in this cell should be moved, if possible. The CRNC  7  therefore comprises selection means  13  for selecting the mobile terminal or terminals communicating with the at least first base station, that should be moved to another carrier if the load in the cell exceeds the first threshold. The CRNC  7  also comprises control node instruction means  15  for instructing the SRNC  9  to instruct the at least one mobile terminal to perform a handover. The SRNC comprises terminal instruction means  17 ,  25  arranged to instruct the mobile terminal or terminals to perform a handover. The CRNC and the SRNC are usually, but not necessarily, implemented in the same physical unit called a Radio Network Controller. 
     In the embodiment shown in  FIG. 1 , the mobile telecommunications network is a WCDMA network. Handover may be performed to another network, or to another frequency in the WCDMA network. In the discussion below it is assumed that the handover should be to another network, such as a GSM network. According to the WCDMA standard, each terminal engaged in communication has a service indicator, also called a service handover, assigned to it. The service indicator is communicated from an exchange (MSC or SGSN) to a service indicator unit  19  in the SRNC  9 . According to this embodiment of the technology disclosed herein, the service indicator unit  19  is arranged to make the service indicator for each connection available to the selection means  13  of the CRNC  7  and the selection means  13  is arranged to base the selection of terminals that are to be moved on the service indicators. The different service indicators, how they should be reported to the selection means  13  and how they may be used in determining which terminals to move, are discussed above. 
     When the selection means  13  has selected the terminal or terminals that are to be instructed to perform a handover to reduce the load in the current cell, it informs the control node instruction means  15  in the CRNC, which instructs a terminal context unit  21  in the SRNC  9  to activate the actions needed for initiating a handover. As, in this case, the handover is to be made from one network (that is, WCDMA) to a different network (that is, GSM), this involves sending an Inter-radio Access Technology (IRAT) action from the control node instruction means  15  to the terminal context unit  21  for initiating an IRAT HO. The terminal context unit  21 , in turn, would instruct an IRAT HO unit  17  to instruct the selected terminal or terminals to perform a handover to the GSM network. 
     Alternatively, the handover could be made to another cell within the same network, in which the load was not so high. In this case, an inter-frequency handover would be carried out. The terminal context unit  21  would then instruct an IF HO unit  25  to instruct the selected terminal or terminals to perform a handover to a selected frequency. Since inter-frequency handover can be performed regardless of the service indicator, the communication between the service indicator unit  19  and the selection unit  13  shown in  FIG. 1  is not needed in this case. 
     The type of handover to be performed, that is, interfrequency or to another network, is usually decided by the terminal context means  21  in the SRNC  9 . It would also be possible to make the decision in the CRNC and include this information in the message from the CRNC to the terminal context means  21 . Alternatively, the CRNC can inform the terminal context means  21  of the preferred type of handover but leave the final decision to the terminal context means. 
     The terminals that are to perform a handover may also be selected on the basis of the type of communication going on between each terminal and the respective base station (speech, CS, multi or packet data). For example it will be suitable to select terminals involved in speech communication for handover to GSM since such communication will not suffer from this. Other parameters that may be used in the decision include the communication rate and the use of resources. The type of communication and/or other parameters can be used in combination with the service indicator. 
     When a handover has been requested from the control node instruction means  15 , the terminal context means  21  preferably responds to the control node instruction means  15  to inform it whether or not the handover was performed successfully. The response may be in the form of an acknowledgement when handover was successful and/or a negative acknowledgement when handover was not successful. It may be feasible to let the negative acknowledgement indicate if the handover was not completed because terminal instruction means decided that it should not be carried out, or if it failed for some other reason. 
       FIG. 2  is an overview of a mobile telecommunications network comprising a first and a second radio network controller (RNC)  31 ,  33 , each controlling a number of base stations  3 . Each base station  3  serves at least one cell, communicating with mobile terminals in the cell. As before, each RNC  31 ,  33  comprises a logical control node  7  and a logical service node,  9  similar to the logical control node and the logical service node of the RNC  1  of  FIG. 1 . To enable communication between the different RNCs  31 ,  33  the second RNC  33  comprises a logical node called the Drift RNC (DRNC)  35 . The skilled person is familiar with the communication between RNCs.  FIG. 2  illustrates a situation when a mobile terminal has started to communicate with a base station  3  controlled by a first RNC  31  and has later performed a handover to another base station  3  controlled by a second RNC  33 . In this case, the logical service node  9  of the first RNC  31  is still responsible for the quality of service of the communication. The load management is, for practical reasons, performed by the logical control node  7  of the second RNC  33 . Thus, the two RNCs  31 ,  33  are both involved in monitoring and controlling the connection. The CRNC  7  of the second RNC  33  communicates with the logical service node  9  of the first RNC  31  through the DRNC  35  of the second RNC  33 . The logical control node  7  of the first RNC  31  and the logical service node  9  of the second RNC  33  are not involved in this example. The SRNC  9  of the second RNC  33  is not needed in this example. 
     The logical control node  7  of the second RNC  33  and the logical service node  9  of the first RNC  31  can be implemented in essentially the same way as shown in  FIG. 1 , the only difference being that the communication passes through the DRNC  35  of the second RNC  33 . Thus, the service indicator unit  19  of the first RNC  31  is arranged to make the service indicator for each connection available to the selection means  13  of the control means  7  of the second RNC  33  through the DRNC  35 . Similarly, the control node instruction means  15  in the CRNC  7  instructs the terminal context unit  21  in the SRNC  9 , through the DRNC  35  of the second RNC  33 , to activate the actions needed for initiating a handover. 
     Between the RNC nodes  31 ,  33  there is an interface Iur, which is defined in the WCDMA standard and is therefore well known to the skilled person. As the skilled person is aware, the Iur interface is adapted to a protocol called the Radio Network Subsystem Application Protocol (RNSAP). The new messages needed according to the technology disclosed herein can easily be implemented in this protocol. For internal communication between an SRNC and a CRNC in the same RNC no standard has been specified.