Abstract:
A telecommunications method for a telecommunications system comprising a user equipment ( 202 ) in dual connection with a primary node ( 204 ) and a secondary node ( 206 ) is disclosed. The method comprises generating configuration information for the user equipment at a virtual radio resource control entity ( 210 ) of the secondary node or at the user equipment; transmitting the configuration information from the secondary node or the user equipment to a radio resource control entity ( 210 ) of the primary node; and transmitting the configuration information from the primary node to the other of the user equipment or secondary node from where the configuration information is received.

Description:
FILED OF THE INVENTION 
       [0001]    The present invention relates to a telecommunications method for a telecommunications system comprising a user equipment in dual connection with a primary node and a secondary node, a telecommunications system, a primary node, a secondary node and to a user equipment. 
       BACKGROUND OF THE INVENTION 
       [0002]    Small Cells are low power, low-cost base stations that are able to provide cellular service in residential or enterprise environments, with a typical coverage range of tens of metres. They have auto-configuration and self-optimization capabilities that enable a simple plug and play deployment, and are designed to automatically integrate themselves into an existing macrocellular network. Small cells, often referred to as pico cell, or metro cell, typically use the customer&#39;s broadband internet connection, for example DSL, cable or the like, as backhaul towards the macrocellular network. Support of non-ideal backhaul (with one way latency of few milliseconds to few tens of milliseconds) between small cells and between small cell and macro cells is considered as the typical deployment scenario. 
         [0003]    Small cell deployment for handling the capacity needs in high traffic areas, such as hot spot areas, is an area of current investigation. One proposal for handling the capacity needs in high traffic areas is to provide dual connectivity support for user equipment. Dual connectivity support allows a User Equipment (UE) to be connected concurrently connected to a macro cell and a small cell, or indeed to two small cells. In other words, the UE can be connected to more than one cell at a time and the UE can be served by more than one cell at a time. Dual connectivity support is considered as a way to enable offloading of traffic when required. 
         [0004]    However, dual connectivity support raises a number of issues relating to Radio Resource Control (RRC) plane architecture. 
         [0005]    It is desirable to provide a RRC architecture which simplifies UE implementation/operation as well as avoiding the need for inter-protocol communication over an open interface. 
       SUMMARY OF THE INVENTION 
       [0006]    According to a first aspect of the invention, there is provided a telecommunications method for a telecommunications system comprising a user equipment in dual connection with a primary node and a secondary node, the method comprising: generating configuration information for the user equipment at a virtual radio resource control (RRC) entity of the secondary node or at the user equipment; transmitting the configuration information from the secondary node or the user equipment to a radio resource control entity of the primary node; and transmitting the configuration information from the primary node to the other of the user equipment or secondary node from where the configuration information is received. 
         [0007]    The proposed radio resource control plane architecture simplifies the UE implementation/operation as well as avoiding the need for inter-protocol communication specification, which is seen cumbersome when considering inter-vendor operation where the inter-protocol layer communication is usually left to the vendor specific macro cell eNB implementation. 
         [0008]    The method may further comprise generating configuration information at a radio resource control entity of the user equipment. 
         [0009]    The radio resource control entity of the primary node may include configuration information from the secondary node in a downlink radio resource control message sent to the user equipment. 
         [0010]    The downlink radio resource control message may be transmitted from the primary node to the user equipment using a radio resource control connection between the radio resource control entity of the primary node and the user equipment. 
         [0011]    The user equipment may decode the radio resource control message as it is received from the primary node, using security and transmission channel parameters of the primary node. 
         [0012]    The radio resource control entity of the primary node may include configuration information from the user equipment in an uplink radio resource control message sent to the secondary node. 
         [0013]    The method may further comprise transmitting the configuration information from the primary node to the user equipment via the secondary node, using layer 2 and/or layer 1 protocols or transmitting the configuration information to the secondary node via the user equipment, using layer 2 and/or layer 1 protocols. 
         [0014]    The configuration information may be transmitted from the secondary node or user equipment to the primary node in a transparent container, wherein the transparent container may be forwarded to the other of the user equipment and secondary node, without the primary node decoding the configuration information in the transparent container. 
         [0015]    The method may further comprise the primary node performing ciphering and/or integrity checks on the configuration information based on security keys. The ciphering and/or integrity checks may be performed by the packet data convergence protocol (PDCP) entity of the primary node. 
         [0016]    The configuration information may be transmitted from the secondary node to the radio resource control entity of the primary node using modified X2 communications protocols. 
         [0017]    An identification may be transmitted with the configuration informing, identifying the origin of the configuration information. 
         [0018]    The primary node may be a macro cell node and the secondary node is a small cell node. 
         [0019]    According to a second aspect of the invention, there is provided a telecommunications system, comprising: a primary node comprising a radio resource control (RRC) entity; a secondary node comprising a virtual radio resource control entity; and a user equipment in dual connection with the primary node and the secondary node, wherein the virtual radio resource control entity is operable to generate configuration information for the user equipment and transmit the configuration information to the radio resource control entity of the primary node, the user equipment is operable to generate configuration information and transmit the configuration information to the radio resource control entity of the primary node; and the radio resource control entity of the primary node is operable to transmit received configuration information to the other of the user equipment or secondary node from where the configuration information is received. 
         [0020]    According to a third aspect of the invention, there is provided a primary node of a telecommunications system comprising a user equipment in dual connection with the primary node and a secondary node, the primary node comprising: a radio resource control (RRC) entity operable to receive configuration information for the user equipment from a virtual radio resource control entity of the secondary node or from the user equipment, and operable to transmit the received configuration information to the other of the user equipment or secondary node from where the configuration information is received. 
         [0021]    According to a fourth aspect of the invention, there is provided a secondary node of a telecommunications system comprising a user equipment in dual connection with the secondary node and a primary node, the secondary node comprising: a virtual radio resource control (RRC) entity operable to generate configuration information for the user equipment and transmit the configuration information to a radio resource control entity of the primary node for subsequent transmission to the user equipment, and operable to receive configuration information from the user equipment via the radio resource control entity of the primary node. 
         [0022]    According to a fifth aspect of the invention, there is provided a user equipment of a telecommunications system comprising a primary node and a secondary node, wherein the user equipment is in dual communication with the primary node and the secondary node, and the user equipment is operable to receive a configuration information for the user equipment from the secondary node via a radio resource control (RRC) entity of the primary node, and is operable to generate configuration information and transmit the configuration information to the radio resource control entity of the primary node for subsequent transmission to the secondary node. 
         [0023]    According to a sixth aspect of the invention, there is provided a computer program product operable when executed on a computer to perform the method of the above first aspect. 
         [0024]    Further particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Some embodiments of the apparatus and/or methods in accordance with embodiment of the present invention are now described, by way of example only, with reference to the accompanying drawings, in which: 
           [0026]      FIG. 1  shows an example of a telecommunications network comprising a small cell cluster and a macro cell; 
           [0027]      FIG. 2  shows proposed control plane architectures; 
           [0028]      FIG. 3  shows the control plane architecture according to a first embodiment; 
           [0029]      FIG. 4  shows the control place architecture according to a second embodiment; 
           [0030]      FIG. 5  shows alternative architecture configurations of layer 2/layer 1; and 
           [0031]      FIG. 6  shows the lower protocol layer control from the virtual RRC at the secondary/assisting cell. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0032]      FIG. 1  illustrates a heterogeneous telecommunications network  10  comprising a macro cell  12  and a cluster of small cells  14 . The cluster of small cells  14  comprises a first small cell  16 , a second small cell  18 , a third small cell  20 , a fourth small cell  22  and a fifth small cell  24 . The small cells are distributed geographically to provide an area of coverage within the macro cell  12 . User equipment (not shown) may roam through the network  10 . When the user equipment is located within the macro cell  12 , communications may be established between the user equipment and the macro cell base station  26  over an associated radio link. If the user equipment is located geographically within one of the small cells  16 ,  18 ,  20 ,  22  and  24 , communications may be established between the user equipment and the base station of the associated small cell over an associated radio link. Of course, it will be appreciated that  FIG. 1  shows only an example heterogeneous network and that a plurality of macro cells may be provided, more or less than five small cells may be provided and a plurality of small cell clusters may be provided. 
         [0033]    As described above, within the macro cell  12 , there is provided a plurality of small cell base stations which provide a plurality of small cells  16 ,  18 ,  20 ,  22 , and  24 . The small cells provide local communications coverage for a user in their vicinity. As a user equipment comes within range of a small cell, such as the first small cell  16 , a handover may occur between the base station  26  of the macro cell and the base station  28  of the small cell, when the base station of the small cell detects that user equipment has come within range. Likewise, as a user equipment comes within range of a different small cell, a handover may occur between the base station of the current small cell and the base station of the new small cell, when the base station of the new small cell detects that user equipment has come within range. 
         [0034]    In order to handle the capacity needs of a high traffic area, a user equipment in the telecommunications network  10  of  FIG. 1  may be provided with dual connectivity support. That is, a user equipment may be connected to both the macro cell  12  and the small cell  16 . Also, it should be appreciated that a user equipment may be dual connected to small cell  16  and any of the other small cells  18  to  24 . 
         [0035]      FIG. 2  shows proposed control plane architectures in which a user equipment (UE) is dual connected to a macro cell and a small cell. 
         [0036]    In  FIG. 2A , a UE  100  is dual connected to a macro cell  102  and a small cell  104 . The macro cell  102  is sometimes referred to as the anchor eNB and the small cell is sometimes referred to the anchor eNB. An RRC entity  106  is maintained in the UE  100  and an RRC entity  108  is maintained in the macro cell eNB  102 . RRC signaling is transmitted and received via radio resources provided by the macro cell  102 . In the control plane architecture of  FIG. 2A , the small cell  104  does not contain a RRC entity. It is therefore necessary for the small cell  104  to communicate control plane/configuration information to the macro cell  102  using Layer 2/Layer 1 protocols, which must then in turn communicate this configuration information to the UE  100  using RRC communication protocols. 
         [0037]    The proposed architecture of  FIG. 2A  has the disadvantage that it requires a new set of specifications for the inter-protocol layer communication between the RRC entity  108  located at the macro eNB  102  and the Layer 2 protocols located at the small cell  104 . Such inter-protocol specifications are not provided for in the current specification of LTE, as defined in 3GPP specification, TS 36.331 v11.3.0. 
         [0038]    In  FIG. 2B , a UE  110  is dual connected to a macro cell  112  and a small cell  114 . An RRC entity  116  is maintained in the UE  110 , an RRC entity  118 , sometimes referred to as an anchor RRC entity, is maintained in the macro cell eNB  112 , and an RRC entity  120 , sometimes referred to as an assisting RRC entity, is maintained in the small cell eNB  114 . In the control plane architecture of  FIG. 2B , each node/cell involved in dual connectivity maintains an RRC entity which partly interacts with the RRC entity  116  in the UE  110 . 
         [0039]    In  FIG. 2B , RRC signaling can be transmitted/received via radio recourses of the cell in which the corresponding function is maintained. For example, it could be that physical radio resource configuration related parameters for the small cell  114  are controlled by and signaled from the small cell  114 , whereas other parameters are controlled by and signaled from the macro cell  112 . 
         [0040]    In  FIG. 2C , a UE  130  is dual connected to a macro cell  132  and a small cell  134 . An RRC entity  138 , is maintained in the macro cell eNB  112  and an RRC entity  140  is maintained in the small cell eNB  114 . The UE  130  maintains a first RRC entity  142  corresponding to the macro cell  132  and a second RRC entity  144  corresponding to the small cell  134 . 
         [0041]    In the control plane architecture of  FIG. 2C , an RRC entity per each node/cell involved in dual connectivity is maintained in the UE  130  and in the network. The RRC entities can be dependent or independent of each other. The mechanism for RRC transmission/reception signalling via radio recourses of the cell are similar those described in relation to  FIG. 2B . 
         [0042]    In the control plane architectures of  FIGS. 2B and 2C , the RRC entities located at the macro and small cell jointly provide the necessary lower parameter configuration for the lower protocol layer operations. The RRC entity at the small cell controls the functions and lower protocol parameters controlled by the small cell, while the RRC entity at the macro cell controls the global UE functions. Therefore, the RRC entity located at small cell is seen as secondary RRC entity while the RRC located at macro cell is seen as the primary RRC entity. From the functionality point of view operation of the control plane architectures of  FIGS. 2B and 2C  is similar, the only difference being the RRC protocol modelling at the UE. RRC is modelled as a single RRC entity in  FIG. 2B  while in  FIG. 2C , the RRC is modelled as two RRC entities. 
         [0043]    The control plane architectures of  FIGS. 2B and 2C  have the disadvantage that they require complex security architecture given that the RRC signal from the macro eNB and small cell eNB is required to be protected with sets of keys which are generated independently. This also increases the complexity at the UE. 
         [0044]    As described above, the proposed control plane architectures of  FIGS. 2A, 2B and 2C  have a number of significant drawbacks. It is desirable to provide an RRC architecture which eliminates the problems seen in control plane architectures of  FIGS. 2A, 2B and 2C  for RRC protocol layer support for dual connectivity. 
         [0045]      FIG. 3  shows a control plane architecture  200  according to a first embodiment. In  FIG. 3 , a UE  202  is provided with two serving cells. UE  202  is dual connected to a macro cell  204  (anchor eNB) and a small cell  206  (assisting eNB). It will be appreciated that although  FIG. 3  shows the UE in connection with a macro cell and a small cell, the UE may be in dual connection to a first and second small cell. 
         [0046]    Both the macro cell  204  and the small cell  206  will have RRC protocol functions/configuration information for the UE  202  during dual connectivity. However, the UE  202  only has one RRC protocol entity/layer communicating with one of the serving cells, in the embodiment shown in  FIG. 3 , this is the macro cell  204 . In  FIG. 3 , the UE  202  has an RRC connection with the macro cell  204 . This RRC connection is established between an RRC entity  208  maintained in the UE  202  and an RRC entity  210  maintained in the macro cell  204 . 
         [0047]    In other words, the small cell  206  must communicate its configuration information to the UE  202  via the macro cell  204 . In view of this, the macro cell  204  may be considered to be a primary cell/node of the telecommunications network and the small cell  206  may be considered to be a secondary cell/node of the telecommunications network. 
         [0048]    As the small cell  206  does not communicate RRC configuration information directly to the UE  202 , the RRC entity  212  in the small cell  206  may be considered to be a virtual RRC entity to the UE  202 . 
         [0049]    The RRC entity  210  in the macro cell and the virtual RRC entity  212  in the small cell may communicate over an Xx interface  214  between small and macro cells. This interface  214  may be a modified version of the X2 interface, or may be a new interface not currently defined in the LTE specification or other backhaul link. 
         [0050]    In the case that the small cell  206  has configuration information to send to the UE  202 , the small cell  206  may generate configuration information for the UE  202  and forward this configuration information to the macro cell RRC entity  210 . The configuration information may be RRC configuration information and may comprise layer 3, layer 2, layer 1 configurations for the small cell. In other words, the virtual RRC protocol layer (entity) located at the small cell (assisting) eNB may generate RRC configuration information relevant to the small cell including the small cell lower protocol parameter configuration, and may transmit this configuration information to the RRC entity  210  of the macro cell  204 . 
         [0051]    The configuration information may be transmitted to the RRC entity  210  of the macro cell  204  in a transparent container. That is, the macro cell RRC entity  212  will not control the message in the transparent container and will not decode the configuration information delivered in the transparent container. The RRC entity  212  will simply forward the configuration information to the UE. 
         [0052]    The RRC entity  212  of the macro cell may encapsulate the configuration information for transmission to the UE in an RRC configuration message. The RRC entity  212  transmits the configuration information delivered from virtual RRC entity  212  of the small cell to the UE  202  over the Uu interface  216 . The Uu interface  216  may be an S1 communications interface or any other suitable radio interface. 
         [0053]    Ciphering and integrity protection for the configuration may be performed at the macro cell  204  based on macro cell eNB security keys. The ciphering and integrity protection on the configuration information may be performed by the packet data convergence protocol (PDCP) located at the anchor eNB (layer L2). 
         [0054]    The UE  202  decodes the configuration information/RRC configuration message as it is received from the macro cell RRC entity  212 , using security and transmission channel parameters of the macro cell eNB for the message decoding. 
         [0055]    In the above architecture RRC protocol located at the small cell may be seen as virtual RRC layer to the UE. However, the lower layers (eg: layer 2/Layer 1) of small cell is controlled directly by the virtual RRC located at the small cell. Therefore, In the embodiment of  FIG. 3 , the need for additional specification to be provided for inter-protocol communication is eliminated as both the controller, the virtual RRC entity in the embodiment of  FIG. 3 , and the layer 2 protocols are located at the same cell, the small cell in the embodiment of  FIG. 3 . 
         [0056]      FIG. 4  shows the control place architecture  201  according to a second embodiment. In the embodiment of  FIG. 4 , the control information generation is the same as that described above in relation to  FIG. 3 , and like features share the same reference numerals. 
         [0057]    However, in  FIG. 4  the transmission of the configuration information from the macro cell RRC entity  210  to the UE  202 , may additionally take a transmission path  218  via the small cell eNB  206 . 
         [0058]    In other words, the virtual RRC entity  212  of the small cell may generate configuration information and this may be transmitted to the RRC entity  210  of the macro cell over Xx interface  214 . The RRC entity may then transmit the configuration information to the UE  202  via the small cell over a transmission path  218 . The transmission path  218  may be an S1 communications interface or any other suitable radio interface. 
         [0059]    The small cell  206  receives the configuration information from the RRC entity  210  of the macro cell over transmission path  218 , and extracts the layer 2/layers 1 protocol information from the configuration information at a layer 2/layer 1 entity  219  and transmits this layer 2/layer 1 protocol information to the UE  202 . 
         [0060]    The UE  202  comprises a first layer 2/layer 1 protocol entity  220  associated with the macro cell  204  and a second layer 2/layer 1 protocol entity associated with the small cell  206 . The second layer 2/layer 1 protocol entity  222  receives the layer 2/layer 1 protocol information from the small cell  206  on transmission path  218 , and decodes as necessary. Although  FIG. 4  shows the UE  202  having first and second layer 2/layer 1 protocol entities, it should be appreciated that the function of these may be combined in a single layer 2/layer 1 protocol entity. 
         [0061]    As layer 2/layer 1 protocol information is sent form the small cell  206  to the UE  202  on transmission path  218 , rather than RRC configuration information, the need for additional specification to be provided for inter-protocol communication is eliminated. 
         [0062]    By providing this additional transmission path for the configuration information from the macro cell RRC entity, transmission diversity for configuration information transmission may be provided, which may be beneficial should the configuration information experience different transmission qualities over different transmission paths. 
         [0063]    It should also be appreciated that a cell identifier may be transmitted together with the configuration information in the embodiments of  FIGS. 3 and 4 , in order to identify the corresponding cell from which the configuration information relates. 
         [0064]    Although  FIGS. 3 and 4  are described with reference to downlink transmissions from the network to the UE, it will be appreciated that the embodiments are equally applicable to uplink transmission from the UE to the network. In other words, the UE may generate configuration and this may be transmitted to the small cell via the macro cell. 
         [0065]      FIG. 5  shows alternative architecture configurations for layer 2/layer 1 for the embodiments of  FIG. 3  and  FIG. 4 . The layer 2/layer 1 protocol architecture of  FIG. 3  and  FIG. 4  may take any of the architecture option shown in  FIGS. 5A, 5B, 5C and 5D . 
         [0066]      FIG. 5A  shows the layer 2/layer 1 architecture for a macro cell  300  and a small cell  302 . The macro cell  300  comprises a Packet Data Convergence Protocol (PDCP) entity  304 , a Radio Link Control (RLC) entity  306  and a Media Access Control (MAC) entity  308 . The small cell  302  comprises a PDCP entity  310 , a RLC entity  312  and a 
         [0067]    MAC entity  314 . In the embodiment of  FIG. 5A , both the PDCP entity  304  of the macro cell  300  and the PDCP entity  310  of the small cell  302  receive information from core network with regards to the EPS bearer through S1 communications interfaces. 
         [0068]      FIG. 5B  shows the layer 2/layer 1 architecture for a macro cell  320  and a small cell  322 . Like  FIG. 5A , the macro cell  320  comprises a PDCP entity  324 , a RLC entity  326  and a MAC entity  328 . The small cell  322  comprises a PDCP entity  330 , a RLC entity  332  and a MAC entity  334 . However, in the embodiment of  FIG. 5B , the PDCP entity  324  of the macro cell  320  receives information through an S1 communications interface and the PDCP entity  330  of the small cell  322  receives information through an Xn interface, which may be a modified X2 interface, via the higher layer RRC protocol of the macro cell  320 . 
         [0069]      FIG. 5C  shows the layer 2/layer 1 architecture for a macro cell  340  and a small cell  342 . In  FIG. 5C , the macro cell  340  comprises a first PDCP entity  344  and a second PDCP entity  346 , a RLC entity  348  and a MAC entity  350 . The small cell  342  comprises a RLC entity  352  and MAC entity  354 . In the embodiment of  FIG. 5C , the first and second PDCP entities  344 ,  346  of the macro cell  340  receive information through S1 communications interfaces. The RLC entity  352  of the small cell  342  receives information through an Xn interface, which may be a modified X2 interface, from the second PDCP entity  346  of the macro cell  340 . 
         [0070]      FIG. 5D  shows the layer 2/layer 1 architecture for a macro cell  360  and a small cell  362 . In  FIG. 5D , the macro cell  360  comprises a first PDCP entity  364  and second PDCP entity  366 , a first RLC entity  368  and a second RLC entity  370  and a MAC entity  372 . The small cell  362  comprises an RLC entity  374  and a MAC entity  376 . The RLC entity  374  is shown with a dotted line, because this RLC at the small cell may not perform the whole of RLC protocol functions/procedures and so may be considered to act as a sub-set of RLC. In the embodiment of  FIG. 5D , the first and second PDCP entities  364 ,  366  of the macro cell  360  receive information through S1 communications interfaces. The RLC entity  374  of the small cell  362  receives information through an Xn interface, which may be a modified X2 interface, from the second RLC entity  370  of the macro cell  360 . 
         [0071]      FIG. 5  shows how lower level protocol control can be achieved in the architectures of the embodiments of  FIGS. 3 and 4 . 
         [0072]      FIG. 6  shows how the lower protocol layers of the small cell of  FIGS. 3 and 4  are controlled by the virtual RRC entity of the small cell. The virtual RRC entity may directly control each of the PDCP entity, RLC entity and MAC entities of the small cell. Given the inter protocol layer communication here all occurs within the same node, it is not necessary to provide and additional control specifications for this inter-protocol layer communication. The inter-protocol layer communication is left to the specific implementation at the small cell eNB. 
         [0073]    In order to distinguish RRC messages which are corresponding to the macro cell from that of small cell, the messages or information could also be tagged with cell specific identification. This may take the form of implicit or explicit indication. if the messages and parameters for small cell is different from that of macro cell, the cell specific identification is implicitly indicated by the message or parameter itself. 
         [0074]    The present inventions may be embodied in other specific apparatus and/or methods. The described embodiments are to be considered in all respects as only illustrative and not restrictive. In particular, the scope of the invention is indicated by the appended claims rather than by the description and figures herein. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.