Centralized radio network controller

In a radio access network, novel systems and methods reduce processing delay, and improve integration with IP networks, by separating user data from connection management and control data at a Node B or at a base station. The user data are routed to an IP (Internet Protocol) switch, whereas the connection management and control data are routed to a centralized radio network controller (RNC). Pursuant to a second embodiment of the invention, a centralized RNC provides improved radio resource management (RRM) functionality by handing all connection management and control data for a plurality of Node B's, thereby simplifying the switching of user data throughout the radio access network. Pursuant to a third embodiment of the invention, a smart IP switch is equipped to switch user data without core network (CN) involvement. Downlink user data are switched independently of uplink user data.

FIELD OF THE INVENTION

The present invention relates generally to wireless communication systems. More specifically, the present invention is directed to an improved radio network controller (RNC) and Universal Terrestrial Radio Access Network (UTRAN) architecture for more efficiently processing of user data and control signaling.

BACKGROUND

Current wireless communication networks typically utilize a distributed radio access architecture. For example, the Third Generation Partnership Project (3GPP) universal terrestrial radio access network (UTRAN), utilizes a distributed RNC architectural configuration as shown inFIG. 1. A serving RNC (S-RNC)104manages one or more user equipment (UEs)114,116. User and control data from an S-RNC104is passed directly through a Node B108via Uu interfaces to the UEs114,116that it manages. The S-RNC is also coupled with the Core Network (CN)100via an Iu interface, which provides a control and user data interface to the regular terrestrial circuit or packet networks. A controlling RNC (C-RNC)106manages one or more Node Bs108,110,112via Iub interfaces. The Node Bs108,110,112, in turn, each control one or more base stations (not shown).

In practice, any RNC takes on the role of both an S-RNC104and a C-RNC106. For example, the RNC may provide S-RNC services to UEs that initiate calls with base stations coupled to Node Bs controlled by the RNC but might have roamed to other base stations controlled by other RNCs; and may also provide C-RNC services to the base stations it controls. As a general consideration, S-RNCs control UEs, whereas C-RNCs control Node Bs. S-RNCs control and receive UE measurements. C-RNCs control and receive Node B measurements.

A distributed RNC architecture is utilized so that user plane (U-Plane) data and control plane (C-Plane) data is combined within the RNC102, for forwarding through the Node Bs, such as Node B108, to the UEs, such as UEs114,116. The U-Plane is responsible for conveying user data to and from UEs. The C-Plane is responsible for setting up and removing UE connections and for implementing network signaling functions. This permits most of the complex processing to be performed within the RNC102, thus simplifying the construction and lowering the costs of the Node Bs108-112.

With reference toFIG. 2, a UE (such as UE X115) may move between Node Bs108-112in a series of inter-Node B cell changes. Although some of the inter-Node B cell changes do not involve a C-RNC change, eventually, such an inter-Node B cell change may involve a change to a new Node B under control of another C-RNC; such as the change between Node B112(which is controlled by C-RNC106) and Node B113(which is controlled by C-RNC107).

It is not practical in many circumstances to move the connection between a first RNC such as RNC1(102) and the CN100, to between a second RNC such as RNC2(103) and the CN100to follow a UE as it moves between Node Bs108-113. Provisions are made to keep the connection between RNC1(102) and the CN100while permitting control of the UE by RNC2(103). In this case, RNC2(103) is referred to as a “drift RNC” (D-RNC). Communications between RNCs are conducted over a connection referred to as an Iur interface.

There is a partial control change between RNCs in that UE X115communicates with RNC2(103), which transparently passes user and control data from RNC1(102) to UE X115. User and control data for UE X115is still controlled by RNC1(102) and all user and control data that goes to UE X115, comes from RNC1(102). Although RNC2(103) does not control UE X115and does not know what user or control data has been sent to or from UE X115, RNC2(107) controls cell measurements (via an Iub interface) pertaining to the Node B113in communication with UE X115. As a result, more than one RNC controls UE X115.

Since the CN100is limited in terms of how fast it can reroute the U-Plane and the C-Plane from one RNC to another, it is not always possible to synchronize the relocation of the U-Plane and the C-Plane functions from the CN100to the new C-RNC107. As a result, measurements necessary to implement radio resource management (RRM) functions for UE X115are distributed between RNCs (i.e., RNC1102and RNC2103). For example, the user admission control function that allows UE X115to establish a connection exists in RNC1(102), but the call admission control function that allocates dedicated resources exists in RNC2(103).

Distributed RNC systems are designed to handle expected or anticipated U-Plane traffic over a wireless system in a given geographic area. In large metropolitan areas, the amount of U-Plane traffic over a wireless system is often orders of magnitude greater than the amount of C-Plane traffic. Thus, U-Plane connectivity requirements generally dictate the location and number of RNCs102,103that are needed to support the wireless system. RNCs are expensive hardware elements since they must support both U-Plane and C-Plane functions. The cost of providing a distributed RNC architecture escalates in regions where RNCs are called upon to handle relatively large amounts of U-Plane traffic. Additionally, in rural areas where U-Plane data communication requirements are distributed over large areas, it may not be economically feasible to provision terrestrial resources in the form of a centralized point of presence.

Another drawback with an architecture having RNCs which are distributed is that the efficiency of RRM functions is reduced. RRM functions are performed most efficiently within a single RNC that has all of the data for an RRM function available to it. For example, as aforementioned, S-RNCs control and receive UE measurements, whereas C-RNCs control and receive Node B measurements. RRM functions often require both UE and Node B measurements. In order to operate most efficiently, the RNC performing the particular RRM function should have all of the information, both uplink (UL) and downlink (DL) for all cells in UE. With the distributed architecture, one RNC will have the information for the cell-based measurements (the UL measurements) whereas another RNC will have the UE-based measurements (the DL measurements). Accordingly, a single RNC does not have all of the information required to efficiently make decisions.

Although is possible to forward or request measurements between S-RNCs and D/C-RNCs, the amount of measurement information that can be forwarded or requested is limited, and the transfer of information incurs delays. Moreover, although it is useful for RRM functions to consider measurements and channel allocations from neighboring cells, this is not always possible, in particular when a neighboring cell is controlled by another RNC.

When RNCs are distributed and each RNC manages fewer cells, less neighbor cell information is available for the performance of RRM functions. Furthermore, as the distribution of RNCs is increased across a given service area, the efficiency of RRM functions is reduced.

What is needed is an improved architectural scheme that overcomes the disadvantages of a distributed RNC configuration.

SUMMARY OF THE INVENTION

In a wireless communication network, the system and method of the present invention separate U-Plane data from C-Plane data at a Node B or at a base station to more efficiently process transmission data, improve Radio Resource Management (RRM), and provide improved integration with Internet Protocol (IP) networks. The user data is routed via the U-Plane to a smart IP switch, whereas the connection management and control data are separately routed via the C-Plane to a centralized RNC. The smart IP switch accepts control input from the centralized RNC specifying the manner in which to route data, and is also equipped to switch DL and UL data independently.

The centralized RNC only handles C-Plane data whereas the smart IP switch only handles U-Plane data. Therefore, the more resource-intensive task of switching potentially large amounts of U-Plane data has been shifted to a less complex and costly component; namely, the smart IP switch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the terminology “wireless transmit/receive unit” (WTRU) includes but is not limited to a user equipment, mobile station, fixed or mobile subscriber unit, pager or any other type of device capable of operating in a wireless environment. In CDMA systems specified by the Third Generation Partnership Project (3GPP), base stations are called Node Bs and subscriber units are called User Equipment (UEs). When referred to hereinafter, the terminology “base station” includes but is not limited to a Node-B, site controller, access point or other interfacing device in a wireless environment.

In accordance with the present invention, transmission data is more efficiently processed, RRM performance is improved, and integration with IP networks is improved by separating user data from connection management and control data, (hereinafter, “control data”). The user data is routed to a smart IP switch, whereas the connection management and control data is routed to a centralized RNC.

Referring toFIG. 3, a first preferred embodiment of a system300in accordance with the present invention is shown. The system300includes a CN100, a centralized RNC303, a smart IP switch309, and first and second Node Bs310,312. A WTRU316is shown as being wirelessly coupled to the second Node B312. Although only one WTRU316is shown for simplicity, it should be understood that a plurality of WTRUs are able to be supported by the present invention. Additionally, although only two Node Bs310,312are shown, it would be appreciated by those of skill of the art that the present invention applies to a single Node B as well as many Node Bs.

A C-Plane runs from the centralized RNC303to each Node B310,312. For example, a first C-Plane329runs between the centralized RNC303and the first Node B310, and a second C-Plane331runs from the centralized RNC303to the second Node B312. A U-Plane couples each Node B310,312to the smart IP switch309. For example, a first U-Plane325couples the IP switch309to the first Node B310, and a second U-Plane327couples the smart IP switch309to the second Node B312.

In contrast to the prior art system shown inFIGS. 1 and 2wherein the user and control data were sent together from the UEs to the RNC for processing, as shown inFIG. 3, control data is separated from user data at the one or more Node Bs310,312. User data is carried on the U-Planes325,327, and control data is carried on the C-Planes329,331. It should be noted that this separation function could also be provided at the base stations (not shown) without departing from the spirit and scope of the present invention.

FIG. 4is a block diagram showing the centralized RNC303, the smart IP switch309and the first Node B310in greater detail. Since control data is separated from user data at the first Node B310, several RNC functions and protocol termination points which traditionally have been handled by the RNC in prior art architectural designs are now performed in a more efficient manner by the smart IP switch309or the first Node B310.

The first Node B310is the logical node responsible for radio transmission and reception in one or more cells with the WTRUs, such as WTRU426. The first Node B310provides a Uu interface to the WTRU426, a control data interface402to the centralized RNC303, and a user data interface417to the smart IP switch309. The first Node B310also includes a resource control unit421.

The Uu interface with the WTRU426is a radio interface. This radio interface is divided into three layers, layer 1 (L1) which is referred to as the “physical layer”; layer 2 (L2) which is referred to the “link layer”; and layer 3 (L3) which is referred to as the “control layer”.

Layer 1 includes both physical channels and transport channels. It provides for the encoding and decoding of the transport channels, and the mapping of transport channels onto physical channels. Layer 1 also includes RF processing, such as modulation, demodulation, spreading and despreading.

Layer 2 is divided into two sublayers: the media access control (MAC) sublayer, and the radio link control (RLC) sublayer. The MAC sublayer is responsible for multiplexing data from multiple sources onto a physical channel. The RLC sublayer segments the data streams into frames that are small enough to be transmitted over the Uu radio interface.

The Layer 3 interface radio resource control (RRC), which controls the use of radio resources, and attributes of physical and transport channels over the Uu interface, (i.e. the air interface).

Employing both a control data interface402to support the C-Plane, (329shown inFIG. 3), and a user data interface417to support the U-Plane, (325shown inFIG. 3), permits user data to be separated from control data at the first Node B310. The control data interface402permits the first Node B310to communicate with the centralized RNC303over an IP network401. The control data interface402may comprise one or more types of interfaces, shown as a Dedicated Control Channel Frame Protocol (DCCH FP) interface407, a Node B Application Part (NBAP) interface405and any other type of control interface (graphically illustrated as an XXAP interface415). Although these particular types of interfaces have been shown by way of example, it should be understood by those of skill in the art that any type of control data interface, either now known or future envisioned, may be employed in a similar manner without departing from the spirit and scope of the present invention.

The DCCH FP interface407provides the frame protocol interface for the DCCH signaling. In the prior art, this function was included within the Dedicated Channel frame protocol within the RNC.

The NBAP interface405provides control signaling between the RNC303and Node B310.

The XXXAP interface415provides the primitives between the RRC and the Layer 2 MAC/RLC functions. In the prior art, this was previously internally transmitted within the prior art RNC.

The user data417interface, such as Iu interface, is similar to the Iu U-Plane connection in the prior art. The user data interface417is first termination point for the U-Plane (such as U-Planes327,331shown inFIG. 3). The second termination point is within the smart IP switch309, which will be described in detail hereinafter. Therefore, the CN100can interoperate between a prior art RNC and the centralized RNC303made in accordance with the present invention.

The resource control unit421, performs Layer 2 MAC and RLC processing by implementing RLC protocols and various MAC functions, such as MAC-common channel (MAC-c), MAC-dedicated channel (MAC-d), MAC-shared channel (MAC-sh), and MAC-paging channel (MAC-p). It should be noted that, prior art approaches performed Layer 2 processing in the RNC.

The centralized RNC303includes a control unit404, a control data interface402, a radio access network application part (RANAP)406interface and an interface to the smart IP switch309. The control unit404supports control signaling for configuring each resource that is needed for the call including the centralized RNC303, the Node B310and the WTRU426. The resource control unit404interface with the first Node B310through the control data interfaces402. The control data interface402supports the C-Plane and includes an NBAP interface405, an XXAP interface415, and DCCH FP interface407, which are the counterpart interfaces to those explained with reference to the first Node B310, and which operate in the same manner. A common control channel (CCCH) interface (not shown) may also be used in the same manner as the DCCH interface407.

The resource control unit404performs control signaling for the Radio Access Network (RAN), and therefore is responsible for controlling and coordinating use of the radio resources. The resource control unit404manages the WTRUs426via RRC signaling, and manages Node Bs310,312using NBAP signaling, both of which are sent over the C-Plane interfaces329,331. This functionality allows the centralized RNC303to function as a common entity for managing both WTRUs316and Node Bs310. These management features, not provided by any known prior art architecture, improve network performance because both UL and DL measurements are available to RRM algorithms with minimal latency. Moreover, measurements from all WTRUs within one or more cells are available to the RRM algorithm at the centralized RNC303. These factors allow improved RRM decisions that result in a more efficient use of physical resources.

The IP switch309includes a router resource control411, and first and second termination points409,410. The first termination point409terminates the U-Planes (such as U-Planes325,327shownFIG. 3) in the IP switch309. The termination point409serves as a location where the Iub protocol headers are added and the other protocol functions like retransmission/error recovery take place. As aforementioned, the first Node B310is the first termination point for the Iub protocol, (at the user data interface417) as in the prior art. However, unlike the prior art, the other termination point was the RNC, not the IP switch309as with the present invention. Since Layer 2 processing requirements are removed from the IP switch309, the IP switch309provides layer 3 switching of user data more efficiently than can be accomplished pursuant to prior art distributed RNC architectures. Termination point410allows for combining or splitting of data when multiple Node B termination points are created during user plane relocation.

The termination points409,410are controlled by the router resource control411. The router resource control411binds together the termination points409and410for each user and forwards the data in each direction between the points. This can include multiple409termination points for the relocation of the user plane.

The smart IP switch309is “smart” in the sense that it is: 1) equipped to accept a control input408from the centralized RNC303specifying the manner in which to route data; and 2) is also equipped to switch DL and UL data independently. In contrast to a traditional IP router/switch which uses a preset operator configuration to statically route IP packets through the network, the IP switch309routes the data streams based on configuration from the centralized RNC303and is modified on a call-by-call basis. Although prior art IP switches normally have the ability to route UL and DL data, the smart IP switch309in accordance with the present invention will perform the actions necessary for UTRAN operation, such as duplicating data paths in one direction while combining data paths in the other. Thus, the call-by-call configuration from the centralized RNC303permits the IP switch309to manipulate the data streams for each user. This configuration may also be modified for a particular user multiple times within a single call. This will be explained further with reference toFIGS. 5A-5D

In order to minimize the requirement for synchronized WTRU316inter-Node B handovers, (such as from the second Node B312to the first Node B310), and U-Plane relocations within the CN100, U-Plane establishment, release, and routing is performed within the IP switch309. The U-Plane is terminated in the Node B310at data interface417. However, for an inter-Node B handover, the data interface point417moves from one Node B to another, since the call is handed off from one Node B to another. Using the mechanisms in accordance with the present invention, the termination point is moved from the data interface417of one Node B to another, without the other end of the Iu U-Plane connection (within the CN100) being aware of the change.

One benefit of the present invention is that since the IP switch309provides IP routing of U-Plane traffic, it is more efficient in data transport processing, and has a greatly reduced cost, relative to a network entity that performs layer 2 processing and CN100U-Plane protocols. In addition to IP routing capability, the IP switch309performs IP address translation and splitting (duplication)/combining multiple IP data streams, which allows U-Plane relocations from one Node B to another (i.e., from Second Node B312to first Node B310to be hidden from CN100.

As shown, since MAC and RLC processing requirements are removed from the centralized RNC303, constraints on designing large RNCs are removed. Layer 2 processing, including MAC and RLC functions, is now provided by one or more Node Bs. This results in further enhancements to RRM functionality, which is attributable to increasing the availability of neighboring cell information. Operator cost is also greatly reduced by the reduction in the number of RNCs required to support a given network.

Since RLC and MAC functions need not be present in centralized RNC303, some internal messaging that used to exist within prior art RNCs is now incorporated into the NBAP405protocol. For example, it is preferred that traffic volume measurements (TVM) and timing deviation measurements (TDM), which in the architecture of the present invention are recorded in first Node B310, are reported to centralized RNC303. This can be accomplished with modification of the NBAP protocol by expanding the reporting mechanism already existing within NBAP for Node B measurement reporting.

As aforementioned, the Iub protocol refers to an interface between a Node B (such as first Node B310) and an RNC (such as centralized RNC303). Iur refers to an interface between two RNCs, such as RNC1(102,FIG. 2) and RNC2(103,FIG. 2). The Iub frame protocol interface between centralized RNC303and first Node B309requires changes to support the dedicated control channel (DCCH)407and common control channel (CCCH) logical channels generated by the control unit404. These channels are used to control the WTRUs in an identical manner as prior art. The Iub frame protocol supports a logical channel, and does not support the transport channels of the Iub frame protocol of the current architecture. By adapting the frame protocols used on the Iur interface for MAC-d/MAC-c service data units (SDUs); (also non-transport channel of MAC424), the logical control channel(s) can be supported between centralized RNC303and first Node B310.

The C-Plane of the Iub is also modified for mobility procedures. Paging and cell update, for example, are transferred from MAC424in the Node B to the centralized RNC303. Mobility control messages previously used on the Iur can be applied to the Iub to support the aforementioned functionality between centralized RNC303and first Node B310.

As in the prior art, the C-Plane exists separately for each RNC/Node B connection. Accordingly, moving from one C-Plane to the other is simple; the centralized RNC303starts transmitting on the new C-Plane when necessary and stops using and releases the old C-Plane when the U-Plane has moved.

However, one of the problems in terminating the U-Plane in a Node B is that inter-Node B handovers are still required to move the U-Plane between Node Bs, such as for example the first Node B310to the second Node B312. Movement of the U-Plane anchor is called relocation, and requiring the CN100to be involved in every inter-Node B cell change is not acceptable.

A sequence within the IP switch309for allowing inter-Node B handovers of the U-Plane without CN100interaction is shown inFIGS. 5A-5D. The IP switch309provides an anchor point to the CN100. A switching mechanism within the IP switch309allows rerouting of the U-Plane from a Source Node B503to a Target Node B505without CN100intervention. The CN100anchor point remains connected to the IP switch309throughout the entire U-Plane rerouting sequence.

FIG. 5Ashows data flow between CN100and Source Node B503prior to a handover. In the case of packet data, the IP switch309terminates a general packet radio services tunneling protocol (GTP) layer (S1). In the case of circuit switched data, IP switch309terminates a real-time transfer protocol (RTP) layer (S1). For both cases (packet switched and circuit switched data), the remaining data are transferred to/from CN100and Source Node B503(S2and S3). The remaining data may include at least one of: (a) Iu-interface frame protocol data (IUFP); (b) user datagram protocol (UDP) data; or (c) Internet Protocol (IP) data.

Referring toFIG. 5B, when a handoff from Source Node B503to Target Node B505is to take place, a new link is activated from Target Node B505to the IP switch309(S4and S5). Data that are queued in Source Node B503but not yet delivered are transferred to Target Node B505using standard tunneling techniques that are used for prior art lossless and seamless handovers. The GTP tunnel is set up so that the user data is forwarded from the source Node B to the target Node B. This is a similar procedure as used in the prior art, with the exception that the tunneling is from Node B to Node B instead of RNC to RNC as it is done in the prior art.

Turning now toFIG. 5C, as the handover from Source Node B503to Target Node B505progresses, the DL stream is multiplexed to both Source Node B503(S6and S7) and Target Node B505(S8and S9). The UL stream coming from either Source Node B503or Target Node B505is sent to the same GTP/RTP termination so that the GTP/RTP can be added for the stream going back to CN100. However, data will be present in only one Node B at a time in a given frame in time division duplex (TDD) systems, since the type of handover employed in such systems is a hard handover. On a frame boundary, data transfer moves from Source Node B503to Target Node B505.

The IP switch309, in accordance with the present invention duplicates the data paths so that the exact moment of handover does not need to be known to the IP switch309. Throughout these procedures an interface between the centralized RNC303and the IP switch309is necessary. This allows for the centralized RNC303to control the setup and release of IP routing, and includes the ability to duplicate or combine data flows as shown inFIGS. 5A-5D. To allow for non time-critical signaling between the centralized RNC303and the IP switch309, both links are present during this time even though only one link will be receiving data at one time. The alternative is to have the RNC attempt to coordinate in exact time the handover at the UE and the switchover at the IP switch309, a difficult process given the variable delays and synchronization throughout the network.

Finally, atFIG. 5D, the handover from Source Node B503to Target Node505is completed. The IP switch309maintains the existing link between CN100and Target Node B505(S10), but releases the link between CN100and Source Node B503.

Pursuant to a further embodiment of the invention, an AP protocol is added between the centralized RNC303(FIG. 4) and first Node B310(FIG. 4) to perform relocation involving only the IP switch309, Source Node B503, and Target Node B505. This AP protocol allows for the centralized RNC303to signal the Node B so that it is properly setup such that the termination point of the U-Plane and C-Plane of the user can be moved, including any contexts that are necessary to make the move transparent to the core network. In this manner, retaining the same anchor point in the IP switch309renders relocation of the U-Plane transparent to CN100. The switching, duplication and combining of data streams in the IP switch309are coordinated by the centralized RNC303. A new interface as shown inFIG. 4, (the router resource control channel between the control unit404and the router resource control411), is defined for this control signaling. In this signaling the centralized RNC303can signal the IP switch to setup additional switching points to allow for the combining and/or splitting of data streams in each direction separately to allow a handover to occur seamlessly without involvement of the CN100. This signaling is used to set up the channels and provide the splitting and/or combining that is necessary during handover as shown inFIGS. 5A-5D.

Although the preferred embodiments are described in conjunction with a 3GPP wideband code division multiple access (W-CDMA) system utilizing the time division duplex (TDD) mode, the embodiments are applicable to any code division multiple access (CDMA) system or hybrid CDMA/time division multiple access (TDMA) communication system.