Integrated Access and Backhaul Mobility

Abstract

To provide a method in which respective small cell base stations transfer packets according to individual QoS and priority.SOLUTION: In a multi-hop wireless backhaul network, a plurality of small cell base stations (SC) are in a state of wireless communication with a microcell base station, the respective SCs are connected to the microcell base station through one or more other SCs connected directly to the microcell base station, and the microcell base station is so arranged that a UE device having an RRC connection with the microcell base station is constituted using a candidate SC and the UE device can autonomously switch among the SCs. The microcell base station is so arranged as to use SC constitution information to constitute the SCs, and makes it possible to: transmit data to the UE device; receive data from the UE device; and multiplex and route data from and to the UE device.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method of operating a mobile communication network in which a User Equipment, UE, device is capable of switching between communication cells.

[0002] Known cellular mobile communication networks include a Core Network (CN) and one or more Radio Access Networks (RANs). The CN includes, among other things, functions for authenticating and authorizing users and devices, managing and controlling Quality of Service (QoS), providing access to various data networks, and routing data between the RANs and data networks. The CN is typically Radio Access Technology (RAT) independent, i.e., it includes only functions that are not related to a particular RAT or RAN.

[0003] Each RAN includes functions that provide user equipment (UE) devices with wireless radio access to the core network. Some of these functions are specific to the RAT used, e.g., UMTS, LTE or 5G New Radio (NR). A RAN consists of multiple macro base stations of a particular RAT (NB, eNB, gNB) and may additionally include a number of small cell base stations (SC) of the same or different RATs.

[0004] A UE device registered with a CN may have a current connection to the RAN and the CN (i.e., in a connected mode) or may not have such a connection (i.e., in an idle or inactive mode). For a UE device in a connected mode, there is usually one base station that controls the device, and is referred to as a serving base station or serving cell throughout this specification. This serving base station uses a Radio Resource Control (RRC) protocol and establishes an RRC context on both the UE and the base station. The RRC context includes the radio capabilities of the UE device, the current setup of bearers with their respective QoS, the multiplexing of services or applications on these bearers, the multiplexing of these bearers onto physical resources, the assigned available resources and measurements performed by the UE device, and triggers and contents for reporting such measurements. The configuration of measurements includes neighboring cells to be measured. The neighboring cells may operate on the same RAT and the same frequency as the controlling base station, on the same RAT and a different frequency or on a different RAT.

[0005] If the measurement report received at the serving base station indicates that the neighboring cell is more suitable for communication than the serving cell, the base station may perform a handover procedure to prepare the selected target cell for handover and instruct the UE to handover to the target cell. During preparation, the target cell receives an RRC context from the serving cell, so that communication between the UE and the target cell may continue essentially from the state it had with the serving cell.

[0006] US 2011 / 0143738 A1 describes an Autonomous Search Function (ASF), which is a function that changes its own function in response to external inputs and optimizes the search strategy for the environment. A mobile device uses the ASF on an LTE network to scan various frequencies and find information broadcast by cells. The information broadcast by UTRA and E-UTRA cells may include the Closed Subscriber Group (CSG) ID of the cell, information identifying the supported protocols, information identifying the supported Radio Access Technology (RAT), and the rating of the cells in that frequency, as well as other information that identifies the cell and its connection method. The mobile device may use the information about the detected cell to initiate a proximity detection message for handover invocation or handover avoidance. If the mobile device enters or leaves the vicinity of another cell while connected to a UTRA or E-UTRA base station, the network may initiate a handover message between the mobile device's current base station and the base station of the detected cell.

[0007] US 9,717,110 provides a wireless communication method between a first wireless communication device and a second wireless communication device, in which the first device transmits a chirp signal to a second device in a mesh network during a first wake-up period common to the first and second devices. The first device further receives a keep-alive signal and connection setup information from a wireless relay device determined from a plurality of second devices during the first wake-up period, where the connection setup information includes resource allocation information. Furthermore, downlink paging can be transmitted to the first device together with the connection setup information.

[0008] US 2017 / 0055192 A1 describes a UE-centric mobility mechanism where the UE performs cell reselection during RRC connected mode when extended DRX is used (i.e. the UE does not receive data for a longer period of time). The reselection criteria is received from the source cell in RRC connected mode, and the UE decides based on the conditions whether network controlled mobility or UE autonomous cell reselection is applied, e.g. whether extended DRX is used. When using UE autonomous reselection in the target cell and signaling is required, an RRC re-establishment procedure is used by the UE to establish a connection to the target cell. As a result, the target cell fetches the UE context from the source cell, similar to the establishment of an RRC connection or resuming from idle mode.

[0009] EP 2 879 440 A1 describes techniques for controlling small cell base stations in a system including small cell base stations controlled by a macro cell base station, the small cells performing measurements and the information being reported to the macro cell base station.

[0010] WO 2017 / 028808 A1 describes a method for connected mode cell reselection, where the UE can perform cell reselection without handover signaling. EP 3 125 640 A1 describes bearer management procedures, where the UE has dual connectivity and changes bearer types between a master cell group and a secondary cell group. WO 2015 / 065010 A1 describes a method for performing dual connectivity in a heterogeneous network, e.g. including macro cell base stations and small cell base stations.

[0011] Wireless relays are known from LTE. They are base stations that connect wirelessly to the core network via so-called donor base stations (DeNBs). To a UE device served by a wireless relay, the relay appears as a normal base station controlling the UE device, i.e. an RRC connection is set up between the relay and the UE device. Wireless relays behave similarly to a UE towards a DeNB, but the radio resources used between the UE and the relay are controlled to some extent by the DeNB or by the CN.

[0012] Dual or multiple connectivity mechanisms are known from LTE and NR, where a single UE device has an RRC connection and an active radio connection to a serving cell (then called a primary cell) and in addition has one or more active radio connections to secondary cells. The primary cell controls the UE device and also controls secondary cells in association with the UE device. A base station providing a secondary cell to a UE device may control other UE devices in parallel as primary or serving cells. Addition and removal of secondary cells to and from the UE is entirely under the control of the primary cell.

[0013] For the transition of LTE networks to the new 5G NR technology, dual connectivity is introduced by a UE device having a primary cell providing LTE connectivity and a secondary cell providing 5G NR connectivity (or vice versa), where the secondary cells also have RRC connections with the UE device for the respective secondary RAT, but the primary cell still controls the connectivity including the addition and removal of the secondary cells.

[0014] For a single UE device, the serving base station is usually the only or main access point to the core network. That is, the exchange of control messages with the core network (so-called NAS signaling) is routed to the core network by this base station. Also, user data is routed through the serving cell, except for some dual connectivity scenarios where multiple CN access points are used for user data routing. When the CN needs to initiate signaling or data forwarding for the UE, it requests signaling or data forwarding in the serving base station.

[0015] 3GPP has recently started a study on the use of 5G NR RAT for wireless backhaul links typically used for small cells (SC). The aim of the study is to enable low-cost and low-effort SC deployment by wirelessly connecting the SC to a controlling base station (so-called Donor Next Generation Node B, DgNB). The study includes multi-hop scenarios where an SC is wirelessly connected to another SC until the last SC in the path provides a direct link to the DgNB.

[0016] The new multi-hop wireless RANs may use different architectural alternatives as to which node, i.e., which base station, has control of the multi-hop RAN and the UE devices connected to that RAN. Each solution has advantages and disadvantages.

[0017] Similar to known wireless relays in LTE, each base station (SC) of a multi-hop RAN may act as an overall base station towards served UE devices or towards served SCs. For its backhaul link, such SC then acts like a next-hop SC or DgNB of the top SC layer towards served UE devices. A drawback of this solution is that each handover of a UE between SCs requires a context transfer between SCs via the hierarchical multi-hop RAN. Since security keys for encryption and integrity protection are set up between the serving base station and the UE device, the SC needs to be built accordingly (i.e., placed in an inaccessible place or protected in a housing that protects the security keys from being read). This significantly increases the price of such SCs. Also, no single node has control of the multi-hop network. Each SC therefore needs knowledge of surrounding neighboring cells to properly configure measurements on served UE devices. This makes the setup of such wireless SCs difficult to set up easily and may require intervention of the operation and maintenance systems required for each newly set up SC. Another drawback is that each SC in the architecture is a serving RAN node for the CN's UEs (i.e., every handover of a UE between SCs requires an update of the respective CN node).

[0018] An alternative approach is to terminate each RRC connection at the DgNB (i.e. all UE devices as well as the SC with radio backhaul through the multi-hop RAN set up RRC connections with the DgNB) and then control all devices in the multi-hop RAN. This allows easy setup of an SC configured entirely by the DgNB. The security of the served devices is not an issue at any SC, since the security in that case is set up between each device and the DgNB. Thus the price of the SC and its location can be reduced.

[0019] However, the latter architectural alternative introduces latency into the connection between the devices and their serving base station (here the DgNB), which conflicts with the requirement that some functions of the serving base station be performed very quickly, resulting in configurations reaching the served devices quickly. One example of such a low-latency procedure is measurement reporting and the resulting handover decision.

[0020] The present invention overcomes the shortcomings of DgNB-centric multi-hop RAN, making the architecture the most beneficial solution for SC deployment.

[0021] The present invention provides a mobile communication system sub-network, comprising a first or macro cell base station and a plurality of second or small cell base stations, the plurality of second base stations being in wireless communication with a first base station, where each second base station is in direct communication with the first base station or is connected to the first base station via one or more other second base stations, where the first base station is arranged to configure a user equipment (UE) device having a radio resource control (RRC) connection with the first base station using candidate second base station information to enable the UE device to autonomously switch between the second base stations; Here, the first base station is arranged to configure the second base station using second base station configuration information, and the second base station configuration information enables the second base station to transmit data to and receive data from the UE device, as well as multiplex and route data from and to the UE device.

[0022] The present invention further provides corresponding UE devices, small cell base stations and methods of operating a mobile communications network.

[0023] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0024] [Figure 1] FIG. 1 illustrates a schematic arrangement of a multi-hop wireless backhaul network. [Figure 2a] FIG. 2 illustrates protocol stack layers. [Figure 2b] FIG. 2 illustrates protocol stack layers. [Figure 2c] FIG. 2 illustrates protocol stack layers. [Diagram 3] FIG. 2 is a schematic diagram of a sub-network. [Figure 4] FIG. 2 is a message sequence chart. [Diagram 5] FIG. 11 is a further message sequence chart. [Figure 6] FIG. 2 is a schematic diagram of a further sub-network arrangement; [Figure 7] FIG. 2 is a message sequence chart. [Figure 8] FIG. 2 is a schematic diagram of a further sub-network arrangement; [Figure 9] FIG. 9 is a message sequence chart of the sub-network of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Figure 1 shows an example of a multi-hop wireless backhaul RAN with a 5G New Radio (NR) Donor Base Station (DgNB) connected to a CN. The DgNB controls a sub-network of multiple cascaded small cell base stations connected wirelessly. Each small cell base station has one wireless backhaul link to another small cell base station or to the DgNB, and zero or more access links to other small cell base stations or UE devices.

[0026] The DgNB has access links 1 and 5 to small cells SC2.1 and SC2.2, respectively.

[0027] Small cell base station SC2.1 has access links 2 and 4 to small cells SC3.1 and SC3.2, respectively. In addition, SC2.1 provides an access link to UE device UE3. Small cell SC2.2 has an access link to small cell SC3.3 and to UE device UE5.

[0028] Via respective access links, small cell SC3.1 provides NR connectivity to two UE devices UE1 and UE2, and small cell SC3.2 provides NR connectivity to UE device UE4.

[0029] According to the present invention, all small cells and UE devices in the given example have active connections to the RAN and via the RAN to the CN, which may further provide connections to various data networks (not shown). UE devices UE1, UE2 and UE4 have established an RRC connection to the DgNB via a first link (e.g., link 3) to a first small cell that is connected to a second small cell via a wireless backhaul link (e.g., link 2). The second small cell is wirelessly connected to the DgNB (e.g., via link 1). UE devices UE3 and UE5 similarly have an RRC connection to the DgNB via a direct connection to a small cell wirelessly connected to the DgNB.

[0030] Every radio link in the UL and DL has a unique identity of the transmitting device, i.e., receiving base stations in all legacy cellular wireless communication systems are able to distinguish data received from different transmitting devices and the devices know which base station they are receiving from.

[0031] According to the present invention, all small cells in this example have an RRC connection to the DgNB, either via a direct wireless backhaul link or via a wireless backhaul to another small cell.

[0032] Small cell base stations in this new architecture are similar to Layer 2 relays. They do not control access to the UE device's RAN or configure the device, both of which are done by the DgNB. They provide radio resources over the access links to the served UE device and the served small cell according to their configuration received from the DgNB. In the downlink, they decode data received over the wireless backhaul link and reconstruct segmented data packets, which they then segment and encode packets to be forwarded over the wireless access link to the next small cell base station or UE device. In the uplink, the small cell base station decodes data received over the access link and reconstructs segmented data packets, which they then segment and encode packets to be forwarded over the wireless backhaul link to the next small cell base station or DgNB.

[0033] To enable QoS to be provided across the described multi-hop network, different bearers from different UE devices need to be differentiated within every small cell. Only then can the small cell apply bearer- and UE device-specific priorities and resource allocations. As a result, an indication of the originating UE device and bearer is needed for every data packet in the air interface between two small cells or between a small cell and a DgNB. That is, small cells need to be able to differentiate data packets from one bearer of a UE from another bearer of the same UE. Similarly, they need to be able to differentiate data packets from one bearer of a UE from another UE's bearer.

[0034] The air interface (e.g., in a wireless backhaul link) inherently provides information which is the originating device (i.e., the peer device for a single hop) that transmitted data on the UL, and provides the bearer identification for that hop, but with each additional hop, the originating device as well as the bearer information is lost.

[0035] According to the present invention, the small cell multiplexes all data received from bearers of the previous hop (potentially from different originating devices) with similar or the same QoS onto one bearer of the next hop with the respective QoS. The data thus multiplexed is transmitted by the air interface between the two small cells. An indication of the originating bearer and device is inserted or added to the data packet. This indication is used by the receiver to again decide on the multiplexing of the data onto the next hop bearer. This allows each small cell base station to forward the packets according to their individual QoS and priority.

[0036] Bearers are indicated on legacy air interfaces (e.g., LTE) by indicating a logical channel identification (LogCh-ID) in the MAC header of the data packet. However, the LogCh-ID is only unique within a single RRC connection between the UE device and the serving base station. Other devices may indicate their bearers using the same LogCh-ID. The base station uses a unique UE device identifier at the physical layer to uniquely identify the packet originator.

[0037] In the present invention, for the processing of packets in a cascaded small cell base station network, an identification combining UE device identifier and bearer is required. Bearer in this sense is the term used for any data flow with common or similar QoS and priority. In legacy radio access networks, this is usually called bearer. In the remainder of the present invention, this terminology is used without loss of generality. The indication of originating UE and bearer together is called Global Logical Channel Identifier (GLogCh-ID), similar to (LogCh-ID), which is then used within the multi-hop network at each hop.

[0038] The GLogCh-ID is unique for every bearer of every UE device served in the sub-network. UE devices can still be identifiable in the GLogCh-ID, for example when this identifier has two parts: a UE device identifier that is unique for UE devices in the sub-network, and a LogCh-ID that is unique for the bearers of a single UE device, similar to the LogCh-ID used in current protocol stacks. Alternatively, the GLogCh-ID does not have separate identifiers for UEs and bearers.

[0039] The DgNB controls the multiplexing: it configures all small cells with the GLogCh-IDs of the devices they are configured to actually or potentially serve, either as routers or to provide access links, and their respective QoS and priorities.

[0040] For simplicity, the following focuses on only a few nodes of those shown in FIG. 1: UE1, SC3.1, SC2.1, links 3, 2 and 1, and DgNB.

[0041] Figures 2a, 2b and 2c show protocol stack layers that may be advantageously used in the relevant nodes based on currently envisaged protocol stack layers of the NR air interface.

[0042] Figure 2a shows the protocol stack for the establishment and maintenance of an RRC connection between a UE device UE1 and a DgNB (control plane) via small cells SC3.1 and SC2.1. The RRC connection is established between the UE UE1 and the DgNB, so that an RRC protocol peer exists in the UE device and the DgNB. A security association is similarly established between these two entities, and the PDCP protocol layer uses the security association (i.e., the respective shared keys) to encrypt and integrity protect the RRC messages. The protocol layers below PDCP, namely the Radio Link Control Protocol (RLC), Medium Access Control (MAC) and the Physical Layer (PHY), are related to the actual radio link. They therefore exist at each associated node, and each hop is established by the respective peer protocols on both sides of the hop.

[0043] For each hop between network nodes (i.e. between two small cells or between a small cell and a DgNB), a function is needed that multiplexes the received packets onto the next-hop bearer and indicates the GLogCh-ID newly introduced in this invention. For this, the protocol stack of each of these hops contains, in addition to the known functions of the RLC, MAC and physical layers, a relay function that keeps the GLogCh-ID in the header fields of the transmitted packets and determines, based on the configuration by the DgNB, the next-hop bearer on which to multiplex the packets. This relay function can be performed in the RLC layer as an additional function with an additional RLC header field. Alternatively, the hop-to-hop protocol stack can include an additional and enhanced PDCP layer for that function. Figure 2a shows another alternative to the function in an additional protocol layer named Relay Protocol (RP) without loss of generality.

[0044] Similarly, FIG. 2b shows the respective protocol stacks for forwarding user data from UE device UE1 to DgNB. In UE1 and DgNB, there is a protocol for multiplexing service data flows onto a data radio bearer (SDAP) newly introduced in 5G NR, and a PDCP protocol for ciphering, integrity protection and control data compression. Again, the protocol layers below PDCP, namely Radio Link Protocol (RLC), Medium Access Control (MAC) and Physical Layer (PHY), are related to the actual radio link and therefore present in each relevant node. The newly introduced relay function with the indication of GLogCh-ID and multiplexing is again denoted as Relay Protocol (RP) while alternatives exist, as mentioned above.

[0045] Figure 2c shows the protocol stack for the establishment and maintenance of the RRC connection between the small cell SC3.1 and the DgNB. The RRC and PDCP peers are present at SC3.1 and the DgNB, respectively, and the RLC, MAC and PHY are hop-by-hop. The relay function (e.g., at the RP layer) is only required at the second hop of the connection (i.e., from SC2.1 to the DgNB). The protocol stack for the establishment and maintenance of the RRC connection between SC2.1 and the DgNB (not shown in any figure) may look very similar to Figure 2c, but with direct peers of every protocol stack layer between SC2.1 and the DgNB.

[0046] Based on the above architecture, one aspect of the present invention is the configuration of candidate handover target small cells by the DgNB, such that the UE device is able to autonomously switch its connection from the current source small cell to one of the candidate target small cells based on criteria configured by the DgNB, but without reporting measurements related to the source and target cells, and without being commanded by the base station to perform a handover.

[0047] The UE device is configured with a set of candidate small cells (i.e., cell identifiers, frequency resources, and radio parameters). The configuration may include further information such as the mode of accessing the target cell, e.g., on the uplink control channel, via RACH or via a direct resource request. The configuration also includes criteria for switching cells, e.g., a threshold below which the current source cell must fall before a cell switch is considered, a threshold for comparing the source and target cells, a duration for which the target cell must have a received signal strength with a higher threshold than the source cell, or other criteria. If the criteria are met, the UE immediately switches to the target cell.

[0048] The above candidate list of potential target cells differs significantly from the known neighbor cell list and includes cells to measure and report to the serving cell under certain criteria, so that the serving cell can decide to prepare a handover and command the UE device to perform the handover. Thus, the legacy neighbor cell list configuration and associated measurement and reporting configuration and performance can continue in parallel with the present invention for potential target cells that are not under the control of the DgNB serving the UE device.

[0049] Also, candidate list and autonomous cell switching is significantly different from cell selection after radio link failure of the serving cell, since it requires the UE to go through an idle state (i.e., to set up a new RRC context with the selected cell).

[0050] The configuration of candidate small cells is not only done by the UE device: the DgNB configures the candidate target small cells as well, so that data transfer via the target cell can start immediately after cell switching.

[0051] The DgNB configures candidate target cells with all the information required to transmit and receive data from and to the UE device, and to multiplex and route data (control and user data). information about existing signaling and data bearers established in the UE device; multiplexing information for multiplexing bearers onto transport channels or physical resources; A MAC layer configuration including priority information (e.g., priority of bearers of the same UE relative to each other and / or priority of a UE device relative to other UE devices or small cells served by the same small cell); A UE device identifier (UE-Id) by which the UE can identify itself when accessing the target cell, for example the C-RNTI known from LTE; the radio capabilities and radio parameters of the UE device; one or more global logical channel identifiers (GLogCh-IDs) transmitted with the data received from the UE device to enable appropriate multiplexing in further hops; and routing information for the conveyance of UL and / or DL ​​information to and from the UE device.

[0052] The DgNB configures the above information in the candidate small cells (i.e., small cells that the UE device can directly access via a radio link connection). In addition, the DgNB configures all small cells on the route between any of the candidate target small cells and the DgNB. These routing small cells that do not provide an air interface to the UE device are: a GLogCh-ID used to identify data of different QoS and / or priority (i.e., different bearers) originating from or addressed to the UE device; relevant QoS and / or priority information; and routing information for conveying UL and / or DL ​​information to or from the UE device.

[0053] In summary, all small cells potentially involved in routing data from the UE device are configured with the information needed to forward data packets to and from the UE device according to the packet's individual QoS requirements. In addition, small cells that are candidates for serving the UE device's radio link are configured with, in addition to the UE device identifier and physical and MAC layer parameters for the setup and maintenance of the radio link.

[0054] The UE switching to the target cell requests UL resources from the target cell with UE-Id. The target cell is capable of identifying the UE based on the pre-configured UE-Id and providing available resources according to bearer, multiplexing and priority information. The resources are requested by the UE for the transmission of user data or control data (e.g. application data or RRC messages), which also serve as an indication to the target small cell base station that the UE has switched cells.

[0055] The UE device ideally resets its RLC and MAC entities so that no further context transfer from the source small cell is required. Depending on the required QoS of the bearer, lost packets may be retransmitted at the PDCP layer between the UE device and the DgNB. Since the UE device has a security association with the DgNB, all data is encrypted and optionally integrity protected, so that the target small cell does not need to perform any security setup procedures with the UE device.

[0056] To ensure a fast route change in the sub-network and route DL traffic to the new small cell, as soon as the UE device arrives at the small cell, the small cell informs the next higher small cell of the UE now served by that target small cell. This is repeated by all small cells towards the top of the hierarchy until a base station that is part of the old route as well as the new route is reached. This base station may be called a co-base station, which can be either a small cell or a DgNB. The co-base station immediately starts routing DL packets along the new route to the target small cell. The trigger for the small cell to inform the next-hop small cell of the arrival of the UE device can be the UE providing its UE-ID in the resource request. A preferred alternative is the arrival of a first data packet at the small cell, for example including an RRC message from the UE to the DgNB. This packet routed along the new path indicates to any small cells on its way to the co-base station that a path change is established. That is, the first UL packet serves as an indication of the arrival of the UE to further small cells. An alternative is for small cells to have peer-to-peer signaling (i.e., via their backhaul MAC layer or via new SC-to-SC protocols).

[0057] As described, one beneficial aspect of the new DgNB-centric architecture is that security is performed between the UE device and the DgNB, so that the UE and small cell do not need to perform additional security procedures that would delay cell switching. One drawback of there being no security association between the UE device and any small cell is the possibility of a security attack from a rogue UE device that simply accesses a small cell with a fake UE-Id or a real UE-Id from the rogue device, inserts false data in the UL, and routes the UE device related data to the new small cell, potentially away from the actual small cell serving the respective UE device.

[0058] The use of integrity protection prevents data from a rogue UE device from successfully inserting any erroneous data into the data stream, and encryption ensures that the data cannot be read by a rogue UE device. However, denial of service attacks can still be a problem, since rerouting to a new target cell initiated by a rogue UE device will prevent the data from reaching the correct target UE device.

[0059] To prevent this type of attack, the co-base station temporarily duplicates packets in the DL to both the new and old routes, and it accepts UL packets from both routes that are to be forwarded along a single route above the co-base station. Any duplicated packets are filtered at the DgNB using PDCP sequence numbers or integrity protection measures.

[0060] Finally, the UE device itself notifies the DgNB of its serving cell switch in an RRC message generated by the UE device, apparently with security, and if received, the DgNB is notified of the cell switch. In addition, the affected small cells may inform the DgNB of the change that has occurred via their RRC or similar protocols. In response, the DgNB informs the affected small cells of the route switch. That is, the small cells under the co-base station on the old path may be notified to stop routing to and from the UE, the co-base station is notified to stop replicating packets and use only the new path, and the UE as well as the small cells are notified of the new candidate small cells for a potential future autonomous handover.

[0061] The co-base station may apply packet duplication only for a limited time, which may start a stopped timer if the new route is confirmed by the DgNB. If the timer expires before confirmation is received, the DgNB may stop packet duplication and revert to the old route assuming that the new route is not suitable.

[0062] With the inventive autonomous cell switching described herein, data transfer between the UE and the core network continues during the time when the DgNB was not notified or did not properly notify the small cell about the cell switch, and data delay is kept at a minimum. Thus, the present invention overcomes the latency introduced by multi-hop radio sub-networks.

[0063] In DL, the new route is used only after the joint base station obtains information about the path switch. Between the switch by the UE device and the first DL packet routed to the target small cell, some packets may be delivered in DL along the old route. To reduce the possibility or number of lost packets, the UE device may continue to receive packets from the source small cell, depending on its capabilities, until the first packet arrives in the DL of the target small cell. Then, the reset of the RLC, MAC and PHY layers in the UE is performed only when the first DL packet of the new cell arrives.

[0064] When a UE device uses a communication service that requires very reliable data transfer, redundant transmission of data may be beneficial to overcome packet loss. The newly introduced architecture of the present invention may be advantageously used in this case as well. A UE may have multiple serving small cells and a configuration of candidate target small cells for autonomous mobility. Here, the UE may use the described mechanism to autonomously switch one of the small cells while keeping the other redundant links unchanged. The other redundant links can be switched only when UL and DL transmissions via the autonomously selected target small cell are confirmed, for example, by the first DL packet arriving or by the respective DL RRC message received from the DgNB. The redundant transmission may be a bearer QoS setting that is used permanently for a particular bearer, or it is a feature that is used temporarily only in conjunction with the described small cell switching to prevent packet loss.

[0065] The present invention can also be used for dual connectivity, where a single UE device is connected in parallel to different base stations. The UE device can be connected to two or more small cells controlled by the same DgNB and use autonomous switching techniques to select the optimal cell. The UE device can alternatively be connected to a first base station and a small cell controlled by a DgNB according to the present invention, where the first base station is not controlled by the DgNB. Then, autonomous switching techniques are used to select the optimal small cell, while the first base station remains the same or is changed by a legacy handover procedure.

[0066] Yet another alternative to the architecture of Figure 1 is a UE with two or more parallel connections to the same DgNB, one over the direct air interface and another to a small cell with wireless backhaul, as described herein. Control signaling can then be sent over a direct link to the DgNB, while the UE is configured to autonomously select the best small cell for the parallel connection. The main reason for autonomous cell switching is to overcome the control signaling delays for measurement reporting and handover performance introduced by the multi-hop architecture of cascaded small cells. However, it is not present in this use case.

[0067] Yet another use case of the present invention is the use of multiple small cells of a single UE device for multiple bearers, so that for different radio bearers the best small cell is selected by the UE device. It may be that some small cells are optimized for some functions, while they only provide limited other functions or none at all. An example may be small cells that are specialized for low latency applications, but cannot provide high data rates. These small cells may broadcast their nature, allowing the UE device to take the information into account when selecting a new small cell, or the candidate cell configuration from the DgNB to include the special functions of the small cell. Then, the autonomous cell switching described in the present invention is performed by the UE device only for a part of the bearers that the UE has set up or is going to set up. The mechanism is applied as described, and the GLogCh-ID in the UL packet allows the joint base station to apply DL route adaptation only for the respective bearer. Also, the route confirmation received later from the DgNB confirms the new route for some bearers of the UE device, while other bearers are still routed along the old route. This use case of the present invention is particularly useful for new data traffic types such as "Ultra-Low Latency (ULL)", "Ultra-High Reliability (URL)" and "Massive Internet of Things (MIoT)" of evolved 5G networks, which may be used for some bearers of UE devices while other bearers may be used for normal broadband traffic. An exemplary deployment may provide low-latency small cell base stations in the coverage of UE devices directly connected to the DgNB to bypass multiple radio backhaul hops of alternative small cell base stations in the UE device coverage. The low-latency small cell base stations provide only limited bandwidth or connection-free data communication, while other small cell base stations provide different services with more efficient but slower multi-hop radio backhaul.

[0068] The above-mentioned mechanism enables autonomous switching of serving cells for UE devices. The new architecture as shown in Fig. 1 is based on the radio backhaul of associated small cell base stations. The radio backhaul between small cells is based on the same or similar air interface as the air interface between the UE device and the small cells. Therefore, the inventive mechanism of the present invention is also applicable to the radio backhaul itself.

[0069] A small cell base station (e.g., SC3.1) served by another small cell base station, SC2.1, can be configured with a candidate small cell (e.g., SC2.2) for autonomous cell switching. The candidate small cells are prepared with routing and multiplexing information and radio and identifier information, so that the small cell SC2.2 can take over the serving of SC3.1 after cell switching. The above-mentioned mechanisms are all available, depending on the route switching, packet duplication and last route specification by the DgNB via layer 3 signaling, for example. The GLogCh-ID is configured only for bearers originating from the small cell SC3.1 itself, since bearers are routed by SC3.1 originating from other devices already associated with the GLogCh-ID, e.g., UE1 and UE2. Assuming that the small cell does not generate any user data, only the signaling radio bearers for the setup and maintenance of the RRC connection between SC3.1 and the DgNB are identified with the GLogCh-ID and associated with QoS and / or priority information in the candidate small cell SC2.2.

[0070] This application of the invention to wireless backhaul connections allows for flexible and dynamic backhaul setup. However, since small cells are assumed not to be mobile, the number of candidate small cells for automatic cell switching in this case is assumed to be much smaller than that of a UE device, which is usually mobile. The switching option may be a countermeasure to dynamic shadowing effects between two small cells or to a small cell outage. However, mobile small cells may benefit from the described network architecture and mechanisms similar to UE devices.

[0071] Preparing a candidate small cell to serve as a radio backhaul for another small cell after an autonomous cell switch requires informing the candidate small cell about all current and potential future bearers served or routed by the source small cell. That is, when the radio backhaul network has a larger and deeper hierarchy than the exemplary network of FIG. 1 and small cell routing traffic of dozens of other small cells, each with a large number of UE devices, the configuration information for preparing each small cell for autonomous switching increases greatly. The configuration and its updates consume a lot of the bandwidth of the radio network and computing resources in the DgNB and small cells.

[0072] An alternative could then be to have the same global configuration of all small cells of the radio backhaul, i.e. every small cell is configured with the global information of the bearers and devices served (e.g. all GLogCh-IDs and associated priorities and QoS). The configuration information could then be broadcast from the DgNB (i.e. the global configuration is provided once by the DgNB to all small cells directly connected to it and to those after receiving the configuration information), which could store and apply the configuration and forward the information to all further small cells served by the direct link. The same mechanism could be applied for configuration updates that only involve changes to the stored global configuration. The broadcast mechanism requires that a common security key with integrity protection is available to all involved small cells to guarantee the accuracy of the configuration information. Security could be achieved either by a symmetric key provided via dedicated Layer 3 signaling from the DgNB to each small cell, or by an asymmetric key pair of the DgNB, whose public key is pre-configured or included in the broadcast as a certificate verifiable by the receiving small cell.

[0073] The described broadcast prepares every small cell as a candidate for cell switching for all devices, UEs and small cells. Candidate configuration of switching devices with candidate small cells ensures that switching is still limited under the control of the DgNB. Also, multicast (i.e. broadcast of different configuration messages addressed to groups of small cells) can be used. This reduces single configuration messages in larger hop-to-hop wireless backhaul sub-networks.

[0074] It should be noted that the description of the present invention does not prevent the wireless backhaul connection of the small cell base station from being protected with a secure tunnel, such as an IPsec tunnel, to prevent eavesdropping and data manipulation at that level. This option does not affect the inventive steps and advantages of the present invention, so it is not further described in the present invention and is simply an implementation option.

[0075] FIG. 3 shows a simplified architecture including a DgNB, three small cell base stations (SC2, SC3.1 and SC3.2) and a UE device UE. The UE device has an access link to the small cell base station SC3.1. The small cells (SC3.1 and SC3.2) have wireless backhaul links to the small cell base station SC2, which has a wireless backhaul link to the DgNB. The DgNB is connected to a core network of the operator network.

[0076] Figure 4 shows in a message sequence chart the exchange of messages and data within the sub-networks shown in Figure 3. As a prerequisite, shown as a single box without further details, according to the base architecture of the present invention it is assumed that all small cell base stations and UE devices have an RRC connection with the DgNB.

[0077] In the initial state of FIG. 4, the UE has an ongoing uplink UL and downlink DL data transfer. For that purpose, the small cells SC3.1 and SC2 are configured according to the present invention so that they are able to provide QoS to the data bearers currently set up by the UE. The UE device has a UE device identifier (e.g. C-RNTI) according to the LTE standard, which is assigned to the UE device and used by the UE device in the UL transmission to indicate the origin of the data. This can be done by scrambling the UL message with the UE device identifier or by transmitting a plane identifier or a part of it as part of the data. The UE device identifier is also used by the serving small cell for DL ​​data transmission to address the resources used to transmit the data to the UE device. Again, scrambling or other techniques can be used to retain the UE device identifier or a part of it in the DL resource allocation. According to the present invention, the small cell base station SC3.1 is configured with the C-RNTI of the UE device. In addition, the UE device can provide small cell specific resources in the time and / or frequency domain to request UL scheduling from the small cell base station SC3.1. Other radio parameters relating to the radio capabilities supported or preferred by the UE device may also be configured similarly to the wireless standards known as LTE or 5G NR.

[0078] The UE may have a total of seven radio bearers (three signaling radio bearers and four data radio bearers) with associated QoS parameters as shown in Table 1. Respective information is configured in the UE device and the small cell base station currently serving the UE device SC3.1.

[0079] [Table 1] The small cell base station SC3.1 has a radio backhaul link to the small cell base station SC2, on which eight radio bearers can be configured (three signaling radio bearers for setting up and managing the RRC connection to its own DgNB, and five data radio bearers for forwarding or relaying data with different QoS). Table 2 shows the radio backhaul bearers configured for SC3.1 in SC3.1 and SC2 in an exemplary format. Only the three signaling radio bearers originating from SC3.1 are assigned a global logical channel identifier, since it is expected that all forwarded or relayed data already contains the GLogCh-ID according to their originating device and bearer.

[0080] [Table 2] Similarly, for small cell SC3.2, the information may be configured in SC3.2 and SC2 according to Table 3.

[0081] [Table 3] The small cell base station SC2 is configured according to the present invention with information of devices potentially served or that can be served by SC2 (e.g. GLogCh-ID, QoS and priority information), which may be different from that configured in the served devices. For example, the priority information of the small cell base station SC2 may take into account that the high priority signaling radio bearers of the small cell base station SC2 itself have a higher priority than similar bearers forwarded or relayed by SC2. Also, the high priority signaling radio bearers of the small cell base stations (e.g. SC3.1 and SC3.2) served by SC2 may have a higher priority than the signaling radio bearers of the UE device. Thus, an example of data related to the UE device UE and the small cell base stations SC3.1 and SC3.2 configured by the DgNB in ​​SC2 is shown in Table 4. In addition, similar to the base stations SC3.1 and SC3.2 in Tables 2 and 3, the small cell base station SC2 is configured with its own signaling and data radio bearers.

[0082] [Table 4] According to the present invention, the small cell base station SC3.1 receives data from the UE device (UE) via one of the radio bearers. It is assumed that user data packets arrive from all data radio bearers (i.e. DRB1, DRB2, DRB3 and DRB4). The small cell base station SC3.1 receives the packets, decodes and demultiplexes them to reconstruct the segmented packets into the original user data packets. In many cases, these are IP packets from the respective applications. In other examples, where packets are received from the signaling radio bearers SRB0, SRB1 or SRB2, the packets are not IP packets but may be RRC messages from the RRC layer of the UE device UE. Here, SC3.1 determines a global logical channel identifier GLogCh-ID for each user data packet based on the radio bearer on which the packet is received and based on the configuration by the DgNB, and attaches the data packet before forwarding the packet to the small cell base station SC2 via the radio backhaul. That is, for packets received from the UE device UE on data radio bearer DRB1, GLogCh-ID=68 is attached before forwarding the data over the radio backhaul. For data radio bearers DRB2, DRB3 and DRB4, GLogCh-IDs 69, 70 and 71 are attached, respectively. The attachment may be performed according to any suitable protocol, for example any of the existing protocols of the 5G NR protocol stack or a new protocol exemplarily named as relay protocol "RP" in Fig. 2a-c. The forwarding of packets is performed according to configuration by the DgNB (i.e. according to the configuration data of Table 2). The table provides, for each of the radio bearers of the UE device, a relative priority with which data is processed with respect to the order of transmission packets multiplexed onto the same resource. A higher priority (i.e. a lower integer value of the relative priority parameter) results in preferential transmission, while a lower priority packet is only transmitted when no higher priority packet is pending transmission.Table 2 also provides for each of the UE device's radio bearers RB-Type information, which may also be referred to as Quality of Service (QoS), indicating the nature of the service from which the data originates. The RB-Type may be used by the small cell base station to select one of the small cell base station's five data radio bearers DRB4 to DRB8 for the transfer of the data packet. The same principle applies to data packets received at the small cell base station SC3.1 from the UE device UE by one of the signaling radio bearers SRB0, SRB1 or SRB2, each having a higher priority and a different QoS or RB-Type, as well as GLogCh-ID 65, 66 or 67, respectively.

[0083] The small cell base station SC2, receiving data packets from the small cell base station SC3.1 via any of the data radio bearers DRB1, DRB2, DRB3, DRB4 or DRB5 on the radio backhaul link of SC3.1, decodes and demultiplexes the packets to reconstruct the segmented packets and determine the attached GLogCh-ID. It searches for the GLogCh-ID according to the configuration by the DgNB. For example, searching for an exemplary packet from a UE device with LogCh-ID=68 results in forwarding by SC2 according to quality of service "best effort" and relative priority 8. The small cell base station SC2 does not have to associate GLogCh-ID=68 with a specific device, since it does not have any information about the UE device UE. However, it receives enough information to determine the forwarding treatment of the packet by forwarding the received data packet together with the GLogCh-ID, in terms of QoS and priority, which provides enough information to the DgNB to associate the packet with a specific UE device, to further small cells to determine the forwarding treatment. Assuming that the small cell base station SC2 has a bearer set up to the DgNB suitable for carrying best effort data, it is used and the data is multiplexed onto the available resources according to priority 8.

[0084] The DgNB has information about the mapping of GLogCh-IDs assigned in the subnetworks controlled by the DgNB to UE devices and their respective radio bearers, so that after successfully receiving a packet, the DgNB can determine, based on the GLogCh-ID, the correct PDCP and / or RRC entity to which the packet is addressed.

[0085] The above describes UL data forwarding from a UE device to a DgNB via a multi-hop sub-network. For DL, the same principle can be applied. That is, a GLogCh-ID is attached by the DgNB to any data packet transmitted to a small cell base station (e.g., SC2). The small cell base station SC2 determines the GLogCh-ID and searches the respective QoS and priority to forward the data packet with the LogCh-ID. In order for the small cell base station to determine the routing (i.e., to which served device the data packet should be routed), the DgNB configured routing information in the small cell of the device that does not serve the access link. In the given example, this is the small cell base station SC2, and the routing configuration is exemplarily illustrated in the "Routing" column of Table 4.

[0086] In that table, all radio bearers to / from the UE device are routed via the small cell base station SC3.1. The routing information may be provided in the form of a next hop address or a next hop device name, the latter shown in Table 4. The routing information may alternatively be provided with an index of the next hop, the index pointing to a pre-configured table.

[0087] Table 4 does not include routing information for the radio bearers of small cell base stations SC3.1 and SC3.2, since both small cell base stations are served on the access link by SC2 and therefore the GLogCh-ID of any packet is mapped to the respective radio bearer of the access link and therefore to the end device.

[0088] Now, looking at Figure 4, the above description mainly describes first the pre-assumption of an established RRC connection between any UE device with the DgNB and the small cell base station, which is shown in the diagram in the top box. Secondly, the above describes data transfer between the UE or other device and the DgNB, which is simplified in the diagram by the top double-headed arrow.

[0089] According to the present invention, the DgNB configures the UE device UE with candidate cell information, which in this embodiment includes information about the cells spanned by the small cell base station SC3.2. The information may include resource information, for example, frequency bands or intermediate frequencies of the cell bandwidth of the candidate cell. The information may also include a cell identifier, for example, a physical cell identifier encoded in a synchronization signal broadcasted in the cell, allowing cell identification based on the synchronization signal. The information may further include a UE device identifier used by the UE device when accessing the candidate cell. In this embodiment, it is assumed that the UE device identifier (e.g., C-RNTI) does not change when switching between cells autonomously. In case of random access or other data-limited methods of accessing the candidate cell, the UE device and the candidate cell may be configured with a short UE device identifier in addition to or instead of the C-RNTI.

[0090] In addition, a candidate small cell SC3.2 is configured so that it can serve the UE device after an autonomous cell switch of the UE device. For that purpose, the SC3.2 is configured with a UE device identifier (in this embodiment, a C-RNTI and / or a short UE device identifier) ​​and further information required to serve the UE. For example, UE radio functions related to the MAC and physical layers are configured.

[0091] In addition, the information according to Table 1 currently present in the UE device and the small cell base station SC3.1 serving the UE device is also configured in the small cell base station SC3.2. This information enables SC3.2 to multiplex DL data onto the appropriate radio bearer, forward UL data with the appropriate QoS and priority, and attach the correct GLogCh-ID, as further explained above for the small cell base station SC3.2.

[0092] Here, the small cell base station SC3.2 broadcasts synchronization and reference signals as well as system information that is received by the UE device and from which measurements of the candidate cell SC3.2 are derived and used by the UE device to decide on a potential cell switch. The information broadcasted by SC3.2 is shown in dashed lines in the figure, as this is just an example and any other kind of trigger for the UE device to decide on a cell switch can be used to implement the invention. The system information may include load information that helps the UE device decide if the service that can be expected from SC3.2 is better than the service currently serving SC3.1.

[0093] According to this embodiment, the UE device decides to autonomously switch cells and request resources from the candidate small cell base station SC3.2. This can be done by performing a random access to the candidate small cell using the configured short UE device identifier. The UE device can request a longer second message in the first random access message resource, transmitted in the granted resource. Alternatively, when random access is not required, for example for timing reasons, the UE can directly use the physical uplink control channel to request UL resources using the C-RNTI.

[0094] During the procedure, DL data transfer via small cell base station SC3.1 may continue. Depending on the radio capabilities of the UE device, the UE device may be able to acknowledge reception in the UL while successfully receiving data from SC3.1 and initiating UL data transfer to SC3.2. This option is indicated by dashed lines in Figure 4.

[0095] The candidate small cell SC3.2 may reply to the UL resource request with a UL resource grant that, when received by the UE device, may change the candidate small cell SC3.2 to the new serving small cell. The UE device compiles, for example, a user data packet or a first UL data packet from a UL RRC message and transmits these to the small cell base station SC3.2. The packet is received and a mapping of the configured radio bearer onto the radio bearer of the wireless backhaul link is performed as described for the UL packet forwarding of the small cell base station SC3.1, including the appending of the GLogCh-ID in the appropriate communication protocol.

[0096] According to the present invention, as soon as UL data packets from a UE device are received at the small cell base station SC2 recognized by their LogCh-ID, duplication of DL data packets to the UE device of the same bearer recognized by the same LogCh-ID is started. Duplication in this sense means that these DL packets are transmitted by the small cell base station along the old route (i.e. to the small cell base station SC3.1 in this embodiment). In addition, they are copied to the new route (i.e. to the small cell base station SC3.2) where the first UL packet was received.

[0097] If a GLogCh-ID is constructed so that it is possible to identify all bearers belonging to a single UE device, the principle of temporarily copying DL data packets in the small cell base station when the first UL data packet is received can be applied to all bearers of the UE. If the GLogCh-ID does not allow UE differentiation, the DL copy can only be applied to bidirectional bearers for which an UL packet was received. In that case, the UE device can be expected to transmit UL dummy packets for bearers that currently do not have UL data to send, to allow fast use of new DL routes for all bearers. These dummy packets can have a user data length of 0, i.e. contain only a small header, or they can be otherwise marked so that they are excluded from the data flow in the radio access sub-network.

[0098] Receiving the first DL packet by the UE via the new small cell base station SC3.2, or the first UL grant, or successfully receiving an acknowledgment of the UL packet by the new small cell base station, may trigger the UE device to inform the DgNB about successfully performing the cell switch with an RRC message (e.g., "path switch" information). Receiving this message at the DgNB may trigger the DgNB to inform all relevant small cells about the path switch (i.e., the small cell base station SC2 is requested to demonstrate a new route for the UE), the small cell base station SC3.2 is requested to act as the serving small cell, and SC3.1 is configured to delete the UE context or as a candidate small cell for future cell switches back to the old cell.

[0099] If the small cell base station SC2 copies DL packets for only some bearers of the UE device, then the DgNB may trigger explicit routes for all bearers of the UE device.

[0100] Now, DL data transfer for all bearers of the UE device is routed to the new small cell base station. A new configuration of the UE serving the new candidate small cell may then be performed by the DgNB.

[0101] The previous variant is shown in Figure 5, based on the same sub-network architecture of Figure 3. The prerequisites for RRC connections with the DgNB of the UE device and all small cell base stations, and the configuration of the small cell base stations SC3.1 and SC2 with the GLogCh-ID and routing information are the same as in the previous embodiment.

[0102] In this embodiment, according to a novel aspect of the invention, the small cell base station SC3.1 is configured to inform the DgNB when the connection to the UE device is lost. The small cell SC3.1 informs the DgNB that the connection to the UE has been lost by transmitting a UE device identifier, or that the connection to the served bearers has been lost by transmitting a list of GLogCh-IDs for which the connection has been lost. Either information can be transmitted to the DgNB in ​​a kind of "Bearer Loss Notification".

[0103] In FIG. 5, at some point in time, the UE device and the small cell base station SC3.1 detect a loss of connection, for example due to a radio link failure resulting from the UE moving away from the cell or UE antenna shadowing or the like. Since there is no link available for transmission, the UE device immediately starts buffering UL data. This is no different from state-of-the-art UE device implementations. According to the present invention, the small cell base station SC3.1 informs the DgNB about the lost connection to the UE device, and the DgNB starts buffering DL data. The DgNB may also start a timer that, if it expires, triggers an implicit release of the RRC connection to the UE device. In this embodiment, it is assumed that the timer does not expire and the RRC connection is maintained.

[0104] The UE device performs an autonomous cell switch to the candidate small cell, which in this embodiment is SC3.2, and transmits an RRC message in the UL (preferably the first UL packet) informing the DgNB about the path switch. The RRC now reconfigures the affected small cells SC2, SC3.1 and SC3.2 for the new path to and from the UE device and starts transmitting buffered DL data before continuing with periodic DL data forwarding of new data. The UE may start UL data forwarding immediately after the autonomously switched cell.

[0105] A further embodiment is now described. This embodiment is a partial correction of the previous embodiment of the architecture according to Fig. 6. Compared to the architecture of Fig. 3, the depicted sub-network has one more hierarchical layer. This embodiment should show a useful aspect of the invention for larger sub-networks.

[0106] Assuming that all five small cell base stations of the sub-network are configured to actually or potentially serve a UE device, the individual configuration of the small cell base stations according to the previous two embodiments consumes radio resources significantly in the radio access link. An alternative is shown in Fig. 7. The DgNB broadcasts a small cell reconfiguration message containing small cell routing preparation information (i.e. GLogCh-ID), related QoS, priority and routing information. Broadcasting in this sense means distributing to all directly connected small cell base stations of the sub-network for the purpose of storing and applying the configuration, and forwarding the information by every small cell base station in parallel to the next directly connected small cell base station via the access link.

[0107] According to figure 7, all small cell base stations receiving the reconfiguration message forward said messages and verify their integrity, for example by verifying their integrity based on certificates stored in each small cell base station previously received from the network operator. If the integrity is verified, the configuration is stored and applied.

[0108] This is an efficient distribution mechanism for the configuration of sub-networks that cannot be combined with the core steps of the invention described in an exemplary manner for the first two embodiments.

[0109] Any reconfiguration of UE devices or small cell base stations of the sub-network resulting in the addition, deletion or major reconfiguration of signaling or data bearers will then result in the broadcast of a small cell reconfiguration message containing updated GLogCh-ID, priority, QoS and / or routing information so that all small cell base stations are prepared to serve the UE device after an autonomous cell switch. When the efficient broadcast mechanism of the third embodiment is not used, any such reconfiguration of UE devices or small cell base stations will result in individual reconfiguration of all affected small cell base stations.

[0110] The fourth embodiment is based on the architecture illustrated in Figure 8, which is similar to the architecture of Figure 3, except that the small cell base station SC3.2 is directly connected to the DgNB. SC3.2 may be optimized for low latency and limited bandwidth communication.

[0111] A UE device may have multiple running applications with QoS that do not require low latency communication. In addition, the UE has one application that sporadically generates data packets (ULL data) that require low latency transmission and typically generates a limited amount of DL traffic, e.g., a single network layer acknowledgment.

[0112] Figure 9 shows the message sequence according to this embodiment. It is assumed that the UE device is connected to a small cell base station SC3.1 and has an RRC connection with the DgNB as in the first embodiment. The UE device configures at least one candidate cell SC3.2, which is a candidate for transmission of ULL data. This cell is not considered in case of autonomous cell switching as in the other embodiments, but is considered in case of autonomous selection of ULL data transmission. Although the small cell base station SC3.2 is configured as a candidate cell, the configuration may be limited to support ULL data radio bearers (e.g. single GLogCh-ID and no signaling radio bearers for the UE device).

[0113] At some point, ULL data is generated by the respective application and the UE device selects a candidate cell SC3.2 for transmission and requests UL transmission resources, while UL and DL transmissions via the small cell base station SC3.1 continue for other applications (i.e., other radio bearers) or RRC signaling. After authorization, the UE device transmits ULL data to the DgNB on the UL routed according to the small cell configuration. The resulting DL data is routed and received on the same route from the UE device's SC3.2. Optionally, the UE device may inform the DgNB about the data transmission on the newly selected small cell base station SC3.2, and the DgNB may reconfigure the small cell base station to confirm the new path. This is described here as optional and is shown in FIG. 9 with dashed lines for a single data transmission, so any involvement of the DgNB over the data routing may be omitted.

[0114] Particular aspects of the present invention can be summarized as follows.

[0115] A base station controlling a radio access sub-network, the radio access sub-network including at least one UE device and a plurality of cascaded small cell base stations, the at least one UE device and the plurality of cascaded small cell base stations having an RRC connection to the base station; The plurality of cascaded small cell base stations further comprises: a plurality of small cell base stations, each having a wireless backhaul link to another small cell base station; at least one small cell base station having a wireless backhaul link to the base station; a plurality of small cell base stations, each having a radio access link to another small cell base station; at least one small cell base station having a wireless access link to at least one UE device; Equipped with The base station Configuring the UE device with candidate small cell information, the candidate small cell information including identification information of at least one candidate small cell spanned by one of a plurality of cascaded small cell base stations for autonomous cell switching and at least one condition for performing autonomous cell switching; configuring at least one small cell base station as a candidate small cell base station having a radio access link to at least one UE device after autonomous switching by the UE device, said configuration as a candidate small cell base station comprising: a UE device identifier used by the UE device when accessing a candidate small cell; and one or more bearer identifiers identifying one or more bearers of the UE device; forwarding treatment information for each of the one or more bearer identifiers, the forwarding treatment information including at least one of a quality of service parameter, priority information, and routing information for forwarding data packets received by the candidate small cell base station from or to the UE device; The composition of The base station receiving information about a cell switch performed autonomously by the UE device (the cell switch execution is not triggered by the station); Base station.

[0116] The base station can configure the UE device with updated candidate small cell information after receiving the information about the cell switch autonomously performed by the UE device, and can also confirm the path switch in the small cell base station associated with the routing data from or to the UE device after receiving the information about the cell switch autonomously performed by the UE device.

[0117] A base station controlling a radio access sub-network, the radio access sub-network including at least one UE device and a plurality of cascaded small cell base stations, the at least one UE device and the plurality of cascaded small cell base stations having an RRC connection to the base station; The plurality of cascaded small cell base stations further comprises: a plurality of small cell base stations having wireless backhaul links to other small cell base stations; at least one small cell base station having a wireless backhaul link to the base station; a plurality of small cell base stations having radio access links to other small cell base stations; at least one small cell base station having a wireless access link to at least one UE device; Equipped with The base station Configuring the UE device with candidate small cell information, the candidate small cell information including identification information of at least one candidate small cell spanned by one of a plurality of cascaded small cell base stations for autonomous cell switching, and at least one condition for performing autonomous cell switching; Configuring at least one small cell base station for one routing data of at least one UE device, the configuration comprising: one or more bearer identifiers identifying one or more bearers of the UE device; forwarding treatment information for each of the one or more bearer identities, the forwarding treatment information including at least one of a quality of service parameter and priority information; routing information for routing downlink data packets received on a wireless backhaul link to a UE device, the routing information including at least one first path for routing the downlink data packets to the UE device; and at least one alternative path for routing the downlink data packets to the UE device after an autonomous cell switch by the UE device. The composition of The base station confirming a path switch to the small cell base station in response to receiving information about a cell switch autonomously performed by the UE device via one of the at least one alternative path; Base station.

[0118] As described above, the base station confirming the path switch to the small cell base station includes requesting an end to the duplication of data packets onto the first path.

[0119] As described above, the base station configuring at least one small cell base station for one routing data of at least one UE device includes providing identical configuration information to all small cell base stations having an access link to the base station for configuration of the small cell base station and forwarding the configuration information by the small cell base station to further small cell base stations, wherein the configuration information is integrity protected, so that the small cell base station can verify the integrity of the configuration data.

[0120] A UE device for performing autonomous cell switching, the UE device comprising: a first small cell base station having a wireless access link to the first small cell base station; having an RRC connection to a macro base station that controls a first small cell base station; The UE device Receive UE device identification information and candidate small cell information from the macro base station, and the candidate small cell information is an identity of at least one candidate small cell; and At least one condition for performing an autonomous cell switchover; Including, the UE device autonomously determines to perform a cell switch to the candidate small cell based on measurements of signals received from the candidate small cell and at least one condition for performing an autonomous cell switch, and uses the UE device identity to request uplink resources for data transmission from the candidate small cell; UE device.

[0121] As mentioned above, the UE device autonomously decides to perform a cell switch without receiving a message triggering a cell switch to the candidate small cell and without informing the first small cell base station about the cell switch execution. Also, as mentioned above, the UE device performs the cell switch while data transfer to and / or from the first small cell base station is ongoing.

[0122] After successfully performing the cell switch, the UE device may be configured to notify the base station about the execution of the cell switch in an RRC message sent via the switched-to small cell, where the execution of the cell switch is considered to be successful after receiving one of an uplink resource grant and a downlink data packet from the switched-to small cell.

[0123] After receiving neighboring cell measurement information from the base station, the neighboring cell measurement information includes identification information of at least one cell not controlled by the base station; While measuring received candidate small cell signals from the identity information of at least one candidate small cell to determine whether to perform an autonomous cell switch (or in parallel but not actually at the same time), the UE device may perform neighboring cell measurements in accordance with the neighboring cell measurement information.

[0124] The UE device may report neighboring cell measurements to the macro base station according to neighboring cell measurement information that is not dependent on autonomous cell switching.

[0125] A small cell base station controlled by a base station having a wireless backhaul link to another small cell base station controlled by the base station, the small cell base station comprising: Receive UE device information from the macro base station; UE device information is a UE device identifier that identifies a UE device that is not currently served by a small cell base station; one or more radio bearer identifiers that uniquely identify (within a sub-network controlled by the base station) one or more radio bearers of the identified UE device; forwarding treatment information associated with one or more radio bearer identifiers, the forwarding treatment information including at least one of quality of service information, priority information, and routing information; Equipped with Small cell base stations are receiving a request for uplink resources from a UE device, the request including a UE device identifier; Identifying the UE device based on respective UE device identifiers received from the UE device and from the macro base station; granting uplink resources to the identified UE device without further communication with the macro base station associated with the UE device; A small cell base station that receives an uplink data packet on a radio bearer from a UE device, determines a radio bearer identifier that uniquely identifies the radio bearer of the UE device, and forwards the data packet together with the determined radio bearer identifier to another small cell base station via a wireless backhaul link in accordance with forwarding processing information.

[0126] A small cell base station controlled by a base station having a wireless backhaul link (to another base station) and having wireless access links to at least two further small cell base stations controlled by the base station, the small cell base station receiving from the base station one or more bearer identifiers, each of which identifies one or more bearers for a particular UE device; forwarding treatment information associated with one or more identified bearers, the forwarding treatment information including at least one of quality of service information and priority information; routing information for routing downlink data packets received on a wireless backhaul link to a particular UE device, the routing information including at least a first path and a second path for routing the downlink data packets to the particular UE device; Receive, While transmitting all downlink data packets identified by the routed bearer identifier to the specific UE device along a first path included in the routing information, the small cell base station, in response to receiving at least one uplink data packet from the specific UE device on (the access link of) a second path included in the routing information, starts transmitting all downlink data packets identified by the routed bearer identifier to the specific UE device along the second path.

[0127] The small cell base station may be arranged such that starting to transmit all downlink data packets identified by the routed bearer identifier to the specific UE device along the second path comprises transmitting copies of all downlink data packets identified by the routed bearer identifier to the specific UE device in addition along the first path included in the routing information, and stopping transmitting copies of all downlink data packets identified by the routed bearer identifier to the specific UE device along the first path included in the routing information after the small cell base station receives a confirmation message from the macro base station via the wireless backhaul link, where the confirmation message confirms the path switch. (Other possible items) (Item 1) 1. A mobile communication system sub-network comprising a macro cell base station and a plurality of small cell base stations, the plurality of small cell base stations being in radio communication with the macro cell base station, each small cell base station being directly connected to the macro cell base station or connected to the macro cell base station via one or more other small cell base stations, the macro cell base station is arranged to configure a user equipment (UE) device having a radio resource control (RRC) connection to the macro cell base station with candidate small cell base station information to enable the UE device to autonomously switch between small cell base stations; The macro cell base station is arranged to configure the small cell base station having small cell base station configuration information, and the small cell base station configuration information includes: a UE device identifier that identifies a UE device configured with the macro cell base station with candidate small cell base station information associated with the small cell base station; one or more radio bearer identifiers that uniquely identify one or more radio bearers of the UE device; having The small cell base station configuration information further enables the small cell base station to receive data from the UE device on a radio bearer, determine a radio bearer identifier that uniquely identifies the radio bearer, and forward the data together with the determined radio bearer identifier. Mobile communication system sub-network. (Item 2) 2. The mobile communication system subnetwork according to claim 1, wherein the candidate small cell base station information comprises information selected from a list comprising a small cell base station identifier, a small cell base station frequency resource, a small cell base station radio parameter, a small cell base station access mode and a small cell base station switching criterion. (Item 3) 3. The mobile communication system subnetwork according to claim 1 or 2, wherein the small cell base station configuration information includes information selected from a list including medium access control (MAC) layer components, physical layer structure elements, global logical channel identifiers transmitted to the macro cell base station together with data received from the UE device, and routing information for conveying uplink and / or downlink information from or to the UE device. (Item 4) 4. The mobile communication system sub-network according to any one of claims 1 to 3, wherein the small cell base station has a cell coverage that is less than the cell coverage of the macro cell base station. (Item 5) 5. A mobile communication system sub-network according to claim 4, wherein the small cell base stations form a network of small cells with certain small cell base stations having a direct connection to the macro cell base station and other small cell base stations having an indirect connection to the first base station via one or more small cell base stations. (Item 6) 6. A mobile communication system subnetwork according to claim 5, wherein each small cell base station is arranged to multiplex data received from different radio bearers onto a single bearer for transmission to the macro cell base station, said multiplexing being dependent on a quality of service setting of the received data radio bearer, and an indication of an outgoing radio bearer being added to the transmitted data packet. (Item 7) 7. A mobile communication system subnetwork according to any one of claims 1 to 6, wherein the macro cell base station is arranged to provide an identifier of the UE device to those of the small cell base stations which may be involved in routing data packets from the UE device to the macro cell base station, the identifier being used by the UE device to request radio resources from the small cell base station. (Item 8) 8. The mobile communication system sub-network according to any one of claims 1 to 7, wherein the macro cell base station is arranged to provide the small cell base station with information about radio bearers and devices served in all sub-networks, together with their radio priority and quality of service settings. (Item 9) The mobile communication system subnetwork according to any one of claims 1 to 8, wherein the small cell base station configuration information includes routing information for routing downlink packets received on a wireless backhaul link to the UE device, the routing information including at least one first path for routing downlink data packets to the UE device and at least one alternative path for routing downlink packets to the UE device after an autonomous cell switch by the UE device. (Item 10) 10. The mobile communication system subnetwork according to item 9, wherein the macro cell base station is configured to confirm a path switch from a first small cell base station to a second small cell base station in response to receiving information about a cell switch performed by the UE device via one of the at least two alternative paths. (Item 11) 11. A mobile communication system subnetwork according to claim 9 or 10, wherein the small cell base station configuration information provides identical configuration information to all small cell base stations having a direct connection to the macro cell base station for configuring the small cell base station and for forwarding the small cell base station configuration information by the small cell base station to further small cell base stations, and the configuration information is integrity protected so that the small cell base stations can verify the integrity of the configuration information. (Item 12) 1. A user equipment (UE) device arranged to enable autonomous cell switching in a mobile communication system sub-network comprising a macro cell base station and a plurality of small cell base stations providing cells between which the UE device can be switched, the UE device comprising: The UE device is arranged to receive a UE device identity and candidate cell information from the macro cell base station having a radio resource control connection, the candidate cell information including the identity and at least one condition for initiating an autonomous cell switch between a first small cell base station and a second small cell base station, and the UE device: Using the UE device identity to request uplink resources for data transmission from a candidate cell; Transmitting uplink data on a radio bearer using the uplink resources received from the candidate cell. It is arranged as follows: A user equipment (UE) device, the UE device identification information enabling the candidate cell to determine a radio bearer identifier that uniquely identifies the radio bearer, and forwarding data packets together with the determined radio bearer identifier to another small cell base station via a wireless backhaul link. (Item 13) A small cell base station controllable by a macro cell base station, the small cell base station being arranged to receive user equipment (UE) device information from the macro cell base station, the UE device information comprising: A UE device identifier that identifies a UE device that is not currently being served by the small cell base station; one or more radio bearer identifiers that uniquely identify one or more radio bearers of the identified UE device; forwarding treatment information associated with the one or more radio bearer identifiers, the forwarding treatment information including at least one of quality of service information, priority information, and routing information; Including, The small cell base station further comprises: receiving a request for uplink resources from the UE device, the request including a UE device identifier; identifying the UE device based on the UE device identifier received from the UE device and from the macrocell base station; granting uplink resources to the identified UE device without further communication with the macrocell base station relating to the UE device; receiving an uplink data packet on a radio bearer from the UE device, determining a radio bearer identifier that uniquely identifies the radio bearer of the UE device, and forwarding the uplink data packet together with the determined radio bearer identifier to another small cell base station via a wireless backhaul link in accordance with the forwarding procedure information; 2. A small cell base station configured to: (Item 14) 1. A method of operating a mobile communications network comprising at least one macro cell base station and a plurality of small cell base stations connected to said macro cell base station by wireless connections, said method comprising the steps of: enabling a UE device connected with the macro cell base station via a first one of the plurality of small cell base stations to autonomously transfer the connection such that the connection passes through a second one of the plurality of small cell base stations by providing the connection with a locally unique identifier and distributing the locally unique identifier to the plurality of small cell base stations via a wireless backhaul link, whereby the UE device communicates the locally unique identifier with the second one of the plurality of small cell base stations during the autonomous transfer; The locally unique identifier is unique to the macro cell base station and the plurality of small cell base stations, identifying a data flow for the UE device on the wireless backhaul link; method.

Claims

1. 1. A method of operating a first small cell base station in a mobile communications system sub-network comprising a macro cell base station and a plurality of small cell base stations including a first small cell base station, the plurality of small cell base stations being in wireless communication with the macro cell base station, the first small cell base station having a direct connection with the macro cell base station or a connection via one or more other small cell base stations; The method comprises: receiving small cell base station configuration information from the macro cell base station in the first small cell base station; receiving, at the first small cell base station, data from a user equipment (UE) device that previously had a connection to a second small cell base station; and using the small cell base station configuration information to forward the received data to the macro cell base station directly or via one or more other small cell base stations; by determining that the UE device has transmitted one of a resource request to the first small cell base station or a first data packet to the first small cell base station, the resource request comprising an identifier of the UE device, the first small cell base station determining that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station; when it is determined that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station, the first small cell base station informs the next highest small cell base station between the first small cell base station and the macro cell base station, or, if there is no such next highest small cell base station, the macro cell base station, about the UE device being served by the first small cell base station so that downlink packets destined for the UE device can be routed to the first small cell base station. method.

2. 2. The method of claim 1, wherein the first small cell base station determines that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station by determining that the UE device has transmitted a first data packet to the first small cell base station, the first data packet including a radio resource control message generated by the UE device destined for the macro cell base station.

3. 3. The method of claim 1 or 2, wherein the first small cell base station determines that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station by determining that the UE device has transmitted a first data packet to the first small cell base station, the first data packet including a locally unique identifier identifying a radio bearer of the UE device, which was provided to the first small cell base station in the small cell base station configuration information.

4. 4. The method according to claim 1, further comprising: when the first small cell base station provides wireless backhaul links to a third small cell base station and a fourth small cell base station and when the first small cell base station determines that a second UE device autonomously switches cells from the third small cell base station to the fourth small cell base station, the first small cell base station is further configured to start routing downlink data packets to the fourth small cell base station based on the small cell base station configuration information upon receiving a locally unique identifier associated with the second UE device from the fourth small cell base station.

5. 5. The method of claim 4, wherein the step of initiating routing of downlink data packets to the fourth small cell base station comprises the step of transmitting duplicated downlink data packets to the third small cell base station and the fourth small cell base station until the first small cell base station is notified by the macro cell base station about a path switch.

6. A first small cell base station in a mobile communication system sub-network, comprising a macro cell base station and a plurality of small cell base stations including a first small cell base station, the plurality of small cell base stations being in wireless communication with the macro cell base station, the first small cell base station having a direct connection with the macro cell base station or a connection via one or more other small cell base stations; The first small cell base station, receiving small cell base station configuration information from the macro cell base station; receiving data from a user equipment (UE) device that previously had a connection to a second small cell base station; configured to forward the received data to the macro cell base station directly or via one or more other small cell base stations using the small cell base station configuration information; the first small cell base station is further configured to determine that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station by determining that the UE device has transmitted one of a resource request to the first small cell base station or a first data packet to the first small cell base station, the resource request comprising an identifier of the UE device; when it is determined that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station, the first small cell base station is configured to inform the next highest small cell base station between the first small cell base station and the macro cell base station, or, if there is no such next highest small cell base station, the macro cell base station, about the UE device being served by the first small cell base station so that downlink packets destined for the UE device can be routed to the first small cell base station. A first small cell base station.

7. 7. The first small cell base station according to claim 6, wherein the first small cell base station is configured to determine that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station by determining that the UE device has transmitted a first data packet to the first small cell base station, the first data packet including a radio resource control message generated by the UE device and destined for the macro cell base station.

8. 8. The first small cell base station according to claim 6 or 7, wherein the first small cell base station is configured to determine that the UE device has autonomously switched its connection from the second small cell base station to the first small cell base station by determining that the UE device has transmitted a first data packet to the first small cell base station, the first data packet including a locally unique identifier identifying a radio bearer of the UE device, which has been provided to the first small cell base station in the small cell base station configuration information.

9. 9. The first small cell base station according to claim 6, further configured to: when the first small cell base station provides wireless backhaul links to a third small cell base station and a fourth small cell base station, and when the second UE device determines to autonomously switch cells from the third small cell base station to the fourth small cell base station, upon receiving a locally unique identifier associated with the second UE device from the fourth small cell base station, the first small cell base station starts routing downlink data packets to the fourth small cell base station based on the small cell base station configuration information.

10. 10. The first small cell base station according to claim 9, wherein the initiating routing of downlink data packets to the fourth small cell base station comprises transmitting duplicated downlink data packets to the third small cell base station and the fourth small cell base station until the first small cell base station is notified by the macro cell base station about a path switch.

11. 1. A macro cell base station in a mobile communication system sub-network, comprising a macro cell base station and a plurality of small cell base stations in wireless communication with the macro cell base station, each small cell base station having a direct connection with the macro cell base station or a connection via one or more other small cell base stations; the macrocell base station is configured to enable a user equipment (UE) device having a radio resource control (RRC) connection to the macrocell base station to autonomously switch between small cell base stations using candidate small cell base station configuration information provided to the UE device by the macrocell base station; The candidate small cell base station configuration information is information that the small cell base station receiving data from the UE device; and configured to enable data transfer to the macro cell base station or another small cell base station; The macrocell base station, receiving an RRC message from a UE device informing a macro cell base station of an autonomous switchover from a first small cell base station to a second small cell base station performed by the UE device; configured to request the first small cell base station to stop routing data to or from the UE device; Macrocell base station.

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