GB2577514A

GB2577514A - Inter-RAT selection

Info

Publication number: GB2577514A
Application number: GB1815708.1A
Authority: GB
Inventors: Assouline Benny; Marco Olivier
Original assignee: TCL Communication Ltd
Current assignee: TCL Communication Ltd
Priority date: 2018-09-26
Filing date: 2018-09-26
Publication date: 2020-04-01
Anticipated expiration: 2038-09-26
Also published as: CN112313995A; WO2020063617A1; GB2577514B; GB201815708D0; CN112313995B

Abstract

Disclosed is a method for facilitating the selection of inter-RAT cells by a mobile device. The method comprises broadcasting a deployment version indicator from a cell of a base station 200, identifying changes in the configuration of inter-RAT neighbouring cells 300, and if changes are identified then the deployment version indicator is updated and broadcast. The deployment version indicator may be an integer value, which may be incremented or decremented when a change in the configuration is detected. There may be a predetermined minimum time between updates of the deployment version indicator, which may be dependent on the maximum sleep time of UEs to be accommodated and the maximum value which can be assigned to the deployment version indicator. The cell may be a Narrowband-IoT (NB-IoT) cell, and the deployment version indicator may be transmitted in a system information broadcast.

Description

Inter-RAT Selection

Technical Field

[1] The following disclosure relates to the selection and reselection of different Radio Access Technologies (RATs) by a mobile device, and in particular to the reselection of a different RAT by an NB-IoT device.

Background

[2] Wireless communication systems, such as the third-generation (3G) of mobile telephone standards and technology are well known. Such 3G standards and technology have been developed by the Third Generation Partnership Project (3GPP). The 3rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Communication systems and networks have developed towards a broadband and mobile system.

[3] Figure 1 shows a schematic diagram of an example of three base stations forming a cellular network. In cellular wireless communication systems User Equipment (UE) is connected by a wireless link to a Radio Access Network (RAN). The RAN comprises a set of base stations which provide wireless links to the UEs located in cells covered by the base station, and an interface to a Core Network (CN) which provides overall network control. As will be appreciated the RAN and CN each conduct respective functions in relation to the overall network. For convenience the term cellular network will be used to refer to the combined RAN & CN, and it will be understood that the term is used to refer to the respective system for performing the disclosed function.

[4] The 3rd Generation Partnership Project has developed the so-called Long Term Evolution (LTE) system, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network where one or more macro-cells are supported by a base station known as an eNodeB or eNB (evolved NodeB). More recently, LTE is evolving further towards the so-called 5G or NR (new radio) systems where one or more cells are supported by a base station known as a next generation NodeB (gNB). NR is proposed to utilise an Orthogonal Frequency Division Multiplexed (OFDM) physical transmission format.

[5] A range of RATs may be offered by a cellular network, each providing particular types of services. Narrowband-loT (NB-IoT) is an example of a RAT developed to support devices with a low cost, long battery life, and high connection density. Accordingly, the wireless protocol provides relatively low data speeds (e.g. 250kbit/s), but with good power efficiency. Another example of a RAT for machine to machine type communications is eMTC (enhanced Machine-Type Communications) which offers higher data rates of 1Mbit/s. Mobile devices are often capable of utilising more than one RAT.

[6] A device's requirements may change over time. For example, an NB-IoT cell usually be optimum for a smart meter, but a RAT with higher data rates may be preferred to perform a software or firmware update. A device RAT preference may thus change over time. A device RAT preference may also change according to the deployment scenario. For example, a smart meter located in both NB-IoT coverage and eMTC coverage may prefer to connect to the eMTC cell if the radio conditions provided by the eMTC cell are significantly better than the radio conditions provided by the NB-IoT cell [7] The deployment of cells changes over time, particularly during the deployment of new technologies. It is therefore likely that a device that is in an area with only coverage of one type of 1 RAT (for example, NB-IoT). The device will thus connect to that cell, even if it is not the optimal RAT. During the life of the device a new cell may be deployed covering the area of the device and offering a more optimum RAT (for example eMTC).

[8] When connected to a first cellular network, mobile devices can search for other cellular networks (for example one offering a different RAT) to which the device could connect, and hence in this example the device could identify the new cell. For example, devices may be configured to conduct a periodic search, or when a different RAT may be preferable. However, such a search requires a scan of all potential frequencies and is expensive from a power consumption perspective. Performing a speculative scan in the hope of identifying a different RAT is thus undesirable as the power expended will be wasted if there is no suitable network.

[9] Figure 2 shows an example of a set of first base station 200 which provides eMTC coverage over a first coverage area 201, and NB-IoT coverage over a second coverage area 202. Devices 203 and 204 are located in the NB-IoT coverage area 202 and hence connect using the NB-IoT RAT.

[10] After initial connection it may be that, as shown in Figure 3, a further base station 300 is deployed which provides eMTC coverage over an additional area 301. Device 203 may detect this network from a periodic search and once identified may connect to it. However, the periodic search may have been performed for an extended period of time before the new base station 300 was identified making the overall process power inefficient. Device 204 may also have been performing periodic searches, but even after deployment of base station 300 the device is still outside of eMTC coverage and hence all power invested in such searches is wasted.

[11] There is therefore a requirement for an improved method of selecting alternative RAT connections.

Summary

[12] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[13] There is provided a method for facilitating connection of a UE to a cell in a cellular network, the method performed at a base station and comprising the steps of broadcasting a deployment version indicator from a cell of the base station; identifying changes in the configuration of inter-RAT neighbouring cells; updating the deployment version indicator if changes are identified; and broadcasting the updated deployment version indicator.

[14] The deployment version indicator may be an integer value.

[15] The deployment version indicator may be incremented or decremented when a change in the configuration is detected.

[16] There may be a predefined minimum time between updates of the deployment version indicator.

[17] The predetermined minimum time may be dependent on the maximum sleep time of UEs to be accommodated and the maximum value that can be assigned to the deployment version indicator.

[18] The cell may be an NB-IoT cell.

[19] The deployment version indicator may be transmitted in a System Information broadcast.

[20] The method may further comprise information regarding neighbouring inter-RAT cells.

[21] The information may be an indication of the frequency of at least one neighbouring inter-RAT cell.

[22] The deployment version indicator may be the SI message value TAG of an SI message containing the SIB comprising the information regarding neighbouring inter-RAT cells.

[23] Changes in the configuration of inter-RAT neighbouring cells may include deployment of a new cell, removal of an existing cell, and reconfiguration of a cell.

[24] The deployment version indicator may relate to a specific RAT and wherein the deployment version indicator is updated only in respect of changes in cells of that RAT.

[25] There may be a plurality of deployment version indicators, each for a respective RAT.

[26] The deployment version indicator may relate to an RAT frequency and wherein the deployment version indicator is updated only in respect of changes in cells of that frequency.

[27] There may be a plurality of deployment version indicators, each for a respective frequency.

[28] A predefined value may be transmitted for the deployment version indicator if there are no neighbouring cells of the relevant RAT.

[29] There is also provided a method for facilitating connection of a UE to a cell in a cellular network, the method performed at a base station providing an NB-IoT cell and comprising the step of broadcasting an indication in the NB-IoT of the availability of an inter-RAT [30] There is also provided a base station configured to performed the methods described herein.

[31] In another aspect, there is provided a non-transitory computer-readable medium. The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory.

Brief description of the drawings

[32] Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

[33] Figure 1 shows an example of a cellular communications network; [34] Figure 2 shows an example deployment, and [35] Figure 3 shows a further example deployment.

Detailed description of the preferred embodiments

[36] Those skilled in the art will recognise and appreciate that the specifics of the examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings.

[37] Figure 1 shows a schematic diagram of three base stations (for example, eNB or gNBs depending on the particular cellular standard and terminology) forming a cellular network.

Typically, each of the base stations will be deployed by one cellular network operator to provide geographic coverage for UEs in the area. The base stations form a Radio Area Network (RAN). Each base station provides wireless coverage for UEs in its area or cell. The base stations are interconnected via the X2 interface and are connected to the core network via the S1 interface. As will be appreciated only basic details are shown for the purposes of exemplifying the key features of a cellular network.

[38] The base stations each comprise hardware and software to implement the RAN's functionality, including communications with the core network and other base stations, carriage of control and data signals between the core network and UEs, and maintaining wireless communications with UEs associated with each base station. The core network comprises hardware and software to implement the network functionality, such as overall network management and control, and routing of calls and data. For convenience the term UE will be used to refer to all types of mobile device.

[39] In order to address at least some of the problems with prior art systems, a base station may include a field in its System Information (SI) broadcast in a cell which identifies the current deployment version of neighbouring cells, which allows changes in deployment status to be identified. In particular, neighbouring cells may be inter-RAT cells to which devices connected to the cell making the broadcast may be able to connect.

[40] A mobile device for which the current RAT is not optimum may utilise the deployment version broadcast to identify if changes have occurred in inter-RAT cells availability, and hence whether a cell of the preferred RAT may be available. If the status indicates a change has occurred, the mobile device may perform a search for a suitable cell, which search may be assisted by information broadcast by the cell with details of neighbouring cells, for example the frequency. If the deployment version indicates no changes, the mobile device can rely on its previous knowledge of potential cells and thus avoid the power consumption incurred by performing a search. The deployment version information thus allows mobile devices to conserve power by avoiding speculative searches.

[41] The deployment version may be indicated in a field in the SI, for example in SIB1-NB or in another SIB dedicated for inter-RAT information, in an NB-IoT cell. As an example only the field may be labelled RATDeploymentValueTag. The deployment version may be defined as an N bit long Integer with integer values in the range 0..2N-1). The deployment version field indicates the latest version of the RAT deployment status and can hence be utilised by UEs receiving the SI to determine if the deployment has changed.

[42] A deployment version may relate to all RATs, or a specific status may be provided for each RAT. For example, one field to indicate the eMTC RAT deployment version and another to indicate the GERAN deployment version. Or per inter-RAT frequency.

[43] The cellular network (in particular the base station) updates the value of the deployment version when it becomes aware of a change in deployment status of neighbouring cells of the relevant RAT. For example, a new cell may be deployed, or a cell removed. In an example the deployment version is an integer and the value is incremented with each change.

[44] The deployment version may be updated following each change, or with a minimum update time such that one change in deployment version indicates one or more changes since the last update. If the tag is updated too frequently (for example after every change) a larger number of bits may be required to avoid the value wrapping-around too quickly. This could cause a UE to consider there had been no changes, when in fact there had been a number of changes and the value has moved through all values and back to the starting point.

[45] NB-IoT networks support a range of applications with widely varying "sleep" periods during which UEs are not active. A sleep time of one week is long, but not impossible. In an example, the minimum update time used for the deployment version field may be set to the maximum supported sleep time divided by 2N-1.

[46] In addition to the deployment version the base station may transmit additional information (for example, in the SI broadcast) on relevant cells. For example, an operating frequency indicator (such as EARFCN for eMTC RAT or ARFCN for GERAN RAT) may be included which allows UEs to restrict their search for a cell to the relevant frequency thus reducing search time and power consumption.

[47] If a new neighbouring cell is deployed, with an operating frequency which is already used by another neighbouring cell, the neighbouring cell information may remain unchanged, but the deployment version will increase to indicate the deployment status change.

[48] The additional information on neighbouring cells may be advertised in a similar manner to the legacy LTE inter-RAT neighbour cells information in SIB7 for GERAN neighbouring cells. in addition, for example, an "eMTC Inter-RAT SIB" may be provided. If such information is provided in new additional SIBs, the value TAG of the SI message containing the new SIBs can also function as the deployment version. That is, a change in the SI message value tag indicates to the UE to reacquire the inter-RAT SIB, and if the acquired information remains unchanged in comparison to the old SI information, it indicates that there was a deployment change.

[49] In another variation the systemInfoValueTagS1 of another SI message, even if not containing a new inter-RAT SIB, may be incremented, without changing the SI message content to indicate a deployment change.

[50] An alternative approach for the base station to signal a deployment change is to temporarily remove the relevant inter-RAT frequency information and to advertise it back again after a break, i.e. after some maximum UE discontinued reception time. That is, once the base station is certain that all UEs had a chance to be updated with the removal of the inter-frequency information.

[51] The deployment version field may be updated following any change in the inter-RAT cells that may be available for a UE connected to the broadcasting cell, for example a new cell being available, a configuration (for example, configuration of the access barring parameters of a cell, for example for the purpose of load balancing) being changed, or removal of a cell from availability.

[52] A value of 0 (or other predefined value) for the deployment version may be reserved to indicate that there are no inter-RAT cells within the serving NB-IoT cell coverage.

[53] Although the above description is given in relation to an NB-IoT transmitting status of other inter-RAT cells, the principles are equally applicable to the cell of any RAT transmitting the deployment version of inter-RAT cells.

[54] While camped on or connected to an NB-IoT cell, a UE which prefers a different RAT may receive and decode SI to identify the deployment version. If the value matches a previously stored value the UE can determine that the deployment status has not changed and there are no new cells to which the UE could connect. In contrast if the value has changed it is an indication that there may be a new inter RAT cell available. The UE may then perform a search for the new cell or may decode information in the SI indicating details of available neighbouring inter-RAT cells. Once details of a preferred cell have been identified the UE can perform a limited search of only the resources indicated for the cell, which may reduce power consumption of the UE.

[55] In an alternative process, a base station may transmit an indication of the availability of an inter-RAT cell within the NB-loT cell coverage. A UE receiving an indication of the inter-RAT cell availability may choose to perform an inter-RAT cell search in order to seek access to that cell. If the cell to which a UE is connected does not indicate the availability of an inter-RAT cell the UE may deactivate any periodic or ad-hoc cell searches to conserve power based on the information that there is not a cell to be found. [56]

[57] <Standard text from here to the end of the description which does not need review> [58] Although not shown in detail any of the devices or apparatus that form part of the network may include at least a processor, a storage unit and a communications interface, wherein the processor unit, storage unit, and communications interface are configured to perform the method of any aspect of the present invention. Further options and choices are described below.

[59] The signal processing functionality of the embodiments of the invention especially the gNB and the UE may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

[60] The computing system can also include a main memory, such as random access memory (RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

[61] The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

[62] In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface, such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

[63] The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

[64] In this document, the terms 'computer program product', 'computer-readable medium' and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally 45 referred to as computer program code' (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

[65] The non-transitory computer readable medium may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory. In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

[66] Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

[67] It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

[68] Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices.

[69] Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term 'comprising' does not exclude the presence of other elements or steps.

[70] Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

[71] Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to 'a', an', 'first', second', etc. do not preclude a plurality.

[72] Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognise that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term 'comprising' or "including" does not exclude the presence of other elements.

Claims

Claims 1. A method for facilitating connection of a UE to a cell in a cellular network, the method performed at a base station and comprising the steps of broadcasting a deployment version indicator from a cell of the base station; identifying changes in the configuration of inter-RAT neighbouring cells; updating the deployment version indicator if changes are identified; and broadcasting the updated deployment version indicator.
2. A method according to claim 1, wherein the deployment version indicator is an integer value.
3. A method according to claim 2, wherein the deployment version indicator is incremented or decremented when a change in the configuration is detected.
4. A method according to any preceding claim, wherein there is a predefined minimum time between updates of the deployment version indicator.
5. A method according to claim 4, wherein the predetermined minimum time is dependent on the maximum sleep time of UEs to be accommodated and the maximum value that can be assigned to the deployment version indicator.
6. A method according to any preceding claim, wherein the cell is an NB-1QT cell.
7. A method according to any preceding claim, wherein the deployment version indicator is transmitted in a System Information broadcast.
8. A method according to any preceding claim, further comprising transmitting information regarding neighbouring inter-RAT cells.
9. A method according to claim 8, wherein the information is an indication of the frequency of at least one neighbouring inter-RAT cell.
10. A method according to any claim 8 or claim 9, wherein the deployment version indicator is the SI message value TAG of an SI message containing the SIB comprising the information regarding neighbouring inter-RAT cells.
11. A method according to any preceding claim, wherein changes in the configuration of inter-RAT neighbouring cells include deployment of a new cell, removal of an existing cell, and reconfiguration of a cell.
12. A method according to any preceding claim, wherein the deployment version indicator relates to a specific RAT and wherein the deployment version indicator is updated only in respect of changes in cells of that RAT.
13. A method according to claim 10, wherein there are a plurality of deployment version indicators, each for a respective RAT.
14. A method according to any preceding claim, wherein the deployment version indicator relates to an RAT frequency and wherein the deployment version indicator is updated only in respect of changes in cells of that frequency.
15. A method according to claim 14, wherein there are a plurality of deployment version indicators, each for a respective frequency.
16. A method according to any preceding claim, wherein a predefined value is transmitted for the deployment version indicator if there are no neighbouring cells of the relevant RAT.
17. A method for facilitating connection of a UE to a cell in a cellular network, the method performed at a base station providing an NB-IoT cell and comprising the step of broadcasting an indication in the NB-IQT of the availability of an inter-RAT
18. A base station configured to performed the method of any of claims 1 to 17.