GB2574854A - Cell selection procedures - Google Patents

Cell selection procedures Download PDF

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Publication number
GB2574854A
GB2574854A GB201810123A GB201810123A GB2574854A GB 2574854 A GB2574854 A GB 2574854A GB 201810123 A GB201810123 A GB 201810123A GB 201810123 A GB201810123 A GB 201810123A GB 2574854 A GB2574854 A GB 2574854A
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United Kingdom
Prior art keywords
system information
terminal device
stored
cell
new
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GB201810123A
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GB201810123D0 (en
GB2574854B (en
Inventor
Magadi Rangaiah Raghavendra
Puthagaram Ghouse Syed Aslam
Rao Anirudh
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ARM Ltd
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ARM Ltd
Advanced Risc Machines Ltd
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Priority to GB1810123.8A priority Critical patent/GB2574854B/en
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Publication of GB2574854A publication Critical patent/GB2574854A/en
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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W76/00—Connection management
    • H04W76/20—Manipulation of established connections
    • H04W76/27—Transitions between radio resource control [RRC] states
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W48/00—Access restriction; Network selection; Access point selection
    • H04W48/20—Selecting an access point
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W48/00—Access restriction; Network selection; Access point selection
    • H04W48/16—Discovering, processing access restriction or access information
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W74/00—Wireless channel access, e.g. scheduled or random access
    • H04W74/002—Transmission of channel access control information
    • H04W74/006—Transmission of channel access control information in the downlink, i.e. towards the terminal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W76/00—Connection management
    • H04W76/30—Connection release
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/70—Services for machine-to-machine communication [M2M] or machine type communication [MTC]
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Abstract

The present disclosure relates to a method in a terminal device, such as a Narrowband Internet of Things, NB­-IoT, terminal device (140), configured to operate in a radio access network (110) in a connected mode and an idle mode during a cell selection procedure. Stored system information of a cell is retained while in connected mode and may be used when the terminal device returns to idle mode (during an RRC connection release). The validity of the stored system information is checked (330) when the terminal device changes from connected mode to idle mode (320). The stored system information is updated with new system information if it is found to be invalid (340), and the terminal device camps on the cell in idle mode (350). Checking the validity 450 of stored system information comprises comparing a change identifier (e.g. SystemInfoValueTag) 420 in the stored system information 410 with a new change identifier 440 in new system information 430 received from the cell. A reduction in the time and processing required to find a suitable cell to camp on can provide a reduction in power consumption for the terminal device, and may extend its lifetime.

Description

CELL SELECTION PROCEDURES
Background
A terminal device may operate in a radio access network in a connected mode and an idle mode. Specifically, the terminal device may connect to a cell of the radio access network in a connected mode to actively transmit and receive data. The cell on which the terminal device is connected may be referred to as a serving cell. If the terminal device stops transmitting and receiving data, the terminal device may transition from a connected mode to an idle mode. In an idle mode, the terminal device may receive control information and system information associated with the serving cell. When the terminal device is operating in an idle mode on a cell, the terminal device may be referred to as being camped on the serving cell. Control information and system information may be kept up-to-date in a terminal device while in idle mode in order, for example, to have the latest parameters available when transitioning from idle mode to connected mode to transmit and receive data. In order to provide optimum conditions for transitioning to connected mode, the terminal device may be required to camp on a suitable cell.
The decision on whether to camp on a particular cell or not may depend on an assessment by the terminal device on whether the cell is a suitable cell. A suitable cell may be a cell which has various characteristics. One characteristic may be that the cell belongs to a preferred public land mobile network (PLMN). The preferred PLMN may be associated with a particular service provider, with whom the user of the terminal device may have a subscription. Another characteristic of a suitable cell is that the terminal device is permitted to camp on the cell: the cell is not barred, reserved for other terminal devices, or restricted to other terminal devices. A further characteristic of a suitable cell is that the cell fulfils a cell selection criterion, which defines the required strength and quality of the signal reception at the terminal device. By only camping on suitable cells, the terminal device can minimise disruptions and provide a reliable service.
To select the most suitable cell for the terminal device to camp on, the terminal device performs a cell selection procedure. There are several cell selection procedures, which are performed based on the status of the terminal device.
An initial cell selection procedure is performed when the terminal device has no prior knowledge of the available cells. For example, the initial cell selection procedure is performed when the terminal device is powered on. The terminal device scans all frequency carriers to search for a suitable cell.
A stored information cell selection procedure may be performed when the terminal device returns to an area of coverage. This procedure uses stored information, such as carrier frequency and cell parameter information, from a selection of potential cells to identify a suitable cell. If no such suitable cell can be found, then an initial cell selection procedure is performed.
A cell selection procedure may also be performed when the terminal device transitions from a connected to an idle mode. Such a transition may occur, for example, when data transfer between the network and the terminal device is complete, and the network releases the connection to the terminal device. The terminal device may be required to find a suitable cell to camp on, as it moves from the connected mode to the idle mode. In such circumstances, the terminal device may be required to scan through all or a select range of frequencies to search for a suitable cell.
A cell selection procedure typically requires the terminal device to scan frequencies across the entire range, or a selected range, of frequencies used by the PLMN, in order to identify the most suitable cell. This scanning is time consuming and can also represent a significant drain on the battery, time and processing resources of the terminal device. There is thus a need for an optimised cell selection procedure to find a suitable cell to camp on, with reduced requirements in terms of time, processing resources and/or power resources.
Summary
According to a first aspect of the present disclosure, there is provided a method in a terminal device configured to operate in a connected mode and an idle mode. The method includes retaining stored system information of a cell of the radio access network while operating in a connected mode, determining that the terminal device should change from connected mode to an idle mode, and checking the validity of the stored system information. The method further includes updating the stored system information with new system information if the stored system information is found to be invalid and camping on the cell in idle mode using the stored system information.
Checking the validity of the stored system information and updating the stored information with new system information if the stored system information is found to be invalid may provide a saving in terms of processing requirements and power resources. For example, certain processes relating to acquiring and updating stored system information in the terminal device may be performed only when the stored system information is determined to be invalid. Camping on the cell in idle mode using the stored system information may provide a time saving as the time-consuming cell selection procedures may be avoided. Such savings are particularly important for terminal devices that are low-power devices which may have very limited computational resources.
According to a second aspect of the present disclosure, there is provided a terminal device configured to retain stored system information of a cell of the radio access network while operating in a connected mode, determine that the terminal device should change from connected mode to an idle mode, and check the validity of the stored system information. The terminal device is further configured to update the stored system information with new system information if the stored system information is found to be invalid and camp on the cell in idle mode using the stored system information.
According to a third aspect of the present disclosure, there is provided a computer program product comprising instructions which, when executed by a computer, cause the computer to retain stored system information of a cell of the radio access network while operating in a connected mode, determine that the terminal device should change from connected mode to an idle mode, and check the validity of the stored system information. The computer program product is further configured to update the stored system information with new system information if the stored system information is found to be invalid and camp on the cell in idle mode using the stored system information.
Further features and advantages of the present disclosure will become apparent from the following description of preferred embodiments of the disclosure, given by way of example only, which is made with reference to the accompanying drawings.
Brief Description of the Drawings
Figure 1 is a schematic representation of a radio access network.
Figure 2 is a schematic representation of signalling within a terminal device when leaving a connected mode, performing a cell search and camping on a cell.
Figure 3 is a diagram of a method in a terminal device operating in a connected mode and an idle mode.
Figure 4 is a flowchart of a method in a terminal device for checking the validity of stored system information
Figure 5 is a schematic diagram showing examples of system information in System Information Block Type 1.
Figure 6 is a schematic diagram showing an example of change identifiers contained in system information.
Figure 7 is a flowchart of a method in a terminal device for checking the validity of stored system information for a System Information Block Type 1.
Figure 8 is a schematic diagram showing examples of system information in a Master Information Block.
Figure 9 is a flowchart of a method in a terminal device for checking the validity of stored system information for a Master Information Block.
Figure 10 is a schematic representation of signalling within a terminal device when leaving a connected mode, validating system information and camping on a cell.
Figure 11 is a schematic diagram of a terminal device configured to operate in a radio access network.
Figure 12 is a block diagram showing an example of a computer system.
Detailed Description
In general, the Internet of Things (loT) describes a set of technologies that enable the connectivity of a large variety of objects to different services via the internet. Such objects are typically connected through a radio interface embedded in or otherwise associated with the object, providing connectivity via radio access networks. Such objects may be referred to as loT devices or more generally terminal devices. The objects have a wide variety of uses and can take a large variety of shapes. Examples include static devices such as gas meters and household appliances, and mobile devices such as vehicles, tracking devices and wearable medical devices. Due to their nature, many loT devices have limited power and processing resources, and are typically battery powered. In many examples, the lifetime of the loT device is limited by the lifetime of the battery. Thus, development of power-efficient processes is important for extending the lifetime of an loT device.
loT systems are characterised by having a large number of terminal devices, each of which requires a relatively small uplink and/or downlink data rate. To meet the requirements for low data transmission, low power consumption, low cost and network expansion capabilities, low power wide area networks (LPWAN) have been developed. Prominent within the LPWAN technologies is the 3GPP LTE Narrowband Internet of Things (NB-IoT) technology standard. Based on the 3GPP LTE standard, but optimised for the requirements of loT technology, NB-IoT provides for a greater number of carriers than conventional telecommunications networks, each of which corresponds to a narrower frequency range than a carrier in a conventional network. Whilst this may improve the network performance in an loT system, it also increases the number of frequencies which must be scanned during a cell selection procedure which in turn increases the time and power resources required.
Reduction in the time and processing required to find a suitable cell to camp on can provide a reduction in power consumption for the terminal device, and thus may extend its lifetime.
Figure 1 shows a schematic representation of a radio access network 100, such as a 3GPP LTE NB-IoT network, in accordance with an example. The radio access network 100 is a cellular communication network comprising multiple cells distributed over a relatively wide geographic area. Figure 1 shows a single cell 120 of the network 100 served by a fixed-location base station 110, which may be referred to as a cell tower. The base station 110 comprises antennae and electronic communication equipment such as transceivers, digital signal processors and control electronics. Multiple cells may be joined together to provide network coverage over a wide geographic area. Terminal devices 130, 140, 150, 160, 170, 180 within the cell 120 may communicate with each other (or with other terminal devices connected to other cells) via the base station 110.
The terminal devices in the NB-IoT network 100 may be for example a mobile phone 130, a smart meter 140 such as a gas meter, a lightbulb 150, a household appliance 160, a wearable medical device 170, or a personal computer 180. A terminal device, for example a mobile phone 130 or a smart meter 140, may be referred to alternatively as operating with the base station 110 or with the corresponding cell 120.
The NB-IoT terminal device, for example smart meter 140, may be in an idle mode when it is not actively connected to the network but is nevertheless receiving NBloT system information broadcast in a cell of the radio access network by the base station 110. In this scenario, the terminal device 140 may be referred to as being camped on the serving cell.
The NB-IoT terminal device 140 may be in a connected mode when it is actively receiving and transmitting data via a radio link with the network. In connected mode, the terminal device 140 may not receive NB-IoT system information broadcast from the cell that it is connected to. The terminal device 140 may only receive NB-IoT system information broadcast from the cell when the terminal device is in idle mode.
The terminal device 140 may move or transition from an idle mode to a connected mode when data is required to be transmitted. Once data transmission is complete, the terminal device may move or transition from the connected mode to the idle mode. During the transition from the connected mode to the idle mode, the terminal device may perform a cell selection procedure to select which cell to camp on.
Static terminal devices, such as smart meters 140, lightbulbs 150, household appliances 160, or personal computers 180, may only infrequently move location, and thus may be connected to the same cell for long durations. By contrast, mobile devices such as mobile phones 130 or wearable medical devices 170, may often change location and thus may often be required to connect to different cells.
Figure 2 is a schematic representation of signalling within a terminal device, for example an NB-IoT terminal device, when leaving a connected mode, performing a cell search and camping on a cell. The signalling diagram describes an example of a system involving a cell search procedure.
Signalling in the terminal device may be performed between different communication layers 201, 202, 203, 204. A non-access stratum (NAS) layer 201 is a functional layer between the core network and the terminal device. The NAS layer 201 establishes and maintains the communication between the core network and the terminal device. A radio resource control (RRC) layer 202 is a protocol layer that functions between the radio access network and the terminal device. The RRC layer
202 is responsible for the broadcast system information of the cell. Both the NAS layer and the RRC layer are sub-layers that form a network layer which may be referred to as layer 3. A layer 2 (L2) layer 203 is a data link layer that functions between the RRC layer 202 and a physical layer 204. The L2 layer 203 enables the transfer of data between the radio access network and the terminal device through the physical layer. In some radio access networks, the L2 layer comprises three sub-layers: packet data convergence protocol (PDCP), radio link control (RLC) and medium access control (MAC). A layer 1 (LI) layer is the physical layer that carries information over the air interface. Among other procedures, the LI layer is responsible for performing cell search procedures.
In Figure 2, the terminal device is initially in connected mode 205, connected 210 to a cell Cl with a frequency FL The terminal device operating in connected mode may be referred to as being in an RRC Connected mode 205. In RRC Connected mode 205, the terminal device may transmit and receive data from the radio access network. Upon completion of the data transfer, the network may inform the terminal device of a connection release. A signalling message 215 is transmitted from the physical LI layer 204 to the L2 layer 203 of the terminal device. The signalling message 215 may be a NPDSCH Data Indicator signal which contains an RRCConnectionRelease message indicating the network release of the connection of the terminal device to the cell CL
The RRCConnectionRelease message 220 is then transmitted from the L2 layer
203 to the RRC layer 202. The terminal device then performs a release of the lower layers 225, for example the L2 layer 203 and the LI layer 204. Upon completion of the release of the lower layers 225, a signalling message 230 is transmitted from the RRC layer 202 to the NAS layer 201 to inform the NAS layer 201 of the connection release of the terminal device.
Upon completion of the signalling 230 informing the NAS layer 201 of the connection release, the terminal device begins the procedure for transitioning from the RRC Connected mode 205 to an idle mode (which is referred to as RRC Idle mode 270).
When leaving RRC Connected mode 205, the terminal device may perform a search in order to select a suitable cell to camp on. The signalling within the terminal device when searching for a suitable cell is described within the dashed box of Figure
2.
In an example as described in Figure 2, the terminal device may perform a cell search procedure starting from the cell the terminal device was last connected to 235.
A cell search procedure is performed by transmitting a signalling message 240 from the RRC layer 202 to the LI layer 204 to request layer LI to perform a cell search.
During the cell search procedure, the terminal device acquires the primary synchronisation signal (PSS) and secondary synchronisation signal (SSS) in order to synchronise on a subframe level. The LI layer 204 decodes the PSS and SSS synchronisation information and determines a physical cell identity (PCI) and frequency of the cell. A signalling message 245 from the LI layer 204 to the RRC layer 202 reports the PCI and frequency of the cell within the terminal device. Synchronisation allows the terminal device to read system information of the cell.
The cell is then evaluated to determine if it is a suitable cell by reading system information of the potential cell, such as a Master Information Block (MIB) and System Information Block Type 1 (SIB1).
A signalling message 250 from the RRC layer 202 to the LI layer 204 is transmitted to read system information comprising a Master Information Block. In some examples where the terminal device is an NB-IoT device operating in an NB-IoT network, the Master Information Block comprises MasterlnformationBlock-NB. The MasterlnformationBlock-NB of a cell of the loT network is broadcast by the loT network and transmitted 255 from the LI layer 204 to the RRC layer 202.
After reception of the Master Information Block, a signalling message 260 from the RRC layer 202 to the LI layer 204 is transmitted to read system information comprising System Information Block Type 1. In the above examples where the terminal device is an NB-IoT device operating in an NB-IoT network, the System Information Block Type 1 comprises SystemlnformationBlockType 1-NB. The SystemlnformationBlockTypel-NB system information of the cell of the loT network is broadcast by the loT network and transmitted 265 from the LI layer 204 to the RRC layer 202.
Using the information contained within the system information, the cell may then be evaluated to determine if the cell is a suitable cell for the terminal device to camp on.
If the cell is determined to be a suitable cell on which to camp, the terminal device may transition to RRC Idle mode 270. A signalling message 275 from the RRC layer 202 to the NAS layer 201 is transmitted to inform the core network that the terminal device has found a suitable cell to camp on. In scenario 280, the terminal device has transitioned to idle mode 270, whereby the terminal device is camped on the cell C1 with the frequency F1.
If the cell is determined to be an unsuitable cell on which to camp, the terminal device may perform an initial cell selection procedure or a stored cell selection procedure. The initial cell selection procedure and the stored cell selection procedure may comprise multiple repetitions of the signalling messages described within the dashed box of Figure 2.
In an initial cell selection procedure, each frequency band supported by the terminal device is searched. Each frequency band is scanned to acquire the received signal strength indicator (RSSI) of each absolute radio frequency channel number (ARFCN) of the frequency band. The ARFCN specifies a pair of carrier frequencies used for transmission and reception in the radio access network. The ARFCNs are arranged in order of decreasing strength of their corresponding RSSI values.
A cell search procedure is then performed on the strongest ARFCN first. Another signalling message 240 is transmitted from the RRC layer 202 to the LI layer 204 to request cell search information. During the cell search procedure, the terminal device acquires the primary synchronisation signal (PSS) and secondary synchronisation signal (SSS) in order to synchronise on a subframe level. A signalling message 245 from the LI layer 204 to the RRC layer 202 reports the physical cell identity (PCI) and the frequency of the cell within the terminal device. Synchronisation allows the terminal device to read system information of the potential cell. A signalling message 250 from the RRC layer 202 to the L1 layer 204 is transmitted to read a Master Information Block of the potential cell. The Master Information Block is broadcast by the network and transmitted 255 from the LI layer 204 to the RRC layer 202. Similarly, a signalling message 260 from the RRC layer 202 to the LI layer 204 is transmitted to read System Information Block Type 1 of the potential cell. The System Information Block Type lis broadcast by the network and transmitted 265 from the LI layer 204 to the RRC layer 202. Using the received information, the cell may then be evaluated to determine if the cell is a suitable cell for the terminal device to camp on.
If the potential cell is determined to be unsuitable, the terminal device continues the cell search and returns to the second-strongest ARFCN to evaluate the suitability of the corresponding cell i.e. perform the cell search procedure to acquire the corresponding PSS, SSS, MIB and SIB1 information. The signalling messages (240, 245, 250, 255, 260, 265) described within the dashed box of Figure 2 are repeated for the corresponding cell.
If all ARFCNs in the frequency band are evaluated and no suitable cell is found, then the terminal device repeats the process of acquiring the RSSI of each ARFCN of the next frequency band. The signalling messages (240, 245, 250, 255, 260, 265) are thus repeated for the next frequency band until a suitable cell is found to camp on.
In a stored cell selection, the terminal device may use a stored list of frequencies corresponding to cells that have previously be measured by the terminal device. The terminal device may acquire a PSS and SSS of the strongest ARFCN in the stored list of frequencies in order to determine a PCI and read system information of the potential cell. From the system information, the suitability of the potential cell may be evaluated.
If the potential cell is determined to be unsuitable, the terminal device may continue the cell search and return to the second-strongest ARFCN to evaluate the suitability of the corresponding cell i.e. perform the cell search procedure to acquire the corresponding PSS, SSS, MIB and SIB1 information. The signalling messages (240, 245, 250, 255, 260, 265) described within the dashed box of Figure 2 are repeated for the corresponding cell.
If all ARFCNs in the stored list of frequencies are evaluated and no suitable cell is found, then the terminal device will initiate an initial cell selection procedure, as described above.
Once a cell is determined to be a suitable cell on which to camp, the terminal device may transition to RRC Idle mode 270. A signalling message 275 from the RRC layer 202 to the NAS layer 201 is transmitted to inform the core network that the terminal device has found a suitable cell to camp on. In scenario 280, the terminal device has transitioned to idle mode 270, whereby the terminal device is camped on the cell C1 with the frequency F1.
In some examples of the method, the terminal device may not have changed location, and thus the cell that the terminal device was previously connected to remains the most suitable cell for the terminal device to camp on. In some examples, performing a cell search and/or a cell selection procedure by the terminal device may be unnecessary. The cell search procedure may use the limited processing resources and power resources of the terminal device unnecessarily. In addition, performing the cell search procedure may be time consuming and may delay the transition of the terminal device to camping on the cell in an idle mode.
Methods of the present disclosure, in addition to apparatus and computerreadable storage media, will now be described. The present disclosure describes a cell selection procedure that may provide a time efficient and power efficient process of selecting a suitable cell to camp on.
Figure 3 is a diagram of a method 300 in a terminal device operating in a connected mode and an idle mode.
The method 300 comprises a step 310 of retaining stored system information of a cell of the radio access network while operating in a connected mode. The stored system information may be stored in memory of the terminal device. In some examples, the memory is a non-volatile memory such as flash memory or a random access memory. This allows the stored system information of the cell to be maintained if the terminal device is powered off. In other examples, the memory is a volatile memory such as a primary storage random access memory.
In some examples, the step 310 of retaining stored system information may comprise retaining the system information in a memory of the terminal device. In other examples, the method comprises a step of receiving and storing the system information of the cell which is broadcast from the radio access network while in idle mode. In such examples, the receiving and storing of the system information while in idle mode is performed prior to retaining the stored system information while in connected mode.
In some examples, the terminal device stores system information comprising a Master Information Block, System Information Block Type 1 and further system information, System Information Block Type 2. In order to identify the cell to which the system information belongs, the terminal device may store further cell-identifying information. The cell-identifying information may comprise a carrier frequency, such as an Absolute Radio Frequency Channel Number (ARFCN), and a cell identifier, such as a Physical Cell ID (PCI).
In further examples, the terminal device may store further system information comprising System Information Block Type 3, 4, 5 and/or 14. The further system information may be acquired and stored if the further system information of the cell is broadcast by the radio access network. In order to acquire the further system information (System Information Block Type 2, 3, 4, 5 and/or 14), it may be necessary to read scheduling information present in System Information Block Type 1 first. The scheduling information present in System Information Block Type 1 determines when the further system information is scheduled and therefore provides the ability for the terminal device to acquire the further system information.
In other examples, the terminal device may acquire additional system information comprising a Master Information Block and System Information Block Type 1 for neighbouring cells. Acquiring the additional system information for neighbouring cells may allow the terminal device to check the suitability of the cell on which the terminal device is camped.
The method 300 comprises a further step 320 of determining that a change of mode from connected mode to idle mode has been triggered. Such a transition may occur, for example, when data transfer between the network and the terminal device is complete, and the network releases the connection to the terminal device.
In some examples, determining that the terminal device should change from connected mode to idle mode is in response to receiving by the RRC layer a radio release message from the LI layer, such as an RRCConnectionRelease message.
The network may release the connection to the terminal device for other reasons not covered by the method of Figure 3, for example, in order for the terminal device to connect to a new cell. In such situations, the RRCConnectionRelease message may comprise re-directed carrier information that provides the terminal device with information about the new cell the network wishes the terminal device to connect to. In such situations, the terminal device does not need to check the validity of the system information of the current cell, as the terminal device will connect to the new cell and thus acquire new system information.
Upon determination of a change from connected mode to idle mode, the method 300 comprises a next step 330 of checking the validity of stored system information of the cell. Checking the validity of the stored system information comprises comparing the stored system information with new system information broadcast from the cell. The stored system information is determined to be valid if the new system information is the same as the stored system information. The stored system information is determined to be invalid if the new system information is not the same as the stored system information.
In some examples, the stored system information can expire and thus become invalid. For example, if the system information has not been updated after a predetermined length of time, the terminal device may presume the system information has expired and is no longer valid. In such examples, checking the expiry of the stored system information may comprise checking the expiration of a timer value in the stored system information. Upon expiry of the timer, the stored system information is determined to be invalid. In examples where the terminal device is an NB-IoT device, the system information may be considered to be invalid 24 hours after it was last confirmed to be valid. The validity of the stored system information may then be checked by comparing the stored system information with new system information broadcast from the cell, as described by step 330.
If the stored system information is determined to be valid, the routine bypasses several steps and transitions to step 350 of the method 300. Step 350 comprises camping on the cell using the stored system information. Valid stored system information signifies that the stored system information of the cell is up to date. In an example, the terminal device may camp on the cell using the stored system information.
In such examples, camping on the cell using the stored system information may reduce the processing power required by the terminal device. The terminal device may save processing power and time by not performing unnecessary cell search procedures or acquiring and reading further blocks of system information.
If the stored system information is determined to be invalid, the routine transitions to step 340 of the method 300. Step 340 comprises updating the stored system information with the new system information so that the stored information now contains the new system information. Invalid stored system information signifies that the stored system information of the cell is no longer up to date. Updating the stored system information may comprise selectively replacing an invalid part of the stored system information with a corresponding part of the new system information.
Upon completion of replacing or selectively replacing the invalid stored system information with new system information, the method comprises a final step 350 of camping on the cell using the stored system information (which may include the new system information). In some examples, the stored system information may be completely replaced by the new system information and the terminal device may camp on the cell using the new system information as the stored system information. In other examples, the stored system information may only be partly replaced by the new system information and the terminal device may camp on the cell using a combination or the existing stored system information and the new system information (which together form the updated stored system information).
In such examples, selectively replacing only the system information that is determined to be invalid reduces the required processing resources of the terminal device. Reduced processing may allow the terminal device to move from a connected mode to an idle mode more quickly, thus saving time and power resources.
Figure 4 is a flowchart of a method 400 in a terminal device for checking the validity of stored system information.
In step 410 of the method 400, stored system information of the cell is recalled in the terminal device. The stored system information of Figure 4 is the system information of the network that may be used by the terminal device in connected mode or in idle more, and is stored in the memory of the terminal device. The stored system information includes a change identifier.
In step 410 of the method 400, the stored change identifier in the stored system information is read from the memory of the terminal device. Once the stored system information is read, the procedure follows a path to step 450 of the method 400.
In step 430 of the method 400, new system information of the cell is received by the terminal device. The new system information in Figure 4 is broadcast by the network within the cell so that it can be received by the terminal device. The new system information includes a change identifier. The change identifier is updated by the network if the system information has been modified since the system information was last broadcast by the network.
In step 440 of the method 400, the new change identifier in the new system information broadcast by the network is read by the terminal device. In some examples, it may be possible to receive a subset of the new system information which may include the new change identifier. In this case, the terminal device may read only the new change identifier in the new system information, instead of all the new system information, which may reduce the time required to identify the invalid stored system information. Receiving and/or reading further system information may only be performed if needed. Once the new system information is read, the routine follows a path to step 450 of the method 400.
In step 450, the stored change identifier is compared with the new change identifier. If the stored change identifier and the new change identifier are the same, the routine follows a path to step 460 of the method 400, whereby the stored system information is considered to be valid. If the stored change identifier and the new change identifier are not the same, the routine follows a path to step 470 of the method 400, whereby the stored system information is considered to be invalid (which may include all the stored system information being invalid or a subset of the stored system information being invalid).
In an example, there is at least one stored change identifier in the stored system information and there is at least one new change identifier in the new system information. Each stored change identifier has a corresponding new change identifier.
In an example, the system information comprises blocks of system information. If the stored change identifier and the new change identifier are the same, a further block of stored system information is determined to be valid 460. If the stored change identifier and the new change identifier are not the same, the further block of stored system information is determined to be invalid 470.
Figure 5 is a schematic diagram showing examples of system information in System Information Block Type 1. In some examples, the system information comprises System Information Block Type 1 information 500. System Information Block Type 1 information 500 may comprise one or more of a SystemlnfoValueTagList
510 and a SchedulinglnfoList 520. In some examples, the system information may comprise further system information blocks such as the System Information Block Types 2, 3, 4, 5, and/or 14 described above. These further system information blocks may be contained in one or more System Information (SI) containers 570, 580, 590. Each SI container 570, 580, 590 may contain one or more System Information Blocks. For example, SI container 570 may contain System Information Block Type 2 530, SI container 580 may contain System Information Block Type 3 540, and SI container 590 may contain System Information Block Type 4 550 and System Information Block Type 5 560.
Figure 5a is a schematic diagram showing an example of System Information Block Type 1 information 500. System Information Block Type 1 information 500 may comprise a plurality of change identifiers 510. The plurality of change identifiers may comprise a SystemlnfoValueTagList 510, wherein each change identifier 511, 512, 513 is an element in the SystemlnfoValueTagList 510. System Information Block Type 1 information 500 may also comprise a plurality of scheduling information 520. The plurality of scheduling information may comprise a SchedulinglnfoList 520, wherein each element 521, 522, 523 contains scheduling information. Each change identifier 511, 512, 513 in the SystemlnfoValueTagList 510 corresponds to an element of scheduling information 521, 522, 523 in the SchedulinglnfoList 520. The number of elements in the SystemlnfoValueTagList 510 is equal to the number of elements in the SchedulinglnfoList 520.
Figure 5b is a schematic diagram showing an example of a SystemlnfoValueTagList 510. While only three change identifiers are shown in Figure 5b, a SystemlnfoValueTagList 510 may contain n number of change identifiers, as indicated by SystemhifoValueTagList\n\. Further change identifiers that may be present in the SystemlnfoValueTag 510 are denoted by an ellipsis. In some examples, the change identifiers 511, 512, 513 in the SystemlnfoValueTagList 510 comprise integer values. In such examples, when the system information in the System Information Blocks 530, 540, 550, 560 has been modified since the system information was last broadcast by the network, the corresponding SI container 570, 580, 590 is also modified accordingly, and the relevant integer value(s) 511, 512, 513 are incremented. In some examples, the integer value 511, 512, 513 follows a sequence of integer numbers from to 3 (which may be represented by 2 binary bits). When the integer value is 3 and the system information is modified, the integer value of the change identifier is reset or cycled to 0.
Modification of a change identifier 511, 512, 513 in SystemlnfoValueTagList 510 signifies that the corresponding SI container 570, 580, 590 has been modified. A change identifier (e.g. 513) in the SystemlnfoValueTagList 510 may correspond to a system information container (e.g. SI container 590) that contains more than one System Information Block (e.g. System Information Blocks 550 and 560). In this case, when the change identifier is modified, all System Information Blocks (e.g. System Information Blocks 550 and 560) of the system information container may be acquired by the terminal device.
Figure 5c is a schematic diagram showing an example of a SchedulinglnfoList 520. While only three elements are shown in Figure 5c, a SchedulinglnfoList 520 may contain n number of elements, as indicated by Scheduling!nfoList\n\. Further elements that may be present in the SchedulinglnfoList 520 are denoted by an ellipsis. In some examples, the elements 521, 522, 523 in the SchedulinglnfoList 520 comprise scheduling information for the SI containers 570, 580, 590. For example, the scheduling information elements may provide information on the periodicity, a timing offset, a repetition pattern and/or mapping information relating to when and how frequently the network sends the corresponding SI container (containing one or more System Information Blocks). In such an example, a terminal device may acquire or read the SchedulinglnfoList 520 when a modification of a change identifier 511, 512, 513 in SystemlnfoValueTagList 510 has been detected in order to know when the relevant system information is being broadcast. Acquiring or reading the corresponding scheduling element 521, 522, 523 allows the terminal device to correctly acquire the modified SI container 570, 580, 590, and in turn the corresponding System Information Blocks 530, 540, 550, 560.
As described in relation to Figure 5b, a change identifier 513 in the SystemlnfoValueTagList 510 may correspond to a SI container containing more than one System Information Block 550, 560. In this case, acquiring the corresponding scheduling element 523 in SchedulinglnfoList 520 allows the SI container to be acquired. Thus, all System Information Blocks of the SI container can be acquired by the terminal device.
Acquisition of the SchedulinglnfoList 520 by the terminal device may occur concurrently with acquisition of the SystemlnfoValueTagList 510 by acquiring the whole of the System Information Block Type 1 500.
Figure 6 is a schematic diagram showing an example of change identifiers 610, 620. In an example, a stored SystemlnfoValueTagList 610 contains a plurality of change identifiers 611, 612, 613 and a new SystemlnfoValueTagList 620 contains a plurality of change identifiers 621, 622, 623. The position of the change identifier 611, 612, 613 and change identifiers 621, 622, 623 corresponds to the position of the change identifiers 511, 512, 513 in Figure 5 i.e. change identifiers 611, 621 and 511 all relate to SIB2. Each change identifier 611, 612, 613, 621, 622, 623 may comprise an integer value.
In the example of Figure 6, each stored change identifier 611, 612, 613 in the stored SystemlnfoValueTagList 610 is compared to the corresponding new change identifier 621, 622, 623 in the new SystemlnfoValueTagList 620. If the stored integer value 611, 612, 613 and the new integer value 621, 622, 623 are the same, the terminal device may consider that the corresponding System Information Block(s) 530, 540, 550, 560 has not been modified and the corresponding stored System Information Block(s) 530, 540, 550, 560 is determined to be valid. If the stored integer value 611, 612, 613 and the new integer value 621, 622, 623 are not the same, the terminal device may consider that the corresponding System Information Block(s) 530, 540, 550, 560 has been modified, and the corresponding stored System Information Block(s) 530, 540, 550, 560 is determined to be invalid.
In the example shown in Figure 6, the first change identifier 611 in the stored SystemlnfoValueTagList 610 equals 0 and the first change identifier 621 in the new SystemlnfoValueTagList 620 equals 1. Therefore, the terminal device will notice that the first change identifier has incremented by 1 and will consider the corresponding stored System Information Block 530 (in this example, the System Information Block Type 2) to be invalid.
In another example shown in Figure 6, the second change identifier 612 in the stored SystemlnfoValueTagList 610 equals 3 and the second change identifier 622 in the new SystemlnfoValueTagList 620 equals 3. Therefore, the terminal device will notice that the first change identifier and the stored change identifier are the same and will consider the corresponding System Information Block 540 (in this example, System Information Block Type 3) to be valid.
Figure 7 is a flowchart of a method 700 in a terminal device for checking the validity of stored system information for System Information Block Type 1. In an example according to a method of the present disclosure, the stored system information comprises System Information Block Type 1 500 and further blocks of system information comprising System Information Blocks 530, 540, 550, 560. The System Information Block Type 1 500 comprises at least a SystemlnfoValueTagList 510 and a SchedulinglnfoList 520.
In step 710 of the method 700, an index for the change identifiers 611, 612, 613 in the SystemlnfoValueTagList 610 is initialised. The index n is initialised by n = 0. A maximum value of the index nmax is defined as the length of the SystemlnfoValueTagList 610, i.e. the number of change identifiers in the SystemlnfoValueTagList 610.
In step 720 of the method, a new change identifier 611 in the new SystemlnfoValueTagList 610 with an index of 0 is read.
In step 730, a stored change identifier 621 in the stored SystemlnfoValueTagList 620 with an index of 0 is recalled. The stored SystemlnfoValueTagList 620 may be stored in the memory of the terminal device.
In step 740, the stored change identifier 611 is compared with the new change identifier 621. If the stored change identifier 611 is the same as the new change identifier 621, then the method comprises bypassing several steps to reach step 780 of evaluating the value of the index, as described later.
If the stored change identifier 611 is not the same as the new change identifier 621, then the method comprises a step 750 of updating the stored change identifier 611 in the stored SystemlnfoValueTagList 610 with the new change identifier 621 in the new SystemlnfoValueTagList 620.
In step 760, the new SchedulinglnfoList 520 in the newly received System Information Block Type 1 500 is read, which may involve reading the new scheduling information element 521 with an index of 0 in the new SchedulinglnfoList 520. Reading the scheduling information element provides the terminal device with timing information for when and how frequently the network broadcasts the SI container containing the System Information Block(s). In this example, reading the new scheduling information element 521 provides the terminal device with information needed to acquire the SI container 570 and hence the System Information Block Type 2 530.
In step 770, the System Information Block 530 is acquired by the terminal device using the scheduling information from step 760. In this example, an index of 0 corresponds to System Information Block Type 2 530. Hence, the system information, comprising the System Information Block Type 1 500 and further blocks of System Information Blocks 530, 540, 550, 560, is updated.
In such examples, the processing requirements are limited to acquiring the System Information Blocks only when the System Information Blocks are determined to be invalid and that need to be updated.
In step 780, the value of the index n is evaluated by comparing the index with the maximum value of the index, nmax. If the value of the index is less than the maximum value of the index, then the value of the index is incremented by 1. If the value of the index is not less than the maximum value of the index, then all change identifiers have been compared, and the method comprises a step of camping on the cell.
In step 785, the index is incremented by 1. The routine then follows a path to step 720, whereby the new SystemlnfoValueTagList 610 is read again. More specifically, reading the new change identifier 612 in the new SystemlnfoValueTagList 610 with in index of n+\. The following steps 730, 740, 750, 760, 770, 780 of the method may then be repeated, using an index of n incremented by 1.
In step 790, the cell is camped on using the stored system information (which may be updated with the new system information). In some examples, the system information 500, 530, 540, 550, 560 may comprise the stored System Information Block Type 1 500 or new System Information Block Type 1 500, in addition to stored further blocks of System Information Blocks 530, 540, 550, 560 or new further blocks of System Information Blocks 530, 540, 550, 560.
Figure 8 is a schematic diagram showing examples of system information in a Master Information Block. System information may comprise a Master Information Block 800.
Figure 8a is a schematic diagram showing an example of a Master Information Block 800. The Master Information Block 800 may comprise a change identifier 810, wherein the change identifier may be a SystemlnfoValueTag 810.
In some examples, a modification of SystemlnfoValueTag 810 (in the Master Information Block 800) indicates a modification in SystemlnfoValueTagList 510 (in System Information Block Type 1 500). As described earlier, the modification in SystemlnfoValueTagList 610 may indicate a modification in further System Information Blocks 530, 540, 550, 560.
Figure 8b is a schematic diagram showing an example of a SystemlnfoValueTag 810. In some examples, the change identifier 811 of the SystemlnfoValueTag 810 comprises an integer value. In such examples, when the system information 500 has been modified since the system information 500 was last broadcast by the network, the integer value 811 of the SystemlnfoValueTag 810 is increased. In some examples, the integer value follows a sequence of integer numbers from 0 to 31 (which may be represented by 5 binary bits). When the change identifier is 31 and the system information is modified, the integer value of the change identifier is reset or cycled back to 0.
In some examples, a change identifier 811 of the SystemlnfoValueTag 810 may correspond to a further block of system information 500, such as System Information Block Type 1. In such an example, modification of a change identifier 811 of the SystemlnfoValueTag 810 signifies to a terminal device that the System Information Block Type 1 500 has been modified.
Figure 8c is a schematic diagram showing an example of two change identifiers.
In this example, a stored SystemlnfoValueTag 820 and a new SystemlnfoValueTag 830 may each contain a change identifier 821, 831. Each change identifier 821, 831 may comprise an integer value. In an example according to a method of the present disclosure, the stored change identifier 821 of the stored SystemlnfoValueTag 820 is compared to the new change identifier 831 of the new SystemlnfoValueTag 830. If the stored integer value 821 and the new integer value 831 are the same, the terminal device may consider that the corresponding System Information Block Type 1 500 has not been modified, and an earlier received and stored version of the System Information Block Type 1 is determined to be valid. If the stored integer value 821 and the new integer value 831 are not the same, the terminal device may consider that the corresponding System Information Block Type 1 500 has been modified by the network, and an earlier received and stored version of the System Information Block Type 1 is determined to be invalid.
In a specific example according to Figure 8c, if the stored change identifier 821 of the stored SystemlnfoValueTag 820 equals 14 and the new change identifier 831 of the new SystemlnfoValueTag 830 equals 15, then the corresponding System Information Block Type 1 500 is determined to be invalid.
In such examples, the processing requirements are limited to acquiring the System Information Block Type 1 500 only when the SystemlnfoValueTag 810 identifies the System Information Block Type 1 500 information as invalid.
Figure 9 is a flowchart of a method 900 in a terminal device for checking the validity of stored system information for a Master Information Block. In an example according to a method of the present disclosure, the stored system information comprises Master Information Block information 800 and a further block of system information comprising System Information Block Type 1 500. The Master Information Block 800 comprises at least a SystemlnfoValueTag 810, 820, 830.
In step 910 of the method 900, a new change identifier 831 in a new SystemlnfoValueTag 830 is read from a newly received Master Information Block.
In step 920 of the method 900, a stored change identifier 821 in the stored SystemlnfoValueTag 820 is recalled. The stored SystemlnfoValueTag 820 may be stored in the memory of the terminal device.
In step 930 of the method 900, the stored change identifier 821 is compared with the new change identifier 831. If the stored change identifier 821 is the same as the new change identifier 831, then the routine bypasses several steps to reach a step 960 of camping on the cell, as described later.
If the stored change identifier 821 is not the same as the new change identifier 831, then the routine follows a path to step 940, whereby the stored change identifier 821 of the stored SystemlnfoValueTag 820 is updated with the new change identifier 831 of the new SystemlnfoValueTag 830.
In step 950 of the method 900, the System Information Block Type 1 500 is acquired. As described above in relation to Figure 5, the System Information Black
Type 1 500 may also comprise a change identifier 510, wherein the change identifier 510 comprises a SystemlnfoValueTagList 510 and may be used to check the validity of further blocks of System Information Blocks 530, 540, 550, 560. In such an example, the method to check the validity of stored system information 500, 530, 540, 550, 560, as described above in relation to Figure 7, may be performed.
In step 960 of the method 900, the cell is camped on using the stored system information and/or the new system information.
In some examples of Figure 9, the method may further comprise replacing the stored Master Information Block 800 with the new Master Information Block 800.
Following a check of the validity of stored System Information Block Type 1 500 in the example of Figure 9, the resulting SIB1 information in the system information may comprise the stored System Information Block Type 1 or the newly acquired System Information Block Type 1. If the resulting SIB 1 information comprises the stored System Information Block Type 1 then the further blocks of system information will also comprise stored further blocks of system information i.e. SIB2, SIB3, SIB4, SIB5 etc.
In the case where System Information Block Type 1 is newly acquired, the resulting further blocks of system information in the system information may comprise stored further blocks of system information or a newly acquired further blocks of system information i.e. SIB2, SIB3, SIB4, SIB5 etc.
In the examples of system information described above in connection with Figures 5 to 9, the radio access network may be a narrow band internet of things (NBloT) network, and the terminal device may be a narrow band internet of things (NBloT) terminal. In this case, the system information may be NB-IoT system information (which may be defined in the FTE NB-IoT technology standard with an “-NB” suffix). In a network which includes NB-IoT co-existing in the same carrier space as non-NBloT FTE, the NB-IoT system information may be different and separate from the FTE system information, and may be sent in a different physical carrier from the FTE system.
Figure 10 is a schematic representation of signalling within a terminal device when leaving a connected mode, checking the system information and camping on the cell. The signalling diagram describes an example of a system involving a system information validity checking procedure, as described in relation to the present disclosure.
Signalling in the terminal device may be performed between different communication layers 201, 202, 203, 204. For a description of said communication layers 201, 202, 203, 204, the reader is referred to the description provided in relation to Figure 2.
In Figure 10, the terminal device is initially in connected mode 205, connected 210 to a cell Cl with a frequency Fl. The terminal device operating in connected mode may be referred to as being in RRC Connected mode 205. In RRC Connected mode 205, the terminal device may transmit and receive data from the radio access network. Upon completion of the data transfer, the network may inform the terminal device of a connection release. A signalling message 215 is transmitted from the physical LI layer 204 to the L2 layer 203 of the terminal device. The signalling message 215 may be a NPDSCH Data Indicator signal which indicates the network release of the connection of the terminal device to the cell CL
A signalling message 220 is transmitted from the L2 layer 203 to the RRC layer 202 comprising an RRCConnectionRelease signal. The terminal device then performs a release of the lower layers 225, for example the L2 layer 203 and the LI layer 204. Upon completion of the release of the lower layers 225, a signalling message 230 is transmitted from the RRC layer 202 to the NAS layer 201 to inform the NAS layer 201 of the connection release of the terminal device.
Upon completion of the signalling 230 informing the NAS layer 201 of the connection release, the terminal device begins the procedure for transitioning from the RRC Connected mode 205 to an idle mode (which is referred to as RRC Idle mode 270).
According to an example of the present disclosure, upon transition from RRC Connected mode 205 to RRC Idle mode 270 by the terminal device, a cell search procedure (as described in relation to the example of Figure 2) may be avoided. In a specific example for aNB-IoT system, the cell search procedure comprises requesting and acquiring a primary synchronisation signal (PSS) that may be transmitted in subframe #5 every 10 ms. Acquiring the PSS information may take a minimum of 10 ms. Additionally, the cell search procedure comprises requesting and acquiring a secondary synchronisation signal (SSS) that may be transmitted in subframe every 20 ms. Acquiring the SSS information may take a minimum of 20 ms. Therefore, avoiding the cell search procedure in order to find a suitable cell to camp on may save time and power resources of the terminal device.
Instead, a signalling message 1000 from the RRC layer 202 to the LI layer 204 is transmitted to read system information comprising the Master Information Block 800. In some examples where the terminal device is an NB-IoT device operating in an NBloT network, the Master Information Block 800 comprises MasterlnformationBlockNB. The MasterlnformationBlock-NB system information of a cell of the loT network is broadcast by the loT network and transmitted 1005 from the LI layer 204 to the RRC layer 202. The Master Information Block 800 may comprise a SystemlnfoValueTag 810.
The signalling within the terminal device when checking the validity of the system information is described within the dashed box of Figure 10. The stored system information may comprise one or more of the Master Information Block 800, the System Information Block Type 1 500 and further System Information Blocks 530, 540, 550, 560. Upon reception of the Master Information Block 800, the terminal device checks 1010, 1015 the validity of the stored system information 500. Checking the validity of the stored system information 1010, 1015 comprises at least checking the SystemlnfoValueTag 810 in the Master Information Block 800.
In scenario 1015, checking the SystemlnfoValueTag 810 in the Master Information Block 800 determines that the stored system information 500 is valid. Therefore, no further blocks of system information, for example the System Information Block Type 1 500, are read 1016.
In a specific example for an NB-IoT system, reading the Master Information Block 800 of the cell that is broadcast by the NB-IoT network may take 640 ms. Additionally, reading System Information Block Type 1 500 of the cell may take 2.5 s. Therefore, if the Master Information Block is determined to be valid, the System Information Block Type 1 does not need to be read, and the terminal device may reduce the time taken to camp on a suitable cell by at least 2.5 s.
In scenario 1010, checking the SystemlnfoValueTag 810 in the Master Information Block 800 determines that at least part of the stored system information 500 is invalid.
A signalling message 1020 from the RRC layer 202 to the LI layer 204 is transmitted to read system information comprising System Information Block Type 1 500. In some examples where the terminal device is an NB-IoT device operating in an NB-IoT network, the System Information Block Type 1 500 comprises SystemlnformationBlockTypel-NB. The SystemlnformationBlockTypel-NB system information of a cell of the loT network is broadcast by the loT network and transmitted 1025 from the LI layer 204 to the RRC layer 202. The System Information Block Type 1 500 may comprise a SystemlnfoValueTagList 510.
The signalling within the terminal device when checking the validity of the further blocks of system information is described within the dot-dashed box of Figure
10. The further blocks of system information may comprise one or more of System Information Blocks 530, 540, 550, 560. Upon reception of the System Information Block Type 1 500, the terminal device checks 1030, 1035 the validity of the stored system information 530, 540, 550, 560. Checking the validity of the stored system information 1030, 1035 comprises at least checking the SystemlnfoValueTagList 510 in the System Information Block Type 1 500.
In scenario 1035, checking the SystemlnfoValueTagList 510 in the System Information Block Type 1 500 determines that the stored system information 530, 540, 550, 560 is valid. Therefore, no further blocks of system information, for example System Information Blocks 530, 540, 550, 560, are read 1036. In such examples, only the System Information Block Type 1 500 is determined to be invalid. Accordingly, the invalid stored System Information Block Type 1 500 is replaced with the new System Information Block Type 1 500, but no further blocks of system information are read.
In scenario 1030, checking the SystemlnfoValueTagList 510 in the System Information Block Type 1 500 determines that at least part of the stored system information 530, 540, 550, 560 is invalid. In order to acquire the required System Information Block 530, 540, 550, 560, it may be necessary to read scheduling information for the SI containers 570, 580, 590 containing the System Information Blocks 530, 540, 550, 560. The System Information Block Type 1 500 may comprise a
SchedulinglnfoList 520, wherein the SchedulinglnfoList 520 comprises scheduling information required to acquire the System Information Blocks 530, 540, 550, 560.
After reading the required elements of scheduling information in the SchedulinglnfoList 520 in System Information Block Type 1 500, a signalling message 1040 from the RRC layer 202 is transmitted to send the scheduling information in the SchedulinglnfoList 520 to the LI layer 204. Upon reception of the scheduling information by the LI layer, a signalling message 1050 from the RRC layer 202 to the LI layer 204 is transmitted to acquire the required System Information Blocks 530, 540, 550, 560. Upon reception 1055 of the required System Information Blocks 530, 540, 550, 560, the invalid stored System Information Blocks 530, 540, 550, 560 are selectively replaced with the required new System Information Blocks 530, 540, 550, 560.
Upon selectively replacement of the invalid system information (for example one or more of the Master Information Block 800, the System Information Block Type 1 500 and further System Information Blocks 530, 540, 550, 560) with valid system information, the terminal device may transition to RRC Idle mode 270. A signalling message 275 from the RRC layer 202 to the NAS layer 201 is transmitted to inform the core network that the terminal device has found a cell to camp on i.e. the terminal device is in possession of valid system information of the cell. In scenario 280, the terminal device has transitioned to idle mode 270, whereby the terminal device is camped on the cell Cl with the frequency FL
Figure 11 is a schematic diagram of a terminal device 1100 configured to operate in a radio access network, for example as described above. The terminal device 1100 comprises a receiver 1110, a memory 1120 and a cell selection procedure module 1130. These components are communicatively coupled. In some examples, the terminal device 1100 is a NB-IoT terminal device. In such examples, the radio access network is a NB-IoT network.
The memory 1120 is configured to store the system information of a cell of a radio access network. In some examples, the system information may comprise one or more Master Information Block 800, System Information Block Type 1 500 and further System Information Blocks 530, 540, 550, 560. In some examples, the memory is a non-volatile memory such as flash memory or a random access memory. This allows the stored system information to be maintained if the terminal device is powered off. In other examples, the memory is a volatile memory such as a primary storage random access memory.
The receiver 1110 is configured to receive a transmission that triggers a change in mode of the terminal device from a connected mode to an idle mode.
The receiver 1110 is further configured to receive new system information 800, 500, 530, 540, 550, 560 of the cell of the radio access network.
The cell selection procedure module 1130 is configured to check the validity of the stored system information 800, 500, 530, 540, 550, 560, update the stored system information with the new system information if the stored system information is found to be invalid, and camp on the cell. In some examples, checking the validity of the stored system information 800, 500, 530, 540, 550, 560 comprises comparing stored change identifiers 820, 610 in the stored system information 800, 500, 530, 540, 550, 560 stored in the memory of the terminal device with new change identifiers 830, 620 in the new system information 800, 500, 530, 540, 550, 560 broadcast from the cell, for example as described above. In some examples, updating the stored system information 800, 500, 530, 540, 550, 560 comprises selectively replacing the stored system information 800, 500, 530, 540, 550, 560 that is found to be invalid with the new system information 800, 500, 530, 540, 550, 560, for example as described above. In some examples, camping on the cell comprises camping on the cell using the stored system information 800, 500, 530, 540, 550, 560 (which may be updated with new system information 800, 500, 530, 540, 550, 560), for example as described above.
Figure 12 is a block diagram showing an example of computer system 1200 comprising a processor 1210 and a computer-readable storage 1220. The computer system 1200 may be a mobile system. The processor 1210 may be implemented as a single processor or multiple processors. The computer-readable storage 1220 may be a non-transitory computer-readable storage medium comprising a set of computer readable instructions 1250 which, when executed by the processor 1210, cause the processor 1210 to perform a method according to examples described herein. The computer readable instructions 1220 may be retrieved from a machine-readable media, for example any media that can contain, store, or maintain programs and data for use by or in connection with an instruction execution system. In this case, machine-readable media can comprise any one of many physical media such as, for example, electronic, magnetic, optical, electromagnetic, or semiconductor media. More specific examples of suitable machine-readable media include, but are not limited to, a hard disk drive, a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory, or a portable disc.
At block 1221 the instructions cause the processor to retain stored system information of a cell of a radio access network in the memory of a terminal device. At block 1222 the instructions cause the processor to determine that a change of mode for the terminal device from connected mode to idle mode has been triggered. At block 1223 the instructions cause the processor to check the validity of the stored system information. Upon determination of the validity of the stored system information, at block 1225 the instructions cause the processor to camp on the cell using the stored system information. Upon determination of the invalidity of the stored system information, at block 1224 the instructions cause the processor to selectively replace the stored system information with new system information broadcast from the cell. At block 1225 the instructions cause the processor to camp on the cell using the stored system information.
The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. For example, the method may be implemented in a cellular telephone. The method may further be implemented in any telecommunications system in which a cell selection procedure is required.
It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims (16)

1. A method in a terminal device configured to operate in a radio access network in a connected mode and an idle mode, the method comprising:
retaining stored system information of a cell of the radio access network while operating in a connected mode;
determining that the terminal device should change from connected mode to an idle mode;
checking the validity of the stored system information;
updating the stored system information with new system information if the stored system information is found to be invalid; and camping on the cell in idle mode using the stored system information.
2. A method according to claim 1, wherein checking the validity of the stored system information comprises checking the validity of the stored system information using a stored change identifier in the stored system information.
3. A method according to claim 2, wherein checking the validity of the stored system information comprises:
receiving new system information from the cell comprising a new change identifier; and comparing the stored change identifier in the stored system information with the new change identifier in the new system information.
4. A method according to claim 3, wherein checking the validity of the stored system information comprises:
determining the stored system information is valid if the stored change identifier is the same as the new change identifier; and determining the stored system information is invalid if the stored change identifier is not the same as the new change identifier.
5. A method according to any preceding claim, wherein the system information comprises multiple blocks of system information.
6. A method according to claim 5, wherein a block of system information comprises a master information block.
7. A method according to claim 5 or claim 6, wherein a block of system information comprises a system information block.
8. A method according to claim 5 dependent on claim 3, wherein the new change identifier is received in a first block of the system information, and the stored change identifier is stored in a corresponding first block of the stored system information, and checking the validity of the stored system information comprises determining the validity of a second block of stored system information based on the comparing step.
9. A method according to any preceding claim, wherein retaining stored system information comprises retaining the system information in a memory of the terminal device.
10. A method according to any preceding claim comprising receiving and storing system information of the cell broadcast from the radio access network while in idle mode prior to retaining the stored system information while in connected mode.
11. A method according to any preceding claim, wherein determining that the terminal device should change from connected mode to idle mode is in response to receiving a radio release message.
12. A method according to any preceding claim, wherein updating the stored system information comprises selectively replacing the stored system information determined to be invalid with new system information.
13. A method according to any preceding claim, wherein the radio access network is a narrowband internet-of-things, NB-IoT, network.
14. A method according to any preceding claim, wherein the terminal device is a 5 narrowband internet-of-things terminal device.
15. A terminal device configured to perform the method of any of claims 1 to 14.
16. A computer program product comprising instructions which, when executed by
10 a computer, cause the computer to carry out the method of any of claims 1 to 14.
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CN115278827B (en) * 2022-07-21 2023-10-13 上海移芯通信科技股份有限公司 Internet of things terminal network residence process control method, system and communication equipment

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