WO2018143868A1

WO2018143868A1 - Methods for adapting cell change based on sfn acquisition

Info

Publication number: WO2018143868A1
Application number: PCT/SE2018/050052
Authority: WO
Inventors: Muhammad Kazmi; Joakim Axmon; Santhan THANGARASA
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-02-03
Filing date: 2018-01-24
Publication date: 2018-08-09

Abstract

The disclosure relates to a method performed by a wireless device in a serving cell of a wireless communication network. The method comprises receiving (151) a request to perform a cell change to a target cell, the request being received from a radio network node (315) operating the serving cell, receiving (152) information about a system frame number, SFN, used in the target cell from the radio network node, and performing (154) the cell change to the target cell in response to the request without acquiring the SFN of the target cell, when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell.

Description

METHODS FOR ADAPTING CELL CHANGE BASED ON SFN ACQUISITION

TECHNICAL FIELD

The present disclosure relates, in general, to wireless communications and, more particularly, to cell change such as handover.

BACKGROUND

The 3rd Generation Partnership Project (3GPP) is responsible for the standardization of Global System for Mobile communications (GSM), Universal Mobile Telecommunication System (UMTS), and Long Term Evolution (LTE). LTE is a technology for realizing highspeed packet-based communication that can reach high data rates both in the downlink and in the uplink, and is a next generation wireless communication system relative to UMTS. LTE brings significant improvements in capacity and performance over previous radio access technologies.

The GSM Edge Radio Access Network (GERAN) is the radio access network of a GSM network, UMTS Universal Terrestrial Radio Access Network (UTRAN) is the radio access network of a UMTS, and E-UTRAN is the radio access network of an LTE system. In a GSM, UTRAN and E-UTRAN, a wireless device, sometimes also called a User Equipment (UE), is wirelessly connected to a Radio Base Station (RBS) commonly referred to as a Base Transceiver station (BTS) in GSM, NodeB (NB) in UMTS, and evolved NodeB (eNodeB or eNB) in LTE. An RBS is a general term for a radio network node capable of transmitting radio signals to the UE and receiving signals transmitted by the UE. The area served by one or sometimes several RBSs may be referred to as a cell.

The fifth generation (5G) of mobile telecommunications and wireless technology is not yet fully defined but in an advanced draft stage within 3rd Generation Partnership Project (3GPP). It includes work on 5G New Radio (NR) Access Technology. Long term evolution (LTE) terminology is used in this disclosure in a forward-looking sense, to include equivalent 5G entities or functionalities although a different term is specified in 5G. A general description of the agreements on the physical layer aspects of 5G NR Access Technology so far is contained in 3 GPP Technical Report 38.802 V14.2.0 (2017-09). Final specifications may be published inter alia in the future 3GPP TS 38.2** series.

Wireless devices, which are referred to as UE in 3 GPP terminology, may comprise, for example, cellular telephones, personal digital assistants, smart phones, laptop computers, handheld computers, machine-type communication/machine-to-machine (MTC/M2M) devices or other devices or terminals with wireless communication capabilities. Wireless devices may refer to terminals that are installed in fixed configurations, such as in certain machine-to- machine applications, as well as to portable devices, or devices installed in motor vehicles. Hereinafter, a wireless device may sometimes be referred to as a UE or simply as a device or terminal.

MTC/eMTC/FeMTC

A Machine-Type-Communication (MTC) device is expected to be of low cost and low complexity. A low-cost User Equipment (UE) envisages that for Machine-to-Machine (M2M) operation, the UE may implement one or more low-cost features like, smaller downlink and uplink maximum transport block size (e.g., 1000 bits) and/or reduced downlink channel bandwidth of 1.4 MHz for data channel such as Physical Downlink Shared Channel (PDSCH). A low-cost UE may also include a Half-Duplex Frequency Division Duplex (HD-FDD) and one or more of the following additional features: single receiver (1 Rx) at the UE, smaller downlink and/or uplink maximum transport block size (e.g., 1000 bits), and reduced downlink channel bandwidth of 1.4 MHz for data channel. The low-cost UE may also be referred to as a low complexity UE.

The path loss between an M2M device and a base station can be very large in some scenarios. One example is when the device is used as a sensor or metering device located in a remote location, such as in the basement of a building. In such scenarios, the reception of signals from the base station is very challenging. For example, the path loss can be 20 dB worse than for normal cellular network operation. In order to cope with such challenges, the coverage in uplink and/or in downlink should be substantially enhanced. This enhancement is realized by employing one or more advanced techniques in the UE and/or in the radio network node for enhancing the coverage. Some non-limiting examples of such advanced techniques are: power boosting of transmission, repetition of transmitted signal, applying additional redundancy to the transmitted signal, and using advanced or enhanced receiver. In general, when employing such coverage enhancing techniques, the M2M device is regarded to be operating in a 'coverage enhancing mode'.

A low complexity MTC UE (e.g. UE with 1 Rx) may also be capable of supporting coverage enhancing mode of operation (e.g., coverage enhancement mode B (CE ModeB)). The normal coverage mode of operation may also be referred to as a coverage enhancement mode A (CE Mode A).

Narrow Band Internet of Things (NB-IOT)

The Narrow Band Internet of Things (NB-IOT) is a radio access for cellular internet of things (IOT), which to a great extent is based on a non-backward-compatible variant of E- UTRA, that addresses improved indoor coverage, support for massive number of low throughput devices, low delay sensitivity, ultra-low device cost, low device power consumption, and optimized network architecture.

The NB-IOT carrier BW (Bw2) is 200 KHz. Examples of operating bandwidth (Bwl) of LTE are 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. B-IoT supports three different deployment scenarios:

1. ' Stand-alone operation' utilizing for example the spectrum currently being used by GERAN systems as a replacement of one or more GSM carriers. In principle, it operates on any carrier frequency which is neither within the carrier of another system, nor within the guard band of another system's operating carrier. The other system can be another NB-IOT operation or any other Radio Access Technology (RAT), e.g. LTE.

2. 'Guard band operation' utilizing the unused resource blocks within an LTE carrier's guard-band. The term guard band may interchangeably be referred to as a guard bandwidth. As an example, in case of LTE BW of 20 MHz (i.e. Bwl= 20 MHz or 100 Resource Blocks (RBs)), the guard band operation of NB-IOT can be placed anywhere outside the central 18 MHz but within the 20 MHz LTE BW.

3. Ίη-band operation' utilizing resource blocks within a normal LTE carrier. The in-band operation may interchangeably be referred to as in-bandwidth operation. More generally, the operation of one RAT within the BW of another RAT is also called in-band operation. As an example, in a LTE BW of 50 RBs (i.e. Bwl= 10 MHz or 50 RBs), NB-IOT operation over one resource block (RB) within the 50 RBs is called in-band operation.

In NB-IOT, the downlink transmission is based on Orthogonal Frequency Division Multiplexing (OFDM) with 15 kHz subcarrier spacing and same symbol and cyclic prefix durations as for legacy LTE for all the deployment scenarios (standalone, guard-band, and in- band). For UL transmission, both multi-tone transmissions with a 15 kHz subcarrier spacing on single-carrier frequency division multiple access (SC-FDMA), and single tone transmission with either 3.75 kHz or 15 kHz subcarrier spacing are supported.

In existing solutions, the MTC and NB-IoT UEs may need to acquire System Frame Number (SFN) of the target cell before performing a cell change. The cell change may e.g. be a handover, a Radio Resource Control (RRC) re-establishment, or an RRC connection release with redirection. In MTC and NB-IoT, when the UE is operating in an enhanced coverage mode with respect to the target cell, the acquisition of SFN of the target cell can be very long (e.g., 1-2 seconds). This significantly increases the cell change delay and therefore degrades mobility performance.

SUMMARY

An object of embodiments is to alleviate or at least reduce one or more of the above- mentioned problems, and to provide a solution improving mobility performance, especially when the UE is operating in an enhanced coverage mode. This object, and others, is achieved by methods and apparatus according to embodiments herein.

According to a first aspect, a method performed by a wireless device or UE in a serving cell of a wireless communication network is provided. The method comprises receiving a request to perform a cell change to a target cell, the request being received from a radio network node operating the serving cell. The method also comprises receiving information about a system frame number, SFN, used in the target cell from the radio network node, and performing the cell change to the target cell in response to the request without acquiring the SFN of the target cell, when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell.

According to a second aspect, a method performed by a radio network node of a wireless communication network is provided. The radio network node is operating a serving cell serving a wireless device or UE. The method comprises transmitting a request to the wireless device to perform a cell change to a target cell. The method also comprises transmitting information about a system frame number, SFN, used in the target cell to the wireless device. The information about the SFN is informing the wireless device whether or not to acquire a SFN of the target cell for performing the requested cell change. The information about the SFN indicates whether the SFN used in the target cell is the same as the SFN used in the serving cell.

According to a third aspect, a wireless device in a serving cell of a wireless communication network is provided. The wireless device is configured to receive a request to perform a cell change to a target cell, the request being received from a radio network node operating the serving cell. The wireless device is also configured to receive information about a system frame number, SFN, used in the target cell from the radio network node. The wireless device is further configured to perform the cell change to the target cell in response to the request without acquiring the SFN of the target cell, when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell.

According to a fourth aspect, a radio network node of a wireless communication network is provided. The radio network node is configured to operate a serving cell serving a wireless device. The radio network node is further configured to transmit a request to the wireless device to perform a cell change to a target cell. The radio network node is also configured to transmit information about a system frame number, SFN, used in the target cell to the wireless device, informing the wireless device whether or not to acquire a SFN of the target cell for performing the requested cell change, wherein the information about the SFN indicates whether the SFN used in the target cell is the same as the SFN used in the serving cell.

According to further aspects, a computer program is provided as well as a carrier containing the computer program. The computer program comprises computer readable code which when executed by at least one processor of a wireless device causes the wireless device to carry out the method according to the first aspect.

According to further aspects, a computer program is provided as well as a carrier containing the computer program. The computer program comprises computer readable code which when executed by at least one processor of a radio network node causes the radio network node to carry out the method according to the second aspect.

Certain embodiments of the present disclosure may provide one or more technical advantages. For example, in certain embodiments, several cell change procedures and corresponding operations (e.g. mobility) are enhanced for the MTC and NB-IoT UEs. As another example, in some embodiments, cell change delay on average is reduced. This delay reduction in turn improves Radio Resource Management (RRM) performance. The delay can be reduced up to 1-2 seconds when the UE is in enhanced coverage in certain instances. In embodiments, the UE does not have to acquire the SFN of the target cell in every cell change. This may reduce the UE complexity and power consumption. Furthermore, informing the wireless device whether to acquire a SFN of the target cell for performing a cell change by indicating whether the SFN used in the target cell is the same as the SFN used in the serving cell provides the above advantages without excessive signaling. Other advantages may be readily apparent to one having skill in the art. Certain embodiments may have none, some, or all of the recited advantages. BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the disclosed embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

FIGURE la is a flowchart illustrating an example method of performing a cell change in a wireless device;

FIGURE lb is a flowchart illustrating a method of performing a cell change in a wireless device according to embodiments;

FIGURE 2a is a flowchart illustrating an example method of performing a cell change in a radio network node;

FIGURE 2b is a flowchart illustrating a method of performing a cell change in a radio network node according to embodiments;

FIGURE 3 is a block diagram illustrating an embodiment of a wireless communication network;

FIGURE 4 is a block diagram illustrating an embodiment of a wireless communication network;

FIGURE 5 is a block schematic of an exemplary wireless device;

FIGURE 6 is a block schematic of an exemplary network node;

FIGURE 7 is a block schematic of an exemplary radio network controller or core network node;

FIGURE 8 is a block schematic of an exemplary wireless device; and

FIGURE 9 is a block schematic of an exemplary network node.

DETAILED DESCRIPTION

General description of scenario

In some embodiments, a more general term "network node" is used and it can correspond to any type of radio network node or any network node which communicates with a UE and/or with another network node. Examples of network nodes are NodeB, Master eNodeB (MeNB), Secondary eNodeB (SeNB), a network node belonging to Master Cell Group (MCG) or Secondary Cell Group (SCG), base station (BS), multi-standard radio (MSR) radio node such as MSR BS, eNodeB, gNodeB, network controller, radio network controller (RNC), base station controller (BSC), relay, donor node controlling relay, base transceiver station (BTS), access point (AP), transmission points, transmission nodes, Radio Resource Unit (RRU), Radio Resource Head (RRH), nodes in distributed antenna system (DAS), core network node (e.g. Mobile Switching Center (MSC), or Mobility Management Entity (MME)), Operation and Maintenance (O&M) node, Operation and Support System (OSS), Self- organizing network (SON) node, positioning node (e.g. Evolved Serving Mobile Location Center (E-SMLC) server), server for Minimized Drive Testing (MDT), and test equipment.

In some embodiments the non-limiting term "user equipment" (UE) is used and it refers to any type of wireless device communicating with a network node and/or with another UE in a cellular or mobile communication system. Examples of UE are target device, device to device (D2D) UE, machine type UE or UE capable of machine to machine (M2M) communication, Personal digital assistant (PDA), tablet computer, mobile terminal, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, ProSe UE, Vehicle-to- Vehicle (V2V) UE, Vehicle-to- Any thing (V2X) UE, MTC UE, enhanced MTC (eMTC) UE, Further enhanced MTC (FeMTC) UE, UE Cat 0, UE Cat Ml, narrowband Internet of Things (NB-IoT) UE, and UE Cat NB 1.

The embodiments are described for LTE or LTE based systems such as MTC, eMTC, NB-IoT. As an example, a UE in such a system may be MTC UE, eMTC UE, and NB-IoT UE also called UE category 0, UE category Ml and UE category NB 1. The embodiments, however, are applicable to any RAT or multi-RAT systems, where the UE receives and/or transmit signals (e.g. data), such as LTE FDD/TDD, WCDMA/HSPA, GSM/GERAN, Wi-Fi, WLAN, CDMA2000, 5G, and NR.

The embodiments are applicable for a UE in a low or high activity state. Examples of low activity state are RRC idle state, or idle mode. Examples of high activity state are RRC CONNECTED state, active mode, or active state. The UE may be configured to operate in DRX or in non-DRX. If configured to operate in DRX, it may still operate according to non- DRX as long as it receives new transmissions from the network node.

The term "cell change" used herein may refer to selection of a target cell or change from one cell to another cell (e.g., target cell). Some examples of cell change are initial cell selection, cell selection when leaving an RRC state (e.g. leaving RRC CONNECTED state), cell reselection, handover, RRC connection release with re-direction, RRC connection re- establishment, Primary Cell (PCell) change, Primary Secondary Cell (PSCell) change, Secondary Cell (SCell) change, and swapping between serving cells such as PCell and SCell. The cell change can be performed by the UE autonomously or it can be performed by the UE based on a message (e.g. a cell change command) received from a network node. The UE may operate under either normal coverage or enhanced coverage with respect to its serving cell. In one example, normal coverage and enhanced coverage levels are interchangeably called CE level 0 and CE level 1 respectively. In another example, normal coverage and enhanced coverage levels are interchangeably called CE Mode A and CE Mode B respectively (only for connected state configured by the network). The enhanced coverage may interchangeably be called extended coverage. The UE may operate in a plurality of coverage enhancement (CE) levels, such as normal coverage enhancement level (CE level 0, or CEO), coverage enhancement level 1 (CE1), coverage enhancement level 2 (CE2), coverage enhancement level 3 (CE3), and so on. For 3GPP MTC there are currently four CE levels specified 0, 1, 2 and 3, but for the rest only two CE levels are specified: normal and enhanced.

The normal and extended coverage operations may typically take place on narrower UE Radio Frequency (RF) bandwidth (BW) compared with the system BW (e.g., cell BW, cell transmission BW, and DL system BW). In some embodiments, the UE RF BW can be the same as the system bandwidth. Examples of narrow RF BWs are 200 KHz, and 1.4 MHz. Examples of system BW include 200 KHz, 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, and 20 MHz. In case of extended/enhanced coverage, the UE may be capable of operating with lower signal quality levels (e.g. Signal to Noise Ratio (SNR), Signal to Interference and Noise Ratio (SINR), ratio of average received signal energy per subcarrier to total received power per subcarrier (Es/Iot)), and Reference Signal Received Quality (RSRQ)) compared to its capabilities when operating in legacy systems. The CE level may vary with the operational scenario and may also depend on the UE type. For example, a UE which is located in a basement with bad coverage may need a larger level of coverage enhancement (e.g. 20 dB) compared to a UE which is at a cell border (e.g. -3 dB).

The coverage level of the UE may be defined with respect to any cell (e.g. serving cell, non-serving cell, or neighbor cell). The coverage level may interchangeably be called the coverage enhancement (CE) level. For example, the CE level with respect to a cell can be expressed in terms of signal level received at the UE from that cell. Alternatively, the CE level of the UE with respect to a cell can be expressed in terms of signal level received at the cell from the UE. As an example, received signal level can be expressed in terms of received signal quality and/or received signal strength at the UE with respect to the cell. More specifically the CE level may be expressed in terms of:

• received signal quality and/or received signal strength at the UE with respect to a cell and/or • received signal quality and/or received signal strength at the cell with respect to the UE. Examples of signal quality are SNR, SINR, Channel Quality Indicator (CQI), RSRQ,

Narrowband Reference Signal Received Quality (NRSRQ), Cell Specific Reference Signal (CRS) Es/Iot, and Shared Channel (SCH) Es/Iot. Examples of signal strength are path loss, path gain, Reference Signal Received Power (RSRP, Narrowband RSRP (NRSRP), and SCH Received Power (SCH RP). The notation Es/Iot is expressed as a ratio of:

• Es, which is the received energy per Resource Element (RE) (power normalized to the subcarrier spacing) during the useful part of the symbol, i.e. excluding the cyclic prefix, at the UE antenna connector.

• lot, which is the received power spectral density of the total noise and interference for a certain RE (power integrated over the RE and normalized to the subcarrier spacing) as measured at the UE antenna connector.

The CE level is also expressed in terms of two or more discrete levels or values (e.g. CE level 1, CE level 2, CE level 3, etc.). Consider an example of two coverage levels defined with respect to signal quality (e.g. SNR) at the UE comprising of:

• Coverage enhancement level 1 (CE1) comprising of SNR > -6 dB at UE with respect to a cell; and

• Coverage enhancement level 2 (CE2) comprising of -15 dB < SNR < -6 dB at UE with respect to a cell.

In the above example, CE1 may also be interchangeably called normal coverage level, baseline coverage level, reference coverage level, or legacy coverage level. On the other hand, CE2 may be referred to as enhanced coverage level or extended coverage level.

In another example, two different coverage levels (e.g. normal coverage and enhanced coverage) may be expressed in terms of signal quality levels as follows:

• The requirements for normal coverage are applicable for the UE category narrowband 1 (NB 1) with respect to a cell, provided that radio conditions of the UE with respect to that cell are defined as follows: SCH Es/Iot > -6 dB and CRS Es/Iot > -6 dB. NBl may also be referred to as NB-IoT UE type 1.

• The requirements for enhanced coverage are applicable for the UE category NB 1 with respect to a cell, provided that radio conditions of the UE with respect to that cell are defined as follows: SCH Es/Iot > -15 dB and CRS Es/Iot > -15 dB.

A parameter defining the coverage level of the UE with respect to a cell may also be signalled to the UE by the network node. Examples of such parameters are CE Mode A and CE Mode B signalled to UE category Ml . The UE configured with CE Mode A and CE Mode B are also said to operate in normal coverage mode and enhanced coverage mode respectively. For example:

• The requirements for CE Mode A apply provided the UE category Ml is configured with CE Mode A, SCH Es/Iot > -6 dB and CRS Es/Iot > -6 dB.

• The requirements for CE Mode B shall apply provided the UE category Ml is configured with CE Mode B, SCH Es/Iot > -15 dB and CRS Es/Iot > -15 dB.

In the above examples, Es/Iot is the ratio of received power per subcarrier to the total interference including noise per subcarrier.

Methods performed in a UE

FIGURE la illustrates an example method 100 of cell reselection which may be performed in a UE. In step 104, the UE obtains a request to perform a cell change to a target cell. In step 108, the UE determines whether the UE should acquire an SFN of the target cell for accessing the target cell for the cell change. If not, then the UE performs step 1 12 to perform the cell change to the target cell based on a first procedure (PI). Otherwise, the UE performs step 116 to perform the cell change to the target cell based on a second procedure (P2). The steps (along with any additions or modifications) are described below.

Step 104

In this step, the UE obtains a request to perform cell change to a target cell (cell2). This request is also called herein as a first message (Ml). The UE may receive the request from higher layers. In one example, the request (Ml) is internally created by the UE's higher layer. In another example, the request (Ml) is received by the UE's higher layer from another node (e.g. serving network node, or core network node). In this case, as an example, the request may be received by the UE from another node via any of: RRC signaling, or NAS signaling. The received message (Ml) may or may not include the identifier of cell2 and/or the identifier of carrier frequency of cell2 (e.g. Absolute radio-frequency channel number (ARFCN), or evolved ARFCN (EARFCN)).

In one example, the cell change to cell2 can be performed from a first cell (celll). Celll and cell2 may operate on the same carrier frequency or on different carrier frequencies. In another example, the cell change to cell2 can be performed by the UE even if the UE does not have any connection or link to celll . Examples of celll are serving cell and non-serving cell. Examples of cell2 are non-serving cell, former serving cell, or serving cell. For example, the cell change may be performed between two serving cells (e.g. swapping between PCell and SCell). Examples of serving cell are PCell, PSCell, SCell, etc. Examples of non-serving cell are neighbor cell on serving carrier (e.g., intra-frequency neighbor cell), neighbor cell on non- serving carrier (e.g., inter-frequency cell, inter-RAT cell).

Step 108

In this step, the UE determines whether or not the UE should acquire a frame number (e.g., SFN) of cell2 for accessing cell2 for performing the cell change operation. Examples of the frame number is a system frame number (SFN), hyper SFN (HSFN), etc. As an example, SFN includes a cycle of 1024 radio frames (e.g. expressed in 10-bit). The frame number of cell2 may be needed in order to access cell2 (e.g. to transmit random access channel (RACH) to cell2 in the resources configured for the RACH transmission).

The UE can determine whether it should acquire the frame number of cell2 based on one or more of the following sets of information:

RACH configuration used in cell2: For example, the UE should not acquire the SFN of cell2 if the RACH is configured in at least one time resource in every radio frame of cell2. But if the RACH is not configured in at least one time resource in every radio frame of cell2, then the UE should acquire the SFN of cell2. For example, if the RACH is configured only in frames with an even frame number or only in frames with an odd frame, then the UE should acquire the SFN of cell2 before sending RACH message to cell2 for accessing cell2 to perform the cell change to cell2. The UE may acquire RACH configuration used in cell2 based on one or more of the following: in the obtained cell change message which triggers the cell change operation, pre-defined RACH configuration, history or statistics of RACH configuration used in cell2, previously used RACH configuration in cell2.

Received information about frame number in cell2: In this example, the UE may receive information about the SFN used in cell2. The information may be received from a network node (e.g., serving network node, core network node, etc.) In one example, the received information may include explicit information indicating the SFN used in cell2 (e.g., SFN used in cell2 at certain reference time). Examples of reference time are Global Navigation Satellite Systems (GNSS) time, SFN used in a reference cell (e.g. serving cell). In this case (e.g., when SFN of cell2 is received), the UE should not acquire the SFN of cell2 for accessing cell2. In another example, the received information may include an implicit indication about the SFN used in cell2 (e.g., SFN used in cell2 is the same as in a reference cell). Examples of reference cell are celll, any serving cell of the UE, any cell whose SFN is known to the UE, etc. In this case, because the UE knows the SFN of the reference cell, the UE should not acquire the SFN of cell2 for accessing cell2. In yet another example, the information may include a relation between SFN used in the reference cell (SFNr) and SFN used in cell2 (SFNcell2). Examples of the relation are difference between SFNr and SFNcell2 or ratio between SFNr and SFNcell2. In this case, based on SFNr and the received relation between SNRr and SFNcell2, the UE determines SFNcell2. The SFNr (e.g. serving cell SFN) is known to the UE.

Pre-defined rule related to frame number used in cell2: In this example, a rule can be specified in the standard or configured at the UE, that the UE shall assume certain SFN is used in cell2 if the SFN of cell2 is not signaled to the UE by the network node. Examples of SFN that the UE can assume based on this rule are same SFN as used in a reference cell (e.g. celll or any cell whose SFN is known) or a certain pre-defined value (e.g. SFN = 0, SFN = 512, etc).

Steps 112 and 116

In these steps, the UE adaptively performs the cell change operation to cell2 based on whether the SFN of cell2 is known to the UE or not before accessing cell2. The adaptive cell change procedure includes the UE:

• applying a first procedure (PI) for performing the cell change to cell2 if the UE should not acquire the SFN of cell2 for accessing cell2, or

• applying a second procedure (P2) for performing the cell change to cell2 if the UE should acquire the SFN of cell2 for accessing cell2.

The term "accessing cell2" herein may include transmitting a message to cell2 as part of a cell change procedure. The cell change procedure starts upon the reception of Ml at the UE and it is completed after the UE has successfully transmitted M2 in cell2 (e.g., cell2 has received M2). The message transmitted to cell2 herein may be called a second message (M2). Examples of such second messages (M2) are random access (RA) messages (e.g. RACH, narrowband RACH (NRACH)), and dedicated channels or signals (e.g. UE specific channel or signal, Physical Uplink Control Channel (PUCCH), Physical Uplink Shared Channel (PUSCH), Sounding Reference Signal (SRS)).

First cell change procedure (PI)

In the first procedure (PI) before accessing cell2 (e.g., before sending RA, PUCCH, or PUSCH), the UE should not acquire the SFN of cell2. This is the case, as described in step 108, wherein the SFN of cell2 is known to the UE before accessing cell2. This in turn leads to shorter cell change delay (TP1) compared to the case when the UE should acquire the SFN of cell2 before accessing cell2.

The cell change delay (TP1) based on procedure PI is the time duration between the moment the UE obtains a cell change request (e.g., first message (Ml)) and the moment the UE has transmitted the second message (M2) to cell2 to access cell2. The TP1 does not include any time to acquire the SFN of cell2.

The TP1 may however depend on:

the time period (TM1) to process the received request to process the obtained cell change message (Ml),

the time period (TM2) to transmit the second message (e.g. RA) to cell2, the time period (Tsearch) to identify or search cell2 or synchronize to cell2 (if cell2 is not already identified). If cell2 is already identified then Tsearch = 0, and

fixed interruption time (a, e.g. time to change the UE physical layer parameters to send M2 to cell2). This is also called herein as UE implementation margin. An example of a= 20 ms.

An example of TP1 is expressed in (1):

TP 1 = f(TM 1 , Tsearch, TM2, a) ( 1 )

A specific example of TP1 based on (1) is expressed in (2):

TP1 = TM1 + Tsearch + TM2 + a (2) The parameters TM1, TM2, and Tsearch may further depend on the coverage enhancement (CE) level of the UE with respect to cell 1 and/or cell2. For example, TM2 in normal coverage is shorter than TM2 in enhanced coverage. This is because in enhanced coverage the message, M2, (e.g. RACH) is transmitted by the UE with certain number of repetitions. Therefore, the UE in enhanced coverage has to transmit multiple M2 (e.g. RACH) transmissions in order to enable cell2 to successfully decode the M2. Examples of TM2 for the UE in normal coverage and in enhanced coverage are 10 ms and 640 ms respectively.

Second cell change procedure (P2)

In the second procedure (P2), before accessing cell2 (e.g., before sending RA, PUCCH, PUSCH, etc.), the UE acquires the SFN of cell2. To acquire the SFN, the UE may read or acquire at least part of the system information (SI) of cell2, which contains SFN of cell2. Examples of SI containing SFN are master information block (MIB), system information block (SIB), etc. As an example, MIB can be transmitted in a physical channel (e.g., Physical Broadcast Channel (PBCH), or NB-IoT PBCH (NPBCH)). The acquisition of the SI of cell2 to read SFN of cell2 involves certain delay (TSFN). This in turn leads to longer cell change delay (TP2) compared to the case when the UE does not need to acquire the SFN of cell2 (e.g., TP2 > TP1 for the UE in the same coverage enhancement level with respect to cell2). The cell change delay (TP2) based on the second procedure P2 is the time duration between the moment the UE obtains a cell change request (e.g., first message (Ml)) and the moment the UE has transmitted the second message (M2) to cell2 to access cell2. The TP2 may depend on at least the time (TSFN) required by the UE to acquire the SFN of cell2.

The TP2 may also further depend on:

the time period (TM2) to transmit the second message (e.g. RA) to cell2, time period (Tsearch) to identify or search cell2 or synchronize to cell2 (if cell2 is not identified) and

fixed interruption time (a, e.g. time to change the UE physical layer parameters to send M2 to cell2). An example of a= 20 ms.

An example of TP2 is expressed in (3):

TP2 = f(TMl, Tsearch, TSFN, TM2, a) (3) A specific example of TP2 based on (3) is expressed in (4):

TP2 = TM1 + Tsearch + TSFN + TM2 + a (4) The parameters TM1, TM2 and Tsearch may further depend on the coverage enhancement (CE) level of the UE with respect to celll and/or cell2 as described in previous sections. The SFN acquisition delay parameter, TSFN, may also further depend on the coverage enhancement (CE) level of the UE with respect to cell2. For example, TSFN in normal coverage is shorter than TSFN in enhanced coverage. This is because in enhanced coverage, the channel containing SFN (e.g. PBCH) is transmitted with a certain number of repetitions. Therefore, the UE in enhanced coverage should receive multiple PBCH transmissions in order to successfully decode the SFN of cell2. Examples of TSFN for the UE in normal coverage and in enhanced coverage are 40 ms and 1280 ms respectively.

FIGURE lb is a flowchart illustrating one embodiment of a method performed by a wireless device 310 in a serving cell of a wireless communication network. In embodiments, the wireless device is an MTC device or an NB-IoT device. The wireless device may operate in an enhanced coverage mode with regards to the target cell. The method comprises:

- 151 : Receiving a request to perform a cell change to a target cell, the request being received from a radio network node operating the serving cell.

- 152: Receiving information about a SFN used in the target cell from the radio network node.

- 154: Performing the cell change to the target cell in response to the request without acquiring the SFN of the target cell. This is done when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell. In embodiments, performing the cell change may comprise transmitting a random access message for accessing the target cell.

In one embodiment, when the received information about the SFN indicates that the SFN used in the target cell is not the same as the SFN used in the serving cell, the method comprises:

- 155: Performing the cell change to the target cell in response to the request, wherein performing the cell change comprises, before transmitting the random access message, acquiring at least part of the system information, SI, of the target cell including the SFN of the target cell.

In embodiments, the cell change may comprise one of: a handover, a RRC re- establishment, a cell selection, a cell reselection, a RRC connection release with redirection, and a swapping between serving cells.

Methods performed in a network node

FIGURE 2a illustrates an example method 200 of cell reselection. In particular embodiments, a network node performs method 200. In step 204, the network node configures a UE to perform a cell change to a target cell (cell2). In step 208, the network node determines whether or not the UE should acquire a system frame number (SFN) of the target cell for accessing the target cell for the cell change operation. If not, then the network node performs step 212 to determine that the UE should perform the cell change to the target cell based on a first procedure (PI). Otherwise, the network node performs step 216 to determine that the UE should perform the cell change to the target cell based on a second procedure (P2). In certain embodiments, the network node receives an access message from the UE in the target cell based on the determined procedure used by the UE for performing cell change to the target cell. The steps (along with any additions or modifications) are described below.

Step 204

In this step, the network node configures the UE to perform the cell change by sending a message (Ml). Examples of Ml are a cell change command, a handover command, RRC connection release with redirection, RRC re-establishment, etc. In one example, the network node may indicate to the UE an identifier of the target cell (e.g., a second cell (cell2)). In another example, the network node only requests the UE to perform cell change to any cell (e.g., strongest cell, cell with largest signal quality, etc.). In yet another example, the network node may provide the UE with identifiers of groups of cells (e.g., cell2, cell3, ... ,cellm, etc.). In yet another example, the network node may provide the UE with identifiers or information (e.g. EARFCN, channel numbers, etc.) of one or plurality of carrier frequencies containing potential target cells or groups of cells. The network node may transmit Ml via RRC signaling, core network node signaling, etc.

Step 208

In this step, the network node determines whether or not the UE should acquire a frame number of cell2 for accessing cell2 for performing the cell change operation. Examples of the frame number include a system frame number (SFN), hyper SFN (HSFN), etc.

The network node determines whether the UE should acquire the frame number of cell2 or not based on one or more of the following principles:

RACH configuration used in cell2:

This is the same principle as described above (e.g., Step 108). The RACH configuration used in cell2 is signaled to the UE in cell change message (M2). The network node acquires the RACH configuration used in cell2 by receiving the information about the RACH configuration used in cell2 from a network node serving cell2.

Whether information about frame number used in cell2 is signaled to UE:

If the network node signals the information about the frame number of cell2, then the UE should not acquire SFN of cell2. The type of information signaled to the UE is the same as described above (e.g., Step 108).

Pre-defined rule related to frame number used in cell2:

This is the same principle as described above (e.g., Step 108).

Step 212

In this step, the network node uses the determined information in step 208 to further determine that the UE should perform cell change to cell2 by applying a first procedure (PI). The first procedure PI is described above.

Step 216

In this step, the network node uses the determined information in step 208 to further determine that the UE should perform cell change to cell2 by applying a second procedure (P2). The second procedure P2 is described above.

In certain embodiments, the network node receives an access message (M2) from the UE within a certain time period (TP) since the network node has transmitted the cell change request message (Ml) to the UE. The value of TP may depend on whether the network node has determined that the UE should apply PI or P2 for doing cell change.

TP = TP1 if it is determined that the UE applies procedure, PI and TP = TP2 if it is determined that the UE applies procedure, P2.

TP1 and TP2 are described above.

FIGURE 2b is a flowchart illustrating one embodiment of a method performed by a radio network node of a wireless communication network, the radio network node operating a serving cell serving a wireless device. In embodiments, the wireless device is an MTC device or an NB-IoT device. The wireless device may operate in an enhanced coverage mode with regards to the target cell. The method comprises:

- 251 : Transmitting a request to the wireless device to perform a cell change to a target cell.

- 252 (optionally): Determining whether or not the UE should acquire the SFN of the target cell for accessing the target cell when performing the cell change. Determining whether or not the UE should acquire the SFN of the target cell may in embodiments comprise determining whether the SFN used in the target cell is the same as the SFN used in the serving cell.

- 253/254: Transmitting information about a SFN used in the target cell to the wireless device, informing the wireless device whether or not to acquire a SFN of the target cell for performing the requested cell change. The information about the SFN indicates whether the SFN used in the target cell is the same as the SFN used in the serving cell.

In embodiments, the radio network node may be operating the target cell, as well as the serving cell. The method may then further comprise receiving a random access message for accessing the target cell from the wireless device.

In embodiments, the method further comprises determining that the wireless device shall perform the cell change to the target cell based on: a first procedure excluding acquisition of SFN of the target cell, if the SFN of the target cell should not be acquired by the wireless device for accessing the target cell, or a second procedure including acquisition of SFN of the target cell, if the SFN of the target cell should be acquired by the wireless device for accessing the target cell.

Embodiments of network and apparatus described with reference to Figures 3-9

FIGURE 3 is a block diagram illustrating a wireless communication network 300, in accordance with certain embodiments. Network 300 includes one or more UE(s) 310 (which may be interchangeably referred to as wireless devices 310) and one or more network node(s) 315 (which may be interchangeably referred to as radio network nodes or e Bs 315). UEs 310 may communicate with network nodes 315 over a wireless interface. For example, a UE 310 may transmit wireless signals to one or more of network nodes 315, and/or receive wireless signals from one or more of network nodes 315. The wireless signals may contain voice traffic, data traffic, control signals, and/or any other suitable information. In some embodiments, an area of wireless signal coverage associated with a network node 315 may be referred to as a cell 325. In some embodiments, UEs 310 may have device-to-device (D2D) capability. Thus, UEs 310 may be able to receive signals from and/or transmit signals directly to another UE.

In certain embodiments, network nodes 315 may interface with a radio network controller. The radio network controller may control network nodes 315 and may provide certain radio resource management functions, mobility management functions, and/or other suitable functions. In certain embodiments, the functions of the radio network controller may be included in network node 315. The radio network controller may interface with a core network node. In certain embodiments, the radio network controller may interface with the core network node via an interconnecting network 320. Interconnecting network 320 may refer to any interconnecting system capable of transmitting audio, video, signals, data, messages, or any combination of the preceding. Interconnecting network 320 may include all or a portion of a public switched telephone network (PSTN), a public or private data network, a local area network (LAN), a metropolitan area network (MAN), a wide area network (WAN), a local, regional, or global communication or computer network such as the Internet, a wireline or wireless network, an enterprise intranet, or any other suitable communication link, including combinations thereof.

In some embodiments, the core network node may manage the establishment of communication sessions and various other functionalities for UEs 310. UEs 310 may exchange certain signals with the core network node using the non-access stratum layer. In non-access stratum signaling, signals between UEs 310 and the core network node may be transparently passed through the radio access network. In certain embodiments, network nodes 315 may interface with one or more network nodes over an internode interface, such as, for example, an X2 interface.

As described above, example embodiments of network 300 may include one or more wireless devices 310, and one or more different types of network nodes capable of communicating (directly or indirectly) with wireless devices 310. In some embodiments, the non-limiting term UE is used. UEs 310 described herein can be any type of wireless device capable of communicating with network nodes 315 or another UE over radio signals. UE 310 may also be a radio communication device, target device, D2D UE, machine-type-communication UE or UE capable of machine to machine communication (M2M), low-cost and/or low-complexity UE, a sensor equipped with UE, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), etc. UE 310 may operate under either normal coverage or enhanced coverage with respect to its serving cell. The enhanced coverage may be interchangeably referred to as extended coverage. UE 310 may also operate in a plurality of coverage levels (e.g., normal coverage, enhanced coverage level 1, enhanced coverage level 2, enhanced coverage level 3 and so on). In some cases, UE 310 may also operate in out-of-coverage scenarios.

Also, in some embodiments generic terminology, "radio network node" (or simply "network node") is used. It can be any kind of network node, which may comprise a base station (BS), radio base station, Node B, multi- standard radio (MSR) radio node such as MSR BS, evolved Node B (eNB), network controller, radio network controller (RNC), base station controller (BSC), relay node, relay donor node controlling relay, base transceiver station (BTS), access point (AP), radio access point, transmission points, transmission nodes, Remote Radio Unit (RRU), Remote Radio Head (RRH), nodes in distributed antenna system (DAS), Multi-cell/multicast Coordination Entity (MCE), core network node (e.g., MSC, MME, etc.), O&M, OSS, SON, positioning node (e.g., E-SMLC), MDT, or any other suitable network node.

The terminology such as network node and UE should be considered non-limiting and does in particular not imply a certain hierarchical relation between the two; in general "eNodeB" could be considered as device 1 and "UE" device 2, and these two devices communicate with each other over some radio channel.

This disclosure contemplates any of the UEs 310 and network nodes 315 in network 300 performing any of the operations and processes described above. For example, any of UEs 310 can obtain a request to perform a cell change to a target cell, determine whether the UE 310 should acquire an SFN of the target cell, and then perform the cell change according to a first procedure PI or second procedure P2 depending on whether the UE 310 should acquire the SFN. As another example, any of network nodes 315 may configure a UE 310 to perform a cell change to a target cell, determine whether the UE should acquire the SFN of the target cell, and then determine whether the UE should perform cell change based on a first procedure PI or a second procedure P2.

Example embodiments of UE 310, network nodes 315, and other network nodes (such as radio network controller or core network node) are described in more detail below with respect to FIGURES 4-9.

Although FIGURE 3 illustrates a particular arrangement of network 300, the present disclosure contemplates that the various embodiments described herein may be applied to a variety of networks having any suitable configuration (e.g., the embodiment illustrated in FIGURE 4). FIGURE 4 illustrates network 300 including one network node 315 in communication with two wireless devices 310a and 310b. Network 300 may include any number of UEs in communication with any number of network nodes. Network 300 may include any suitable number of UEs 310 and network nodes 315, as well as any additional elements suitable to support communication between UEs or between a UE and another communication device (such as a landline telephone). Furthermore, although certain embodiments may be described as implemented in a Long Term Evolution (LTE) network, the embodiments may be implemented in any appropriate type of telecommunication system supporting any suitable communication standards (including 5G standards) and using any suitable components, and are applicable to any radio access technology (RAT) or multi-RAT systems in which a UE receives and/or transmits signals (e.g., data). For example, the various embodiments described herein may be applicable to LTE, LTE-Advanced, 5G, UMTS, HSPA, GSM, cdma2000, WCDMA, WiMax, UMB, WiFi, another suitable radio access technology, or any suitable combination of one or more radio access technologies.

FIGURE 5 is a block schematic of an exemplary wireless device 310, in accordance with certain embodiments. Wireless device 310 may refer to any type of wireless device communicating with a node and/or with another wireless device in a cellular or mobile communication system. Examples of wireless device 310 include a mobile phone, a smart phone, a PDA (Personal Digital Assistant), a portable computer (e.g., laptop, tablet), a sensor, an actuator, a modem, a machine-type-communication (MTC) device / machine-to-machine (M2M) device, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, a D2D capable device, or another device that can provide wireless communication. A wireless device 310 may also be referred to as UE, a station (STA), a device, or a terminal in some embodiments. Wireless device 310 includes transceiver 510, processing circuitry 520, and memory 530. In some embodiments, transceiver 510 facilitates transmitting wireless signals to and receiving wireless signals from network node 315 (e.g., via an antenna), processing circuitry 520 executes instructions to provide some or all of the functionality described above as being provided by wireless device 310, and memory 530 stores the instructions executed by processing circuitry 520.

Processing circuitry 520 may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of wireless device 310, such as the functions of wireless device 310 described above in relation to FIGURES la, lb, 2a and 2b. In some embodiments, processing circuitry 520 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, one or more application specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs) and/or other logic.

Memory 530 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by processing circuitry 520. Examples of memory 530 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non-transitory computer-readable and/or computer- executable memory devices that store information, data, and/or instructions that may be used by processing circuitry 520.

FIGURE 5 is a block diagram illustrating a wireless device 310 in a serving cell of a wireless communication network 300 according to one embodiment. The wireless device is configured to receive a request to perform a cell change to a target cell, the request being received from a radio network node 315 operating the serving cell. The wireless device is further configured to receive information about a system frame number, SFN, used in the target cell from the radio network node, and perform the cell change to the target cell in response to the request without acquiring the SFN of the target cell, when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell.

The wireless device may be configured to perform the cell change by being configured to transmit a random access message for accessing the target cell.

The wireless device may be further configured to perform the cell change to the target cell in response to the request, when the received information about the SFN indicates that the SFN used in the target cell is not the same as the SFN used in the serving cell. Performing the cell change comprises in this embodiment, before transmitting the random access message, acquiring at least part of the system information, SI, of the target cell including the SFN of the target cell.

In embodiments, the wireless device is a Machine Type Communication, MTC, device or a Narrowband Internet of Things, NB-IoT, device. The wireless device may be configured to operate in an enhanced coverage mode with regards to the target cell.

The cell change may comprise one of: a handover, a RRC re-establishment, a cell selection, a cell reselection, a RRC connection release with redirection, and a swapping between serving cells.

As illustrated in FIGURE 5, the wireless device may comprise a processing circuitry 520 and a memory 530, the memory containing instructions executable by the processing circuitry whereby the wireless device is configured to receive a request to perform a cell change to a target cell, the request being received from a radio network node (315) operating the serving cell, receive information about a system frame number, SFN, used in the target cell from the radio network node, and perform the cell change to the target cell in response to the request without acquiring the SFN of the target cell, when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell.

The memory may contain instructions executable by the processing circuitry, whereby the wireless device is configured to perform the method as described previously with reference to FIGURE lb.

Other embodiments of wireless device 310 may include additional components beyond those shown in FIGURE 5 that may be responsible for providing certain aspects of the wireless device's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above). As just one example, wireless device 310 may include input devices and circuits, output devices, and one or more synchronization units or circuits, which may be part of the processing circuitry 520. Input devices include mechanisms for entry of data into wireless device 310. For example, input devices may include input mechanisms, such as a microphone, input elements, a display, etc. Output devices may include mechanisms for outputting data in audio, video and/or hard copy format. For example, output devices may include a speaker, a display, etc. FIGURE 6 is a block schematic of an exemplary network node 315, in accordance with certain embodiments. Network node 315 may be any type of radio network node or any network node that communicates with a UE and/or with another network node. Examples of network node 315 include an eNodeB, a node B, a base station, a wireless access point (e.g., a Wi-Fi access point), a low power node, a base transceiver station (BTS), relay, donor node controlling relay, transmission points, transmission nodes, remote RF unit (RRU), remote radio head (RRH), multi-standard radio (MSR) radio node such as MSR BS, nodes in distributed antenna system (DAS), O&M, OSS, SON, positioning node (e.g., E-SMLC), MDT, or any other suitable network node. Network nodes 315 may be deployed throughout network 300 as a homogenous deployment, heterogeneous deployment, or mixed deployment. A homogeneous deployment may generally describe a deployment made up of the same (or similar) type of network nodes 315 and/or similar coverage and cell sizes and inter-site distances. A heterogeneous deployment may generally describe deployments using a variety of types of network nodes 315 having different cell sizes, transmit powers, capacities, and inter-site distances. For example, a heterogeneous deployment may include a plurality of low-power nodes placed throughout a macro-cell layout. Mixed deployments may include a mix of homogenous portions and heterogeneous portions.

Network node 315 may include one or more of transceiver 610, processing circuitry 620, memory 630, and network interface 640. In some embodiments, transceiver 610 facilitates transmitting wireless signals to and receiving wireless signals from wireless device 310 (e.g., via antenna 650), processing circuitry 620 executes instructions to provide some or all of the functionality described above as being provided by a network node 315, memory 630 stores the instructions executed by processing circuitry 620, and network interface 640 communicates signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), core network nodes or radio network controllers 130, etc.

Processing circuitry 620 may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of network node 315, such as those described above in relation to FIGURES 2a and 2b. In some embodiments, processing circuitry 620 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic. Memory 630 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by processing circuitry 620. Examples of memory 630 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non-transitory computer-readable and/or computer- executable memory devices that store information.

In some embodiments, network interface 640 is communicatively coupled to processing circuitry 620 and may refer to any suitable device operable to receive input for network node 315, send output from network node 315, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface 640 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

FIGURE 6 is a block diagram illustrating a radio network node 315 of a wireless communication network according to one embodiment. The radio network node is configured to operate a serving cell serving a wireless device 310. The radio network node is further configured to transmit a request to the wireless device to perform a cell change to a target cell, and transmit information about a system frame number, SFN, used in the target cell to the wireless device, informing the wireless device whether or not to acquire a SFN of the target cell for performing the requested cell change, wherein the information about the SFN indicates whether the SFN used in the target cell is the same as the SFN used in the serving cell.

The radio network node may be configured to operate the target cell, and to receive a random access message for accessing the target cell from the wireless device. In embodiments, the radio network node may be further configured to determine whether or not the UE should acquire the SFN of the target cell for accessing the target cell when performing the cell change. The radio network node may be configured to determine whether or not the UE should acquire the SFN of the target cell by being configured to determine whether the SFN used in the target cell is the same as the SFN used in the serving cell.

The radio network node may be configured to operate a serving cell serving a wireless device, wherein the wireless device is a Machine Type Communication, MTC, device or a Narrowband Internet of Things, NB-IoT, device.

In embodiment, the radio network node may be further configured to determine that the wireless device shall perform the cell change to the target cell based on: a first procedure excluding acquisition of SFN of the target cell, if the SFN of the target cell should not be acquired by the wireless device for accessing the target cell, or a second procedure including acquisition of SFN of the target cell, if the SFN of the target cell should be acquired by the wireless device for accessing the target cell.

As illustrated in FIGURE 6, the radio network node may comprise a processing circuitry 620 and a memory 630. The memory may contain instructions executable by the processing circuitry whereby the radio network node is configured to transmit a request to the wireless device to perform a cell change to a target cell, and transmit information about a system frame number, SFN, used in the target cell to the wireless device, informing the wireless device whether or not to acquire a SFN of the target cell for performing the requested cell change, wherein the information about the SFN indicates whether the SFN used in the target cell is the same as the SFN used in the serving cell.

In embodiments, the memory may contain instructions executable by the processing circuitry, whereby the radio network node is configured to perform the method as described above with reference to FIGURE 2b.

Other embodiments of network node 315 may include additional components beyond those shown in FIGURE 6 that may be responsible for providing certain aspects of the radio network node' s functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solutions described above). The various different types of network nodes may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

FIGURE 7 is a block schematic of an exemplary radio network controller or core network node 700, in accordance with certain embodiments. Examples of network nodes can include a mobile switching center (MSC), a serving GPRS support node (SGSN), a mobility management entity (MME), a radio network controller (RNC), a base station controller (BSC), and so on. The radio network controller or core network node 700 includes processing circuitry 720, memory 730, and network interface 740. In some embodiments, processing circuitry 720 executes instructions to provide some or all of the functionality described above as being provided by the network node, memory 730 stores the instructions executed by processing circuitry 720, and network interface 740 communicates signals to any suitable node, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), network nodes 315, radio network controllers or core network nodes 700, etc.

Processing circuitry 720 may include any suitable combination of hardware and software implemented in one or more modules to execute instructions and manipulate data to perform some or all of the described functions of the radio network controller or core network node 700. In some embodiments, processing circuitry 720 may include, for example, one or more computers, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic.

Memory 730 is generally operable to store instructions, such as a computer program, software, an application including one or more of logic, rules, algorithms, code, tables, etc. and/or other instructions capable of being executed by processing circuitry 720. Examples of memory 730 include computer memory (for example, Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (for example, a hard disk), removable storage media (for example, a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non-transitory computer-readable and/or computer- executable memory devices that store information.

In some embodiments, network interface 740 is communicatively coupled to processing circuitry 720 and may refer to any suitable device operable to receive input for the network node, send output from the network node, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface 740 may include appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

Other embodiments of the network node may include additional components beyond those shown in FIGURE 7 that may be responsible for providing certain aspects of the network node' s functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above). FIGURE 8 is a schematic block diagram of an exemplary wireless device, in accordance with certain embodiments. Wireless device 310 may include one or more modules. For example, wireless device 310 may include an obtaining module 810, a determining module 820, and a performing module 830, and any other suitable modules. In some embodiments, one or more of obtaining module 810, determining module 820, performing module 830, or any other suitable module may be implemented using one or more processors, such as processing circuitry 520 described above in relation to FIGURE 5. In certain embodiments, the functions of two or more of the various modules may be combined into a single module. Wireless device 310 may perform the methods for cell change described above with respect to FIGURES 1-7.

Obtaining module 810 may perform the obtaining functions of wireless device 310. As one example, obtaining module 810 may obtain a request to perform a cell change (e.g., to a target cell) as described above in relation with FIGURES la-2a. In response to obtaining such a request, wireless device 310 may proceed to determine how to perform the cell change. Obtaining module 810 may include or be included in one or more processors, such as processing circuitry 520 described above in relation to FIGURE 5. Obtaining module 810 may include analog and/or digital circuitry configured to perform any of the functions of obtaining module 810 and/or processing circuitry 520 described above. The functions of obtaining module 810 may, in certain embodiments, be performed in one or more distinct modules.

Determining module 820 may perform the determining functions of wireless device 310. As one example, determining module 820 may determine whether wireless device 310 should acquire an SFN of a target cell as described above in relation with FIGURES la-2a. After determining whether wireless device 310 should acquire the SFN, wireless device 310 may determine how to perform the cell change. Determining module 820 may include or be included in one or more processors, such as processing circuitry 520 described above in relation to FIGURE 5. Determining module 820 may include analog and/or digital circuitry configured to perform any of the functions of determining module 820 and/or processing circuitry 520 described above. The functions of determining module 820 may, in certain embodiments, be performed in one or more distinct modules.

Performing module 830 may perform the cell change functions of wireless device 310. For example, performing module 830 may perform the cell change based on a first procedure PI or a second procedure P2 depending on whether wireless device 310 should acquire the SFN of the target cell as described above in relation with FIGURES la, and 2a. Performing module 830 may include analog and/or digital circuitry configured to perform any of the functions of performing module 830 and/or processing circuitry 520 described above. Performing module 830 may include or be included in one or more processors, such as processing circuitry 520 described above in relation to FIGURE 5. The functions of performing module 830 may, in certain embodiments, be performed in one or more distinct modules.

Obtaining module 810, determining module 820, and performing module 830 may include any suitable configuration of hardware (e.g., processing circuitry 520) and/or software. Wireless device 310 may include additional modules beyond those shown in FIGURE 8 that may be responsible for providing any suitable functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the various solutions described herein).

FIGURE 9 is a schematic block diagram of an exemplary network node 315, in accordance with certain embodiments. Network node 315 may include one or more modules. For example, network node 315 may include configuring module 910, determining module 920, and any other suitable modules. In some embodiments, one or more of configuring module 910, determining module 920, or any other suitable module may be implemented using one or more processors, such as processing circuitry 620 described above in relation to FIGURE 6. In certain embodiments, the functions of two or more of the various modules may be combined into a single module. Network node 315 may perform the methods for cell change described above with respect to FIGURES 2a, and 2b.

Configuring module 910 may perform the configuring functions of network node 315. As an example, configuring module 910 may configure a UE to perform a cell change to a target cell as described above with relation to FIGURES 2a. Configuring module 910 may include or be included in one or more processors, such as processing circuitry 620 described above in relation to FIGURE 6. Configuring module 910 may include analog and/or digital circuitry configured to perform any of the functions of configuring module 910 and/or processing circuitry 620 described above. The functions of configuring module 910 may, in certain embodiments, be performed in one or more distinct modules.

Determining module 920 may perform the determining functions of network node 315. As one example, determining module 920 may determine whether a UE should acquire an SFN of a target cell as described with relation to FIGURES 2a. As another example, determining module 920 may determine whether a UE should perform a cell change based on a first procedure or a second procedure as described with relation to FIGURES 2a. Determining module 920 may include or be included in one or more processors, such as processing circuitry 620 described above in relation to FIGURE 6. Determining module 920 may include analog and/or digital circuitry configured to perform any of the functions of determining module 920 and/or processing circuitry 620 described above. The functions of determining module 920 may, in certain embodiments, be performed in one or more distinct modules.

Configuring module 910 and determining module 920 may include any suitable configuration of hardware and/or software. Network node 315 may include additional modules beyond those shown in FIGURE 9 that may be responsible for providing any suitable functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the various solutions described herein).

Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the disclosure. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. Additionally, operations of the systems and apparatuses may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, "each" refers to each member of a set or each member of a subset of a set.

Modifications, additions, or omissions may be made to the methods described herein without departing from the scope of the disclosure. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order.

Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure.

Further examples of methods

1. An example method includes:

obtaining a request to perform a cell change to a target cell (cell2);

determining whether or not a UE should acquire a system frame number (SFN) of cell2 for accessing cell2 for the cell change operation; and

performing the cell change to cell2 based on a first procedure (PI) if the SFN of cell2 should not be acquired by the UE for accessing cell2 or based on a second procedure (P2) if the SFN of cell2 should be acquired by the UE for accessing cell2. 2. The method of example 1, wherein P2 includes acquiring at least part of the system information (SI) of the target cell, the SI including the SFN of the target cell.

3. The method of example 1, wherein determining whether or not the UE should acquire the SFN includes determining whether the UE already knows the SFN.

4. The method of example 1, wherein determining whether or not the UE should acquire the SFN includes referencing a rule that indicates whether to assume the SFN.

5. An example method includes:

configuring a UE to perform a cell change to a target cell (cell2);

determining whether or not the UE should acquire a system frame number (SFN) of cell2 for accessing cell2 for the cell change operation; and

determining that the UE shall perform the cell change to cell2 based on a first procedure (PI) if the SFN of cell2 should not be acquired by the UE for accessing cell2 or based on a second procedure (P2) if the SFN of cell2 should be acquired by the UE for accessing cell2.

6. The method of example 5 further including receiving a cell change message from the UE in cell2 based on the determined procedure used by the UE for performing cell change to cell2.

7. The method of example 5, wherein P2 includes acquiring at least part of the system information (SI) of the target cell, the SI including the SFN of the target cell.

8. The method of example 5, wherein determining whether or not the UE should acquire the SFN includes determining whether the UE already knows the SFN.

9. The method of example 5, wherein determining whether or not the UE should acquire the SFN includes referencing a rule that indicates whether to assume the SFN.

Claims

1. A method performed by a wireless device (310) in a serving cell of a wireless communication network, the method comprising:

- receiving (151) a request to perform a cell change to a target cell, the request being received from a radio network node (315) operating the serving cell,

- receiving (152) information about a system frame number, SFN, used in the target cell from the radio network node,

- performing (154) the cell change to the target cell in response to the request without acquiring the SFN of the target cell, when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell.

2. The method according to claim 1, wherein performing the cell change comprises:

- transmitting a random access message for accessing the target cell.

3. The method according to claim 2, further comprising:

- performing (155) the cell change to the target cell in response to the request, when the received information about the SFN indicates that the SFN used in the target cell is not the same as the SFN used in the serving cell, wherein performing the cell change comprises, before transmitting the random access message:

• acquiring at least part of the system information, SI, of the target cell including the SFN of the target cell.

4. The method according to any of the preceding claims, wherein the wireless device is a Machine Type Communication, MTC, device or a Narrowband Internet of Things, NB- IoT, device.

5. The method according to any of the preceding claims, wherein the wireless device operates in an enhanced coverage mode with regards to the target cell.

6. The method according to any of the preceding claims, wherein the cell change comprises one of: a handover, a RRC re-establishment, a cell selection, a cell reselection, a RRC connection release with redirection, and a swapping between serving cells.

7. A method performed by a radio network node (315) of a wireless communication network, the radio network node operating a serving cell serving a wireless device (310), the method comprising:

- transmitting (251) a request to the wireless device to perform a cell change to a target cell,

- transmitting (253, 254) information about a system frame number, SFN, used in the target cell to the wireless device, informing the wireless device whether or not to acquire a SFN of the target cell for performing the requested cell change, wherein the information about the SFN indicates whether the SFN used in the target cell is the same as the SFN used in the serving cell.

8. The method according to claim 7, wherein the radio network node is operating the target cell, the method further comprising:

- receiving a random access message for accessing the target cell from the wireless device.

9. The method according to any of claims 7-8, the method further comprising:

- determining (252) whether or not the UE should acquire the SFN of the target cell for accessing the target cell when performing the cell change.

10. The method according to claim 9, wherein determining whether or not the UE should acquire the SFN of the target cell comprises:

- determining whether the SFN used in the target cell is the same as the SFN used in the serving cell.

11. The method according to any of claims 7-10, wherein the wireless device is a Machine Type Communication, MTC, device or a Narrowband Internet of Things, NB-IoT, device.

12. The method according to any of claims 7-11, wherein the wireless device operates in an enhanced coverage mode with regards to the target cell.

13. The method according to any of claims 7-12, the method further comprising: - determining that the wireless device shall perform the cell change to the target cell based on: a first procedure excluding acquisition of SFN of the target cell, if the SFN of the target cell should not be acquired by the wireless device for accessing the target cell, or a second procedure including acquisition of SFN of the target cell, if the SFN of the target cell should be acquired by the wireless device for accessing the target cell.

14. The method according to any of claims 7-13, wherein the cell change comprises one of: a handover, a RRC re-establishment, a cell selection, a cell reselection, a RRC connection release with redirection, and a swapping between serving cells.

15. A wireless device (310) in a serving cell of a wireless communication network (300), the wireless device being configured to:

- receive a request to perform a cell change to a target cell, the request being received from a radio network node (315) operating the serving cell,

- receive information about a system frame number, SFN, used in the target cell from the radio network node,

- perform the cell change to the target cell in response to the request without acquiring the SFN of the target cell, when the received information about the SFN indicates that the SFN used in the target cell is the same as the SFN used in the serving cell.

16. The wireless device according to claim 15, configured to perform the cell change by being configured to transmit a random access message for accessing the target cell.

17. The wireless device according to claim 16, further configured to:

- perform the cell change to the target cell in response to the request, when the received information about the SFN indicates that the SFN used in the target cell is not the same as the SFN used in the serving cell, wherein performing the cell change comprises, before transmitting the random access message:

18. The wireless device according to any of claims 15-17, wherein the wireless device is a Machine Type Communication, MTC, device or a Narrowband Internet of Things, NB- IoT, device.

19. The wireless device according to any of claims 15-18, wherein the wireless device is configured to operate in an enhanced coverage mode with regards to the target cell.

20. The wireless device according to any of claims 15-19, wherein the cell change comprises one of: a handover, a RRC re-establishment, a cell selection, a cell reselection, a RRC connection release with redirection, and a swapping between serving cells.

21. A wireless device (310) in a serving cell of a wireless communication network (300), the wireless device comprising a processing circuitry (520) and a memory (530), the memory containing instructions executable by the processing circuitry whereby the wireless device is configured to:

22. The wireless device of claim 21, wherein the memory contains instructions executable by the processing circuitry, whereby the wireless device is configured to perform the method of any of claims 2-6.

23. A radio network node (315) of a wireless communication network, the radio network node being configured to operate a serving cell serving a wireless device (310), the radio network node being further configured to:

- transmit a request to the wireless device to perform a cell change to a target cell,

- transmit information about a system frame number, SFN, used in the target cell to the wireless device, informing the wireless device whether or not to acquire a SFN of the target cell for performing the requested cell change, wherein the information about the SFN indicates whether the SFN used in the target cell is the same as the SFN used in the serving cell.

24. The radio network node according to claim 23, wherein the radio network node is configured to operate the target cell, and to receive a random access message for accessing the target cell from the wireless device.

25. The radio network node according to any of claims 23-24, further configured to:

- determine whether or not the UE should acquire the SFN of the target cell for accessing the target cell when performing the cell change.

26. The radio network node according to claim 25, configured to determine whether or not the UE should acquire the SFN of the target cell by being configured to determine whether the SFN used in the target cell is the same as the SFN used in the serving cell.

27. The radio network node according to any of claims 23-26, configured to operate a serving cell serving a wireless device, wherein the wireless device is a Machine Type Communication, MTC, device or a Narrowband Internet of Things, NB-IoT, device.

28. The radio network node according to any of claims 23-27, further configured to:

- determine that the wireless device shall perform the cell change to the target cell based on: a first procedure excluding acquisition of SFN of the target cell, if the SFN of the target cell should not be acquired by the wireless device for accessing the target cell, or a second procedure including acquisition of SFN of the target cell, if the SFN of the target cell should be acquired by the wireless device for accessing the target cell.

29. The radio network node according to any of claims 23-28, wherein the cell change comprises one of: a handover, a RRC re-establishment, a cell selection, a cell reselection, a RRC connection release with redirection, and a swapping between serving cells.

30. A radio network node (315) configured to, the radio network node comprising a processing circuitry (620) and a memory (630), the memory containing instructions executable by the processing circuitry whereby the radio network node is configured to: - transmit a request to the wireless device to perform a cell change to a target cell,

31. The radio network node of claim 30, wherein the memory contains instructions executable by the processing circuitry, whereby the radio network node is configured to perform the method of any of claims 8-14.

32. A computer program comprising computer readable code which when executed by at least one processor of a wireless device causes the wireless device to carry out the method according to any of claims 1-6.

33. A computer program comprising computer readable code which when executed by at least one processor of a radio network node causes the radio network node to carry out the method according to any of claims 7-14.

34. A carrier containing the computer program of any of claims 32-33, wherein the carrier is a computer readable storage medium.