Patent ID: 12245063

DETAILED DESCRIPTION OF THE EMBODIMENTS

Conventional Communications System

FIG.1provides a schematic diagram illustrating some basic functionality of a mobile telecommunications network/system100operating in accordance with LTE principles and which may be adapted to implement embodiments of the disclosure as described further below.

Various elements ofFIG.1and their respective modes of operation are well-known and defined in the relevant standards administered by the 3GPP® body, and also described in many books on the subject, for example, Holma H. and Toskala A [1]. It will be appreciated that operational aspects of the telecommunications network which are not specifically described below may be implemented in accordance with any known techniques, for example according to the relevant standards.

The network100includes a plurality of base stations101connected to a core network102. Each base station provides a coverage area103(i.e. a cell) within which data can be communicated to and from communications devices104. Data is transmitted from base stations101to communications devices104within their respective coverage areas103via a radio downlink. Data is transmitted from communications devices104to the base stations101via a radio uplink.

The uplink and downlink communications may be made using radio resources that are licenced for exclusive use by the operator of the network100. The core network102routes data to and from the communications devices104via the respective base stations101and provides functions such as authentication, mobility management, charging and so on. Communications devices may also be referred to as mobile stations, user equipment (UE), user device, mobile radio, and so forth. Base stations may also be referred to as transceiver stations/NodeBs/eNodeBs (eNB for short), and so forth.

Wireless communications systems such as those arranged in accordance with the 3GPP defined Long Term Evolution (LTE) architecture use an orthogonal frequency division modulation (OFDM) based interface for the radio downlink (so-called OFDMA) and a single carrier frequency division multiple access scheme (SC-FDMA) on the radio uplink. Other examples of wireless communications systems include those operating in accordance with 5G in which a radio network is formed by infrastructure equipment referred to as wireless transceiver units.

Embodiments of the present technique can provide an arrangement in which a communications device is configured to more efficiently evaluate a neighbour cell and to select the neighbour cell by adapting the rate at which measurements are performed of the neighbour cell in accordance with a set of predetermined conditions with respect to signals received from a serving cell. In particular the present invention for example is configured to provide a more efficient technique for allowing a communications device to perform cell reselection in a situation where the communications device may be disposed indoors in which it is attached to a relatively weak serving cell and may proceed to move out of doors in which case it receives an increase in signal strength from a neighbour cell and by configuring the rate of measurements of the neighbour cell to be adapted in accordance with a relative threshold to the serving cell a communications device can sample the signal strength of neighbour cells in a way which utilises unavailable power of the communications device in a more efficient way.

Embodiments of the present technique therefore relate to a mode in which a communications device is for example in an idle mode in which it performs cell reselection in order to attach to a cell or infrastructure equipment such as an eNB in order to receive downlink signals when these are to be transmitted to the communications device. Accordingly the communications device selects a cell or reselects a cell based upon a relate quality of signals received from the available cells and therefore clamps on to the cell so that the communications device can transition to an active mode for example in order to transmit or receive data from the wireless communications network.

FIG.2provides a schematic representation of a conventional arrangement in which one of the communications devices104shown inFIG.1is configured to perform a reselection technique in which the communications device104selects a neighbour cell to attach to for receiving downlink communications.

As shown inFIG.2the communications device104includes a transmitter circuit201, a receiver circuit202and a controller circuit204. The controller circuit204controls the transmitter circuit and the receiver circuit to transmit and receive signals via a wireless access interface performed by a radio network part of a mobile communications network. The radio network part may include a plurality of infrastructure equipment such as eNB's as shown inFIG.1. As shown inFIG.2, three infrastructure equipment are shown,210,212,214.

InFIG.2, each of the eNBs210,212,214, provides a single coverage area (or cell), such as the cells103ofFIG.1. In some situations, a base station or eNB, such as eNB210may generate multiple coverage areas or cells (not shown). Whether or not they are generated by the same eNB, cells may overlap in their geographic coverage, and may use the same or different frequency and/or time resources.

In the following description, it is assumed that each eNB generates one cell and hence the terms eNB and cell are used interchangeably. However it will be readily apparent that the embodiments described herein are equally applicable regardless of the number of cells generated by an eNB.

According to the example illustrated inFIG.2the communications device104is currently camped on a serving eNB210. That is to say the communications device104has selected the serving eNB210in order to receive downlink signals should these be transmitted by the wireless communications network and/or to initiate uplink communications should the need arise. As such, at any given instant, the UE104may or may not have an active connection with serving eNB210(in other words, there may be no ongoing data transfer in either the uplink or downlink). According to a conventional arrangement the serving eNB is identified by the network with respect to the communications device104by storing an indication of the serving eNB210in mobility management entity forming part of the communications core network102.

Cells generated by eNBs212,214, which are not the serving cell may include neighbour cells. These neighbour cells may be identified to the UE by means of signalling from the serving eNB210. Additionally or alternatively, these cells may be identified autonomously by the UE.

In accordance with a conventional arrangement the communications device104performs measurements of neighbour cells which are transmitting signals such as synchronisation signals or broadcast signals including cell-specific reference signals which can be measured by the communications device104using the receiver202.

The communications device104monitors signals transmitted by the serving eNB210such as from the SIB or beacon transmissions and determines a received signal strength metric of the serving cell.

The received signal strength metric maybe for example a Reference Signal Received Power (RSRP) or Received Signal Strength Indicator (RSSI) which are measurements used in LTE. The RSSI is a measure of the total received power observed only in OFDM symbols containing reference symbols for an antenna port in the measurement bandwidth over N reference Blocks. RSRP is defined as the linear average over the power contributions of the resource elements which carry cell-specific reference signals. The signal strength metric may be a metric indicative of the path loss incurred by signals transmitted by an eNB (such as serving eNB210) and received by the communications device104. As such, the signal strength metric may indicate that there is a high likelihood that signals transmitted by eNB210will be received with sufficient received signal power by communication device104's receiver circuit202that error-free or at least a low error rate decoding of encoded data therein is possible and, similarly, that signals transmitted by communication device104's transmitter circuit201can be received and decoded by eNB210.

In some examples of NB-IoT devices, repetition coding is used in which signals are transmitted repeatedly in order to improve a likelihood of correctly receiving the data which they are carrying. As such a so-called ‘coverage extension’ is achieved for such devices. However this can mean that such devices are operating at relatively low signal to noise ratios, which can affect a cell reselection procedure.

The communications device104compares the determined received signal strength metric of the serving cell with respect to a predetermined threshold. Only if the metric falls below this predetermined threshold does the communications device begin to monitor signals transmitted by the neighbour eNB's212,214in order to determine whether the communications device should reselect one of these eNB's, that is to say, should perform the actions necessary for the selected one of the eNBs212,214to become the communication device's serving eNB.

In some examples, these actions may include identifying to the communications network that the communications device has selected the one of the eNBs212,214as its new serving eNB and can receive signals from this reselected cell if the communications network wishes to transmit signals or data to the communications device104. In some examples these actions may be conditional on an identifier associated with the selected one of the eNBs being different from a corresponding identifier associated with the serving cell. In some examples, these actions may include identifying to an entity within the core network102the identifier associated with the selected one of the eNBs.

FIG.3provides a graphical representation of a conventional arrangement in which the communications device104determines whether or not it should perform measurements of neighbour cells.FIG.3provides a graphical plot of possible signal quality and signal strength metrics based on the measurements of signals transmitted by the serving eNB210and received by the receiver circuit202.

The received signal strength metric may be, for example, RSRP as described above. The signal quality metric may be an Reference Signal Received Quality (RSRQ) metric, defined as the ratio N×RSRP/(E-UTRA carrier RSSI), wherein N is the number of resource blocks of the E-UTRA carrier RSSI measurement bandwidth. The signal quality metric may indicate the absolute or relative (with respect to the strength of the desired signal from e.g. serving eNB210) extent of interference detected in the signal received by the receiver202of communications device104. The metric may be an Squal metric, defined as Qqualmeas-Qqualmin-Pcompensation-Qoffset in accordance with 3GPP TS 36.304 v14.2.0.

As shown inFIG.3a threshold300is shown with respect to the signal strength of the serving cell. If the signal strength of the received signals has for example calculated in accordance with an RSRP measurement falls below the threshold300then the metrics associated with the signals received from the serving cell form part of a region302in which the communications device104begins to measure signals received from the neighbour eNBs212,214in order to determine whether or not to perform cell reselection. If however the RSRP or signal strength value received by the receiver circuit202is above the threshold300then no measurements are performed of the signals transmitted by the neighbour cells because the strength of the signal received from the serving cell210is sufficient for the communications device to transmit or receive signals to the mobile communications network.

A flow diagram representing the operation of the communications device in order to perform a conventional cell reselection is shown inFIG.4.FIG.4will be briefly summarised as follows:

S1: At a starting operation a communications device proceeds to step S2to perform measurements of the RSRP value of the serving cell provided for example by the serving eNB210.

S4: The signal strength measurements received by the receiver unit of circuit202are compared to a predetermined threshold Thresh_1. Thresh_1may correspond to an S-IntraSearchP parameter. The signal strength measurement may be evaluated as Srxlev=Qrxlevmeas-Qrxlevmin-Pcompensation-Qoffsettemp in accordance with an LTE standard, such as 3GPP TS 36.304, where Qrxlevmin may be a minimum required signal level for a cell to be suitable to camp on (i.e. act as serving cell). If the RSRP signal strength value exceeds the predetermined threshold Thresh_1then processing proceeds to step S2in order to continue to monitor the signal strength of signals received from the serving cell. In some examples a delay may be incurred before proceeding back to S4in order to re-evaluate the received signal strength measurements or RSRP with respect to the threshold Thresh_1.

S6: If however the evaluation at step S4the signal strength or RSRP is determined to be below the threshold Thresh_1then the communications device104begins to perform measurements of the signals received from one or more neighbour cells provided by the neighbour eNBs212,214.

Depending on the relative location of the device104and eNBs212and214, the device may not be able to identify any signals as having been transmitted by the neighbour eNBs. Alternatively, the device may be able to identify and measure one or more metrics associated with the transmissions from eNB212and/or eNB214. The measurements of the neighbour cells may be signal strength measurements, signal quality measurements, or any other measurement appropriate to form the basis of a determination as to whether a particular neighbour cell should be selected as a new serving cell for the communications device.

The terms “measure neighbour cells” or “measure signals received from a neighbour cell” and the like may, therefore, refer to the step of attempting to identify signals associated with one or more candidate cells (e.g. transmitted by a respective eNB) for reselection, as well as measuring one or more properties of such signals if any are identified.

S8: The controller circuit of the eNB104performs an evaluation of the neighbour cell measurements. The device104determines whether it should select any of the identified neighbour cells (which may be provided by the neighbour eNBs212,214) in order to receive downlink communications or effectively camp on to this cell. In other words, the device104determines whether to perform cell reselection to an identified neighbour cell. The determination of whether it should select any neighbour cell to be a new serving cell (i.e. perform cell reselection) may be in accordance with a conventional reselection algorithm, such as those defined in 3GPP TS 36.304 for LTE and NB-IoT communications systems.

EXAMPLE EMBODIMENTS

FIG.5provides an illustrative example with which the present technique finds application in order to perform a more efficient way of cell reselection. As shown inFIG.5, two cells500,502are shown which are formed by two eNBs or infrastructure equipment210,212. As for the example shown inFIG.2, a first eNB210forms a serving cell to two communications devices504,506. The second eNB212forms a neighbour eNB and therefore forms the neighbour cell502. As shown inFIG.5, the first UE504is mobile as represented by an arrow510and is moving away from the serving eNB210towards the neighbour eNB212. In contrast the second UE506is in an indoor environment because it is installed or present within a house or building512. As a result of the relative positions of the UE's504,506the signal strength of received signals in the form for example of RSRP is illustrated by the graphical plot shown inFIG.6.

FIG.6provides a graphical plot of signal strength or RSRP value associated with the signals transmitted by eNB210, with respect to distance from the serving eNB210. As shown by first plot600for the first UE504, there is a decline in signal strength value as the UE504moves away from the serving eNB210. However the signal strength only gradually approaches the predetermined threshold Thresh_1, below which device504triggers a process in which it monitors the signal strength of the neighbour cells (such as neighbour cell502) and enters a situation corresponding to region302ofFIG.3. In contrast the second UE506experiences a sudden decline in signal strength or RSRP value with respect to distance because the second UE506moves within the house512which means that it observes significantly greater path loss with respect to the communications link between it and eNB210. Since it determines that the RSRP value associated with the serving cell has fallen below the threshold Thresh_1, it is in a situation corresponding to region302ofFIG.3, and device506initiates the measurement and evaluation of signals received from neighbour cells.

As can be seen fromFIGS.5and6, neither device504nor device506is served effectively by the existing neighbour cell reselection approach. Device504is entering coverage of cell502, but because it determines that the signal strength metric associated with its serving cell remains above the threshold Thresh_1, it does not initiate the measurement and/or evaluation of the signals received from eNB212providing cell502, even though cell502provided by eNB212is a more appropriate cell. Although it is still able to obtain service from cell500, it will require higher transmit power for UE504to transmit at a given data rate to eNB210than it would if it were to transmit to eNB212. Furthermore, transmissions between device504and eNB210will give rise to unnecessary levels of interference to other devices operating on the same frequency (which may include eNB212). This may in turn reduce the overall system capacity (i.e. considering the transmissions of a plurality of eNBs and associated devices).

On the other hand, device506is required to perform neighbour cell measurements based on the high path loss experienced by signals from eNB210. However, in this case, it is already camped on the most appropriate cell, and (since it is stationary) is unlikely to determine that any other cell is more appropriate in the future.

When applied to radio technologies provided enhanced coverage, such as in accordance with a NB-IoT standard, which may provide coverage enhancements of up to 20 dB compared to conventional LTE, the measurement threshold Thresh_1may be set to a relatively low absolute value to ensure that indoor/stationary UEs are not required to continuously measure. While a low threshold may address the problems described above in respect of device506, it exacerbates the problems described above, related to device504.

Some embodiments of the present technique to enhance the neighbour cell measurement process recognise that when a UE such as device504moves from a serving cell (such as cell500) towards a neighbouring cell (such as cell502), both the measured signal strength (e.g. RSRP) and signal quality (e.g. RSRQ) of the signals received from the serving cell500will drop; however, the signal quality may drop more quickly due to the effect of interference from the neighbour cell.

Some example embodiments of the present technique can enhance a neighbour cell measurement process by arranging a rate at which neighbour cell measurements in response to a requirement to more quickly evaluate neighbour cells to perform more urgently a cell reselection process. Furthermore the urgency with which cell reselection is required may depend on one or both of the path loss and interference which affects signals transmitted by a serving eNB and which are received by a device.

Embodiments of the present technique can provide a more efficient cell reselection process which reduces the power consumption of a communications device and also provides an earlier measurement of neighbour cell signals so that the communications device can more quickly reselect a neighbour cell if there is some degradation in the received signal strength from the serving cell.FIG.7provides an example block diagram of the operation of the communications device such as that shown inFIG.2but according to an embodiment of the present technique.FIG.7is summarized as follows:

S100—At the start the communications device is already attached to or camped on a serving eNB or a serving cell. The communications device may have ongoing data communications with the serving eNB, for example it may have established a bearer and/or may be encoding and transmitting data and/or receiving signals and decoding them to recover the transmitted underlying data. Alternatively the device may be in an idle state with no ongoing communications.

S102—The communications device first performs a measurement of the signal strength of signals received from the serving cell or serving eNode B such as in the form of the RSRP measurement. In some embodiments, step S102may be substantially the same as step S2ofFIG.4.

S104—The communications device then compares the RSRP value or signal strength of signals received from the serving cell with respect to a predetermined threshold Thresh_1which may be the same threshold as the threshold300shown inFIG.3for a conventional arrangement. If the received signal strength is below the threshold then processing proceeds to step S106. If however the received signal strength or RSRP value is above the predetermined threshold then processing proceeds to step S108. In some embodiments step S104may be substantially the same as step S4ofFIG.4.

S106—If the RSRP signal strength value is above the threshold Thresh_1then processing proceeds to evaluate the radio signals received from the serving cell and compare the results of this evaluation with respect to predetermined conditions. In accordance with these predetermined conditions, if these conditions are satisfied then processing proceeds to step S110. If not, then measurements of neighbour cells ceases if they are currently occurring and processing proceeds back to step S102and the communications device continues to measure the signal strength of the serving cell.

In some embodiments, the measurements of neighbour cells ceases only after an elapsed time has occurred. The elapsed time may be calculated starting at the point where the evaluation at step S106determined that the serving cell signal measurements no longer fulfilled the requirements for neighbour cell measurements to occur, or the elapsed time may be a minimum time, starting at the time where measurements were most recently started.

If the predetermined conditions in step S106are satisfied then in step S110the communications device begins to measure the signals received from the neighbour cells at a second rate. In some embodiments the second rate is different from the first rate as is performed in step S108. In some embodiments, the second rate is selected from the range of approximately once every second to approximately once every minute.

S108—If the RSRP or signal strength value is below the predetermined threshold Thresh_1then the communications device begins to evaluate signals received from neighbour cells at a first rate.

Since the signal strength or RSRP value has fallen below the predetermined threshold Thresh_1then the rate at which the signals are sampled or measured from the neighbour cells is at the first rate. As described above in respect of step S6, the evaluation of neighbour cell signals may include an identification step to determine if in fact, any signals can be identified has having been transmitted by a neighbour cell. The evaluation of neighbour cell signals may be include determining a signal strength (or other measure generally indicative of path loss), signal quality (or other measure generally indicative of a signal to noise ratio, a signal to interference ratio, or an absolute interference measurement), or both, in respect of signals identified as being transmitted by a particular neighbour cell.

In some embodiments, the first rate is higher than the second rate. This is because the communications device is already in a position in which the signal strength has fallen below the predetermined threshold in which the communications device should consider reselecting another cell than the serving cell. In some embodiments, the first rate may be in accordance with the requirements of a conventional LTE or an NB-IoT standard. In some embodiments, the first rate may correspond to a gap between measurements in the order of a few milliseconds, for example, once every five milliseconds. In some embodiments, the first rate and the second rate are the same.

In some embodiments, the measurements of neighbour cells starts only after an elapsed time has occurred. The elapsed time may be calculated starting at the point where the evaluation at step S106or step S104determined that the serving cell signal measurements fulfilled the relevant criteria, or the elapsed time may be a minimum time, starting at the time where measurements were most recently stopped.

S112—Based on the measurements received or evaluated from the neighbour cells, the communications device then determines if it should reselect to a neighbour cell based on these measurements acquired at the second rate R2. If no, then processing proceeds back to S102but if yes then processing proceeds to step S114in which the communications device performs cell reselection and processing stops at S116.

S118—If the measured values of the neighbour cells signal strength at the first rate indicate that cell reselection should be performed to select a neighbour cell then again processing proceeds from step S118to perform cell reselection in step S114. Otherwise processing proceeds back to the measured signal strength of the serving cell in step S102. In some embodiments, step S118proceeds in a similar manner to step S8ofFIG.4.

The determination that a neighbour cell meets the criteria for reselection may be based the absolute values of the measurement of signals received from the neighbour cell or the relative values of the measurements (compared to those of either the serving cell, other neighbour cells, or both). The neighbour cell reselection criteria may be based on a ranking of cells (which may include the serving cell). The reselection criteria may be the same for both steps S112and S118, in which case the determination as to whether the reselection criteria are met may be made without regard to whether the measurements were obtained at the first rate R1or at the second rate R2. In some embodiments, the determination as to whether the reselection criteria are met may be made based on one or more measurements obtained at the first rate R1(e.g. obtained as part of step S108) and one or more measurements obtained at the second rate R2(e.g. obtained as part of step S110). In some embodiments, the reselection criteria for steps S112and S118may differ in light of the different rates at which measurements are obtained. Reselection may be based on one or more parameters in addition to the signal strength and/or signal quality, and may include restrictions (e.g. by means of hysteresis offsets or timing constraints) to avoid reselection ping-pong whereby a device repeatedly changes serving cell with high frequency.

Cell reselection criteria may include one or more of an absolute threshold applicable to the signal strength of a neighbour cell, an absolute threshold applicable to the signal quality of a neighbour cell, a relative threshold comparing the signal strength of a neighbour cell with the signal strength of the serving cell, a relative threshold comparing the signal strength of a neighbour cell with the signal quality of the serving cell, a ranking algorithm, an algorithm based on absolute priorities (which may be individual priorities applicable to the device, or priorities applicable to all devices in the serving cell).

The Cell reselection criteria may be based on a plurality of comparable measurements, which are combined by averaging or filtering. The cell reselection criteria may include a time threshold, such that the criteria must be fulfilled for a continuous time period exceeding the time threshold.

S114—If in either step S112or step S118the device determines that a neighbour cell fulfils the neighbour cell reselection criteria, then control passes to step S114and the device performs cell reselection. That is to say, the device performs the necessary steps to receive service in the selected neighbour cell. This may include one or more of receiving and decoding system information of the neighbour cell, performing an update to inform the network of the cell reselection, and updating the internal state of the device to reflect the cell reselection.

S116—On completion of the cell reselection procedure, the device may start the entire process from step S100, with the newly-selected cell being the serving cell.

FIGS.8a,8band8cprovide graphical representations of the relative rates of sampling of the measured neighbour cell signal strength performed by the steps S108and S110shown inFIG.7and the corresponding conditions (as evaluated in steps S104and S106) in which they are applicable. As shown inFIG.8a, if the signal strength or RSRP value of the serving cell falls below the second threshold Thresh_2800(which is higher than the first threshold Thresh_1806) the signal strength of the neighbour cells is sampled at the second rate802which is slower than the first rate R1804. Neighbour cell measurements are evaluated at the first rate if the signal strength or RSRP value is below the first threshold Thresh_1806.

FIG.8bprovides a further example in which the communications device performs the measurements of the neighbour cells at the second sampling rate only if the signal strength or RSRP of received signals from the serving cell is above the first threshold Thresh_1806and the signal quality or the RSRQ of the signals received from the serving cell is below a quality threshold Q_Thresh_1810.

In the third example shown inFIG.8c, if the strength or RSRP of signals received from the serving cell are above the first threshold Thresh_1806but below a third threshold Thresh_3816(higher than the first threshold Thresh_1806) then no measurements are performed whereas if the signal quality or RSRQ value is below a second threshold Q_Thresh_2820and the strength or RSRP of signals is above the third threshold Thresh_3816then the signals are measured of the neighbour cells at the second rate R2.

In some embodiments, Thresh_1is set to ensure that the device is, with high likelihood, able to obtain service from the serving cell when the measured RSRP of the serving cell is at or above Thresh_1.

In some embodiments, Thresh_2or Thresh_3is set such that the device is likely to initiate measurements of neighbour cells once it is able to obtain better service (e.g. to be able to transmit at the same data rate using lower transmit power) from a neighbour cell than from the serving cell.

In some embodiments, a threshold may be adapted based on the signal strength or signal quality of the serving cell crossing another threshold. For example, with respect to the conditions illustrated inFIG.8B, in some embodiments, Thresh_1is increased (e.g. by a predetermined factor) when the signal quality (RSRQ) falls below Q_Thresh_1.

In some embodiments, the rate of measurements R1and R2are equal, but a third rate (higher than rates R1and R2and, in some embodiments, equal to the rate at which measurements occur according to a conventional arrangement) applies if and only if both a signal strength measurement (e.g. RSRP) and a signal quality measurement (e.g. RSRQ) fall below their respective thresholds (e.g. Thresh_1and Q_Thresh_1respectively ofFIG.8B).

In some embodiments in accordance with the scheme illustrated inFIG.8C, the third threshold Thresh_3816is set such that, with increased likelihood, indoor devices receive signals from the serving cell with an RSRP lower than the third threshold, while devices which are outdoors receive signals from the serving cell with an RSRP greater than the third threshold.

In some embodiments, some or all of the thresholds may be predetermined and specified in an appropriate specification, for example 3GPP TS 36.304. In such embodiments, the thresholds may be specified as being relative to a threshold which is transmitted in broadcast signalling by the serving cell.

In some embodiments, some or all of the thresholds are transmitted in broadcast signalling by the eNB associated with the serving cell, such as by eNB210. Each threshold may be signalled explicitly (e.g. based on encoding an absolute value) or relatively (e.g. where the difference between two thresholds is encoded), or determined according to a predetermined relationship, for example, Thresh_2may be defined as being three times Thresh_1.

In some embodiments, the evaluations of the neighbour cell signals occur periodically in accordance with a rate determined according to the descriptions above. In some embodiments, the evaluation of the reselection criteria (e.g. in steps S118and S112ofFIG.7) occur more or less frequently than the evaluation of the serving cell signal in step S102.

In some embodiments, events which are described as happening “at a rate” or similar, may occur periodically. In some embodiments, events may occur at times scheduled by the controller204which are sufficiently close together to ensure that outcomes (such as cell reselection) may occur within a predetermined time starting from a time at which certain predetermined conditions are met. This may include the possibility that such events occur at an instantaneous rate which is higher or lower than a rate described herein.

Various aspects and features of the present technique are defined in the appended claims. Various modifications may be made to the example embodiments as disclosed above as appreciated by the skilled person within the scope of the appended claims. Various further example embodiments and features are defined in the following numbered paragraphs:

Paragraph 1. A method of performing cell reselection by a wireless communications device, the method comprising:measuring a signal strength of radio signals received from a serving cell,determining whether the signal strength of the signals received from the serving cell is lower than a first predetermined signal strength threshold,if the signal strength is lower than the first predetermined signal strength threshold measuring signals received from a neighbour cell operating on the same frequency as the serving cell to generate neighbour cell measurements at a first rate, andin accordance with the neighbour cell measurements of the neighbour cell generated at the first rate determining whether to reselect to the neighbour cell, andif the signal strength of the signals received from the serving cell is greater than the first predetermined signal strength threshold and the radio signals received from the serving cell satisfy one or more predetermined conditions based on at least one of the measured signal strength of the signals received from the serving cell and a measured signal quality of the signals received from the serving cell, measuring the signals received from the neighbour cell to generate neighbour cell measurements at a second rate, and in accordance with the neighbour cell measurements of the neighbour cell generated at the second rate determining whether to reselect to the neighbour cell.

Paragraph 2. A method of paragraph 1, wherein the second rate is less than the first rate.

Paragraph 3. A method of paragraph 1, wherein the second rate is different to the first rate.

Paragraph 4. A method of paragraph 1, 2 or 3, wherein the one or more predetermined conditions of the radio signals received from the serving cell for measuring the signals received from the neighbour cell at the second rate, include a condition that the measured signal strength of the radio signals received from the serving cell is higher than the first predetermined signal strength threshold and a condition that the measured signal strength of the radio signals received from the serving cell is lower than a second predetermined signal strength threshold.

Paragraph 5. A method of paragraph 1, 2 or 3, wherein the one or more predetermined conditions of the radio signals received from the serving cell for measuring the signals received from the neighbour cell at the second rate, include a condition that the measured signal strength of the radio signals received from the serving cell is higher than the first predetermined signal strength threshold and a condition that the measured signal quality of the signals received from the serving cell is lower than a first predetermined signal quality threshold.

Paragraph 6. A method of paragraph 5, wherein the one or more predetermined conditions of the radio signals received from the serving cell for measuring the signals received from the neighbour cell at the second rate, include a condition that the measured signal strength of the radio signals received from the serving cell is higher than a third predetermined signal strength threshold and the measured signal quality of the signals received from the serving cell is lower than a second predetermined signal quality threshold.

Paragraph 7. A method of any of paragraphs 1 to 6, comprisingdetermining that the signal strength of the radio signals received from the serving cell is greater than the first predetermined signal strength threshold and determining that the signals received from the serving cell do not satisfy the predetermined conditions, and if the signal strength of the radio signals is greater then the first predetermined threshold and the signals received from the serving cell do not satisfy the predetermined conditions, stopping the measurement of the signals received from the neighbour cell.

Paragraph 8. A method of any of paragraphs 1 to 7, wherein the neighbour cell measurements comprise at least one of a signal strength measurement and a signal quality measurement.

Paragraph 9. A method of any of paragraphs 2 to 8, comprising:receiving from an infrastructure equipment associated with the serving cell at least one of the first predetermined signal strength threshold, the second predetermined signal strength threshold, the third predetermined signal strength threshold, the first predetermined signal quality threshold and the second predetermined signal quality threshold.

Paragraph 10. A communications device configured to transmit radio signals to and/or receive radio signals from an infrastructure equipment of a wireless communications network, the communications device comprisinga receiver circuit configured to receive radio signals transmitted by the infrastructure equipment via a wireless access interface,a transmitter circuit configured to transmit radio signals to the infrastructure equipment via the wireless access interface, anda controller circuit configured to control the transmitter circuit and the receiver circuit to transmit data to or receive data from the wireless communications network via the infrastructure equipment, wherein the controller circuit is configured to control the receiver circuitto measure signals strength of the radio signals received from a serving cell formed by an infrastructure equipment of the wireless communications network,to determine whether the signal strength of the signals received from the serving cell is lower than a first predetermined signal strength threshold, andif the signal strength is lower than the first predetermined signal strength threshold measuring a signal received from a neighbour cell operating on the same frequency as the serving cell to generate neighbour cell measurements of the neighbour cell at a first rate, andin accordance with the neighbour cell measurements of the neighbour cell generated at the first rate determining whether to reselect to the neighbour cell, andif the signal strength of the signals received from the serving cell is greater than the first predetermined signal strength threshold and the radio signals received from the serving cell satisfy one or more predetermined conditions based on at least one of the measured signal strength of the signals received from the serving cell and a measured signal quality of the signals received from the serving cell, to measure the signals received from the neighbour cell to generate neighbour cell measurements at a second rate, and in accordance with the neighbour cell measurements of the neighbour cell generated at the second rate to determine whether to reselect to the neighbour cell.

Paragraph 11. A communications device according to paragraph 10, wherein the second rate is less than the first rate.

Paragraph 12. A communications device according to paragraph 10, wherein the second rate is different to the first rate.

Paragraph 13. A communications device according to any of paragraphs 10, 11 or 12, wherein the one or more predetermined conditions of the radio signals received from the serving cell for measuring the signals received from the neighbour cell at the second rate include a condition that the measured signal strength of the radio signals received from the serving cell is higher than the first predetermined signal strength threshold and a condition that the measured signal strength of the radio signals received from the serving cell is lower than a second predetermined signal strength threshold.

Paragraph 14. A communications device according to any of paragraphs 10, 11 or 12, wherein the one or more predetermined conditions of the radio signals received from the serving cell for measuring the signals received from the neighbour cell at the second rate, include a condition that the measured signal strength of the radio signals received from the serving cell is higher than the first predetermined signal strength threshold and a condition that the measured signal quality of the signals received from the serving cell is lower than a first predetermined signal quality threshold.

Paragraph 15. A communications device according to any of paragraphs 10, 11 or 12, wherein the one or more predetermined conditions of the radio signals received from the serving cell for measuring the signals received from the neighbour cell at the second rate, include a condition that the measured signal strength of the radio signals received from the serving cell is higher than a third predetermined signal strength threshold and the measured signal quality of the signals received from the serving cell is lower than a second predetermined signal quality threshold.

Paragraph 16. A communications device according to any of paragraphs 10 to 15, wherein the controller circuit is configured to control the receiver circuitto determine that the signal strength of the radio signals received from the serving cell is greater than the first predetermined signal strength threshold and determining that the signals received from the serving cell do not satisfy the predetermined conditions, andif the signal strength of the radio signals is greater than the first predetermined threshold and the signals received from the serving cell do not satisfy the predetermined conditions, to stop the measurement of the signals received from the neighbour cell.

Paragraph 17. A communications device according to any of paragraphs 10 to 16, wherein the neighbour cell measurements comprise at least one of a signal strength measurement and a signal quality measurement.

Paragraph 18. A communications device according to any of paragraphs 10 to 16 whereinthe controller circuit is configured to control the receiver circuit to receive from the infrastructure equipment at least one of the first predetermined signal strength threshold, the second predetermined signal strength threshold, the third predetermined signal strength threshold, the first predetermined signal quality threshold and the second predetermined signal quality threshold.

REFERENCES

[1] LTE for UMTS: OFDMA and SC-FDMA Based Radio Access, Harris Holma and Antti Toskala, Wiley 2009, ISBN 978-0-470-99401-6.[2] “(draft) Email discussion report [97bis #31][NB-IoT] Cell reselection for NB-IoT”, Ericsson, published on 3GPP TSG RAN WG2 email reflector, 18 Apr. 2017[3] 3GPP TS 36.304[4] R2-1702929 “Cell reselection issue for NB-IoT”, China Mobile Communications (CMCC)