Paging procedure at a user equipment

Abstract

A user equipment (UE) comprises a primary (main) communication unit which is configured to support communications with a network over at least a first and second frequency band. The UE also comprises

Description

Field of the Disclosure The present disclosure relates to the paging procedure at a user equipment (UE). More specifically, the disclosure relates to a UE and a method for configuring a UE. The UE may comprise a low power receiver and a main receiver. The main receiver supports operation on at least a first and a second frequency band and the low power receiver supports operation on a third frequency band. The first frequency band is different to the second and third frequency band. Background to the Disclosure The battery life of a mobile device or user equipment (UE) is an important consideration in all telecommunication systems (and especially 5G), along with throughput, latency, and reliability. The set of possible use cases for a particular device is affected by the length of its battery life, and therefore several efforts have been undertaken in order to achieve a higher energy efficiency or reduced battery consumption of UEs in 5G. In 3rd Generation Partnership Project, 3GPP Release 16 and 17, it was recognized that one of the procedures that consumes a substantial amount of power in a UE is the paging procedure. The paging procedure is the mechanism by which an entity in a telecommunication network alerts a user equipment (UE) or user device that there is data waiting to be received at said UE. The network entity will send a paging message during a specific paging occasion. The paging message may be sent to a group of UEs connected to a certain cell, and the paging message includes information on the identity of the specific UE to which the subsequent data (e.g. a message, or call to connect) is addressed. The paging occasion denotes a specific period in which the paging message will be sent, allowing the UE to only be ‘woken’ during the paging occasion in order to receive the paging message. This reduces energy usage at the device, as in periods outside of paging occasions and where the UE is not in use, the UE can be placed in an idle state. Said wake-up periods to be able to monitor a Paging Occasion (PO) are determined by a discontinuous reception (DRX) cycle. The DRX cycle can be extended to allow the UE to sleep during longer periods of time; however, this will lead to increased latency, which may not be suitable for certain use cases. Nevertheless, according to the provisions of Release 16, even during periods where there is no signalling or data traffic, the UE will still need to periodically wake up once per DRX cycle (during the paging occasion, regardless of whether a paging message was sent by the network or not. In view of this, to further reduce power consumption, in 3GPP Release 17 a new procedure was introduced to provide a Paging Early Indication (PEI), through which the gNB or the core network provides an indication to the UE whether or not to monitor the next PO (whereby the PEI provides the UE an indication if it is going to be paged). In the case in which a UE is indicated by the PEI not to monitor the next paging occasion, then the UE will go to a sleep or remain in idle mode and so reduce its power consumption. A further extension to this concept was suggested in 3GPP Release 18 and specified in 3GPP Release 19. This suggested employing an additional receiver at the UE, specifically for monitoring for receipt of a wake-up signal (largely equivalent to the PEI in Release 17). More specifically, this approach provides a low-powered receiver in the UE, separate from the main radio receiver, that can be configured to send a trigger to wake up the main receiver i.e. in order to receive a paging message. Said Low-Power Wake Up Receiver (LP-WUR) can monitor an ultra-low power wake-up-signal (LP-WUS) sent by the gNB, wherein the LP-WUS indicates whether to wake up the main receiver (MR) to receive paging message or to allow it to be in a deeper sleep mode if not triggered. The aim of adding low powered wake up receivers to an UE architecture is to allow the main receiver (MR) of the device to be kept in lower energy consumption states (i.e. sleep states) for longer periods of time, only “waking up” whenever it is triggered by a low-power low complexity receiver (LP-WUR). The overall architecture described in this prior art approach can be seen in FIGURE 1. Here, the main radio receiver 140 remains “off” (i.e. in a sleep mode) as long as a wakeup signal has not been received at an ultra-low-power wake-up receiver 150. . However, when the ultra-low-power wake-up receiver 150 receives a signal 155 that the main radio receiver 140 should ‘wake-up’ to receive a paging message, then the ultra-low-power wakeup receiver 150 sends a trigger 165 to the main radio receiver 140 to “wake-up”. In many cases, the UE manufacturers have preferred to implement the low-power low complexity receiver (LP-WUR) to operate on only a subset of the frequency bands supported by the main receiver. This is because the addition of more frequency bands increases overall complexity and costs, and can also increase the battery consumption of the low complexity receiver. In this case, the main receiver (MR), once woken up to receive a paging message, may receive the paging message on a different frequency band than the low complexity receiver which received the LP-WUS. Preferably, the low complexity receiver will operate on a lower frequency band (for instance, below 1 GHz) as this will provide a greater range (and so coverage) than use of the higher frequency bands supported by the main receiver (for instance, bands up to and including 3.5 GHz). As such, in a particular example as shown in FIGURE 3 (and discussed in greater detail below), the low complexity receiver may monitor for a LP-WUS on a band at 700 MHz, and then ‘wake-up’ the main receiver to receive a paging message on a band at 3.5 GHz. In principle, it should be possible to allow the low complexity receiver and the main receiver to operate using different frequencies in this way. However, some drawbacks have been identified. In particular, the different inherent range or coverage of the low frequency signal 200 (e.g. at 700 MHz) compared to the high frequency signal 250 (e.g. at 3.5 GHz) (see FIGURE 2) can mean that, although a LP-WUS is received by a UE 300, the signal at the main receiver may be poor or insufficient to receive the paging message. This can cause the paging message not to be received, even though the main receiver has been woken by the low-power receiver, Moreover, in an attempt to further conserve energy usage, the low complexity receiver can perform serving cell measurements (i.e. measurement of signal strength) in place of the main receiver. However, where the low complexity receiver and main receiver operate on different frequency bands, this can result in an inaccurate measurement of the signal strength for the main receiver when based on measurements at the low complexity receiver. A number of approaches have been proposed to counteract these problems. In relation to the signal strength measurements, one proposal is to impose a delta factor when performing measurements of signal strength, in order to take account of the difference in the estimated signal strength at the main receiver when based on measurements at the low complexity receiver using a different frequency band than the main receiver. However, this would not necessarily mitigate against receipt of a LP-WUS at the low complexity receiver whilst having insufficient coverage at the main receiver. An alternative approach has been suggested to maintain operation of the main receiver and the low complexity receiver in the same frequency band, but for the network entity (gNB) to assign a higher priority to the frequency with LP-WUS deployment. However, this could severely limit user traffic capacity, particularly in the case where the low complexity receiver only supports lower frequency bands. Low frequency bands have limited band width, and so there would be a risk of overloading such bandwidth limited bands (e.g. low frequency bands e.g. 700 MHz typically provide only 10 MHz of bandwidth, and may often have further capacity reduction from the use of 4G / 5G Dynamic Spectrum Sharing). Thus, it is an objective of the present invention to address these problems. Summary of the Disclosure In view of the above, the present disclosure describes a method for configuring a UE according to claim 1 and a user equipment according to claim 20. The UE has at least one primary communication unit (being a main radio transceiver) and a secondary communication unit (being a low-power radio receiver). The secondary communication unit is arranged to receive a low power ‘wake-up’ signal from a network entity or node (such as a gNodeB, gNB), at which time the secondary communication unit sends a trigger signal to “wake-up” the primary communication unit. The primary communication unit may then proceed to receive a paging message (and further communications, if the paging message is addressed to the UE). According to the present disclosure, the wake-up message is received at the secondary communication unit over a particular frequency (being in a frequency band or carrier, denoted a third frequency band). This may be a relatively low frequency band, i.e. below 1 GHz, such as 700 MHz. Once woken, the primary communication unit receives the paging message using a second frequency band or carrier (which is also a low frequency band i.e. below 1 GHz, and which may be the same as the third frequency band). However, if, after the paging message is received at the primary communication unit and then subsequently decoded, the paging message is addressed to the UE, then the UE is synchronised and reconfigured to send and receive data (specifically at least the call or message data preceded by the paging message) over a further frequency band or carrier (denoted the first frequency band). The first frequency band is preferably different to the second and third frequency bands, and may comprise higher frequencies (i.e. greater than 1 GHz, for instance 3.5 GHz) than both the first and second frequency bands. Thus, the wakeup signal and paging message benefit from the use of relatively longer-range, lower frequency bands, but the call or message data transmitted between the UE and the network benefits from a relatively higher frequency band with a larger bandwidth. This approach has a number of advantages. In particular, in comparison to a scenario in which the higher frequency band is used at the main receiver for both the paging message and for subsequent call or message data, the use of a lower frequency band (with greater range) for receiving the paging message reduces the likelihood that the paging message is not received at the UE after a wake-up message (also sent via a lower frequency, greater range band) has been received. In particular, if the wake-up message at the third frequency band is received at the UE, the paging message over the second frequency band should also be received at the UE, as in both cases these are low frequency bands (with similar or the same frequencies). However, as the UE subsequently switches to the higher frequency band for receiving the call or message data addressed to the UE (rather than to continue using the frequency band over which the paging message was received), then overloading of the lower frequency and bandwidth limited lower frequency band is avoided. Moreover, prior to wake-up, the low power receiver can be used for serving cell measurements (i.e. signal strength any synchronisation measurements to the serving network entity). These serving cell measurements by the low-power receiver will be more representative of signal strength measurements for the main receiver at the lower (second) frequency band used for receiving the paging message without requiring adjustment (such as a delta factor) to account for a substantial frequency difference with the frequency band used by the low power receiver. As such, the serving cell measurements at the low power receiver are more representative and better reflect the ability of the main receiver to receive the paging message. Finally, if the main receiver is woken in order to receive the paging message over the lower frequency band, then if required (i.e. if the paging message is addressed to the UE) signal strength measurements at the higher (first) frequency band can be obtained by the main receiver before handover to the higher frequency band. Thus, said handover to the higher (first) frequency band for subsequent communications may be enacted only if the signal characteristics at the higher frequency band are assessed to be sufficient and suitable. In view of this, the present disclosure describes a system and method that benefits from the lower power consumption provided by the use of a low-power receiver for receipt of a low-frequency wake-up signal, whilst also benefiting from the use of different frequency bands at the low-power receiver and the main receiver. In a first aspect, there is described a method for configuring a user equipment (UE), the UE comprising a primary communication unit configured to support communications with a telecommunications network over at least a first and a second frequency band, and a secondary communication unit in communication with the primary communication unit and configured to communicate with the telecommunications network over a third frequency band, wherein the secondary communication unit is configured to draw less power than the primary communication unit, the method comprising: receiving, by the secondary communication unit, a wake-up signal over the third frequency band; and in response to receiving the wake-up signal, causing, by the secondary communication unit, the primary communication unit to transition from a lower power consumption mode to a higher power consumption mode; receiving, by the primary communication unit, a paging message over the second frequency band; decoding, by the primary communication unit, the paging message to identify if the paging message is addressed to the UE; and if the paging message is addressed to the UE, initiating the primary communication unit for sending and receiving communications over the first frequency band. The UE comprises at least one primary communication unit, but may comprise a plurality of primary communication units. Each communication unit may be a transceiver or a transmitter and receiver, although typically the second communication unit will be a receiver configured to receive only. The primary communication unit may be a main radio receiver for sending and receiving communications over at least two supported frequency bands. In some cases, more than two frequency bands may be supported by the primary communications unit. The primary communication unit may comprise any one or more of: a modem; a bi-directional radio unit; and a main radio of the UE. The secondary communication unit may be a low-power receiver, for receiving communications operating on a particular frequency band. The secondary communication unit is configured to draw less power than the higher power consumption mode of the primary communication unit. The secondary communication unit may comprise any one or more of: a low-power receiver; an ultra-low power receiver; a passive receiver; a wake-up receiver; an almost-zero-power (AZP) receiver. The higher power consumption mode for the primary communication unit is an awake mode or a connected mode, whereas the lower power consumption mode is any one or more of: an off mode; a deep sleep mode; an idle mode; and an inactive mode. The wake-up signal and the paging message are received from a network entity of the telecommunications network. The wake-up signal and paging message maybe sent by the same or different network entities. Each network entity is a base station (e.g. gNodeB), a core network element or another network node of a telecommunications network. The wake-up signal is a low power wake-up signal, LP-WUS, broadcast by a given network entity to indicate that a paging message will be sent to the connected UE (and therefore acts as a trigger for the second primary communication unit to “wake” the primary communication unit). The paging message may take the format of paging messages in the art. The paging message typically will be sent to a group of UEs connected to a particular network entity or node, and will include encoded within the paging message an identifier for the specific UE to which the subsequent data (call or message data) is addressed. A frequency band or carrier refers to a segment of the radio electromagnetic spectrum, comprising a range of frequencies higher or lower than a particular designated frequency. Thus, where for example the 3.5 GHz frequency band is mentioned, this frequency band comprises a small range of frequencies above and below 3.5 GHz. The primary communication unit supporting communications with a telecommunications network over a first and a second frequency band means the primary communication unit is enabled to send and receive communications over the first and the second frequency band. Initiating the primary communication unit for sending and receiving communications over the first frequency band may comprise initiating a communication session between the primary communication unit and a network entity of the telecommunications network over the first frequency band. Preferably, the second and third frequency bands or carriers are not overlapping with the first frequency band or carrier. In other words, the second and third frequency band are different from (comprise different frequencies than) the first frequency band. The first frequency band may comprise higher frequencies than the second and third frequency band. For instance, the first frequency band may be at frequencies greater than 1 GHz (e.g. centred at 2.1 GHz, or 3.5 GHz), whereas the second and third frequency band may be less than 1 GHz (e.g. centred at 700 MHz, 800 MHz or 900 MHz). In some examples, the second and third frequency band comprise the same frequencies (i.e. represent a single or identical frequency band). Prior to receiving, by the primary communication unit, a paging message over the second frequency band, the method comprises synchronising the primary communication unit for receiving communications over the second frequency band. For example, the primary communication unit may receive or obtain one or more synchronisation signal block, SSB, allowing the correct synchronisation for timing of the paging occasion prior to receipt of a paging message. Initiating the primary communication unit for sending and receiving communications over the first frequency band may comprise measuring, at the primary communication unit, signal characteristics of a reference signal over the first frequency band to determine if the signal characteristics are suitable to receive communications at the primary communication unit from the telecommunications network over the first frequency band. For instance, signal characteristics may include signal strength and / or time and / or frequency synchronisation. Measurement of signal strength may include Reference Signal Received Power (RSRP) measurements (for instance, measurements of Synchronization Signal Reference Signal Received Power (SS-RSRP) or Channel State Information Reference Rignal Receive Power (CSI-RSRP)). The reference signal may be a synchronization signal block which includes a Primary Synchronization Signal (PSS), a Secondary Synchronization Signal (SSS) and / or a Physical Broadcast Channel (PBCH). The refence signal may also include any other reference signal (and specifically a downlink reference signal) such as demodulation reference signal (DMRS), or Channel State Information Reference Signal (CSI-RS). The determination of suitability for the signal characteristics may be by comparison with a threshold for each parameter. For instance, the signal strength at the first frequency band may be required to exceed a specific threshold in order to be considered suitable. In addition, the UE checks that the primary communications unit is connected to the network entity or cell for which it has stored the various parameters (for instance, random access channel, RACH parameters). To do this, the UE receives the PSS and SSS, in order to obtain the Physical Cell ID (PCI) of the network cell to which it is connected. If the signal characteristics are determined to be suitable to receive communications at the primary communication unit from the telecommunications network over the first frequency band, then the method may further comprise: configuring the primary communication unit to send and receive communications over the first frequency band; and sending, by the primary communication unit over the first frequency band, a response to the paging message. Configuring the primary communication unit may comprise synchronising the primary communication unit for sending and receiving communications over the first frequency band. The primary communication unit may be configured to send and receive communications over the first frequency band based on configuration parameters for the first frequency band stored at the UE. The configuration parameters for the first frequency band stored at the UE may be previously used configuration parameters for sending and / or receiving previous communications over the first frequency band (for instance during a previous communication session, in which previous communications were sent or received prior to the primary communication unit being transitioned to the lower power consumption mode). Alternatively, the primary communication unit may be configured to send and receive communications over the first frequency band based on configuration parameters for the first frequency band acquired from the telecommunications network after receiving the paging message. For instance, new configuration parameters may be required if the UE has connected to a different network entity or cell of the telecommunications network than compared to the network entity or cell used for the previous communications sent or received prior to the primary communication unit entering the lower power consumption mode (and for which the configuration parameters will typically be stored at the UE). The configuration parameters may include one or more of: a physical layer cell identifier (PCI), one or more System Information Blocks (SIB), and / or an index value for the selected network. It should be noted that the UE will also have stored configuration parameters for the primary communication unit to be used for configuration of the primary communication unit to receive the paging message on the second frequency band. Sending, by the primary communication unit over the first frequency band, a response to the paging message may comprise sending a random-access preamble over a randomaccess channel, RACH, in the first frequency band. This process initiates a channel between the UE and the telecommunications network (more specifically between the UE and a network entity or node of the telecommunications network) for exchange of call and / or message data. If the signal characteristics are determined to be unsuitable to receive communications at the primary communication unit from the telecommunications network over the first frequency band, then the method may further comprise: configuring the primary communication unit to send and receive communications over the second frequency band; and sending, by the primary communication unit over the second frequency band, a response to the paging message. In other words, if the coverage at the first frequency band is found to be insufficient to receive the data addressed to the UE, then the primary communication unit can send a response to the paging message over the second frequency band (i.e. the same frequency band over which the paging message was received). Configuring the primary communication unit to send and receive communications over the second frequency band may comprise synchronising the primary communication unit for sending and receiving communications over the second frequency band. The primary communication unit may be configured to send and receive communications over the second frequency band based on configuration parameters for the second frequency band stored at the UE. The configuration parameters for the second frequency band stored at the UE may be configuration parameters that were used for sending and / or receiving previous communications over the second frequency band. Alternatively, the primary communication unit may be configured to send and receive communications over the second frequency band based on configuration parameters for the second frequency band acquired from the telecommunications network. For example, new configuration parameters may be acquired from the telecommunications network if the network entity (or cell) serving the UE has changed since previous communications were sent over the second frequency band. Once again, the configuration parameters may include one or more of: a physical layer cell identifier (PCI), one or more System Information Blocks (SIB), and / or an index value for the selected network. Sending, by the primary communication unit over the second frequency band, a response to the paging message may comprise: sending a random-access preamble over a random-access channel (RACH) in the second frequency band. Prior to receiving the paging message over the second frequency band, the method further comprises: receiving, by the UE from the telecommunications network, an indication that the paging message will be sent over the second frequency band. In other words, the primary communication unit will be primed to expect the paging message on the second frequency band, including synchronisation of the correct paging occasion and offset. Prior to receiving a wake-up signal over the third frequency band, the method may further comprise: performing, at the secondary communication unit, serving cell measurements and / or neighbour cell measurements on the third frequency band. The serving cell measurements may be used to inform a reselection of the network entity or cell to which a UE is connected. If the serving cell measurements at the secondary communication unit fall below a predefined threshold, then primary communication unit may be woken to perform serving cell measurements on either second or first frequency band at the serving and / or neighbouring cell for use in the determination of the cell reselection. In a second aspect there is described a user equipment, UE, comprising: a primary communication unit configured to support communications with a telecommunications network over at least a first and a second frequency band; and a secondary communication unit in communication with the primary communication unit and configured to communicate with the telecommunications network over a third frequency band, wherein the secondary communication unit is configured to draw less power than the primary communication unit; wherein the secondary communication unit is configured to: receive a wake-up signal over the third frequency band; and in response to receiving the wake-up signal, cause the primary communication unit to transition from a lower power consumption mode to a higher power consumption mode; and wherein the primary communication unit is configured to: after transitioning to the higher power consumption mode, receive a paging message over the second frequency band; decode, by the primary communication unit, the paging message to identify if the paging message is addressed to the UE; and if the paging message is addressed to the UE, initiate the primary communication unit for sending and receiving communications over the first frequency band. Characteristics and advantages of features described above in relation to the disclosed method will be understood equally to apply to like features of the UE. The primary communication unit configured to initiate for sending and receiving communications over the first frequency band may comprise the primary communication unit configured to initiate a communication session for sending and receiving communications over the first frequency band. The primary communication unit configured to initiate the primary communication unit for sending and receiving communications over the first frequency band may comprise the primary communication unit configured to: measure signal characteristics of a reference signal over the first frequency band to determine if the signal characteristics are suitable for receiving communications at the primary communication unit from the telecommunications network over the first frequency band. The UE may be further configured such that, if the signal characteristics are determined to be suitable for receiving communications at the primary communication unit from the telecommunications network over the first frequency band, the primary communication unit may be configured to: configure to send and receive communications over the first frequency band; and send a response to the paging message over the first frequency band. The primary communication unit configured to send and receive communications over the first frequency band may comprise the primary communication unit configuring a communication session for sending and receiving communications over the first frequency band. The primary communication unit configured to send a response over the first frequency band, may comprise the primary communication unit configured to: send a random-access preamble over a random-access channel, RACH, in the first frequency band. The UE may be further configured such that, if the signal characteristics are determined to be unsuitable to receive communications at the primary communication unit from the telecommunications network over the first frequency band, the primary communication unit may be configured to: configure to send and receive communications over the second frequency band; and send a response to the paging message over the second frequency band. The primary communication unit configured to send and receive communications over the second frequency band may comprise the primary communication unit configuring a communication session for sending and receiving communications over the second frequency band. The primary communication unit configured to send a response over the second frequency band, may comprise the primary communication unit configured to: send a random-access preamble over a random-access channel, RACH, in the second frequency band. Brief Description of the Figures Specific embodiments of the present disclosure will be described by way of example with reference to the accompanying drawings, in which: FIGURE 1 shows a schematic representation of the states of the low-power receiver and the main radio receiver in a UE; FIGURE 2 schematically illustrates the different coverage regions for communications to and from a UE at 700 MHz than compared to 3.5 GHz; FIGURE 3 shows a process diagram for a method, not according to the claimed invention, which uses two different frequency bands for the wake-up signal and subsequent communications at a UE; FIGURE 4 shows a schematic diagram of the system according to the claimed invention; and FIGURE 5 shows a process diagram for the method according to the claimed invention. Corresponding features within the figures are labelled with like reference numerals. The figures are not to scale. Detailed Description of Specific Examples FIGURE 3 shows, as an illustrative example and not conforming to the present invention, a schematic diagram showing the receipt of communications at a primary communication unit 140 (being a main radio receiver, MR) and at secondary communication unit 150 (being a low-power radio receiver, LR). This example is provided for information only, in order to allow the reader to better understand the presently claimed method and UE. In this illustrative example, the main receiver 140 and the low power receiver 150 operate on different frequency bands or carriers. In the particular example of FIGURE 3, the low-power receiver, LR, 150 operates on a comparatively lower frequency band such as 700 MHz, whereas the main receiver, MR, 140 operates on a comparatively higher frequency band such as 3.5 GHz. The main receiver 140 obtains over the higher frequency band (i.e. 3.5 GHz) configuration parameters such as a Physical Cell Identifier (PCI) of the network node (i.e. gNodeB) or base station to which the UE is connected, a Master Information Block (MIB) and / or System Information Block (SIB1). These configuration parameters are parameters which can be used to configure the main receiver 140 so as to communicate via the higher frequency band. The configuration parameters are stored at the UE 120 to be used in future configuration of the main receiver. In most cases, the configuration parameters will be stored during or at the termination of a previous communication session during which data has been received via the higher frequency band at the main receiver from the network node or base station to which the UE is connected. The main receiver 140 is subsequently placed in a “sleep” or “idle” mode, which is a relatively low power mode. This acts to reduce energy consumption of the UE 120, and so conserve energy in the battery. Whilst the main receiver 140 is in sleep mode, the low power receiver 150 monitors for a wake-up message (Low Power Wake-Up Signal, LP-WUS), which is sent by the telecommunications network (more specifically, from a network entity or network node) in the event that a paging message will be sent to a UE 120 connected to said network entity. As noted above, the low power receiver 150 consumes less energy than the main receiver 140, and so relatively little energy is consumed whilst the main receiver is in sleep or idle mode. The low-power receiver 150 receives a LP-WUS 155 via the lower frequency band (i.e. 700 MHz). This indicates that a paging message will be sent by the network entity to which the UE is connected. Accordingly, the low-power receiver 150 sends a trigger signal to the main receiver, to “wake” the main receiver 140 to a relatively higher power consumption “alert” or “active” mode. The main receiver 140 then monitors for the paging message 175, which is received after elapse of the paging occasion, PO, (a predefined period of time, synchronised with the network entity). The paging message 175 is sent and received at the main receiver 140 via the higher frequency band (i.e. the 3.5 GHz band). Subsequently, the main receiver 140 decodes the paging message 175. Upon identifying that the paging message 175 is addressed to the UE 120, the main receiver 140 then synchronises and reconfigures to send a response 185 over the higher frequency band. The reconfiguration is based on the configuration parameters stored prior to entry of the main receiver into the sleep or idle mode. The response 185 sent by the main receiver 140 to the network node may be a random-access preamble over a random-access channel, RACH, in the higher frequency band. This commences a communication session between the UE 120 and the network entity or network node via the main receiver and over the higher frequency band. As noted above, there are a number of problems that may occur in this procedure. For instance, the low frequency band inherently may have a greater reception range (i.e. a greater coverage area) than the higher frequency signal. Therefore, according to this approach the wake-up signal 155 may be received by the low power receiver 150 having adequate signal on the lower frequency band, but the paging message 175 may fail to be received by the main receiver 140 due to insufficient signal on the higher frequency band. Consequently, as paging message 175 will not be received or decoded, a communication session will not be initiated by the UE irrespective of whether it is addressed in the paging message. Furthermore, each freqeuncy band may have a different paging occasion configuration, for example a different periodicity. Since there may be multiple frequency bands or carriers provided by a single network entity or base station, multiple offsets between the wake up signal 155 sent over the lower frequency band (e.g. the LP-WUS transmitted at 700 MHz) and the paging occasion in the given frequency band used by the main radio receiver (e.g., the paging occasions associated with the 700MHz, 1800 MHz, 2.1 GHz, or 3.5GHz higher frequency bands) would need to be defined. This can result in many more wake-up signal transmissions over the lower frequency band, reducing the capacity of that frequency band and risking overloading and subsequent deterioration of user experience. In view of these shortcomings, the inventors for the present invention have developed the method and system of the present disclosure. FIGURE 4 illustrates a schematic diagram of a system for implementation of the disclosed method described with reference to FIGURE 5. Looking to FIGURE 4, the system 10 incorporates a UE 20 and a network entity or node 30 (which in this example is a gNB base station) connected to other parts of a telecommunications network 70. The system 10 may include a plurality of network entities 30 and many UEs 20, but FIGURE 4 shows only a single UE 20 and single network entity 30 for simplicity. In particular, it will be understood that the wake-up signal and paging message (as discussed below) could be sent to the UE from the same or different network entities or nodes. A primary communication unit (or main radio receiver) 40 and a secondary communication unit (or low power receiver) 50 are shown within the UE 20. It will be understood that more than one primary communication unit could be included in the UE, for instance separate radio receivers could be provded for use in 4G and 5G communications. However, only a single primary communication unit 40 is shown in FIGURE 4 for simplicity. All communication units are associated with an antenna 90 of the UE. Although a single antenna is shown in FIGURE 4, there may be separate antennae, and each communication unit may be connected to its own antenna in certain implementations. The network entity 30 has its own antenna 85, and further comprises a processor 80 that controls how and when signals are sent from the network entity 30 via the antenna 85. Each primary communication unit 40 may include any type of processor 60 that contains logic to control the way in which the respective communication unit 40 operates. The processor 60 may comprise or be a modem. In FIGURE 4, communication over a radio access network (RAN) 45 is shown between the network entity 30 and the primary communication unit 40 of the UE 20. The primary communication unit supports (i.e. can send and receive) communications over at least a first relatively higher frequency band or carrier (for example, a frequency band above 1 GHz, such as 3.5 GHz or 2.1 GHz) and a second relatively lower frequency band or carrier (for example, a frequency band below 1 GHz, such as 800 MHz or 700 MHz). The secondary communication unit 50 is shown in communication with the primary communication unit 40 and the network entity 30. The secondary communication unit 50 is configured to receive communications from the network entity over a third frequency band or carrier (also being a relatively lower frequency band below 1 GHz, for example 800 MHz or 700 MHz). Notably, the first frequency band or carrier is different to (in other words, does not overlap in frequency with) the second and third frequency band or carrier, although the second and third frequency band or carrier may be overlapping or identical. In the presently described example and in most implementations, the first frequency band or carrier will be a band at higher frequencies than the second and third frequency carrier or band, although this is not a requirement for working the disclosed method. The system 10 in use is now described with reference to FIGURE 5. With the UE 20 in an idle or inactive mode during which no active communication sessions are in underway between the UE 20 and the network entity 30, the primary communication unit 40 (e.g. the main radio receiver) is placed in a lower power consumption (e.g. “deep sleep”) mode. Prior to entering the lower power consumption mode (e.g. during previous connection 95 in FIGURE 5), configuration parameters for connection over the first frequency band (including information on the random-access channel, RACH, for the connected network entity or cell, as well as other stored information) can be stored at the UE 20 (the UE may comprise memory for storage of the configuration parameters, although this is not shown in FIGURE 4)- Whilst the primary communication unit 40 is in the lower power consumption mode, the secondary communication unit 50 (e.g. the low-power receiver) performs monitoring at the third frequency band, in order to detect a wake-up signal 55. In this state, the secondary communication unit 50 draws relatively little power from the UE battery (not shown in FIGURE 4) compared to the primary communication unit 40 in a higher power consumption mode. Therefore, overall, the UE 20 in the idle or inactive mode can minimise its energy usage even though the secondary communication unit 50 is actively monitoring. A wake-up signal 55 (for instance, a low power wake-up signal, LP-WUS) is sent from the network entity 30 to the UE 20 over the third frequency band. The wake-up signal indicates to the UE 20 that it should expect to receive a paging message, and thus provides notice (provided by the core network) that the primary communication unit 40 should wake during the paging occasion (being a predetermined time interval) associated with the second frequency band. Upon receiving the wake-up signal 55, the secondary communication unit 50 subsequently communicates with the primary communication unit 40, for instance by sending a trigger signal 65. This causes the primary communication unit 40 to “wake up” within the paging occasion, by changing its power consumption state from a lower power consumption mode (e.g. inactive, idle or sleep state) to a higher power mode (e.g. active, connected or awake state). In the higher power consumption mode, the primary communication unit 40 will perform synchronisation at the second frequency band, in order to receive communications over the RAN 45 from the network entity 30 over the second frequency band. In particular, from the time of receipt of the low power wake up signal at the secondary communication unit 50, after elapse of the paging occasion and offset associated with the second frequency band then the primary communication unit 40 receives a paging message 75. The paging message 75 is received over the second frequency band (which may comprise the same frequencies as the third frequency band). The primary communication unit 40 then proceeds to decode the paging message 75. If the paging message 75 is addressed to the UE 20 (i.e. the paging message identifies the UE 20 as the intended destination for subsequent call or message data sent by the network entity 30), then the primary communication unit 40 begins initiation for sending and receiving communications (more specifically the call or message data) over the first frequency band. In this way, the low power wake up signal 55 and the paging message 75 are both received at the UE 20 over the third and second frequency band respectively (which may be bands at the same frequencies) whereas subsequent call or message communications are sent and received by the primary communication unit 40 over a first frequency band (which is a different, non-overlapping frequency band compared to the second and third frequency bands). In many examples, the first frequency band is a higher frequency band than the second and third frequency band. This allows the wake-up message 55 and paging message 75 to be sent over longer range (although bandwidth limited) bands, whilst the communication session used for the call or message data makes use of other frequency bands to increase capacity. As noted above, once it has been established that the paging message 75 is addressed to the UE 20, the primary communication unit 40 is initiated for sending and receiving communications over the first frequency band (via the RAN 45). More specifically, this may comprise the primary communication unit 40 being configured to initiate a communication session for sending and receiving communications over the first frequency band. As part of the initiation, the primary communication unit 40 measures certain signal characteristics of a reference signal over the first frequency band, to determine if the first frequency band is sufficient and suitable to send a response to the paging message. The reference signal may be a Synchronization Signal Block (SSB), including a Primary Synchronisation signal, a Secondary Synchronization Signal, or a Physical Broadcast Channel (PBCH). Alternatively, the reference signal could be any other downlink reference signal such as a demodulation reference signal (DMRS), a Channel State Information Reference Signal (CSI-RS). The signal characteristics may include the signal strength (Reference Signal Received Power, RSRP), as well as time and frequency synchronisation of the reference signal over the first frequency band. The first frequency band may be considered suitable if each of the signal characteristics are above predetermined levels (i.e. exceed predetermined thresholds). In a particular example, after it has been established that the paging message 75 is addressed to the UE 20, the primary communication unit 40 performs some rapid, successive measurements over the first frequency band. For example, the primary communication unit 40 may measure three successive SSBs on the first frequency band of 3.5 GHz. Measurement of three such successive SSB is expected to take around 60-80ms, which would not significantly increase the latency of forming a connection for sending and receiving between the UE 20 and the network entity 30 via the first frequency band. By taking said measurements, the primary communication unit 40 can determine if the coverage at the first frequency band is sufficient to proceed with forming a communication channel for sending and receiving data over the first frequency band. If the measurements during initiation of the primary communication unit 40 for sending and receiving communications over the first frequency band determine that the signal characteristics of the first frequency band are sufficient, then the primary communication unit 40 responds 85 to the paging message 75 using the first frequency band (over the RAN 45). This may require configuration and synchronisation of the primary communication unit 40 to the first frequency band, before responding to the paging message 75 by sending a randomaccess preamble over a random-access channel, RACH, in the first frequency band. The configuration parameters used for configuration of the primary communication unit 40 on the first frequency band may be those stored at the UE 20, being the set of configuration parameters used for a previous communication session 95 over the first frequency band prior to the most recent idle period of the primary communication unit 40. The configuration parameters may include, for example, a physical layer cell identifier (PCI), one or more System Information Blocks (SIB), and / or an index value for the selected network (such as a Public Land Mobile Network, PLMN, identifier). However, in some cases the UE 20 may be connected to a different network entity (i.e. a different network node or network cell) than used for the previous communication session over the first frequency band. In this case, the configuration parameters can be acquired from the network before responding to the paging message. For instance, in this case the UE 20 acquires a System Information Block (SIB1) prior to responding to the paging message. Although this will cause a possible 40-160ms delay, this period is short compared to the time taken for connection, and such a delay will not significantly affect latency in the connection process. In some cases, the measurement during initiation of the primary communication unit 40 for sending and receiving communications over the first frequency band will determine that the signal characteristics of the first frequency band are insufficient or unsuitable. For instance, said measurements may show that, although the paging message 75 was adequately received at the primary communication unit 40 over the second frequency band, the signal characteristics (signal strength, synchronization) are insufficient to send a response to the paging message 75 over the first frequency band (in other words, that there is poor coverage in the first frequency band). In this case the primary communication unit 40 may send a response to the paging message 75 over the second frequency band (i.e. the same frequency band as that by which the paging message 75 was received). Here, responding to the paging message 75 may comprise synchronising and configuring the primary communication unit 40 for sending and receiving over the second frequency band, and then sending a response to the paging message 75 over the second frequency band (i.e. by sending a random-access preamble over a random-access channel, RACH, in the second frequency band via the RAN 45). The UE 20 may look to reselect the network entity or network cell to which it is connected if the coverage of the serving network cell 30 becomes too poor (for instance, due to relocation of the UE 20, thereby increasing its distance to the network entity). While the UE 20 is in the idle mode and the secondary communication unit 50 (e.g. the low-power receiver) is used to monitor for a wake-up message 55, the UE 20 performs serving cell measurements on the lower frequency, third frequency band via the second communications unit 50, at least until the signal strength for the third frequency band goes below a predetermined threshold. Below this threshold, the UE 20 can use the primary communication unit 40 (e.g. the main receiver) to perform serving cell measurements on either the first frequency band or on the second frequency band. Moreover, neighbour cell measurements (for the purposes of cell reselection) could be made by the primary communication unit 40 on either the second frequency band (depending on receiver implementation) or the first frequency band. After cell reselection, relevant system information is acquired at the UE for use by the primary communication unit 40 on the new network entity’s (e.g. gNB’s) priority band. It is noted that the re-selection parameters are controlled by the network operator, and the re-selection criteria may take into account a coverage gap difference between the second frequency band (on which the paging message 75 is received by the primary communication unit 40) and the first frequency band (on which subsequent communications are sent and received by the primary communication unit 40). Overall, the reception of the paging message 75 via the second frequency band and subsequent re-configuration at the primary communication unit 40 to the first frequency band should not significantly impact the latency of an initial access procedure to a UE 20 (i.e. connection of a call or receipt of a message) than compared to the already expected delay for the primary communication unit 40 to be ‘woken-up’ from a deep sleep mode to an active mode. Furthermore, the offset between the low power wake up signal occasions on the third frequency band (e.g. lower frequency bands such as 700 MHz, 800 MHz or 900 MHz) and the paging occasions may be selected to take into consideration the extra delay in this procedure. In any case, any such delays are small compared to the time interval for typical discontinuous reception (DRX) cycles of 1.28 or 2.56s. Furthermore, said delays are smaller than the access and mobility management function (AMF) retransmission timers that are likely to be 2 and 3 seconds, respectively, denoting the time for which a paging message would be resent if no response had been received by the network. The entity causing the page (e.g., the remote person making the phone call) has no idea of the timing of the paging occasion, and the proposed method would not be expected to increase noticeably the time taken to connect a call. Finally, it is noted that (in 2G, 3G, 4G or 5G) the RAN and core network are indifferent to whether the UE responds to the paging message on the same or a different cell (i.e. via a different network entity) than the cell from which the UE received the paging message. Although FIGURE 4 shows only a single network entity or network node 30 from which both the wake-up signal and the paging message are sent to the UE, it will be understood that these could be sent by two different network entities or nodes. In one possible implementation, the wake-up signal is transmitted by a dedicated network node, independent from the network node (i.e. a gNodeB) sending the paging message to the UE and to which a subsequent communication session is initiated. It is noted that, in the examples above, the wake-up signal 55 is received over a third frequency band, the paging message 75 is received over a second frequency band and a subsequent communication session 45 may be initiated to send and receive communications over a first frequency band. As already discussed, the first frequency band will be different to the second and third frequency band, and in some implementations the second and third frequency band may be the same or an identical frequency band. Nevertheless, in some implementations the second and third frequency band will represent different frequencies. For instance, in the case where a network has more than one coverage band, three different frequency bands maybe used in order to better distribute the load (i.e. network traffic), especially if there is a coverage gap between the higher frequency bands. In an alternative implementation a dedicated frequency band could be used for sending the wake-up signal (for instance, on an especially low frequency band e.g. below 700MHz, analogous to the legacy paging network band). Such an especially low frequency band may not be supported by the primary communication unit for sending and receiving (noting that the secondary communications unit may be configured for receiving only). Although examples according to the disclosure have been described with reference to specific illustrative examples, other approaches according to the disclosure may be used. Certain features may be omitted or substituted, for example as indicated herein. Each feature disclosed in this specification, unless stated otherwise, may be replaced by alternative features serving the same, equivalent or similar purpose. Thus, unless stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. In this detailed description of the various examples and / or embodiments, for the purposes of explanation, numerous specific details are set forth to provide a thorough understanding of the examples and / or embodiments disclosed. One skilled in the art will appreciate, however, that these various examples and / or embodiments may be practiced with or without these specific details. Furthermore, one skilled in the art can readily appreciate that the specific sequences in which methods are presented and performed are illustrative and it is contemplated that the sequences can be varied and still remain within the scope of the various examples and / or embodiments disclosed herein. As used herein, including in the claims, unless the context indicates otherwise, singular forms of terms are to be construed as including the plural form and vice versa. For instance, unless the context indicates otherwise, a singular reference herein including in the claims, such as "a" or "an" means "one or more". Throughout the description and claims of this disclosure, the words "comprise", "including", "having" and "contain" and variations of the words, for example "comprising" and "comprises" or similar, mean "including but not limited to", and are not intended to (and do not) exclude other components. Also, the use of “or” is inclusive, such that the phrase “A or B” is true when “A” is true, “B” is true, or both “A” and “B” are true. The use of any and all examples, or exemplary language ("for instance", "such as", "for example" and like language) provided herein, is intended merely to better illustrate the disclosure and does not indicate a limitation on the scope of the disclosure unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the disclosure. The terms “first” and “second” may be reversed without changing the scope of the disclosure. That is, the terms are relative such that an element termed a “first” element or position may instead be termed a “second” element or position and an element termed a “second” element or position may instead be considered a “first” element or position. Any steps described in this specification may be performed in any order or simultaneously unless stated or the context requires otherwise. Moreover, where a step is described as being performed after another step, this does not preclude intervening steps being performed. It is also to be understood that, for any given component, example or embodiment described herein, any of the possible candidates or alternatives listed for that component may generally be used individually or in combination with one another, unless implicitly or explicitly understood or stated otherwise. It will be understood that any list of such candidates or alternatives is merely illustrative and not limiting, unless implicitly or explicitly understood or stated otherwise.

Claims

1. A method for configuring a user equipment, UE, the UE comprising a primary communication unit configured to support communications with a telecommunications network over at least a first and a second frequency band, and a secondary communication unit in communication with the primary communication unit and configured to communicate with the telecommunications network over a third frequency band, wherein the secondary communication unit is configured to draw less power than the primary communication unit, the method comprising:receiving, by the secondary communication unit, a wake-up signal over the third frequency band; andin response to receiving the wake-up signal, causing, by the secondary communication unit, the primary communication unit to transition from a lower power consumption mode to a higher power consumption mode;receiving, by the primary communication unit, a paging message over the second frequency band;decoding, by the primary communication unit, the paging message to identify if the paging message is addressed to the UE; andif the paging message is addressed to the UE, initiating the primary communication unit for sending and receiving communications over the first frequency band.

2. The method of claim 1, wherein the second and third frequency bands are not overlapping with the first frequency band.

3. The method of claim 1 or claim 2, wherein the first frequency band comprises higher frequencies than the second and third frequency band.

4. The method of any preceding claim, wherein the second and third frequency band comprise the same frequencies.

5. The method of any preceding claim, wherein initiating the primary communication unit for sending and receiving communications over the first frequency band comprises:measuring, at the primary communication unit, signal characteristics of a reference signal over the first frequency band to determine if the signal characteristics are suitable toreceive communications at the primary communication unit from the telecommunications network over the first frequency band.

6. The method of claim 5, wherein if the signal characteristics are determined to be suitable to receive communications at the primary communication unit from the telecommunications network over the first frequency band, then the method further comprises:configuring the primary communication unit to send and receive communications over the first frequency band;sending, by the primary communication unit over the first frequency band, a response to the paging message.

7. The method of claim 6, wherein the primary communication unit is configured to send and receive communications over the first frequency band based on configuration parameters for the first frequency band stored at the UE.

8. The method of claim 7, wherein the configuration parameters for the first frequency band stored at the UE are configuration parameters used for sending and / or receiving previous communications over the first frequency band.

9. The method of claim 6, wherein the primary communication unit is configured to send and receive communications over the first frequency band based on configuration parameters for the first frequency band acquired from the telecommunications network.

10. The method of any one of claims 7 to 9, wherein the configuration parameters include one or more of: a physical layer cell identifier (PCI), one or more System Information Blocks (SIB), and / or an index value for the selected network.

11. The method of any one of claims 6 to 10, wherein sending, by the primary communication unit over the first frequency band, a response to the paging message comprises:sending a random-access preamble over a random-access channel, RACH, in the first frequency band.

12. The method of any one of claims 5 to 11, wherein if the signal characteristics are determined to be unsuitable to receive communications at the primary communication unit from the telecommunications network over the first frequency band, then the method further comprises:configuring the primary communication unit to send and receive communications over the second frequency band;sending, by the primary communication unit over the second frequency band, a response to the paging message.

13. The method of claim 12, wherein the primary communication unit is configured to send and receive communications over the second frequency band based on configuration parameters for the second frequency band stored at the UE.

14. The method of claim 13, wherein the configuration parameters for the second frequency band stored at the UE are configuration parameters used for sending and / or receiving previous communications over the second frequency band.

15. The method of claim 12, wherein the primary communication unit is configured to send and receive communications over the second frequency band based on configuration parameters for the second frequency band acquired from the telecommunications network.

16. The method of any one of claims 13 to 15, wherein the configuration parameters include one or more of: a physical layer cell identifier (PCI), one or more System Information Blocks (SIB), and / or an index value for the selected network.

17. The method of any one of claims 12 to 16, wherein sending, by the primary communication unit over the second frequency band, a response to the paging message comprises:sending a random-access preamble over a random-access channel (RACH) in the second frequency band.

18. The method of any preceding claim, wherein prior to receiving the paging message over the second frequency band, the method further comprises:receiving, by the UE from the telecommunications network, an indication that the paging message will be sent over the second frequency band.

19. The method of any preceding claim, wherein prior to receiving a wake-up signal over the third frequency band, the method further comprises:performing, at the secondary communication unit, serving cell measurements and / or neighbour cell measurements on the third frequency band.

20. A user equipment, UE, comprising:a primary communication unit configured to support communications with a telecommunications network over at least a first and a second frequency band; anda secondary communication unit in communication with the primary communication unit and configured to communicate with the telecommunications network over a third frequency band, wherein the secondary communication unit is configured to draw less power than the primary communication unit;wherein the secondary communication unit is configured to:receive a wake-up signal over the third frequency band; andin response to receiving the wake-up signal, cause the primary communication unit to transition from a lower power consumption mode to a higher power consumption mode; andwherein the primary communication unit is configured to:after transitioning to the higher power consumption mode, receive a paging message over the second frequency band;decode, by the primary communication unit, the paging message to identify if the paging message is addressed to the UE; andif the paging message is addressed to the UE, initiate the primary communication unit for sending and receiving communications over the first frequency band.

21. The UE of claim 20, wherein the primary communication unit configured to initiate the primary communication unit for sending and receiving communications over the first frequency band comprises the primary communication unit configured to:measure signal characteristics of a reference signal over the first frequency band to determine if the signal characteristics are suitable for receiving communications at the primary communication unit from the telecommunications network over the first frequency band.

22. The UE of claim 21, wherein the UE is further configured such that, if the signal characteristics are determined to be suitable for receiving communications at the primary communication unit from the telecommunications network over the first frequency band, the primary communication unit is configured to:configure to send and receive communications over the first frequency band; send a response to the paging message over the first frequency band.

23. The UE of claim 22, wherein the primary communication unit configured to send a response over the first frequency band, comprises primary communication unit configured to:send a random-access preamble over a random-access channel, RACH, in the first frequency band.

24. The UE of any one of claims 21 to 23, wherein the UE is further configured such that, if the signal characteristics are determined to be unsuitable to receive communications at the primary communication unit from the telecommunications network over the first frequency band, the primary communication unit is configured to:configure to send and receive communications over the second frequency band; send a response to the paging message over the second frequency band.

25. The UE of claim 24, wherein the primary communication unit configured to send a response over the second frequency band, comprises primary communication unit configured to:send a random-access preamble over a random-access channel, RACH, in the second frequency band.s

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