Wake-up signals in a cellular radio telecommunication system

Abstract

A cellular radio telecommunication system, radio apparatus, and method of operating the same are disclosed. The system includes a cellular network and a radio apparatus having a wake-up radio module and a main radio module. The cellular network transmits a wake-up signal in a first frequency band, the wake-up radio module detects the wake-up signal, and, in response to detecting the wake-up signal, activates the main radio module. After transmitting the wake-up signal, the cellular network transmits a paging signal including paging information and frequency-band indication information in the first frequency band, and the activated main radio module receives the paging signal. At least partly in dependence upon the received frequency-band indication information, the radio apparatus determines whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band, different from the first frequency band. The main radio module thereafter starts the initial access procedure with the cellular network on the determined frequency band.

Description

[0001] 174975 / 01

[0002] Wake-Up Signals in a Cellular Radio Telecommunication System

[0003] TECHNICAL FIELD

[0004] This invention relates to wake-up signals for cellular telecommunication systems.

[0005] BACKGROUND OF THE INVENTION

[0006] User equipment (UE) devices in cellular radio telecommunication systems can save power by entering a lower-power or ultra-low power “sleep” state when not receiving information over a radio channel. This may involve powering down a portion of their receiver circuitry, whilst a wake-up radio module in the UE device remains active. A wake-up radio module typically consumes less power than a main radio module. This can reduce power consumption and prolong battery life of the UE device.

[0007] In order for a device in a sleep state to become awake again, it is known for the cellular network to transmit a relatively simple wake-up signal (WUS) to the device (e.g. a 3GPP 5G new radio (NR) wake-up signal), which the device can listen for efficiently using the wake-up radio module while in the sleep state. Following detection of this wake-up signal, the device can enter a wake state in which it is able to exchange more complex information through the cellular radio system. For example, a device may wake to monitor a particular paging occasion, but only if it detects a wakeup signal within a predetermined time window prior to the paging occasion.

[0008] Wake-up signals can desirably facilitate reduced power consumption by receiving devices.

[0009] However, embodiments of the present invention seek to provide an approach to wakeup signalling that enables improved network efficiency.

[0010] SUMMARY OF THE INVENTION

[0011] From a first aspect, the invention provides a method of operating a cellular radio telecommunication system comprising a cellular network and a radio apparatus, the method comprising: the cellular network transmitting a wake-up signal in a first frequency band; the radio apparatus using a wake-up radio module to detect the wake-up signal, and, in response to detecting the wake-up signal, activating a main radio module of the radio apparatus; the cellular network thereafter transmitting a paging signal in the first frequency band, wherein the paging signal comprises paging information and further comprises frequency-band indication information; the radio apparatus, after activating the main radio module, receiving the paging signal using the main radio module, and, at least partly in dependence upon the frequency-band indication information, determining whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band different from the first frequency band; and the radio apparatus using the main radio module to start the initial access procedure with the cellular network on the determined frequency band.

[0012] From a further aspect the invention provides a radio apparatus for use with a cellular network of a cellular radio telecommunication system, the radio apparatus comprising a wake-up radio module and a main radio module, wherein: the radio apparatus is configured to use the wake-up radio module to detect a wake-up signal from the cellular network in a first frequency band, and, in response to detecting the wake-up signal, activate the main radio module; the radio apparatus is configured, after activating the main radio module, to use the main radio module to receive a paging signal from the cellular network in the first frequency band, the paging signal comprising paging information and further comprising frequency-band indication information; and the radio apparatus is configured, at least partly in dependence upon the received frequency-band indication information, to determine whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band different from the first frequency band, and thereafter to use the main radio module to start the initial access procedure with the cellular network on the determined frequency band.

[0013] From a further aspect a cellular radio telecommunication system comprising a cellular network and a radio apparatus, the radio apparatus comprising a wake-up radio module and a main radio module, wherein: the cellular network is configured to transmit a wake-up signal in a first frequency band; the radio apparatus is configured to use the wake-up radio module to detect the wake-up signal, and, in response to detecting the wake-up signal, to activate the main radio module; the cellular network is configured, after transmitting the wake-up signal, to transmit a paging signal in the first frequency band, wherein the paging signal comprises paging information and further comprises frequency-band indication information; the radio apparatus is configured, after activating the main radio module, to use the main radio module to receive the paging signal; and the radio apparatus is configured, at least partly in dependence upon the received frequency-band indication information, to determine whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band different from the first frequency band, and thereafter to use the main radio module to start the initial access procedure with the cellular network on the determined frequency band.

[0014] Thus, in accordance with embodiments of the invention, paging information can be transmitted in the same frequency band as the wake-up signal, and frequency-band indication information in the paging signal can enable the network to influence which frequency band the main radio module of the radio apparatus uses for carrying out an initial access procedure — i.e. influencing whether to start the initial access procedure in the same frequency band as the wake-up signal or in a second frequency band.

[0015] This can simplify synchronization on both the cellular network and the radio apparatus, compared with transmitting paging information and the wake-up signal on different respective frequency bands (and so may reduce the risk of the main radio module missing paging occasions that follow the wake-up signal), while also helping to prevent too many radio apparatuses in the system all using the first frequency band for subsequent communication following paging, which might otherwise overload the network.

[0016] In any of the aspects disclosed herein, the main radio module may have a wake state (i.e. an activated state) and a sleep state, which may correspond to a wake state and a sleep state for the radio apparatus. The main radio module may be configured to consume less power in the sleep state than in the wake state. At least a portion of the electrical circuitry of the main radio module may be powered down when in the sleep state. The wake-up radio module may be at least partly distinct from the main radio module (e.g. comprising distinct circuitry). The wake-up radio module may be active when the radio module is in the sleep state. The wake-up radio module may be inactive when the radio module is in the wake state, although in other embodiments it may be active continuously.

[0017] The wake-up radio module may be coupled to the main radio module (e.g. by a wakeup line) for sending an electrical wake-up signal to activate the main radio module.

[0018] The main radio module may be provided by a semiconductor chip. The wake-up radio module may be integrated on this chip, or it may be separate. The wake-up radio module may be provided by a separate wake-up semiconductor chip.

[0019] The system may be any type of cellular telecommunication system. It may support one or more current or future 3GPP standards. It may comprise a 4G and / or 5G system. The radio signals may conform to current or future 5G new radio (NR) specification. The cellular network may comprise one or more base stations. The paging information may comprise paging information as specified in a current or future 3GPP standard.

[0020] The radio apparatus may support one or more current or future 3GPP standards. It may be a 4G and / or 5G apparatus. It may be part or all of a user equipment (UE) device. The system may comprise a plurality of radio apparatuses, some or all of which may comprise a wake-up radio module. As such, some or all of the radio apparatuses may comprise a main radio module which has a wake state and a sleep state. The system may further comprise one or more other radio apparatuses which do not comprise a wake-up radio module, and do not comprise main radio modules having a wake state and a sleep state. Radio apparatuses comprising a wake-up radio module may be referred to herein as having wake-up functionality. Radio apparatuses without a wake-up radio module may be referred to herein as being without wake-up functionality. Each radio apparatus may be any respective radio device, such as a wireless sensor, industrial machine, vehicle, home appliance, mobile telephone, etc., or may be a radio component thereof.

[0021] The first frequency band may span a first range of frequencies, and the second frequency band may span a second range of frequencies, which is preferably nonoverlapping (disjoint) with the first range. The ranges may be contiguous or may be separated by one or more further frequency bands.

[0022] In some preferred embodiments, the first range of frequencies is lower than the second range of frequencies. This may beneficially allow the wake-up signal to have a greater range than it would if it were transmitted on the second frequency band. The first range of frequencies may comprise frequencies that are equal to or less than 2GHz, e.g. less than 1GHz. The first frequency band may be a frequency-division duplexing (FDD) band below 2GHz. The first frequency band may be a 3GPP 600 MHz, 700 MHz, 800 MHz or 900 MHz band. The second range of frequencies may be greater than or equal to 3GHz, e.g. greater than or equal to 3.3GHz. For example, the second frequency band may comprise frequencies in the range 3.3MHz to 3.8MHz. The second frequency band may be a 3GPP 3.5GHz band (e.g. n77 or n78). The second frequency band may comprise frequencies in the range 2GHz to 3GHz , e.g. the second frequency band may be a time-division duplexing (TDD) band such as n41.

[0023] In some embodiments, information indicating that a wake-up signal will be transmitted in the first frequency band may have been sent by the cellular network to the radio apparatus when the radio apparatus was previously in a wake state. The cellular network may be configured to transmit a wake-up allocation signal to one or more radio apparatuses with wake-up functionality in the system, e.g. being received when the main radio modules of said radio apparatuses are in a wake state. The wake-up allocation signal may comprise information indicating that a wake-up signal will be transmitted in the first frequency band. The main radio module of the radio apparatus may receive and decode the wake-up allocation signal, may determine one or more frequency bands to monitor for wake-up signals at least partly in dependence on the information in the wake-up allocation signal, and may store information identifying the one or more frequency bands in a memory of the radio apparatus. As such, the radio apparatus may gain knowledge of the range(s) of frequencies which the wake-up signal could be transmitted in. This may advantageously allow the wake-up radio module to be configured by the radio apparatus for detecting the wake-up signal, and for activating the main radio module to receive a paging signal in the same frequency band as the wake-up signal. The wake-up allocation signal may additionally comprise an indication of one or more frequency channels (e.g. carriers) within the first frequency band which the wake-up signal may be transmitted on. Such an indication may indicate a particular cell or carrier frequency. It may be provided by one or more channel numbers, e.g. one or more EARFCNs. Each channel number may uniquely designate a predetermined carrier frequency.

[0024] The cellular network may be configured to transmit a plurality of wake-up signals, each followed by a respective paging signal, at a plurality of different times. The plurality of wake-up signals and / or paging signals may be transmitted to a respective plurality of different radio apparatuses. Each of the plurality of wake-up signals may be transmitted in the first frequency band. In some embodiments, the cellular network is configured to transmit wake-up signals exclusively in the first frequency band. Restricting the transmission of wake-up signals to the first frequency band may advantageously prevent the wake-up signals from using signalling overhead in a wider range of frequency bands in the cellular network.

[0025] Each paging signal transmitted to a radio apparatus with wake-up functionality following the transmission of a wake-up signal may be transmitted in the first frequency band. The cellular network may transmit paging signals to other radio apparatuses which do not have wake-up functionality, and such paging signals may not be restricted to being transmitted exclusively in the first frequency band. However, paging signals transmitted to radio apparatuses with wake-up functionality, following corresponding wake-up signals, may be transmitted exclusively in the first frequency band. More generally, in some embodiments, each paging signal transmitted to a radio apparatus with wake-up functionality, following the transmission of a wake-up signal, may be transmitted in a same frequency band as the preceding wake-up signal.

[0026] In some embodiments, the frequency-band indication information may indicate whether the radio apparatus is permitted to start the initial access procedure in the first frequency band. The radio apparatus may determine whether to start the initial access procedure on a channel in the first frequency band solely in dependence upon the frequency-band indication information in the paging signal, or it may be configured to do so in additional dependence upon one or more further factors. In some embodiments, the frequency-band indication information may indicate whether the radio apparatus is required to start the initial access procedure in the first frequency band.

[0027] Allowing a radio apparatus which detects a wake-up signal to continue to use the first frequency band for initial access to the cellular network after the main radio module has been activated may reduce latency associated with synchronisation for subsequent transmission and reception of radio signals. However, the applicant has appreciated that it may be undesirable for every radio apparatus with wake-up functionality to always to continue to communicate with the cellular network in the first frequency band after the main radio module has been activated. This may, on occasions, cause too much congestion in the first frequency band. This may be the case if, for example, all radio apparatuses using a wake-up radio module were to perform initial access on the same channel in the first frequency band. Thus, the proportion of the plurality of radio apparatuses which continue to use the first frequency band for communication following activation of the main radio module may, at least in some embodiments, be controlled by the cellular network using the frequency-band indication information in the paging signal.

[0028] In some embodiments, the frequency-band indication information indicates that the initial access procedure should be carried out in frequency band other than the first frequency band. This may be desirable for situations where there is high demand for use of the first frequency band. The frequency-band indication information may, in some embodiments, identify the second frequency band, but in other embodiments it indicates only that the first frequency band should not be used or should not always be used. The identity of the other frequency band may be fixed (e.g. always being the second frequency band), or the radio apparatus or cellular network may be configured to choose the second frequency band from among a plurality of candidate frequency bands. The cellular network may transmit information identifying one or more candidate frequency bands to the radio apparatus. For example, the frequency-band information in the paging signal may comprise information identifying one or more candidate frequency bands. This information may comprise one or more channel numbers, each channel number designating a carrier frequency for initial access. Where a plurality of candidate frequency bands are communicated to the radio apparatus, the radio apparatus may select one based on previous measurement history.

[0029] However, carrying out the initial access procedure in a different frequency band from the first frequency band can introduce additional delay and / or complexity. Therefore, the applicant has recognised that it may be desirable for some of the radio apparatuses of the system to carry out the initial access procedure on the first frequency band, e.g. depending on the demands on the cellular network and / or on the type or requirements of each radio apparatus.

[0030] Therefore, in some embodiments, the frequency-band indication information in the plurality of paging signals transmitted to the respective plurality of radio apparatuses may indicate, for a first subset of the radio apparatuses, that an initial access procedure should be carried out in the first frequency band, and indicate, for a second subset of the radio apparatuses, that an initial access procedure should be carried out in a frequency band other than the first frequency band. These respective paging signals may all comprise the same frequency-band indication information, or the frequency-band indication information may differ between the paging signals. The subset may be determined at least in part in dependence upon a type capability of each radio apparatus — e.g. reduced capability (RedCap) apparatuses may be permitted to use the first frequency band while radio apparatuses of a different type capability may be required to use a frequency band other than the first frequency band.

[0031] The subset may additionally or alternatively be determined at least in part stochastically — e.g. based on a random or pseudo-random process carried out by each radio apparatus and / or by the cellular network. By controlling the size of the subset, the cellular network may control the proportion of radio apparatuses that continue to use the first frequency band for subsequent communication with the cellular network. The proportion of transmitted paging signals which comprise frequency-band indication information that indicates that an initial access procedure should be carried out in a different band may be a configurable parameter for the system. The value of this parameter may be variable responsive to the demands on the cellular network. Thus, each radio apparatus may determine whether to start an initial access procedure in the first frequency band partly in dependence upon the frequency-band indication information and partly stochastically.

[0032] The cellular network may determine the frequency-band indication information in dependence on radio resource management (RRM) measurements by the cellular communication system. Such measurements may measure network congestion, or a co-channel interference level, or a number of access points per channel, or any other similar metric, or any combination of these.

[0033] The frequency-band indication information in each paging signal sent to a respective plurality of radio apparatuses may be specific to the radio apparatus that receives the paging signal. Alternatively, each of a plurality of radio apparatuses with wake-up functionality may receive the self-same paging signal or may receive respective paging signals but comprising the same frequency-band indication information. The frequency-band indication information may be generic for a portion of the telecommunication system, e.g. applying to all radio apparatuses in a geographic area.

[0034] In some embodiments, the frequency-band indication information consists of a flag, which may be a single bit flag. This can desirably be transmitted very efficiently. If the frequency-band indication information has a first binary value (e.g. zero), the main radio module of the radio apparatus may start an initial access procedure in the first frequency band, and if the frequency-band indication information indicates an opposite binary value (e.g. one), the main radio module of the radio apparatus may start an initial access procedure on the second frequency band.

[0035] In other embodiments, the frequency-band indication information comprises a stochastic threshold value — e.g. a float value between zero and one. The cellular network may determine a proportion of radio apparatuses in the system to use the first frequency band for further communication (e.g. without causing undue congestion) (for example, by using RRM measurements described above), and determine the stochastic threshold value in dependence on this proportion. The main radio module may be configured to determine whether to start an initial access procedure in the first frequency band or in the second frequency band at least partly in dependence on the stochastic threshold value. It may use a random number generator to randomly generate a random value (which may be a pseudorandom value) in a predetermined interval (e.g. zero to one), and may determine whether the random value is above or below the stochastic threshold value. It may use this determination to determine whether or not to use the first frequency band for the initial access procedure. The probability of each radio apparatus determining that it should use the first frequency band may correspond to the determined proportion. As such, across a plurality of radio apparatuses with wake-up functionality in the system, a predetermined proportion of radio apparatuses may start an initial access procedure in the first frequency band. This use of a stochastic threshold value may enable the cellular network to control capacity in a straightforward and bandwidth efficient manner.

[0036] The frequency-band indication information may comprise an indication that the radio apparatus is indefinitely barred from using the first frequency band for initial access. Alternatively, the frequency-band indication information may comprise an indication that the radio apparatus should not carry out initial access in the first frequency band for a predetermined length of time following reception of the paging signal. The frequency-band indication information may indicate a time period, and / or a number of resource blocks or symbol periods for which the main radio module is barred from initially attempting to use the first frequency band for further transmission or reception of radio signals.

[0037] The frequency-band indication information may comprise channel selection information. The main radio module may determine which channel, of a plurality of channels in the second frequency band, to start the initial access procedure on, in dependence on the channel selection information. The channel selection information may comprise one or more channel numbers, e.g. one or more EARFCNs. Each channel number may uniquely designate a predetermined carrier frequency in the second frequency band.

[0038] The paging signal may further comprise synchronisation update information. The main radio module may determine whether synchronisation information (e.g. within a System Information Block (SIB)) has been updated for a selected channel (i.e. carrier) depending upon the synchronisation update information. The synchronisation update information may indicate whether synchronisation information has been updated since a predetermined time-stamp. The predetermined time-stamp may comprise the timeend of a previous hyper-frame where the main radio module transmitted radio signals on the selected channel. The previous hyper-frame may be the most recent hyperframe when the main radio module was in a wake state, or it may be a hyper-frame which occurred a predetermined number of hyper-frames in the past. The time-stamp may comprise the end-time of the previous sleep cycle of the radio apparatus, e.g. the end of the previous eDRX cycle. This may be applicable for paging signals where the frequency-band indication information indicates that the main radio module should start an initial access procedure on a selected channel that the main radio module previously used for transmission and reception of radio signals before entering a wake state. As such, if the synchronisation update information indicates that synchronisation information has not been updated, the main radio module may retrieve synchronisation information from a memory of the radio apparatus, and use the retrieved synchronisation information to carry out the initial access procedure on the selected channel. This may advantageously reduce latency of the main radio module following activation and paging.

[0039] In some embodiments, the synchronisation update information comprises a single bit flag. If the synchronisation update information indicates a first binary value (e.g. of 0), the main radio module may retrieve synchronisation information from a memory of the radio apparatus, and if the frequency-band indication information indicates an opposite binary value (e.g. a value of 1), the main radio module may start the initial access procedure without accessing stored synchronisation information.

[0040] In some embodiments, starting an initial access procedure on a channel comprises transmitting an access request radio signal to the cellular network on the channel. The cellular network may exchange one or more further radio transmissions with the main radio module of the radio apparatus to establish synchronisation and / or reserve at least a portion of the channel for subsequent communication with the cellular network. The channel may be a random-access channel, e.g. a 3GPP Random Access Channel (RACH). The initial access procedure may comprise a 3GPP Random Access Channel (RACH) procedure, either contention-based or contention free.

[0041] The second frequency band may be selected (by the radio apparatus or by the cellular network) from a plurality of available frequency bands in the cellular network. The channel on which the initial access procedure is performed may be selected (by the radio apparatus or by the cellular network), e.g. randomly, from a plurality of channels available within the second frequency band. The selected channel and / or second frequency band may be selected according to a selection algorithm. The selected channel and / or second frequency band may be selected at least partly in dependence upon an indication provided by the frequency-band indication information.

[0042] In some scenarios, the initial access procedure in the second frequency band may fail or the radio apparatus may be out of coverage or cells or channels in the second frequency band. Thus, in some embodiments, the main radio module is configured, if it is not possible to complete the initial access procedure on the second frequency band, to start a new initial access procedure on a channel in the first frequency band. As such, subsequent communication with the cellular network following the initial paging signal may be carried out on a channel in the first frequency band, even if the main radio module first attempted an initial access procedure in the second frequency band according to the frequency-band indication information provided in the paging message. This may advantageously ensure that connectivity for the device is maintained.

[0043] The wake-up signal may be encoded across two or more subcarriers in the first frequency band, but is preferably encoded on a single subcarrier.

[0044] In some embodiments, the wake-up signal comprises an orthogonal frequency- divisional multiple-access (OFDMA) radio signal comprising a predetermined temporal pattern of modulated and unmodulated symbol periods on one or more subcarriers in the first frequency band. The wake-up radio module of the radio apparatus may detect the predetermined temporal pattern of modulated and unmodulated symbol periods in the transmitted wake-up signal, and, in response to detecting the predetermined temporal pattern in the received wake-up signal, generate the electrical wake-up signal.

[0045] The modulated and unmodulated sets of symbol periods may be interleaved. The temporal pattern may have any length, e.g. consisting of 4, 8, 16, 32 or more symbol periods. It may conform to a Gold, Walsh, Barker, Hadamard, Kasami or M-sequence code, or any other binary pattern having strong auto-correlation performance, wherein one of the sets of symbol periods corresponds to the “1” bits and the other set of symbol periods corresponds to the “0” bits. By transmitting unmodulated symbol periods within the wake-up signal, the radio signal may contain no or negligible energy within the second set of symbols (e.g. not significantly greater than a noise floor for the radio system). This can enable the wakeup signal to detect the wake-up signal efficiently.

[0046] In some embodiments, the same modulated symbols in the wake-up signal can be used both to transmit data to one radio apparatus and to wake up another radio apparatus. In these embodiments, the cellular network may send allocation information to a second radio apparatus indicating that one or more of the modulated symbol periods in the predetermined pattern of the wake-up signal are allocated to the second radio apparatus. The second apparatus may subsequently receive the wake-up signal, and demodulate and use information from the one or more allocated modulated symbol periods. This may advantageously efficiently use of some of the network bandwidth used to send the wake-up signal for a dual purpose.

[0047] The information carried by the wake-up signal and paging signal may be modulated using any type of modulation, but in some embodiments it is modulated using quadrature amplitude modulation (QAM). Each modulated symbol period may contain a respective QAM symbol. The symbol periods may all be of equal duration.

[0048] The wake-up radio module of the radio apparatus may detect the predetermined temporal pattern by determining a time-series of energy values, each energy value representing an energy of the wake-up signal received by the radio apparatus at a respective time. It may cross-correlate the time-series of energy values with data representative of the predetermined temporal pattern, thereby determining a correlation value. It may determine if the correlation value satisfies a wake-up condition, and may, in response, generate the electrical wake-up signal.

[0049] The wake-up radio module may comprise an envelope detector for determining the time-series of energy values. The envelope detector may comprise analogue circuitry, e.g. rectification circuitry. It may additional comprise digital circuitry for determining the energy values. The envelope detector may be configured to sample received energy, to determine the energy values. It may measure total received energy across one or more subcarriers within the first frequency band. It may sample received energy at least once every symbol period, for the duration of the predetermined temporal pattern. The wake-up radio module may comprise a correlator for performing the cross-correlation.

[0050] The predetermined temporal pattern may be continuous, or it may be spread across a plurality of spaced-apart time intervals. These intervals may be spaced apart by one or more temporal gaps (e.g. in which the modulation status of the resource units may be variable). The wake-up radio module may exclude energy values corresponding to the one or more temporal gaps when performing the cross-correlation.

[0051] The wake-up radio module may comprise a memory for storing the data representative of the predetermined temporal pattern. The data may be permanently stored in memory, e.g. from manufacture, or the radio apparatus may be configured to receive the data representative of the predetermined temporal pattern in a radio signal which is decoded by the main radio module. The wake-up radio module may be coupled to the main radio module for receiving configuration data from the main radio module (e.g. the data representative of the predetermined temporal pattern). The memory may store a plurality of predetermined temporal patterns, and the radio apparatus may cross-correlate the time-series of energy values with data representative of each of the predetermined temporal patterns.

[0052] The main radio module may comprise logic for decoding information from received radio signals using a fast Fourier transform (FFT). The wake-up radio module, by contrast, preferably does not have FFT logic, but instead detects the wake-up signal using the correlator. The wake-up radio module preferably has a lower power consumption when active than does the main radio module when decoding a radio signal. Therefore, using a wake-up signal in accordance with embodiments of the present invention when the apparatus is in the sleep state allows saving of power.

[0053] The radio apparatus may perform any of the operations disclosed in hardware or in software or using a combination or hardware and software. It may, in some embodiments, comprise a processor and a memory storing software which, when executed by the processor, causes the radio apparatus to perform any one or more of the operations disclosed herein. Features of any aspect or embodiment described herein may, wherever appropriate, be applied to any other aspect or embodiment described herein. Where reference is made to different embodiments or sets of embodiments, it should be understood that these are not necessarily distinct but may overlap.

[0054] BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0056] Figure 1 is a schematic diagram of a multi-device cellular telecommunication system;

[0057] Figure 2 is a schematic diagram of an exemplary UE device that can be switched between a wake state and a sleep state;

[0058] Figure 3 is a signal timing diagram showing communication between a base station and a UE device switch the UE device to a wake state from a sleep state and establish initial access to the cellular network;

[0059] Figure 4 is a diagram showing a first example of the allocation of different frequency channels to the different signals exchanged between the UE device and the base station shown in Figure 3; and

[0060] Figure 5 is a diagram showing a second example of the allocation of different frequency channels to the different signals exchanged between the UE device and the base station shown in Figure 3.

[0061] DETAILED DESCRIPTION

[0062] Figure 1 shows a multi-device cellular telecommunication system 100 embodying an aspect of the present invention. The system 100 may support a present or future mobile telecommunications standard. It may support at least 3GPP 4G and / or 5G. The system 100 comprises a number of user equipment (UE) devices 101-104 that are in radio range of a base station 105. The UE devices 101-104 may include mobile telephones, wireless sensors, machinery, vehicles, home appliances, etc. The base station 105 may be a component of a telecommunications network 107 that also comprises a backhaul network, which may be coupled to further base stations, as well as a mobile core and other conventional components. The system 100 may include other UE devices. The base station 105 can transmit information to the UE devices 101-104 by one or more downlink radio signals using digital modulation, according to an orthogonal frequency-division multiple access (OFDMA) system. At least some of the UE devices 101-104 embody an aspect of the present invention, and have a wake state and a sleep state and are designed to use less power when they are in the sleep state than they do when in the wake state. In particular, they can conserve electrical energy by powering down some of their radio transceiver circuitry when in the sleep state. However, the UE device then needs to be set to the wake state in order to decode information transmitted to it by the base station 105. During a particular time period represented in Figure 1, three of the UE devices 101-103 are in a wake state, while one UE device 104 is in the sleep state.

[0063] Different UE devices may communicate with the base station 105 using different frequency bands in the cellular spectrum. In the example shown in Figure 1 , the base station 105 communicates with the first UE device 101 and the second UE device 102 using downlink radio signals 106 in a 3GPP 3.5GHz frequency band. Each of the first UE device 101 and the second UE device 102 are allocated different resources in frequency and time. The first UE device 101 and the second UE device 102 communicate with the base station using respective uplink radio signals 108 also in the 3GPP 3.5GHz frequency band. The base station 105 communicates with the third UE device 103 using a downlink radio signal 110 in a sub-1GHz 3GPP frequency band. The third UE device 103 communicates with the base station 105 using an uplink radio signal 108 in the sub-1 GHz frequency band.

[0064] The second downlink signal 110 can, when required, include a low-power wake-up signal (LP-WUS) for setting the fourth UE device 104 to a wake state. The resources in the second downlink signal used to transmit the wake-up signal to the fourth UE device 104 may be distinct from the resources used to transmit information to the third UE device 103, or they may overlap. For example, the wake-up signal may use on-off keying to create a predetermined pattern of modulated and unmodulated symbol periods, and the modulated symbols in the wake-up signal can be used to transmit data to the third UE device 103. This may advantageously efficiently use of some of the network resources used to send the wake-up signal for a dual purpose. Although this can somewhat reduce the overhead of network resources required to implement wake-up signals, wake-up signals still add to resource demands on the cellular network. In order to provide greater control over the congestion that could be caused by wake-up signals, and better predictability, it can be preferable to restrict the transmission of wake-up signals 110 to a specific frequency band, or set of frequency bands. In the example described herein, the base station 105 only transmits wake-up signals in a low frequency band, e.g. a frequency band below 1GHz.

[0065] Figure 2 shows a schematic diagram of an exemplary UE device 104 that can be switched between a wake state and a sleep state. The UE device 104 comprises a main radio module 200 and a wake-up radio module 201 , each of which are electrically coupled to a radio antenna 202 of the device 104.

[0066] The main radio module 200 comprises standard radio transceiver circuitry capable of decoding OFDMA signals, including the downlink signals 106, 110 from the base station 105. It contains hardware logic for performing a fast Fourier transform (FFT) on radio signals received at the antenna 202, and for processing the transformed data to decode information from the received radio signals. It also contains circuitry for transmitting uplink signals 108 to the base station 105. The UE device 104 may comprise a processor 240 and a memory 250 storing software for execution by the processor for performing one or more operations, which may include operations disclosed herein. These may be separate from the main radio module 200, as shown in Figure 2, or may be part of the main radio module 200.

[0067] The wake-up radio module 201 is also connected to the antenna 202, but, in contrast to the main radio module 200, it does not contain FFT logic for decoding information from incoming signals; instead it comprises an envelope detector 203, a correlator 204, a memory 205, and control logic 206. The correlator 204 could be implemented in software but in this embodiment is a hardware correlator.

[0068] The main radio module 200 and wake-up radio module 201 may be integrated in a common semiconductor chip, but in some embodiments the main radio module 200 is provided by a semiconductor radio transceiver chip and the wake-up radio module 201 is separate, e.g. being provided by discrete circuitry or as a semiconductor wake-up chip. The main radio module 200 is electrically coupled to the wake-up radio module 201 by a wake-up signal line 210 and by a configuration-data channel 211.

[0069] Figure 3 is a signal timing diagram showing communication between the base station 105 and the UE device 104 to wake up the UE device 104. Figure 4 is a resourcing diagram showing the allocation of different frequency channels (carriers) to the different signals exchanged between the UE device 104 and the base station 105 shown in Figure 3. The channels CH1 and CH2 are shown for a first, low frequency band (<1GHz), and the channels CH3 and CH4 are shown for a second, higher frequency band (~3.5GHz). Each channel comprises a range of frequencies used by a mobile network operator to provide service to subscribers. Typically, a network operator may have only one channel within a given frequency band, although it could have more. Each range of frequencies associated with a channel is a sub-range of the range of frequencies covered by the broader frequency band. For simplicity, only two channels are shown in Figure 4 for each frequency band. However, it should be appreciated that, in practice, each frequency band may be divided up into many more frequency channels.

[0070] Referring again to Figure 3, initially, the UE device 104 is shown in the sleep state. When the UE device 104 is in the sleep state, the main radio module 200 does not attempt to decode the incoming downlink signal 110 comprising the wake-up signal transmitted from the base station 105. Instead, the wake-up signal is processed by the wake-up radio module 201 to detect when the signal 110 contains a predetermined wake-up signal.

[0071] The UE device 104 is configured with a predetermined set of one or more frequency bands or ranges over which the wake-up signal 110 could be received. The base station 105 (e.g. gNB) may send this information to the UE device 104 earlier, when the UE device 104 is in a wake state. This may advantageously allow the wake-up radio module 201 to be configured optimally for detecting the wake-up signal when the UE device 104 is in a sleep state.

[0072] More specifically, in some examples, a gNB may send a filter list of supported / queried frequencies (bands) by the network to the UE device during a 3GPP UE Capability transfer. A novel form of UE-CapabilityRAT-RequestList entry (a UE-CapabilityRAT- Request IE) with RAT-Type set to nr may include a sequence of flags that indicate support for LP-WUS for a given band. It may, for example, have the following structure: UE-CapabilityRAT-RequestList ::= SEQUENCE (SIZE (1..maxRAT-

[0073] CapabilityContainers)) OF UE-CapabilityRAT-Request

[0074] UE-CapabilityRAT-Request ::= SEQUENCE { rat-Type, capabilityRequestFilter OCTET STRING OPTIONAL, - Need N

[0075] IpwusRequestFilter SEQUENCE (SIZE (1..maxBandsMRDC)) OF LPWUSInformation OPTIONAL - NEED R }

[0076] LPWUSInformation ::= SEQUENCE {

[0077] IpwusSupport ENUMERATED {supported} OPTIONAL - NEED R bandNR reqBandlndicatorNR OPTIONAL - NEED R

[0078] }

[0079] The size of the lowusRequestFilter here matches the size of the frequencyBandListFilter sequence in the UE-CapabilityRequestFilterNR. The LPWUSInformation is present when the matching band supports LP-WUS. From the above the UE device 104 can learn the bands with LP-WUS and can combine a Capability Response to the network about those bands it can use or wants to use for LP-WUS monitoring.

[0080] The frequency channel which the wake-up signal is transmitted on could vary depending on the system which the UE device 104 is deployed in. For example, it may vary depending on the geographical area. In the example described herein, as mentioned above, the wake-up signal 110 (and all other wake-up signals transmitted by the base station 105) is transmitted on a channel in the low-frequency band.

[0081] In some embodiments, the main radio module 200 may operate on a cell in a high- frequency band (e.g. 3.5GHz NR band), and receive a broadcast indication in SIBx that LP-WUS is supported by a cell in a different band (e.g. a <1GHz band) within the area, or the network 107 may indicate the bands where the LP-WUS is supported during the capability negotiation during the ATTACH procedure. The main radio module 200 may perform a re-selection to the indicated low-band and check for sleep entry conditions to be able to enter LP-WUR monitoring. The UE may decide to move to different cell on a different band to save power. Once entry conditions are satisfied, the wake-up radio unit 201 starts monitoring for LP-WLIS. The entry conditions may be based on serving cell RRM measurements, by both wake-up radio module 201 and main radio module 200.

[0082] The wake-up radio module 201 detects the wake-up signal by listening for a predetermined pattern of radio energy in the low-frequency band. Typically, wake-up signals comprise a sequence of ON-OFF keying symbols. ON-OFF keying creates a predetermined pattern of modulated and unmodulated symbol periods. As described above with reference to Figure 1 , to make efficient use of some of the network resources used for the wake-up signal, the modulated symbols in the wake-up signal can be used as part of an OFDMA signal to transmit data to other devices. Wake-up signals may use any binary pattern with good autocorrelation properties, such as a Gold, Walsh, Barker, Hadamard, Kasami or M-sequence code, and may be of different bit lengths. If the wake-up signal is transmitted more than once, with the same temporal pattern, its resources will have the same relative positions in time at every transmission. The wake-up radio module 201 does not demodulate and decode the incoming downlink signal 110, and therefore consumes much less energy than the main radio module 200 does when the main radio module 200 is actively receiving information by radio. Alternatively, in some embodiments, the wake-up radio module 201 may demodulate the downlink signal 110 but using a low-power OFDMA receiver. In all cases, the wake-up radio module 201 may require less precise synchronisation compare to the main radio module 200, which may further reduce unit complexity and such power consumption.

[0083] At least in some embodiments, whenever the UE device 104 is in the sleep state, the wake-up radio module 201 constantly establishes whether a wake-up signal has been received by the UE device 104. After appropriate tuning and filtering, the incoming radio-frequency (RF) spectrum is passed to the envelope detector 203, which repeatedly samples the received signal strength across the low frequency band. The received signal is filtered such that the envelope detector only samples signal strength in the low frequency band. Resource units in the wake-up signal that contain modulated symbols will be determined to have a relatively high received energy, for example above -72dBm, while resource units that are unmodulated will carry only background noise and so be determined to have a relatively low received energy. The envelope detector 203 outputs a sample stream representative of a temporal pattern 220 of received energy that depends on which of the wake-up resource units contain modulated symbols and which do not. This temporal pattern 220 of received energy is then passed to the correlator 204. The correlator 204 cross-correlates the incoming temporal pattern 220 with sample data representative of a predetermined expected wake-up pattern 221 which has been stored in the memory 205. If the predetermined wake-up physical resource blocks are not contiguous in time, the correlator 204 may be configured to correlate only on those energy samples that correspond to symbol periods of the wake-up resource units (i.e. to filter out energy samples from the envelope detector 203 from time periods lying outside the predetermined wake-up resource units).

[0084] Although the wake-up signal 110 is described herein as being sent to wake a single UE device 104, the same signal could be used to wake multiple devices simultaneously, so long as the multiple devices have been configured to correlate against stored data representative of the same predetermined temporal pattern (e.g. by the network 107 having sent appropriate template data to be stored in the local memories 205 of the wake-up radio modules 201 of the devices before they entered a sleep state).

[0085] The control logic 206 coordinates the behaviour of the components of the wake-up radio module 201. In particular, it may configure the correlator 204 with the predetermined wake-up resource blocks and symbols that make up the resource units, e.g. based on configuration data 230 it receives from the main radio module 200 over the data channel 211. It may comprise a processor and software, or may implement a finite state machine in hard-wired digital logic.

[0086] The use of energy envelope detection limits the power which the wake-up radio module 201 needs to use to detect the wake-up signal. It avoids the need for processes such as a Fourier transform to decode the received downlink signal 110, which would require more complex logic and consume greater power. This use of envelope detection, rather than a more complex decoding process, effectively uses on-off keying (OOK) to detect the wake-up pattern 221 as a binary string. The expected wake-up pattern 221 may have been pre-loaded into the memory 205 when the device was manufactured or with a firmware update, or alternatively the expected wake-up pattern may have been previously transmitted to the UE device 104 by the telecommunications network 107 when the device 104 was in the wake state and connected to the network. Thus the control logic 206 may be configured to receive configuration data 230 encoding an updated wake-up pattern from the main radio module 200 over the configuration data channel 211 , which it may store in the memory 205.

[0087] The correlator 204 outputs correlation strength information (e.g. as a stream of correlation coefficients) to the control logic 206, which may detect a correlation peak in any appropriate, e.g. by detecting when the correlation strength passes above a predetermined threshold. If the correlation between the incoming temporal pattern of signal energy 220 and the expected wake-up pattern 221 indicates a match, the control logic 205 causes a wake-up command signal 231 to be sent from the wake-up radio module 201 to the main radio module 200 over the wake-up line 210. Alternatively, the wake-up command signal 231 may be sent to separate power management unit of the device 104, which may in turn wake the main radio module 200. The main radio module 200 enters a wake state and powers up its receiver circuitry. The UE device 104 is thus restored to a wake state, ready to receive and decode information from an incoming paging signal 112 from the base station 105.

[0088] According to embodiments described herein, the paging signal 112 is transmitted on the same frequency band as the second downlink signal 110 containing the wake-up signal - i.e. the low frequency band. The main radio module 200 is therefore configured to start listening to paging on the same frequency channel which the second downlink signal 110 was transmitted on. This avoids the need for a timeconsuming cell reselection process. The applicant has appreciated that minimising latency between wake-up and paging is beneficial, so that the UE device 104 does not miss paging occasions. Allowing the UE device 104 to continue to use the low frequency band for paging, after the UE device 104 has been set to a wake state, reduces delay compared to needing to perform cell reselection and obtain new synchronisation information for receiving paging information on a different frequency channel (i.e. carrier). However, in a busy network with potentially large numbers of UE devices, it is undesirable for every UE device with wake-up functionality to continue to use the low frequency band for transmitting and receiving further radio signals after paging has been completed. This could cause excessive congestion on the low frequency band, which is typically also used for other devices in the system 100, not all of which will be configured with wake-up functionality.

[0089] Therefore, in accordance with some embodiments described herein, at least some of the plurality of UE devices stop using the low frequency band for communication after the paging signal 112 has been received. Instead, the network 107 requires these UE devices to switch to using a channel in a higher frequency band after the paging signal 112 has been received. The proportion of UE devices that switch channel after paging is controlled by the network 107 using frequency-band indication information included in each paging signal 112 as described in more detail below.

[0090] This frequency-band indication information is encoded in each paging signal 112 along with typical paging information. The frequency-band indication information at least partly determines whether the main radio module 200 of the UE device 104 should continue to use the low frequency band for carrying out an initial access procedure, or switch to using a different frequency band for requesting initial access to the cellular network.

[0091] In some embodiments, the paging signals may include the following fields:

[0092] PagingRecord ::= SEQUENCE { ue-ldentity PagingUE-ldentity, accessType ENUMERATED, cell-Barred, cell-sibs-modified ...} where cell-Barred is a single-bit or multi-bit value providing frequency-band indication information, and cell-sibs-modified is a single-bit value providing synchronisation update information, both of which are described in more detail below. As shown in Figure 3, the main radio module 200 receives the paging signal 112, decodes information from the paging signal 112, selects a frequency channel for carrying out an initial access procedure, and initiates carrying out a RACH procedure by transmitting an initial access request 114 to the base station 105. The frequency channel that the UE device 104 uses for transmitting the initial access request 114 is selected at least partly in dependence upon the frequency-band indication information included in the paging signal 112. Figure 4 shows an example where the UE device 104 switches to a frequency channel labelled CH3 in the 3.5GHz band for initial access. In this scenario, the UE device 104 proceeds to operate in a similar manner to the first UE device 101 and second UE device 102 shown in Figure 1. Figure 5 shows an example where the UE device 104 continues to use the same frequency channel, CH1 , as the low-band frequency channel which the paging signal 112 was received on. In this scenario, the UE device 104 proceeds to operate in a similar manner to the third UE device 103 shown in Figure 1.

[0093] In some embodiments, the frequency-band indication information could comprise a single bit flag. For example, if the frequency-band indication information in the paging signal 112 indicates a value of 0, the main radio module 200 of the UE device 104 starts an initial access procedure on a selected channel in the low frequency band (e.g. CH1 or CH2 shown in Figure 4 and 5), and if the frequency-band indication information indicates a value of 1 , the main radio module 200 of the UE device 104 starts an initial access procedure on a selected channel in the 3.5GHz frequency band (e.g. CH3 or CH4 shown in Figures 4 and 5).

[0094] The proportion of transmitted paging signals 112 sent to different respective UE devices 101-104 where the frequency-band indication information indicates that an initial access procedure should be carried out in the higher frequency band may be controlled by the system 100 (e.g. being a configurable parameter for the system 100). In some examples the parameter could be configured as a constant value, e.g. set by the network operator. For example, for specific geographical regions, the frequencyband indication information may specify that all UE devices with wake-up functionality (i.e. 100%), or may be such that a specific proportion of them (e.g., 50%, 75%, 90%) switch to a higher frequency band after paging. However, in other examples, the value of this parameter varies responsive to the demands on the cellular network. For example, the system 100 may take resource management measurements (RRM) of the cellular network to determine measures of network congestion, co-channel interference levels, the number of access points per channel, and other similar information. The proportion of transmitted paging signals 112 which request that the UE device switches to the higher frequency band after paging would then vary in dependence of these measurements.

[0095] In some embodiments, the frequency-band indication information in a paging signal may be depend on a type capability of the UE device 101-104 to which the paging signal is sent. For example, paging signals may always permit use of the first (<1GHz) frequency band for reduced capability (RedCap) NR UEs.

[0096] In other embodiments, rather than comprising single bit flag, the frequency-band indication information may alternatively comprise a stochastic threshold value between zero and one. In these examples, the cellular network determines a proportion of UE devices in the system that could use the low frequency band for further communication without causing undue congestion, and determines the threshold value in dependence on this proportion. This could be determined according to RRM measurements, as described above. The main radio module 200 then decodes the threshold value from the paging signal, and provides it as input to a process which determines whether to use the low frequency band or a higher frequency band after paging, where the likelihood of determining that the UE device 104 should use a higher frequency band for further communication depends on the threshold value. The main radio module 200 may comprise a pseudo-random number generator and may select a value between zero and one, and compare this with the stochastic threshold. If the random value is lower than the threshold, the main radio module 200 uses the first (<1GHz) frequency band, and if it is higher the main radio module 200 uses the second (3.5GHz) frequency band. The same stochastic threshold value can therefore be included in each paging signal transmitted to a plurality of UE devices after transmitting respective wake-up signals. Across a large number of similarly-configured UE devices, a desired proportion of the UE devices will thus switch to a higher frequency band for starting an initial access procedure.

[0097] In the example described in detail herein, the initial access procedure carried out by the main radio module 200 is a Random Access Channel (RACH) procedure. As shown in Figure 3, the UE device 104 transmits a RACH access request signal 114 to the base station 105, and in reply, the base station transmits an access grant signal 116 if the request for initial access is successful. The access request signal 114 is transmitted on a channel in the low frequency band or a higher frequency band, depending on the frequency-band indication information in the paging signal, as explained above. A sequence of transmissions may be exchanged between the base station 105 and the UE device 104 in order to establish uplink and downlink synchronisation on the selected channel. The access grant signal 116 indicates that access is granted to the UE device to establish an uplink for sending subsequent radio signals to the base station 105, and typically includes timing information so that synchronisation can be established between the UE device 104 and the base station 105. The base station 105 may exchange one or more further radio transmissions with the main radio module 200 of the UE device to establish synchronisation and reserve resources on the selected channel for subsequent communication with the base station 105.

[0098] For occasions where the UE device 104 continues to use the first frequency band after paging, it may start the initial access procedure on the same channel as the paging signal 112 was received on. For occasions where the UE device 104 starts initial access in a higher frequency band, the selected channel may be selected from a plurality of channels available within the higher frequency band. The selected channel may be selected randomly, or according to a predetermined channel selection algorithm. The channel may be selected according to data stored in memory of the UE device 104. For example, the same channel may be selected as one which the UE device 104 has used before when the main radio module 200 was previously awake. The UE device 104 may store an EARFCN uniquely identifying the channel previously used for communication with the cellular network in memory. Alternatively, the frequency-band indication information could include further information which specifies which channel the UE device 104 should select for carrying out the initial access procedure, e.g. the frequency-band indication information could include an EARFCN that identifies the channel. The UE device 104 would then initiate access using the instructed frequency channel in the frequency-band indication information. Specifying the frequency channel may provide greater centralised control over the cellular network resources. Various further information can be included in the frequency-band indication information. For example, the frequency-band indication information could further comprise an indication that the UE device 104 is indefinitely barred from using the first frequency band for communication other than paging. Alternatively, the frequencyband indication information may comprise an indication that the UE device should not communicate in the first frequency band for a predetermined length of time after paging, after which it is permitted to use the first frequency band again. The frequencyband indication information may indicate a time period, and / or a number of resource blocks or symbol periods for which the main radio module 200 is barred from initially attempting to use the first frequency band for further transmission or reception of radio signals.

[0099] To reduce latency between reception of the paging signal and the main radio module 200 of the UE device 104 being ready to initiate access to the network, the paging signal 112 may further comprise synchronisation update information. The synchronisation update information indicates whether synchronisation information has been updated for a selected frequency channel since a predetermined time-stamp. In some examples, the time-stamp is the time when the previous hyper-frame for communication between the main radio module 200 and the base station 105 ended. In this manner, the synchronisation update information informs the UE device 104 whether information critical to synchronisation that would be contained in a system information block (SIB), such as timing, has been updated while the main radio 200 of the UE device 104 switched to a sleep state. The time-stamp does not need to be associated with the immediately preceding hyper-frame, for example, the time-stamp could comprise the time-end of a hyper-frame which occurred several hyper-frames in the past. Similarly, the time-stamp may comprise the end-time of the previous eDRX cycle. The synchronisation update information could take various formats, but in its simplest form could comprise a single bit flag.

[0100] Since synchronisation information (e.g. provided in a System Information Block (SIB)) is specific to each frequency channel, including synchronisation information may only be applicable in a scenario where the frequency-band indication information from the base station 105 indicates that the UE device 104 should use a frequency channel which it has already used on a previous occasion. If a UE device is configured to make use of synchronisation update information, when a UE device uses a frequency channel in a wake state, the main radio module 200 of the UE device stores the synchronisation information, e.g. from a SIB, for said channel, in memory. Then, subsequently, when the UE device receives a paging signal 112 after waking up from being in a sleep state, if the synchronisation update information indicates that synchronisation information has not been updated, the main radio module 200 retrieves synchronisation information for the selected channel from memory, and uses the retrieved synchronisation information to carry out the initial access procedure on the selected channel. If the synchronisation update information indicates that the synchronisation information has been updated, the main radio module 200 proceeds to acquire suitable synchronisation information during the initial access procedure.

[0101] Thus, using mechanisms described herein, a base station (e.g. gNB) can control the amount of RACH procedures performed on a low-band carrier. If traffic is low, it may allow performing RACH on the low-band. If the carrier becomes busy, it can direct all or a proportion of UEs to perform RACH on higher bands.

[0102] Although in general it is expected that the WUS will be sent on a lower-frequency band, in some embodiments the first frequency band could be higher than the second frequency band.

[0103] It will be appreciated by those skilled in the art that the invention has been illustrated by describing one or more specific embodiments thereof, but is not limited to these embodiments; many variations and modifications are possible, within the scope of the accompanying claims.

Claims

CLAIMS1. A method of operating a cellular radio telecommunication system comprising a cellular network and a radio apparatus, the method comprising: the cellular network transmitting a wake-up signal in a first frequency band; the radio apparatus using a wake-up radio module to detect the wake-up signal, and, in response to detecting the wake-up signal, activating a main radio module of the radio apparatus; the cellular network thereafter transmitting a paging signal in the first frequency band, wherein the paging signal comprises paging information and further comprises frequency-band indication information; the radio apparatus, after activating the main radio module, receiving the paging signal using the main radio module, and, at least partly in dependence upon the frequency-band indication information, determining whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band different from the first frequency band; and the radio apparatus using the main radio module to start the initial access procedure with the cellular network on the determined frequency band.

2. The method of claim 1 , wherein the first frequency band spans a first range of frequencies, the second frequency band spans a second range of frequencies, and the first range of frequencies is non-overlapping with, and is lower than, the second range of frequencies.

3. The method of claim 1 or 2, further comprising: the cellular network transmitting a wake-up allocation signal to the radio apparatus, wherein the wake-up allocation signal comprises information indicating that a wake-up signal will be transmitted in the first frequency band; the radio apparatus receiving and decoding the wake-up allocation signal using the main radio module, and, at least partly in dependence upon the information in the wake-up allocation signal, determining one or more frequency bands to monitor for wake-up signals.

4. The method of any preceding claim, further comprising the cellular network determining the frequency-band indication information in dependence upon radioresource management (RRM) measurements by the cellular radio telecommunication system.

5. The method of any preceding claim, wherein the frequency-band indication information consists of a single bit flag, and wherein, if the frequency-band indication information has a first binary value, the main radio module of the radio apparatus starts the initial access procedure on a channel in the first frequency band, and if the frequency-band indication information indicates an opposite binary value, the main radio module of the radio apparatus starts the initial access procedure on a channel in the second frequency band.

6. The method of any of claims 1 to 4, wherein the frequency-band indication information comprises a stochastic threshold value, and the method further comprises: the radio apparatus generating a random value in a predetermined interval; the radio apparatus determining whether the random value is above or below the stochastic threshold value, and the radio apparatus determining, at least partly in dependence upon whether the random value is above or below the stochastic threshold value, whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in the second frequency band.

7. The method of any preceding claim, wherein the frequency-band indication information comprises an indication that the radio apparatus should not carry out initial access in the first frequency band for a predetermined length of time following reception of the paging signal.

8. The method of any of claims 1 to 6, wherein the frequency-band indication information comprises an indication that the radio apparatus is indefinitely barred from using the first frequency band for initial access.

9. The method of any preceding claim, wherein the paging signal further comprises synchronisation update information, and the method further comprises the main radio module determining whether synchronisation information has been updated for a selected channel depending upon the synchronisation update information, and if the synchronisation update information indicates that synchronisation information hasnot been updated, the main radio module retrieving synchronisation information from a memory of the radio apparatus and using the retrieved synchronisation information to carry out the initial access procedure on the selected channel.

10. The method of any preceding claim, wherein the system comprises a plurality of different radio apparatuses, each comprising a main radio module and a wake-up radio module, and wherein the method comprises the cellular network transmitting a plurality of wake-up signals, each followed by a respective paging signal, to a respective plurality of the radio apparatuses, wherein each of the plurality of wake-up signals and plurality of paging signals is transmitted in the first frequency band.

11. The method of claim 10, wherein the frequency-band indication information in the plurality of paging signals transmitted to the respective plurality of radio apparatuses indicates, for a first subset of the radio apparatuses, that an initial access procedure should be carried out in the first frequency band, and indicates, for a second subset of the radio apparatuses, that an initial access procedure should be carried out in a frequency band other than the first frequency band.

12. The method of any preceding claim, wherein the initial access procedure comprises a 3GPP Random Access Channel (RACH) procedure.

13. The method of any preceding claim, wherein at least the wake-up signal conforms to a 5G new radio (NR) specification.

14. A radio apparatus for use with a cellular network of a cellular radio telecommunication system, the radio apparatus comprising a wake-up radio module and a main radio module, wherein: the radio apparatus is configured to use the wake-up radio module to detect a wake-up signal from the cellular network in a first frequency band, and, in response to detecting the wake-up signal, activate the main radio module; the radio apparatus is configured, after activating the main radio module, to use the main radio module to receive a paging signal from the cellular network in the first frequency band, the paging signal comprising paging information and further comprising frequency-band indication information; andthe radio apparatus is configured, at least partly in dependence upon the received frequency-band indication information, to determine whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band different from the first frequency band, and thereafter to use the main radio module to start the initial access procedure with the cellular network on the determined frequency band.

15. The radio apparatus of claim 14, wherein the radio apparatus is configured to support at least one 3GPP standard.

16. The radio apparatus of claim 14 or 15, wherein the radio apparatus is further configured to: use the main radio module to receive and decode a wake-up allocation signal from the cellular network, and, at least partly in dependence upon the information in the wake-up allocation signal, determine one or more frequency bands to monitor for wake-up signals; and store information identifying the one or more frequency bands in a memory of the radio apparatus.

17. The radio apparatus of any of claims 14 to 16, wherein the frequency-band indication information consists of a single bit flag, and the radio apparatus is configured: if the frequency-band indication information has a first binary value, to use the main radio module of the radio apparatus to start an initial access procedure in the first frequency band, and if the frequency-band indication information indicates an opposite binary value, to use the main radio module of the radio apparatus to start an initial access procedure on the second frequency band.

18. The radio apparatus of any of claims 14 to 16, wherein the frequency-band indication information comprises a stochastic threshold value, and the radio apparatus is configured to: use a random number generator to generate a random value in a predetermined interval;determine whether the random value is above or below the stochastic threshold value, and use the determination to determine whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band different from the first frequency band.

19. The radio apparatus of any of claims 14 to 18, wherein the paging signal further comprises synchronisation update information, and the radio apparatus is configured to use the main radio module to determine whether synchronisation information has been updated for a channel depending upon the synchronisation update information, and, if the synchronisation update information indicates that synchronisation information has not been updated, use the main radio module to retrieve synchronisation information from a memory of the radio apparatus, and use the retrieved synchronisation information to carry out the initial access procedure on the selected channel.

20. A cellular radio telecommunication system comprising a cellular network and a radio apparatus, the radio apparatus comprising a wake-up radio module and a main radio module, wherein: the cellular network is configured to transmit a wake-up signal in a first frequency band; the radio apparatus is configured to use the wake-up radio module to detect the wake-up signal, and, in response to detecting the wake-up signal, to activate the main radio module; the cellular network is configured, after transmitting the wake-up signal, to transmit a paging signal in the first frequency band, wherein the paging signal comprises paging information and further comprises frequency-band indication information; the radio apparatus is configured, after activating the main radio module, to use the main radio module to receive the paging signal; and the radio apparatus is configured, at least partly in dependence upon the received frequency-band indication information, to determine whether to start an initial access procedure with the cellular network on a channel in the first frequency band or on a channel in a second frequency band different from the first frequency band, andthereafter to use the main radio module to start the initial access procedure with the cellular network on the determined frequency band.

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