Power optimisation for NB-iot devices
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-02-04
- Publication Date
- 2026-08-13
Smart Images
Figure EP2026052938_13082026_PF_FP_ABST
Abstract
Description
[0001] 175651 / 01
[0002] Power Optimisation for NB-loT Devices
[0003] TECHNICAL FIELD
[0004] This disclosure relates to radio systems, radio devices and methods for operating the same.
[0005] BACKGROUND OF THE INVENTION
[0006] Non-Terrestrial Networks (NTNs) are wireless communication networks that include at least one node at high altitude, such as a satellite in low-earth orbit. NTNs are able to provide radio coverage also in remote locations where traditional terrestrial cellular coverage is limited or absent.
[0007] It is desirable to enable Narrow Band Internet-of-Things (NB-loT) operation over NTNs. However, due to power limitations or coexistence in some NTNs and / or NTN bands, the availability of radio resources over NTNs may differ significantly from traditional cellular networks, necessitating changes to conventional NB-loT procedures for NTN applications. The Applicant has recognised that implementing NB-loT operation over NTN using existing approaches would require relatively high power consumption for radio devices connected to these NTNs.
[0008] Embodiments of the present invention seek to provide a more power-efficient approach for NB-loT operation over NTN.
[0009] SUMMARY OF THE INVENTION
[0010] According to a first aspect of the invention, there is provided a method of operating a radio device, the method comprising:
[0011] receiving, at the radio device, channel information for a first carrier and a second carrier, the channel information encoding at least i) a frequency of the first carrier and the second carrier and ii) a time offset between respective downlink bursts transmitted on each of the first and second carriers;
[0012] receiving, at the radio device, a first synchronisation signal on the first carrier;
[0013] synchronising an oscillator of the radio device to the second carrier based on the first synchronisation signal and the channel information;receiving first data on the second carrier;
[0014] after receiving the first data, switching off the oscillator for a predetermined duration set based on the time offset and a known periodicity of signals transmitted on the first and second carriers;
[0015] at the end of the predetermined duration:
[0016] switching on the oscillator of the radio device;
[0017] receiving, at the radio device, a second synchronisation signal on the first carrier;
[0018] synchronising the oscillator to the second carrier based on the second synchronisation signal and the channel information; and
[0019] receiving data on the second carrier.
[0020] From a second aspect, the invention provides a radio device for use within a system comprising the radio device and a satellite configured to communicate with the radio device on a first carrier and a second carrier, wherein the radio device is configured to:
[0021] receive channel information encoding at least i) a frequency of the first carrier and the second carrier and ii) a time offset between respective downlink bursts transmitted on each of the first and second carriers;
[0022] receive a first synchronisation signal on the first carrier;
[0023] synchronise an oscillator of the radio device to the second carrier based on the first synchronisation signal and the channel information;
[0024] receive first data on the second carrier;
[0025] after receiving the first data, switch off the oscillator for a predetermined duration set based on the offset and a known periodicity of signals transmitted on the first and second carriers; and
[0026] at the end of the predetermined duration:
[0027] switch on the oscillator;
[0028] receive a second synchronisation signal on the first carrier; synchronise the oscillator to the second carrier based on the second synchronisation signal and the channel information; and
[0029] receive data on the second carrier.
[0030] Thus it will be seen that, in accordance with at least some embodiments of the invention, a radio device is able to synchronise to a second carrier using asynchronisation signal received on a first carrier in combination with frequency and timing information for the first and second carriers. By using a synchronisation signal received on the first carrier, the radio device can synchronise to the second carrier in advance of receiving data on the second carrier. The radio device can thus be ready to receive data on the second carrier without having to receive synchronisation signals on the second carrier itself. This early synchronisation advantageously allows the radio device to make more efficient use of radio resources on the second carrier. In the context of satellite carriers, which may only transmit data periodically (i.e. at intervals) with a large time offset between transmissions, this approach enables the radio device to switch off its oscillator, thereby reducing power consumption, during periods in which no transmissions will be received from the second carrier, without restricting its ability to synchronise to the second carrier.
[0031] Thus, in some embodiments, the radio device switches off its oscillator after receiving the first data on the second carrier, and the oscillator remains switched off until the second synchronisation signal can be received on the first carrier. The predetermined duration for which the oscillator is switched off may therefore depend on the delay between transmission of first data on the second carrier and transmission of the second synchronisation signal on the first carrier.
[0032] The radio device may be a 4G LTE or 5G device, such as an LTE-enabled appliance, vehicle, cell phone, etc. Alternatively, the radio device may be a component within such a device (e.g. a system-on-chip radio). The radio device may be a terrestrial device, e.g. it may be ground-based.
[0033] The satellite may be a mobile-satellite radiocommunication service (MSS) satellite. The satellite may be a low Earth orbit (LEO) satellite, a medium Earth orbit (MEO) satellite, or a geostationary Earth orbit (GEO) satellite. In some embodiments, the satellite may form part of a constellation of satellites.
[0034] In a set of embodiments the radio device and the satellite support a legacy Narrowband-lnternet-of-Things (NB-loT) radio protocol, preferably as defined in accordance with the Third Generation Partnership Project (3GPP) Release 19, further preferably as defined in the loT-NTN TDD mode feature. Thus, in someembodiments, the first synchronisation signal and / or the second synchronisation signal comprises a synchronisation signal according to the legacy NB-loT protocol. For example, the first synchronisation signal and / or the second synchronisation signal may comprise a narrowband primary synchronisation signal (NPSS) or a narrowband secondary synchronisation signal (NSSS). In some embodiments the first synchronisation signal and / or the second synchronisation signal comprises broadcast information for the first carrier, e.g. it may comprise a system information block (SIB) or a master information block (MIB).
[0035] The first carrier may be an NB-loT anchor carrier, configured to provide broadcast information and synchronisation signals. The NB-loT anchor carrier may provide the Narrowband Reference signal (NRS), NPSS, NSS, Narrowband Physical Broadcast Channel (NPBCH), NPDSCH, and Narrowband Physical Downlink Control Channel (NPDCCH). Alternatively, the first carrier may be an NB-loT non-anchor carrier which does not transmit broadcast signals. The non-anchor carrier may only provide the NRS, NPDCCH and NPDSCH. The non-anchor carrier may also provide the initial access procedure and paging in some embodiments. The second carrier may also be an NB-loT anchor carrier or an NB-loT non-anchor carrier. In preferred embodiments, the first carrier is an NB-loT anchor carrier and the second carrier is an NB-loT non-anchor carrier.
[0036] In some embodiments, the radio device receives the channel information over a third carrier, which may be an NB-loT anchor carrier or an NB-loT non-anchor carrier. However, in some embodiments, the channel information is stored in a memory of the radio device, for example during an initial set up procedure of the radio device.
[0037] In some embodiments, the frequency information for the first carrier and / or second carrier is encoded in the channel information in the form of a frequency channel number for the carrier, e.g. as an E-LITRA Absolute Radio Frequency Channel Number (EARFCN) for each respective carrier. However, in some embodiments the frequency information for the first carrier and / or second carrier is encoded in the form of an absolute frequency value for each respective carrier, e.g. the centre frequency of the respective carrier.The first carrier and / or the second carrier may operate in the mobile-satellite radiocommunication service (MSS) allocated band. In some embodiments, the first carrier and the second carrier operate in the 1616-1626.5 MHz MSS allocated band.
[0038] In some embodiments, the time offset between downlink bursts transmitted on each of the first and second carriers is encoded in the form of a number of frames or subframes between periodic downlink bursts on each of the first and second carriers and a common reference signal. The time difference between the downlink bursts transmitted on the first carrier and the second carrier may be greater than or equal to 10 ms in some embodiments, e.g. it may be 10 ms, 20 ms, 30 ms, 40 ms, 50 ms or more. In some preferred embodiments the time difference is between 8 ms and 32 ms.
[0039] The interval between the periodic downlink or uplink signals transmitted on the first carrier and the second carrier may be dependent on the round-trip time of data transmitted over the carrier between the radio device and the satellite, and / or on radio resource constraints at the satellite. In contrast to terrestrial radio systems, in which a typical transmission interval on a carrier may be 5 ms or 10 ms, the interval between signals in satellite-based systems may be significantly greater than this. In some embodiments, the interval of the signals transmitted on the first carrier and / or the second carrier is greater than 50 ms. For example, it may be 60 ms, 70 ms, 80 ms, 90 ms, or 100 ms. In some embodiments the periodicity of the signals transmitted on the first carrier and the second carrier is greater than 100 ms, e.g. it may be 150 ms, 200 ms, 250 ms or more. In a preferred embodiment, the interval of the signals transmitted over the first carrier and the second carrier is 90 ms.
[0040] Signals are typically transmitted for the radio device on the first carrier and the second carrier periodically. The signal transmitted on the carrier in each period may comprise one or more NB-loT downlink frames allocated to the radio device. The radio device may be allocated a plurality of subframes within the one or more allocated frames. In some embodiments, the radio device is allocated eight downlink subframes within one or two frames. The eight subframes may be subframes within the same frame, or they may be consecutive subframes of two consecutive frames. In preferred embodiments, the eight allocated subframes aresubframes [34567890] across two consecutive radio frames, or subframes [45 6 789 0 1] across two consecutive frames. Using one of these two sets of subframes allows for each of the NPBCH, NPSS, NSSS and SUB-1 signals to be provided within the eight consecutive subframes according to the legacy NB-loT protocol. Using one of these two sets of subframes also guarantees that NPSS immediately precedes NSSS, which is beneficial when performing an initial cell search using the radio device.
[0041] The radio device may thus receive downlink signals (e.g. downlink bursts) comprising a set of one or more downlink frames allocated to the radio device on each of the first carrier and the second carrier. As downlink signals transmitted on the first carrier and second carrier are periodic, there may be a predetermined time offset between each set of one or more downlink frames allocated to the radio device on the first carrier and a respective set of one or more downlink frames allocated to the radio device on the second carrier.
[0042] The radio device may thus receive the first synchronisation signal in a first instance of a set of one or more downlink frames allocated to the radio device on the first carrier, and synchronise to the second carrier based on the first synchronisation signal and the channel information. After receiving the first data on the second carrier, the oscillator may be switched off until a next instance of a set of one or more downlink frames allocated to the radio device on the first carrier is scheduled for transmission. The radio device may then receive the second synchronisation signal in the next (e.g. second) instance of a set of one or more downlink frames allocated to the radio device on the first carrier, and synchronise to the second carrier based on the second synchronisation signal and the channel information.
[0043] Thus, in some embodiments, after receiving the first data on the second carrier, the oscillator is switched off until a next instance of a set of one or more allocated downlink frames on the first carrier is scheduled for transmission.
[0044] In some embodiments, the first synchronisation signal and / or the second synchronisation signal transmitted on the first carrier comprises a further copy of the NSSS in addition to the NSSS required by the legacy NB-loT protocol. In contrast to the NSSS required by the legacy NB-loT protocol, which is transmittedin subframe 9 of every other NB-loT frame on the carrier, the further copy of the NSSS is provided in another, earlier subframe within the downlink bursts transmitted on the first carrier, and is provided in the same subframe of every downlink burst transmitted on the first carrier.
[0045] Preferably, the further copy of NSSS is provided in the first subframe of each downlink burst allocated to the radio device on the carrier (e.g. in the first of eight subframes allocated to the radio device). This may be subframe 3 or subframe 4 of each downlink burst allocated to the radio device. By providing a further copy of NSSS in the first subframe of each downlink burst allocated to the radio device, the radio device may be able to receive synchronisation data without needing to receive control or data channels in the first subframe. In addition, the use of NSSS allows synchronisation to be performed even in low SNR conditions, as NSSS carries more power within the subframe than NRS.
[0046] In some embodiments in which a further copy of NSSS is provided, the further copy of NSSS is transmitted in a set of subframes only if NPDCCH and / or NPDSCH has been transmitted to the radio device or another radio device on the carrier in that set of subframes. In such embodiments, the radio device may switch off its oscillator and / or enter a sleep mode in response to the absence of the further NSSS signal in the first subframe. The radio device may switch on its oscillator and / or exit the sleep mode for the next transmission on the first carrier. The presence of additional NSSS can be indicated in a dedicated user equipment configuration for the radio device.
[0047] The provision of an additional synchronisation signal in an NB-loT subframe to facilitate faster synchronisation is considered to be inventive in its own right. Thus, according to a third aspect, the invention provides a method of synchronising a radio device with a carrier, wherein the radio device is operable to receive signals according to a legacy NB-loT protocol, the method comprising using the carrier to transmit an additional synchronisation signal to those required by the legacy NB-loT protocol, and the radio device using the additional synchronisation signal to synchronise to the carrier. This aspect of the invention also extends to a radio device configured to receive an additional synchronisation signal on such a carrier and to use it to synchronise to the carrier.In some embodiments of the third aspect, the additional synchronisation signal is a further copy of the NSSS. Thus, in such embodiments, the carrier transmits a further copy of the NSSS in addition to the NSSS (if any) required by the legacy NB-loT protocol on a particular carrier. In some such embodiments, the further copy of NSSS is provided in the first subframe of each downlink burst allocated to the radio device on the carrier (e.g. in the first of eight subframes allocated to the radio device). This may be subframe 3 or subframe 4 of each downlink burst allocated to the radio device. By providing a further copy of the NSSS in the first subframe allocated to the radio device, the radio device may be able to receive synchronisation data without needing to receive control or data channels in the first subframe. In addition, the use of NSSS allows synchronisation to be performed even in low SNR conditions.
[0048] In some embodiments, the carrier transmits a system information block (SIB) in a predetermined subframe at a predetermined interval, e.g. in every second instance of the subframe, and transmits the additional synchronisation signal in instances of the subframe that do not include the system information block. In some such embodiments, the carrier transmits a SIB in a predetermined subframe of every other frame (e.g. of every even frame), and transmits the additional synchronisation signal in the predetermined subframe in frames in which the SIB is not transmitted. In some preferred embodiments, the predetermined subframe is subframe 4. The additional synchronisation signal may be a further copy of the NSSS in addition to the NSSS (if any) required by the legacy NB-loT protocol on a particular carrier. Alternatively, the additional synchronisation signal may be a System Information Block that is not required to be read during radio resource controlled connected mode, e.g. SIB2. Providing an additional synchronisation signal in this way ensures that the radio device is able to synchronise to the carrier based on signals received in every frame. For example, it may allow the radio device to synchronise to the carrier based on the content of subframe 4 of both odd and even frames. Where the radio device is allocated eight downlink subframes in a downlink burst as described above, and the eight allocated subframes are subframes [34567890] across two consecutive radio frames, or subframes [45678901] across two consecutive frames, providing an additional synchronisation signal in subframe 4 in this way ensures that the radio device is able to synchronise to the carrier within thefirst one or two subframes of every downlink burst. This allows the radio device to synchronise to the carrier while still leaving sufficient time to download data in later subframes of each downlink burst. Similarly to NSSS, the content of SIB1 or SIB2 can be known a priori, and thus can serve as synchronisation signal.
[0049] As above the legacy NB-loT protocol is preferably as defined in accordance with the Third Generation Partnership Project (3GPP) Release 19.
[0050] In some embodiments of the third aspect, the additional synchronisation signal is only transmitted if one or more of NPDCCH or NPDSCH are transmitted at least to one radio device by the carrier. In such embodiments, the radio device may modify its operation based on the content of the predetermined subframe (e.g. the first subframe of each downlink burst allocated to the radio device on the carrier, or subframe 4 of each downlink burst).
[0051] Thus, in some embodiments, if neither SIBIor NSSS is present in subframe 3 or 4 of a downlink burst, the radio device can determine that there is no data to receive in that downlink burst, and can therefore switch off its oscillator and / or enter a sleep mode until the next transmission by the carrier without monitoring the rest of the downlink subframes of that downlink burst, resulting in a further power saving. The radio device may switch on its oscillator and / or exit the sleep mode for the next transmission on the carrier.
[0052] In an analogous manner, if NSSS is not present in the first subframe allocated to the radio device on the carrier (for an NB-loT non-anchor carrier), or if neither NSSS or a system information block is present in the first subframe allocated to the radio device on the carrier (for an NB-loT non-anchor carrier) the radio device can determine that there is no data to receive in that downlink burst, and can therefore switch off its oscillator and / or enter a sleep mode until the next transmission by the carrier without monitoring the rest of the downlink subframes of that downlink burst, resulting in a further power saving. The radio device may switch on its oscillator and / or exit the sleep mode for the next transmission on the first carrier.
[0053] 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 this disclosure will now be described, byway of example only, with reference to the accompanying drawings, in which:
[0056] FIG. 1 shows a radio system comprising a radio device and a satellite configured to communicate with the radio device using a legacy NB-loT protocol in accordance with the present invention;
[0057] FIG. 2 shows a system frame structure according to a first embodiment of the present invention;
[0058] FIG. 3 shows a system frame structure according to a second embodiment of the present invention;
[0059] FIG. 4 shows a system frame structure according to a third embodiment of the present invention; and
[0060] FIG. 5 shows a system frame structure according to a fourth embodiment of the present invention.
[0061] DETAILED DESCRIPTION
[0062] Figure 1 shows radio system 100 comprising a radio device 1 communicating with a satellite 2 over a NB-loT network 3.
[0063] In the embodiment shown in Figure 1, the radio device 1 is a terrestrial device, (e.g. the radio device 1 is ground based or air-borne such as on an aeroplane), and the satellite 2 is a low Earth orbit (LEO) mobile-satellite radiocommunication service (MSS) satellite located at a height of 600 km above the surface of the Earth. In other embodiments the satellite may have a different orbit, e.g. a medium Earth orbit (MEO), a geostationary Earth orbit (GEO), or a LEO of a different height, e.g.
[0064] 1200 km above the surface of the Earth. Although a single satellite 2 is shown in Figure 1, the satellite 2 may form part of a constellation of satellites, and the radio device 1 may be configured to communicate with any satellite of the constellation.
[0065] Where a satellite of the constellation is in a geostationary orbit, the satellite may be an “Earth fixed cell” configuration, covering a stationary region on the Earth’ssurface having permanent fixed boundaries. However, where a satellite of the constellation has a non-geostationary orbit, the satellite may be in an “Earth moving cell” configuration covering an area on the Earth’s surface that changes over time as the satellite orbits the Earth.
[0066] The radio device 1 may be a 4G LTE or 5G device, such as an LTE-enabled appliance, vehicle, cell phone, etc. Alternatively, the radio device may be a component within such a device (e.g. a system-on-chip radio). The radio device 1 supports the Narrowband-lnternet-of-Things (NB-loT) radio standard developed by 3GPP, and communicates with the satellite 2 over the NB-loT network 3, as explained in the following. Although Figure 1 shows a single radio device 1, it will be appreciated that there may be any number of radio devices in the system 100 in practice.
[0067] The radio device 1 includes a System on Chip integrated circuit (IC) 10, a battery 20, and a transceiver antenna 30 for sending / receiving radio transmissions to / from the satellite 2.
[0068] It will be appreciated that the radio device 1 may contain other discrete components, such as PCBs, oscillators, capacitors, resistors, a housing, user interface features, etc. which are not shown in Figure 1 for the sake of simplicity.
[0069] The IC 10 includes an LTE radio portion 11, a processor 12, a memory 13 (which may include volatile and non-volatile types) and general peripherals 14 (e.g. timers, digital-to-analogue converters, etc.). These elements are all connected to a bus system 15 which facilitates communication between each module in the IC 10.
[0070] The LTE radio 11 portion communicates with the satellite 2 over the MSS allocated band, specifically over the 1616-1626.5 MHz range of the MSS allocated band. The LTE radio portion 11 contains digital and analogue logic for implementing the Narrowband-lnternet-of-Things (NB-loT) radio protocol.
[0071] Of particular relevance to the present invention, the radio portion 11 includes a high frequency temperature-controlled crystal oscillator TCXO 111 that acts as a clock for the radio 11 , allowing the operating frequency of the radio 11 to be controlled inorder to synchronise with carriers of the satellite 2. The radio 11 may also contain conventional components, such as DSPs, amplifiers, etc, as is known in the art. Although the radio device of the embodiment shown in Figure 1 includes a temperature-controlled crystal oscillator 111, in some embodiments the radio device may comprise a high frequency crystal oscillator compensated using software.
[0072] The memory 13 stores software which is executed by the processor 12 for controlling operation of the radio device 1. The software comprises instructions for implementing part of the methods described below with reference to Figure 2-5.
[0073] The satellite 2 contains a radio processing module 200, used to communicate with the radio device 1 over a set of M dedicated NB-loT carriers (i.e. frequency channels). The M carriers comprise both NB-loT anchor carriers, which primarily serve to provide broadcast information and synchronisation signals, and nonanchor carriers, which are used to transmit data to terrestrial radio devices including the radio device 1. In the embodiment shown in Figure 1, the satellite 2 is configured to transmit signals using four different carriers, 201-204. Carrier 201 is an NB-loT anchor carrier, while carriers 202, 203 and 204 are non-anchor carriers.
[0074] The radio device 1 and the satellite 2 communicate using an NB-loT time division duplexing (TDD) mode as described in more detail hereinbelow.
[0075] As explained below, the TDD mode of the embodiment of the present invention described here is a modification of the existing legacy FDD frame structure used for NB-loT in non-terrestrial networks (NTN). The frame structure of the NB-loT NTN TDD mode of the present invention is made up of a set of N 10 ms radio frames, comprising a set of contiguous upload frames, a set of contiguous download frames, and guard periods. The structure is periodic every N frames, where N is set depending on the requirements of the particular carrier.
[0076] Figure 2 shows an exemplary frame structure used in a first embodiment of the invention in which N=9, such that the frame structure is repeated periodically every 90 ms. This period is significantly longer than that used in conventional, terrestrial networks, and is the consequence of the much greater round-trip time of datatransmitted from the ground-based radio device 1 and the satellite 2 in low earth orbit.
[0077] As illustrated in Figure 2, the 90 ms period comprises a simplex time slot, four contiguous uplink slots UL1-UL4, and four contiguous download slots DL1-DL4. The simplex time slot has a length 20.32 ms, and the uplink / downlink slots each have a length of 8.28 ms. The sum of the lengths of the time slots is thus 86.56 ms. However, each slot also has a respective guard period (omitted from Figure 2 for simplicity of illustration) such that the total length of the period over which the frame structure repeats is 90 ms.
[0078] Each frame comprising an uplink slot UL1-UL4 or a downlink slot DL1-DL4 comprises ten subframes (labelled #0 through #9), as illustrated for the slot DL1 in Figure 2. As shown in Figure 2, certain subframes within slot DL1 are reserved for broadcast information and synchronisation signals that are required to operate in accordance with the existing NB-loT protocol. Other subframes are free to be used for data transmission. In particular, subframe #0 is reserved for the Narrowband Physical Broadcast (NPBCH) in every frame, subframe #4 is reserved for the system information block SIB-1 in frames where this is required (as explained below), subframe #5 is reserved for the Narrowband Primary Synchronisation Signal (NPSS) in every frame and subframe #9 is reserved for the Narrowband Secondary Synchronisation signal (NSSS) on even frames only. Subframe #3 may also be used to transmit SIB-1 , however this is not essential. As is known in the art, SIB-1 is transmitted in every other frame, and hence will only be present in either every odd frame or every even frame in practice. Hence, the term “if present”, in Figure 2 will be understood as being dependent on whether it is even or odd frames that are used to carry the SIB-1 signal.
[0079] As well as the requirement that broadcast information and synchronisation signals be provided in certain subframes, there are two additional constraints on the frames and subframes that can be used in the non-terrestrial network of the present invention.
[0080] First, any individual carrier (e.g. carriers 201-204 in Figure 1) is configured to use a single one of the downlink slots DL1-DL4, and a corresponding single one of theuplink slots UL1-UL4 within one 90 ms period, and to use this same slot across all 90 ms periods. A carrier may thus use the slots UL1 and DL1, or UL2 and DL2, or UL3 and DL3 or UL4 or DL4. By contrast, it may not use, for example UL1 and DL2, or UL2 and D3, or UL4 and DL1, etc.
[0081] Secondly, each carrier is configured to use only eight consecutive downlink or uplink subframes (i.e. one 8 ms downlink burst or one 8 ms uplink burst) within any 90 ms period. This may be achieved by using eight subframes in a single frame, or eight subframes across two consecutive frames However, the eight consecutive downlink subframes must include the NPBCH, NPSS, NSSS and SIB-1 signals in order to operate according to the legacy NB-loT protocol.
[0082] As each carrier can only use a single downlink burst of 8 ms in a 90 ms period, and may only use eight subframes within this period, there is a significant delay between successive downlink or uplink windows available on any individual carrier when compared to conventional terrestrial networks. The presence of these long “silent” gaps, in which neither uplink nor downlink occurs, presents challenges for channel estimation and synchronisation between a radio device and the carriers. In particular, it can be difficult to maintain synchronisation between a radio device and a carrier between successive downlink bursts.
[0083] One option to maintain synchronisation would be to keep the TCXO of the radio device running during the silent gaps between successive downlink bursts.
[0084] However, this can impose a power consumption of 1 mA or greater on the radio device which would often be prohibitive for a battery powered device.
[0085] In accordance with the present invention however, the delay between successive downlink bursts can be used to reduce power consumption of the radio device by going into sleep mode without loss of synchronisation, as explained in the following.
[0086] In accordance with the invention, the subframes of each downlink burst used by the radio device are selected as either subframes [34567890] across two consecutive frames, or as subframes [4567890 1] across two consecutive frames. By selecting either of these sequences of subframes, a radio device is able to receive all of the signals (MIB, SIB, NPSS and NSSS) required to operate inaccordance with the legacy NB-loT protocol within the eight consecutive subframes of each downlink burst. In addition, both sequences of subframes allow broadcast information and synchronisation signals to be received by the radio device at an early stage in the sequence of subframes. Specifically, SIB-1 (in subframe #4) and NPSS (in subframe #5) can be received within the first two or three subframes of the eight subframes of the downlink burst, depending on which order is selected. This ordering allows the radio device 1 to switch off its TCXO 111 between successive downlink bursts, while still allowing it to perform synchronisation.
[0087] With further reference to Figure 3, it will be explained how the radio device 1 can be synchronised to a carrier 201-204 according to the first embodiment. In the embodiment shown in Figure 3, the radio device 1 receives downlink signals in the form of downlink bursts, over two different carriers 201 , 202 having a predetermined time offset between their respective downlink bursts. The time offset between respective downlink bursts transmitted on the two carriers may be defined with respect to a common timing reference.
[0088] Specifically, the satellite 2 transmits downlink signals over both a first (unconfigured) carrier 201, and a second (configured) carrier 202, and the radio device 1 receives downlink bursts on both carriers 201, 202. The time offset between the two carriers 201, 202 is stored in the memory 13 of the radio device 1. Frequency information for each of the carriers 201 , 202 is also stored in the memory 13 of the radio device 1 e.g. in the form of an E-LITRA Absolute Radio Frequency Channel Number (EARFCN) of the carriers 201, 202.
[0089] The unconfigured carrier 201 is an NB-loT anchor carrier, which primarily serves to provide broadcast information and synchronisation signals. The NB-loT anchor carrier 201 is configured to transmit all of the broadcast and synchronisation information necessary for the radio device 1 to operate in accordance with the NB-loT standard. The NB-loT anchor carrier 201 therefore provides all of the NPBCH, NPSS, NSSS and SIB-1 signals, and hence has little capacity for transmitting data. The configured carrier is an NB-loT non-anchor carrier 202 which does not transmit broadcast or synchronisation signals, and is used by the radio device 1 for data transmission.The satellite 2 transmits signals in a plurality of frames on the carriers 201, 202, each frame comprising ten subframes [0 1 23456789] respectively. The radio device 1 is configured to use a downlink burst comprising subframes [3456789 0 1] across respective sets of two consecutive frames to communicate with each of the carriers. As there is a time offset between downlink bursts transmitted on the NB-loT anchor carrier 201 and the non-anchor carrier 202, the radio device 1 is able to tune to each of the carriers 201 , 202 at different times. As explained below, the radio device 1 leverages the time offset between downlink bursts transmitted on the two carriers 201 , 202 stored in its memory, along with EARFCN of the carriers and the known length of the frame structure to determine a period in which its TCXO 111 can be switched off without interfering with its ability to synchronise with the carriers.
[0090] The radio device 1 listens for the downlink burst on the NB-loT anchor carrier 201 in its allocated downlink frame for the NB-loT anchor carrier 201 (shown as frame 0 in Figure 3), and uses the synchronisation information obtained in this frame to synchronise the TCXO 111 with the non-anchor carrier 202 ahead of its allocated downlink frame for the non-anchor carrier 202 (shown as frame 2 in Figure 3).
[0091] Specifically, with the TCXO 111 switched on, the radio device 1 receives the SIB-1 signal from the NB-loT anchor carrier 201 in subframe #4 of frame 0, as well as the NPSS signal in subframe #5 of frame 0. Based on the received SIB-1 and NPSS signals, as well as the time offset between downlink bursts transmitted on the NB-loT anchor carrier 201 and non-anchor carrier 202 and the EARFCN of the two carriers 201 , 202, the radio device 1 synchronises the TCXO 111 to the frequency of the non-anchor carrier 202 ahead of its allocated downlink frame for the non-anchor carrier 202 (frame 2 of Figure 3).
[0092] With the TCXO 111 synchronised to the non-anchor carrier 202, the radio device 1 downloads a first data instance from the non-anchor carrier 202 after the known time offset has elapsed, i.e. in frame 2. After frame 2, the TCXO 111 is turned off until the next instance of its allocated downlink frame for the NB-loT anchor carrier 201 (frame 9 of Figure 3), i.e. until the 90 ms silent gap between frame 0 and frame 9 has elapsed. At this time, the TCXO 111 is switched back on, and the nextinstances of SIB-1 and NPSS from the NB-loT anchor carrier 201 (in subframes #4 and #5 of frame 9) are received.
[0093] Based on the received SIB-1 and NPSS from the NB-loT anchor carrier 201, in combination with the time offset between the downlink bursts transmitted on the NB-loT anchor carrier 201 and the non-anchor carrier 202 and the EARFCN on the two carriers 201, 202 stored in the memory 13, the radio device 1 synchronises the TCXO 111 to the non-anchor carrier 202 ahead of the next instance of the downlink burst in its allocated downlink frame for the non-anchor carrier 202 (frame 11 of Figure 3).
[0094] With its TCXO 111 synchronised to the non-anchor carrier 202, the radio device 1 downloads a second data instance from the non-anchor carrier 202 after the time offset has elapsed. The TCXO 111 is then switched off until the next instance of the allocated downlink burst on the NB-loT anchor carrier 201 , and the process can then be repeated for third, fourth, fifth data blocks etc. For example, the process may be repeated until all required data transmission has completed.
[0095] In this way, the radio device 1 is able to leverage synchronisation data transmitted on a first (NB-loT anchor) carrier 201 to synchronise to a second (non-anchor) carrier 202 ahead of an allocated downlink burst on the second carrier. This allows the radio device 1 to switch off its TCXO 111 during a period between sequential transmissions, resulting in a power saving for the radio device 1.
[0096] The method described above relies on multiple carriers 201, 202 to synchronise the radio device 1 after switching the TCXO 111 off during a silent gap between downlink windows. However, in accordance with an alternative synchronisation method the radio device can switch off its TCXO between successive downlink bursts without requiring the use of multiple carriers. Instead, a modification to the NB-loT subframe structure is used to allow the radio device to both synchronise with a carrier and receive data from said carrier in the same frame.
[0097] More particularly, additional instances of synchronisation data are provided in early subframes of downlink bursts transmitted to the radio device. This allows the radio device to synchronise with the carrier while still leaving sufficient time to downloaddata in later subframes. Two ways in which this can be achieved are described below with reference to Figures 4 and 5.
[0098] In the first method, the frame structure is modified such that subframe #4 contains synchronisation information in both odd and even frames, as shown in Figure 4. In the modified frame structure, frames in which subframe #4 does not include SIB-1 in the existing NB-loT protocol (i.e. in either all odd frames or all even frames), are modified to include additional broadcast or synchronisation information.
[0099] In the example shown in Figure 4, an extra copy of NSSS is included in subframe #4 of frames that do not carry SIB-1 (i.e. odd frames in this example). However, in some alternative examples, subframe #4 may instead be modified to carry another essential SIB, such as SIB2.
[0100] With this modification, the radio device 1 configured to use downlink bursts comprising subframes [34567890] across two consecutive frames, as described above, may turn off its TCXO 111 and wake up at the next valid downlink subframe #4 (subframe #4 of frame 2 in Figure 4). The radio device 1 can then receive subframes #4 and #5, and based on the content of these subframes (regardless of whether the frame is an even frame or an odd frame) the radio device 1 can synchronise its downlink frequency to the carrier after the TXCO 111 is switched on. More particularly, in radio frames where SIB1 is present in subframe #4 (i.e. even frames), the NPSS signal used in subframe #5 is used for resynchronisation to the carrier, while in radio frames where an extra copy of NSSS is present in subframe #4 (i.e. odd frames), the re-synchronisation of the radio device 1 is performed using the extra NSSS signal.
[0101] Having synchronised to the carrier, the radio device 1 may receive data in later subframes of the eight consecutive subframes of the downlink burst allocated to the radio device, before turning the TXCO 111 off again at the end of the 8 consecutive subframes (i.e. at the end of the downlink burst). The radio device 1 can then switch the TXCO 111 back on before the next valid downlink subframe #4 (subframe #4 of frame 11 in Figure 4), and repeat the process. This allows the TXCO 111 to be switched off during the period between sequential transmissions, i.e. for almost 80ms in the example shown in Figure 4, resulting in a power saving for the radio device 1.
[0102] The additional synchronisation signal in subframe #4 is only transmitted if one or more of NPDCCH or NPDSCH are transmitted at least to one radio device by the carrier. This allows the radio device 1 to modify its operation based on the content of subframe #4. In particular, if neither SIBIor NSSS is present in subframe #4, the radio device determines that there is no data to receive in that frame, and therefore switches off its TCXO 111 until the next transmission by the carrier without monitoring the rest of the downlink subframes of that radio frame, resulting in a further power saving.
[0103] Another way of achieving a similar effect is illustrated by the modified frame structure shown in Figure 5, whereby the first subframe of the eight consecutive subframes used by the radio device 1 (i.e. subframe #3) contains additional synchronisation information in the form of an extra copy of NSSS in both odd and even frames. This method can be used so long as the first subframe is not subframe #9, which would disrupt cell timing recovery in the radio system.
[0104] Providing an extra copy of NSSS in the first subframe of the eight downlink subframes available to the radio device 1 in each downlink burst ensures that the radio device 1 does not need to receive control or data channels in the first subframe it receives in the downlink burst, and also provides sufficient energy to perform synchronisation even in low signal to noise ratio conditions.
[0105] With this modification, a radio device 1 configured to use downlink bursts comprising subframes [34567890] across two consecutive frames (as shown in Figure 5) may turn off its TCXO 111 and wake up at the next valid downlink frame (frame 2 in Figure 5). The radio device 1 can then download the extra NSSS provided in subframe #3 of frame 2, can use the received NSSS to synchronise timing and frequency with the carrier, such that the radio device 1 is ready to receive data on the carrier in subframe #4.
[0106] Having synchronised to the carrier, the radio device 1 may receive data in later subframes of the eight consecutive subframes allocated to the radio device 1 ineach downlink burst, before turning the TXCO 111 off again at the end of the eight consecutive subframes. The radio device 1 can then switch the TXCO 111 back on before the next valid downlink frame (frame 11 in Figure 5), and repeat the process. This allows the TXCO 111 to be switched off during a period between sequential transmissions, i.e. for almost 80 ms in the example shown in Figure 5, resulting in a very significant power saving for the radio device 1.
[0107] Where this method is employed by an NB-loT anchor carrier, the extra copy of NSSS can only be present in a downlink burst provided it does not collide with the transmission of a System Information transmission. However, for non-anchor carriers, the extra copy of NSSS is transmitted in every downlink burst for the radio device (i.e. with a with periodicity of 90 ms in the embodiment shown in Figure 5).
[0108] In this embodiment, the extra copy of NSSS is only transmitted if one or more of NPDCCH or NPDSCH are transmitted at least to one radio device on the carrier within the set of eight consecutive downlink subframes of the downlink burst. The absence of the extra NSSS signal therefore acts as a sleep signal for the radio device 1. The radio device 1 modifies its operation based on the content of the first subframe of the 8 consecutive subframes of the downlink burst. In particular, if NSSS is not present in the first subframe of a downlink burst (on an NB-loT nonanchor carrier), or if neither NSSS or a system information block is present in the downlink burst (on an NB-loT anchor carrier) the radio device 1 determines that there is no data to receive in that frame and therefore switches off its TCXO 111 until the next transmission by the carrier without monitoring the rest of the downlink subframes of that radio frame, resulting in a further power saving.
[0109] It will be appreciated by those skilled in the art that the present disclosure has been illustrated by describing one or more specific examples thereof, but is not limited to these examples; many variations and modifications are possible, within the scope of the accompanying claims.
Claims
CLAIMS1. A method of operating a radio device, the method comprising:receiving, at the radio device, channel information for a first carrier and a second carrier, the channel information encoding at least i) the frequency of the first carrier and the second carrier and ii) a time offset between respective downlink bursts transmitted on each of the first and second carriers;receiving, at the radio device, a first synchronisation signal on the first carrier;synchronising an oscillator of the radio device to the second carrier based on the first synchronisation signal and the channel information;receiving first data on the second carrier;after receiving the first data, switching off an oscillator of the radio device for a predetermined duration, wherein the predetermined duration is set based on the offset between the two carriers and a known periodicity of signals transmitted over the first and second carriers;at the end of the predetermined duration: andswitching on the oscillator;receiving a second synchronisation signal at the radio device on the first carrier;synchronising the oscillator to the second carrier based on the second synchronisation signal and the channel information; and receiving data on the second carrier.
2. The method of claim 1 , wherein the first synchronisation signal and / or the second synchronisation signal comprises a synchronisation signal according to a legacy NB-loT protocol.3 The method of claim 2, wherein the first synchronisation signal and / or the second synchronisation signal comprises a narrowband primary synchronisation signal or a narrowband secondary synchronisation signal (NSSS).
4. The method of claim 2 or 3, wherein the first synchronisation signal and / or the second synchronisation signal comprises a further copy of the NSSS in addition to the NSSS required by the legacy NB-loT protocol5. The method of claim 4, wherein the further copy of NSSS is provided in the first subframe of each downlink burst allocated to the radio device on the carrier.
6. The method of claim 4 or 5, wherein the further copy of NSSS is transmitted in a downlink burst only if NPDCCH and / or NPDSCH has been transmitted to the radio device or another radio device on the carrier in said downlink burst.
7. The method of claim 5 or 6, wherein the first subframe of each downlink burst allocated to the radio device is subframe 3 or subframe 4.
8. The method of any preceding claim, wherein the first carrier is an NB-loT anchor carrier, and wherein the second carrier is an NB-loT non-anchor carrier.
9. The method of any preceding claim, wherein the first carrier and the second carrier operate in the 1616-1626.5 MHz MSS allocated band.
10. The method of any preceding claim, wherein an interval between signals being transmitted on the first carrier and / or the second carrier is greater than 50 ms.
11. The method of any preceding claim, wherein a time difference between the downlink bursts transmitted on the first carrier and second carrier is greater than 8 ms.
12. The method of any preceding claim, wherein receiving the first synchronisation signal on the first carrier comprises receiving the first synchronisation signal in a first instance of a set of one or more downlink frames allocated to the radio device on the first carrier; and whereinswitching off the oscillator of the radio device comprises switching off the oscillator until a next instance of a set of one or more allocated downlink frames on the first carrier is scheduled for transmission.
13. A radio device for a system comprising a radio device and a satellite configured to communicate with the radio device on a first carrier and a second carrier, wherein the radio device is configured to:receive channel information encoding at least i) a frequency of the first carrier and the second carrier and ii) a time offset between respective downlink bursts transmitted on each of the first and second carriers ;receive a first synchronisation signal on the first carrier; synchronise an oscillator of the radio device to the second carrier based on the first synchronisation signal and the channel information; receive first data on the second carrier;after receiving the first data, switch off the oscillator for a predetermined duration set based on the offset and a known periodicity of signals transmitted on the first and second carriers; andat the end of the predetermined duration:switch on the oscillator;receive a second synchronisation signal on the first carrier; synchronise the oscillator to the second carrier based on the second synchronisation signal and the channel information; andreceive data on the second carrier.
14. A method of synchronising an NB-loT radio device with a carrier, wherein the radio device is operable to receive signals according to a legacy NB-loT protocol, the method comprising using the carrier to transmit an additional synchronisation signal to those required by the legacy NB-loT protocol, and the radio device using the additional synchronisation signal to synchronise to the carrier.
15. The method of claim 14, wherein the additional synchronisation signal is provided in the first subframe of each downlink burst allocated to the radio device on the carrier.
16. The method of claim 14, wherein the carrier is configured to transmit a system information block in a predetermined subframe of every other frame, and to transmit the additional synchronisation signal in the predetermined subframe in frames in which the system information block is not transmitted.
17. The method of any of claims 14-16, wherein the additional synchronisation signal is a further copy of NSSS in addition to the NSSS required by the legacy NB-loT protocol.
18. The method of claim 16, wherein the additional synchronisation signal is a System Information Block that is not required to be read during radio resource controlled connected mode.