EP4659420A1

EP4659420A1 - A radio network node, a wireless communications device and methods for synchronization provision in a wireless communications network

Info

Publication number: EP4659420A1
Application number: EP23702793.3A
Authority: EP
Inventors: Henrik Sjöland; Gang ZOU; Andres Reial; Sina MALEKI
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2023-01-31
Filing date: 2023-01-31
Publication date: 2025-12-10
Also published as: WO2024160356A1; CN120569942A

Abstract

A method, performed by a radio network node, for synchronization provision in a wireless communications network. The method comprises broadcasting (703) to one or more wireless communications devices within the wireless communications network a single- tone synchronization signal according to a configuration of the single-tone synchronization signal.

Description

A RADIO NETWORK NODE, A WIRELESS COMMUNICATIONS DEVICE AND METHODS

FOR SYNCHRONIZATION PROVISION IN A WIRELESS COMMUNICATIONS NETWORK

TECHNICAL FIELD

The embodiments herein relate to a radio network node, a wireless communications device and methods for synchronization provision in a wireless communications network. A corresponding computer program and a computer program carrier are also disclosed.

BACKGROUND

In a typical wireless communication network, wireless devices, also known as wireless communication devices, mobile stations, stations (STA) and/or User Equipments (UE), communicate via a Local Area Network such as a Wi-Fi network or a Radio Access Network (RAN) to one or more core networks (CN). The RAN covers a geographical area which is divided into service areas or cell areas. Each service area or cell area may provide radio coverage via a beam or a beam group. Each service area or cell area is typically served by a radio access node such as a radio access node e.g., a Wi-Fi access point or a radio base station (RBS), which in some networks may also be denoted, for example, a NodeB, eNodeB (eNB), or gNB as denoted in 5G. A service area or cell area is a geographical area where radio coverage is provided by the radio access node. The radio access node communicates over an air interface operating on radio frequencies with the wireless device within range of the radio access node.

Specifications for the Evolved Packet System (EPS), also called a Fourth Generation (4G) network, have been completed within the 3rd Generation Partnership Project (3GPP) and this work continues in the coming 3GPP releases, for example to specify a Fifth Generation (5G) network also referred to as 5G New Radio (NR). The EPS comprises the Evolved Universal Terrestrial Radio Access Network (E-UTRAN), also known as the Long Term Evolution (LTE) radio access network, and the Evolved Packet Core (EPC), also known as System Architecture Evolution (SAE) core network. E-UTRAN/LTE is a variant of a 3GPP radio access network wherein the radio access nodes are directly connected to the EPC core network rather than to RNCs used in 3G networks. In general, in E-UTRAN/LTE the functions of a 3G RNC are distributed between the radio access nodes, e.g. eNodeBs in LTE, and the core network. As such, the RAN of an EPS has an essentially “flat” architecture comprising radio access nodes connected directly to one or more core networks, i.e. they are not connected to RNCs. To compensate for that, the E-UTRAN specification defines a direct interface between the radio access nodes, this interface being denoted the X2 interface. Wireless communication systems in 3GPP

Figure 1 illustrates a simplified wireless communication system. Consider the simplified wireless communication system in Figure 1 , with a UE 12, which communicates with one or multiple access nodes 103-104, which in turn is connected to a network node 106. The access nodes 103-104 are part of the radio access network 10.

For wireless communication systems pursuant to 3GPP Evolved Packet System, (EPS), also referred to as Long Term Evolution, LTE, or 4G, standard specifications, such as specified in 3GPP TS 36.300 and related specifications, the access nodes 103-104 corresponds typically to Evolved NodeBs (eNBs) and the network node 106 corresponds typically to either a Mobility Management Entity (MME) and/or a Serving Gateway (SGW). The eNB is part of the radio access network 10, which in this case is the E-UTRAN (Evolved Universal Terrestrial Radio Access Network), while the MME and SGW are both part of the EPC (Evolved Packet Core network). The eNBs are inter-connected via the X2 interface, and connected to EPC via the S1 interface, more specifically via S1-C to the MME and S1-U to the SGW.

For wireless communication systems pursuant to 3GPP 5G System, 5GS (also referred to as New Radio, NR, or 5G) standard specifications, such as specified in 3GPP TS 38.300 and related specifications, on the other hand, the access nodes 103-104 corresponds typically to an 5G NodeB (gNB) and the network node 106 corresponds typically to either an Access and Mobility Management Function (AMF) and/or a User Plane Function (UPF). The gNB is part of the radio access network 10, which in this case is the NG-RAN (Next Generation Radio Access Network), while the AMF and UPF are both part of the 5G Core Network (5GC). The gNBs are inter-connected via the Xn interface, and connected to 5GC via the NG interface, more specifically via NG-C to the AMF and NG-U to the UPF.

To support fast mobility between NR and LTE and avoid change of core network, LTE eNBs may also be connected to the 5G-CN via NG-U/NG-C and support the Xn interface. An eNB connected to 5GC is called a next generation eNB (ng-eNB) and is considered part of the NG-RAN. LTE connected to 5GC will not be discussed further in this document; however, it should be noted that most of the solutions/features described for LTE and NR in this document also apply to LTE connected to 5GC. In this document, when the term LTE is used without further specification it refers to LTE-EPC.

NR uses Orthogonal Frequency Division Multiplexing (OFDM) with configurable bandwidths and SubCarrier Spacing (SOS) to efficiently support a diverse set of use-cases and deployment scenarios. With respect to LTE, NR improves deployment flexibility, user throughputs, latency, and reliability. The throughput performance gains are enabled, in part, by enhanced support for Multi-User Multiple-Input Multiple-Output (MU-MIMO) transmission strategies, where two or more UEs receives data on the same time frequency resources, i.e., by spatially separated transmissions.

For a mobile device equipped with a mmWave communication circuit, the power consumption in active mode by its millimeter wave phased array system is high, since many receivers or transmitters must be operated in parallel. The high operating frequency also makes the power consumption high. Means to increase the battery life in mobile devices are thus needed. mmWave communication systems require accurate frequency synchronization, since even a small relative frequency error becomes large in absolute terms. For instance, a 50 ppm error corresponds to 5 MHz error at 100 GHz. A receiver and transmitter are synchronized when their frequency references are adjusted to be substantially equal in frequency, i.e. for the same frequency setting in receiver and transmitter they should generate almost the same carrier frequency. The time must also be accurately synchronized due to shorter symbol time being used in high frequency systems.

Synchronization is for example required for detectors to recover digital data properly from the modulated signal. In the case of coherent phase demodulation, such as phase shift keying, the receiver is assumed to be able to generate reference signals whose phases are identical (except perhaps for a constant offset) to those of the signaling alphabet at the transmitter.

With present solutions, a wireless communications device must use a full antenna array at frequent time intervals to receive synchronization information from the wireless communications network. Conventional synchronization using existing Reference Signals (RS) has a high energy overhead. In wireless communications devices with low traffic, this will be a main limitation to achievable battery time.

On the other hand, to ensure frequency synchronization accuracy by a wireless communications device, the synchronization signals broadcasted from the wireless communications network generally contain multiple subcarriers in frequency domain and multiple symbols in time domain. For example, in 3GPP NR, the synchronization signal, i.e., the Synchronisation Signal Block (SSB), contains 240 subcarriers and 4 symbols in time duration. The subcarrier spacing is 15kHz or 30kHz for NR FR1 , and 120kHz or 240kHz for NR Frequency Range 2 (FR2). The corresponding frequency bandwidth of SSB is 3.6MHz, 7.2MHz, 28.8MHz and 57.6MHz respectively. Moreover, when waking up from deep sleep, a wireless communications device may have to perform synchronization by monitoring multiple instances of the synchronization signal to meet the frequency synchronization accuracy.

SUMMARY There is thus a need for a more efficient approach for frequency synchronization. For example, it would be beneficial if a full antenna array with all transceivers were active only during actual transmission or reception of data.

An object of embodiments herein may be to obviate some of the problems related to frequency synchronization mentioned above.

According to a first aspect, the object is achieved by a method, performed by a radio network node, for synchronization provision in a wireless communications network (100).

The method comprises broadcasting to one or more wireless communications devices within the wireless communications network a single-tone synchronization signal according to a configuration of the single-tone synchronization signal.

According to a second aspect, the object is achieved by a radio network node, such as a base station. The radio network node is configured to perform the method according to the first aspect above.

According to a third aspect, the object is achieved by a method, performed by a wireless communications device, for synchronization of wireless communication between the wireless communications device and a radio network node of a wireless communications network operating at a first frequency range, for example within mmWave. The wireless communications device comprises a first Radio Frequency, RF, receiver for wireless communication of data or control signals or both within the wireless communications network at the first frequency range and a second RF receiver operating at the first frequency range and at a reduced power consumption compared to a power consumption of the first RF receiver when active.

The method comprises receiving, from the radio network node, a single-tone synchronization signal within the first frequency range using the second RF receiver. The first RF receiver may be in an inactive mode when the single-tone synchronization signal is received by the second RF receiver.

The method further comprises comparing a carrier frequency of the single-tone synchronization signal and a frequency of a Local Oscillator, LO, of the second RF receiver. The first RF receiver may be in the inactive mode when comparing the carrier frequency of the single-tone synchronization signal and the frequency of the LO of the second RF receiver.

The method further comprises tuning a common reference oscillator of the first RF receiver and the second RF receiver based on a frequency difference between the carrier frequency of the single-tone synchronization signal and the frequency of the LO of the second RF receiver such that the frequency difference is tuned to a target value. The first RF receiver may be in the inactive mode when tuning the common reference oscillator. The method further comprises synchronizing the wireless communications device in time with the radio network node based on the second RF receiver correlating the received modulating data sequence with a reference data sequence in time domain. The first RF receiver may be in the inactive mode when synchronizing the wireless communications device in time with the radio network node.

The method further comprises communicating, by the first RF receiver, control or data signals or both with the radio network node at the first frequency range based on the tuned common frequency reference and the time synchronization of the wireless communications device with the radio network node. The first RF receiver may be activated before communicating control or data signals or both with the radio network node. The above operations of the second RF receiver may be performed between transmissions to or from the radio network node or between measurements or between transmissions and measurements using the first RF receiver. The second RF receiver may perform the above actions continuously.

According to a fourth aspect, the object is achieved by a wireless communications device, such as a UE. The wireless communications device is configured to perform the method according to the third aspect above.

According to a further aspect, the object is achieved by a computer program comprising instructions, which when executed by a processor, causes the processor to perform actions according to any of the aspects above.

According to a further aspect, the object is achieved by a carrier comprising the computer program of the aspect above, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

Since the high-power first RF receiver communicates control or data signals or both with the radio network node based on a synchronization achieved by the low-power second RF receiver receiving the single-tone synchronization signal synchronization using the high-power first RF receiver is not necessary.

The above aspects enable synchronisation of the wireless communications device with a small overhead and a low power consumption of the wireless communications device. The low power consumption improves battery time in low-traffic wireless communications devices. Further, since the power consumption due to synchronization is low the wireless communications device may perform the synchronisation often, e.g., continuously, which means that embodiments herein enable a quick response for data reception and transmission.

Specifically, embodiments herein enable millimeter wave connection in loT sensors and other low power applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of embodiments disclosed herein, including particular features and advantages thereof, will be readily understood from the following detailed description and the accompanying drawings, in which:

Figure 1 illustrates a simplified wireless communication system,

Figure 2 is a block diagram schematically illustrating a wireless communications network wherein embodiments herein may be implemented,

Figure 3 is a block diagram schematically illustrating a wireless communications device according to embodiments herein,

Figure 4 is a block diagram schematically illustrating further details of a wireless communications device according to embodiments herein,

Figure 5 is a block diagram schematically illustrating further details of a wireless communications device according to some embodiments herein,

Figure 6 is a graph illustrating examples of a modulation pattern,

Figure 7 is a flow chart describing a method performed by a radio network node according to embodiments herein,

Figure 8 is a flow chart describing a method performed by a wireless communications device according to embodiments herein,

Figure 9 is a block diagram schematically illustrating a radio network node according to embodiments herein,

Figure 10 is a block diagram schematically illustrating a wireless communications device according to embodiments herein,

Figure 11 schematically illustrates a telecommunication network connected via an intermediate network to a host computer.

Figure 12 is a generalized block diagram of a host computer communicating via a base station with a user equipment over a partially wireless connection.

Figures 13 to 16 are flowcharts illustrating methods implemented in a communication system including a host computer, a base station and a user equipment.

DETAILED DESCRIPTION

Embodiments herein relate to frequency synchronization in a wireless communications network. Figure 2 is a schematic overview depicting a wireless communications network 100 wherein embodiments herein may be implemented. The wireless communications network 100 comprises one or more RANs and one or more CNs. The wireless communications network 100 may use a number of different technologies, such as Wi-Fi, Long Term Evolution (LTE), LTE- Advanced, 5G, New Radio (NR), Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications/enhanced Data rate for GSM Evolution (GSM/EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible implementations. Embodiments herein relate to recent technology trends that are of particular interest in a 5G context. However, embodiments are also applicable in further development of other existing wireless communication systems such as e.g. WCDMA and LTE and in future wireless communication systems, such as 6G systems.

Access nodes operate in the wireless communications network 100 such as a radio access node 111. The radio access node 111 provides radio coverage over a geographical area, a service area referred to as a cell 115, which may also be referred to as a beam or a beam group of a first radio access technology (RAT), such as 5G, LTE, Wi-Fi or similar. There may be more than one cell. For example, there may be a second cell 116 as well. The radio access node 111 may be a NR-RAN node, transmission and reception point e.g. a base station, a radio access node such as a Wireless Local Area Network (WLAN) access point or an Access Point Station (AP STA), an access controller, a base station, e.g. a radio base station such as a NodeB, an evolved Node B (eNB, eNode B), a gNB, a base transceiver station, a radio remote unit, an Access Point Base Station, a base station router, a transmission arrangement of a radio base station, a stand-alone access point or any other network unit capable of communicating with a wireless device within the service area depending e.g. on the radio access technology and terminology used. The respective radio access node 111 may be referred to as a serving radio access node and communicates with a UE with Downlink (DL) transmissions to the UE and Uplink (UL) transmissions from the UE.

A number of wireless communications devices operate in the wireless communication network 100, such as a wireless communications device 121. The wireless communications device 121 may be connected to the wireless communications network 100 through the radio access node 111. The wireless communications device 121 may communicate with the radio access node 111 by transmitting data or control signals on an UL communications link UL- 123 illustrated in Figure 2. The wireless communications device 121 may also receive data or control signals from the radio access node 111 on a DL communications link DL-123 illustrated in Figure 2. Each of the UL communications link UL-123 and the DL communications link DL-123 may use a mmWave-frequency band, e.g. NR FR2.

The UE 121 may be a mobile station, a non-access point (non-AP) STA, a STA, a user equipment and/or a wireless terminal, that communicate via one or more Access Networks (AN), e.g. RAN, e.g. via the radio access node 111 to one or more core networks (CN) e.g. comprising a CN node 130, for example comprising an Access Management Function (AMF). It should be understood by the skilled in the art that “UE” is a non-limiting term which means any terminal, wireless communication terminal, user equipment, Machine Type Communication (MTC) device, Device to Device (D2D) terminal, or node e.g. smart phone, laptop, mobile phone, sensor, relay, mobile tablets or even a small base station communicating within a cell.

Embodiments herein disclose methods for improved synchronization of the wireless communications device 121 by synchronizing the wireless communications device 121

Figure 3 is a block diagram schematically illustrating the wireless communications device 121 according to embodiments herein. The wireless communications device 121 is configured for communication with the radio network node 111. The wireless communications device 121 comprises a first RF receiver 410 for wireless communication of data or control signals or both with the radio network node 111. The wireless communications device 121 further comprises a second RF receiver 420 operating at a reduced power consumption compared to a power consumption of the first RF receiver 410 when active. That is, when the second RF receiver 420 is active it operates at a reduced power consumption compared to the power consumption of the first RF receiver 410 when the first RF receiver 410 is active. In some embodiments herein the first RF receiver 410 is referred to as a full receiver. The full receiver may also be referred to as a main receiver. Both the first RF receiver 410 and the second RF receiver 420 may operate at mmWave frequencies.

The reduced power consumption may for example be due to front end amplifiers with lower power demands due to relaxed noise or linearity requirements or local oscillators with relaxed phase noise requirements or fewer front-end branches. In some other embodiments the reduced power consumption is due to analog to digital converters with less bandwidth and hence less power consumption. The second RF receiver 420 may also be connected to fewer antennas than the first RF receiver 410. For example, the first RF receiver 410 may be a wideband, multi-antenna receiver, and the second RF receiver 420 may be a narrow-band, singleantenna receiver. The second RF receiver 420 may be a separate receiver hardware block or a reduced-power operating mode of the first RF receiver 410. A bandwidth of the second RF receiver 420 may be narrower than one to five subcarrier spacings, such as narrower than one subcarrier spacing. In some embodiments herein the bandwidth of the second RF receiver 420 is within 1-1000 kHz, preferably within 3-20 kHz, such as 10 kHz.

In Figure 3 the first RF receiver 410 is connected to a first primary antenna element 411 and a second primary antenna element 412 while the second RF receiver 420 is connected to a secondary antenna element 421. The antenna elements may be part of a phased array antenna system. The antenna elements may be configured to operate at mmWave frequencies. The wireless communications device 121 comprises at least one local oscillator (LO), e.g., for frequency conversion of received and transmitted RF signals. In electronics, an LO is an electronic oscillator used with a mixer to change the frequency of a signal. This frequency conversion process, also called heterodyning, produces signals at the sum and difference of the frequency of the LO and the frequency of the input signal. Processing a signal at a fixed center frequency after conversion gives a radio receiver improved performance. In many receivers, the function of LO and mixer is combined in one stage called a "converter".

In some embodiments herein the first RF receiver 410 comprises or is connected to a first LO 441 , while the second RF receiver 420 comprises or is connected to a second LO 442. The first and second LOs 441 , 442 may for example be used for frequency conversion by the respective first and second RF receiver 410, 420.

The second LO 442 may be used for frequency conversion of a single-tone synchronization signal from the radio network node 111. The first LO 441 may be used for frequency conversion of data or control signals, e.g., to and from the radio network node 111. The first LO 441 may be optimized for high performance, while the second LO 442 may be optimized for low power. In some embodiments herein the second LO 442 comprises common components with the first LO 441. For example, all components of the first LO 441 may be common with the second LO 442. In such embodiments the common components may be reconfigurable. An advantage of using common components for the first LO 441 and the second LO 442 is that less space is needed for the first and second RF receivers 410, 420. The frequency of the single-tone synchronization signal may be in a same frequency range as used for the carrier for the connection between the radio network node 111 and the wireless communications device 121. For example, the single-tone synchronization signal may be in the mmWave range, such as in 3GPP FR2. Using the mmWave spectrum for broadcasting the single-tone synchronization signal is advantageous since currently there are many free frequencies in this frequency range.

The second LO 442 may be a low-power and low-cost LO compared to the first LO 441.

Figure 4 is a block diagram schematically illustrating further details of the wireless communications device 121 and the second RF receiver 420 according to embodiments herein.

In Figure 4 the second RF receiver 420 is illustrated as a heterodyne receiver. However, a homodyne receiver may also be used at the expense of using quadrature mixers and quadrature LO signal. With quadrature LO, twice as many LO signal phases are needed, and the generation of quadrature LO signals also requires a 90-degree phase shift at high frequency, which may be created in different ways all costing power. Thus, the heterodyne receiver may save power compared to a homodyne receiver with quadrature RF mixers, e.g., when operating with a low Intermediate Frequency (IF) and operating the heterodyne receiver so that the image frequency falls inside a quiet band, such as a guard band. When the image frequency falls in a quiet band, image rejection is not necessary, which saves power.

The first and second LOs 441, 442 may each comprise a frequency synthesizer such as a frequency synthesizer 510 of the second LO 442 illustrated in Figure 4. Each frequency synthesizer may comprise an oscillator controlled by a signal, such as a Voltage-Controlled Oscillator (VCO) or a digitally controlled oscillator. Each frequency synthesizer may further comprise or be connected to a reference oscillator such as a common reference oscillator XO. Each reference oscillator, such as the common reference oscillator XO, may be a crystal oscillator. The crystal oscillator may be an electronic oscillator circuit that uses a piezoelectric crystal as a frequency-selective element. The crystal oscillator may maintain a reference frequency with high stability.

Although the first RF receiver 410 and the second RF receiver 420 may have separate LOs they may still use the same frequency reference, that is the same reference oscillator XO. By using the same reference oscillator XO it is possible to adjust the frequency reference of the first RF receiver 410 based on the synchronization signal received with the second RF receiver 420.

Each frequency synthesizer may be based on a Phased-Locked Loop (PLL). Figure 5 shows basic elements and an arrangement of a PLL-based frequency synthesizer, such as the frequency synthesizer 510 of the second LO 442. Thus, the second LO 442 may comprise a PLL. In Figure 5 the PLL is an example of an analog PLL. The analog PLL may comprise a VCO while a digital PLL may comprise a digitally controlled oscillator. The PLL-based frequency synthesizer 510 is a feedback control system. It compares the phases of two input signals at a phase-frequency detector 512 and produces an error signal that is proportional to the difference between their phases. A first input signal is derived from a signal from the common reference oscillator XO. The error signal may pass through a charge pump 513 and is then low pass filtered in a low-pass filter 514 and used to drive a VCO 511 which creates an output frequency. The output frequency is fed through a frequency divider 515 back to the input of the system, producing a negative feedback loop. Thus, a second input signal is derived from the output of the VCO 511 after frequency division by the frequency divider 515.

If the output frequency of the VCO 511 drifts, the phase error signal will increase, driving the frequency in the opposite direction so as to reduce the error. Thus, the output is locked to the frequency of the reference oscillator XO at the other input.

Turning back to Figure 4, the second RF receiver 420 may comprise one or more receiver branches Rx1, Rx2, Rx3, Rx4. Each receiver branch Rx1 , Rx2, Rx3, Rx4 may be connected to an antenna element A11, A12, A21, A22. For example, a first receiver branch Rx1 may be connected to a first secondary antenna element A11. A second receiver branch Rx2 may be connected to a second secondary antenna element A12 and so forth.

In Figure 4 only the components of the first receiver branch Rx1 is shown for simplicity. However, each receiver branch Rx1 , Rx2, Rx3, Rx4 may comprise the components of the first receiver branch Rx1. Thus, according to Figure 4 each receiver branch Rx1, Rx2, Rx3, Rx4 may comprise the following components in the following or any other suitable order: an RF filter 520, a Low Noise Amplifier (LNA) 530, an RF Mixer 540, an IF filter 550, an Analog Digital Converter (ADC) 560, a first digital filter 570, a Digital DownConverter (DDC) 575, a second digital filter 576, an envelope detector 577 for rectification of the signal and a correlator 580. The second digital filter 576, after the DDC 575, will remove unwanted mixing components around 2*IF frequency. The envelope detector 577 may be disabled when the frequency synchronization is accurate enough to support Angle of Arrival (AoA) detection of signals from the radio network node 113, such as synchronisation signals. If the envelope detector 577 is used then the output of the correlator is a real number. If the envelope detector 577 is not used, the correlator works on complex input data: I and Q. The correlator in each active receiver branch then outputs a complex number which may be described with a magnitude and a phase and may be used to estimate AoA.

As shown in Figure 4 the second RF receiver 420 in the wireless communications device 121 may be equipped with four separate antenna elements arranged in a 2x2 matrix (two horizontal and two vertical antenna elements illustrated in the lower left corner of Figure 4), to which four receiver branches are connected, with separated LNA, down-conversion mixer, filter, ADC, digital filter, correlator etc. The receiver branches, using the same LO signal for all the mixers and the same digital LO signal for the digital downconversion when applicable, e.g., in the heterodyne case, may then be used to detect a synchronization signal which is transmitted by the radio network node 111.

Although Figure 4 illustrates the wireless communications device 121 comprising four secondary antenna elements A11 , A12, A21, A22 connected to four receiver branches Rx1, Rx2, Rx3, Rx4 of the second RF receiver 420 some embodiments herein disclose a singleantenna and single-receiver branch second RF receiver 420.

The wireless communications device 121 may further comprise a nullforming unit 590. The nullforming unit 590 may be digital. The second RF receiver 420 may comprise the nullforming unit 590. The nullforming unit 590 is connected to two or more of the receiver branches Rx1 , Rx2, Rx3, Rx4. For example, in some embodiments herein the nullforming unit 590 is connected to all receiver branches Rx1 , Rx2, Rx3, Rx4. Some embodiments herein utilize the fact that when the number of antenna elements is small, an RF reception null is sharper than the corresponding receive beam, which may be used for estimating an AoA of the transmitted beam.

After the nullforming unit 590, there may also be a bank of parallel complex digital bandpass filters 591, each followed by a respective envelope detector 577 and correlator 580. The respective digital filter of the bank of digital filters is tuned to a centre frequency which is different from the other centre frequencies of the other digital filters of the bank of digital filters, to find if the received synchronization signal has a corresponding frequency offset from the frequency where the synchronization signal would occur without frequency errors.

In embodiments disclosed herein the radio network node 113 transmits a reference signal intended for synchronization of frequency and time at one or more pre-determined frequencies. In embodiments herein the synchronization signal may also be referred to as a Frequency Reference Signal (FRS). The synchronization signal may have a very low bandwidth. Despite the synchronization reference signal having limited power, the low bandwidth allows it to be received with a single antenna receiver, such as the second RF receiver 420, of the wireless communications device 121. The low bandwidth and single antenna receiver may be implemented with low power consumption.

The frequency of the FRS may be fixed and known to the wireless communications device 121. The wireless communications device 121 uses the second RF receiver 420 to track the FRS and continually tunes the second LO 442 to minimize the frequency offset to the FRS. Thus, the wireless communications device 121 is able to continuously maintain an accurate frequency and time synchronization with the wireless communications network 100 and is therefore ready for immediate data transmission or reception without requiring additional synchronization operations.

By tuning the second RF receiver 420 to the synchronization signal, e.g., by tuning the second LO 442 to the synchronization signal, accurate frequency synchronization between the wireless communications network 100 and the wireless communications device 121 is achieved and maintained. When communication is to occur, no additional frequency synchronization is needed for using the first RF receiver 410 having high power consumption. Furthermore, by tuning to the synchronization signal, e.g. by tuning the common reference oscillator XO of the wireless communications device 121, a clock timing of the wireless communications device 121 may accurately track that of the wireless communications network 100. This means that after correct timing has been established by the wireless communications device 121 using the first RF receiver 410, correct timing may be maintained for a long time with low power consumption using just the second RF receiver 420.

The frequency reference signal may be transmitted out-of-band with respect to data or integrated into OFDM signal transmission, e.g. using one subcarrier location, including Modulation Coding Scheme (MCS) modification to make the transmission of the frequency reference signal transparent to legacy wireless communications devices.

For the synchronization signal a constant amplitude and frequency tone may be used, but for increased robustness it is preferred to overlay a modulation to identify that the proper signal is received. For simplicity and not to compromise the frequency reference properties, the frequency of the synchronization signal may be kept constant, while the modulation may be of the amplitude only. One example is a periodic on-off keying pattern with 90% on and 10% off, where the power is reduced by just 0.46dB compared to a non-modulated tone being on 100% of the time.

Embodiments herein may be applied to different Radio Access Technologies (RATs) such as IEEE 802.11/Wifi, 3GPP LTE or NR, particularly in contexts where the wireless communications device 121 needs to be monitoring the control channel for data or paging transmissions where conventional synchronization cost ahead of data or paging monitoring is significant. The approach is particularly suited for Massive Machine-Type Communications (M- MTC) or Internet of Things (loT) UEs with strict energy budgets and limited data activity.

Modulated signature/ID

To identify the FRS, to differentiate among multiple overlapping FRSs, or to carry relevant status information, the tone of the FRS may be amplitude-modulated, e.g. using a periodic On- Off Keying (OOK) pattern, or a similar Amplitude Shift Keying (ASK) or other amplitude modulation. Amplitude modulation is particularly suitable since amplitude modulation causes least spectral expansion. A sequence period may be varied to differentiate different sequences, or more elaborate periodic patterns may be used to differentiate different sequences. The receiver bandwidth of the second RF receiver 420 may be selected to not be narrower than an inverse of a shortest symbol time of the modulating data sequence.

The periodicity of the modulation pattern may be selected based on multiple considerations. For example, the off-segment(s) may be kept as short a fraction of the period as possible, to avoid losing energy, e.g., total FRS energy. Alternatively, the FRS signal may be power-boosted with the inverse of the duty cycle, in which case the received power is not affected. The modulation pattern may be kept as long as possible in absolute terms to allow as narrow receiver bandwidth of the second RF receiver 420 as possible to maximize the Signal to Noise ratio (SNR). If the period of the modulation pattern is for instance 1 ms and the duty cycle of the modulation pattern is 90 %, a channel filter of the second RF receiver 420 may have as low bandwidth as 10 kHz and still capture waveforms. The bandwidth may be just 3-4 kHz if the duty cycle is reduced to 70%. The channel filter may be the most narrowband filter in the receive chain, or a combination of the most narrowband filters. In Figure 4 it may be the filters in the bank of parallel complex digital bandpass filters 591 that act as channel filter when determining the frequency error. When determining AoA using the phases of the correlated signals, the DF 576 may act as channel filter, so also in the alternative method of sweeping the frequency to find the error.

If the second RF receiver 420 further reduces the bandwidth of the second RF receiver 420, the modulation pattern may not be detected but the FRS may still be used for frequency tracking. In one embodiment, the second RF receiver 420 may operate with minimal bandwidth most of the time and occasionally switch to a wider bandwidth to detect or verify the modulation pattern. For example, the second RF receiver 420 may reconfigure the channel filter to a different bandwidth, or switches between filters with different bandwidth. As the filters acting as channel filters in this case are digital, switching or reconfiguration is facilitated.

Transmission of the FRS

Since the transmitted frequency reference signal is rather low in power, for example representing about a 1 MHz fraction of a signal that may be several GHz in total, i.e. parts of a per mille of the total power, it may be transmitted in different ways from the base-station. It may be transmitted with the regular antenna array, covering an area with many different beams, following other beam sweep patterns (e.g. SSB, Tracking Reference Signal (TRS), Channel State Information Reference Signal (CSI-RS) sweeps in NR). Another option is to have dedicated antennas and transmitters for transmitting the FRS, with wider beams covering the area with fewer beams. Since the power level of the narrow-band signal is so low, wider beams may be used without requiring excessive transmit power.

In some embodiments, the FRS may be transmitted outside the communications band, at a predefined frequency offset in relation to known signals, e.g. in relation to an SSB frequency location in NR.

In some alternative embodiments, the FRS may be transmitted in a guard band which is reserved at the edge of the allocated bands to reduce the impact of adjacent channel interference.

The wireless communications network 100 may preferably provide FRS configuration information, such as location, offset to other conventional reference signals etc. in the SI. This information may for example be provided by the radio network node 111. If the RAT in question includes signal components with stable discrete spectral component(s), one or more of these may be indicated as FRS, instead of a separate FRS transmission.

In some OFDM embodiments, the FRS may be embedded in-band in a known subcarrier position. This is achieved by inserting a constant value, e.g. a known Quadrature Phase Shift Keying (QPSK) symbol, in the selected frequency bin that does not change over time, at least over a large number of adjacent symbols. OOK modulation may then be applied by turning off the subcarrier, i.e., inserting zeros, during symbols corresponding to off-segments of the OOK signal. In some embodiments, a single subcarrier frequency is reserved. The FRS may be provided transparently to other data transmission by adjusting link adaptation, e.g. lowering MCS of data transmitted in the same physical resource block (PRB) to compensate for the missing data energy and the interference introduced in the form of the FRS component. In some other embodiments, the wireless communications network 100 may reserve a PRB where no data is transmitted and use one subcarrier for FRS transmission.

The wireless communications network 100 may transmit the FRS continuously or activate it in a cell when there are wireless communications devices in the coverage area.

The FRS may be transmitted by a separate always-on transmitter, which may include carrier generation and power amplifier circuitry, with low energy consumption in order to avoid the need to have a full transceiver of the radio network node 111 to be always on. In case the FRS is embedded in the OFDM signal, the full transceiver of the radio network node 111 may omit transmitting anything on the corresponding subcarrier. In one embodiment, a separate transmitter is used in low load scenarios with gNB sleep opportunities while, for high load, the FRS may be included in the OFDM signal generation and the always-on transmitter is not used.

The wireless communications network 100 may provide FRS configuration information in its system information transmission or alternatively via dedicated signaling to individual wireless communications devices. The FRS configuration information may include a frequency offset to a system synchronisation signal and a signature or identity value.

The FRS may be transmitted with wide or omni-directional beams. Then, in a typical scenario, omni-directional transmission may be considered to be Quasi Co-located (QCL) with any narrow beam, such as a beam used for Physical Downlink Control Channel (PDCCH), from the same transmission point, assuming that the narrow beam is a best beam. Certain Doppler differences may occur if the narrow beam is a suboptimal, i.e., a non-primary, reflection. In one embodiment, the wireless communications device 121 may determine whether the FRS is sufficiently QCLed with data or PDCCH transmissions, e.g. in terms of a frequency offset between the FRS and a carrier of the data or control signal being below a threshold. If not, the wireless communications device 121 may choose to not use the FRS but revert to traditional synchronization methods.

LPR design

The second RF receiver 420 may use a number of different architectures, like homodyne, heterodyne, or low-IF. The frequency synthesizer 510 of the second RF receiver 420 may use the same crystal oscillator as the first RF receiver 410, so that the first RF receiver 410 may be calibrated by receiving the frequency reference signal with the second RF receiver 420.

The selectivity filter, or in other words the channel filter, such as one of the digital filters, is tuned to the FRS frequency, preferably with as low bandwidth as possible that captures the modulation. When a homodyne architecture is used the filters become particularly simple, being low pass filters and hence having poles with minimum Q-values. For a heterodyne receiver with a high IF-frequency the Q-value may be so high that the filter may need to be implemented off- chip, but for a single antenna receiver, requiring a single filter, that is still feasible.

In one embodiment, the PLL-based frequency synthesizer 510 may be used to allow the second LO 442 of the second RF receiver 420 to track the frequency of the received FRS. A PLL tracking bandwidth of the PLL may be based on a Doppler spread of the received FRS from the wireless communications network 100. The Doppler spread may be estimated based on an LO or PLL stability and variation rate of either the first RF receiver 410 or second RF receiver 420. The tracking bandwidth should not be narrower than the Doppler spread of the received signal and may be adapted dynamically or set to a worst-case expected value.

In an alternative embodiment, the frequency of the second LO 442 is adjusted by estimating a frequency error, or in other words a frequency offset, between the frequency of the second LO 442 and the frequency of the received FRS in baseband. The second RF receiver 420 in the wireless communications device 121 estimates the frequency offset, e.g, by measuring a rotation speed of the received l/Q vector which is directly proportional to the frequency error and adjusts the frequency of the second LO 442 to minimize the rotation speed and thus the frequency offset.

In one embodiment, the received and down-converted FRS is filtered suitably for modulation detection and fed to both the modulation detector, comprising the envelope detector 577 and the correlator 580, and the PLL. The PLL then includes one or more additional Low Pass Filters (LPF) that removes the modulation component.

When the wireless communications device 121 is in deep sleep, e.g., when all circuitry is off except the clock, the first LO 441 of the first RF receiver 410 is powered off to save power while the second LO 442 of the second RF receiver 420 is always synchronized to the wireless communications network 100. Once the wireless communications device 121 wakes up, e.g., when it turns on its circuitry in order to receive a signal or channel, the first LO 441 of the first RF receiver 410 is also powered up. The wireless communications device 121 may perform frequency or phase synchronization or both between the first and second LOs 441, 442. The synchronization may be realized by using the common reference oscillator XO, such as the same crystal oscillator, as a frequency reference for the first and second LOs 441 , 442.

In one embodiment, the second RF receiver 420 may utilize one element in its regular antenna array or a separate antenna for FRS reception. For wireless communications devices with large antenna arrays, one array element may be reserved for FRS without severely impacting normal operation. In another embodiment, the second RF receiver 420 may adapt the number of antennas invoked and/or the receiver bandwidth to ensure sufficient SNR for FRS tracking, based on the channel quality of the FRS. The channel quality may be found e.g. by the level of the peak from the correlator. For example, if channel quality is bad, the number of antennas may be increased, or the receiver bandwidth may be increased, the former provides more spatial diversity, and the latter access to more Resource Elements for synchronization. More antennas may be used by the second RF receiver 420, or the second RF receiver 420 may be omitted and the full receiver used, in cell regions with FRS signal power below a threshold.

Receiver procedures

The wireless communications device 121 may initially operate its full receiver, i.e. , the first RF receiver 410, to find a cell, obtain conventional time or frequency synchronization or both, extract FRS configuration information from System Information (SI), or dedicated signaling, e.g., RRC, and start operation of the second RF receiver 420. Start operation of the second RF receiver 420 may comprise to turn on the second RF receiver 420 and configure it according to a configuration information. For example, in case the FRS is a specific TRS configuration or used as a perceived FRS, i.e., a subset of TRS chosen by the wireless communications device 121 , the configuration may be obtained through a SIBn, if for example provided to idle wireless communications devices, or as part of RRC signaling when in the connected mode.

The received FRS may first be analyzed by amplitude demodulation, e.g., by sweeping the LO frequency (e.g. by adjusting the common crystal oscillator) while trying to identify the transmitted modulation pattern. If no matching modulation pattern is detected, the operation of the second RF receiver 420 may be terminated. When the modulation pattern is found, a second mode may be entered where a rotation of a received l/Q vector is investigated and the LO frequency of the second LO 442 is adjusted to minimize the rotation speed, which is directly proportional to the frequency error. If the FRS is not detected during the second mode, e.g., due to that the base station beam does not point in the direction of the second RF receiver 420, the amplitude modulation pattern will no longer be seen by the second RF receiver 420. Then the wireless communications device 121 makes no frequency adjustments until the modulation pattern is detected again. Then the wireless communications device 121 continues in the second mode to make adjustments based on the l/Q vector rotation.

The wireless communications device 121 may detect the presence or absence of the FRS autonomously by observing a magnitude of the received signal after the narrowband digital filtering of the second RF receiver 420 and compare to a threshold, or alternatively be made aware of it by implicit or explicit indication from the wireless communications network 100. For example, in case the FRS is a specific TRS configuration, then in the connected mode, the wireless communications device 121 is aware of the presence of it on a periodic basis and occasionally aperiodic if triggered by the wireless communications network 100. But if the wireless communications device 121 is in idle mode, the wireless communications device 121 may either be indicated by the wireless communications network 100 of the presence of the TRS, or that the wireless communications device 121 may apply additional blind detection to detect TRS. The blind detection operation may be performed at the same time as the frequency synchronization.

If the PLL indicates a rate of change of the reference frequency exceeding a threshold, or if the wireless communications device 121 ceases to track the single-tone FRS, the full first receiver 410 may be invoked to re-acquire the frequency synchronization or perform other synchronization maintenance operations. In case synchronization is lost, re-acquiring may be necessary, otherwise other operations may suffice to maintain synchronization.

If the RAT in question includes signal components with one or more stable discrete spectral components, one or more of these may be used as FRS by the wireless communications device 121.

In some embodiments herein the modulating data sequence comprises a first data sequence 601 and a second data sequence 602, both illustrated in Figure 6. The second data sequence 602 has a higher bit rate than the first data sequence 601. Thus, the second data sequence 602 may be a high bit rate data sequence and the first data sequence 601 may be a low bit rate data sequence. Then the synchronizing may comprise a first rough time synchronization by correlating the received first data sequence 601 with a first reference data sequence, and then a second refined time synchronization by correlating the received second data sequence 602 with a second reference data sequence over a time interval, such as a time synchronization hypothesis interval, derived from the first rough time synchronization.

Exemplifying methods according to embodiments herein will now be described with reference to a flow chart in Figure 7 and with continued reference to Figures 2, 3, 4 and 5. The flow chart illustrates a method, performed by the radio network node 111.

The method is for synchronization provision in the wireless communications network 100.

The method actions may be performed in any suitable order. Some method actions may be optional.

Action 701

In some embodiments herein the radio network node 111 provides the configuration of the synchronization signal to the one or more wireless communications devices 121 in a System Information, SI, transmission or in dedicated signalling, such as RRC signalling. However, the configuration may also be provided to the one or more wireless communications devices 121 by another network node or by encoding it on a Subscriber Identity Module (SIM).

Action 702

The method may further comprise adjusting a link adaptation scheme for Physical

Resource Blocks, PRBs, overlapping with the single-tone synchronization signal. For example, the radio network node 111 may adjust OFDM signal MCS to compensate for interference caused by the synchronization signal to legacy users receiving data in a PRB overlapping with the synchronization signal.

Action 703

In action 703, the radio network node 111 broadcasts to one or more wireless communications devices 121 within the wireless communications network 100 a single-tone synchronization signal according to the configuration of the single-tone synchronization signal.

In some embodiments herein broadcasting the single-tone synchronization signal comprises embedding the single-tone synchronization signal in a subcarrier location of an OFDM signal.

Further, broadcasting the single-tone synchronization signal may comprise modulating the single-tone synchronization signal with a modulating data sequence.

In some embodiments herein modulating the single-tone synchronization signal with the modulating data sequence comprises modulating an amplitude of the single-tone synchronization signal.

A bandwidth of the modulating data sequence may be within 1-1000 kHz.

The modulating data sequence may indicate any one or more of: an identity of the radio network node 111 or an identity of the one or more wireless communications devices 121.

The bandwidth of the single-tone synchronization signal may be narrower than one per mille of a carrier frequency of the single-tone synchronization signal, or narrower than 10 MHz, such as narrower than 1 MHz.

In some embodiments herein the single-tone synchronization signal is broadcasted at a mmWave frequency. Embodiments herein are particularly advantageous at mmWave frequencies due to the high power consumption of the RF circuitry at these frequencies.

In some embodiments herein the radio network node 111 comprises a first RF transmitter 1010 illustrated in Figure 9 for wireless communication of data or control signals or both with the one or more wireless communications devices 121 within the wireless communications network 100 and a second RF transmitter 1020 operating at a reduced power consumption compared to a power consumption of the first RF transmitter 1010 when active, wherein broadcasting the single-tone synchronization signal comprises transmitting the single-tone synchronization signal using the second RF transmitter 1020. The second RF transmitter 1020 may be a simple transmitter just for transmitting the single-tone synchronization signal, e.g., with OOK. The second RF transmitter 1020 may be for example be implemented with a lower linearity than the first RF transmitter 1010. Exemplifying methods according to embodiments herein will now be described with reference to a flow chart in Figure 8 and with continued reference to Figures 2, 3, 4 and 5. The flow chart illustrates a method, performed by the wireless communications device 121.

The method is for synchronization of wireless communication between the wireless communications device 121 and the radio network node 111 of the wireless communications network 100.

The method may be performed when the wireless communications device 121 is in a low power mode in which the first RF receiver 410 is not operable, such as in an idle or inactive state in which the wireless communications device 121 does not receive any data or control signaling from the wireless communications network 100.

Action 801

In some embodiments herein the wireless communications device 121 receives a configuration of the single-tone synchronization signal in the SI transmission or via dedicated signaling from the radio network node 111.

Action 802

The wireless communications device 121 receives, from the radio network node 111 , the single-tone synchronization signal within the first frequency range using the second RF receiver 420. The wireless communications device 121 may receive the single-tone synchronization signal continuously. Continuously means that the single-tone synchronization signal is received without interruptions. However, the single-tone synchronization signal may also be received duty-cycled, in repeated receptions with interruptions between. For example, the wireless communications device 121 may repeatedly receive the single-tone synchronization signal in the low power mode in which the first RF receiver 410 is not operable.

As mentioned above, the single-tone synchronization signal may be modulated with the modulating data sequence, for example with an amplitude modulation. When the amplitude of the single-tone synchronization signal is modulated with the modulating data sequence, then the bandwidth of the second RF receiver 420 may be broader than an inverse of a shortest symbol time of the modulating data sequence.

Action 803

The wireless communications device 121 then compares a carrier frequency of the singletone synchronization signal and a frequency of the second LO 442 of the second RF receiver 420. The comparison may for example take place by examining the received single-tone synchronization signal using the narrowband digital filters. Either by investigating the rotation of the single-tone synchronization signal after correlation without envelope detector when the target frequency after the DDC 575 is zero, or by comparing the envelope detected and correlated outputs from the different filter banks.. The comparison may produce an error signal that may be used to correct, that is synchronize, the frequency of the second LO 442 to the synchronization signal.

Action 804

The wireless communications device 121 tunes the common reference oscillator XO of the first RF receiver 410 and the second RF receiver 420 based on a frequency difference between the carrier frequency of the single-tone synchronization signal and the frequency of the LO 442 of the second RF receiver 420 such that the frequency difference is tuned to a target value. In case the second RF receiver is a homodyne receiver the target value may be zero.

Action 805

The wireless communications device 121 then synchronizes the wireless communications device 121 in time with the radio network node 111 based on the second RF receiver 420 correlating the received modulating data sequence with a reference data sequence in time domain as described in more detail above. The reference data sequence may be selected from a few known sequences.

Action 806

In some embodiments herein the wireless communications device 121 activates the first RF receiver 410 from an inactive state.

Action 807

The wireless communications device 121 then communicates, by the first RF receiver 410, control or data signals or both with the radio network node 111 at the first frequency range based on the tuned common frequency reference XO and the time synchronization of the wireless communications device 121 with the radio network node 111.

The communication by the first RF receiver 410, control or data signals or both may be performed without a preceding frequency or time synchronization of the first RF receiver 410 based on receiving a second synchronization signal with the first RF receiver 410 from the wireless communications network 100 at the first frequency range.

Action 808

In some embodiments herein the second RF receiver 420 is configured to receive two or more synchronization signals, each synchronization signal of the two or more synchronization signals being modulated with a respective modulating data sequence. Then the method may further comprise determining an identification of the received synchronization signal based on demodulating the modulated synchronization signal with the second RF receiver 420.

Action 809

In some embodiments herein the wireless communications device 121 determines the bandwidth of the second RF receiver 420 based on any one or more of: a target Signal-to-Noise Ratio, SNR, for the received synchronization signal; properties of the modulating data sequence; an estimated stability of the LO 442 or a Phased-Locked Loop 510 of the second RF receiver 420; and a Doppler spread of the received synchronization signal.

The wireless communications device 121 may determine the bandwidth of the second RF receiver from a set of different selectable bandwidths.

The wireless communications device 121 may estimate a suitable bandwidth based on one or more of the above. Estimations may be made before receiving the synchronization signal to set an initial bandwidth value, and when measurements become available during reception, some changes in bandwidth may be necessary based on the measurement results. Thus, in some embodiments herein action 809 or part of action 809 is performed before action 802.

Action 810

In some embodiments herein the wireless communications device 121 increases the bandwidth of the second RF receiver 420. For example, after reception and measurements of the synchronization signal the bandwidth of the second RF receiver 420 may be increased in order to capture the modulating data sequence correctly. That is, the bandwidth of the second RF receiver 420 may be dynamically increased to detect or verify the modulation pattern.

Numerical examples

To illustrate feasibility of a single antenna receiver, an effective receiver bandwidth of 10 kHz may be assumed. It may further be assumed that 1 MHz of the downlink signal bandwidth is allocated to the frequency synchronization signal, so that the frequency synchronization signal has about 0.5 MHz at each side of empty space. It may be further assumed that the power allocated to that 1 MHz band is concentrated on the frequency synchronization signal in the center. This means that the power spectral density is 100 times higher (1 MHz/10 kHz) in the frequency synchronization signal than in a normal communication signal transmitted in the wireless communications network 100. It is then possible to receive the frequency synchronization signal with 100 times fewer antenna elements. Furthermore, the simple modulation used requires less SNR than a high order modulation that may be used in e.g. a 5G downlink signal. This further strengthens the case of the single antenna reference signal receiver. Since wireless communications devices may have up to about 100 antenna elements, a single-antenna auxiliary reference receiver is feasible.

In the context of an NR FR2 operation, the FRS may be embedded in one subcarrier of the 240 kHz SCS OFDM signal, assigned the power equal to the average power in the corresponding data subcarrier. A UE with a full receiver employing panels with 8 antenna elements may use a single element for FRS reception with 30 kHz modulation bandwidth superimposed, corresponding to e.g. 90 % modulation duty cycle and up to 3 kHz period.

Embodiments herein have disclosed the FRS transmitted by the radio network node 111. The FRS may be a narrow-band amplitude modulated signal. The FRS may be received by an auxiliary receiver, such as a single-antenna narrow-band receiver in the wireless communications device 121 and used for frequency synchronization of the wireless communications device 121. The auxiliary receiver may be implemented as a separate receiver or as a low-power mode of the normal receiver.

The FRS may also be used to adjust the crystal oscillator in the wireless communications device 121, minimizing the clock time drift. Since all timing in the wireless communications device 121 is derived from the crystal oscillator, continuously adjusting it to track the frequency of the radio access node 111, will minimize clock time drift between the two units. The wireless communications device 121 will then not need to use the power-hungry first RF receiver 410 as often for synchronization, and when communication is needed the wireless communications device 121 is sufficiently well synchronized in time and frequency for direct operation.

Advantages of embodiments herein

• The overhead to transmit the narrowband synchronization signal from the wireless communications network 100 is small.

• In embodiments wherein the second RF receiver 420 is a narrow-band single-antenna receiver the power consumption for the wireless communications device 121 to perform frequency or time synchronization and tracking will be lower than using the high-power full receiver for frequency or time synchronization. In embodiments herein tracking has the meaning of continuously follow the FRS.

Since the main or full transceiver is always synchronized in time and frequency there will be a quick response for data reception and transmission.

Embodiments herein improves battery time in low traffic devices. Embodiments herein enable millimeter wave connections in loT sensors and other low power devices.

Figure 9 illustrates an example of the radio network node 111. The radio network node 111 may be configured to perform the method actions of Figure 7 above. Thus, the radio network node 111 may be configured for synchronization provision in the wireless communications network 100.

The radio access node 111 is further configured to broadcast to the one or more wireless communications devices 121 within the wireless communications network 100 the single-tone synchronization signal according to the configuration of the single-tone synchronization signal.

In some embodiments herein the radio access node 111 is further configured to broadcast the single-tone synchronization signal by being configured to embed the single-tone synchronization signal in the subcarrier location of the OFDM signal.

The radio access node 111 may be further configured to adjust the link adaptation scheme for PRBs overlapping with the single-tone synchronization signal.

In some embodiments herein the radio access node 111 is further configured to broadcast the single-tone synchronization signal by being configured to modulate the single-tone synchronization signal with the modulating data sequence.

The radio access node 111 may further be configured to modulate the single-tone synchronization signal with the modulating data sequence by being configured to modulate the amplitude of the single-tone synchronization signal.

The radio access node 111 may further be configured to broadcast the single-tone synchronization signal by being configured to transmit the single-tone synchronization signal using the second RF transmitter 420.

Figure 10 illustrates an example of the wireless communications device 121. The wireless communications device 121 may be configured to perform the method actions of Figure 8 above. The wireless communications device 121 may be configured for synchronization of wireless communication between the wireless communications device 121 and the radio network node 111. The wireless communications device 121 is configured to receive, from the radio network node 111 , the single-tone synchronization signal within the first frequency range using the second RF receiver 420.

The wireless communications device 121 is further configured to compare the carrier frequency of the single-tone synchronization signal and a frequency of the LO 442 of the second RF receiver 420.

The wireless communications device 121 is further configured to tune the common reference oscillator XO of the first RF receiver 410 and the second RF receiver 420 based on a frequency difference between the carrier frequency of the single-tone synchronization signal and the frequency of the LO 442 of the second RF receiver 420 such that the frequency difference is tuned to a target value.

The wireless communications device 121 is further configured to synchronize the wireless communications device 121 in time with the radio network node 111 based on the second RF receiver 420 correlating the received modulating data sequence with the reference data sequence in time domain.

The wireless communications device 121 is further configured to communicate, by the first RF receiver 410, control or data signals or both with the radio network node 111 at the first frequency range based on the tuned common frequency reference XO and the time synchronization of the wireless communications device 121 with the radio network node 111.

In some embodiments herein the activating wireless communications device 121 is further configured to activate the first RF receiver 410 from an inactive state. Then, the wireless communications device 121 may be further configured to communicate, with the first RF receiver 410, control or data signals or both without a preceding frequency or time synchronization of the first RF receiver 410 based on receiving the second synchronization signal with the first RF receiver 410 from the wireless communications network 100 at the first frequency range.

The radio network node 111 and the wireless communications device 121 may each comprise a respective input and output interface, IF, 1006, 1106 configured to communicate, e.g., with each other. The input and output interface 1006,1106 may comprise one or more receivers and one or more transmitters. For example the IF 1006 of the radio network node may comprise the first RF transmitter 1010 and the second RF transmitter 1020. The IF 1106 of the wireless communications device 121 may comprise the first RF receiver 410 and the second RF receiver 420. Both the respective one or more receivers and the respective one or more transmitters may be wireless. The embodiments herein may be implemented through a respective processor or one or more processors, such as the respective processor 1004, and 1104, of a processing circuitry in the radio network node 111 and the wireless communications device 121 , and depicted in Figures 9-10 together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the respective radio network node 111 and the wireless communications device 121. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the respective radio network node 111 and the wireless communications device 121.

The radio network node 111 and the wireless communications device 121 may further comprise a respective memory 1002, and 1102 comprising one or more memory units. The memory comprises instructions executable by the processor in the radio network node 111 and the wireless communications device 121.

Each respective memory 1002 and 1102 is arranged to be used to store e.g. information, data, configurations, and applications to perform the methods herein when being executed in the respective radio network node 111 and the wireless communications device 121.

In some embodiments, a respective computer program 1003 and 1103 comprises instructions, which when executed by the at least one processor, cause the at least one processor of the respective radio network node 111 and the wireless communications device 121 to perform the actions above.

In some embodiments, a respective carrier 1005 and 1105 comprises the respective computer program, wherein the carrier is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

Those skilled in the art will also appreciate that the units described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in the respective radio network node 111 and the wireless communications device 121 , that when executed by the respective one or more processors such as the processors described above. One or more of these processors, as well as the other digital hardware, may be included in a single Application-Specific Integrated Circuitry (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC).

With reference to Figure 11 , in accordance with an embodiment, a communication system includes a telecommunication network 3210, such as a 3GPP-type cellular network, which comprises an access network 3211 , such as a radio access network, and a core network 3214. The access network 3211 comprises a plurality of base stations 3212a, 3212b, 3212c, such as the source and target access node 111 , 112, AP STAs NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 3213a, 3213b, 3213c. Each base station 3212a, 3212b, 3212c is connectable to the core network 3214 over a wired or wireless connection 3215. A first user equipment (UE) such as a Non-AP STA 3291 located in coverage area 3213c is configured to wirelessly connect to, or be paged by, the corresponding base station 3212c. A second UE 3292 such as a Non-AP STA in coverage area 3213a is wirelessly connectable to the corresponding base station 3212a. While a plurality of UEs 3291, 3292 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 3212.

The telecommunication network 3210 is itself connected to a host computer 3230, which may be embodied in the hardware and/or software of a standalone server, a cloud- implemented server, a distributed server or as processing resources in a server farm. The host computer 3230 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections 3221 , 3222 between the telecommunication network 3210 and the host computer 3230 may extend directly from the core network 3214 to the host computer 3230 or may go via an optional intermediate network 3220. The intermediate network 3220 may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network 3220, if any, may be a backbone network or the Internet; in particular, the intermediate network 3220 may comprise two or more sub-networks (not shown).

The communication system of Figure 11 as a whole enables connectivity between one of the connected UEs 3291, 3292 such as e.g. the UE 121, and the host computer 3230. The connectivity may be described as an over-the-top (OTT) connection 3250. The host computer 3230 and the connected UEs 3291 , 3292 are configured to communicate data and/or signaling via the OTT connection 3250, using the access network 3211 , the core network 3214, any intermediate network 3220 and possible further infrastructure (not shown) as intermediaries. The OTT connection 3250 may be transparent in the sense that the participating communication devices through which the OTT connection 3250 passes are unaware of routing of uplink and downlink communications. For example, a base station 3212 may not or need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 3230 to be forwarded (e.g., handed over) to a connected UE 3291. Similarly, the base station 3212 need not be aware of the future routing of an outgoing uplink communication originating from the UE 3291 towards the host computer 3230.

Example implementations, in accordance with an embodiment, of the UE, base station and host computer discussed in the preceding paragraphs will now be described with reference to Figure 12. In a communication system 3300, a host computer 3310 comprises hardware 3315 including a communication interface 3316 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 3300. The host computer 3310 further comprises processing circuitry 3318, which may have storage and/or processing capabilities. In particular, the processing circuitry 3318 may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The host computer 3310 further comprises software 3311 , which is stored in or accessible by the host computer 3310 and executable by the processing circuitry 3318. The software 3311 includes a host application 3312. The host application 3312 may be operable to provide a service to a remote user, such as a UE 3330 connecting via an OTT connection 3350 terminating at the UE 3330 and the host computer 3310. In providing the service to the remote user, the host application 3312 may provide user data which is transmitted using the OTT connection 3350.

The communication system 3300 further includes a base station 3320 provided in a telecommunication system and comprising hardware 3325 enabling it to communicate with the host computer 3310 and with the UE 3330. The hardware 3325 may include a communication interface 3326 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 3300, as well as a radio interface 3327 for setting up and maintaining at least a wireless connection 3370 with a UE 3330 located in a coverage area (not shown in Figure 12) served by the base station 3320. The communication interface 3326 may be configured to facilitate a connection 3360 to the host computer 3310. The connection 3360 may be direct or it may pass through a core network (not shown in Figure 12) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 3325 of the base station 3320 further includes processing circuitry 3328, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The base station 3320 further has software 3321 stored internally or accessible via an external connection. The communication system 3300 further includes the UE 3330 already referred to. Its hardware 3335 may include a radio interface 3337 configured to set up and maintain a wireless connection 3370 with a base station serving a coverage area in which the UE 3330 is currently located. The hardware 3335 of the UE 3330 further includes processing circuitry 3338, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The UE 3330 further comprises software 3331 , which is stored in or accessible by the UE 3330 and executable by the processing circuitry 3338. The software 3331 includes a client application 3332. The client application 3332 may be operable to provide a service to a human or non-human user via the UE 3330, with the support of the host computer 3310. In the host computer 3310, an executing host application 3312 may communicate with the executing client application 3332 via the OTT connection 3350 terminating at the UE 3330 and the host computer 3310. In providing the service to the user, the client application 3332 may receive request data from the host application 3312 and provide user data in response to the request data. The OTT connection 3350 may transfer both the request data and the user data. The client application 3332 may interact with the user to generate the user data that it provides.

It is noted that the host computer 3310, base station 3320 and UE 3330 illustrated in Figure 12 may be identical to the host computer 3230, one of the base stations 3212a, 3212b, 3212c and one of the UEs 3291, 3292 of Figure 11 , respectively. This is to say, the inner workings of these entities may be as shown in Figure 12 and independently, the surrounding network topology may be that of Figure 11.

In Figure 12, the OTT connection 3350 has been drawn abstractly to illustrate the communication between the host computer 3310 and the use equipment 3330 via the base station 3320, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE 3330 or from the service provider operating the host computer 3310, or both. While the OTT connection 3350 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network).

The wireless connection 3370 between the UE 3330 and the base station 3320 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 3330 using the OTT connection 3350, in which the wireless connection 3370 forms the last segment. More precisely, the teachings of these embodiments may improve the data rate, latency, power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime.

A measurement procedure may be provided for the purpose of monitoring data rate, latency and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 3350 between the host computer 3310 and UE 3330, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 3350 may be implemented in the software 3311 of the host computer 3310 or in the software 3331 of the UE 3330, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 3350 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software 3311, 3331 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 3350 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the base station 3320, and it may be unknown or imperceptible to the base station 3320. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer’s 3310 measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that the software 3311 , 3331 causes messages to be transmitted, in particular empty or ‘dummy’ messages, using the OTT connection 3350 while it monitors propagation times, errors etc.

FIGURE 13 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to Figure 11 and Figure 12. In a first action 3410 of the method, the host computer provides user data. In an optional subaction 3411 of the first action 3410, the host computer provides the user data by executing a host application. In a second action 3420, the host computer initiates a transmission carrying the user data to the UE. In an optional third action 3430, the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional fourth action 3440, the UE executes a client application associated with the host application executed by the host computer.

FIGURE 14 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to Figure 11 and Figure 12. In a first action 3510 of the method, the host computer provides user data. In an optional subaction (not shown) the host computer provides the user data by executing a host application. In a second action 3520, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third action 3530, the UE receives the user data carried in the transmission.

FIGURE 15 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to Figure 11 and Figure 12. In an optional first action 3610 of the method, the UE receives input data provided by the host computer. Additionally or alternatively, in an optional second action 3620, the UE provides user data. In an optional subaction 3621 of the second action 3620, the UE provides the user data by executing a client application. In a further optional subaction 3611 of the first action 3610, the UE executes a client application which provides the user data in reaction to the received input data provided by the host computer. In providing the user data, the executed client application may further consider user input received from the user. Regardless of the specific manner in which the user data was provided, the UE initiates, in an optional third subaction 3630, transmission of the user data to the host computer. In a fourth action 3640 of the method, the host computer receives the user data transmitted from the UE, in accordance with the teachings of the embodiments described throughout this disclosure.

FIGURE 16 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station such as a AP STA, and a UE such as a Non-AP STA which may be those described with reference to Figures 11 and 12. In an optional first action 3710 of the method, in accordance with the teachings of the embodiments described throughout this disclosure, the base station receives user data from the UE. In an optional second action 3720, the base station initiates transmission of the received user data to the host computer. In a third action 3730, the host computer receives the user data carried in the transmission initiated by the base station.

When using the word "comprise" or “comprising” it shall be interpreted as non- limiting, i.e. meaning "consist at least of".

The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used.

Claims

1. A method, performed by a radio network node (111), for synchronization provision in a wireless communications network (100), the method comprises: broadcasting (703) to one or more wireless communications devices (121) within the wireless communications network (100) a single-tone synchronization signal according to a configuration of the single-tone synchronization signal.

2. The method according to claim 1 , wherein broadcasting the single-tone synchronization signal comprises embedding the single-tone synchronization signal in a subcarrier location of an Orthogonal Frequency Division Multiplexing, OFDM, signal.

3. The method according to any of the claims 1-2, further comprising: adjusting (702) a link adaptation scheme for Physical Resource Blocks, PRBs, overlapping with the single-tone synchronization signal.

4. The method according to any of the claims 1-3, wherein broadcasting the single-tone synchronization signal comprises modulating the single-tone synchronization signal with a modulating data sequence.

5. The method according to claim 4, wherein modulating the single-tone synchronization signal with the modulating data sequence comprises modulating an amplitude of the single-tone synchronization signal.

6. The method according to any of the claims 4-5, wherein a bandwidth of the modulating data sequence is within 1-1000 kHz.

7. The method according to any of the claims 4-6, wherein the modulating data sequence indicates any one or more of: an identity of the radio network node (111) or an identity of the one or more wireless communications devices (121).

8. The method according to any of the claims 1-7, wherein a bandwidth of the single-tone synchronization signal is narrower than one per mille of a carrier frequency of the singletone synchronization signal, or narrower than 10 MHz, such as narrower than 1 MHz.

9. The method according to any of the claims 1-8, wherein the network node (111) comprises a first Radio Frequency, RF, transmitter (410) for wireless communication of data or control signals or both with the one or more wireless communications devices (121) within the wireless communications network (100) and a second RF transmitter (420) operating at a reduced power consumption compared to a power consumption of the first RF transmitter (410) when active, wherein broadcasting the single-tone synchronization signal comprises transmitting the single-tone synchronization signal using the second RF transmitter (420).

10. The method according to any of the claims 1-9, further comprising: providing (701) the configuration of the synchronization signal to the one or more wireless communications devices (121) in a System Information, SI, transmission or in dedicated signaling.

11. The method according to any of the claims 1-10, wherein the single-tone synchronization signal is broadcasted at a mmWave frequency.

12. A method, performed by a wireless communications device (121), for synchronization of wireless communication between the wireless communications device (121) and a radio network node (111), of a wireless communications network (100) operating at a first frequency range, the wireless communications device (121) comprising a first Radio Frequency, RF, receiver (410) for wireless communication of data or control signals or both within the wireless communications network (100) at the first frequency range and a second RF receiver (420) operating at the first frequency range and at a reduced power consumption compared to a power consumption of the first RF receiver (410) when active, the method comprises: receiving (802), from the radio network node (111), a single-tone synchronization signal within the first frequency range using the second RF receiver (420); comparing (803) a carrier frequency of the single-tone synchronization signal and a frequency of a Local Oscillator, LO, (442) of the second RF receiver (420); tuning (804) a common reference oscillator (XO) of the first RF receiver (410) and the second RF receiver (420) based on a frequency difference between the carrier frequency of the single-tone synchronization signal and the frequency of the LO (442) of the second RF receiver (420) such that the frequency difference is tuned to a target value; synchronizing (805) the wireless communications device (121) in time with the radio network node (111) based on the second RF receiver (420) correlating the received modulating data sequence with a reference data sequence in time domain; and communicating (807), by the first RF receiver (410), control or data signals or both with the radio network node (111) at the first frequency range based on the tuned common frequency reference (XO) and the time synchronization of the wireless communications device (121) with the radio network node (111).

13. The method according to claim 12, further comprising: activating (806) the first RF receiver (410) from an inactive state; and wherein communicating (807), with the first RF receiver (410), control or data signals or both is performed without a preceding frequency or time synchronization of the first RF receiver (410) based on receiving a second synchronization signal with the first RF receiver (410) from the wireless communications network (100) at the first frequency range.

14. The method according to any of the claims 12-13, wherein the first RF receiver (410) is a wide-band, multi-antenna receiver, and the second RF receiver (420) is a narrow-band, single-antenna receiver.

15. The method according to any of the claims 12-14, wherein a bandwidth of the second RF receiver (420) is narrower than one to five subcarrier spacings, such as narrower than one subcarrier spacing.

16. The method according to any of the claims 12-15, wherein an amplitude of the single-tone synchronization signal is modulated with a modulating data sequence, and the bandwidth of the second RF receiver (420) is broader than an inverse of a shortest symbol time of the modulating data sequence.

17. The method according to any of the claims 12-16, wherein the bandwidth of the second RF receiver (420) is within 1-1000 kHz, preferably within 3-20 kHz, such as 10 kHz.

18. The method according to any of the claims 12-17, wherein the second RF receiver (420) is configured to receive two or more synchronization signals, each synchronization signal of the two or more synchronization signals being modulated with a respective modulating data sequence and the method further comprises: determining (808) an identification of the received synchronization signal based on demodulating the modulated synchronization signal with the second RF receiver (420).

19. The method according to any of the claims 12-18, further comprising: determining (809) the bandwidth of the second RF receiver (420) based on any one or more of: a target Signal-to-Noise Ratio, SNR, for the received synchronization signal; properties of the modulating data sequence; an estimated stability of the LO (442) or a Phased-Locked Loop (510) of the second RF receiver (420); and a Doppler spread of the received synchronization signal.

20. The method according to any of the claims 12-19, further comprising increasing (810) the bandwidth of the second RF receiver (420).

21. The method according to any of the claims 12-20, further comprising: receiving (801) a configuration of the single-tone synchronization signal in a System Information, SI, transmission or via dedicated signaling from the radio network node (111).

22. The method according to any of the claims 12-21, performed when the wireless communications device (121) is in a low power mode in which the first RF receiver (410) is not operable, such as in an idle or inactive state in which the wireless communications device (121) does not receive any data or control signaling from the wireless communications network (100).

23. A radio network node (111) for synchronization provision in a wireless communications network (100), wherein the radio access node (111) is configured to: broadcast to one or more wireless communications devices (121) within the wireless communications network (100) a single-tone synchronization signal according to a configuration of the single-tone synchronization signal.

24. The radio network node (111) according to claim 23, configured to perform the method of any of the claims 2-11.

25. A wireless communications device (121) for synchronization of wireless communication between the wireless communications device (121) and a radio network node (111) of a wireless communications network (100) operating at a first frequency range, the wireless communications device (121) comprising a first Radio Frequency, RF, receiver (410) for wireless communication of data or control signals or both within the wireless communications network (100) at the first frequency range and a second RF receiver (420) operating at the first frequency range and at a reduced power consumption compared to a power consumption of the first RF receiver (410) when active, wherein the wireless communications device (121) is configured to: receive from the radio network node (111), a single-tone synchronization signal within the first frequency range using the second RF receiver (420); compare a carrier frequency of the single-tone synchronization signal and a frequency of a Local Oscillator, LO, (442) of the second RF receiver (420); tune a common reference oscillator (XO) of the first RF receiver (410) and the second RF receiver (420) based on a frequency difference between the carrier frequency of the single-tone synchronization signal and the frequency of the LO (442) of the second RF receiver (420) such that the frequency difference is tuned to a target value; synchronize the wireless communications device (121) in time with the radio network node (111) based on the second RF receiver (420) correlating the received modulating data sequence with a reference data sequence in time domain; and communicate, by the first RF receiver (410), control or data signals or both with the radio network node (111) at the first frequency range based on the tuned common frequency reference (XO) and the time synchronization of the wireless communications device (121) with the radio network node (111).

26. The wireless communications device (121) according to claim 25, wherein the reduced power consumption of the second RF receiver (420) compared to the power consumption of the first RF receiver (410) is due to any one or more of: front end amplifiers with lower power demands, local oscillators with relaxed phase noise requirements, fewer front-end branches, analog to digital converters with less bandwidth or fewer antennas.

27. The wireless communications device (121) according to according to claim 25 or 26, configured to perform the method of any of the claims 12-22.

28. A computer program (1003), comprising computer readable code units which when executed on a radio network node (111) causes the radio network node (111) to perform the method according to any one of claims 1-11.

29. A computer program (1103), comprising computer readable code units which when executed on a wireless communications device (121) causes the wireless communications device (121) to perform the method according to any one of claims 12-22.

30. A carrier (1005, 1105) comprising the computer program (1003, 1103) according to the claim 28 or 29, wherein the carrier (1005, 1105) is one of an electronic signal, an optical signal, a radio signal and a computer readable medium.