Low power receivers with intermediate frequency (IF) detection and local oscillator (LO) frequency correction

Abstract

A method, system and apparatus for a wireless receiver with intermediate frequency (IF) detection and local oscillator (LO) frequency correction are disclosed. According to one aspect, the wireless receiver is configured to include an LO configured to generate a local oscillator signal, the LO not being phased-locked. The wireless receiver includes a mixer configured to mix the LO signal with an amplitude shift keyed (ASK) modulated signal to produce an intermediate frequency (IF) signal. The wireless receiver also includes tuning circuitry configured to estimate a frequency of the IF signal and to tune the LO according to the estimated intermediate frequency and tune the LO to compensate for an IF frequency drift. The IF frequency estimate is based on correlations of signals in a plurality of frequency bins of a fast Fourier transform (FFT) of the IF signal.

Description

[0001] LOW POWER RECEIVERS WITH INTERMEDIATE FREQUENCY (IF) DETECTION AND LOCAL OSCILLATOR (LO) FREQUENCY CORRECTION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to wireless communications, and in particular, to a low power receiver with intermediate frequency (IF) detection and local oscillator (LO) frequency correction.

[0004] BACKGROUND

[0005] The Third Generation Partnership Project (3GPP) has developed and is developing standards for Fourth Generation (4G) (also referred to as Long Term Evolution (LTE)) and Fifth Generation (5G) (also referred to as New Radio (NR)) wireless communication systems. Such systems provide, among other features, broadband communication between network nodes, such as base stations, and mobile wireless devices (WD), as well as communication between network nodes and between WDs. The 3GPP is also developing standards for Sixth Generation (6G) wireless communication networks.

[0006] To save power, a wireless device (e.g. 3GPP WD) shall go to idle / inactive mode when there is no downlink (DL) / uplink (UL) data traffic to it or from it. The WD needs to wake up for a Discontinuous Reception (DRX) cycle to receive paging information transmitted from a radio node. For each wakeup, prior to paging reception, the WD has to perform frequency synchronization to correct the frequency drift of its clock system so that its local oscillator (LO) frequency is tuned to align with the carrier frequency transmitted from the radio node. The radio node may be a base station, an access point (AP) or another WD.

[0007] For an NR WD, when waking up from idle / inactive, it performs frequency synchronization by using Synchronization Signal Block (SSB) signaling. A radio node transmits SSBs with a certain bandwidth (BW) (e.g. 5G mmW SSB BW=29MHz) and a repetitive rate. A WD detects the reference signals, calculates a phase shift between two successive reference symbols or blocks to estimate frequency error, and adjusts its local Crystal Oscillator (XO) frequency or Phase-Locked Loop (PLL) frequency divider. The frequency synchronization process leads to energy consumption overhead and time latency. Specially, for a 5G mmW WD, the energy consumption overhead for frequency tracking may be very costly.

[0008] To overcome these issues, methods and low-power topologies using a free- running oscillator in place of a PLL to reduce the overall energy consumption have been proposed, as shown in the examples of FIGS. 1 and 2. They are not without drawbacks. In a transmitter, receiver, or transceiver, uncertainty as to intermediate frequency (IF) may cause a signal loss if the IF falls outside of the IF filter bandwidth. In low power receivers using a free running oscillator, the free running oscillator frequency may drift and ultimately cause a similar signal loss. There is no way to compensate or control this frequency drift. If the low power receiver also uses a correlator, no peak may be observed in the correlation window if the signal frequency falls outside the IF filter passband. This means that there is no XO frequency compensation possible.

[0009] SUMMARY

[0010] Some embodiments advantageously provide methods and low power receiver implementations with intermediate frequency (IF) detection and local oscillator (LO) frequency correction.

[0011] Low power solutions to detect the IF frequency drift and tune the free running oscillator to compensate this drift are disclosed. Some embodiments improve low power receiver topologies using a free running oscillator and improve the spectral efficiency and energy consumption at the network level.

[0012] In some embodiments, a hardware block that includes an analog IF detector and LO corrector, and a control block, is configured to detect and correct a potential IF frequency drift introduced by a free-running oscillator used as an LO for low-power receivers.

[0013] By being able to detect the IF frequency and tune the LO accordingly, the IF signal frequency may be contained inside the IF filter passband. This may eliminate the signal loss in filters occurring when the signal falls outside the IF filter bandwidth.

[0014] At the low-power receiver topology level it is possible to keep the IF signal inside the IF filter bandwidth so that the baseband clock drift may be detected. For low- power receivers containing a correlator, the LO may be tuned so that the sequence correlation peak may be observed in the correlation window. Moreover, for low-power receivers containing a correlator, coarse frequency synchronization may be employed. In some embodiments, the tuned LO may be used for transmitting signals with the low power transmitter and setup low data rate communication between low power devices which may be in a cluster of devices. Correcting the LO frequency drift makes it possible to transmit closer to the receive frequency of other receivers and thus enable energy savings on a network scale.

[0015] A low-power receiver configured according to principles disclosed herein may be used in an uncertain frequency environment such as a cluster of low-power devices, and may provide information concerning an interferer and other causes of IF uncertainty sources at the network level.

[0016] According to one aspect, a wireless receiver includes a local oscillator , LO, configured to generate a local oscillator signal, the LO not being phase-locked. The wireless receiver includes a mixer configured to mix the local oscillator signal with a received Amplitude-shift Keying ASK modulated signal to produce an intermediate frequency (IF) signal. The wireless receiver also includes tuning circuitry configured to estimate a frequency of the IF signal and tune the LO to compensate for an IF frequency drift, the tuning circuitry including an analog fast Fourier transform circuit configured to perform a fast Fourier transform, FFT, of the IF signal to obtain signals in a plurality of frequency bins, the IF frequency estimate being based on correlations of the signals in the plurality of frequency bins with a reference sequence.

[0017] According to this aspect, in some embodiments, the LO is tuned according to a digital control signal based at least in part on the FFT of the IF signal. In some embodiments, the wireless receiver includes comprising an envelope detector to detect an envelope of the FFT of the IF signal and a baseband filter to filter the detected envelope. In some embodiments, the wireless receiver includes at least one correlator configured to correlate a sequence detected in the filtered detected envelope of the FFT of the IF signal with a reference sequence. In some embodiments, the tuning circuitry is configured to tune the LO so that a correlation peak occurs in a frequency bin- associated with at least one correlator. In some embodiments, the FFT is disabled when no peak is observed In some embodiments, the at least one correlator (90) is configured to perform a coarse frequency estimate using an FFT frequency window of a first width followed by a fine frequency estimate using an FFT frequency window of a second width narrower than the first width. In some embodiments, the ASK modulated signal is an on-off keying OOK modulated signal, wherein each one of the at least one correlator is configured to search for an on-off keying, OOK, modulated signal in a different frequency bin of the FFT. In some embodiments, each correlator of the at least one correlator performs a correlation between a reference sequence and a sequence associated with a different frequency bin of the FFT of the IF signal. In some embodiments, In some embodiments, the tuning circuitry is configured to determine a frequency bin of the FFT that is associated with a strongest correlation peak. In some embodiments, the tuning circuitry is configured to tune the LO to a frequency that, when mixed with the received signal, provides the IF signal at a frequency that is within a bandwidth of operation of an IF filter of a receiver chain of the wireless receiver. In some embodiments, the wireless receiver includes, for each frequency bin of the plurality of frequency bins, an envelope detector and a baseband filter to detect and filter an envelope of a signal in the frequency bin. In some embodiments, the wireless receiver is comprised in a wireless device.

[0018] According to another aspect, a method is provided for compensating for frequency drift of a local oscillator, LO, in a wireless receiver, the wireless receiver configured to provide a tuning control signal to the LO. The method incudes searching for a peak of a correlation in an FFT frequency window; and tuning the LO based on a frequency bin where a peak is found.

[0019] According to this aspect, in some embodiments, searching for the correlation peak includes: searching for the correlation peak in a first FFT frequency window of a first width; and when the correlation peak is found in the first window, searching for the correlation peak in a second FFT frequency window of a second width that is narrower than the first width. In some embodiments, searching for the correlation peak includes: searching for the correlation peak in a first FFT frequency window of a first width; and when the correlation peak is not found in the first FFT frequency window, searching for the correlation peak in a second FFT frequency window of a second width that is wider than first width. In some embodiments, tuning the LO includes , when a correlation peak is not found in any FFT frequency window, tuning the LO with a step wider than a portion of a maximum width of an FFT frequency window, said portion having a width of at least 20% of the maximum width. In some embodiments, tuning the LO includes tuning the LO to a local oscillation frequency that results in a strongest correlation peak within a correlation window. In some embodiments, searching for a correlation peak in a correlation window includes correlating a sequence detected in an envelope of a frequency component of an intermediate frequency, IF, signal with a reference sequence. In some embodiments, the method includes continuing to narrow an FFT frequency search window for each search of a plurality of successive searches until a predetermined number of searches have been performed. In some embodiments, the method includes continuing to widen an FFT frequency search window for each search of a plurality of successive searches until a predetermined number of searches have been performed.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] A more complete understanding of the present embodiments, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

[0022] FIG. l is a schematic of a known low power receiver;

[0023] FIG. 2 is a more detailed schematic of a known low power receiver;

[0024] FIG. 3 is a schematic diagram of an example network architecture illustrating a communication system according to principles disclosed herein;

[0025] FIG. 4 is a block diagram of a network node in communication with a wireless device over a wireless connection according to some embodiments of the present disclosure;

[0026] FIG. 5 is a flowchart of an example process in a wireless device for tuning a free running LO according to some embodiments of the present disclosure;

[0027] FIG. 6 is a block diagram of an example low power receiver configured according to principles disclosed herein;

[0028] FIG. 7 is a block diagram of another example low power receiver configured according to principles disclosed herein;

[0029] FIG. 8 illustrates peak search and related correlation windows;

[0030] FIG. 9 illustrates a low power receiver and a low power transmitter;

[0031] FIG. 10 is a block diagram of yet another example low power receiver configured according to principles disclosed herein;

[0032] FIG. 11 is a block diagram of another example low power receiver configured according to principles disclosed herein;

[0033] FIG. 12 is a flowchart of an example process in a wireless device for adjusting correlation windows when searching for a correlation peak; and FIG. 13 is a block diagram of an example low power receiver having a digital processor for tuning a free running local oscillator.

[0034] DETAILED DESCRIPTION

[0035] Before describing in detail exemplary embodiments, it is noted that the embodiments reside primarily in combinations of apparatus components and processing steps related to a low power receiver with intermediate frequency (IF) detection and local oscillator (LO) correction. Accordingly, components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

[0036] As used herein, relational terms, such as “first” and “second,” “top” and “bottom,” and the like, may be used solely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and / or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0037] In embodiments described herein, the joining term, “in communication with” and the like, may be used to indicate electrical or data communication, which may be accomplished by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling or optical signaling, for example. One having ordinary skill in the art will appreciate that multiple components may interoperate and modifications and variations are possible of achieving the electrical and data communication.

[0038] In some embodiments described herein, the term “coupled,” “connected,” and the like, may be used herein to indicate a connection, although not necessarily directly, and may include wired and / or wireless connections. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts described herein. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes” and / or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0039] The term “network node” used herein may be any kind of network node comprised in a radio network which may further comprise any of base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), g Node B (gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio (MSR) radio node such as MSR BS, multi-cell / multicast coordination entity (MCE), relay node, donor node controlling relay, radio access point (AP), transmission points, transmission nodes, Remote Radio Unit (RRU) Remote Radio Head (RRH), a core network node (e.g., mobile management entity (MME), selforganizing network (SON) node, a coordinating node, positioning node, MDT node, etc.), an external node (e.g., 3rdparty node, a node external to the current network), nodes in distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network node may also comprise test equipment. The term “radio node” used herein may be used to also denote a wireless device (WD) such as a wireless device (WD) or a radio network node.

[0040] In some embodiments, the non-limiting terms wireless device (WD) or a user equipment (UE) are used interchangeably. The WD herein may be any type of wireless device capable of communicating with a network node or another WD over radio signals, such as wireless device (WD). The WD may also be a radio communication device, target device, device to device (D2D) WD, machine type WD or WD capable of machine to machine communication (M2M), low-cost and / or low-complexity WD, a sensor equipped with WD, Tablet, mobile terminals, smart phone, laptop embedded equipped (LEE), laptop mounted equipment (LME), USB dongles, Customer Premises Equipment (CPE), an Internet of Things (loT) device, or a Narrowband loT (NB-IOT) device etc. Also, in some embodiments the generic term “radio network node” is used. It may be any kind of a radio network node which may comprise any of base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, Multi-cell / multicast Coordination Entity (MCE), relay node, access point, radio access point, Remote Radio Unit (RRU) Remote Radio Head (RRH).

[0041] Note that although terminology from one particular wireless system, such as, for example, 3GPP LTE and / or New Radio (NR), may be used in this disclosure, this should not be seen as limiting the scope of the disclosure to only the aforementioned system. Other wireless systems, including without limitation Wide Band Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB) and Global System for Mobile Communications (GSM), may also benefit from exploiting the ideas covered within this disclosure.

[0042] Note further, that functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and / or network nodes. In other words, it is contemplated that the functions of the network node and wireless device described herein are not limited to performance by a single physical device and, in fact, may be distributed among several physical devices.

[0043] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0044] Some embodiments are directed to a low power receiver with intermediate frequency (IF) detection and local oscillator (LO) frequency correction.

[0045] Returning to the drawing figures, in which like elements are referred to by like reference numerals, there is shown in FIG. 3 a schematic diagram of a communication system 10, according to an embodiment, such as a 3 GPP -type cellular network that may support standards such as LTE and / or NR (5G), which comprises an access network 12, such as a radio access network, and a core network 14. The access network 12 comprises a plurality of network nodes 16a, 16b, 16c (referred to collectively as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (referred to collectively as coverage areas 18). Each network node 16a, 16b, 16c is connectable to the core network 14 over a wired or wireless connection 20. A first wireless device (WD) 22a located in coverage area 18a is configured to wirelessly connect to, or be paged by, the corresponding network node 16a. A second WD 22b in coverage area 18b is wirelessly connectable to the corresponding network node 16b. While a plurality of WDs 22a, 22b (collectively referred to as wireless devices 22) are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole WD is in the coverage area or where a sole WD is connecting to the corresponding network node 16. Note that although only two WDs 22 and three network nodes 16 are shown for convenience, the communication system may include many more WDs 22 and network nodes 16.

[0046] Also, it is contemplated that a WD 22 may be in simultaneous communication and / or configured to separately communicate with more than one network node 16 and more than one type of network node 16. For example, a WD 22 may have dual connectivity with a network node 16 that supports LTE and the same or a different network node 16 that supports NR. As an example, WD 22 may be in communication with an eNB for LTE / E-UTRAN and a gNB for NR / NG-RAN.

[0047] A wireless device 22 is configured to include a wireless receiver 24 which is configured to compensate for drift in an IF frequency. The WD 22 may also include a low power transmitter 26. Both the wireless receiver 24 and the low power transmitter 26 are referred to as “low power” because they are designed to consume less power than a main transceiver 25 that is used for primary communication with the network node and / or another WD 22. A wireless receiver 24 is designed to consume less power than the main transceiver 25 by performing a reduced set of functions and using components that consume as little power as necessary to perform the reduced set of functions.

[0048] Example implementations, in accordance with an embodiment, of the WD 22 and network node 16 discussed in the preceding paragraphs will now be described with reference to FIG. 4.

[0049] The communication system 10 includes a network node 16including hardware 28 enabling it to communicate with the WD 22. The hardware 28 may include a radio interface 30 for setting up and maintaining at least a wireless connection 32 with a WD 22 located in a coverage area 18 served by the network node 16. The radio interface 30 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and / or one or more RF transceivers. The radio interface 30 includes an array of antennas 34 to radiate and receive signal(s) carrying electromagnetic waves.

[0050] In the embodiment shown, the hardware 28 of the network node 16 further includes processing circuitry 36. The processing circuitry 36 may include a processor 38 and a memory 40. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 36 may comprise integrated circuitry for processing and / or control, e.g., one or more processors and / or processor cores and / or FPGAs (Field Programmable Gate Array) and / or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 38 may be configured to access (e.g., write to and / or read from) the memory 40, which may comprise any kind of volatile and / or nonvolatile memory, e.g., cache and / or buffer memory and / or RAM (Random Access Memory) and / or ROM (Read- Only Memory) and / or optical memory and / or EPROM (Erasable Programmable Read- Only Memory).

[0051] Thus, the network node 16 further has software 42 stored internally in, for example, memory 40, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the network node 16 via an external connection. The software 42 may be executable by the processing circuitry 36. The processing circuitry 36 may be configured to control any of the methods and / or processes described herein and / or to cause such methods, and / or processes to be performed, e.g., by network node 16. Processor 38 corresponds to one or more processors 38 for performing network node 16 functions described herein. The memory 40 is configured to store data, programmatic software code and / or other information described herein. In some embodiments, the software 42 may include instructions that, when executed by the processor 38 and / or processing circuitry 36, causes the processor 38 and / or processing circuitry 36 to perform the processes described herein with respect to network node 16.

[0052] The communication system 10 further includes the WD 22 already referred to. The WD 22 may have hardware 44 that may include a radio interface 46 configured to set up and maintain a wireless connection 32 with a network node 16 serving a coverage area 18 in which the WD 22 is currently located. The radio interface 46 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and / or one or more RF transceivers. The radio interface 46 includes an array of antennas 48 to radiate and receive signal(s) carrying electromagnetic waves. The radio interface of the wireless device 22 may include a wireless receiver 24 which is configured to compensate for an unknown IF frequency.

[0053] The hardware 44 of the WD 22 further includes processing circuitry 50. The processing circuitry 50 may include a processor 52 and memory 54. In particular, in addition to or instead of a processor, such as a central processing unit, and memory, the processing circuitry 50 may comprise integrated circuitry for processing and / or control, e.g., one or more processors and / or processor cores and / or FPGAs (Field Programmable Gate Array) and / or ASICs (Application Specific Integrated Circuitry) adapted to execute instructions. The processor 52 may be configured to access (e.g., write to and / or read from) memory 54, which may comprise any kind of volatile and / or nonvolatile memory, e.g., cache and / or buffer memory and / or RAM (Random Access Memory) and / or ROM (Read-Only Memory) and / or optical memory and / or EPROM (Erasable Programmable Read-Only Memory).

[0054] Thus, the WD 22 may further comprise software 56, which is stored in, for example, memory 54 at the WD 22, or stored in external memory (e.g., database, storage array, network storage device, etc.) accessible by the WD 22. The software 56 may be executable by the processing circuitry 50. The software 56 may include a client application 58. The client application 58 may be operable to provide a service to a human or non-human user via the WD 22.

[0055] The processing circuitry 50 may be configured to control any of the methods and / or processes described herein and / or to cause such methods, and / or processes to be performed, e.g., by WD 22. The processor 52 corresponds to one or more processors 52 for performing WD 22 functions described herein. The WD 22 includes memory 54 that is configured to store data, programmatic software code and / or other information described herein. In some embodiments, the software 56 and / or the client application 58 may include instructions that, when executed by the processor 52 and / or processing circuitry 50, causes the processor 52 and / or processing circuitry 50 to perform the processes described herein with respect to WD 22. For example, the radio interface of the wireless device 22 may include a wireless receiver 24 which is configured to compensate for an IF frequency drift.

[0056] In some embodiments, the inner workings of the network node 16 and WD 22 may be as shown in FIG. 4 and independently, the surrounding network topology may be that of FIG. 3. The wireless connection 32 between the WD 22 and the network node 16 is in accordance with the teachings of the embodiments described throughout this disclosure. More precisely, the teachings of some of these embodiments may improve the data rate, latency, and / or power consumption and thereby provide benefits such as reduced user waiting time, relaxed restriction on file size, better responsiveness, extended battery lifetime, etc. In some embodiments, 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.

[0057] Various units for implementing the low power receiver functionality disclosed herein may be implemented such that a portion of the unit is stored in a memory within processing circuitry. In other words, the units may be implemented in hardware or in a combination of hardware and software within the processing circuitry.

[0058] FIG. 5 is a flowchart of an example process in a wireless receiver 24 according to some embodiments of the present disclosure. One or more blocks described herein may be performed by one or more elements of wireless receiver 24 such as by one or more of LO 60, tuning circuitry 62 and mixer 64. The method incudes searching (Block S10) for a peak of a correlation in a FFT frequency window; and tuning (Block S12) the LO 60 based on a frequency bin where a peak is found.

[0059] In some embodiments, searching for the correlation peak includes: searching for the correlation peak in a first FFT frequency window of a first width; and when the correlation peak is found in the first window, searching for the correlation peak in a second FFT frequency window of a second width that is narrower than the first width. In some embodiments, searching for the correlation peak includes: searching for the correlation peak in a first FFT frequency window of a first width; and when the correlation peak is not found in the first FFT frequency window, searching for the correlation peak in a second FFT frequency window of a second width that is wider than first width. In some embodiments, tuning the LO 60 includes , when a correlation peak is not found in any FFT frequency window, tuning the LO 60 with a step wider than a portion of a maximum width of an FFT frequency window, said portion having a width of at least 20% of the maximum width. In some embodiments, tuning the LO 60 includes tuning the LO 60 to a local oscillation frequency that results in a strongest correlation peak within a correlation window. In some embodiments, searching for a correlation peak in a correlation window includes correlating a sequence detected in an envelope of a frequency component of an intermediate frequency, IF, signal with a reference sequence. In some embodiments, the method includes continuing to narrow an FFT frequency search window for each search of a plurality of successive searches until a predetermined number of searches have been performed. In some embodiments, the method includes continuing to widen an FFT frequency search window for each search of a plurality of successive searches until a predetermined number of searches have been performed.

[0060] Having described the general process flow of arrangements of the disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the disclosure, the sections below provide details and examples of arrangements for a low power receiver with intermediate frequency (IF) detection and local oscillator (LO) correction.

[0061] In some embodiments, an analog IF detection and LO correction block is implemented. Some embodiments are applicable to any kind of low-power receiver architecture using a free-running oscillator (meaning an oscillator with no phase lock), but are not limited to this particular architecture.

[0062] FIG. 6 is one example of a low power receiver, herein referred to as wireless receiver 24, configured according to principles disclosed herein. The wireless receiver 24 includes the LO 60, the tuning circuitry 62, a mixer 64, an IF filter 66, an envelope detector 68 and baseband circuitry 70, which controls the tuning circuitry 62 via control circuitry 72. The mixer 64 mixes a received signal with the local carrier signal from the LO 60 to produce an IF signal. The IF signal is filtered by the IF filter 66 and the envelope detector 68 detects the envelope of the filtered IF signal. Baseband circuitry 70 may be configured to generate a control signal that is sent to control circuitry 72 to control the analog IF detection and LO correction functions of the tuning circuitry 62. The LO 60 may be a free running oscillator that is not controlled by a frequency locked or phase locked loop.

[0063] Referring to the example wireless receiver 24 of FIG. 7:

[0064] The receiver chain of the wireless receiver 24 may include the baseband filter 74, hard limiter 76, a correlator 78 and a sequency generator 80. The correlator 78 may output a control signal that is used to control the crystal oscillator of a main receiver of the WD 22.

[0065] The wireless receiver 24 includes tuning circuitry 62 that performs analog IF detection and LO correction functions to estimate the IF frequency and tune the LO frequency, (i.e., detecting the frequency and tune the LO 60 in the right direction to compensate for drift of the LO 60). For example, the LO 60 may be tuned by tuning circuitry 62 so that a correlation peak is observed in the correlation window to enable compensation for an IF frequency drift. In some embodiments, the tuning circuitry may include a low power analog fast Fourier transform (FFT); Signals relating to each of a plurality of bins of the FFT output can be used for correlation to a predetermined sequence, such as a preamble sequence. Correlation is performed by at least one correlator. In some embodiments, there is only one correlator doing the correlation for all FFT bins in sequence. In some embodiments, the correlation is performed by separate correlators, one for each FFT bin. In some embodiments, the number of correlators may be optimized based on power and area and performance. The bin or bins corresponding to a highest correlation, or at least a peak in correlation, or at least a peak higher than a threshold, are used to identify the IF frequency drift and to tune the local oscillator. One advantage of the analog FFT is the fact that it is low power. Another advantage is that all the frequency bins at the output of the FFT are available simultaneously and in parallel. With parallel processing, by correlation of those output signals, it is possible to identify the bin or bins that are mostly correlating and therefore identify what is the frequency drift to be compensated. If no peak is found, the IF signal is outside of the FFT window, and therefore the LO may be calibrated. That is, the LO may be tuned with a larger step, equal to a portion of a maximum FFT window width, for example between 20% and 100% of such maximum width.

[0066] FIG. 8 illustrates an example correlation process. When the output of the mixer 64 is outside the passband of the IF filter 66, the output of the correlation process is without a clear peak. When the output of the mixer 64 is within the passband of the IF filter 66, the output of the correlation process has a detectable peak.

[0067] FIG. 9 shows a WD 22 sharing the same LO 60 between a wireless receiver 24 and the low power transmitter 26. Thus, the tuned LO 60 may also be used for transmitting signals by a low power transmitter 26.

[0068] Referring to FIG. 10, the control circuitry 72 may be used to control an analog FFT unit 84 so that the FFT unit 84 is only running when necessary (e.g., when no peak is observed in the correlation window of FIG. 8). Envelope detectors 86 may be configured to detect an envelope of the signal in each frequency bin of the FFT output by the FFT unit 84. Baseband filters 88 filter the outputs of the envelope detectors 86 and output filtered signals that are correlated by correlators 90 with a locally generated sequence from the sequency generator 92.

[0069] In general low-power receivers topologies, some embodiments provide the IF signal inside the bandwidth of the IF filter 66 so that the baseband clock drift may be detected. Indeed, with no possibilities to detect the IF frequency and tune the LO 60 accordingly, the IF signal may drift outside the IF filter bandwidth window, and it would not be possible to detect and compensate a baseband clock drift. (See Figure 8);

[0070] Referring to FIG. 11, for low-power receivers containing a correlator 78 and sequence generator 80 in baseband, the LO 60 may be tuned so that the sequence correlation peak may be observed in the correlation window. In the absence of such a control loop, it would be possible for the received signal to be outside the IF filter bandwidth and it would not be possible to perform further compensations. (See FIG. 8);

[0071] For low-power receivers containing a correlator 78, a coarse frequency synchronization (i.e., a “quick way to find” the frequency peak) may be performed followed by use of the correlator for fine frequency synchronization; and / or

[0072] It is possible to use a more narrow-band IF filter 66 in a low-power receiver, which improves receiver sensitivity as well as immunity to interference.

[0073] There are also a number of network scale advantages enabled in some embodiments, such as one or more of the following:

[0074] In a WD 22 sharing the same LO 60 between a wireless receiver 24 and a low power transmitter 26 as described in FIG. 9, the tuned LO 60 may also be used for transmitting signals. Low data rate communication may be setup between low power devices. Correcting the LO frequency drift makes it possible to transmit closer to the center frequency of other receivers and thus enable energy savings at the network scale;

[0075] It possible to derive extra information when it comes to interferer and other causes of IF uncertainty sources at the network level; and / or

[0076] A wireless receiver 24 in an uncertain frequency environment such as a cluster of low-power devices may be implemented.

[0077] Low Power Analog FFT implementation:

[0078] An example implementation of the FFT unit 84 is a 16-point analog domain FFT using a Charge Re-use Analog Fourier Transform (CRAFT) engine. It demonstrates a power consumption of 3.8mW for a of 5GS / s (meaning a sampling rate of 5GHz) and a 16 bins definition. Anticipating a maximum IF frequency of 250 MHz (in line with the targeted device to device application), then a sampling rate of only 500 MHz is sufficient. As the analog FFT power consumption may be scaled linearly with respect to the sampling rate, a known FFT architecture implemented in accordance with principles disclosed herein may consume only around 0.38mW, making it compatible with low power receiver applications.

[0079] The dynamic range of the analog FFT unit 84 may be reduced to further reduce the power consumption by at least 50%.

[0080] Also, because of the introduction of the tuning circuitry 62 and the baseband feedback from the baseband circuitry 70 or correlator 78, the FFT unit 84 may be turned off when not needed, meaning even more energy consumption reduction at the system level.

[0081] IF detection and LO correction implementation: Implementation option: using correlators.

[0082] In some embodiments, the tuning circuitry 62 uses envelope detectors 86, baseband filters 88, comparators and correlators 90 and a frequency control unit 92 to process the outputs of the FFT unit 84. A correlator 90 uses a sequence generator 94 to look for the desired OOK-modulated signal at different frequency bins provided by the FFT unit 84. The frequency control unit 92 controls the frequency of the LO 60. An example of this topology is provided in FIG. 10 for a wireless receiver 24 using a free running oscillator as LO 60 (no PLL). FIG. 11 is another example topology for a wireless receiver 24 using an LO 60 according to principles disclosed herein.

[0083] By performing correlations for the different FFT frequency bin signals, it is possible to distinguish between the desired IF signal and interference. In case multiple bins contain signal energy, the correlators 90 may then be used to determine which one contains the desired signal. Another situation where correlation is beneficial is when the signal is very weak, at or below the noise floor, and it is therefore not possible to determine its presence from observing the signal power level alone.

[0084] When equipped with correlators 90 after the analog FFT 84, a faster operation is possible than without such correlators, since several FFT bins may in parallel be investigated for the modulated signal. There may be different numbers of correlators 90 and associated analog signal chains, each analog signal chain including an envelope detector 86 and baseband filter 88. To reduce chip area, there may not be an analog signal chain and a correlator 90 implemented for each FFT unit output signal. In that case, the signals may be investigated in an order depending on their power level, starting with the strongest and moving to weaker ones, until the desired IF signal is found. Switches may be used to connect the FFT unit outputs to the envelope detectors 86. In case each envelope detector 86 may be connected to a separate subset of FFT unit outputs using a multi-through switch, to reduce switch complexity compared to a full switch matrix, the search may start with the strongest signal in each subset, move on to the second strongest, and so on.

[0085] The flowchart in FIG. 12 is one example process for the implementations of FIGS. 10 and 11.

[0086] During the ON mode of the FFT unit 84 in the tuning circuitry 62, the FFT unit 84 starts with a default user-defined sequence code and window width for the peak search (Block S14). A correlator 90 correlates and integrates the signal received from a baseband filter 88 with the defined sequence code from the sequence generator 92 to obtain the desired peak which will be at the frequency fRF-fio (S20).

[0087] Once the desired peak is found (Block SI 8), the FFT peak search window frequency width may be narrowed (Block S20) to increase frequency resolution. The LO frequency may be tuned according to the FFT output bin where the peak was found.

[0088] In the case where a peak is not found (Block SI 8), the peak search frequency window may be widened (Block S22) by consuming more power. In the worst-case scenario where the peak is not found even at the maximum window width (Block S24), a suitable calibration needs to be done to the free-running oscillator to ensure fro > JRF- max. window width and LO < RF (assuming low-side mixing) (Block S26).

[0089] Another possible implementation: Using ADCs

[0090] Other implementations of the IF detection and LO correction block are possible. Some examples are described as follows. In some embodiments, the IF frequency may be searched by detecting energy with the FFT (detecting at which frequency a peak of energy is observed). It is then possible to adjust the oscillator frequency of the LO 60 and investigate the peaks one by one with the main path. Moreover, in order to detect the FFT energy peaks, envelope detectors 86 may be implemented, as well as ADCs 96 to quantize the signal from the envelope detectors 86. FIG. 13 shows an example embodiment where a digital processor 98 between the ADCs 96 and the LO 60 is configured to tune the LO 60.

[0091] Some non-limiting embodiments may include one or more of the following. An implementation of a low power receiver to perform IF frequency detection and LO frequency correction without using a PLL, wherein:

[0092] Embodiment 1. A low power receiver including: a. A low power free-running oscillator generates the local carrier frequency (LO) which is fed to a down-conversion mixer; b. A baseband circuit; and / or c. A controllable analog IF detection and LO correction block.

[0093] Embodiment 2. The controllable analog IF detection and LO correction block from 1c. including: a. An analog IF detection and LO correction block to estimate the IF frequency and tune the LO accordingly, including an analog FFT block; b. A control block to turn on / off the analog IF frequency detection and LO correction block;

[0094] Embodiment 3. The low power receiver in Embodiment 1 further including: a. A correlator that correlates the received OOK sequence with the local -generated sequence; b. the baseband circuit from lb also includes a circuit that generates a clock signal with the same period time as the modulation.

[0095] Embodiment 4. The IF frequency drift estimate is used to adjust the LO.

[0096] Embodiment 5. The mm-wave and analog parts may be in idle-mode between measurements.

[0097] Embodiment 6. A WD comprising a main transceiver and a low power receiver. The reference clock of the main transceiver is from the output of a crystal oscillator (XO) which also serves as system clock for the low power receiver baseband. The low power transmitter using the same LO as the low power receiver to transmit at a frequency close to the frequency of other receivers in the network.

[0098] Embodiment 7. The analog IF detection and LO correction block from Embodiment 2. a. further including (main implementation): a. Envelope detectors; b. Baseband filters; c. Correlators; d. A sequence generator. Embodiment 8. The analog IF detection and LO correction block from Embodiment 2. a. further including (other implementation): a. Envelope detectors; b. ADCs.

[0099] As will be appreciated by one of skill in the art, the concepts described herein may be embodied as a method, data processing system, computer program product and / or computer storage media storing an executable computer program. Accordingly, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit” or “module.” Any process, step, action and / or functionality described herein may be performed by, and / or associated to, a corresponding module, which may be implemented in software and / or firmware and / or hardware. Furthermore, the disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that may be executed by a computer. Any suitable tangible computer readable medium may be utilized including hard disks, CD- ROMs, electronic storage devices, optical storage devices, or magnetic storage devices.

[0100] Some embodiments are described herein with reference to flowchart illustrations and / or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, may be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer (to thereby create a special purpose computer), special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0101] These computer program instructions may also be stored in a computer readable memory or storage medium that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instruction means which implement the function / act specified in the flowchart and / or block diagram block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks.

[0102] It is to be understood that the functions / acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality / acts involved. Although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.

[0103] Computer program code for carrying out operations of the concepts described herein may be written in an object oriented programming language such as Python, Java® or C++. However, the computer program code for carrying out operations of the disclosure may also be written in conventional procedural programming languages, such as the "C" programming language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0104] Many different embodiments have been disclosed herein, in connection with the above description and the drawings. It will be understood that it would be unduly repetitious and obfuscating to literally describe and illustrate every combination and subcombination of these embodiments. Accordingly, all embodiments may be combined in any way and / or combination, and the present specification, including the drawings, shall be construed to constitute a complete written description of all combinations and subcombinations of the embodiments described herein, and of the manner and process of making and using them, and shall support claims to any such combination or subcombination.

[0105] Abbreviations that may be used in the preceding description include: Abbreviation Explanation

[0106] AP Access Point

[0107] BW Bandwidth

[0108] DL Downlink

[0109] DRX Discontinuous Reception fRF Input RF signal frequency fro LO frequency

[0110] IF Intermediate Frequency

[0111] LO Local Oscillator mmW Milli-meter Wave

[0112] OOK On-Off Keying

[0113] NR Next generation radio

[0114] RF Radio frequency

[0115] SSB Synchronization Signal Block

[0116] UE User Equipment

[0117] UL Uplink

[0118] VCO Voltage Control Oscillator

[0119] XO Crystal Oscillator

[0120] It will be appreciated by persons skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. In addition, unless mention was made above to the contrary, it should be noted that all of the accompanying drawings are not to scale. A variety of modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.

Claims

What is claimed is:

1. A wireless receiver (24) comprising: a local oscillator , LO (60), configured to generate a local oscillator signal, the LO (60) not being phase-locked; a mixer (64) configured to mix the local oscillator signal with a received Amplitude-shift Keying ASK modulated signal to produce an intermediate frequency (IF) signal; and tuning circuitry (62) configured to estimate a frequency of the IF signal and tune the LO (60) to compensate for an IF frequency drift, the tuning circuitry (62) including an analog fast Fourier transform circuit (84) configured to perform a fast Fourier transform, FFT, of the IF signal to obtain signals in a plurality of frequency bins, the IF frequency estimate being based on correlations of the signals in the plurality of frequency bins with a reference sequence.

2. The wireless receiver (24) of Claim 1, wherein the LO (60) is tuned according to a digital control signal based at least in part on the FFT (84) of the IF signal.

3. The wireless receiver (24) of any of Claims 1 and 2, further comprising an envelope detector to detect an envelope of the FFT (84) of the IF signal and a baseband filter (88) to filter the detected envelope.

4. The wireless receiver (24) of Claim 3, further comprising at least one correlator (90) configured to correlate a sequence detected in the filtered detected envelope of the FFT (84) of the IF signal with a reference sequence.

5. The wireless receiver (24) of Claim 4, wherein the tuning circuitry (62) is configured to tune the LO (60) so that a correlation peak occurs in a frequency bin- associated with at least one correlator (90).

6. The wireless receiver (24) of Claim 5, wherein the FFT (84) is disabled when no peak is observed7. The wireless receiver (24) of any Claims 4-6, wherein the at least one correlator (90) is configured to perform a coarse frequency estimate using an FFT frequency window of a first width followed by a fine frequency estimate using an FFT frequency window of a second width narrower than the first width.

8. The wireless receiver (24) of any of Claims 4-7, wherein the ASK modulated signal is an on-off keying OOK modulated signal, wherein each one of the at least one correlator (90) is configured to search for an on-off keying, OOK, modulated signal in a different frequency bin of the FFT (84).

9. The wireless receiver (24) of any of Claims 4-8, wherein each correlator (90) of the at least one correlator (90) performs a correlation between a reference sequence and a sequence associated with a different frequency bin of the FFT of the IF signal.

10. The wireless receiver (24) of any of Claims 4-10, wherein the tuning circuitry (62) is configured to determine a frequency bin of the FFT that is associated with a strongest correlation peak.

11. The wireless receiver (24) of any of Claims 4-9, wherein the tuning circuitry (62) is configured to tune the LO (60) to the frequency of an FFT frequency bin having a strongest correlation peak.

12. The wireless receiver (24) of any of Claims 1-11, wherein the tuning circuitry (62) is configured to tune the LO (60) to a frequency that, when mixed with the received signal, provides the IF signal at a frequency that is within a bandwidth of operation of an IF filter of a receiver chain of the wireless receiver (24).

13. The wireless receiver (24) of any of Claims 1-12, further comprising, for each frequency bin of the plurality of frequency bins, an envelope detector and a baseband filter to detect and filter an envelope of a signal in the frequency bin.

14. The wireless receiver (24) of any of Claims 1-13, wherein the wireless receiver (24) is comprised in a wireless device (22).

15. A method for compensating for frequency drift of a local oscillator, LO (60), in the wireless receiver (24) of any of Claims 1-14, the wireless receiver (24) configured to provide a tuning control signal to the LO (60), the method comprising: searching (S10) for a peak of a correlation in a FFT frequency window; and tuning (S12) the LO (60) based on a frequency bin where a peak is found.

16. The method of claim 15, wherein searching for the correlation peak includes: searching for the correlation peak in a first FFT frequency window of a first width; and when the correlation peak is found in the first window, searching for the correlation peak in a second FFT frequency window of a second width that is narrower than the first width.

17. The method of any of Claims 15 and 16, wherein searching for the correlation peak includes: searching for the correlation peak in a first FFT frequency window of a first width; and when the correlation peak is not found in the first FFT frequency window, searching for the correlation peak in a second FFT frequency window of a second width that is wider than first width.

18. The method of any of Claims 15-17, wherein tuning the LO (60) includes , when a correlation peak is not found in any FFT frequency window, tuning the LO (60) with a step wider than a portion of a maximum width of an FFT frequency window, said portion having a width of at least 20% of the maximum width.

19. The method of any of Claims 1-15, wherein tuning the LO (60) includes tuning the LO (60) to a local oscillation frequency that results in a strongest correlation peak within a correlation window.

20. The method of any of Claims 15-19, wherein searching for a correlation peak in a correlation window includes correlating a sequence detected in an envelope of a frequency component of an intermediate frequency, IF, signal with a reference sequence.

21. The method of any of Claims 15-20, further comprising continuing to narrow an FFT frequency search window for each search of a plurality of successive searches until a predetermined number of searches have been performed.

22. The method of any of Claims 15-20, further comprising continuing to widen an FFT frequency search window for each search of a plurality of successive searches until a predetermined number of searches have been performed.

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