Patent Description:
Wireless communication networks, including geographically fixed network nodes and often mobile radio network devices such as cellphones and smartphones, are ubiquitous in many parts of the world. These networks continue to grow in capacity and sophistication. To accommodate both more users and a wider range of types of devices that may benefit from wireless communications, the technical standards governing the operation of wireless communication networks continue to evolve. The fourth generation (<NUM>) of network standards has been deployed, and the fifth generation (<NUM>, also known as New Radio, or NR) is in development.

Cellular wireless communication systems are currently being developed and improved for machine-to-machine (M2M) or machine type communication (MTC), which is characterized by lower demands on data rates than, e.g., mobile broadband, but with higher requirements on aspects such as low cost device design (e.g., below USD $<NUM>), and very long battery life (device lifetime). In Release <NUM>, the Third Generation Partnership Project (3GPP) standardized two different approaches for MTC. Enhanced MTC (eMTC), also known as Long Term Evolution - Machine-to-machine (LTE-M), includes cost reduction measures such as lower bandwidth, lower data rates, and reduced transmit power, as compared to legacy (broadband) LTE. Narrowband Internet of Things (NB loT) more aggressively addresses the extremely low cost market with less than <NUM> of channel bandwidth and flexibility to be deployed concurrently with legacy networks or outside of active legacy spectrum.

An important aspect to M2M and MTC type device design is ultra-low power consumption. For example, it is envisioned that sensors and other devices may be deployed with a battery that outlasts the useful device life, such as <NUM> years. Another approach to powering M2M/MTC devices is energy scavenging, where power is captured and stored (e.g., in a battery or capacitor) from, e.g., solar cells, temperature or salinity gradients, kinetic energy, and the like. In such devices, power management is a major design concern. Selective activation - e.g., sleep mode - is heavily exploited. While it is straightforward to only activate circuits to serve the device's needs, such as to transmit sensed or accumulated data, connectivity is a two-sided activity, and the device must consume power to "listen" to the network if it is to be reachable.

One approach to conserving power while operating a receiver is to activate it on a duty cycle, with dormant periods between receiver activations. Such a receiver activation duty cycle directly affects the response time - the lower the duty cycle, the longer the network must on average repeat the paging messages to contact the device. Repeated paging messages consume air interface resources, increase interference to other devices, and may cause congestion in heavy traffic loads. A lower duty cycle also necessarily increases the delay for obtaining a response from the device.

Another approach is to utilize a very low-power, limited-function receiver, called a "wakeup" receiver, which is operated at a higher duty cycle (or even continuously) and consumes far less power than a main receiver. The wake-up receiver's functionality is limited to detecting a wakeup request from the network. Upon such detection, the wake-up receiver alerts the device (e.g., a power management system), which brings the main receiver out of sleep mode to establish connectivity and engage the device's full communications capabilities.

To achieve ultra-low power consumption (e.g., below 100uW), the wakeup receiver is typically based on amplitude detection of on-off keying (OOK) signals. This avoids the need for highly accurate local oscillator (LO) clock signals, which are typically generated by power-hungry phase locked loop (PLL) circuits. However, due to the resulting inaccuracy and uncertainty in a local oscillator frequency, only relatively wideband filtering can be realized prior to the amplitude detection. In this case, immunity to interference is essentially limited to what can be achieved by correlation of PN-sequences.

Due to the limited amount of filtering prior to amplitude detection, the wakeup receivers are very vulnerable to interference. All interference and noise entering the amplitude detector, having amplitude modulation in the same frequency range as the wakeup message, will mask the signal. It is not necessary that the interference utilize the same frequency channel. Rather, because of the limited ability to filter out signals adjacent to the wakeup signal, signals transmitted in adjacent channels, and potentially even further away (in frequency), will effectively have as detrimental an effect as a co-channel interferer. More narrowband filtering would eliminate most such interference; however the accurate frequency generation required for that would consume significant power, defeating the purpose of the wakeup receiver.

Compounding the interference problem, the amplitude detector is also heavily non-linear and therefore produces very small outputs for weak input signals. For example, assuming a quadratic gain characteristic for small signals means that the signal to noise ratio (SNR) falls off by 20dB for each reduction of 10dB of the received signal level. With even modest amounts of interference at the detector input, the gain is therefore often insufficient for reliable operation with small input signal amplitudes.

The Background section of this document is provided to place embodiments of the present invention in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Approaches described in the Background section could be pursued, but are not necessarily approaches that have been previously conceived or pursued.

Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.

Two examples of the prior art are disclosed in <NPL> and in <CIT>.

The following presents a simplified summary of the disclosure in order to provide a basic understanding to those of skill in the art. This summary is not an extensive overview of the disclosure and is not intended to identify key/critical elements of embodiments of the invention or to delineate the scope of the invention. The sole purpose of this summary is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

According to embodiments of the present invention described and claimed herein, a wakeup receiver is based on frequency shift keying (FSK) instead of amplitude modulation (AM). The inherent problems of AM-demodulation are then avoided. Most importantly, the nonlinearity of the amplitude detector, which is a severe bottleneck in receiving weak signals, is removed from the signal chain. The FSK detector is easily realized in the digital domain, and due to the time discrete nature of digital signals, it has a periodic response in frequency (also known as frequency folding). Wakeup receivers according to embodiments of the present invention exploit this property by demodulating FSK at different offsets from the center frequency. This does not impose high accuracy demands on the local oscillator frequency, and a power-hungry phase locked loop (PLL) is therefore not necessary. However, the sensitivity of the receiver is very low at regular frequencies - that is, there are periodic "nulls" in the transfer function. To address this potential loss of reception, the network at least occasionally transmits the FSK wakeup signal at a slightly shifted frequency. The delay between an FSK wakeup signal transmission and a frequency-shifted transmission is significantly smaller than the time for the wakeup receiver frequency to drift, resulting in at least one of the FSK wakeup signals being received at a frequency where the receiver has good sensitivity. FSK wakeup signals (and frequency-shifted ones) are transmitted often, so that wakeup receivers can continuously keep their center frequency and filter bandwidth tuned for best reception. In some embodiments, because FSK detection is wideband, channel filters in a wakeup receiver are set to different bandwidths. Wider filters are used to speed up acquisition and finding proper oscillator settings to generate the proper center frequency, and more narrow filters are employed during tracking.

One embodiment relates to a method of operating a low-power wakeup receiver in a wireless device operative in a wireless communication network. Operation of a primary receiver circuit is suspended to conserve power. A limited-function, low-power wakeup receiver circuit is operated. A wakeup signal transmitted by the network at a first frequency is received. The wakeup signal is transmitted using Frequency Shift Keying (FSK), wherein a state of an information bit is encoded as a positive or negative offset from the first frequency. The wake-up signal is frequency down-converted from the first frequency to a second frequency lower than the first frequency. The received FSK wakeup signal is demodulated at the second frequency using first and second matched filters in the discrete time domain. The first filter is configured to detect odd numbered members of an ordered set of equidistant frequencies, and reject even numbered ones. A separation between two frequencies in the ordered set is equal to two times the offset frequency of the FSK signal. The second filter is configured to detect even numbered members of the ordered set and reject odd numbered ones. In this manner, data modulated onto the FSK wakeup signal is recovered. If the demodulated data identifies the wireless device, operation of the primary receiver circuit is resumed.

Another embodiment relates to a wireless device operative in a wireless communication network. The wireless device includes a primary receiver circuit adapted to be suspended to conserve power, and further adapted to resume operation if data demodulated from a received FSK wakeup signal identifies the wireless device. The wireless device further includes a limited-function, low-power wakeup receiver circuit. The wakeup receiver circuit is adapted to receive a wakeup signal transmitted by the network at a first frequency. The wakeup signal is transmitted using Frequency Shift Keying (FSK), wherein a state of an information bit is encoded as a positive or negative offset from the first frequency. The wakeup receiver circuit includes a digitally controlled oscillator adapted to generate a local oscillator signal, and a mixer adapted to frequency down-convert the wake-up signal from the first frequency to a second frequency lower than the first frequency. The wakeup receiver circuit further includes a demodulator comprising first and second matched filters in the discrete time domain. The first filter is configured to detect odd numbered members of an ordered set of equidistant frequencies, and reject even numbered ones. A separation between two frequencies in the ordered set is equal to two times the offset frequency of the FSK signal. The second filter is configured to detect even numbered members of the ordered set and reject odd numbered ones. In this manner, data modulated onto the FSK wakeup signal is demodulated.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention and examples of an interacting network node and a method therein are shown. However, this invention should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

For simplicity and illustrative purposes, the present invention is described by referring mainly to an exemplary embodiment thereof. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be readily apparent to one of ordinary skill in the art that the present invention may be practiced without limitation to these specific details. In this description, well known methods and structures have not been described in detail so as not to unnecessarily obscure the present invention.

<FIG> depicts functional blocks of a wireless device <NUM> according to one embodiment. The wireless device <NUM> includes a battery <NUM> (or power scavenging device), power management circuit <NUM>, and baseband processor <NUM> connected to memory <NUM>. When actively connected to a wireless network, the baseband processor <NUM> communicates with the network (e.g., a base station) via a transmitter <NUM> and primary receiver <NUM>. A duplexer <NUM> provides isolation between FDD transmit and receive functions (which could be a switch in a TDD implementation), in connecting them both to an antenna <NUM> (which may be internal or external, as indicated by the dashed lines). Of course, the wireless device <NUM> may include other functions not depicted in <FIG>, such as sensors, cameras, monitors, actuators, control circuits, other communication interfaces, a user interface, and the like, depending on the specific purpose of the wireless device <NUM>.

As indicated by dashed arrows, the power management circuit <NUM> controls the provision of power (and/or clock signals) to other circuits and functions of the wireless device <NUM>. In particular, the power management circuit <NUM> places circuits in a "sleep," or inactive mode, when the relative functionality is not being currently utilized, to conserve power. As discussed above, the power management circuit <NUM> may efficiently and accurately control the provision of power to circuits such as the baseband processor <NUM> and transmitter <NUM>, in response to current computational or outgoing communication demands. However, the wireless device <NUM> has no knowledge when incoming communications, such as paging messages, may be directed to it from the network, and continuously monitoring the network consumes large amounts of power. While the power management circuit <NUM> can reduce the power consumption of the primary receiver <NUM> by operating it in a duty cycle, this results in wasted air interface resources, increased interference, and possible congestion as the network is required to repeatedly transmit paging messages until one coincides with a primary receiver <NUM> "on" time.

Accordingly, the wireless device includes a wakeup receiver <NUM>. The wakeup receiver <NUM> is a low-power, limited-functionality circuit, the purpose of which is to monitor the network for an indication of pending transmissions directed to the wireless device <NUM> when operation of the primary receiver <NUM> is suspended for power savings. This indication may be in the form of a wakeup signal transmitted by the network and identifying the wireless device <NUM> (or a group, of which the wireless device <NUM> is a member). Upon detecting such a signal, the wakeup receiver alerts the power management circuit <NUM>, which in turn activates the primary receiver <NUM>, which e.g., monitors the network for paging messages, performs a random access procedure, or otherwise engages in conventional (and higher power consuming) communication protocols with the network. When the wireless device <NUM> completes a task, or otherwise believes no further network transmissions directed to it are likely for a time, the power management circuit <NUM> again suspends operation of the primary receiver <NUM>, and activates the wakeup receiver <NUM>.

<FIG> depicts the architecture of a wakeup receiver <NUM> according to one embodiment. The wakeup receiver <NUM> is a limited-function, low-power receiver intended to be activated by a wireless device <NUM> when a primary, full-function receiver <NUM> is in "sleep" mode for power conservation. The wakeup receiver <NUM> searches for a wakeup signal transmitted by the network (e.g., by a base station or eNB). If the decoded wakeup signal includes an ID of the wireless device <NUM>, the wakeup receiver <NUM> outputs a signal to the wireless device <NUM> - such as to a power management system <NUM> on the wireless device <NUM> - to activate the primary receiver <NUM>. The primary receiver <NUM> may then receive broadcasts such as System Information, and search for paging messages. In this manner, the wireless device <NUM> may remain dormant, in a very low power consumption mode, for extended periods. However, during such dormant times, the wireless device <NUM>, via the wakeup receiver <NUM>, continues to monitor network transmissions, and hence the network need not repeat paging messages directed to the wireless device <NUM> when it has downlink data to transfer.

The wakeup receiver <NUM> comprises a front-end filter <NUM>, mixer(s) <NUM>, amplifier(s) <NUM>, narrowband filter(s) <NUM>, Analog to Digital (ADC) converter(s) <NUM>, digital processing and control logic <NUM>, and a Digitally Controlled Oscillator (DCO) <NUM>. The dual paths depicted in <FIG> reflect In-phase (I) and Quadrature (Q) mixing, although other mixers <NUM> may be employed. Operation of the wakeup receiver <NUM> is straightforward to those of skill in the art. A signal received at an antenna <NUM> (<FIG>), and passed through a duplexer <NUM> for isolation from transmitter circuits <NUM>, is initially filtered by front-end filter <NUM>. Mixers <NUM> frequency downconvert received signals by mixing them with Local Oscillator (LO) signals generated by the DCO <NUM>, under the control of control logic <NUM>. The mixer <NUM> is a passive structure, to minimize power consumption and flicker noise. Because the mixer <NUM> precedes the baseband amplifiers <NUM> and filters <NUM>, the signal frequency is low, and narrowband filtering can be applied to minimize interference, reducing the dynamic range needed in the ADCs <NUM>. Further filtering and signal processing is then performed in the digital domain, in digital processing circuits <NUM>. If data decoded from a received wakeup signal indicate the wakeup signal targeted the wireless device <NUM> (for example, the data match a unique identifier of the wireless device <NUM>, such as IMSI, C-RNTI, or the like), the primary receiver <NUM> is activated to receive further messages from the network.

The DCO <NUM> is the major power consumer of the wakeup receiver <NUM>. To minimize power consumption, no external frequency reference, such as a crystal oscillator, is used. Furthermore, phase locked loop designs are avoided, as they are heavy consumers of power. In one embodiment, a ring oscillator is used in the DCO <NUM> for ultra-low power consumption. Due to these power-saving design considerations, the DCO <NUM> is neither highly accurate nor particularly stable. That is, the output frequency of the DCO <NUM> LO signal will drift over time.

The demodulation of the wake-up signal is performed in the digital processing circuit <NUM>. The signal is modulated using FSK, in which a state of an information bit is encoded as a positive or negative offset from a carrier frequency. <FIG> depicts FSK, where fc denotes a center, or carrier, frequency. A digital "<NUM>" is represented by a tone at frequency fc + foffset, and a digital "<NUM>" is represented by a tone at frequency fc - foffset (or vice versa). At the wakeup receiver <NUM>, the frequency of the FSK wakeup signal is detected from discrete time signal samples. A highly efficient FSK demodulator using discrete samples is presented in the papers, <NPL>, and <NPL>.

The FSK demodulation is performed using two matched filters, one for a transmitted negative frequency offset (fc - foffset,), and one for a transmitted positive offset (fc + foffset,). The sign of the frequency offset contains the digital information to receive: for example, a negative offset could mean a digital zero, and a positive a digital one (or vice versa). The modulation index is chosen so that each symbol represents a full <NUM> degrees rotation of the complex baseband signal. The sample rate is chosen to be four samples per symbol. The matched filters are then very simple to implement, as the signal will rotate <NUM> degrees between each sample, clockwise or counterclockwise. The two matched filters consist of multiplying the samples of a symbol by <NUM>, j, -<NUM>, -j and <NUM>, -j, -<NUM>, j, respectively, and then summing the result. These multiplications are very easy to realize for a baseband signal in I, Q representation, by swapping the I, Q signals and the signs. This demodulation also suppresses flicker noise and DC-offsets, as the sum of coefficients in the filters are zero. A DC input will therefore result in a zero output of the filters.

<FIG> depicts the periodic response of the two matched filters (one solid and one dashed-line) for a sample rate of <NUM>. Since one filter detects the positive offset tone and the other the negative, the filter outputs are separated by two times the offset frequency. As <FIG> shows, not only will the filters detect the rotations of the signal at the targeted offset frequencies of ¼ of the sample rate, but each filter will also detect offset frequencies an integer number of sample rates higher or lower. This is normally an undesired property, requiring filtering (or otherwise discarding) the duplicate responses. However, according to embodiments of the present invention, this feature is exploited to increase the wakeup receiver robustness. In a wake-up receiver <NUM>, the DCO <NUM> is not locked to a reference in a phase locked loop, since that would consume too much power. This makes the local oscillator (LO) frequency uncertain, and at baseband the wakeup signal could have higher offset frequencies, positive or negative. The FSK demodulator will anyway demodulate the signal, as long as the frequency separation between the two FSK tones is twice the offset frequency, or ½ the sample rate.

The frequencies corresponding to the matched filter peak outputs are collected in an ordered set. Arbitrarily beginning by numbering a first frequency, detected by one filter, as <NUM>, the other filter will detect the next frequency numbered <NUM>, and so on. One example of such numbering is indicated in <FIG>. Hence, the first filter detects all odd-numbered frequencies in the ordered set and rejects the even-numbered ones. Similarly, the second filter detects the even-numbered frequencies in the ordered set, and rejects the odd-numbered ones. The frequencies in the ordered set are equidistant, and the separation between two frequencies in the ordered set is equal to twice the offset frequency of the FSK signal.

Depending on the offset frequency, however, which matched filter detects the lower frequency tone and which detects the higher may switch. Furthermore, at certain frequency offsets, the two tones will be located at zero response of the filters, if they occur at DC or plus/minus integer multiples of half the sample rate. Both of these factors must be addressed for the wake-up receiver to be reliable.

The uncertainty of which filter detects which tone can be addressed by correlating for both polarities of the wakeup signal. A single correlator is used; it yields a positive result for the regular polarity of the wakeup message, and a negative result for the inverse, where each bit has been reversed (or vice versa). In one example of an interacting method, the network transmits the wakeup signal with an initial preamble in the message, which is known a priori by the receiver. Once the preamble is detected, the polarity is known for the rest of that wakeup signal.

To eliminate the risk of a wakeup signal being lost by coinciding with zeros in the matched filter responses, the wakeup signal is at least occasionally re-transmitted shortly after a first transmission, at a shifted center frequency. In one example of an interacting method, as depicted in <FIG>, the re-transmission is shifted by the FSK offset frequency foffset, which may for example be <NUM>. By making the re-transmission soon after the first transmission, the local oscillator will not have experienced any significant frequency drift. If the first message was lost due to the zeros in the transfer function of the filter response, the second one will be received with close to maximum gain. The maximum frequency error will occur if the two transmissions occur at frequencies located symmetrically at each side of a zero in the matched filter responses, or symmetrically at each side of a peak. In this case both situations yield a frequency error of <NUM>/<NUM> of the offset frequency, i.e., <NUM> in <FIG>.

Transmitting the shifted-frequency wakeup signal increases power consumption; however, this occurs at the transmitter, where power consumption is typically not a concern. In addition, the shifted-frequency wakeup signal is quite short, and only transmitted relatively seldom, for example, for a duration of <NUM>-<NUM> sent every <NUM>, so the increase in channel usage is also insignificant.

If higher performance is required, more shifted-frequency transmissions are made. In one example of an interacting method, three wakeup signals are transmitted, with two being shifted, relative to the third, in frequency by -<NUM>/<NUM> and <NUM>/<NUM> of the FSK offset frequency (that is, yielding wakeup signals at -<NUM>/<NUM>, <NUM>, and <NUM>/<NUM> of the offset frequency). In this example, the maximum error is <NUM>/<NUM> of the offset frequency, which is equal to <NUM> in <FIG>. In another example of an interacting method, four wakeup signals are transmitted, with frequency shifts of - <NUM>/<NUM>, -<NUM>/<NUM>, <NUM>/<NUM>, and <NUM>/<NUM> of the FSK offset frequency, relative to a nominal center, or carrier frequency. In this example, the maximum error is <NUM>/<NUM> of the offset frequency, which is equal to <NUM> in <FIG>.

<FIG> depicts the loss in sensitivity due to frequency errors, for different Bit Error Rates (BER). In a wake-up receiver <NUM> the raw bit error rate can be quite high, so the curve for BER=<NUM>-<NUM> is relevant. As can be seen with four shifted-frequency wakeup signal transmissions, yielding a maximum error of <NUM>, the sensitivity is degraded by less than <NUM>. With three shifted-frequency wakeup signal transmissions, yielding an error of <NUM>, the degradation is about 3dB. With two shifted-frequency wakeup signal transmissions the maximum error is outside the graph, but the maximum degradation can be estimated to slightly above 5dB. To summarize, the minimum number of shifted-frequency wakeup signal transmissions for robust operation is two, but better performance is achieved with three or four, while using more than four shifted-frequency wakeup signal transmissions yields diminishing returns.

In one embodiment, different modes of the wakeup receiver circuit <NUM> are used when acquiring the FSK wakeup signal sequence, and when staying tuned by tracking it. For example, wider bandwidth filters <NUM> are used during signal acquisition, such as when the wakeup receiver circuit <NUM> is activated, following inactivation of the primary receiver circuit <NUM>. The wideband filters speed up the signal acquisition, and finding the proper DCO setting for generating the right center frequency. Then, more narrowband filters <NUM> are employed while tracking the FSK wakeup signals, to provide the best immunity to interference. In some embodiments, there is a gradual transition, using shrinking filter bandwidths, between these modes.

<FIG> depicts a method <NUM> of operating a low-power wakeup receiver <NUM> in a wireless device <NUM> operative in a wireless communication network, in accordance with particular embodiments. Operation of a primary receiver circuit <NUM> is suspended to conserve power (block <NUM>). A limited-function, low-power wakeup receiver circuit is operated (block <NUM>). A wakeup signal, transmitted by the network at a first frequency, is received (block <NUM>). The wakeup signal is transmitted using Frequency Shift Keying (FSK), wherein a state of an information bit is encoded as a positive or negative offset from the first frequency. The first received FSK wakeup signal is frequency down-converted from the first frequency to a second frequency lower than the first frequency (block <NUM>). The received FSK wakeup signal is demodulated at the second frequency using first and second matched filters in the discrete time domain. The first filter is configured to detect odd numbered members of an ordered set of equidistant frequencies, and reject even numbered ones. A separation between two frequencies in the ordered set is equal to two times the offset frequency of the FSK signal. The second filter is configured to detect even numbered members of the ordered set and reject odd numbered ones. In this manner, data modulated onto the FSK wakeup signal is recovered (block <NUM>). If the demodulated data identifies the wireless device <NUM> (block <NUM>), operation of the primary receiver circuit <NUM> is resumed (block <NUM>).

<FIG> depicts a method <NUM> of operating a base station serving one or more low-power wireless devices <NUM> in a wireless communication network, in accordance with particular examples of an interacting method. A first wakeup signal is generated at a first frequency (block <NUM>). The first wakeup signal is transmitted using Frequency Shift Keying (FSK), wherein a state of an information bit is encoded as a positive or negative frequency offset from the first frequency. The first FSK wakeup signal is transmitted (block <NUM>). A second FSK wakeup signal is generated at a second frequency (block <NUM>). The second FSK wakeup signal frequency is shifted from the first FSK wakeup signal frequency by the FSK offset frequency or a fraction thereof. The second FSK wakeup signal is transmitted after transmitting the first FSK wakeup signal (block <NUM>).

Apparatuses described herein may perform the methods <NUM>, <NUM> described herein, and any other processing, by implementing any functional means, modules, units, or circuitry. In one example of an interacting apparatus, the apparatuses comprise respective circuits or circuitry configured to perform the steps shown in the method figures. The circuits or circuitry in this regard may comprise circuits dedicated to performing certain functional processing and/or one or more microprocessors in conjunction with memory. For instance, the circuitry may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory may include program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein, in several examples. In examples that employ memory, the memory stores program code that, when executed by the one or more processors, carries out the techniques described herein.

As described above, <FIG> for example illustrates a wireless device <NUM> as implemented in accordance with one or more embodiments. In general, a wireless device <NUM> is any type of device capable of communicating with a network node and/or base station using radio signals. A wireless device <NUM> may therefore refer to a machine-to-machine (M2M) device, a machine-type communications (MTC) device, a Narrowband Internet of Things (NB loT) device, etc. The wireless device <NUM> may also be a User Equipment (UE); however it should be noted that the UE does not necessarily have a "user" in the sense of an individual person owning and/or operating the device. A wireless device <NUM> may also be referred to as a radio device, a radio communication device, a wireless communication device, a wireless terminal, or simply a terminal - unless the context indicates otherwise, the use of any of these terms is intended to include device-to-device UEs or devices, machine-type devices, or devices capable of machine-to-machine communication, sensors equipped with a radio network device, wireless-enabled table computers, mobile terminals, smart phones, laptop-embedded equipped (LEE), laptop-mounted equipment (LME), USB dongles, wireless customer-premises equipment (CPE), etc. In the discussion herein, the terms machine-to-machine (M2M) device, machine-type communication (MTC) device, wireless sensor, and sensor may also be used. It should be understood that these devices may be UEs, but may be configured to transmit and/or receive data without direct human interaction.

A wireless device <NUM> as described herein may be, or may be comprised in, a machine or device that performs monitoring or measurements, and transmits the results of such monitoring measurements to another device or a network node. Particular examples of such machines are power meters, industrial machinery, or home or personal appliances, e.g. refrigerators, televisions, personal wearables such as watches etc. In other scenarios, a wireless device <NUM> as described herein may be comprised in a vehicle and may perform monitoring and/or reporting of the vehicle's operational status or other functions associated with the vehicle.

<FIG> illustrates a schematic block diagram of a wireless device <NUM> operative in a wireless communication network according to still other embodiments. As shown, the wireless device <NUM> implements various functional means, units, or modules, e.g., via the baseband processor <NUM>, power management circuit <NUM>, primary receiver <NUM>, or wakeup receiver <NUM> in <FIG> and/or via software code. These functional means, units, or modules, e.g., for implementing method <NUM> herein, include for instance: primary receiver suspending/resuming unit <NUM>, wakeup receiver operating unit <NUM>, wakeup signal receiving unit <NUM>, wakeup signal frequency converting unit <NUM>, and wakeup signal demodulating unit <NUM>.

The primary receiver suspending/resuming unit <NUM> is configured to suspend operation of a primary receiver circuit <NUM> to conserve power. If a received wakeup signal identifies the wireless device <NUM>, the primary receiver suspending/ resuming unit <NUM> is further configured to resume operation of the primary receiver circuit <NUM>. The wakeup receiver operating unit <NUM> is configured to operate a limited-function, low-power wakeup receiver circuit <NUM>. The wakeup signal receiving unit <NUM> is configured to receive a wakeup signal transmitted by the network at a first frequency, the wakeup signal being transmitted using FSK , wherein a state of an information bit is encoded as a positive or negative offset from the first frequency. The wakeup signal frequency converting unit <NUM> is configured to frequency down-convert the wake-up signal from the first frequency to a second frequency lower than the first frequency. The wakeup signal demodulating unit <NUM> is configured to demodulate the received FSK wakeup signal at the second frequency using first and second matched filters in the discrete time domain, wherein the first filter is configured to detect odd numbered members of an ordered set of equidistant frequencies, and reject even numbered ones, a separation between two frequencies in the ordered set being equal to two times the offset frequency of the FSK signal, and wherein the second filter is configured to detect even numbered members of the ordered set and reject odd numbered ones, thereby recovering data modulated onto the FSK wakeup signal.

<FIG> illustrates an example of an interacting network node <NUM>. In particular, the network node <NUM> may function as a base station in a wireless communication network. As those of skill in the art are aware, a base station is a network node <NUM> providing wireless communication services to one or more wireless devices <NUM> in a geographic region (known as a cell or sector). The base station <NUM> in LTE is called an e-NodeB or eNB; in NR it is known as gNB. However the present invention is not limited to LTE or NR. As shown, the network node <NUM> includes processing circuitry <NUM> and communication circuitry <NUM>. The communication circuitry <NUM> is configured to transmit and/or receive information to and/or from one or more other nodes, e.g., via any communication technology. The communication circuitry <NUM> is connected to one or more antennas <NUM>, to effect wireless communication across an air interface to one or more wireless devices <NUM>. As those of skill in the art are aware, and as indicated by the continuation lines in the antenna feed line of <FIG>, the antenna(s) <NUM> may be physically located separately from the network node <NUM>, such as mounted on a tower, building, or the like. Although the memory <NUM> is depicted as being internal to the processing circuitry <NUM>, those of skill in the art understand that the same or additional memory <NUM> may be separate from the processing circuitry <NUM>. Those of skill in the art additionally understand that virtualization techniques allow some functions nominally executed by the processing circuitry <NUM> to actually be executed by other hardware, perhaps remotely located (e.g., in the so-called "cloud"). The processing circuitry <NUM> is configured to perform processing described above, such as by executing instructions stored in memory <NUM>. The processing circuitry <NUM> in this regard may implement certain functional means, units, or modules.

<FIG> illustrates a schematic block diagram of a network node <NUM> in a wireless network according to another example. As shown, the network node <NUM> implements various functional means, units, or modules, e.g., via the processing circuitry <NUM> in <FIG> and/or via software code. These functional means, units, or modules, e.g., for implementing the method <NUM> herein, include for instance: wakeup signal generating unit <NUM> and wakeup signal transmitting unit <NUM>.

The wakeup signal generating unit <NUM> is configured to generate a first wakeup signal at a first frequency, the first wakeup signal being transmitted using Frequency Shift Keying (FSK), wherein a state of an information bit is encoded as a positive or negative frequency offset from the first frequency. The wakeup signal generating unit <NUM> is further configured to generate a second FSK wakeup signal at a second frequency, shifted from the first FSK wakeup signal frequency. The wakeup signal transmitting unit <NUM> is configured to transmit the first FSK wakeup signal, and is further configured to transmit the second FSK wakeup signal after transmitting the first FSK wakeup signal.

Those skilled in the art will also appreciate that embodiments and examples herein further include corresponding computer programs.

A computer program comprises instructions which, when executed on at least one processor of an apparatus, cause the apparatus to carry out any of the respective processing described above. A computer program in this regard may comprise one or more code modules corresponding to the means or units described above.

Claim 1:
A method (<NUM>) of operating a low-power wakeup receiver (<NUM>) in a wireless device (<NUM>) operative in a wireless communication network, comprising:
suspending (<NUM>) operation of a primary receiver circuit (<NUM>) to conserve power;
operating (<NUM>) a limited-function, low-power wakeup receiver circuit (<NUM>);
receiving (<NUM>) a wakeup signal transmitted by the network at a first frequency, the wakeup signal being transmitted using Frequency Shift Keying, FSK, wherein a state of an information bit is encoded as a positive or negative offset from the first frequency;
frequency down-converting (<NUM>) the wake-up signal from the first frequency to a second frequency lower than the first frequency;
demodulating (<NUM>) the received FSK wakeup signal at the second frequency using first and second matched filters in the discrete time domain, wherein the first filter is configured to detect odd numbered members of an ordered set of equidistant frequencies, and reject even numbered ones, a separation between two frequencies in the ordered set being equal to two times the offset frequency of the FSK signal, and wherein the second filter is configured to detect even numbered members of the ordered set and reject odd numbered ones, thereby recovering data modulated onto the FSK wakeup signal; and
if the demodulated data identifies the wireless device (<NUM>), resuming (<NUM>) operation of the primary receiver circuit (<NUM>).