System and method for low-power wireless beacon monitor

Selectively enabling an amplitude processing circuit and a phase processing circuit of a wireless station's polar receiver with respect to reception of a beacon signal. Such systems and methods may include sequentially demodulating symbols of the received beacon signal using at least the phase processing circuit to detect a traffic indication signal value in a data payload portion of the received beacon signal. Upon detecting a condition indicating no data traffic for the wireless station, the phase processing circuit may be turned off. The polar receiver may demodulate symbols of the received beacon signal and upon detecting a beacon preamble symbol sequence, shut off the amplitude processing circuit and set the amplitude to a fixed value. The phase processing circuit in conjunction with the fixed amplitude value may be used to demodulate symbols of the beacon signal.

BACKGROUND

Some WiFi receivers consume significant amounts of power. Such wireless devices may process all traffic received by the wireless device.

The entities, connections, arrangements, and the like that are depicted in—and described in connection with—the various figures are presented by way of example and not by way of limitation. As such, any and all statements or other indications as to what a particular figure “depicts,” what a particular element or entity in a particular figure “is” or “has,” and any and all similar statements—that may in isolation and out of context be read as absolute and therefore limiting—may only properly be read as being constructively preceded by a clause such as “In at least one embodiment, . . . .” For brevity and clarity of presentation, this implied leading clause is not repeated ad nauseum in the detailed description of the drawings.

DETAILED DESCRIPTION

This application is related to U.S. patent application Ser. No. 15/655,676, filed Jul. 20, 2017 and entitled “Polar Receiver System and Method for Bluetooth Communications,” now U.S. Pat. No. 10,122,397, the entirety of which is hereby incorporated by reference, and which claims the benefit of U.S. Provisional Patent Application No. 62/477,999, filed Mar. 28, 2017, the entirety of which is hereby incorporated by reference.

FIG. 1is a functional block diagram of gain and event processing components for a wireless reception and power control system100according to some embodiments. For some embodiments, a Wi-Fi beacon signal may be received by antenna102. A beacon signal, e.g., a modulated beacon signal such as a binary phase-shift keying (BPSK) or quadrature phase-shift keying (QPSK) signal, may be processed by an RF circuit104. In some embodiments, the RF circuit104may include a receiver, e.g., a polar receiver. The RF circuit104implemented as, e.g., a polar receiver, may have an amplitude processing path and a phase processing path. An example configuration of an RF circuit implemented as a polar receiver may be the configurable receiver200shown inFIG. 2. In some embodiments, the RF circuit104, when implemented as a receiver, may provide digital output signals to a baseband circuit106. The baseband circuit106may be configured to receive, e.g., I and Q (rectangular format) symbols for some embodiments. In some embodiments, the baseband circuit106may be configured to receive, e.g., amplitude and phase (polar format) signals.

In some embodiments, AGC circuit108may be configured to regulate a gain of the RF circuit104. In some embodiments, the RF circuit104may include one or more low-noise amplifier (LNA) stages. In some embodiments, the AGC circuit108may be configured to regulate a gain of, e.g., the low-noise amplifier (LNA) to account for differences in signal strength of received beacon RF signals. In some embodiments, the AGC circuit108may converge an AGC value in an iterative manner after detecting a large signal power jump (such as detecting a signal level or signal power that exceeds a threshold), where the signal power jump requires a corresponding decrease in LNA gain. Gain related events, such as a detected large signal change and corresponding gain change by the AGC circuit108, may be indicated to a coprocessor (COP)110, e.g., a MAC coprocessor, using an event signal (e.g., “GAIN”) provided to the COP110, directly, or, e.g., by way of an events circuit112. In some embodiments, the events circuit112may be used in conjunction with, e.g., gain values received from the AGC circuit108to generate a gain related event signal (such as a large gain change event signal, or AGC gain convergence subsequent to a large gain change) sent to the MAC coprocessor110. Some embodiments use an AGC hardware accelerator to detect large signal level/power changes and to send event messages to the MAC coprocessor110. For some embodiments, an AGC accelerator circuit calculates power, as shown in Eq. 1, using, e.g., I and Q values outputted from the RF circuit104(see, e.g., the receiver200ofFIG. 2), according to the following relationship:
Power=I2+Q2Eq. 1
Some embodiments calculate power, as shown in Eq. 2, using amplitude values from, e.g., an amplitude path, such as amplitude values outputted by RF circuit104(see, e.g., example amplitude detection circuit266from example configurable receiver200shown inFIG. 2):
Power=(Amplitude)2Eq. 2

In some embodiments, the gain of the LNA stage(s) of the RF circuit104is adjusted until the power (which may be calculated as shown in Eq. 1 or Eq. 2 for some embodiments), or a low-pass filtered version of the power, is between two thresholds. For example, a low-pass filtered version of the power may be calculated. A large jump in receive signal power may be caused by the reception of a new beacon frame, which begins with a synchronization pattern. For some embodiments, the AGC value is adjusted based on received signal power. The AGC value may be adjusted until the output power level of the LNA does not exceed a threshold or is between two thresholds. Alternatively, the AGC may adjust the gain of the LNA based on sample values from the ADC260such that the conversion range of the ADC260is not exceeded. In some embodiments, detection of the synchronization pattern (which may cause a beacon detection signal to be generated) may be used to directly adjust receiver processing paths within the RF circuit104, e.g., with direct control from the COP110(via a feedback path shown inFIG. 1) based on analysis of, e.g., digital signals from the baseband circuit106. Upon occurrence of one or more events (e.g., reported to the COP110directly or by the events circuit112), such as generation of a beacon detection signal (which may occur upon AGC convergence or detection of the synchronization pattern), some embodiments turn off an amplitude path of the RF circuit104and may replace the amplitude path result with a fixed amplitude value (such as a “1”) for demodulating and processing symbols. In some embodiments, a beacon detecting signal may be an automatic gain control adjustment signal or a beacon preamble symbol sequence detection signal (e.g., based on a known or expected synchronization pattern in a beacon preamble).

The polar receiver generates amplitude and phase values associated with a received beacon signal. In some modes, for part of a beacon message, receive amplitude values may be replaced by fixed values (e.g., a “1”, when an amplitude processing path is turned off), and phase values may be processed by the CORDIC to generate I and Q values used to further demodulate the received signal to recover beacon message data values. The baseband circuit106for some embodiments may include, e.g., circuits for correlation and detection of Barker sequences, Fast-Fourier Transform (FFT), interleaving, and Viterbi decoding algorithms. Some embodiments use a coprocessor to control operation of the correlation, Fast-Fourier Transform (FFT), interleaving, and Viterbi decoding circuits and algorithms. In some embodiments, control signals and/or power values are received by the AGC circuit108. These control signals and/or power values are used to adjust the AGC value and resistive feedback and thereby the gain of the RF circuit104(e.g., one or more LNA stages in the circuit104). The AGC circuit108outputs to the RF circuit104a control signal to control the gain of the LNA. The AGC circuit108outputs to the events circuit112a gain signal to indicate the gain value. In some embodiments, the events circuit112may receive events such as (and may combine events such as) the gain value with data values received from the baseband circuit, to, e.g., determine the occurrence of events associated with receiving a beacon message. The coprocessor110may be used in conjunction with the events circuit112to determine the timing of events for some embodiments. In some embodiments, the coprocessor110may provide, directly or indirectly, control signals and/or power values to affect power management of the RF circuit104. In some embodiments, the coprocessor110may provide control signals to any of, e.g., the power supply120, the RF circuit104, the transmitter122, and the AGC circuit108, and so on. In some embodiments, the coprocessor110stores beacon message data values and event timing data in RAM114,116(which may be internal or external to the coprocessor110for some embodiments). The coprocessor110has access to an external RAM bus for storage of data.

In some embodiments, further AGC adjustment may be inhibited after shutting off the amplitude processing circuit. For some embodiments, MAC coprocessor110, for some embodiments, is used to sequentially process demodulated symbols in real-time. In some embodiments, a polar receiver may be configured to set a gain control value (e.g., an AGC value) to a fixed value and turn off the amplitude processing circuit. The amplitude processing circuit may be turned off based on one of the scenarios mentioned above. In some embodiments, the amplitude path may be turned off and a fixed value provided without using, e.g., gain control provided by the AGC circuit108. Additional symbols (such as symbols received after turning off the amplitude processing circuit) may be sequentially demodulated using received phase values in combination with a fixed amplitude value.

As described further herein, the system100may include (or may communicate with) a timing control circuit such as a crystal oscillator118or an RC timing circuit. In some embodiments, the crystal oscillator118may continue to operate during a sleep mode of the wireless station, and may keep precise timing over extended time periods, e.g., during a sleep mode. A symbol demodulation crystal oscillator124is used to generate clock signals for demodulation. The bias current to the symbol demodulation crystal oscillator124may be increased for high resolution symbol demodulation. In some embodiments, the crystal oscillator118, via a coprocessor110, may communicate with a power supply120to power the system100(including RF circuit104) back on. In some embodiments, a counter within the power supply may be programmed by the coprocessor, or the coprocessor may monitor the time/clock generated by the crystal, and responsively enable the power supply circuits to initiate the wake-up process. In some embodiments, during a sleep mode, in addition to the system100being turned off (which includes turning off the symbol demodulation crystal oscillator124ofFIG. 1), a transmitter block (e.g., transmitter122) may be turned off as well, and the crystal oscillator118may indirectly via a coprocessor110, for example, turn the transmitter122back on. For simplicity, power supply lines are shown coming from the power supply120to, e.g., the RF circuit104and the coprocessor110and the transmitter122, but generally the power supply120may power any number of circuits in the system100. In some embodiments, the coprocessor110may communicate directly with the power supply120to control or adjust all or some of the power supplied by the power supply120to other circuits in the system100. In some embodiments, the coprocessor110may include a power management unit (PMU). In some embodiments, the PMU may be located external to the coprocessor110.

In some embodiments, the power supply120may include, or may interface with, low-drop out (LDO) voltage regulator circuits that may provide on-chip power management, which may be used to turn off specific circuits during a low power mode of operation. In some embodiments, a bias current control circuit may be used to cause selected circuits to shut off.

FIG. 2is a functional block diagram of a configurable multi-mode receiver200according to some embodiments. In some embodiments, a configurable multi-mode receiver system and method for modulated signal communications is presented. In some embodiments, Wi-Fi communications using, e.g., constant envelope magnitude information and polar to rectangular (IQ) conversion and baseband low pass filtering are presented. It will be understood that examples presented in accordance with some embodiments may relate to Wi-Fi communications as well as, e.g., other communication specifications, e.g., low energy communication specifications. Some examples of a configurable receivers having, e.g., a low energy mode are described in U.S. Pat. No. 10,122,397, entitled “Polar Receiver System and Method for Bluetooth Communications”, issued Nov. 6, 2018, which claims priority to a provisional application No. 62/477,999, filed Mar. 28, 2017, both of which are hereby incorporated by reference herein in their entirety.

In accordance with some embodiments,FIG. 2shows an example configurable multi-mode receiver200receives an incoming radio-frequency (RF) signal through an input node (not shown), such as an antenna. In some embodiments, the incoming radio-frequency signal, which may be implemented as a modulated carrier signal, has a frequency in the range of 2412 MHz-2484 MHz, although, as appreciated by one of skill in the art, the use of the configurable receiver200is not limited to that frequency range. The incoming radio-frequency signal may be filtered by a bandpass filter (not shown) and amplified by a low-noise amplifier (LNA)205(e.g., one or more LNA stages205). The configurable receiver200operates to receive and decode frequency modulated or phase-modulated radio-frequency signals, such as signals modulated using phase shift keying (PSK) or quadrature amplitude modulation (QAM). As the term is used in the present disclosure, phase-modulated signals include signals that are modulated in phase (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), 8-PSK, or 16-PSK) as well as signals that are modulated in both phase and amplitude (e.g., 16-QAM, 64-QAM, or 256-QAM). Frequency modulated signals include, among others, frequency shift keying (FSK) signals such as binary frequency-shift keying (BFSK) signals, multiple frequency-shift keying (MFSK) signals, and minimum-shift keying (MSK) signals.

In some embodiments, BPSK or QPSK modulated signals transmitted as beacons (from, e.g., an access point) are received and processed by the example configurable multi-mode receiver200. It will be understood that BPSK and QPSK modulated signals are merely one example of received signals. While some of the embodiments described herein refer to the demodulation of phase-modulated signals (such as, e.g., QPSK), some embodiments also may be used to demodulate frequency-modulated (FM) signals, based on the mathematical relationship between changes in frequency and changes in phase.

The configurable receiver200may be provided with frequency division circuitry210. The frequency division circuitry has an input for receiving the modulated radio-frequency input signal from the low-noise amplifier205and a frequency-divided output for providing a frequency-divided output signal to a trigger input of a time-to-digital converter (TDC)220. The frequency division circuitry operates to divide the frequency of the input signal by a frequency divisor. In some embodiments, the frequency division circuitry may be implemented using a harmonic injection-locked oscillator, a digital frequency divider, or a combination thereof, among other possibilities. In one embodiment, the frequency division circuitry210may comprise an injection-locked oscillator212, an amplitude limiter214, and a frequency divider216(having a divisor such as 4, 8, 16, etc.).

A time-to-digital converter220may operate to measure a characteristic time of the frequency-divided signal, such as the period of the frequency-divided signal. The time-to-digital converter220may operate to measure the period of the frequency-divided signal by measuring an elapsed time between successive corresponding features of the frequency-divided signal. For example, the time-to-digital converter may measure the period of the frequency-divided signal by measuring a time between successive rising edges of the frequency-divided signal or the time between successive falling edges of the frequency-divided signal. In alternative embodiments, the time-to-digital converter may measure a characteristic time other than a complete period, such as an elapsed time between a rising edge and a falling edge of the frequency-divided signal. In a further embodiment, the TDC may measure features (i.e., rising edges, or falling edges) of the modulated signal with respect to an internal reference clock. In this manner, the phase measurement of the received signal may be made with respect to the internal timing signal. Frequency offsets between the received modulated signal (after frequency division, when present) may be accounted for by repeatedly removing a time increment equal to predetermined difference in period between the internal reference and the received modulated signal.

In some embodiments, the time-to-digital converter220operates without the use of an external trigger such as a clock signal. That is, the time-to-digital converter220measures the time between two features (e.g., two rising edges) of the frequency-divided signal rather than the time between an external trigger signal and a rising edge of the frequency-divided signal. Because the start and end of the time period measured by the time-to-digital converter220are both triggered by the frequency-divided signal, rather than an external clock signal, the time-to-digital converter220, is referred to herein as a self-triggered time-to-digital converter. In some embodiments, the time-to-digital converter220may be implemented by comparing, e.g., the frequency-divided signal with an external clock signal, such that the time-to-digital converter220may be triggered externally.

In the example ofFIG. 2, the self-triggered time-to-digital converter220may provide a digital time output that represents the period of the frequency-divided output signal. The digital time output may be provided to a digital subtractor225. The digital subtractor225operates to subtract a period offset value T from the digital time output, thereby generating an offset digital time output signal. The period offset value may be a constant value corresponding to an expected period of the frequency-divided signal in an unmodulated state, which may be expressed in native units used by the time-to-digital converter. For example, where the frequency of the frequency-divided signal is expressed by fd, the period offset value T may be expressed by:

T=1fd·L⁢⁢S⁢⁢BEq.⁢3
where LSB is the amount of time represented by the least significant bit of the time-to-digital converter. The offset digital time output is thus at or near zero when no shift is occurring in the phase of the frequency-divided signal.

To generate a phase shift, a momentary frequency shift does occur in the modulated radio-frequency signal. This results in a temporary change in the period of the modulated radio-frequency signal, which in turn causes a temporary change in the period of the frequency-divided signal. This temporary change in the period of the frequency-divided signal is measured as a temporary change in the digital time output (and in the offset digital time output). In some embodiments, the offset digital time output is at or near zero during periods when the phase of the modulated radio-frequency signal remains steady, while a shift in the phase of the modulated radio-frequency signal results in the offset digital time output signal briefly taking on a positive or negative value, depending on the direction of the phase shift.

The offset digital time output signal is provided to a digital integrator230, which may be implemented in configurable receiver200using a digital adder232and a register234. In other embodiments, alternative implementations of the digital integrator may be used. The digital integrator generates an integrated time signal. The register234may be clocked using the frequency-divided signal, resulting in one addition per cycle of the frequency-divided signal. In embodiments in which the offset digital time output signal represents a change in the phase of the modulated radio-frequency signal, the integrated time signal provides a value that represents the current phase of the modulated radio-frequency signal.

In configurable receiver200, the integrated time signal may be resampled using a register235, which may be clocked by a clock source (not shown). In some embodiments, the register235operates to sample the integrated time signal at 160 Msps, although other sampling rates may alternatively be used. In some embodiments, the phase signal generation is synchronous with the receiver clock, and no resampling is used.

In some embodiments, the beacon transmission is rapidly detected by a beacon identification signal generated in response to certain events, such as (i) the identification of Barker sequences by a Barker sequence correlator, or (ii) by a large AGC adjustment followed by AGC gain convergence. In such scenarios, the continuing BPSK beacon signal may be processed by freezing the AGC adjustment, and setting the amplitude value provided to (or processed by) the CORDIC to a constant value (e.g., an amplitude of “1”).

In particular, in some embodiments, configurable receiver200may further comprise an amplitude path. Elements of the amplitude path include amplitude detection circuit266having mixer245, low pass filter250, analog-to-digital circuit260and alignment logic265. In one embodiment, amplitude detection circuit266may be implemented as an envelope detector, operating to provide a signal representing the amplitude of the modulated radio-frequency signal. The envelope detector may operate using various techniques such as, for example, signal rectification followed by low-pass filtering. In one embodiment, the amplitude path may include mixer245and low pass filter250. In one embodiment, mixer245receives the output of LNA205and the output of XOR246, which is coupled to oscillator212and generates a frequency, such as a carrier frequency. The signal representing the amplitude of the modulated radio-frequency signal may be converted to a digital form with an analog-to-digital converter (ADC)260. In some embodiments, ADC260samples the amplitude of the modulated radio-frequency signal at 160 Msps.

In some embodiments, an alignment logic265may be provided to provide temporal alignment between the amplitude signal from ADC260and the phase signal from register235, accommodating different processing delays in the generation of the amplitude signal versus the phase signal.

In one embodiment, the aligned amplitude and phase signals may be provided to coordinate rotation digital computer (CORDIC) logic circuit270. The CORDIC logic270is operative to identify in-phase (I) and quadrature (Q) components corresponding to a phase-modulated radio-frequency input signal. In some embodiments, the identified I and Q components may be processed and/or analyzed to demodulate the received signal, as known to those of skill in the art.

In some embodiments, the configurable receiver200may operate on a constant envelope modulated signal, such as a BPSK-modulated beacon signal. In such cases, the configurable receiver200may operate in a reduced power mode. In such a reduced power mode, the amplitude path of the signal may be selectively disabled, and rather than a received and processed amplitude signal, a constant amplitude value (such as a constant amplitude of 1) may be input to the CORDIC logic270to process the phase signal. For example, in one embodiment, configurable receiver200includes mode control circuit290at least coupled to the input of CORDIC270and, in one embodiment, coupled to the input of configurable receiver200, such as at the input or output of LNA205to control the mode of operation for configurable receiver200. A beacon detection signal295may be generated if (i) the AGC settles following a large jump, or (ii) a beacon synchronization pattern is detected. If a beacon detection signal295is generated, a low power mode may be implemented by turning off the amplitude path290and injecting, for example, a constant “1” to a multiplexer297and selecting the constant “1” to be outputted to CORDIC270as representative of the amplitude signal. If no beacon detection signal295is detected, the amplitude signal provided to CORDIC270may default to the amplitude signal generated by the amplitude detection circuit266. For some embodiments, the beacon detection signal295may be generated by a MAC coprocessor, such as the MAC coprocessor110shown inFIG. 1.

The CORDIC converts the polar signals to I and Q signals, which are output to the baseband circuit296. Of course, it will be understood that variations on the specific example configurable multi-mode receiver200illustrated inFIG. 2may also be implemented. For example, instead of being connected between the digital integrator and the digital subtractor, the digital divider216may be positioned after the time-to-digital converter220in some embodiments, reflecting the distributive property of multiplication.

FIG. 3is a flowchart300for turning off amplitude and phase paths of a receiver upon detecting conditions of a beacon message according to some embodiments. A wireless station may perform, for some embodiments, a process that includes: enabling302, at an estimated time of a beacon signaling interval, an amplitude processing circuit, a phase processing circuit, and a medium access control (MAC) coprocessor of a polar receiver of a wireless station; demodulating304symbols of a received beacon signal by processing amplitude values from the amplitude processing circuit and phase values from the phase processing circuit; responsive to detecting a beacon detection signal, turning off306the amplitude processing circuit; sequentially demodulating308additional symbols of the received beacon signal by processing the phase values in combination with a fixed amplitude value; processing310the sequentially demodulated additional symbols using the MAC coprocessor; detecting312a traffic indication signal value in a data payload portion of the received beacon signal; and turning off314the phase processing circuit upon detecting a traffic indication signal value indicating no data traffic for the wireless station.

For some embodiments, a wireless station operations may include: enabling, at an estimated time of a beacon signaling interval, an amplitude processing circuit and a phase processing circuit of a polar receiver of wireless station; sequentially demodulating symbols of the received beacon signal using at least the phase processing circuit to detect a traffic indication signal value in a data payload portion of the received beacon signal; and shutting off the phase processing circuit upon detecting a traffic indication signal value indicating no data traffic for the wireless station. The wireless station's operations, in some embodiments, may further include: demodulating symbols of the received beacon signal with the polar receiver; and responsive to detecting a beacon preamble symbol sequence, shutting off the amplitude processing circuit and setting an amplitude, wherein sequentially demodulating symbols of the received beacon signal is performed using the phase processing circuit.

Some embodiments of a wireless station apparatus may include: an amplitude processing circuit of a polar receiver of a wireless station, configured to generate amplitude values of a received beacon signal; a phase processing circuit configured to generate phase values of the received beacon signal; a medium access control (MAC) coprocessor configured (i) to demodulate symbols of the received beacon signal by processing the amplitude values and the phase values, (ii) upon receiving indication of a synchronization pattern of the received beacon signal, to turn off the amplitude processing circuit, and (iii) upon receiving a traffic indication signal value indicating no data traffic for the wireless station, to turn off the phase processing circuit; an events circuit configured (i) to detect the synchronization pattern and indicate detection of the synchronization pattern to the MAC coprocessor, and (ii) to detect a traffic indication signal value in a data payload portion of the received beacon signal and send the traffic indication signal value to the MAC coprocessor; and a beacon timing circuit configured to enable, at an estimated time of a beacon signaling interval, the amplitude processing circuit, the phase processing circuit, the medium access control (MAC) coprocessor; and the events circuit.

FIG. 4is a flowchart400for turning off the phase path of a receiver upon detecting conditions of a beacon message according to some embodiments. A wireless station may perform, for some embodiments, a process that includes: enabling402, at an estimated time of a beacon signaling interval, an amplitude processing circuit and a phase processing circuit of a polar receiver of wireless station. The process also may include sequentially demodulating404symbols of the received beacon signal using at least the phase processing circuit to detect a traffic indication signal value in a data payload portion of the received beacon signal. The process may include shutting off406the phase processing circuit upon detecting a traffic indication signal value indicating no data traffic for the wireless station.

FIG. 5is a timing diagram500for TIM and DTIM beacon messages (sent by, e.g., an access point (AP)), broadcast, and unicast messages according to some embodiments. A beacon message may be sent generally at a periodic rate according to a beacon interval value. For example, a beacon message may be sent every 100 ms according to a WiFi protocol standard.FIG. 5labels the beacon messages as TIM beacons504,506,510,512and DTIM beacons502,508,514. The interval between TIM beacons504,506,510,512and DTIM beacons502,508,514may be configured. TIM beacons include a DTIM count field, and DTIM beacons correspond to DTIM count=0. The beacons also include a bitmap control byte680, which is described below with regard toFIG. 6C, that indicates whether multicast/broadcast packets are buffered for transmission following the DTIM beacon. A wireless station, upon receiving a TIM beacon message that indicates unicast data is waiting for the wireless station, may respond back to the access point (AP) with an “awake” message, such as a “PS-Poll” message. The AP may send a unicast message upon receiving the “awake” message. For some embodiments, at certain times, a wireless station may ignore TIM beacons and enter sleep mode while awaiting reception of the next DTIM beacon message. For some embodiments, a wireless station may turn off the wireless station's polar receiver for a period of time exceeding the DTIM beacon signaling interval. For example, if beacon messages are sent every 100 ms, and the DTIM interval is set to 3, then a wireless station may sleep for a period exceeding 200 ms (e.g., 500 ms) and process only every other DTIM beacon message. During sleep mode, the wireless station may turn off the polar receiver completely (including the symbol demodulation crystal oscillator124ofFIG. 1) and use a crystal oscillator (see, e.g., crystal oscillator118ofFIG. 1) that is used to determine the wake-up time. The wake-up time may be adjusted iteratively each sleep period to determine a peak wake-up time and to increase the sleep time.

For some embodiments, a DTIM beacon is sent every DTIM interval, which is described in regards toFIG. 6C. TIM beacons are sent in between DTIM beacons. A wireless station may skip TIM beacons when in power saving mode. For example, a DTIM interval may be 3 with beacons sent every 100 ms. At t=0 ms, a DTIM beacon502is sent. A broadcast message516is sent following the DTIM beacon. The DTIM count, which is described in regards toFIG. 6C, is 0 because the beacon is a DTIM beacon. The wireless station expects to receive another DTIM beacon at t=300 ms. At t=100 ms, a TIM beacon504is received, and the DTIM count is two. At t=200 ms, a TIM beacon506is transmitted, and the DTIM count is one. At t=300 ms, a DTIM beacon508is sent, and the DTIM count is zero. If the wireless station is configured to skip TIM beacons504,506at t=100 and t=200, the wireless station's receiver and transmitter may be in sleep mode a threshold time period prior to t=300 ms. A crystal oscillator118may be used to turn on the system at a threshold time period prior to 300 ms. For some embodiments, the threshold time period may be equal to the length of time the receiver (and transmitter for some embodiments) takes to power up plus a safety factor. In some embodiments, the wireless station may skip DTIM beacons if configured to do so. For example, a wireless station may skip every other DTIM beacon. Hence, the wireless station may not exit sleep mode until a threshold time period prior to 600 ms, which is shown as DTIM beacon514.

FIG. 6Ais message structure diagram600for a beacon message according to some embodiments. A synchronization pattern602(“SYNC”) may be received at the beginning of a beacon message, e.g., in the preamble prior to other fields and the payload of the beacon message. The sync pattern602may be identified by a Barker sequence correlator for some embodiments. More generally, in some embodiments. the sync pattern may be used by, e.g., the system100ofFIG. 1to recognize a beacon and to, e.g., determine whether an amplitude path of the RF circuit104(e.g., implemented as a polar receiver, in accordance with some embodiments) may be turned off, e.g., by providing a fixed amplitude value in place of the amplitude processing path.

A beacon message may include three components: a Media Access Control (MAC) header604, a frame body606, and a frame check sequence (FCS)608. For some embodiments, referring to the example shown inFIG. 1, a synchronization pattern602is detected and an event is generated and sent to a MAC coprocessor (such as the coprocessor110shown inFIG. 1) indicating detection of the synchronization pattern602. In some embodiments, the baseband circuit106may detect the synchronization pattern602and may send a signal to the events circuit112indicating detection of the synchronization pattern. The events circuit112may generate and send to the MAC coprocessor110a signal indicating detection of the synchronization pattern602for some embodiments. The frame body component606of a beacon signal is expanded into the fields shown inFIG. 6B. One of the frame fields, the TIM information element642, is expanded to show the TIM information element's structure inFIG. 6C.

FIG. 6Bis a message structure diagram for frame body fields630according to some embodiments. Frame body, or payload, fields may include many different fields in accordance with a WiFi protocol. Some embodiments may include 8 bytes for a timestamp632, 2 bytes for a beacon interval field634, 2 bytes for a capability information field636, up to 32 bytes for a service set identifier (SSID) field638, and a variable number of bytes for a supported rates field640. Additional frame fields (not all shown inFIG. 6B) may include, e.g., a frequency-hopping (FH) parameter set field, a direct-sequence (DS) parameter set field, a contention-free (CF) parameter set field, an independent basic service set (IBSS) parameter set field, and a traffic indication map (TIM) information element field642. Other frame fields, indicated inFIG. 6Bwith ellipses and the label “other frame body fields”644, are available per a WiFi protocol

For some embodiments, the beacon interval field634indicates the quantity of time units (TU) between the start of one beacon signal and next beacon signal. A time unit is equal to 1.024 ms. If the beacon interval field is equal to 100, then a beacon signal may be sent every 102.4 ms. The beacon interval field634is used to determine the length of time between beacon signals received by a wireless station. Some embodiments of a wireless station may be in sleep mode for a portion of time between received beacon signals. To determine how long a wireless station may be in sleep mode, some embodiments of a wireless station increment a counter using a crystal oscillator (or other clock device), e.g., crystal oscillator118ofFIG. 1. If the counter is equal to an estimated wake-up time count, the wireless station exits sleep mode and configures the receiver to receive a beacon signal for some embodiments. An iterative process may be performed to adjust the estimated wake-up time count. Some embodiments of the iterative process include comparing a prior estimated time of the beacon signal interval with an actual time of the beacon signal interval to generate an estimated time adjustment; and updating the estimated time of the beacon signaling interval using the estimated time adjustment. For example, the estimated time may be calculated using Eqs. 4 and 5:

FIG. 6Cis a message structure diagram for a TIM information element670according to some embodiments. The TIM information element (shown as TIM642in condensed form inFIG. 6Band expanded form inFIG. 6C) may be sent with every beacon signal. Each of the fields shown inFIG. 6Cis one byte, except the partial virtual bitmap682, which may be 1 to 251 bytes. For a TIM information element, the element ID field672is equal to 5. The length field674indicates the number of bytes in the TIM information element.

For some embodiments, the DTIM count field676is a countdown counter value that indicates the count until a DTIM beacon is scheduled to be sent. The DTIM count field676is decremented with each successive beacon signal transmitted by the access point. If the DTIM count field676is zero, the beacon signal is a DTIM beacon signal and a broadcast (multicast) packet may be scheduled to be transmitted by the access point following the beacon message.FIG. 6Dwill be used to discuss whether broadcast data is available for the wireless station. The DTIM period field676indicates the quantity of beacon signals to be transmitted by an access point for each DTIM interval of time.

The partial virtual bitmap field682is a variable length bit mask array indicating the presence of buffered frames (such as unicast messages) available from the access point. For example, if the access point has a unicast message for a wireless station, the access point may indicate the presence of the unicast message by setting to 1 the bit within the bit mask corresponding to the wireless station. In some embodiments, this bit within the bit mask may be described as a TIM value. To reduce the size of the partial virtual bitmap field682, a bitmap control field680is used to indicate which portion of the full traffic indication map (251 bytes) is sent via the partial virtual bitmap field682.

In some embodiments, a wireless station may analyze the TIM vector, the partial virtual bitmap682, to determine if the access point has unicast data for the wireless station. If the access point does not have unicast data (corresponding to a TIM value of 0), the receiver and transmitter may be powered down to enter sleep mode and wait until the next DTIM beacon. Some embodiments power down and wait for the next TIM beacon.

FIG. 6Dis a message structure diagram for a bitmap control byte within a TIM information element according to some embodiments.FIG. 6Dindicates the structure690of the bits within the bitmap control byte680of a TIM information element. For some embodiments, bit 0 (least significant bit) indicates the availability of broadcast data buffered at an access point for the wireless station. If bit 0 (692) is equal to 1, broadcast data is available at an access point (AP). If bit 0 (692) is equal to 0, no broadcast data is buffered at the AP. Bits 1 to 7 (694) represent an offset to the start of the portion of the full traffic indication map sent via the partial virtual bitmap field682. Combining the bitmap offset694with the TIM information element's length field674, a wireless station may be able to determine which portion of the full traffic indication map is sent.

In some embodiments, a wireless station may process any broadcast message transmitted by the access point. The MAC coprocessor may determine if bit 0 (692) of the bitmap control byte680is set to one. If bit 0 (692) is a one, the access point has broadcast data to send. This bit may be described as a broadcast D value in some portions of this application. In some embodiments, the receiver and transmitter may be shutdown even if bit 0 (692) of the bitmap control byte680is a one and the partial virtual bitmap682(TIM value) is zero. In some embodiments, the receiver and transmitter may stay powered up if bit 0 (692) of the bitmap control byte680is a one and the partial virtual bitmap682(TIM value) is zero so that the coprocessor may process the broadcast message that follows the beacon message.

Table 1 shows different scenarios of the TIM value (partial virtual bitmap682) and the broadcast D value (bit 0 (692) of bitmap control680).

TABLE 1Broadcast DTIM ValueValueResult0 (no unicast0 (noShutdown the receiver (and thedata waiting forbroadcasttransmitter) and go into sleep modethe wirelessdata)until a threshold period of time prior tostation)transmission of the next DTIM beacon.The crystal oscillator is running,awaiting the end of the DTIM interval.The crystal oscillator causes a wakeupsignal to be generated a thresholdperiod of time prior to transmission ofthe next DTIM beacon if the wirelessstation is configured to process thenext DTIM beacon.0 (no unicast1 (broadcastThe receiver stays powered up so thatdata waiting fordata will bethe coprocessor may process thethe wirelesssent by thebroadcast message if the wirelessstation)access point)station is configured to process thebroadcast message.The system is shutdown if the wirelessstation is configured to ignore thebroadcast message.1 (unicast data is0 or 1The receiver stays powered up so thatwaiting for thethe coprocessor may process thewireless station)unicast message if the wireless stationis configured to process the broadcastmessage. The wireless station wakes upthe transmitter and transmits an“AWAKE” message and listens for aresponse from the access point. Afterfinishing processing the unicast and/orbroadcast message(s), the system enterssleep mode until a threshold period oftime prior to the next DTIM beaconmessage if configured to not skip DTIMbeacons.

For some embodiments, the MAC coprocessor may be shut off upon detecting a traffic indication signal value indicating no data traffic for the wireless station. Detection of a traffic indication signal value indicating no data traffic for the wireless station may be performed in one of multiple ways for some embodiments, such as: (i) detecting a TIM value indicating no unicast traffic for the wireless station, (ii) detecting a TIM value indicating no unicast traffic for the wireless station in combination with a broadcast D value indicating no broadcast traffic, or (iii) detecting a TIM value indicating no unicast traffic for the wireless station in combination with a broadcast D value indicating the presence of broadcast traffic in combination with a broadcast ignore condition. For example, a broadcast ignore condition may occur if the wireless station is a device with a low amount of functionality, and the wireless station is configured to ignore a certain percentage of broadcast messages. For example, the wireless station may be configured to alternate between ignoring and processing broadcast messages.

For some embodiments, the traffic indication map or the partial virtual bitmap682may be used to determine the TIM value to indicate no unicast traffic for the wireless station. The traffic indication map is the full unicast data bitmap, and the partial virtual bitmap682is a portion of the traffic indication map. The TIM value is the bit within the traffic indication map corresponding to the wireless station.

A broadcast ignore condition, for some embodiments, may indicate that a wireless station will not process (e.g., is configured to ignore) one or more broadcast messages. A broadcast ignore condition may occur, for some embodiments, if the wireless station is fully configured, has limited functionality, and is able to ignore conditions related to other portions of the SSID network unrelated to the wireless station. Some embodiments of a wireless station may limit a broadcast ignore condition such that the wireless station processes a broadcast message every threshold number of broadcast messages. For example, the broadcast ignore condition may have a threshold of 10 broadcast messages so that at least every tenth broadcast message is processed. For some embodiments, upon detecting a traffic indication signal value indicating no data traffic for the wireless station, the wireless station may responsively turn off the receiver (which may be a polar receiver). Detecting a traffic indication signal value indicating no data traffic for the wireless station may be performed by demodulating a beacon signal and detecting a data indicator field that indicates no data traffic for the wireless station. A data indicator field may be a TIM value, a broadcast D value, a traffic indication map, or a partial virtual bitmap682.

FIG. 7is a graph700of current vs. time for a wireless station receiver receiving a beacon message according to some embodiments. The graph is not generally drawn to scale and is intended for purposes of explanation. The left portion716ofFIG. 7left of the spike714in current indicates a low-level current (for example, 12 μA), during, e.g., a sleep mode of the device. The low level current, indicated as I3712, may be used to power a crystal oscillator or other time keeping device. A beacon signaling interval may be determined using the beacon interval value shown inFIG. 6B. The beacon interval value may be multiplied by 1.024 ms to calculate a time value for the beacon signal interval. Some embodiments may use units of TU for the beacon signal interval. The receiver current may have a spike714upon exiting sleep mode prior to receiving a beacon signal706. The spike714may correspond to powering on the receiver prior to receiving a beacon message. The spike714may be due to charging up of capacitors within the power supply of the receiver. The increase in current718just prior to receipt of a beacon message corresponds to the start of adjustment of the AGC value using the beacon synchronization pattern. Upon receipt of a beacon signal706, the receiver's current may increase rapidly and plateau at a current indicated by I1708. The current may stay at a high level until the beacon detection signal is identified, either as an AGC convergence event or synchronization pattern identification event. For some embodiments, the envelope off point702may occur with the generation of a beacon detection signal. In some embodiments, a beacon detection signal may be generated upon matching the synchronization pattern with a Barker code or sequence of Barker codes. In some embodiments, a beacon detection signal may be generated upon detecting an increase in received signal power exceeding a threshold (indicated by, e.g., a 33 dB AGC adjustment) followed by a settling of an AGC value. The amplitude path (e.g.,266ofFIG. 2) may be turned off and a fixed value may be used for the amplitude value for some embodiments. With the amplitude path turned off at the envelope off point702, the receiver's current may decrease to the current level indicated by I2710. Upon generation of a traffic indication signal such as by the reception of, e.g., the TIM information element (IE) portion of a beacon signal (shown inFIG. 6C), the receiver may determine that no broadcast and/or unicast message is available for the wireless station, and the wireless station may, e.g., enter a sleep mode, and, e.g., may turn off the receiver, decreasing the current to a low level used to maintain, e.g., operation of the crystal oscillator or other timing reference. In some embodiments, the transmitter of the wireless station may be turned off as well, since there may be no need to for the wireless station to send messages if, e.g., no data traffic is expected or available, per the TIM information element portion.FIG. 7indicates reception of the TIM information element as the TIM IE point704. The receivers current may decrease and return to the low-level indicated by I3712. For some embodiments, a bias current of a low-noise amplifier (LNA) may be set to a low level value at the TIM/IE point704in time.

Some embodiments may set a bias current of a symbol demodulation crystal oscillator to a low level value for processing a beacon message. Upon determining that a broadcast message and/or a unicast message is to be processed by the receiver, the bias current to a symbol demodulation crystal oscillator (such as the symbol demodulation crystal oscillator124ofFIG. 1) may be increased to enable more accurate demodulation of symbols in broadcast and/or unicast messages. Some embodiments of a wireless station's beacon signal reception process may include: enabling, at the estimated time of the beacon signaling interval, a symbol demodulation crystal oscillator with a bias current; generating, by the symbol demodulation crystal oscillator, a timing reference for the polar receiver to process the beacon signal; and upon detecting a traffic indication signal value indicating a presence of data traffic for the wireless station, increasing the bias current to the symbol demodulation crystal oscillator.

Some embodiments may set a bias current of a low noise amplifier (LNA) to a low level value for processing a beacon message. Upon determining that a broadcast message and/or a unicast message is to be processed by the receiver, the bias current to the LNA may be increased to provide a higher signal to noise ratio to provide for more accurate demodulation of symbols in broadcast and/or unicast messages. The beacon signal reception process, for some embodiments, may include: enabling with a bias current, at the estimated time of the beacon signaling interval, a wideband gain stage of a low noise amplifier (LNA); amplifying, by the LNA, the received beacon signal; and upon detecting the traffic indication signal value indicating the presence of traffic data for the wireless station, increasing the bias current to the LNA. The increase in the bias current to the symbol demodulation crystal oscillator or the LNA may not be immediate but may occur prior to reception and subsequent demodulation of unicast frames for some embodiments.

FIG. 8is a graph800of power vs. time for a beacon message according to some embodiments. The graph is not generally drawn to scale and is intended for purposes of explanation and not limitation. The left portion806of the graph800left of the envelope AGC interval802indicates that the receiver is adjusting an AGC setting at the beginning of the reception of the beacon. The envelope AGC interval802indicates for some embodiments the time period over which the AGC value may be adjusted. The envelope AGC interval802may start with the reception of a beacon synchronization pattern prior to a beacon signal. The envelope AGC interval802may end804with the beacon identification signal. Specifically, if a beacon indication signal is used to turn off the amplitude processing path, no further amplitude information may be available for further assessing a gain setting. For some embodiments, a crystal oscillator indicates a threshold period of time prior to an estimated point in time for reception of a beacon signal. The receiver may be powered up at this point in time as the receiver prepares to receive a beacon signal. An AGC value may be adjusted to increase the gain for the low noise amplifier (LNA). An increase in received signal power exceeding a threshold (e.g., greater than 33 dB) may be detected, such as by large adjustments in AGC settings. At the envelope off point804, the AGC adjustment period ends. The AGC envelope may end with the detection of the settling of the AGC value, or by a Barker sequence detection, and the amplitude path may be turned off. The wireless station may determine that a fixed value may be used for the amplitude of a beacon signal instead of the actual received amplitude.

For some embodiments, an AGC circuit may detect saturation and a change in gain that exceeds a threshold (such as an increase in gain by more than 33 dB). The AGC circuit may trigger an event circuit to send an event indication to the MAC coprocessor to turn off the amplitude path. Some embodiments of a baseband circuit may detect a barker code that matches the beacon synchronization pattern, and the baseband circuit may trigger the event circuit to send an event indication to the MAC coprocessor to turn off the amplitude path. In some embodiments, the amplitude path is effectively turned off by reducing or shutting off the bias current to one or more signal processing circuit elements in the amplitude signal processing path.

The receiver RF circuit and baseband circuit is controlled by a co-processor. The co-processor will receive events from the baseband circuit and/or event circuits. The co-processor keeps track of the length of the packet and restarts the baseband circuit when needed. Restarting will happen after receiving a beacon frame or falsely detecting a beacon frame. Note that the co-processor is able to use the RF and baseband circuits to process the received beacon on a symbol-by symbol basis, and thus is able to rapidly determine TIM bits and traffic indication signal values. Thus, the receiver architecture utilizing a MAC co-processor provides the ability to rapidly power down the receiver prior to complete demodulation of the beacon frame.

FIG. 9is a system interface diagram showing an access point and wireless stations according to some embodiments. A Wi-Fi network900may include an access point902that communicates with one or more wireless stations904,906,908,910,912. Such communications are shown as wireless RF signals914,916,918,920,922between the access point902and the wireless stations904,906,908,910,912. Wireless stations may include, for example, smart phones and laptops, which are both depicted, as well as other electronic devices, such as desktops, tablets, watches, printers, servers, switches, routers, speakers, displays, appliances, televisions, radios, and remote controls, among other Wi-Fi capable devices.

Accordingly, some embodiments of the present disclosure, or portions thereof, may combine one or more processing devices with one or more software components (e.g., program code, firmware, resident software, micro-code, etc.) stored in a tangible computer-readable memory device, which in combination form a specifically configured apparatus that performs the functions as described herein. These combinations that form specially programmed devices may be generally referred to herein as “modules.” The software component portions of the modules may be written in any computer language and may be a portion of a monolithic code base, or may be developed in more discrete code portions such as is typical in object-oriented computer languages. In addition, the modules may be distributed across a plurality of computer platforms, servers, terminals, and the like. A given module may even be implemented such that separate processor devices and/or computing hardware platforms perform the described functions.

The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. The Abstract is submitted with the understanding that the Abstract will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, the Abstract may be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.