US20130121398A1 - Timing and Time Information Extraction from a Phase Modulated Signal in a Radio Controlled Clock Receiver - Google Patents
Timing and Time Information Extraction from a Phase Modulated Signal in a Radio Controlled Clock Receiver Download PDFInfo
- Publication number
- US20130121398A1 US20130121398A1 US13/563,246 US201213563246A US2013121398A1 US 20130121398 A1 US20130121398 A1 US 20130121398A1 US 201213563246 A US201213563246 A US 201213563246A US 2013121398 A1 US2013121398 A1 US 2013121398A1
- Authority
- US
- United States
- Prior art keywords
- timing
- phase
- modulation
- time
- information
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000605 extraction Methods 0.000 title claims description 5
- 238000000034 method Methods 0.000 claims abstract description 35
- 230000000875 corresponding effect Effects 0.000 claims description 14
- 230000010363 phase shift Effects 0.000 claims description 10
- 238000001914 filtration Methods 0.000 claims description 6
- 238000012937 correction Methods 0.000 claims description 5
- 238000012935 Averaging Methods 0.000 claims description 4
- 230000003044 adaptive effect Effects 0.000 claims description 2
- 230000002596 correlated effect Effects 0.000 claims description 2
- 230000007704 transition Effects 0.000 abstract description 6
- 238000009825 accumulation Methods 0.000 abstract description 3
- 238000010586 diagram Methods 0.000 description 54
- 238000004891 communication Methods 0.000 description 18
- 239000003550 marker Substances 0.000 description 10
- 230000018199 S phase Effects 0.000 description 4
- 230000005540 biological transmission Effects 0.000 description 4
- 238000001514 detection method Methods 0.000 description 4
- 230000006872 improvement Effects 0.000 description 4
- 238000012986 modification Methods 0.000 description 4
- 230000004048 modification Effects 0.000 description 4
- 239000000654 additive Substances 0.000 description 3
- 230000000996 additive effect Effects 0.000 description 3
- 230000008901 benefit Effects 0.000 description 3
- 238000005192 partition Methods 0.000 description 3
- 239000013078 crystal Substances 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000001747 exhibiting effect Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- HVUMOYIDDBPOLL-XWVZOOPGSA-N Sorbitan monostearate Chemical compound CCCCCCCCCCCCCCCCCC(=O)OC[C@@H](O)[C@H]1OC[C@H](O)[C@H]1O HVUMOYIDDBPOLL-XWVZOOPGSA-N 0.000 description 1
- 230000001427 coherent effect Effects 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 230000003442 weekly effect Effects 0.000 description 1
- 210000000707 wrist Anatomy 0.000 description 1
Images
Classifications
-
- G—PHYSICS
- G04—HOROLOGY
- G04G—ELECTRONIC TIME-PIECES
- G04G7/00—Synchronisation
- G04G7/02—Synchronisation by radio
-
- G—PHYSICS
- G04—HOROLOGY
- G04R—RADIO-CONTROLLED TIME-PIECES
- G04R20/00—Setting the time according to the time information carried or implied by the radio signal
- G04R20/08—Setting the time according to the time information carried or implied by the radio signal the radio signal being broadcast from a long-wave call sign, e.g. DCF77, JJY40, JJY60, MSF60 or WWVB
- G04R20/10—Tuning or receiving; Circuits therefor
Definitions
- the present invention relates to the field of wireless communications, and more particularly relates to a radio controlled clock receiver adapted to extract timing and time information from a phase modulated signal.
- Radio-controlled-clock (RCC) devices that rely on time signal broadcasts have become widely used in recent years.
- a radio-controlled-clock (RCC) is a timekeeping device that provides the user with accurate timing information that is derived from a received signal, which is broadcast from a central location, to allow multiple users to be aligned or synchronized in time. Colloquially, these are often referred to as “atomic clocks” due to the nature of the source used to derive the timing at the broadcasting side.
- NIST National Institute of Standards and Technology
- NIST National Institute of Standards and Technology
- the information encoded in this broadcast includes the official time of the United States. This also includes information regarding the timing of the implementation of daylight saving time (DST), which has changed in the United States over the years due to various considerations.
- DST daylight saving time
- the present invention is a system and method for a radio controlled clock receiver adapted to extract timing and time information from a phase modulated signal.
- the system and method of the present invention provide a modified modulation scheme for transmission of the official time signal that is broadcast from a central location, and a receiver adapted to extract the timing and time information from this broadcast.
- the modified modulation scheme adds phase modulation that allows for greatly improved performance.
- the information modulated onto the phase contains a known synchronization sequence, error-correcting coding for the time information and notifications of daylight-saving-time (DST) transitions that are provided months in advance.
- DST daylight-saving-time
- the structure and method of operation of the receiver allows the timekeeping functionality of a device to be accurate, reliable and power efficient.
- the communication protocol of the present invention is adapted to allow prior-art devices to operate in accordance with the legacy communication protocol such that they are unaffected by the changes introduced to the protocol by the present invention, whereas devices adapted to operate in accordance with the present invention benefit from various performance advantages. These advantages include (1) greater robustness of the communication link; (2) allowing reliable operation at a much lower signal-to-noise-and-interference-ratio (SNIR); (3) greater reliability in providing the correct time; and (4) reduced energy consumption which leads to extended battery life in battery-operated devices.
- SNIR signal-to-noise-and-interference-ratio
- the modulation applied to the carrier is limited to its phase, thereby allowing existing devices that operate in accordance with the legacy communication protocol, whereby the information may be extracted through envelope detection, to continue to operate with the modified protocol without being affected.
- this backward compatibility property of the communication protocol of the present invention may represent a practical need when upgrading an existing system, the scope of the invention is not limited to the use of this modulation scheme and to operation in conjunction with an existing communication protocol.
- the enhanced robustness offered by the present invention is a result of the use of (1) a known synchronization sequence having good autocorrelation properties; (2) coding that allows for error detection and correction within the fields of information bits that are part of each data frame; and (3) the use of a superior modulation scheme, such as binary-phase-shift-keying (BPSK) (also known as phase-reversal keying or PRK) in one embodiment of the present invention.
- BPSK binary-phase-shift-keying
- PRK phase-reversal keying
- the PRK modulation representing an antipodal system, provides the largest distance in the signal space with respect to signal power, whereas the historical modulation schemes that are used for time broadcasting worldwide are based on pulse width modulation (PWM) that relies on amplitude demodulation, requiring a higher SNIR to achieve the same decision error probability or bit-error-rate (BER).
- PWM pulse width modulation
- BER bit-error-rate
- the enhanced reliability in assuming or setting the right time in a device of the present invention may be partly achieved through the use of a time-computing procedure that considers not only the information extracted from the received frame, but also the time that has been assumed in the timekeeping device. For example, if the information extracted from a received frame suggests that the year is many years ahead of what the timekeeping device has been assuming for a long time, it is likely that the reception is in error and should be disregarded.
- the receiver may apply averaging filtering, wherein the timing extracted from the received signal is weighted against the locally assumed time in the device such that the timing adjustment considers them both instead of being determined based solely on the received signal, as is typically done in existing prior art devices.
- the system is scalable in that it allows for receivers experiencing different reception conditions to use the received signal differently.
- it is designed to allow for the accumulation of received energy over multiple one-minute frames (i.e. throughout a one-hour superframe or a portion thereof), to provide for a corresponding gain in the receiver (e.g., reception for a whole hour may provide a gain of 60, or 18 dB, with respect to a single minute).
- the features described supra serve to greatly increase the robustness and reliability of the time signal communication system, allowing it to operate at signal-to-noise ratios that are several orders of magnitude lower than those required in the existing scheme, while exhibiting even higher gains in scenarios of on-frequency jamming, to which the existing receivers are particularly vulnerable.
- a radio receiver comprising a receiver circuit operative to receive a phase modulated (PM), pulse width modulation (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing and time information, the timing information based on a known synchronization sequence and a circuit operative to extract the timing and time information from the phase of the received signal.
- PM phase modulated
- PWM pulse width modulation
- ASK amplitude shift keyed
- a radio receiver method comprising receiving a phase modulated (PM), pulse width modulated (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing and time information, the timing information based on a known synchronization sequence and extracting the timing and time information from the phase of the received signal.
- PM phase modulated
- PWM pulse width modulated
- ASK amplitude shift keyed
- a radio receiver method for use in a timekeeping device comprising receiving a phase modulated (PM), pulse width modulated (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing and time information, the timing information based on a known synchronization sequence, extracting the timing and time information from the phase of the received signal and correlating the timing information against a known synchronization sequence so as to establish frame and symbol timing.
- PM phase modulated
- PWM pulse width modulated
- ASK amplitude shift keyed
- a radio receiver method comprising receiving a phase modulated (PM) broadcast signal encoded with timing and time information, wherein the timing and time information, intended for synchronization and time reference purposes, is conveyed in the phase of the carrier portion of the broadcast signal and extracting the timing and time information from the phase of the received signal.
- PM phase modulated
- FIG. 1 is a high level block diagram illustrating an example timing and time information transmitter of a system operating in accordance with the present invention
- FIG. 2 is a high level block diagram illustrating an example timing and time information receiver constructed in accordance with the present invention
- FIG. 3 is a diagram illustrating a first example pulse-width modulated AM signal representing a ‘0’ bit
- FIG. 4 is a diagram illustrating a second example pulse-width modulated AM signal representing a ‘0’ bit
- FIG. 5 is a diagram illustrating a first example pulse-width modulated AM signal representing a ‘1’ bit
- FIG. 6 is a diagram illustrating a second example pulse-width modulated AM signal representing a ‘1’ bit
- FIG. 7 is a diagram illustrating a first example pulse-width modulated AM signal representing a marker ‘M’;
- FIG. 8 is a diagram illustrating a second example pulse width modulated AM signal representing a marker ‘M’;
- FIG. 9 is a diagram illustrating the structure of an example data frame incorporating timing and time information
- FIG. 10 is a diagram illustrating an example embodiment of phase modulation, shown at baseband, added to a pulse-width amplitude modulated carrier;
- FIG. 11 is a diagram illustrating the signal space representation of the prior art AM/pulse-width ‘0’ and ‘1’ signals, as well as that of the an example embodiment of the present invention, where PRK is added onto the AM/pulse-width modulation;
- FIG. 12 is a diagram illustrating an example receiver incorporating both amplitude and phase modulation receiver paths
- FIG. 13 is a diagram illustrating an example receiver adapted to receive a phase modulated signal
- FIG. 14 is a diagram illustrating a first example waveform of phase modulation added to a pulse-width amplitude modulated carrier in an example communication protocol
- FIG. 15 is a diagram illustrating a second example phase modulation added to a pulse-width amplitude modulated carrier in an example communication protocol
- FIG. 16 is a diagram illustrating an example phase modulated carrier in an example communication protocol.
- FIG. 17 is a diagram illustrating the structure of an example super-frame incorporating timing and time information.
- FIG. 1 A high level block diagram illustrating an example timing and time information transmitter a system operating in accordance with the present invention is shown in FIG. 1 .
- the equipment at the transmitter end generally referenced 10 , comprises a high accuracy clock source (frequency source) 12 from which a clock signal (timing information) is derived, a time-code-generator 14 having user-interface 16 , a source of time data 13 , a transmitter 18 generating a TX signal 19 and coupled to transmitting antenna 11 .
- a high accuracy clock source frequency source
- timing information timing information
- the time code generator 14 keeps track of time based on the high-accuracy frequency source input to it from source 12 , constructs the frames of data representing the time information received from time data source 13 and other information that is to be transmitted, modulates the data frames onto the RF carrier in accordance to a protocol and allows time initialization and other controls to be set in it through its user interface 16 .
- the transmitter 18 amplifies the modulated signal to generate an output TX signal 19 at the desired levels, e.g., 50 kW, and drives the antenna 11 that is used for the wide-coverage omnidirectional broadcasting of the signal.
- FIG. 2 A high level block diagram illustrating an example timekeeping device constructed in accordance with the present invention is shown in FIG. 2 .
- the timekeeping device is incorporated into low cost consumer market products, but may be implemented in any device that requires a precision time reference.
- the timekeeping device generally referenced 20 , comprises receiving antenna 21 , receiver module 24 operative to receive RX signal 22 , processor and controller 26 , timekeeping function 30 , internal or external clock source 31 , display 32 and user interface 34 .
- the receiver module 24 extracts timing and time information from the received signal 22 , in accordance with the modulation scheme and protocol in use, and provides the processing and control function 26 with the extracted timing and time information. Controller function/processor 26 appropriately enables/disables the operation of the receiver module through control line 28 such that it is limited to the intervals of interest to minimize energy consumption in those applications where it may be critical to do so (e.g., wrist watches).
- the timekeeping function 30 keeps track of the time based on pulses provided by clock source 31 having limited accuracy.
- the clock source 31 may comprise any suitable clock source or clock signal such as a crystal oscillator and may be provided internal to the timekeeping device 20 or supplied from a source external to the timekeeping device.
- the timekeeping may be adjusted by the processor/controller in accordance with an estimated drift at a specific instant, which is either measured or calculated or a combination of the two.
- the display function 32 may be used to display the time as well as various indications to the user, including reception quality, estimated bound for error in displayed time, battery status, etc.
- the user interface function 34 based on pushbuttons, slide-switches, a touch-screen, keypad, computer interface, a combination therefrom, or any other form of human interface, may be used to set the initial time, define the maximal allowed timing error, the time-zone according to which time is to be calculated, the use of daylight saving time, etc.
- the timekeeping device is operative to extract timing and time information conveyed in a broadcast signal.
- Timing information denotes information related to synchronization and tracking and is used, e.g., for bit and frame synchronization.
- Time information denotes information related to the current time being communicated, such as the date and the time of day (hours, minutes, etc.), as well as scheduled events, such as an upcoming DST transition, leap second, etc.
- Typical available time-broadcast signals employ some form of amplitude modulation combined with some form of pulse width modulation (PWM) to send binary data bits.
- PWM pulse width modulation
- the WWVB signal comprises a 60 second frame consisting of 60 one second bits. Each bit, of one second duration, is sent as a pulse width modulated signal where carrier signal is transmitted at a low amplitude or a high amplitude for different portions of the bit.
- the frame also consists of several marker bits spread out evenly through the frame, which serve only to indicate timing and do not convey time information. Representations of the different possible signal waveforms transmitted by WWVB are presented below.
- the existing WWVB system transmits a pulse-width modulated amplitude-shift keyed waveform on a 60 kHz carrier.
- the one-second duration ‘0’ and ‘1’ symbols are represented by a power reduction of ⁇ 17 dB at the start of the second for 0.2 s and 0.5 s, respectively.
- FIGS. 3 , 5 , 7 show the baseband waveforms for the ‘0’ (denoted x 0 (t)), ‘1’ (denoted x 1 (t)) and Marker (‘M’) symbols for the existing WWVB system where the low portion of the symbols are reduced in power ⁇ 17 dB, corresponding to an amplitude reduction to about 0.14 of the high amplitude.
- FIG. 3 A diagram illustrating a first example pulse width modulated AM signal representing a ‘0’ bit is shown in FIG. 3 .
- the signal x 0 (t) 40 (upper diagram) represents the envelope or baseband waveform of a ‘0’ bit and consists of 0.2 seconds of low amplitude carrier (e.g., 0.14 amplitude) and 0.8 seconds of high amplitude carrier.
- the lower diagram shows the corresponding carrier waveform 42 of 0.2 seconds low amplitude followed by 0.8 seconds of high amplitude.
- FIG. 4 A diagram illustrating a second example pulse width modulated AM signal representing a ‘0’ bit is shown in FIG. 4 .
- the signal x 0 (t) 44 (upper diagram) represents the envelope or baseband waveform of a ‘0’ bit and consists of 0.2 seconds of zero amplitude carrier and 0.8 seconds of high amplitude carrier.
- the lower diagram shows the corresponding carrier waveform 46 of 0.2 seconds zero amplitude followed by 0.8 seconds of high amplitude.
- FIG. 5 A diagram illustrating a first example pulse width modulated AM signal representing a ‘1’ bit is shown in FIG. 5 .
- the signal x 1 (t) 48 (upper diagram) represents the envelope or baseband waveform of a ‘1’ bit and consists of 0.5 seconds of low amplitude carrier (e.g., 0.14 amplitude) and 0.5 seconds of high amplitude carrier.
- the lower diagram shows the corresponding carrier waveform 50 of 0.5 seconds low amplitude followed by 0.5 seconds of high amplitude.
- FIG. 6 A diagram illustrating a second example pulse width modulated AM signal representing a ‘1’ bit is shown in FIG. 6 .
- the signal x 1 (t) 52 (upper diagram) represents the envelope or baseband waveform of a ‘1’ bit and consists of 0.5 seconds of zero amplitude carrier and 0.5 seconds of high amplitude carrier.
- the lower diagram shows the corresponding carrier waveform 54 of 0.5 seconds zero amplitude followed by 0.5 seconds of high amplitude.
- FIG. 7 A diagram illustrating a first example pulse width modulated AM signal representing a marker ‘M’ bit is shown in FIG. 7 .
- the signal x 1 (t) 56 (upper diagram) represents the envelope or baseband waveform of a ‘M’ bit and consists of 0.8 seconds of low amplitude carrier (e.g., 0.14 amplitude) and 0.2 seconds of high amplitude carrier.
- the lower diagram shows the corresponding carrier waveform 58 of 0.8 seconds low amplitude followed by 0.2 seconds of high amplitude.
- FIG. 8 A diagram illustrating a second example pulse width modulated AM signal representing a marker ‘M’ bit is shown in FIG. 8 .
- the signal x 1 (t) 60 (upper diagram) represents the envelope or baseband waveform of a ‘M’ bit and consists of 0.8 seconds of zero amplitude carrier and 0.2 seconds of high amplitude carrier.
- the lower diagram shows the corresponding carrier waveform 62 of 0.8 seconds zero amplitude followed by 0.2 seconds of high amplitude.
- FIG. 9 A diagram illustrating the structure of an example data frame incorporating timing and time information in an example communication protocol is shown in FIG. 9 .
- the frame N generally referenced 70 , comprises timing data 74 , time data 76 and a field of zero or more additional information bits 78 .
- the N th transmitted frame is preceded by frame N ⁇ 1 72 and followed by frame N+1 79 , both of which span 60 seconds and represent the minute before and the minute after frame N, respectively.
- the transmitted frame 70 comprises a synchronization sequence 74 spanning m seconds, a field of information 73 spanning k seconds that precedes the synchronization sequence and a field 78 spanning the remaining time 60 ⁇ (m+k) seconds following the synchronization sequence, such that the four fields together span the total of 60 seconds.
- the values of m and k are preferably fixed and their sum is less than 60, such that the location of the synchronization sequence is predictable in a frame, allowing the receiver to search for it at the expected timing, while ignoring the information bits if there is no need to receive them.
- the timing data field 74 comprises a known synchronization sequence (e.g., barker code, modified barker code, pseudo random sequence, or any other known word or bit/symbol sequence) at a known timing within the one minute frame of 60 bits that is transmitted every 60 seconds.
- a known synchronization sequence e.g., barker code, modified barker code, pseudo random sequence, or any other known word or bit/symbol sequence
- the synchronization sequence may be placed within the frame such that it overlaps or straddles the frame N ⁇ 1 before it or frame N+1 after it.
- phase modulation is added to an amplitude modulated carrier.
- a diagram illustrating phase modulation added to an amplitude modulated carrier in an example communication protocol is shown in FIG. 10 .
- This diagram describes the amplitude/pulse width modulation (PWM) used in the historical WWVB broadcast as well as the phase modulation introduced in accordance with an embodiment of the present invention.
- PWM pulse width modulation
- the diagram shows the baseband representation of the ‘0’ and ‘1’ symbols in both the historical WWVB modulation and in one that is modified in accordance with an example embodiment of the present invention.
- the enhancement in the communication protocol offered by the present invention in the form of independently defined phase modulation and the use of a known synchronization sequence, is not limited to the broadcast of WWVB and may be applied to other timing/time information broadcast systems such as those in other countries around the world where similar AM/pulse-width schemes are used or where no AM/pulse-width modulation needs to be supported, allowing for continuous BPSK to be used.
- the additional phase modulation added to the signal is binary phase shift keying (BPSK) having an 180° difference in the carrier's phase between the ‘0’ and ‘1’ symbols, also known as antipodal phase modulation or Phase Reversal Keying (PRK).
- BPSK binary phase shift keying
- PRK Phase Reversal Keying
- the enhanced modulation scheme can be accomplished through simple sign inversion for the waveform representing the ‘1’ symbol. It is noted that since the existing envelope detector based receivers designed to receive and decode the current WWVB AM/PWM based broadcast signal do not consider the carrier's phase, they are not impacted by the modification of phase inversion of the ‘1’ symbol.
- FIG. 11 A diagram illustrating the signal space representation of AM only and PM over AM ‘0’ and ‘1’ symbols is shown in FIG. 11 .
- the new pair of waveforms, x 0 (referenced 88 ) and ⁇ x 1 (referenced 86 ) having the same amount of energy (corresponding to their distances from origin), exhibit a much greater distance between the ‘0’ and ‘1’ symbols (as compared to waveform pair x 0 and x 1 (referenced 90 ), thereby allowing for more robust reception in the presence of additive noise.
- the existing symbols x 0 and x 1 are strongly correlated, i.e. they have a very short distance between them in the signal space with respect to their energies.
- the Euclidean distance between the two amplitude modulated waveforms x 0 and x 1 is shown to be 0.47, whereas the Euclidean distance for the two phase modulated waveforms x o and ⁇ x 1 increases to 1.55. Therefore, the modulation gain (denoted m g ) representing the power ratio by which the detection capability in the presence of additive noise is improved, is given by
- AWGN additive white Gaussian noise
- the information represented by the phase modulation in each bit is independent from that represented by the existing (legacy) AM/pulse-width modulation, such that an inverted phase would not necessarily be tied to the shorter waveform 82 , represented by inverted waveform ⁇ x 1 (t) 84 in FIG. 10 .
- a phase inverted bit which may represent a “1”, for example, may be combined with either a “0” or a “1” in the AM/PWM signal, resulting in the example waveform shown in FIG. 14 .
- the receiver extracting the information from the phase may limit the phase demodulation operation to the last 0.5 sec of each bit, where both the “0” and “1” symbols of the AM/PWM scheme shown in this example are at high amplitude.
- the receiver may extend the demodulation of phase during those symbols to 0.8 sec when the content is of the AM/PWM modulation is known to be “0”.
- phase modulated information may consider the predicted durations of the time-information bits as they are defined by the particular AM/PWM protocol, thereby further optimizing reception.
- a receiver operating in accordance with the present invention may also consider some or all of the energy that a transmitted bit may have in the low amplitude portion of it, if it is greater than zero. This is to be done by weighting that portion of the signal in accordance with the theory of matched filtering, i.e. if the lower amplitude portion is at a normalized level of 0.14, the correlation operation in the receiver must provide it with such weighting with respect to the weighting of 1 that is applied during the high level duration in the receiver symbol.
- the receiver determines the current time in accordance with a nonlinear function that disregards the timing and time information extracted from the received frame (along with its weighting) if its distance from the local currently assumed time in the timekeeping device is greater than a predefined or dynamic threshold. This it to avoid incorrect timing adjustments that could be caused by erroneous reception of the timing or time information, the likelihood of which increases as the SINR conditions are more severe.
- a dynamically adaptive threshold considers the duration over which the time-keeping device has been maintaining the time and the statistics of the time corrections applied throughout that duration. For example, a time keeping device that has been tracking the time for an entire year, while performing weekly timing adjustments averaging 0.8 sec, with the greatest correction being below 1.5 seconds in magnitude, may act to disregard a reception instance suggesting a timing correction of 4 seconds, whereas it would have been considered and weighted at an earlier point in time during that year.
- an example embodiment of the present invention may perform such an operation utilizing linear combining wherein the coefficient applied towards the timing extracted from the received signal and the coefficient applied for the locally assumed time depend on the levels of confidence in these two timings variables. If, for example, the reception conditions are determined to be excessively noisy, for which the probability of inaccurate timing extraction is higher, whereas the locally assumed time is based on a relatively recent adjustment and a good record of successive timing adjustments suggests that not much drift could have been experienced up until the instance of the reception at question, then relatively low weighting may be applied towards the received timing versus the locally assumed one. If, in contrast, the received timing is accompanied by an indication of high SINR, suggesting a high probability that it is accurate, then it may receive higher weighting compared to that of the locally assumed timing.
- a time-keeping device operating in accordance with the present invention applies non-linear logic in its reception of time information when a locally assumed time is available and has been validated over time. If the device attempts to extract from a received frame not only the timing information, for the purpose of timing adjustment, but also time information, despite such information already being available to it, then rather than computing a new time based on a linear combination of the received time and the locally assumed one, it is to select one of the two. If the locally assumed time has been validated over time and the received frame is received with errors or is accompanied by a low SINR indication, then the device may disregard the information extracted from the receiver. If, however, the device's confidence in its locally assumed time is low and the received signal is accompanied by an indication of reliable reception, then the received time may be selected, or one or more additional frames may be received to further increase the confidence in the received information.
- non-antipodal phase modulation can be used to modulate the PWM signal.
- the magnitude of phase modulation applied may be set at any value less than 180°, e.g., ⁇ 45°, ⁇ 25°, ⁇ 13°, etc.
- Use of a lower value such as ⁇ 13° ensures that the modulated signal is contained within a narrow bandwidth and does not escape the narrow filtering in typical existing AM receivers, which is on the order of 10 Hz.
- narrowband PM is not comparable in performance to antipodal BPSK, where the two symbols are 180° apart exhibiting a correlation factor of ⁇ 1.
- FIG. 12 A diagram illustrating an example receiver incorporating both amplitude and phase modulation receiver paths is shown in FIG. 12 .
- the receiver is operative to receive both a legacy PWM/AM modulated broadcast signal as well as a phase modulated signal which is transmitted over the legacy PWM/AM signal.
- the receiver generally referenced 100 , comprises an AM receiver block 104 and a PM receiver block 102 , both of which are connected to antenna 106 at their input and to processor 124 at their output.
- Amplitude modulation receiver 104 comprises an envelope-detector-based receiver of the type that is typically used in consumer market RCC devices.
- the AM receiver 104 comprises band pass filter (e.g., crystal filter) 110 , envelope detector 112 and threshold block 114 .
- band pass filter e.g., crystal filter
- envelope detector 112 envelope detector
- threshold block 114 threshold block 114 .
- the AM signal is converted into an analog equivalent baseband signal by use of a conventional nonlinear envelope detector 112 (similar to the diode-based circuit in traditional AM receivers).
- a threshold operation 114 that follows serves to determine the middle level, around which the voltages below it would be converted to a logic low level and the voltages above it to a logic high level.
- the digital processing stage that follows this operation measures the pulse durations and accordingly recovers the symbols (‘1’, ‘0’, or ‘marker’).
- an on-frequency interferer can cause the receiver to decode that symbol incorrectly.
- the effect of the interferer is greatest when the signal is at a “low”. If the interferer is exactly on-frequency, however, then it has a very significant effect when it is out of phase and added to the high state of the transmitted signal (e.g., the WWVB signal).
- the modulated signal input to the receiver has two different amplitude levels with the information represented in the durations of each of these levels.
- the high/low decision is made by following the “low” and “high” levels with dedicated peak holders (with appropriate time-constants) and deriving the middle (average) of these two.
- a threshold operation e.g., a simple comparator
- a threshold operation is then used to create the logic level signals for the digital stage that follows where the pulse durations are measured and the ‘1’/‘0’/‘marker’ symbol decision is made.
- the phase modulation receiver 102 comprises a demodulator 118 , correlator 120 and decoder 122 .
- the PM receiver 102 is operative to receive the signal broadcast from WWVB in Fort Collins, Colo. This broadcast signal adds phase modulation (PM) to the WWVB broadcast while maintaining the existing AM code, so as not to impact the existing time-of-day RCC devices.
- PM phase modulation
- the receiver comprises a coherent BPSK optimal receiver that may be implemented digitally.
- the PM receiver 130 comprises antenna 132 coupled to analog front end (AFE) 134 , low pass filter (LPF) 136 , analog to digital converter (ADC) 138 , mixer 140 , local synthesized carrier (e.g., local oscillator (LO)) 146 , correlator 143 and threshold detector 144 .
- AFE analog front end
- LPF low pass filter
- ADC analog to digital converter
- mixer 140 mixer 140
- local synthesized carrier e.g., local oscillator (LO)
- bit-error-rate (BER) performance of the receiver for a signal to noise ratio E b /N o , is given by
- E b is the energy per bit and N o is the noise density.
- the threshold decision block 144 is where the decisions are made and the errors occur, in direct relation to the variance of noise, which is assumed to have Gaussian nature and equal variances around the ‘0’ and ‘1’ symbols.
- the BER may also be expressed as a function of the distance between the symbols in the signal space, as follows
- Q(x) is the tail probability of the normal distribution, i.e.
- FIG. 14 A diagram illustrating a first example phase modulation added to an amplitude modulated carrier in an example communication protocol is shown in FIG. 14 .
- the waveform illustrates three consecutive example bits in the transmission as a time-domain waveform 150 .
- the three bits 152 , 154 and 156 each span a duration of one second.
- Each of the one second bits is divided into a first portion 160 for which the carrier power is low and a second portion 162 for which the carrier power is high.
- the information in each bit depends on the durations of these two portions with an even 0.5/0.5 sec partition representing a “1” bit, and the uneven 0.2/0.8 sec partition representing a “0” bit.
- a 0.8/0.2 sec partition represents a ‘marker’ bit, which may be used for timing identification, but does not carry information.
- the bits represented under the legacy PWM/AM modulation are indicated at the top portion of the diagram. For example, the three PWM/AM bits shown are “1”, “0” and “1”.
- While the information represented by the pulse widths is shown to be “1”, “0”, “1”, the information that is sent in parallel, in accordance with the example BPSK (or PRK) protocol of the present invention, is shown to be “0”, “0”, “1” (as shown along the bottom portion of the diagram). Note that there is not necessarily any relationship between the bit pattern transmitted using PWM/AM and that transmitted using PM as they can be completely independent. It is noted that the carrier frequency is not shown to scale in the figure to enhance clarity, but it is preferable for the phase transitions to occur at zero crossing instances of the carrier.
- FIG. 15 A diagram illustrating a second example phase modulation added to an amplitude modulated carrier in an example communication protocol is shown in FIG. 15 .
- the carrier amplitude transmitted during the low portions of a bit is zero rather than reduced to a lower value (e.g., ⁇ 17 dB or 0.14 amplitude level) as is the case in FIG. 14 .
- the waveform illustrates three consecutive example bits in the transmission as a time-domain waveform 170 .
- the three bits 172 , 174 and 176 each span a duration of one second.
- Each of the one second bits is divided into a first portion 178 for which the carrier power is zero and a second portion 180 for which the carrier power is high.
- the modulation of information is added to the existing modulation using BPSK modulation.
- bit pattern transmitted using PWM/AM and that transmitted using PM as they can be completely independent.
- carrier frequency is not shown to scale in the figure to enhance clarity, but it is preferable for the phase transitions to occur at zero crossing instances of the carrier.
- FIG. 16 A diagram illustrating an example phase modulated carrier in an example communication protocol is shown in FIG. 16 .
- the phase modulation is not added to a PWM/AM signal but rather is sent as the entire bit duration.
- the waveform illustrates three consecutive example bits in the transmission as a time-domain waveform 190 .
- the three bits 192 , 194 and 196 each span a duration of one second.
- the carrier power is high.
- the modulation of information is performed using BPSK (or PRK) modulation, in accordance with an embodiment of the present invention.
- the information sent in accordance with the BPSK protocol of the present invention is shown to be “0”, “0”, “1” (as shown along the bottom portion of the diagram). It is noted that the carrier frequency is not shown to scale in the figure to enhance clarity, but it is preferable for the phase transitions to occur at zero crossing instances of the carrier, as may be implemented easily when a bit spans an integer number of carrier cycles, as is the case for WWVB, where the carrier frequency is 60 kHz (i.e. 60,000 cycles per bit).
- FIG. 17 A diagram illustrating the structure of an example super frame incorporating timing and time information is shown in FIG. 17 .
- information is recovered not only from the bits of a frame, but may also be recovered by using multiple consecutive frames making up a superframe.
- additional information may be conveyed using the superframe, or the same information from each frame may be repeated to allow for improved reception based on the accumulated energy of multiple frames.
- the use of superframes can potentially improve performance of the receiver by nearly two orders of magnitude, which may be critical in low SNR conditions.
- the polarity of each of the one-minute frames in an hour is modulated (e.g., differentially or otherwise) by a corresponding bit in a 60-bit hour-synchronization sequence.
- the preserved consistency between the polarities of the synchronization sequence and the information in each of one-minute frames permits the receiver to resolve the 180-degree phase ambiguity of BPSK reception.
- the receiver can accurately adjust its timing and can then use recorded data from an entire hour to perform long-term integration for the hour field (i.e. soft addition). This provides an improvement in gain of 60 (i.e. 18 d B), which enables operation at SNIR values well below 0 dB (when evaluated in a 1 Hz bandwidth). While the minute and parity fields for the time information vary from one minute to the next in the course of an hour, all other fields, however, remain fixed. Thus, simple addition can be used to increase the total amount of energy involved in the information recovery. Since the pattern according to which the minute frame is changing is also known, it too can serve in the extended reception operation.
- the receiver may determine its timing with respect to the beginning of an hour based on the identification of a portion of the hour-synchronization sequence (at least six bits, collected over seven minutes) with or without recovering information from the minute fields in the received frames.
- a frame 216 comprises a synchronization sequence field 218 , hour field 220 , minute field 222 and zero or more additional fields 224 .
- a superframe e.g., superframe P 212
- Each synchronization sequence i.e. sync seq 0 , sync seq 1 , . . .
- sync seq 59 is assigned a particular phase wherein the pattern is known to all receivers.
- the receivers use their knowledge of the super-synchronization sequence to aid in adjusting their time to a particular minute within the hour without having to recover the information from the minute field.
- Such a super-synchronization sequence provides additional information for receivers to aid in acquisition and tracking at low SINR conditions.
- superframes provides system scalability in that it allows for receivers experiencing different reception conditions to use the received signal differently.
- superframes (or the use of a number of multiple frames) allow for the accumulation of received energy over multiple one-minute frames to provide for a corresponding gain in the receiver. For example, reception for an entire hour may provide a gain of 60 or 18 dB with respect to reception over a single minute (i.e. a single frame).
Abstract
Description
- This application is a continuation of U.S. application Ser. No. 13/345,084, filed Jan. 6, 2012, now U.S. Pat. No. 8,233,525, entitled “Timing and Time Information Extraction from a Phase Modulated Signal in a Radio Controlled Clock Receiver,” incorporated herein by reference in its entirety.
- This invention was made with Government support under National Institute of Standards and Technology SBIR Grant No. NB401000-11-04154. The Government has certain rights in the invention.
- The present invention relates to the field of wireless communications, and more particularly relates to a radio controlled clock receiver adapted to extract timing and time information from a phase modulated signal.
- Radio-controlled-clock (RCC) devices that rely on time signal broadcasts have become widely used in recent years. A radio-controlled-clock (RCC) is a timekeeping device that provides the user with accurate timing information that is derived from a received signal, which is broadcast from a central location, to allow multiple users to be aligned or synchronized in time. Colloquially, these are often referred to as “atomic clocks” due to the nature of the source used to derive the timing at the broadcasting side. In the United States, the National Institute of Standards and Technology (NIST) provides such broadcast in the form of a low-frequency (60 kHz) digitally-modulated signal that is transmitted at high power from radio station WWVB in Fort Collins, Colo. The information encoded in this broadcast includes the official time of the United States. This also includes information regarding the timing of the implementation of daylight saving time (DST), which has changed in the United States over the years due to various considerations.
- Reception of the time signal, however, is being challenged by a growing number of sources of electromagnetic interference. In particular, the on-frequency interference from the MSF radio station in the United Kingdom has been identified as a particularly challenging jammer for receivers on the East Coast.
- There is thus a need for a new protocol for time signal broadcasts, such as that provided by WWVB, that attempts to cost-effectively address the reception challenges. Such a new protocol should preserve existing amplitude modulation properties of the transmitted signal, in order to maintain backwards compatibility and not impact existing devices.
- The present invention is a system and method for a radio controlled clock receiver adapted to extract timing and time information from a phase modulated signal. The system and method of the present invention provide a modified modulation scheme for transmission of the official time signal that is broadcast from a central location, and a receiver adapted to extract the timing and time information from this broadcast. The modified modulation scheme adds phase modulation that allows for greatly improved performance. The information modulated onto the phase contains a known synchronization sequence, error-correcting coding for the time information and notifications of daylight-saving-time (DST) transitions that are provided months in advance.
- The structure and method of operation of the receiver allows the timekeeping functionality of a device to be accurate, reliable and power efficient. The communication protocol of the present invention is adapted to allow prior-art devices to operate in accordance with the legacy communication protocol such that they are unaffected by the changes introduced to the protocol by the present invention, whereas devices adapted to operate in accordance with the present invention benefit from various performance advantages. These advantages include (1) greater robustness of the communication link; (2) allowing reliable operation at a much lower signal-to-noise-and-interference-ratio (SNIR); (3) greater reliability in providing the correct time; and (4) reduced energy consumption which leads to extended battery life in battery-operated devices.
- In one embodiment of the present invention, the modulation applied to the carrier is limited to its phase, thereby allowing existing devices that operate in accordance with the legacy communication protocol, whereby the information may be extracted through envelope detection, to continue to operate with the modified protocol without being affected. Although this backward compatibility property of the communication protocol of the present invention may represent a practical need when upgrading an existing system, the scope of the invention is not limited to the use of this modulation scheme and to operation in conjunction with an existing communication protocol.
- The enhanced robustness offered by the present invention, resulting in reliable reception at lower SNIR values with respect to those required for proper operation of prior art devices, is a result of the use of (1) a known synchronization sequence having good autocorrelation properties; (2) coding that allows for error detection and correction within the fields of information bits that are part of each data frame; and (3) the use of a superior modulation scheme, such as binary-phase-shift-keying (BPSK) (also known as phase-reversal keying or PRK) in one embodiment of the present invention. The PRK modulation, representing an antipodal system, provides the largest distance in the signal space with respect to signal power, whereas the historical modulation schemes that are used for time broadcasting worldwide are based on pulse width modulation (PWM) that relies on amplitude demodulation, requiring a higher SNIR to achieve the same decision error probability or bit-error-rate (BER).
- The enhanced reliability in assuming or setting the right time in a device of the present invention may be partly achieved through the use of a time-computing procedure that considers not only the information extracted from the received frame, but also the time that has been assumed in the timekeeping device. For example, if the information extracted from a received frame suggests that the year is many years ahead of what the timekeeping device has been assuming for a long time, it is likely that the reception is in error and should be disregarded.
- On a finer scale, when the correlation operation that makes use of the known synchronization sequence in the received signal produces a noisy result (i.e. the correlation peak is closer to the low-correlation results), based on which the timing extraction may be inaccurate, the receiver may apply averaging filtering, wherein the timing extracted from the received signal is weighted against the locally assumed time in the device such that the timing adjustment considers them both instead of being determined based solely on the received signal, as is typically done in existing prior art devices.
- Furthermore, the system is scalable in that it allows for receivers experiencing different reception conditions to use the received signal differently. In particular, it is designed to allow for the accumulation of received energy over multiple one-minute frames (i.e. throughout a one-hour superframe or a portion thereof), to provide for a corresponding gain in the receiver (e.g., reception for a whole hour may provide a gain of 60, or 18 dB, with respect to a single minute).
- The features described supra serve to greatly increase the robustness and reliability of the time signal communication system, allowing it to operate at signal-to-noise ratios that are several orders of magnitude lower than those required in the existing scheme, while exhibiting even higher gains in scenarios of on-frequency jamming, to which the existing receivers are particularly vulnerable.
- There is thus provided in accordance with the invention, a radio receiver comprising a receiver circuit operative to receive a phase modulated (PM), pulse width modulation (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing and time information, the timing information based on a known synchronization sequence and a circuit operative to extract the timing and time information from the phase of the received signal.
- There is also provided in accordance with the invention, a radio receiver method, the method comprising receiving a phase modulated (PM), pulse width modulated (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing and time information, the timing information based on a known synchronization sequence and extracting the timing and time information from the phase of the received signal.
- There is further provided in accordance with the invention, a radio receiver method for use in a timekeeping device, the method comprising receiving a phase modulated (PM), pulse width modulated (PWM)/amplitude shift keyed (ASK) broadcast signal encoded with timing and time information, the timing information based on a known synchronization sequence, extracting the timing and time information from the phase of the received signal and correlating the timing information against a known synchronization sequence so as to establish frame and symbol timing.
- There is also provided in accordance with the invention, a radio receiver method, the method comprising receiving a phase modulated (PM) broadcast signal encoded with timing and time information, wherein the timing and time information, intended for synchronization and time reference purposes, is conveyed in the phase of the carrier portion of the broadcast signal and extracting the timing and time information from the phase of the received signal.
- The invention is herein described, by way of example only, with reference to the accompanying drawings, wherein:
-
FIG. 1 is a high level block diagram illustrating an example timing and time information transmitter of a system operating in accordance with the present invention; -
FIG. 2 is a high level block diagram illustrating an example timing and time information receiver constructed in accordance with the present invention; -
FIG. 3 is a diagram illustrating a first example pulse-width modulated AM signal representing a ‘0’ bit; -
FIG. 4 is a diagram illustrating a second example pulse-width modulated AM signal representing a ‘0’ bit; -
FIG. 5 is a diagram illustrating a first example pulse-width modulated AM signal representing a ‘1’ bit; -
FIG. 6 is a diagram illustrating a second example pulse-width modulated AM signal representing a ‘1’ bit; -
FIG. 7 is a diagram illustrating a first example pulse-width modulated AM signal representing a marker ‘M’; -
FIG. 8 is a diagram illustrating a second example pulse width modulated AM signal representing a marker ‘M’; -
FIG. 9 is a diagram illustrating the structure of an example data frame incorporating timing and time information; -
FIG. 10 is a diagram illustrating an example embodiment of phase modulation, shown at baseband, added to a pulse-width amplitude modulated carrier; -
FIG. 11 is a diagram illustrating the signal space representation of the prior art AM/pulse-width ‘0’ and ‘1’ signals, as well as that of the an example embodiment of the present invention, where PRK is added onto the AM/pulse-width modulation; -
FIG. 12 is a diagram illustrating an example receiver incorporating both amplitude and phase modulation receiver paths; -
FIG. 13 is a diagram illustrating an example receiver adapted to receive a phase modulated signal; -
FIG. 14 is a diagram illustrating a first example waveform of phase modulation added to a pulse-width amplitude modulated carrier in an example communication protocol; -
FIG. 15 is a diagram illustrating a second example phase modulation added to a pulse-width amplitude modulated carrier in an example communication protocol; -
FIG. 16 is a diagram illustrating an example phase modulated carrier in an example communication protocol; and -
FIG. 17 is a diagram illustrating the structure of an example super-frame incorporating timing and time information. - A high level block diagram illustrating an example timing and time information transmitter a system operating in accordance with the present invention is shown in
FIG. 1 . The equipment at the transmitter end, generally referenced 10, comprises a high accuracy clock source (frequency source) 12 from which a clock signal (timing information) is derived, a time-code-generator 14 having user-interface 16, a source oftime data 13, atransmitter 18 generating aTX signal 19 and coupled to transmittingantenna 11. - The
time code generator 14 keeps track of time based on the high-accuracy frequency source input to it fromsource 12, constructs the frames of data representing the time information received fromtime data source 13 and other information that is to be transmitted, modulates the data frames onto the RF carrier in accordance to a protocol and allows time initialization and other controls to be set in it through itsuser interface 16. Thetransmitter 18 amplifies the modulated signal to generate anoutput TX signal 19 at the desired levels, e.g., 50 kW, and drives theantenna 11 that is used for the wide-coverage omnidirectional broadcasting of the signal. - A high level block diagram illustrating an example timekeeping device constructed in accordance with the present invention is shown in
FIG. 2 . Typically, the timekeeping device is incorporated into low cost consumer market products, but may be implemented in any device that requires a precision time reference. The timekeeping device, generally referenced 20, comprises receivingantenna 21,receiver module 24 operative to receiveRX signal 22, processor andcontroller 26,timekeeping function 30, internal orexternal clock source 31,display 32 anduser interface 34. - The
receiver module 24 extracts timing and time information from the receivedsignal 22, in accordance with the modulation scheme and protocol in use, and provides the processing andcontrol function 26 with the extracted timing and time information. Controller function/processor 26 appropriately enables/disables the operation of the receiver module throughcontrol line 28 such that it is limited to the intervals of interest to minimize energy consumption in those applications where it may be critical to do so (e.g., wrist watches). Thetimekeeping function 30 keeps track of the time based on pulses provided byclock source 31 having limited accuracy. Note that theclock source 31 may comprise any suitable clock source or clock signal such as a crystal oscillator and may be provided internal to thetimekeeping device 20 or supplied from a source external to the timekeeping device. - The timekeeping may be adjusted by the processor/controller in accordance with an estimated drift at a specific instant, which is either measured or calculated or a combination of the two. The
display function 32 may be used to display the time as well as various indications to the user, including reception quality, estimated bound for error in displayed time, battery status, etc. Theuser interface function 34, based on pushbuttons, slide-switches, a touch-screen, keypad, computer interface, a combination therefrom, or any other form of human interface, may be used to set the initial time, define the maximal allowed timing error, the time-zone according to which time is to be calculated, the use of daylight saving time, etc. - In one embodiment of the invention, the timekeeping device is operative to extract timing and time information conveyed in a broadcast signal. Timing information denotes information related to synchronization and tracking and is used, e.g., for bit and frame synchronization. Time information denotes information related to the current time being communicated, such as the date and the time of day (hours, minutes, etc.), as well as scheduled events, such as an upcoming DST transition, leap second, etc.
- Typical available time-broadcast signals employ some form of amplitude modulation combined with some form of pulse width modulation (PWM) to send binary data bits. As an example consider the WWVB signal broadcast from Fort Collins, Colo. in the United States of America. The WWVB signal comprises a 60 second frame consisting of 60 one second bits. Each bit, of one second duration, is sent as a pulse width modulated signal where carrier signal is transmitted at a low amplitude or a high amplitude for different portions of the bit. The frame also consists of several marker bits spread out evenly through the frame, which serve only to indicate timing and do not convey time information. Representations of the different possible signal waveforms transmitted by WWVB are presented below.
- The existing WWVB system transmits a pulse-width modulated amplitude-shift keyed waveform on a 60 kHz carrier. The one-second duration ‘0’ and ‘1’ symbols are represented by a power reduction of −17 dB at the start of the second for 0.2 s and 0.5 s, respectively.
FIGS. 3 , 5, 7 show the baseband waveforms for the ‘0’ (denoted x0(t)), ‘1’ (denoted x1(t)) and Marker (‘M’) symbols for the existing WWVB system where the low portion of the symbols are reduced in power −17 dB, corresponding to an amplitude reduction to about 0.14 of the high amplitude.FIGS. 4 , 6, 8 show the baseband waveforms for the ‘0’ (denoted x0(t)), ‘1’ (denoted x1(t)) and Marker (‘M’) symbols for an example broadcast system where the low portion of the symbols are zero amplitude. - A diagram illustrating a first example pulse width modulated AM signal representing a ‘0’ bit is shown in
FIG. 3 . The signal x0(t) 40 (upper diagram) represents the envelope or baseband waveform of a ‘0’ bit and consists of 0.2 seconds of low amplitude carrier (e.g., 0.14 amplitude) and 0.8 seconds of high amplitude carrier. The lower diagram shows the correspondingcarrier waveform 42 of 0.2 seconds low amplitude followed by 0.8 seconds of high amplitude. - A diagram illustrating a second example pulse width modulated AM signal representing a ‘0’ bit is shown in
FIG. 4 . The signal x0(t) 44 (upper diagram) represents the envelope or baseband waveform of a ‘0’ bit and consists of 0.2 seconds of zero amplitude carrier and 0.8 seconds of high amplitude carrier. The lower diagram shows the correspondingcarrier waveform 46 of 0.2 seconds zero amplitude followed by 0.8 seconds of high amplitude. - A diagram illustrating a first example pulse width modulated AM signal representing a ‘1’ bit is shown in
FIG. 5 . The signal x1(t) 48 (upper diagram) represents the envelope or baseband waveform of a ‘1’ bit and consists of 0.5 seconds of low amplitude carrier (e.g., 0.14 amplitude) and 0.5 seconds of high amplitude carrier. The lower diagram shows the correspondingcarrier waveform 50 of 0.5 seconds low amplitude followed by 0.5 seconds of high amplitude. - A diagram illustrating a second example pulse width modulated AM signal representing a ‘1’ bit is shown in
FIG. 6 . The signal x1(t) 52 (upper diagram) represents the envelope or baseband waveform of a ‘1’ bit and consists of 0.5 seconds of zero amplitude carrier and 0.5 seconds of high amplitude carrier. The lower diagram shows the correspondingcarrier waveform 54 of 0.5 seconds zero amplitude followed by 0.5 seconds of high amplitude. - A diagram illustrating a first example pulse width modulated AM signal representing a marker ‘M’ bit is shown in
FIG. 7 . The signal x1(t) 56 (upper diagram) represents the envelope or baseband waveform of a ‘M’ bit and consists of 0.8 seconds of low amplitude carrier (e.g., 0.14 amplitude) and 0.2 seconds of high amplitude carrier. The lower diagram shows the correspondingcarrier waveform 58 of 0.8 seconds low amplitude followed by 0.2 seconds of high amplitude. - A diagram illustrating a second example pulse width modulated AM signal representing a marker ‘M’ bit is shown in
FIG. 8 . The signal x1(t) 60 (upper diagram) represents the envelope or baseband waveform of a ‘M’ bit and consists of 0.8 seconds of zero amplitude carrier and 0.2 seconds of high amplitude carrier. The lower diagram shows the correspondingcarrier waveform 62 of 0.8 seconds zero amplitude followed by 0.2 seconds of high amplitude. - A diagram illustrating the structure of an example data frame incorporating timing and time information in an example communication protocol is shown in
FIG. 9 . The frame N, generally referenced 70, comprises timingdata 74,time data 76 and a field of zero or moreadditional information bits 78. The Nth transmitted frame is preceded by frame N−1 72 and followed by frame N+1 79, both of which span 60 seconds and represent the minute before and the minute after frame N, respectively. - In one embodiment, the transmitted
frame 70 comprises asynchronization sequence 74 spanning m seconds, a field ofinformation 73 spanning k seconds that precedes the synchronization sequence and afield 78 spanning the remainingtime 60−(m+k) seconds following the synchronization sequence, such that the four fields together span the total of 60 seconds. The values of m and k are preferably fixed and their sum is less than 60, such that the location of the synchronization sequence is predictable in a frame, allowing the receiver to search for it at the expected timing, while ignoring the information bits if there is no need to receive them. - The timing
data field 74 comprises a known synchronization sequence (e.g., barker code, modified barker code, pseudo random sequence, or any other known word or bit/symbol sequence) at a known timing within the one minute frame of 60 bits that is transmitted every 60 seconds. Note that in alternative embodiments the synchronization sequence may be placed within the frame such that it overlaps or straddles the frame N−1 before it or frame N+1 after it. - In one embodiment of the invention, phase modulation is added to an amplitude modulated carrier. A diagram illustrating phase modulation added to an amplitude modulated carrier in an example communication protocol is shown in
FIG. 10 . This diagram describes the amplitude/pulse width modulation (PWM) used in the historical WWVB broadcast as well as the phase modulation introduced in accordance with an embodiment of the present invention. The diagram shows the baseband representation of the ‘0’ and ‘1’ symbols in both the historical WWVB modulation and in one that is modified in accordance with an example embodiment of the present invention. It is noted that the enhancement in the communication protocol offered by the present invention, in the form of independently defined phase modulation and the use of a known synchronization sequence, is not limited to the broadcast of WWVB and may be applied to other timing/time information broadcast systems such as those in other countries around the world where similar AM/pulse-width schemes are used or where no AM/pulse-width modulation needs to be supported, allowing for continuous BPSK to be used. - In one embodiment, the additional phase modulation added to the signal is binary phase shift keying (BPSK) having an 180° difference in the carrier's phase between the ‘0’ and ‘1’ symbols, also known as antipodal phase modulation or Phase Reversal Keying (PRK). Hence, the modulated waveforms representing these symbols may be expressed as the products of the sinusoidal 60 kHz carrier (in the case of WWVB) and the baseband waveforms s0(t)=x0(t) (waveform 80) and s1(t)=−x1(t) (waveform 84), respectively, as shown in
FIG. 10 .Waveform 82 represents the original ‘1’ symbol s1(t)=x1(t) that is replaced by itsinverse waveform 84 in one example embodiment of the present invention. As is shown inFIG. 10 , the enhanced modulation scheme can be accomplished through simple sign inversion for the waveform representing the ‘1’ symbol. It is noted that since the existing envelope detector based receivers designed to receive and decode the current WWVB AM/PWM based broadcast signal do not consider the carrier's phase, they are not impacted by the modification of phase inversion of the ‘1’ symbol. - A diagram illustrating the signal space representation of AM only and PM over AM ‘0’ and ‘1’ symbols is shown in
FIG. 11 . As shown in the diagram, the new pair of waveforms, x0 (referenced 88) and −x1 (referenced 86), having the same amount of energy (corresponding to their distances from origin), exhibit a much greater distance between the ‘0’ and ‘1’ symbols (as compared to waveform pair x0 and x1 (referenced 90), thereby allowing for more robust reception in the presence of additive noise. Note that the existing symbols x0 and x1 are strongly correlated, i.e. they have a very short distance between them in the signal space with respect to their energies. - The Euclidean distance between the two amplitude modulated waveforms x0 and x1 is shown to be 0.47, whereas the Euclidean distance for the two phase modulated waveforms xo and −x1 increases to 1.55. Therefore, the modulation gain (denoted mg) representing the power ratio by which the detection capability in the presence of additive noise is improved, is given by
-
- Thus, by simply adding such phase modulation, an order of magnitude of improvement may be achieved when assuming additive white Gaussian noise (AWGN). This analysis implicitly assumes that the receivers for both schemes would be optimal, i.e. based on correlation or matched filtering. In practice, the BPSK receiver may be implemented digitally in a near-optimal fashion, whereas the receivers for the existing AM/pulse-width scheme, not designed as a classical digital-communications system, are based on envelope detection, as previously noted. This adds an additional gap of 2 to 4 dB between the two when only AWGN is considered. In the presence of on-frequency interference, however, the gain offered by realizing a near-optimal BPSK receiver may be arbitrarily higher. Furthermore, additional gains can be offered, such as (1) through encoding of the information, (2) use of a known synchronization sequence, and (3) extended-duration reception in the receiver over multiple frames (i.e. superframes).
- In an embodiment of the present invention, the information represented by the phase modulation in each bit is independent from that represented by the existing (legacy) AM/pulse-width modulation, such that an inverted phase would not necessarily be tied to the
shorter waveform 82, represented by inverted waveform −x1(t) 84 inFIG. 10 . In an example embodiment, with independent data being communicated through the carrier's phase, a phase inverted bit, which may represent a “1”, for example, may be combined with either a “0” or a “1” in the AM/PWM signal, resulting in the example waveform shown inFIG. 14 . - The receiver extracting the information from the phase may limit the phase demodulation operation to the last 0.5 sec of each bit, where both the “0” and “1” symbols of the AM/PWM scheme shown in this example are at high amplitude. Alternatively, in order to gain from the additional energy in the longer “0” pulses (0.8 sec in this example), the receiver may extend the demodulation of phase during those symbols to 0.8 sec when the content is of the AM/PWM modulation is known to be “0”. In the existing WWVB protocol, for example, there are several such bits fixed at “0”. Additionally, when a device operating in accordance with the present invention has already acquired the time and is tracking it, its reception of the phase modulated information may consider the predicted durations of the time-information bits as they are defined by the particular AM/PWM protocol, thereby further optimizing reception.
- Furthermore, a receiver operating in accordance with the present invention may also consider some or all of the energy that a transmitted bit may have in the low amplitude portion of it, if it is greater than zero. This is to be done by weighting that portion of the signal in accordance with the theory of matched filtering, i.e. if the lower amplitude portion is at a normalized level of 0.14, the correlation operation in the receiver must provide it with such weighting with respect to the weighting of 1 that is applied during the high level duration in the receiver symbol.
- In one embodiment, the receiver determines the current time in accordance with a nonlinear function that disregards the timing and time information extracted from the received frame (along with its weighting) if its distance from the local currently assumed time in the timekeeping device is greater than a predefined or dynamic threshold. This it to avoid incorrect timing adjustments that could be caused by erroneous reception of the timing or time information, the likelihood of which increases as the SINR conditions are more severe.
- In one embodiment, a dynamically adaptive threshold considers the duration over which the time-keeping device has been maintaining the time and the statistics of the time corrections applied throughout that duration. For example, a time keeping device that has been tracking the time for an entire year, while performing weekly timing adjustments averaging 0.8 sec, with the greatest correction being below 1.5 seconds in magnitude, may act to disregard a reception instance suggesting a timing correction of 4 seconds, whereas it would have been considered and weighted at an earlier point in time during that year.
- When the time-keeping device takes into account the timing information extracted by correlating the appropriate portion of the received signal against the known synchronization sequence, an example embodiment of the present invention may perform such an operation utilizing linear combining wherein the coefficient applied towards the timing extracted from the received signal and the coefficient applied for the locally assumed time depend on the levels of confidence in these two timings variables. If, for example, the reception conditions are determined to be excessively noisy, for which the probability of inaccurate timing extraction is higher, whereas the locally assumed time is based on a relatively recent adjustment and a good record of successive timing adjustments suggests that not much drift could have been experienced up until the instance of the reception at question, then relatively low weighting may be applied towards the received timing versus the locally assumed one. If, in contrast, the received timing is accompanied by an indication of high SINR, suggesting a high probability that it is accurate, then it may receive higher weighting compared to that of the locally assumed timing.
- In one embodiment, a time-keeping device operating in accordance with the present invention applies non-linear logic in its reception of time information when a locally assumed time is available and has been validated over time. If the device attempts to extract from a received frame not only the timing information, for the purpose of timing adjustment, but also time information, despite such information already being available to it, then rather than computing a new time based on a linear combination of the received time and the locally assumed one, it is to select one of the two. If the locally assumed time has been validated over time and the received frame is received with errors or is accompanied by a low SINR indication, then the device may disregard the information extracted from the receiver. If, however, the device's confidence in its locally assumed time is low and the received signal is accompanied by an indication of reliable reception, then the received time may be selected, or one or more additional frames may be received to further increase the confidence in the received information.
- In an alternative embodiment, non-antipodal phase modulation can be used to modulate the PWM signal. For example, the magnitude of phase modulation applied may be set at any value less than 180°, e.g., ±45°, ±25°, ±13°, etc. Use of a lower value such as ±13° ensures that the modulated signal is contained within a narrow bandwidth and does not escape the narrow filtering in typical existing AM receivers, which is on the order of 10 Hz. Note that such narrowband PM is not comparable in performance to antipodal BPSK, where the two symbols are 180° apart exhibiting a correlation factor of −1.
- A diagram illustrating an example receiver incorporating both amplitude and phase modulation receiver paths is shown in
FIG. 12 . In this example embodiment, the receiver is operative to receive both a legacy PWM/AM modulated broadcast signal as well as a phase modulated signal which is transmitted over the legacy PWM/AM signal. The receiver, generally referenced 100, comprises anAM receiver block 104 and aPM receiver block 102, both of which are connected toantenna 106 at their input and toprocessor 124 at their output. -
Amplitude modulation receiver 104 comprises an envelope-detector-based receiver of the type that is typically used in consumer market RCC devices. TheAM receiver 104 comprises band pass filter (e.g., crystal filter) 110,envelope detector 112 andthreshold block 114. As shown in this block diagram, the AM signal is converted into an analog equivalent baseband signal by use of a conventional nonlinear envelope detector 112 (similar to the diode-based circuit in traditional AM receivers). Athreshold operation 114 that follows serves to determine the middle level, around which the voltages below it would be converted to a logic low level and the voltages above it to a logic high level. The digital processing stage that follows this operation measures the pulse durations and accordingly recovers the symbols (‘1’, ‘0’, or ‘marker’). Note that, with such a receiver topology, an on-frequency interferer can cause the receiver to decode that symbol incorrectly. Typically, the effect of the interferer is greatest when the signal is at a “low”. If the interferer is exactly on-frequency, however, then it has a very significant effect when it is out of phase and added to the high state of the transmitted signal (e.g., the WWVB signal). - In operation of a typical envelope detector based receiver, the modulated signal input to the receiver has two different amplitude levels with the information represented in the durations of each of these levels. The high/low decision is made by following the “low” and “high” levels with dedicated peak holders (with appropriate time-constants) and deriving the middle (average) of these two. A threshold operation (e.g., a simple comparator) is then used to create the logic level signals for the digital stage that follows where the pulse durations are measured and the ‘1’/‘0’/‘marker’ symbol decision is made.
- The
phase modulation receiver 102 comprises ademodulator 118,correlator 120 anddecoder 122. In one embodiment, thePM receiver 102 is operative to receive the signal broadcast from WWVB in Fort Collins, Colo. This broadcast signal adds phase modulation (PM) to the WWVB broadcast while maintaining the existing AM code, so as not to impact the existing time-of-day RCC devices. - A diagram illustrating an example receiver adapted to receive a phase modulated signal is shown in
FIG. 13 . In one embodiment, the receiver, generally referenced 130, comprises a coherent BPSK optimal receiver that may be implemented digitally. ThePM receiver 130 comprisesantenna 132 coupled to analog front end (AFE) 134, low pass filter (LPF) 136, analog to digital converter (ADC) 138,mixer 140, local synthesized carrier (e.g., local oscillator (LO)) 146, correlator 143 andthreshold detector 144. The filtering of the signal is based on the correlation operation which is followed by a decision that is made in the presence of AWGN. - The bit-error-rate (BER) performance of the receiver, for a signal to noise ratio Eb/No, is given by
-
- where Eb is the energy per bit and No is the noise density.
- The Eb/No ratio is equivalent to the ratio between the power of the signal and the power of the noise in a bandwidth that is equal to the bit rate, i.e. Eb/No=SNR @ BW=Rb, where Rb represents the bit rate. The
threshold decision block 144 is where the decisions are made and the errors occur, in direct relation to the variance of noise, which is assumed to have Gaussian nature and equal variances around the ‘0’ and ‘1’ symbols. The BER may also be expressed as a function of the distance between the symbols in the signal space, as follows -
- where Q(x) is the tail probability of the normal distribution, i.e.
-
- As previously noted, the analysis presented for the improvement obtained through the introduction of the phase modulation scheme assumed only the presence of AWGN in the receiver. In the presence of radio frequency interference (RFI), and particularly on-frequency interference, the performance improvement could be much more significant and stems from the structure of the BPSK receiver, where the demodulation is based on correlation.
- A diagram illustrating a first example phase modulation added to an amplitude modulated carrier in an example communication protocol is shown in
FIG. 14 . The waveform illustrates three consecutive example bits in the transmission as a time-domain waveform 150. The threebits first portion 160 for which the carrier power is low and asecond portion 162 for which the carrier power is high. In the WWVB protocol, the information in each bit depends on the durations of these two portions with an even 0.5/0.5 sec partition representing a “1” bit, and the uneven 0.2/0.8 sec partition representing a “0” bit. A 0.8/0.2 sec partition represents a ‘marker’ bit, which may be used for timing identification, but does not carry information. The bits represented under the legacy PWM/AM modulation are indicated at the top portion of the diagram. For example, the three PWM/AM bits shown are “1”, “0” and “1”. - In accordance with an embodiment of the present invention, information is added to the existing modulation using BPSK modulation. A “1” is represented by a carrier having an inverted phase, with the
phase inversion 158 occurring at the beginning of the bit, as shown for thethird bit 156 at t=2 sec. It is noted that the phase inversion may also be performed at any other instance, e.g., during the low amplitude portion of the carrier if the receiver's phase demodulation operation is limited to the high-amplitude duration and disregards the low amplitude portion. While the information represented by the pulse widths is shown to be “1”, “0”, “1”, the information that is sent in parallel, in accordance with the example BPSK (or PRK) protocol of the present invention, is shown to be “0”, “0”, “1” (as shown along the bottom portion of the diagram). Note that there is not necessarily any relationship between the bit pattern transmitted using PWM/AM and that transmitted using PM as they can be completely independent. It is noted that the carrier frequency is not shown to scale in the figure to enhance clarity, but it is preferable for the phase transitions to occur at zero crossing instances of the carrier. - A diagram illustrating a second example phase modulation added to an amplitude modulated carrier in an example communication protocol is shown in
FIG. 15 . In this second example, the carrier amplitude transmitted during the low portions of a bit is zero rather than reduced to a lower value (e.g., −17 dB or 0.14 amplitude level) as is the case inFIG. 14 . As inFIG. 14 , the waveform illustrates three consecutive example bits in the transmission as a time-domain waveform 170. The threebits first portion 178 for which the carrier power is zero and asecond portion 180 for which the carrier power is high. - In accordance with the present invention, the modulation of information is added to the existing modulation using BPSK modulation. A “1” is represented by a carrier having an inverted phase, with the
phase inversion 182 occurring at the beginning of the bit as shown for thethird bit 176 at t=2.5 sec. While the information represented by the pulse widths is shown to be “1”, “0”, “1”, the information that is sent in parallel, in accordance with the BPSK (or PRK) protocol of the present invention, is shown to be “0”, “0”, “1” (as shown along the bottom portion of the diagram). - Note that there is not necessarily any relationship between the bit pattern transmitted using PWM/AM and that transmitted using PM as they can be completely independent. It is noted that the carrier frequency is not shown to scale in the figure to enhance clarity, but it is preferable for the phase transitions to occur at zero crossing instances of the carrier.
- A diagram illustrating an example phase modulated carrier in an example communication protocol is shown in
FIG. 16 . In this third example, the phase modulation is not added to a PWM/AM signal but rather is sent as the entire bit duration. The waveform illustrates three consecutive example bits in the transmission as a time-domain waveform 190. The threebits phase inversion 198 occurring at the beginning of the bit, as shown for thethird bit 196 at t=2 sec. The information sent in accordance with the BPSK protocol of the present invention is shown to be “0”, “0”, “1” (as shown along the bottom portion of the diagram). It is noted that the carrier frequency is not shown to scale in the figure to enhance clarity, but it is preferable for the phase transitions to occur at zero crossing instances of the carrier, as may be implemented easily when a bit spans an integer number of carrier cycles, as is the case for WWVB, where the carrier frequency is 60 kHz (i.e. 60,000 cycles per bit). - A diagram illustrating the structure of an example super frame incorporating timing and time information is shown in
FIG. 17 . In an alternative embodiment, information is recovered not only from the bits of a frame, but may also be recovered by using multiple consecutive frames making up a superframe. In this embodiment, additional information may be conveyed using the superframe, or the same information from each frame may be repeated to allow for improved reception based on the accumulated energy of multiple frames. - The use of superframes can potentially improve performance of the receiver by nearly two orders of magnitude, which may be critical in low SNR conditions. In one embodiment, the polarity of each of the one-minute frames in an hour is modulated (e.g., differentially or otherwise) by a corresponding bit in a 60-bit hour-synchronization sequence. The preserved consistency between the polarities of the synchronization sequence and the information in each of one-minute frames permits the receiver to resolve the 180-degree phase ambiguity of BPSK reception.
- By correlating against multiple consecutive synchronization sequences, the receiver can accurately adjust its timing and can then use recorded data from an entire hour to perform long-term integration for the hour field (i.e. soft addition). This provides an improvement in gain of 60 (i.e. 18 d B), which enables operation at SNIR values well below 0 dB (when evaluated in a 1 Hz bandwidth). While the minute and parity fields for the time information vary from one minute to the next in the course of an hour, all other fields, however, remain fixed. Thus, simple addition can be used to increase the total amount of energy involved in the information recovery. Since the pattern according to which the minute frame is changing is also known, it too can serve in the extended reception operation. The receiver may determine its timing with respect to the beginning of an hour based on the identification of a portion of the hour-synchronization sequence (at least six bits, collected over seven minutes) with or without recovering information from the minute fields in the received frames.
- With reference to
FIG. 17 , aframe 216 comprises asynchronization sequence field 218,hour field 220,minute field 222 and zero or moreadditional fields 224. A superframe (e.g., superframe P 212) is defined as a set of multiple frames (e.g., 60 frames) wherein the phase of one or more fields in each frame may be modulated to convey information on a superframe basis. For example, additional timing information can be conveyed by modulating the phase of the synchronization sequence field to define a super-synchronization sequence. Each synchronization sequence (i.e. sync seq 0, sync seq 1, . . . , sync seq 59) is assigned a particular phase wherein the pattern is known to all receivers. The receivers use their knowledge of the super-synchronization sequence to aid in adjusting their time to a particular minute within the hour without having to recover the information from the minute field. Such a super-synchronization sequence provides additional information for receivers to aid in acquisition and tracking at low SINR conditions. - The use of superframes provides system scalability in that it allows for receivers experiencing different reception conditions to use the received signal differently. In particular, superframes (or the use of a number of multiple frames) allow for the accumulation of received energy over multiple one-minute frames to provide for a corresponding gain in the receiver. For example, reception for an entire hour may provide a gain of 60 or 18 dB with respect to reception over a single minute (i.e. a single frame).
- The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
- The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. As numerous modifications and changes will readily occur to those skilled in the art, it is intended that the invention not be limited to the limited number of embodiments described herein. Accordingly, it will be appreciated that all suitable variations, modifications and equivalents may be resorted to, falling within the spirit and scope of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.
Claims (30)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/563,246 US20130121398A1 (en) | 2011-11-15 | 2012-07-31 | Timing and Time Information Extraction from a Phase Modulated Signal in a Radio Controlled Clock Receiver |
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US201161559966P | 2011-11-15 | 2011-11-15 | |
US13/345,084 US8270465B1 (en) | 2011-11-15 | 2012-01-06 | Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver |
US13/563,246 US20130121398A1 (en) | 2011-11-15 | 2012-07-31 | Timing and Time Information Extraction from a Phase Modulated Signal in a Radio Controlled Clock Receiver |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/345,084 Continuation US8270465B1 (en) | 2011-11-15 | 2012-01-06 | Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver |
Publications (1)
Publication Number | Publication Date |
---|---|
US20130121398A1 true US20130121398A1 (en) | 2013-05-16 |
Family
ID=46800747
Family Applications (8)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/345,084 Expired - Fee Related US8270465B1 (en) | 2011-11-15 | 2012-01-06 | Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver |
US13/422,601 Expired - Fee Related US8774317B2 (en) | 2011-11-15 | 2012-03-16 | System and method for phase modulation over a pulse width modulated/amplitude modulated signal for use in a radio controlled clock receiver |
US13/424,733 Expired - Fee Related US8300687B1 (en) | 2011-11-15 | 2012-03-20 | Timing and time information extraction in a radio controlled clock receiver |
US13/424,807 Expired - Fee Related US8467273B2 (en) | 2011-11-15 | 2012-03-20 | Leap second and daylight saving time correction for use in a radio controlled clock receiver |
US13/563,246 Abandoned US20130121398A1 (en) | 2011-11-15 | 2012-07-31 | Timing and Time Information Extraction from a Phase Modulated Signal in a Radio Controlled Clock Receiver |
US13/591,757 Abandoned US20130121118A1 (en) | 2011-11-15 | 2012-08-22 | Leap Second and Daylight Saving Time Correction in a Radio Controlled Clock Receiver |
US13/663,184 Abandoned US20130121399A1 (en) | 2011-11-15 | 2012-10-29 | Timing and Time Information Extraction in a Radio Controlled Clock Receiver |
US13/678,223 Expired - Fee Related US8605778B2 (en) | 2011-11-15 | 2012-11-15 | Adaptive radio controlled clock employing different modes of operation for different applications and scenarios |
Family Applications Before (4)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/345,084 Expired - Fee Related US8270465B1 (en) | 2011-11-15 | 2012-01-06 | Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver |
US13/422,601 Expired - Fee Related US8774317B2 (en) | 2011-11-15 | 2012-03-16 | System and method for phase modulation over a pulse width modulated/amplitude modulated signal for use in a radio controlled clock receiver |
US13/424,733 Expired - Fee Related US8300687B1 (en) | 2011-11-15 | 2012-03-20 | Timing and time information extraction in a radio controlled clock receiver |
US13/424,807 Expired - Fee Related US8467273B2 (en) | 2011-11-15 | 2012-03-20 | Leap second and daylight saving time correction for use in a radio controlled clock receiver |
Family Applications After (3)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/591,757 Abandoned US20130121118A1 (en) | 2011-11-15 | 2012-08-22 | Leap Second and Daylight Saving Time Correction in a Radio Controlled Clock Receiver |
US13/663,184 Abandoned US20130121399A1 (en) | 2011-11-15 | 2012-10-29 | Timing and Time Information Extraction in a Radio Controlled Clock Receiver |
US13/678,223 Expired - Fee Related US8605778B2 (en) | 2011-11-15 | 2012-11-15 | Adaptive radio controlled clock employing different modes of operation for different applications and scenarios |
Country Status (2)
Country | Link |
---|---|
US (8) | US8270465B1 (en) |
WO (5) | WO2013074159A1 (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20100124331A1 (en) * | 2008-11-18 | 2010-05-20 | Qualcomm Incorprated | Spectrum authorization and related communications methods and apparatus |
Families Citing this family (35)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US8401600B1 (en) | 2010-08-02 | 2013-03-19 | Hypres, Inc. | Superconducting multi-bit digital mixer |
US8533516B2 (en) | 2010-09-22 | 2013-09-10 | Xw Llc | Low power radio controlled clock incorporating independent timing corrections |
US8270465B1 (en) | 2011-11-15 | 2012-09-18 | Xw Llc | Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver |
US8693582B2 (en) | 2012-03-05 | 2014-04-08 | Xw Llc | Multi-antenna receiver in a radio controlled clock |
JP5842908B2 (en) * | 2013-12-26 | 2016-01-13 | カシオ計算機株式会社 | Radio clock |
JP6075297B2 (en) * | 2014-01-14 | 2017-02-08 | カシオ計算機株式会社 | Radio clock |
EP4277170A3 (en) * | 2014-11-20 | 2024-01-17 | Panasonic Intellectual Property Corporation of America | Transmitting method, receiving method, transmitting device, and receiving device |
US9537687B2 (en) | 2015-02-04 | 2017-01-03 | Qualcomm Incorporated | Multi-modulation for data-link power reduction and throughput enhancement |
US9948920B2 (en) | 2015-02-27 | 2018-04-17 | Qualcomm Incorporated | Systems and methods for error correction in structured light |
US9621197B2 (en) | 2015-03-10 | 2017-04-11 | Samsung Electronics Co., Ltd. | Bi-phased on-off keying (OOK) transmitter and communication method |
US10068338B2 (en) | 2015-03-12 | 2018-09-04 | Qualcomm Incorporated | Active sensing spatial resolution improvement through multiple receivers and code reuse |
US9530215B2 (en) | 2015-03-20 | 2016-12-27 | Qualcomm Incorporated | Systems and methods for enhanced depth map retrieval for moving objects using active sensing technology |
US9712188B2 (en) | 2015-05-04 | 2017-07-18 | International Business Machines Corporation | Decoding data stored with three orthogonal codewords |
US9606868B2 (en) * | 2015-05-04 | 2017-03-28 | International Business Machines Corporation | Encoding and writing of data on multitrack tape |
US9635339B2 (en) | 2015-08-14 | 2017-04-25 | Qualcomm Incorporated | Memory-efficient coded light error correction |
US9846943B2 (en) | 2015-08-31 | 2017-12-19 | Qualcomm Incorporated | Code domain power control for structured light |
US9747790B1 (en) * | 2016-02-12 | 2017-08-29 | King Fahd University Of Petroleum And Minerals | Method, device, and computer-readable medium for correcting at least one error in readings of electricity meters |
JP6508096B2 (en) * | 2016-03-16 | 2019-05-08 | カシオ計算機株式会社 | Satellite radio wave receiver, radio wave clock, date and time information output method, and program |
DE102016014375B4 (en) * | 2016-12-03 | 2018-06-21 | Diehl Metering Systems Gmbh | Method for improving the transmission quality between a data collector and a plurality of autonomous measuring units and communication system |
FR3071688B1 (en) * | 2017-09-22 | 2019-09-27 | Thales | METHOD FOR SYNCRONIZING A DEVICE ASSEMBLY, COMPUTER PROGRAM, AND SYNCRONIZATION SYSTEM THEREOF |
JP6825525B2 (en) * | 2017-09-27 | 2021-02-03 | カシオ計算機株式会社 | Electronic clocks, control methods and programs |
KR102397095B1 (en) | 2017-11-17 | 2022-05-12 | 삼성전자주식회사 | Method and apparatus for detecting object using radar of vehicle |
US10581684B2 (en) | 2017-12-06 | 2020-03-03 | Schweitzer Engineering Laboratories, Inc. | Network management via a secondary communication channel in a software defined network |
US10560390B2 (en) | 2018-03-05 | 2020-02-11 | Schweitzer Engineering Laboratories, Inc. | Time-based network operation profiles in a software-defined network |
US10756956B2 (en) | 2018-03-05 | 2020-08-25 | Schweitzer Engineering Laboratories, Inc. | Trigger alarm actions and alarm-triggered network flows in software-defined networks |
US10812392B2 (en) * | 2018-03-05 | 2020-10-20 | Schweitzer Engineering Laboratories, Inc. | Event-based flow control in software-defined networks |
CN108762048A (en) * | 2018-06-01 | 2018-11-06 | 齐鲁工业大学 | A method of realizing distribution terminal clock synchronization using power frequency current signal |
CN110290090B (en) * | 2019-07-09 | 2021-08-10 | 南京航空航天大学 | Time amplitude phase joint modulation and demodulation method |
US11425033B2 (en) | 2020-03-25 | 2022-08-23 | Schweitzer Engineering Laboratories, Inc. | SDN flow path modification based on packet inspection |
US11201759B1 (en) | 2020-07-08 | 2021-12-14 | Schweitzer Engineering Laboratories, Inc. | Reconfigurable dual-ring network redundancy |
CN112034698B (en) * | 2020-08-31 | 2021-07-02 | 天津津航计算技术研究所 | Universal time service and timing method |
US20220407528A1 (en) * | 2021-06-22 | 2022-12-22 | Texas Instruments Incorporated | Methods and systems for atomic clocks with high accuracy and low allan deviation |
US11677663B2 (en) | 2021-08-12 | 2023-06-13 | Schweitzer Engineering Laboratories, Inc. | Software-defined network statistics extension |
CN113917833A (en) * | 2021-09-18 | 2022-01-11 | 广西电网有限责任公司柳州供电局 | Time synchronization device and time synchronization method |
US11882002B2 (en) | 2022-06-22 | 2024-01-23 | Schweitzer Engineering Laboratories, Inc. | Offline test mode SDN validation |
Family Cites Families (55)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3406343A (en) | 1965-07-01 | 1968-10-15 | Rca Corp | Pm/am multiplex communication |
US3648173A (en) | 1970-08-07 | 1972-03-07 | Us Navy | Time recovery system from a pulse-modulated radio wave |
US4217467A (en) | 1974-07-19 | 1980-08-12 | Nippon Telegraph & Telephone Public Corporation | Amplitude and periodic phase modulation transmission system |
US4117661A (en) | 1975-03-10 | 1978-10-03 | Bryant Jr Ellis H | Precision automatic local time decoding apparatus |
JPS5920860A (en) | 1982-07-28 | 1984-02-02 | Hitachi Ltd | Digital output type integration circuit |
US4500985A (en) | 1982-12-08 | 1985-02-19 | At&T Bell Laboratories | Communication path continuity verification arrangement |
US4525685A (en) * | 1983-05-31 | 1985-06-25 | Spectracom Corp. | Disciplined oscillator system with frequency control and accumulated time control |
US4768178A (en) | 1987-02-24 | 1988-08-30 | Precision Standard Time, Inc. | High precision radio signal controlled continuously updated digital clock |
DE3726524A1 (en) | 1987-08-10 | 1989-02-23 | Fresenius Ag | HAEMOGLOBIN DETECTOR |
DE19514031C2 (en) | 1995-04-13 | 1997-07-10 | Telefunken Microelectron | Method for detecting the beginning of time frames |
US6041082A (en) | 1996-09-06 | 2000-03-21 | Nec Corporation | Digital amplitude modulation amplifier and television broadcasting machine |
US6124960A (en) | 1997-09-08 | 2000-09-26 | Northern Telecom Limited | Transmission system with cross-phase modulation compensation |
US6295442B1 (en) | 1998-12-07 | 2001-09-25 | Ericsson Inc. | Amplitude modulation to phase modulation cancellation method in an RF amplifier |
US7027773B1 (en) | 1999-05-28 | 2006-04-11 | Afx Technology Group International, Inc. | On/off keying node-to-node messaging transceiver network with dynamic routing and configuring |
US6212133B1 (en) | 1999-07-26 | 2001-04-03 | Mccoy Kim | Low power GPS receiver system and method of using same |
US6862317B1 (en) | 2000-07-25 | 2005-03-01 | Thomson Licensing S.A. | Modulation technique providing high data rate through band limited channels |
US6937668B2 (en) | 2001-03-28 | 2005-08-30 | Spectra Wireless, Inc. | Method of and apparatus for performing modulation |
CA2443992A1 (en) | 2001-04-13 | 2002-10-24 | Salton, Inc. | Appliance having a clock set to universal time |
US20030169641A1 (en) | 2002-03-08 | 2003-09-11 | Quartex A Division Of Primex, Inc. | Time keeping system with automatic daylight savings time adjustment |
US7402897B2 (en) | 2002-08-08 | 2008-07-22 | Elm Technology Corporation | Vertical system integration |
US7394870B2 (en) | 2003-04-04 | 2008-07-01 | Silicon Storage Technology, Inc. | Low complexity synchronization for wireless transmission |
US20040239415A1 (en) * | 2003-05-27 | 2004-12-02 | Bishop Christopher Brent | Methods of predicting power spectral density of a modulated signal and of a multi-h continuous phase modulated signal |
DE10334990B4 (en) | 2003-07-31 | 2016-03-17 | Atmel Corp. | Radio Clock |
US20050073911A1 (en) | 2003-10-06 | 2005-04-07 | Barnett Steven R. | Electronic prayer alert |
US7346098B2 (en) | 2003-11-25 | 2008-03-18 | Freescale Semiconductor, Inc. | Communication receiver |
US7324615B2 (en) * | 2003-12-15 | 2008-01-29 | Microchip Technology Incorporated | Time signal receiver and decoder |
US20050141648A1 (en) * | 2003-12-24 | 2005-06-30 | Microchip Technology Incorporated | Time signal peripheral |
DE102004004416A1 (en) * | 2004-01-29 | 2005-08-18 | Atmel Germany Gmbh | Method for determining the signal quality of a transmitted time signal |
DE102004005340A1 (en) | 2004-02-04 | 2005-09-01 | Atmel Germany Gmbh | Method for obtaining time information, receiver circuit and radio clock |
JP2005227203A (en) * | 2004-02-16 | 2005-08-25 | Citizen Watch Co Ltd | Radio controlled watch and its control method |
US20050213433A1 (en) * | 2004-03-24 | 2005-09-29 | Mah Pat Y | Localized signal radio adjusted clock |
GB2417860A (en) * | 2004-09-01 | 2006-03-08 | Tak Ming Leung | Identifying the modulation format of a received signal |
US7411870B2 (en) | 2004-09-30 | 2008-08-12 | Casio Computer Co., Ltd. | Radio-wave timepieces and time information receivers |
JP4322786B2 (en) | 2004-11-29 | 2009-09-02 | Okiセミコンダクタ株式会社 | Multiple standard radio wave decoding method and standard radio wave receiver |
US7684473B2 (en) | 2005-06-01 | 2010-03-23 | Qualcomm Incorporated | Receiver for wireless communication network with extended range |
US7636397B2 (en) * | 2005-09-07 | 2009-12-22 | Mclaughlin Michael | Method and apparatus for transmitting and receiving convolutionally coded data for use with combined binary phase shift keying (BPSK) modulation and pulse position modulation (PPM) |
JP2007139703A (en) * | 2005-11-22 | 2007-06-07 | Casio Comput Co Ltd | Time receiving apparatus and radio controlled timepiece |
JP4699882B2 (en) | 2005-11-22 | 2011-06-15 | ルネサスエレクトロニクス株式会社 | Voltage-pulse conversion circuit and charge control system |
DE102005056483B3 (en) | 2005-11-26 | 2007-01-11 | Atmel Germany Gmbh | Time information receiving e.g. for radio clock, involves having characteristic value of temporal duration compared to signal phase of certain signal level of digital signal with desired value |
JP4882610B2 (en) * | 2005-12-20 | 2012-02-22 | セイコーエプソン株式会社 | Radio correction clock and radio correction clock time correction method |
US7719928B2 (en) | 2006-06-08 | 2010-05-18 | Seiko Epson Corporation | Radio watch |
JP4882561B2 (en) * | 2006-07-12 | 2012-02-22 | セイコーエプソン株式会社 | Receiver circuit and radio correction clock |
JP2008051705A (en) * | 2006-08-25 | 2008-03-06 | Seiko Epson Corp | Radio-controlled timepiece and method of modifying its waveform discrimination standard |
US7215600B1 (en) | 2006-09-12 | 2007-05-08 | Timex Group B.V. | Antenna arrangement for an electronic device and an electronic device including same |
US8468244B2 (en) | 2007-01-05 | 2013-06-18 | Digital Doors, Inc. | Digital information infrastructure and method for security designated data and with granular data stores |
JP2008241354A (en) | 2007-03-26 | 2008-10-09 | Casio Comput Co Ltd | Time information receiving device and radio controlled timepiece |
US7903501B2 (en) * | 2007-07-10 | 2011-03-08 | Seiko Epson Corporation | Radio-controlled timepiece and control method for a radio-controlled timepiece |
US8249616B2 (en) | 2007-08-23 | 2012-08-21 | Texas Instruments Incorporated | Satellite (GPS) assisted clock apparatus, circuits, systems and processes for cellular terminals on asynchronous networks |
US7974580B2 (en) | 2007-08-28 | 2011-07-05 | Qualcomm Incorporated | Apparatus and method for modulating an amplitude, phase or both of a periodic signal on a per cycle basis |
JP5168164B2 (en) * | 2008-05-02 | 2013-03-21 | セイコーエプソン株式会社 | Radio correction clock and control method thereof |
US7872545B2 (en) | 2008-09-18 | 2011-01-18 | Infineon Technologies Ag | Jumpless phase modulation in a polar modulation environment |
JP2010199799A (en) | 2009-02-24 | 2010-09-09 | Renesas Electronics Corp | Analog/digital conversion circuit |
JP5609310B2 (en) | 2009-09-01 | 2014-10-22 | セイコーエプソン株式会社 | Antenna built-in clock |
US8533516B2 (en) | 2010-09-22 | 2013-09-10 | Xw Llc | Low power radio controlled clock incorporating independent timing corrections |
US8270465B1 (en) | 2011-11-15 | 2012-09-18 | Xw Llc | Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver |
-
2012
- 2012-01-06 US US13/345,084 patent/US8270465B1/en not_active Expired - Fee Related
- 2012-03-16 US US13/422,601 patent/US8774317B2/en not_active Expired - Fee Related
- 2012-03-20 US US13/424,733 patent/US8300687B1/en not_active Expired - Fee Related
- 2012-03-20 US US13/424,807 patent/US8467273B2/en not_active Expired - Fee Related
- 2012-07-31 US US13/563,246 patent/US20130121398A1/en not_active Abandoned
- 2012-07-31 WO PCT/US2012/049029 patent/WO2013074159A1/en active Application Filing
- 2012-08-22 US US13/591,757 patent/US20130121118A1/en not_active Abandoned
- 2012-10-29 US US13/663,184 patent/US20130121399A1/en not_active Abandoned
- 2012-11-13 WO PCT/US2012/064807 patent/WO2013074510A1/en active Application Filing
- 2012-11-13 WO PCT/US2012/064799 patent/WO2013074505A1/en active Application Filing
- 2012-11-13 WO PCT/US2012/064823 patent/WO2013074519A1/en active Application Filing
- 2012-11-15 WO PCT/US2012/065278 patent/WO2013074789A2/en active Application Filing
- 2012-11-15 US US13/678,223 patent/US8605778B2/en not_active Expired - Fee Related
Non-Patent Citations (2)
Title |
---|
Cherenkov, "Employment of phase modulation to transmit standard signals", Plenum 1984. * |
Lichtenecker, "Terrestrial time signal dissemination", Kluwer 1997, discloses the use of BPSK in DCF77 system (see section 3.4). * |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20100124331A1 (en) * | 2008-11-18 | 2010-05-20 | Qualcomm Incorprated | Spectrum authorization and related communications methods and apparatus |
US8848914B2 (en) * | 2008-11-18 | 2014-09-30 | Qualcomm Incorporated | Spectrum authorization and related communications methods and apparatus |
Also Published As
Publication number | Publication date |
---|---|
US8300687B1 (en) | 2012-10-30 |
US8774317B2 (en) | 2014-07-08 |
US8270465B1 (en) | 2012-09-18 |
US8605778B2 (en) | 2013-12-10 |
WO2013074789A2 (en) | 2013-05-23 |
WO2013074789A3 (en) | 2013-07-11 |
WO2013074519A1 (en) | 2013-05-23 |
WO2013074510A1 (en) | 2013-05-23 |
US20130121397A1 (en) | 2013-05-16 |
WO2013074159A1 (en) | 2013-05-23 |
WO2013074505A1 (en) | 2013-05-23 |
US8467273B2 (en) | 2013-06-18 |
US20130121399A1 (en) | 2013-05-16 |
US20130121118A1 (en) | 2013-05-16 |
US20130121117A1 (en) | 2013-05-16 |
US20130121400A1 (en) | 2013-05-16 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US8270465B1 (en) | Timing and time information extraction from a phase modulated signal in a radio controlled clock receiver | |
US8533516B2 (en) | Low power radio controlled clock incorporating independent timing corrections | |
US8693582B2 (en) | Multi-antenna receiver in a radio controlled clock | |
US20070140064A1 (en) | Radio-controlled timepiece and method of adjusting the time kept by a radio-controlled timepiece | |
JP4631667B2 (en) | Time receiver and radio clock | |
JP3903986B2 (en) | Time information transmission / reception device and time information transmission / reception circuit | |
CN103620443A (en) | Navigation signal transmitter and navigation signal generating method | |
Engeler | Performance analysis and receiver architectures of DCF77 radio-controlled clocks | |
JP4264494B2 (en) | Standard radio wave reception time device | |
JP2010019617A (en) | Time information acquisition apparatus and radio-controlled timepiece | |
Lowe et al. | New improved system for WWVB broadcast | |
Liang et al. | WWVB time signal broadcast: An enhanced broadcast format and multi-mode receiver | |
US10165530B2 (en) | Verification of time information transmitted by time signals or time telegrams | |
Liang et al. | A new broadcast format and receiver architecture for radio controlled clocks | |
Mills | A precision radio clock for WWV transmissions | |
JP2002286877A (en) | Method and apparatus of deciding start timing of time frame, time information detector and radio-controlled clock | |
Liang | An enhanced broadcast format and multi-mode receiver for WWVB time signal radio | |
JP5810978B2 (en) | Time information acquisition device and radio clock | |
Liang et al. | Interference-robustness improvement in BPSK receivers for the enhanced WWVB broadcast | |
Series | Protection criteria for systems in the standard frequency and time signal services | |
US11119449B2 (en) | Electronic timepiece | |
JP2005062077A (en) | Electric wave receiving device, electric wave clock and repeater | |
Huber et al. | Clock Synchronisation and Time Dissemination | |
Barman et al. | Maximum likelihood clock and carrier recovery in a direct sequence spread spectrum communication system | |
JP2004354304A (en) | Time signal converter |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: GRINDSTONE CAPITAL, LLC, MICHIGAN Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:XW, LLC;REEL/FRAME:029210/0527 Effective date: 20121015 |
|
AS | Assignment |
Owner name: GRINDSTONE CAPITAL, LLC, MICHIGAN Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:XW, LLC;REEL/FRAME:030186/0156 Effective date: 20121231 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |
|
AS | Assignment |
Owner name: GRINDSTONE CAPITAL, LLC, MICHIGAN Free format text: SECURITY INTEREST;ASSIGNOR:EVERSET TECHNOLOGIES, INC.;REEL/FRAME:033279/0918 Effective date: 20140225 |