Wireless System Using Sleep State Modulation

Abstract

A low-power transmission system for periodic data transmissions communicates the periodic data as the interval between two transmitted anchor symbols when the transmitter and associated circuitry are off. Significant power savings are achieved for short data words by using a star topology that eliminates receiver power consumption. Multi-bit anchor symbols provide improved error detection and allow for separation of simultaneous transmissions from multiple transmitters by a single receiver.

Description

[0001] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. patent application 16 / 456,299, filed June 28, 2019, which is hereby incorporated by reference. Background Art

[0004] The present invention relates generally to radio transmitters and receivers and, in particular, to a low power data transmission system suitable for battery powered remote sensors.

[0005] Real-time data monitoring using wireless sensors can be useful in a wide range of applications including, for example, “smart agriculture,” where such sensors can perform soil moisture measurements or provide livestock monitoring, and medicine, where wearable sensors can monitor the vital signs of ambulatory patients, as well as a range of other similar mobile and fixed applications.

[0006] Ideally, these wireless sensors offer long communication range (to provide flexibility for remote sensing) and low power consumption (to manage battery power and long life).

[0007] The balance between long communication range and low power consumption is typically managed by placing the transmitter in a low-power mode between sensor reading transmissions. In this low-power mode, the transmitter and sensor inputs can be disabled, and the receiver operates in a reduced power configuration to monitor for incoming messages. When data collection is needed, the transmitter wakes up, and sensor readings can be acquired and transmitted, after which the transmitter is placed back into low-power mode until the next transmission time. This approach essentially balances transmit power with data rate, reducing the average transmit power but also reducing the transmit time and, therefore, the amount of data communicated.

[0008] An interesting possibility for further reducing transmission power is to transmit the data not by transmitting a radio signal holding the data, but rather by sending two anchor symbols (a start symbol and a stop symbol) and turning off the transmitter between these transmissions. The data is then derived from the length of the transmitter "off" time. A discussion of this possibility is provided in the 2005 paper by Zhu and Sivakumar entitled "Challenges: Communication through Silence in Wireless Sensor Networks," which is incorporated herein by reference.

[0009] This "powerless" transmission technique has not been widely adopted, if at all. This is likely because significant energy savings can only be achieved with long data words, and the technique has so far been fundamentally limited in data word length. This limitation arises because the amount of time required for data transmission is exponentially related to the data word length. For example, consider a 20-bit data word that is typically transmitted in 20 clock cycles. Transmitting this data word by measuring the duration between two anchor symbols would require over a million clock cycles.

[0010] Attempts to enhance energy savings in transmitters employing powerless transmission have led researchers to explore complex techniques such as single-bit anchor symbols that can be transmitted with low power and baseband radio transmitters to eliminate carrier synchronization time, but these approaches are difficult to implement with existing hardware or have significant range limitations. Summary of the Invention

[0011] The present invention has recognized that an important class of data monitoring applications can be implemented in a star topology, thereby eliminating the need for radio receiver circuitry. By eliminating the power consumption of such circuitry and employing "deep" sleep during periods of no-power transmission for both the transmitter and the transmitter processor, the present invention can provide up to three times the energy savings of comparable low-power transmission techniques. Importantly, the savings are achieved using standard carrier modulation transmission, which provides substantial range, and multi-bit anchor data, which allows for robust addressing and collision avoidance in multi-sensor environments.

[0012] Specifically, in one embodiment, the present invention provides a wireless data transmitter, comprising: a radio transmitter that modulates a radio frequency carrier according to a data pattern in an awake state and shuts off transmission of the radio frequency carrier in a sleep state, wherein the sleep state consumes less power than the awake state. A controller communicates with the radio transmitter and receives data to be transmitted, and the controller executes a program stored in a non-transitory medium to: (a) switch the radio transmitter to the awake state to transmit a multi-bit preamble by carrier modulation; (b) after transmitting the preamble, switch the radio transmitter to the sleep state for a data duration according to a function that maps a data duration to a unique value of the data to be transmitted; (c) switch the radio transmitter to the awake state to transmit a multi-bit postamble by carrier modulation to signal the end of the data duration; and (d) repeat steps (a) to (d).

[0013] It is thus a feature of at least one embodiment of the invention to exploit the benefits of powerless data transmission using common carrier modulation and multi-bit anchor symbols.

[0014] The controller may repeat steps (a) to (d) with a different data transmission and without radio reception.

[0015] It is thus a feature of at least one embodiment of the invention to eliminate the overhead of receiver circuitry to enhance the effect of powerless data transmission.

[0016] The controller may operate in an awake state during steps (a) and (c) and switch itself to a sleep state during step (b).

[0017] It is thus a feature of at least one embodiment of the invention to drastically reduce energy consumption during transmission by shutting down not only the transmitter but also the controller itself and relying on a sleep state timer.

[0018] The consumption during step (b) performed by the wireless data transmitter is less than 1 / 1000 (one thousandth) of the power consumption during steps (a) and (c).

[0019] It is thus a feature of at least one embodiment of the invention to significantly reduce energy consumption during intervals of no power transmission to enhance the utility of the technology.

[0020] At step (b), the transmitted preamble and postamble may convey data uniquely identifying them to the data to be transmitted.

[0021] It is thus a feature of at least one embodiment of the invention to link preambles and postambles to allow different messages to be interleaved without interference, taking advantage of the sparsity of actual data transmission to reduce collisions.

[0022] In each repetition of step (d), the preamble and postamble may remain unchanged.

[0023] It is therefore a feature of at least one embodiment of the invention to remove the data communication load from the preamble and postamble to minimize their length and energy consumption.

[0024] At least one of the preamble and the postamble may be adapted to provide a coded address that uniquely identifies the wireless data transmitter relative to other wireless data transmitters.

[0025] It is thus a feature of at least one embodiment of the invention to provide robust addressing to allow transmissions from multiple transmitters associated with different sensors.

[0026] The wireless transmitter may further comprise an analogue to digital converter and be operable to read a sensor attached to the analogue to digital converter to provide data to be transmitted prior to step (c).The repetition of step (d) may be greater than 100 times the data duration pattern.

[0027] It is thus a feature of at least one embodiment of the invention to provide extremely low power data communication utilizing the high delay tolerance of sensor data, such as soil moisture data.

[0028] The data may have a predetermined frequency distribution that describes how common a given value of the data is, and the most frequent data value may be mapped by a function to the smallest data duration.

[0029] It is therefore a feature of at least one embodiment of the invention to minimize transmission duration, potentially increasing the amount of data that can be transmitted in a given interval.

[0030] The controller may further delay by a pseudo-random or random interval after step (d) and before step (a).

[0031] It is therefore a feature of at least one embodiment of the invention to minimize collisions between different transmitters by randomizing the repetition rate, thereby improving the use of the system in multi-sensor applications in the context of a star network.

[0032] The data to be transmitted may include error correction data and payload data, the error correction data being operated upon to allow error detection or correction in the payload data.

[0033] It is thus a feature of at least one embodiment of the invention to relax synchronization requirements and maximize range transmission for a given power by using error correction techniques built into the data transmitted through silence.

[0034] The controller may periodically use predetermined calibration data as the data to be transmitted, the calibration data providing an indication of the clock speed of the controller which controls the duration of the data in step (b).

[0035] It is thus a feature of at least one embodiment of the invention to eliminate the need for clock synchronization information in the preamble and postamble while accommodating clock offsets.

[0036] The modulation rate of the preamble and postamble may be different from the clock rate of the timer that measures the data duration.

[0037] It is thus a feature of at least one embodiment of the invention to allow the clock rate to be sized, for example, to relax synchronization and offset requirements between a transmitter and a receiver, to be smaller than the limitations imposed by the bandwidth of a communication channel.

[0038] The preamble and postamble may be narrowband signals, wherein the frequency of the carrier wave is at least 5000 times the bandwidth of the preamble and postamble.

[0039] It is thus a feature of at least one embodiment of the invention to eliminate the need for wide bandwidth communications and reception, simplifying and reducing power consumption for data transmission of a given range.

[0040] The wireless data transmitter may also provide: a radio receiver that provides demodulation of a radio frequency carrier of a wirelessly received radio transmitter, and a receiver controller in communication with the radio receiver to: (a) detect transmission of a preamble by the radio transmitter; (b) start a timer based on detection of the preamble; (c) detect transmission of a postamble by the radio transmitter to stop the timer and provide the data duration; (d) decode a transmitter address from at least one of the preamble and the postamble; and (e) use a function of the data duration to decode data to be transmitted and associated with the decoded address.

[0041] It is thus a feature of at least one embodiment of the invention to provide a system that can be implemented in a star topology with many transmitters communicating with a central receiver and distinguished by preamble-based addressing.

[0042] The radio receiver may also provide a signal strength measurement of the radio frequency carrier, and the receiver controller may detect a transmission error if the signal strength measurement fails to drop by a predetermined amount after detecting a preamble or postamble.

[0043] It is thus a feature of at least one embodiment of the invention to provide improved error detection by monitoring carrier signal strength.

[0044] Additionally or alternatively, the controller may reject the decoded data if a postamble associated with the decoded data is not followed by a matching preamble.

[0045] It is thus a feature of at least one embodiment of the invention to use concatenated preambles and postambles to detect loss of an anchor signal associated with a data error.

[0046] These specific objects and advantages may apply only to some embodiments falling within the scope of the claims and therefore do not limit the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a block diagram of a star topology network of a transmitter system providing multiple transmitters communicating with a central receiver employing the present invention;

[0048] Figure 2 yes Figure 1 Block diagram of the main components of the transmitter and receiver;

[0049] Figure 3 It is shown by Figure 1 and Figure 2 A flowchart of steps performed by a transmitter controller of a transmitter;

[0050] Figure 4 is with Figure 3 The steps are similar to those shown by Figure 1 and Figure 2 A flowchart of the steps performed by a receiver;

[0051] Figure 5 is a graph showing a mapping of data word frequency to delay time for improving transmission throughput;

[0052] Figure 6 is shown during a normal transmission period Figure 2 Timing diagram of the operation of the transmitter and receiver;

[0053] Figure 7 is a graph illustrating collision avoidance during multiple simultaneous transmissions from different transmitters;

[0054] Figure 8 is with Figure 7 A similar diagram showing combined preamble and postamble transmission; and

[0055] Figure 9 is a diagram showing decoded data of a payload and an error correction portion. DETAILED DESCRIPTION

[0056] Now refer to Figure 1 , a wireless data transmitter 10 may provide a plurality of transmitter units 12a and 12b (only two are shown for clarity) that communicate via radio signals 14 with a common receiver 16 in a so-called "star" topology, in which there is unidirectional communication from each transmitter unit 12 to the common receiver 16. In one application, each of the transmitter units 12 may be associated with one or more sensors 18, such as soil moisture sensors, to read data from those sensors 18 and transmit the data collected by the sensors 18 to the common receiver 16. This sensor data 43 may be received by the receiver units 20 of the common receiver unit 20 and transmitted to, for example, a terminal 22 for displaying and further processing the sensor data.

[0057] Now refer to Figure 2, each transmitter unit 12 may be provided with a transmitter controller 24 and a transmitter 26. The transmitter 26 may receive data regarding a preamble 28 or a postamble 124 (discussed below) from the transmitter controller 24, as well as a power state signal 30 that controls the operating power of the transmitter 26. The power state signal 30 may define an active or "wake-up" state during which radio transmissions may occur and during which the transmitter unit 12 may consume more than 10 mA and more typically more than 40 mA. Alternatively, the power state signal 30 may define a "sleep" state in which the transmitter is turned off, such that the transmitter unit 12 consumes less than 1000 nanoamps and, in some cases, less than 200 nanoamps. During the sleep state, no data transmission may occur.

[0058] The transmitter 26 may provide standard carrier-modulated transmitter circuitry, for example, providing frequency shift keying as discussed below. Transmitters 26 suitable for use with the present invention include, but are not limited to, the Linx-NT transceiver module available from Linx Technologies of Merlin, Oregon, USA, the CC1101 high-performance RF transceiver available from Texas Instruments of Dallas, Texas, USA, or the nRF24L01 single-chip 2.4 GHz transceiver available from Nordic Semiconductors of Trondheim, Norway. Although these circuits include receiver circuitry, during use with the present invention, the receiver circuitry will be disabled or placed in sleep mode during most or all of the operating time of the wireless status transmitter 10. It should be understood that such receiver circuitry is not required.

[0059] The transmitter 26 will include a carrier signal generator 32 that provides a radio frequency carrier signal to a modulator / RF amplifier 34, which receives a baseband signal from an amplifier 38, which in turn receives the data of the preamble 28 or postamble 124. The modulator / RF amplifier 34 transmits a carrier signal modulated by the baseband signal from the carrier signal generator 32 and transmits the modulated carrier signal on an antenna 39. A power status signal 30 communicates with these various components to turn them on or off to control power consumption.

[0060] The transmitter controller 24 can be a standard microcontroller, such as, for example, the MSP430FR2355 or MSP430FR599x available from Texas Instruments or the STM32L available from ST Microelectronics in Shanghai, China. Typically, the transmitter controller 24 will include a processor 40, such as a von Neumann-type microprocessor that will execute a program 42 stored in a computer memory 45, as will be discussed below. The transmitter controller 24 may also include standard input and output circuitry, such as an A / D converter 44 that can be connected to the sensor 18 to obtain data therefrom to be provided as sensor data 43. The sensor data 43 may be represented as one or more binary words, such as, for example, a binary word having a total length of 2 to 16 bits, as will be discussed below.

[0061] The transmitter controller 24 may also include a set of timers 46 that may operate independently of the execution of the program 42 by the processor 40 to communicate with the processor 40, for example, through interrupt circuitry of a type known in the art.

[0062] Transmitter controller 24, like transmitter 26, can also operate in multiple power modes including an awake mode (active) and a sleep mode. In the latter sleep mode, timer 46 can continue to operate to count the relevant clock, while other major systems of transmitter controller 24, including processor 40 and A / D converter 44, are shut down to reduce power. As is generally understood in the art, when the active timer 46 reaches a preprogrammed count value, it can wake up processor 40 and remove it from the sleep state to resume execution of program 42.

[0063] Example power consumption of suitable circuits in awake (active) and sleep states is shown below in Table I. However, it should be emphasized that the present invention is not limited to use with these particular circuits which are shown by way of enabling examples only.

[0064] Table I

[0065]

[0066] The transmitter unit 12 may also provide a battery 50 for powering the transmitter unit 12 and may optionally provide a programming port 52, such as a mechanical electrical connector or a low-energy radio receiver, such as an RFID circuit or the like, for receiving programming data from a programming device 54. Such programming data may be used to assign an address to the transmitter unit 12 or to change any of the transmission parameters described below (length of the preamble 28 or postamble 124, transfer function, error correction, etc.).

[0067] Still refer to Figure 2Receiver unit 20 may be any receiver compatible with transmitter 26, having a receiver 60 of a type known in the art in communication with an antenna 62 to receive transmissions from transmitter unit 12 and provide demodulated data 64 and a received signal (carrier) strength signal 66 to a receiver controller 68. Receiver controller 68 may be a general-purpose microprocessor that may communicate with terminal 22, which includes a processor 70 executing a program 72 stored in computer memory 76.

[0068] Now refer to Figure 3 and Figure 6 During the operation of the wireless data transmitter 10, the processor 40 will be awakened by the expiration of the first timer 46 (set at the previous cycle) at time t0. Upon awakening, the processor 40 jumps to a predetermined interrupt vector of the program 42 to read the sensor 18 through the A / D converter 44, as indicated by process block 80.

[0069] Prior to this time t0, the transmitter controller 24 and the transmitter 26 are in a dormant state during an inter-sampling duration 85 with a sleep state current consumption 89, for example, on the order of microamperes and ideally less than 10 μA. After waking up the transmitter controller 24 at time t0, the current consumption of the wireless data transmitter 10 may rise to a pre-transmission level, for example, greater than 1 μA and less than 2 mA during a ramp-up interval 88. The time required to wake up the transmitter controller 24 and acquire sensor data may be a few microseconds, for example, less than 50 μs.

[0070] The first timer 46 is typically set to a length of time that matches the desired inter-sampling duration 85 between readings of the sensor 18 , which may be on the order of minutes or hours, for example.

[0071] After acquiring data from sensor 18, processor 40 determines at decision block 82 whether wireless data transmitter 10 needs to be calibrated, and if so, exchanges the data read from sensor 18 with calibration data per process block 84. Typically, as discussed below, the calibration data provides predefined data values that can be used by receiver 16 to calibrate its clock for timing purposes. This calibration process is performed infrequently, as determined by the stability of the internal clock of transmitter controller 24, which controls timer 46, and the corresponding clock circuitry in receiver unit 20. For example, the calibration process may occur on a daily basis, as opposed to an inter-sampling duration 85 of hours or less. The calibration process may be triggered by timer 46 or by counting the occurrences of sampling by sensor 18.

[0072] Typically, at decision block 82 , no calibration will be required and the data obtained from the sensor 18 will be the transmitted data.

[0073] In either case, the program 42 then proceeds to process block 86 and the transmitter controller 24 begins ramping up at interval 88, during which the current consumption rises to a value between 2 μA and 5 μA, for a duration between 2 ms and 10 ms, as the energy and time required for the transmitter 26 to prepare for transmission are increased. Typically, interval 88 is selected to be slightly longer than the maximum expected duration required for the ramp-up. Following this transmitter ramp-up time of interval 88, the transmission of the preamble 28 occurs during interval 90. In one example, for a 16-bit preamble 28 transmitted at a modulation frequency of 96 kHz, this interval 90 may last 3.9 ms or less. The preamble 28 may be represented as a set of binary pulses 92 having a value of one or zero, with a word size 93 ranging from 2 bits to 18 bits. In one embodiment, the preamble 28 may encode the address of the transmitter controller 24, as previously programmed by the programming device 54, as discussed above. Additionally, preamble 94 may uniquely identify itself as preamble 28 rather than postamble 124, as will be discussed below, and may uniquely link itself to postamble 124 through a common address.

[0074] In one embodiment, the transmitter 26 may transmit the preamble 94 (and subsequently the postamble 124) using narrowband modulation, such as dual-frequency frequency shift keying, operating on a carrier frequency of approximately 902 MHz to 928 MHz and having a modulation bandwidth of approximately 100 kHz. Narrowband transmission allows the wireless data transmitter 10 to have a long range at reduced power; however, the present invention also contemplates possible wideband transmission if faster data communication is desired.

[0075] At the end of the transmission of the preamble, a timer 46 is set for encoding the sensor data 43 to be transmitted according to an encoding function that encodes the sensor data 43 as a duration. A simple encoding system takes only less than or equal to 2 N duration of , where N is the sensor data 43. However, in an alternative embodiment, and with reference to Figure 5 , the values of the sensor data 43 can be arranged according to their expected transmission frequency (obtained through empirical measurement or during a dynamic analysis process). The values of the sensor data 43 arranged in this manner are then mapped to the delay times 100 such that more frequent values of the sensor data 43 are mapped to shorter delay times 100, while maintaining a one-to-one mapping between the data values of the sensor data 43 and the delay times 100. The effect of this mapping is to reduce the average delay time 100 during use of the wireless data transmitter 10, and thus increase the transmission frequency, reducing errors caused by clock offsets, etc.

[0076] Refer again Figure 3 and Figure 6 Once timer 46 is set, transmitter controller 24, via program 42, places itself and transmitter 26 into a sleep state at time t1 (transmitter controller 24 is awakened by timer 46 in the future), as indicated by process block 87. An interval 102 is placed in timer 46 that is equal to delay time 100 minus ramp-up interval 88 and transmitter 26 transmission interval 90.

[0077] With the transmitter controller 24 and transmitter 26 in sleep mode, the transmission interval 102 passes with extremely low power consumption, for example, less than 2 μA of current consumption, which is comparable to the power consumption during the inter-sampling duration 85. The clock signal 104 that controls the interval 102 (in the delay time 100) by the incrementing timer 46 is typically much faster than the modulation frequency of the preamble 28, which may be 9.6 kHz, although the clock signal 104 may operate at 32 kHz. Typically, the frequency of the clock signal 104 is also much less than the maximum bandwidth of the communication channel defined by the frequency of the carrier signal, and may be varied as needed to reduce errors caused by offsets between the comparable clocks of the receiver 16 and the transmitter unit 12 used to measure this delay time 100.

[0078] Now also refer to Figure 4 , the program 72 executing on the receiver unit 20 during this transmission by the transmitter 26 can monitor the antenna 23 to detect a carrier signal from the transmitter 26 during the interval 90 (and slightly before), as provided by the received signal strength signal 66. When a carrier signal is detected, as indicated by the decision block 108, the receiver unit 20 can collect data for the preamble 28 per the processing block 110 by demodulating the carrier signal. For example, the demodulation can employ a correlation process to detect the pulse 92 without requiring prior synchronization of the demodulator with the transmitter 26. However, the correlation process can be informed by the known modulation frequency and expected word length of the preamble 28. These values (and any other necessary values that need to be shared between the transmitting unit 12 and the receiving unit 20) can be pre-programmed into the components of the wireless data transmitter 10 or communicated during a commissioning process that occurs prior to the transmission now being described.

[0079] The demodulation of process block 110 not only extracts the data of the preamble indicating the address, but also captures the setup time t l The time of the last bit of preamble 28.

[0080] During the demodulation process, the receiver unit 20 also determines whether the previously decoded bit sequence is a postamble 124 and if not then throws an error per process block 112, discarding the current timer value timing the delay time 100 based on an indication that there was a missing postamble 124 and therefore the data has been corrupted.

[0081] Once the setup time t is determined l , then, for example, a timer in the processor 70 is started at time t2, and the time indicating the arrival of the last symbol of the preamble 94 is set at time t2 and the time t l The interval between (eg, the timestamp data from before the correlation) is added to the timer to begin measuring the time delay time 100 , as indicated by process block 116 .

[0082] Refer again Figure 3 and Figure 6 At time t3, timer 46 on transmitter unit 12, measuring interval 102, again wakes up transmitter controller 24 and transmitter 26, moving them to the awake state, as indicated by process block 120. Transmitter controller 24 initiates ramp-up interval 88 and causes transmitter 26 to begin transmitting postamble 124 over interval 90, which is timed to complete at the end of delay time 100.

[0083] Postamble 124 may be similar to preamble 28 in terms of carrier frequency and modulation frequency, but may differ in the data conveyed by the modulated bits to the extent that postamble 124 identifies itself as postamble 124 (rather than preamble 28) to allow detection of lost anchor transmissions, as briefly discussed above with respect to process block 112. Postamble 124 may link itself to preamble 28, for example, by encoding a public address of transmitter unit 12 or by other linking data.

[0084] After completing the transmission of the postamble 124 of each process block 120, the transmitter controller 24 and the transmitter 26 return each process block 130 to the sleep state for the inter-sampling duration 85 at time t4 after setting the timer 46. Process blocks 84, 82, 86, 87, 120, and 130 may then repeat after the inter-sampling duration 85. Because the preamble 94 and postamble 124 do not contain the sensor data 43 to be transmitted, the preamble 94 and postamble 124 generally remain unchanged during this repetitive process; the sensor data 43 to be transmitted is instead conveyed by the sleep interval 102.

[0085] Refer again Figure 4 and Figure 6, slightly prior to the transmission of postamble 124, receiver unit 20 may use received signal strength 66 to detect the carrier again as indicated by decision block 134, and may begin a demodulation process as indicated by process block 136, similar to that described with respect to process block 110. Likewise, if demodulation indicates that preamble 28 has been received when postamble 124 is expected, it may be assumed that there has been a loss of an anchor symbol and an error may be thrown as indicated by process block 138, resulting in resetting and discarding the value of the timer counting delay time 100.

[0086] Otherwise, the end of the preamble is detected, for example, at time t5, which is fixed to the earlier time stamp data at time t4, and by the necessary subtraction, the end of the preamble is determined using the time stamp data for Figure 5 The inverse function of the described function is used to determine and decode the delay time 100 .

[0087] In a subsequent process block 140, if the data is calibration data (e.g., determined by a particular preamble 94 or postamble 124 or by a particular value of the data transmitted by the delay time 100), the decoded data is compared to a predefined calibration value and used to make an adjustment in the clock of the receiver unit 20 per process block 142. This adjustment process can simply provide for calibration without changing the actual clock speed. Figure 5 The factor adjustment of the function or the adjustment process can adjust the clock speed.

[0088] At process block 142, the decoded data may be corrected according to error detection techniques and then output, for example, to a Figure 1 The terminal 22 shown. In this regard, and with temporary reference to Figure 9 It will be appreciated that the sensor data 43 may be coupled to an error correction code 144 by the transmitter controller 24 during transmission according to known error correction techniques that allow detection and correction of bit errors in the received data. For example, the error correction code may use cyclic redundancy coding or other techniques known in the art.

[0089] Any error correction code can be enhanced by error reduction techniques that reduce the Figure 6 The sensor data 43 operates at the speed of the clock signal 104 as shown, which substantially increases the timing (Hamming) distance between adjacent values of the sensor data 43.

[0090] Now refer to Figure 7It should be understood that when there are multiple transmitting units 12, transmissions by transmitter unit 12a may potentially collide with simultaneous transmissions from other transmitter units 12b or 12c. However, because sensor data 43 is transmitted during times when there are no transmissions (intervals 102), collisions with interfering transmissions may only occur during the relatively short transmission times of the preamble 28 or postamble 124 indicated by interval 150, rather than during interval 102 or the inter-sampling duration 85. To this end, transmissions by other transmitter units 12b and 12c may occur at times that overlap with transmissions by transmitter unit 12a, as long as the various preambles 28 and postambles 124 (indicated by the letters A, B, and C) do not overlap.

[0091] Occasional collisions can be resolved simply by detecting the collision (either through error detection or missing anchor symbol detection) and discarding the data to wait for the next data transmission. This is possible and feasible by sending data at a higher rate than required, because the data is transmitted based on the Figure 7 For the actual transmissions shown, collisions are statistically unlikely.

[0092] To prevent the sampling duration 85 between multiple transmitter units 12 (in Figure 6 To avoid repeated conflicts caused by alignment of the two samples (as shown in ), the length of the inter-sampling duration 85 can be perturbed by a random amount 160.

[0093] Now refer to Figure 8 Although the present invention contemplates that an inter-sampling duration 85 may separate a postamble 124 from a subsequent preamble 28, and that a different transmission interval 102 may separate a preamble 28 from a subsequent postamble 124, it should be understood that these anchor transmissions of the preamble 28 and postamble 124 can actually be combined by appropriate scaling of the clock signal 104 so that the averaging interval 102 is equal to the desired inter-sampling duration 85 (assuming that variations in the inter-sampling duration 85 can be tolerated). In this case, the preamble 28 and postamble 124 can be linked to each other by proximity rather than by data.

[0094] As described herein, during sleep time of the transmitter unit 12 , the carrier will be turned off and any receiver circuitry will be turned off; however, this should be understood to include any significant reduction in carrier output or receiver detection capability below the level required for communication with the receiver 16 .

[0095] Certain terms are used herein for reference purposes only and are not intended to be limiting. For example, terms such as "upper," "lower," "above," and "below" refer to directions in the accompanying drawings to which reference is made. Terms such as "front," "rear," "back," "bottom," and "side" describe the orientation of portions of a component within a consistent but arbitrary frame of reference, as will become clear by reference to the text and the associated drawings depicting the component in question. Such terms may include the words specifically mentioned above, their derivatives, and words of similar meaning. Similarly, the terms "first," "second," and other such numerical terms referring to structures do not imply a sequence or order unless the context clearly indicates otherwise.

[0096] When introducing elements or features of the present disclosure and exemplary embodiments, the articles "a," "an," "the," and "said" are intended to mean that there are one or more such elements or features. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements or features other than those specifically noted. It should also be understood that, unless specifically identified as an order of execution, the method steps, processes, and operations described herein should not be construed as necessarily being performed in the particular order discussed or illustrated. It should also be understood that additional or alternative steps may be employed.

[0097] References to "microcontroller" and "controller" or "the microcontroller" and "the controller" may be understood to include one or more microcontrollers that may communicate in (one or more) independent and / or distributed environments, and thus may be configured to communicate with other controllers via wired or wireless communications, wherein such one or more controllers may be configured to operate on one or more controller-controlled devices that may be similar or different devices. Additionally, unless specifically stated otherwise, references to memory may include one or more controller-readable and accessible memory elements and / or components that may be internal to a controller-controlled device, external to a controller-controlled device, and accessible via a wired or wireless network.

[0098] In particular, the present invention is not intended to be limited to the embodiments and descriptions contained herein, and the claims should be understood to include modifications of these embodiments, including portions of the embodiments and combinations of elements of different embodiments, as long as they fall within the scope of the appended claims. All publications described herein, including patent and non-patent publications, are hereby incorporated by reference in their entirety.

[0099] To assist the Patent Office and any reader of any patent issuing based on this application in interpreting the appended claims, Applicant wishes to point out that unless the words "means for" or "step for" are expressly used in a particular claim, Applicant does not intend that any appended claim or claim element invoke 35 U.S.C. §112(f).

Claims

1. A wireless data transmitter, comprising: a radio transmitter that provides modulation of a radio frequency carrier according to a data pattern in an awake state and switches off transmission of the radio frequency carrier in a sleep state, the sleep state providing less power consumption than the awake state; a controller that communicates with the radio transmitter and receives data to be transmitted, the controller executing a program stored in a non-transitory medium to: (a) switching the radio transmitter to the awake state to transmit a multi-bit preamble by modulation of the carrier; (b) after transmitting the preamble, switching the radio transmitter to the sleep state for the data duration according to a function that maps a data duration to a unique value of the data to be transmitted; (c) switching the radio transmitter to the awake state to transmit a multi-bit postamble by modulation of the carrier to signal the end of the data duration; as well as (d) Repeat steps (a) to (d), Wherein, at step (b), the transmitted preamble and postamble convey data uniquely identifying them to the data to be transmitted.

2. The wireless data transmitter according to claim 1, wherein The controller repeats steps (a) to (d) with different data transmissions and without radio reception.

3. The wireless data transmitter according to claim 1, wherein The controller operates in an awake state during steps (a) and (c) and switches itself to a sleep state during step (b).

4. The wireless data transmitter according to claim 3, wherein: The power consumption during step (b) performed by the wireless data transmitter is less than one thousandth of the power consumption during steps (a) and (c).

5. The wireless data transmitter according to claim 1, wherein In each repetition of step (d), the preamble and postamble remain unchanged. The wireless data transmitter according to claim 1 , wherein: At least one of the preamble and the postamble is adapted to provide a coded address that uniquely identifies the wireless data transmitter relative to other wireless data transmitters.

7. The wireless data transmitter according to claim 1 , further comprising an analog-to-digital converter and further comprising the steps of: reading a sensor attached to the analog-to-digital converter to provide the data to be transmitted before step (c); as well as Wherein, the repetition of step (d) is greater than 100 times of the data duration pattern.

8. The wireless data transmitter according to claim 1, wherein The data has a predetermined frequency distribution that describes how common a given value of the data is, and wherein the most frequent data value is mapped by the function to the smallest data duration.

9. The wireless data transmitter according to claim 1, wherein: The controller further delays by a pseudo-random or random interval after step (d) and before step (a).

10. The wireless data transmitter according to claim 1, wherein The data to be transmitted includes error correction data and payload data, the error correction data operating to allow error detection or correction in the payload data.

11. The wireless data transmitter according to claim 1, wherein: The controller also periodically uses predetermined calibration data as the data to be transmitted, the calibration data providing an indication of a clock speed of the controller that controls the duration of the data in step (b).

12. The wireless data transmitter according to claim 1, wherein The modulation rate of the preamble and the postamble is different from the clock rate of a timer that measures the data duration.

13. The wireless data transmitter according to claim 1, wherein: The function has a domain equal to the bit length of the data to be transmitted and a range equal to the bit length raised to a power of two, and provides a one-to-one mapping between the domain and the range.

14. The wireless data transmitter according to claim 1, wherein The preamble and the postamble are narrowband signals, wherein the frequency of the carrier is at least 5000 times the bandwidth of the preamble and the postamble.

15. The wireless data transmitter according to claim 1, further comprising: a radio receiver providing demodulation of the radio frequency carrier of the radio transmitter received wirelessly; as well as a receiver controller that executes a program stored in a non-transitory medium and communicates with the radio receiver to: (a) detecting, by the radio transmitter, transmission of the preamble; (b) starting a timer based on detection of the preamble; (c) detecting, by the radio transmitter, transmission of the postamble to stop the timer and provide the data duration; (d) decoding a transmitter address from at least one of the preamble and the postamble; as well as (e) using the function on the data duration to decode the data to be transmitted and associated with the decoded address.

16. The wireless data transmitter according to claim 15, wherein: The radio receiver also provides a signal strength measurement of the radio frequency carrier, and wherein the receiver controller further executes the procedure to detect a transmission error if the signal strength measurement fails to drop by a predetermined amount after detecting the preamble or the postamble.

17. The wireless data transmitter according to claim 15, wherein: If a postamble associated with the decoded data is not followed by a matching preamble, the receiver controller refuses to decode the data.

18. The wireless data transmitter according to claim 15, wherein: The receiver controller further executes the program to operate on the decoded data to isolate a payload from an error correction code to provide error correction to the payload of the decoded data.

Images