METHOD FOR CONTROLLING THE TRANSMISSION OF SELF-ADAPTING RADIO SIGNALS

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a method for transmitting radio signals carrying useful data. STATE OF THE ART

[0002] Devices intended to periodically transmit useful data to remote equipment, such as water meters, are known from the state of the art.

[0003] Some of these devices are powered by a battery that stores a limited amount of energy. Each time a signal carrying useful data is emitted by such a device, energy is consumed from the battery. When the battery is empty, the device can no longer operate, and, in particular, can no longer send useful data.

[0004] It should be noted that the amount of energy consumed to transmit a signal carrying useful data varies depending on the device's installation location. This is because the device's network coverage depends on the installation location. For example, if network coverage is poor, the device may consume additional energy by repeatedly sending fragments or increasing its transmission power.

[0005] As a result, the respective batteries of two identical devices placed in different locations may drain at different rates. As a result, the actual lifespans of these devices may sometimes be very different, which is not desirable.

[0006] Document US 2006 / 270385 describes a method in which a transmission duty cycle is modified when an estimated energy cost falls below a threshold. STATEMENT OF THE INVENTION

[0007] One aim of the invention is to remedy this situation.

[0008] For this purpose, according to a first aspect, a method is proposed comprising the steps set out in claim 1.

[0009] The method according to the first aspect may also comprise the following features, taken alone or in combination where technically possible.

[0010] Preferably, the first factor and the second coefficient are equal.

[0011] Preferably, the method according to the first aspect further comprises a step of calculating the reference energy quantity from the stored period and a quantity of energy remaining in a battery 6 of the transmitter.

[0012] Preferably, the amount of energy consumed to transmit the first ratio signal is estimated from a transmission duration of the first signal and a transmission power of the first signal.

[0013] Preferably, the useful data comprises at least one measurement of consumption of a fluid.

[0014] Also provided, according to a second aspect, is a computer program product comprising program code instructions for executing the steps of the method according to the first aspect, when this program is executed by a transmitter.

[0015] Also provided in a third aspect is a computer-readable memory storing computer-executable instructions for performing the steps of the method according to the first aspect.

[0016] Also provided, according to a fourth aspect, is a transmitter comprising a radio communication interface, and a control unit configured to implement the steps of the method according to the first aspect, such that a first radio signal and the second radio signal are transmitted by the radio communication interface.

[0017] Also provided, according to a fifth aspect, is a meter for measuring fluid consumption, the meter comprising a transmitter according to the fourth aspect. DESCRIPTION OF FIGURES

[0018] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which: There Figure 1 schematically illustrates a device according to one embodiment. The Figure 2 is a flowchart of steps of a method according to one embodiment. The Figure 3 represents the evolution of a quantity of energy consumed to emit a radio signal over time.

[0019] Throughout the figures, similar elements have identical references. DETAILED DESCRIPTION OF THE INVENTION

[0020] We have represented in Figure 1a device 1. Device 1 is, for example, a meter whose general function is to measure fluid consumption, for example water consumption in an installation.

[0021] Device 1 comprises a sensor 2, a transmitter 4 and a battery 6.

[0022] Sensor 2 is configured to acquire measurements indicative of fluid consumption in the installation.

[0023] The transmitter 4 is configured to transmit radio signals repeatedly over time in a network, so that these radio signals are received by remote equipment.

[0024] The network considered is typically a Low Power Wide Area Network (LPWAN). For example, the LPWAN network is one of the following: SigFox, LoRaWAN, NB-IOT, CAT-M, WAZE, wMBUS.

[0025] The battery 6 constitutes an energy source which makes it possible to supply energy to the other components of the device 1, in particular the transmitter 4. The battery 6 stores a limited quantity of energy: this quantity of stored energy decreases over time, in particular each time the transmitter 4 emits a radio signal. The battery 6 may or may not be rechargeable. The battery 6 comprises, for example, one or more electric batteries.

[0026] The transmitter 4 comprises a radio communication interface 8, a memory 10 and a control unit 12.

[0027] The radio communication interface 8 is adapted to generate the aforementioned radio signals. The radio communication interface 8 comprises one or more antennas.

[0028] Memory 10 stores two parameters: a transmission period Pt and a frame size Tt. We will see later that these two parameters have an influence respectively on the transmission times and the lengths of the radio signals emitted by transmitter 4.

[0029] The control unit 12 is configured to control the transmission of radio signals by the radio communication interface 8, so as to take into account the two aforementioned parameters. In particular, the control unit 12 is capable of modifying the values ​​of the two parameters Pt, Tt which are stored in the memory 10.

[0030] The control unit 12 is further configured to generate payload data frames intended to be communicated to a remote device. The generated frames typically comprise measurements provided by the sensor, or data derived therefrom.

[0031] The control unit 12 may comprise one or more processors, programmable (FPGA for example) or not (ASIC). The or each program may be adapted to execute a control program comprising code instructions for implementing a method which will be described later. The control program is for example stored in the memory 10.

[0032] Generally, the transmitter 4 is configurable in two operating modes which will be detailed below: a static operating mode, and a dynamic operating mode. The operating mode in which the transmitter 4 is configured is for example indicated in data stored in the memory 10, for example a Boolean. The transmitter 4 can change operating mode, typically upon receipt of a request to this effect received via the radio communication interface 8, and previously transmitted by a remote device.

[0033] In reference to the Figure 2 , a method implemented by transmitter 4 comprises the following steps.

[0034] In a step 100, the control unit 12 detects that a radio signal is to be transmitted. We will see later that this detection is based on an elapsed time.

[0035] In a step 102, the control unit 12 determines the operating mode in which the transmitter 4 is configured (static or dynamic). Depending on the determined mode, different steps are implemented by the control unit 12. Static operating mode

[0036] When the operating mode of the transmitter 4 is the static mode, the control unit 12 constructs a frame containing useful data (step 104). The control unit 12 imposes as a constraint that the constructed frame has a size equal to the frame size Tt as stored in the memory 10.

[0037] Then, the radio communication interface 8 transmits a radio signal carrying the constructed frame. The radio signal is a time signal of limited duration. The transmission of the signal begins at one instant, and ceases at a later instant, the interval between these two instants constituting the duration of the transmitted radio signal. This duration depends on the size of the constructed frame.

[0038] We have represented in Figure 3 schematically the evolution of the quantity of energy consumed by the transmitter 4 to transmit the radio signal at step 106 in an LPWAN network. Thus, several phases are distinguished: a network search phase: This phase is dominant in so-called connected networks (i.e. with signals exchanged between the transmitter 4 and remote recipient equipment such as gateways. Its duration can range from a few seconds to several minutes depending on the frequency bands to be covered. This phase allows: ∘ determining a listening frequency for the remote equipment(s), ∘ initiating a dedicated channel configuration for the transmitter 4 ∘ attaching to the network. a signaling phase: This phase allows alerting on the start or end of a transmission phase. Data transfer: Depending on the protocol layers involved, encapsulation and fragmentation mechanisms apply. The useful data is transmitted in this phase. Reception window: Depending on the network, one or more reception windows are activated after a transmission of useful data.

[0039] It should be noted that the phases that constitute the transmission session, their durations, frequencies and energy impact vary from one technology to another but overall, they are generally present. For example, in an NBIOT network, the network search phase and transmission times are longer than in a CAT-M network because the modulation of the latter allows higher throughputs. Furthermore, LoRa and SigFox networks have a very low throughput compared to other technologies, which lengthens transmission times.

[0040] Back to the Figure 2, the transmitter 4 then waits for a period equal to the period stored in the memory 10 (step 108). Concretely, the control unit 12 starts a time counter at the instant at which the communication interface began to transmit the radio signal, and waits. When the time counter reaches a value equal to the period stored in the memory 10, the waiting period is over, and the method returns to step 100.

[0041] Finally, it is detected that a new frame is to be transmitted at step 100 when a time equal to the period Tt has elapsed from the time when a previous radio signal was transmitted (more precisely, the time at which this transmission started).

[0042] Assuming that the operating mode of the transmitter 4 has not changed (static mode), a new radio signal is transmitted during a new implementation of step 104. Thanks to the preceding mechanism, the control unit 104 ensures that: the duration which separates the respective emissions of two consecutive radio signals is equal to the period Pt stored by the transmitter 4, the two consecutive radio signals transport respective frames having sizes equal to the frame size Tt stored by the transmitter 4.

[0043] The preceding steps are repeated over time.

[0044] Thus, as long as transmitter 4 is in the static operating mode, transmitter 4 transmits radio signals periodically, based on the period Pt stored in memory 10. Furthermore, all signals carry the same amount of useful data, this amount being dictated by the stored frame size. Dynamic operating mode

[0045] We will now describe the steps implemented by the transmitter 4 when the control unit 12 notes in step 102 that the operating mode in which the transmitter 4 has been configured is the dynamic mode. We will see that in the dynamic mode, self-adaptation is implemented by the transmitter.

[0046] It is assumed that transmitter 4 has already emitted at least one radio signal in the past. By convention, the last radio signal emitted is considered to be a radio signal of index k-1, and the frame carried by this signal is a frame of index k-1.

[0047] In a step 110, the control unit 12 estimates a quantity of energy consumed by the transmitter 4 to transmit the radio signal of index k-1. This estimation 110 can be carried out in different ways.

[0048] In a first embodiment, this estimation 110 is carried out from the duration of the signal of index k-1 and a transmission power of the radio signal of index k-1.

[0049] The duration of the radio signal with index k-1 can be calculated as follows: Nb de fragments = Nb de r é p é tition ∗ Arrondi sup Taille payload octets Taille fragment octets Dur é e é mission fragment = Nb de fragments ∗ Taille fragment octets D é bit octets / s Or : Number of repetitions is a number of times a fragment is transmitted (parameter depends on network configuration) Payload size in bytes is the size of the useful data carried by the k-1 index ratio signal (this parameter corresponds to the size Tt discussed previously), Fragment size bytes is the size of a low layer packet (MAC), Speed bytes / s is a transmission rate that depends on signal quality, modulation etc. Number of signals is a number of signaling messages, Duration of a signaling is an approximate value retrieved from the radio module, Number of fragments is the number of fragments to transmit, Duration of fragment broadcastis the average transmission time of a fragment.

[0050] A transmission power of the signal of index k-1 is measured by the transmitter 4.

[0051] The control unit 12 can estimate in step 110 a current intensity consumed from the transmission power of the radio signal of index k-1. This estimation can be carried out from a conversion table stored in the memory 10, this table associating power values, for example expressed in dBm, with current intensity values, for example expressed in milliamperes (mA).

[0052] Table 1 below is an example of a usable conversion table: [table 1] Power (dBm) Fluent 0 30 mA 1 32 mA 2 35 mA 3 40 mA 4 52 mA ... 18 120 mA 19 140 mA 20 160 mA

[0053] Then, the control unit 12 can estimate the amount of energy consumed by multiplying the determined current intensity by the transmission duration of the radio signal of index k-1. In this case, the estimated amount of energy consumed can be expressed in mAh.

[0054] In a second embodiment, the estimation of step 110 is carried out from actual current measurements acquired by a suitable device. The estimate could be more precise than with the first embodiment, but the incorporation of the device represents an additional manufacturing cost.

[0055] In a step 112, the control unit 12 obtains a reference amount of energy. This step can be carried out in different ways.

[0056] In a first embodiment, the reference quantity of energy is a quantity determined in advance and stored in the memory 10. This quantity is determined as a function of a desired lifetime for the transmitter 4, and of the maximum quantity of energy that can be stored in the battery 6.

[0057] In a second embodiment, the reference energy quantity is calculated by the control unit 12, in particular from the period stored in the memory 10. We will see in the following that, in the dynamic operating mode, the stored period can vary over time; this also results in a variation of the reference energy quantity over time.

[0058] More precisely, the reference energy quantity can be calculated as follows Cr é dit mAh = Capacit é mAh Dur é e vie jours ∗ Nb transmissions / jour Or : mAh capacity denotes a quantity of energy remaining in the battery 6, Life span daysis the number of days remaining that transmitter 4 is expected to operate before battery 6 is empty, Number of transmissions / day is the number of signals to be emitted per day (applying the stored period).

[0059] The reference energy quantity thus represents a maximum quantity allocable for the transmission of a signal so that the battery can operate for the number of days indicated.

[0060] In a step 114, the control unit 12 compares the quantity of energy consumed to transmit the radio signal k-1, having been estimated in step 110, and the reference quantity of energy obtained in step 112. We will see that the control unit 12 will decide whether or not to update the parameters Pt, Tt stored in the memory 10 (frame size and / or transmission period) depending on the comparison.

[0061] The control unit 12 calculates a difference between these two quantities of energy. The threshold is an absolute value. The control unit 12 compares the difference with a predefined threshold. This threshold is preferably strictly greater than zero.

[0062] When the deviation is less than the threshold, then the parameters stored in memory 10 (frame size and transmission period) are not modified (step 116.

[0063] When the deviation is greater than or equal to the threshold, then the parameters stored in memory 10 (frame size Tt and transmission period Pt) are modified (steps 118, 120).

[0064] These changes differ depending on whether the estimated amount of energy consumed is less than the reference amount of energy.

[0065] When the deviation is greater than or equal to the threshold and in addition the estimated energy quantity is less than the reference energy quantity, then the control unit 12 reduces the stored period and / or reduces the stored frame size, preferably both (step 118).

[0066] Preferably, the stored period is reduced in step 118 by a first factor, and the stored size is reduced by the same first factor. In the present text, "reducing X by a factor Y" designates an operation taking X as input and producing a result equal to X multiplied by a multiplicative factor Y, Y being strictly greater than 1. Using the same factor to modify (here increase) the period Pt and the frame size Tt makes it possible to maintain the quantity of useful data transmitted by the transmitter 4 in the very long term.

[0067] For example, when the first factor is chosen equal to 2, the reductions are carried out as follows: Pt = Pt 2 Tt = Tt 2

[0068] When the deviation is greater than or equal to the threshold and in addition the estimated energy quantity is greater than the reference energy quantity, then the control unit 12 increases the stored period and / or increases the stored frame size, preferably both (step 120).

[0069] Preferably, the stored period is increased at step 120 by a second factor, and the stored size is increased by the second factor. In this text, “increasing X by a factor Y” designates an operation taking X as input and producing a result equal to X multiplied by a factor Y, Y being strictly less than 1. In other words, “increasing X by a factor Y” amounts to “reducing X by a factor 1 / Y”.

[0070] For example, when the second factor is chosen equal to 2, the increases are carried out as follows: Pt = 2 ∗ Pt Tt = 2 ∗ Tt

[0071] Most preferably, the first factor and the second factor are equal (as in the example presented above). This allows to preserve a certain balance between the different ways of modifying the two aforementioned parameters, and to avoid a long-term drift of the values ​​of the parameters Pt, Tt. However, the two factors could be different.

[0072] Then, the control unit 12 implements step 104 to construct a new frame, of index k. As indicated previously, the control unit 12 relies on the value of the size Tt as present in the memory 10 to ensure that the frame of index k has a size equal to the stored size Tt. If the frame size was updated during step 118 or step 120, then it is this updated size which is used at this stage. Thus, it can be seen that the frame of index k can have a size equal to, greater than or less than that of the frame of index k-1, depending on the decision taken by the control unit in step 114.

[0073] Then, the transmission step 106 is implemented as indicated previously, so as to transmit a new radio signal carrying this new frame.

[0074] Then, the waiting step 108 is implemented, on the basis of the period Pt as stored in the memory 10, having therefore potentially been updated in step 118 or step 120. Thus, the duration which separates the respective transmissions of the radio signal of index k and of a following radio signal of index k+1 will, depending on the case, be equal to, greater than or less than the duration which separates the respective transmissions of the radio signal of index k-1 and of the radio signal of index k.

[0075] The inventors found that distributing a quantity of useful data into several radio signals spaced apart in time consumes more energy than transmitting this quantity at once in a longer radio signal threshold, under the assumption that all the other parameters used by the transmitter are identical (selected modulation, signal power, etc.). In the example of the Figure 3, this comes from the fact that the transmitter 4 must carry out the network search phase and the reception window phase, regardless of the quantity of useful data transmitted in the radio signal between these two phases. In return, distributing a quantity of useful data in several spaced radio signals allows the device 1 to be more responsive.

[0076] Thus, the implementation of step 120 makes it possible to ensure that the amount of energy that will be consumed to transmit the radio signal k is less than the amount of energy consumed to transmit the radio signal k-1. Furthermore, the implementation of step 118 makes it possible to make the device more responsive. Indeed, the device 1 will have to wait less time at step 108 to transmit the next signal. The dynamic mode described previously is advantageous, because it allows the transmitter to find an interesting compromise between responsiveness and energy consumption, and this in a manner that evolves over time.

[0077] The process described above in relation to the Figure 2 may be subject to variations. In particular, it will be noted that this method allows the device 1 to change its operating mode (static or dynamic). It may be envisaged that the device 1 only operates in dynamic mode. Furthermore, the first factor and the second factor may be modified, for example at the request of a remote device. The processing unit 12 may maintain the parameters Pt and Tt within predefined value ranges. Thus, the period Pt or the size Tt may be reduced in step 118 provided that a minimum value is not exceeded; similarly, the period Pt or the size Tt may be increased in step 120 provided that a maximum value is not exceeded. For example, the control unit may impose a minimum period of 24 hours (otherwise sending one frame per day) and / or a frame size that remains between 64 and 256 bytes.

Claims

1. A method implemented by a transmitter, comprising: • causing a transmission (106) of a first radio signal carrying a first payload data frame, such that: • a time interval separating the transmission of the first radio signal and a transmission of a preceding radio signal by the transmitter is equal to a stored period, Pt, which is stored by the transmitter, and • the first payload data frame has a size equal to a stored size, Tt, which is stored by the transmitter, • estimating (110) a quantity of energy consumed by the transmitter to transmit the first radio signal, • comparing (114) the quantity of energy and a reference quantity of energy, • updating (118, 120) the stored period, Pt, and the stored size, Tt, on the condition that a difference between the quantity of energy and the reference quantity of energy is greater than a threshold, • after updating, causing a transmission of a second radio signal carrying a second payload data frame, such that: • a time interval separating the transmission of the second radio signal and a transmission of the first radio signal by the transmitter is equal to the stored period, and • the second payload data frame has a second size equal to the stored size, Tt, • characterized by: • reducing the stored period by a first factor and reducing the stored size by the first factor whenever the difference is greater than the threshold and the quantity of energy is less than the reference quantity of energy, or • increasing the stored period by a second factor and increasing the stored size by a second factor whenever the difference is greater than the threshold and when the quantity of energy is greater than the reference quantity of energy.

2. The method as claimed in claim 1, wherein the second factor is equal to the first factor.

3. The method as claimed in any one of claims 1 to 2, further comprising computing (112) the reference quantity of energy from the stored period and a remaining quantity of energy in a battery of the transmitter.

4. The method as claimed in any one of claims 1 to 3, wherein the quantity of energy is estimated (112) from a duration of transmission of the first signal and a transmission power of the first signal.

5. A computer program product comprising program code instructions for the execution of the steps of the method as claimed in any one of claims 1 to 4, when this program is executed by a transmitter (4).

6. Computer-readable medium comprising code instructions for causing a transmitter to perform the method as claimed in any one of claims 1 to 4.

7. A transmitter (4) comprising: • a radio communication interface (8), • a control unit (12) configured to implement the method as claimed in any one of claims 1 to 4, such that the first radio signal and the second radio signal are transmitted by the radio communication interface.

8. A meter (1) for measuring a consumption of fluid, the meter (1) comprising a transmitter as claimed in claim 7, wherein the first payload data frame or the second payload data frame comprise at least a measurement of consumption of a fluid.