Data transmission/reception by frequency hopping

Abstract

The invention relates to a method for the telecommunication of data by frequency hopping in a first frequency band, wherein the frequency hops follow a predetermined time sequence, known at least to a data transmitter, characterized in that it comprises the following steps implemented by said data transmitter: defining, from a pseudo-random sample, successive values of respective differences in frequency (fs1, fs2, fs3, . . . ; fd1, fd2, fd3, etc.) in order to determine the hopping time sequence starting at a first frequency (f1), transmitting to at least one data receiver at a first frequency (f1), said first frequency being randomly selected (S1) within the first frequency band, then at successive frequencies (S5) which, starting at the first frequency, comply with said successive values of respective differences in frequency, said successive values of differences in frequency defining, at reception, a succession of reception frequencies for useful data to be received from said data transmitter.

Claims

1. A method for the telecommunication of data by frequency hopping in a first frequency band, wherein the frequency hops follow a predetermined time sequence, known at least to a data transmitter, characterized in that it comprises the following acts implemented by said data transmitter: defining, from a pseudo-random sample, successive values of respective differences in frequency (fs1, fs2, fs3, . . . ; fd1, fd2, fd3, . . . ) in order to determine the hopping time sequence starting at a first frequency (f1), transmitting to at least one data receiver at a first frequency (f1), said first frequency being randomly selected (S1) within the first frequency band, then at successive frequencies (S5) which, starting at the first frequency, comply with said successive values of respective differences in frequency, said successive values of differences in frequency defining, at reception, a succession of reception frequencies for useful data to be received from said data transmitter.

2. The method of claim 1, comprising an act prior to transmission, wherein: after randomly selecting the first frequency, the transmitter listens (S2) in the first band for said first frequency before any transmission, to verify the availability of a transmission channel corresponding to the first frequency, and: if the channel is free, proceeds with a transmission on the first frequency and then at successive frequencies in compliance with said differences in frequency, if the channel is busy: randomly selects another first frequency, and repeats the verification of availability of the corresponding transmission channel, until an available channel is found.

3. The method of claim 1, wherein the transmitter sends: synchronization data at the first frequency (fs1=f1), then at a first set of successive frequencies (fs2, fs3, . . . ) with differences in frequency (fs1, fs2, fs3, . . . ) between the successive frequencies of this first set, starting at the first frequency, which are representative of said successive values of respective differences in frequency of the time sequence (fd1, fd2, fd3, . . . ), then useful data, at the first frequency (fd1=f1) then at a second set of successive frequencies which, starting at the first frequency, comply with said successive values of respective differences in frequency of said time sequence (fd1, fd2, fd3, . . . ).

4. The method of claim 3, wherein the first set (fs2, fs3, . . . ) is identical to the second set (fd2, fd3, . . . ).

5. The method of claim 1, wherein the first frequency and the successive frequencies define a data transmission sequence, and further wherein the transmitter repeats said data transmission sequence (S7; S13) a predefined number of times, at said first frequency then at said successive frequencies.

6. The method of claim 1, wherein at least a portion of the respective differences in frequency of the sequence contributes to defining an identifier of the transmitter (S29).

7. The method of claim 6, wherein a first portion of the respective differences in frequency of the sequence contributes to defining a membership group (GpY) of the transmitter and a second portion of the respective differences in frequency of the sequence contributes to defining the identifier specific to the transmitter (EmX) within that group.

8. The method of claim 6, wherein the hops from one frequency to another in the sequence are defined at successive time intervals which are variable within the sequence, and wherein said successive time intervals further contribute to defining an identifier of the transmitter.

9. The method of claim 1, wherein a receiver, to which data is to be sent, scans the first frequency band (S21) to identify the first frequency (S24) and a first portion at least of said successive frequencies which, starting at the first frequency, comply with said successive values for the respective differences in frequency (fi, fi+1, . . . ), said first portion at least of said successive frequencies allowing the receiver to identify (S28) the succession of reception frequencies for useful data to be received from the data transmitter.

10. The method of claim 9, wherein the receiver is connected to a database (DB) storing pseudo-random samples defining sequences used in transmission by one or more transmitters, and wherein, on the basis of said first portion at least of said successive frequencies, the receiver: determines successive differences in frequency (S25) starting at the first frequency identified by scanning the first frequency band (S24), compares (S27) said successive differences in frequency, to differences in frequency of sequences corresponding to the pseudo-random samples stored in the database, and identifies (S28), on the basis of said comparison, the time sequence used by the transmitter for receiving (S30) useful data on the successive frequencies of the sequence thus identified.

11. A non-transitory computer-readable storage medium storing a code of a computer program, characterized in that said computer program comprises instructions for implementing the method according to claim 1 when this program is executed by a processor.

12. A method for the telecommunication of data by frequency hopping in a first frequency band, wherein the frequency hops follow a predetermined time sequence, known at least to a data transmitter, characterized in that it comprises the following acts implemented by said data transmitter: defining, from a pseudo-random sample, successive values of respective differences in frequency (fs1, fs2, fs3, . . . ; fd1, fd2, fd3, . . . ) in order to determine the hopping time sequence starting at a first frequency (f1), transmitting to at least one data receiver at a first frequency (f1), said first frequency being randomly selected (S1) within the first frequency band, then at successive frequencies (S5) which, starting at the first frequency, comply with said successive values of respective differences in frequency, said successive values of differences in frequency defining, at reception, a succession of reception frequencies for useful data to be received from said data transmitter; wherein the transmitter sends: synchronization data at the first frequency (fs1=f1), then at a first set of successive frequencies (fs2, fs3, . . . ) with differences in frequency (fs1, fs2, fs3, . . . ) between the successive frequencies of this first set, starting at the first frequency, which are representative of said successive values of respective differences in frequency of the time sequence (fd1, fd2, fd3, . . . ), then useful data, at the first frequency (fd1=f1) then at a second set of successive frequencies which, starting at the first frequency, comply with said successive values of respective differences in frequency of said time sequence (fd1, fd2, fd3, . . . ) wherein a receiver, to which data is to be sent, scans the first frequency band (S21) to identify the first frequency (S24) and a first portion at least of said successive frequencies which, starting at the first frequency, comply with said successive values for the respective differences in frequency (fi, fi+1, . . . ), said first portion at least of said successive frequencies allowing the receiver to identify (S28) the succession of reception frequencies for useful data to be received from the data transmitter; wherein the receiver is connected to a database (DB) storing pseudo-random samples defining sequences used in transmission by one or more transmitters, and wherein, on the basis of said first portion at least of said successive frequencies, the receiver: determines successive differences in frequency (S25) starting at the first frequency identified by scanning the first frequency band (S24), compares (S27) said successive differences in frequency, to differences in frequency of sequences corresponding to the pseudo-random samples stored in the database, and identifies (S28), on the basis of said comparison, the time sequence used by the transmitter for receiving (S30) useful data on the successive frequencies of the sequence thus identified, wherein the database stores pseudo-random samples defining sequences used for the transmission of synchronization data, and wherein the transmitter and receiver use a predetermined rule (F), known to the transmitter and receiver, to define a sequence for respectively transmitting (S9) and receiving useful data based on a sequence used for the transmission of synchronization data.

13. A data transmitter (Em1), comprising a logic circuit programmed to implement a method for the telecommunication of data by frequency hopping in a first frequency band, wherein the frequency hops follow a predetermined time sequence, known at least to a data transmitter, characterized in that it comprises the following acts implemented by said data transmitter: defining, from a pseudo-random sample, successive values of respective differences in frequency (fs1, fs2, fs3, . . . ; fd1, fd2, fd3, . . . ) in order to determine the hopping time sequence starting at a first frequency (f1), transmitting to at least one data receiver at a first frequency (f1), said first frequency being randomly selected (S1) within the first frequency band, then at successive frequencies (S5) which, starting at the first frequency, comply with said successive values of respective differences in frequency, said successive values of differences in frequency defining, at reception, a succession of reception frequencies for useful data to be received from said data transmitter.

14. A system comprising at least one data transmitter (Em1), comprising a logic circuit programmed to implement a method for the telecommunication of data by frequency hopping in a first frequency band, wherein the frequency hops follow a predetermined time sequence, known at least to a data transmitter, characterized in that it comprises the following acts implemented by said data transmitter: defining, from a pseudo-random sample, successive values of respective differences in frequency (fs1, fs2, fs3, . . . ; fd1, fd2, fd3, . . . ) in order to determine the hopping time sequence starting at a first frequency (f1), transmitting to at least one data receiver at a first frequency (f1), said first frequency being randomly selected (S1) within the first frequency band, then at successive frequencies (S5) which, starting at the first frequency, comply with said successive values of respective differences in frequency, said successive values of differences in frequency defining, at reception, a succession of reception frequencies for useful data to be received from said data transmitter; and a receiver (REC), to which data is to be sent, comprising a logic circuit programmed to scans the first frequency band (S21) to identify the first frequency (S24) and a first portion at least of said successive frequencies which, starting at the first frequency, comply with said successive values for the respective differences in frequency (fi, fi+1, . . . ), said first portion at least of said successive frequencies allowing the receiver to identify (S28) the succession of reception frequencies for useful data to be received from the data transmitter.

15. The receiver (REC) of a system according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features and advantages of the invention will be apparent from examining the following detailed description of some exemplary embodiments and the appended drawings in which:

(2) FIG. 1 shows a flowchart illustrating the steps implemented by a transmitter within the meaning of the invention.

(3) FIG. 2 shows a flowchart illustrating the steps implemented by a receiver within the meaning of the invention.

(4) FIG. 3 schematically illustrates a system comprising a transmitter and a receiver within the meaning of the invention

DETAILED DESCRIPTION OF THE INVENTION

(5) Referring to FIG. 1 which illustrates the implementation of an exemplary embodiment of the method at a transmitter, in a first step S1, the transmitter randomly selects a frequency f1 within the entire band of available frequencies (said first frequency band, for example around 868 MHz for LoRA or Sigfox).

(6) In one particular embodiment, in step S2, the transmitter listens for whether or not the channel corresponding to this frequency f1 is busy, and if this frequency is busy (KO arrow exiting test S2), randomly selects a different other frequency f1, and again checks the availability of the corresponding channel. The transmitter may for example perform this verification step according to the principle of CSMA (Carrier sense multiple access) or LBT (Listen before talk). The new frequency tested is different from the initial value, for example by a selected distance (typically greater than the bandwidth of the useful signal). In this manner it is possible to take advantage of the degree of freedom provided by the random selection of the first frequency f1, to limit the risk of collision between transmissions from different transmitters even if they share a same portion at least of the hop sequence fs1, fs2, fs3, . . .

(7) After choosing a frequency f1 whose channel is available, in step S3 a processor comprised in the transmitter finds, by accessing a memory MEM comprised in the transmitter, the data of a previously saved pseudo-random code. The data in this code indicate in step S4 the respective differences in frequency fs1, fs2, fs3, . . . to be applied, starting at an initial frequency f1, for transmitting the synchronization data SYNC in the corresponding frequencies fs1, fs2, fs3, fs4, . . . , in the embodiment described by way of example here.

(8) Thus, in step S5, these successive frequencies fs1, fs2, fs3, fs4, . . . , are constructed as follows: fs1=f1, fs2=f1+fs1, fs3=f1+fs2, fs4=f1+fs3, etc.

(9) Alternatively, these frequencies may be defined differently, for example as follows: fs1=f1, fs2=fs1+fs1, fs3=fs2+fs2, fs4=fs3+fs3, etc.

(10) In one embodiment, the data of the code may define a transmission duration at each frequency (for example, 500 ms at fs1, then 300 ms at fs2, then 600 ms at fs3, etc.). In a simpler embodiment, the durations may instead be constant.

(11) A synchronization signal may then be sent at a first time, in step S6, to these transmission frequencies fs1, fs2, fs3, fs4, . . . and at a rhythm as defined above.

(12) Preferably, the transmitter redundantly sends the synchronization signal at these successive frequencies in step S7. This redundancy defines the sending of the sequence a predefined number of times (for example two or three times, or more), so that a receiver can find the entire sequence of successive frequencies.

(13) The transmitter can then send the useful data DAT. In one particular embodiment described below, the frequencies chosen for sending useful data are different from the frequencies used for sending synchronization data.

(14) In one possible embodiment, the transmitter may have in its memory MEM another sequence that defines another pseudo-random code for the sending of useful data, or may use the memory MEM in step S8 to find a function F which enables, in step S9, in general obtaining the differences in frequency to use to define the transmission frequencies of the useful data, based on the differences in frequency used to send synchronization data.

(15) Thus in step S10, the transmitter can obtain the differences in frequency for sending useful data, denoted fd1, fd2, fd3, . . . and obtained by applying function F to the differences in frequency for sending synchronization data fs1, fs2, fs3, . . . , which is: fd1, fd2, fd3, . . . =F (fs1, fs2, fs3, . . . )

(16) For example, by using the following numerical values: fs1=+30 Hz, fs2=50 Hz, fs3=+80 Hz, . . . one can define a very simple affine function of the type: fdi=10fsi, such that fd1=+300 Hz, fd2=500 Hz, fd3=+800 Hz, . . .

(17) Such an embodiment allows for example reducing the complexity of the receiver and only having to listen for the sequence of the synchronization signal on a reduced frequency band (for example 100 Hz+f1 to 100 Hz+f1). Once the synchronization sequence is recognized, the receiver can then progressively be positioned in all the frequencies for receiving useful data, which may be located in a wider band (for example said first frequency band).

(18) This embodiment more generally allows preventing an intruder receiver which has received the sequence of synchronization data, from immediately identifying the sequence of useful data.

(19) Moreover, the sequence used for synchronization can be shorter than the sequence used for the transmission of useful data (the second sequence always being deduced from the first by a predefined function, or storage of corresponding code in memory), to allow a transmitter to reduce the amount of data to be transmitted and thus save resources.

(20) Next, in the following step S11, the set of transmission frequencies for the useful data may be constructed as follows: fd1=f1, fd2=f1+fd1, fd3=f1+fd2, fd4=f1+fd3, etc.

(21) Here, for the sake of simplicity, the first frequency f1 is chosen to be the same for the transmission of synchronization data and the transmission of useful data, since the associated channel has been detected as available. However, alternatively, the sequence of differences in frequency for synchronization may also define a first frequency fd1 that is different from f1, for the transmission of useful data.

(22) In step S12, the useful data can be sent to these successive transmission frequencies fd1, fd2, fd3, . . . , possibly with redundancy in step S13.

(23) We now refer to FIG. 2 to describe an exemplary embodiment of a counterpart process performed by the receiver. In step S21 of FIG. 2, the receiver scans the entire frequency band (said first band) and receives in step S22 a succession of synchronization data at different reception frequencies fi, fi+1, . . . , fn, f1, f2, f3, . . . , the redundancy in receiving these data in step S23 making it possible to define all of these reception frequencies.

(24) If a synchronization pulse is provided between transmission at and transmission at f1, then it is possible to determine f1 and from this the differences in frequency f1, f2, f3, etc.

(25) Alternatively, in one exemplary embodiment, one can require that the pseudo-random sequence for the transmission/reception of synchronization data at least, satisfies a selected property, for example that the algebraic sum of the differences in frequency f1, f2, f3 . . . is zero.

(26) Thus, the average of the received frequencies fi, fi+1, . . . , fn, f1, f2, f3, . . . , must equal the first frequency f1. One can also verify that the algebraic sum of the differences between frequencies received is zero, to ensure that the different frequencies received do indeed come from the same transmitter for example, and typically to ignore the frequencies that no longer appear in the redundancies.

(27) From the first frequency f1 thus determined in step S24, the associated differences in frequency are determined in step S25: fi=fif1, fi+1=(fi1)(f1), etc.

(28) In step S26, the receiver refers to a previously saved database DB of sequences of differences in frequency, each sequence being for example specific to a transmitter (or group of transmitters) with which it can communicate. The receiver thus has, in the received differences fi, fi+1, etc., at least a portion of the corresponding sequence previously saved in a memory MEM of the receiver. In step S27, the receiver can execute for example a comparison routine (matching algorithm) in order to identify in step S28, in the database DB, the sequence fs1, fs2, fs3, . . . , fsi, fsi+1, . . . , fsn, corresponding to that received sequence portion fi, fi+1, etc. Optionally, the respective reception delays at each frequency fi, fi+1, etc. may also help identify the sequence in the database DB.

(29) At this stage, in step S29, the receiver can deduce from the identified sequence that the transmitter listed as corresponding to this sequence in the database DB is a transmitter of identifier EmX, belonging to a group of transmitters GpY because it has for example a sequence portion in common with the transmitters of this group GpY (for example the beginning of the sequence: fs1, fs2, fs3).

(30) In step S30, the receiver constructs the succession of frequencies in order to await the reception of useful data in the successive channels corresponding to these frequencies, starting with the sequence fs1, fs2, fs3, etc. so identified. In one exemplary embodiment, the reception frequencies are defined, as indicated above with reference to FIG. 1, from the frequency f1 and the sequence fs1, fs2, fs3 . . . , as follows: fd1=f1, fd2=f1+fd1, fd3=f1+fd2, fd4=f1+fd3, etc.
where fd1, fd2, . . . =F(fs1, fs2, . . . ), F being the function predefined in the transmitter and receiver and for which the data can be stored in a memory MEM of the receiver.

(31) For example: fd1=10 fs1; fd2=10 fs2; etc.

(32) In the above example, different differences in frequency are described for the transmission of synchronization/timing data and for the transmission of useful data. However, the differences may be the same in these two transmissions. Moreover, one will further note that it is not necessarily required to provide a transmission of synchronization data, the redundancy in the transmission of useful data making it possible to ensure the reception of all frequencies fd1, fd2, fd3, . . . fdn, and from this to deduce the first frequency f1 and the sequence used fd1, fd2, fd3, for the transmission of useful data. It should be more generally noted that the sequence generated pseudo-randomly at the transmitter does not need to be known to the receiver. Indeed, due to redundancy, knowledge of the entire sequence can be deduced from a predetermined rule (for example the algebraic sum of the differences f1, f2, f3, etc., is zero, and the average frequency corresponds to the first frequency f1).

(33) Illustrated in FIG. 3 are the hardware components of a system having a receiver and one or more transmitters according to an exemplary embodiment of the invention. In the illustrated example, the receiver REC comprises a reception antenna RA, connected by an interface R1 to a processor R3 capable of interpreting the received signals and deducing the respective sequences therefrom, by communicating with a memory R4 which typically stores instructions of a computer program within the meaning of the invention, as well as any temporary data. This memory R4 may further store the contents of the database, or alternatively may communicate via the interface R2 with a remote database DB which also stores transmitter identifiers ID EMI, ID EM2, etc. (and/or transmitter groups).

(34) For example, a corresponding transmitter EMI typically comprises an antenna EA connected via an interface E1 to a processor E3 in order to form the data signals to be transmitted (synchronization or useful data), in a sequence constructed by communicating with a memory E4 which typically stores instructions of a computer program within the meaning of the invention (as well as any temporary data). The transmitter EMI may further comprise another interface E2 for accessing the memory E4 and storing in it said instructions, as well as the pseudo-random code defining the sequence used for the transmission of synchronization data and/or the sequence used for the transmission of useful data.

(35) Compared to the prior art, the approach of the invention provides the following advantages over conventional frequency hopping systems: it requires no prior synchronization, neither in time nor in frequency, between transmitter and receiver, since the receiver fully adapts to the transmissions of the transmitter: the receiver is therefore particularly suitable for transmitters equipped with oscillators of low quality and therefore having very limited control over their actual transmission frequency, which is typically the case for the low-cost, low-power terminals in the Internet of Things; unlike most frequency hopping systems, no agreement on an initial frequency or initial transmission channel is required to trigger the start of the frequency hopping (typical case of the first hop frequency, used in common channels): this first transmission can occur anywhere in the spectrum; it is not more indispensable than the signal fragments that follow, which can also increase system robustness against interference; the ability to transmit information in the hop sequence itself is another advantage (even during the receiver's synchronization search): this allows considering a frequency hopping system that uses a plurality of hop sequences in a same transmission, to optimize use of the radio resource, for example, a unique starting hop sequence associated with a given group of transmitters can be used to initiate synchronization (possibly including basic information concerning this group of transmitters), then a complementary portion in the synchronization sequence can be characteristic of one of those transmitters for the actual communication portion with that transmitter.

(36) The result is essentially better stealth and greater ruggedness, and in particular a general relaxation of the constraints on radio implementation, which makes frequency hopping systems accessible to the most limited radio systems.

(37) However the bitrates necessarily remain low, and some of the complexity is transferred to the receiver. Nevertheless, in an application in connected objects, this constraint can be satisfied since the receivers are much less limited than the transmitters. This is already the case in very narrowband systems. Compared to conventional narrowband systems, the main advantage of the invention is that it enables them to take advantage of a broadband radio channel without compromising their goals of cost and very low power consumption, or the sensitivity of the system.

(38) The algorithm enabling the receiver to synchronize to the frequency hop sequence by using only the distances between consecutive hops, without the use of an absolute reference, provides both robustness against the loss of information, and reliability in the acquisition of synchronization in a legitimate signal (in the sense where the identity of the transmitter is assured by this means).

(39) The invention is advantageous for use in an Internet of Things context, which requires a capacity for communication that is both robust and reliable but also inexpensive and energy efficient, for objects incapable of receiving the usual communications means primarily for reasons of cost and energy consumption. In fact, for a negligible additional cost, this invention provides increased flexibility and robustness to existing radio interfaces designed for this type of use, while rendering the radio link more reliable.