BE1024408B1 - Method and device for wireless communication - Google Patents

Abstract

Methods of communication in a wireless communication network comprising a plurality of connected objects, a gateway and a central server. These elements communicate with each other by messages sent and received on frequency channels. A channel is reserved for the periodic transmission of messages tagged by the gateways, which allows the organization and optimization of the time of use and communication of the network.

Description

(73) Holder (s):

CROHAS Henri 1160, AUDERGHEM Belgium (72) Inventor (s):

CROHAS Henri 1160 AUDERGHEM Belgium (54) Wireless communication method and device (57) Communication methods in a wireless communication network comprising a plurality of connected objects, a gateway and a central server. These elements communicate with each other by messages sent and received on frequency channels. A channel is reserved for the periodic emission of beacon messages by the gateways, which allows the organization and optimization of the network usage and communication time.

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BELGIAN INVENTION PATENT

FPS Economy, SMEs, Middle Classes & Energy

Publication number: 1024408 Deposit number: BE2016 / 5737

Intellectual Property Office International Classification: H04W 74/08 H04B 7/26 H04W 92/20 Date of issue: 02/08/2018

The Minister of the Economy,

Having regard to the Paris Convention of March 20, 1883 for the Protection of Industrial Property;

Considering the law of March 28, 1984 on patents for invention, article 22, for patent applications introduced before September 22, 2014;

Given Title 1 “Patents for invention” of Book XI of the Code of Economic Law, article XI.24, for patent applications introduced from September 22, 2014;

Having regard to the Royal Decree of 2 December 1986 relating to the request, the issue and the maintenance in force of invention patents, article 28;

Given the patent application received by the Intellectual Property Office on 04/10/2016.

Whereas for patent applications falling within the scope of Title 1, Book XI of the Code of Economic Law (hereinafter CDE), in accordance with article XI. 19, §4, paragraph 2, of the CDE, if the patent application has been the subject of a search report mentioning a lack of unity of invention within the meaning of the §ler of article XI.19 cited above and in the event that the applicant does not limit or file a divisional application in accordance with the results of the search report, the granted patent will be limited to the claims for which the search report has been drawn up.

Stopped :

First article. - It is issued to

CROHAS Henri, Avenue Louis Berlaimont 5A, 1160 AUDERGHEM Belgium;

represented by

FISHING Nicolas, Rue Louis de Geer 6, 1348, LOUVAIN-LA-NEUVE;

a Belgian invention patent with a duration of 20 years, subject to payment of the annual fees referred to in article XI.48, §1 of the Code of Economic Law, for: Wireless communication method and device.

INVENTOR (S):

CROHAS Henri, Avenue Louis Berlaimont 5A, 1160, AUDERGHEM;

PRIORITY (S):

DIVISION:

divided from the basic application: BE2015 / 5622 filing date of the basic application: 05/10/2015

Article 2. - This patent is granted without prior examination of the patentability of the invention, without guarantee of the merit of the invention or of the accuracy of the description thereof and at the risk and peril of the applicant (s) ( s).

Brussels, 08/02/2018, By special delegation:

BE2016 / 5737

Wireless communication method and device

Technical Field [0001] The invention relates to communication protocols in a radio frequency network and more particularly to methods allowing this type of communication within a long range and low power wireless network. In its application in a layered model, the invention relates to the protocol of the link layer (layer comprising the Media Access Control MAC). The invention also relates to devices implementing these methods.

PRIOR ART [0002] Data exchange methods are known in a wireless network comprising connected objects, gateways and a central server. For example, patent application US 2014/0111313 discloses a communication method in which a connected object must perform many steps before connecting to a gateway. These steps consist of:

• listening to a periodic signal containing a beacon signal sent by at least one gateway;

• synchronization of the internal clock of the connected object with the beacon signal;

• the identification of the gateway by the connected object thanks to the beacon signal;

• selection of the gateway with the strongest beacon signal;

• the sending of a message on a time slot for a join request by the connected object;

• the identification of the object connected by the gateway and allocation of a time slot for communications;

• the reception of the time slot by the connected object during a time slot for acknowledgment of junction receipt (join acknoledgement);

• the communication between the connected object and the gateway on the allocated time slot.

BE2016 / 5737

This type of protocol has several limitations. First, the management of usage time is far from optimal since the splitting of the periodic signal into time windows and time sub-windows lengthens the time between communications. Second, if the number of gateways is increased, the duration of the periodic signal increases (or the number of sub-windows decreases), which further increases the time between communications (or reduces the number of sub-windows attributable by a bridge). Third, the number of time slots that a gateway can assign to connected objects is limited so that the periodic signal does not become too long. The risks of network saturation therefore become significant. In conclusion, this protocol lacks flexibility, is poorly suited to objects communicating on an ad hoc basis and does not optimize the use of time useful for communications.

Another method of exchanging data in a wireless network is described in the LoRa communication protocols (https://www.loraalliance.org/) which describes a network comprising a set of macro-cells each comprising connected objects and a macro-gateway (of the type placed on a roof - rooftop). Each macro-gateway is capable of receiving several messages simultaneously on different frequency channels and at transfer rates (or bit rate, i.e. the amount of digital data transmitted per unit of time expressed in bit / s or bytes / s) different (about 8 channels and 8 transfer rates). A connectable connected object having a message to send semi-randomly selects a channel and a compression factor (depending on its distance from the macro-gateway) and sends its message. This protocol also has several flaws. First, the usage time is not organized: each connected object sends its data when it wants, on the sole condition of not exceeding any legal usage limits. Therefore, given the large number of connected objects potentially linked to a macro-gateway, the probability of message collision can become significant. Second, the macro gateway only exceptionally sends information. The reasons are that when the macro gateway transmits a signal, it dazzles the uplink signals and is therefore unable to receive a message. Another reason is that the broadcast time

BE2016 / 5737 in a public frequency band and / or the rate of use of this band by a transmitter are in most cases severely restricted by the radio regulatory authority and as these macro-gateways aim to serve a large number of objects, the emission time which they can devote to individual objects is thereby extremely limited. Consequently, if the macro-gateway transmits, it will occupy part of the time which will reduce the time available for listening to uplink messages and will contribute to exhausting the downtime capital allocated by the authority of regulation. This will therefore increase the waiting time for connected objects to communicate and the risk of message collisions. In addition, if the macro-gateway regularly sends messages, it risks quickly reaching the legal time limits. For the same reasons, the macro-gateway only exceptionally sends an acknowledgment to the connected objects which can also be problematic.

In other words, the network usage time is not optimal and the network is saturated. This situation is all the more probable that the macroploves serve macro-cells potentially comprising a large number of connected objects.

Summary of the invention The invention is defined by the independent claims. The dependent claims define preferred embodiments of the invention.

According to a first aspect, the invention relates to communication methods in a wireless communication network using a plurality of channels each having a central frequency and a bandwidth, said network comprising a plurality of connected objects and at least one gateway, said connected objects and at least one gateway being capable of transmitting and receiving messages in each of the channels, at least one of these channels, called beacon channel, being reserved for the periodic or quasiperiodic emission of messages tagged by gateways.

BE2016 / 5737 [0006] One of the aims of the invention is to solve the problems of network saturation as described above and to optimize the use of time. The proposed solution consists of the use of beacon messages sent on a beacon channel and sent periodically by gateways. These beacon messages are used to warn connected objects of the availability of a gateway to send or receive messages. They also allow connected objects to select a gateway with which they will have good communication. In addition, the communication procedure is simple because connected objects can send a message at any time from the moment they receive a beacon message. Connected objects no longer need to maintain a perfectly synchronized internal clock. Communication times are therefore well organized and profitable. Finally, the gateways are organized without external intervention and the addition of a gateway allows (without external intervention) to increase the network capacities.

The first method of communication in a wireless communication network relates to communications between a plurality of connected objects and at least one gateway. In this method, the beacon message comprises at least the following elements: either an indication that the gateway wants to deliver a message or that it is capable of receiving at least one message and an indication of at least one channel for exchanging at least one message. This process is a process by which:

a) a connectable connected object transfers a message to a gateway. For this, the connected object listens to the tag channel or channels to detect at least part of at least one tag message, said part of the tag message making it possible to determine an RSSI of the signal carrying said tag message. Then, the connected object selects a gateway according to the RSSI, then it receives the beacon message sent by the selected gateway and it verifies that this gateway is able to receive a message. Finally, the connected object sends a message to the selected gateway on at least one channel indicated in the beacon message.

b) a connectable connected object receives a message from a gateway For this, the connected object listens to the beacon channel or channels to receive at

BE2016 / 5737 minus a beacon message. Then the connected object checks that the gateway wants to deliver a message to it. Finally, the connected object receives a message on at least one channel indicated in the tag message.

Preferably, the tag message further comprises a preamble and a connected object listens to the tag channel or channels to detect at least part of at least one preamble, said part of the preamble making it possible to determine an RSSI of the signal. The advantage of this preamble is on the one hand, to avoid losing a useful part of the message and, on the other hand, to allow an easy detection of the signal, the preamble being, for example, made up of powerful chirps signals and easily detectable.

Preferably, the beacon message further comprises at least one identifier of at least one connected object and a connected object verifies that the gateway wants to deliver a message to it and verifying that the at least one identifier contained in the beacon message is hers. This is a simple and efficient method for the connected object to ensure that the message is intended for it. Preferably, the connected object which wishes to send a message chooses its transfer rate according to the RSSI so that this rate is higher when the RSSI is high and lower when the RSSI is lower. This step, which can be repeated with each sending, thus minimizing the hazards inherent in the fluctuations of the radio channel over time, makes it possible to better use the useful time by minimizing the transfer times when the connected objects are close to the gateway. On the other hand, this ensures good transmission of long-range, low-power signals when the connected object is further from the gateway. The transfer rate or bit rate is defined as the measure of the amount of digital data transmitted per unit of time.

Preferably, the connected object waits for a period of time which is a function of the transfer rate chosen before sending its message. Indeed, the gateway that receives the messages may have to scan the different transfer rates to detect the message, so it must be sent at the right time.

Preferably, the connected object or the gateway transmits or receives an acknowledgment of receipt of the radio frequency transmission on the same channel as

BE2016 / 5737 the one used either for transmission or for reception. This acknowledgment is issued by the connected object or the gateway which received a message after reception. The purpose of this step is to notify the sender that their message has been received. The purpose of this accused is that if a sender does not receive an accused, he knows that his message has not been delivered and he can try to send it again at a later time.

Preferably, the acknowledgment is an acknowledgment of receipt of the RF transmission and is sent directly after receipt of a message. Preferably, the acknowledgment is sent or received with a transfer rate equal to or less than that of the message received or sent. This eliminates the need to scan all transfer rates to find the acknowledgment.

Preferably, the gateway chosen by a connected object when it wants to send a message is one of the gateways with the highest RSSI. The goal is to ensure rapid transfer and to optimize network usage time.

Preferably, the gateway chosen by a connected object when it wants to send a message is a gateway having a high quality of service (QoS). Preferably, the gateway chosen by a connected object is the one which makes it possible to transport in good conditions a given type of traffic, that which is available, which has a good speed, good transmission times, a low packet loss rate. Alternatively, the gateway selected is the one with a high signal to transmission noise ratio.

Preferably, the network further comprises a central server, said central server being able to assign a gateway to a connected object. For various reasons: quality of service, economic, it may be interesting to link an object connected to a gateway.

According to a second aspect, the invention consists of a device comprising a radiofrequency modem characterized in that it implements a procedure described above.

The second method of communication in a wireless communication network relates to communications between a gateway and a connectable connected object. In this process, the tag message includes at

BE2016 / 5737 minus the following: either an indication that the gateway wants to deliver a message or that it is able to receive at least one message and an indication of at least one channel for exchanging at least one message. This process is a process by which:

a) a gateway emits, in its time window, a signal carrying a beacon message.

b) a gateway receives at least one message from a connected object. In this case, the gateway begins by listening to the channel or channels assigned in the beacon message in order to detect a message. Then the gateway receives the message it detected.

c) a gateway sends at least one message to at least one object connected on the at least one channel indicated in the beacon message.

Preferably, the tag message further comprises at least one identifier of at least one connected object. A gateway wishing to send a message to at least one connected object sends the identifier of the connected object (s) in its beacon message to inform them that the said gateway has a message for them or deliver them.

Preferably, the gateway which wants to receive a message scans different transfer rates simultaneously or sequentially and listens on the channel or channels assigned in the beacon message to detect a message. This step makes better use of the useful time by minimizing the transfer times when the connected objects are close to the gateway and when they use a high transfer rate. On the other hand, this ensures good transmission of long-range, low-power signals when the connected object is further from the gateway and uses a low transfer rate.

Preferably, the message sent by the connected object comprises a preamble and the gateway scans different transfer rates and listens on the channel or channels assigned in the beacon message to detect at least part of a preamble. The advantage of this preamble is on the one hand, to avoid losing a useful part of the message and, on the other hand, to allow an easy detection of the signal, the preamble being made up of powerful and easily detectable chirps signals.

BE2016 / 5737 Preferably, the gateways can send their beacon message on two parallel beacon channels. The signals transmitted carrying the beacon messages on the two channels are preferably orthogonal.

Preferably, the connected object or the gateway transmits or receives an acknowledgment of receipt of the radiofrequency transmission on the same channel as that used either for transmission or for reception. This acknowledgment is issued by the connected object or the gateway which received a message after reception. The purpose of this step is to notify the sender that their message has been received. The purpose of this accused is that if a sender does not receive an accused, he knows that his message has not been delivered and he can try to send it again at a later time.

Preferably, the acknowledgment is an acknowledgment of receipt of the RF transmission and is sent directly after receipt of a message. Preferably, the acknowledgment of receipt is sent or received with a transfer rate equal to or lower than that of the message received or sent. This eliminates the need to scan all transfer rates to find the acknowledgment.

According to a third aspect, the invention consists of a device comprising a radio frequency modem characterized in that it implements a procedure described in the paragraphs concerning the second method (that is to say those included between the paragraph starting with "The second process" and the paragraph preceding this one).

The third method of communication in a wireless communication network relates to communications between at least two gateways. In this method, the tag message includes at least one preamble. This method is a method by which a time window is associated with a gateway. For this, the gateway listens to the beacon channel or channels for at least a whole period. Then, if the gateway has detected at least part of a preamble and at least one time window is available, the gateway chooses one of these windows and said gateway begins to send its beacon message. If the gateway has detected at least part of a preamble and no time window is available, the

BE2016 / 5737 gateway goes to sleep. If the gateway does not detect any preamble, it chooses a time window and it begins to transmit its beacon message. Preferably, a gateway which has paused because no time window was available wakes up after at least one period of issuing beacon messages and begins to search again for an available time window.

Preferably, the network further comprises a central server, said server determining the order of the time windows of each of the gateways.

Preferably, the server assigns the time windows to the gateways.

Preferably, the server assigns a companion channel to a gateway, this companion channel allowing only the gateway to receive messages in a time window used by another gateway.

The fourth method of communication in a wireless communication network relates to the resynchronization of the gateways. In this method, the tag message includes at least one preamble. This method is a method by which a gateway listens to at least a portion of the beacon messages of the other gateways during at least one whole period of transmission of beacon messages. Then, said gateway calculates a reference time as a function of the beacon message or messages received and finally, the gateway adjusts its time window.

Preferably, the network further comprises a central server, said server controlling and initiating the synchronization of each gateway after a predefined number of period for issuing beacon messages.

Brief description of the drawings These aspects as well as other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, reference being made to the drawings of the figures, in which:

- Fig. 1 shows an example of a wireless communication network;

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- Fig.2a shows an example of simplified ISM 868MHz frequency band;

- Fig.2b shows an example of time division;

- Fig.2c shows an example of scanning two frequencies with a preamble of 10 symbols;

- Fig.3 shows a diagram of the communication method between a connected object and a gateway according to the invention;

- Fig.4 shows a diagram of the communication method between a gateway and at least one connected object according to the invention;

- Fig.5 shows a diagram of the communication method between several gateways according to the invention;

- Fig.6 shows a diagram of the synchronization method between several gateways according to the invention;

- Fig.7 shows a device implementing the methods according to the invention relating to gateways.

The drawings of the figures are not to scale. Generally, similar elements are denoted by similar references in the figures. The presence of reference numbers in the drawings cannot be considered to be limiting, including when these numbers are indicated in the claims.

Detailed description of certain embodiments of the invention [0036] Figure 1 shows an example of a wireless communication network 100 comprising a plurality of wirelessly connected objects 110, at least one gateway 120. The usual term "connected object Should be understood as an object which is actually connected to a network or which is connectable to a network. Preferably, the network 100 comprises a plurality of gateways 120. Preferably, the gateway or gateways 120 are connected to a central server 130. This connection can be a local area network connection, a wired (Ethernet) or wireless internet connection ( Wireless). Preferably, the server 130 is a cloud type server. Preferably, the object network 110 - gateways 120 is a long range and low power wireless network (Low-Power Wide Area Network, LP-WAN).

BE2016 / 5737 Preferably, the network uses a plurality of frequency channels characterized by a central frequency and a bandwidth. Connected objects 110 and gateways 120 can send and receive messages in each of the channels. Figure 2a shows an example of a simplified ISM 868MHz frequency band, the percentages indicate the temporal occupancy rate of the legally authorized band (duty cycle) by a connected object. Preferably, the communications between the connected objects 110 and the gateways 120 take place in this frequency band. Alternatively, any other frequency band can be used.

Preferably, at least one of the channels, called the beacon channel, is reserved for the periodic or quasi-periodic transmission of beacon messages by the gateways 120. For example, in the ISM band 868 MHz (the ISM bands, industrial , scientific and medical, are frequency bands which can be used for industrial, scientific, medical, domestic or similar applications, without request for authorization), the beacon channel or channels can be located in sub-band 869.40 to 869.65 MHz with an occupancy rate of 10%. Preferably, there can be 2 beacon channels of 62.5 kHz bandwidth and respectively centered on the frequencies 869.46825 MHz and 869.58175 MHz. Alternatively, you can have 1 beacon channel of 125 kHz bandwidth, or 4 beacon channels of 41.7 kHz bandwidth. These channels can have different spreading factor (SF). Preferably, the number of beacon channels will be adjusted to the frequency subband used as a function of the frequency width thereof and any constraints of the authorized occupancy rate of the band or frequency subband.

FIG. 2b shows an example of the division of time according to the periodic transmission of period T, of a beacon message. In this figure, the arrows to the right indicate the transmission of a beacon message, the double arrows indicate either a descending message (to the right) or an ascending message (only one of these two operations can be performed during a period T, the start of the communication always being at the left origin of the arrow, the duration of the communication being able to be variable. For example, the n gateways 120 (PO, P1, ...) transmit one after the other their

BE2016 / 5737 beacon message. Preferably, each gateway 120 transmits its beacon message in its own time window. Once its beacon message has been sent, a gateway 120 either listens to receive an uplink message, or sends a downlink message for a connected object 110 (Oi, j, k, m). Preferably, the duration of the transmission depends on the size of the message to be transmitted and can be variable. Preferably, the maximum number of gateways 120 depends on the possible constraints of the authorized occupancy rate and the number of beacon channels. For example, in the case of a 10% limit and a single beacon channel, the maximum number of gateways making it possible to optimize the time is 10 gateways if we consider an average beacon message time of Tb = 50 ms for a cycle period T of 500 ms and a processing time with the chips of Tp = 4 ms. Indeed we have then that: Tb / (Tb + Tp) / 10 = 50 / (50 + 4) / 10 = 9.25%. Alternatively, two gateways 120 can simultaneously transmit their beacon message on two separate channels, which makes it possible to double the number of gateways 120 maximum. In addition, these simultaneously transmitting gateways 120 can transmit on orthogonal channels overlapping one another but without interfering due to the orthogonality of their signals at the level of the physical layer (for example by using orthogonal chirps).

The possibility that two gateways 120 simultaneously transmit their beacon message is all the more interesting as some radio frequency (RF) transceiver chips, such as the SX127x chips from Semtech based on the LoRa transmission protocol at the physical layer level , for example, can detect activity on a frequency channel (Channel Activity Detection CAD) in a very short time by analyzing very few signal symbols. This CAD allows a connected object 110 to detect a signal with only 1.8 symbols. Preferably, the messages exchanged in the network 100 include a preamble of ten symbols. FIG. 2c shows an example of scanning two frequency channels with a preamble of 10 symbols, these symbols preceding the useful data of the message. For example, in the case of a network 100 comprising two beacon channels, a connected object 110 can detect activity on a first channel by analyzing 1.8 symbols of a preamble sent on this first channel, then it can change the channel and detect an activity on a second channel by analyzing 1.8

BE2016 / 5737 symbols (if the signals are transmitted at the same time they are symbols 2 to 3.8) of a preamble transmitted on this second channel. This CAD characteristic of chips like SX127x chips, also allows to evaluate the power in reception of a received signal (Received Signal Strength Indication or RSSI) in a very short time in the same way.

Preferably, the tag message comprises at least part of the following elements:

a) a preamble: for example, a series of chirps signals each representing a symbol of the signal. Preferably this series comprises 5 to 20 signals. Even more preferably from 8 to 12.

b) either an indication that the gateway wants to deliver a message or that it is able to receive at least one message: for example, this can result in the presence of an Uplink bit: if Uplink = 1 (uplink: the gateway is able to receive at least one message), if Uplink = 0 (downlink: the gateway wants to deliver a message).

c) an indication of at least one channel for exchanging at least one message: for example, this indication can be expressed by a series of bits (preferably 4 bits for 16 channels), this series of bits coding a number associated with a particular channel. For example, if the bit codes the number 1, this means that the message exchange will take place on channel 1 corresponding to a bandwidth and a central frequency agreed in advance and predefined for example in the manufacture of connected objects 110 and gateways 120.

d) an identifier of a connected object 110: for example, this identifier can be expressed by a series of bits (preferably 1 to 40, or preferably 10 to 30, or preferably 16 bits), if the bit Uplink = 0, this series includes an identifier of a connected object 110 or of a group of connected objects 110 for which the message is intended. If the bit Uplink = 1, this part of the tag message can, for example, make it possible to transmit flags of information to the connected objects 100.

e) a companion channel indication: for example, this indication can result in a series of bits of the same length as the series to indicate a channel for exchanging at least one message. This indication

BE2016 / 5737 can be used in the case where the maximum number of gateways 120 is reached in the network 100. This indication can alternatively be used in the case where two gateways 120 are very close to each other. In these exemplary cases, a new gateway 120 can become a silent companion to a gateway 120 emitting a beacon signal. The companion channel indication allows a connected object to send a message not only to the transmitting gateway 120 but to the silent one, which doubles the reception capacity.

f) an indication of the beacon channel used: for example, this indication can be translated by a bit in the case where there are only two beacon channels.

g) an indication of the time window used: for example, this indication can be expressed by a series of bits (preferably 1 to 20, or preferably 2 to 10, or preferably 4 bits), which, associated with the indication of the beacon channel used, allow the gateways 120 to identify or be identified.

h) control information: for example, a cyclic redundancy check (CRC).

i) a group identification (cluster): when several networks 100 come together to form a larger network 100, the central server 130 can group them into subnets or clusters which are identified by a number coded by a series of bits.

Figure 3 shows a diagram of the communication method between a connected object 110 and a gateway 120 according to the invention. The first step consists in listening to at least one beacon channel 310. The second step depends on the type of communication: either the connected object 110 wants to transmit a message to the gateway 120, or the connected object wants to verify that the gateway 130 possibly wants to deliver a message to it and if necessary, receive this message from gateway 120. In the first case, the connected object 110 which wants to transmit a message to a gateway 120 performs the steps of detecting at least one part of at least one tag message. Preferably, the tag message includes a preamble and the detected part is a part of the preamble. Preferably this part of the beacon message makes it possible to evaluate the power in reception of a received signal (RSSI) 320. The RSSI makes it possible to provide an indication

BE2016 / 5737 on the strength of the received signal. Alternatively, other methods of assessing the signal strength can be used.

The next step is to select a gateway 120 according to the RSSI 321. Preferably, the gateway 120 selected is the one with the highest RSSI. Alternatively, the gateway 120 selected is the one with sufficient quality of service (quality of service QoS) and therefore the one which allows a given type of traffic to be carried in good condition, the one which is available, which has good speed, good transmission delays or a low packet loss rate. Alternatively, the gateway 120 selected is the one having a high signal to transmission noise ratio.

Alternatively, the central server 130 can link a connected object 110 to a preferred gateway 120. The connected object 110 will always try to connect in priority to this preferred gateway 120. In case it does not succeed, it can connect to a gateway with a good RSSI.

The goals of this privileged link can be varied but an economic goal can be put forward. In fact, the payment for the use of the network is usually made from the point of view of the connected objects 110. Each connected object 110 connecting to a gateway pays a “charge for access” to the network 100. For example, the costs of connection can be 0.5 € / connected object / year. The 120 gateways are inexpensive to produce and can be sold, for example, € 50 and can be installed very easily (power supply via a power outlet or via an Ethernet outlet, for example). A gateway installer 120 can then become a radio frequency (RF) network access provider quite easily. It is then very advantageous to be able to link a connected object 110 to a particular gateway 120 so that the service provider can be better paid according to the traffic which passes through its own gateways.

Once a gateway 120 has been selected by a connected object 110, the latter receives the entire beacon message and verifies that the gateway 120 is capable of receiving a message 322. For this, the connected object 110 can , for example, checking the value of the Uplink bit contained in the beacon message. The beacon message also includes an indication of at least one channel for exchanging messages and on which the gateway 120 is listening.

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If the gateway 120 is able to receive a message, the connected object 110 sends a message 324 to this gateway 120 on the channel indicated by the gateway

120 in its beacon message.

Preferably, the connected object 110 chooses a transfer rate 323 of its message as a function of the RSSI so that the transfer rate is higher if the RSSI is high and that the transfer rate is lower if RSSI is low. For example, SX127x chips use the spread spectrum technique at the radio frequency (RF) physical layer which is a transmission method in which the emitted energy is deliberately spread or distributed in the frequency domain. The purpose of this technique is to ensure good communication. Indeed, the most distant connected objects will use a larger spread and the closest connected objects will use a lower spread. Over a given time, the data transfer rate will therefore be lower for the most distant connected objects and greater for the nearby connected objects. The spreading factor, which is defined as the ratio between the spread bandwidth and the non-spread bandwidth, is therefore an indirect measure of the transfer rate. Consequently, the higher the RSSI the less the spectrum is spread and the lower the SF and the higher the transfer rate. Low SF is also synonymous with faster transmission since the transfer rate is higher. For example, the number of transfer rates can be between 1 and 20. Preferably, it is between 1 and 10. Even more preferably between 4 and 8. Preferably, the SFs range from 7 to 12.

Preferably, at the end of the sending of its message, a connected object 110 goes into listening mode and waits to receive an acknowledgment of receipt of the radio frequency transmission RF 325 emitted by the gateway 120. The purpose of this Acknowledgment of receipt is, for example, to indicate to the connected object that the RF transmission has gone well. In another example, this acknowledgment may contain information on the correct transmission of the message by the central server 130.

Preferably, this acknowledgment is received on the same channel as that used for the transmission of the message. Preferably, the acknowledgment of receipt is received with a transfer rate equal to or lower than that of the transmission of the

BE2016 / 5737 message. Preferably, this acknowledgment is a short message, the useful part of which comprises between 8 and 32 bits, preferably the useful part comprises bits.

If the connected object 110 does not receive an acknowledgment, it can try again to send its message during the following period T. The reasons why a connected object 110 may not receive an acknowledgment can be varied: interference, instability of the communication channel, fading, multiple signal reflections, poor communication, communication interruption, power failure depriving the gateway 120 one of the most common reasons is the collision of messages. If two connected objects 110 send their message at the same time, these messages can collide. There are then two possible scenarios: either one of the messages is well received and the other is not, or none of the messages is correctly received. In both cases, at least one of the two connected objects will not receive its acknowledgment of receipt. In this case, the connected object or objects 110 will try to send their message again after a random number of period T (this number being included, for example between 1 and 3). If a new collision occurs, the connected object or objects will retry after a random number of period T greater than the previous one (for example between 4 and 8).

In the case where the connected object 110 wants to verify that the gateway 120 possibly wants to deliver a message to it and if necessary, receive this message from the gateway 120, the latter begins by receiving the tag messages 330 from the various gateways 120 The connected object 110 verifies that the beacon message indicates that the gateway 120 which sent it has a message to deliver to it 331.

Preferably, the tag message includes an identifier specific to the connected object 110. Preferably, this identifier can be common to a group of connected objects 110. Alternatively, the identifier can include a part common to a group of objects connected 110 and a specific part for each connected object 110. This makes it possible to deliver messages to groups of connected objects 110 or to deliver individual messages to each connected object 110. Alternatively, any means making it possible to identify directly or

BE2016 / 5737 indirectly a connected object 110 or a group of connected objects 110 can be used (sending a message at a specific time, specific encryption, specific channel, ...).

Preferably, the beacon message of the gateway 120 indicates on which channel the message is sent. Preferably, the beacon message of the gateway 120 indicates the transfer rate used to send the message to be delivered.

If the message is intended for the connected object 110, the latter receives the message 332 on the channel indicated by the gateway 120.

Preferably, the connected object 110 which has correctly received a message, sends an acknowledgment to the gateway 120. Preferably, this acknowledgment is received on the same channel as that used for the transmission of the message. Preferably, the acknowledgment of receipt is received with a transfer rate equal to or lower than that of the transmission of the message. Preferably, this acknowledgment is a short message, the useful part of which comprises between 8 and 32 bits, preferably the useful part comprises 16 bits. Preferably, the connected object 110 issues its acknowledgment of receipt immediately after receipt of the message.

Preferably, when the connected object 110 has no message to send, it listens continuously to the beacon channel or channels to verify that a gateway 120 has no message to deliver to it or, for select the gateway with the best RSSI. Alternatively, when the connected object 110 has no message to send, it can go to sleep and wake up periodically to check that a gateway 120 has no message to send it. Preferably, it wakes up after a predefined number of periods T. Alternatively, a connected object 110 does not receive messages until it has sent them. Preferably, it receives this message after a predefined number of periods T, for example, after 2 periods.

Figure 4 shows a diagram of the communication method between a gateway 120 and at least one connected object 110 according to the invention. The first step consists in the transmission of a beacon message 410 by a gateway 120 in its transmission time window in the period T. Then, either the gateway 120 can receive one or more messages, or it has a message to deliver to one or more connected objects 110.

BE2016 / 5737 In the first case, the gateway 120 listens to the channel or channels that it indicated in its beacon message 420. Then, the gateway 120 possibly detects a message 422 then receives it 423. Preferably, the gateway 120 scans different transfer rates simultaneously or sequentially to detect a message 421. Preferably, these transfer rates depend on the SF of the message. Preferably, the message sent by the connected object 110 comprises a preamble and the gateway 120 detects at least part of a preamble.

Preferably, when the message received has been sent with a high transfer rate (otherwise a low SF), the transmission time is less than half a period T (transfer time < ¹ Λ T) it is then possible receiving a second message during the same period T. for this, the gateway 120 seeks a second preamble from time t = _^1/2 T. If it detects one, it receives the second message.

Preferably, the gateway sends an acknowledgment of receipt of the radio frequency (RF) transmission 424. Preferably, this acknowledgment of receipt is sent directly after the reception of a message. Preferably, this acknowledgment is sent on the same channel and, preferably with a transfer rate equal to or less than that of the message sent.

In the second case, the gateway 120 has a message to deliver to one or more connected objects 110. In this case, the gateway sends a message 431 to one or more connected objects 110 identified in the beacon message on the indicated channel in the same tag message. Alternatively, the gateway 120 sends a message to a connected object 110 or to a group of connected objects 110 only when they themselves have sent a message a predefined number of periods T (for example, 2 periods) before. Preferably, the beacon message includes the identifier 430 of the connected object 110 or of the group of connected objects 110. Preferably, the gateway listens directly after having sent its message and waits to receive one or more acknowledgments of reception of the radio frequency (RF) transmission 432. Preferably, this acknowledgment of receipt is received on the same channel and, preferably with a transfer rate equal to or less than that of the message transmitted.

BE2016 / 5737 [0056] FIG. 5 shows a diagram of the communication method between several gateways 120 according to the invention. When a gateway 120 connects to the network 100, a time window must be allocated to it. For this, the gateway 120 listens to the tag channel or channels for at least one period T 510. Preferably the gateway 120 listens to the tag channel or channels a sufficient number of periods T only to be able to listen to all the tag channels at least one period. Once the beacon channel or channels have been listened to, either the gateway 120 has detected and received at least part of at least one preamble of a beacon message 520 from another gateway 120 already connected to the network 100, or the gateway 120 has not detected any preamble 530.

In the case where the gateway 120 has detected and received at least part of at least one preamble of a beacon message 520 from another gateway 120 already connected to the network 100, the gateway 120 checks that there is at least one time window available 521. If at least one time window is available, the gateway allocates this window 540. Then, the gateway transmits its beacon message in its window 541. If no time window is available, the gateway starts standby 522. Preferably, the gateway 120 put on standby again searches for a free time window after a predefined number of periods T. Preferably, the gateway 120 again searches for a free time window after at least one period T.

In the case where the gateway 120 has not detected any preamble 530, it assigns itself a time window 540. Then the gateway transmits its beacon message in its window 541.

Preferably, a gateway 120 connecting to the network 100 for the first time identifies itself with the central server 130 and, preferably, sends it information on the surrounding gateways 120 which it has detected.

Preferably, a new connected object 110 connecting to the network 100 for the first time identifies itself to the central server 130 via a gateway 120 for example by sending it its identifier. Preferably, the connected object 110 receives a short identifier from the central server 130 via a gateway 120 to identify itself in its subsequent communications and, in particular, for the exchange of acknowledgments of receipt.

BE2016 / 5737 [0057] Alternatively, the central server 130 can schedule the order of the time windows. Preferably, the central server 130 can allocate the time windows to the gateways 120.

When the network 100 includes a maximum number of gateways 120 to optimize the use of time and a new gateway 120 is introduced, it does not find a free time window. The central server 130 can designate this gateway 120 as a companion gateway. In this case, the new gateway 120 does not emit a beacon message but positions itself as an additional receiver of another gateway 120 which emits a beacon message. The central server 130 commands this transmitting gateway 120 to supply companion channel information in its beacon message so that a connected object 110 can send a message to the companion gateway 120. This makes it possible, in the best of cases, to double the reception capacity of the network 100. Preferably, a connected object 110 transmitting a message will choose in a pseudo-random manner between the companion channel and the normal channel for its communication, the information on these channels being transmitted in the beacon message.

Figure 6 shows a diagram of the synchronization method between several gateways 120 according to the invention. Preferably, the central server 130 monitors and controls the synchronization 610 between the gateways 120 after a predefined number of periods T. Preferably, this number of periods is at least 10 periods.

A gateway 120 which wants to resynchronize begins by listening to at least part of the beacon message from the other gateways 620. During the resynchronization, a gateway therefore does not transmit its beacon message for at least one period T and preferably no more of 4 periods T. Then, from the times at which the gateway 120 has heard the (parts of) beacon messages from the other gateways 120, it calculates a reference time 630. From this reference time, the gateway adjusts its window 640 to send its beacon message at the right time. Finally, the gateway resumes sending its tag message 650 in its time window. For example, if we consider an accuracy of around 5 ppm for the internal clock of a gateway, the deviation will be around 0.6 ms for a cycle of 128 s.

BE2016 / 5737

Taking into account other uncertainties, we can take a safety factor of 3, that is to say that the deviation will be approximately 2 ms on a cycle of 128 s, which constitutes an acceptable deviation. For a gateway to send its beacon message in its time window, all the gateways must resynchronize at least once per 128s (Tsync) cycle, preferably twice. If we consider a set of 10 gateways, this means that each gateway synchronizes with the others every 12 periods of T-tag message transmission (in other words, once in 12, the gateway does not transmit its beacon message) . Which gives: 12 * T ~ = 6.5 s and 10 * 12 * T ~ = 64 s ~ = Vi Tsync.

Figure 7 shows a device implementing the methods relating to gateways as described above. The device includes a radio frequency (RF) modulator-demodulator (modem). Preferably, this device comprises an Ethernet socket and / or a Wi-fi connection. The device can be powered, for example, through a power outlet or an Ethernet cable. Preferably, the device uses an SX127x chip and even more preferably the SX1276 chip as described in patent application US2014219329. Preferably, this device operates in the ISM 868 MHz frequency band. Preferably, the device has a maximum size of less than 30 cm.

The devices implementing the methods relating to connected objects include a radio frequency (RF) modulator-demodulator (modem). Preferably, the device comprises its own power supply such as a battery or a battery. Preferably, the device uses an SX127x chip and even more preferably the SX1276 chip as described in patent application US2014219329. Preferably, this device operates in the ISM 868 MHz frequency band. Preferably, the device is compatible with the MAC LoRaWAN ™. Preferably, the device is also compatible with the MAC Sigfox ™.

One of the aims of the invention was to solve the problems of network saturation and to optimize the use of time. This goal has been achieved by the use of beacon messages sent on a beacon channel and periodically sent by gateways. These beacon messages allow

BE2016 / 5737 to organize the time by warning the connected objects of the availability of a gateway to send or receive messages. These messages also allow connected objects to select a gateway with which they will have good communication. The communication procedure is also simple because connected objects can send a message at any time from the moment they receive a beacon message. Finally, the gateways are organized without external intervention and the addition of a gateway makes it possible (without external intervention) to increase the network's capacities and avoid its saturation.

The present invention has been described in relation to specific embodiments, which have a purely illustrative value and should not be considered as limiting. In general, the present invention is not limited to the examples illustrated and / or described above. In particular, the invention also relates to combinations of the technical characteristics of the embodiments set out above. The use of the verbs "to understand", "to include", "to include", or any other variant, as well as their conjugations, cannot in any way exclude the presence of elements other than those mentioned. The use of the indefinite article "a", "an", or of the definite article "the", "the" or "I", to introduce an element does not exclude the presence of a plurality of these elements. Reference numbers in the claims do not limit their scope.

In summary, the invention can also be described as follows. Communication methods in a wireless communication network 100 comprising a plurality of connected objects 110, a gateway 120 and a central server 130. These elements communicate with each other by messages sent and received on frequency channels. A channel being reserved for the periodic emission of beacon messages by the gateways, which allows the organization and optimization of the usage and communication time of the network 100.

BE2016 / 5737

Claims (7)

Claims 1. A method of communication in a wireless communication network (100) using a plurality of channels each having a central frequency and a bandwidth, said network (100) comprising a plurality of connected objects (110) and a set of gateways (120) said connected objects (110) and said gateways (120) being capable of transmitting and receiving messages in each of the channels, at least one of these channels, called beacon channel, being a unidirectional communication channel reserved for periodic or quasi-periodic transmission of beacon messages by the gateways (120), said beacon messages being transmitted in time windows specific to each gateway (120) and comprising: • a preamble; • either an indication that the gateway (120) wants to deliver a message or that it is able to receive at least one message; • an indication of at least one channel for exchanging at least one message; method by which a time window is associated with a gateway (120) by performing the steps of: a) listening by the gateway (120) of the beacon channel or channels during at least one whole period of emission of beacon messages (510); b) either, the gateway (120) detects at least part of a preamble and at least one time window is available (521), the gateway (120) chooses one of these windows (540) and the gateway (120) transmits its beacon message (541); c) either, the gateway (120) detects at least part of a preamble and no time window is available (521), the gateway (120) goes into standby (522); d) or the gateway (120) does not detect any preamble, it chooses a time window (540) and it transmits its beacon message (541). BE2016 / 5737 2. Method according to claim 1, in which a gateway which was put on standby in step b) wakes up after at least one period of transmission of beacon messages and repeats steps a), b) and / or d). 3. Method according to any one of claims 1 to 2, wherein the network (100) further comprises a central server, said server determining the order of the time windows of each of the gateways (120). 4. Method according to any one of claims 1 to 3, wherein the network (100) further comprises a central server, said server allocating the time windows to the gateways (120). 5. Method according to any one of claims 1 to 4, in which the network (100) further comprises a central server, said server assigning a companion channel to a gateway, this companion channel allowing only the gateway (120) to receive messages in a time window used by another gateway (120). 6. Method according to any one of claims 1 to 5, in which a gateway (120) resynchronizes by performing the steps: • listens to at least part of the beacon messages from the other gateways (120) during at least one whole beacon message transmission period (620); • the gateway (120) calculates a reference time as a function of the beacon message (s) received (630); • the gateway (120) adjusts its time window (640). 7. Method according to any one of claims 1 to 6, in which the network (100) further comprises a central server, said server controlling and initiating the synchronization of each gateway (120) after a predefined number of message transmission periods. beacon (610). BE2016 / 5737 100