GB2530019A

GB2530019A - A method for controlling a communication system

Info

Publication number: GB2530019A
Application number: GB1415265.6A
Authority: GB
Inventors: Mickaã L Lorgeoux; Alain Caillerie; Francois Thoumy
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2014-08-28
Filing date: 2014-08-28
Publication date: 2016-03-16
Anticipated expiration: 2034-08-28
Also published as: GB201415265D0; GB2530019B

Abstract

Controlling a communication system 100 comprising a mobile node 130, such as a camera on a robot arm 120, communicating wirelessly with a plurality of fixed nodes 140 and moving between a plurality of stationary positions P0, P1, P2, at least some of which being stored, as predetermined stationary positions in said communication system, in association with predetermined operation settings and with at least one context parameter value, the method comprising each time the mobile node has reached a predetermined stationary position: measuring at least one current value of at least one of said context parameters; determining whether environmental conditions of the communication system have changed based on the measured current value and the stored value of said context parameter associated with the stationary position, if conditions havent changed retrieving and re-using said predetermined operation settings associated with the stationary position, or, if conditions have changed, computing new operation settings for the stationary position. The arrangement may relate to a camera on a robot arm photographing an object in a working cycle and sending the photographs to multiple fixed receivers around the working area over a 60 GHz millimetre wave network. Operation settings may include modulation and or coding scheme, a sub-set of the fixed nodes to use among the plurality or camera capture settings such as exposure, aperture, ISO, size or flash/lighting. Context parameters may include light levels, humidity, temperature, quality of the communication link or quality of the image captured. New settings are only calculated when necessary as settings are re-used if conditions havent changed.

Description

A METHOD FOR CONTROLLING A COMMUNICATION SYSTEM

FIELD OF THE INVENTION

The present invention relates in general to capture and wireless transmission of image data at a mobile node of a communication system. In particular, the present invention provides a method for controlling a communication system in dynamic operation conditions.

BACKGROUND OF THE INVENTION

Wireless applications such as capture of High Definition (HD) images, are now increasingly numerous and require high data bit rates and high quality of service (e.g. low Bit Error Rate BER and low latency transmission). Such applications may be implemented for instance in wireless vision sensors in an industrial context. A robot arm may carry an image sensor for performing a visual check of an object under test or construction on a production line in a factory.

A communication system using the millimetre wave frequency band (60GHz) is well adapted to the transmission of uncompressed HD video or image data from the sensor to a central processing unit. Indeed, the authorized band around a carrier frequency of 60GHz provides a wide bandwidth which makes the transportation of a large quantity of data with a high data rate transmission (>3Gbps) possible.

Moreover, the radio range of such systems is limited to about ten meters, thus frequencies can be reused in time and space. Typically, in the above exemplary industrial context, using several 60GHz communication systems may advantageously make it possible to have several check points in the same factory and possibly on the same production line.

However, a typical characteristic of millimeter waves is the sensitivity to masking phenomena. Certain static or moving obstacles such as furniture, objects, and human beings, can interrupt or disturb the communication path and cause transmission errors. In order to decrease the transmission errors due to physical obstacles, the communication system preferably uses multi-reception techniques that create spatial diversity and allow implementation of a multi-reception error correction code for achieving a low BER and low latency transmission required by the application. In practice, the communication system comprises several fixed nodes that are spaced apart (thus creating spatial diversity) and that receive captured data from a mobile node at which the capture application is implemented. These fixed nodes are connected to a system controller device that implements the aforementioned multi-reception error correction code (Multi-RX ECC) on the copies of the captured data received by the fixed nodes.

Typically, the mobile node is moving from one stationary position to another one. For example, a stationary position may be considered as a position of the mobile node such that when arriving at this position, the application running at the mobile node becomes operational. In practice, the environmental conditions experienced by the mobile node may change from one stationary position to another. For instance, the mobile node may come closer to a heat source, to a humidity source or to a light source. A change in ambient temperature or in humidity is known to impact wireless communications, and a change in lighting conditions may degrade captured image data (e.g. through over-exposure). Also, some obstacles may appear on the path between the mobile node and some of the fixed nodes even though they were not there when the mobile node was at the previous stationary position.

Consequently, the operation settings such as radio communication settings (e.g. transmission power level, modulation scheme, number of active fixed receiving nodes) and image (capture) application settings (e.g. exposure time, aperture value, and ISO sensitivity value of the capture means (sensor) attached to the mobile node) have to be adapted to the local environmental conditions at each new stationary position of the mobile node. A setup of the communication system is thus necessary to adapt the operation settings.

In some contexts, the mobile node may be displaced from a starting (initial) stationary position through several other intermediary stationary positions before returning to the starting (or initial) stationary position. This particular cycle of displacement, called a working cycle, may be reproduced several times. Also, several different working cycles may be formed from the same starting stationary position.

Since the above-mentioned setups are performed at each stationary position, they usually represent an important part of the working cycle duration.

In some cases, it may be very important to have a short working cycle, for instance when the application captures image data used in a real-time check of a dynamic environment (i.e. in movement). The visual check of an object under construction on a production line, as mentioned above, is a typical example.

A solution for reducing the setup duration over a cycle is to use predetermined operation settings stored for each predetermined stationary position of the mobile node.

However, another concern is that environment conditions may also change over time (i.e. not only in space). Hence, predetermined operation settings may be no longer relevant in case of environmental changes over time.

SUMMARY OF THE INVENTION

The present invention has been devised to address one or more of the foregoing concerns.

In this context, according to a first aspect, there is provided a method for controlling a communication system comprising a mobile node communicating wirelessly with a plurality of fixed nodes, the mobile node moving between a plurality of stationary positions, at least some of which being stored, as predetermined stationary positions in said communication system, in association with predetermined operation settings and with at least one value of at least one context parameter, the method comprising the following steps implemented each time the mobile node has reached a predetermined stationary position: measuring at least one current value of at least one of said context parameters; determining whether environmental conditions of the communication system have changed based on the measured current value and the stored value of said context parameter associated with the stationary position, upon negative determination, performing a fast control phase using said predetermined operation settings associated with the stationary position, upon positive determination, performing a slow control phase comprising computing new operation settings for the stationary position.

The present invention makes it possible to control the communication system without having to compute operation settings at each of its setups, in particular when the environmental conditions correspond to predetermined conditions, thus optimizing the setup of the communication system during the movement of the mobile node between the plurality of stationary positions, while keeping adapted operation settings for the setup.

This is achieved by using predetermined operation settings for setting up the communication system (fast phase), when it is determined, based on measured current values of context parameters, that environmental conditions of the communication system have not changed since the computing of the predetermined operation settings stored in association with the stationary position. Therefore, the predetermined operation settings are still relevant and can be directly used, and setup time is saved.

Optional features of the invention are further defined in the dependent appended claims.

In some embodiments, said new operation settings are computed under the current environmental conditions defined by said at least one measured current value of at least one context parameter.

In some embodiments, new operation settings are computed for each stationary position of the mobile node. In a variant, they may optionally be computed only for one or few stationary positions.

In some embodiments, the method further comprises storing, in association with each stationary position of the mobile node, the new operation settings computed for said stationary position and the at least one measured current value, as predetermined operation settings and context parameter value.

Thanks to this provision, the next time the mobile node reaches this stationary position, if no change in environmental conditions is determined since the update time, the updated operation settings will be directly retrieved from memory and used for the setup.

In practice, a preliminary step of computing (also called "learning phase") is performed at the start-up of the communication system.

In some embodiments, said context parameter is one of the following: light level, temperature, humidity, quality of the wireless communication path between the mobile node and the fixed nodes, quality of image data captured at the mobile node by an application for capturing image data.

These parameters may have an impact on the operation settings used for setup. This is why they have to be measured to verify that they have not drastically changed in comparison to the environmental conditions in which the predetermined operation settings were determined. In practice, the variation between the stored (predetermined) value and the measured current value may be compared to a threshold. Hence, time setup may be saved when permitted, while avoiding inappropriate reuse of operation settings for the setup when environmental conditions have changed.

In some embodiments, an application for capturing image data is implemented at the mobile node, and operation settings comprise capture seftings.

For example, capture settings may comprise features such as exposure time, aperture value, ISO sensibility value, image size, lighting parameters (flash).

In some embodiments, operation settings comprise communication settings.

For example, communication settings may comprise features such as transmission power level for communicating wirelessly between the mobile node and the fixed nodes, modulation and coding scheme (e.g. Quadrature phase-shift keying modulation associated with a Convolutional code with rate 1/3 or 2/3 (QPSK;1/3 or QPSK;2/3) or 16 states Quadrature amplitude modulation associated with a Convolutional code with rate 2/3 (16QAM;2/3)), and/or communication scheme to be used for uplink communications with the mobile node.

In some embodiments, the communication scheme comprises an indication of at least one subset of fixed nodes to be used for uplink communications with the mobile node.

For instance, the communication settings may comprise a plurality of subsets stored in a subset table. The subsets may be sorted according to a preference order. The criterion used to sort the subsets may be, for example, the space between the nodes of the subset.

Advantageously, the latency of uplink communication is reduced in comparison to a regular communication scheme in which all the fixed nodes generally successively perform uplink communications with the mobile node. Indeed, according to the communication scheme indicated in the communication settings, only one fixed node belonging to a subset of fixed nodes is used for uplink communications with the mobile node.

In some embodiments, a set of fixed nodes is selected from among the fixed nodes of the communication system based on a quality criterion, and said subset is built from the selected set.

The quality criterion is for instance the signal reception level (RSSI level) and/or the reception quality (BER) of the mobile node, when one of the fixed nodes is transmifting data.

In some embodiments, the fixed nodes of said subset indicated in the communication scheme are spaced apart so that when an obstacle arises on the path between the mobile node and one of the fixed nodes of the subset, said obstacle is not on the path between the mobile node and another fixed node of the subset.

In some embodiments, the subset indicated in the communication scheme comprises a main fixed node and at least one spare fixed node, and the method further comprises: sending an uplink message from the main node to the mobile node; and in case the uplink message is not received correctly by the mobile node, transmitting the uplink message from the spare fixed node to the mobile node.

Thanks to these two provisions, since an obstacle on the path between the main fixed node and the mobile node cannot be also on the path between the spare fixed node and the mobile node, the operation settings do not have to be recomputed every time such an obstacle arises.

According to a second aspect, there is provided a system controller device for controlling a communication system comprising a mobile node communicating wirelessly with a plurality of fixed nodes, the mobile node moving between a plurality of stationary positions, at least some of which being stored as predetermined stationary positions in said communication system, in association with predetermined operation settings and with values of at least one context parameter, the system controller device comprising: a module for sending a moving command to the mobile node, for reaching a predetermined stationary position; a module for measuring at least one current value of at least one of said context parameters when the mobile node has reached the stationary position; a module for determining whether environmental conditions of the communication system have changed based on the measured current value and the stored value of said context parameter associated with the stationary position; and wherein the mobile node and the fixed nodes are configured to perform, upon negative determination, a fast control phase, using said predetermined operation settings associated with the stationary position, and upon positive determination, a slow control phase comprising computing new operation seftings for the stationary position.

At least parts of the method according to the invention may be computer implemented. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "circuit", "module" or "system".

Furthermore, the present invention may take the form of a computer program product embodied in any tangible medium of expression having computer usable program code embodied in the medium.

Since the present invention can be implemented in software, the present invention can be embodied as computer readable code for provision to a programmable apparatus on any suitable carrier medium. A tangible carrier medium may comprise a storage medium such as a floppy disk, a CD-ROM, a hard disk drive, a magnetic tape device or a solid state memory device and the like. A transient carrier medium may include a signal such as an electrical signal, an electronic signal, an optical signal, an acoustic signal, a magnetic signal or an electromagnetic signal, e.g. a microwave or RF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, and with reference to the following drawings in which: -Figure 1 schematically shows a communication system according to some embodiments; -Figure 2 schematically shows an example of architecture for a mobile node or a fixed node of a communication system according to some embodiments; -Figure 3 schematically shows an example of architecture for a wireless controller of a system controller device of a communication system according to some embodiments; -Figure 4 schematically shows an example of architecture for a main controller of a system controller device of a communication system according to some embodiments; -Figure 5 schematically shows general steps of a method for controlling a communication system, according to some embodiments; -Figures 6a and 6b schematically show steps of a method for controlling a communication system, with Figure 6a showing steps during which operation settings for the setup are re-computed ("slow phase") and

B

Figure 6b showing other steps during which predetermined operation settings are retrieved from the memory ("fast phase"); -Figures 7a and 7b schematically represent two exemplary communication schemes for uplink communications towards a mobile node of the communication system; -Figures 8a and 8b respectively show steps for obtaining the communication scheme shown in Figure 7b, and steps for controlling communication troubles according to this communication scheme; and -Figures 9a and 9b respectively show a table of quality measurements possibly obtained during the computing of the communication scheme of Figure 8a, and an example of configuration of the communication system corresponding to the table of Figure 9a.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention provides methods for controlling a communication system comprising a mobile node that communicates wirelessly with a plurality of fixed nodes, and that moves between a plurality of stationary positions, each stationary position being stored in said communication system in association with predetermined operation settings and with a value of at least one context parameter. The predetermined operation settings are adapted to specific environmental conditions that may be described by context parameter values stored in association with the predetermined operation settings and the associated stationary position.

Such methods take advantage of the fact that without change in environmental conditions in comparison to the environmental conditions in which operation settings have been determined, these operation settings are still relevant.

In particular, the value of at least one context parameter is measured in order to verify if the current environmental conditions are the same as the environmental conditions in which operation settings associated with the stationary position have been determined. If so, these predetermined operation settings are merely retrieved from the memory and used for the setup of the communication system.

Otherwise, when the measured value shows that environmental conditions are not those in which the operation settings associated with the stationary position have been determined, operation settings are computed from scratch.

Consequently, such a method allows re-computation of the operation settings to be avoided in some cases, while taking into account changes in environmental conditions that may occur over time, and may impact the performances of the system.

As will be described hereafter in details, in some industrial contexts, an advantage to reuse the stored operation settings may be to minimize the duration of a working cycle of an articulated arm achieving a visual check on a production line, thus increasing the productivity of the whole production line.

Figure 1 represents a communication system 100 according to embodiments. Such communication system 100 is adapted to implement a method according to some embodiments, as will be described below with reference to Figure 5, Figures 6a and 6b.

In the present example, the communication system 100 is used in an industrial environment, for instance in a factory.

The communication system 100 comprises a mobile node 130, a plurality of fixed nodes (here five: 140a, 140b, 140c, 140d, 140e) and is controlled by a system controller device 150.

The mobile node 130 is for instance attached to a source device configured to capture data such as image data or video data, for instance an HO image or video data sensor. For instance, the sensor may be an HO digital camera, an HD digital camcorder or the like. The mobile node 130 is also configured to process image data captured by the sensor and to send them to the fixed nodes 140a to 140e. Thus, the mobile node 130 is configured to wirelessly communicate (or broadcast) with the fixed nodes, using one or more antennas, and for instance by means of 60GHz millimetre waves.

The mobile node 130 may send the processed data from several different stationary positions P0, P1, P2, P3, P'1, P'2, P'3, P'4 within an area 110, in the present example, thanks to an articulated arm 120 to which the mobile node is attached.

For instance, in Figure 1, the mobile node 130 is initially positioned at stationary position P0. After a first data capture and communication sequence(s), it may move towards one of the stationary positions P1 or P'1 from which a new data capture and communication sequence(s) will be performed. Next, another stationary position is reached by the mobile node 130, for instance P2 or P'2 from which another new data capture and communication sequence(s) will be performed, and so on. More than one data capture and communication sequence may be performed at a stationary position, and a given stationary position other than the initial position may be reached several times. Once the mobile node 130 has reached again the initial position P0, a cycle of displacement terminates.

Thus, two cycles of displacement are shown in Figure 1, namely {P0, P1, P2, P3, P0} and {P0, P'1, P'2, P'3, P'4 P0}. The represented cycles are given only for illustrative purposes and the present invention is not limited thereto. It is worth noting that the presence of cycles is not mandatory for the invention.

The fixed nodes 140a to 140e are located at fixed positions, in the mobile node 130 wireless coverage area. Five fixed nodes are shown in Figure 1; however the invention is not limited thereto. The number of fixed nodes generally provided is a compromise between the cost of fixed nodes and the need to create spatial diversity to avoid shadowing effects due to obstacles on the wireless communication paths between the mobile node and the fixed nodes.

Depending on the position of the mobile node 130 within the area 110 and depending on the position of possible obstacles, one or more line of sight communication paths between the mobile node 130 and the fixed nodes 140a to 140e may be disturbed or totally cut. As a result, the fixed nodes 140a to 140e may have different reception quality, notably different Bit Error Rates (BER) and/or different RSSI levels.

Each fixed node may also send data (e.g. capture settings, triggering commands) to the mobile node (uplink communication). Also, the fixed nodes may receive acknowledgements from the mobile node 130 (see for instance Figures 7a and 7b). These secondary communications use around 10% of the total bandwidth of the communication system 100 against 90% for transmission of captured data from the mobile node 130 to the fixed nodes 140a to 140e.

Fixed nodes 140a, 14Db, 140c, 140d, and 140e, are respectively connected to the system controller device 150, in particular to a wireless controller 152 of the system controller device 150 (see below), by means of wired or wireless links 180a, 18Db, 180c, 180d, and 180e.

3D Each fixed node may comprise a radio transceiver module and a modem and the interconnection between the fixed nodes and the system controller device may be performed using digital high speed interfaces with differential signals. These high speed wired interfaces may be point-to-point interfaces, or bus-oriented interfaces.

They may be of the l000BaseT type or compliant with any other standard, or may be proprietary and use any physical medium allowing a high data rate such as twisted pairs, optical fibre, coaxial cable, or be wireless.

Other embodiments may be provided wherein the interconnection physical medium is analog and modems are not included in the fixed nodes, but rather in the system controller device 150. This list of interconnection possibilities is not exhaustive.

The system controller device 150 here comprises a wireless controller 152 that controls operational settings such as the radio communication settings for the wireless communications between the mobile and fixed nodes 140a to 140e.

The wireless controller 152 is thus connected to the fixed nodes by means of wires 180a to 180e, and is furthermore connected to a main controller 154 (for instance a Personal Computer) which is also part of the system controller device 150, through a wire interface 156. The wire interface 156 can be an Ethernet connection, an USB connection or other kind of connexion. This connexion 156 is used to exchange capture settings and triggering commands for the sensor at the mobile node 130, and to retrieve captured image data from the sensor at the mobile node 130.

The main controller 154 controls the displacement of the sensor at the mobile node 130 attached to the articulated arm 120. In practice, the main controller 154 sends displacement commands to the articulated arm 154 through the wire interface 160. The wire interface 160 is typically a CAN bus (Controller Area Network).

The main controller 154 may also control the setup of the capture application implemented at the mobile node 130 and the triggering of image capture by the sensor at the mobile node 130, through the wireless controller 152 and the fixed nodes 140a to 140e.

Also, the system controller device 150 may forward data received from the fixed nodes to an application device, for instance a display, a recorder, or any other equipment configured to interpret and use the received data.

The representation of the system controller device 150 is not limitative. The wireless controller 152 and the main controller 154 may be implemented as part of the same device or may be physically independent.

Thus, in practice, when the mobile node 130 has reached a stationary position, such as P0, when the required operation settings are tuned on, the wireless controller 152 receives several copies (here five) of the same original image data from the fixed nodes 140a to 140e. The wireless controller 152 may embed a Multi-rx ECC module which allows the BER of the received image data to be improved.

Next, the wireless controller 152 foiwards the corrected uncompressed HD image data to the main controller 154 through the wire interface 156 that performs image processing on the received image data. Depending on the image processing result, the main controller 154 may send a command though interface 160 of the articulated arm 120 to move the sensor at the mobile node 130 to another stationary position (e.g. F1 or F'1), or it may send a command to tune different operation settings (see Figure 6a -"slow phase") and trigger the capture of new image data without moving the sensor.

Figure 2 schematically shows an example of architecture 200 for a mobile node 130 or a fixed node 140a-140e of a communication system 100 as shown in Figure 1.

The architecture 200 of a node comprises: -a processing unit pc (for micro-controller) 201 whose capacity can be extended by an optional random-access memory connected to an expansion port (not shown in Figure 2); -a volatile memory denoted RAM (for Random Access Memory) 202 working as a main memory, in which instructions and temporary variables and parameters for implementing steps of a method according to particular embodiments may be loaded from a non-volatile memory; -a non-volatile memory denoted ROM (for Read Only Memory) 203 in which instructions for implementing steps of a method according to particular embodiments may be stored; -a block RF-FE (for RF-front-end) 210 configured to process an output signal of a baseband block RF-BB (for RF-baseband) 205 to transmit it through an antenna 204. For example, the output signal may be processed by applying frequency transposition and power amplification processes. Block 210 is also configured to process a signal received by antenna 204 to transmit it to baseband block 205.

Baseband block 205 is configured to perform modulation and demodulation on the digital data exchanged with block 210. Block 210 comprises a sub-block RM (for Reception Measurement) 212, for example an analog/digital converter, configured to measure the power of the signal received through antenna 204, the power measurement value being then communicated to processing unit 201; and -an input/output interface I/O IF 206 for instance to connect the sensor that captures image or video data (for the mobile node 130), or to communicate with a wireless controller 152 of a system controller device 150 (for the fixed nodes 140a-1 40e).

Figure 3 schematically shows an example of architecture for a wireless controller 152 of a system controller device 150 of a communication system 100 as shown in Figure 1.

The wireless controller 152 comprises: -a processing unit r.ic (for micro-controller) 301 whose capacity can be extended by an optional random-access memory connected to an expansion port (not shown in Figure 3); -a volatile memory denoted RAM (for Random Access Memory) 302 working as a main memory, in which instructions and temporary variables and parameters for implementing steps of a method according to some embodiments may be loaded from a non-volatile memory; -a non-volatile memory denoted ROM (for Read Only Memory) 303 in which instructions for implementing steps of a method according to some embodiments may be stored; -a Multi-Rx unit (for multi-reception unit) 300 configured to receive digital data signals from the fixed nodes 140a, 14Db, 140c, 140d, and 140e, respectively through the links 180a, 18Db, 180c, 180d, and 180e and to combine these signals.

Such combination could be a simple selection of the best copy of data from among the multiple received copies. In a variant, the combination may be more complex and the best copy of a sub-part of data may be selected for each sub-part of the received data; and -an input/output interface I/O IF 305 configured to connect the main controller 154 of the system controller device 150, or any other device configured to interpret and use the received data, via link 156. The interface 305 may also be configured to exchange commands and status messages, typically with the main controller 154 of the system controller device 150, via link 156.

Figure 4 schematically shows an example of architecture for a main 3D controller 154 of a system controller device 150 of a communication system 100 as shown in Figure 1.

The main controller 154 comprises: -a processing unit pc (for micro-controller) 401 whose capacity can be extended by an optional random-access memory connected to an expansion port (not shown in Figure 4); -a volatile memory denoted RAM (for Random Access Memory) 402 working as a main memory, in which instructions and temporary variables and parameters for implementing steps of a method according to some embodiments may be loaded from a non-volatile memory; -a non-volatile memory denoted ROM (for Read Only Memory) 403 in which instructions for implementing steps of a method according to some embodiments may be stored; -an input/output interface I/O IF 404 configured to connect the articulated arm 120 of Figure 1 (not shown in Figure 4) of communication system 100, by means of link 160 (wired or not) for exchanging data, commands and status messages. The interface 404 may also be configured to exchange data, commands and status messages with the wireless controller 152 of the system controller device 150, by means of link 156 (wired or not); and -an image processing unit 405 configured to process image data received from the input/output interface I/O IF 404. For example, such process may be a quality check of received data and an analysis of the corresponding image, for instance in order to determine if the device under test or under construction on the production line satisfies the expected requirements.

Optionally, the main controller 154 may comprise a Man-Machine-Interface (MMI) 406, for instance a display and-or a keyboard, which allows an operator to use, control and check the behaviour of the communication system 110 through main controller 154 of the system controller device 150.

The wireless controller 152 and the main controller 154 of system controller device 150 have been independently described respectively with reference to Figure 3 and 4, however, in other embodiments, they may share for instance the same processing unit, the same volatile memory, the same non-volatile memory and/or the same input/output interface to exchange data with the fixed nodes 140a to 140e on the one hand and with the articulated arm 120 in the other hand. Also, the wireless controller 152 and the main controller 154 may be integrated as one and a same unit (referred to as system controller device 150).

General steps of a method for controlling the communication system 100 according to some embodiments are now described with reference to Figure 5. Such method may be implemented by the system controller device 150, in particular some steps may be performed by the wireless controller 152 described with reference to Figure 3 and some steps may be performed by the main controller 154 described with reference to Figure 4.

In this example, the method starts at step 500 when the mobile node 130 has reached a stationary position P. In practice, the main controller 154 has sent a moving command to the articulated arm 120 in order to make it move the sensor at the mobile node 130 towards stationary position F. Step 500 thus results from the execution of the moving command by the articulated arm 120.

At step 510, the current value of at least one context parameter is measured.

For example, this context parameter may be the Received Signal Strength Intensity (RSSl) measured at the fixed nodes 140a to 140e or at the mobile node during successive uplink communications from each of the fixed nodes 140a to 140e (see Figure 7a). The context parameter may also be a variable indicating the communication scheme applied or a variable indicating whether the communication scheme is new or not. Such variables may be stored in the wireless controller 152. The context parameter may also be the temperature, the humidity, the light intensity.

Typically, the sensors used to measure these environmental parameters may be located in the working area 110 of the mobile node 130. These sensors are connected to the wireless controller 152.

At step 520, a test is performed by the system controller device 150 to determine whether environmental conditions have changed, based on the context parameter values measured at step 510 and based on predetermined context parameter values stored in advance in association with the stationary position and operation settings, for instance during a preliminary learning step as will be described below with reference to Figure 6a. This test may be performed by the wireless controller 152 or by the main controller 154.

During this test, the measured value may be compared to a threshold corresponding to the stored context parameter value. When the values of several context parameters have been measured, the test may comprise evaluating the number of measured values that are larger or lower than their respective thresholds. In variants, the difference between the measured value and the stored value of a same context parameter (e.g. the temperature) may be compared to a threshold (triggering condition). Other kinds of tests may be performed based on the measured values and on the stored values.

If it is determined at step 520 that the context conditions have not changed, a control phase called "fast control phase" or "fast phase" is performed using said predetermined operation settings associated with the stationary position.

This control phase is called "fast phase" since it allows time saving in comparison with a control phase (called hereafter "slow phase") during which the operation settings are computed from scratch.

In this example, two kinds of operations settings are considered: first, capture settings (e.g. image size, lighting parameters, aperture value, exposure time) to be used by the sensor for capturing image data at mobile node 130, and second, communication settings (e.g. transmission power level, modulation and coding scheme (for example QPSK;1/3 or QPSK;213 or 16QAM;2/3), communication scheme for uplink communications with the mobile node 130).

An exemplary fast control phase will be described hereafter with reference to Figure 6b.

Otherwise, if it is determined at step 520 that the environmental conditions have changed, a slow control phase is performed at step 550, during which new operation settings (capture settings and communication settings) are computed 0 Thus, new operation settings are computed for the current stationary position of the mobile node 130. In some embodiments, new operation settings are also computed for some other stationary positions, for instance for the stationary positions surrounding it, or in variants for all the stationary positions.

The predetermined operation settings initially stored in the communication system (and which are used at step 530 for the setup if there is no change in environmental conditions) have been computed during a preliminary step similar to the slow control phase that will be described hereafter for the current stationary position with reference to Figure 6a.

In practice, capture settings are determined step by step. In other words, several capture settings are successively tuned until the quality (e.g. contrast, brightness) of the resulting image captured by the sensor at the mobile node 130 is satisfactory. A detailed example of an algorithm that may be used to determine the capture settings leading to an image with a satisfying quality will be described with reference to Figure Sa (left side).

Similarly, communication settings are determined step by step. For example, at first the less robust (but fastest) modulation/coding scheme is used (ex:16QAM;2/3) with a maximum power level, and the power level is decreased until the highest acceptable BER is reached. In case the highest acceptable BER cannot be reached with the 16QAM;2/3 and the maximum power level, a more robust (but less fast) modulation/coding scheme is used (ex: QPSK;2/3) with the maximum power level, and the power level is decreased until the highest acceptable BER is reached.

Thus, when environmental conditions make it possible, reducing the power level of transmission to the minimum power level needed to achieve the transmission may suffice to achieve satisfying reception of captured image data sent by the mobile node 130. Thus, the communication settings may comprise the minimum power level allowing good data reception by the maximum number of fixed nodes. It may be determined for instance using a technique described in document GB2502108 by Lorgeoux et al. Correspondingly, when satisfying quality communications over the communication system can be performed, for instance when the Bit Error Rate is lower than an acceptable threshold when using only some of the fixed nodes, a specific communication scheme indicated in the communication settings may be used for uplink communication (i.e. transmission towards the mobile node). As will be described with reference to Figure 7b, at least one subset of fixed nodes may be used for uplink wireless communications with the mobile node (the other fixed nodes not being used), whereas by default, all the fixed nodes are used for uplink communications with the mobile node.

In practice, once the new operation settings are computed, they are used to update the predetermined operation settings stored in memory, that are no longer relevant given the measured environmental conditions. Thus, the context parameter values stored in memory for the stationary position are also replaced by the measured current context parameter values.

An exemplary slow control phase during which operation settings are computed will be described hereafter with reference to Figure 6a.

Figures 6a and 6b represent a detailed example of a method for controlling a communication system according to a particular embodiment.

For the sake of clarity, in this example, stationary positions forming a cycle are identified. However, the present invention is not limited to cycles, and contexts other than cyclic displacements may be considered.

In particular, Figure 6a illustrates steps that may be performed during a preliminary learning phase, or each time that new operation settings have to be computed typically because of a change in environmental conditions. Figure 6a also illustrates the protocol of data exchange between the main controller 154 and the wireless controller 152.

As explained before, this phase during which the operation settings are computed from scratch is called "slow phase" because it last longer than a phase during which predetermined operation settings are retrieved from the memory ("fast phase") as will be described with reference to Figure 6b.

In this example, the algorithm shown on the left side of Figure 6a is launched at step 600 by the main controller 154.

At step 601, the main controller 154 forces the slow phase operational mode and sends a "slow phase" indicator 601b to the wireless controller 152 to let it know that (new) operation settings have to be computed.

At step 602, the main controller 154 sends a moving command to the articulated arm 120 to moves the sensor attached to the mobile node 130 to the stationary position number n (Pa) of working cycle m. In the meantime, the main controller 154 sends a message 602b to the wireless controller 152 indicating the stationary position n of the cycle m which isto be reached by the mobile node 130.

At step 603, the main controller 154 checks if a "ready for capture" indicator 653b from the wireless controller 152 has been received. This check is performed regularly until the indicator 653b is received. The indicator "ready for capture" 653b indicates that communication settings (e.g. modulation and coding scheme, transmission power, and sub-set of fixed nodes to be used for uplink wireless communications with mobile node 130) for stationary position number n (Pa) of cycle m, have been tuned by the wireless controller 152.

Once the "ready for capture" indicator has been received, the algorithm goes to step 604 during which the main controller 154 tunes capture settings corresponding to stationary position number n (Pa) of cycle m. The capture settings are re-tuned here in the loop comprising the steps 604-605. For the first iteration of the loop, the initial value of capture settings can be the default application settings or the previously stored values.

As described before with reference to Figure 5, the capture settings may be the exposure time, the aperture, and other values to be used by the sensor at the mobile node 130.

Once the main controller 154 has chosen the initial values of the capture settings corresponding to stationary position number n (Pa) of cycle m, it sends a message 604b to the wireless controller 152 comprising the capture settings to be used by the sensor at the mobile node 130 and a triggering command. The triggering command aims at triggering the image capture by the sensor attached to the mobile node 130, upon setup of the application with capture settings comprised in the message 604b.

At step 605, the main controller 154 receives image data 654b resulting from image data captured by the sensor at the mobile node 130, sent from the mobile node 130 to the fixed nodes 140a-140e, and then transmitted to the wireless controller 152 to be processed. The quality of the resulting image data 654b is then measured by the main controller 154 and compared to a predetermined threshold. In practice, the quality check comprises a checking of the brightness and the contrast of the received image data 654b.

If the quality of the received image data 654b is not satisfactory, the algorithm goes back to step 604 in order to tune other capture settings. The main controller 154 needs to re-tune the capture settings until an image of satisfying quality is achieved. For instance, if brightness is detected as too low, the ISO value or the exposure time is increased.

Once the quality of the received image data is satisfactory, the algorithm switches to step 606 during which the main controller 154 stores the corresponding capture settings, that are the capture settings lastly tuned.

Next, the main controller 154 sends an "image processing ok' indicator 606b to the wireless controller 152 indicating that new capture settings leading to a satisfactory quality of image have been computed and stored.

At step 607, the main controller 154 checks if all stationary position n (Pn) of each cycle m have been iterated. If not, the algorithm goes to step 609 where the next stationary position number n (Pa) of the current cycle m is considered or where another cycle m is considered. Then the algorithm loops to step 602.

In the present example, each position of each cycle is processed once. It is worth noting that generally, all the positions of all the cycles are processed at the initialization of the system, in order to have them in memory as predetermined stationary positions. However, in case of a slow phase occurring because of a change in environmental conditions, only one or some of the positions may be processed.

In a variant, during the learning phase (initialization of the system) each cycle m could be iterated several times in order to get several values of capture settings for each position n (Pa) of each cycle m. Thus, an average value of satisfying capture settings could be computed for each position n of each cycle.

Next, in the present example, if all the stationary positions of all the cycles have been processed, the algorithm goes to step 608 where the main controller 154 sends a "slow phase done" indicator 608b to the wireless controller 152, and the "fast phase" may then be performed starting from step 610. This "fast phase" will be described later in detail with reference to Figure 6b.

Back to the example of Figure 6a, the algorithm shown on the right side of the figure is launched at step 650 by the wireless controller 152.

At step 651, the wireless controller 152 checks if a "slow phase" indicator 601 b indicating that (new) operation settings have to be computed, has been received from the main controller 154. This check is performed regularly until the message 601b is received.

Once the "slow phase" indicator 601b has been received, the algorithm goes to step 652, during which the wireless controller 152 receives the message 602b from the main controller 154, indicating the stationary position number n (Pa) of the cycle m which isto be reached by the mobile node 130.

Next, the wireless controller 152 tunes communication settings corresponding to stationary position number n (Pa) of cycle m.

As described before with reference to Figure 5, the communication settings may be the modulation and coding scheme, the power level of transmission, the subset of fixed nodes to be used for transmission (uplink) towards the mobile node 130. A detailed example of an algorithm that may be used to build the subsets of fixed nodes during the "slow phase" will be described hereafter with reference to Figure 8a.

For instance, the less robust (but fastest) modulation/coding scheme (e.g. 16QAM;2/3) and a maximum power level are tuned as starting communication settings.

Next, the power level is decreased until the highest acceptable BER is reached. In case the highest acceptable BER cannot be reached with the less robust modulation/coding scheme and the maximum power level, a more robust modulation/coding scheme is tuned, and the same operation is performed to reach the minimum power level acceptable (in terms of BER). Once the best set of modulation/coding scheme, minimum power level and acceptable BER is reached, they are stored as communication settings for cycle m, position n.

Also, during step 652, sensors linked to the wireless controller 152 measure and store one or several values of context parameters that are stored in the wireless controller 152 in order to represent the current environmental conditions of the system.

These values will be used during the "fast phase' (see Figure 6b) for determining (at step 658) whether the environmental conditions of the system have changed or not.

Once the wireless controller 152 has tuned and stored the best communication settings for stationary position number n (Pa) of cycle m, it sends a "ready for capture" indicator 653b to the main controller 154 indicating that the communication settings have been tuned by the wireless controller 152. At step 654, the wireless controller 152 receives the message 604b from the main controller 154, comprising the capture settings to be used by the sensor at the mobile node 130 and the triggering command, and forwards this message wirelessly to the mobile node 130 through all the fixed nodes 140a to 140e.

Next, after a setup of the application with the capture settings, the application executes the triggering command so that the sensor at the mobile node 130 captures image data. The captured image data are sent back to the wireless controller 152 from the mobile node 130 through the fixed nodes 140a to 140e. The wireless controller 152 forwards these image data to the main controller 154.

At step 655, the wireless controller 152 checks the reception of the "image processing ok' indicator 606b from the main controller 154, indicating that new capture settings leading to a satisfactory quality of image have been computed by the main controller 154.

If the "image processing ok' indicator 606b has been received, the algorithm goes to step 656.

Otherwise, if the "image processing ok' indicator 606b is not received, the algorithm loops to the step 654.

At step 656, the wireless controller 152 checks the reception of the "slow phase done" indicator 608b indicating that all the stationary positions of all the cycles have been processed. If no "slow phase done" indicator 608b is received, the algorithm loops back to step 652 described above.

On the contrary, if the "slow phase done" indicator 608b has been received, a "fast phase" may then be performed starting from step 610. This "fast phase" is now described with reference to Figure 6b.

Figure Sb illustrates steps of a controlling method according to embodiments. As mentioned above, these steps may be performed after the steps described with reference to Figure 6a, i.e. after a preliminary phase of learning, and/or after each time that new operation settings have to be computed typically because of a change in environmental conditions. Figure Gb also illustrates the protocol of data exchange between the main controller 154 and the wireless controller 152.

As mentioned above, the fast phase" described here below allows time saving during the working cycle of the sensor since predetermined operation settings (capture settings and communication settings) are retrieved from the memory for the setup of the communication system. In particular, the "fast phase" is shorter than the "slow phase" described with reference to Figure 6a, during which the operation settings are computed from scratch.

In this example, the algorithm shown on the left side of Figure 6b is performed by the main controller 154.

At step 610, the main controller 154 forces the fast phase operational mode and sends a "fast phase" indicator 61 Ob to the wireless controller 152 to let it know that if no change occurred in environmental conditions, predetermined operation settings have to be used for the setup At step 611, the main contioller 154 sends a moving command to the articulated arm 120 to moves the sensor attached to the mobile node 130 to the stationary position number n (Pa) of working cycle m. In the meantime, the main controller 154 sends a message 611b to the wireless controller 152 indicating the stationary position number n (Pa) of the cycle m which is to be reached by the mobile node 130. This step is similar to step 602 in Figure 6a.

At step 612, the main controller 154 checks if a "slow phase request" 659b is received from the wireless controller 152. Such request is received only if environmental conditions have changed, in which case new operation settings have to be computed, as described with reference to Figure Ga.

If no request is received at this step, the algorithm goes to step 613 during which the main controller 154 checks if a "ready for capture" indicator 661b from the wireless controller 152 has been received. This check is performed regularly until the indicator 661b is received. The indicator "ready for capture" 661b indicates that communication settings (e.g. modulation and coding scheme, transmission power, and sub-set of fixed nodes to be used for uplink wireless communications with mobile node 130) for stationary position number n (Pa) of cycle m, have been set by the wireless controller 152. These communication settings have been determined and stored previously during the slow phase. This step is similar to step 603 in Figure 6a.

Once the "ready for capture" indicator 661b has been received, the algorithm goes to step 614 during which the main controller 154 retrieves from memory predetermined capture settings that have been stored during the last slow phase (at step 606) described with reference to Figure 6a.

Next, the main controller 154 sends a message 614b to the wireless controller 152 comprising the predetermined capture settings (retrieved from memory) that have to be used by the sensor at the mobile node 130, and a triggering command.

The message 614b is similar to message 604b, the difference between these two messages being the way to obtain the capture settings embedded in the message.

At step 615, the main controller 154 receives image data 662b resulting from image data captured by the sensor at the mobile node 130, sent from the mobile node 130 to the fixed nodes, and then transmitted to the wireless controller 152 to be processed. The quality (e.g. contrast, brightness) of the resulting image data 662b is then checked at step 615 by the main controller 154.

If the quality of the received image data 662b is not satisfactory, it means that communication settings or capture settings (e.g. current lighting conditions) are not adapted to the current environment, and the algorithm goes back to step 601 of the slow phase (Figure 6a) in order to compute new operation settings. At step 616, the main controller 154 sends an image processing not ok' indicator 616b to the wireless controller 152 to indicate that the main controller 154 considers it is necessary to compute new operation settings.

On the contrary, if the quality of the received image data 662b is satisfactory, the algorithm goes to step 617 where a new stationary position n (in this example: of the current cycle m or of another cycle) is considered, and the algorithm starts again from step 611.

In this example, the algorithm shown on the right side of Figure 6b is performed by the wireless controller 152.

At step 657, the wireless controller 152 checks if a "fast phase" indicator 61Db indicating that if no change occurred in environmental conditions, predetermined operation settings have to be used for the setup. This check is performed regularly until the message 61Db is received.

Once the "fast phase" indicator 610b has been received, the algorithm goes to step 658, during which the wireless controller 152 receives the message 611b from the main controller 154, indicating the stationary position number n (Pa) of the cycle m which is to be reached by the mobile node 130.

Next, the current value of at least one context parameter is measured by sensors linked to the wireless controller 152. For instance, this context parameter may be the RSSI levels of the fixed nodes (or an average RSSI level), the temperature, the humidity rate, the lighting, the communication scheme (variable Change_communication_scheme -see hereafter Figure 8b).

For instance, for measuring the RSSI levels of the fixed nodes, the wireless controller 152 sends a wireless control message to the mobile node 130 through one or several of fixed nodes 140a-140e. The wireless control message comprises a command for triggering the emission from the mobile node 130 of a signal during a given amount of time. In response to this message, the mobile node 130 emits the signal during the given amount of time and each of the fixed nodes receives a copy of the signal, based on which they may measure their respective RSSI levels. Next, each fixed node 140a-140e communicates its RSSI level to the wireless controller 152. In a variant, the raw copies of the signal as received by the fixed nodes 140a-140e may be transmifted to the wireless controller 152 that deduces the RSSl levels of the different fixed nodes 140a-140e from the received copies of the signal.

The wireless controller 152 then checks the status of various possible triggers based on the measured current values, in order to determine whether environment conditions have changed or not. These triggers are based on values of context parameters that have been previously stored during the last "slow phase", in particular at step 652. As explained before, sensors attached to the wireless controller 152 measure these values.

For instance, measured RSSI levels are compared to RSSI levels stored during the slow phase at step 652. If a change of one or several RSSI levels is detected, the wireless controller 152 will consider that environment conditions have changed. A change of one or several RSSI levels may indicate that a new obstacle is present in the area surrounding one or several fixed nodes.

According to another example, if the variable Change_communication_scheme described hereafter with reference to Figure Sb indicates that the communication scheme has changed, the wireless controller 152 will consider that environment conditions have changed.

According to a further example, if a measured value indicates a large temperature raise (or humidity) in comparison to the temperature (or humidity) measured and stored during the last slow phase, the wireless controller 152 will consider that environment conditions have changed.

A large change in lighting conditions compared to the last stored lighting measurements is also considered as a change in environment conditions.

The reference environment conditions are represented by one or several values of context parameters that are stored in the wireless controller 152, for instance during step 652.

If the check is positive for at least one of these triggers, predetermined operation settings are considered as no longer relevant because environmental conditions have changed since the computing and storing of these operation settings.

Therefore, the wireless controller 152 goes to the step 659 and sends a "slow phase request" 659b to the main controller 154 in order to indicate that new operation settings have to be computed. Next, the algorithm thus goes to step 651 of the slow phase, as described with reference to Figure 6a.

On the contrary, if it is determined at step 658 that the environment conditions are the same as the last slow phase during which the operation settings were computed and stored, the algorithm goes to step 660 during which the wireless controller 152 retrieves from memory predetermined communication settings that were stored during the last slow phase for stationary position number n (Pa) and cycle m (at step 652), as described with reference to Figure 6a.

At step 661, the wireless controller 152 sends a "ready for capture" indicator 661b to the main controller 154 indicating that the communication settings have been retrieved and set by the wireless controller 152. This step is similar to step 653 in Figure 6a.

At step 662, the wireless controller 152 receives the message 614b from the main controller 154, comprising the capture settings to be used by the sensor at the mobile node 130 and the triggering command, and forwards this message wirelessly to the mobile node 130 through at least one of the fixed nodes 140a-140e. An example of an algorithm for controlling the uplink transmission using only one of the fixed nodes will be described with reference to Figure 8b.

At step 663, the wireless controller 152 checks the reception of an "image processing not ok" indicator 616b indicating that the main controller 154 considers it is necessary to compute again the operation settings due to the bad quality of the received image data 662b. Indeed, a bad quality of image means that communication settings or capture settings (e.g. current lighting conditions) are not adapted to the current environment.

If such indicator 616b is received, new operation settings have to be computed during a "slow phase" as described with reference to Figure 6a, starting from step 651.

Otherwise, it means that the quality of image data 662b is satisfactory, and the algorithm loops to step 658 of the fast phase" already described above.

The algorithms described with reference to Figures Ba and Sb are not limitative and some variants may exist.

Figure 7a and 7b represent two examples of communication schemes that may be indicated in the operation settings for each stationary position of the mobile node 130, in particular in the communication settings, for use for uplink radio communications between at least one of the fixed nodes 140a-140e controlled by the wireless controller 152 and the mobile node 130.

In particular, Figure 7a represents a communication scheme hereafter called high latency scheme", and according to which all the fixed nodes successively send the uplink message to be sent (e.g. messages 604b and 614b) to the mobile node in order to increase the chances of successful reception of the uplink message by the mobile node 130.

In this example, a first transmission 700a of the uplink message is performed by the wireless controller 152 that sends it to the fixed node 140a (A) through the wired link 180a (not shown) that forwards the uplink message over-the-air to the mobile node 130. However, in this example, the wireless transmission of the uplink message between the fixed node 140a (A) and the mobile node 130 is not successful due to the presence of an obstacle 19 on the Line Of Sight (LOS) path between the fixed node 140a (A) and the mobile node 130.

The second (and respectively third, fourth, fifth) transmission 700b (and respectively 700c, 700d, 700e) of the uplink message is performed by the wireless controller 152 that sends it to the fixed node 140b (B) (and respectively fixed node 140c (C), fixed node 140d (0), fixed node 140e (E)) through the wired link 180b (and respectively 180c, 180d, 180e) that forwards the uplink message over-the-air to the mobile node 130. In this example, the wireless transmissions of the uplink message between each of the fixed nodes 140b (B), 140c (C), 140d (D), and 140e (E), and the mobile node 130 are all successful.

Thus, in the example of Figure 7a, the uplink message has been sent five times by the wireless controller 152 whereas it has been received correctly only four times by the first node 130.

In practice, the mobile node 130 acknowledges the reception of the uplink message through the transmission 701. The acknowledgment is received simultaneously by all fixed nodes 140a-140e which forward it to the wireless controller 152 for instance respectively through the wired links 180a-lBOe.

The latency of this high latency communication scheme is schematized by a double-arrow 702. As noticed before, this high latency communication scheme increases the chances that an uplink message is received correctly by the mobile node but its high latency impacts the duration of the displacements (working cycle).

Usually, at the start-up of the communication system, the radio communication status (i.e. satisfying quality/bad quality) between each fixed node 140a-140e and the mobile node 130 is unknown as the environment (e.g. obstacles) may not be known. As a result, the high latency communication scheme is used to determine the status/quality of each link during a preliminary phase of learning. More generally, the high latency scheme may be applied each time that new operation settings have to be computed, i.e. during the slow phase in Figure 6a, in particular at step 652. Indeed, environmental conditions may have changed due to the presence of a new obstacle on the path between one of the fixed nodes and the mobile node.

However, when it is determined that environmental conditions have not changed for instance at step 658 in Figure 6b (fast phase), it may be advantageous to reduce the latency of the communication scheme by selecting only some of the fixed nodes for the uplink transmission, based on the knowledge of the quality of the different paths between the fixed nodes and the mobile node acquired during the latest slow phase during which the high latency scheme has been applied.

In practice, this knowledge of the path quality may be acquired thanks to the mobile node 130 that may estimate the reception quality (e.g. BER) of each fixed node 140a-140e and also the signal reception level (RSSI level) based on the uplink message successively received by the mobile node 130 as shown in Figure 7a.

The reception quality and the signal reception level for each fixed node (called here before the "knowledge of the path quality") may be then sent by the mobile node 130 in the acknowledgment (transmission 701) so that the wireless controller 152 may use the reception quality and the signal reception level provided by the mobile node 130 to build a table 900 of quality features for each stationary position of the mobile node 130, as will be described with reference to Figure 9a.

Based on such table 900, the wireless controller 152 will be configured to select the fixed node(s) that may be used for the transmission of an uplink message to the mobile node 130, when the environment conditions have not changed. An example of an algorithm that may be used for the selection of these fixed node(s) will be described with reference to Figure 8a.

An example of "low latency scheme" is shown in Figure 7b. According to this example, the uplink message is sent through only one fixed node called the main fixed node, and another fixed node called a "spare node" is provided as a "fallback solution" in case the transmission through the main fixed node fails.

In this example, the fixed node 140e is selected as the main fixed node for the transmission 700e' of the uplink message from the wireless controller 152 (e.g. messages 604b and 614b) to the mobile node 130. And, in case of failure of the transmission over-the-air from the fixed node 140e to the mobile node 130, for instance due to the presence of an obstacle between them, the fixed node 140c (C) will be used for the transmission of the uplink message to the mobile node 130.

In this example, the transmission of the uplink message through the main fixed node 140e (E) is successful. Thus, the mobile node 130 acknowledges the reception of the uplink message through the transmission 701'. The acknowledgment is received by all the fixed nodes 140a to 140e and then forwarded to the wireless controller 152 for instance through the wired links 180a to lSOe.

The latency of this low latency communication scheme is schematized by a double-arrow 702', which is shorter than the high latency arrow 702. This is because the fewer the transmissions (i.e. the number of fixed nodes transmitting the same uplink message) the lower is the latency of the uplink communication.

If there had been trouble (case not shown) at the main fixed node 140e (E), the spare fixed node 140c (C) would have been used for the transmission of the uplink message to the mobile node 130, and the acknowledgement would also have been sent to all the fixed nodes 140a to 140e. The latency would have been also shorter than with the high latency communication scheme since only two transmissions would have been performed instead of five (see Figure 7a).

As will be described later, several subsets of main and spare nodes may be provided so that in case of sudden path shadowing at the main and at the spare nodes, a main node of another subset may be used for the uplink transmission. The use of the low latency communication scheme is thus maximized and the latency optimized.

The selection of the main fixed node from among the fixed nodes 140a to 140e and the determination of its spare fixed node to be used according to the low latency communication scheme of Figure 7b are now described with reference to Figure 8a. This algorithm may be performed at step 652 of Figure 6a (slow phase), during which new communication settings are determined.

The present algorithm is implemented by the wireless controller 152 and starts at step 800.

At step 801, the wireless controller 152 selects a high latency communication scheme as described with reference to Figure 7a, according to which a same uplink message is successively transmifted to the mobile node 130 through all the fixed nodes 140a to 140e.

At step 802, the wireless controller 152 receives from the main controller 154 a message 602b indicating the stationary position number n (Pa) of the cycle m which is to be reached by the mobile node 130.

Next, the wireless controller 152 obtains the quality measurements (reception quality and signal reception level of each fixed node) forwarded by the fixed nodes 140a to 140e upon receiving the acknowledgment from the mobile node 130, as described with reference to Figure 7a and 7b. The wireless controller 152 then stores these quality measurements in association with their respective fixed node and the stationary position of the mobile node 130, in a table 900 as will be described with reference to Figure 9a.

At step 803, the wireless controller 152 builds a set of fixed nodes which have a satisfying path quality with the mobile node 130, based on the quality measurements stored in table 900.

At step 804, the wireless controller 152 builds one or several subsets of fixed nodes from the set of fixed nodes built at step 803. In the example of Figures 9a and 9b that will be described later, the subset is a pair of fixed nodes, and this pair is built as the best compromise between a satisfying quality of path with the mobile node and a satisfying spatial diversity between the fixed nodes of the pair (i.e. they are spaced apart in order to not be both impacted when an obstacle arise on the path with the mobile node). In a variant (not shown on Figures 9a and 9b), subsets of more than two fixed nodes may be built at step 804.

At step 805, the wireless controller 152 builds a subsets table. In this table, the subsets of fixed nodes may be sorted in preference order, for instance according to their spatial diversity or based on the highest quality of the fixed node of each subset, or based on any other criterion. Once the subsets table has been built, the wireless controller 152 can implement the corresponding communication scheme, i.e. the low latency communication scheme, provided that the environmental conditions remain the same. As explained earlier with reference to Figure 6a, the subset table is indicated in the operation settings as communication settings, during the slow phase of Figure 6a.

At step 806, the algorithm stops.

Figure 8b represents the steps of an algorithm for controlling the transmission of an uplink message from the wireless controller 152 to the mobile node 130, in particular during the fast phase shown in Figure 6b.

This algorithm may be for instance used at step 662 of Figure 6b, for transmitting the message 614b comprising the capture settings to be used by the sensor at the mobile node 130 and the triggering command, to the mobile node.

This algorithm is implemented by the wireless controller 152 and starts at step 850.

At step 851, the wireless controller 152 identifies that the mobile nodes has reached the stationary position number n (Pa) of cycle m, thanks to message 611b, (see Figure 6b).

At step 852, the wireless controller 152 selects a low latency communication scheme, for instance the low latency scheme described earlier with reference to Figure 7b, for the transmission of uplink messages to the mobile node 130. The wireless controller 152 also selects a subset and a main fixed node corresponding to the current stationary position number n (Pa) of cycle m, in the subset table included in the operation settings stored previously at step 652 of the latest slow phase (Figure 6a).

For instance, the best sorted subset ("preferred subset") may be chosen in the table.

At step 853, the wireless controller 152 determines whether the main node selected at step 852 has communication trouble. In practice, this determination is based on the acknowledgment received correctly or not by the fixed nodes 140a to 140e as described with reference to Figure 7b. If no communication trouble is detected, the algorithm stops at step 860.

On the contrary, when the main node encounters communication trouble, the wireless controller 152 checks at step 854 if a variable Change_subset stored in memory is equal to 1'. This variable indicates whether the subset currently used (i.e. the subset selected at step 852) has to be changed (Change_subset = 1) or not (Change_subset = 0).

If the subset currently used does not have to be changed (Change_subset = 0), a spare node of this subset is selected for the transmission at step 853 and the variable Change_subset is set to 1. In this example, we assume that the subset is a pair and so comprises only one spare fixed node. Consequently, if it is then determined at a new step 853 that there is still communication troubles with the selected node (now the spare node), the subset will have to be changed.

If it is determined at step 854 that the subset currently used has to be changed (Change_subset = 1), the wireless controller 152 checks at step 856 whether an alternative subset is available in the table included in the operation settings. In practice, it may happen that the table comprises only one subset, for instance when the path quality is bad for a several fixed nodes.

If there is an alternative subset available in the table, it is selected at step 857, and the former selected subset (at step 852) is no longer the best sorted (preferred") in the table. The selected alternative subset is updated (step 858) in the table to become the "preferred subset" (best sorted) and the variable Change_subset is set to 0'. Next, the algorithm goes back to step 852 described above.

If there is no alternative subset available in the table, the wireless controller 152 switches at step 859, to the high latency communication scheme as described with reference to Figure 7a, and a variable Change_communication_scheme in memory is set to 1'. This variable (when it is set at 1) indicates that the environmental conditions have changed too much to be handled by the "fallback solution(s)" of the low latency scheme provided in the stored operation settings, and so, a request for computing new operation settings is sent (corresponds to step 659 of Figure 6b).

At step 860, the algorithm stops. The algorithms described with reference to Figures 8a and Sb are not limitative and some variants may exist.

Figure 9a illustrates an example of table that may result from quality measurements recorded for each stationary position of the mobile node 130.

As described above with reference to Figure 7a, the wireless controller 152 enables successively each fixed nodes 140a to 140e, to transmit a frame to the mobile node 130. For each corresponding copy of the frame received, the mobile node 130 performs path quality and signal level measurements. Next, the mobile node 130 gathers all these measurements and sends a frame (corresponds to the above-mentioned acknowledgment) embedding all the results to the wireless controller 152 through all fixed nodes 140a to 140e, based on which the wireless controller 152 is configured to build the table shown in Figure 9a.

In this table, the first raw 910 corresponds to the fixed nodes 140a to 140e, the second raw 920 corresponds to the path quality (BER) and the third row 930 corresponds to the reception signal level (RSSI). Each column corresponds to the reception status of the mobile node for a given fixed node (e.g. column 913 corresponds to fixed node 140a).

Each intersection between the first row and any column comprises a path quality indicator "OK" or "NOK" that indicates whether the BER of the path between the mobile node 130 and the fixed node corresponding to the column, is below (OK) or above (NOK) a quality threshold. In an example shown in Figure 9a, the quality is satisfactory for the wireless communication path between the mobile node 130 and each of the fixed nodes 140b to 140e but the quality is not satisfactory for the wireless communication path between the mobile node 130 and the fixed node 140a.

Also, each intersection between the second row and any column comprises an indication of the power level of the wireless signal received by the mobile node 130 when a fixed node is transmitting a signal. This indication may correspond to the RSSI (Received Signal Strength Indication) or the value of the VGA (Variable-Gain Amplifier) since it is used to set the amplification of the received signal to a predetermined value.

In the example shown in Figure 9b, the power level of the signal received by the mobile node 130 is 3 when the fixed node 14Db is transmitting a signal, 5 when the fixed node 140c is transmitting, 9 when the fixed node 140d is transmitting and 6 when the fixed node 140e is transmitting a signal.

Based on this table 900, the set of fixed nodes with a satisfying quality path for the current stationary position of the mobile node 130 is selected, here fixed nodes 14Db to 140e, and the fixed node 140a is thus not selected. An indication of the selected fixed nodes 140b-140e to be activated may be included in the operation settings associated with the current stationary position.

Next, also based on this table 900, the wireless controller 152 builds the subset of fixed nodes to be used during the fast phase described with reference to Figure 6a and Figure Sb. The main fixed node of the subset is used for transmission in the uplink direction from the wireless controller 152 towards the mobile node 130. As mentioned before, the interest of such selection is to prevent from successive transmissions through all the fixed nodes 140a to 140e.

In case of a sudden path shadowing between the mobile node and the main fixed node, it is possible to immediately use a spare fixed node of the subset without having to go back to a high latency communication scheme.

Figure 9b describes an example of configuration in line with the quality measurements of table shown in Figure 9a.

As mentioned above, according to some embodiments, subsets of fixed nodes are built from among the fixed nodes with a satisfying path quality with the mobile node 130, so that the corresponding fixed nodes of a subset achieve satisfying spatial diversity (i.e. they are spaced apart in order to not be all impacted when an obstacle arise on the path with the mobile node). An example of selection of subsets has been detailed with reference to Figure 8a. These subsets are used in the low latency communication scheme in a way described with reference to Figure 8b.

The present example aims to illustrate the principle of spatial diversity that may be used to build the subsets.

In the present example, for the sake of clarity, the selection of only one subset is described. However, embodiments are not limited thereto and several subsets may be selected. The number of subsets depends on the environment conditions, and on the total number of fixed nodes.

When considering the quality measurements stored in the table 900 of Figure 9a, the fixed node 140a is discarded due to its bad path quality with the mobile node 130. Between the remaining fixed nodes, a subset (here a pair) of a main and spare fixed nodes having a satisfying spatial diversity is selected in order to reduce the probability of having unexpected shadowing impacting both of them.

Generally, in communication systems using multi-reception techniques, all the fixed nodes are not located close to each other, but are spread all around the working area of the mobile node in order to always have at least one fixed node configured to wirelessly communicate with the mobile node for the various stationary positions that the mobile node can reach.

In the example of Figure 9b, the farthest fixed nodes thus forming the pair of fixed nodes achieving the best spatial diversity are the fixed nodes 140c and 140d.

However, the selection of the subset should also take into account the signal level measurements. Preferably, the fixed nodes selected should lead to similar reception signal levels for the mobile node 130. Considering table 900 shown in Figure 9a, when the fixed node 140c is transmitting, the mobile node 130 measures a signal level of about 5, and when the fixed node 140e is transmitting, the mobile node 130 measures a signal level of about 6, so these two fixed nodes provide similar reception levels to the mobile node 130. In such case, as represented in Figure 9b, this means the mobile node 130 is almost located on the perpendicular bisector 940 between the fixed nodes 140c and 140e. As the fixed nodes 140c and 140e are not closely located, a satisfying spatial diversity is achieved with this solution, and these two fixed nodes may thus form a subset as used in the algorithm described with reference to Figures 8a and 8b. In this example, the fixed node 140e is selected as the main node of the subset since it provides a better signal reception than the other fixed node 140c which is thus selected as the spare node of the subset.

The composition of each selected subset (main and spare(s)) is stored in a subsets table in sorting preference order. As mentioned above, this table may be included in operation settings as communication settings, in order to be (re)used if environmental conditions are unchanged (fast phase).

Thanks to the described algorithms and communication schemes, the main controller 154 is configured to always optimize the average duration of displacement of the sensor at the mobile node 130 while ensuring satisfactory behavior of the overall communication system 100.

Although the present invention has been described hereinabove with reference to specific embodiments, the present invention is not limited to the specific embodiments, and modifications which lie within the scope of the present invention will be apparent to a person skilled in the art. Many further modifications and variations will suggest themselves to those versed in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the invention as determined by the appended claims. In particular different features from different embodiments may be interchanged, where appropriate.

Claims

CLAIMS1. A method for controlling a communication system comprising a mobile node communicating wirelessly with a plurality of fixed nodes, the mobile node moving between a plurality of stationary positions, at least some of which being stored, as predetermined stationary positions in said communication system, in association with predetermined operation settings and with at least one value of at least one context parameter, the method comprising the following steps implemented each time the mobile node has reached a predetermined stationary position: measuring at least one current value of at least one of said context parameters; determining whether environmental conditions of the communication system have changed based on the measured current value and the stored value of said context parameter associated with the stationary position, upon negative determination, performing a fast control phase using said predetermined operation settings associated with the stationary position, upon positive determination, performing a slow control phase comprising computing new operation settings for the stationary position.
2. The method of claim 1, wherein operation settings comprise at least one of the following communication settings: the transmission power level for communicating wirelessly between the mobile node and the fixed nodes, the modulation and coding scheme, the communication scheme to be used for uplink communications with the mobile node.
3. The method of claim 2, wherein the communication scheme comprises an indication of at least one subset of fixed nodes to be used for uplink communications with the mobile node.
4. The method of claim 3, wherein a set of fixed nodes is selected from among the fixed nodes of the communication system based on a quality criterion, and the subset indicated in the communication scheme is built from said selected set.
5. The method of claim 4, wherein the fixed nodes of said subset indicated in the communication scheme are spaced apart so that when an obstacle arises on the path between the mobile node and one of the fixed nodes of the subset, said obstacle is not on the path between the mobile node and another fixed node of the subset.
6. The method of claim 3, wherein said subset indicated in the communication scheme comprises a main fixed node and at least one spare fixed node, and the method further comprises: sending an uplink message from the main fixed node to the mobile node; and in case the uplink message is not received correctly by the mobile node, transmitting the uplink message from the spare fixed node to the mobile node.
7. The method of claim 1, wherein an application for capturing image data is implemented at the mobile node and operation settings comprise at least one of the following capture settings: exposure time, aperture value, image size, lighting parameters, ISO sensibility value.
8. The method of claim 1, wherein said context parameter is one of the following: light level, temperature, humidity, quality of the wireless communication path between the mobile node and the fixed nodes, quality of image data captured at the mobile node by an application for capturing image data.
9. The method of claim 1, further comprising storing, in association with each stationary position of the mobile node, the new operation settings computed for said stationary position and the at least one measured current value, as predetermined operation settings and context parameter value.
10. A system controller device for controlling a communication system comprising a mobile node communicating wirelessly with a plurality of fixed nodes, the mobile node moving between a plurality of stationary positions, each stationary position being stored in said communication system in association with predetermined operation settings and with at least one value of at least one context parameter, the system controller device comprising: a module for sending a moving command to the mobile node, for reaching a stationary position; a module for measuring at least one current value of at least one of said context parameters when the mobile node has reached the stationary position; a module for determining whether environmental conditions of the communication system have changed based on the measured current value and the stored value of said context parameter associated with the stationary position; and wherein the mobile node and the fixed nodes are configured to perform, upon negative determination, a fast control phase using said predetermined operation settings associated with the stationary position, and upon positive determination, a slow control phase comprising computing new operation settings for the stationary position
11. A computer program product for a programmable apparatus, the computer program product comprising a sequence of instructions for implementing a method according to any one of claims 1 to 9, when loaded into and executed by the programmable apparatus.
12. A computer-readable storage medium storing instructions of a computer program for implementing a method according to any one of claims 1 to 9.
13. A communication system as hereinbefore described, with reference to, and as shown in, Figure 1 of the accompanying drawings.
14. A node of a communication system as hereinbefore described, with reference to, and as shown in, Figure 2 of the accompanying drawings.
15. A wireless controller of a system controller device as hereinbefore described, with reference to, and as shown in, Figure 3 of the accompanying drawings.
16. A main controller of a system controller device as hereinbefore described, with reference to, and as shown in, Figure 4 of the accompanying drawings.
17. A method as hereinbefore described, with reference to, and as shown in, Figures 5, 6a and 6b, of the accompanying drawings.