GB2524974A

GB2524974A - Method for monitoring the displacement of a mobile node in a communication system

Info

Publication number: GB2524974A
Application number: GB1406243.4A
Authority: GB
Inventors: Alain Caillerie; Mickaã L Lorgeoux; Francois Thoumy
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2014-04-07
Filing date: 2014-04-07
Publication date: 2015-10-14
Anticipated expiration: 2034-04-07
Also published as: GB2524974B; GB201406243D0

Abstract

There is provided a method for monitoring the displacement of a mobile node 130 in a communication system, the mobile node communicating wirelessly with a plurality of fixed nodes 140 of the communication system, and the mobile node moving between a plurality of rest positions P. The mobile node transmits a monitoring signal (which may be intermittent) which is received by the fixed nodes; this allows the fixed nodes to determine when the mobile node has reached or left a particular rest position. The monitoring signal transmitted by the mobile node is modified, for an energy saving period, between the rest positions. The modification may be an increase in the period of the intermittent transmission of the monitoring signal, a reduction in the power of the monitoring signal, an increase in the transmission period or a combination of these. The energy saving period is selected to be smaller than upon the minimum transit time between rest positions. The mobile node may be a HD camera transmitting uncompressed image data to the fixed nodes using a millimetre radio waves (i.e. 60GHz or terahertz communication).

Description

METHOD FOR MONITORING THE DISPLACEMENT OF A MOBILE NODE IN A

COMMUNICATION SYSTEM

FIELD OF THE INVENTION

The present invention relates in general to the wireless transmission of data between a mobile node and a plurality of fixed nodes, in a geographically limited context. In particular, the present invention provides a method for monitoring the displacement of a mobile node in a communication system.

BACKGROUND OF THE INVENTION

Wireless NV (audio/video) applications such as capture of High Definition (HD) video or image, are now increasingly numerous and require even higher data bit rates and higher quality of service.

A wireless network system using the millimetre wave frequency band (60GHz) is well adapted to the transmission of such uncompressed HD video or image data.

Indeed, the authorized band around a carrier frequency of 60GHz offers a wide bandwidth thus enabling the transportation of a large quantity of data with a high data rate transmission (>3Gbps). Moreover, the radio range of such systems is limited to about ten meters, thus favoring the reuse of frequencies in time and space.

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 create space diversity, wireless network systems comprising a single moving emitting node and several fixed receiving nodes connected to a system controller device are considered.

Typically, the mobile node is moving from a rest position to another one. A position is considered as a rest position when the application, for instance image capture, running at the mobile node thus positioned, becomes operational. Then, the captured data have to be transmitted to the system controller device, preferably using direct transmission without reflection, also called Line Of Sight (LOS), between the mobile node and the receiving nodes connected to the system controller device.

Starting from a rest position, several next rest positions, called next possible rest positions, may be reached.

In some contexts, the mobile node may move from a starting rest position and passes through several other intermediary rest positions before reaching again the starting rest position, thus forming a particular cycle of displacement. The latter may eventually be reproduced several times. Also, several different cycles may be formed for the same starting rest position.

Methods are known that allow determination of the optimal power level to be used for transmitting data from a given rest position, based on the reception quality of the receiving nodes.

However, such solutions are not adapted to control the overall power consumption over an entire cycle of displacements.

In addition, detecting the rest positions of the mobile node is costly in terms of power and energy since it requires the mobile node to transmit data during the whole cycle of displacements, and the receiving nodes to be active even when the mobile node is between two rest positions.

SUMMARY OF THE INVENTION

The present invention has been devised to address one or more of the foregoing concerns, with the aim of saving energy.

In this context, according to a first aspect of the invention, there is provided a method for monitoring the displacement of a mobile node in a communication system, the mobile node communicating wirelessly with a plurality of fixed nodes of the communication system, and the mobile node moving between a plurality of rest positions, the method comprising the steps of: transmitting a monitoring signal from the mobile node to the fixed nodes; and determining that the mobile node has reached or left a rest position based on reception parameters of the monitoring signal by the fixed nodes; and wherein, the method further comprises modifying the transmission of the monitoring signal upon determination that the mobile node has left a current rest position, for a period, called energy saving period, based on a predetermined time value selected from among a plurality of predetermined time values, wherein each of said predetermined time values is associated with the current rest position and a next possible rest position, as the amount of time necessary to reach the next possible rest position from the current rest position, the predetermined time value being selected as the minimum time value among the plurality of predetermined time values.

The present invention makes it possible to monitor the displacement of the mobile node between several rest positions without continuously transmitting a monitoring signal from the mobile node to the fixed nodes, thus optimizing energy consumption between rest positions.

This is achieved by modifying the transmission of the monitoring signal upon determination that the mobile node has left a current rest position, until expiry of the energy saving period which is based on the minimum amount of time necessary to reach a next possible rest position, i.e. until the closest next possible position can be reached.

Thanks to this, no rest position is missed while the energy due to the transmission of the monitoring signal for determining that the mobile node is at a rest position is saved, in comparison with the prior art.

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

In some embodiments, the above-mentioned energy saving period is smaller than the selected predetermined time value, so that it allows determination that the mobile node has reached the next possible rest position associated with the selected predetermined time value.

An analysis of the reception parameters of the monitoring signal by the fixed nodes may thus increase the precision of the determination of the point when the mobile node is at a rest position.

In some embodiments, the step of modifying the transmission of the monitoring signal comprises transmitting the monitoring signal periodically with a period lower than the above-mentioned energy saving period.

Thus, the monitoring signal is transmitted at least once to the fixed nodes between two rest positions of the mobile node.

In some embodiments, the monitoring signal is transmitted periodically.

The energy due to the transmission of the monitoring signal for determining that the mobile node is at a rest position is saved even more in comparison with a continuous transmission of data near a rest position.

In some embodiments, the step of modifying the transmission of the monitoring signal comprises increasing the period of transmission of the monitoring signal during the above-mentioned energy saving period.

Thus, upon determination that the mobile node has left a current rest position, the monitoring signal is transmitted less often than when the mobile node is far from any rest position. Consequently, the energy consumption is decreased.

In some embodiments, modifying the transmission of the monitoring signal includes switching off the transmission during the above-mentioned energy saving period.

Consequently, no energy is consumed for transmitting the monitoring signal during this energy saving period.

In some embodiments, upon determination that the next possible rest position associated with the selected predetermined time value has not been reached on expiry of the selected predetermined time value, the method further comprises another step of modifying the transmission of the monitoring signal for a period, also called energy saving period, based on another predetermined time value selected from among the above-mentioned plurality of predetermined time values, the other predetermined time value being selected as the minimum time value among the plurality of predetermined time values which have not been selected yet.

Thus, the transmission of the monitoring signal is modified until expiry of the energy saving period which is based on the minimum amount of time necessary to reach another next possible rest position, i.e. until the closest next possible position, which is different from the initial closest next possible position considered, can be reached.

In some embodiments, the method further comprises a step of adjusting the power level of the monitoring signal transmitted from the mobile node based on the current rest position and on the selected predetermined time value.

The power level of the transmission of the monitoring signal is thus optimized.

In some embodiments, the monitoring signal is a dummy signal.

In some embodiments, the method comprises a preliminary step of learning which comprises: identifying a plurality of possible rest positions; for each possible rest position identified, computing a plurality of time values, each defining the amount of time necessary to reach a different next possible rest position; and associating with each pair of identified rest positions, the corresponding computed time value as a predetermined time value.

In a variant, a table of predetermined time values associated with each pair of rest positions is received from a third party electronic entity.

In some embodiments, the preliminary step of learning also comprises: determining the optimal power level for the transmission of the monitoring signal from each possible rest position; and associating with each identified possible rest position, the corresponding determined optimal power level.

In a variant, a table of possible rest positions associated with optimal power level is received from a third party electronic entity.

In some embodiments, the power level of the monitoring signal transmitted from the mobile node is adjusted according to the optimal power level associated with the next possible rest position which is associated with the selected predetermined time value during the learning step.

The power level of the transmission of the monitoring signal is thus optimized and the energy consumption is thus minimized.

In some embodiments, if all the predetermined time values have been selected without any positive determination, the method comprises, on expiry of the selected predetermined time value to reach the next possible rest position associated with the selected predetermined time value, a new step of learning.

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 system controller device of a communication system according to some embodiments; -Figure 4 schematically shows general steps of a method for monitoring the displacement of a mobile node in a communication system, according to some embodiments; and -Figure 5 schematically shows a preliminary step of learning, according to some embodiments.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention provides methods for monitoring the displacement of a mobile node in a communication system, such that the mobile node communicates wirelessly with a plurality of fixed nodes connected to a system controller device and moves between a plurality of rest positions.

As described below with reference to several examples, a method according to the invention comprises a step of transmitting a monitoring signal from the mobile node to the fixed nodes, so that the system controller device can evaluate reception parameters such as quality parameters, based on the monitoring signal received by each fixed node. Based on these reception parameters and their evolution, it is determined whether the mobile node has reached or left a rest position, or not.

According to the method, in case it is determined that the mobile node has left a current rest position, the monitoring signal is modified, so that less energy is consumed until the mobile node comes close to the next rest position.

All the same, in order to detect the reaching of the next rest position, the transmission of the monitoring signal is modified only during a period, called energy saving period, which is based on the minimum time necessary to reach the next possible rest position starting from the current rest position of the mobile node. Thus, even if the transmission of the monitoring signal is modified when leaving a rest position, no next rest position is missed.

Such method takes advantage of the preliminary knowledge of the possible next positions that may exist for a given rest position and of the associated amount of time necessary to reach each of these positions from the current rest position.

Indeed, since the modification of the transmission of the monitoring signal terminates upon expiry of a period based on the time to reach the closest next possible rest position, the system controller device can evaluate reception parameters when the mobile node is in the neighbourhood of the closest next possible rest position, so as to determine whether the mobile node will actually reach that next possible rest position, or not.

Consequently, energy is saved during the displacement of the mobile node while still making it possible to determine that the mobile node reaches or leaves a rest position.

Figure 1 represents a communication system comprising a mobile node 130, a plurality of fixed nodes 140a, 140b, 140c, 140d, 140e, 140f, and a system controller device 150. Such communication system is adapted to implement a monitoring method according to some embodiments, as will be described below with references to Figure 4.

The mobile node 130 is for instance a source device configured to capture data such as image data or video data. Some embodiments of the present invention have a particular application in the context of HD image or video capture and transmission.

The mobile node wirelessly communicates (broadcasts) with the fixed nodes, for instance by means of 60GHz millimetre waves. The fixed nodes 140a to 140f are located in fixed places in the mobile node wireless coverage area. Six fixed nodes are shown in Figure 1; however the invention is not limited thereto. The number of fixed nodes generally used is a compromise between the cost of fixed nodes and the need to create space diversity to avoid shadowing effects due to obstacles on the wireless communication paths between the mobile node and the fixed nodes.

Each fixed node may also send data to the mobile node, and the mobile node may also receive data from the fixed nodes.

Fixed nodes 140a, 140b, 140c, 140d, 140e, and 140f are respectively connected to the system controller device 150, by means of wired or wireless links 180a, 18Db, 180c, 180d, 180e, and 180f.

Each fixed node may comprise a modem and the interconnection between the fixed nodes and the system controller device may be performed thanks to digital high speed interfaces using differential signals. These high speed wired interfaces may be point-to-point organized, or may be bus oriented. They may be of l000BaseT type or compliant to 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 even be wireless.

Other embodiments may be envisaged where the interconnection physical medium is analogue 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 acts as a central unit and may forward data received from the fixed nodes to an application device, for instance a display, a recorder, or any other equipment able to interpret and use the received data.

The mobile node 130 may move between two data communication sequences. Thus, a path between the mobile node and a given fixed node may for example be cut during a given sequence but not during another sequence.

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

Thus, four cycles of displacement are shown in Figure 1, namely {P0, P1, P if 11 1 1 * * 2, 3, 01, t 0, 1, 2, 3, 01, t 0, 1, 2, 3. 01, an 0, 1, 2, 3, 0 Obviously, 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 provided some expected possible next rest positions may be determined for each current rest position.

Figure 2 schematically shows an example of architecture 200 for a mobile node 130 or a fixed node 140a-140f of a communication system 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-enci) 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 Recept/on 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; -an input/output interface I/O IF 206 for instance to capture image or video data (for the mobile node 130) through the link 207, or to communicate with a system controller device 150 (for the fixed nodes 140a-140f) through the link 207.

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

In that example, the system control device 150 comprises: -a processing unit pc (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, 140b, 140c, 140d, 140e and 140f, respectively through the links 180a, 180b, 180c, iBOd, 180e and 180f 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; -an input/output interface I/O IF 305 configured to connect an application device 306 which could be a display, a recorder, or any other equipment able to interpret and use the received data. The interface 305 may also be able to exchange commands and status messages.

A method for monitoring the displacement of the mobile node 130 according to some embodiments is now described with reference to Figure 4. Such method may be implemented by the communication system shown in Figure 1 comprising mobile node 130, fixed nodes 140a-140f and system controller device 150 that have been described with references to Figures 2 and 3.

In this example, the method starts at step 400 during which an index i of a current rest position is set to zero. The current rest position i=0 is for instance the initial position P0 on Figure 1.

At step 405, the mobile node 130 starts the transmission (broadcast) of a monitoring signal to fixed nodes 140a to 140f This transmission is called normal transmission".

The monitoring signal is for instance a dummy signal so that the processing of the signals received by fixed nodes 140a to 140f by the system controller device 150 is simple.

The monitoring signal may be continuous. In a variant, the monitoring signal may be periodically transmitted with a predetermined period.

At step 410, an index j of a next possible rest position starting from current rest position i, is set to zero.

At step 415, system controller device 150 tests if mobile node 130 has left the current rest position i which is the initial rest position P0 in the first implementation of step 415.

In practice, system controller device 150 analyses reception parameters of the monitoring signal by fixed nodes 140a-140f. For instance, system controller device computes the change in the power level of reception, and/or of other quality parameters, and when no change is detected for a while, it means that mobile node is in a rest position. Otherwise, when there is a change in the reception parameters, it means that the mobile node is moving.

In case of a negative test, i.e. if no change in the reception parameters is detected, mobile node 130 is still at rest position i. Next, test 415 is repeated after a short amount of time.

In case of a positive test, i.e. if a change in the reception parameters is detected, mobile node 130 has left rest position i. A timer T is then started at step 420 by system controller device 150. Timer T1 measures the time passed since the mobile node started leaving rest position i. Upon detection (step 415) that mobile node 130 has left rest position i, the transmission of the monitoring signal is modified for an energy saving period (step 425) as opposed to the normal transmission started at step 405. The transmission may be modified in different ways.

One way of modifying the transmission is to merely switch off the transmission. Thus, no more energy is consumed for the transmission of the monitoring signal.

Another way of modifying the transmission consists in transmitting periodically the monitoring signal, while the normal transmission is continuous. Thus, the energy consumption due to the transmission of the monitoring signal is decreased in comparison with the normal transmission which is continuous.

Again another way of modifying the transmission consists in modifying the period of transmission of the monitoring signal while the normal transmission is periodic. Typically, the monitoring signal is transmitted less often in order to decrease the energy consumption. In other words, the period of transmission (i.e. the amount of time between two emissions of the monitoring signal) is increased.

In practice, when the modified transmission is periodic, the transmission period is shorter than said energy saving period during which the transmission is modified so that the monitoring signal is transmitted at least once. Otherwise, the modification is equivalent to a switch off.

Also, the power level of the monitoring signal may be modified in comparison with the power level of the normal transmission.

Obviously, other ways of modifying the transmission of the monitoring signal may be considered. For instance, they may combine some features pertaining to different ways described above, or others.

The energy saving period Dii of the modified transmission of the monitoring signal, is linked to a predetermined time value corresponding to the minimum amount of time necessary to reach the next possible rest position j from the current rest position i, i.e. the predetermined time value corresponding to the amount of time necessary to reach the closest next possible rest position j.

Generally, is slightly smaller than the predetermined time value of the closest next possible rest position. "slightly" means enough to allow system controller device 150 to determine whether mobile node 130 is actually reaching the closest next possible rest position or not.

This predetermined time value is selected from among a plurality of predetermined time values respectively corresponding to the amount of time required to reach each next possible rest position j from the current rest position i.

In practice, one or more tables of predetermined time values is stored in the memory of system controller device 150 so that, for each rest position i, all the next possible rest positions j are associated with the amount of time required to reach each next possible j from the considered rest position i.

One table may be stored for each rest position i, or only one table may be stored for all the rest positions i. The pairs of rest position i and next possible rest position j may be sorted based on their associated time value. The selection of the minimum time value is thus facilitated.

Let N denote the total number of next possible rest position j existing for the considered rest position i. Taking the example of Figure 1, the rest position P0 has N = 3 next possible rest positions: P1, P'1 P"1. Among them, the closest one seems to be P1, then P'1, and the farthest from P0 seems to be P"1. Consequently, in a sorted table dedicated to rest position P0, next possible rest position P1 will be the first one (i.e. j = 1), then next possible rest position P'1 will be the second one (j=2), and next possible rest position P"1 will be the last one Q=3). The same kind of table may be computed for each rest position.

Also, the table(s) may comprise, for each next possible rest position j, a value of optimal power level for the transmission of the monitoring signal.

This or these table(s) may be obtained by system controller device 150 from a third party entity, for instance on powering up of the communication system.

In a variant, the table(s) is(are) constructed and stored by system controller device 150 during a preliminary step of learning. During this optional preliminary step of learning, a signal is transmitted from mobile node 130, for example at a maximum available power level.

System controller device 150 computes the variations of the above-described reception parameters, and checks the periods of stability of the signal, which corresponds to rest positions of mobile node 130.

The position of moving device 130 is preferably characterized by a set of RSSI (forReceivedsigna/Strength Indication) values. In other words, mobile node 130 is determined to be at a given position if the RSSI values to the different fixed nodes are equal to specific predetermined values associated with the given position.

For all identified rest positions, the amount of time to reach a next rest position from a given identified rest position is then stored in the table in association with the pair of corresponding rest positions.

Next, system controller device 150 may determine, for each identified rest position, the minimum power level allowing good data reception by the maximum number of fixed nodes. To that end, system controller device 150 may use a technique described in document GB2502 108 by Lorgeoux et al. Optionally, as mentioned above, the table may present, for each rest position, the next possible rest positions which may be sorted so that the corresponding time values are in increasing order. In other words, for each rest position, the next possible rest positions are sorted from the closest to the farthest from the considered rest position.

Figure 5 represents an example of implementation of this optional preliminary step of learning. For the sake of clarity, in this example, rest positions forming a cycle are identified. However, the present invention is not limited to cycles and tables may be computed in contexts other than cyclic displacements.

At step 500, the identification of rest positions forming a considered cycle starts by setting an index i corresponding to a current rest position at zero. The rest position i = 0 corresponds to the initial or starting position of the considered cycle.

At step 505, mobile node 130 starts transmitting a signal at the maximum power level available, to fixed nodes 140a, 140b, 140c, 140d, 140e and 140f.

At step 510, system controller device 150 checks if the signal level received by all the fixed nodes from mobile node 130 is changing.

If so, this means the mobile node has left rest position i, and a timer T is started at step 515. One may note that at the first implementation of step 510, it is tested whether the mobile node has left the starting position i = 0.

At step 520 (similar to step 455 in Figure 4), it is determined whether the mobile node has reached a new rest position H-i, or not.

If so, the timer I is stopped and its value is stored (step 525) in a table in association with rest positions i and i+1. One may note that this value corresponds to the amount of time taken to reach rest position H-i from rest position i.

Next, system controller device 150 may determine for each newly identified rest position, the minimum power level allowing good data reception by the maximum number of fixed nodes. To that end, system controller device 150 may use a technique described in document GB2502 108 by Lorgeoux et al. Also, the optimal power level for transmission of the signal may be stored at step 530, in association with rest position i+1.

It is then tested (step 535) whether rest position i corresponds to the initial rest position of the considered cycle. If not, index i is incremented (step 540) and steps 510 and the following ones are performed again with the new value of index i.

On the contrary, if the rest position i is the initial position of the cycle, the learning step ends (step 545).

Returning to the example of Figure 4, after starting the modified transmission of the monitoring signal as described above with reference to step 425, it is determined (step 430) whether the next possible rest position j currently considered is the last one for the given rest position i, or whether there is another next possible rest position j that has not been considered yet.

If all the next possible rest solutions have been considered, i.e. if j = N, it means that for current rest position i, no rest position of the table has been reached.

Thus, the process ends at step 435. A new table may be then obtained, for instance by performing a new learning step as depicted in Figure 5, or from a third entity. In a variant, the existing table may be uploaded (or refreshed) by performing a new step of learning as aforementioned.

On the contrary, if there is at least one other next possible rest position j that has not been considered yet for the current rest position j, the index j is incremented (step 440). For instance, at first implementation of step 440, j = 1.

At step 445, it is tested whether the value of the timer T is equal to the energy saving period At first implementation, i = 0 and j = 1, thus is based on the minimum amount of time to reach P1 or P'1 or P"1 from P0. In the example of Figure 1, P1 is the closest next possible rest position from P0. Consequently, Dii is based on the amount of time necessary to reach P1.

When the timer T is equal to the energy saving period Dii, the transmission of the monitoring signal stops being modified and the transmission returns to normal (i.e. as at step 405).

Based on the reception parameters determined from the monitoring signal normally transmitted from the mobile node 130, system controller device 150 determines (step 455) whether mobile node 130 has reached the closest next rest position j, or not.

In case mobile node 130 reaches the closest next rest position j, the index of the current rest position i is set at j (step 460) since the closest next rest position becomes the current rest position (index i) and the method follows on with step 410 and the next ones as described above.

For instance, let's suppose that mobile node 130 has reached the next possible rest position P1 (corresponding to j = 1 since it is the closest next possible rest position) after having left the initial rest position P0 at T = 0. The new current rest position i is thus set toj = 1, i.e. i =1, and the transmission of the monitoring signal is back to normal. The steps 410 and following ones are performed again with the current rest position i = 1.

On the contrary, let's suppose that mobile node 130 has never reached the closest next possible rest position P1, corresponding to j = 1. The second closest next possible rest position P'1 corresponding to j = 2 is thus considered, and the transmission of the monitoring signal is again modified until the timer T = T0 becomes equal to Dij = D02.

If mobile node 130 reaches that second closest next possible rest position P'1, the new current rest position i is set to j = 2 so that i = 2, and the transmission of the monitoring signal is returned to normal. The steps 410 and following ones are performed again with the current rest position i = 2.

On the contrary, if mobile node 130 does not reach the second closest next possible rest position P'1, the third closest next possible rest position P"1 corresponding to j = 3 is considered, and the transmission of the monitoring signal is again modified until the timer T = T0 becomes equal to Dii = D03.

If mobile node 130 reaches that third closest next possible rest position P"1, the new current rest position i is set to j = 3 so that i = 3, and the transmission of the monitoring signal is back to normal. The steps 410 and following ones are performed again with the current rest position i = 3.

On the contrary, if mobile node 130 does not reach the third closest next possible rest position F"1, since there is no other next possible rest position in the table (j = 3 = N), the method ends (step 435).

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 ad. 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 monitoring the displacement of a mobile node in a communication system, the mobile node communicating wirelessly with a plurality of fixed nodes of the communication system, and the mobile node moving between a plurality of rest positions, the method comprising the steps of: transmitting a monitoring signal from the mobile node to the fixed nodes; and determining that the mobile node has reached or left a rest position based on reception parameters of the monitoring signal by the fixed nodes; and wherein, the method further comprises modifying the transmission of the monitoring signal upon determination that the mobile node has left a current rest position, for a period, called energy saving period, based on a predetermined time value selected from among a plurality of predetermined time values, wherein each of said predetermined time values is associated with the current rest position and a next possible rest position, as the amount of time necessary to reach the next possible rest position from the current rest position, the predetermined time value being selected as the minimum time value among the plurality of predetermined time values.
2. The method of claim 1, wherein said energy saving period is smaller than the selected predetermined time value, so that it allows determining that the mobile node has reached the next possible rest position associated with the selected predetermined time value.
3. The method of any one of claims 1 to 2, wherein the step of modifying the transmission of the monitoring signal comprises transmifting the monitoring signal periodically with a period lower than said energy saving period.
4. The method of any one of claims 1 to 3, wherein the monitoring signal is transmitted periodically.
5. The method of claim 4, wherein the step of modifying the transmission of the monitoring signal comprises increasing the period of transmission of the monitoring signal during said energy saving period.
6. The method of any one of claims 1 to 4, wherein modifying the transmission of the monitoring signal includes switching off the transmission during said energy saving period.
7. The method of any one of claims 1 to 6, wherein upon determination that the next possible rest position associated with the selected predetermined time value has not been reached after the selected predetermined time value expired, the method further comprises another step of modifying the transmission of the monitoring signal for a period, also called energy saving period, based on another predetermined time value selected from among said plurality of predetermined time values, the other predetermined time value being selected as the minimum time value among the plurality of predetermined time values which have not been selected yet.
8. The method of any one of claims 1 to 7, further comprising a step of adjusting the power level of the monitoring signal transmitted from the mobile node based on the current rest position and on the selected predetermined time value.
9. The method of any one of claims 1 to 8, wherein the monitoring signal is a dummy signal.
10. The method of any one of claims ito 9, further comprising a preliminary step of learning which comprises: identifying a plurality of possible rest positions; for each possible rest position identified, computing a plurality of time values, each defining the amount of time necessary to reach a different next possible rest position; and associating with each pair of identified rest positions, the corresponding computed time value as a predetermined time value.
11. The method of claim 10, wherein the preliminary step of learning also comprises: determining the optimal power level for the transmission of the monitoring signal from each possible rest position; and associating with each identified possible rest position, the corresponding determined optimal power level.
12. The method of claim 11, wherein the power level of the monitoring signal transmitted from the mobile node is adjusted according to the optimal power level associated with the next possible rest position which is associated with the selected predetermined time value during the learning step.
13.The method of any one of claims 10 to 12, comprising, if all the predetermined time values have been selected without any positive determination, on expiry of the selected predetermined time value, that the next possible rest position associated with the selected predetermined time value has been reached, a new step of learning.
14. 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 13, when loaded into and executed by the programmable apparatus.
15. A computer-readable storage medium storing instructions of a computer program for implementing a method according to any one of claims 1 to 13.
16. A method or apparatus as hereinbefore described, and with reference to the accompanying drawings Amendments to the claims have been made as follows:CLAIMS1. A method for monitoring the displacement of a mobile node in a communication system, the mobile node communicating wirelessly with a plurality of fixed nodes of the communication system, and the mobile node moving between a plurality of rest positions, the method comprising the steps of: transmitting a monitoring signal from the mobile node to the fixed nodes, such transmission being called normal transmission; and determining that the mobile node has reached or left a rest position based on reception parameters of the monitoring signal by the fixed nodes; and wherein, the method further comprises modifying the normal transmission of the monitoring signal upon determination that the mobile node has left a current rest position, for a period, called energy saving period, based on a predetermined time value selected from among a plurality of predetermined time LCD 15 values, . . . . . wherein each of said predetermined time values is associated with the current rest position and a next possible rest position, as the amount of time necessary o to reach the next possible rest position from the current rest position, the predetermined time value being selected as the minimum time value among the plurality of predetermined time values.2. The method of claim 1, wherein said energy saving period is smaller than the selected predetermined time value, so that it allows determining that the mobile node has reached the next possible rest position associated with the selected predetermined time value.3. The method of any one of claims 1 to 2, wherein the step of modifying the normal transmission of the monitoring signal comprises transmitting the monitoring signal periodically with a period lower than said energy saving period.4. The method of any one of claims 1 to 3, wherein the monitoring signal is transmifted periodically during the normal transmission, with a predetermined period.5. The method of claim 4, wherein the step of modifying the normal transmission of the monitoring signal comprises increasing the predetermined period of normal transmission of the monitoring signal during said energy saving period, thereby transmifting the monitoring signal less often during the energy saving period than during normal transmission.6. The method of any one of claims 1 to 4, wherein modifying the normal transmission of the monitoring signal includes switching off the transmission during said energy saving period.7. The method of any one of claims 1 to 6, wherein upon determination that the next possible rest position associated with the selected predetermined time value has not been reached after the selected predetermined time value expired, the method further comprises another step of modifying the normal transmission of the monitoring signal for a period, also called energy saving period, based on another predetermined time value selected from among said plurality of predetermined time values, the other predetermined time value being selected as the minimum time value among the plurality of predetermined time values which have not been selected yet. IC)8. The method of any one of claims 1 to 7, further comprising a step of I'-. adjusting the power level of the monitoring signal transmitted from the mobile node 0 based on the current rest position and on the selected predetermined time value.(\J 9. The method of any one of claims 1 to 8, wherein the monitoring signal is a dummy signal.10. The method of any one of claims ito 9, further comprising a preliminary step of learning which comprises: identifying a plurality of possible rest positions; for each possible rest position identified, computing a plurality of time values, each defining the amount of time necessary to reach a different next possible rest position; and associating with each pair of identified rest positions, the corresponding computed time value as a predetermined time value.11. The method of claim 10, wherein the preliminary step of learning also comprises: determining the optimal power level for the transmission of the monitoring signal from each possible rest position; and associating with each identified possible rest position, the corresponding determined optimal power level.12. The method of claim 11, wherein the power level of the monitoring signal transmitted from the mobile node is adjusted according to the optimal power level associated with the next possible rest position which is associated with the selected predetermined time value during the learning step.13. The method of any one of claims 10 to 12, wherein, when all the next possible positions associated with the current rest position have been considered without being reached, a new step of learning identifying a plurality of new possible rest positions associated with a plurality of new computed time values is performed.14. A computer program product for a programmable apparatus, the 15 computer program product comprising a sequence of instructions for implementing a method according to any one of claims ito 13 when loaded into and executed by the programmable apparatus.15. A computer-readable storage medium storing instructions of a computer program for implementing a method according to any one of claims 1 to 13.16. A method or apparatus as hereinbefore described, and with reference to the accompanying drawings.