FIELD OF THE INVENTION

The present invention relates to wireless networks, and more particularly to ZigBee

Green Power (ZGP) personal area networks.

This invention is, for example, relevant for bi-directional communication between an energy-restricted device, for example a ZigBee Green Power Device, and a receiver. In such bi-directional communication mode, the energy-restricted ZigBee Green Power Device (ZGPD) is required to be able not only to transmit information on a radio channel, but also to receive information.

BACKGROUND OF THE INVENTION

The ZGP specification allows that the ZGPD transmits the same information in multiple identical frames; the set of frames corresponding to the same information is called a Green Power Frame Sequence (GPFS). This redundant transmission increases the likelihood that the information conveyed by the ZGPD reaches its destination(s), since ZGPD do not perform CSMA/CA, not even CCA, and don't receive the MAC ACKnowledgements. The ZGP specification also allows the ZGPD to apply bidirectional communication, i.e. to receive some information in specific cases like configuration parameters (e.g. security key) in the commissioning procedure and requested attributes during operation.

If bi-directional communication is being applied according to the ZGP specification, if the ZGPD sets in its transmitted GPDF (Green Power Device Frame) the RxAfterTx sub field of the extended NWK header equal to Obi, then it will enter receive mode 3ms after sending the GPDF, for a specific duration, but not shorter than 0.672ms.

If bidirectional communicaiton is applied and the ZGPD sends a set consisting of multiple GPDFs (desired for obtaining a sufficiently high reliability), the receiver must still send its reply to the ZGPD at a moment that the ZGPD is in receive mode. This means that the receiver must send its reply 3 ms after transmission of the final GPDF of the set. However, as all frames of the GPFS according to the ZGP specification at the time of the invention are identical, the receiver cannot tell if its most recently received GPDF is the final one of the GPFS or not, and hence does not know when to start sending.

This results in a robustness and reliability issue of the system, since the devices capable of bidirectional communication can only send one frame when they also want to receive, otherwise the receiver would not send a response in a proper time slot, i.e. when the ZigBee Green Power Device is in a receive mode.

Another issue araises when an energy-restricted device, more particularly a ZigBee Green Power Device, sends the same GPDF on several channels. The commissioning procedure for the ZGPD allows the ZGPD to determine the operational channel of the network, by sending a ZGPD Beacon Request frames on a number of channels per commissioning attempt, and then listening once for a Beacon command.

The receiver hears a GPDF on just one channel, and must somehow determine when it can reply, but it does not know if the channel was the first one that the device sent on, or the final one, or an intermediate one. Accordingly, similar to the previous case, the device can only send one frame, which leads to reliability issue and/or negatively influences the user experience by making the commissioning procedure (the channel finding part of it) long.

The present invention aims at solving such issue by providing a method allowing the ZGPD to send multiple frames while still receiving a reply from the receiver in proper time.

SUMMARY OF THE INVENTION

The present invention relates to a method for exchanging information between an energy- restricted device and a receiver in a wireless network compliant with a ZigBee Green Power specification, the method comprising the following steps:

- the energy-restricted device sending a set of Green Power Device Frames (GPFS) wherein each frame comprises at least an information part identical in all frames of the GPFS and a counter in each frame i indicating the position of the frame in the set of Green Power Device Frames,

- the receiver receiving a frame, and determining the value of the counter,

the receiver transmitting the reply to the energy-restricted device after the last frame in the set.

In a preferred embodiment of the invention, the set of Green Power Device Frames is a Green Power Frame Sequence, wherein all frames are sent successively on one single radio channel, and wherein the counter indicates the number of frames in the Green Power Frame Sequence after frame i. In another embodiment, all frames are sent successively on more than one channel, and wherein the counter indicates the number of frames still to be sent in this set of frames

In another embodiment, a method according to the present invention comprises the following steps:

upon receipt of a frame, the receiver estimating a time t to wait before sending a reply as a function of the counter value x, the duration T(f) of the received frame, for example as t = x ^■ ( Τ(ΐ) + Δ)

where Δ is an estimate for the time elapsing between transmission of two consecutive frames.

after a duration t, the receiver sending a reply, even in case where the last frame of the set is not received.

In one specific embodiment, the value of the counter included in a frame i is a 2-bits value.

In this case, the value of the counter included in a frame i is, for example, comprised in the group comprising:

11, where 3 frames are comprised in the GPFS after frame i, or 3 frames of the set are still to be sent,

- 10, where 2 frames are comprised in the GPFS after frame i, or 2 frames of the set are still to be sent ,

01, where 1 frame is comprised in the GPFS after frame i, or 1 frame is still to be sent 00, where frame i is the last frame of the GPFS or the last frame to be sent on any channel.

The invention also relates to a method wherein the Green Power Device Frame is compliant with the ZigBee Green Power Specification, and wherein for the frames which have the RxAfterTx subfield of the Extended NWK Frame Control field set to Obi, the Most Significant Bit of the counter value is included in the Auto-Commissioning subfield of the NWK Frame Control field of the GPDF, and the Least Significant Bit is included in the Direction subfield of the Extended NWK Frame Control field.

In one embodiment the two bits of the counter value are stored in the two final bits of the Extended NWK Frame Control field. Other embodiments of a method according to the invention are as follows :

the frame sent by the ZGPD contains the ZGPD Beacon Request command and the reply contains ZGPD Beacon command,

the frame sent by the ZGPD contains the ZGPD Commissioning command and the reply contains ZGPD Commissioning Reply command.

the frame sent by the ZGPD contains any ZGPD Data command and the reply contains either ZGPD Commissioning Reply command or ZGPD Data command.

In another embodiment, a method according to the present invention comprises the step for the energy-restricted device and/or for the receiver of performing a security processing once for all frames in a Green Power Frame Sequence.

In yet another embodiment, a method according to the present invention comprises the step for the receiver of replacing the counter bit value of each received frame by 00 and of performing security processing computations for each frames separately from the others.

The invention also relates to a ZigBee Green power device comprising means for carrying out a method according to the invention.

The invention also relates to a receiver for use in a ZigBee Green Power-compliant system, comprising means for carrying out a method according to the invention.

The invention also relates to a Green Power Device Frame according to any of claims 1 to 10.

The invention also relates to a Green Power Device Frame according to any of claims 1 to 9.

These and other aspects of the invention will be apparent from and will be elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail, by way of example, with reference to the accompanying drawings, wherein:

Fig. 1 is a block diagram representing a network in which an embodiment of the invention is implemented. Fig. 2 is a block diagram representing a frame used in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In accordance to an embodiment of the present invention, a network 100 shown in

Figure 1, comprises a plurality of nodes being of different types. Energy restricted devices 101, like batteryless devices may be ZigBee Green Power Devices, for example switches that harvest energy from the actuation of the switch by a user. To communicate with this kind of devices, receivers or proxies 102 are used as an interface with the rest of the network 103.

The present invention relates to a method wherein, for the case of bi-directional communication, the frames sent by a ZigBee Green Power Device within a GPFS are distinct, allowing a receiver to estimate how long it has to wait before sending a reply. To this end, we use a 2-bit counter, indicating how many frames still have to arrive in this set (e.g., the value 00 meaning the present GPDF is the final one in the GPFS, the value 01 meaning the present GPDF is the penultimate, the value 10 indicating the GPFS contains two future GPDFs, and the value 11 meaning the GPFS contains three future GPDFs. The receiver can estimate the time t to wait before sending a reply as a function of the counter value x, the duration T(f) of the received frame, for example as t = x ^■ ( Τ(ΐ) + Δ) where Δ is an estimate for the time elapsing between two consecutive GPDFs.

More precisely, in one embodiment of the present invention shown on figure 2, the two bits for the counter are proposed to be included in the GPDFs by redefining the value of two particular bits in the NWK Frame Control field and the Extended NWK Frame Control field.

More specifically: if the RxAferTx subfield in the Extended NWK header 210 of the GPDF has value Obi, then the Most Significant Bit (MSB) of the counter is placed into the Auto-Commissioning subfield in the NWK Frame Control field 220, and the Least Significant Bit (LSB) of the counter is placed into the Direction subfield of the Extended NWK Frame Control field 230. Also, if the RxAfterTx subfield in the Extended NWK header 210 has value Obi, the receiver shall apply the following default values to the redefined fields, if required for GPDF handling: for the AutoCommissioning subfield, the value Obi shall be applied (meaning that the ZGPD implements the Commissioning GPDF), and for the Direction subfield, the value ObO shall be applied (meaning the GPDF is transmitted by the ZGPD).

If the RxAfterTx bit has value ObO, the interpretation of the two above sub fields remains as defined in the ZigBee Green Power specification at the time of the present invention

In another embodiment of the invention, the Frame type subfield of the NWK Frame Control field is used for re-defining the meaning of two bits in the Extended NWK Frame Control field. More specifically: if the value of the Frame type subfield to a value X not yet used in the specification (at the time of the present invention, 00, 01 and 11 can be used), then the counter value is stored in the two final bits of the Extended NWK Frame Control field; moreover, the Frame type subfield having value X also implies that the frame has been sent by a ZGPD and that the ZGPD will enter the receive mode, as defined by the ZGP specification.that will enter the receive mode after sending the GPDF frame, for a device- specific duration.

In one embodiment, entrance into the receive mode is planned, for example, to begin 3 ms after having sent the frame, and the duration of the specific mode is not shorter than

0.672 ms.

Moreover, a security processing is defined in the ZigBee Green Power Specification.

In case all sent frames are identical, as in GPFS according to the specification at the time of the present invention, the ZigBee Green Power Device can perform once the security processing on one frame, and then use it for other frames.

In the present situation, wherein the frames differ one from each other, it is still proposed that - if security processing of the GPDF is required - the ZGPD performs the processing once for all GPDF in the GPFS, based on the GPDF with the bits of the counter set to 00; in the security processing steps, the receiver replaces the bits of the counter by 00 as well. The trigger for the receiver for doing so is the indicator of the counter's presence.

1. e. in the first embodiment, it is the RxAferTx subfield being equal to Obi, in the second embodiment it is the value X in the Frame Type subfield. Such method presents advantages both from a security perspective, since an attacker sees only one the authentication of one frame, and from a processing perspective, since the authentication-related computations only have to be done once, despite slightly different frame content. The invention as described above is applicable to a ZGPD sending multiple ZGPD Beacon Request frames on multiple channels as part of the channel finding of the commissioning procedure, to allow the receiver to determine when to send the GPDF containing the ZGPD Beacon command. In this embodiment and in any other embodiment described in the present invention, the receiver is, for example, a ZGP proxy or a ZGP target+ or a combination of both.

The invention is further applicable to ZGPD sending as part of the commissioning procedure a GPFS consisting of GPDFs containing a ZGPD Commissioning command, to allow the receiver to determine when to send the GPDF containing the ZGPD Commissioning Reply command.

The invention is further applicable to ZGPD sending, during operation, a GPFS consisting of GPDFs containing ZGPD Data command, such as the bidirectional operation command ZGPD Request Attributes command or any other ZGPD Data command, to allow the receiver to determine when to send the GPDF containing the ZGPD bidirectional operation commands: ZGPD Write Attributes command or ZGPD Read Attributes command.

The invention is further applicable to ZGPD sending, during operation, a GPFS consisting of GPDFs containing any ZGPD Data command to allow the receiver to determine when to send the GPDF containing the ZGPD Commissioning command, to carrying, i.e. changing configuration parameters, such as channel, security key or PANId and/or as a confirmation of network's presence.

The invention is further applicable to ZGPD sending during operation a GPFS consisting of GPDFs containing any ZGPD Data command to allow the receiver to determine when to send the GPDF containing the ZGPD Beacon command, to carry, i.e. change configuration parameters, such as channel, and/or as a confirmation of network's presence.

In the present specification and claims the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. Further, the word "comprising" does not exclude the presence of other elements or steps than those listed.

The inclusion of reference signs in parentheses in the claims is intended to aid understanding and is not intended to be limiting.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art of wireless networks and which may be used instead of or in addition to features already described herein.