WO2010067278A1

WO2010067278A1 - Method for sending packets by a relay station based on monitoring packets

Info

Publication number: WO2010067278A1
Application number: PCT/IB2009/055494
Authority: WO
Inventors: Lei Feng; Daiqin Yang
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2008-12-12
Filing date: 2009-12-04
Publication date: 2010-06-17

Abstract

To alleviate the problem of high complexity and low robustness of alternate control in the current alternate relay technology, the present invention proposes a method and an apparatus for relay. At first, a relay device monitors the receiving channel to receive a data packet from the previous device; then, it determines a monitoring duration based on the forward priority of the relay device; after that, it monitors the sending channel before the expiration of the monitoring duration to decide whether or not another relay device in the same relay group as the present relay device has sent a data packet, in order to decide whether or not to send the received data packet. According to the present invention, alternate relay and fault tolerance are implemented in a way that relay devices perform priority-based monitoring with different durations to monitor whether another relay device has conducted relay, and no extra control overhead is introduced. The requirement for the device complexity is low. The alternate relay and fault tolerances provided in the present invention have good robustness and are particularly applicable for systems with low device complexity, such as wireless illuminating control networks and so on.

Description

METHOD FOR SENDING PACKETS BY A RELAY STATION BASED ON MONITORING PACKETS

FIELD OF THE INVENTION

The present invention relates to wireless communication technology, and particularly relates to methods and apparatus for a wireless relay network controlling a lighting system.

BACKGROUND OF THE INVENTION

Currently, wireless communication technology is more and more utilized in lighting systems. It uses wireless networks to carry through the commissioning and controlling of lighting systems, so that the complexity of the deployment and operation of lighting systems is reduced. In wireless lighting systems, control signaling, feedback signals and the like as data borne by wireless control networks are typically exchanged between central controllers and individual nodes (i.e. luminaires). Since the scale of lighting systems, for instance outdoor beautification lighting systems is larger and larger, it comprises more and more luminaires and its range is wider and wider. In order to control a large amount of luminaires within a large area, the control lighting systems raise higher and higher requirements for data throughput, coverage range and reliability of wireless networks. Therefore, subject to the constraints of the interference level or the transmission power of communication devices in wireless control networks, it is an effective way to arrange certain relay nodes (relay devices) in the network to perform multi-hop relays to increase the system throughput and coverage range of the control system.

In order to fulfill the relay task of "receive-and-forward", a relay device can be a specially designed specific device, or it can also be a relay device reused as a luminaire and selected from all of the luminaires based on a certain rule. The latter solution is very convenient, in that a relay device can be optimally selected from all of the luminaires of the whole lighting system, based on the wireless communication condition of the practical system, after the arrangement and commissioning of the lighting system, and the relay device can be adapted to other luminaires at other suitable locations. In the former solution, however, as practical wireless communication changes, it is very difficult to re-locate an already-mounted specific relay device to other locations in a timely fashion. Owing to cost constraint, each luminaire generally has only one RF transceiver. Therefore, in the latter solution wherein a relay device is selected in real time, the relay device has also only one RF transceiver. This makes a relay device work only in the half-duplex relay mode, i.e. a relay device can only work under the receiving state or the sending state at the same time, so that a relay device cannot receive subsequent data packets from a previous device when it forwards data packets to be relayed to a next device. Therefore, a source network device of data packets cannot send data packets to a relay device continuously and must wait until a relay device returns to the receiving state after it has finished sending packets, then subsequent data packets can be sent. Apparently, as compared with no relay or full duplex relay technology wherein a relay device can receive and send data packets simultaneously, the data throughput of the half-duplex relay is greatly reduced.

In a thesis "RELAY NODE DIVISION DUPLEX" RELAYING APPROACH FOR MIMO RELAY NETWORKS, published by Hui Shi, Takahiro Asai, and Hitoshi Yoshino in the 17th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications,PIMRC06, half-duplex relay nodes are divided into two groups. The nodes of the two groups receive and forward continuous data packets alternately, so that a relay form similar to a full duplex relay is fully implemented. SUMMARY OF THE INVENTION

In prior art where relay is performed alternately based on half-duplex, although its relay communication capacity is higher than the relay merely employing half-duplex, relay nodes need to be divided into two groups, and the alternate relay of the nodes of the two groups needs to cooperate specially, e.g. alternation flags are added in data packets etc. This causes extra overhead to the two communication parties and relay nodes in the wireless network. Therefore, the requirements for the processing functions of these devices are relatively high. Furthermore, this kind of relay technology lacks sufficient robustness: when relay nodes of one group fail, the alternate relay cannot continue to be performed; or when the relay nodes of one group are subject to high interference and cannot receive and forward data packets normally, data packets need to be sent again by the source network devices of the data packets. All these reduce the fault tolerance capacity of the system and the throughput of the data.

In order to reduce or even avoid the disadvantages of the aforementioned technical problem, it is necessary to reduce the control complexity of the alternate relay of a plurality of half-duplex relay devices. Furthermore, half-duplex relay technology also needs better robustness, so that the normal relay communication capacity can be guaranteed when some relay devices fail.

According to an embodiment of one aspect of the invention, a method for use in a relay device is provided. It comprises the following steps: I), monitoring a receiving channel to receive a data packet from a previous device, the previous device comprises any one of a source network device and a relay device in a previous relay group; II). determining a monitoring duration based on a forward priority of the present relay device; III), monitoring a sending channel before the expiration of the monitoring duration, to decide whether or not another relay device in the same relay group as the present relay device has sent a data packet, in order to decide whether or not to send the received data packet.

According to an embodiment of another aspect of the invention, a relay device for wireless relaying is provided. The device comprises: a receiver, configured to monitor a receiving channel to receive a data packet from a previous device, the previous device comprising any one of a source network device and a relay device in a previous relay group; a first determining means, configured to determine a monitoring duration based on a forward priority of the present relay device; a monitor, configured to monitor whether or not another relay device in the same relay group as the present relay device has sent a data packet in a sending channel before the expiration of the monitoring duration; a second determining means, configured to decide whether or not to send the received data packet according to the result of the monitor and a predefined rule; and a transmitter, configured to transmit the received data packet.

According to an embodiment of the invention, a relay method and a relay device with lower complexity for controlling half-duplex relay devices to perform the alternate relay are provided. When it has monitored that relay devices with higher forward priority are not forwarding data, a relay device with lower forward priority forwards data. Additional information, such as alternate relay flags etc. need not be added into data packets by a sender to specially assist the relay device to carry through the cooperative alternate relay, so that the overhead of the relay communication is less. Furthermore, in another embodiment of the invention, a relay method with higher robustness is provided. When a relay device has not monitored that another relay device in the same relay group as the present relay device in the receiving channel is sending a data packet, it automatically resets the other relay device to forward, which possibly fails, so that the fault tolerance of the alternate relay is achieved with low complexity, and thus normal relay communication capacity is guaranteed. Since relay methods and devices with less overhead and low complexity of fault tolerance are provided by the embodiments of the invention, the embodiments of the invention are particularly suitable for reuse in the luminaires of the wireless control network, and thus the wireless lighting control network is enabled to deploy and adjust relay topology in the network flexibly.

The above and other features of the present invention will be elucidated in the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS The features, objects and advantages of the present invention will be easily understood with the following detailed and non-limited embodiments with reference to the accompanying drawings, wherein same or similar reference signs denote same or similar devices.

Fig.l shows the schematic block diagram of major components of the relay device, according to an embodiment of the invention;

Fig.2 is a schematic view of data relays performed by a multi-hop relay network between wireless controllers and luminaires in a manner that half-duplex relay devices work alternately, according to an embodiment of the invention;

Fig.3 shows a flowchart of a relay method performed by the relay devices, according to an embodiment of the invention;

Fig.4 is a schematic view of respective monitoring durations of each relay device in the relay device groups;

Fig.5 is a schematic view of receiving and sending a collision of relay devices possibly caused by the difference in the monitoring durations of each relay devices; Fig.6 is a schematic view of receiving and sending a collision of relay devices possibly caused by the unfixed length of packets continuously sent by the wireless controllers;

Fig.7 is a schematic view of data relays performed by the multi-hop relay network comprising backup relay devices, according to another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to Fig.l to Fig.7, the embodiments of the invention will be elucidated in aspects of the method, and necessary explanations about the embodiments of the relay devices of the invention will also be made at the same time in aspects of the apparatus.

First Embodiment As shown in Fig. 1, each relay device includes a wireless communication module 220, a processor 230, a memory 240 and a power supply 250, wherein the wireless communication module 220 can communicate with the wireless controller C, wireless communication modules of other relay devices and wireless communication modules of the luminaires to build a wireless network. The processor 230 can implement relay processing such as the decapsulation of data packets, adding, deleting or modifying certain fields of data packets and the encapsulation of data packets etc. The memory 240 stores multiple instructions required by the processor for the relay processing, and can also be used to store the received data packets. The power supply 250 provides the working electrical energy to the wireless communication module 220, the processor 230 and the memory 240.

These relay devices receive lighting control signaling (i.e. downstream load data) coming from a wireless controller for the control luminaires from a previous relay device or directly from the wireless controller, and then forward it to a next relay device or to the target luminaire of the control signaling. Generally, each relay device maintains a local relay table, which lists the target luminaire, or the next relay devices of the data packet to be relayed by the present relay device.

The present relay device forwards the data packet, if the target luminaire or the next hop relay device contained in the received data packet corresponds to the content in the relay table. The relay table is generally determined by the wireless lighting control network after its deployment and commissioning, and can also be sent to the present relay device by the wireless network controllers in advance before the relay communication. The relay table can also be adjusted and updated in real time by the wireless lighting control network based on the actual wireless communication condition.

As described above, in some embodiments of the invention, a relay device is also reused as a luminaire. In detail, a luminaire includes a luminaire (not shown in the figure), and reuses the aforementioned wireless communication module 220, the processor 230, the memory 240 and the power supply 250. The relay device is further configured to decide whether the received signaling is sent to itself or to other luminaires; to forward the signaling intended to be sent to other luminaires, or extract the control commands from the data packets sent to itself, then controls the lighting features of the reused luminaire, such as its on/off, brightness, color and so on, based on the control commands.

The above relay functions can be pre-stored in the form of software programs in the memory of each luminaire, and read and executed by its processor. A general luminaire does not use these functions; after an operator or a lighting system has selected the location of a relay device, a control device sends signaling and a relay table to the luminaire in the corresponding location, to indicate to the luminaire to work also as a relay device. After receiving the signaling, the luminaire can load the pre-stored relay function program to implement the relay function. If the operator or the lighting system decides to cancel the relay device in this location, it sends a signaling to the relay device, which shuts down its relay function after receiving the signaling. Since the cost of implementation of the relay function in the form of software in a luminaire is very low, this reuse solution is very convenient.

The application of the invention in the wireless lighting control network will be elucidated in detail through this embodiment. It can be appreciated that the invention can also be applicable to the control network of various devices, such as temperature control devices, audio devices and so on. Fig.2 illustrates a schematic view of data relays performed by a multi-hop relay network between wireless controllers and luminaires in the manner that half-duplex relay devices work alternately, according to an embodiment of the invention. The lighting system can be located in an indoor environment e.g. in a room, in several rooms adjacent to each other, in a house, in an office building etc., or it can also be located in an outdoor environment, e.g. in a garden, in a stadium, at a building site. Luminaires can be various luminaires, e.g. decoration lights, illuminating lights, guiding lamps etc.

As shown in Fig. 2, the wireless controller C needs to send control signaling to luminaires in the regions A, B, C and D. The control signaling can be a control signaling of various lighting functions such as controlling the on/off, the brightness, the color, the focus and the rotation of a luminaire etc. Wherein the luminaires La, Lb, Lc and Ld (deep color circular points in the figure) are located in the region A, B, C and D respectively to represent the luminaires in the regions. The relay devices RIa and RIb, R2a and R2b, R3a and R3b have been selected and commissioned by the wireless control network to relay alternately respectively in relay group Rl, R2 and R3. Wherein the forward priority of RIa is set higher than that of RIb, the forward priority of R2a is higher than that of R2b, the forward priority of R3a is higher than that of R3b.

Each forward priority can be set by the wireless controller in advance. Relay devices of the relay group R3, R2 and Rl can cover the region A, B and C respectively, that is, they can forward the control signaling directly to the luminaires in the same region, and to the relay devices in the adjacent regions; the wireless controller C can cover the region D. It can be understood that the control signaling created by the wireless controller C can be contained in data packets; one data packet can contain a signaling sent to only one luminaire, or can contain multiple signaling sent to several luminaires. After the data packet has been received by the corresponding luminaire, if there is a signaling sent to itself in the data packet, the corresponding luminaire will extract the signaling from the data packet to perform corresponding operations. Concretely, in the first data packet time tl, the wireless controller C first sends a control signaling contained in the data packet Pl to control the luminaire La in the farthest region. The reason why a signaling sent to a luminaire in farther regions earlier than that sent to a luminaire in nearer regions is the fact that it can allow luminaires with different distances from the wireless controller C or with different numbers of hops to receive the signaling at almost the same time, which is very advantageous in controlling the luminaires synchronously. Under the circumstance that no synchronization is required, the wireless controller can also not follow the sending sequence of the above reverse sequence. In the embodiment, a data packet can contain a control signaling completely. In other cases, if a control signaling is longer, for instance if it contains a large quantity of color information, several continuous data packets can be employed to contain each segment of the control signaling respectively. This will not be elucidated further by the present invention herein.

With reference to Fig. 2 and Fig. 3, in detail, in the step S20 and S30, the two relay devices RIa and RIb in the relay group Rl respectively monitor a receiving channel to receive the data packet Pl from the wireless controller C in the data packet time tl. Then, in steps S21 and S31, RIa and RIb determine the monitoring duration T_ml and T_m2 based on their forward priority respectively. The monitoring duration is employed to decide whether or not another relay device in the same relay group as the present relay device is sending a data packet. In a preferred embodiment, the monitoring duration is determined by a relay device in accordance with a rule: the higher the forward priority, the shorter the monitoring duration. In this embodiment, RIa is set to have the highest forward priority and RIb is set to have the lowest forward priority. Then the monitoring duration T_ml determined by RIa is shorter than the monitoring duration T_m2 determined by RIb. Preferably, T_ml is set to 0, T_m2 is the sum of the time T_s needed for RIa to start a data packet transmission and the time Ta needed for RbI to detect the data packet transmission of RIa, as shown in Fig.4. T_s and Ta are relevant to the performance of the wireless communication modules of RIa and RIb respectively.

After that, RIa and RIb are switched from the receiving state, in which they monitor a receiving channel, to the monitoring state, in which they monitor a sending (relay) channel. In the monitoring state, RIa and RIb monitor the sending channel before the expiration of their monitoring durations respectively to decide whether or not other relay devices in the same relay group as the present relay device have forwarded the data packet. With respect to the practical system, as shown in Fig. 4, the switching needs a certain turnaround time T_t, and this time is relevant to the performance of the wireless communication modules and the processors of RIa and RIb.

Then, in step S22, since the monitoring duration T_ml of RIa is 0, RIa does not monitor and directly decides to forward the data packet Pl in the sending channel, and starts to send.

Therefore, in step S32, RIb has monitored that RIa had forwarded the data packet Pl in the sending channel before the expiration of the monitoring duration T_m2, decides to abandon the forwarding,switches back to the receiving channel immediately and will monitor the receiving channel in the second data packet duration t2 to receive the next data packet P2 following the data packet Pl from the wireless controller C. RIb can use multiple monitoring methods for determining whether the data packet has been relayed in the sending channel, e.g. measuring the received signal strength indicator (abbr. RSSI) of the radio signal in the channel, or monitoring the preamble or synchronization field of the data packet. This monitoring method is known to those skilled in the art, and thus the present invention will not give further details herein. In order to eliminate the interference between the forwarding of the data packet Pl by RIa and the receipt of the data packet P2 by RIb, the sending channel used by RIa and the receiving channel used by RIb can be different. To save the channel resources, the relay devices in the relay group work in the same receiving channel alternately, and in the same sending channel alternately. It can be understood that the receiving channel and the sending channel can be fixed or be changed.

Then, in the second data packet duration t2, the wireless controller C continues to send data packets P2 to the luminaire Lb in the relative further region B and the relay device RIb receives the data packet P2 in the receiving channel in step S30'. At the same time, the relay device RIa forwards the data packet Pl, and the relay device R2a and R2b of the relay group R2 which are in the receiving state receive the data packet Pl in the receiving channel. After that, the relay device RIb determines its monitoring duration T_m2 in step S31', and monitors the sending channel in step S32'. Since at this time the relay device RIa finishes sending the data packet Pl and returns to the receiving state, the relay device RIb does not detect that the relay device RIa with a higher forward priority forwards a data packet before the expiration of the monitoring duration T_m2 determined by the relay device RIb itself, and then the relay device RIb decides to forward P2 in the sending channel. Furthermore, the operations performed by the relay device R2a and R2b of the relay group R2 are similar to the forgoing steps S21 to S22 and S31 to S32 respectively. In detail, at first, the relay device R2a and R2b determine their monitoring durations respectively according to their forward priority. In this embodiment, the forward priority set for R2a is higher than that of R2b, and thus the monitoring duration determined by R2a is 0, which is shorter than the monitoring duration T_s+T_d of R2b. Then the relay device R2a with a higher forward priority decides to forward the data packet Pl to the relay group R3, and starts to forward it; the relay device R2b with a lower forward priority has detected that R2a started to forward Pl before the expiration of its monitoring duration, then it switches back to the receiving state, monitors the receiving channel and prepares to receive P2.

After that, in the third data packet duration t3, the wireless controller C continues to send data packets P3 to the luminaire Lc in the relative nearer region C. The relay device RIa monitors the receiving channel and receives the data packet in step S20'; at this time, the relay device RIb forwards the data packet P2 in the sending channel to the relay device R2b of the relay group R2 that is in the monitoring state. The relay device R2b of the relay group R2 receives the data packet P2. At this time, the relay device R2a forwards the data packet Pl to the relay devices R3a and R3b of the relay group R3 that are in the receiving state.

Then the relay device RIa of the relay group Rl determines its monitoring duration T_ml in step S21' and decides to forward the data packet P3 to the luminaire Lc in the region C in step S22'. The relay device R2b of the relay group R2 determines its monitoring duration and does not detect that R2 sends a data packet before the expiration of the monitoring duration, and thus decides to forward the data packet P2 to the luminaire Lb in the region B. The operations performed by the relay devices R3a and R3b of the relay group R3 are similar to the forgoing steps S21 to S22 and S31 to S32 respectively. R3a and R3b determine their monitoring durations respectively. R3a with a higher forward priority judges to forward to the luminaire La in the region A. The relay device R3b detects that R3a sends a data packet, and thus abandons sending this data packet.

At last, in the fourth data packet duration t4, the wireless controller C sends the data packet P4 directly to the luminaire Ld in the nearest region D; the relay device RIa of the relay group Rl sends P3 to the luminaire Lc in the region C; the relay device R2b of the relay group R2 sends

P2 to the luminaire Lb in the region B; the relay device R3a of the relay group R3 sends Pl to the luminaire La in the furthest region A. This kind of reverse -order sending enables luminaires with different distances to receive control signals almost at the same time.

In the embodiment of the present invention, in comparison with the traditional half-duplex communication, the relay communication capacity is significantly increased. In a same relay group, when a relay device with a lower forward priority detects that a relay device with a higher forward priority does not forward a data packet, it starts to forward the data packet, so that the introduction of extra control overhead into the source network device of the data packet or into the data packet itself is avoided, which reduces the complexity of implementation of the half-duplex alternate relay network. As the present invention provides a relay method and device with lower overhead, the requirements for the complexity of the communication parties and relay devices in the communication network is relatively low, and the embodiment of the present invention is particularly applicable for being reused with the luminaire of the wireless illuminating control network, and then enables the wireless illuminating control network to adjust the deployed relay structure of the network flexibly. In the above embodiment, since the processing time used from the completing receipt of a data packet and to the forwarding of this data packet is different for relay devices with different forward priorities in a same relay group, for example for the relay device with the highest forward priority, the time it uses includes the switching time T_t employed to switch from the receiving state to the forwarding state; for another relay device, the used time includes not only the above switching time T_t, but also its monitoring duration T_m, namely the time T_s needed for the relay device with the highest forward priority to start a data packet transmission and the time Ta needed for the relay device itself to detect the data packet transmission. Under the circumstances where there are more relay devices, e.g. in the preferred embodiment to be described below, which employs at least three relay devices with different forward priority in a same relay group, and uses a backup relay device to perform fault tolerance, the monitoring duration of each relay device includes the monitoring duration of a prior relay device whose forward priority is just higher than that of the relay device, namely whose forward priority is higher than and adjacent to that of the relay device, the time T_s needed for the prior relay device to start a data packet transmission and the time Ta needed for the relay device to detect the data packet transmission. As can be seen , the data packet processing time is different for each relay device and will increase with the reduction of the forward priority. Under the circumstances that the time interval for the wireless controller to send data packets is small, for example it is smaller than T_t +T_d, relay devices with lower forward priority may experience conflict. Concretely, as shown in Fig.5, owing to the long monitoring duration of the relay device RIb, RIb starts to forward the data packet P2 after the expiration of the monitoring duration; while RIb has not finished forwarding the data packet P2, the wireless controller C has already started to send another data packet P4 which should be received by RIb, which leads to a receive-and-transmit conflict of the relay device RIb (as is shown in the parts of the figure in shadow with oblique line). Therefore, in order to guarantee that no receive-and-transmit conflict occurs for each relay device, in an embodiment of the present invention, it is preferably proposed that synchronization is performed between the wireless controller and each relay device. Concretely, the wireless controller C chooses the longest monitoring duration T_mmax among the monitoring durations of all relay devices of all relay groups in the network as the synchronization duration and sends data packets with the interval of

T_mmax+T_t, which is the sum of the synchronization duration and the switching time T_t of the relay device between the receiving state and the sending state. Herein, the present invention defines a relay frame, the time length of the whole relay frame is RelayFrameTime, including the time length of the data packet PacketTime (namely the time needed for transmitting the data packet), the synchronization duration T_mmax deployed by the wireless controller C to perform synchronization after finishing transmitting a data packet and the switching time T_t,, the RelayFrameTime can be expressed as follows:

RelayFrameTime = PacketTime + T_mmax+ T_t ( 1 )

And, in the above steps S22 and S32', if the relay devices RIa and RIb judge to send a data packet, before sending a data packet, they wait a corresponding synchronization duration T_syCi which is the difference between the synchronization duration T_mmax of the wireless controller C and the monitoring duration T_m' of the previous device sending the data packet:

1 syc ⁼ 1 mmax ^~ I m \ ^ I Wherein, the previous device can add its monitoring duration T_m' into the header of the received and forwarded data packet, and the relay device receiving the data packet can extract this duration from the packet.

In practical systems, if the type or performance of the deployed relay devices is same, the time T_s needed for each relay device to start a data packet transmission and the time Ta needed for other relay devices to detect the data packet transmission should be same. Therefore, for each relay device of a relay group, a forward priority value n can be preset: n=l represents the highest forward priority, n increases with the decrease of the forward priority. Then the monitoring duration of each relay device can be:

T_m = ( n - 1 ) x T_umt ( 3 ) Wherein

Then the Relay FrameTime expressed in formula (1) can be simplified as:

ReI ay FrameTime = PacketTime +

( maxPrioLevel - 1 ) xT_umt+T_t ( 4 )

Wherein maxPrioLevel is the forward priority number of the relay device with the lowest forward priority among all relay devices of all relay groups in the whole wireless relay network.

The synchronization duration of a relay device expressed in formula (2) can be simplified as:

T_syc = ( maxPrioLevel - pktPrioLevel ) x T_umt ( 5 )

Wherein pktPrioLevel is the forward priority number of the previous device sending the data packet. The pktPrioLevel can be added to the header of the received and forwarded data packet by the previous device and can be extracted by the relay device receiving the data packet.

For each relay device, the aforementioned T_umt and the switching time T_t can be measured by itself, and can also be informed and set by the wireless controller in advance. As for the longest monitoring duration T_mmax and the largest priority maxPrioLevel, they can be informed and set by the wireless controller in advance.

The above embodiment describes the synchronization solution of the present invention in detail under the circumstances that the time length of each data packet to be transmitted is fixed. It can be understood that, in practical systems, the length of each data packet to be transmitted can be unfixed. For example, there are more luminaires in the region A, and the data packet Pl comprises control signaling for controlling a plurality of luminaires in the region, and thus the length of Pl is greater; there are fewer luminaires in the region B, and thus the length of P2 is smaller; and there are more luminaires in the region C, and thus the length of P3 is greater. Since the length of each data packet is not same, if the wireless controller sends data packets continually, receive-and-transmit conflict of relay devices may occur. As shown in Fig. 6, the length of Pl is greater and the length of

P2 is smaller; after finishing sending P2, the wireless controller sends P3 immediately; at this time, the relay device RIa has not finished forwarding Pl, however, the wireless controller C has already started to send P3, which causes a receive-and-transmit conflict. Therefore, if the length of data packets to be sent is not the same, in order to guarantee that no receive-and-transmit conflict occurs for each relay device, in another embodiment of the present invention, it is preferably proposed that the wireless controller and each relay device synchronize data packets with different lengths. Concretely, on the basis of the above synchronization of different monitoring durations, the synchronization duration that the wireless controller C waits after finishing sending each data packet further comprises the difference between the longest data packet time among all data packets to be transmitted

(namely the time needed to transmit the longest data packet) maxPacketTime and the time length of the current data packet (namely the time needed to transmit the current data packet) currentPacketTime. In other words, the relay frame time comprises the time of the longest data packet maxPacketTime, the longest monitoring duration of all relay devices (maxPrioLevel - l)xT_umt and the switching time T_t, expressed as the following formula:

RelayFrameTime = maxPacketTime +

( maxPrioLevel - 1 ) xT_umt+T_t ( 6 )

On the basis of formula (5), the synchronization duration T_syc of each relay device further comprises the difference between the data packet time of the longest data packet maxPacketTime and the data packet time of the current data packet currentPacketTime, namely:

T_syc = maxPacketTime - currentPacketTime +

( maxPrioLevel - pktPrioLevel ) xT_umt ( 7 )

The above longest data packet time maxPacketTime can be informed and set by the wireless controller in advance.

It can be seen that, since monitoring durations with different lengths and data packet times with different lengths need to be synchronized, each relay frame time in the above embodiment of the present invention is larger than the data packet time and has certain overhead. However, generally speaking, T_{umt ,} which is the sum of the time T_s needed for a relay device to start a data transmission and the time Ta needed for a relay device in the next hop to detect the data packet, is relatively small; and the difference between the lengths of time for illuminating control data packets is not large. Therefore, the synchronization duration T_syc is relatively much shorter than the data packet time. Then, under the circumstances that there are fewer relay devices in a relay group, for example, under the circumstances that a relay group comprises three relay devices to implement fault tolerance, which will be described in the second embodiment below, the synchronization performed for monitoring durations with different lengths and data packet times with different lengths in the embodiment of the present invention will not obviously influence the efficiency of the system. Above, steps performed by relay devices to relay control signaling sent from the wireless controller C to luminaires in each region are described in detail according to an embodiment of the present invention. It can be understood that the present invention can also be applicable for relay devices to relay signals sent by each luminaire or relay device to the wireless controller C. According to the above detailed description wherein the wireless controller C is the source network device of data packets, those skilled in the art can foresee embodiments of the present invention in other application scenarios without inventive step, wherein the source network device of data packets is luminaires or relay devices etc. The present invention will not give further details herein.

In wireless illuminating control networks, relay devices are reused as luminaires, and thus they should also receive control signaling sent from the wireless controller. But since they work in the manner of alternate relay, they will miss approximately half of the data packets, some of which may contain control signaling sent to the relay device. With the gradual enlargement of the system topology structure and its becoming complex, it is hard to guarantee that a relay device would not miss a data packet sent to the reused luminaire. To solve this problem, it is proposed in an embodiment of the present invention that the same control signaling is contained in multiple continuous data packets sent to a relay device to ensure that the relay device receives at least one data packet containing the control signaling sent to it in its working process as alternate relay.

Above, several embodiments of the present invention are elucidated in detail in the aspect of method. It can be understood that the prevent invention can also be implemented in the aspect of apparatus. According to an embodiment of the present invention, a relay device can comprise the following means:

- a receiver, configured to monitor a receiving channel to receive a data packet from a previous device, the previous device comprising any one of a source network device and a relay device in a previous relay group. The receiver can be the aforementioned wireless communication module 220.

- a first determining means, configured to determine a monitoring duration based on a forward priority of the present relay device. The aforementioned processor 230 can be used as the first determining means. - a monitor, configured to monitor the sending channel to judge whether or not another relay device in the same relay group as the present relay device sends a data packet. The wireless communication module 220 can be used as the monitor.

- a second determining means, configured to decide whether or not to send the received data packet according to the result of the monitor and a predefined rule. The processor 230 can be used as the second determining means.

- a transmitter, configured to transmit the data packet. The wireless communication module 220 can be used as the transmitter.

Wherein the monitor, the second determining means and the transmitter are configured to cooperatively monitor the sending channel to judge whether or not another relay device in the same relay group as the present relay device sends a data packet, and then decide whether or not to send the data packet received by the present relay device.

Preferably, when the first determining means determines the monitoring duration, it follows the rule: the higher the forward priority, the shorter the monitoring duration.

Preferably, the relay device with the highest forward priority has the shortest monitoring duration. And the monitoring duration of each other relay device is no less than the sum of the monitoring duration of a prior relay device whose forward priority is only higher than that of the present relay device, the time needed for the prior relay device to start a data packet transmission and the time needed for the present relay device to detect the data packet transmission. Preferably, the predefined rule employed by the second determining means comprises: i). sending the received data packet after the expiration of the monitoring duration, if it has not monitored that other relay devices send a data packet before the expiration of the monitoring duration; ii). monitoring the receiving channel to receive a data packet from the previous device, if it has monitored that other relay devices send a data packet before the expiration of the monitoring duration.

If synchronization is required to be performed for monitoring durations with different lengths of relay devices with different forward priorities and data packets with unfixed length, the above relay device further comprises: - a synchronization means, configured to delay by a synchronization duration T_syc before sending a data packet, and the synchronization duration T_syc is no less than the sum of the difference between a synchronization duration of the source network device and a monitoring duration of the previous device and the difference between the duration for sending the longest data packet and the duration for sending the received data packet. The processor 230 can be used as the synchronization means.

Preferably, since a relay device is reused as a luminaire, a relay device further comprises:

- a controller, configured to extract commands from the data packet to control a corresponding luminaire. The processor 230 can be used as the controller.

Above, the method and apparatus used by a relay device of a wireless relay network for relaying control signaling between a wireless controller and luminaires have been elucidated according to an embodiment of the present invention. Below, a wireless relay network with fault tolerance function will be elucidated according to another embodiment of the present invention.

Second embodiment

As shown in Fig. 7, the relay group Rl comprises three relay devices RIa, RIb and RIc. Their forward priorities are different and decrease in turn, namely RIa has the highest forward priority, RIb has the second highest forward priority and RIc has the lowest forward priority. The deployment of other relay groups and other relay devices are similar to that in the first embodiment. Concretely, in the first data packet duration tl, the three relay devices RIa, RIb and RIc of the relay group Rl monitor the receiving channel respectively to receive the data packet Pl from the wireless controller C. Then, the operation performed by RIa, RIb and RIc is similar to that in the aforementioned first embodiment. After detecting that the data packet has been received correctly, they determine the monitoring durations T_ml, T_m2 and

T_m3 respectively, before whose expiration the data packet is monitored to judge whether or not it is forwarded, according to their forward priorities. Wherein, T_ml is 0, T_m2 is the sum of the time T_s needed for RIa to start a data transmission and the time Ta needed for RIb to detect the data transmission, T_m3 is the sum of T_m2, the time T_s needed for RIb to start a data transmission and the time Ta needed for RIc to detect the data transmission, as shown in Fig. 4. After that, the relay device RIa with the highest forward priority judges to forward the data packet to the relay group R2 and forwards it. The relay device RIb and RIc monitor the sending channel. After monitoring that the relay device RIa with higher forward priority has forwarded the data packet, they monitor the receiving channel again to get ready to receive next data packet P2 in the second data packet duration t2.

Then, in t2, the wireless controller C sends the data packet P2. In practical systems, due to factors such as wireless channel interference etc., data packets may have various errors, e.g. they are lost, they are not completely received, they are broken etc., which will lead to the incorrectness of data packets received by a relay device, and those data packets with errors cannot be forwarded. In the prior art where half-duplex alternate relay is used, since only one relay device receives the data packet, when an error occurs, the only solution is that the wireless controller C is requested to retransmit the data packet by means of a feedback retransmission mechanism, which will result in an increase in the communication delay. And, when a relay device in an alternate relay mode cannot work because of failure such as power off etc., the alternate relay cannot continue. An extra backup relay device is employed in the embodiment of the present invention to receive a data packet simultaneously. When a relay device with higher forward priority receives a data packet incorrectly or does not forward the data packet owing to failure, the backup relay device automatically replaces the relay device with error to forward the data packet. Concretely, in one situation, in the data packet duration t2, relay devices RIb and RIc of the relay group Rl monitor the receiving channel to receive the data packet P2 sent from the wireless controller C and judge whether the data packet is received correctly based on a check mechanism such as CRC (Cyclic Redundancy Check). If RIb finds the check is wrong, it will not forward the wrong data packet to the next relay and will switch back to the receiving state and monitor the receiving channel to receive the data packet P3 from the wireless controller C in the third data packet duration t3. If RIc finds the data packet is correct after check, it will determine its monitoring duration T_m3 and monitor whether a relay device with higher forward priority forwards the data packet before the expiration of the monitoring duration T_m3. Since at this time the relay device RIa has finished forwarding Pl and returned to the receiving state, and owing to the wrong receipt of P2 the relay device

RIb has abandoned forwarding and returned back to the receiving state too, both of them monitor the receiving channel to receive subsequent data packets and do not send any information in the sending channel. Therefore, RIc has not monitored that any relay device sent a data packet within the monitoring duration T_m3, and thus it decides to forward the data packet P2 and forwards it.

In the duration of t3, the relay devices RIa and RIb are in the receiving state and monitor in the receiving channel to receive the data packet P3 from the wireless controller C; the relay device RIc is in the forwarding state and forwards the data packet P2 in the sending channel. The subsequent steps are similar to those of the aforementioned embodiments and will not be described further herein. In another situation, in the data packet duration t2, the relay device RIb cannot work owing to failure or power off. Then, the relay device RIc having received the data packet P2 correctly will not detect that the relay device RIa or RIb sends a data packet within its monitoring duration T_m3. Therefore, the relay device RIc judges to forward the data packet P2 and forwards it. In the data packet duration t3, the relay device RIa is in the receiving state and monitors the receiving channel to receive the data packet P3 from the wireless controller C; the relay device RIc is in the forwarding state, forwards the data packet P2 in the sending channel and takes over the job of RIb thereafter. If the relay device RIb returns to work normally, it will rejoin the relay group Rl and replace RIc. According to this embodiment of the present invention, a wrong receipt of a data packet in a relay device will not mean that the data packet cannot be forwarded; other relay devices having received the data packet successfully would monitor according to their forward priority, and after detecting that no other relay devices with higher forward priority forwarded the data packet, the relay device with the highest forward priority forwards the data packet automatically. When a relay device fails, there are other relay devices working as backup relay devices to perform the similar forwarding. The robustness of the multi-hop relay network is significantly increased. As can be seen, in respect of the fault tolerance mechanism according to this embodiment of the present invention, there is no need to specially set and monitor each relay device in real time. To implement the automatic switching, we only need to deploy three relay devices with different forward priorities in a relay group, and then the complexity requirement of relay devices is reduced. Therefore, it is particularly applicable for a wireless illuminating control network etc.

The above description is made by means of an embodiment where a relay group comprises three relay devices. It can be understood that a relay group can comprise more than three relay devices, in which case the fault tolerance capacity of the relay group can be further improved.

Similar to the first embodiment, preferably, synchronization is done between the wireless controller C and each relay device, so that receive-and-transmit conflict, which may be caused owing to different monitoring durations of each relay device, can be eliminated. The method for synchronization and its implementation has been elucidated in the above first embodiment in detail, those skilled in the art should be able to implement synchronization in this embodiment according to the description in the first embodiment, and the present invention will not give further details herein. It should be noted that, with the increase in the number of relay devices in a relay group, a relay device with lower forward priority correspondingly needs a longer monitoring duration to monitor whether the relay devices with higher forward priorities forward a data packet, which extends the relay frame time, the synchronization duration T_mmax of the wireless controller C and the synchronization duration T_syc and thus increases the overhead of the synchronization. However, the increased overhead time is an integer multiple of the sum T_umt of the time T_s needed for a relay device to start a data transmission and the time Ta needed for the next relay device to detect the data transmission, and T_umt is by far smaller than the packet time. Therefore, under the circumstances that there are a few backup relay devices, the increased overhead will not have any apparent influence on the efficiency of the system and can provide the relay network with better fault tolerance function. Further, under the circumstances that the length of each data packet to be sent is unfixed, the synchronization performed between the wireless controller and each relay device should eliminate receive-and-transmit conflict, which may be caused due to unfixed length of data packets. The method for synchronization and its implementation has been elucidated in the above first embodiment in detail and will not be described further herein. In the above embodiments, the description of the present invention is made by way of examples where all relay devices work in the half-duplex mode. It can be understood that the prevent invention is not limited to be based on half-duplex mode, it is also applicable for other relay modes, e.g. it provides relay devices working in full-duplex mode with fault tolerance function having small overhead. The fault tolerance function can be realized by forwarding monitoring based on priority, which is similar to that in the second embodiment.

All luminaires in the above embodiments are stationary; it can be understood that the present invention can also be applicable for relay devices to provide the communication between the wireless controller C and luminaires in the moving state with multi-hop relay.

Based on the teaching of the present invention, in conjunction with available relay technologies in moving state, those skilled in the art can carry out the present invention without inventive work.

As many different embodiments of the present invention can be made without departing from the spirit and scope thereof, it should be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.

Claims

What is claimed is:

1. A method for use in a relay device, comprising the steps of:

I), monitoring a receiving channel to receive a data packet from a previous device, the previous device comprising any one of a source network device and a relay device in a previous relay group;

II). determining a monitoring duration based on a forward priority of the present relay device;

III).monitoring a sending channel before the expiration of the monitoring duration, to decide whether or not another relay device in the same relay group as the present relay device has sent a data packet, in order to decide whether or not to send the received data packet.

2. The method according to claim 1, wherein, in the step II), the monitoring duration is determined in accordance with a rule: the higher the forward priority, the shorter the monitoring duration. 3. The method according to claim 2, wherein, in one relay group, the relay device with the highest forward priority has the shortest monitoring duration, and the monitoring duration of each other relay device is no less than the sum of the monitoring duration of a prior relay device whose forward priority is only higher than that of the other relay device, the time needed for the prior relay device to start a data packet transmission and the time needed for the other relay device to detect the data packet transmission.

4. The method according to claim 1 , wherein the step III further comprises any one of the following steps: i). sending the received data packet after the expiration of the monitoring duration, if it has not monitored that other relay devices sent a data packet before the expiration of the monitoring duration; ii). monitoring the receiving channel to receive a data packet from the previous device, if it has monitored that other relay devices sent a data packet before the expiration of the monitoring duration.

5. The method according to claim 4, wherein step i) further comprises the step of: delaying by a synchronization duration before sending the received data packet, the synchronization duration is no less than the difference between a synchronization duration of the source network device and a monitoring duration of the previous device.

6. The method according to claim 5, wherein the delaying by the synchronization duration further comprises the difference between the duration for sending the longest data packet and the duration for sending the received data packet, if data packets to forward have unfixed lengths.

7. The method according to claim 1, wherein the relay devices are further configured to extract commands from the data packet to control corresponding luminaires.

8. A relay device for wireless relaying, comprising: - a receiver, configured to monitor a receiving channel to receive a data packet from a previous device, the previous device comprising any one of a source network device and a relay device in a previous relay group;

- a first determining means, configured to determine a monitoring duration based on a forward priority of the present relay device; - a monitor, configured to monitor whether or not another relay device in the same relay group as the present relay device has sent a data packet in a sending channel before the expiration of the monitoring duration;

- a second determining means, configured to decide whether or not to send the received data packet according to the result of the monitoring and a predefined rule; and - a transmitter, configured to transmit the received data packet.

9. The relay device according to claim 8, wherein the first determining means determines the monitoring duration following a rule: the higher the forward priority, the shorter the monitoring duration.

10. The relay device according to claim 9,wherein, in one relay group, the relay device with the highest forward priority has the shortest monitoring duration, and the monitoring duration of each other relay device is not less than the sum of the monitoring duration of a prior relay device whose forward priority is only higher than that of the other relay device, the time needed for the prior relay device to start a data packet transmission and the time needed for the other relay device to detect the data packet transmission. 11. The relay device according to claim 10, wherein the predefined rule comprises: i). sending the received data packet after the expiration of the monitoring duration, if it has not monitored that other relay devices sent a data packet before the expiration of the monitoring duration; ii). monitoring the receiving channel to receive a data packet from the previous device, if it has monitored that other relay devices sent a data packet before the expiration of the monitoring duration.

12. The relay device according to claim 8, wherein the relay device further comprises:

- a synchronization means, configured to delay by a synchronization duration before sending the received data packet, and the synchronization duration is no less than the difference between a synchronization duration of the source network device and a monitoring duration of the previous device.

13. The relay device according to claim 13, wherein the delaying by the synchronization duration further comprises the difference between the duration for sending the longest data packet and the duration for sending the received data packet, if data packets to transmit have unfixed lengths.

4. The relay device according to claim 8, wherein the relay device further comprises:

- a controller, configured to extract commands from the data packet to control corresponding luminaires.