WO2013030715A1

WO2013030715A1 - Device for controlling communication of a node in a wireless network

Info

Publication number: WO2013030715A1
Application number: PCT/IB2012/054216
Authority: WO
Inventors: Marc Aoun; Tim Corneel Wilhelmus Schenk; Javier Espina Perez; Daniel Martin Goergen; Oscar Garcia Morchon
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-09-02
Filing date: 2012-08-21
Publication date: 2013-03-07

Abstract

A device for controlling communication of at least one node in a wireless network is provided, the wireless network having a plurality of nodes, wherein the device is adapted to monitor communication statistics of at least one node associated to the device, wherein the device is adapted to initiate an adjustment of a communication mode of the at least one node based on the communication statistics and/or the device is adapted to output interference information of the at least one node based on the communication statistics.

Description

Device for controlling communication of a node in a wireless network

FIELD OF THE INVENTION

The invention relates to a device, a method and a system for controlling communication of a node in a wireless mesh network.

BACKGROUND OF THE INVENTION

Recently, wireless mesh networks attract more and more attention, e.g. for remote control of illumination system, building automation, monitoring applications, sensor systems, medical applications and air condition systems. In particular, a remote management of outdoor luminaires, so-called telemanagement becomes increasingly important. On the one hand, this is driven by environmental concerns, since telemanagement systems enable the use of different dimming patters, for instance as function of time, weather conditions and season, allowing a more energy efficient use of the outdoor lighting system or other systems as mentioned above. On the other hand, this is also driven by economical reasons, since the increased energy efficiency also reduces operation costs. Moreover, the system can remotely monitor power usage and detect failures of the controlled elements, e.g. lamp failure or driver failure, which allows for determining the best time for repairing or replacing the element of the network, e.g. the lamp.

Current radio frequency (RF) based wireless solutions use either star network topology or mesh network topology for communication between the elements of the network. In a star network, a data collector has a direct communication path to every node in a network. However, this typically requires a high power/high sensitivity base station like controller, which makes the solution cumbersome to deploy and expensive. In a mesh network, the plurality of nodes in general does not communicate directly with the central controlling device, but via so-called multi-hop communications. In a multi-hop

communication, a data packet is transmitted from a sender node to a destination node via one or more intermediate nodes. Nodes act as routers to transmit data packets from neighboring nodes to nodes that are too far away to reach in a single hop, resulting in a network that can span larger distances. By breaking long distances into a series of shorter hops, signal strength is sustained. Consequently, routing is performed by all nodes of a mesh network, deciding to which neighboring nodes the data packet is to be sent. Hence, a mesh network is a very robust and stable network with high connectivity and thus high redundancy and reliability.

Mesh network transmission techniques can be divided into two groups:

flooding-based and routing-based mesh networks. In a flooding-based mesh network, data packets are forwarded by all nodes in the network. Therefore, a node does not have to make complicated routing decisions, but just broadcasts the data packet. By these means, the technique is quite robust. However, in large networks, the data overhead due to forwarding impacts the overall data rate. Moreover, collisions of data packets are more likely to occur, further reducing the overall performance. Routing-based mesh networks can be further divided into pro-active and re-active schemes. In a pro-active routing-based network, immediate network paths are stored in routing tables in each node. The routing tables are kept up to date, e.g. by sending regular beacon messages to neighboring nodes to discover efficient routing paths. However, the pro-active update of the routing tables consumes large parts of network resources. In contrast, reactive schemes avoid a permanent overhead and large routing tables by discovering routes on demand. They use flooding to discover a network path and cache active routes or nodes. When routes are only used scarcely for single data packets, flooding the data packets instead of performing a route discovery might be more efficient. If routes are kept long enough to avoid frequent routing, reactive schemes degenerate to pro-active schemes. An example for a re-active routing-based mesh network is used in ZigBee.

Mesh networks, as discussed herein, mostly refer to networks having a plurality of nodes which are stationary, wherein the communication between the nodes is performed wirelessly.

One of the challenges with these wireless solutions is that they are susceptible to electromagnetic interference. This is especially true, since these solutions typically apply communications in a shared RF band, also referred to as an ISM band. As such, also other devices and services can, and are allowed, to apply the same frequency band. Moreover, a mesh solution typically applies short-range communication solution, which apply low transmit powers. Other devices might use the same frequency bands with higher transmit power. Accordingly, nodes in a system may experience interference from devices/collection of devices that are foreign to the system and that are transmitting in the same or in

neighboring frequency bands as the nodes.

Further, e.g. in case of outdoor luminaires, the wireless controllers in the luminaires can also experience interference from the lamp driver located in a same luminaire. This is especially the case for high frequency electronic drivers, which are used for LED and fluorescent light sources.

In general, interference results in a reduced communication ability that causes non- stable behavior of the system, which is not desired and may result in a plurality of retransmissions of messages between the nodes wasting network resources. In some cases interferences may even lead to a breakdown of communication.

Further, the described mesh technology relies on the knowledge of

neighboring nodes, which can act as routers of the messages sent to, and from, the central controlling device or a data collector node. Due to foreign and/or in-network electromagnetic interference (EMI), the communication abilities of the nodes are influenced and the routing table in the node is no longer up to date, which causes routing/communication errors. State of the art mesh network communications are not designed to deal with foreign and/or in- network EMI.

This situation also occurs in other systems, like air-conditioner systems, including a plurality of indoor units and outdoor units connected and controlled wirelessly.

US 2003/0123420 Al describes a system for monitoring interference in a wireless communication system. The system monitors error statistic data at one or more devices in the wireless communication system. If any unusual error statistic data is present at the one or more of the devices, raw unprocessed data is provided from the devices experiencing unusual error activity. The raw unprocessed data can be utilized to characterize the interference. For example, the raw unprocessed data can be compared to one or more interference templates to determine an interference type.

SUMMARY OF THE INVENTION

In view of the above disadvantages and problems associated with the prior art, it is an object of the present invention to provide a device, a method and a system for controlling communication of a node of a wireless network that provide an improved transmission efficiency in the presence of interferences.

The object is solved by the features of the independent claims.

The present invention is based on the idea of identifying interference by monitoring communication statistics of the nodes and to adapt the

communication/transmission behavior of one or more nodes of the network according the identified interference. Accordingly, proper communication/transmission modes or parameters are selected and transmission efficiency and transmission reliability is improved. The term 'node' refers to a device with wireless transmission and reception capability. 'Network' refers to a collection of nodes that function cooperatively as a system. The term 'foreign interferer' refers to a device that does not belong to the network under consideration, and that has the capability of interfering with the wireless transmissions that take place within the network. Interferers are in general external devices, but may as well be devices that are controlled by and/or attached to the node, such as load drivers and a load itself, e.g. a motor.

The object is solved by a device for controlling communication of a node of a wireless network, like a star network or a mesh network. The wireless network has a plurality of nodes, wherein the device is adapted to monitor communication statistics of at least one node associated to the device, wherein the device is adapted to initiate an adjustment of a communication mode of the at least one node based on the communication statistics and/or the device is adapted to output interference information of the at least one node based on the communication statistics.

In a preferred embodiment the wireless network is realized as a mesh-network or a star-network. The wireless network may employ any kind of wireless transmission techniques, such as RF, Bluetooth, light (infrared or visible), acoustic energy, and the like. However, the present invention is not limited to wireless networks and could also be applied to wired networks. Even a combination of wired and wireless is possible. The network may include a central contra ller/central controlling device or back-end, which is connected to some collector nodes. The collector nodes act as distributing nodes receiving and transmitting information from a plurality of nodes of the network. The collector node may for example be wire-connected to a central controlling device, and the remaining nodes may be connected to the collector node wirelessly. Accordingly, the present invention is open to a variety of application.

The node may apply a suitable communication protocol for communicating with other nodes, in particular with communication units of the nodes. The node may be associated to a single load unit or to a plurality of load units. The node may include a control unit, a communication unit and other functional units, e.g. memory etc.

The device is associated to at least one node. This includes a respective connection for requesting and/or receiving data/information/signals regarding communication statistics of the node. The device may further be adapted to request and/or receive further information from the at least one node, such as an operation state thereof. The device is adapted to initiate an adjustment of a communication mode of the associated node and/or any node within the wireless network based on communication statistic received from the at least one node. Here, the device may evaluate the received communication statistics and identify interferences based on said statistics. Then, the device may instruct one or more nodes to adjust their communication mode or may directly adjust said communication mode in order to mitigate the effect of interference on the transmission/reception behavior of the node under consideration.

Alternatively or additionally the device is adapted to output interference information of the at least one node based on the communication statistics. The interference information may include at least one of a presence, source, location, type, magnitude and duration of interference and time per day thereof.

In a centralized embodiment the device may be a stand-alone device or be integrated in or attached to a central controller of the network. The device may centrally decide on the communication mode to be used by one or more nodes of the wireless network. Here, it is preferred that one or more nodes send communications statistics to the

device/central controller. The device then decides on the communication mode based on the received information and instructs at least one of the nodes of the network to change its communication mode. This procedure can be performed periodically in certain time intervals or aperiodically, but may as well be performed upon request of one of the nodes or a user. Additionally or alternatively the nodes may store the communication mode associated with a particular interference pattern as provided by the device, and apply the respective

communication mode automatically upon a request/interference information received from the device. Alternatively, the respective communication mode can be applied autonomously by the node if it deduces a known interference pattern or a similar one thereto, without the need to first inform the centralized entity and then waiting for the request from it.

In a decentralized embodiment of the present invention the device may be integrated in or attached to a node of the network. The device may be adapted to monitor communications statistics of the respective node only, or may be adapted to monitor communications statistics of multiple nodes of the network. Preferably, the device receives communications statistics from the multiple nodes. The multiple nodes may include or be the neighboring nodes. The device may then initiate the adjustment of the communication mode of at least one of the nodes of the network based on the monitored communications statistics. Additionally, the device may send the determined interference information and/or information about the communication mode of at least one node to a central controller of the network. The operation(s) of the device is/are identical for the centralized and the decentralized solution.

In a preferred embodiment, the device may be partially integrated in at least one of the nodes, and the rest at the backend/central controller. Further, the device may be implemented as software and/or a hardware module inside one single node or be distributed over multiple nodes.

In a preferred embodiment, interference detection can also be performed in a distributed fashion, where the nodes propagate the information to their direct neighbors or generally to collection of direct/indirect neighbors, and a distributed algorithm can be used to detect interference in the network. A node can be chosen as cluster node or cluster head and all the information forwarded to it. The cluster node can then aggregate the information it receives and either directly conclude that interference exists, or contact neighboring cluster nodes to exchange additional information and reach a conclusion. In this embodiment, the device is associated with the cluster node. However, the device can also be distributed, e.g. partially at the cluster node and partially at the node(s) that communicate(s) with the cluster node. Preferably, a plurality of devices are provided, wherein at least two of them

communicate with each other to exchange (interference) information. A decision on a presence, source, location, type, magnitude and duration of interference and time per day thereof and/or a decision to change the communication mode of at least one of the nodes of the network may then be made by the nodes collectively or independently. In particular, in the independent case a node may decide only on the communication mode of its associated node(s). However, instead of one single node also a collection/plurality of nodes can be chosen as cluster nodes or cluster heads.

Communication statistics include, but are not restricted to: number of (MAC) channel access failures, number of access attempts per packet before transmission success (in case of successful transmission), number of retransmissions before receiving an ACK, signal strength indicator when sampling the channel, difference between the sampled signal strength, the specified strength threshold that defines a channel as being busy, delay parameters and transmission success rate. In addition, the communication statistics and in particular the included channel access statistics may include the packet arrival rate at the nodes as well as the neighbor table of the nodes, i.e. the list of nodes in the network that a node can communicate with.

As mentioned above, the device may be adapted to determine interference information based on communication statistics. The device may evaluate communication statistics of the at least one node, e.g. by using an algorithm, and determine if the node is affected by interference. The device may then identify at least one of a location, a source and a type of interference and output this information. For instance, the device may use position information of the node to determine the location. Position information, i.e. a spatial identifier, of the node under consideration may be stored in a memory of the device or may be received from the node e.g. together with the communications statistics. Further, the node under consideration may deduce its position from the positions of the other nodes. The position information may include a GPS position of the node. The source of interference may for instance be determined by analyzing at least one of frequency information, a temporal behavior obtained from/included in the communications statistics and a power level e.g. of a known load unit that may be associated to the node or be positioned in close proximity to the node. The same information may be used to determine/identify a possible source of interference. The device may output the determined information on a display thereof. The device may alternatively or additionally send the information to the central controller, where the information may be accessible and/or visibly and/or audibly presented to a user.

Alternatively or additionally, the device may send the information to any other device, such as a mobile device carried by a network administrator that is debugging the network.

Additionally or alternatively, the device may be adapted to identify network locations/areas affected by interference based on communication statistics of at least one node and spatial (position) information of the node or a group of nodes in a certain area. The spatial information may include a GPS position of the nodes. Accordingly, the device may identify areas that are affected by interference. The device may then adjust the

communication mode of at least one of the nodes of the network based on the identified network locations.

Electromagnetic interference will mostly affect the reception performance of a node, in particular by decreasing the sensitivity of a receiver of said node. Accordingly, in a preferred embodiment the communication mode of a transmitting node is changed/adjusted based on the identified network locations. Preferably, a transmit power of the transmitting node is increased and/or MAC parameters (number of retries etc.) are modified in order to maintain/restore a communication link to a neighboring, e.g. a receiving, node. Neighboring nodes may be defined as the nodes within transmission range of the transmitting node, or may be pre-defined e.g. in the form of a table that is stored in a memory of the device.

Preferably the device runs an algorithm based on a model, which takes into account the identified network locations. For instance, in case that communication statistics of a plurality of nodes are monitored, the node with the worst performance degradation within the identified network location is taken into account, and the communication mode of at least one node of the network is adjusted accordingly. Preferably, a transmit power of at least one node is increased in order to maintain/restore a communication link to the node with the worst performance degradation.

In another preferred embodiment the adjustment of the communication mode of the at least one node includes at least one of resetting and/or updating a routing table, increasing and/or decreasing a beaconing frequency, increasing or decreasing a transmit power of the node, selecting a different frequency band for transmission, switching to a different communication technology (e.g. from infrared to Bluetooth) and increasing the number of channel access attempts.

According to the present invention, in a routing-based multi-hop network data packets or messages are forwarded by means of routing tables stored in the nodes (ad hoc on- demand distance vector (AODV) routing can also be used), wherein it is preferred to route messages differently depending on the detected interferences. The routing table may be reset and/or updated based on the detected interference/interference locations, since the routing table is likely no longer up to date due to the interference. For updating the routing table the frequency of beaconing, which can be used to build up or update the routing table, can be increased to enable a fast building or modification of the routing table. For observing the neighborhood a node may send periodically a beacon prompting the neighboring node to answer on the received beacon. The received answers are used to build up the routing tables. Further, the routing table may be first reset to a default setting and then be updated.

Alternatively, different routing tables for different operation states may be stored in a memory of the device and the routing table may be updated by activating a stored routing table. In this case it is not necessary to build up new routing tables. In the memory-based solution two routing tables could be used, wherein one is used in the presence of interference and one in the absence thereof. In a preferred embodiment during updating the routing table another routing method can be applied, e.g. flooding which does not require routing tables.

The adjustment of the communication mode may also include a change of certain parameters of the physical layer (PHY). One parameter may by the transmit power, that can be increased or decreased based on the detected interference, and in particular on the strength/intensity of the interference. This can be done in a control loop (learning) manner until a certain performance is achieved, such as communication delay, number of observed neighbors, and/or success rate in communications. Preferably, the transmit power is increased when interference is present, and is decreased when interference is absent. By increasing the transmit power of the node a transmission range of the node is increased and therefore, more neighboring nodes can be reached by the node, leading to an increased transmission efficiency and reliability. Additionally, the transmission power of neighboring nodes might also be adjusted. Additionally or alternatively, also the PHY data rate can be decreased, which typically increases the receiver sensitivity. Another possibility is to change the length of CRC (cyclic redundancy check) and/or to send the message multiple times consecutively, to increase the reliability. The adjustment of the communication mode may be made dependent on how urgent the information the node wants to transmit is, i.e. on a priority of the message to be transmitted.

It is noted, that the above-mentioned control loop (or learning) approach is not limited to the adjustment of the parameters of the physical layer, and in particular not to the adjustment of the transmit power, but can be used to adjust any of the parameters of the communication mode.

In a preferred embodiment the adjustment of the communication mode includes a change of the frequency band for transmission. In particular, the device may determine that a certain frequency band is affected by interference. The device may then instruct at least one node to change its transmission frequency. Further, the number of retransmissions of a message to be sent from one node to another can be changed. More retransmissions increase the reliability of success, which can mitigate the effect of interference. It may be further preferred to increase the counts of the counters in the presence of interference, to thereby increase the chance of receiving a packet before dropping a packet and requesting a new one. When no interference is present, the counts of the counters in the receiving node may be reduced again. Again, this may be dependent on a priority of the message to be transmitted.

In another preferred embodiment, on the detection of interference, for at least one node of the wireless network a different communication mode is activated for a predetermined time. The different communication mode may be applied during updating a routing table, wherein the predetermined time preferably corresponds to the time that is required to update the routing table. The communication mode that is activated for a predetermined time may include high-level transmission parameters, such as maximum transmit power. This ensures a sufficient transmission efficiency and transmission reliability although e.g. the routing table has not been updated yet. Thus, it is possible to communicate with nodes, although noise levels and/or interferences are high. In a preferred embodiment the device is further adapted to distinguish between in-network interference and foreign interference. The adjustment of the communication mode may then be done differently for in-network interference and foreign interference. In case of in-network interference, the adjustment of the communication mode may include a certain timing for transmission attempts, e.g. by using time division multiple access (TDMA). For instance, time slots for transmission might be assigned to each node. Preferably, for neighboring nodes the assigned time slots do not overlap. In case of foreign interference, the change of the communication mode may include an increase of the transmit power and/or a change of the frequency band for transmission. This distinction allows a proper and sophisticated adjustment of the communication modes.

To distinguish between in-network interference and foreign interference, the device may first determine which nodes are experiencing interference, e.g. by recognizing a high channel access failure rate of the nodes, and map these nodes to their geographical locations, and then determine the geographical proximity of these nodes with respect to each other or to a specific location. Subsequently, the device may deduce whether areas can be labeled as interference-affected, or deduce that the geographical locations do not map into a geographical area, i.e. that the affected nodes are too dispersed and cannot be clustered in a continuous or near-continuous geographical area. With this, generic interference can be ruled out. For instance, in case of an outdoor lighting system streets and building distribution information can be taken into account.

It is to be noted, that e.g. a high number of (MAC) channel access failures can be attributed to the high interference of foreign interferers that are operating in the neighboring frequency band (and potentially ones that are operating in the same frequency band of the nodes) as well as to in-network interference e.g. caused by a high level of communication congestion between the nodes.

In-network interference may be identified by determining a level of communication congestion between the nodes. For instance, when nodes belonging to the network are heavily accessing a channel, a high number of channel access attempt/failures can be attributed to in-network interference, since successful communication becomes more and more difficult due to high congestion. A packet arrival rate information and/or a queue size can be used to deduce the level of congestion. Additional information such as timestamps of the channel access attempts moments can be used to correlate channel access attempts at different nodes and deduce the level of congestion the channel is experiencing. Time synchronization can be used to provide a global notion of time in the network. Alternatively or additionally a density parameter of the nodes can be deduced from the spatial information and the in-network interference can be identified based on said density parameter. By this density parameter it is possible to identify whether e.g. an observed high failure rate is due to the own network. A density parameter of the nodes can be derived from the spatial locations of the set of nodes, but also by the size of the neighbor table of the specific node, or the number of neighbors tables a node appears in, i.e. the higher this number the higher the (radio) density. This is very applicable, since a higher density will result to a higher congestion, which can cause the failures. For instance, if all nodes run approximately the same application they will generate about the same amount of traffic. Moreover, the distance to a data collector of the network can be calculated, either in actual (geographic) distance or in number of network hops. This is useful because the traffic density will also be higher closer to the data collector. A threshold for the number of access failures can then be set based on these spatial parameters. If the number of access failures (observed in a period of time) is above the threshold, congestion due to own network, i.e. in-network interference, is ruled out.

Either one or a combination of both approaches described above can be used to distinguish in-network from foreign interference. Using a combination of both approaches results in an increased certainty in the identification.

In a preferred embodiment of the present invention the communications statistics are determined by performing medium assessment (fake-transmission mode), in which the nodes simulate actual transmission attempts. Here, the device may instruct nodes to stop all attempts to access the channel for packet transmission, and enter, for a certain period of time, a medium assessment phase where the nodes simulate actual transmission attempts by continuously or regularly/periodically attempting to access the channel, registering all required channel access statistics, but without actual physical data

transmissions even if the channel is assessed as free. Such an approach can be adopted in the whole network, or in areas that were flagged as interference-affected (in the aforementioned possible approach to detect interference-affected geographical areas). In the latter case, the device can choose those areas that it already labeled or identified as interference-affected, and instruct the nodes in these areas to enter this fake-transmission attempts mode. The frequency with which this information is provided to the device determines the

responsiveness of the system in determining interference-affected areas. After this testing the statistics are fed back to the device, which makes the decision on the levels of interference and actual areas affected by interference, thereby ruling out in-network interference. This information on interference affected areas can be, subsequently, be applied to change the communication mode of the network/system. One example of this changing is by selecting a different frequency band or a different communication technology to operate in, and informing all the nodes to switch over. Alternatively, the number of channel access attempts might locally be increased in the areas identified as affected by foreign interference.

In a preferred embodiment, a first node that notices a high number of transmission failures may also instruct its direct neighbors, and through them its indirect neighbors if necessary, to refrain from sending data for a certain amount of time. The node can then enter the fake-transmission mode described above. Although interference at this node might then be detected, other nodes in the neighborhood should also perform this procedure to identify whether interference is affecting the area in general. All nodes or a subset of the nodes can be randomly chosen from the neighbor table of the first node to perform the fake-transmission phase by silencing their neighbors and then listening to the channel. The procedure can be repeated periodically or aperiodically in a synchronized manner in order to delimit the affected geographical region. Multiple nodes can be concurrently chosen to perform the fake-transmission phase. The procedure can be performed in a fine-grained or coarse fashion. In a fine-grained fashion, all nodes or a high proportion of them performs the fake-transmission phase. In a coarse approach, the nodes are chosen in such a way that the area covered becomes larger. In other words, fine-grained and coarse approaches differ in the geometric distance that separates two consecutive choices of nodes that enter a fake-transmission phase.

Preferably the device is operatively coupled to or integrated in the node. The device may be attached in a removable and/or reusable manner to a node, or the device may be integrated into the node. Referring to the latter, the device may be part of or integrated in a CPU of the node. The device may also be implemented partially or entirely as software or as a software module. Further, it is possible to upgrade existing nodes with the device.

In a preferred embodiment the device is used in a lighting control system. The lighting control system may be an outdoor lighting control system for telemanagement (remote control) of luminaire nodes. The device of the present invention may also be used in indoor lighting control systems. However, the present invention is not limited to lighting systems and may as well be applied to air-conditioning systems and other kinds of networks using communication suffering from interference. In another aspect of the present invention a method for controlling

communication of at least one node in a wireless network, wherein the wireless network having a plurality of nodes, comprises the steps of monitoring communication statistics of at least one node and adjusting a communication mode of the at least one node based on the communication statistics and/or outputting interference information of the at least one node based on the communication statistics.

In still another aspect of the present invention a system for controlling communication of at least one node in a wireless network is provided, the system comprising a plurality of nodes a device adapted to monitor communication statistics of at least one node and to adjust a communication mode of the at least one node based on the communication statistics and/or to output interference information of the at least one node based on the communication statistics.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows an example of a wireless mesh network;

Fig. 2 shows a flow diagram of a method according to a first embodiment of the present invention;

Fig. 3 shows a flow diagram of a method according to a second embodiment of the present invention;

Fig. 4 shows a flow diagram of a process included in the second embodiment of the present invention;

Fig. 5 shows a flow diagram of a method according to a third embodiment of the present invention; DETAILED DESCRIPTION

Preferred applications of the present invention are outdoor lighting systems (e.g. for streets, parking and public areas), indoor lighting systems for general area lighting (e.g. for malls, arenas, parking, stations, tunnels etc.) or sensor networks. In the following, the present invention will be explained further using the example of an outdoor lighting system for street illumination. In the field of lighting control, the telemanagement of outdoor luminaires via radio-frequency network technologies is receiving increasing interest, in particular solutions with applicability for large-scale installations (say above 200 luminaires).

In fig. 1 , a typical network with mesh topology is shown. A plurality of nodes 10 (N) is connected to each other by wireless communication paths 40. Some of the nodes 10 function as data collector nodes 50 (N/DC), which receive data packets from the surrounding nodes 10 via single-hop or multi-hop transmissions and transmit them to a control center 60 and vice versa. Thus, the data collector nodes 50 may operate in the manner of gateways between the nodes 10 and the central controlling device or control center 60. The wireless communication path 40 between the nodes 10 and data collector nodes 50 may be constituted by radio frequency transmissions, while the connection 70 between the data collector nodes 50 and the control center 60 may make use of the Internet, mobile communication networks, radio systems, Ethernet, DSL, cable or other wired or wireless data transmission systems.

In case of a lighting system, the central controlling device may be used by a lighting system operator to control and monitor the luminaires of the lighting system, e.g. by uploading dimming schedules to the luminaires and monitoring energy consumption. For this application the central controlling device knows the exact positions of all the luminaires. This is used for intuitive control, e.g. by selecting relevant luminaires on a map, but also to signal were a luminaire is failing and needs to be serviced. This spatial information of the nodes may be applied to the advantage in the present invention.

Compared to other so-called ad-hoc mesh networks, the telemanagement system for an outdoor lighting control network is stationary, i.e. the nodes 10 do not move. Also, all nodes 10 may be connected to mains power. Consequently, network changes will be mainly due to a changing environment, e.g. due to traffic. Since the nodes 10 are stationary, the physical positions of the nodes 10, for instance GPS coordinates, may be known in the system, enabling geographic or position-based routing.

For data packet transmission from the luminaire nodes 10 to the data collector nodes 50, sink distance vector routing is preferred, wherein every node 10 selects as intermediate node 10 the neighboring node 10 that is closer to one of the data collector nodes 50 (so-called sinks). Preferably, a routing solution is used, since the routes to the data collector nodes 50 are regularly used. Preferably, a routing table is stored in every node 10, indicating which neighboring node 10 is closer to one of the data collector nodes 50. Thus, data packets can be sent to the closest data collector node 50 in a very efficient and fast way. Advantageously, each node 10 keeps information about multiple downlink neighboring nodes 10 as alternative routes in order to increase reliability.

Every node in the network is endowed with a transceiver module responsible for the physical transmission and reception of packets. The operation of this transceiver module can be mapped to the first layer (PHY layer) of the OSI communication layering model. In general, a module, implemented in software, hardware, or combination of software and hardware, functions at the second OSI layer (data link), on top of the PHY layer, and is responsible for arbitrating channel access among nodes.

The IEEE 802.15.4 Medium Access Control (MAC) and the IEEE 802.11 MAC protocols are examples of protocols that are adopted in such a module. In Contention- based Medium Access Control protocols such as IEEE 802.15.4 and IEEE 802.11, nodes contend for channel access. The contention procedure consists of a channel listening phase where the status of the channel (free or busy) is assessed, a potential back-off phase where a node that finds the channel to be busy waits for a random amount of time before trying to access the channel again, and an execution phase where the node either starts transmitting its packet or reports a channel access failure to the upper layer (the Network layer in the OSI model). Instead of a channel access failure, a transmission failure might be reported in case the node manages to send its packet but does not receive a reception acknowledgment from the receiver node (in case of unicast transmission). Multiple transmissions/transmission attempts might be initiated by the MAC layer of the node before reporting a failure.

To detect regions of high interference, and more specifically regions where channel access failures are due to devices that do not belong to the network, communication statistics, in particular MAC and channel statistics, may be correlated with location information of the nodes and/or temporal information and/or failures at other nodes in order to determine network regions that are affected by interference, and further to differentiate between regions where access failures are due to in-network interference, and regions where interference are due to foreign interferers.

Figure 2 shows a flowchart of a method according to a first embodiment of the present invention. In step S210 the device monitors communication statistics of at least one node. In the centralized approach the device may be integrated in or attached to a central controlling device of the network or be a separate, stand-alone device. In the decentralized approach the device may be attached to or integrated in a data collector node, or any other node of the network.

The device receives communications statistics from at least one node of the network via a wireless (or wired) connection. The device evaluates/analyzes the

communication statistics. For example, the analysis may reveal that a channel access failure rate of one or more nodes of the network is high. A certain threshold may be predefined so that the device can distinguish between normal (acceptable) and abnormal (unacceptable) channel access failure rate. Based thereon the device then concludes, that a node showing an abnormal channel access failure rate experiences interference (step S220). It is to be noted, that the device might also analyze and consider a plurality of information included in the communication statistics in order to achieve a higher level of certainty in the conclusion that the node experiences interference.

The device may then adjust the communication mode (step S230) of at least one of the nodes being affected by interference, or of any other node in the network. For instance, if it is determined that node A is affected by interference, a transmit power of node B, which may be a neighboring node of node A, is increased. This could be done in a control/learning loop manner. In particular, the transmit power of node B could be increased stepwise until a satisfying communication connection between node A and B is established. Alternatively or additionally data prioritization may be used, wherein e.g. more important data may be sent more frequently and/or at a higher power level.

Figure 3 shows a flowchart of a method according to a second embodiment of the present invention. In step S310 the device gathers/collects communications statistics of multiple nodes, similar to the first embodiment. In step 320 the device combines the communication statistics of the nodes with spatial information of the nodes. The spatial information may be included in a data package comprising the communication data/statistics sent from a node to the device, for example a spatial identifier. However, the node may also send a separate message including the spatial information to the device upon request of the device or automatically. Alternatively, the device may have prestored the spatial information and a corresponding unique node identifier in a memory thereof, wherein the node identifier is preferably included in each message sent from the node to the device. The spatial information may include a GPS position of the nodes.

From the combined statistics and/or spatial information and/or time information the device then determines locations/areas of the network that are subject to interference. For example, the device may determine that a number N of neighboring nodes experience interference. Accordingly, the area spanned by the N nodes is considered to be affected by interference.

If the procedure results in a defined geographical area, the device has to further identify whether the low performance (e.g. high failure rate) is due to in-network interference, e.g. due to a high level of communication congestion between the nodes, or due to foreign interferers e.g. operating at the same or neighboring frequency bands (step S340).

In order to determine, if the interference is due to in-network congestion, for instance a packet arrival rate information of the node is leveraged to deduce the level of congestion between the nodes. Additional information such as timestamps of the channel access attempts moments can be used to correlate channel access attempts at different nodes and deduce the level of congestion the channel is experiencing. Time synchronization can be used to provide a global notion of time in the network. Further, task synchronization can be used to coordinate actions of the nodes.

A further method to identify whether the interference is due to the own network is by the use of the available spatial information. A density parameter of the nodes {NodeDensity) can be derived from the spatial locations of the nodes under consideration, but also from the size of the neighbor table of the specific node, or the number of neighbor tables a node appears in, i.e. the higher this number the higher the (radio) density. This is very applicable, since a higher density will result to a higher congestion, which can cause the failures. This is specifically valid for telemanagement since the all nodes run approximately the same application, hence generation about the same traffic. Moreover, the distance to the data collector (DC in fig. 1) can be calculated, either in actual distance (DistanceNodeDC) or in number of network hops. This is useful because the traffic density will also be higher closer to the DC. A threshold Th can then be set based on these spatial information/density for e.g. the expected number of MAC access failures, e.g. defined as:

Th = {(NodeDensity, DistanceNodeDC)

= A* NodeDensity + B* DistanceNodeDC,

If the number of access failures (observed in a period of time) is above the threshold Th, congestion due to own network, i.e. in-network interference, is ruled out, and those nodes may be removed from the list of potential interfered nodes/areas. Providing such a threshold is not limited to the number of access failures, but may additionally or

alternatively be set for other information included in or deduced from the communication statistics, such as transmission success rate. Once the possibility of abnormal congestion between the nodes is ruled out, the device concludes/deduces that the major interference source(s) is/are foreign to the network, i.e. due to foreign interferers. Additionally or alternatively, if all nodes are operating in the same channel, a node or device can decide to sniff on a neighboring channel (still within the possible channels specified by the protocol). If interference is also witnessed on that channel, then it deduces that there is a higher probability that foreign interference is also occurring, at that channel and in the original channel. The adjustment of the communication mode is then performed depending on if the interference is in-network or foreign (S350). In case of in-network interference, the adjustment of the communication mode may include a certain timing for transmission attempts and/or some frequency hopping technique. In particular, time slots for transmission might be assigned to each node. Preferably, the assigned time slots do not overlap for neighboring nodes. In case of foreign interference, the change of the communication mode may include an increase of the transmit power and/or a change of the frequency band for transmission and/or a prioritization of data, wherein the latter can e.g. be mapped to different power levels.

Figure 4 shows a flow diagram of a process that can be performed as a part of the method of the second embodiment described above. The process allows to rule out generic interference. The process shown in figure 4 is preferably performed between steps S330 and S340 shown in figure 3 and described above. The device processes the combined statistics and spatial information obtained in step S330 to determine a proximity of the nodes experiencing interference. For instance, the device can determine which nodes are experiencing a high channel access failure rate, and map these nodes to their geographical locations (step S330), and then determine the geographical proximity of these nodes experiencing this high rate (S331). Subsequently, the device may deduce whether areas can be labeled as interference-affected, or deduce that the geographical locations do not map into a geographical area, i.e. that the affected nodes are too dispersed and cannot be clustered in a continuous or near-continuous geographical area (S332). If the geographical locations map into a geographical area, generic interference can be ruled out. Once generic interference is ruled out, the method proceeds to step S340 to distinguish between in-network and foreign interference. Ruling out generic interference facilitates and enhances the reliability of identifying in-network and foreign interference. It should be noted, that also metadata information can be taken into account, such as proximity to places that produce a high level of interference, e.g. to a center that uses WIFI, to a hospital etc..

Figure 5 shows a method according to a third embodiment of the present invention. In step S510 the device instructs the nodes of the network to stop all attempts to access the channel for packet transmission, and enter, for a certain period of time, a medium assessment phase where the nodes simulate actual transmission attempts by continuously or regularly/periodically attempting to access the channel, registering all required channel access statistics, but without actual physical transmissions even if the channel is assessed as free (step S520). Such an approach can be adopted in the whole network, or in the areas that were flagged as interference-affected in the aforementioned possible approach to detect interference-affected geographical areas. In the latter case, the device can choose those areas that it already labeled or identified as interference- affected, and instruct the nodes in these areas to enter the fake-transmission attempts mode. If required, the fake transmission attempts may be synchronized for some or all nodes.

The frequency with which this information is provided to the device determines the responsiveness of the system in determining interference-affected areas. After this testing the statistics are fed back to the device (step S530), which makes the decision on the levels of interference and actual areas affected by interference (S540). The statistics and/or the decisions may be exchanged with other nodes/devices. Step S540 may include the different approaches for e.g. detecting/determining interference/areas affected by interference described with respect to the first and second embodiment of the present invention.

This information on interference can subsequently be used to change the communication mode of the network/system (step S550), as described for the first and second embodiment.

The invention provides the advantage to adapt the communication mode of at least one node of a wireless network based on detected interference. Thus, an intelligent solution is provided reflecting the interference a network is experiencing and influencing the communication behavior of the nodes.

Claims

CLAIMS:

1. A device for controlling communication of at least one node in a wireless network, the wireless network having a plurality of nodes (10), wherein the device is adapted to monitor communication statistics of at least one node associated to the device, wherein the device is adapted to initiate an adjustment of a communication mode of the at least one node based on the communication statistics and/or the device is adapted to output interference information of the at least one node based on the communication statistics.

2. Device according to claim 1, wherein the device is adapted to receive communication statistics of multiple nodes of the network, and to process the received communication statistics of the multiple nodes to control the communication mode of the multiple nodes in the network based on the received communication statistics.

3. Device according to claim 1 or 2, wherein the communication statistics includes at least one of channel access statistics, positive or negative acknowledgement statistics, wherein the channel access statistics includes at least one of a number of channel access failures, a number of channel access attempts, a number of retransmissions, a signal strength indicator, delay parameters and a transmission success rate.

4. Device according to any one of the preceding claims, wherein the device is adapted to determine interference information based on communication statistics.

5. Device according to any one of the preceding claims, wherein the device is adapted to identify network locations affected by interference based on communication statistics of the nodes and spatial information of the nodes, wherein the device is in particular adapted to adjust a communication mode of at least one of the nodes based on the identified network locations.

6. Device according to any one of the preceding claims, wherein the adjustment of the communication mode of the at least one node includes at least one of modifying parameters of the routing layer, resetting and/or updating a routing table, increasing and/or decreasing a beaconing frequency, increasing or decreasing a transmit power of the node, selecting a different frequency band for transmission, selecting a different communication technique and increasing the number of channel access attempts.

7. Device according to any one of the preceding claims, wherein the device is further adapted to distinguish between in-network interference and foreign interference.

8. Device according to claim 7, wherein the in-network interference is identified by determining a level of communication congestion between the nodes.

9. Device according to claim 7 or 8, wherein in-network interference is identified based on the spatial information of the at least one node and/or a proximity of the node to known interference sources.

10. Device according to any one of the claims 7-9, wherein a density parameter of the nodes is deduced from the spatial information and the in-network interference is identified based on said density parameter.

11. Device according to any one of the preceding claims, wherein the channel access statistics are determined by performing medium assessment, in which the nodes simulate actual transmission attempts.

12. Device according to one of the preceding claims, wherein the device is attached to or integrated into a node or is provided separately in the wireless network and/or is partially or entirely implemented as a software module.

13. Device according to one of the preceding claims, wherein the device is used in telemanagement of an outdoor lighting system.

14. Method for controlling communication of at least one node in a wireless network, wherein the wireless network having a plurality of nodes, comprising the steps of:

- monitoring (S210) communication statistics of at least one node, - adjusting (S230) a communication mode of the at least one node based on the communication statistics and/or outputting interference information of the at least one node based on the communication statistics.

15. System for controlling communication of at least one node in a wireless network, the system comprising:

a plurality of nodes (10); and

a device adapted to monitor communication statistics of at least one node to adjust a communication mode of the at least one node based on the communication statistics and/or to output interference information of the at least one node based on the communication statistics.