WO2012080893A1

WO2012080893A1 - Control unit, node and method for addressing multicast transmissions in a wireless network

Info

Publication number: WO2012080893A1
Application number: PCT/IB2011/055424
Authority: WO
Inventors: Marc Aoun; Daniel Martin Goergen; Javier Espina Perez; Tim Corneel Wilhelmus Schenk; Oscar Garcia Morchon
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2010-12-15
Filing date: 2011-12-02
Publication date: 2012-06-21
Also published as: TW201233209A

Abstract

For a fine-grained flexible addressing of nodes in a wireless network with increased network scalability and transmission efficiency, a control unit, a node and a method is provided, wherein an addressee group of a plurality of destination nodes (11) is created by including at least one addressee condition in a multicast data packet for transmission of the multicast data packet.

Description

CONTROL UNIT, NODE AND METHOD FOR ADDRESSING MULTICAST

TRANSMISSIONS IN A WIRELESS NETWORK

FIELD OF THE INVENTION

The invention relates to a control unit, a node and a method for addressing multicast data packets in a wireless network. BACKGROUND OF THE INVENTION

Recently, wireless mesh networks attract more and more attention, e.g. for remote control of illumination systems, building automation, monitoring applications, sensor systems and medical applications. 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 patterns, for instance as a function of time, weather conditions and season, allowing a more energy-efficient use of the outdoor lighting system. On the other hand, this is also driven by economical reasons, since the increased energy efficiency also reduces operational costs. Moreover, the system can remotely monitor power usage and detect lamp failures, which allows for determining the best time for repairing luminaires or replacing lamps.

Current radio-frequency (RF) based wireless solutions use either a star network topology or a mesh network topology. In a star network, a control center has a direct wireless communication path to every node in the network. However, this typically requires a high-power/high-sensitivity base-station-like control center to be placed at a high location (e.g. on top of a building), which makes the solution cumbersome to deploy and expensive. In a mesh network, the plurality of nodes does in general not communicate directly with the control center, 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 in a series of shorter hops, signal strength is sustained. Consequently, routing is performed by all nodes of a mesh network, deciding to which neighboring node 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. In the prior art, mesh network transmission techniques can be divided in two groups: flooding-based and routing-based mesh networks. In a flooding-based mesh network, all 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 achievable data rate. Moreover, collisions of data packets are more likely to occur, further reducing the overall performance. Hence, the main problem of this solution is the scalability. Routing-based mesh networks can be further divided into proactive and reactive schemes. In proactive routing-based mesh networks, all needed 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. Although the data transmission is very efficient in such kind of network, the scalability is still low, since in big networks, the proactive update of the routing tables consumes large parts of network resources. Moreover, the routing tables will grow with the scale of the network. In addition, the setup of the network requires time and resources in order to build up the routing tables. Reactive schemes, in contrast, avoid the permanent overhead and large routing tables by discovering routes on demand. They use flooding to discover network paths 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 proactive schemes. An example for a reactive routing-based mesh network protocol is used in ZigBee. However, the main problem of this protocol scheme is still the scalability of the network.

For controlling a large number of nodes, efficient communication methods such as multicasting are indispensable to achieve the required scalability. Multicasting does refer to the transmission of a data packet to several (but not all) destination nodes. Thus, only one multicast data packet is required, instead of transmitting a data packet to each destination node separately. In general, a multicast data packet includes a multicast group address or identity corresponding to a predefined multicast group comprising several nodes. However, although multicasting is a known concept, previous approaches do not take key parameters into account, e.g. geographical and context characteristics of network nodes, when defining multicast groups during a commissioning phase of the system. In particular, for large sensor or actuator networks, such as lighting systems for illuminating streets or other public grounds, these features are intrinsic for the function and controlling. For example, luminaire nodes of a lighting system, which are located in the same street, will very likely share identical control requirements. Moreover, the creation of a multicast group is commonly performed during commissioning of the system by allocating a multicast group identity to the individual nodes. Therefore, multicast groups are predefined and cannot simply be modified. In order to create a new multicast group in prior art networks, an extensive set-up routine is required, wherein every node to be included in this new multicast group has to be subscribed individually and has to be then informed about the multicast group identity. However, this is a very time-intensive task and causes a large data overhead increasing considerably the network load. In particular, when creating multicast groups, which are only used once or which comprise a large number of nodes, this set-up procedure is very disadvantageous. Therefore, when only a few interactions with a set of nodes are required in prior art networks, unicast data transmissions are preferred, instead of creating new multicast groups. However, this approach is not suited for high scalability. Therefore, big disadvantages in common wireless networks are the tedious configuration of the network, the inflexibility and preset definitions of multicast groups and the extensive setting-up of new multicast groups with respect to time and network resources.

In many situations, it would be preferable to modify predefined multicast groups on demand, in order to include or exclude nodes from the multicast group

communication. Moreover, an efficient way to address an arbitrary set of nodes is required, which is both suited for high scalability and flexible control of a large wireless network.

WO 2009/128001 describes a method of commissioning an arrangement of devices communicating with each other over a wireless network control system, wherein a unique identity of each device to be installed is read and compiled in an inventory of the installed devices. SUMMARY OF THE INVENTION

In view of above disadvantages and problems in the prior art, it is an object of the present invention to provide a control unit and a method for addressing nodes of a wireless network in a flexible manner, while maintaining the network scalability and communication efficiency.

The invention is based on the idea to include at least one addressee condition in a multicast data packet, which has to be satisfied by a node for being addressed as a destination node. Thus, this addressee condition defines an addressee group of destination nodes without any pre-setting or prior grouping of multicast groups. The multicast data packet may then be transmitted using flooding or broadcasting. In this case, many or even all nodes of the network will receive the multicast data packet, but only those, which are addressed by the addressee condition, will act as destination nodes of the data packet, e.g. decode the data packet and use its contents accordingly. By these means, the complex and time-consuming explicit creation of multicast groups can be avoided, thus avoiding extensive use of network resources and providing high scalability and communication flexibility. This is in particular useful for ad-hoc or on-demand addressing, for addressing a large number of destination nodes or for addressee groups that will be addressed only once or very seldom.

According to one aspect of the present invention, a control unit for a wireless network having a plurality of nodes is provided. The control unit is adapted to include an addressee condition in a multicast data packet for creating an addressee group of destination nodes. Thus, a plurality of nodes can be addressed without requiring unicast data

transmissions to the individual destination nodes or a pre-grouping into one multicast group having a preset group address or group identity. This drastically increases the flexibility and efficiency of data transmission and of the control in a wireless network. The control unit may be included or installable in at least one of a network node, a collector node or a control center of the network.

The wireless network may have mesh topology, wherein each node may act as a router. Such a network has increased redundancy and reliability. Preferably, the nodes of the wireless network are stationary, as it is mainly the case for large actuator or sensor networks, such as lighting systems for public grounds. Alternatively or additionally, the positions of at least some nodes may be known to at least some of the other nodes of the network.

In one example, the addressee condition may be related to node characteristics, such as network characteristics, a geographical position, context characteristics and additional characteristics of a respective node. Network characteristics may refer to a node address or node identity, to a multicast group to which the node is allocated, to a function of the node within the wireless network, e.g. whether the node is a collector node, to a position within the network, e.g. to a hop distance of the node to a collector node, or the like. The geographical position of a node may refer to GPS coordinates, to a geometric position within the wireless network defined in arbitrary units, to a relative position to other elements of the network or the like. Moreover, context characteristics may correspond to a street, a building or place of interest in the neighborhood, etc., whereas additional characteristics may refer to a version of firmware, a fabrication type or other properties of the node itself. Since nodes sharing at least some node characteristics are very likely to have the same control or communication requirements, it may be advantageous to cluster them as an addressee group of a multicast data packet by including a corresponding addressee condition. For instance, in a telemanagement network for controlling a large sensor or actuator network, such as a lighting system, luminaire nodes can thus be grouped together by defining at least one shared node characteristic as addressee condition, e.g. being located in the same specified street or having the same software version or lamp type.

Preferably, an addressing information corresponding to a multicast group is included in the multicast data packet in addition to the at least one addressee condition, so that the addressee group of destination nodes is defined by the combination of the addressing information and the addressee condition. In this case, the multicast group addressed by the addressing information may be modified according to the requirements, e.g. ad-hoc or on- demand, using the addressee condition. When the addressing information and the addressee condition are both included in the multicast data packet, they are both considered by a node receiving the data packet for determining whether the node belongs to the addressee group of the data packet. The addressing information may include geographical addressing

information defining a multicast group by specifying geographical area, within which all nodes are addressed as destination nodes of the multicast data packet. For instance, the geographical addressing information may specify a GPS position and a radius, the specified GPS position being the center of a circular geographical area having the specified radius. Alternatively, the geographical addressing information may relate to intervals of GPS positions, so that the specified geographical area has a rectangular shape. Instead of globally defined GPS position, also other geographically based position data may be used, e.g. relative position coordinates or position coordinates only defined within a deployment map of the network. Thus, the geographical addressing information may be used for defining a geographical area usually having a simple geometric shape. Alternatively or additionally, the addressing information may include a group address or group identity of a predefined group of nodes, e.g. a multicast group. These predefined multicast groups may be set up having an allocated group identity or group address, e.g. during a commissioning phase of the network. Hence, if a node corresponds to the addressing information and satisfies the addressee condition, it will act as a destination node of the multicast data packet. Using the example of a lighting system, the GPS position of a hospital and a radius of 200 m may be included in the multicast data packet as geographical addressing information, whereas a further addressee condition may include the context characteristics of belonging to an access road of the hospital. Thus, by using the addressing information in addition to the addressee condition, the advantages of a simple but general addressing and of a fine-grained addressing can be combined. By these means, the number of data packets can be reduced, thus increasing the efficiency and scalability of the network. Moreover, the addressing information and the addressee condition may be based on different routing algorithms, as in above example on geographic and characteristic based routing. Therefore, different routing algorithms become compatible and advantages thereof can be combined.

In a preferred embodiment, the addressee condition relates to an open- addressing condition, by which not only nodes included in the multicast group of the addressing information are addressed, but also all nodes, which belong to one or more predefined multicast groups, whereof at least one node is included in the multicast group corresponding to the addressing information. In this case, an addressee condition as well as an addressing information may be included in the multicast data packet, wherein the addressing information corresponds to a predefined multicast group. Then, if a node included in the multicast group corresponding to the addressing information is also member of another preset multicast group, all nodes of this other predefined multicast group are also addressed as destination nodes. This may be in particular advantageous, if the addressing information is a geographical addressing information based on geographical routing. As an example, if the geographical addressing information defines a crossing and if luminaire nodes of a street are pre-grouped in a predefined multicast group, it is sufficient to include the addressing information of the crossing as well as the open-addressing identity in the multicast data packet, in order to address the luminaire nodes at the crossing as well as all luminaire nodes within streets leading to this crossing. However, side streets of these streets are not addressed. In other words, when addressing a multicast group by means of the addressing information and including an addressee condition related to open-addressing, nodes of the multicast group corresponding to the addressing information and nodes of all other multicast groups, which overlap with the multicast group corresponding to the addressing information, are addressed. Therefore, a precise addressing can be performed in a very efficient way. By these means, the payload of a single multicast data packet as well as the overall number of data packets can be reduced.

In a further embodiment, the addressee condition may relate to a filtering condition for selecting a sub-set of nodes within a predefined multicast group. This multicast group may relate to the multicast group defined by an addressing information included in the data packet. The filtering addressee condition may include a disclaimer for de-selecting nodes of the multicast group. This may be denoted as negative filtering or masking of nodes. In the terminology of logic, this filtering condition may be thought of as an "AND NOT" condition. Likewise, when considering the multicast group defined by the addressing information as a first set and nodes satisfying the filtering condition as a second set, the disclaimer may act as a set difference operator, e.g. all nodes of the first set without the nodes of the second set. Alternatively or additionally, the filtering condition may include an additional or compulsory condition. In this case, when an addressing information is also included in the multicast data packet, only those nodes of the multicast group defined by this addressing information are destination nodes, which also comply with the compulsory filtering condition. This may be denoted as positive filtering. In the terminology of logic, the additional compulsory condition can be referred to as an "AND" condition, or in the terminology of set theory, the compulsory condition may be considered as an intersection operator forming the intersection between sets. Alternatively or additionally, the addressee condition may include an optional condition. When an addressing information is included in the data packet defining a multicast group of nodes, all nodes belonging to this multicast group as well as all nodes complying with the optional condition are addressed as destination nodes. By these means, predefined or geographically defined multicast groups can be expanded, without the necessity of allocating a group address to this addressee group. In the terminology of logic, this optional condition may be referred to as an "OR" condition, or in terminology of set theory, as a union operator, combining several sets.

Furthermore, the control unit may be adapted to create a new multicast group based on node characteristics. As an example for creating a new multicast group, the control unit may cluster all nodes having the same software version or being in the same street in one multicast group. Possibly, the control unit is further adapted to allocate a group address or identity to the new multicast group. The group identity may be communicated to the nodes of the multicast group by transmitting at least one data packet containing the group identity and the node identities of the individual nodes belonging to this multicast group. In general, a group or node identity may also refer to a group or node address, respectively. Possibly, the control unit is adapted to generate a new multicast group by using map information in combination with geographical position information of nodes. Thus, individual nodes can be localized within a map and may then be grouped in one or more multicast groups based on their position. For instance, the map can be divided into a plurality of sectors, so that nodes included in one sector may be defined as one multicast group. Alternatively or additionally, context characteristics may be used, i.e. luminaire nodes of the same street or all luminaire nodes in the neighborhood of one or more hospitals may be clustered in multicast groups. Possibly, the control unit uses image analysis together with geographical position data of nodes in order to allocate nodes to one or more multicast groups. Here, the control unit may be able to recognize context characteristics of the individual nodes based on their relative positions from each other or from the arrangement of nodes. In the example of a street lighting system, nodes arranged along a straight line may thus be recognized as nodes being localized in the same street and so on. Moreover, third-party information may be available to the control unit when creating multicast groups, such as geographical positions of important buildings or places, e.g. hospitals, governmental buildings, airports, harbors and the like. By these means, multicast groups can be defined automatically based on geographical characteristics or context characteristics.

Preferably, the control unit may be adapted to create one or more compound multicast groups by combining at least one multicast group with at least one node or at least one other predefined multicast group or a combination thereof. Thus, a multicast group may be a simple multicast group or a compound multicast group. Preferably, a compound multicast group comprises nodes having same or similar communication or control requirements or characteristics. Possibly, the compound multicast group is only defined locally at the control unit, i.e. the control unit processes the nodes or elements of this compound multicast group as one multicast group, but when transmitting a multicast data packet, each element, e.g. predefined multicast group or node, is addressed individually. That is, in case of a compound multicast group consisting of a multicast group and one single node, a multicast data packet is transmitted to the multicast group and a unicast data packet is transmitted to the single node. Alternatively, a single data packet including the addressing information of both the multicast group and the single node is transmitted. The local definition of the compound multicast group is advantageous for compound multicast groups that will be used only rarely. Alternatively, the compound multicast group may be globally defined by generating a compound identity or compound address corresponding to the compound multicast group. This compound identity may be communicated to each node of the compound multicast group and stored at each node as a group identity. This may be useful, when establishing new frequently used multicast groups after a commissioning phase.

According to another aspect of the present invention, a node of a wireless network comprising a plurality of nodes is provided, wherein the node is adapted to recognize, whether it is addressed as a destination node of a received multicast data packet at least based on one or more addressee conditions included in the multicast data packet. In case that the node is addressed and thus belongs to the addressee group of the data packet, the node acts as a destination node of the multicast data packet. For instance, if the data packet comprises operation commands, the destination node is operated according to the commands included in the multicast data packet. In addition to the at least one addressee condition, the node may also consider at least one addressing information when determining whether it is a destination node. Hence, the node is adapted to determine whether it is part of an addressee group created by a control unit according to one of the above-described embodiments. In a preferred embodiment, the node is a sensor or actuator node of a sensor or actuator network, e.g. a luminaire node of a lighting system.

In a further aspect of the present invention, a system for addressing nodes in a wireless network is provided, the network comprising a plurality of nodes, wherein the system comprises at least one of a control unit and/or at least one node according to any embodiment described above. Preferably, the system is a sensor or actuator system, e.g. a lighting system. Therefore, in a preferred embodiment, at least some of the nodes and/or a collector node are associated with luminaire nodes of a lighting system. Furthermore, the system according of the present invention may be used in telemanagement of a lighting system, e.g. for switching on/off luminaire nodes, for controlling dimming patterns of luminaire nodes and/or for updating schedules or software of the luminaire nodes. Employing a system according to the present invention for telemanagement of a lighting system will result in a high-performance lighting system with high scalability.

According to another aspect of the present invention, a method for addressing nodes in a wireless network comprising a plurality of nodes is provided. In this method, an addressee group comprising a plurality of destination nodes can be created by including at least one addressee condition in a multicast data packet. By these means, the multicast data packet can be transmitted to an arbitrary addressee group, without including the single node addresses of the individual nodes in the data packet or setting-up a multicast group by allocating a corresponding group address to the individual nodes of the multicast group by means of unicast transmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures:

Figure 1 illustrates an example of a wireless mesh network;

Figure 2 schematically illustrates a multicast transmission; Figure 3 illustrates an example of creating new multicast groups based on node characteristics;

Figure 4 illustrates creating a compound multicast group;

Figure 5A illustrates data fields of a multicast data packet according to one embodiment the present invention;

Figure 5B illustrates possible ways of addressing the compound multicast group of Figure 4;

Figure 6A illustrates an addressee group of destination nodes being a subset of a multicast group;

Figure 6B illustrates possible ways of addressing the addressee group of

destination nodes of Figure 6A;

Figure 7A illustrates another possible addressee group of destination nodes according to the present invention;

Figure 7B illustrates possible ways of addressing the addressee group of

Figure 7A;

Figure 8A illustrates a further possible addressee group of destination nodes according to the present invention;

Figure 8B illustrates a possible way of addressing the addressee group of

Figure 8A;

Figure 8C illustrates possible ways of addressing the compound multicast group of Figure 4;

Figure 9A illustrates a further possible addressee group of destination nodes according to the present invention;

Figure 9B illustrates a possible way of addressing the addressee group of

Figure 9A; and

Figure 10A illustrates a further possible addressee group of destination nodes according to the present invention;

Figure 10B illustrates a possible way of addressing the addressee group of

Figure 10A.

DETAILED DESCRIPTION

Preferred applications of the present invention are actuator networks, sensor networks or lighting systems, such as outdoor lighting systems (e.g. for streets, parking and public areas) and indoor lighting systems for general area lighting (e.g. for malls, arenas, parking, stations, tunnels etc.). In the following, the present invention will be explained further using the example of an outdoor lighting system for street illumination, however, without being limited to this application. 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 with segments of above 200 luminaires.

In Figure 1, a typical network with mesh topology is shown. A plurality of nodes 10 (N) is connected one to another by wireless communication paths 40. Some of the nodes 10 function as 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 collector nodes 50 may operate in the manner of gateways between the nodes 10 and the control center 60. Optionally, the collector nodes might act as control center themselves. The wireless communication paths 40 between the nodes 10 and collector nodes 50 may be constituted by RF transmissions, while the connection 70 between the collector nodes 50 and the control center 60 may make use of the Internet, mobile communication networks, radio systems or other wired or wireless data transmission systems. Therefore, the nodes 10 and the collector nodes 50 comprise a transceiver for transmitting or receiving data packets via wireless communication paths 40, e.g. via RF transmission. Since RF transmissions do not require high transmission power and are easy to implement and deploy, costs for setting up and operating a network using the device can be reduced. This is especially important for large RF networks, e.g. a RF telemanagement network for lighting systems. However, the data packet transmission may alternatively use infrared communication, free-space-visible-light communication or powerline communication. In the following, data packet transmitted from a node 10 to the collector node 50 are referred to as uplink data packets, whereas data packets transmitted from the collector node 50 to one or more nodes 10 are denoted downlink data packets. Moreover, when a data packet is addressed to all nodes 10 of the network, this is referred to as broadcasting, whereas a data packet directed to a group of nodes 10 is called a multicast or groupcast data packet. A data packet directed to a single node 10 is denoted a unicast data packet.

In a telemanagement system for lighting control, the number of luminaire nodes 10 is extremely high. Hence, the size of the network is very large, especially when compared to common wireless mesh networks, which typically contain less than 200 nodes. In addition, the nodes 10 typically have limited processing capabilities due to cost

considerations, so that processing and memory resources in the luminaire nodes 10 will be limited. Thus, communication protocols for transmitting data packets between single nodes 10 should consider the limited resources for efficient and fast data packet transmission.

Furthermore, 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.

Nevertheless, it may be required to flexibly define addressee groups of destination nodes, e.g. due to changing requirements. In a lighting system, 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. If 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. Furthermore, telemanagement of an outdoor lighting system does not require a high data throughput. That means that a large part of the data traffic consists of time- uncritical data packets, e.g. status report data, statistical data, schedule updates or the like. Moreover, in a lighting system such as a street lighting system, communication is very asymmetric. Most of the traffic is generated by the luminaire nodes 10, e.g. reporting their status, their dimming profile, sensor values or power usage to the control center 60. The other traffic consists of control commands from the control center 60 to the different nodes 10, e.g. for adjusting a dimming pattern or switching on/off lamps. The traffic from the control center 60, or data collector 50, to the nodes 10 consists of 1 :N traffic, either in unicast, multicast or broadcast mode. Therefore, while it is worth to use efficient collector-oriented routing protocols for the uplink, downlink paths would be much more costly to create or maintain, since they are much less frequently used. Thus, downlink data packets are transmitted from the collector node 50 to one or more destination nodes B by flooding, as shown in Figure 2. In a flooding process, data packets are forwarded to all luminaire nodes 10 in the network

(arrows), but only the destination nodes B (shaded circles), whose node address is included in the flooded data packet, decode the data packet. This flooding approach can be applied to unicast, multicast or broadcast downlink data packets. Preferably, nodes 10 that often require the same data transmission are grouped as a multicast group Gi. Thus, data for the nodes 10 of this multicast group Gi is transmitted as a multicast data packet. Thus, a control center 60 or a collector node 50 can communicate with several nodes 10 of a multicast group Gi by means of a multicast transmission instead of addressing each node separately using unicast transmissions. When setting up a lighting system, a commissioning phase takes place before the system becomes functional. In one scenario, a commissioning person sets up every node 10 in the network on an individual basis, providing it with information such as its GPS- coordinates and with data such as a group identity of a multicast group Gi the node 10 is allocated to, a node identity, node address, street pole identity or street identity or the like. This can be achieved by means of a handheld device having either street layout information locally stored or retrieving this information via internet or the like by querying for the street corresponding to its current geographical location. In the simplest case, the commissioning person can also enter the street identity into the handheld device on the spot. By these means, also simple multicast groups Gi can be created by allocating a group address to the single nodes 10.

In order to create new multicast groups, the control center 60 or a collector node 50 can create multicast groups Gi using GPS position data of nodes 10 in combination with a city map or street map. By these means, the control center 60 or the collector node 50 can generate a deployment map representing the absolute positions of all luminaire nodes 10, e.g. within a city. Preferably, locations of buildings or structures of interest are also added in this map, for instance as metadata provided by a third party and considered for generating multicast groups Gi. An alternative way for setting up multicast groups by the control center 60 or collector node 50, which can expense with map information, is the usage of image analysis. For this, the control center 60 or the collector node 50 creates a deployment map using absolute or relative geographical positions of the nodes 10, thus identifying the position of the nodes 10 relative to each other. Then, streets, crossings, junctions, market squares, open areas and the like can be identified based on the layout of the deployment map using image analysis. After that, nodes 10 can be allocated to different multicast groups Gi based on their position relative to the identified structures.

Moreover, the control center 60 or the collector node 50 can create new multicast groups Gi based on a geographical position, context characteristics, network characteristics or other additional characteristics of a node 10 or a combination thereof. The geographical position of a node 10 can refer to an absolute geographical position defined by GPS data or to a relative geographical position defined by relative distances between the individual nodes 10 or based on a hop distance of a node 10 to the collector node 50.

Network characteristics are related to the function of a node 10 within the network, e.g. whether the node 10 is a collector node 50. Similarly, context characteristics include functional properties of a node 10, which are defined by the surroundings or context of the node 10, e.g. the street of the node 10, buildings or structures of interest in the neighborhood of the node 10, an operation status of the node 10, an alarm situation detected by the node 10 and the like. In contrast, the additional characteristics include all stationary hardware or software properties of the individual node 10, e.g. a luminance or light power of a lamp, a firmware version, a luminaire type, etc.

As illustrated in Figure 3, the control center 60 or the collector node 50 can for example specify that all nodes 10 within a certain distance to a hospital Hi belong to the same multicast group Gi. Here, the multicast group Gi is geographically defined, e.g. by specifying the geographical position of the hospital Hi and a radius within which all nodes 10 belong to the multicast group Gi. In general, such geographically defined multicast groups Gi have a very simple shape. Multicast groups G₂ and G₃ relate to preset multicast groups comprising nodes 10, which have been individually allocated to the multicast group, e.g. based on context characteristics or the like. Therefore, when including the group address of a multicast group Gi in a multicast data packet, all nodes 10 of the group are addressed as destination nodes 11.

As shown in Figure 4, the control center 60 or the collector node 50 can also generate a compound multicast group CG by combining a multicast group with another multicast group or with single nodes 10 or a combination thereof, e.g. based on node characteristics. Here, multicast groups Gi may be compound multicast groups CG

themselves. For instance, as shown in figure 4, all multicast groups Gi comprising nodes 10 in the neighborhood of hospitals Hi may be combined, thus creating a compound multicast group CG related to hospitals Hi. Therefore, instead of transmitting data packets to the simple multicast groups Gi, G₂ and G₃, the nodes 10 of the simple multicast groups Gi, G₂ and G₃ can be addressed together as destination nodes 11 of one multicast data packet addressed to the compound multicast group CG. This is in particular advantageous, if multicast groups Gi share the same node characteristics or control requirements and are regularly used. In one embodiment, the multicast groups Gi, G₂ and G₃ can be informed that they have been allocated to the compound multicast group CG via multicast transmissions to the individual multicast groups Gi, G₂ and G₃. Alternatively, the notion of the compound multicast group CG can remain localized at the control center 60 or collector node 50. In this case, the compound group CG is treated as one multicast group Gi within the control center 60 or collector node 50, e.g. when preparing controls, commands or updates or the like. However, when a data packet has to be transmitted to the compound group CG that is only locally defined, three multicast data packets are transmitted for Gi, G₂ and G₃, respectively. If the group addresses of the multicast groups Gi, G₂ and G₃ can be included in one data packet, it is possible to transmit only one multicast data packet comprising all group addresses of the multicast groups Gi, G₂ and G₃. Any node 10 belonging to at least one of these multicast groups Gi, G₂ and G₃ will act as destination node 1 1 and decodes the received data packet. By these means, creation of new multicast groups or new compound groups can be efficiently performed at a later stage, e.g. after a commissioning phase of the network.

After a multicast group Gi has been generated, a group address or identity ID(Gi) is stored together with node identities of the included nodes 10. Likewise, when creating a compound multicast group CG, the group identity ID(CG) and the identities of the included network elements are stored. Instead of identities, also corresponding addresses can be used, and vice versa. This information is stored at least locally at the control center 60, but preferably also at the included nodes 10. In the latter case, the nodes 10 of the multicast group Gi can be informed about their group assignment by transmitting either a unicast data packet including the respective node address and the group address of the created multicast group Gi or by flooding a multicast data packet including the group address together with all included node addresses. However, such a group setup should only be used for frequently used multicast groups Gi, since the data overhead required for the group setup is considerably large.

As mentioned above, nodes 10 having the same node characteristics often require data transmissions with the same control data or information data. However, they are not always pre-grouped in a multicast group Gi, which can be used for addressing them together for transmitting a single multicast data packet. Yet, creating new multicast groups Gi on demand drastically increases the network load, since the control center 60 or the collector node 50 has to inform the nodes 10 about a corresponding group address. Moreover, setting- up all possible multicast groups Gi would require a lot of time and network resources and would moreover result in a highly complex network, requiring large memories for group addresses at the individual nodes 10. In addition, also these newly created multicast groups Gi are then fixed or unchangeably defined. In order to save network resources, multicast data packets should be used, when the same data has to be provided to more than one node 10. Hence, means are required for more flexibly and more precisely addressing a multicast data packet.

In Figure 5A, an address format according to the present invention is shown. According to the present invention, data fields of a data packet related to addressing comprise an addressee condition field. The addressee condition is preferably related to node characteristics shared by at least some of the destination nodes 11 of the data packet. For instance, network characteristics may be used for defining the addressee group of destination nodes 11, these characteristics relating to the function or position of the respective node 10 within the wireless network, e.g. whether the node 10 is a collector node 50 or based on the hop distance between the node 10 and a collector node 50. The node characteristics can also relate to the geographical position of the respective node 10, e.g. determined by GPS data or arbitrarily defined coordinates x and y. Furthermore, context characteristics of a node may be used, which relate to a status of the node 10 or to its surroundings, e.g. a street of the luminaire node 10, buildings or places of interest in the neighborhood of the node 10, an operation status of the luminaire node 10, sensor data or alarm situation detected by the luminaire node 10 and the like. Moreover, additional characteristics of a node 10 can be used for addressing related to fixed properties of the node 10, such as an average power consumption, a fabrication type, a lamp type, a software version or driver capabilities etc. Therefore, by including an addressee condition in a data packet, a plurality of nodes 10 can be addressed based on one or more node characteristics they have in common.

Preferably, the data packet further includes an addressing information field. In the addressing information field, identities or addresses of a predefined network element can be included, such as the identity of a multicast group Gi or of a single node 10. Alternatively or additionally to predefined identities or addresses, also geographical addressing information can be included in the addressing information field. For instance, a geographical destination area may be defined by including position data such as GPS data of a hospital Hi specified as a center of a circular area and a radius Ri, so that all nodes 10 within a circle with radius Ri around the hospital Hi are addressed. An example of this geographical addressing has been described for hospital Hi of Figure 4. Thus, the multicast group Gi can be either addressed using geographical addressing information or using a group identity ID(Gi) of the predefined multicast group. Of course, geographical addressing is not limited to circular areas, but can also define rectangular areas or other areas having a simple geometric shape. In case of a rectangular area, intervals of coordinates x and y defining a geographical position can be specified in the addressing information field, e.g. 10 < x < 15 and 300 < y < 510 in arbitrary units. If the field of addressing information is empty, the data packet is a broadcast data packet directed to all nodes 10 of the network. Thus, it is not required to include addressing information in the data packet.

In Figure 5B, two possibilities for addressing the compound group CG shown in Figure 4 are illustrated. As shown in the upper part of Figure 5B, the compound multicast group CG can be addressed using a given group identity ID(CG). However, for this, the compound multicast group CG has to be either preset involving the distribution of the group identity to the associated nodes 10 or the compound multicast group CG is only set up locally at the control center 60 or collector node 50, thus often requiring separate transmissions to the included preset multicast groups Gi, G₂ and G₃. According to the present invention, the compound group CG can also be addressed as shown in the lower part of Figure 5B, e.g. using an addressee condition. In this example, the addressee condition corresponds to the context information {related to a hospital Hi}, identifying all nodes 10 being related to a hospital Hi as destination nodes 11. The context information, i.e. that a node 10 is related to a hospital Hi may be stored locally at the respective nodes 10. In this example, the compound group CG can thus also be addressed by including only an addressee condition in the multicast data packet without any addressing information. Therefore, the addressee condition may be used alone for addressing a multicast data packet.

In Figures 6 to 10, further examples for addressee conditions are shown. In Figure 6A, only some nodes of a preset multicast group Gi should be addressed as destination nodes 11. This can be achieved by including a filtering addressee condition for selecting a subset of destination nodes 11 from the nodes 10 of the multicast group Gi. This filtering condition can be either a negative condition for de-selecting or masking nodes 10 of the multicast group Gi, as shown in the upper part of Figure 6B, or a positive condition, representing an additional compulsory condition for specifying selected destination nodes 11 , as shown in the lower part of Figure 6B. By these means, a subset of destination nodes 11 can be filtered from a predefined multicast group Gi identified in the addressing information field, thus providing the possibility to modify predefined multicast groups Gi.

In Figure 7, another example for modifying a preexisting multicast group Gi based on geographical selection criteria is shown. Here, the addressee group of destination nodes 11 can be selected by addressing the predefined multicast group Gi in the addressing information field and by postulating that the position coordinate x of a node 10 must not be lower than 10. This is a further example for a compulsory addressee condition. Alternatively, the compulsory filtering condition can require that a destination node 11 must have a position coordinate x larger than 10. This negative filtering condition can also be considered as a condition for deselecting some of the nodes 10 addressed in the addressing information field.

While Figures 6 and 7 illustrate the addressing of a subset of nodes 10 of a predefined multicast group Gi, it can also be required to expand a preexisting multicast group Gi by one or more nodes 10. For this, an optional or alternative addressee condition can be included in the data packet. As shown in Figure 8A, the destination nodes 1 1 belong either to the predefined multicast group Gi or are allocated along a road R to the hospital Hi . As shown in Figure 8B, these destination nodes 1 1 can be addressed by including the group identity ID(Gi) together with the optional addressee condition referring to the position at the road R. Likewise, using again the example of the compound multicast group CG of Figure 4, this compound multicast group CG can also be addressed by including the group identifiers ID(G₂) and ID(G₃) of the preset multicast groups G₂ or G₃ as addressing information and a geographical addressing as an addressee condition, as shown in Figure 8C. Here, all nodes 10 are destination nodes 1 1 of the data packet, which are either part of the preset multicast groups G₂ or G₃ or whose node position r; is located within a radius Ri from the position of the hospital Hi . Therefore, by means of such an addressee condition also denoted alternative or optional condition, existing multicast groups can be expanded for nodes 10 with a certain node characteristic.

Sometimes, a preset multicast group Gl has to be addressed together with other preset multicast groups Gi, which are at least partially overlapping with the multicast group Gl . For instance, if Gl corresponds to a group of luminaire nodes 10 surrounding a hospital HI , it may be required to control the luminaire nodes surrounding the hospital HI as well as all luminaire nodes 10 located at streets leading to the hospital HI . If the luminaire nodes 10 of the streets are approved in predefined multicast groups G2 and G4 (see Figure 9A), open addressing may be used instead of including the group identities of the single multicast groups ID (Gl), ID (G2) and ID (G4). As shown in the second example of Figure 9B, in this case only the central multicast group Gl has to be explicitly addressed, whereas when including the open addressing identity in the addressee condition field, also all nodes 1 1 are addressed, which belong to a multicast group, which has at least one node included in the addressed multicast group Gl . The open addressing may also be combined with further addressee conditions selecting from the multicast groups concerned by the open addressing nodes having certain node characteristics. In one example, open addressing can be performed as follows. If an open addressing identity is included in addition to addressing information such as a group identity or geographical addressing information, in the data packet, destination nodes 1 1 corresponding to the addressing information can forward the data packet further, while appending the group identity or group address of the multicast group the destination node 1 1 belongs to. Any node 10, which receives the data packet, but does not belong to the addressee group specified by the addressing information, will behave as a destination node 11 , if it has the same group identity as one of those added in the data packet. Such a node 11 , which is not addressed by the addressing information, but has a group identity corresponding to a newly added identity, may forward the data packet further, but without including other group identities.

This principle is further illustrated in Figure 10, using geographical addressing. Here, multicast group Gl is defined by geographical addressing information, e.g. by specifying GPS data of a center of a circle and the radius of the circle. In this case, all nodes 10 within the circle belong to the multicast group Gl . However, alternatively, a rectangular area may be specified by including intervals for position coordinates. As mentioned before, the position coordinates can be either GPS based or arbitrarily defined within the network. When using geographical addressing, a geographical area having in general a very simple geometric shape is specified. Thus, due to such a rudimentary specification of the addressee group, some nodes 10 may be unintentionally left out. For instance, nodes 10 having the same context characteristics, e.g. are located in the same street, should also be addressed although they do not fall within the specified geographical area. In other words, when including addressing information, either geographical based or group identity based, for addressing a multicast group Gl as well as an open addressing identity in the data packet, the multicast group Gl specified by the addressing information and all multicast groups Gi overlapping at least partially with the specified multicast group Gl will be addressed.

In the example of Figure 10A, a node A included in the multicast group Gl, which corresponds to the addressing information, also belongs to a second multicast group G2. If node A receives a data packet including addressing information corresponding to the multicast group Gl and an open addressing identity, node A will include group identities of all other predefined multicast groups G2 it belongs to in the data packet and forward the data packet. If a node 10 of multicast group G2 receives this modified data packet, it will act as a destination node 11 , although it does not correspond to the original addressing of the data packet. This node B may forward the data packet further, but without including new group identities.

It should be noted that in the whole description, a multicast group Gi may relate to a simple multicast group consisting of individual nodes 10 or to a compound multicast group CG, which can include individual nodes 10, simple multicast groups, other compound multicast groups or a combination thereof. The multicast group Gi can be either predefined having a group identity or group address known to all nodes 10 belonging to the multicast group Gi or it may be geographically addressed by specifying a certain geographic area. Both, the geographical based and identity based addressing is included as addressing information in the corresponding data field of the data packet. However, these modes of addressing only allow for a very coarse addressing. In order to address a plurality of nodes 10 belonging to different multicast groups Gi or to no multicast group at all, extensive addressing information has to be included in the data packet, leading to a large data overhead. This is resolved according to the present invention by including an addressee condition in the data packet, by which nodes 10 sharing at least one specified node characteristic can be selected as destination nodes 11 or by which a multicast group Gi can be modified. By these means, a very fine-grained addressing can be performed, without increasing the network load or requiring time-consuming definitions of multicast groups. This is in particular useful for addressee groups of destination nodes 11 , which are not repeatedly used or which are very large.

Claims

CLAIMS:

1. A control unit for a wireless network, the network comprising a plurality of nodes (10), wherein the control unit is adapted to create an addressee group of a plurality of destination nodes (11) by including at least one addressee condition in a multicast data packet for transmission of the multicast data packet.

2. A control unit according to claim 1, wherein the control unit is further adapted to include in the multicast data packet at least one addressing information corresponding to a multicast group (Gi) in addition to the at least one addressee condition.

3. The control unit according to claim 2, wherein the addressing information includes at least one group address (ID(Gi)) of the multicast group (Gi) and/or at least one geographical addressing information defining the multicast group (Gi) as a group of nodes (10) within a specified geographical area.

4. The control unit according to claim 2 or 3, wherein the addressee condition includes an open-addressing identity for addressing one or more nodes (10) that belong to a multicast group (Gi) comprising at least one node (10), which is also included in the multicast group (Gi) corresponding to the addressing information.

5. The control unit according to any of claims 2-4, wherein the addressing information and the addressee condition are based on different routing algorithms.

6. The control unit according to any of claims 2-5, wherein the addressee condition includes a filtering condition for filtering one or more destination nodes (11) out of the multicast group (Gi) corresponding to the addressing information.

7. The control unit according to claim 6, wherein the filtering condition is a disclaimer for excluding at least one node (10) of the multicast group (Gi) corresponding to the addressing information from being addressed and/or wherein the filtering condition is an compulsory condition that has to be satisfied by a node (10) of the multicast group (Gi) corresponding to the addressing information for being addressed.

8. The control unit according to any of claims 2-7, wherein the addressee condition includes an optional condition for expanding the multicast group (Gi)

corresponding to the addressing information by nodes (10) complying with the optional condition.

9. The control unit according to any of the preceding claims, wherein the addressee condition is related to node characteristics including at least one of network characteristics, a geographical position, context characteristics and additional characteristics of a node (10).

10. The control unit according to any of the preceding claims, wherein the control unit is further adapted to create a multicast group (Gi) based on geographical position data of nodes (10) and at least one of map information and image analysis.

11. The control unit according to any of the preceding claims, wherein the control unit is further adapted to create a compound multicast group (CG) by combining at least one multicast group (Gi) with at least one node (10) and/or at least one other multicast group (Gi) based on node characteristics of the included nodes (10).

12. The control unit according to any of the preceding claims, wherein the control unit is included in a luminaire node (10), a collector node (50) or a control center (60) of a lighting system.

13. A node of a wireless network comprising a plurality of nodes (10), wherein the node (10) is adapted to determine at least based on one or more addressee conditions included in a received multicast data packet, whether it belongs to an addressee group of destination nodes (11) of the received multicast data packet.

14. The node according to claim 13, wherein the node is a luminaire node (10) of a lighting system.

15. A method for addressing nodes (10) in a wireless network comprising a plurality of nodes (10), the method comprising the steps of:

creating an addressee group of a multicast data packet by including at least one addressee condition in the multicast data packet, the addressee group comprising a plurality of destination nodes (11); and

transmitting the multicast data packet to the addressee group.