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WO2012009849A1 - Système de routage destiné à des réseaux de capteurs sans fil - Google Patents

Système de routage destiné à des réseaux de capteurs sans fil Download PDF

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Publication number
WO2012009849A1
WO2012009849A1 PCT/CN2010/075286 CN2010075286W WO2012009849A1 WO 2012009849 A1 WO2012009849 A1 WO 2012009849A1 CN 2010075286 W CN2010075286 W CN 2010075286W WO 2012009849 A1 WO2012009849 A1 WO 2012009849A1
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WIPO (PCT)
Prior art keywords
data processing
processing apparatus
path
source
message
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PCT/CN2010/075286
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English (en)
Inventor
Canfeng Chen
Jian Ma
Chengcheng Long
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Nokia Inc
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Nokia Inc
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Priority to PCT/CN2010/075286 priority Critical patent/WO2012009849A1/fr
Publication of WO2012009849A1 publication Critical patent/WO2012009849A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/023—Limited or focused flooding to selected areas of a network
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
    • H04W40/20—Communication route or path selection, e.g. power-based or shortest path routing based on geographic position or location
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W40/00—Communication routing or communication path finding
    • H04W40/24—Connectivity information management, e.g. connectivity discovery or connectivity update
    • H04W40/28—Connectivity information management, e.g. connectivity discovery or connectivity update for reactive routing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W84/00—Network topologies
    • H04W84/18—Self-organising networks, e.g. ad-hoc networks or sensor networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

Definitions

  • the present invention relates to the field of communication, and more particularly to a routing scheme for networks, especially for wireless sensor networks.
  • Wireless sensor networks have attracted intensive attention in recent years due to their wide variety of potential applications.
  • a sensor network always consists of spatially distributed autonomous sensor nodes and sink nodes, to cooperatively monitor physical or environmental conditions (such as temperature, sound, vibration, pressure and pollutants), and capture events of interest (such as object tracking, event monitoring).
  • MEMS Micro Electro-Mechanical Systems
  • multifunctional senor nodes such as image sensor, audio sensor, and video sensor or the like, reflect and describe the physical phenomenon.
  • An example is the SenseCam made by Microsoft, which can provide the information which cannot be easily described by simple sensor node.
  • streaming data to represent a sequence/number of data packets waiting for transmission in a sensor node. It is believed that streaming data transmission will be a very common situation for wireless sensor networks, such as for audio, image, and video sensor nodes, which can dramatically enhance the event description in wireless sensor networks. Another situation is that a bunch of buffered sensor data which are collected for a certain time period waiting for transmission. As sensor data usually needs to be disseminated from the source sensors to sink nodes, thus data dissemination is one of the fundamental problems in WSNs. In addition, as these sensors usually operate on limited non-rechargeable battery power and are expected to last over several months or years, energy efficiency becomes one of the most critical design issues for WSNs.
  • the existing solutions on data dissemination in WSNs with mobile sink can be classified into four categories based on how to disseminate data to sinks: (1 ) flooding or hierarchical flooding approach; (2) position estimation based on geographic routing approach; (3) controlled sink mobility approach; and (4) opportunistic forwarding approach.
  • Directed Diffusion is also a flooding based approach.
  • the sink floods interests for desired data.
  • Some nodes sense the data matching the interests, they send the data back to the sink with a low data reporting rate along the reverse paths of cached interests.
  • the major problem in the flooding approach is that it costs too much energy.
  • hierarchical structure for data dissemination was proposed, wherein flooding only occurs among backbone/partial nodes, such as Two-Tier Data Dissemination (TTDD), Scalable Energy-efficient Asynchronous Dissemination (SEAD), Hierarchical Cluster-based Data Dissemination (HCDD), etc.
  • TTDD Two-Tier Data Dissemination
  • SEAD Scalable Energy-efficient Asynchronous Dissemination
  • HCDD Hierarchical Cluster-based Data Dissemination
  • the problem for the hierarchical flooding approach is the poor scalability.
  • a more efficient approach to find the paths between data sources and mobile sinks is the position estimation approach, such as Query Based Data Collection (QBDCS).
  • QBDCS Query Based Data Collection
  • the motion trajectory of mobile sinks can be predictable in a short period, e.g., a vehicle moves along the road and the digital map is available, the prediction of its future mobility becomes possible.
  • Another assumption is that all nodes know their location information and where the destination is.
  • the source node since it knows the mobility information of the mobile sink, it can estimate the mobile sink's instantaneous position; hence it can disseminate data to the mobile sink using geographic routing protocol.
  • the position estimation approach relies on the sensor's location information. However, the location and mobility information may not be always available in many practical situations, because it is heavily power-consumed to equip expensive GPS devices in the cheap sensor nodes.
  • Another alternative solution is the opportunistic forwarding, where the collected data is often delay tolerant, i.e., its delivery to the sinks is not time critical, e.g., Data Mobile Ubiquitous LAN Extensions (MULEs) and Transmission Scheduling Algorithm for wireless Sensor Networks with Mobile Sinks (TSA-MSSN).
  • MULEs Data Mobile Ubiquitous LAN Extensions
  • TSA-MSSN Transmission Scheduling Algorithm for wireless Sensor Networks with Mobile Sinks
  • the basic strategy only allows data delivery when sensors are in direct proximity of the mobile sink and this technique has very little communication overhead.
  • the disadvantage is obvious, i.e., it may experience very long delivery delay, a few hours or even days.
  • This invention designs an efficient routing solution for networks, especially for WSNs. Using such routing solution, a lightweight scheme for disseminating streaming data to a mobile sink is obtained, without the knowledge of any node's or sink's location information and avoid the high cost of global flooding of sink's mobility information throughout the network at the same time.
  • the invention aims to find a path with which a bunch of data packets can be disseminated to a data processing apparatus.
  • the following routing method, apparatus and corresponding computer programs are proposed to solve or at least alleviate at least one of the existing problems.
  • a method comprising: flooding a message within limited hops to discover at least one data processing apparatus of a network;
  • the related routing information maintained by an intermediate apparatus is recent.
  • the method can further comprising:
  • said selecting can be made on the basis of at least one of the following: distance, the cost of energy, the cost of time, security, confidence, the processing and forwarding ability/speed, application-specific preferences/characteristics, whether the maintained routing information is recent.
  • an end-to-end path can be built to the discovered data processing apparatus, then data, preferably streaming data can be transmitted to the discovered or selected preferred data processing apparatus.
  • the request is further forwarded by the intermediate apparatus to a data processing apparatus on the basis of its routing information or the combination of its routing information and the moving trajectory of the data processing apparatus.
  • the network is a wireless network or a wireless sensor network
  • the data processing apparatus is a mobile sink or a static sink.
  • the mobile sink is discovered by the intermediate apparatus based on routing information or routing information in combination with moving trajectory of the mobile sink maintained by the intermediate apparatuses; if the data processing apparatus is a static sink, the mobile sink is discovered based on routing information maintained by the intermediate apparatus directly.
  • a discovered data processing apparatus can rebuild a path (to the source flooding the message) through geographic greedy forwarding based on location information.
  • an apparatus comprising
  • At least one memory including computer program code
  • the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to perform at least following:
  • a method comprising: receiving a message for discovering a data processing apparatus flooded within limited hops of a network;
  • a request for discovering a data processing apparatus is feedback, addressing to at least one data processing apparatus with maintained routing information.
  • a path from a source sending the message to the discovered data processing apparatus can be built, and data can be transmitted to the data processing apparatus.
  • the network is a wireless sensor network
  • the data processing apparatus is a mobile sink or a static sink; and/or if the data processing apparatus is a mobile sink, it is discovered based on maintained routing information or routing information in combination with its moving trajectory; and/or if the data processing apparatus is a static sink, it is discovered based on maintained routing information directly.
  • said addressing comprising forwarding the feedback request from the intermediate apparatus to a data processing apparatus.
  • an apparatus comprising
  • At least one memory including computer program code
  • the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least following:
  • a request for discovering a data processing apparatus is feedback, address to at least one data processing apparatus with maintained routing information.
  • a method comprising determining whether to rebuild a path to a source
  • the message is further transmitted to the source by an intermediate apparatus with its maintained routing information.
  • the intermediate apparatus locates within a limited flooding range of the source in which a message for discovering a data processing apparatus has been flooded.
  • the determination can be made based on the required probability of rebuilding a path, or a path shorter than the current path connecting the source to the data processing apparatus, and/or an energy cost analysis.
  • a path can be built if the flooding hop-count is no less than the difference of hop-count of the current path and the flooding hop-count of the source, or if there is an apparatus locate within the limited flooding range of the source and limited flooding range of the data processing apparatus.
  • the probability of rebuilding a shorter path can be estimated on the trajectory of the current path, or angles of segments of the current path together with location information.
  • the energy cost analysis comprising the energy cost for building a shorter path and/or the energy saving brought out by the shorter path.
  • the energy cost and energy saving can be estimated from the one or more of the following factors maintained by a data processing apparatus or derived/estimated from its maintained routing information with experiences: node density, flooding area, the number of nodes within the flooding rage, the number of paths that the message will be transmitted to the source, the hop-count from the intermediate apparatus to the source, the amount of data to be transmitted from the source to the data processing apparatus, the reduced hop-count by the shorter path comparing with the current path.
  • a method of numerical integration can be used to reduce the computation complexity.
  • duplicate transmissions can be avoided; and/or an intermediate apparatus overhearing the flooded message can update its related routing information; and/or the message is transmitted unicastly.
  • the flooding of the data processing apparatus can be approximately a circular or fan-shaped region.
  • an apparatus comprising
  • At least one memory including computer program code
  • the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to perform at least following:
  • apparatuses comprising respective means for implementing the steps of the above methods or apparatus are proposed.
  • the location knowledge of any sensor node or the mobile sink is released, this is especially useful for a mobile sinks as they usually move randomly and unpredictably.
  • the advantages brought out by the invention are obvious as the invention applicable for general and practical application scenarios, where the accurate location information is unavailable. However, it should be noted that this doesn't mean the invention exclude such utilization of location information whenever these location information are available. For example, as more and more mobile devises are equipped with GPS receivers, thus when the mobile sink's location is available, another advantage is that after the Route Rediscovery with chasing mode, a rough estimation on the location of the source can be obtained.
  • existing mobile objects such as mobile handsets, laptops and vehicles
  • mobile objects can initiate a reroute procedure for building a shorter path.
  • software for implementing the preferred solution can be embodied in the existing mobile objects. With this preferred reroute solution, an efficient path can be built, and lower communication overhead can be achieved.
  • the proposed scheme allows a source to select a preferred apparatus for further processing or forwarding its data if multiple apparatuses are available, and also allows a longer distance routing path connecting the source to an discovered apparatus to be redirected to a shorter distance routing path in an energy efficient manner.
  • Fig.1 is a flowchart performed at a source node according to one exemplary embodiment of the present invention
  • Fig.2 shows a simplest circumstance in which a source discovers a mobile sink directly in the flooding process according to one exemplary embodiment of the present invention
  • Fig.3 is a flowchart performed at an intermediate node according to one exemplary embodiment of the present invention.
  • Fig.4 and 7 shows a flowchart according to one preferred exemplary embodiment of the present invention
  • Fig. 5 shows a network environment and the moving trajectory of a mobile sink according to one exemplary embodiment of the present invention
  • Fig.6 is a flowchart performed at a mobile sink according to one exemplary embodiment of the present invention.
  • Fig. 8 illustrates the route rediscovery mechanism according to one preferred exemplary embodiment of the present invention
  • Figs. 9 and 10 illustrate an exemplary algorithm for determining whether to perform the reroute procedure from the energy point of view according to one preferred exemplary embodiment of the present invention
  • Figs. 11 and 12 show how to avoid the transmissions of duplicate messages according to one preferred exemplary embodiment of the present invention
  • Figs. 13a-c illustrate simplified function block diagram of apparatus capable of embodied in a source, an intermediate node and a mobile sink respectively according to one exemplary embodiment of the present invention.
  • a wireless sensor network consists of a number of static sensor nodes and one or multiple mobile sinks, wherein each sensor node has a fixed level of transmission power and has the same transmission range. A packet will be received successfully if the received signal power is greater than the receiving power threshold. Nodes (including both sinks and sensor nodes) have limited transmission range and multihop paths are in general needed for data dissemination among nodes, such as from sensors to the sink.
  • a routing solution will be described in detail in reference to the figures. With such routing solution, a path, preferably an efficient path will be found between a sensor node and a mobile sink on which a data processing apparatus is embodied. Therefore, a lightweight streaming data dissemination scheme for wireless sensor networks with mobile sinks is achieved.
  • the mobile sinks being studied here refers to all existing mobile objects, so long as they can be equipped/enhanced with wireless communication interfaces to communicate with ambient wireless sensor networks, such as mobile handsets, PDA, portable PC, cellular handset, internet tablet, user mobile terminal, laptops, vehicles or the like.
  • a mobile sink can move randomly and unpredictably. Since the mobile sink operates on a rechargeable battery and has much higher computation and communication capabilities than sensor nodes, it is reasonable that we assume the mobile sink sends out a message/frame announcing the presence of a mobile sink periodically as it moves.
  • the existing mobile objects are already required to do so in some environments.
  • beacon frames are used to announce the presence of a Wi-Fi network (as a result, an 802.11 client receives the beacons sent from all nearby APs, even when it is not connected to any network).
  • Other examples are HELLO message, beacon or heartbeat message. We refer to the message periodically sent from a mobile sink to announce its presence as the Hello message hereafter.
  • the source node when a sensor has a bunch of data packets to send, if there is no recent route toward a sink in its routing table, the source node can utilize the routing method illustrated in Fig. 1 to find at least one mobile sink.
  • a sensor node When a sensor node has streaming data to send (refer to as the source node), e.g., it detects a physical event of interest or the buffered data exceeds a certain amount, and if it finds there is no recent route to a sink in its routing table, at step 101 , it will flood a message (sometimes we call it RouteDiscovery message hereinafter) within K hops to search any available sink nearby.
  • a localized flooding (controlled within K hops) is adopted.
  • K can be a predefined constant or a variant.
  • K should be a small value compared with the network diameter.
  • selection of an appropriate K value depends on the particular environment, such as density and mobility characteristics of the mobile data collectors, thus different regions may have difference K values. If it is found not suitable anymore, such as a source node fails to receive responses (or enough responses) in step 102 (which will be explained below), K value can be increased without exceeding its upper bound (if any).
  • the source node receives one or more replies.
  • the source node can find one or more mobile sinks. If more than one mobile sinks are found, the source node can select a preferred one.
  • the source node can also select more than one sinks. For example, if an application has the reliability or delivery latency constraint, the source sensor may send data to multiple sinks along multiple paths in a parallel manner to improve the reliability or delivery latency.
  • Such selection can be made upon taking into account at least one of the following factors: cost of energy; the distance between the source and the discovered mobile sink; cost of time; the processing and forwarding ability/speed of the mobile sink; the security and/or confidence degree of the mobile sink; other application-specific preferences, or the like.
  • cost of energy the distance between the source and the discovered mobile sink
  • cost of time the processing and forwarding ability/speed of the mobile sink
  • security and/or confidence degree of the mobile sink other application-specific preferences, or the like.
  • this is an ideal and also the simplest case, i.e., there is at least one mobile sink located within K hops range of the source node.
  • RouteDiscovery message the control message sent by source sensor node is named as RouteDiscovery message.
  • the source sensor node after receiving RouteReply sent by the mobile sink, the source sensor node can send data to it.
  • the source sensor node transmits a request (this request is named as SinkRequest in the following description) to at least one intermediate node to find a mobile sink.
  • this request is named as SinkRequest in the following description
  • the source sensor node exploits the nearby existing recent route information (i.e., routing information maintained by the selected intermediate node) to discover a mobile sink. Then an end-to-end route from the source to a mobile sink can be built.
  • the criterions for making a selection including selecting a preferred intermediate node by the source sensor node, and selecting a preferred mobile sink by an intermediate node, are similar with the selection of mobile sinks by the source sensor node. Such as the most recent and nearest intermediate node is selected.
  • Fig. 3 shows the flowchart implemented on an intermediate node according to an exemplary embodiment of the invention.
  • an intermediate node receives a message from a source sensor node.
  • the message may be the aforementioned RouteDiscovery.
  • this intermediate node knows some existing recent route to a mobile sink according to its routing table, in other words, if it maintains routing information regarding to a mobile sink, it transmit a reply back to the source sensor node.
  • the reply may be the aforementioned RouteReply.
  • a message (such as the aforementioned SinkRequest) sent from the source sensor node is received (in the case that there is no sink nearby and the source node selects one existing recent route to an intermediate node who returns a RouteReply message back, and sends a SinkRequest message, in order to reach the mobile sink)
  • the intermediate node (who replies a RouteReply to the source) utilizes the routing information it maintained to address at least one mobile sink.
  • an end-to-end path can be built.
  • Fig. 4 shows how the mobile sink is discovered by an intermediate node in detail.
  • an intermediate node with the knowledge of an existing recent route to a mobile sink receives the SinkRequest message, it forwards this message along its pre-known existing route to the mobile sink.
  • the sensor node nearest to the mobile sink along this existing route as the access node.
  • the SinkRequest arrives at the access node, there are two cases: 1 ) the mobile sink is still in its radio range; 2) Due to the random mobility of a sink, it may move out of the access node's radio range. Note this is possible because that the existing route is not so fresh.
  • the SinkRequest will be forwarded along the mobile sink's moving trajectory until reaching that mobile sink, which we call chasing mode (in which the SinkRequest message chases the mobile sink along its moving trajectory). Then when the mobile sink receives such SinkRequest message, it makes a decision whether to initiate a route rediscovery process (which will be explained with reference to Fig. 6 later) to rebuild a path. In this example, it does not perform this process. Thus, it replies a SinkReply message to the source node. Upon the received SinkReply message, the source sensor node can send data to the mobile sink along the discovered end-to-end path.
  • the moving trajectory can be obtained easily and the specific method for getting such information depending on the particular network environment. For example, obtain such information from other nodes along the moving trajectory, or from a central device serving as a server or the like.
  • the SinkRequest message will be cooperatively forwarded by qualified neighbours toward the moving direction of the mobile sink.
  • the qualified neighbours are defined as the nodes that have fresher HELLO message timestamp than the current forwarding node's (the last hop node) or at least the same HELLO message timestamp with the current forwarding node (depends on the HELLO message broadcasting cycle). It is a contention-based forwarding process, that is, each qualified neighbour who correctly receives this SinkRequest will start timer to contend to be the next-hop forwarder. The timer's value depends on the selected criteria.
  • the selected criteria is that the fresher the HELLO message timestamp is, the higher priority it should be assigned to take the forwarding task, hence the shorter the timer will be.
  • the neighbor whose timer first expires wins the competition to be the downstream next-hop node. Then when the timer expires, the neighbor will broadcast the received SinkRequest until a mobile sink is addressed to, do like the current-hop node.
  • the timer value can be calculated according to different metrics.
  • One common contention policy is that the fresher the HELLO message timestamp is; the higher priority it should be assigned to take the forwarding task, hence the shorter the timer will be.
  • Fig. 5 gives a more intuitionistic view of the aforementioned Route Discovery and Chasing process.
  • the source node S has data to send, it first checks whether there is a recent route to a sink. If not, it will flood a RouteDiscovery to search any available sink nearby within K hops. There is no available sink within K hops.
  • an intermediate node A knows an existing recent route to a mobile sink according to its routing table; thus, A replies a RouteReply to S. Then S unicasts a SinkRequest to A, and node A forwards this SinkRequest along the existing route to reach that sink.
  • the mobile sink Because the route to a mobile sink is recent but not freshly discovered, when this SinkRequest arrives at node B (access node), the mobile sink has moved out of B's radio range. In this case, the SinkRequest is forwarded along the mobile sink's moving trajectory until reaching the sink.
  • the mobile sink receives the SinkRequest, according to its own judgment, it may return a SinkReply message along the reverse path to the source node, or it initiate a Route Rediscovery procedure, which will be described in the subsequent portion of this description.
  • This Route Rediscovery procedure allows a longer distance routing path connecting the source node to a mobile sink to be redirected to a shorter distance routing path in an energy efficient manner.
  • the Route Rediscovery is composed of two phases: 1 ) flooding a message (such as a RouteRediscovery message shown in Fig. 7) from the mobile sink within limited hops (the hop-count of this flooding operation is denoted as L); 2) the nodes who have a route to the source will forward the flooded message to the source (such as the nodes who have received the RouteDiscovery message in the previous Route Discovery phase will transmit, preferably unicast this RouteRediscovery along their reverse pathes to the source node).
  • 1 flooding a message (such as a RouteRediscovery message shown in Fig. 7) from the mobile sink within limited hops (the hop-count of this flooding operation is denoted as L); 2) the nodes who have a route to the source will forward the flooded message to the source (such as the nodes who have received the RouteDiscovery message in the previous Route Discovery phase will transmit, preferably unicast this RouteRediscovery along their reverse pathes to the source node).
  • Fig. 6 shows the route rediscovery process implemented by a mobile sink.
  • a discovered mobile sink can make a decision to determine whether to rebuild a path to a source. If it determines to rebuilt a path, at step 602, it floods a message (such as RouteRediscovery message shown in Fig. 7) within limited hops of a network.
  • a message such as RouteRediscovery message shown in Fig. 7
  • the nodes who maintain related routing information to the source will transmit the received RouteRediscovery message to the source.
  • Such nodes can be the nodes who have received the RouteDiscovery message in the previous (in other words, nodes locate within the flooding range of the source sensor node), those nodes will unicast the flooded message to the source.
  • a mobile sink will determine to rebuild a path to a source, if it founds the probability of rebuilding a path, preferably a path shorter than the current path connecting the source to this mobile sink is very high, or its estimated probability is higher than a required value/threshold.
  • a mobile sink can estimate the probability of rebuilding such (shorter) path by its experiences and/or its maintained routing information. For example, if the flooding hop-count is no less than the difference of hop-count of the current path and the flooding hop-count of the source (which will be explained with reference to Figs.
  • At least a path can be built. Or the probability can be estimated on the trajectory of the current path, or analysis of angles of segments of the current path (preferably with location information).
  • some location information may be necessary obtained for example, by using directional antennas or other existing methods.
  • the source node may have stronger capability (i.e., knows its location) than other neighboring nodes, the source will take charge of the local data collection and aggregation/fusion and send the aggregated data to a mobile sink. That is to say, the source node, access node and the mobile sink know their locations.
  • the invention doesn't exclude such utilization of location information. This is because some location information may facilitate a mobile sink to get angles between segments of a path.
  • the current path into several segments, such as the path connecting the source node and the intermediate node (denoted as HCi in Figs.7, 9, 10), the path connecting the access node (if any) and the mobile sink (denoted as HC 3 in Figs.7, 9, 10), and the path connecting the intermediate node and the mobile sink (denoted as HC 2 in Fig. 9), we can consider the angles between those segments (with obtained location information), and the smaller those angles are, the more curve the current path is. If we go to Figs. 9 and 10, we can see that the smaller the angles between the shown segments, the higher possibility for a mobile sink to find a shorter path.
  • a mobile sink can make a determination on the basis of the value of those angles.
  • the angles can be compared with certain predefined thresholds.
  • one or more parameters can be set appropriately depending on such as the routing experience and the specific application circumstances. Then if the angles are smaller than the parameters, a route rediscovery process can be initiated.
  • estimations maybe a rough one
  • an intuitionistic estimation can be made based on the graphic of the current routing path from the source, such as the one as shown in Fig. 5.
  • a mobile sink can make the determination based on the energy cost analysis.
  • a mobile sink can simply make the determination on the comparison of an estimation of the energy cost with a threshold (which can be set predefined or can be adjust timely to accommodate the current network circumstances). In this case, if the energy cost is acceptable, a route rediscovery will be initiated.
  • the mobile sink can compare the energy cost for building a shorter path and the energy saving brought our by the shorter path, and only if energy saving dominates (the cost of energy for building a shorter path is less than the saving energy brought out by the rebuild path) the route rediscovery operation will be initiated.
  • the energy cost for building a shorter path can comprise the cost of the above flooding operation and the cost of the aforementioned preferred unicasting operation.
  • the energy cost for building a shorter path can comprise the cost of the above flooding operation and the cost of the aforementioned preferred unicasting operation.
  • one or more of the following factors can be taken into account: the number of nodes within the flooding rage (or node density, flooding area), the number of paths that the message will be transmitted to the source, the hop-count from the intermediate apparatus to the source, the amount of data to be transmitted from the source to the data processing apparatus, the expected reduced hop-count by the shorter path comparing with the current path.
  • the above information can be maintained by a mobile sink, or it can be derived/estimated from the mobile sink's maintained routing information with experiences.
  • the determination can be made based on the application-specific requirements and characteristics, or the specific network circumstances or the like.
  • a mobile sink after the Route Rediscovery, if a mobile sink knows location information, a rough estimation on the location of the source can be made by the mobile sink. For example, after Route Rediscovery, a mobile sink in chasing mode can make such estimation based on HC3, HC4 and HC5 as shown in Fig. 10 with its current location and previous location. Simply speaking, a combination of the length of some segments of the current path and the rebuild path together with certain location information, it is possible for the mobile sink to make said estimation. Then the mobile sink can report its estimated location information to others. Preferably, the estimated location information is sent together with the sensor data to an intended destination, such as a remote data center through some other access method, e.g, through 3G to access the Internet.
  • an intended destination such as a remote data center through some other access method, e.g, through 3G to access the Internet.
  • a mobile sink can rebuild a path to the source through geographic greedy forwarding based on location information. Specifically, the mobile sink knows the source's location and all nodes are location-aware, then as the location are available, there is no need to using hop count to estimate the distance. In geographic routing, nodes need to know only the location information of their direct neighbors and where the destination is. A person skilled in the art knows that the basic idea for geographic routing is greedily forwarding data packets to the neighbor geographically closest to the destination. For each hop in greedy forwarding, the neighbor closest to the destination will be selected as the next-hop node. Thus in this invention, when the mobile sink receives the SinkRequest message from the source, if it knows the soure's location, the mobile sink will send a RouteRediscovery message to notify the source through geographic greedy forwarding.
  • Fig. 7 shows a flowchart of another embodiment in which the discovered mobile sink decides to perform the route rediscovery process.
  • the mobile floods a RouteRediscovery message within L (as illustrated with reference to Figs. 9 and 10, L is no less than HC1 +HC2+HC3-K), which can guarantee that the RouteRediscovery can find a path to the source node.
  • L is no less than HC1 +HC2+HC3-K
  • the node within the flooding range of the source node has a route to the source (this route can be learned when the source node sends out the RouteDiscovery message) will send the RouteRediscovery message along the RouteDiscovery's reverse path to the source node.
  • Route Rediscover mechanism An example of the Route Rediscover mechanism is given in Fig. 8.
  • the flooding of RouteRediscovery is limited in a certain range.
  • the nodes who have received the RouteDiscovery message in the previous Route Discovery phase will unicast this RouteRediscovery along their reverse paths to the source node.
  • the source node may receive multiple RouteRediscovery messages, and it will select a preferred path, e.g., the path with least hop count.
  • the objective of the Route Rediscovery is trying to find a shorter path to the source and therefore save energy consumption for the subsequent data dissemination. This is important for not only mobile sinks but also static sinks. For a mobile sink, the new shorter path can save energy. For a static sink, maybe initiate this process will not save much energy for the current data dissemination, or maybe the energy cost dominates, but this process is still useful for the following/subsequent data transmission.
  • a current path connecting a source to a discovered mobile sink is divided into several segments.
  • HC1 denote the hop-count connecting the source node to the selected intermediate node, e.g., the route SA in Fig. 5.
  • HC2 denotes the hop-count connecting the selected intermediate node to the access node, e.g., the route AB in Fig. 5.
  • HC3 denotes the hop-count connecting the access node to the mobile sink, e.g., the route BC in Fig. 5.
  • the mobile sink knows HC1 , HC2 and HC3 (if any).
  • Let HC5 denote the hop-count of the new discovered route between the source node and the mobile sink when adopting the Route Rediscovery scheme. We normalize one hop as one unit of length.
  • the sensor nodes are evenly distributed, i.e., the number of nodes receiving a broadcast packet is roughly equal.
  • the cost of a transmission consists of the sending cost of the sender, and the receiving cost of a fixed number of receivers. Hence, the transmission cost is proportional to the sending cost.
  • the node density NodeDensity as the average number of nodes deployed per unit area. That is to say, given the size of an area, we can estimate the number of sensor nodes in this area.
  • the upper bound of the cost (here "upper bound” means the upper bound of the cost for guarantee a path can be found in the RouteRediscovery procedure, if L is set less than (HC1 +HC2-K), energy cost will be reduced, but it maybe failed to find a path to the source in the rediscovery procedure, the vaule of L can be set on basis of the required probability of find a path to the source; if L is set larger than (HC1 +HC2-K), the energy cost will certainly increase, however, the larger value is not necessary for the above "guarantee”) introduced by the Route Rediscovery, denoted by£ , is composed of two parts, the RouteRediscovery flooding cost ⁇ (HC i + HC i - K) 2 - NodeDesity - ⁇ > and the unicasting cost along a RouteDiscovery reverse path. K ⁇ $ the estimated upbound cost of the unicasting along a RouteDisc
  • HC5 is a deterministic value.
  • HCs VHCi 2 + HCi - 2 ⁇ HCi ⁇ HCi ⁇ cos ⁇
  • the mobile sink When the mobile sink receives a SinkRequest, it checks whether Inequality (4) holds. If yes, it will adopt the Route Rediscovery mechanism. If a new route is built, the source will send Data packets to the mobile sink along the new route.
  • Fig. 10 shows when a SinkRequest arrives at the access node B, due to the random mobility of a sink, it moves out the access node's radio range.
  • SinkRequest will be forwarded along the mobile sink's moving trajectory until reaching the mobile sink, which we call the packet chasing mode.
  • is the upper bound of HC5. Since the source node has flooded a RouteDiscovery message within K hops, i.e., all nodes in the RouteDiscovery flooding area will receive this message, as shown in Fig.10. Thus, similarly, the flooding range (parameter L) of RouteRediscovery message needs to be set no less than (HC1 +HC2+HC3-K), to guarantee that the RouteRediscovery can find a path to the source node.
  • the upper bound of the cost introduced by the Route Rediscovery, denoted by£ is:
  • the mobile sink receives a SinkRequest, it checks whether Inequality (8) holds. If yes, it will adopt the Route Rediscovery mechanism. If a new route is built, the source will send Data packets to the mobile sink along the new route.
  • the protocol can define a system parameter, which is the maximum hop count it will flood the RouteRediscovery message. Its value can be smaller than (HC1 +HC2-K) or (HC1 +HC2+HC3-K). As aforementioned, this depends on the required probability of finding a path in a RouteRediscovery procedure.
  • Route Rediscovery mechanism Another benefit from the Route Rediscovery mechanism is that all nodes having received the RouteRediscovery message, such as nodes within the RouteRediscovery flooding area, can take this opportunity to update their related routing information (such as routing tables) toward that mobile sink, i.e., recording that it has recently witnessed a mobile sink nearby.
  • routing information such as routing tables
  • the cost of flooding the RouteRediscovery message from the mobile sink can be calculated based on estimation of the node density (which is defined as the average number of nodes deployed per unit area based on either the pre-configuration or local neighborhood knowledge, e..g., by calculating the number of one-hop neighbors), the flooding area (it is assumed as a circle here, but certainly other shapes are also applicable, such as a fan-shaped region towards the source), then obtains the number of nodes within the flooding range.
  • the node density which is defined as the average number of nodes deployed per unit area based on either the pre-configuration or local neighborhood knowledge, e..g., by calculating the number of one-hop neighbors
  • the flooding area it is assumed as a circle here, but certainly other shapes are also applicable, such as a fan-shaped region towards the source
  • the cost of unicasting the RouteRediscovery message can be obtained based on estimation of the number of paths that the RouteRediscovery will be unicasted to the source node, and K hop of the upper bound of the unicasting along the RouteDiscovery reverse path (then the transmission cost of unicasting the RouteRediscovery message can be obtained).
  • the energy saving when a shorter distance routing path is found can be calculated based on, the number of the packets to be transmitted to the selected mobile sink, the estimated deduced hopcout by adopting the Route Rediscovery mechanism (the difference between the total hop-count of the longer distance routing path connecting the source node to a mobile sink and the expected hop-count of the shorter distance routing path Calculating), then the reduced transmission cost (the energy saving) brought the Route Rediscovery mechanism can be calculated.
  • the Route Rediscovery mechanism the difference between the total hop-count of the longer distance routing path connecting the source node to a mobile sink and the expected hop-count of the shorter distance routing path Calculating
  • Newton-Cotes formula a method of numerical integration, can be applied to calculate the approximate value of expected hop-count.
  • any node will take the forwarding task once at most.
  • the principle of overhearing is that because the wireless medium is shared, each node can overhear packets sent by its neighbours. Then if a node founds the same packet has been forwarded by its neighbour, it drops such packet.
  • Fig. 11 shows an example illustrating such optimization mechanisms.
  • a source node S sends a RouteDiscovery.
  • Nodes A, B, C, D and E know an existing route to the same mobile sink.
  • A first replies a RouteReply to S, which includes the sink id and the hop-count to that mobile sink.
  • Nodes C, B, D overhear this RouteReply. Since A has replied the RouteReply, they know that their replies are redundant.
  • Node E does not know A has replied the RouteReply, it sends a RouteReply to B. Then upon overhearing, B will drop this RouteReply.
  • Fig. 12 shows another example of forwarding the SinkRequest in chasing mode, in which newly broadcasted SinkRequest will also suppress other neighbours' contention, i.e., other neighbours who overhear this SinkRequest will cancel their contention timer.
  • node A forwards a SinkRequest along the sink moving trajectory.
  • Nodes B, C, D are qualified to forward the SinkRequest (i.e., they have the same timestamps and are no less than As timestamp). They contend to serve as the next forwarder. D wins the contention and forwards the SinkRequest to its downstream neighbours.
  • B is out of the radio range of D, thus B will also forward the SinkRequest to its downstream neighbours, e.g., node E. In this case, the packet duplication problem would occur.
  • E witnesses that F has forwarded the SinkRequest to G.
  • E receives the SinkRequest from B, it will drop this message.
  • Figs. 13a-13c shows exemplary embodiments of the implementations of apparatus operating on the source sensor node, an intermediate node and a mobile sink respectively.
  • the apparatus have respective means for performing each step of respective methods.
  • the apparatus in 13a to be deployed in an existing source sensor node has a flooding means, receiving means and transmitting means.
  • the structure of this apparatus can be changed as comprising a transceiver/wireless interface and a control unit/means.
  • the transceiver/wireless interface will be responsible for communicating, including sending and receiving, while the control unit will perform other operations, such as deciding to perform the flooding operation and instructing the interface to perform the specific flooding.
  • the apparatus shown in Fig. 13b can be embodied in an intermediate node. Similarly, it has receiving means, transmitting means and addressing means for implementing corresponding method. In addition, it may have a cash area, such as a memory, a disk or the like to maintain its routing information. Certainly, instead of storing in the apparatus of the invention, such routing information can be stored in the intermediate node itself or some peripheral equipment. Also, such apparatus can be realized in other structure, such as a hardware interface, and a central processing unit or a processor for performing other functions of this apparatus.
  • the apparatus shown in Fig. 13c can be embodied in a mobile sink. It has decision making means and flooding means, and similarly, it can also embodied as other forms, such as hardware, the combination of hardware and software, etc. In a preferred embodiment in which energy cost is considered when making a decision, the apparatus may further comprise a calculating means for implementing the specific calculating function.
  • the invention should not be limited thereto.
  • the invention is also applicable for a network in which a plurality of data packet often needs to be transmitted.
  • the sink can also be static. In this case, the chasing process and the route rediscovery are not necessary.
  • sink of the invention it can be any kind of data processing apparatus with necessary interface for communications of the network, and it also has certain ability of processing data, such as gathering/receiving/transmitting data from the source.
  • the data transmission is comparatively simple.
  • a bunch of data packets will be forwarded along the discovered route to the mobile sink. Since the end-to-end route is fresh enough (the mobile sink replies the SinkReply to the source or the mobile sink initiates a Route Rediscovery procedure immediately), during the data packets being forwarded toward the mobile sink, considering the limited moving speed of mobile sinks (e.g., for mobile users, the walking speed is among 1 -2m/s, while the sensor node radio range is 50m on average), that mobile sink won't move far away from the new access node.
  • the data packets can be delivered to the mobile sink following the sink moving trajectory within limited hops. This process is similar as the chasing mode, it is expected that the data packet can chase the mobile sink within limited hops, e.g., one or two hops, because the end-to-end route is fresh. Therefore, with the routing scheme of the invention, a lightweight streaming data dissemination scheme for wireless sensor networks with mobile sinks is achieved.
  • the invention release the necessity of utilizing any location information.
  • the invention establishes the route to a mobile sink.
  • it is scalable because the flooding scale will not increase as the network size increases. Compared with the hierarchical flooding approach, it avoids the construction of the hierarchical structures.
  • localized flooding enables the source node to select the least cost route to send data and introduces shorter reply latency. Therefore, the routing scheme presented in this invention achieves timely delivery of collected data.
  • the present invention can be realized in hardware, software, firmware or a combination thereof. It is applicable for the present invention to be implemented as a computer program product, which comprises all the features enabling the implementation of the methods and devices or modules described herein, and when being loaded into a computer system or a processing device, is able to carry out these methods or constitute the functional means/modules in the apparatuses or devices according to embodiments of the present invention.
  • said program products can be embodied in computer readable medium.
  • a program of the computer program product can be loaded into/embodied in a memory of the processing device.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)

Abstract

La présente invention propose un système de routage destiné à des réseaux, en particulier à des réseaux de capteurs sans fil. Grâce à l'invention, il est possible de construire un chemin de bout en bout, et on obtient alors un système léger de diffusion de données en continu destiné à des réseaux de capteurs sans fil avec des collecteurs de données mobiles. Le procédé selon l'invention comprend les étapes consistant à : diffuser en abondance un message à l'intérieur de sauts limités de façon à découvrir au moins un appareil de traitement de données d'un réseau ; en réponse à ladite diffusion en abondance, recevoir au moins une réponse ; s'il n'y a aucune réponse en provenance d'un appareil de traitement de données, transmettre au moins une demande à un appareil intermédiaire à partir duquel la réponse est envoyée, de façon à découvrir au moins un appareil de traitement de données avec les informations de routage mises à jour par l'appareil intermédiaire.
PCT/CN2010/075286 2010-07-20 2010-07-20 Système de routage destiné à des réseaux de capteurs sans fil Ceased WO2012009849A1 (fr)

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