Abstract:
Wireless sensor platforms ( 10 ), when deployed, can ascertain whether they can meaningfully participate in communications with more than one cluster ( 22, 23 ) of such devices. When true, such multi-cluster platforms can serve as bridge nodes to facilitate the passing of data collected from one cluster to or through another cluster. In a preferred embodiment, the platforms serving as bridge modes ( 24  and  25 ) utilize a communication schedule that imposes no greater work load than the load the platform would otherwise have served as an ordinary node, and preferably the workload is considerably reduced. This aids in ensuring that the portable power reserves of the bridge nodes will support bridge operations for at least as long as the clusters are otherwise functioning.

Description:
TECHNICAL FIELD 
     This invention relates generally to wireless communications and more particularly to wireless sensor platforms and systems. 
     BACKGROUND 
     Wireless sensors are known. Such devices typically comprise an integral device having one or more sensors (to sense any of a wide variety of conditions and parameters) and a transmitter or transceiver to support wireless telemetry of sensor data. Many such devices further include a portable power supply (such as a battery pack and/or a solar cell array) and/or control logic to facilitate various actions and responses. 
     Networks of such wireless sensors have also been proposed. Proliferation of corresponding system designs has occurred as various enabling technologies (such as microelectromechanical system (MEMS) design to facilitate the provision of very small, accurate, cost effective, and low power sensor mechanisms) have become available. Pursuant to one deployment scheme, a plurality of wireless sensors are strewn over a geographic area of interest (such as, for example, a farm or ranch). These sensors then communicate with one another pursuant to a pre-arranged or self-organized communication protocol and schedule. In many such proposals, the wireless sensors communicate in this fashion pursuant to a relatively fixed or otherwise predictable schedule. So configured, the wireless sensors are then able to assume a so-called sleep mode during intervening periods in order to conserve power. 
     In many wireless sensor networks, one or more collection points serve to receive the sensor data as generated by the various wireless sensors that comprise the network. For a variety of reasons, however, such collection points are often not able to receive such information directly from each wireless platform (for example, the collection point may be located beyond the transmission range of a given wireless sensor). One useful proposal suggests relaying data from one wireless sensor to another as needed in order to transport sensor data from a given source to a desired endpoint. In a relatively simple configuration, such an approach may prove acceptable. 
     There are other circumstances where such an approach remains insufficient, however. In some systems, groups of wireless sensors are organized into clusters (such clusters may be differentiated by range, purpose, wireless communications protocol and/or modulation, or any number of other causes or criteria). Relaying data from one cluster to a collection point via another cluster can be accomplished using so-called bridge nodes (these being wireless sensors that are able to function compatibly in both clusters), but such an approach gives rise to a new set of problems. In particular, the communications duty cycle of such a bridge node will typically at least double as compared to the wireless sensors that otherwise comprise these clusters. This occurs because the bridge node becomes active during the communication cycles of both clusters that it serves to link. As a result, the bridge nodes will deplete their portable power source more rapidly than other platforms within these clusters and therefore fail sooner. When this occurs, the link between the clusters breaks and the collection point no longer has access to data still being collected by the now-stranded cluster of wireless sensors. 
     One simple solution would be to provide the bridge nodes with a larger portable source. Such an approach, however, dictates that some wireless platforms within a given deployment are different than others. This can raise costs significantly, both to provide and supply a plurality of platforms and to ensure that each type of sensor is deployed properly (that is, to ensure that bridge nodes are positioned where they can, in fact, usefully serve as a bridge node). Problems such as these tend to militate against the use of such a solution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above needs are at least partially met through provision of wireless sensor apparatus and method described in the following detailed description, particularly when studied in conjunction with the drawings, wherein: 
         FIG. 1  comprises a block diagram of a wireless sensor platform as configured in accordance with an embodiment of the invention; 
         FIG. 2  comprises a schematic top plan view of a deployment of wireless sensor platforms as configured in accordance with an embodiment of the invention; 
         FIG. 3  comprises a flow diagram as configured in accordance with an embodiment of the invention; 
         FIG. 4  comprises an illustrative communications timing diagram as configured in accordance with an embodiment of the invention; 
         FIG. 5  comprises a communication schedule as configured in accordance with an embodiment of the invention; 
         FIG. 6  comprises a schematic top plan view of a deployment of wireless sensor platforms as configured in accordance with another embodiment of the invention; and 
         FIG. 7  comprises a detailed flow diagram as configured in accordance with an embodiment of the invention. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. 
     DETAILED DESCRIPTION 
     Generally speaking, pursuant to these various embodiments, a wireless sensor platform can operate to determine whether it can detect wireless communications amongst a plurality of sensor clusters. When true, the wireless sensor platform identifies the communications schedule for each such cluster (such communications schedules identifying, in one embodiment, times when the wireless sensor platforms that comprise each cluster are to be powered up and communicating or be ready to communicate amongst themselves). The wireless sensor platform then determines a communication schedule for itself that represents a reduced time requirement for communications as compared to a combination of the first communications schedule and the second communications schedule. In one embodiment, the newly determined communication schedule will serve to both conserve the power reserves of the wireless sensor platform while simultaneously facilitating a passing of data from one cluster to the other. 
     In one embodiment, the wireless sensor platform can determine an ability of other wireless sensor platforms to also inter-communicate with these same clusters (or, in another embodiment, with at least one other cluster) and to use that information when devising and using its communications schedule. In one embodiment the wireless sensor platforms that can serve to link multiple clusters can divide the offering of such services amongst themselves over time. This will permit the power requirements to support such linking services to be spread over multiple platforms and thereby serve to preserve the individual power reserves of each such platform. In another embodiment, such multi-cluster capable wireless sensor platforms can transfer data amongst themselves to thereby further facilitate the transfer of data within a multi-cluster deployment of such platforms. 
     So configured, wireless sensor platforms that have inter-operable communications access to multiple clusters and/or other platforms that possess such access can serve as data bridges to facilitate the flow of data throughout the network. By establishing such services in a dynamic fashion, multiple platforms can be leveraged to thereby permit power usage for any given wireless sensor platform to be substantially reduced or minimized. So configured, bridge platforms will typically retain useful power reserves at least as long as the wireless sensor platforms that do not serve this purpose. Furthermore, by facilitating such configurations in a dynamic fashion, the wireless sensor platforms can be essentially identical to one another to thereby achieve corresponding economies of scale and ease of deployment. 
     Referring now to  FIG. 1 , a suitable wireless sensor platform  10  will typically include a control unit  11  such as a microprocessor, microcontroller, programmable gate array, or other programmable logic platform (if desired, of course, and particularly where the intended and desired service of the wireless sensor platform  10  is likely to remain continuously specific and well defined, a more hard-wired non-programmable architecture can be utilized instead). The control unit  11  can be programmed or otherwise configured and adapted to permit effectuation of the various processes and operational modes described herein. A sensor  12  (or sensors  13 ) couples to the control unit  11  and provides data regarding whatever parameter the sensor(s)  12 ( 13 ) detects. A wide variety of sensors are presently known and more are sure to be introduced. It should be understood that these teachings are not limited to any particular sensor technology or sensed parameter. It should also be understood that, to the extent that multiple sensors are used, mixed sensor technologies and/or monitoring of multiple sensor parameters are also readily accommodated within these teachings. 
     If desired, one or more memories  14  are coupled to the control unit  11  (to store, for example, sensor data as received from the sensor  12  (or sensors) and/or sensor data as received from other wireless sensor platforms and/or clusters as described below (it would also be possible to include such memory integral to the control unit  11  if desired). Such a memory  14  can also serve to retain programming for the control unit  11  and/or communications schedule information as developed pursuant to these embodiments. 
     At least one transceiver  15  couples to the control unit  11  to permit wireless communications with, for example, other wireless sensor platforms. Such a transceiver can facilitate communications via radio frequency-based emissions, light frequency-based emissions, or any other wireless medium as appropriate to a given application. In addition, there are no particular limitations with respect to the modulation technique and/or communications protocol as regards these embodiments. Instead, the designer is free to select whichever techniques and approaches may best serve the immediate needs of a given deployment. If desired, additional transceivers (and/or transmitters or receivers) can also be provided. Depending upon the needs of the moment, such additional platforms can provide redundant back-up communications services and/or can facilitate parallel communications using alternative technologies. For example, a wireless sensor platform  10  could be provided with a first transceiver that utilizes amplitude modulation and a second transceiver that utilizes frequency modulation techniques. So configured, the platform would be able to communicate with other sensor platforms using either approach, either in parallel or in seriatim fashion. 
     So configured, the wireless sensor platform  10  can readily support various modes of operation. For example, pursuant to a first mode of operation, the wireless sensor platform  10  can detect the wireless communications of any number of clusters of wireless sensor platforms and also determine the communications schedule to be used by each such cluster. Pursuant to a second mode of operation, the wireless sensor platform  10  can interact with other wireless sensor platforms that are also able to interact wirelessly with a plurality of such clusters. For example, such platforms can self-organize during such a mode of operation and determine which amongst them are to serve as bridge platforms. Pursuant to a third mode of operation, the wireless sensor platform  10  can serve as a bridge platform and inter-operate with at least one cluster to provide a data bridge service. When serving as a bridge platform, and in accordance with a preferred embodiment, the wireless sensor platform  10  will observe a communications schedule that is no more demanding, and usually less frequent, than the communications schedule that the platform  10  would have to observe when maintaining communications with all of the available clusters (in effect, bridge services are preferably shared across a number of wireless sensor platforms  10  to thereby leverage their collective power reserves). 
     Referring now to  FIG. 2 , a deployed sensor network  20  will typically include one or more base units  21  that serve to ultimately receive the sensor data from the dispersed wireless sensor platforms  10 . Such a base unit  21  can be a fixed-location platform or can be mobile as appropriate to the needs of a given application. Similarly, the base unit  21  can operate autonomously or under the control of one or more operators (either on-site or remotely). The deployed wireless sensor platforms  10  themselves are geographically dispersed (in this example) over a geographic area. Also in this example, and pursuant to ordinary cluster architecture and process, the dispersed platforms  10  self-organize themselves into two clusters denoted here as cluster A  22  and cluster B  23  (as already noted, there are numerous ways and various cluster-membership criteria by which such clusters can be identified and organized). For purposes of this illustration, it will be presumed that each wireless sensor platform  10  within a given cluster  22  or  23  is able to wireless communicate with every other wireless sensor platform  10  that also comprises a part of that cluster. It will also be presumed that such communications occur pursuant to a specific communication schedule (which schedule can be previously determined and/or dynamically determined as part of the self-organization activity) in order to permit the wireless sensor platforms  10  to effect a sleep mode of operation during at least some other periods. 
     For purposes of this illustrative example, there are two wireless sensor platforms  24  and  25  that are able to communicate with platforms  10  belonging to both clusters  22  and  23 . Pursuant to these embodiments, such wireless sensor platforms  24  and  25  are able to determine their inter-operation capacity and to work together to exploit that capacity to permit data as collected by one cluster (such as cluster B  23 , which cluster, in this example, is beyond an effective communications range of the base unit  21 ) to be passed on to the other cluster (such as cluster A  22 , which cluster, in this example, is suitably positioned to pass on data from cluster B  23  to the base unit  21 ). And, as already noted, in a preferred embodiment such wireless sensor platforms  24  and  25  further work together to establish a communications schedule that will permit them to support such bridge services while simultaneously conserving their on-board power reserves to ensure availability of the bridge service for the full operating lifetime of the bulk of the wireless sensor platforms  10  that comprise each cluster  22  and  23 . 
     Referring now to  FIGS. 3 and 4 , a general process to effect such behavior along with an illustrative example will be described. Upon initial deployment (or as otherwise triggered or initiated in accordance with the needs of a given application) a wireless sensor platform searches for and detects  31  the communications of a first cluster of other wireless sensor platforms (presuming, of course, that such a first cluster exists). Upon detecting  31  such a cluster, the process then identifies  32  the communications schedule by which the wireless sensor platforms of that cluster communicate with one another. As one illustrative example, and referring momentarily to  FIG. 4 , a first wireless sensor platform (WSP) can detect the communications  40  of cluster A and then ascertain the communications schedule for that cluster A. Similarly, a second, third, and fourth wireless sensor platform in this example also detect such communications  41  and likewise obtain the corresponding communications schedule. 
     Referring again to  FIG. 3 , the process then searches for other clusters. If no additional clusters are detected  33 , then the wireless sensor platform proceeds in accord with its normal functionality  34  as well understood in the art. When the platform detects  33  other sensors, however, the process again provides for identifying  35  the communication schedules for each such cluster. To continue the example of  FIG. 4 , the first wireless signal platform, having already detected and characterized cluster A, then notes the communications and determines the communications schedule  42  of cluster B. In similar fashion, the other three wireless sensor platforms also detect the communications and corresponding schedule  43  of cluster B. So configured, these four wireless sensor platforms are now each apprised of two clusters and the communications schedule by which such clusters organize their communications. To illustrate this concept with a simple example,  FIG. 5  presents cluster A as having communications scheduled for Mondays, Wednesdays, Fridays, and Sundays while cluster B has communications scheduled for Tuesdays, Thursdays, Saturdays, and Sundays. (It should be emphasized that these are simple examples being provided for explanatory purposes only.) 
     Referring again to  FIG. 3 , the process next permits a wireless sensor platform to determine  36  whether it should serve as a bridge (between, for example, clusters and/or other bridges). When, for whatever reason, a particular candidate bridge platform is not scheduled for bridge service, that particular wireless sensor platform can simply proceed with its normal functionality  34 . Such a decision may occur, for example, when the candidate bridge platform has a relatively small power reserve as compared to other candidates, when the sheer number of candidates is more than sufficient to enable the provision of appropriate bridge services without this particular candidate&#39;s participation, when no bridge services are necessary, or any number of other reasons. 
     For those wireless sensor platforms that are to serve as bridge platforms, however, the process provides for determination  37  of a communications schedule for that particular platform. To continue the illustrative example of  FIG. 4 , and pursuant to one embodiment, the four wireless sensor platforms that comprise the candidate bridge platforms can communicate  44  amongst themselves to determine which of them, if any, should serve as bridge platforms (as well as for which cluster(s)/bridge(s)) and pursuant to what communications schedule). All of these decisions, but especially the scheduling determinations, can be based upon a variety of criteria, including but not limited to the frequency or periodicity by which sensor data is to be forwarded from a given cluster, the memory available to each wireless sensor platform (as is available to store, for example, data to be passed from one cluster to another), the population size of the clusters in question, the respective energy reserves of the candidate bridge platforms, the communication schedules of the various clusters (including, for example, the mechanism by which so-called pseudo-random wake-up times are scheduled), and so forth. 
     In general, the communications schedule for a given bridge platform should be no more demanding than the communications schedule for that particular wireless sensor platform would be were it to conduct ordinary functions with the clusters in question (and preferably should be less demanding). For example, in the illustrative example at hand, and referring again momentarily to  FIG. 5 , a first wireless sensor platform serving as bridge A can be assigned to communicate with cluster A on Mondays and Fridays and with cluster B on Tuesdays and Saturdays. This represents four scheduled communications windows per week which is only half the total number of scheduled communications that would be required if this platform were to communicate with both clusters pursuant to the full-time schedules of both clusters. In effect, this bridge A is communicating no more frequently on a weekly basis than it would be communicating if it were operating as part of only a single cluster. This example also illustrates that a second wireless sensor platform, serving as bridge B, can be scheduled to communicate with cluster A on Wednesdays and Sundays and cluster B on Thursdays and Sundays. Again, the total number of communications as scheduled for the platform as a bridge platform comprises a reduced schedule as compared to a non-bridge schedule for this same platform. 
     Returning again to  FIG. 3 , the wireless sensor platforms that are selected and scheduled as bridge platforms then proceed to function  38  as communication bridges between clusters and/or other bridges. So configured, of course, the bridge platforms can be placed in a partial or full sleep mode for at least a substantial amount of the time that is outside the reduced time schedule for communications to thereby reduce their respective power consumption. When serving as a bridge platform, of course, these platforms generally serve to receive data from one cluster and to pass that data on to another cluster. For example, as illustrated in  FIG. 2 , data from cluster B  23  can be passed to cluster A  22  via one of the wireless sensor platforms  24  and  25  that are positioned to serve as bridge platforms. 
     Returning again to the illustrative example of  FIG. 4 , the first wireless sensor platform, operating as a bridge platform during a scheduled communication period for cluster A, can transmit an announcement message  45  to indicate its presence and availability to receive data to be forwarded to cluster B. With appropriate programming, the wireless sensor platforms of cluster A can respond by transmitting their data  46  to the first wireless sensor platform. Such data can then be locally stored as necessary. Later, when the first wireless sensor platform communicates as scheduled with cluster B, the cluster A data is then transmitted  47  to cluster B to complete the forwarding process via the bridge. These same communications (including the availability announcement, receipt of data, and forwarding of data) with these same clusters are then done at other times by the second wireless sensor platform. So configured, the bridge duties are shared between two wireless sensor platforms to accrue the benefits already noted above. 
     In the scenarios presented above, the wireless sensor platforms are able to identify other clusters with which they can communicate. It is also possible, however, for such a wireless sensor platform to also sense other bridge platforms, which bridge platforms may be communicating with one or more other clusters that are not otherwise available to the sensing platform. It is within the scope of these teachings to facilitate a transfer of data via these connections as well. For example, with reference to  FIG. 6 , data from a first cluster B  61  can be transferred via a bridge platform  62  to either of two other clusters C and D  65  and  64  through another bridge platform  63 . Such connection opportunities can be ascertained at the same time that a given wireless sensor platform detects other clusters and/or other bridge platform candidates, and the scheduling of communications with such platforms can be similarly determined when the communications schedule for a given platform is otherwise determined as described above. So configured, and as illustrated in  FIG. 4 , data  49  can be readily forwarded from one bridge platform to another. 
     As already noted, there are numerous ways to specifically embody a given wireless sensor platform and/or sensor network to behave compatibly with these various teachings.  FIG. 7  presents one particular illustrative approach. Pursuit to this embodiment, a given wireless sensor platform engages in its ordinary cluster setup routine  70  (for example, upon initiation or deployment) and then determines  71  whether scheduled communications in the form of wakeup times for have found for more than one cluster. When only one such cluster has been found, the platform behaves as an ordinary node  72  within that cluster. When more than one cluster has been scheduled, however, the platform initiates a bridge startup mode  73 . 
     During the bridge startup mode  73 , the platform notes and records  74  corresponding indicia for all accessible clusters and then seeks to discover  75  any neighboring bridge nodes as otherwise noted above. Information regarding reachable clusters (and the corresponding wakeup times/communication schedules for such clusters) is obtained  76  and shared amongst the neighboring bridge nodes and a resultant collection time schedule formed  77  for each cluster for which this particular platform will serve as a bridge node. The platform then calculates  78  a corresponding bridge wakeup time (or times) B time  following which the platform can enter a powered down mode of operation to thereby conserve energy. 
     When the bridge wakeup time expires a bridge mode  79  becomes active. In this mode, the platform determines  80  whether it has a next-hop bridge or cluster data packet available. When a bridge data packet exists, the platform passes  81  the packet to a next bridge node (for example, as described earlier). When a cluster data packet exists, the platform accesses  82  the priority and/or other duty cycle indicia that may apply to the data in question. When a high priority or other indicia of desired rapid service exists, a new delivery time is set  83  and the process switches to the deliverer process  86  described below. When a low priority exists, collector times are obtained  84  and a corresponding wakeup time scheduled  85 . When the appropriate wakeup time arrives, the process switches to the collector mode  87  described below. 
     Pursuant to the deliverer mode  86 , the platform transmits  88  its announcement regarding its availability to deliver forwarded data, following which the platform transmits  89  buffered packets that include the data to be forwarded. The platform then determines  90  whether a collector mode is on or off. When off, the process  86  returns to the bridge mode  79 . When the collector mode is on, however, the process  86  switches to the collector mode  87 . 
     Pursuant to the collector mode  87 , the platform transmits  91  its announcement regarding its availability as a data collector. As an optional step, the platform can then deliver  92  any outgoing data that it might otherwise have and can then receive  93  data from the cluster in question (at least until the platform&#39;s resident buffer memory becomes full  94 ). Upon concluding this process, the platform then transmits  95  an announcement that it is leaving. 
     So configured, a wireless sensor platform can serve as an ordinary wireless sensor platform within a cluster of similar devices or can support a specialized bridge service to thereby facilitate extension of the effective range of a given deployment of such devices. Significant economies of scale can be realized in part because each device can be made essentially identical to every other device (with changes obviously being appropriate where necessary to support different sensor technologies, wireless technologies, and so forth). Furthermore, no special additional hardware elements need be provided to permit such a device to function as a bridge nor is a larger capacity energy reserve necessary. 
     Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the ambit of the inventive concept. For example, when a given bridge platform can determine that two clusters happen to share a common communication window (as can happen either pursuant to a set schedule or by happenstance when two pseudo-random-based schedules coincidentally produce a common wake-up time), that bridge platform can effect its services by using that common window to again aid in minimizing its own on-time requirements. To illustrate, in  FIG. 5  it can be seen that both cluster A and cluster B have a communication scheduled on Sunday. By utilizing this particular window of commonly scheduled communications, the bridge platform can serve as a bridge while simultaneously likely minimizing its own required service time.