Patent Document

CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This application is related to the application Ser. No. 10/125,939 filed Apr. 19, 2002, entitled “Communication Network Utilizing a Cluster Tree Protocol,” by Maeda et al.; application Ser. No. 09/803,259 filed Mar. 9, 2001, entitled “A Protocol for a Self-Organizing Network Using a Logical Spanning Tree Backbone,” by Lee et al.; and application Docket No. CML00414J entitled “Network Architecture, Addressing and Routing,” by P. Chen et al., filed Nov. 26, 2002, which are hereby incorporated herein by reference and assigned to Motorola, Inc. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates in general to networking. More particularly, the present invention relates to ad hoc wireless networking.  
         BACKGROUND OF THE INVENTION  
         [0003]    Advances in electronics manufacturing technology have enabled the manufacture of inexpensive wireless devices in large quantities. Presently there is an interest in greatly expanding the use of wireless devices and networks of wireless devices beyond traditional communication uses.  
           [0004]    Examples of applications of networks of inexpensive wireless devices, include sensor systems that include a large number of spatially distributed sensors, and distributed control systems that include both a large number of spatially distributed sensors, and a large number of spatially distributed actuators. In the former application one or more nodes can serve as data sinks at which data from the sensors is collected, and in the latter application sensors may in some case route data directly to actuators, and also route data to one or more nodes that are linked to data monitoring stations. Examples of distributed control systems include a fire control system for a large facility that includes a plurality of smoke detectors, and a plurality of sprinkler valve actuators.  
           [0005]    One type of wireless network that is of interest is that which is termed an ‘ad hoc’ network. In forming an ad hoc network, wireless devices that have been positioned as needed in building or outdoor area, upon being turned on, interoperate in order to form a cohesive network that is able to route messages from one wireless device to another as needed. A variety of routing protocols have been proposed for use in ad hoc wireless device networks. Certain routing protocols are suitable for certain types of applications. For example if much of the communication activity on an ad hoc network involves sending data to and from a particular node e.g., a node acting as a central controller, then a routing protocol based on an organization of the ad hoc network according to a hierarchical tree topology is appropriate. For applications of ad hoc networks which do not require a central node, peer-to-peer routing protocols are appropriate, and can be more efficient for routing messages between nodes. Different routing protocols can be associated with different network topologies. In each case, the network topology determines which wireless devices send messages to each other in operating according to the protocol. The optimum choice of routing protocol and corresponding network topology is application dependent.  
           [0006]    It would be desirable to be able to enjoy the performance characteristics of a variety of routing protocols in a single network. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0007]    The present invention will be described by way of exemplary embodiments, but not limitations, illustrated in the accompanying drawings in which like references denote similar elements, and in which:  
         [0008]    [0008]FIG. 1 is a graph showing a hierarchical tree topology wireless communication network of wireless devices in accordance with the present invention;  
         [0009]    [0009]FIG. 2 is a graph showing a second topology wireless communication network of the wireless devices shown in FIG. 1 in accordance with the present invention;  
         [0010]    [0010]FIG. 3 is a functional block diagram of a wireless device of the networks shown in FIGS.  1 - 2  according to the preferred embodiment of the invention;  
         [0011]    [0011]FIG. 4 is a flow chart of a method of operating a wireless device of the networks shown in FIGS.  1 - 2  according to the preferred embodiment of the invention;  
         [0012]    [0012]FIG. 5 is a flow chart of a method of operating a wireless device of the networks shown in FIGS.  1 - 2  according to the preferred embodiment of the invention; and  
         [0013]    [0013]FIG. 6 is a hardware block diagram of a wireless device of the networks shown in FIGS.  1 - 3  according to the preferred embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention.  
         [0015]    [0015]FIG. 1 is a graph showing a hierarchical tree topology  100  wireless communication network in accordance with the present invention. The network includes a central wireless device  102  in a root position of the hierarchical tree topology and a plurality of other wireless devices  104 . The central wireless device  102  is distinguished by its position in the network. The central wireless device  102  optionally has increased processing power. On the other hand, the central device  102  is optionally identical in hardware design to other nodes of the network. The edges shown in FIG. 1 represent paths over which messages are routed according to a routing scheme used in the network  102  that is consistent with the hierarchical tree topology.  
         [0016]    One routing scheme that is consistent with the hierarchical tree topology is described in co-pending application “Network Architecture, Addressing and Routing” by Priscilla Chen et al. According to the network addressing and routing scheme, described in the latter application each nodes of the network are assigned addresses such that routing decisions can be made based on numerical comparisons that involve the assigned addresses.  
         [0017]    Alternatively, routing tables maintained at each wireless device are used in routing messages through the network  100 .  
         [0018]    Routing protocols that use hierarchical tree topologies are efficient in the case that a large fraction of network traffic includes messages from or to the root position wireless device  102 .  
         [0019]    Although, the network  100 , as shown in FIG. 1 includes only twelve wireless devices  102 ,  104 , more wireless devices can be included in the network. Large networks can be divided into a plurality of sub-trees also referred to as ‘clusters’. Each particular cluster is preferably identified by a cluster address that is common to all wireless devices in the particular cluster. Within each particular cluster specific wireless devices are identified by network addresses.  
         [0020]    The edges shown in FIG. 1 represent network layer level connections, i.e., paths over which messages are sent. Depending on the distances between devices,  102 ,  104 , some of the devices  102 ,  104  that are not shown to be connected by edges will be within range, and aware of devices in addition to those with which logical links are established. Devices may become aware of devices in addition to those with which network layer level connections are maintained via communications at a lower levels of a communication protocol stack. Such lower level connections, allow the network layer level connections to be reconfigured according to other network routing protocols.  
         [0021]    [0021]FIG. 2 is a graph showing a peer-to-peer topology wireless communication network  200  of the wireless devices shown in FIG. 1 in accordance with the present intention. Although the peer-to-peer topology includes the same wireless devices  102 ,  104 , as shown in FIG. 1, the topology indicated by the arrangement of edges in FIG. 2 is different. Note that edges corresponding to network layer level connections can in certain routing protocols be dynamic. For example logical layer level connections can be established for each messages to be sent if they do not already exist, and can be expired if not used within a certain period. Examples of non-hierarchical tree topologies, in which logical layer level connections are changeable include ‘Dynamic Source Routing Protocol” and “Ad hoc On-Demand Distance Vector protocol”.  
         [0022]    Routing protocols that do not use hierarchical tree topologies can be more efficient when network traffic is not heavily centered on one particular wireless device.  
         [0023]    In the case that more than one application is to be run on a single network, it is desirable to be able to optimally choose the routing scheme, and network layer topology of the network for each application.  
         [0024]    [0024]FIG. 3 is a functional block diagram of the wireless device  102  of the networks shown in FIGS.  1 - 2  according to the preferred embodiment of the invention. The other wireless devices  104  are also preferably described by the same functional block diagram as shown in FIG. 3. A number of the blocks shown in FIG. 3 correspond to layers of the International Organization for Standards Open System Interconnection (ISO/OSI) model. Referring to FIG. 3, a physical layer  302  includes a radio frequency transceiver. A media access control (MAC)/logical link control (LLC) layer  304  is coupled to the physical layer  304 . The MAC/LLC layer  304  is in charge of low-level communications. The MAC/LLC layer coordinates the timing of communications. Low-level communications use MAC layer addresses which are preferably factory set and permanently stored in each wireless device  102 ,  104 . Such addresses preferably comprises sixty-four bit IEEE addresses.  
         [0025]    A network layer module  306  is coupled to the MAC/ILLC layer  306 . The network layer  306  comprises a plurality of different network routing protocol modules  308 ,  310 ,  312 , including a first network routing protocol module  308 , a second network routing protocol module  310 , and an nth network routing protocol module  312 . The network routing protocol modules  308 ,  310 ,  312 , preferably comprise at least one routing protocol that is based on a hierarchical tree topology such as shown in FIG. 1, and at least one peer-to-pear routing protocol. The network routing protocol modules preferably support diverse routing protocols such as Dynamic Source Routing (DSR), location/geographic routing, and/or Ad hoc On-demand Distance Vector (AODV) routing. The network layer can also comprises other network layer functionality.  
         [0026]    An application layer  314  is coupled to the network layer  306 . The application layer  314  comprises a plurality of application programs  316 ,  318 ,  320 , including a first application program  316 , a second application program  318 , and a third application program  320 . Each application program  316 ,  318 ,  320  routes messages through a network (e.g.,  100 ,  200 ) of which the wireless device  102  is a part. For each application  316 ,  318 ,  320  a particular network routing protocol  308 ,  310 ,  312  works best. Which routing protocol works best for each application can be determined based on trial and error, or simulation. In certain cases the network routing protocol that is best suited for a particular application will be readily apparent. For example for a sensor network application in which a particular wireless device serves as a data sink, a routing protocol based on a hierarchical tree topology in which the data sink wireless device occupies the root position is appropriate.  
         [0027]    [0027]FIG. 4 is a flow chart of a method  400  of operating a wireless device of the networks shown in FIGS.  1 - 2  according to the preferred embodiment of the invention. The method  400  is shown from the perspective of a particular device hereinafter referred to as the kth device. The method  400  starts prior to the kth device having joined a network (e.g.,  100 ,  200 ).  
         [0028]    In step  402  communication is initiated between the kth device and another device, hereinafter referred to as the ith device, that is already part of the network. The communication can be initiated by the kth device or the ith device. Initiation of communication is preferably based on MAC/LLC layer protocols. Initiation of communication preferably involves transmitting a beacon signal from one device (e.g., the kth device), and listening for a beacon signal (e.g., from the ith device).  
         [0029]    In step  404  the kth node transmits a message to or through the ith device requesting to join the network. The message transmitted in step  404  includes or is supplemented by a further message that includes information identifying routing protocols that the kth device supports. Such information preferably takes the form of a set of binary flags each of which specifies whether or not a particular routing protocol is supported. The message sent in step  404  is preferably sent using MAC/LLC layer protocols, e.g., using a physical address, and not assuming a particular routing protocol. The message is sent to or through one or more neighbors of the kth device that are discovered through MAC/LLC layer processes. The message is optionally sent to a device in the network that is responsible for supervisory functions.  
         [0030]    In step  406  the kth device listens for a command to operate according to a specified routing protocol for a predetermined period of time. The command is preferably sent in response to the message sent in step  404 . Block  408  is a decision block the outcome of which depends on whether a command to operate according to a specified routing protocol was received. If not then the method  400  continues with decision block  410  the outcome of which depends on whether a preprogrammed retransmit limit has been reached. If not the method loops back to step  404  and retransmits the message requesting to join the network. If in step  410  it is determined that the retransmit limit has been reached then the method  410  halts at step  412  in which a disconnected alert of the kth device is activated. The disconnected alert preferably takes the form of a light (e.g., a flashing light), or an audible alarm. The disconnected alert signals that human intervention may be required to trouble shoot network problems and get the kth device connected to the network (e.g. by moving the kth device to a position of higher signal strength).  
         [0031]    Preferably, at least initially, the network is operated using a routing protocol that all wireless devices in the network can support. The command received in step  406  can be sent from a wireless device that has supervisory authority for the network, or supervisory authority for a part of the network that includes the kth device, or from a wireless device that is merely a nearest neighbor or parent (in a hierarchical tree topology) of the kth device. According to an alternative embodiment each device is programmed to start operating according to a preprogrammed routing protocol upon being powered on, and need not initially receive a command to operate according to a particular routing protocol.  
         [0032]    If in block  408  it is determined that a command to operate according to a specified protocol has been received, then the method  400  continues with decision block  414  the outcome of which depends on whether the kth device is able to support the specified protocol indicated in the command received in block  406 . If it is determined in block  414  that the kth device is able to support the specified protocol, the method  400  continues with block  416  in which the kth device operates according to the specified protocol. When operating according to the specified protocol, the kth device preferably periodically transmits a beacon that indicates that the kth device is participating in the network. The beacon indicates that messages can be routed through the kth device (unless the kth device is at a leaf position, in a hierarchical tree topology network).  
         [0033]    Thereafter, at any time, while the kth device is operating in the network, a command may be received instructing the kth device to operate according to another routing protocol. For example in the case that, initially the network is operating according to a routing protocol based on a hierarchical tree topology, a command to change to a different routing protocol can be broadcast from a wireless device that is located at the root position. Information used to operate according to a first protocol can be stored when switching to another protocol.  
         [0034]    The possibility of receiving a command to operate according to another protocol is reflected in FIG. 4 in block  418  which follows step  416 , and is a decision block. The outcome of decision block  418  depends on whether a command to operate according to a new routing protocol is received. If not then the kth device continues to operate according to the protocol according to which it is currently operating.  
         [0035]    If on the other hand a command is received instructing the kth device to operate according to a new protocol, then the method  400  loops back to decision block  414 .  
         [0036]    If on reaching decision block  414 , either from decision block  408  or decision block  418 , it is determined that the kth device is not able to support the routing protocol according to which it has been requested to operate, then the method  400  continues with step  420 . In step  420  a negative response that indicates that the kth device is not able to operate according to the commanded protocol is transmitted. In step  422  a beacon signal that includes an indication that the kth wireless device cannot establish links with other devices in order to route messages according to the commanded protocol is transmitted.  
         [0037]    Following block  422  after a predetermined delay  424 , the device  402  loops back to step  402 . Note that during the delay  424 , or after multiple delay  424  periods have elapsed, the network may have been switched to a protocol that the kth device is able to support (as determined in step  414 ) and the kth device will be able to join or rejoin the network.  
         [0038]    [0038]FIG. 5 is a flow chart of a method  500  of operating a wireless device of the networks  100 ,  200  shown in FIGS.  1 - 2  according to the preferred embodiment of the invention. The wireless device that executes the method  500  shown in FIG. 6, herein after referred to as the mth wireless device, performs a control function in the networks  100 ,  200 . In particular, in block  502 , messages are received from a plurality of wireless devices indicating what routing protocols each of the wireless devices supports. The messages received in step  502  are equivalent to the message sent step  404  of method  400 . Alternatively, the messages received in step  502  are sent by an intermediate wireless device (e.g., a wireless device having special status among a subset of the wireless devices of a network) based on information extracted from the message sent in step  404 . Step  502 , takes place over at least a period of time as wireless devices join the network.  
         [0039]    In step  504  a determination to switch to another routing protocol is made based on the information collected in step  502 .  
         [0040]    In step  506  a command is transmitted to at least a subset of the wireless devices  102 ,  104  in the network (e.g.,  102 ,  104 ) to switch to a specified routing protocol. Either the entire network can be commanded to switch to a new routing protocol, or a part of the network can be commanded to switch to a new protocol.  
         [0041]    [0041]FIG. 6 is a hardware block diagram of the central wireless device  102  that is included in the networks shown in FIGS.  1 - 2  according to the preferred embodiment of the invention. The other wireless devices  104  preferably have the same basic internal structure. Optionally the wireless devices (e.g., central wireless device  102 ) that in carrying out certain routing protocols perform more functions (e.g., control functions) are connected to external power sources, and/or have higher processing power. The wireless device  102  comprises a transceiver  602  a processor  604 , a program memory  606 , a workspace memory  608  and an indicator  614  coupled together through a signal bus  610 . The control processor  604  controls the overall operation of the wireless device  102 , and is used to execute programs embodying the methods shown in FIG. 4 or  5 . The control processor  604  also serves to generate packets for transmission, and process received packets. The program memory  606  is used to store the programs executed by the control processor  604 . The program memory  606  is a type of computer readable medium. Programs embodying the method shown in FIGS. 4, 5 are alternatively stored in other types of program memories. The works space memory  608  is used as a workspace by the control processor  604  in executing the programs stored in the program memory  606 . The transceiver  602  is coupled to an antenna  612 . The indicator  614 , which can be audible or visual or both is used to indicate that a wireless device  102  is not connected to the network (e.g.,  100 ,  200 ) and human intervention may be necessary to get the wireless device  102  connected to the network.  
         [0042]    The computer readable medium used in connection with the present invention as a memory for storing programs can comprise volatile memory such as RAM, or a medium that contains data in a transient state, such as a communication channel, network circuits, or a wireless communication link, or preferably nonvolatile memory including but not limited to, flash memory, Read Only Memory (ROM), EPROM, EEPROM, disk drive. The computer readable medium used as a workspace for signal processing operations, can comprise Random Access Memory (RAM). The present invention, as would be known to one of ordinary skill in the art could be produced in hardware or software, or in a combination of hardware and software. The system, or method, according to the inventive principles as disclosed in connection with the preferred embodiment, may be produced in a single computer system having separate elements or means for performing the individual functions or steps described or claimed or one or more elements or means combining the performance of any of the functions or steps disclosed or claimed.  
         [0043]    While the preferred and other embodiments of the invention have been illustrated and described, it will be clear that the invention is not so limited. Numerous modifications, changes, variations, substitutions, and equivalents will occur to those of ordinary skill in the art without departing from the spirit and scope of the present invention as defined by the following claims.

Technology Category: 5