Abstract:
A method for sharing thermal load between nodes in a communication network includes monitoring the thermal load of a first node in the communication network. The first node is an advantaged node. When the thermal load of the first node is a predetermined value, a second node is selected as an advantaged node. A notification message is transmitted to the plurality of nodes in the communication network identifying the second node as an advantaged node for at least a subset of message traffic of the first node.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to communication networks and in particular, to a system and method for thermal load sharing between nodes in a communications network. 
     BACKGROUND OF THE INVENTION 
     Wireless communication networks may be used for numerous applications including tactical military and commercial applications. In an exemplary military application, military vehicles (e.g., tanks, trucks, airplanes, etc.) may include radios that act as nodes in the wireless communication network. One type of radio is a software defined radio (SDR). A software defined radio may be implemented in existing radios and the existing physical enclosures of these radios (i.e., the legacy radio form factors). As a result, the thermal limitations of the existing radio structure is imposed on the software defined radio. A digital radio, such as an SDR, may generate more power and heat than a legacy radio and a legacy radio enclosure may not have appropriate fans or fins to dissipate the heat and power. In addition, the radio temperature may be affected by the temperature of the external environment as well as the duty cycle of the radio (e.g., an SDR may transmit greater percentage of time than a legacy radio). 
     Thermal limitations of the physical enclosure of legacy radios can impact the ability of an SDR to operate in an ad hoc manner. In particular, thermal constraints of the radio enclosure may impact the ability of an SDR to function as an ad hoc relay (e.g., a cluster head or advantaged node). A wireless communication network may include advantaged nodes (e.g., on a ground platform, an airborne platform, a naval based platform, etc.) which have enhanced visibility or connectivity to other nodes in the network and therefore may have a larger number of one-hop neighbor nodes than a non-advantaged node. For example, a node may be selected as a relay node if the node can reach a particular destination or destinations in less hops. An advantaged node typically processes a large amount of traffic and therefore may generate more power and heat. When the thermal capacity of the ad hoc relay node is exceeded, the relay node must shut down which can disrupt the entire communication network. As a result, the performance of the network may be limited to the throughput of a single relay node. 
     There is a need, therefore, for a system and method to share (or shift) the thermal load of a relay node in a communication network. There is also a need for a system and method to assign a new relay node with additional thermal capacity and shift at least a portion of the thermal load from an original relay node. Accordingly, a system and method may be provided to select a new cluster head in response to the thermal load of an original cluster head and shift at least a portion of traffic to the new cluster head (i.e., other nodes in the network may direct/send traffic to the new cluster head) to prevent shut down of the original cluster head and disruption of the communication network. 
     SUMMARY OF THE INVENTION 
     In accordance with one embodiment, a method for sharing thermal load between nodes in a communication network includes monitoring the thermal load of a first node in the communication network, the first node being an advantaged node, selecting a second node as an advantaged node when the thermal load of the first node is a predetermined value, transmitting a notification message to the plurality of nodes in the communication network identifying the second node as an advantaged node for at least a subset of message traffic of the first node. 
     In accordance with another embodiment, a node for a communications network includes an antenna, a transceiver coupled to the antenna and configured to transmit and receive messages, and a control circuit coupled to the transceiver and configured to monitor the thermal load of the node, to select a second node in the communication network as an advantaged node when the thermal load of the node is a predetermined value, and to transmit a notification message identifying the second node as an advantaged node. 
     In accordance with one embodiment, a method for sharing thermal load of a relay node in a communication network having a plurality of nodes includes monitoring the thermal load of a first relay node in the communication network, selecting a node as a second relay node when the thermal load of the first relay node is a predetermined value, transmitting a notification message to the plurality of nodes in the communication network identifying the second relay node as a relay node for at least a subset of message traffic of the first relay node and transmitting the subset of message traffic through the second relay node. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more readily understood by reference to the following description taken with the accompanying drawings, in which: 
         FIG. 1  is a diagram of a wireless communication network having a plurality of nodes in accordance with an embodiment. 
         FIG. 2  is a schematic block diagram of a node in a wireless communication network in accordance with an embodiment. 
         FIG. 3  illustrates a method of sharing a thermal load between nodes in a communication network in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  is a diagram of a wireless communication network  100  including a plurality of nodes in accordance with an embodiment. In an exemplary embodiment, wireless communication network  100  may be a Joint Tactical Radio System (JTRS) or other ad hoc wireless network. Nodes  1  through  14  in network  100  may be, for example, a ground based node (e.g., a radio in a tank or other military vehicle), an airborne based node, a naval based node, or other appropriate platform. Each node in network  100  may be a software defined radio (SDR). Preferably, each node in network  100  communicates in accordance with a structured wireless channel access scheme such as Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA). Slot assignments may be coordinated by a protocol such as Unifying Slot Assignment Protocol (USAP). 
     Network  100  may include both non-advantaged nodes. e.g., nodes  1 - 6  and  8 - 14  and advantaged nodes (i.e., a cluster head or relay node) such as node A 7 . An advantaged node, such as node A 7 , has enhanced visibility and connectivity to other nodes in network  100  and therefore may have a larger number of one-hop neighbor nodes than a non-advantaged node. Non-advantaged nodes in network  100  may use advantaged node A 7  as a relay node (or cluster head) to reach other nodes in network  100 . Various algorithms may be used to appoint a node as an advantaged node. For example, a node may be appointed as an advantaged node if the node has the widest coverage, the shortest paths, the most addresses with direct access, etc. 
     A plurality of nodes may contend for access to and use advantaged node A 7 . As advantaged node A 7  is used to receive, process and transmit traffic, it generates power and heat (i.e., a thermal load). The thermal load of the node may be affected by operation of the node, the number of messages processed by the node as well as the duty cycle of the node. In addition, the temperature of the external environment may cause an increase of the thermal load of the node. Advantaged node A 7  is configured to share or shift the thermal load with another node or nodes in network  100  in order to prevent overheating and shut down of advantaged node A 7  as well as disruption of network  100 . The other nodes in network  100  may also be configured to share or shift thermal load. 
       FIG. 2  is a schematic block diagram of a node in a wireless communication network in accordance with an embodiment. In an exemplary embodiment, node  200  is a radio in a military vehicle, such as a software defined radio. Node  200  includes an antenna  204 , a transceiver  206 , a control circuit  208  and a memory  210 . Node  200  also has a physical enclosure  202 , for example, a software defined radio may be implemented in an existing radio enclosure (i.e., a legacy radio form factor). Physical enclosure  202  may have thermal limitations that may effect the operation of node  200 . 
     Transceiver  206  is coupled to antenna  204  and control circuit  208 . Transceiver  206  includes transmit and receive circuitry and is configured to transmit and receive signals via antenna  204 . Node  200  is configured to communicate with (e.g., receive signals from and transmit signals to) other nodes in a communication network  100  (shown in  FIG. 1 ). Control circuit  208  is coupled to transceiver  206  and memory  210 . Control circuit  208  may include various types of control circuitry, digital and/or analog, and may include a microprocessor, microcontroller, application specific integrated circuit (ASIC), or other digital and/or analog circuitry configured to perform various input/output, control, analysis, and other functions described herein. Memory  210  includes volatile and/or non-volatile memory to, for example, store a computer program or software to perform the functions described herein. Control circuit  208  may execute sequences of instructions contained in memory  210 . In an exemplary embodiment, node  200  is configured to communicate in an ad hoc manner using a structured wireless channel access scheme such as TDMA. 
     Node  200  may be designated as an advantaged node. Various algorithms known in the art may be used to appoint node  200  as an advantaged node. For example, a node may be appointed as an advantaged node if the node has the widest coverage, the shortest paths, the most addresses with direct access, etc. As node  200  processes message traffic to/from other nodes in the network, node  200  generates power and heat (i.e., a thermal load). In order to prevent overheating and possible shut down, control circuit  208  of node  200  is configured to share traffic (and the thermal load caused by processing the traffic) with another node (e.g., a radio) in the network that can also act as a relay or advantaged node. Accordingly, node  200  may appoint another node in the network as a relay node for at least a portion of the message traffic directed to node  200 . Accordingly, other nodes in the network will direct/transmit traffic through the new relay node. Node  200  is also configured to notify the network that it is no longer a relay node for this portion of message traffic. Node  200  may continue to process the portion of traffic that must be delivered to or by node  200 . By assigning a new relay node for at least a portion of traffic, the thermal load is shifted from one node to another across the network. By sharing the traffic load of a relay or advantaged node, a plurality of nodes are involved with carrying the thermal load for periods of time. Accordingly, the overall network performance is not restricted by the thermal capacity limitations of any one single node and the network is able to continue to operate. Each node in a network may be configured to shift traffic (and therefore thermal load) when it is appointed as a relay node and its thermal load reaches a predetermined level, i.e., when the thermal load of the node rises too high to be sustained. In this manner, the quality of service (QoS) handling of messages is based at least in part on the thermal capacity of the advantaged node, for example, a message of lower QoS may be routed a longer, slower path through the newly designated advantaged node to preserve the thermal capacity of a key advantaged node for messages with higher QoS. 
       FIG. 3  illustrates a method for sharing a thermal load between nodes in a communication network. At block  302 , an advantaged node (e.g., a cluster head or relay node) of a network is configured to monitor its thermal load. If the power and heat generated (i.e., the thermal load) does not exceed a predetermined level (i.e., the advantaged node is capable of handling the sustained relayed traffic) at bock  304 , the advantaged node operates as normal and processes all traffic at block  306 . If the power and heat generated by the advantaged node is greater than a predetermined level (i.e., the thermal load rises too high to be sustained) at block  304 , another node in the network is assigned as a new advantaged node for predetermined portion of traffic (e.g., traffic for a selected destination) at block  308 . Preferably, the new advantaged node has excess thermal capacity. Accordingly, other nodes in the network will direct traffic through the new advantaged node. The original advantaged node also sends a message throughout the network announcing it will no longer be handling at least a portion of the message traffic and identifies the new advantaged node for this traffic at block  310 . The original advantaged node may continue to process a portion of (or subset of) traffic that must be delivered to or delivered by the original advantaged node at block  312  as determined by the QoS level of the messages. Each new advantaged node may also be configured to share traffic with another node in the network if its thermal load rises too high to be sustained. 
     While the detailed drawings, specific examples and particular formulations given describe preferred and exemplary embodiments, they serve the purpose of illustration only. The inventions disclosed are not limited to the specific forms shown. For example, the methods may be performed in any of a variety of sequence of steps. The systems and methods depicted and described are not limited to the precise details and conditions disclosed. Furthermore, other substitutions, modifications, changes, and omissions may be made in the design and arrangement of the exemplary embodiments without departing from the scope of the invention as expressed in the appended claims.