Time synchronization for distributed mobile ad hoc networks
Time synchronization among nodes in a wireless mobile ad hoc network (MANET) is obtained using a cross layer approach. Each node maintains a routing table that contains entries corresponding to other nodes of the network that are one or more hops away from the node, and topology messages are exchanged periodically among the nodes in order to update their routing tables. A network master node is selected, and remaining nodes that are one or more hops away from the master node are defined as slave nodes. The master node includes master timing information in the topology messages it transmits. The timing information is concatenated to include a first time (T 1 ) at which a topology message was received by the master from each of the slave nodes, and a second time (td) at which the master node transmits a topology message after receiving all the topology messages from the slave nodes.
1. A method of obtaining synchronization among nodes in a wireless mobile ad hoc network (MANET), comprising:
maintaining, at a given node of the network, a routing table containing entries corresponding to other nodes of the network that are one or more hops away from the given node;
periodically exchanging topology messages among nodes of the network for updating the routing tables at each of the nodes of the network;
selecting a network master node, and defining remaining nodes that are one or more hops away from the network master node as slave nodes;
including master timing information in topology messages transmitted by the network master node, wherein the master timing information corresponds to first times (T 1 ) at which the network master node received a topology message from each of the slave nodes, and a second time (td) at which the network master node sends a topology message after receiving the topology messages from each of the slave nodes; and
implementing a distributed scheduling protocol for transmitting the topology messages from each of the slave nodes in order to resolve contention for channel access among each of the nodes of the network.
2. The method of claim 1 , including selecting a node activation multiple access (NAMA) protocol as the distributed scheduling protocol.
3. A method of obtaining synchronization among nodes in a wireless mobile ad hoc network (MANET), comprising:
maintaining, at a given node of the network, a routing table containing entries corresponding to other nodes of the network that are one or more hops away from the given node;
periodically exchanging topology messages among nodes of the network for updating the routing tables at each of the nodes of the network;
selecting a network master node, and defining remaining nodes that are one or more hops away from the network master node as slave nodes;
including master timing information in topology messages transmitted by the network master node, wherein the master timing information corresponds to first times (T 1 ) at which the network master node received a topology message from each of the slave nodes, and a second time (td) at which the network master node sends a topology message after receiving the topology messages from each of the slave nodes; and
providing a given slave node with a controller or processor for determining a time offset estimation (D) according to the master timing information in a topology message received by the given slave node from the network master node.
4. The method of claim 3 , including configuring the controller or processor at the given slave node to determine the time offset estimation (D) according to D=(½)(T 1 +td−T 2 ) wherein T 2 corresponds to a time at which the given slave node received the master timing information.
5. A method of obtaining synchronization among nodes in a wireless mobile ad hoc network (MANET), comprising:
operating the network according to a time domain multiple access (TDMA) protocol having time slots of a determined size available for transmissions from the nodes;
maintaining, at a given node of the network, a routing table containing entries corresponding to other nodes of the network that are one or more hops away from the given node;
periodically exchanging topology messages among nodes of the network for updating the routing tables at each of the nodes;
implementing a distributed scheduling protocol for transmitting the topology messages in order to resolve contention among the nodes of the network for access to the time slots;
selecting a network master node, and defining remaining nodes that are one or more hops away from the master node as slave nodes; and
including master timing information in topology messages transmitted by the network master node, wherein the master timing information corresponds to first times (T 1 ) at which the network master node received a topology message from each of the slave nodes, and a second time (td) at which the network master node sends a topology message after receiving the topology messages from the slave nodes.
6. The method of claim 5 , including selecting a node activation multiple access (NAMA) protocol as the distributed scheduling protocol.
7. The method of claim 5 , including providing a given slave node with a controller or processor for determining a time offset estimation (D) according to the master timing information in a topology message received by the slave node from the given, network master node.
8. The method of claim 7 , including configuring the controller or processor at the given slave node to determine the time offset estimation (D) according to D=(½)(T 1 +td−T 2 ) wherein T 2 corresponds to a time at which the given slave node received the master timing information.
9. The method of claim 7 , including implementing a coarse network time synchronization among the nodes of the network before including the master timing information in the topology messages transmitted by the network master node.
10. The method of claim 9 , including configuring the controller or processor at the given slave node to determine the time offset estimation when a topology message exchange between the given slave and the network master nodes is completed over a time greater than the size of one time slot.