Patent ID: 8565214

Claim:
A method for scheduling downlink packets to be transmitted in a hybrid communication network for a transportation safety system, wherein the hybrid communication network includes a wired network and a wireless network, wherein the wired network includes a set of fixed nodes, wherein the set of fixed nodes includes a head node at a first end of the wired network connected to a controller via a wired interface, a terminal node at a second end of the wired network, and a set of relay nodes arranged between the head node and the terminal node, wherein the wireless network includes a set of mobile nodes, wherein each mobile node is arranged in a moveable car associated with the transportation safety system, wherein the controller includes means for generating the downlink packets and transmitting the downlink packets to the head node via the wired interface, wherein the downlink packet are asynchronously relayed to the set of relay nodes and the terminal node via the wired network, wherein all the fixed nodes synchronously retransmit the downlink packets via the wireless network to the set of mobile nodes after the terminal node receives the downlink packet, and wherein the set of fixed nodes are arranged sequentially along a trajectory of the moveable cars, comprising: determining a downlink travel time for the downlink packets to travel from the controller to the set of fixed nodes and from the set of fixed nodes to the set of mobile nodes, wherein a downlink travel time T D for the downlink packet from the controller to a mobile node MN i is T D =T CH +T HF +T FM , where T CH is a time from when the controller be ins transmitting the downlink packet to a time a head node (FN 0 ) has received the downlink packet, T HF is a time from when the head node has received the downlink packet to a time when all the fixed nodes begin transmitting the packet synchronously, and T FM is a time from when all the fixed nodes synchronously transmit the packet to a time when the mobile node MN i has received the packet; scheduling downlink data intervals (DDI) based on the downlink travel time; and transmitting the downlink packets to the set of mobile nodes during the DDI, such that a latency requirement of the transportation system is satisfied.