Vehicle-mounted ad hoc network communication system based on OFDMATechnical Field
The invention belongs to the technical field of mobile communication, and particularly relates to a vehicle-mounted ad hoc network communication system based on OFDMA.
Background
The vehicular ad hoc network technology is used as a key component of an intelligent traffic system, and aims to improve traffic management efficiency and traffic safety through communication between vehicles and road facilities. The original purpose of development is to provide vehicles and road condition information beyond the conventional visual range for drivers by utilizing the characteristics of the self-organizing network, thereby reducing traffic accidents and optimizing traffic flow. The vehicle-mounted ad hoc network plays a very important role in the current technical advanced traffic management method, and is also a core of an intelligent traffic system. Researchers realize vehicle networking through new generation communication technologies such as 5G, and some people try to establish an ad hoc network protocol to realize vehicle ad hoc network.
In the direction of research on the ad hoc network, due to limitation of resources, protocols of a communication system are related to how to effectively utilize limited bandwidth resources, and a time division multiplexing method is often adopted, so that each vehicle only transmits in a specific time slot. Due to the rapid mobility of nodes and the complexity of the communication environment, conventional ad hoc network communication technology has not been able to adapt to the development thereof.
Disclosure of Invention
In view of this, the present invention proposes an OFDMA-based vehicular ad hoc network communication system. The invention adopts OFDMA system to divide different sub-channels for different communication nodes, improves the spectrum utilization efficiency, carries out fine granularity perception on the running state of the mobile node, improves the communication reliability, and obviously reduces the maintenance scale of the routing network by adopting the regional routing protocol type mixed routing protocol.
The invention adopts the technical scheme that:
A vehicle-mounted self-networking communication system based on OFDMA comprises fixed nodes and mobile nodes, wherein the fixed nodes adopt a 4-antenna transmission mechanism to form space diversity, the mobile nodes adopt a 2-antenna transmission mechanism to form space diversity, each communication period is divided into a control time slot, a sensing time slot and a data time slot, the system adopts a regional routing protocol, each node only maintains a routing table in a regional radius which is within 1 hop, a table-driven routing mode is adopted in the region, an active routing mode is adopted among the regions, and the routing discovery between a source node and a destination node is completed through the routing discovery of boundary nodes;
The communication process between the mobile node A and the mobile node B is as follows:
1) The mobile node A sends an information sending request to the fixed node in a control time slot;
2) After receiving the request, the fixed node inquires a routing table, if the routing information of the mobile node B is found, the data time slot distribution of the data transmitted from the mobile node A to the fixed node and from the fixed node to the mobile node B is defined, and then the step 3) is executed, otherwise, the routing information of the mobile node B is broadcasted and found to the adjacent fixed node, the propagation path is determined, and then the step 4) and the step 5) are executed;
3) After the time slot allocation is completed, the mobile node A transmits information to the fixed node in the defined data time slot, and the fixed node forwards signals to the mobile node B as a relay in the defined data time slot;
4) In the control time slot, all relay fixed nodes plan the data time slot allocation of the data transmitted to the mobile node B by the mobile node A;
5) The mobile node A and each data relay fixed node perform data transmission in the respective assigned data time slots.
Further, the duration of the communication period is 1s, the beginning of the communication period is a control time slot of 10ms, and then the communication period is divided into four sections, each section is composed of a sensing time slot and a data time slot, and the lengths of the first three sections are all 250ms.
Further, the control time slot is responsible for constructing a regional network topology, forming a network transmission path, and dividing the time-frequency structure of each node of the data time slot in the future 1 s.
Further, the sensing time slot occupies 10ms, in the sensing time slot, the fixed node sequentially sends sensing trigger signaling to each mobile node to be communicated, the mobile communication node replies the sensing trigger signaling to the fixed node after receiving the sensing trigger signaling, the mobile node and the communication node obtain relative moving speed by detecting Doppler frequency shift of the sensing trigger signaling, and according to the relative moving speed and receiving level of the trigger signaling, the fixed node and the mobile node regulate respective transmitting power to ensure effective transmission of signal transmission in a communication period.
Further, the whole bandwidth is divided into a plurality of sub-channels overlapped with each other among the sub-bands, each sub-channel comprises a plurality of orthogonal modulation sub-carriers, and each sub-channel is distributed to a mobile node, so that the utilization efficiency of network channel resources is improved.
The invention has the beneficial effects that:
1. the invention improves the communication reliability under the high dynamic condition, improves the network communication capacity, and has good adaptability and flexibility.
2. In the invention, the fixed node and the mobile node evaluate the relative moving speed through exchanging sensing signaling, then adjust the transmitting power according to the receiving level, reduce the energy loss of the mobile node and ensure that the signal in the next data time slot is effectively transmitted.
3. The invention divides the network into different areas, adopts a table-driven routing mode in the areas, adopts an active routing mode among the areas, and completes the route discovery between the source node and the destination node through the route discovery of the boundary node.
Drawings
Fig. 1 is a schematic diagram of an OFDMA-based vehicular ad hoc network communication system.
Fig. 2 is a schematic diagram of time slot division.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
An OFDMA-based vehicular ad hoc network communication system, as shown in fig. 1, includes a fixed node and a mobile node. The fixed node is installed in the urban traffic network, is a network skeleton of the system, is mainly responsible for relay, is connected with a mains supply, and forms space diversity by adopting a 4-antenna transmitting mechanism. The mobile node is arranged on a motor vehicle and is a communication terminal, has energy sensing and adjusting capability, adopts a vehicle-mounted power supply to supply power, and adopts a 2-antenna transmitting mechanism to form space diversity. The mobile node communicates only with the fixed node, and the fixed node may also communicate with the fixed node within the coverage area.
The system employs an OFDMA communication scheme, where time slots are divided into control, sense and data slots every 1s in time for one period, as shown in fig. 2.
The control time slot occupies 10ms, is responsible for constructing a regional network topology, forms a network transmission path, and divides the time-frequency structure of each node of the data time slot in the future 1 s. The sensing time slot occupies 10ms, the time slot fixed node sequentially sends sensing trigger signaling to each mobile node to be communicated, the mobile communication node replies the sensing trigger signaling to the fixed node after receiving the sensing trigger signaling, the mobile node and the communication node can obtain relative moving speed by detecting Doppler frequency shift of the sensing trigger signaling, and according to the relative moving speed and the receiving level of the trigger signaling, the two types of nodes regulate respective transmitting power, so that signal transmission is effectively sent in a period, and the sensing time slot is carried out once every 250ms for ensuring the timeliness of the position and the speed of the mobile node.
The system divides the whole bandwidth into a plurality of sub-channels overlapped with each other among the sub-bands, each sub-channel comprises a plurality of orthogonal modulation sub-carriers, each sub-channel is distributed to a mobile node, and the utilization efficiency of network channel resources is improved.
The system adopts Zone Routing Protocol (ZRP), each node only maintains a routing table in a zone radius, the zone radius is set to be within 1 hop, a network is divided into different zones according to the rule, a table-driven routing mode is adopted in the zones, an active routing mode is adopted among the zones, and the routing discovery between a source node and a destination node is completed through the routing discovery of boundary nodes.
The communication process between different mobile nodes a and B within a single node coverage area of a fixed node is described as:
1) A sends an information transmission request to the fixed node in a control slot.
2) After receiving the request, the fixed node performs a routing table query and demarcates the allocation of data time slots from the a to the fixed node and from the fixed node to the B.
3) After the slot allocation is completed, a sends information to the fixed node in the specified data slot, and the fixed node forwards the signal to B as a relay in the defined data slot.
The communication procedure between two mobile nodes a and C within the coverage of different fixed nodes can be described as:
1) A sends an information transmission request to the fixed node in a control slot.
2) After receiving the request, the fixed node performs a routing table query, in which case no routing information of C is found, and then broadcasts the routing information of finding C to the neighboring fixed nodes, and determines a propagation path, which can be completed in a control slot and an idle data slot.
3) In the control time slot, all relay fixed nodes plan the data time slot allocation of the data transferred from A to C.
4) And the A node and each data relay fixed node perform data transmission in the respectively allocated data time slots.
In the system, the fixed node is arranged at the roadside and is responsible for constructing the regional network topology, and the mobile node is arranged on the automobile and is a communication terminal. The fixed node and the mobile node both adopt multiple antennas to realize the multipath resistance of the space diversity improving system.
The system adopts an OFDMA communication system, time slots are divided into control time slots, sensing time slots and data time slots every 1s in time, as shown in fig. 2, the control time slots are responsible for generating propagation paths, the time and frequency structures of the data time slots in the period are allocated, meanwhile, regional routes in 1 hop are maintained, the sensing time slots are used for evaluating the relative moving speed by exchanging sensing signaling between a fixed node and a mobile node, then the energy loss of the mobile node is reduced according to a receiving level, the signals in the next data time slots are guaranteed to be effectively transmitted, and the data time slots are used for transmitting service data according to the time and frequency structures allocated by the control time slots and the transmitting power obtained by the sensing time slots. In order to adapt to the high dynamic characteristic of the vehicle-mounted ad hoc network communication system, sensing needs to be carried out once every 250ms, a data time slot in every 1s is divided into four data time slots, and the receiving and transmitting power of each time slot needs to be regulated.
When the fixed nodes need to communicate with the fixed nodes and the mobile nodes distributed in different fixed nodes communicate, an active route mode is adopted among the areas, and route discovery between the source node and the destination node is finally completed through a route discovery process among the fixed nodes. The route discovery process between the fixed nodes is in an active route form and can be initiated at any time point at any time.
In short, the nodes of the invention adopt an OFDMA mechanism to communicate, and different vehicles divide different communication sub-channels in a time-frequency domain. And sensing the motion state of the mobile node through the sensing time slot, and adjusting the communication signal strength and the network connection form. By adding energy awareness and management, the energy consumption of the mobile node is reduced. The system remarkably increases the spectrum utilization efficiency of the vehicle-mounted ad hoc network communication system, and can adapt to the high dynamic movement characteristic of the vehicle.