A vehicle-mounted ad hoc network communication system based on OFDMA

Abstract

The present invention relates to an OFDMA-based on-vehicle ad hoc network communication system, belonging to the field of mobile communication technology. The system includes fixed nodes and mobile nodes, and each communication cycle is divided into a control time slot, a sensing time slot, and a data time slot. The system adopts a regional routing protocol, and each node only maintains a routing table within the regional radius, which is within a single hop. A table-driven routing method is used within the regional area, and an active routing method is used between regional areas. Route discovery between source and destination nodes is completed through route discovery at boundary nodes. The present invention can improve communication reliability and significantly reduce the maintenance scale of the routing network.

Description

Technical Field

[0001] The present invention belongs to the technical field of mobile communications, and in particular relates to an OFDMA-based vehicle-mounted ad hoc network communication system. Background Art

[0002] Vehicle-based ad hoc networking (VAN) technology, a key component of intelligent transportation systems (ITS), aims to improve traffic management efficiency and driving safety through communication between vehicles and between vehicles and road infrastructure. Its development was originally intended to leverage the characteristics of self-organizing networks to provide drivers with vehicle and road condition information beyond their normal visual range, thereby reducing traffic accidents and optimizing traffic flow. In-vehicle ad hoc networking plays a crucial role in today's technologically advanced traffic management methods and is the core of intelligent transportation systems. Researchers are primarily implementing VANs through next-generation communication technologies such as 5G, while others are attempting to establish ad hoc networking protocols to achieve this goal.

[0003] In the field of ad hoc networking research, due to resource constraints, communication system protocols must fully consider how to effectively utilize limited bandwidth resources. Time division multiplexing is often used, with each vehicle transmitting only during specific time slots. Due to the rapid mobility of nodes and the complexity of the communication environment, traditional ad hoc network communication technologies are no longer adaptable. Summary of the Invention

[0004] In light of this, the present invention proposes an OFDMA-based vehicular ad hoc network communication system. This system uses OFDMA to divide different communication nodes into different subchannels, improving spectrum utilization efficiency, providing fine-grained awareness of the operating status of mobile nodes, and enhancing communication reliability. Furthermore, it employs a hybrid routing protocol with a regional routing protocol to significantly reduce the maintenance scale of the routing network.

[0005] The technical solution adopted in the present invention is:

[0006] An OFDMA-based vehicular ad hoc network communication system includes fixed nodes and mobile nodes. The fixed nodes use a four-antenna transmission mechanism to achieve spatial diversity, while the mobile nodes use a two-antenna transmission mechanism to achieve spatial diversity. Each communication cycle is divided into a control time slot, a sensing time slot, and a data time slot. The system uses a regional routing protocol, and each node only maintains a routing table within the regional radius, which is within a 1-hop radius. A table-driven routing method is used within the regional area, and an active routing method is used between regional areas. Route discovery between source and destination nodes is completed through route discovery at boundary nodes.

[0007] The communication process between mobile node A and mobile node B is as follows:

[0008] 1) Mobile node A sends a message sending request to the fixed node in the control time slot;

[0009] 2) After receiving the request, the fixed node searches its routing table. If it finds routing information for mobile node B, it allocates data time slots for transmitting data from mobile node A to the fixed node and from the fixed node to mobile node B, and then executes step 3). Otherwise, it broadcasts routing information for mobile node B to neighboring fixed nodes, determines the propagation path, and then executes steps 4) and 5).

[0010] 3) After completing the time slot allocation, mobile node A sends information to the fixed node in the designated data time slot. The fixed node acts as a relay and forwards the signal to mobile node B in the designated data time slot.

[0011] 4) In the control time slot, all relay fixed nodes plan the data time slot allocation for data to be transmitted from mobile node A to mobile node B;

[0012] 5) The mobile node A and each data relay fixed node perform data transmission in their respective allocated data time slots.

[0013] Furthermore, the duration of the communication cycle is 1s. The communication cycle starts with a 10ms control time slot and is then divided into four segments. Each segment consists of a sensing time slot and a data time slot. The length of the first three segments is 250ms.

[0014] Furthermore, the control time slot is responsible for constructing the regional network topology, forming the network transmission path, and dividing the time-frequency structure of each node in the data time slot within the next 1 second.

[0015] Furthermore, the perception time slot occupies 10ms. In the perception time slot, the fixed node sends perception trigger signaling to each mobile node to communicate in turn. After receiving the perception trigger signaling, the mobile communication node replies with the perception trigger signaling to the fixed node. The mobile node and the communication node obtain the relative moving speed by detecting the Doppler frequency shift of the perception trigger signaling. According to the relative moving speed and the receiving level of the trigger signaling, the fixed node and the mobile node adjust their respective transmission power to ensure the effective delivery of the signal transmission within the communication cycle.

[0016] Furthermore, the entire bandwidth is divided into multiple sub-channels with overlapping sub-bands. Each sub-channel includes multiple orthogonally modulated sub-carriers. Each sub-channel is allocated to a mobile node, thereby improving the utilization efficiency of network channel resources.

[0017] The beneficial effects of the present invention are:

[0018] 1. The present invention improves communication reliability under highly dynamic conditions, increases network communication capacity, and has good adaptability and flexibility.

[0019] 2. In the present invention, the fixed node and the mobile node evaluate the relative moving speed by exchanging perception signaling, and then adjust the transmission power according to the reception level to reduce the energy loss of the mobile node and ensure that the signal in the next data time slot is effectively transmitted.

[0020] 3. The present invention divides the network into different areas, adopts table-driven routing within the area, adopts active routing between areas, and completes routing discovery between source nodes and destination nodes through routing discovery of boundary nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of a vehicle-mounted ad hoc network communication system based on OFDMA.

[0022] Figure 2 This is a schematic diagram of time slot division. DETAILED DESCRIPTION

[0023] The present invention will be described in further detail below with reference to the accompanying drawings.

[0024] A vehicle-mounted ad hoc network communication system based on OFDMA, such as Figure 1 As shown in the figure, the system consists of fixed nodes and mobile nodes. Fixed nodes are installed in the urban transportation network and serve as the network backbone of the system. They are primarily responsible for relaying, connected to the mains power supply, and use a four-antenna transmission mechanism to achieve spatial diversity. Mobile nodes are installed in vehicles and serve as communication terminals. They have energy sensing and regulation capabilities, are powered by the vehicle's power supply, and use a two-antenna transmission mechanism to achieve spatial diversity. Mobile nodes communicate only with fixed nodes, while fixed nodes can also communicate with other fixed nodes within their coverage area.

[0025] The system adopts OFDMA communication system, and divides the time slot into control slot, sensing slot and data slot every 1s. Figure 2 shown.

[0026] The control time slot, which takes up 10ms, is responsible for building the regional network topology, forming the network transmission path, and dividing the time-frequency structure of each node in the data time slot within the next 1s. The sensing time slot, which takes up 10ms, is where the fixed node sequentially sends sensing trigger signaling to each mobile node to communicate. After receiving the sensing trigger signaling, the mobile communication node replies to the fixed node. The relative movement speed of the mobile node and the communication node is determined by detecting the Doppler frequency shift of the sensing trigger signaling. Based on the relative movement speed and the received level of the trigger signaling, the two types of nodes adjust their respective transmit power to ensure that the signal transmission within the period is effectively delivered. To ensure the timely location and speed of the mobile node, the sensing time slot is performed every 250ms.

[0027] The system divides the entire bandwidth into several overlapping sub-channels between sub-bands. Each sub-channel includes several orthogonally modulated sub-carriers. Each sub-channel is assigned to a mobile node, improving the utilization efficiency of network channel resources.

[0028] The system adopts the Zone Routing Protocol (ZRP). Each node only maintains the routing table within the zone radius. The zone radius here is set to within 1 hop. The network is divided into different zones according to the above rules. Table-driven routing is adopted within the zone, and active routing is adopted between zones. The route discovery between the source node and the destination node is completed through the route discovery of the boundary node.

[0029] Within the coverage area of ​​a single fixed node, the communication process between different mobile nodes A and B is described as follows:

[0030] 1) A sends an information sending request to the fixed node in the control time slot.

[0031] 2) After receiving the request, the fixed node performs a routing table query and allocates the data time slots for data transmission from A to the fixed node and from the fixed node to B.

[0032] 3) After completing the time slot allocation, A sends the information to the fixed node in the specified data time slot, and the fixed node acts as a relay to forward the signal to B in the designated data time slot.

[0033] The communication process between two mobile nodes A and C in different fixed node coverage areas can be described as:

[0034] 1) A sends an information sending request to the fixed node in the control time slot.

[0035] 2) After receiving the request, the fixed node performs a routing table query. In this case, if C's routing information is not found, it broadcasts C's routing information to adjacent fixed nodes and determines the propagation path. This process can be completed in the control time slot and the idle data time slot.

[0036] 3) In the control time slot, all relay fixed nodes plan the data time slot allocation for data to be transmitted from A to C.

[0037] 4) Node A and each data relay fixed node perform data transmission in their respective allocated data time slots.

[0038] In this system, fixed nodes are installed on roadsides and are responsible for building the regional network topology. Mobile nodes are installed in vehicles and serve as communication terminals. Both fixed and mobile nodes use multiple antennas to achieve spatial diversity, improving the system's anti-multipath capability.

[0039] This system adopts OFDMA communication system, and divides the time slot into control time slot, sensing time slot and data time slot every 1s. Figure 2 As shown in the figure, the control slot is responsible for generating propagation paths, allocating the time and frequency structure of data slots within the current cycle, and maintaining regional routing within a single hop. During the sensing slot, fixed and mobile nodes exchange sensing signaling to assess relative movement speeds. Transmit power is then adjusted based on the received power level, minimizing energy loss at the mobile node and ensuring effective signal transmission in the next data slot. In the data slot, service data is transmitted according to the time-frequency structure allocated by the control slot and the transmit power obtained during the sensing slot. To accommodate the highly dynamic nature of VANET communication systems, sensing is performed every 250ms, splitting each 1s data slot into four data slots. Transmit and receive power adjustments are required for each slot.

[0040] When fixed nodes need to communicate with other fixed nodes, or when mobile nodes distributed within different fixed nodes communicate, active routing is used between regions. This process of route discovery between fixed nodes ultimately completes the route discovery between the source and destination nodes. This route discovery process between fixed nodes is an active routing process and can be initiated at any time.

[0041] In summary, the present invention utilizes OFDMA for inter-node communication, assigning different communication sub-channels to different vehicles in the time-frequency domain. By sensing time slots, the motion state of mobile nodes is detected, adjusting communication signal strength and network connection mode. Energy sensing and management are incorporated to reduce energy consumption in mobile nodes. This system significantly improves the spectrum utilization efficiency of vehicular ad hoc network communication systems and can adapt to the highly dynamic mobility characteristics of vehicles.

Claims

1. A vehicle-mounted ad hoc network communication system based on OFDMA, characterized in that: The system includes fixed nodes and mobile nodes. Fixed nodes use a 4-antenna transmission mechanism to form spatial diversity, while mobile nodes use a 2-antenna transmission mechanism to form spatial diversity. Each communication cycle is divided into a control time slot, a sensing time slot, and a data time slot. The system uses a regional routing protocol. Each node only maintains a routing table within the regional radius, which is within a 1-hop radius. Table-driven routing is used within the region, and active routing is used between regions. Route discovery between source and destination nodes is completed through route discovery at the boundary nodes. The communication cycle lasts 1 second and begins with a 10ms control slot. It is then divided into four segments, each consisting of a sensing slot and a data slot. The first three segments are 250ms long. The sensing slots are 10ms long. During these slots, the fixed node sends a sensing trigger signaling message to each mobile node in communication. Upon receiving the sensing trigger signaling message, the mobile communication node replies to the fixed node with a similar signaling message. The mobile and communication nodes detect the Doppler shift of the sensing trigger signaling message to determine their relative speed. Based on the relative speed and the received level of the trigger signaling message, the fixed and mobile nodes adjust their transmit power. The communication process between mobile node A and mobile node B is as follows: 1) Mobile node A sends a message sending request to the fixed node in the control time slot; 2) After receiving the request, the fixed node searches its routing table. If it finds routing information for mobile node B, it allocates data time slots for transmission from mobile node A to the fixed node and from the fixed node to mobile node B, and then proceeds to step 3. Otherwise, it broadcasts the routing information for mobile node B to neighboring fixed nodes, determines the propagation path, and then proceeds to steps 4 and 5. 3) After the time slots are allocated, mobile node A sends information to the fixed node in the designated data time slot. The fixed node acts as a relay and forwards the signal to mobile node B in the designated data time slot. 4) In the control time slot, all relay fixed nodes plan the data time slot allocation for data to be transmitted from mobile node A to mobile node B; 5) Mobile node A and each data relay fixed node transmit data in their respective allocated data time slots.

2. The OFDMA-based vehicle-mounted ad hoc network communication system according to claim 1, characterized in that: The control time slot is responsible for constructing the regional network topology, forming the network transmission path, and dividing the time-frequency structure of each node in the data time slot within the next 1 second.

3. The OFDMA-based vehicle-mounted ad hoc network communication system according to claim 1, characterized in that: The entire bandwidth is divided into multiple overlapping sub-channels between sub-bands. Each sub-channel includes multiple orthogonally modulated sub-carriers. Each sub-channel is assigned to a mobile node, improving the utilization efficiency of network channel resources.

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