In-vehicle mobile heterogeneous wireless network architecture and key technologies

The rapid development of computer technology, communication technology and microelectronics technology, as well as the mutual penetration and integration of the three, have laid the foundation for the application of communication network technology and promoted the development of social informatization. In recent years, the explosive growth of vehicles and the ubiquitous demand for information have increasingly closely integrated communication networks and vehicles. People's demand for communication services during vehicle mobility is increasing, and the research on vehicle-mounted mobile networks has become the focus of world attention, while also promoting the development of vehicles towards intelligence and networking.

Traditional vehicle communication networks are usually closed communication networks designed for purposes such as highway toll collection. Recent developments have enabled vehicle networks to support autonomous communication between vehicles to exchange safety information. Due to defects in network architecture, existing systems can only provide information exchange within a local area for vehicles traveling at high speeds. The new generation of vehicle networks will provide ubiquitous services, including: various vehicle safety message transmissions, intelligent traffic information services, multimedia digital services, etc. Therefore, in the new generation of vehicle mobile networks, how to ensure the exchange of safety information between vehicles, realize real-time data services between vehicles and intelligent traffic control centers (such as providing road conditions information, map download services based on location information, etc.), and broadband wireless access to the Internet for users in the car to obtain multimedia entertainment and information has become a very important and urgent topic in the study of vehicle mobile networks. In response to this situation, this paper proposes a vehicle mobile network architecture that integrates heterogeneous wireless networks, mainly based on vehicle self-organizing communication technology based on Wireless Access in Vehicle Environments (WAVE) (IEEE 802.11p) and vehicle broadband wireless access technology based on Worldwide Interoperability for Microwave Access (WiMAX) (IEEE 802.16e), and discusses and studies its related key technologies.

Research status and development trend of vehicle network communication

In recent years, vehicle communication networks have gradually become a hot topic in the field of intelligent transportation systems (ITS). All countries are committed to applying advanced communication technologies to vehicle transportation systems to make them safer, smarter and more efficient. Vehicle Ad Hoc Networks (VANETs) can realize communication between vehicles (V2V) during movement, and between vehicles and roadside infrastructure (V2I) when moving at low speed or stationary, and can provide vehicles with a variety of safety applications and non-safety applications. In 2004, IEEE established the IEEE 802.11p working group to develop the IEEE 802.11 version in WAVE, and used the IEEE 1609 series of protocols as the upper layer protocol to form the basic protocol architecture for vehicle wireless communication [1]. A team led by Professor Nitin Vaidya of the University of Illinois at Urbana Champaign developed a wireless mesh network test bench for multi-channel testing. Professor G. Pau of UCLA proposed the Vehicle-to-Vehicle Routing Protocol (PVRP) and built a system test platform for verification. Professors Jinhua Guo and Weidong Xiang from the University of Michigan developed a 5.9 GHz-based WAVE system channel test platform.

From the perspective of vehicle wireless access technology, most of the current vehicle mobile communication network research is based on IEEE 802.11 communication technology. However, 802.11 has the following weaknesses: small coverage, frequent switching of roadside units during vehicle movement, weak quality of service (QoS) support, and inability to provide high-quality support for multimedia information [2-3]. To this end, we proposed a study on vehicle communication networks based on IEEE 802.16 (which has the characteristics of wide coverage and strong QoS support). References [4-5] proposed the use of WiMAX (IEEE 802.16)-based technology to provide on-board mobile broadband wireless access for vehicles and their internal users, applying WiMAX technology to vehicle communication networks for the first time. This idea essentially breaks the pattern of IEEE 802.11 dominating vehicle communication networks, and opens up a new direction for the development and research of vehicle communication networks. Broadband wireless access systems based on the IEEE 802.16 technical standard have attracted widespread market attention in recent years. According to the results of actual network planning, the reasonable coverage radius of WiMAX base stations in urban areas is about several kilometers, which can provide higher data transmission rates and wider coverage. In order to solve the broadband wireless access problem of in-vehicle user terminals in high-speed mobile conditions, the IEEE 802.16 standard development group established the Mobile Relay Service (MRS) working group based on IEEE 802.16j in March 2006 to study the feasibility of using MRS. It intends to use vehicle-mounted MRS stations to provide broadband wireless access services for group user terminals in the vehicle[6].

At present, the research hotspots of vehicle mobile networks are mainly concentrated on multi-channel coordination applications and multicast routing management of vehicle communications based on the WAVE protocol (IEEE 802.11p), and switching and resource scheduling of fixed relay technology based on the WiMAX protocol (IEEE 802.16).

In the self-organizing communication network between vehicles based on the WAVE protocol, the safety and non-safety applications of the entire vehicle network are completed on one channel, which makes it difficult to ensure the QoS of safety applications. This is because a large amount of non-safety information may cause network congestion, making it impossible to effectively transmit safety messages, which seriously weakens the important role of VANET in active safety. The use of a multi-channel media access control (MAC) mechanism is one of the direct and effective methods to solve the above problems [7]. After using multiple channels, nodes can use different channels for communication, and the access method is more flexible and changeable, which can obtain network throughput and delay characteristics that are better than a single channel. In view of this situation, the time slot interval method is generally used to alternately divide the time into a control interval and a data exchange interval [8-9]. In the control interval (CCH), all nodes jump to the control channel for channel negotiation, and in the data exchange interval (SCH), they jump to different channels for data transmission. The detailed architecture is shown in Figure 1.

The original routing mechanism in the WAVE protocol is not fully suitable for vehicle communication networks with dynamically changing topologies. The table-driven proactive routing protocol cannot coordinate nodes that are uncertain in advance in the traffic environment, and the frequent changes in the topology structure seriously affect the performance of the protocol; the source-driven reactive routing protocol only establishes routes when messages need to be sent, and will expire after a period of time. As the number of communication hops increases and the speed of vehicle movement increases, the delay in establishing routes for these routing protocols increases accordingly, making it difficult to meet low-latency safety applications. Therefore, location-based multicast routing has emerged [10-11]. The goal of multicast routing is to transmit messages from the source node to all nodes within the associated zone (ZOR). For the multicast routing mechanism, the concept of clustering is proposed, which organizes the vehicle network into multiple peer units (clusters) to improve scalability in mobile environments [12]. In VANET, clustering mechanism is adopted. In-cluster communication can be used to quickly and effectively transmit safety-related emergency messages, while inter-cluster communication is used to transmit messages that need to cross multiple hops to reach farther areas. This cluster-based routing method can provide full coverage of messages while ensuring low transmission delay, and is suitable for distributing various emergency messages while driving. In the future, the routing concept of cluster multicast will be used in the safety applications of vehicle networks. The cluster head, as a coordinator, collects and distributes safety warning messages in real time within the cluster on the one hand, and forwards the processed safety messages to neighboring cluster heads on the other hand.

The communication between vehicles and roadside infrastructure is only suitable for vehicles traveling at low speeds or in relatively static environments. Vehicles cannot provide long-term information interaction with the infrastructure of roadside units during high-speed driving. In vehicle-mounted broadband wireless access, a vehicle-mounted MRS site is introduced between the in-vehicle user terminal and the roadside base station to coordinate the communication between the in-vehicle user and the base station. The base station and the in-vehicle user terminal will interact with each other through the MRS site instead of direct communication between the two.

In this system, the concepts of hierarchical scheduling and group mobility emerge. The base station and the in-vehicle user terminal exchange information through MRS, and the MRS obtains the allocated resources from the service base station, and the in-vehicle user obtains the allocated resources from the in-vehicle relay, which is a two-level resource scheduling. At the same time, after the introduction of MRS nodes, the mobility management is greatly improved. The relay node can bundle the communication links of the same type of services with similar QoS requirements from the in-vehicle user terminal, and centrally process them for group switching, reducing the process of separate signaling interaction between each terminal user and the base station in the previous switching process. Reference [13] proposed a two-level resource scheduling mechanism based on fixed relay, which improved the system throughput and reduced the packet loss rate and delay time of the service. Reference [14] proposed a multi-hop cellular network relay-assisted switching technology. The mobile terminal transmits information through the relay node. This technology is used to ensure the QoS parameters of the channel and reduce the call drop rate. Reference [15] first proposed a group switching based on MRS. The mobile relay station assists the in-vehicle user terminal to complete the switching of access to the target base station, and improves the switching success rate and reduces the switching congestion and delay by reallocating resources during the switching process.

In summary, the WAVE protocol can provide real-time text and image information to road intersections, gas stations, parking lots, etc. within a radius of hundreds of meters with a communication speed of tens of megabits per second. At the same time, this communication technology can also be used for vehicle-to-vehicle communication to provide emergency safety message communication for moving vehicles to prevent vehicle collisions. The maximum communication radius of WiMAX can reach several thousand meters and can be used in high-speed moving vehicles with a speed of more than 120 km/h. At the same time, the outstanding system gain of its MRS station can also provide higher-speed communication services for in-vehicle user terminals. Therefore, we proposed a vehicle mobile network architecture that integrates WiMAX and WAVE new heterogeneous networks, thereby forming a vehicle mobile communication network for vehicle safety communication, traffic information transmission, and broadband wireless multimedia data transmission.