Network Protocols for Vehicle Platoon Control and Management Essay Example

and radar systems among the vehicles. The velocity and distance between vehicles are constantly monitored and updated [3]. Lateral control is achieved by aligning the following vehicle's direction with that of the front vehicle using magnetic sensors and markers to determine the vehicle's position.

The on-board computers process the data of the vehicle’s route and transfer the command to the brakes and actuators to maintain the correct direction [4]. 1. 1. 2 Vehicle Management The vehicle platoon system enables vehicles to join and leave the platoon during the route. The system creates a common travel plan with the same route for all vehicles in the platoon. A platoon is established with a known group of vehicles, with one vehicle designated as the lead. Common travel plans can be developed while traveling when a new platoon is formed.

When a vehicle is joining or leaving the platoon, the communication system will coordinate the maneuvers among the platoon [5]. If a vehicle in the platoon wants to leave, it will notify the lead vehicle. The lead vehicle will analyze the route situation and decide whether to grant leave permission. If the vehicle is given permission to leave, it will move back to a long distance behind the front vehicle along with the vehicles following it, and then drive away from the platoon. The following vehicles will catch up with the front.

The lead vehicle will analyze the new platoon and update the platoon's settings, including speed and distance. If a vehicle wants to join the platoon, it must send its travel plan to the lead vehicle. The lead vehicle will review the travel plan and determine whether to grant permission

to join. Once permission is granted, the lead vehicle will determine where to insert the joining vehicle in the platoon. The vehicles following the joining vehicle will move back to a significant distance behind the front vehicle, allowing the new vehicle to join the platoon.

The lead vehicle updates the platoon's settings and the common travel plan [6]. One benefit of vehicle platooning is enhanced fuel efficiency. By planning the route for all vehicles in the platoon, fuel efficiency can be improved. Through vehicle control and management, the platoon can adjust vehicle operation and timing to avoid stop lights, reducing drag and decreasing fuel consumption. This ultimately leads to greater fuel efficiency.

The most efficient way to reduce drag is for vehicles to maintain a distance between them equal to half the length of the car. This can result in a 20-25% decrease in fuel consumption [4] [5]. Additionally, vehicle platooning allows vehicles to travel closely and safely. In the platoon, the gap between vehicles can be smaller than those outside the platoon, which reduces space occupancy on the highway for each vehicle. Consequently, more vehicles can be accommodated, significantly increasing the capacity of the highway.

According to research, increasing the separation between vehicles by 25% and allowing for a 200 ft separation between different platoons can double the normal capacity of the highway. Reduced congestion is achieved through tight coordination among vehicles within a platoon, enabling them to react appropriately to various road situations. By utilizing malfunction management software, vehicles can automatically take corrective actions such as increasing the distance between vehicles and decreasing speed in the event of an accident.

The vehicle platoon system monitors the

traffic to avoid traffic jams and reduce congestion. By implementing vehicle platooning for all vehicles, it becomes easier to increase traffic stability and ultimately reduce congestion [6]. Furthermore, automated driving improves safety and comfort by providing a smooth acceleration and minimizing changes for passengers. Additionally, it allows the driver to relax as the vehicle platoon system continuously monitors and updates the ride's safety.

The vehicle's longitudinal control and lateral control exhibit much higher performance as compared to human beings when it comes to keeping the vehicle in the center of the lane and maintaining a stable distance from the front vehicle, among other things. However, there are disadvantages to vehicle platooning. The driver of the lead vehicle bears most of the driving responsibility, making it crucial to select a competent professional driver. Determining the requirements for professional driving is indeed challenging. Additionally, since most people are unfamiliar with vehicle platooning, it is difficult for drivers to place trust in the vehicle platoon systems.

Currently, vehicle platooning is primarily applicable to motorways, but it becomes more complicated when considering different road types that have pedestrians [6][7].

Part 2: Overview of Network Protocols

1. Protocol 1: RNP and Related Protocols

Neighborcast is an innovative communication technique used to exchange information on position, speed, and state among vehicles. Each vehicle communicates with its nearby vehicles, known as its neighborhood (also referred to as a communication group), as shown in the figure above.

The neighborhoods of vehicles in close proximity may overlap but they are distinct. Each vehicle's neighbors communicate with different vehicles within the neighborhood, excluding the vehicle itself. The transmitter uses the overlay to establish a neighborhood

that includes the vehicles intended to receive its transmitted information [8]. The reliable neighborcast protocol (RNP) provides assurances such as message sequencing, delivery, and delay. RNP can be seen as an overlay on multiple reliable broadcast protocols with overlapping coverage. RNP can be implemented on any reliable broadcast protocol as its foundation.

The RNP overlay utilizes neighborcast to transmit motion state, maneuver operations, and warning messages between vehicles in different platoons [9]. For mobile ad hoc networks, the RNP is constructed as a layer above the mobile reliable broadcast protocol (M-RBP). Both RNP and M-RBP are application-level protocols. [pic] M-RBP consists of reliable broadcast protocols (RBP) and timed reliable multicast protocol (T-RMP), both of which are P2P protocols. M-RBP functions on top of various transmission layers, such as MAC lay or wireless interface.

M-RBP is a mechanism that ensures dependable delivery and continuous message ordering within a broadcast group. It allows all members of the group to utilize the same messages. In the provided illustration, M-RBP employs a token ring consisting of receivers. These receivers exchange a token at regular intervals, enabling them to receive messages in turns. Each time a receiver passes the token, it sends a control message containing acknowledgements for all previously unacknowledged source messages that have been received.

The control message contains a unique sequence number which is transmitted along with each source message. Each source message is assigned a unique identifier. The sequence number assigned to the source message determines the sequence number and position of the control message in the control message list. Receivers are able to recover missing control messages and place source messages in the correct order. M-RBP utilizes aggressive

token passing to handle situations when receivers leave the broadcast group. Receivers use a voting process to determine if the scheduled control message sender has left the group.

If the majority of receivers vote a receiver as failing to transmit the control message, that receiver will be removed from the token list [8]. Based on the M-RBP operations discussed above, it becomes clear that M-RBP ensures the transmission of all source messages to all receivers. It also notifies each receiver when the message has been transmitted to all other receivers. M-RBP guarantees a delay in order to ensure that messages are transmitted by a specific deadline by utilizing the timed passing mechanism [9]. Additionally, M-RBP permits changes to the broadcast group.

When a group changes, the protocol will halt and establish a new group with a new token ring for the group members. If a vehicle wishes to join the broadcast group, it will send a message to the group and wait until the message transmission is finished. RNP expands on M-RBP's capabilities by transforming the broadcast group into a neighborhood. This enables a source to identify the receivers that receive the transmitted message. RNP incorporates M-RBP groups to encompass all the vehicles and neighborhoods of the vehicles in a specific area.

RNP is implemented in every vehicle and consolidates the messages from each M-RBP group that covers the vehicle's location [8]. RNP, when implemented on the highway, can be represented as one-dimensional overlays. The accompanying graph illustrates how vehicles in a platoon are divided among several M-RBP broadcast groups. [pic] It is evident that all vehicles on the highway can be assigned to a single broadcast group.

However, this allocation has several disadvantages: certain guarantees can only be provided after the token has been transmitted through all vehicles, a significant number of unnecessary messages need to be transmitted and received, and the channel becomes shared by a large number of sources.

The implementation of the broadcast group should be relatively small. The following graph illustrates how the 2Dl reliable neighborcast and underlying broadcast groups are implemented [8]. [pic]
2. 2 Protocol 2: WTRP and Related Protocols
The IEEE 802.11 protocol has a medium access control (MAC) protocol and various signaling techniques. The MAC protocol of IEEE 802.11 in DCF mode is based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme. [pic] [pic] [pic]
From the timing diagram of IEEE 802.1 in DCF mode above, we can determine the following: If a station detects that the carrier signal is busy, the station will wait until the carrier signal becomes idle. Then, the station enters the "backoff" state and waits for a random backoff interval. If the station attempts to transmit information while in the "backoff" state, it will postpone the transmission and switch to the carrier sense state. It will then wait until the carrier signal becomes idle again before resuming from where it left off. After the "backoff" state comes the "Tx" state, in which the station waits for ACK or CTS to ensure successful transmission.

If the transmission is successful, the state changes to "Sequence & Retry" state [10]. The wireless token ring protocol (WTRP) is a wireless LAN protocol that was inspired by the IEEE 802.4 Token Bus Protocol for the MAC layer in wireless networks for

intelligent transportation systems (ITS). WTRP ensures bounded delay and all stations in the network share bandwidth. To overcome partial connectivity, WTRP adds a manager, special tokens with additional fields, and a new timer. The decision for a node to join or leave the ring depends on its connectivity table.

The text describes the implementation of a unique priority assignment scheme for tokens in the WTRP protocol. This scheme allows a station to accept a token with a higher priority than the last accepted token. The transmission order in the ring is determined by the successor and predecessor fields of each station. The WTRP token frame includes several fields such as Frame Control, Ring Address, Destination Address, Source Address, Sequence Number, and Generation Sequence Number.

Additionally, WTRP creates a connectivity table that lists the ordered stations within its ring and the unordered stations outside of it. An example of this connectivity table for station E is shown in a figure.

In order for a station to join a ring using WTRP, it must be connected to its prospective predecessor and successor according to its connectivity table.

The joining station listens for a request from the successor station and switches to the joining state. Within a random timeframe, it detects a request from its own successor station. If the joining station successfully competes for access, the successor station will send a request for a predecessor update to the joining station, and the joining station will forward this request to its predecessor station. The following diagram demonstrates the entire process of joining. [pic] When a station departs from the ring, it sends a request for a successor update to its predecessor station.

The predecessor station retrieves the next available station from its connectivity table and sends a request for a predecessor update to that station.

The graph below displays the entire process of leaving [11]. [pic] The WTRP ensures that each ring address remains unique to support multiple rings. In WTRP, the ring address corresponds to the address of any station within the ring, as depicted in the figure below. The station is the current owner of the ring. It is important to note that the MAC addresses of two distinct rings are always unique. [pic] When comparing WTRP to IEEE 802.11 DCF, the following points stand out: 1. WTRP utilizes a deterministic MAC protocol, whereas IEEE 802.11 DCF employs a randomized one. WTRP outperforms IEEE 802.11 DCF when waiting for an idle carrier signal. 2. WTRP supports partial connectivity, unlike IEEE 802.11 DCF. A station only needs to establish connections with its successor and predecessor. 3.

WTRP ensures ordered transmission while IEEE 802. 11 DCF does not, thus reducing collision probability compared to IEEE 802. 11 DCF. Additionally, WTRP is highly bounded while IEEE 802. 11 DCF is not, resulting in decreased delay [10]. However, WTRP is not reliable for warning messages and is not adaptable for fast topology change. On the other hand, the overlay token ring protocol (OTRP) can achieve efficient coordination among nearby vehicles, high quality data transmission, and reliable safety message transmission [11]. In OTRP, vehicles are logically set into several overlapped virtual rings, where each ring uses a unique token to determine transmission rights.

The OTRP system allows for the changing of the ring based on current traffic conditions, allowing vehicles to enter and

exit the ring. There are two modes in OTRP: normal mode for communication between vehicles and emergency mode for the exchange of safety messages. In emergency mode, the priority of messages is set higher than in normal mode to ensure desired quality of service. In OTRP, vehicles are divided into three states: free (vehicles not belonging to any ring), inring idle (vehicles belonging to a ring but not currently holding the token), and inring busy (vehicles belonging to a ring and currently holding the token). The following graph depicts the vehicle network in OTRP [12]: [pic]

When a free vehicle is unable to join an existing ring after a certain period of time, a new ring should be created to accommodate the free vehicle. Once the ring is established, the vehicle will generate a token and transition to a state of being inring busy. The OTRP protocol utilizes five types of tokens: data token, open token, responding message (RS), acknowledgement token (ACK), and request for message (RQ). A new vehicle can join the ring as long as it is not already full. The current token holder will broadcast the open token, allowing the free vehicle to join the ring. If a vehicle is unable to receive communication from the next vehicle for an extended period of time, it is assumed that the next vehicle has left the ring. The vehicle address is then removed and the token is passed to the following vehicle. As a result, the leaving vehicle becomes free [12].

The process has a timer, and if there is no response for a certain time, related operations will be taken. OTRP has several advantages: it

minimizes the risk of token collision, is easy to implement, and transmits emergency messages with higher reliability and lower latency than normal messages. However, the challenge of OTRP is to avoid losing tokens. Protocol 3, known as DOLPHIN and Related Protocols, utilizes Carrier Sense Multiple Access (CSMA) for establishing autonomous decentralized networks in the MAC layer. There are two types of CSMA: non-persistent CSMA and p-persistent CSMA.

CSMA is a transmission method that waits for the carrier signal to be idle before sending a packet. There are two types of CSMA that behave differently when the carrier signal is busy. [pic] [pic] In the case of non-persistent CSMA, if the carrier signal is busy, it will wait for a random interval before sensing the carrier signal again. On the other hand, p-persistent CSMA will continuously sense the carrier signal until it becomes idle. Since CSMA involves contention in the MAC method, there is a possibility of packet loss during transmission. For instance, if multiple vehicles transmit their packets at the same time while the carrier signal is idle, none of these collision packets will successfully transmit. [pic]

The figure above illustrates the transmission of emergency information within a vehicle platoon using CSMA. Vehicle No. 5 acts as the source, transmitting the emergency information to its surrounding vehicles (No. 1, 2, 3, 4, 6, 7, 8, and 9). These surrounding vehicles will check if the forward vehicle has transmitted the emergency information. If so, they will in turn transmit the information to the vehicle behind them. The main challenge for CSMA, whether it is non-persistent or p-persistent, is the delay time in the process. However, p-persistent CSMA has

a slight advantage. The packet format for DOLPHIN includes various components such as PR (Preamble), SD (Start Delimiter), MPDU (MAC layer Protocol Data Unit), FC (Packet Control Field), ID (Vehicle Identity Field), DATA (Data Field), CRC (Cyclic Redundancy Check), and FEC (Forward Error Control). The DATA field of the packet contains road information, vehicle control information, hopping information, message, and Road-Vehicle Communication information.

The DATA field has three types of information: emergency, normal, and another normal. The transmission interval varies depending on the type of information. The table below displays the DOLPHIN function specification for receiving information from the front vehicle to the following vehicle. DOLPHIN offers the advantage of low end-to-end message latency, but it also restricts its usefulness for other applications [13]. [pic] The DOLPHIN frame consists of three layers: traffic control layer, vehicle management layer, and vehicle control layer, as shown in the figure below [14]. [pic]

Part 3 New Protocol The new protocol I have created combines OTRP and DOLPHIN. In DOLPHIN, if the lead vehicle is at the front of the platoon and a collision occurs in the middle of the platoon, the emergency information is transmitted to the lead vehicle relatively late. This means that the lead vehicle will not have enough time to set operations for the vehicles after the collision vehicles. In ORTP, it is also relatively late for the emergency information to be transmitted to the vehicles nearby the collision, and information transmitted between the platoons is not very efficient. The MAC layer protocol uses CSMA protocol. The packet frame is the same as DOLPHIN: . This time, the DATA field in the packet includes road information, vehicle

control information, hopping information, messages, and Road-Vehicle Communication information. There are still three types of information for the DATA field: emergency information, normal information, and another normal information. The transmission interval for each type of information remains the same as DOLPHIN, which are 5msec, 20msec, and 200msec respectively. This time, when transmitting information among the vehicles, a token with the same purpose as in ORTP is used in the transmission process instead of a carrier signal. The token contains the priority of the message.

The highest priority in the platoon is given to emergency information that is not transmitted to the leader vehicle. Following that, vehicle control information from the leader vehicle is set as the second highest priority. In the event of a collision, nearby vehicles will receive the emergency data and the leader platoon will generate vehicle control information upon receiving the emergency information. This vehicle control information then becomes the highest priority in the platoon. The vehicles following the lead vehicle can promptly adjust their motion based on this vehicle control information. The ORTP timer will consider these updates in the new protocol. Any process that takes a relatively long time to respond will be disregarded. If a vehicle fails to respond when passing on information, it will be compelled to leave the vehicle platoon.

This guarantees that information continues to be transmitted within the platoon even if a collision causes a vehicle to lose communication with others. If a vehicle wants to join or leave the platoon, it sends a request for information to the leader vehicle. Only the information containing the leader vehicle's operation will be transmitted through the platoon. In

the case of transmitting emergency information, a vehicle detects the danger and becomes the emergency site, rapidly generating emergency information. Each vehicle that receives the emergency information will generate an acknowledgement, and then pass on the emergency information.

This report provides a comprehensive overview of vehicle platooning, detailing its functionality and operations. It discusses the main objectives, crucial controls, and the management system employed in vehicle platooning. Additionally, it highlights the advantages, such as improved fuel efficiency, increased highway capacity, reduced congestion, and enhanced safety and comfort for drivers and passengers. However, it also mentions the limitations of vehicle platooning due to its limited application.

In the second part of the report, we provide examples of protocols for platoon control and management. The report discusses the mechanisms, advantages, and disadvantages of these protocols. Firstly, it covers the RNP protocol and the M-RBP protocol. RNP can be viewed as overlays of M-RBP and is suitable for VANETs due to its design for a rapidly changing environment and provision of various guarantees for VANET applications. RNP ensures minimal delays in transmitting information, allowing vehicles to quickly detect collisions. Additionally, the report introduces the IEEE 802.11 protocol in DCF mode along with WTRP. It demonstrates the data transmission process in both protocols and compares them.

WTRP outperforms IEEE 802.11 in DCF and has the ability to support partial connectivity. This protocol reduces collision probability and decreases delay. However, it is not reliable for warning messages and is not adaptable to fast topology changes.

The report introduces the OTRP protocol, which is easy to implement for fast-changing VANETs. OTRP minimizes the risk of token collision and prioritizes emergency messages for transmission.

The report also

discusses the process for vehicle joining or leaving a platoon in both WTRP and OTRP protocols. In the last section of part 2, the report examines the DOLPHIN and CSMA protocols.

The report demonstrates how non-persistent CSMA and p-persistent CSMA operate differently. It also showcases the process of transmitting emergency information in DOLPHIN. The report includes the specifications and framework of the DOLPHIN function for information transmission. Additionally, it presents a new protocol that extends the DOLPHIN protocol by combining it with the OTRP protocol. This new protocol designates the lead vehicle in the platoon as unique, and gives high priority to the vehicle control information generated by the lead vehicle. This makes it convenient for other vehicles in the platoon to perform operations based on the lead vehicle's control information in order to avoid collisions.

The OTRP protocol prioritizes emergency information, as mentioned in reference [1]. Additional references [2], [3], [4], [5], [6], [7], and [8] provide further details on vehicle platooning and its application. In their article titled "A Survey of Inter-vehicle Communication Protocols and Their Applications," T. L. Willke, P. Tientrakool, and N. F. Maxemchuk conducted a survey on inter-vehicle communication protocols and their applications, which was published in the IEEE Communications Surveys and Tutorials journal in the second quarter of 2009.In their paper titled "Wireless Token Ring Protocol - Performance Comparison with IEEE 802.11," M. Ergen, D. Lee, R.Sengupta,and P.Varaiya compared the performance of the wireless token ring protocol with IEEE 802.11 at ISCC 2003.D.Lee et al.presented a wireless token ring protocol for intelligent transportation systems in their paper titled "A Wireless Token Ring Protocol for intelligent transportation systems" at the 2001 IEEE

Intelligent Transportation Systems Conference in Oakland, California.Jingqiu Zhang,Kuang-Hao Liu,and Xuemin Shen proposed a novel overlay token ring protocol for inter-vehicle communication in their paper titled "A Novel Overlay Token Ring Protocol for Inter-Vehicle Communication." This paper titled "DOLPHIN for inter-vehicle communications system" was presented at the 2008 IEEE International Conference on Communications (ICC '08) by K.Tokuda et al.
In addition, L. D. Baskar, B. De Schutter, and H. Hellendoorn presented a paper titled "Hierarchical traffic control and management with intelligent vehicle" at the IEEE Intelligent Vehicles Symposium in Dearborn, Michigan in 2000. They also discussed this topic at the 2007 IEEE Intelligent Vehicles Symposium (IV'07) in Istanbul, Turkey.