Simulation and Analysis of Extended Brake Lights for Inter-Vehicle Communication Networks

Transcription

1 Simulation and Analysis of Extended Brake Lights for Inter-Vehicle Communication Networks Jason D. Watson, Mark Pellerito, Charlie Gladden, and Huirong Fu Abstract The goal of this research is to simulate and analyze an Inter-Vehicle Communication (IVC) Mobile Ad hoc Network (MANET). Automobiles of the future will take advantage of IVC capabilities, in which vehicles will communicate with one another wirelessly. The Crash Avoidance Metrics Partnership (CAMP) Vehicle Safety Communications Consortium (VSCC) has identified three scenarios that are representative of the capabilities of future vehicular networks: Curve Speed Warning (CSW), Traffic Signal Violation Warning (TSVW), and Extended Brake Lights (EBL). We consider only EBL, as it is the only scenario that involves direct communication between vehicles. This research aims to simulate the EBL scenario over an IVC network, and analyze the network using accepted metrics and benchmarks. The resulting performance data may influence and motive future research efforts. Keywords Inter-Vehicle Communication, Mobile Ad hoc Networks, Simulation, Throughput, One-way Delay I. INTRODUCTION Vehicles of the future will be driven and controlled by a network. Vehicles will not be independent of one another. The goal of this research was to collect data about the interaction of the vehicle network through computer simulation. Performance metrics used in this study are communication delay (one-way, max) and data throughput. The goal is to simulate inter-vehicle communications and to determine the feasibility of implementing crash avoidance systems. Current technologies used in vehicle communications are discussed briefly here as a background to IVC technologies. The Opticom System, which is developed by Federal Signal and 3M, is a priority control system. It controls traffic lights to provide emergency vehicles the right-of-way to traffic situations. It is a wireless, infrared, authenticated, vehicle communications emergency vehicle system. Police cars, fire trucks, and emergency vehicles can be prioritized on the road in emergency situations. These vehicles are allowed to safely pass through the light. The Intelligent Transportation Society of America (ITS) This material is based upon work supported by the National Science Foundation under Grant No Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The authors are with Oakland University, Rochester Hills, MI, USA. The authors may be reached by s: {watsonj9@gmail.com, mjpeller@gmail.com, cegladde@oakland.edu, and fu@oakland.edu}, phone: , or fax: has developed and deployed Intelligent Transportation Systems (ITS) for 5 years. It improves safety, security, and efficiency of transportation. It helps vehicles to avoid crashes and to eliminate traffic delays. Real-time travel information and efficient traffic management are also a few of its capabilities. The FastTRAC System enables fast and safer travel routing and advanced controls of vehicles. It is a real-time computer-controlled traffic management system. It determines traffic flow, and helps to reduce serious intersection accidents. The Traffic Information System (TIMS) automatically shares information with the Michigan Department of Transportation. The system video cameras can be pole mounted. Longer duration green lights for heavier traffic flows are enabled to allow emergency vehicles to pass through. The Fleetnet System is the equivalent of the Internet on the road. It is an inter-vehicle communication platform. There is a need for local information while driving to extend a driver s range of awareness. Fleetnet can provide a service to create greater driver awareness. It can notify drivers of upcoming traffic jams. It can query the system for available alternate routes. In the future, children may make chat friends or play interactive games with other neighbor traffic flow children. Drivers may also receive detailed fuel station prices and services. II. THEORETICAL ASPECTS While vehicle-to-infrastructure communication is quite prevalent in many production systems, vehicle-to-vehicle communications are currently limited in general to signal lights for drivers to indicate to others of current and anticipated driving actions. Because wireless data communications can be performed with relatively high bandwidth as compared to a signal light, more information about a driver s or car s actions can be relayed more quickly using MANETs than with conventional signals. Additionally, coupling the MANET to an automated driving or braking system would be more straightforward than to conventional signals. Modes of communication including link protocol as well as packet size are yet to be determined. We investigate these variables through simulations. Some terms and concepts used throughout this research are presented here as background knowledge. The drop-tail queuing method drops packets from the tail of the queue when a routing

2 buffer is full [3]. The Ad hoc On-demand Distance Vector (AODV) routing algorithm is an algorithm for routing data across Wireless Mesh Networks, in which a route to a destination is established only on demand [4]. Media Access Control (MAC) provides addressing and channel access control mechanisms that make it possible for several network nodes to communicate within a multipoint network [5]. Time Division Multiple Access (TDMA) is a channel access method for shared medium (usually radio) networks that allows several users to share the same frequency channel by dividing the signal into different timeslots [6]. The 8. standard is the set of Wireless LAN/WLAN standards developed by working group of the IEEE LAN/MAN Standards Committee (IEEE 8) [3]. III. SIMULATION RESULTS A. Simulation Overview The objective of this research is to simulate and analyze an Inter-Vehicle Communication (IVC) Mobile Ad hoc Network (MANET), and then analyze the network using accepted metrics and benchmarks. The Extended Brake Lights (EBL) scenario was chosen for this simulation [5]. The goal of this scenario is to extend the range of brake lights in emergency braking situations via radio transmission. The network reference model consisted of two vehicle platoons with three vehicles each. Communication between the vehicles occurs only when the vehicles are braking or stopped. The fixed parameters that were used were drop-tail queuing, the AODV routing protocol, and a velocity of 5 mph (.4 m/s). Example scenarios are listed below. When the simulation begins, the first vehicle platoon is moving vertically, while the second vehicle platoon is stopped and communicating at an intersection, as illustrated in Fig.. Fig.. Subsequent movement of the two vehicle platoons in the simulation. Performance metrics that were most applicable to intervehicular communications were chosen for this simulation, including one-way delay, max delay, and throughput. Packet size and Medium Access Control (MAC) type were chosen as the variable parameters for this simulation. The packet size was varied from 5 to bytes. The MAC type was either TDMA or 8.. The NS- Network Simulator was chosen as the simulation tool for this research [9]. NS- was executed on a Windows XP system using the Cygwin environment. The network model was written in Tcl. The fixed parameters were configured in the Tcl code as shown in Fig. 3. set val (ifg) Queue/DropTail / PriQueue set val (rp) AODV $ns_ node-config -adhocrouting $val (rp) \ -ifqtype $val (ifq) $ns_ at. $node_ () setdest Fig. 3. Tcl code sample showing configuration of fixed parameters. The one-way delay and max delay were computed offline by parsing the trace file. Throughput was collected in the Tcl file as shown in Fig.4. set time. set bw [$tcpsink set bytes_] set now [$ns_ now] puts $thrufd $now [expr $bw/$time*8/] $ns_ at [expr $now+$time] record Fig. 4. Tcl code sample showing throughput data collection. Fig.. Initial movement of the two vehicle platoons in the simulation. When the first vehicle platoon reaches the intersection, it stops and begins communicating. The second vehicle platoon then begins to move horizontally and stops communicating, as illustrated in Fig.. The following command was used to execute the simulation: ns.exe vanet-test.tcl (NOTE: ns.exe and nam.exe must both be in the Cygwin PATH). The above command automatically launches the Nam network animator when the simulation completes. The performance data was then written to trace files. B. Trial Results Recall that the variable parameters for this simulation were packet size and MAC type. The packet size for trial was, bytes, and the MAC type was Time-Division Multiple Access (TDMA). Trial was used as the base trial

3 to which the subsequent trials were compared. ) One-way Delay: An analysis of the one-way delay was performed for the trial scenario. One-way delay data was overall and transient state one-way delay data for the first vehicle platoon are presented in Fig. 5 and Fig. 6. One-way Delay (Platoon ) Fig. 5. One-way delay for the first vehicle platoon of Trial as a function of packet ID. The transient state for the one-way delay lasts until approximately packet 5, at which point it enters the steady state with a oneway delay of approximately.6 seconds. Transient State One-way Delay (Platoon ) Fig. 6. Transient state one-way delay for the first vehicle platoon of Trial as a function of packet ID. average one-way delay was.945 s, the minimum was.4 s, and the maximum was.636 s. For the trailing vehicle in the platoon, the average one-way delay was.3 s, the minimum was.76 s, and the maximum was.63 s. platoon. For the middle vehicle in the platoon, the average one-way delay was.99 s, the minimum was.4 s, and the maximum was.636 s. For the trailing vehicle in the platoon, the average one-way delay was. s, the minimum was.76 s, and the maximum was.63 s. ) Throughput: An analysis of the throughput was performed for the trial scenario. Throughput data was throughput data for the first vehicle platoon is presented in Fig. 7. Throughput (in Mbps) Throughput (Platoon ) Time (in sec) Fig. 7. Throughput for the first vehicle platoon of Trial as a function of time. The vehicles begin communicating at approximately seconds, at which point packets are sent at a constant bit rate until the simulation ends. The average, minimum, and maximum throughput were calculated for the platoon. The average throughput was.988 Mbps, the minimum was Mbps, and the maximum was.54 Mbps. platoon. The average throughput was.94 Mbps, the minimum was Mbps, and the maximum was.54 Mbps. A confidence level analysis was performed for the throughput data of trial. It was determined that the actual average throughput for such a scenario is within.596 Mbps of the observed value, with a 95% confidence and a 5.3% relative precision. C. Trial Results The packet size for trial was 5 bytes, and the MAC type was Time-Division Multiple Access (TDMA). Trial was compared to trial to determine the impact of packet size on the IVC network. ) One-way Delay: An analysis of the one-way delay was performed for the trial scenario. One-way delay data was overall and transient state one-way delay data for the first vehicle platoon are presented in Fig. 8 and Fig. 9. One-way Delay (Platoon ) Fig. 8. One-way delay for the first vehicle platoon of Trial as a function of packet ID. The transient state for the one-way delay lasts until

4 approximately packet 5, at which point it enters the steady state with a oneway delay of approximately.6 seconds. Transient State One-way Delay (Platoon ) Fig. 9. Transient state one-way delay for the first vehicle platoon of Trial as a function of packet ID. average one-way delay was.943 s, the minimum was.38 s, and the maximum was.634 s. For the trailing vehicle in the platoon, the average one-way delay was.9 s, the minimum was.74 s, and the maximum was.68 s. platoon. For the middle vehicle in the platoon, the average one-way delay was.97 s, the minimum was.38 s, and the maximum was.634 s. For the trailing vehicle in the platoon, the average one-way delay was. s, the minimum was.74 s, and the maximum was.68 s. ) Throughput: An analysis of the throughput was performed for the trial scenario. Throughput data was throughput data for the first vehicle platoon is presented in Fig.. Throughput (in Mbps) Throughout (Platoon ) Time (in sec) Fig.. Throughput for the first vehicle platoon of Trial as a function of time. The vehicles begin communicating at approximately seconds, at which point packets are sent at a constant bit rate until the simulation ends. The average, minimum, and maximum throughput were calculated for the platoon. The average throughput was.5 Mbps, the minimum was Mbps, and the maximum was.34 Mbps. platoon. The average throughput was.497 Mbps, the minimum was Mbps, and the maximum was.34 Mbps. A confidence level analysis was performed for the throughput data of trial. It was determined that the actual average throughput for such a scenario is within.45 Mbps of the observed value, with a 95% confidence and a 4.8% relative precision. D. Trial 3 Results The packet size for trial 3 was, bytes, and the MAC type was 8.. Trial 3 was compared to trial to determine the impact of MAC type on the IVC network. ) One-way Delay: An analysis of the one-way delay was performed for the trial 3 scenario. One-way delay data was overall and transient state one-way delay data for the first vehicle platoon are presented in Fig. and Fig One-way Delay (Platoon ) Fig.. One-way delay for the first vehicle platoon of Trial 3 as a function of packet ID. The transient state for the one-way delay lasts until approximately packet 5, at which point it enters the steady state with a one-way delay of approximately.5 seconds..5.5 Transient State One-way Delay (Platoon ) 5 5 Fig.. Transient state one-way delay for the first vehicle platoon of Trial 3 as a function of packet ID. average one-way delay was.459 s, the minimum was.4 s, and the maximum was.8 s. For the trailing vehicle in the platoon, the average one-way delay was.9 s, the minimum was. s, and the maximum was.485

5 s. The overall and transient state one-way delay data for the second vehicle platoon are presented in Fig. 3 and Fig One-way Delay (Platoon ) Fig. 3. One-way delay for the second vehicle platoon of Trial 3 as a function of packet ID. The transient state for the one-way delay lasts until approximately packet, at which point it enters the steady state with a one-way delay of approximately.5 seconds..5.5 Transient State One-way Delay (Platoon ) 5 5 Fig. 4. Transient state one-way delay for the second vehicle platoon of Trial 3 as a function of packet ID. average one-way delay was.48 s, the minimum was. s, and the maximum was.477 s. For the trailing vehicle in the platoon, the average one-way delay was.59 s, the minimum was.54 s, and the maximum was.487 s. ) Throughput: An analysis of the throughput was performed for the trial 3 scenario. Throughput data was throughput data for the first vehicle platoon is presented in Fig. 5. Throughput (in Mbps) Throughput (Platoon ) Time (in sec) Fig. 5. Throughput for the first vehicle platoon of Trial 3 as a function of time. The vehicles begin communicating at approximately seconds, at which point packets are sent at a constant bit rate until the simulation ends. The average, minimum, and maximum throughput were calculated for the platoon. The average throughput was.346 Mbps, the minimum was Mbps, and the maximum was.678 Mbps. platoon. The average throughput was.3 Mbps, the minimum was Mbps, and the maximum was.59 Mbps. A confidence level analysis was performed for the throughput data of trial 3. It was determined that the actual average throughput for such a scenario is within.358 Mbps of the observed value, with a 95% confidence and a.8% relative precision. E. Analysis of Results A comparison of trials and demonstrates the impact of packet size on the one-way delay and throughput of the IVC network. Recall that the packet size was, bytes in trial, and was reduced to 5 bytes in trial. As expected, the reduced packet size results in a reduction in throughput, since fewer bytes are being sent across the network. Somewhat unexpectedly, however, are the results of the oneway delay comparison. The one-way delay for trial and trial is essentially unchanged, suggesting that the primary source of the delay was not the size of the packets being exchanged, but rather the overhead associated with the TCP and TDMA protocols. A comparison of trials and 3 demonstrates the impact of the MAC type on the one-way delay and throughput of the IVC network. Recall that the MAC type was TDMA in trial, and was changed to 8. in trial 3. The throughput for trial 3 was significantly greater than the throughput for trial. This is due largely to the fact that packets are sent with a greater frequency when using 8., as compared to using TDMA. Also, the one-way delay for trial 3 was significantly less than the one-way delay for trial. This confirms that the primary source of delay with trial is associated with the use of TDMA. In TDMA, senders and receivers must wait until their assigned time slice before they can process packets, which may cause unnecessary overhead. There is a tradeoff involved with the decision to use TDMA or 8.. As shown, the use of 8. can greatly

6 improve network performance. An important consideration for IVC networks, however, is security. It has been suggested that a combination of TDMA and Frequency Hopping Spread Spectrum (FHSS) may be used as a means to help prevent Denial-of-Service (DoS) attacks on IVC networks []. Therefore, they may be a tradeoff between performance and security when faced with the decision of which MAC type to use. This research suggests, however, that the one-way delay associated with the use of TDMA may not be practical in emergency braking situations. The one-way delay statistics can be used to assess whether or not drivers will have sufficient time to stop under the scenarios presented here. The one-way delay of the initial packet will be used for this assessment, since this will be the first indication to trailing vehicles that a lead vehicle is applying its brakes. Under trials and, in which the one-way delay was essentially unchanged, the average oneway delay for the initial packet was.4 s. At.4 m/s (5 mph), a trailing vehicle would travel approximately 5.38 meters. The vehicles in the simulation were positioned at a distance of 5 m. Therefore, a trailing vehicle will have traveled over % of the separating distance before receiving indication that the lead vehicle has applied its brakes. This may or may not leave the vehicle with a sufficient stopping distance, depending on a number of other parameters, including the condition of the brakes, the condition of the tires, the condition of the road, and the reaction time of the driver, among others. Under trial 3, however, the average one-way delay for the initial packet was only.8 s. At the same velocity, a trailing vehicle would travel only.4 meters, only.8% of the separating distance. This would likely provide the driver enough time to stop under most conditions. IV. CONCLUSION AND FUTURE WORK The results produced through simulation strongly suggest that an IVC MANET implementation would be feasible. Simulation results indicate a holistically reasonable amount of communication delay to corresponding overall throughput. For greater accuracy, the study would require further simulation with a larger and more complex vehicular configuration to more closely mimic that of actual traffic scenarios. Because the performance of 8.-based communications appeared to be much more efficient and capable of handling a greater load, it is the wireless protocol we suggest as a basis for continued research in the area of IVC MANETs. Additionally, a packet size of bytes is suggested as a basis for work to determine ideal 8.- based IVC MANET packet sizes. We have therefore determined that 8. technologies, as well as larger data packet sizes, are a basis for continued research. REFERENCES [] Aijaz, Amer, B. Bochow, F. Dotzer, A. Festag, M. Gerlach, R. Koch, and T. 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