DIFTOS: A Distributed Infrastructure-Free Traffic Optimization System Based on Vehicular Ad Hoc Networks for Urban Environments
- DIFTOS is completely infrastructure-less and does not rely on any other network (cellular network, RSU), and it is totally distributed and does not rely on a centralized server.
- DIFTOS is designed in a hierarchical fashion, thus short length path requests are resolved locally, and does not need to travel long distances.
- To demonstrate the validity of DIFTOS, we have conducted a thorough comparison with existing approaches.
2. Related Works
3. System Architecture
- All vehicles are equipped with a dedicated short-range communication (DSRC) device.
- All vehicles are equipped with a GPS-based navigation system that has a digital roadmap.
- All communications are done using multi-hop vehicle-to-vehicle communication model (V2V).
- Drivers input the destination into their GPS-based navigation system as a navigation request when they start traveling. The VVS computes the shortest non-congested path and reserves it for them.
- Vehicles report the updates about their travel experience in road segments and at intersections along their travel path to their corresponding VVS.
- Since the travel paths are very sensitive information, all the communications between DIFTOS-Client and DIFTOS-Server are encrypted.
- The road segments are reserved in the order of a first come first served policy.
3.2. System Components
3.3. Virtual Vehicular Server
3.3.1. Hierarchical Partitioning
3.3.2. Server Selection
4. System Modelling
4.2. Road Network Graph
4.3. Traffic Flow and Travel Delay
4.4. Road Reservation Matrix
4.5. Problem Formulation
4.6. Priority Quota
4.7. Shortest Path and Road Rerouting
|Algorithm 1 Priority Quota Constrained Shortest Path|
|1: Function Shortest-Path-Quota-Priority ()|
|3: for each road segment do|
|4: if () then|
|6: if () then|
|8: end if|
|9: end if|
|10: end for|
4.8. Path Reservation
4.8.1. Path Request
4.8.2. Path Reply
4.8.3. Path Update
5.1. Map Extraction
5.2. Network Simulation
V2V Communication Parameters
6. Performance Evaluation
- Request Round Trip Time (RRTT): The time required to send a path request packet and receive the path reply.
- Computation Cost (CC): The number of operations the server performs to determine the optimal path for a given RReq and maintain the road reservations.
- Trip Time (TT): The time required by a vehicle to reach its destination after receiving the RRep packet from the server.
- Traffic Messages (TM): The number of exchanged messages to compute and maintain the optimal path. In this context, only the traffic related messages are counted, such as route request messages, server election messages, route reply messages and route update messages.
6.3. Evaluation Parameters
6.4. Results Analysis
- The inter-vehicle communications are encrypted. However, as long as vehicles’ traces are fully disclosed, the user’s identity in some cases can be inferred even if pseudonyms are used. Therefore, DIFTOS still needs to be improved from the privacy point of view. Enhancing DIFTOS with an additional security and privacy framework is one of our future research directions.
- DIFTOS’s distributed architecture improves the scalability of the system and reduces the load on servers, as the path requests are treated as different servers. However, at upper-level servers, it becomes difficult for a single vehicle to maintain the RRM, due to the large size of data, and the huge amount of computation needed to resolve many path requests simultaneously. Therefore, optimizing DIFTOS to distribute the server calculation as a vehicular cloud server, where many vehicles collaborate to maintain RRM, is one of our future directions.
- The current hierarchical partition still needs improvements, as cross levels paths still need to solicit upper levels servers. In our next work, we will try to change the path request procedure, where two adjacent servers of the same level can cooperate to solve a path request without the need to forward it to higher level servers.
Conflicts of Interest
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|System||Infrastructure Dependency||Server Architecture||Server Design||Congestion Treatment Policy|
|DIFTOS||Infrastructure-Less||Distributed||Hierarchy of Vehicular Servers (Vehicles)||Path requests for roads reservation (Congestion will never occur)|
|SAINT ||RSU + Cellular network||Centralized||Traffic Center (Computer)||Traffic estimation (Possible congestion)|
|DIVERT ||Cellular network||Partially Distributed||Traffic Center + Vehicular Servers (Computer + Vehicles)||Congestion detection (Possible congestion)|
|RTP ||RSU + Cellular network||Centralized||Traffic Center (Computer)||Congestion mitigation based on path planning (Possible congestion)|
|NRR ||RSU + Cellular network||Centralized||Traffic Center (Computer)||Heuristic rerouting to avoid congestion (Possible congestion)|
|RoadRunner ||Cellular network||Distributed||Mobile app + Centralized Server (Computer + smart phones)||Tokens for road reservation (Congestion will never occur)|
|Road network graph that represents the city map|
|I||Set of all vertices in the road network graph|
|Set of all edges in the road network graph|
|Set of all vehicles in the city|
|The road segment from intersection to intersection|
|Set of successive time slots|
|The mean of the speed of all vehicles driving within the traffic flow on the road segment within the time slot|
|The velocity of the vehicle in road segment during time slot t|
|Travel delay required to cross road segment|
|The length of the road segment|
|The waiting delay at intersection|
|The capacity of the road segment|
|The number of available positions in the road segment during time slot .|
|The weight of road segment during time slot t|
|The path yielded by connecting the road segments from to|
|Road reservation matrix of the road set during the period|
|The quota limit of the road during time slot|
|Network simulator||Omnet++ 5|
|Traffic simulator||SUMO 0.27.1|
|Map source||Open street map|
|Simulated location||Part of Beijing city, China|
|Simulated area||10 km × 10 km|
|PHY model||802.11 p|
|Channel frequency||5.890 × 109 Hz|
|Propagation model||Two ray|
|Propagation distance||450 m|
|Fading model||Jakes model rayleigh fading|
|Transmission power||20 mW|
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Zhang, W.; Aung, N.; Dhelim, S.; Ai, Y. DIFTOS: A Distributed Infrastructure-Free Traffic Optimization System Based on Vehicular Ad Hoc Networks for Urban Environments. Sensors 2018, 18, 2567. https://doi.org/10.3390/s18082567
Zhang W, Aung N, Dhelim S, Ai Y. DIFTOS: A Distributed Infrastructure-Free Traffic Optimization System Based on Vehicular Ad Hoc Networks for Urban Environments. Sensors. 2018; 18(8):2567. https://doi.org/10.3390/s18082567Chicago/Turabian Style
Zhang, Weidong, Nyothiri Aung, Sahraoui Dhelim, and Yibo Ai. 2018. "DIFTOS: A Distributed Infrastructure-Free Traffic Optimization System Based on Vehicular Ad Hoc Networks for Urban Environments" Sensors 18, no. 8: 2567. https://doi.org/10.3390/s18082567