VANET MAC Protocol Time Slot Reservation for Collision Avoidance
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Solution Overview
Problem
Existing VANET MAC protocols, such as IEEE 802.11p, face limitations in reliable broadcast services for safety messages due to the absence of RTS/CTS exchange and ACK packets, leading to reduced successful packet delivery rates and increased transmission collisions, especially in broadcast-based safety applications.
Innovation Solution
A time division scheme-based MAC protocol that synchronizes nodes using external time reference signals, allowing nodes to select and verify unoccupied time slots for message broadcasting, and dynamically reassign slots to avoid collisions and deadlocks, ensuring timely and reliable delivery of safety messages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If IEEE 802.11p standard is used for broadcast communications, then unicast communication mechanisms (RTS/CTS) are avoided, but successful packet delivery rate decreases due to hidden terminal problem
Solution Approach 1:
The broadcast transmission process is segmented into multiple phases: reservation phase where nodes send RSV packets to claim time slots, and transmission phase where actual data is sent in assigned slots. This segmentation allows collision avoidance through prior reservation while maintaining broadcast efficiency.
Solution Approach 2:
Nodes perform preliminary actions by sending RSV (Reservation) packets before actual data transmission. This preliminary reservation of time slots prevents hidden terminal collisions by establishing prior claims on transmission resources, ensuring reliable packet delivery without requiring RTS/CTS handshaking.
2Loss of time
If small contention window size is used for safety messages, then transmission delay is reduced, but collision probability increases among simultaneous broadcasts
Solution Approach 1:
The RSV packet mechanism performs preliminary action by reserving time slots before actual safety message transmission. This eliminates the need for small contention windows by pre-establishing transmission rights, thus avoiding both delays and collisions.
Solution Approach 2:
The system dynamically assigns time slots based on node activity and message priorities. Active nodes receive time slot allocations through RSV exchanges, while inactive nodes remain silent. This dynamic resource allocation optimizes both delay and collision probability adaptively.
3Productivity
If no ACK packets are transmitted for broadcast messages, then protocol overhead is reduced, but reliable delivery verification becomes impossible
Solution Approach 1:
The RSV packet serves as a preliminary acknowledgment mechanism. By requiring nodes to send RSV packets to reserve time slots, the system implicitly verifies that receivers are present and functional, providing delivery verification without traditional ACK packets.
Solution Approach 2:
The RSV packet acts as an intermediary mechanism that provides verification functionality without using traditional ACK packets. The reservation process itself serves as implicit acknowledgment that the broadcast medium is accessible and receivers are active.
Data Source
AI summary
The invention generally relates to the field of vehicular communications. In particular, the invention relates to method, system and apparatus for establishing and maintaining vehicular communications, such as wireless vehicular communications in a vehicular ad hoc network (VANET).