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LTE-direct broadcast of periodic safety messages

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(1)LTE-Direct Broadcast of Periodic Safety Messages Laurent Gallo, Jérôme Härri - Mobile Communications Department - e-mail: {gallo, haerri}@eurecom.fr. Highly Autonomous Driving Vehicles • Need for periodic safety communications between road users: ‣ Autonomous driving requires awareness of surrounding traffic ‣ Information from local sensors might not be sufficient (reactions could be delayed and non optimal) ‣ Cooperative mapping and localization applications. LTE broadcast of safety messages - Issues with LTE-based periodic safety transmissions:. + Advantages of LTE-based periodic safety transmissions: ‣ Network widely available and in expansion ‣ PHY optimized for high speed mobility ‣ Allows for integration with smartphones, which: 1) will initially compensate for slower adoption rate of connected cars 2) will extend safety features to vulnerable users (pedestrians, cyclists). ‣ Latency ‣ Basestation (eNodeB) becomes a single point of failure ‣ Massive mobility management by the network can cause further delay ‣ Can generate considerable traffic (that must coexist with regular traffic) ‣ Broadcast of safety messages difficult to handle. Proposed solution: broadcast LTE-direct •Safety messages follow a direct Device-to-Device path •Control plane transmitted by the eNodeBs •D2D and commercial LTE traffic can coexist, multiplexed in time •Energy efficient for battery-powered devices •Divided in two phases: 1) Resource Allocation 2) Distributed Resource Access Scheduling. Resource Allocation. Distributed Resource Access Scheduling Organization of LTE Resource Blocks into a TDMA-like scheme. Safety Broadcast Area: periodic pool of common dedicated resources (LTE subframes) allocated over an area covering multiple cells, allowing broadcast among users spread over neighboring cells. Resource blocks belonging to the subframes dedicated to LTE D2D broadcast are collected into slots the size of a CAM packet The slots within 100 ms form a frame (transmission rate of 10 Hz) Multiple access can be treated as a TDMA-like system. Operation modes: Band sharing with LTE: D2D subframes interweaved with commercial LTE subframes. Dedicated band: D2D subframes allocated in reserved band (5.9 GHz). Allows time sharing with DSRC. TDMA scheme: Optical Orthogonal Codes (OOC) ‣ Repetition based: multiple (re)transmissions per frame (w) ‣ Max number of collisions per frame between two users: bounded to λ Congestion Control: ‣ same Decentralized Congestion Control as DSRC can be applied Performance comparison with DSRC (802.11p). Features: ‣ Quasi static pool of resources available over a wide area (time/frequency coordinates are periodically broadcast in control channel) ‣ Does not require connection procedure with eNodeB ‣ No network-side mobility management ‣ Network has the flexibility to reallocate resources ‣ Periodic pattern: ‣ Provides a certain degree of eNodeB failure-resilience ‣ Allows for energy saving (TX/RX duty cycle) without losing awareness ‣ Allows for time sharing with other D2D technologies as DSRC. Metric: Packet Delivery Ratio Channel Rate: 6 Mbps Modulation: QPSK TX Rate: 10 packets/s Bandwidth: 10 MHz Packet size: 300 bytes LTE D2D time occupation: 50% LTE D2D outperforms DSRC up to ∼ 80 neighbors Current and future development: ‣ Adoption of location aware multiple access: Self Organizing TDMA ‣ Definition of a suitable waveform for LTE-direct. Reference: Gallo L., Härri J. “Short Paper: A LTE-Direct Broadcast Mechanism for Periodic Vehicular Safety Communications” 2013 IEEE Vehicular Networking Conference (VNC), 16-18 December 2013, Boston USA. EURECOM – CAMPUS SOPHIATECH 450 route des Chappes F-06410 BIOT Sophia ddddddAntipolis www.eurecom.fr. http://systuf.ifsttar.fr.

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