Needs & Objectives

1. CAR-TO-CAR SAFETY BROADCAST WITH INTERFERENCE USING RAPTOR CODES Nor Fadzilah Abdullah, Angela Doufexi, Robert J. PiechockiUniversity of Bristol, UK • This work considered car-to-car (V2V) safety applications, with decentralized design (ad-hoc) in the Control Channel (CCH). • Safety applications have stringent requirement for real-time and reliable communications. Repetition coding proposed in the standard is inefficient for lossy highway environment with huge Doppler spread and multipath fading. • A novel coding technique such as fountain coding is required. • More than 40,000 road fatality and millions of injury every year in the EU causing billions of economic loss. • Increasing car ownership (EU: >200mil vehicles) leads to traffic congestion, reduced air quality, unpredictable travel time, and increased petrol cost. • IEEE 802.11p draft standard (an extension to the IEEE 802.11) at 5.9 GHz band, specifically to allow direct communication between vehicles (V2V) and to roadside infrastructure (V2I). Needs & Objectives Numerical analysis • 2 types of safety messages: • (1) Post-crash warning (by tagged vehicle) • (2) Status beacon (source of interference) Methodology • 1. Detailed physical layer simulator • An OFDM-based simulator considering channel coding (multi-rate convolutional coding), multipath and fast-fading Rayleigh channel in accordance to V2V highway measurements, and training-aided channel estimation. This gives a more realistic and accurate representation to the analysis. • STBC (space-time block code) is considered to exploit the diversity gain. STBC 2x2 and 4x4 gives ~5-10 dB gain against SISO (single antenna). • 2. Analytical MAC model (Bianchi’s) with consideration of multi-nodes interference • Take into consideration the IEEE 802.11p parameters and the random back-off DCF procedure. • 3. Systematic Raptor-coded FEC at the application layer • Most successful of fountain code family (3GPP-MBMS and DVB-H standard). • Low complexity, O(K) vs. LT code O(K log K), where K=source block length. • Systematic design allows immediate decoding for nodes with good channel condition. Conclusions • Raptor codes decreased the end-to-end delay by around 50% to 60% of for high density traffic and around 60% to 70% for low density traffic. • Raptor codes allow the end-to-end delay that meets the ETSI specification of 100ms maximum latency for safety messages. • For high density traffic using repetition codes, this requirement can only be met by vehicles located very near to the tagged vehicle (<200m for SISO, <400m for STBC 2x2 and <800m for STBC 4x4). • Spatial diversity benefit is twofold: (1) extends the communication distance, (2) reduces the end-to-end delay.