Successive Interference Cancellation in Vehicular Networks to Relieve the Negative Impact of the Hidden Node Problem. Carlos Miguel Silva Couto Pereira. Outline. Introduction Objectives How to characterize packet collision Outlook. Introduction. Vehicular Ad-Hoc NETworks (VANETs):
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Successive Interference Cancellation in Vehicular Networks to Relieve the Negative Impact of the Hidden Node Problem Carlos Miguel Silva Couto Pereira
Outline • Introduction • Objectives • How to characterize packet collision • Outlook
Introduction • Vehicular Ad-Hoc NETworks (VANETs): • Communications between vehicles. • Increase safety on roads by cooperative awareness. • Two types of safety messages: alarm and beacon. • High probability of beacon reception is desirable
Introduction • Technology • IEEE 802.11p standard based on modifications and amendments to IEEE 802.11-2007 to adapt it to vehicular environments. • IEEE 802.11 DCF introduces carrier-sense-based random multiple access scheme known as the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).
Challenges • Scalability/Congestion • Hidden Node • Same Backoff Slot A B C RTS/CTS
Challenges • Mobility and Fading • High Mobility of nodes leads to: • Highly dynamic channel conditions • Variation in the vehicular density • Fading - deviation of the attenuation that a carrier-modulated signal experiences over certain propagation media. • Nodes mobility and fading characteristics of the received signal introduce additional collisions.
Successive Interference Cancellation in Vehicular Networks to Relieve the Negative Impact of the Hidden Node Problem Objectives • Characterize packet collisions • Answer the question: • How much could interference cancellation help to deal with packet collisions in vehicular communications? • Possibly implement SIC What is SIC? SIC (Successive Interference Cancellation) is a physical layer technique that allows a receiver to decode packets that arrive simultaneously.
SIC SIC permits the recovery even of the weaker signal by subtracting the stronger signal (highest SINR) to the combined signal and extracting the weaker signal from the residue.
How to characterize packet collision? • Packet collision happens when two or more packets overlap in time, at a given receiver, due to unsynchronized transmissions. • A packet is considered interference to other packets when its reception power is higher than thermal noise power. • However, a packet can be recovered from a collision, if during the reception its power is higher than the accumulated powers of the all other interfering packets plus a capture threshold. P t
How to characterize packet collision? • Primary Metrics • Packet drop probability with respect to distance between sender and receiver • Independent of the circumstances • Dependent of the circumstances • Due to own transmission • Due to signal attenuation • Due to channel fading • Due to a collision • How many packets did interfere? (minimum, maximum, and average values) • Would it be possible to decode the dropped packet in case all interfering packets can be cancelled out perfectly? • Identify the interfering users.
How to characterize packet collision? • Secondary Metrics • Packet reception probability with respect to the distance between sender and receiver • Independent of the circumstances • Dependent of the circumstances • Without Interference • With Interference • The load that is put on the channel (in Mbps).
How to characterize packet collision? • Scenario • Communication scenario: Highway with 4 or 6 lanes. • Static scenario: No mobility. • Distribution: Uniform. • Configurations: • Data Rate: 6 Mbps in a 10MHz channel (QPSK). • Simulation Parameters • Channel Configuration: Two-ray Ground model. • Packet size: 200 bytes, 400 bytes, and 600 bytes. • Node Density: 20 nodes/km, 60 nodes/km, 100 nodes/km. • Transmission Frequency: 2Hz, 6Hz, and 10Hz. • Transmission Power: 5 dBm, 10 dBm, 15 dBm, and 20 dBm. + Mobility based on the mobility traces of the FleetNet project • + Distribution based on the mobility traces of the FleetNet project • +Fading Model
Outlook • Quantification and characterization of packet collisions. • Determine the amount of unsynchronized packet transmissions in different scenarios. • Determine the situations as well as the geographic relationship between a sender and an unsynchronized interferer. • Evaluate the impact of collisions in VANET scenarios and the impact of the hidden node. • Determine the importance of a possible development of an interference cancellation to ease collisions in VANETs, considering effort and complexity of its implementation in real transceivers. • Possibly develop an interference cancellation algorithm within the NS-3. • Develop code. • Perform operational tests. • Optimization. • Performance evaluation. • Write the master thesis.