dysco: a dynamic spectrum and contention control framework for enhanced broadcast communication in...
DESCRIPTION
Presentation at MOBIWAC 2012, about a MAC protocol to reduce the collision in Vehicular Networks (VANETS). The paper won the Best Paper Award.TRANSCRIPT
DySCO: a Dynamic Spectrum and Contention Control
Framework for Enhanced Broadcast Communication in
Vehicular Networks
Marco Di Felice, Luca Bedogni and Luciano Bononi
Department of Computer Science
University of Bologna - Italy
Outline
System model
Analytical Results
The DYSCO framework
Performance evaluation
Conclusions
Introduction
Introduction
VANETs – Vehicular Adhoc NETworks● Safety related messages to reduce car accidents● Notification messages for better route planning
WAVE – Wireless Access in Vehicular Environment● DSRC frequencies● IEEE 802.11p and 1609.4 protocols● Switch every 50 ms from CCH to one of the SCH
50ms 100 ms 150ms 200ms 250ms 300ms
CCH SCH CCH SCH CCH SCH
Issues
Synchronous collisions● At the start of each CCH, every one could transmit a
packet
Bandwidth shortage● At the end of each CCH, one could not had the time to
transmit everything
Underutilization of the spectrum● Even in congested scenarios, every 50 ms the CCH or
the SCHs are not used
Contributions
Analytical model to investigate the PDR of broadcast applications
● Derive probabilities of succesfull transmissions
Study on the impact of changing communication parameters
● Change CW and rate to lower collisions
Evaluation in a scenario● By simulation
WAVE - IEEE 802.11p 1609.4
DSRC frequencies – V2V and V2I● 1 control channel (CCH) 10MHz wide● 6 service channels (SCH) 10 MHz wide
802.11p● EDCA mechanism
1609.4● On top of the 802.11p MAC protocol● Strict synchronization between the vehicles● Safety related messages are transmitted on the CCH● The lenght of the interval is 50 ms
System Model
Each vehicle is equipped with a SDR – WAVE stackNo queuing mechanismQoS requirements
Analytical model
W is the CW size is the probability of a succesfull transmission Is the backoff state with CW equal to i
B0
Bi
Evaluation
We can derive the probability of transmitting a message as
The packet delivery ratio is given by
More metrics are on the paper
τ=P(B0)=2
W+1
PDR=NumPkts−Succesfully−Transmitted
NumPkts−Transmitted
=κ⋅psp
λ
PDR computation
Probabilities of:
Idle slot
Busy slot
Succesfull transmission
Collision
pi=(1−τ)N
pb=1−pi
ps=N⋅τ⋅(1−τ)N−1
pc=1−pi−ps
PDR computation
Probabilities of:
Succesfull transmission knowing that the slot isbusy
Avg of transmittedSAFETY messages
psp=ps
pb
=N⋅τ⋅(1−τ)N−1
1−(1−τ)N
κ=min (λ ,E [T access ]
T cch
)
Evaluation
PDR varying the CW
PDR varying the CW
DYSCO – RSU operations
Centralized● Distributed as a future work
During the SCH interval → NETCONF packet● Propagates the network configuration
< W , RCCH , Tstamp >
DYSCO - algorithm
Step 1● Try to determine the best CW
Step 2● Verify if current rate is enough
● If not, using cognitive technology, try to increase it
W>2⋅(N−1)
ϵ
RCCH⩾S⋅λ⋅β
T CCH−α−λ
Comparison varying the density
Comparison varying the density
Comparison varying the load
Comparison varying the scenario
Conclusions
Simultaneous collisions Untransmitted security packets
Characterization of MAC/PHY parameters
Outcomes● Reduced collisions● Better spectrum utilization● Fullfilling of QoS requirements
Major issue in VANETs
Future works
Extend the algorithm to a distributed fashion● To minimize the risks of a centralized architecture
Inclusion of additional network parameters
Extend the study also for non safety related applications
THANK YOU FOR YOUR ATTENTION
Marco Di Felice <[email protected]>Luca Bedogni <[email protected]>Luciano Bononi <[email protected]>
Collisions probability varying the CW
Comparison varying the scenario