It is a TDMA MAC protocol based model designed for vehicular network. Paper is in the link -- https://www.dropbox.com/s/6gnkl3tfjsxc1s7/Game-based%20TDMA%20MAC%20Protocol%20for%20Vehicular%20Network.pdf?dl=0

1. Game-based TDMA MAC
Protocol for Vehicular
Network

2. Flow of Talk
 Introduction
 System Model
 Game-Based Slot Reservation
Mechanism
 Performance Analysis
 Simulation Result and Analysis
 Conclusion
 References

3. Introduction
 Challenges in VANET
◦ Topology is highly dynamic due to the moving vehicles.
◦ Frequent path breaks and high density of nodes.
◦ Interference because of movement of intermediate nodes or
end nodes.
◦ Routing protocol should aware of frequent topology changes.
◦ Frequent disconnection of nodes create problem in designing
protocol for traffic information exchange.
◦ Heterogeneous vehicle management
◦ Uses both push and pull models for data exchange.
The vehicular ad hoc network (VANET) is a special network
that applies the mobile ad hoc network (MANET) to traffic
scenarios.

4. Contd…
 Some previously used protocols for VANET
◦ IEEE 802.11p, HER-MAC, CFR-MAC, CAH-MAC .
 Disadvantages of above protocols
◦ Hidden terminal problem.
◦ Reserve the time slots with the same priority.
◦ Continuous reservation collisions.
◦ Non-Cooperative connections.
◦ Some nodes may not get time slots.
◦ Less overall throughput.
◦ Markov chain model can not be implemented.
◦ Network intelligence is not possible.
In one scenario, Station
A can communicate
with Station B. Station
C can also
communicate with
Access Point Station B.
However, Stations A
and C cannot
communicate with each
other as they are out of
range of each other.

5. Contd…
 Advantages of Game-Based MAC protocol
◦ Assigns priority to nodes.
◦ Time slot reservation based on priority.
◦ Priority decided based on waiting counter
◦ Analysis can be done using Markov chain.
◦ Provides colliding nodes two strategies to
reserve new time slots
• Reserving the original conflicting slots again
• Choose new idle slots to reserve

6. System Model
 Each vehicle has its own ID
◦ ID ∈ {1, 2, ・ ・ ・,N} for N vehicle
 Initial position of vehicles are random.
 Transmission range of each vehicle is r(assigned by system)
 All the vehicles have GPS.
 The neighboring nodes are of two types
◦ One-hop nodes
◦ Two-hop nodes
 One-hop sets (OHSs) and two-hop sets (THSs) are
defined as the sets of nodes whose relative distance is
shorter than the communication range r or 2r.
 THS = OHS1 U OHS2 .

7. Contd…
 For a node x,
◦ N(x) - set of IDs of one-hop neighbours of node x.
◦ S(x) - set of time slots where node x cannot reserve.
 Transmission collisions are of two types
◦ Access collision : when two or more nodes reserve the same time
slot when they are in the same THS.
◦ Merging collision : when two nodes communicate with another
node in a two-hop set .

8. Game-Based Slot Reservation
Mechanism
 The Structure of Control Message and Frame
◦ Nodes reserve slots on a unique control channel.
◦ Control channel is used to broadcast control messages(vehicles’
position, speed, moving direction, the occupied slot number).
◦ Control channel is also used to transmit high-priority messages.
M – no. of slots in frame
𝑀 𝑎- no. traditional time slots
L – no. of special slots(0,M/2)
𝑀 𝑎=M – L

9. Contd…
 Two types of time slots :-
◦ Traditional time slots(𝑀 𝑎) - This let those occupied slots’
nodes broadcast the control messages periodically or let
the nodes that need to reserve slots broadcast the
reservation message.
◦ Special Slots(L) - This let those colliding nodes reserve
slots again.
 The broadcasting sequence in the special slots is arranged according
to the number of the conflicting slots.
 Number of special nodes depends on the node density in the network.
 This slot arrangement reduces the total number of
slots for reserving, but it does increase the success
rate of reservation, and the total number of
occupied slots is increased in the high-density
network.

10. Contd…
Fig 2. The structure of control message
• Modifications in control message
• Slot Information – Records the status of slots.
• Waiting Counter(W(x)) - record the total times that node
x chooses to reserve a new slot after the reservation
collision happens.
• The value of W(x) is a number, it just occupies 8 bits
which is much less than the payload data.

11. The Reservation Procedure
 Information Synchronization
◦ When a new node joins to the network it has to monitor at
least one frame to collect control messages from other
nodes.
◦ Then it updates following sets :
 𝑁(𝑥) – Set of one-hop neighbours of x.
 𝑆 𝑜ℎ𝑠 𝑥 − Set of time slots occupied by one-hop neighbours of
x.
 𝑊𝑜ℎ𝑠 𝑥 −Set of waiting count of one-hop neighbours of x.
 𝑆𝑡ℎ𝑠 𝑥 − Set of time slots occupied by two-hop neighbours of
x.
 𝑊𝑡ℎ𝑠 𝑥 − Set of waiting count of two-hop neighbours of x.
 𝑆 𝑥 = 𝑆 𝑜ℎ𝑠(𝑥) ∪ 𝑆𝑡ℎ𝑠 (𝑥)
 𝑊 𝑥 = 𝑊𝑜ℎ𝑠(𝑥) ∪ 𝑊𝑡ℎ𝑠 (𝑥)

12. Contd…
 Available Slots Reservation
◦ A node x can choose any slot k for reservation
from available set.
◦ Changes mark of slot k from 0 to 1.
◦ Update the set N(x).
◦ Broadcast updated control message.
◦ Node x will monitor the control message one
frame after reservation.
◦ The reservation will end only when the node x
and its neighbours have updated the related
sets.

13. Contd…
 Slot Allocation

14. Contd…
 The Collision Judgement
◦ The reservation collision is of two types:
 Access collision
 Merging collision
◦ Both of them are the collision that two or more
nodes within two-hop range acquired the same
slot.
◦ When a reservation collision occurs the slot
broadcasts a notice message.
◦ The notice is like a urgent notice to all other
nodes in network.

15. Contd…
 The Time Slot Competition Game
◦ When the collision happens both the nodes have to play
the game.
◦ According to the game theory the strategy status of nodes
are{R,W}
 R indicates that colliding nodes reserve the original slot again.
 W indicates that colliding nodes choose another slot to reserve.
◦ The colliding nodes will choose the strategy R or W
according to the probability calculated through the game.
◦ There are three different cases for the colliding nodes
according to the strategy. In each case Utility value is
calculated.
◦ Utility values are the probabilities of the nodes getting the
slot under a particular case.

16. Contd…
 Example of Time–Slot Competition Game
◦ Let there are v colliding nodes.[ I = {1,2,…,v} ]
◦ The three cases for node i
 If node i reserves the original slot again and other colliding
nodes gives up reserving the original slot, it will occupy the time
slot successfully, in this case, the utility value is 𝑢𝑖
𝑟
.
 if node i reserves the original slot again and there exists other
colliding nodes reserve the original slot, it fails to occupy the
time slot, in this case, the utility value is 𝑢𝑖
𝑐
.
 if node i chooses a new slot to reserve, it won’t affect other
colliding nodes reserve the original slot, in this case, the utility
value is 𝑢𝑖
𝑤
.
◦ The larger the waiting count of a node , the
higher priority is given to it.

17. Contd…
 𝑈𝑖: The utility function of node i.
 ϕ(v): The probability that the slot is reserved successfully in v-points
game.
 𝑃𝑖: The probability that node i chooses the strategy R
 The utility value of node i is
 Calculating partial derivative of (1)
 Substitute 𝑃𝑗 = 1 − 𝑃𝑖 in (2)
 (3) gives the Nash equilibrium solution or the probability set of nodes
choosing the strategy R.

18. Contd…
 Extending 2-point model to v-point model the
equations will be

19. Performance Analysis
 Assumptions before analysis
◦ All the nodes are in the same THS;
◦ All the nodes remain still in one frame;
◦ Any node i has updated N(i), S(i),W(i) before reserving the
slots.
 The Distribution of chosen slots
 Calculate the lower bound and the upper bound

20. Simulation Result And
Analysis
Fig 4. The simulation result
compared with the theoretical
upper and lower bound.
Fig 5. The reservation speed of
GAH-MAC compared with VeMAC

21. Contd…
Fig 6. The performance of
normalized throughput in the city
scenario.
Fig 7. The performance of
packet drop rate in the city
scenario.

22. Conclusion
 This presents a GAH-MAC protocol.
 This protocol sacrifices part of the available slots as special
slots. The colliding nodes play games with each other to decide
whether to reserve the original slot or a new one, and use the
special slots to broadcast messages.
 The success rate for a reservation is increased, and fairness in
the reservation of nodes is ensured by a new modular waiting
counter.
 The reservation speed, throughput performance, and packet
drop rate are simulated and compared with those of the
VeMAC protocol.
 The simulation results show that the performance of GAH-MAC
is superior to VeMAC in high-density networks.
 GAH-MAC decreases the packet drop rate and increases
network throughput.

23. References
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25. Thank you