1. LOAD SENSITIVE CONTENTION RESOLUTION MAC-PROTOCOL
MAC-Layer Protocol for
Wireless Ad-hoc Networks
Shachar Siboni
Department of Communication System Engineering
Ben-Gurion University of the Negev

2. INTRODUCTION WIRELESS AD-HOC NETWORK Decentralized Wireless Network
No Base-Stations
Topology defined by connectivity
Station Capabilities:
Maintain MAC-Layer algorithm
Operate as Relay-node
Suitable for a variety of applications
Where central nodes can't be relied on
Minimal configuration and quick deployment

3. INTRODUCTION SHARED WIRELESS MEDIA CHALLENGE
Transmissions Collisions Avoidance
Hidden and Exposed Node Problems
Contention Resolution Mechanism
Distributed Wireless Network
Adapt to Topology Changes
Performance Requirements
Fairness in Resources Allocation
Achieve High Channel Utilization
Guaranty Low end-to-end message Delay X
Collision A B C

4. INTRODUCTION LOAD SENSITIVE CONTENTION RESOLUTION MAC-PROTOCOL
The most Loaded Station gain the grant to transmit data S1 S6 S2 S4 S5 S3

5. SYSTEM MODEL PROTOCOL STATION DEFINITION
Each station can function as “MASTER” or “SLAVE”
Depending on Network Topology
The “MASTER” manages and supervises contention resolution
between all stations in It’s transmission/reception range
Protocol Cluster definition
According to “MASTER” station
The “SLAVE”s respond to
“MASTER” decisions
SLAVE
MASTER

6. STATION LOAD PARAMETER
STATION LOAD FUNCTION
Global Cluster Parameters
Local Station Parameters
max{Qi} – Maximum Queue Size in Cluster
Qi – Station Queue Size [Bytes]
max{Dmaxi} – Maximum Accumulated
Message Delay in Cluster
Dmaxi – Station Maximum Accumulated
Message Delay [sec]
 - Equilibrium parameter [0  1]

7. PROTOCOL IMPLEMENTATION
LOAD SENSITIVE CONTENTION OPERATION:
“MASTER” initiates new session in the protocol
Stations compete to gain channel access using RTS\CTS Mechanism
Each station defines Access Time (AT) interval before transmit RTS signal
According to Station Load parameter:
Station Load
Access
Time 1
f(Qx, Dmaxx)
f(Qy, Dmaxy)
f(Qz, Dmaxz)
ATy
ATx
ATz
MASTER Tx Rx
Start Session
(max{Qi}, max{Dmaxi}, )
“RTS”
ATM
t (µsec)
RTS
SLAVEi
ATi

8. PROTOCOL IMPLEMENTATION
LOAD SENSITIVE RESOLUTION OPERATION:
“MASTER” decides according to the first RTS indication that is received
Estimates the highest load in cluster:
Detects RTS collision occurrence indication
Send it’s decision with {estLoad} parameter: CTS{estLoad} or COL{estLoad}
Update global cluster parameters: max{Qi}, max{Dmaxi}
MASTER
RTS
estAT Tx Rx
RTS Collision
stSess
COL
(estLoad)
Contention Round (CR) Period
CR2
“RTS”
ATM
t (µsec)
Collision-Free
CTS
Tx_DATA
Period

9. PROTOCOL IMPLEMENTATION
LOAD SENSITIVE RESOLUTION OPERATION (cont.):
“SLAVE”s respond to these decisions using Loads Comparison criteria
myLoad > estLoad
Return To IDLE
CTS\COL
Gain a grant to transmit Data
Continue to compete with Random Access No
Yes
COL
CTS
Executes a Stop-&-Wait transmission mechanism
Retransmit Data packet if necessary
Relay-node operation

10. PROTOCOL UTILIZATION ANALYSIS

11. LOAD SENSITIVE CONTENTION RESOLUTION MAC PROTOCOL FOR WIRELESS AD-HOC NETWORKS