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

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

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

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

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

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]

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

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

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

PROTOCOL UTILIZATION ANALYSIS

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