A Multi-Channel CSMA MAC Protocol with Receiver Based Channel Selection for Multihop Wireless Networks Nitin Jain, Samir R. Das Department of Electrical & Computer Engineering and Computer Science University of Cincinnati Reporter: Chang, Pei-Chen ICCCN 2001

Outline  Introduction  Motivation  Receiver-Base Channel Selection Protocol  Performance Evaluation  Conclusions

Introduction  Multihop Store-and-Forward routing  MAC Protocol is responsible for minimizing conflicts  Distributed Coordination Function  CSMA/CA technique  RTS-CTS-data-ACK handshake

Motivation  Mulitple Channels Advantages  Reducing collisions  Enabling more concurrent transmissions  Better bandwidth usage  Aggregate capacity

Receiver-Base Channel Selection  Carrier Sensing  Find the clearest channel for transmission  Support CDMA  Receiver may also receive multiple signals form difference sources at the same time.  Two classification  First Class (dedicated channel)  Transmitter-Oriented  Receiver-Oriented  Second Class  Bandwidth divided into number of channels  A node may transmit and receive on any channels

RCBS Protocol (cont)  RTS-CTS avoid hidden terminal problems at low load  Control Channel  Exchange RTS and CTS shared for all node  N traffic channels (Data Only)  Exchange data packet only  Signal to Interference plus Noise Ration(SINR)

Assumption  Total bandwidth W is divided into N+1  Control channel Wc  Data channels  Node could simultaneously sense all the channel  Nodes are equipped with Half-duplex radios  Nodes could access on all channels.  One packet can be transmitted on any channel  Multuple packets can be received at different channels

Protocol Description  RCBS  Sender  Sender create own free-channel list  If free channel list is empty then go to Backoff  Else Sender node send RTS packet in control channel  Include free data channel list  When receives CTS packet go to data channel to transmit data  Receiver  After reception RTS then Create own free-channel list  Compare free-channel list from RTS  Select best common channel included in CTS  Receive data packet on data channel then transmit ACK  Other nodes  Record used channel, transmit duration from CTS  Defer only until the duration of CTS (not ACK)

Performance Evaluation  Compare with DCF MAC  Throughput  Delay Performance  Optimum bandwidth of Control Channel  Optimum number of Data Channels

Simulation Model  Use ns-2 network simulator  2Mbps nominal bit rate  250 meters transmission range  Omni-directional antenna  Assume noiseless and error-free  Fixed packet size of 1.5Kb  Simulation duration 500 seconds  Two model  100 nodes in a 10 x 10 grid with 175 m grid size  255 nodes in a 15 x 15 grid with 125 meters

Throughput Performance

Delay Performance

Optimum Number of Channels

Optimum Number of Channels (2)

Conclusions  Receiver-Base Channel Selection  Reducing collisions  Enabling more concurrent transmissions  Better bandwidth usage  Aggregate capacity  Lower delay  High throughput  Comment  With SINR, node could receive packets and assign best common channel for transmit  Maybe we could add the Multi-Rate function on it