Wireless Ad Hoc and Sensor Networks

Background on Networking 29Carrier sensing range: This is the distance range around the transmitterwithin which any user in the network can sense the informationsent by the transmitter. When highest transmitter power is used,the carrier sensing range is 500 m.Carrier sensing zone: This is the distance range around the transmitterwithin which any user in the network can sense the informationsent by the transmitter but cannot decode it correctly. When highesttransmitter power is used, the carrier sensing zone is between 250and 500 m.Figure 1.3 shows transmission range, carrier sensing range, and carriersensing zone for the user C. Here, users B and D are in the transmissionrange of C as per the definition of transmission range. Users A and E arein the carrier sensing zone. All the nodes shown in the figure are in thecarrier sensing range.The DCF in IEEE 802.11 works on the principle of carrier sense multipleaccess with collision avoidance (CSMA/CD). Carrier sensing is performedusing physical carrier sensing through air as an interface, and also byvirtual carrier sensing. Virtual carrier sensing uses the duration of thepacket transmission, which is included in the header of RTS, CTS, andDATA frames. The duration included in each of these frames can be usedto infer the time when the source node would receive an ACK frame fromthe transmitter. The duration in RTS signifies the time needed for CTS,Carrier sensing zoneA B CD ETransmission rangeFIGURE 1.3An IEEE 802.11 wireless LAN.