Wireless Ad Hoc and Sensor Networks

Distributed Fair Scheduling in Wireless Ad Hoc and Sensor Networks 3477.6.3.1 SchedulingTo store packet’s weight, each user data packet is extended with ADFSheader. The source node allocates the initial weight according to the trafficflow the packet belongs to. The MAC layer updates the packet’s weightafter the packet is received. Next, this weight is used by queuing algorithmto store and dispatch packets. When the packet is released from the queueand passed to the MAC layer, a backoff interval is calculated and thebackoff timer is set accordingly. After the timer expires, the packet istransmitted using standard RTS-CTS-DATA-ACK procedure.7.6.3.2 DPC ProtocolThe DPC scheme is used to calculate transmission power for all, exceptbroadcast, messages that are sent over the radio interface. However, simplereduction of a transmission power leads to the degradation of qualityof service due to increased hidden-terminal problem, as indicated in Jungand Vaidya (2002) and Zawodniok and Jagannathan (2004). In consequence,more collisions occur reducing throughput and yielding higherenergy consumption. By using a train of pulses presented in Chapter 6with increased power magnitude will reduce the hidden terminal problem,which in turn increased throughput.In the energy-aware protocol, only the initial RTS-CTS frames duringlink set up have to be transmitted using maximum power defined by thelink. Subsequently, all frames, including RTS-CTS-DATA-ACK frames,will use transmission power calculated according to the DPC. To accommodatethe DPC, the MAC header was changed to allow power informationto be sent between the communicating nodes. As a result, an increasein overhead is observed, which could cause a decrease in throughput.However, it is found that the increase in throughput, due to better channelutilization, overcomes the penalty introduced by the additional overhead.7.6.3.3 Sleep Mode ImplementationThe packets to the sensor nodes are buffered at the local CHs. The MAClayer allocates memory for such a buffer. Any buffered packet at the CHis delivered after the sensor node wakes up and sends the RTS frame.First, the CH responds with the CTS frame. This frame contains a flagindicating that there is a buffered packet to a particular sensor node. Next,the sensor node sends the DATA frame with most recent collected data.Afterward, the acknowledgment frame is sent from the CH to the sensornode, where the packet to the sensor node is piggybacked. Finally, thesensor node acknowledges the correct reception of the packet by sendinga standard ACK message.In case of a sensor node, the computational and RF circuits are turnedoff but the MAC frames are exchanged with the CH. To enable periodic