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A/J.c/ruci-ln packet radio networks, especially an ad hoc wirclcss netw,ork using IEEE 802.11 as the MAC (multiple access control) protocol, power control is a crucial issue. By using a judicious power control mechanism. co-channel interference can be significantly reduced, thus improving the channel spatial reuse and network capacity. However, efficient power control i n an IEEE 802.1 I system i s very challenging because according to the slandard, fixed power i s used lor transmitting packets, atid there is only one channel. In this paper. we propose an enhancement t o the standard I E E E 802.11 MAC protocol by improving the handshaking mechanisms and adding one separate power control channel. With the control channel, the receiver notifies i t s neighbors i t s noise tolerance. Thus, the neighbors can adjust their transmission power levels to avoid packet collisions at the receiver. Through extcnsiye simulations using NS-2, our proposed power control mechanism is found to be effective in h i t network lhroughput can be increased by about IO%, a n d the battery utilization can also be improved at the same I i m e .

Ad hoc routing is important for mobile devices, when they are out of each other's transmission range, to communicate in an IEEE 802.11b based wireless LAN using the distributed coordination function. While traditional table-based or on-demand routing protocols can be used, it is much more efficient to use a routing protocol that is channel-adaptivejudiciously selecting links that can transmit at higher data rates to form a route. However, devising channel-adaptive routing protocols is still largely unexplored. In this paper, we propose a reactive ad hoc routing algorithm, called RICA (receiver-initiated channel-adaptive) protocol, to intelligently utilize the multi-rate services (based on different modulation schemes) provided by the IEEE 802.11b standard. Our NS-2 simulation results show that the RICA protocol is highly effective.