New MAC schemes: CTMA and CRMA-one approach for `hidden terminal problem´

The authors propose two new media access control (MAC) schemes to resolve the hidden terminal problem in the radio LAN environment. These schemes, called channel tone multiple access (CTMA) and channel reservation multiple access (CRMA), were compared with carrier sense multiple access (CSMA) through computer simulations in terms of throughput and delay characteristics. With the CTMA scheme, the maximum throughput and packet delay are sensitive to nomalized propagation delay. For small propagation delays, performance with hidden terminals is better than that of CSMA without hidden terminals, making CTMA attractive for the radio LAN environment. The CRMA scheme uses a control channel based on CSMA and is basically affected by hidden terminals. However, due to dynamic arrangement of reservations at a central station, CRMA performs much better than CSMA with hidden terminals. Making the request packet length sufficiently short compared with the data packet length can significantly reduce wasted transmissions caused by hidden terminals