Combating the effects of Hidden Terminals in Multi-channel MAC Protocols

Abstract—Multiple channels present IEEE 802.11 MAC protocol designers with a number of options in their attempt to calm the effects of Hidden Terminal Problems (HTPs). The research on multi-channels shows that the effects of HTPs can be reduced and limited to Request To Send/Clear To Send (RTS/CTS) control packets. Unfortunately our analysis shows that data packets can be affected by HTPs. An effective HTP control channel solution may effectively protect data packets in data channels. Our previous work revealed that HTPs can be completely eliminated through the implementation of Long InterFrame Space (LIFS) and an intelligent MAC in single channel systems. An intelligent MAC divides terminals into two segments, the Transmitter Carrier Sensing Zone (CSZ) and the Receiver CSZ for the implementation of Extended Inter-Frame Space (EIFS) and LIFS respectively. The extension of our LIFS and CSZ concepts to Multi-channel environments reveals interesting developments that need to be tackled. The HTP may not be completely eliminated as new challenges arise in multichannel environments. Multiple channels have a delayed effect on HTP manifestation. They do not solve the HTP but they reduce its effects. Our analytical results suggest the existence of a theorem mapping the occurrence of HTPs onto the number of channels implemented.