ABSTRACT
Contents Abstract ..................................................................................................................................... 78 4.1 Introduction ..................................................................................................................... 78
4.1.1 Functions of the Medium Access Control Layer ................................................... 78 4.1.2 Contention versus Contention-Free ...................................................................... 78 4.1.3 Power Management .............................................................................................. 79 4.1.4 IEEE 802.11 (Wi-Fi) ............................................................................................ 79
4.2 Directional Antennas: Opportunities at the Medium Access Layer ...................................81 4.2.1 Increased Capacity through Spatial Reuse ............................................................ 82 4.2.2 Transmission Range Extension ............................................................................. 83 4.2.3 Improved Energy Efficiency .................................................................................. 83 4.2.4 Enhanced Reliability ............................................................................................ 84 4.2.5 Increased Capacity Due to Higher Data Rates ...................................................... 84 4.2.6 Enhanced Security ................................................................................................ 84
4.3 Design Issues of MAC Using Directional Antennas ..........................................................85 4.3.1 Hidden Node Problem (Hidden Terminals) ..........................................................85 4.3.2 Deafness ............................................................................................................... 87 4.3.3 Communication Range Utilization ....................................................................... 89 4.3.4 Exposed Node Problem ........................................................................................ 90 4.3.5 Minor Lobe Problem .............................................................................................91 4.3.6 Miss-Hit Problem and Neighbor Discovery ......................................................... 92 4.3.7 Head-of-Line Blocking ......................................................................................... 93 4.3.8 Power Management .............................................................................................. 93
4.4 Selected MAC Protocols for Directional Antennas ........................................................... 93 4.4.1 Single-Channel (Foundational): Basic DMAC ..................................................... 94
Abstract The use of directional antennas in wireless networks offers a wide variety of potential gains, including increased capacity and range, improved reliability and energy efficiency, and enhanced security. To realize these potential gains, the medium access layer must be designed to effectively utilize the unique capabilities of directional antennas. In this chapter, we review the fundamentals of medium access for wireless networks, highlight the opportunities presented by directional antennas as they apply to medium access, and discuss the medium access control (MAC) layer design issues relevant to effective utilization of directional antennas. We close with a sampling of medium access control protocols that have been proposed for directional antennas, discussing both their operation and their performance.
