To improve physical layer performance in a wireless environment, a common technology is to consider directional communications or use multiple antennas on the same communication node. It should be noted that a multi-antenna communication system consists of both RF components and baseband processing.
Directional Antenna
Directional antennas enable directional transmission and reception in a wireless network, and thus have several advantages.
• Better spatial reuse efficiency. Since transmission and reception are directional, channel reuse does not need to rely on spacial separation, which significantly improves channel spatial reuse efficiency. This feature helps to increase network capacity.
• Lower interference. Directional transmission and reception reduces the collisions and interference among different nodes. This feature improves the QoS and throughput of a network.
• Less energy consumption for the same network capacity. For the same transmission range, less transmit power is needed by a directional antenna than an omni-directional antenna. Thus, for the same transmission rate, less interference will produce by a node to other nodes. In other words, this feature not only improves the energy efficiency , but also increases the network capacity.
• Better security. Due to directional transmission, eavesdropping becomes much more difficult, and thus enhances security of the network at the physical layer. Directional antennas can be realized in the following methods.
• Steerable antenna. In this case, one antenna is used on each node, pointing in a specific direction. For networking with other nodes, the antenna needs to be mechanically or electronically steerable so that the antenna points to the right direction at the right time . Since the process of changing the direction of a steerable antenna may be slower than ad hoc networking needs, it is not always a good choice for WMNs.
