Capture-Aware Protocols for Wireless Multihop Networks Using MultiBeam Directional Antennas

We define a node to be “captured” when its receiver is engaged in receiving a packet that is not intended for that node. A unicast transmission using IEEE 802.11, although intended for a single destination node, can result in capturing several other nodes located within the interference footprint of the transmitter. Capture is mostly unproductive, because the physical layer of a captured node is kept occupied in receiving a packet which will eventually get dropped at the MAC layer. This can degrade network capacity because captured nodes refrain from scheduling useful communication during the period of capture. Antennas capable of beamforming may be able to overcome capture by spatially filtering directions from which signals lead to capture. As a result, nodes might be able to gain more free time to simultaneously schedule their own productive communication. This paper presents protocols that utilize multi-beam antennas to minimize the impact of capture. At the MAC layer, nodes characterize ongoing transmissions based on their directions, and use multi-beam antenna patterns to suppress unwanted signals – thus, the antenna can implement a spatial filter. The network layer assists the MAC layer by using a new capture-aware routing metric that prefers routes less prone to capture. Simulation results show that reducing the impact of capture can help improve performance in wireless multihop networks.