Null placement configurations for radio network capacity enhancement

The use of array antennas in the radio nodes of a wireless network will increase the capacity since by appropriate null placement, the cochannel interference can be suppressed and the channel reuse will be enhanced. A radio network with arbitrary topology and array antennas in the nodes is considered in this paper. Each radio node may act either as a receiver or as a transmitter and can place a number of nulls in its radiation pattern. A collection of links may share the same channel if the interfering transmitters within the range of each receiver are cancelled out by null placement either at the receiver or at the transmitter side. The following problem is considered. Given a collection of links, identify a null placement configuration such that the links share the same channel without interference. It is shown that such a null placement configuration can be found by solving a maximum flow problem in an appropriately defined capacitated network.