Overlapped transmission in wireless ad hoc networks

In wireless ad hoc networks that do not employ code-division multiple access, medium access control (MAC) protocols are used to allocate the channel to specific transmitters and receivers, typically to the exclusion of all other users within the interference ranges of the transmitters and receivers. A few authors have proposed the use of multiuser detection (MUD) or dirty paper coding (DPC) to allow transmissions in an ad hoc network to occur simultaneously, even when the transmissions cause interference to each other. However, such proposals usually assume that the MUD or interference cancellation (IC) schemes can completely excise the interference without knowing the interfering signals. We consider a more practical approach in which multiple transmissions are allowed only when the information in the interfering signal is known at the receiver and thus simpler MUD schemes can be applied. This may often occur in ad hoc networks because multihop routing causes the information that was transmitted by a node to be transmitted later by one of that node's neighbors. We call this approach overlapped transmission. The restriction that the interference is known places some limits on when the MUD techniques can be applied. We investigate these limits for random networks with non-fading channels. We then propose a simple protocol for scheduling overlapped transmissions and investigate its performance.