Multi-Access Spreading over Time: MAST

In this paper, we consider a multi-access communication channel with many transmitters that randomly enter a channel and send their data to a receiver. The transmitters are not synchronized and the receiver does not send any feedback to the transmitters. We propose a Medium Access Control (MAC) protocol, which we call Multi-Access Spreading over Time (MAST). In this protocol, in order to mitigate the effects of user interference, each transmitter spreads its access over a time frame that is much larger than its encoded and modulated packet size. In order to perform this operation, the transmitters choose a spreading matrix from a set, which is known by all the transmitters and the receiver. We obtain the packet decoding probability analytically under user interference conditions, and substantiate our results with simulations. We finally compare the symbol-error probability performance of our protocol with the one of the Zig-zag protocol, and show that MAST outperforms the Zig-zag protocol under the same spreading conditions in both low and high signal-to-noise ratio regimes.