On Faster-than-Nyquist Transmission over a Multiple-Access Channel

This paper explores faster-than-Nyquist transmission over a multiple-access channel (MAC) when (joint) multi-user demodulation and decoding are utilized at the receiver. We first obtain the appropriate discrete-time channel model, then derive a formula to evaluate the sum capacity of this FTN-MAC channel. Next, we use eigen-value decomposition to facilitate the capacity evaluation of FTN-MAC when large-sized matrices are involved. We conjecture a further simplified capacity formula and also present numerical capacity results showing the improvements of FTN-MAC transmission with different FTN factors and signal-to-noise ratios. Finally, we discuss potential benefits and issues of using FTN transmission in various communication systems.