FTN-Based MIMO Transmission as a NOMA Scheme for Efficient Coexistence of Broadband and Sporadic Traffics

In this paper, the concept of faster-than Nyquist (FTN) transmission is used as a non-orthogonal multiple access scheme to interlace sporadic traffic into a broadband service traffic so that radio resources can be efficiently shared by both traffics, beyond the Nyquist rate. We have extended the concept of a 2-dimensional faster- than Nyquist (2D-FTN) transmission where some time-frequency resources are offloaded (turned off) from a broadband transmission to a time- frequency- space 3DFTN system. A broadband user transmitting in multiple- input multiple-output (MIMO) mode turns-off some set of transmit antennas for few subcarriers, which will be allowed for sporadic traffic. Furthermore, we show that turning-off subcarriers with the ill- conditioned channel matrices reduces the performance penalty of FTN transmission. For example, we have have shown that turning-off 12.5% of subcarriers from broadband transmission of 256 OFDM-symbol block costs only 0.3dB transmit power per bit while allowing up to 64 single- carrier grant-free transmission over the offloaded subcarriers.