Channel Division Multiple Access for MTC under Frequency-Selective Fading

In this paper, we study random access for machine-type communications (MTC) based on a multiple access scheme that exploits different channel state information (CSI) from active devices under frequency-selective fading, which is called channel division multiple access (ChDMA). In ChDMA, in order to use a low-complexity compressive sensing (CS) algorithm for multiuser detection (MUD) with a high transmission rate, we employ index modulation. Since the CSI is used as a signature for MUD, the CSI estimation becomes crucial, but suffers from the pilot collision. In order to lower the probability of pilot collisions, multiple transmissions of randomly selected pilots are considered.