Compressive sensing for MTC in new LTE uplink multi-user random access channel

In LTE, establishing a connection requires a relatively complex handshaking procedure. Such an approach is suitable for a system serving only a few high activity users, but it becomes very cumbersome for machine to machine (M2M) traffic, where large amounts of low activity users intermittently transmit a small number of packets. To avoiding excessive signaling overhead, each packet has to facilitate user detection, channel estimation, and data decoding. Even in the case of limited network activity, users may transmit simultaneously, resulting in packet collisions. It has been shown that such traffic can be best served by a Compressive Sensing (CS) detector. However, most of the CS-based multi-user detection (CS-MUD) research deals with Code Division Multiple Access (CDMA) type systems. In this work we propose a CS-MUD algorithm that is designed for single carrier OFDM (SC-OFDM) systems and, as such, can be integrated into LTE uplink subframes. Each packet contains both a user identification code (ID) and data. The CS algorithm uses the ID not only for user detection, but also for channel estimation. We investigate random and structured ID code generation and report system performance in both cases.