Non-orthogonal direct access for small data transmission in cellular MTC networks

In conventional LTE networks, user equipments (UEs) access the network via a four-step random access procedure. When small amount of data is transmitted, such as in the scenarios of machine-type communications (MTC), signaling overhead resulted from the random access procedure becomes a critical issue. To enable an efficient small data transmission, a direct access scheme utilizing code division multiplexing (CDM) is proposed in this paper. Instead of transmitting on the resource blocks indicated by eNB, UEs randomly select resource blocks for direct data transmission without signaling eNB, with CDM used to resolve the collision problem. Under the proposed architecture, however, the data transmission is inherently non-orthogonal and the eNB has to detect the data without any information from UEs, making the receiver too complex to implement. To ease the burden of the receiver, we design a pseudo-random resource selection scheme such that the search space of the data detection is reduced. The analysis and simulation results show the advantage of using the proposed direct access scheme to improve the efficiency of small data transmission in cellular networks.