Enhanced LTE physical downlink control channel design for machine-type communications

The application of LTE to the machine-type communications (MTC) poses some serious challenges due to the large performance mismatch between the regular LTE user equipment and the MTC device, caused mainly by the physical limitations of MTC devices. This paper addresses these limitations and their implications to the communication signal´s link performance and the corresponding link budget. The focus of this paper is on the downlink control channel design. We analyze the issues of the existing LTE control channels and propose an enhanced design specifically-tailored to overcome the limitations of MTC devices and the stringent link budget by applying repeated transmissions, frequency retuning, and the orthogonal spatial precoding based joint channel estimation, fully exploiting the time, frequency, as well as spatial diversities. The basic schemes proposed in this paper apply to other LTE channels as well, such as the uplink control channel, and the random access channel.