Improved Physical Downlink Control Channel for 3GPP Massive Machine Type Communications

To provide cellular connectivity to massive machine type communications, 3rd Generation Partnership Project (3GPP) has come up with an enhanced machine type communications (eMTC) standard. The eMTC is a low power wide area network technology. It can cater to the needs of massive MTC devices providing voice support, required data rates, low latency, wide area coverage, and mobility. The eMTC is built on LTE framework and necessary modifications are made as per the requirements of MTC. A chunk of 1.4 MHz from the LTE bandwidth is required to deploy eMTC. Similar to LTE, delivering Downlink Control Information (DCI) to end devices is crucial in eMTC. The DCI carries information about modulation and coding scheme, uplink grant, and scheduling of downlink resources. The DCI of multiple eMTC devices are multiplexed over a region of time and frequency resources. Hence, the eMTC devices have to blindly decode this control channel region. Significant computational power is required from an eMTC device to decode this region. This paper explains the processes involved in the delivery of DCI for eMTC. We propose a novel mapping of repetition and aggregation level to each eMTC device based on the available channel state information. We identify the under utilization of the time and frequency resources in the existing eMTC scheme used for rate matching the DCI information bits. We present system level simulations considering the proposed novel mapping. Further, through extensive simulations and hardware emulations, we show that the proposed rate matching scheme results in significant improvement in performance as compared to the existing scheme.