Removing the PDCCH Bottleneck and Enhancing the Capacity of 4G Massive MIMO Systems

Abstract

The Full Dimension-MIMO (FD-MIMO) technology is capable of achieving huge improvements in network throughput with simultaneous connectivity of a large number of mobile wireless devices, unmanned aerial vehicles, and the Internet of Things (IoI). With large antennae at the base station, an enhanced multi-user transmission is performed to increase the capacity of physical downlink shared channel (PDSCH). However, the current 3 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sup> Generation Partnership Project (3GPP) specifications of Long Term Evolution (LTE) do not allow the base station to perform any beamforming techniques for the physical downlink control channel (PDCCH). The PDCCH capacity dictates the number of users scheduled in a subframe, and thus, the PDCCH limits the cell capacity. Motivated by this, we propose a novel beamformed PDCCH (BF-PDCCH) design for LTE which strictly adheres to the 3GPP specifications. With just software-based changes at the base station, the proposed design significantly enhances the PDCCH capacity. The proposed design uses the sounding reference signals (SRS) transmitted in the uplink to decide the best beam for a user, and then ingeniously schedules the users in PDCCH. Since the performance of the proposed BF-PDCCH heavily relies on this SRS reception, we model the SRS channel estimation errors while evaluating the performance of the proposed BF-PDCCH. Through system-level simulations, we show that the proposed design achieves significant network throughput, and outperforms the current state of art algorithms and also the existing 3GPP schemes.