Hosein Nikopour

Massive machine-type communications in 5g: physical and MAC-layer solutions

MTC are expected to play an essential role within future 5G systems. In the FP7 project METIS, MTC has been further classified into mMTC and uMTC. While mMTC is about wireless connectivity to tens of billions of machinetype terminals, uMTC is about availability, low latency, and high reliability. The main challenge in mMTC is scalable and efficient connectivity for a massive number of devices sending very short packets, which is not done adequately in cellular systems designed for human-type communications. Furthermore, mMTC solutions need to enable wide area coverage and deep indoor penetration while having low cost and being energy-efficient. In this article, we introduce the PHY and MAC layer solutions developed within METIS to address this challenge.

FDD massive MIMO with analog csi feedback

Massive multiple-input multiple-output (MIMO) is a breakthrough in cellular networking, through using a large number of antennas to serve simultaneously many users. Most prior work on massive MIMO assumes time-division duplex (TDD) operation to take advantage of channel reciprocity. Typical cellular systems, however, make use of spectrum dedicated for frequency-division duplex (FDD) operation. In this paper, we consider an FDD massive MIMO network where the base stations obtain downlink channel estimates via analog feedback from the users. Assuming an uncorrelated channel model, we derive closed-form expressions of the downlink achievable signal-to-interference-plus-noise ratio (SINR) and the corresponding rates. These expressions provide a means for studying rate with and without feedback overhead penalties. A surprising result is that depending on system parameters like the Doppler shift, it is desirable to shut off a subset of antennas at the base stations to maximize achievable downlink sum-rates.