Ansuman Adhikary

A Primer on 3GPP Narrowband Internet of Things

Narrowband Internet of Things (NB-IoT) is a new cellular technology introduced in 3GPP Release 13 for providing wide-area coverage for IoT. This article provides an overview of the air interface of NB-IoT. We describe how NB-IoT addresses key IoT requirements such as deployment flexibility, low device complexity, long battery lifetime, support of massive numbers of devices in a cell, and significant coverage extension beyond existing cellular technologies. We also share the various design rationales during the standardization of NB-IoT in Release 13 and point out several open areas for future evolution of NB-IoT.

Massive-MIMO Meets HetNet: Interference Coordination Through Spatial Blanking

In this paper, we study the downlink performance of a heterogeneous cellular network (HetNet) where both macro and small cells share the same spectrum and hence interfere with each other. We assume that the users are concentrated at certain areas in the cell, i.e., they form hotspots. While some of the hotspots are assumed to have a small cell in their vicinity, the others are directly served by the macrocell. Due to a relatively small area of each hotspot, the users lying in a particular hotspot appear to be almost co-located to the macrocells, which are typically deployed at some elevation. We assume a large number of antennas at the macrocell relative to the number of users simultaneously served. In this “massive MIMO” regime, the channel vectors become highly directional. We exploit this directionality in the channel vectors to obtain spatial blanking, i.e., concentrating transmission energy only in certain directions while creating transmission opportunities for the small cells lying in the other directions. In addition to this inherent interference suppression, we also develop three low-complexity interference coordination strategies: turn off small cells based on the amount of cross-tier interference they receive or cause to the scheduled macrocell hotspots; schedule hotspots such that treating interference as noise is approximately optimal for the resulting Gaussian interference channel; and offload some of the macrocell hotspots to nearby small cells to improve throughput fairness across all hotspots. For all these schemes, we study the relative merits and demerits of uniform deployment of small cells vs. deploying more small cells towards the cell center or the cell edge.

Random Access Preamble Design and Detection for 3GPP Narrowband IoT Systems

Narrowband Internet of Things (NB-IoT) is an emerging cellular technology that will provide improved coverage for massive number of low-throughput low-cost devices with low device power consumption in delay-tolerant applications. A new single tone signal with frequency hopping has been designed for NB-IoT physical random access channel (NPRACH). In this letter, we describe this new NPRACH design and explain in detail the design rationale. We further propose possible receiver algorithms for NPRACH detection and time-of-arrival estimation. Simulation results on NPRACH performance including detection rate, false alarm rate, and time-of-arrival estimation accuracy are presented to shed light on the overall potential of NB-IoT systems.

Performance Evaluation of NB-IoT Coverage

Narrowband Internet of Things (NB-IoT) is a new radio access technology, recently standardized in 3GPP to enable support for IoT devices. NB-IoT offers a range of flexible deployment options and provides improved coverage and support for a massive number of devices within a cell. In this paper, we provide a detailed evaluation of the coverage performance of NBIoT and show that it achieves a coverage enhancement of up to 20 dB when compared with existing LTE technology.

JSDM and multi-cell networks: Handling inter-cell interference through long-term antenna statistics

Joint Spatial Division and Multiplexing (JSDM) is a novel paradigm for splitting the functions of multiuser MIMO precoding into a concatenation of blocks: a pre-beamforming projection depending only on the channel covariances, and a precoder achieving multiplexing gain over the effective channel including pre-beamforming. In this paper, we extend our study of JSDM to a multi-cell system, where the pre-beamforming projections are jointly selected across cells together with user scheduling, such that inter-cell interference can be handled using only the channel covariances (the so-called “long-term” antenna statistics), which are much easier to collect than the classical instantaneous channel state information.