Distributed Massive MIMO in Cellular Networks

Abstract

Introduction Wireless communications, together with its underlying applications, is among today's most active areas of technology development, with the demand for data rates expected to grow to unprecedented levels by 2020. Cisco's latest report predicts a monthly mobile traffic of 24.3 exabytes (2 60 bytes) in 2019, which represents a 57% compound annual growth rate compared with 2014 [1]. The catalyst for this seminal development is 5G, the fifth generation of wireless systems, which denotes the next major phase of mobile telecommunications standards beyond the current fourth generation (4G) International Mobile Telecommunications-Advanced (IMT-Advanced) standards and promises speeds far beyond what the current 4G can offer. This represents a radically new paradigm in the field of wireless communications and promises to substantially improve the area spectral efficiency (measured in bit/s/Hz/km2) and energy efficiency (EE) (measured in bit/J). According to [2], there are three symbiotic technologies that can support the required “data-rate boom”: 1. extreme densification and offloading to serve more active nodes per unit area and Hz, also known as massive multiple-input multiple-output (MIMO); 2. increased bandwidth, primarily by moving toward and into the millimeter wave spectrum (from 30 to 300 GHz); 3. increased spectral efficiency, primarily through advances in MIMO, to support more bits/s/Hz per node. In this chapter, we will elaborate exclusively on item 1 above, namely massive MIMO, which represents a disruptive technological paradigm and is considered by many experts as the “next big thing in wireless” [3, 4]. We will first delineate the basic principles behind the operation of massive MIMO and then review some of its applications. Finally, we will conclude this chapter by presenting some directions for future work along with open challenges in the general field of massive MIMO. Table 8.1 lists the nomenclature used in this chapter. Massive MIMO: Basic Principles The massive MIMO technology originates from the seminal paper of Marzetta [5], and since then has been at the forefront of wireless communications research, with numerous papers reported in the literature along with huge industrial investments. Generally speaking, in a massive MIMO topology, a number K of user terminals (UTs) communicate simultaneously with a base station (BS) over the same time–frequency resources.