**3. The massive MIMO systems**

Massive MIMO is a rising technology that considerably enhances the basic MIMO features. The term massive MIMO is referred to the whole of systems that use antenna arrays with at least few hundred antennas, simultaneously serving multiple terminals in the same time frequency resource.

**Figure 3** illustrates the basic operation principle of a massive MIMO; few users are served from a macrodevice (for example a rectangular array) having a large number of base stations (antennas). Generally, massive MIMO is an instrument that allows to enable the development of future broadband (fixed and mobile) networks which will satisfy special requirements in terms of energy-efficiency, security,

**91**

**3.1 Planar massive MIMO**

*Smart Antenna Systems Model Simulation Design for 5G Wireless Network Systems*

and robustness. Structurally, a massive MIMO system consists of a group of small (relatively) antennas, supplied from an optical or electric digital bus that operates simultaneously related to a certain task. Massive MIMO, as well as the SAS systems are able to well exploit the spatial division multiple access (SDMA) allowing for an efficient resource channel utilization, both on the uplink and the downlink [18, 19]. In conventional MIMO systems, like the long-term evolution (LTE), the base station transmits waveforms depending on terminals channel response estimation, and then these responses are quantized by some processing units and sent out back to the base station. Fundamentally, this is not possible in massive MIMO systems, especially concerning high-mobility environments [20], because optimal downlink pilots should be mutually orthogonal between the antennas. Therefore, in spite of the difficult hardware and designing implementation, these systems are becoming increasingly prevalent in the modern applications due to the great benefits that could introduce; in particular, massive MIMO can increase the wireless channel capacity up to 10 times and the radiated energy-efficiency up to 100 times with respect to the traditional LTE systems. This translates into higher gains and higher performance. However, the employment of these systems entails a series of issues that should be properly considered, for example, the interferences between terminals increase as the data rate increases. Other issue is the fact that terminals consume a lot of energy during the communication process in spite of the well SDMA exploitation. Finally, the difficulty of designing a system of limited size improves proportionally with the increasing of the number of antennas in the system. For this reason, it is necessary to find a trade-off between the number of elements and the requirements. Although there exist several kinds of massive MIMO systems depending on the geometry pattern, in this chapter, only the planar massive MIMO technology is exposed. We use the term planar to indicate that the array can scan the beam along the elevation plane *θ* and the azimuth plane *ϕ* as opposed to the linear arrays that scan the main beam only along *θ* or *ϕ* [21]. Planar arrays offer more gain and lower sidelobes than linear arrays at the expense of using more elements [22].

From an architectural point of view, a massive MIMO is structured depending on the geometry pattern that is able to form. There exist several design configurations that usually are function of the kind of application to which these systems are destined. Anyway, in this chapter, we consider three different types of planar antenna arrays: the uniform rectangular planar array (URPA), the hexagonal planar array (HPA), and the circular planar array (CPA). Substantially, the term uniform means that the weight parameters *w*1,*w*2,.…,*wM* are all unity, thus it cannot be readjusted as mentioned earlier in Section 2, **Figure 2**. The following subsections

synthesize the main feature of the mentioned configurations.

*DOI: http://dx.doi.org/10.5772/intechopen.79933*

**Figure 3.**

*Massive MIMO operation principle.*

*Smart Antenna Systems Model Simulation Design for 5G Wireless Network Systems DOI: http://dx.doi.org/10.5772/intechopen.79933*

**Figure 3.** *Massive MIMO operation principle.*

*Array Pattern Optimization*

**Figure 2.**

*SAS basic operation principle.*

Switched beam antenna systems form multiple fixed beams with high sensitivity in particular directions. These antenna systems detect signal strength, choose from one of several predetermined, fixed beams, and switch from one beam to another as the mobile moves throughout an area. So, they produce a static fixed beam that could be electronically controlled. Adaptive antenna technology, instead, uses adaptive algorithm because of its ability to effectively locate and track various types of signals to dynamically minimize interference and maximize the intended signal reception. In this case, produced beam is variable and adapts itself depending on transmission channel conditions and a weight array that dynamically varies in time. In this context, the spatial structure is used to estimate the direction of arrive (DOA) or angle of arrive (AOA) by nodes. However, both systems attempt to increase gain according to the location of the user. The basic SAS operation prin-

In **Figure 2**, inputs *<sup>x</sup>*1(*t*),.…,*xM*(*t*) are multiplied by elements of a weight vector *<sup>W</sup>*¯ <sup>=</sup> [*w*1,*w*2,.…*wM*] that varies according to an adaptive algorithm (used only in the adaptive array version); *y*(*t*) is the output, while *e*(*t*) denotes the error; all terms are defined in functions of the discrete time *t*. Instead, when a switched beam approach is employed, because any adaptive algorithm is executed, the weight array can be considered missing or simply as a constant. Based on the kind of produced geometry pattern, SAS can be categorized into different ways. The most common categories include, rectangular, hexagonal, and the circular arrays. However, in 5G technology, the antenna arrays should be adaptive, and it is required that they have an adaptive capability to point the main beam toward the desired direction and steer the nulls toward the undesired interfering directions. In all cases, this adaptive mechanism should be optimized to get best performance or maximum signal to

Massive MIMO is a rising technology that considerably enhances the basic MIMO features. The term massive MIMO is referred to the whole of systems that use antenna arrays with at least few hundred antennas, simultaneously serving

**Figure 3** illustrates the basic operation principle of a massive MIMO; few users are served from a macrodevice (for example a rectangular array) having a large number of base stations (antennas). Generally, massive MIMO is an instrument that allows to enable the development of future broadband (fixed and mobile) networks which will satisfy special requirements in terms of energy-efficiency, security,

interference plus noise ratio (SINR) at the system's output [15–17].

multiple terminals in the same time frequency resource.

ciple can be summarized by the following figure.

**3. The massive MIMO systems**

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and robustness. Structurally, a massive MIMO system consists of a group of small (relatively) antennas, supplied from an optical or electric digital bus that operates simultaneously related to a certain task. Massive MIMO, as well as the SAS systems are able to well exploit the spatial division multiple access (SDMA) allowing for an efficient resource channel utilization, both on the uplink and the downlink [18, 19]. In conventional MIMO systems, like the long-term evolution (LTE), the base station transmits waveforms depending on terminals channel response estimation, and then these responses are quantized by some processing units and sent out back to the base station. Fundamentally, this is not possible in massive MIMO systems, especially concerning high-mobility environments [20], because optimal downlink pilots should be mutually orthogonal between the antennas. Therefore, in spite of the difficult hardware and designing implementation, these systems are becoming increasingly prevalent in the modern applications due to the great benefits that could introduce; in particular, massive MIMO can increase the wireless channel capacity up to 10 times and the radiated energy-efficiency up to 100 times with respect to the traditional LTE systems. This translates into higher gains and higher performance. However, the employment of these systems entails a series of issues that should be properly considered, for example, the interferences between terminals increase as the data rate increases. Other issue is the fact that terminals consume a lot of energy during the communication process in spite of the well SDMA exploitation. Finally, the difficulty of designing a system of limited size improves proportionally with the increasing of the number of antennas in the system. For this reason, it is necessary to find a trade-off between the number of elements and the requirements. Although there exist several kinds of massive MIMO systems depending on the geometry pattern, in this chapter, only the planar massive MIMO technology is exposed. We use the term planar to indicate that the array can scan the beam along the elevation plane *θ* and the azimuth plane *ϕ* as opposed to the linear arrays that scan the main beam only along *θ* or *ϕ* [21]. Planar arrays offer more gain and lower sidelobes than linear arrays at the expense of using more elements [22].
