**1. Introduction**

The proliferation of smartphone devices has enabled the expansion of Location Based Services (LBS) [1]. With the increasing popularity of LBS applications, there is a growing demand for more accurate localization solutions. Wireless MIMO localization is an alternative solution to the widely accepted Global Positioning System (GPS) in environments where GPS falls short. Specifically, GPS faces a challenge in maintaining accuracy and availability with urban canyons and indoor environments

[2]. Wireless MIMO systems already exist in these environments for communication purposes. Therefore, the existing wireless communication infrastructure can also be leveraged to provide localization services without investing in additional equipment. In fact, many LBS applications are enabled by wireless MIMO localization. While compiling a comprehensive list of these applications would be difficult, the following subsections provide an overview of some interesting LBS applications.

### **1.1 Applications**

#### *1.1.1 Emergency services*

The purpose of emergency services is to identify a caller's location and provide this information to the emergency responders. Emergency service is the oldest LBS application. The need to position mobile users was first advocated back in 1996 when the Federal Communication Commission (FCC) announced its mandate to enhance emergency services. During that time, the main motivation was mostly centered around locating emergency calls [3]. Since then, both FCC Enhanced 911 (E911) and 3rd Generation Partnership Project (3GPP) requirements for localization accuracy have become more stringent [4, 5].

#### *1.1.2 Autonomous vehicles and urban air mobility*

Precise positioning systems play a crucial role in autonomous vehicles and Unmanned Aerial Systems (UASs) [6]. The purpose of these positioning systems is to provide accurate estimations of the vehicle's location and orientation relative to the road and other vehicles (whether terrestrial or aerial). Moreover, the localization systems facilitate tracking of other vehicles, pedestrians, and obstacles in the surroundings. This information is utilized to plan safe and efficient routes, and to avoid collisions. The wireless MIMO system can provide primary location estimation or a backup in the event of GPS failure or loss of other proximity sensors [2]. Several studies have explored using MIMO localization for vehicles [7–11] and UASs [12–14].

#### *1.1.3 Field surveying and mapping*

Field surveying and mapping has both civilian and military applications including creating detailed topographical maps, measuring land boundaries, and collecting data on natural resources. For example, in construction surveying, positioning and localization systems are used to ensure that buildings and infrastructures are positioned and aligned correctly. In military applications, these systems can be used for reconnaissance of enemy territory and targeting of enemy or enemy assets. Simultaneous Localization and Mapping (SLAM) is often employed in these types of applications. SLAM is an active area of research and over the past few years, various surveys have been published that summarize the state-of-the-art SLAM solutions [15–17].

#### *1.1.4 Indoor tracking and localization*

Indoor tracking and localization technology have numerous practical applications across various industries. In healthcare, it can be used to track the location of medical

#### *Localization Techniques in Multiple-Input Multiple-Output Communication: Fundamental… DOI: http://dx.doi.org/10.5772/intechopen.112037*

equipment, staff and patients, ensuring efficient use of resources and timely delivery of care [18]. In the retail industry, it can help to optimize store layouts and improve the customer experience by providing personalized recommendations and targeted advertising. In industrial settings, it can improve warehouse logistics and inventory management by providing real-time tracking of goods and equipment [19]. Additionally, indoor tracking and localization can be used to enhance the safety of buildings and occupants by detecting and responding to emergencies, such as fires or security breaches. The technology also has potential applications in the field of smart architectures (smart homes [20], smart buildings [21], smart cities [22], and smart grids [23]) where it can be used to automate and optimize tasks and energy consumption.

#### *1.1.5 Agriculture*

Highly accurate localization systems have a wide range of applications in agriculture, including precision farming, autonomous equipment, livestock tracking, and soil mapping [24–28]. In precision farming, localization systems are used to collect data on soil conditions, crop growth, weather patterns, and other factors, which can then be analyzed to make informed decisions about crop management, including planting, fertilization, irrigation, and harvesting. Moreover, the accurate localization systems are also used to guide autonomous equipment to carry out tasks such as planting, spraying, and harvesting with greater precision and efficiency.

#### *1.1.6 Social networking*

LBS-enabled social networking applications aim to connect people who are located near each other and share similar interests. These applications use location data to recommend nearby events, activities, or groups that users might be interested in, and facilitate connections with others who are nearby. This approach offers benefits for both individuals and businesses. Some popular LBS-enabled social networking applications include Meetup, Foursquare, Yelp, and Facebook Places.

### **2. Wireless MIMO system**

#### **2.1 Sub-6 GHz and mmWave massive MIMO systems**

Fifth-Generation and Beyond (5G&B) mobile networks offer the potential for significantly greater communication capacity and ultra high-speeds that exceed those of previous generations by several orders of magnitude [29]. The large number of antennas in massive MIMO allows for more precise control of the signals, leading to increased capacity, better coverage, improved energy efficiency and reliability [30, 31]. Specifically, massive MIMO antennas enable the generation of narrow and highly directional signal beams. A beam can be steered towards a user to provide a high-quality signal that is less susceptible to interference and fading.

Sub-6 GHz bands are typically between 1 and 6 GHz. This frequency range is commonly used for wireless communication technologies such as cellular networks (3G, 4G, and 5G), Wi-Fi, Bluetooth, and other wireless communication standards. Sub-6 GHz systems are typically implemented using small-scale MIMO antennas. Regarding the sub-6 GHz channel, several measurement campaigns have been carried out to characterize it [32–34]. The propagation that depends on path-loss and shadowing results in large-scale fading, and multi-path propagation, results in small-scale fading [35].

The massive increase in data traffic has made the sub-6 GHz spectrum congested. This results in limited bandwidth for users, causing slower and unreliable connections [36]. One solution to this problem is to move to a different frequency band such as milimeter-Wave (mmWave) frequency channels. The channels are called mmWave because their wavelength ranges between 1 mm and 10 mm, which is equivalent to a frequency range between 30 GHz and 300 GHz. The mmWave channels can provide significantly more bandwidth compared to sub-6 GHz, which will be required for next generation wireless communication systems. Therefore, mmWave frequency has been identified as a key technology-enabler in 5G&B [30, 35, 36]. However, there are some disadvantages in mmWave communication such as severe signal attenuation and blockage. The signals cannot penetrate obstacles and tend to get absorbed by rain [37, 38].

In an experimental study, a comprehensive channel measurement campaign was conducted in Europe in 2014–2016 in numerous indoor and outdoor scenarios. The study showed that geometry of the main propagation paths at sub-6 GHz and mmWave bands are almost similar [39]. However, the blockage at mmWave band causes higher losses, rendering the path completely blocked. This experimental outcome has motivated several recent studies to use sub-6 GHz channel information for mmWave applications [40–42].
