Fifth generation (5G) wireless systems

Recent decades have experienced an unparalleled evolution of analog and digital technologies that are categorized as information and communication technologies (ICT), as well as radar, industrial, consumer, and medical applications. They have become universal, and are available worldwide [14], but are causing energy consumption levels to reach worrying rates. The next big advance in wireless communications will be 5G technology, which will deploy large numbers of low-powered smartphones, notebooks, tablets, access networks, and other transmitters [15].

This technology will provide the public with an infinite capability communication network in terms of speed, volume of data, and number of devices; however, it will lead to further emissions, with many of those devices intended to be used close to the body.

Millimeter wave (MMW) communications

MMWs refer to EM fields ranging from 30 to 300 GHz in terms of frequency, from 1 to 10 mm in terms of wavelength in free space, and from about 10'⁴ to 1СИ eV in terms of photon energy. They constitute the extremely high frequency portion of the RF band. They are considered nonionizing radiation because the photon energy is not nearly sufficient to remove an electron from an atom or a molecule. They remain several orders of magnitude below the level required to ionize biological molecules (typically 12 eV is required). Therefore, at MMW frequencies, the photon energy is more than four orders of magnitude weaker than ionizing radiation and is thus not capable of displacing electrons, which disrupts molecular bonds; this disruption is linked to health implications including cancer [16]. However, MMWs can induce rotation of some free molecules with a dipole moment. The applications of MMWs may be broadly classified as shown in Figure 1.17, in which MMWs are used in applications beyond ICT.

Compared to other wireless technologies already available at lower RF frequencies, MMWs offer several advantages, including faster data rates (over 2 Gbit/s), compact size of radiating structures and electronic components, and lower interference between devices [17]. MMW plays a big role in 5G RAN system due to higher bandwidth. It is expected (although not fully demonstrated) that devices

employing MMW will work with low power and, due to the small penetration depth of the radiation, the exposure should involve only superficial tissues. However, mainly due to the low power, this technology requires a high density of small cells and a proliferation of devices is expected. This combination of factors will increase chance of human exposure to RFR.

5G will use higher MMW frequencies never before used for communications. In terms of spectrum, 5G systems will operate over a very wide frequency range from below 1 GHz up to and including MMW frequencies (Figure 1.18). The 5G deployment proposes to add frequencies in the low- (0.6 GHz-3.7 GHz), mid- (3.7 GHz-24 GHz), and high-band frequencies (24 GHz and higher) for faster communications. As these higher frequencies do not travel far and are blocked by buildings, 5G will have to use a dense network of fixed antennae outdoors as well as indoor systems. Among future candidates for 5G networks are the 24.25 to 27.5 GHz, 27.5 to 29.5 GHz, 37 to 39 GHz, and 57 to 71 GHz ranges. While operating at MMW frequencies has its advantages, a significant disadvantage is system path loss.

MMWs have been in use for various applications such as passive imaging for surveillance, active anti-collision automotive radars, security body scanners, radio astronomy, military radars, and non-lethal weapons. Moreover, MMWs have been used for therapy in some Eastern European countries. MMWs alone, or in combination with other treatments, may give promising clinical results in the cure of various diseases, including ulcers, pain relief, cardiovascular diseases, wound healing, bronchial asthma, skin disorders, and cancers [18].

Using frequencies much higher in the frequency spectrum opens up more spectra and also provides the opportunity of having much wider channel bandwidth, possibly 1-2 GHz. For 5G, frequencies of above 50 GHz are being considered and this will present some real challenges in terms of the electronic design and signal propagation, as these frequencies do not travel as far and are absorbed almost completely by obstacles.

State of knowledge

Today, wireless mobile systems using different technologies, frequency bands, and output power receive the most attention as potential sources of RF energy. In the past years, analog technology produced the highest average power levels compared to digital technology. The reason is because no power control was available and analog phones were always operating at maximum power. Today, much of the attention goes to 5G, which is currently under early adoption with expected full implementation between 2020 and 2030. The predecessors of 5G are the first generation analog cellular networks designed for voice communications (1980); Global System for Mobile communication (GSM) through the use of digital modulations and time division multiple access (TDMA) or code division multiple access (CDMA) (1992); Universal Mobile Telecommunications System (UMTS) with extensive data usage and high efficiency through the utilization of high-speed internet access, and highly improved video and audio streaming capabilities by employing technologies such as wideband CDMA (W-CDMA) and high-speed packet access (HSPA) (2001); and longterm evolution (LTE) to offer a fully capable mobile broadband platform (2011) [19]. The above technologies are also referred to as first generation (1G), second generation (2G), third generation (3G), and fourth generation (4G) technologies, respectively. The above progress is made achievable by the use of additional higher frequency bands.

5G will be similar to 4G systems that are already in use. The evolution toward 5G will happen in two concurrent phases: first, the improvement of current cellular networks (modulation and coding schemes) and second, the integration of advanced cellular networks with emerging wireless communication systems based on new standards. In the first stage of 5G implementation (for example, during the next few years), 5G networks will operate in parallel with current mobile systems, with an unavoidable global increase in the exposure level. It has been designed to carry a massive amount of data and provide ubiquitous connectivity for applications as diverse as the IoT, automated cars, smart cities, virtual reality, drones, and huge video streaming (Figure 1.19). A differentiating characteristic of 5G is a much denser network with more cellular towers and the employment of smart antennas which can transmit numerous beams (up to 64 with present designs, or even more) that can be independently steered to individual subscribers.

The future 5G network is envisioned to be soft, green, and fast. It will operate within several frequency bands of which the lower frequencies are being intended for the first phase of the 5G networks. Additionally, much higher frequencies are also intended to be employed at later stages of 5G evolution. The total amount of power transmitted from a 5G cell site may exceed that from a 4G site of an otherwise similar size (microcell or

Figure 1.19 Wireless communication roadmap.

small cell). Based on the above, a change in the exposure to EM fields of humans and the environment is anticipated.

Soft and green network

The 5G network is anticipated to be soft, with reconfigurable software- defined networking and air interface. A soft network is intended to generate agility into employment of each network component from core network to access network, as well as the building blocks of the air interface. A green network is a social obligation to reduce energy consumption and increase capacity with the minimum burden of spectrum resources, as well as being an economic goal for wireless industry [20]. To achieve the goals of 5G, a new and efficient radio access network (RAN) as well as a core network are required to provide the anticipated performance (Figure 1.20).

Radio Access Network (RAN)

Traditional RAN has been the air interface in application since the beginning of cellular technology and has evolved through the generations (1G through 5G). Small low-powered cells such as RAN nodes having a range of few meters to few hundred meters in diameter will play an essential role in major applications of 5G. Small cells compromise three types namely femto (~0.1 km), pico (~1 km), and microcells (~2 km). However, a macrocell is used in the cellular network to offer radio coverage to a wide area of mobile network access (~2 km). By using small cells, the network can increase area spectrum efficiency by reusing a

Figure 1.20 9 5G radio access and core networks.

higher frequency [21]. Elements of the RAN comprise a base station that connects to sector antennas which cover a small region depending on their capacity and can handle the communication within this small sector only.

• 5G RAN is the upcoming air interface supporting the next generation of mobile communication to enable wireless connectivity everywhere, at any time, to anyone and anything, with low latency and a much faster, efficient, and scalable network which can support billions of devices and emerging technologies like the IoT. It can be plugged into a 4G core and co-exist with 4G radios as part of a network to speed deployments. Moreover, the unlicensed spectrum has unlimited opportunities due to higher bandwidth even up to 500 MHz.
• 5G RAN utilizes modulation, waveforms, and access technologies that will enable the system to meet the needs of high data rate services that requires low' latency, small data rates, and long battery lifetimes amongst others. The advantage of using higher frequency bands is that they are much wider and they will be able to allow' much higher signal band- widths and hence support much higher data throughput rates. However, the disadvantage is that they w'ill have a much shorter range, but this is also an advantage because it will allow' much greater frequency re-use.

G core network

Although initial deployments of 5G w'ill utilize the core netw'ork of LTE, or possibly even 3G, networks, the ultimate aim is to have a new' netw'ork that is able to handle the much higher data volumes whilst also being able to provide a much lower level of latency. The core networks of 5G will move from copper and fiber to MWW connections, allowing rapid deployment and mesh-like connectivity with cooperation between base stations.

As a result, the 5G network will need to accommodate a huge diversity in types of traffic and it will need to be able to accommodate each one with great efficiency and effectiveness. Often it is thought that a "one type suits all" approach does not give the best performance in any application, but this is what is needed for the 5G network.

Beamforming

5G will be characterized by a set of large antennas, MIMO arrays, and beamforming techniques to concentrate the radiated power into small portions of territory. Arrays of up to hundreds of small antennas at the base station will enable focusing the RF transmission to various devices. Antennas and devices operating at MMW frequencies have a reduced size compared to their counterparts in the lower part of the RF spectrum, a fact that largely reduces the propagation range. To overcome this problem, beamforming antennas help offset the effect of reduced propagation of very high frequency carriers and enable the beam from the cellular base station to be directed towards the receiving mobile device. Such antennas will have narrow antenna beams with direct alignment to the receiving device (Figure 1.21). This characteristic allows controlling the directionality of the radiated power in space. Therefore, it is possible to concentrate the power into the locations where the 5G service is requested. This gives communication operators the choice of sending information to multiple devices simultaneously or directing multiple beams at one device to enhance download speed.

By using MIMO technology, downlink speeds of up to 1 Gbps may be achieved. Although this technology is being used in many applications from LTE to Wi-Fi, the number of antennas is fairly limited. Using MMW frequencies opens up the possibility of using many tens of antennas on a single piece equipment; it becomes a real possibility because of the antenna sizes and spacing in terms of a wavelength. In this way, the optimum signal can be transmitted to the mobile device and received from it, whilst also cutting interference to other mobiles. This could possibly reduce EM environmental exposure compared to the current exposure situation. However, it is also disputed that the accumulation of a very high number of 5G network elements will increase the total EM exposure in the environment.

Satellite and non-terrestrial networks

5G will be a network of networks, a set-up with numerous technologies sustaining a global infrastructure of satellite, small cells, Wi-Fi, typical mobile wireless networks, and enormous machine-type communications, among many others. The development of 5G networks provides a distinctive opportunity for a seamless combination of satellite with terrestrial networks, where MMWs are ideal because of their significant bandwidth. Due to their fundamentally large footprint, reliability, and cost effectiveness, satellites can offer complementary connectivity options and a smooth user experience. They can provide significant benefits when integrated in the overall 5G system, owing to its key advantages including worldwide coverage and multicasting and broadcasting potential. They will supplement as well as compete with other technologies in meeting the needs of users globally. The satellite solutions of trunking, back-haul, mobility, and hybrid multiplay will be employed to complement other high-bandwidth connectivity links.

In addition to the current fleet of geostationary earth orbit (GEO) satellites, the next generation of medium earth orbit (MEO) and low earth orbit (LEO) satellite systems will be highly flexible and up to ten times more powerful than the current constellations. GEO is about 35,800 km above the equator, MEO is between 5,000-12,000 km above the earth, and LEO is between 500-1,500 km above the earth, so the delay is very small and the losses are small. A single GEO satellite can provide communications downlinks over wide areas, such as whole countries or continents, including to areas with no terrestrial connections. Constellations of MEO and LEO satellites can deliver high-capacity services to localized areas with low latency. Several companies (for example, SpaceX, OnWeb, Boing, Spir Global, Telesat) are proposing to provide 5G from space utilizing a combined 20,000 satellites in MEO and LEO that will blanket the earth with powerful, focused, and steerable beams.

Internet of Things

5G and Wi-Fi 6 are expected as a major driver for the growth of IoT, industrial IoT (IIoT), and Industry 4.0. These new technologies are expected to transform IoT, and wireless communications in general, with high speeds, low power requirements, and superior bandwidth.

IoT is a vision of connecting everything possible to the Internet including machines, appliances, devices, animals and insects, and even human brains. In addition, the IoT will include artificial intelligence (AI), virtual reality, robots, microchipped humans, and augmented humans (humans with a type of technology implanted into their biology to improve human characters or competences). When connecting digital and physical by leveraging IoT and cyber-physical systems and when striving towards ever more automation and autonomous decisions in environments such as the smart factory, smart hospital, autonomous vehicles, smart buildings, smart, to name a few more, we do need quite some resources to deal with the resulting flood of data that needs to be analyzed and gathered to begin with as well as flood of EM signals resulting from the broad range of sensors and wearables, along with other devices.

Such devices will make it easier for organizations to constantly collect, report, and transmit information to monitoring centers. However every IoT elements, including sensors, robots, surveillance cameras, devices, and other machines, will increase people exposure to EM fields, the fact that might impact humans and wildlife.

The questions of electromagnetic constraint

The number of connected devices is expected to cross the 50 billion benchmark in the next decade, all of them being connected to the cloud, for anywhere and anytime access to data [22]. Planning a universal deployment of 5G networks to accommodate the above devices under stringent EM exposure limits without compromising the quality of service (QoS) in the networks is not an easy task, especially in densely populated urban areas where multiple 5G RAN infrastructures of different operators have to coexist, jointly adding EM fields to the exposure already produced by pre-5G technologies. Service provisioning to the expected enormous number of users causes a surge in the energy consumption of the RAN as well the corresponding emission. Clearly, the amount of power consumed by the next generation networks must be scaled to enhance energy efficiency as well as for a greener EM environment. Network modernization and the efficient design of RAN through the implementation of antenna muting and power allocation techniques are essential in determination of its impact on the environment.

Despite its importance for the success of 5G, the challenge of 5G network planning under EM exposure limits is still completely open. As a result, the planning has to integrate suitable exposure limits by considering the most recent regulating guidelines. All the above gives rise to several key questions, such as: how do current EM exposure limits affect the 5G deployment? What is the EM impact of already installed pre-5G sites on the deployment of future 5G sites? How do different regulations on EM emissions influence 5G planning [23]?

The combination of many new cellular and satellite networks being installed in ground and space appear to be main factors in regard to public concerns about 5G technology. Here, the uncertainty begins. What do we know so far about the effects on biological systems, on health and environment, due to exposure to the higher frequency bands (6-100 GHz)? The lower frequencies have been considerably investigated due to their use already in current wireless communication networks. Now other key questions arise: do supposed nonthermal effects (effects that occur below the thermal effect threshold) occur that may lead to health effects? Is there relevant health-oriented research investigation using the 5G technology related frequencies? Is there relevant research that can make a significant contribution to improving the risk assessment of EM exposure to the public?

Answers to all above questions are needed for the quick and safe employment of the 5G technology. One of the major goals of this book is to shed light on the above questions by outlining the research challenges and opportunities that they generate.

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