MASSIVE MIMO, MM WAVE AND

5G TECHNOLOGY INSIGHTS AND

CHALLENGES

Sara Bhatti

Sir Syed University of Engineering & Technology. Karachi (Pakistan)

E–mail: sarab@ssuet.edu.pk

Recepción: 05/03/2019 Aceptación: 05/04/2019 Publicación: 17/05/2019

Citación sugerida:

Bhatti, S. (2019). Massive MIMO, MM wave and 5G Technology insights and challenges.

3C Tecnología. Glosas de innovación aplicadas a la pyme. Edición Especial, Mayo 2019, pp. 498–

517. doi: http://dx.doi.org/10.17993/3ctecno.2019.specialissue2.498–517

Suggested citation:

Bhatti, S. (2019). Massive MIMO, MM wave and 5G Technology insights and challenges.

3C Tecnología. Glosas de innovación aplicadas a la pyme. Special Issue, May 2019, pp. 498–517.

doi: http://dx.doi.org/10.17993/3ctecno.2019.specialissue2.498–517

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ABSTRACT

The global broadband cellular demand is increasing exponentially resulting in a

worldwide shortage of available bandwidths allocated for wireless transmission,

leading to in–depth research being carried out in the underutilized Millimeter

Wave (mmWave) bands which occupy the frequencies above 3GHz in the

frequency spectrum. The 5G technology is evolving rapidly from the current

3G and 4G networks deployed worldwide, and the mmWave technology plays

a vital role in the future 5G networks. Massive MIMO will be unprecedented

during the design considerations when utilizing mmWave data streams with not

only less complexity but will also enhance the spectral eciency of the wireless

system economically. This paper looks at the 5G revolution, its advantage over

4G, the incorporation between 5G and mmWave technologies, and MIMO

antenna design considerations. It will also highlight the challenges facing the

above technologies, and some new technologies such as Ultra Dense Networks

(UDN), smart cities and Li–Fi which will incorporate mmWave, MIMO and 5G

technology.

KEYWORDS

3GHz, Millimeter Wave, 3G, 4G, 5G, MIMO, UDN, Smart cities, Li–Fi.

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1. INTRODUCTION

The expeditious increase in the worldwide demand for high speed, secure,

bi–directional and fully networked wireless communications has led forward

vast research towards alternate frequencies in the spectrums. The limited

bandwidth resources which are currently available are being exhausted due to

the high Compound Annual Growth Rate (CAGR) of wireless trac, and this

has prompted research into the previously untapped high–frequency bands of

3GHz to 300GHz in the frequency spectrum as shown in Sharma (2013), also

known as Millimeter Wave (mmWave) spectrum. This spectrum shares similar

propagation characteristics and can be incorporated relatively easily with the

wireless technologies currently deployed worldwide (Pi & Khan, 2012).

1.1. MMWAVE FREQUENCY ALLOCATION

Figure 1. The frequency range of the mmWave (Pi & Khan, 2012).

The mmWave range within the frequency spectrum is between 3GHz to 300GHz,

as illustrated in Figure 1. It is shown that the 57–64GHz band is limited to oxygen

absorption and the 164–200GHz band is not suitable for propagation due to

severe water vapor attenuation, with maximum losses at 180GHz. Therefore,

only around 252GHz of the spectrum is available for mobile broadband

communication (Federal Communications Commission, 1997). If it is assumed

that only 40% of the mmWave spectrum is available for mobile broadband

communication, it still provides more than 100 GHz of unused frequencies, which

are about 200 times more than the current 4GHz frequency bands deployed

worldwide (Pi & Khan, 2012).

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1.2. (5G) DEPLOYMENT WORLDWIDE

Table 1. Frequency Allocations for Cellular Usage within different generations.

800MHz

D AMPS 800MHz–1.9GHz

GSM 800MHz–1.9GHz

AS95 A/B 800MHz–1.9GHz

UMTS 2GHz

WCDMA 2GHz

CDMA2000 2GHz

LTE 1.8–2.5GHz

LTE 600 MHz–6 GHz

mmWave 24–86 GHz

As seen in Table 1, the current mobile networks which utilize their allotted radio

frequencies to provide cellular services don’t exceed 780MHz, and each provider

has about 200MHz of spectrum available to them (Rappaport, et al., 2013). This

bandwidth is proving to be insucient for the explosive trac volumes, even for

the most advanced 4G technologies.

To meet these unprecedented magnitudes in demands, 5G networks, which are

still under research, are proving to be a promising solution and are expected to

hit initial phases of commercialization by 2020, with global adoption by 2025

(Sharma, 2013). To reach the 5G design target, there are three paramount

approaches: Ultra–dense Networks (UDN), large spectrum eciency and

increase bandwidth allocation. This is harnessed by mmWave incorporated with

a large number of antennae, also referred to as mmWave massive Multiple Input

Multiple Output (MIMO) antennae, to provide a wireless network with high

speeds and smaller cell sizes to support not only the cellular demands, but also

backhaul and Wi–Fi services (Rappaport, et al., 2013).

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2. 5G EVOLUTION

Each new cellular generation, when compared to the previous generation, is an

enhancement the system electronics, security, speed, frequency, data capacity and

latency. This journey began with 1G, followed by 2G, 3G, the currently deployed

4G and the newly emerging 5G technologies. A new generation has appeared

every ten years since 1981 and has followed its own evolutionary path towards

achieving higher speeds and better performance, as the global market of mobile

and wireless communication has increased exponentially.

The rst generation (1G) used the analog transmission to fulll basic mobile

voice transmission. The 2G systems used digitally enhanced multiple access

technologies such as TDMA (Time Division Multiple Access) and CDMA (Code

Division Multiple Access) leading towards early data services and enhanced

spectral eciency, under the Enhanced Data for Global Evolution (EDGE)

standard. However, the standards were found to dier globally, and a network

was developed where the design standards would not dier and be independent

of the technology platform. And hence 3G was implemented (Sharma, 2013;

Swindlehurst, Ayanoglu, Heydari & Capolino, 2014).

In 3G, technologies such as Wideband Code Division Multiple Access

(W–CDMA) and High–Speed Packet Access (HSPA) resulted in enhanced

improvements within video and audio streaming capabilities (Rappaport, et al.,

2013) by supporting information transfer rate of at least 2Mbps.

3G was a family of standards working together to meet the IMT–2000 technical

standards (Bangerter, Talwar, Are, & Stewart, 2014). Universal Terrestrial

Mobile System (UMTS) was adopted in Europe, while the American 3G

technology is named as cdma2000 (Hossain, 2013) and both were developed by

the Third Generation Partnership Project (3GPP).

3GPP also developed the Long–Term Evolution (LTE) to oer a complete 4G capable

mobile broadband and an upgrade to the existing 3G network. LTE uses Orthogonal

Frequency–Division Multiplexing (OFDM) to support a transmission bandwidth

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of 20 MHz, while also supporting MIMO antenna arrays. These combined with

dynamic channel allocation and channel–dependent scheduling allows for the

utilization of propagation via multiple paths, in order to improve signal performance,

spectral eciency and diversity (Bangerter, Talwar, Are & Stewart, 2014).

The predicted increase in mobile broadband demands is up to a thousand fold

by the year 2020, which has led to the motivation behind research in alternate

spectrums beyond the 4G standard.

5G is the latest generation to be developing in the wireless revolution. It promises

speeds of up to 10 Gbps, 100 times faster than 4G. It has low latency of 1 ms

or less, and mobility with larger coverage areas. The higher data rates will

allow services beyond cell phones, and base stations will provide the necessary

bandwidth for oce and home usage, which was not possible in previous

generations (Rappaport, et al., 2013).

3. 5G AND MMWAVE INCORPORATION

Currently, the 700 MHz to 2.6 GHz radio spectrum is highly saturated for all

wireless applications, and the 5G mmWave technological advances will support

the imminent congestion by providing at least 100GHz of bandwidth which

is substantially greater and would allow 4G service providers to expand their

channel bandwidths signicantly.

The incorporation of 5G with the mmWave spectrum will also allow antennae

with highly directional beam–forming at the base stations and mobile phones,

lower infrastructure costs due to smaller base stations, longer battery life and

provisions of uniform, uninterrupted and consistent connectivity.

This will be achieved with the usage of steerable antenna arrays as the mmWave

spectrum will simultaneously support mobile communications as well as backhaul,

and possibly allow for the convergence of both cellular and Wi–Fi services

(Swindlehurst, et al., 2014). The smaller wavelengths allow for physically smaller

antenna arrays, which is discussed in detail in the following section.

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Recent developments into CMOS technology operating within the mmWave

spectrum, as well as antennas that are steerable both at the base station as well as

the mobile phone has further enhanced the operation of 5G within this spectrum

(Gutierrez, Agarwall, Parrish & Rappaport, 2009). The smaller component

sizes, about 40nm, allows them to be applicable in numerous areas such as radar

transceiver and in chipsets employed in automotive and industrial applications.

The higher frequencies and bandwidth allocations in the mmWave spectrum

allow for a signicant increase in data transfers. This, in turn, reduces latency,

which is invaluable for digital internet–based applications and access requiring

minimal latency.

The mmWave spectral band results in smaller cell sizes as RF path loss increases

with frequency. This increase can be overcome by the large beamforming gains

obtained through massive antenna arrays, and simultaneously increase the

coverage areas (Swindlehurst, et al., 2014). Operating in smaller cells reduce the

channel coherence time and allow higher channel coherence bandwidth and

lower mobility. All these factors, as well as the smaller wavelengths and higher

frequencies, resulting in a reduction in the antenna sizes and electronics, which

are appealing for massive MIMO transceiver design (Swindlehurst, et al., 2014).

As compared to the 4G networks in populous areas, mmWaves oer such a high

jump in bandwidth that links between station–to–device, as well as backhaul,

can be established wirelessly and would be capable to handle the larger trac.

Using smart, steerable antennas would allow the base station cost to be reduced

as their numbers would increase in urban environments, thus increasing wireless

backhaul even more achievable and necessary (Rappaport, et al., 2013).

4. MASSIVE MIMO AND 5G

Millimeter–wave (mmWave) (30–300 GHz) Multiple–Input Multiple–Output

(MIMO) with large antenna array, incorporating 5G technology, has been

considered as a promising solution to meet the one thousand times increase

in data trac predicted in the near future (Marzetta, 2010). Besides providing

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larger bandwidth compared to the current 4G wireless communications,

antenna arrays can now be packed into a smaller physical size due to the

shorter wavelengths associated with mmWave frequencies. This means that

the spectral eciency can be improved considerably as MIMO with a large

antenna array eectively compensate for the high path loss induced by high

frequencies (Hossain, 2013).

To increase the diversity or the number of degrees of freedom in the wireless

communication system, the usage of multiple antennas is essential. Compared to

the conventional single antenna channels, a system with multiple transmits and

receive antennas (MIMO) has higher spectral eciency and higher bandwidth,

as each pair of transmitting and receiving antennas will provide separate signal

paths from the transmitter to receiver.

Reception reliability is therefore increased as signals carrying the same information

are transmitted on dierent paths, and multiple independently faded replicas of

the data symbols are received at the receiver (Zheng & Tse, 2003). Therefore,

the probability that all signal symbols fade simultaneously reduces as the receiver

receives multiple independently faded replicas of the same information symbol.

At higher frequencies, rain, foliage and atmospheric absorption are a serious

impediment to mmWave mobile communication. The attenuation caused

by rain and oxygen absorption is around 10–20 dB/km. These issues can be

overcome when we consider that the cell sizes have been reduced to about 50–

200m, especially at 28 GHz and 38 GHz, equating to about 1.4 dB over 200m

(Rappaport, et al., 2013; Gao, Dai, Mi, Wang, Imran & Shakir, 2015).

The primary imposing factor on the cell size in mmWave massive MIMO would

be free space path loss. In smaller cells, this loss can limit intercell interference,

and allow for greater frequency reuse.

In a wireless communication downlink system, the relationship between

Transmitted Power (P

), Received Power (P

), Transmitted Gain (G

) of entire

transmit array and Received Gain (G

) is given by

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(1)

In reference to Eq. (1), the path loss is given by

, and is directly proportional

to wavelength,

, where r is the range (Zheng & Tse, 2003). A larger path loss value

can be compensated by increasing the transmitted power, receiver sensitivity,

antenna array gain and reducing channel noise. Hence, equipping massive

antennas at macro and small–cell base–stations (BSs) can not only compensate

for severe path loss whilst achieving larger coverage distances, but also improve

signal directivity. Deploying antenna arrays with a large number of antennas will

increase the antenna gain (Gao, et al., 2018).

To achieve dramatic gains, MIMO envisions BSs with antennas numbering

100 or more, and this concept leads to massive MIMO. BSs with a very large

number of antennas N

, serve a group of single antenna co–channel users. It can

be concluded that as N

approaches innity, where throughput and quantity of

terminals are independent of cell size, the eects of uncorrelated noise and fast

fading vanish and the spectral eciency is independent of bandwidth, with the

required transmitted energy per bit vanishes (Swindlehurst, et al., 2014; Marzetta,

2010).

A larger N

enables a substantial increase in capacity, but in reality causes

interference problems which can be alleviated by using beamforming antennas

as opposed to the conventional ones (Ali, Ismail, Nordin & Abdulah, 2017).

In MIMO, beamforming is a signal processing procedure where the radiated

beam patterns of the antenna are produced by formulating the processed signal

in the direction of the desired terminals while cancelling interfering signals. This

enhances the energy eciency, spectral eciency while increasing system security

(Jungnickel, et al., 2014).

As the value of N

increases, more orthogonal pilots are required for channel

estimation, which is exhausting for the radio resources (Lu, Li, Swindlehurst,

Ashikhmin & Zhang, 2014). As the number of independent pilot sequences is

limited, they are reused between dierent cells and can cause conicts in antenna

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arrays known as pilot contamination (Jungnickel, et al., 2014). Pilot contamination

in massive MIMO systems limits the spectral eciency and increases with an

increase in N

It is assumed that as N

increases, the user channels remain spatially uncorrelated

and remain orthogonal with their respective pairs given proper propagation

conditions. However, increasing the number of antennas cannot provide

orthogonality in the highly correlated channels and user scheduling can render

a problem and signal processing of higher complexity is needed to separate

spatially correlated users (Ali, et al., 2017).

5. APPLICATIONS OF 5G

As wireless access techniques are being deployed extensively due to the rapid

convergence of computational technologies and information communication,

5G can no longer be constricted to conventional technical characteristics. 5G

is a cloud of multiple technologies, a diverse system of air interfaces, frequency

bands, protocols, network types and access node classes which are integrated to

provide smart and customized services, ranging from medicine to smart cities and

the more obvious cellular technologies. 5G should not be viewed as a solution to

replacing the current 4G LTE systems, but the seamless and ecient utilization

of advanced technologies and spectrum–usage schemes.

5.1. ULTRA–DENSE RADIO ACCESS NETWORKS

Ultra–Dense Radio Access Networks (UDRANETS) is seen as a promising

system architecture to enable high trac capacity over extremely reliable short–

range links (Chávez–Santiago, et al., 2015).

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Figure 2. MmWave massive MIMMO based 5G UDN (Skouby & Lynggaard, 2014).

A macro–cell base station with large coverage areas is responsible for the user

scheduling and resource allocation of high mobility users, while the various

ultra–dense smaller BSs provide a very high data rate for low mobility users

(Gao, et al., 2015), as illustrated in Figure 2. The UDRANETS allow for better

frequency reuse and improving energy eciency and reduction in path loss.

There is a possibility of completely wireless backhaul based on the mmWave

massive MIMO in the future (Sulyman, et al., 2014).

These cells do pose several problems, such as frequent handovers due to small cell

sizes, higher energy consumption and backhaul, which will increase interference

and mobility (Hao, Yan, Yu–Ngok & Yuan, 2016).

5.2. SMART CITIES AND 5G

The deployment of new ecosystems utilizing 5G technologies for the combination

of smart cities and homes has huge potential, with a focus on compatibility

with existing infrastructures to create sustainable and cost–ecient urban

environments. This will provide multiple options in a smart city in areas of health

care, green ecosystems and intelligent community services such as e–businesses,

security surveillance, social networks, intelligent transportation, telemedicine,

logistical management, Internet of things (IoT) and Cloud of Things (CoT),

Articial Intelligence (AI) just to name a few (Lynggaard & Skouby, 2015).

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Smart homes are targeted towards enriching the living environment and

improving the quality of life of its inhabitants. This targets the home automation

area, where embedded devices such as light, heating, entertainment systems

security are controlled remotely (Skouby & Lynggaard, 2014).

The wireless technologies such as Bluetooth, Radio Frequency Identication

(RFID), ZigBee, Wireless Local Area Networks (WLANs), sensor networks

along with ber communication and cable networks form the basis of smart city

infrastructures (Han, Ge, Wang, Kwak, Han & Liu, 2017). All these together with

IoT produces a huge amount of information that needs to be securely stored for

processing. Hence, the incorporation of CoT with rest of these technologies is

crucial as it provides resources and calculation capabilities which are accessible

via the internet and can store the IoT data eciently.

There are various challenges that face the development of such ambitious

technologies. The complexity of the movement of various mobile terminals

increases and becomes more varied. The data transmission can be of a

pedestrian with a cellular phone, a laptop device on a high–speed train or even a

navigational device on a moving car. There are also various obstacles in a dense

urban environment, especially in the mmWave spectrum.

The security and privacy of networks users pose a serious threat to the

development of 5G technologies. Sensitive and personal information such as

banking information would have to be shared on a cloud platform and could

pose a threat of being disclosed to the wrong persons. This would require highly

complex data security management with strong encryption and cryptographic

tools to maintain network system condentiality and also to identify vulnerabilities

in networks that could serve as weak points for various attacks (Gao, et al., 2015;

Mehmood, et al., 2017).

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5.3. LI–FI AND 5G

High–speed wireless data communication using infrared and visible light spectrum

is being deployed and is predominantly known as Li–Fi. The concept of Visible

Light Communication (VLC) is used to achieve bi–directional high–speed, secure

and fully networked wireless communication.

Figure 3. Comparison of the Radio Frequency (RF) Spectrum and the Visible Light Spectrum (Haas,

2018).

As illustrated in Figure 3, the bandwidth occupied by VLC is approximately

2600 times greater than the currently employed radio frequencies for wireless

communication. The conventional VLC system was being conceived as a single

point–to–point wireless communication between a LED source and a receiver

that is equipped with a photodetection device. The data rates required to depend

on digital modulation and lighting technology.

Adoption of wireless networks based on light as opposed to pointing to point

links pose several challenges. As each cell can have several users, multiple access

schemes are required. Uplink provisions can be the dierence from downlink

ones, as the portable device requires lower energy consumption, and the user is

not likely to be distracted by the visible light source (Swindlehurst, et al., 2014),

and therefore infrared spectrum is the most desirable for uplink (Bangerter, et al.,

2014).

The high–speed uplink requires its modulation to be both power and spectrum

ecient simultaneously. Handovers will be complicated as connectivity needs to

be maintained as a user leaves a certain premise for an area without any Li–Fi

coverage (Ayyash, et al., 2016).

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However, the incorporation between Wi–Fi and Li–Fi proves promising and

it is a possibility for the two of them to co–exist. It will allow for o–loading

opportunities for the Wi–Fi network as immobile users would be utilizing the Li–

Fi technology. With this collaboration, the total number of users can more than

triple, and throughput can increase exponentially, by enhancing indoor coverage

and providing high data rates.

6. CONCLUSION

To achieve dramatic demands that wireless technologies will need in terms of

capacity and spectral eciency, 5G systems embracing mmWave spectrum

from 3300GHz is promising. It promises high speed, low latency amongst

other advantages, and would meet the predicted demands that 4G networks

will meet by 2020. It will result in smaller cell sizes, and wireless backhauls to

be implemented. Higher spectrums allow for utilization of highly directional

antennas to be packed into larger arrays with smaller physical sizes. This is

appealing for the massive MIMO transceiver design. To reduce the path loss

mmWaves experience, increasing the number of antennas can lead to high

capacity, but also high interference. Signal analysis complexity increases, and

results in pilot contamination.

The Ultra–Dense Radio Access Networks (UDRANETS) is a system architecture

to meet high trac and handle large capacity. 5G technologies are being deployed

in smart cities, embracing IoT and CoT technologies. This would meet some

challenges such as data security, privacy and an increase in overall signal analysis

complexity.

Li–Fi would be a promising solution as it would be able to integrate with Wi–Fi

and increase the capacity, while also enhancing indoor and outdoor coverage.

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Edición Especial Special Issue Mayo 2019

DOI: http://dx.doi.org/10.17993/3ctecno.2019.specialissue2.498-517

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AUTHOR

Sara Bhatti

Sara is a lecturer in Sir Syed University of Engineering and

Technology. She completed her Bachelors of Engineering in Electrical

and Electronic Engineering from the University of Auckland in 2002.

Her areas of interest include wireless Communications, Satellite

Communications and Communication Systems.