Wireless Pers Commun https://doi.org/10.1007/s11277-017-5217-9

Spectrum for 5G Services P. S. M. Tripathi1

•

Ramjee Prasad2

 Springer Science+Business Media, LLC, part of Springer Nature 2017

Abstract The unprecedented growth in mobile data traffic has choked network capacity of existing IMT/IMT-A (3G/4G) networks. Work on next generation mobile communication system (5G) i.e. IMT 2020 is underway and likely to come in the year 2020. The 5G network envisages data speed of 1 Tbps and beyond. To realise the IMT 2020, radio spectrum is an essential element. Presently, mobile communications are operating between 700 and 3600 MHz. These spectrum bands do not have the capacity to carry such enormous data. Millimeter (mm) frequency band beyond 10 GHz is the most preferred band for 5G. Radiocommunication sector of ITU is in the process to identify the frequency bands for IMT 2020, which will be finalised in the WRC 2019. There are considerable differences in the spectrum bands currently in use and MM waves in terms of propagation characteristics, interference management and system design etc. In this paper, frequency bands under consideration for 5G services has been discussed. Keywords Radio spectrum  5G  WISDOM  IMT 2020  MM waves

1 Introduction Evolution in mobile communication has made peoples life easier. Mobile phone is now one-point solution for most of the daily life chores, whether it is ordering food, accessing bank, filing government taxes, searching an address in a city or connecting with others. Essential services such as e-commerce, e-banking, e-governance, e-health etc. can be & P. S. M. Tripathi [email protected] Ramjee Prasad [email protected] 1

Department of Telecom, Ministry of Communications, New Delhi, India

2

Department of Business Development and Technology, Aarhus University, Aarhus, Denmark

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accessed through mobile phone and these are continue expanding their coverage and heading towards more mobility [1]. These expansions will lead to need for enormous wireless traffic in future. Ericsson has predicted that the wireless traffic would be increased by 1000 times in 2020 than seen in 2010. This traffic is primarily driven by increased usage of mobile multi-media services [2]. Cisco has predicted that mobile data traffic will grow at a compound annual growth rate (CAGR) of 47 percent from 2016 to 2021 and there will be 11.6 billion mobile-connected devices by 2021 [3]. Today’s wireless traffic is largely contributed by human centric applications. Machine centric traffic will contribute equally (or even more than human centric) in the future with a growth of 34 percent CAGR from 2016 to 2021 [3]. The combination of human and machine centric applications will diversify the landscape of the mobile industry in terms of size, cost, energy dissipation and services. Machine centric applications require data delivery of high reliability, and on the other side human centric applications require data delivery at high speed and always connected. Therefore, the next generation of mobile communication will be moving towards to a future state of everything everywhere and always connected with reliability [4, 5]. The existing 4th generation mobile communications (also known as IMT-A [International Mobile Telecommunications-Advanced]) is all IP based network with packet switched delivery with high data rates of 100 Mbps (high mobility)/1 Gbps (low mobility). The 4th generation network is IP based network which able to communicate with PSTN (Public Switched Telephone Networks), LAN (Local Area Networks), IP based mobile network, 2G and 3G network, nomadic, ad-hoc and sensor networks etc. LTE (Long Term Evolution) and LTE-A are the 4G technology, which based on the OFDMA technology and can operate with maximum bandwidth of 20 MHz. The LTE network is fulfilling the present demands but it may not be able to meet future requirements of high bandwidth demanding applications such as entertainment, multimedia, Intelligent Transport Systems (ITS), telemedicine, emergency, safety/security applications and other futuristic applications. These applications will push the demand for real-time, symmetric, wireless ubiquitous connectivity to an individual with a data rate that far exceeds the capacity offered by the current 4G network [6, 7]. The 5G network, also known as IMT-2020, is universally deployable converging technologies, which enable wireless services and applications at a data rate more than one terabit per second (Tbit/s) with coverage extending from a city to a country to the continents and to the world that will enable user-centric mega-communications [6]. 5G services cover a wide range of applications, mainly enhanced Mobile Broadband (eMBB), Ultra-reliable and Low Latency Communications (URLLC) and massive Machine Type Communications (mMTC) [8]. The eMBB is extension of existing 4G network and URLCC and mMTC are new dimensions added to 5G network. Therefore, growth of 5G network would drive substantial economic benefits by serving as a platform for innovation in many areas of public and commercial importance, and benefits will lead to more investment, faster economic growth and new jobs. As per IHS report, 5G network will generate $3.5 trillion in output and will generate 22 million jobs by 2035 [9]. Radio spectrum is a prime factor in driving the growth of mobile services. The success of 5G network is based on the unrestricted availability of spectrum. In the ITU-R M.2290 report, future spectrum requirement for terrestrial IMT services has been given taking into account market, service, radio, traffic distributions related parameters. As per the estimation, total spectrum requirement by 2020 for both low and high user density would be around 1340 and 1960 MHz respectively. However, this spectrum requirement may vary from country to country. It has also been estimated that traffic growth would be at least 25

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times more in 2020 as compared to 2010. Further this IMT traffic will increase in the range of 10–100 times from 2020 to 2030 [10]. About 1200 MHz of spectrum in the frequency bands below 5 GHz has been identified for IMT services during the World Administrative Radio Conference (WARC)-92, World Radiocommunication Conference (WRC)-2000, WRC-2007 and WRC 2015 as per detail given in the Table 1. In the above frequency bands, spectrum available for cellular mobile services does not exceed beyond a total of 780 MHz, and an operator is having approximately 200 MHz spectrum across all IMT bands for providing telecom services using different access technologies from GSM to LTE [11]. However, 1200 MHz non-contiguous spectrum will not hold the pressure of high mobile data growth, demand for convergence of different varieties of services and speed. Therefore, more spectrum bands would need to be explored. Presently, frequency bands under consideration in the framework of WRC-19 agenda item No. 1.13 (Table 2, 3). The paper provides an overview of spectrum requirement for 5G services. This paper is organised as follows: Concept of 5G network discussed in Sect. 2 and challenges and spectrum requirements for 5G services is discussed in Sects. 3 and 4 respectively followed by conclusion in Sect. 5.

2 Concept of 5G Network The upcoming 5G wireless network envisages with capabilities for supporting high capacity and massive connectivity for diverse set of services, application and users, and flexible and efficient use of all available contiguous/non-contiguous, licensed/unlicensed spectrum. Convergence of technologies, ultra-high capacity, universal coverage, minimum energy usage and cost-efficiency are key characteristics of the 5G wireless system concept [7]. Currently, operators are providing services using multiple RATs (2G, 3G, WiMAX, LTE, WLAN and Bluetooth etc.). For example, operators rely on unlicensed Wi-Fi network to offload traffic demand at hot-spots. Devices are equipped with multiple RATs like cellular, Wi-Fi and Bluetooth to connect the peripheral devices and internet. The 5G network should have the capability to integrate multiple radio access technologies Table 1 Spectrum identified for IMT services IMT frequency band (MHz)

Identified in WRC

Frequency arrangements

450–470

WRC-15

FDD/TDD

470–608

WRC-15

–

694–960

WRC-2000, 2007, 2012

FDD/TDD

1427–1518

WRC-15

1710–2200

WARC-92, WRC-2000

FDD

2300–2400

WRC-07

TDD

2500–2690

WRC-2000

TDD/FDD

3300–3400

WRC-15

TDD

3400–3600

WRC-07

TDD/FDD

4800–4990

WRC-15

–

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P. S. M. Tripathi, R. Prasad Table 2 Technical parameters for 5G services Parameter

Description

Values

Peak data rate

Maximum achievable data rate under ideal conditions per user/device (in Gbit/s)

10–20 Gbit/s

User experienced data rate

Achievable data rate available ubiquitously across the coverage area to a mobile user/device (in Mbit/s or Gbit/s)

100 mbit/s for wide area coverage and 1Gbit/s for hotspot

Latency

The contribution by the radio network to the time from when the source sends a packet to when the destination receives it (in ms)

1 ms

Mobility

Maximum speed at which a defined QoS and seamless transfer between radio nodes (in km/h)

500 km/h

Connection density

Total number of connected and/or accessible devices per unit area (per km2)

106 devices/km2

Energy efficiency

Energy efficiency on the network side, quantity of information bits transmitted to/received from users per unit of energy consumption of the RAN (in bit/Joule) and on the device side, quantity of information bits per unit of energy consumption of the communication module (in bit/Joule)

100 times more than IMTAdvanced

Spectrum efficiency

Average data throughput per unit of spectrum resource and per cell (bit/s/Hz)

3 times more than IMTAdvanced

Area traffic efficiency

Total traffic throughput served per geographic area (in Mbit/s/m2)

10 Mbit/s/m2

seamlessly and to choose a suitable one among them, and to switch over between various access technologies, combine different streams coming from different technologies during a session to meet capacity demands [12]. The future 5G network will have a relatively large number of small cell sites with different cell size from macro to femto and with low/medium transmit power to meet the high traffic demand. The low-powered small cell sites are used for the capacity, whereas macro cells are deployed for coverage. Therefore, 5G networks offer multiple options in respect of transmit power, coverage, capacity, spectrum usage and choice of RATs. The 5G network would also create a dynamic environment for device to device (D2D), communications to enable to communicate directly between user’s equipment or between machines (in the context of Internet of Thing) without using base stations or core network, and machine to machine (M2 M), to communicated between massive numbers of devices using base station [13]. Such type of communications will coexist dynamically within the network and will help to improve the area spectral efficiency, cellular coverage and reduce end-to-end latency and power consumption. According to ITU-R Recommendation M.2083, IMT Vision—Framework and overall objectives of the future development of IMT for 2020 and beyond, identified the following three usage scenario for 5G services [14]: 1.

Enhanced Mobile Broadband (eMBB) Mobile Broadband addresses the human-centric use cases for access to multi-media content, services and data. eMBB has two key features; the first one is extending cellular coverage, which covers a range of cases, including small and wide-area coverage and hotspot, which have different

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Spectrum for 5G Services Table 3 Available spectrum for IMT services in India IMT frequency band (MHz)

Quantum of spectrum available for IMT ( MHz)

Remarks

450–470

–

Identified but not yet allotted

700 (698–806 MHz)

35 ? 35 (FDD)

Available but not yet allotted

800 (824–844/869–889 MHz)

20 ? 20 (FDD)

900 (890–915/945–960 MHz)

25 ? 25 (FDD)

1800 1710–1785/ 1805–1880 MHz)

55 ? 55 (FDD)

2100 1920–1980/ 2110–2190 MHz)

40 ? 40 (FDD)

2300–2400

100

2500–2690

40

3300–3400

100

Identified but not yet allotted

3400–3600

175

Identified but not yet allotted

4800–4990

–

Not identified

2.

3.

requirements such as high user density, very high traffic capacity, seamless connectivity with low and high mobility, and the other one is handling of large number of devices using high volume of data. Ultra-Reliable and Low Latency Communications (URLC) This includes very low latency with high availability and strong reliability. This will be used for wireless control of industrial manufacturing or production processes, remote medical surgery, distribution automation in a smart grid, transportation safety, etc. Massive Machine Type Communications (mMTC) Very large number of connected devices typically transmitting a relatively low volume of non-delay-sensitive data with low cost, and long battery life such as sensor. This application is combination of traditional machine to machine (M2 M) and internet of thing (IOT).

The eMBB is extension of existing 4G network but other two usage URLC and mMTC are new phenomenon which have been introduced in 5G network. Therefore, 5G covers all possible mobile communications, which are presently provided through various platforms such as sensors, robotics and smart metering etc. Figure 1 illustrates some examples of envisioned usage scenarios for IMT for 2020 and beyond. The following eight parameters are considered for IMT-2020 [14]. The key capabilities of IMT-2020 are shown in Fig. 2, compared with those of IMTadvanced. With the above attributes, the 5G network will support everything from simple M2 M/ D2D devices to high speed data streaming, monitoring and control of various kinds of millions of sensors, multiple simultaneous streaming services, and will support the massive

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Enhanced mobile broadband Gigabytes in a second 3D video, UHD screens Work and play in the cloud

Smart home/building

Augmented reality Industry automation Mission critical application

Voice Smart city

Self driving car

Future IMT

Massive machine type communications

Ultra-reliable and low latency communications M.2083-02

Fig. 1 Usage scenarios of IMT for 2020 and beyond [14]

data collection and distribution needs of the Internet of Things (IOT) [4]. There are three main aspects to realizing 5G communication systems in Fig. 3 [6]. 5G intelligent core: Intelligent core will be the soul of the 5G network. M2M and IoT are keys for realizing the intelligent core which provides seamless ubiquitous networking and connectivity in the 5G network. Ubiquitous connectivity Ubiquitous connectivity will be for coverage under high mobility and data rates, and to moving application from device to device without any content interruption. Use of millimeter wave links, high-order spatial multiplexing (MIMO) antenna, virtualization, small cell deployments and novel spectrum usage methods, are some of the keys for ubiquitous connectivity. Ubiquitous networking The ubiquitous net-working will provide the same quality of services to end users, regardless of how many access networks, and spectrum bands are integrated for connectivity purposes. The 5G network has been envisaged as a multi-layers heterogeneous network in which primary layer will be a macro layer responsible for ubiquitous connectivity and secondary layers, embedded in the primary layer, will be a combination of several small cells (micro, pico and femto) to provide additional capacity to end users. This additional capacity will be in the form of larger bandwidth on the same carrier, different access technology or an additional stream on a different carrier. The network will be controlled by an intelligent unit called, WISDOM (Wireless Innovative System for Dynamic Operating Mega communications) [6, 7, 15, 16]. The function of multilayer network is conceived as initially a user will be connected to the primary layer. When data requirements go beyond the primary layer network capacity even after providing the additional spectrum (if available) and change in radio access technology within the primary layer, the user will also get connected to the nearest secondary layer through the WISDOM network. This has been depicted in the Fig. 4, where three users A, B and C have been shown. The requirements of

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Fig. 2 Enhancement of key capabilities from IMT-Advanced to IMT-2020 [14]

Fig. 3 Concept of 5G network

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Fig. 4 5G network: primary and secondary layers

the user A and B is beyond the capacity of primary layer, they have also been connected to secondary layers, whereas the user C requirement is within the capacity of primary layer. With the above- mentioned features, a modification in 4G networks could be the best solution for 5G network. Based on this assumption, the concept of 5G has been introduced as integration of 4G with WISDOM as given below [15, 16]: 4G&WISDOM ¼ 5G The Wireless Innovative System for Dynamic Operating Mega Communications (WISDOM) is a communication system for ubiquitous trustworthy human-centric connectivity via an arbitrary infrastructure support. The WISDOM principle, as shown in Fig. 5, brings unlimited wireless world interconnection, convergence, and cooperation (geographically including cities, countries, continents, and finally, the whole world), together with a large variety of multimedia services at very high data rates, and becomes the main 5G definition point.

Fig. 5 WISDOM principle [6]

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The three founding pillars of WISDOM are [16]: • An information theoretic performance/capacity estimation of different types of networking paradigms. • Design of protocols based on end-to-end, cross- layer and cross-network-domain performance optimization. • Cognitive radio (CR) network based self-organizing networks for management of possible usage scenarios and minimize the spectrum and energy requirements. WISDOM aims to design and develop technologies, system that could globally integrate, interconnect and communicate into a flexible and dynamic system for the humancentric and machine centric communications in 2020 and beyond [15]. The operational domain of WISDOM concept requires well-defined network protocols, architecture for heterogeneous network, integration between different kinds of terrestrial and satellite network to provide applications up to 1 Tbps link rate at short distance or as system aggregate operating in burst mode, and at least 250 Mbps to the end user for real time applications with coverage extending from a city, to a country, the continent and the world (Fig. 6). The WISDOM concept will lead wireless communications beyond the emerging technologies and towards the realization of that new paradigm, based on the combination of five independent elements, Communication, Connectivity, Convergence, Content and Cooperation [16].

3 Implementation Challenges 5G networks is basically delivery of services at any user platform using various wireless access technologies over any kind of network (all kinds of wireline, wireless, satellite networks) and frequency band with a speed of more than 250 Mbps at end user. Therefore, a general framework should be developed to evaluate the performance of 5G wireless systems, taking into account as many performance metrics as possible from different

Fig. 6 Global connectivity through WISDOM

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perspectives. Besides, coexistence study between heterogeneous, the following implementation challenges should also need to be addressed. 5G network envisages delivery over any kind of network. Therefore, a realistic channel models with proper accuracy complexity trade-off are required for 5G network. Massive MIMO channel model is an option. The technical challenge in developing massive MIMO systems is the signal processing complexity. Simplification of algorithm in massive MIMO system is a challenge. The massive MIMO should have the capability [17]: (1) to support 10–100 times more devices than today (2) to allow very long battery lifetimes of the wireless device (3) to incur minimum signalling overhead (4) to enable low cost wireless devices (5) to support efficient transmission of small payloads with fast setup and low latency. At the same, it is desirable to have 99.999% coverage, while energy consumption and cost for the infrastructure should not increase. The network should be energy efficient. Energy efficiency has two aspects; the first one is energy spend for maintaining infrastructure, which have a direct link with operational overhead, and the other one is energy consumption in the end user’s devices. There are communication strategies, which require high energy for computation. Such applications will drain user’s device battery. To reduce energy consumption, two different approaches are under consideration. The first approach is creation of small cells with high capacity density. The main challenges of this approach are related to providing an economic backhaul solution and to minimise the additional deployment cost. The second one is use of massive MIMO system. The challenges of massive MIMO include the diffusion of energy due to scattering in NLOS scenarios, limiting the achievable directivity, and the complexity of spatial multiplexing of users. The interference-tolerant CR networks is very much part of the 5G network. Reliable and practical management of the mutual interference of CR and primary systems is essential for 5G network. Therefore, regulation of the transmit power is essential for the CR system to coexist with other licensed systems. 5G network will be a step further towards low cost, plug and play, self-configuring and self-optimising networks. 5G systems will be combination of macro and several micro, pico and femto cells embedded within the macro cell and will be deployed dynamically and in a heterogeneous manner, combining different radio technologies. Such configuration will improve spectral efficiency and coverage within an area. A massive deployment of small access nodes induces several challenges such as an adverse interference scenario or additional backhaul and mobility management requirements, which 5G needs to address. Different levels of coordination/cooperation among small cells are keys to enhance the network capacity and keep interference at an adequate level, to manage mobility and spectrum, to ensure service availability and response to non-uniform traffic distribution between neighbouring access points [17].

4 Spectrum for 5G Services The network capacity depends on the number of base stations, radio access technology and frequency bandwidth. The 5G network will have several short range cell base stations for capacity boosting, which works alongside macro cells. The spectrum requirements for macro cell and short range cells are different. Macro cells will be for ubiquitous connectivity, and small cells will be for capacity booster [13]. Low frequency waves are suitable for macro cells due to its wide coverage and better penetration, and high frequency

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waves are suitable for booster cells due to large data carrying capacity. Therefore, spectrum requirements for the 5G networks could be divided into two different categories, low and high frequency waves.

4.1 Lower Spectrum Bands As stated, approximately 1200 MHz of spectrum has been identified for IMT-A services in various frequency bands below 5 GHz. These frequency bands are suitable for macro cell sites due to better propagation and penetration properties, especially bands below 1 GHz. 5G envisage massive IoT connectivity and ultra-reliable communication. Ubiquitous coverage is important factor for ultra-reliable connectivity, which can be provided with low frequency bands spectrum only. Therefore, lower bands spectrum will be backbone for success of 5G as it provides ubiquitous wide area coverage. As per the frequency allocation plan, almost 50% of the total spectrum between 300 MHz and 6 GHz has been earmarked for mobile services as primary services. It means that this 50% of the total spectrum can be utilized for mobile services alone or in sharing with other primary/secondary services. The frequency bands below 6 GHz have already been allocated to legacy services long back and is very difficult to relocate legacy services in other frequency bands. Therefore, no vacant spectrum is available below 6 GHz at present. The two options are available to increase the spectrum availability for 5G services; spectrum re-farming and spectrum sharing. The spectrum re-farming is basically allowing incumbent license holders to utilise the allocated spectrum for some other services or relocation of licensees to some other band from the existing band and reuse this band for other radio services. For example, refarming of 900 or 1800 MHz band, which was earlier allotted for 2G GSM services, is now being replaced by 4G network. Another example is the vacation of spectrum in the 700 MHz band by broadcasting services due to the digital switch over. Re-farming is a cumbersome process involve protracted negotiations with existing operators for migration with financial implications. Spectrum sharing is another option, where two or more than two operators share the same spectrum in frequency, time and geographic dimensions for providing same or different services. For example, there are several services, which use spectrum for a certain period of time or at certain locations. Such spectrum could be considered vacant, during the period or at the locations, where existing licensed operator is not using and the same could be utilised by mobile operators to provide IMT services. This type of sharing is known as static spectrum sharing. Another possibility is the dynamic spectrum access (DSA) that allows to access spectrum in opportunistic manners. CR is the basic tool for exploiting DSA. The CR enabled system sense the vacant spectrum and operates from the vacant spot, and retreat occupied spectrum on arrival of the primary user. A big chunk of already identified 1200 MHz spectrum has not yet been freed for IMT services worldwide. Spectrum crunch for the 5G network in lower bands would be resolved without doing large scale spectrum re-farming if DSA is allowed. In India, IMT services are presently available in 800, 900, 1800, 2100, 2300 and 2500 MHz bands. IMT services in India are being provided on GSM, CDMA, WCDMA and LTE platform. GSM and CDMA services are being rapidly replaced by LTE services. A total of 315 MHz (out of which 175 MHz in FDD and 140 MHz in TDD) has so far been available for IMT services. A detail of available spectrum in various bands for IMT services in India is given in the table.

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Spectrum in 700 MHz was put to auction in October 2016 but it was not sold. At present, services in 700 MHz band are not available in India. The frequency bands 450, 3300 and 3400 MHz have not yet been made available for IMT services even after identification of these bands for IMT services long back in 2011. Recently, it has been decided to make available spectrum in 3300 and 3400 MHz for IMT services [18].

4.2 Higher Spectrum Band: MM-WAVES The spectrum bands identified under the IMT umbrella do not have the capacity to carry such enormous data which required for 5G services. Therefore, mm-waves could be the candidate bands for 5G mobile communications, especially for second layer network due to high data carrying capacity. The mm-waves have the following advantages [19]: • • • • • •

Not much operation at mm-waves so more spectrum is available at mm-waves. Very large blocks of contiguous spectrum to support future applications. Due to high attenuation in free space, frequency reuse is possible at short distance. Spatial resolution is better at mm-waves hardware with CMOS technology. Advancement in semiconductor technology allows low cost. Small wave-length makes possible use of large antenna arrays for adaptive beam forming. • The small size of the antenna at mm-waves facilitates easy integration on chip and installation at suitable locations. Millimeter waves allow larger bandwidth and offer high data transfer and low latency rate that are suitable for high speed reliable internet services. The small wavelength facilitates small size antenna and radio hardware, which reduces cost and easy to install. The transmitter’s antenna would be of the size of lamppost, which could be installed on building, street lamppost, etc. MM Waves provide the scalability, capacity and density required for a seamless integration of these cells into the cellular network infrastructure. These bands offer prospects for increased network capacity and network densification. All of these benefits, on the other hand, come with complex system design and higher losses. The recent technical developments have produced cost effective solutions that can be used to manage many of these challenges. Propagation conditions at high frequency have several issues. Propagation loss at high frequency is high. As per ITU-R Report ITU-R M.2376, Line of Sight (LOS) and NonLine of Sight (NLOS) path loss is always more than 100 dB for the average distance of 20 m and more, and difference of path loss between LOS and NLOS conditions is around 25 dB for distance more than 100 m at 38 and 60 GHz. At such high frequency, waves are more prone to rain and other atmospheric attenuation. Figure 7 shows the specific gas, rain and fog attenuation (dB/km) as a function of frequency. It can be seen that these effects show a high degree of frequency dependent variation [20]. Rain loss can be more significant compared to other atmospheric losses, except near the peaks in gaseous attenuation, but is relatively infrequent. The wavelength is in the order of millimeters, and rain drops are also of the same size. Rains absorb high frequency waves and make it difficult for propagation. However, the experimental results show that in heavy rain condition, attenuation is 1. and 1.6 dB for 200 m distance at 28 and 38 GHz respectively [11]. Therefore, slight high transmit power may be required to take care of rain attenuation. Some other factors such as trees and buildings etc. may also be taken into account for outdoor environment as these factors cause additional attenuation of the

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Fig. 7 Rain and gas attenuation with respect to frequency [20]

millimetric signal. The associated loss is caused by a combination of diffraction, ground reflection and through-vegetation scattering. Wavelength at such high frequencies is in the range of millimeters. Any slight change in the position would affect the signal strength at the receiving end, due to which mm-waves are deeply affected by scattering, reflection and refraction. The r.m.s. delay spread for mmwave is of the order of few nano seconds, and it is high for are non-line of sight (NLOS) links than line of sight (LOS) links [13]. Similarly, path loss exponent for NLOS links is higher than LOS links. Due to higher path loss and r.m.s delay spread, it is assumed that mm-waves are not suitable for non-line of sight (NLOS) links. The r.m.s. delay spread can be minimised using high gain antenna with narrow bandwidth. The narrow beam width transmission from the base station limits the direction of the generated energy, which reduce the opportunities to scatter. Further r.m.s. delay spread could be minimised using carrier aggregation, high order MIMO, steerable antenna and beamforming techniques etc. Propagation feasibility studies for mm waves have been carried out at research institutes, and concluded that propagation is feasible up to 200 m of distance [8, 21] in both the conditions i.e. line of sight (LOS) and non-line of sight (NLOS) with transmit power of the order of 40–50 dBm in a difficult urban environment. The cell size in dense urban areas normally varies between 100 and 300 m. These results support the feasibility of IMT at mm-waves. The traditional uses of the mm-waves include radio navigation, space research, radio astronomy, earth exploration satellite, radar, military weapons and other applications. The backbone/backhaul networks (point to point network) for existing telecom network to connect base station to main switching centre (MSC), Local Multipoint Distribution System (LMDS), indoor WLAN, high capacity dense networks are also present in the mmwaves. The Radiocommunication Sector of International Telecom Union (ITU) is responsible for management of radio spectrum at international level. As per ITU-R frequency allocation plan, the frequency bands above 10.0 GHz has been earmarked majority for satellite based services in all the three regions along with Fixed and mobile services. Local

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Multipoint Distribution System WLAN, Satellite services and High capacity dense network etc. are main services present in mm-waves. Several point to point fixed microwaves links are also working in this band. These links are basically for backbone/backhaul network for GSM and other services. As per the agenda item 1.13 of WRC-19, the following frequency bands have been identified for the future development of IMT, including possible additional allocations to the mobile services on primary basis [22].

Frequency bands under study (GHz)

Allocation as per RR 2016

Frequency bands with mobile services as primary allocation 24.25–27.50

RADIONAVIGATION, FIXED-SATELLITE (Earth-to-space), EARTH EXPLORATION-SATELLITE (space-to Earth), FIXED, INTERSATELLITE, MOBILE, SPACE RESEARCH (space-to-Earth), Standard frequency and time signalsatellite (Earth-to-space)

37.00–40.50

FIXED, FIXED-SATELLITE (space-to-Earth), MOBILE except aeronautical mobile, SPACE RESEARCH (space-to-Earth), Earth exploration-satellite (space-to-Earth), MOBILE-SATELLITE (space-to-Earth)

42.50–43.50 GHz

FIXED, FIXED-SATELLITE (Earth-to-space), MOBILE except aeronautical mobile, RADIO ASTRONOMY

45.50–47.00

MOBILE, MOBILE-SATELLITE, RADIONAVIGATION RADIONAVIGATION-SATELLITE

47.20–50.20

FIXED, FIXED-SATELLITE (Earth-to-space), MOBILE

50.40–52.60

FIXED, FIXED-SATELLITE (Earth-to-space), MOBILE, Mobile-satellite (Earth-to-space)

66.00–76.00

INTER-SATELLITE, MOBILE, MOBILE-SATELLITE RADIONAVIGATION, RADIONAVIGATION-SATELLITE, FIXED, FIXED-SATELLITE, BROADCASTING, BROADCASTING-SATELLITE Space research (space-to-Earth)

81.00–86.00

FIXED, FIXED-SATELLITE (Earth-to-space), MOBILE MOBILESATELLITE (Earth-to-space), RADIO ASTRONOMY, Space research (space-to-Earth)

Frequency bands—Not have mobile services as primary allocation 31.80–33.40

FIXED, RADIONAVIGATION, SPACE RESEARCH (deep space) (space-to-Earth)

40.50–42.50

FIXED, FIXED-SATELLITE (space-to-Earth), BROADCASTING, BROADCASTING-SATELLITE Mobile

47.00–47.20

AMATEUR, AMATEUR-SATELLITE

The above spectrum bands it is clear that frequency bands above 24 GHz are key bands for 5G networks. Out of above bands, most of the administrations are ready to adopt part of 24–27 GHz band for IMT services. This band is most pioneering band for 5G services. In totality, 33.25 GHz spectrum is under consideration for IMT services in higher frequency bands. Out of which, 29.45 GHz spectrum has provision for mobile services as a primary service in all the 3 ITU regions. Presently, in these bands, spectrum has been allotted majority to satellite services, which require low transmit power. These identified spectrum

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blocks cannot be made available exclusively for IMT services as once a satellite is launched, assigned cannot be shifted during its life. Therefore, co-existence study between satellite services and IMT services must be carried out before the utilisation of these frequency bands for IMT services. Three another frequency bands 31.8–33.4, 40.5–42.5 and 47.0–47.2 GHz with a total of 3.8 GHz spectrum are under consideration for IMT services but these bands do not have mobile services as primary services. Therefore, a provision needs to be made for these bands, mobile as a primary service. Research for utilising these bands for 5G services is underway by research institutes worldwide. Results would be presented in the meetings of Working Party 5D of the study group 5 of ITU—R and it anticipated that 5G radio interface would be launched before 2020. Regulation of Millimeter waves is little bit more complex as compared to Lower frequency bands. As stated, higher frequency bands are more susceptible to the specific gas and rain absorption. Due to which coverage shrinks as we move towards higher frequency bands. Due to high data carrying capacity and small coverage, higher frequency bands are suitable for hot spots or dense populated areas. Light licensing is good for frequency bands above 60 GHz [23] as the coverage is limited to 2–4 kms. Most of the countries have adopted light licensing method of allocation of spectrum in the frequency bands more than 60 GHz. It may not be suitable for frequency bands between 24 and 60 GHz frequency bands as coverage is larger up to 10 kms in light dense areas. Therefore, two different approach should be adopted for allotment of spectrum in higher frequency bands, the first one for the spectrum between 24 and 50 GHz and the second one for spectrum in the frequency bands beyond 60 GHz. Generally, IMT identified frequency bands are allotted through auction in which, spectrum auctioned for wide area (normally called service area). Such type of auction may not be suitable for higher frequency bands from spectrum utilisation point. Moreover, spectrum requirements at any location may vary with respect to time and traffic. To enhance the spectrum utilisation, service area may further be divided into small areas based on the volume of traffic and reserve price would also be fixed accordingly [24]. Spectrum in these small areas should be put for auction. With such kind of auction, administration will get more revenue and provide better spectrum utilisation and co-existence with existing services. Small area basis spectrum auction is suitable for the spectrum between 24 and 50 GHz. Light Licensing is good for the spectrum beyond 60 GHz. Another aspect of regulation is harmonisation of frequency bands identified for IMT services as harmonisation facilitates economies of scale and global roaming [8]. Harmonisation is basically re-arrangement of allotted spectrum in such a way that a certain block of spectrum can be made available for IMT services. There are various challenges in the harmonisation process, such as equipment compatibility, relocation of existing users some other frequency bands and other administrative challenges etc., which have to be addressed very judiciously and resolved in consultation with the concerned stakeholders. Harmonisation of spectrum is desirable at global level, if not possible, it must be done at regional level. Harmonisation must be done not only in IMT bands but in adjacent bands also to improve the reliability.

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5 Conclusion In this paper frequency bands for 5G mobile communications services have been discussed. Lower band is suitable for the primary layer due to better propagation characteristics. Exclusive spectrum below 6 GHz is not available. The avail-ability can be increased through spectrum sharing as primary and secondary user concept. The Millimeters waves are most suitable candidate bands for secondary layer of 5G network. Analysis of candidate bands shows that sufficient spectrum is available, which could be allocated for the 5G services. However, extensive co-existence study with existing usage is required to be carried out for making provision for the 5G communications services. Traditional regulation may be adopted for spectrum in lower frequency bands whereas small area spectrum auction and light licensing may be used for regulating the spectrum in higher spectrum bands.

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Mobile commerce essay. https://brightkite.com/essay-on/mobile-business. Ericsson, L. (2011). More than 50 billion connected devices, White Paper. Cisco visual networking index: Global mobile data traffic forecast update, 2016–2021. Agilent, current activity in 5G. www.agilent.co.in/about/news-room/tmnews/background/5g/. A primer on 5G. https://ipfiles.wordpress.com/2014/05/14/a-primer-on-5g/. Prasad, R. (2013). Global ICT standardisation forum for India (GISFI) and 5G standardization. Journal of ICT Standardization, 1, 123–136. https://doi.org/10.13052/jicts2245-800X.12a. Prasad, R., & Mihovska. A. (2013). Challenges to 5G standardization. https://itunews.itu.int/En/4619Challenges-to-5G-standardization.note. ITU—R Report M.2290. https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-M.2290-2014-PDF-E.pdf. The 5G economy: How 5G technology will contribute to the global economy. HIS Economics/HIS Technology. https://www.qualcomm.com/media/documents/files/ihs-5g-economic-impact-study.pdf. G Americas. 5G spectrum recommendations http://www.5gamericas.org/files/9114/9324/1786/5GA_ 5GSpectrum_Recommendations_2017_FINAL.pdf. Rappaport, T. S., et al. (2013). Millimeter wave mobile communications for 5G cellular: It will work. IEEE Open Access. https://doi.org/10.1109/AC-CESS.2013.2260813. Badoi, C. I., et al. (2011). 5G based on cognitive radio. Wireless Personal Communications, 57, 441–464. https://doi.org/10.1007/s11277-010-0082-9. Demestichas, P., et al. (2013). 5G on the horizon: Key challenges for the radio-access network. IEEE Vehicular Technology Magazine, 8(3), 47–53. ITU—R Recommendations M. 2083. www.itu.int. Prasad, R. (2012). Introducing 5G standardisation. In 11th GISFI standardisation series meeting, 17 Dec 2012, Bangalore, India. Prasad, R. (2009). Convergence: A step towards unpredictable future. In Wireless technology conference, EuWIT, European, 28–29 Sept. 2009 (pp. 187–191). Radio access and spectrum FP7 future networks cluster. http://www.academia.edu/9872297/Radio Access and Spectrum FP7 FutureNetworksCluster. Consultation paper on auction of spectrum dated 28 Aug 2017. www.trai.gov.in. Yu, Y., et al. (2011). Integrated 60 GHz RF beamforming in CMOS. Berlin: Springer. https://doi.org/10. 1007/978-94-007-0662-0-2. ITU—R Report M. 2376. www.itu.int. Geng, S., et al. (2009). Millimeter-wave propagation channel characterisation for short-range wireless communication. IEEE Transaction on Vehicular Technology, 58(1), 3. Radio regulation 2016 edition. www.itu.int. E-band communications corp. ‘‘light licensing’’. www.e-band.com/get.php?f.848. Tripathi, P. S. M. (2014). Radio spectrum management for future wireless communication services. Denmark: Aalborg University Press.

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P. S. M. Tripathi is currently Deputy Wireless Adviser in in Wireless Planning and Coordination (WPC) Wing of Department of Telecommunications, Ministry of Communications, Government of India. In his current position, he is associated with radio spectrum management and planning and engineering activities for telecom services in India especially for telecom services in 900, 1800 and 2100 MHz bands and also associated with spectrum auction held in India since 2010 onwards. He has more than 15 years of experience in management, strategy in Radio Spectrum Management and Radio Spectrum Monitoring Sector including implementation of a very prestigious World Bank Assisted Project on ‘‘National Radio Spectrum Management and Monitoring System (NRSMMS)’’ in the WPC Wing. He was graduated from M M M Technical University, Gorakhpur (India). He worked as Research fellow at Center for Tele-infrastructure (CTIF), Italy, Department of Electronics, University of Tor Vergata, Rome, Italy. He was selected in the year 2010 under Erasmus Mundus ‘‘Mobility for Life’’ scholarship programme of European Commission for doing Ph.D. at Department of Electronic Systems, Aalborg University, Denmark. The Degree of Doctor of Philosophy has been awarded in the 2014. Ramjee Prasad is currently Professor, Department of Business Development and Technology, Aarhus University, Aarhus, Denmark. Ramjee Prasad is the Founding Chairman of the Global ICT Standardisation Forum for India (GISFI: www.gisfi.org) established in 2009. GISFI has the purpose of increasing of the collaboration between European, Indian, Japanese, North-American and other worldwide standardization activities in the area of Information and Communication Technology (ICT) and related application areas. He was the Founding Chairman of the HERMES Partnership—a network of leading independent European research centres established in 1997, of which he is now the Honorary Chair. He is the founding editor-in-chief of the Springer International Journal on Wireless Personal Communications. He is a member of the editorial board of other renowned international journals including those of River Publishers. Ramjee Prasad is a member of the Steering, Advisory, and Technical Program committees of many renowned annual international conferences including Wireless Personal Multimedia Communications Symposium (WPMC) and Wireless VITAE. He is a Fellow of the Institute of Electrical and Electronic Engineers (IEEE), USA, the Institution of Electronics and Telecommunications Engineers (IETE), India, the Institution of Engineering and Technology (IET), UK, and a member of the Netherlands Electronics and Radio Society (NERG), and the Danish Engineering Society (IDA). He is also a Knight (‘‘Ridder’’) of the Order of Dannebrog (2010), a distinguished award by the Queen of Denmark.

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