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Abstract

With the exponential growth of wireless communication services that require ever increasing data throughputs. 5G mobile networks are expected to achieve high data rates and high network capacities with a very low latency to fulfill the demands of future mobile networks. However, it presents a great challenge and raise high capacity need for mobile backhauling. Accordingly, much more transmission systems and innovative solutions are required to support this growth. Millimeter wave communications play a key role in the mobile traffic backhauling as deploying optical fiber to every small node is most likely going to be too cost intensive for mobile operators. The purpose of this thesis is to show how combining microwave and millimeter wave technologies is able to fulfil 5G requirements especially high data rates and low latency, increase the backhauling link range and service availability. This solution maximize spectrum efficiency, with a promise to deliver a massive improvement in the capacity and performance levels of microwave backhaul, while at the same time accelerating the much needed shift toward the use of higher frequency bands because of the higher bandwidth availability.

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1. Introduction
1.1 Motivation

Mobile traffic has significantly increased over the last decade mainly due to the increasing number of devices accessing mobile networks, Bandwidth-hungry applications and machine type communication. 5G mobile networks are aimed at meeting the requirements for mobile communications beyond 2020. It is expected that the fifth generation of cellular networks is able to achieve 1000 times the system capacity, 10 times the spectral efficiency, 10 times the energy efficiency, 10-100 times the data rate, and 25 times the average cell throughput, compared to the fourth generation 1.

Figure 1.1: The evolution of mobile communications requirements in the upcoming decade 1.
Current cellular networks are mostly built with microwave links and fiber/copper-based links, cannot cope with the capacity, latency, reliability, energy efficiency, and cost effectiveness required for the 5G mobile networks. Mobile wireless networks should expand greatly their capacities for supporting high-density mobile users with high speed throughput services, so networks are getting denser than ever before. This results in a larger number of smaller cells producing massive data traffic. The massive data traffic shall be connected through the mobile backhaul network with extreme requirements in terms of capacity, latency, reliability, energy efficiency, and cost effectiveness to the core network. Millimeter wave communications play an important role in mobile backhauling as deploying optical fiber to every small node is most likely going to be too intensive high cost for Mobile operators. Millimeter wave systems operating for example at 70-80 GHz (E-Band) can provide high throughput with very high frequency reuse by utilizing very narrow beams.

Motivated by the above discussion, the 5G backhaul research has been triggered, aiming at bridging the gap between the requirements stipulated by the 5G RAN and the realistic backhaul capabilities, evolving the current backhaul to meet 5G expectations. In this thesis, we will investigate feasibility, advantages, and challenges of future wireless communications backhauling over the millimeter wave frequencies then we will discuss point-to-point link bonding / carrier aggregation of different carriers and frequency band combinations to meet the extreme requirements of the future 5G backhaul networks.

1.2 Purpose and Scope

With the advance of broadband wireless access and next generation mobile systems, huge demands are being placed on backhaul infrastructure. As cost-effective alternatives to fiber backhaul, high speed and long distance wireless backhauls are becoming increasingly attractive. However, there are significant technical challenges such as how to achieve higher spectral efficiency and extend transmission range. For long range wireless backhaul, the major challenge is to achieve multi-Gigabit throughput rate at microwave frequencies. We therefore purpose dual band solution combining both microwave and millimeter wave backhaul technologies to provide up to 10 Gbps data rates over several kilometers range. Combining multiple carriers in the same or different frequency bands into a single link referred as Multiband or Carrier Aggregation, will provide the benefits of lower frequency availability alongside higher frequency band capacity. This new wireless transmission solution will can significantly increase transmission capacity, availability and leading to an efficient use of the available spectrum.

1.3 Structure of the thesis

Chapter 2 will introduce the necessary background knowledge of wireless cellular and chapter 3 provides the basic theory about mobile backhaul, technologies and challenges. Chapter 4 focuses on millimeter wave and microwave Backhauling design, challenges, and attenuation and losses. Chapter 5 contains the technical study of multiband / carrier aggregation, purposes the dual band solution, and contains complete link budget and performance simulation for a dual band solution example. Finally conclusions are given in with proposals for further research.

2. Mobile networks evolution

2.1. Introduction

Mobile communication has achieved extreme technology innovations and commercial success over several generations of evolution. The explosive growth of data traffic, great increase of services in connection and continuous emergence of new services are main drivers of future mobile networks. Over the years, mobile wireless communications have evolved from analog voice calls to current digital technologies, which are able to provide many services with data rate up to megabits per second. This rapid development in mobile communications as well as the ever-increasing number of Internet mobile devices, e.g. smart phones, tablets, and laptops, leads to the exponential growth in broadband traffic. This chapter will introduce the mobile networks evolution path towards the fifth generation. 5G is not yet standardized at this time, it is still in pre-standardization phase. Large players in the industry are investing so much on the research of the next generation mobile networks which are expected to launch commercially in 2019 and beyond.

2.2. The First Generation (1G)

First generation mobile radio networks were the first wireless networks utilizing cellular concept introduced in the 1980s. They were based on analog technology operating on 150MHz and up. There were no international standards available, each country had their own 1st generation radio network system (where deployed). Some most known 1G standards were NMT (Nordic Mobile Telephone) in Nordics, Switzerland, the Netherlands, Eastern Europe and Russia and eastern Europe, AMPS (Advanced Mobile Phone System) in North America and TACS (Total Access Communications System) in UK. Multiple access scheme used in most 1st generation mobile radio networks was based on FDMA (Frequency Division Multiple Access), where mobile stations were allocated a specific frequency channel for a call. At that time, 1G has a lot of disadvantages, for example, low capacity, no handover, high interference, and no security as voice calls were stored and played in radio towers 2.

2.3. The Second Generation (2G)

The Second generation was later appeared in late 1990’s, based on digital technology which improved the quality, security, and capacity of the network tremendously led to the explosive increase in mobile phone usage. Voice quality was much improved and short message service was provided. Also the power consumption of mobile terminals was greatly reduced which improved the mobility. There were several 2nd generation standards, but GSM (Global System for Mobile communications) became the most widely spread of all, with data rate up to 64 kbps. The multiple access method in GSM was based on combination of FDMA (Frequency Division Multiple Access), and TDMA (Time Division Multiple Access), where the allocated spectrum was divided to narrow carriers, then again were divided to time slots while IS-95 (Interim Standard 95) was based on CDMA (code division multiple access). These resources were allocated according to need. GSM was first designed for traditional circuit switched speech traffic only, but later packet switching was added as extension. GPRS (General Packet Radio Service), which was considered as “2.5G” technology, brought packet switching to GSM with data rates reaching up to 172 kbps. Later the data rates were further expanded by EDGE (Enhanced Data rates for GSM Evolution) standard, so called “2.75G” technology, which used higher modulation and coding schemes combined with timeslot aggregation. The maximum theoretical net throughput in EDGE network could reach 384 kbps. 2 3.

2.4. The Third Generation (3G)

In late 2000, the 3G was first introduced with the capability of providing data rate up to 2 Mbps, which high-speed mobile access was merged to Internet Protocol (IP) based services. Third generation networks were defined by International Telecommunications Union (ITU) in recommendation called IMT-2000. The most widely used 3G standard called 3GPP (3rd Generation Partnership Project), whose system based on WCDMA (Wideband Code Division Multiple Access) which was deployed internationally by all major network vendors. The 3GPP used an umbrella term called Universal Mobile Telecommunications System (UMTS) as it was designed to be used worldwide. The initial 3GPP Release 99 (refers to 1999) based 3G UMTS network changed from narrow FDMA based carriers to a 5 MHz wide band from which capacity was allocated to users simultaneously using orthogonal codes instead of frequency channels.
The 3rd generation standards focused more on packet switching data services while maintaining the circuit switched speech services. In addition, global roaming and improved voice quality were made possible in 3G. However, the major disadvantage in 3G handsets was the increase in power requirement, compared to that in 2G. With some added improvement, 3G is able to support data rate of up to 5-30 Mbps by utilizing advanced technologies like High Speed Uplink/Downlink Packet Access (HSUPA/HSDPA) and Evolution-Data Optimized (EVDO). 3.5G also plays the role of an intermediate generation bridging 3G and the fourth generation 2 3.

2.5. The Fourth Generation (4G)

The fourth generation mobile radio networks were defined in IMT-Advanced recommendation by ITU. There were initially two competing 4G standards; WiMAX (Worldwide Interoperability for Microwave Access) by IEEE (Institute of Electrical and Electronics Engineers) and LTE (Long Term Evolution) by 3GPP. Later releases of LTE called LTE-Advanced (focus is on higher capacity) integrated the functions defined in IMT-Advanced to officially be categorized as a 4G network, such as coordinated multipoint transmission (CoMP) and inter cell interference cancellation (ICIC). The spectrum usage was further expanded from 3G networks 5 MHz up to 20 MHz in a single channel. It is possible to aggregate multiple 20 MHz blocks to increase the throughput (e.g. 2 x 20 MHz channels can offer 300Mbps).
The multiple access method was selected to be OFDMA (Orthogonal Frequency Division Multiple Access), which utilizes a range of orthogonal narrow carriers inside the (e.g. 20 MHz) channel. The mainstream variant is FDD (Frequency Division Duplexing) based system which is used almost everywhere used. The other variant is TDD (Time Division Duplexing) based. FDD uses separate frequency bands for uplink and downlink, where TDD uses single frequency band and divides uplink and downlink based on ratio of uplink and downlink timeslots.
The additional advancement in 4G is to be fully packet based solution based on IP, in which voice, data, and multimedia are imparted to subscribers on every time and everywhere basis, while supporting higher network speed, faster download speed and lower latency, compared to previous generations. 4G networks could accommodate applications that utilize large bandwidth such as Multimedia Messaging Service (MMS), Digital Video Broadcasting (DVB), High Definition TV content, Video Chat, and Mobile Television.
Voice service over 4G network has not been widely used, but operators tend to use a technology called Circuit Switched Fallback (CSFB), where the network instructs the handset to change from 4G network to 3G or 2G network. Fallback to 3G network will still enable simultaneous data while calling, but in case fallback to 2G, mobile data will be put on hold until the call has finished. In any case the data performance will be greatly affected during a call when CSFB is used. After the call the handset will eventually switch back to 4G network for better data performance. Voice over LTE (VoLTE) has been already deployed by some operators, but globally many operators are still planning or testing. 3 4 5

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