Handoff Management in Radio over Fiber 60 GHz Indoor Networks

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Handoff Management in

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Handoff Management in

Radio over Fiber 60 GHz Indoor Networks

Proefschrift

ter verkrijging van de graad van doctor aan de Technische Universtiteit Delft,

op gezag van de Rector Magnificus prof. ir. K.C.A.M. Luyben, voorzitter van het College voor Promoties,

in het openbaar te verdedigen op dinsdag 11 November 2014 om 12:30 uur

door

Quang Van BIEN

MSc in Electronics & Telecommunication at Hanoi University of Technology, Vietnam

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Dit proefschrift is goedgekeurd door de promotor: Prof. dr. ir. Ignas G. M. M. Niemegeers

Copromotor:

Dr. R. R. Venkatesha Prasad

Samenstelling promotiecommissie: Rector Magnificus,

Prof. dr. ir. Ignas G. M. M. Niemegeers, Dr. R. R. Venkatesha Prasad,

Prof. dr. ir. P. G. M. Baltus,

Prof. dr. ir. S.M. Heemstra de Groot, Prof. Bala Natarajan,

Dr. ir. M. J. Bentum, Dr. ir. J. H. Weber, Prof. dr. ir. R. E. Kooij,

voorzitter

Technische Universiteit Delft, promotor Technische Universiteit Delft, copromotor Technische Universiteit Eindhoven Technische Universiteit Eindhoven Kansas State University, USA Universiteit Twente

Technische Universiteit Delft

Technische Universiteit Delft, reservelid

Copyright c 2014, Quang Van Bien

ISBN 978-90-6464-830-4

Printed in the Netherlands by GVO drukkers & vormgevers B.V. Typeset by the author with the LA_{TEX Documentation System.}

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Contents

Introduction

1.1 Indoor Wireless Networks

Wireless communication is playing an important role in our daily life since it offers flexibility and mobility. Currently, there are more than 3.2 billion users and a hundredfold increase of traffic is expected by the year 2017 [1]. In the future, the home and office networking environments are predicted to be dominated by a variety of multimedia services like wireless High-definition and Ultra High-definition television (HD and UHDTV), wireless home entertainment and virtual wireless offices [2]. In order to support these applications, the indoor wireless network should provide the user with a transmission capacity of hundreds of Mbps using short-range Gbps wireless technology and using techniques like antenna diversity, beam-forming, sophisticated coding schemes, etc. With 5 GHz of unlicensed spectrum available at the 60 GHz band, the millimeter wave radio at 60 GHz becomes a promising air interface for future home networks.

1.1.1 Multimedia Applications

In an indoor environment, there are many types of devices such as HD and UHDTVs, DVD players, laptops, tablets, and smart phones which should be connected in a wireless network. On top of that there will be Machine to Machine (M2M) communication, involving a multitude of consumer electronic devices that need to communicate and be controlled remotely. Indoor networks were typically for sharing data, Internet access and peripherals. Now, they are dominated by advanced

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1. Introduction

multimedia applications such as HD and UHDTV, IPTV, on-line games, virtual offices, etc. People should be free to move around in their home with their mobile devices while watching a UHD movie from a storage device located in another room, transferring it to a display in the meeting room, and controlling the lighting. Six application categories for indoor networks are presented in [3].

• Broadband Internet sharing - Cloud services, which demand broadband Internet access from multiple devices in the house, is growing faster than expected. People can access their data, files and multimedia applications using cloud computing. The ability to have broadband Internet connection in the house is of special importance. It can be through digital subscriber line (DSL) technologies (summarized as xDSL), Fiber to the home (FTTH) or wireless. This is a key driver for a total solution for connected homes.

• Communication and collaboration - Instant Messaging, VoIP, Skype or Facetime-like applications, online games etc. are ubiquitous.

• Peripheral and device sharing - Devices such as scanners and printers are already accessible from any location in the building through an indoor network. • File sharing - Calendars, address books, documents etc. can be accessed from

any devices in the home.

• Sensing, remote control and monitoring (M2M) - These applications are intended for realizing smart building. The demand for these applications in residential homes is increasing. Traditional applications such as automation of lighting, security, surveillance etc. and new applications like demand-side energy management and health care monitoring will be an important part of a home network.

• Game, audio and video distribution: real-time or stored audio and video etc. can be distributed to any device in the home. In [4] this is further grouped into four categories: (U)HD streaming, (U)HD interactive, (U)HD messaging, and (U)HD broadcasting. This requires 1 Gb/s data rate and 500 GB storage per hour.

Table 1.1 illustrates the required data rates for wireless applications in the six categories. In the six categories, the first four categories are provided in the traditional Local Area Networks (LAN). The last two categories are becoming the indispensable part of indoor networks. Most of them require the wireless networks to provision high data rates of several hundred of Mbps.

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1.1. Indoor Wireless Networks

Table 1.1: Wireless applications

Application Capacity per user (Mb/s) Uncompressed 8K UHDTV (7680x4320) 47776

Uncompressed 4K UHDTV (3840x2160) 11944 Current Uncompressed HDTV (1920x1080) 2986 Current Compressed HDTV (1920x1080 - MPEG2) 20

Wireless LAN Bridge 100-1000 Virtual Reality 450 Wireless IEEE 1394 300 High quality video conference 10-100

Wireless surveillance camera 4-10 Wireless Video Phone 1.5 Wireless remote control 0.01 Wireless embedded systems 0.01

1.1.2 Indoor Wireless Technologies

One of the radio technologies introduced in the early stage of indoor wireless networking is Digital Enhanced Cordless Telecommunications (DECT). The DECT standard was developed by European Telecommunications Standards Institute (ETSI) for wireless communications over unlicensed spectrum 1880 - 1900 MHz. This standard can offer upto 2 Mbps data rate and communications range of upto 200 m indoor and upto 6 km using a directional antenna outdoors. In 2006, DECT Forum introduced a new DECT based home networking technology, named "Cordless Advanced Technology - internet and quality (CAT-iq)" [5], which aims for VoIP and other Internet-based services on the standard cordless DECT phones. There are roughly 800 million DECT devices in the world. DECT is optimized for the new emerging M2M wireless communications, which is expected to grow exponentially.

Wireless Personal Area Networking (WPAN) is also an indispensable part of the ubiquitous communication landscape, it is designed for low power and short ranges. The dominant WPAN technologies are part of the IEEE 802.15 standards suite [6]. The best known is Bluetooth operating in the 2.4 GHz band. It was standardized as IEEE 802.15.1. The latest version is Bluetooth v4.0 with low energy, known as Bluetooth Low Energy (BLE). HomeRF is a wireless technology for home networking [7]. It is based on the IEEE 802.11 FHSS standard. HomeRF supports high-quality voice communication and incorporates with DECT. Another standard released in 2001, IEEE 802.15.4 known as ZigBee, is for low-cost and low power ubiquitous wireless networking. IEEE 802.15.4 operates at the 868/915 MHz and

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1. Introduction

2.4 GHz to provide 20/40 Kbps and 250 Kbps. Thus, ZigBee is mainly designed for command and control, not for video and high quality audio, although it can send text or voice messages. Moreover, ZigBee has no mechanism for QoS provisioning. IEEE 802.15.3 specifies MAC/PHY standards to provide high data rate connectivity among devices for WPAN communication [8]. Sub-task group 802.15.3c formed in 2005 specifies a new millimeter wave based PHY which operates in the unlicensed 57-64 GHz band. It can support high data rate (over 3 Gbps) applications, e.g., high speed Internet access, HDTV, etc. WPAN and Wireless LAN (WLAN) technologies are expected to complement each other to provide connectivity to end-users in the indoor environment.

Table 1.2 presents a summary of some current and emerging wireless standards and their operating frequencies. Most of the standardized in-home radio technologies have been concentrating on the 2.4 GHz range (e.g., Bluetooth, IEEE 802.11b/g, HomeRF, IEEE 802.15.3) and 5 GHz (e.g., IEEE 802.11a, HIPERLAN/2) unlicensed bands. The limited bandwidth restricts the highest achievable data rate to the order of 100 Mbps. These radios are designed to support the home networks today, as they are typically oriented towards sharing data, Internet access and peripheral devices. However, they are not sufficient for the future of advanced multimedia applications like UHDTV, IPTV, multi-player gaming, and VoIP. These HD or UHD multimedia applications require new radio solutions for enabling Gbps high speed indoor communications. There have been many research initiatives on seeking solutions from millimeter wave radios. With the huge unlicensed bandwidth of 5 GHz, 60 GHz radio has recently been a promising candidate for providing multi-Gbps radio links for short range line-of-sight (LOS) communications. Currently, six standards define physical layer (PHY) specifications operating at the 60 GHz band. They are IEEE 802.15.3 c, IEEE 802.11 ad, IEEE 802.16 e, Wireless HD, ECMA, and WiGig. The investigations have focused on using 60 GHz radio as a means of cable replacement for high data rate communication between HD multimedia devices; for example, a HDTV set and a Blueray player in close vicinity within a room. The future home network will require high speed connectivity in the entire physical dwelling site, e.g., people would like to have their bedroom (U)HDTV display connected to a media player in the living room; therefore, a 60 GHz indoor network for connecting all devices in indoor would be a solution.

1.1.3 Radio over Fiber 60 GHz indoor networks

The factors driving the demand of the indoor networks are electronic consumer devices, wireless technologies, high bandwidth multimedia and M2M applications. The indoor network should support many types of devices via many standards, and

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1.1. Indoor Wireless Networks

Table 1.2: Indoor wireless standards

Wireless Standards Frequencies [GHz] Data Rate [Mbps]

IEEE 802.11 2.4 2 ETSI HomeRF 2.4 1.6 IEEE 802.11b 2.4 11 IEEE 802.11a 5 54 IEEE 802.11n 2.4/5 300–450 ETSI HiperLAN/2 5 54 IEEE 802.11g 2.4 54 IEEE 802.15.1 (Bluetooth) 2.4 3-24 IEEE 802.16 2-60 54 IEEE 802.15.3 (UWB) 60 3000 WirelessHD 60 4000 IEEE 802.11ad 60 6500

with multiple bandwidth-level applications. In addition, it must be easy to use, reliable and low cost. Thus, when designing an indoor network, it is necessary to consider the following requirements:

• Multi-standard support.

• A wide range of data rates, extending to 1 Gbps.

• Quality of Service (QoS) support. crucial for interactive and streaming appli-cations.

• Ease of use: installing and managing the network should be simple. Home networking products and solutions target a large audience of residential users who should not be assumed to have technological know-how.

• Low cost: it is a consumer product.

The 60 GHz band offers an opportunity to cope with the increasing demand of high bandwidth multimedia applications. However, the high attenuation loss of a 60 GHz channel reduces the coverage. Each antenna can normally cover only one room, thus, a number of antennas is required to cover a whole building, at least one antenna per room. This means that the complexity of networking and the cost of the antenna points could become significant issues.

The massive penetration of last mile access technologies such as xDSL and cable are proposed in the business and household environments. FTTH is one member of the

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1. Introduction

to-the-x (FTTx) family which includes to-the-building (FTTB), Fiber-to-the-premises (FTTP), Fiber-to-the-desk(FTTD), Fiber-to-the-curb (FTTC), and Fiber-to-the-node (FTTN). The use of optical fiber can bring higher data rates over longer distances (in order of kilometers). FTTH is the most future-proof broadband infrastructure capable of delivering media-rich applications such as HDTV. For example, GPON as ITU-T Recommendation G.983 series can provide triple play services with a data rate of up to 2.488 Gbps downstream and 1.244 Gbps upstream. Since the walls and windows of buildings can block cellular radio signal, these (outside) networks (3 G, 4 G) may not cover the indoor areas. This requires the deployment of a distributed antenna system (DAS) inside the building. This also creates an opportunity to offload the (3G and 4G) traffic from the cellular system to an indoor network, directly connected to the core of the cellular networks, bypassing the radio access networks.

Radio over Fiber (RoF) 60 GHz indoor networks, which utilize the flexibility and mobility of 60 GHz and the low cost and high capacity of optical fiber, have been recognized as enablers of a flexible, cost-effective wireless broadband access infrastructure. In such systems, the radio access control, signal generation, and signal processing are carried out at a centralized control station. The radio signal (RF) is delivered to simplified remote antenna sites via an optical fiber distribution network. These systems can take the advantages of optical fiber such as low cost, light weight, and huge transmission bandwidth to be the distribution medium for delivering 60 GHz radio signals. The antenna simplification is one reason to reduce the complexity and the deployment cost of RoF systems. RoF systems could be the answer for future indoor networks [9].

1.2 The Problem Statement

To provide the high data rates for future multimedia applications, one way is extending the spectrum efficiency by using complex techniques such as diversity and coding schemes. The other way is by studying new air interfaces with a vast available spectrum, for instance: 17 GHz, 30 GHz and 60 GHz. With valuable characteristics, the 60 GHz band has been selected in this dissertation. Some properties of 60 GHz radio are listed below.

1. The vast unlicensed 5 GHz spectrum.

2. The large oxygen absorption – short propagation distances enabling higher frequency reuse (spatial multiplexing) as well as better security (more difficult

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1.2. The Problem Statement

to eavesdrop of radio signals).

3. Millimeter wavelength enabling small size antennas and beam-forming antennas with a small form factor [10].

By extending the coverage of 60 GHz, reducing the complexity of a network and simplifying antennas, the 60 GHz indoor network employing RoF is very suitable for high data rates and QoS stringent multimedia application delivery. However, the disadvantages of 60 GHz radio and the delay introduced by the optical distribution network bring some challenges when designing such a network.

1. The propagation path attenuation of a 60 GHz channel is quite high. It is in the range from 3 dB to 7 dB due to glass, and 36 dB due to 15 cm thick concrete. Therefore a radio cell is small and typically confined to a room; and walls become the cell boundaries. Therefore, to cover a whole building, a considerable number of antennas are deployed, which increases the infrastructure cost and the complexity of the network. To reduce the complexity of the network and the deployment cost, the simplification of antennas by employing RoF is a promising solution. In this thesis, we explore Radio over Fiber 60 GHz indoor networks (called RoF network).

2. The location of an mobile station (MS) can be used for location-based services, improving the performance of wireless networks including network planning, network adaptation, resource management and load balancing. In an indoor environment, a number of location systems have been researched and developed by universities, research centers and companies. Several artificial intelligent techniques such as Markov chains, Bayesian networks, hidden Markov models (HMM), and neural networks, have been proposed to address this. Thus the challenge is how to choose the right technique and model for the requirements of RoF networks, and apply it in an indoor environment. The HMM is a promising prediction model for using both historical location patterns of MSs and the location of antennas to predict the future location of MSs.

3. Because the 60 GHz cell size is very small, handoff in the proposed indoor network is frequent. Moreover, the overlapping between two adjacent cells is small, narrow and directional and usually in open areas such as doors [11]. In addition, the distribution optical network has an influence on handoff delay due to its introduced extra delay. Consequently, a handoff should be completely processed in a small overlapping area and in a short time (of the order of a few milliseconds). Thus, to solve this problem, a proper handoff algorithm is

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1. Introduction

required. If the handoff algorithm uses the location information of a mobile user, a handoff could be fast.

4. One of the challenges of mobile networks is the dynamic traffic due to the mobility of users. It is difficult to guarantee QoS in terms of the call dropping probability (CDP) and the call blocking probability (CBP). Thus, several handoff schemes have been proposed to manage bandwidth resources efficiently. Many of them are operating with the support of the location information of the MS from GPS. However, GPS cannot work properly in an indoor environment. Thus, in order to improve QoS, the handoff scheme using the indoor prediction location system is potentially a good solution.

5. Besides the advantages of optical fibers, the optical distribution network also introduces additional propagation delay with respect to a non-RoF wireless network. As the requirements of the future home network, the proposed indoor network should support multiple MAC (Media Access Control) standards such as IEEE 802.11, IEEE 802.16, IEEE 802.11 ad and IEEE 802.15.3 c. The feasibility of each MAC protocol to operate in a RoF network should be investigated.

1.3 Summary of Main Contributions

The main contributions of this dissertation are listed as follows.

1. The dissertation introduces a novel Radio over Fiber 60 GHz Indoor Network for advanced high speed applications. Handoff research in wireless networks and in RoF networks is discussed and accessed. Two additional components prediction model and positioning system are introduced to improve the handoff performance.

2. A movement prediction model is proposed in indoor environments, which is based on the HMM. This model could provide a more accuracy estimation via the prior knowledge. The proposed prediction model is examined by experiments with two datasets: a real data for an employee and simulated data for a guest.

3. Predicting the next location of the MS can help the system to know the direction information of the MS for improving the handoff performance. A direction assisted handoff algorithm is designed for RoF networks. The simulation of this algorithm and conventional handoff algorithms has been performed in this dissertation.

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1.4. Thesis Outline

4. The bandwidth allocation problem in a cell in RoF networks is formulated. Using the next location of the MS, we propose a handoff scheme that allows the system to reserve a specific resource on the potential cells for handoff calls. Therefore, the system can improve QoS and handoff performance.

5. The feasibility to support multiple MAC standards, IEEE 802.15.3 c and IEEE 802.11 ad, has been analytically investigated in terms of throughput and bandwidth efficiency for different ACK mechanisms. The ACK mechanisms are compared. Thus, depending on the requirements of system, the designer could choose the most adaptive ACK mechanism. The effect of fiber length on the throughput is also examined.

1.4 Thesis Outline

The dependency among chapters of this dissertation is indicated in Fig. 1.1. The remaining of this dissertation is organized as follows. Chapter 2 introduces the Radio over Fiber indoor network operating at 60 GHz. We also present necessary background material on 60 GHz networks and Radio over Fiber techniques. In Chapter 3, handoff requirements and issues in wireless networks (such as GSM, WLAN) and 60 GHz network are investigated and simulated. Chapter 4 has pre-sented movement prediction techniques and proposed the adaptive indoor movement prediction developed from the HMM. With the use of direction information, a handoff algorithm has been proposed in Chapter 5. In order to improve QoS by managing the bandwidth resource, the new handoff scheme based on the movement prediction is present in Chapter 6. As the requirement of supporting multiple MAC standards, IEEE 802.15.3 c and IEEE 802.11 ad are introduced and compared in Chapter 7. The IEEE 802.15.3 c is modeled and analysed in this chapter. Finally, Chapter 8 summarizes the main contributions of the work and proposes the possible directions of future research.

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1. Introduction

Chapter 2 Radio over Fiber 60 GHz

Indoor Networks

Chapter 3 Handoff in Wireless Networks

Chapter 7 Feasibility of IEEE 802.15.3c

and IEEE 802.11ad for RoF Networks

Chapter 5 A Direction Assisted Handoff

Algorithm

Chapter 4 Movement Prediction in Indoor

Environments

Chapter 6 Bandwidth Resource Management in RoF Networks

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Chapter 2

Radio over Fiber 60 GHz Indoor

Networks

60 GHz radio is a promising technology that can enable wireless transmission data rates of the order of Gbps. In this chapter, we introduce the background of 60 GHz radio, i.e. the worldwide regulations and standardization activities, and the fun-damental propagation properties, (in Section 2.1). Then Section 2.3 gives a brief introduction of RoF technology using Optical Frequency Multiplication (OFM). Thereafter, by combining two technologies, an RoF network for high data rate multimedia applications is presented in Section 2.3. Finally, Section 2.4 concludes this chapter.

2.1 60 GHz Radio Background

The 60 GHz is a new emerging technology for broadband multimedia applications, however 60 GHz and higher radio research has been done since the early 1900’s by J.C.Bose, who conducted experiments using wavelengths from 2.5 cm to 5 mm (60 GHz radio) [12]. However, it was too early to use 60 GHz for any applications at that time. Until now, when modern optical transmission techniques in outdoors can reach up to Tb/s, 60 GHz radio is now considered as the promising candidate to Gbps data rate wireless communications in indoor environments. 60 GHz radio has several special characteristics which give it great commercial potential. First, one can use the unlicensed 5 GHz of spectrum, a very high bandwidth. Second, the 60 GHz circuitry can be easily integrated in to electronics devices. Beside its

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2. Radio over Fiber 60 GHz Indoor Networks

advantages, there are some issues of the 60 GHz band that the network designer should consider when designing 60 GHz networks. In this section, we discuss the basic characteristics of this 60 GHz band.

2.1.1 Worldwide Regulation and Standardization

Currently, several organizations are standardizing 60 GHz short-range wireless com-munications, e.g., IEEE 802.15.3 c, WirelessHD, IEEE 802.11 ad, Wireless Gigabit Alliance, and ECMA. Let us examine their activities.

IEEE 802.15.3 c

IEEE 802.15 is a working group of the IEEE which specifies WPAN standards. It includes seven task groups. Task Group 3 is responsible for high data rate WPAN. IEEE 802.15.3 defines a standardization of MAC and PHY for such WPANs (11 to 55 Mbit/s, which aims to enable wireless connectivity of high-speed, low-power, low-cost, and multimedia-capable portable consumer electronic devices [13]. IEEE 802.3 a specifies a high rate UWB PHY, an enhanced amendment to IEEE 802.15.3 for applications of imaging and multimedia. In May, 2006, the IEEE802.15.3 b enhanced IEEE 802.15.3 to improve implementation and interoperability of the MAC. However, these standards are still not satisfying the demand for very high data rate applications. Thus, in March 2005, the IEEE 802.15.3 Task Group 3c [13] was formed to develop a 60 GHz based alternative PHY for the existing IEEE 802.15.3 WPAN. This standard operates in the range of 57-64 GHz (mmWave), the mmWave unlicensed band defined by FCC 47 CFR 15.255. It was approved in September 2009 and called the IEEE 802.15.3c-2009. The 60 GHz based WPAN has a coupe of valued features.

Firstly, the mmWave–based WPAN can support data rates of at least 1 Gb/s, making it suitable for applications such as broadband Internet access, video on de-mand, and optional data rates in excess of 3 Gb/s applications such as uncompressed HDTV.

Secondly, the mmWave–based WPAN systems can coexist with existing wireless communication systems such as WiFi, Bluetooth, 2 G/3 G/4 G networks, and UWB systems due to the large frequency difference.

The IEEE 802.15.3c–2009 specifies three PHY modes for different purposes. The first is a single carrier mode (SC) for low power and low complexity devices. The second is a high–speed interface mode for low–latency bidirectional data transfer.

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2.1. 60 GHz Radio Background

And the third one is an Audio/Video mode for uncompressed high definition video and audio applications.

WirelessHD

The WirelessHD Consortium was formed by leading technology and consumer electronics companies, such as Intel Corporation, LG Electronics Inc, Panasonic Corporation in 2006 to develop the first industry–standard next generation wireless digital interface specification for consumer electronics, PC, and portable prod-ucts [14]. Their main focus is to enable wireless HDMI for streaming compressed and uncompressed Audio/Video at resolutions of up to 1080p. It may be the first global standard for 60 GHz applications based on the standard IEEE 802.15.3 c. The first version of Wireless HD specification (version 1.0) was released in January 2008. The second version, WirelessHD specification version 1.1 published in May 2010, specifies several capabilities including:

• Supports data rates of at 10 – 28 Gb/s, more than 20x faster than the highest 802.11n data rates,

• Support of portable devices,

• Defines 3D formats and resolutions for WirelessHD devices, • Data networking using IP,

• HDCP 2.0 content protection over WirelessHD.

IEEE 802.11 ad

The IEEE 802.11 is a set of standards to implement WLANs which have been developed successfully in the commercial market. IEEE 802.11 networks can provide data rates of up to 150 Mb/s (IEEE 802.11 n). This is less than the requirements of high speed multimedia applications such as HDTV and definitely UHDTV. In order to meet the high data rate demand, the IEEE 802.11 ad Task Group [15] was formed to modify both the IEEE 802.11 PHY and the IEEE 802.11 MAC to enable it to operate in the 60 GHz band. IEEE 802.11 ad is developed from the IEEE 802.11 VHT (Very High Throughput – IEEE 802.11 ac) study group and should compete with Gigabit WiFi in some applications in the future. It featured devices that are expected to be compatible with the existing IEEE 802.11 services, facilities and network structures since it supports session switching between 2.4 GHz, 5 GHz and 60 GHz bands.

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The final IEEE 802.11ad-2012 specification was published in December 2012. This standard is expected to reach the market sometime in 2014.

Wireless Gigabit Alliance

Another industry-led organization promoting mmWave based wireless communication is the Wireless Gigabit Alliance (WiGig), established in May 2009 [16]. WiGig Alliance is defining a unified specification that enables PCs, consumer electronics and hand-held devices in a typical room to communicate without wires at Gbps data rates. The speed specified by WiGig is more than 10 times higher than current wireless LANs. The version 1.0 of the WGA MAC and PHY, named as WiGig, was published in February 2010, and the version 1.1 was released in April 2011. Since a proposal based on the WiGig version 1.0 specification was contributed to IEEE 802.11 ad Task Group, so that the published IEEE 802.11ad and WiGig v1.2 MAC/PHY final specifications are essentially identical.

ECMA

European Computer Manufacturers Association (ECMA) was founded in 1961 to develop the standards for Information and Communication Technology and consumer electronics [17]. ECMA International published their standard of 60 GHz for short range communication as ECMA-387. The first edition of the standard ECMA-387 was published in December 2008 and the second edition in December 2010. This standard was passed through the ISO/IEC fast-track approval procedure to become ISO/IEC 13156:2011.

This ECMA-387 standard provides high rate wireless personal area network (including point-to-point) for multimedia streaming and data transfer by specifying a PHY, distributed MAC sub-layer and an HDMI protocol adaptation layer (PAL) for 60 GHz wireless networks. It also specifies high data rates WPANs (including Point-to-Point) for transporting both bulk data and multimedia streaming.

2.1.2 The 60 GHz Band

Spectrum Allocation

Many countries and regions in the world have their own regulations about the unlicensed frequency bands around 60 GHz. The unlicensed frequency allocations at around 60 GHz is not the same in each region, but there is substantial overlap; at least 3.5 GHz. Currently, the US and Canada, the European Union, Japan, South

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2.1. 60 GHz Radio Background 57 58 59 60 61 62 63 64 65 66 67 57.05-64 United States 57.05-64 Canada 57-66 EU 59-66 Japan 57-64 Korea 59.4-62.9 Australia

Figure 2.1: The unlicensed frequency bands around 60 GHz in different regions in the world.

Korea, and Australia have approved an unlicensed spectrum allocation in the 60 GHz region. The situation is illustrated in Figure 2.1.

Transmit power

The emission power is also regulated differently by the different countries similar to the spectrum allocation. In Europe, the Equivalent Isotropic Radiated Power (EIRP) of the transmitter is limited to 57 dBm. 500 mW (27 dBm) is the peak transmit power imposed by the USA and Canada. The average and the peak transmission power densities at 3 m distance should be controlled below 9 and 18µW/cm2_{, equivalent}

to EIRP of 40 and 43 dBm. In Japan, the average transmission power should be less than 10 mW (10 dBm) and the transmit antenna gain is limited to 47 dBi. In Australia the peak transmission power and EIRP are limited to 10 mW, and 52 dBm, respectively. In worldwide regulations, the transmission power is limited to 10 dBm and the EIRP is limited to 25 dBm for portable devices and 37 dBm for mobile devices.

Oxygen absorption

The millimeter wave region of the electromagnetic spectrum is characterized by high levels of atmospheric radio frequency energy absorption. The transmitted energy is quickly absorbed by oxygen molecules in the atmosphere over a long distance. Thus the coverage of 60 GHz is limited. The path attenuation due to oxygen absorption is typically around 15 dB/km and due to water vapor is 0.2 dB/km [18]. However, in an indoor environment, the oxygen absorption is not a real issue. Thus, an indoor propagation model should be useful to evaluate the performance of a high data rate

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wireless network. It is even better if the indoor environment is completely specified in detail such as room size, presence of furniture, wall materials, etc.

Wavelength

The wavelength of the 60 GHz band is around 5 mm. This is an advantage. 60 GHz antennas are small and can be easily integrated 60 GHz transceivers for portable electronic devices. Moreover antenna-arrays for beamforming are also feasible.

Multi-path channel

Why is the multi-path channel considered for the 60 GHz band? The main reason is the strong multi-path behavior of the 60 GHz band. Typical root mean square delay spread in an office is 10 to 20 ns and excess delay spread for 30 dB attenuation is 70 ns [19]. This multi-ray propagation model considers the effects of reflected com-ponents. The propagation losses with the presence of N single reflected components and M double reflected components are given by the Eq. 2.1:

Lp(d) = 68 + 20log   1 d0 + N X i=1 ri di ei∆φi₊ M X j=1 rja.rjb di ej∆φi   (2.1)

where 68 dB is the free path loss at 1 m distance; d0 is the path length of the

direct component and di. ri is the reflection coefficient of i single reflected ray, rja,

rjb are the reflection coefficients of the j double reflected rays on a and b surfaces.

∆φi= 2π_λ∆li and ∆φj = 2π_λ∆lj are the phase differentials between the direct ray

and the reflected rays with ∆li and ∆lj the differential path lengths between the

direct and the i single and j double reflected rays, and λ is the wavelength (5 mm). However, the third and fourth reflected components do not contribute to the average power at 60 GHz because of high attenuation loss. So, we should reduce the number of rays by ignore such components in the considered model. The two-ray model is one case of the multi-ray model and it is usually used for many simulations due to it is lower complexity. It may be enough to describe the indoor signal propagation without affecting the accuracy.

Coverage

At 60 GHz there is much more free space loss than at 2.4 GHz or 5 GHz. The Friis free-space propagation model [20] shows the relationship between the transmit power

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Pt, received power Pr and the radio wavelength λ as follows.

Pr Pt = GtGr _λ 4πd 2 (2.2)

where Gt, Gr are the transmit and receiving antenna gain respectively, and d is the

distance between the transmit antenna and the received antenna. λ is the wavelength (5 × 10−3m). Therefore, the free-space path loss at 1 m for 2.4 GHz, 5 GHz and 60 GHz are consequently 40.05 dB, 46.42 dB, and 68 dB. In principle, this high path loss can be compensated by the use of antennas with more directive patterns.

Walls also may attenuate millimeter waves significantly. This attenuation depends on the type of wall material and its thickness (Table 2.1). The propagation path attenuation due to glass is in the range from 3 dB to 7 dB, and due to 15 cm thick concrete it can be 36 dB. This high penetration loss for most materials in the 60 GHz band is an advantage because it limits interference and isolates from 60 GHz radios in adjacent rooms. But it is also a disadvantage, because any obstacle can block a line-of-sight or alternative path and produce strong shadow fading. Now, let us

Table 2.1: The attenuation of 60 GHz channel through materials

Material Loss at 60 GHz Loss at 2.5 GHz Drywall 2.4 (dB/cm) 2.1(dB/cm) Clear Glass 11.3 (dB/cm) 20.0(dB/cm) Whiteboard 5 (dB/cm) 0.3 (dB/cm) Mesh Glass 31.9 (dB/cm) 24.1(dB/cm)

Clutter 1.2 (dB) 2.5 (dB)

estimate the range of the 60 GHz channel. At first, the received power should be greater than the receiver sensitivity, which includes thermal noise power N , shadow margin M , and the needed signal-to-noise ratio SN R as the following equation:

Pr≥ N + M + SN R (2.3)

Secondly, considering a signal with bandwidth B = 100 MHz, the noise floor power is -94 dBm. The thermal noise power N is calculated by the equation: N = F kT B, where F = 10 is the noise figure of the receiver, k is the Boltzmann constant, and T = 290K. Shadow-margin M should be taken into account, which is assumed 10 dB on average. The transmitting power is Pt = 100 mW EIRP (20 dBm) according to

European regulations. Assuming Eb/N0is higher than 10 dB to achieve a bit error

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Using both equations Eq. 2.2 and Eq. 2.3, with the antenna gains equal to one, we can estimate the range of the 60 GHz antenna (or access point) is approximately 25 m. Hence it is suitable for short-range indoor communication. Therefore, in order to deploy a 60 GHz network, it requires a large number of antennas which operate as access points, which means that the cost of 60 GHz deployment might be a challenge.

Due to the limits imposed on the emitted power, the high temperature noise, and the high oxygen absorption, the range of 60 GHz system is short. The propagation of 60 GHz signal is easily obstructed by the movement of people, and the presence of furniture and walls. This however opens up the opportunity for spatial reuse of channels. Channels in the indoor or open areas show a strong multipath behavior because of easy reflection. So 60 GHz is usually envisaged for communication confined to a room or an open area where LOS signals from the antennas can be expected. In Fig. 4.6(b), the comparison of the coverage between the 60 GHz band and the 2.4 GHz band has been illustrated using the measured data. The 2.4 GHz system requires only three antennas or access points (AP) to cover the whole building while for the 60 GHz band we need at least one antenna per room. In [21] it is shown that the signal to interference ratio (SIR) can drop from 20 dB to 0 dB within a few centimeters in the indoor environment (Fig. 2.3).

(a) 2.4 GHz (b) 60 GHz

(a) 2.4 GHz(a) 2.4 GHz (b) 60 GHz(b) 60 GHz

Figure 2.2: The coverage of 60 GHz compared with that of 2.4 GHz in the same building

The detailed 60 GHz wireless physical layer and antenna designs are out of the scope of this dissertation. For more details on 60 GHz PHY, readers please refer to [8, 22]. In the rest of this thesis, we assume that a non-obstructed room with the

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Figure 2.3: The variant SIR along the hallway path [21]

size 10 × 10 m should be covered by a sufficient 60 GHz signal.

2.1.3 Potential Applications

Applications that might benefit from the advantages of 60 GHz are present briefly bellow.

Indoor Broadband Wireless Communication

As the explosive growth in broadband wireless networks, multimedia applications will dominate the future home wireless communications [2, 23]. They require the new wireless interfaces to offer the high data rates. The 60 GHz small cells is suitable for those indoor applications in large buildings. Some scenarios are presented in [2], which express the need of the high speed applications in practice. Two network architectures of the 60 GHz band are proposed in [2, 23]. The first one is the 60 GHz ad-hoc network. The second one is the 60 GHz employing Radio over Fiber technique. Both approaches are for the future broadband indoor networks.

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Vehicle-to-highway Communication

The leisure traveler can receive traffic information (such as traffic jams, road ac-cidents) from audio as well as video in high quality. They also want to access a limitless library of music and travel information or play on-line games. The use of millimeter waves also appears to be convenient for inter-vehicle or vehicle-to-fixed-infrastructure communication [24]. In [25], the proposed vehicle-to-fixed-infrastructure is providing high-bandwidth communication services with a uniform user interface independent of the location or speed of the user.

Railway Communication

In a modern railway transportation system, not only efficient communication be-tween railway traffic control and the trains in the network is vital, but also the communication needs of the passengers with the external world is important. Rail-way communication these days is about high speeds and high density because of a high number of passengers. During their journey, the demand of entertainment (for example playing online game, Video on Demand (VoD)) or exchanging information with the external world is high. They require the telecommunication operators to provide the large bandwidth (in orders of Gbps) and high QoS. Thus, 60 GHz is proposed to be used in railway communication [26]. With such proposed architecture, the passengers should be able to have access high speed Internet.

Aircraft Communication

What do you do on the long journey on the flight? The demand of reading news, watching films, playing games on the fight is growing higher day by day. An in-flight entertainment system for passenger aircraft requires a total data rate of the order of several Gbps with user densities of up to one thousand passengers per system. A well designed 60 GHz WLAN system is very appropriate for in-flight entertainment [27, 28]. In this design [28], each antenna serves 36 seats (passengers), antenna diversity schemes are investigated.

Inter-satellite Communication

The use of the 60 GHz band for inter-satellite links has been investigated by The National Aeronautics and Space Administration (NASA) and presented in [29]. Since satellite is totally outside the atmosphere, signals are subject to only free-space propagation loss. Thus, the 60 GHz link is working well. The proposed application uses the 60 GHz band for transmission between two or more satellites to relay signals from two stations on earth which are too far to be served by only one satellite.

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2.2. RoF technology

2.2 RoF technology

2.2.1 Optical Access Networks

The wired broadband services are mainly driven by the platforms of DSLs, cable and fiber-optic. DSLs have still been the dominant technology for broadband access, and a variety of improvements of DSLs have been proposed that will increase the data rate and line-length limitations. However, in recent years, there has been a remarkable shift from DSLs to optical fiber since the high demand of high speed Internet multimedia services as well as the rise in services and pricing competition among operators and service providers (Fig. 2.4).

The point-to-multipoint optical network known as Passive Optical Networks (PONs) is the dominant broadband network today. The simple PON includes a telecoms central stattion (CS) connecting to subscribers by using a couple of wavelengths for downstream and upstream from optical line terminal (OLT) to optical network units (ONU) and vice versa. The first PON activity was initiated in the mid-1990s by the Full Service Access Network (FSAN) group [30]. It was soon standardized by ITU – Telecommunication Standardization Sector, the ITU-T Recommendation G.983 series of standards. Based on current standards, a PON provides higher bandwidth for data applications than DSL and Cable Modem, as well as in a larger area (it can be maximum of 20 km from the OLT to the ONU). Three drivers that make the large deployment of PONs around the world have higher bit rates, high service capacity and greater service integration.

Current PON standards such as Broadband PON (B-PON) and Gigabit-capable PON (G-PON) is bases on time division multiplexing (TDM) with fiber reach up to 20 km (loss budget of 28 dB with typical split ratio 1 × 32 or smaller. B-PON is specified in ITU-T Recommendation G.983 series [31] offering numerous broadband services including Ethernet access and video distribution. G-PON is specified in ITU-T Recommendation G.984 series [32]. The G-PON is a PON technology operating at bit-rates of above 1 Gb/s. Its fiber can reach at least 20 km with a logical support within the protocol of 60 km. The recommendations can support various bit-rate options using the same protocol, including symmetrical 622 Mb/s, symmetrical 1.25 Gb/s, 2.5 Gb/s in downstream and 1.25 Gb/s in upstream and more. The IEEE 802.3 ah (E-PON) is the IEEE standard of Gigabit-Ethernet PON (1 Gb/s) [33]. In early 2006, work began on an even higher-speed 10 Gbps/second Ethernet Passive optical network (XEPON or 10G-EPON) standard, ratified in 2009 as IEEE 802.3 av [34].

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2. Radio over Fiber 60 GHz Indoor Networks Figure 2.4: Fib er-T o-The-Home (FTTH) p enetration in Dec. 2011 (sour ce: FTTH Council, publishe d in F eb. 2012)

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2.2. RoF technology

2.2.2 RoF system

A simple RoF system includes three main components (depicted in Fig. 2.5): (i) a CS controls the radio access, generates signal and process signal, (ii) antennas that contain only RF modules and (iii) the optical distribution network. The CS manages all signal processing, generating as well as centralized controlling of resources. It can help in reducing power, optimizing bandwidth utilization and channel allocation. The antenna is simply to repeat the radio signal and convert signal from electrics to optical and vice verse. Each antenna has two parts: the first part for downlink including photo-diode circuity (O/E) and RF power amplifier (PA), the second part for uplink consisting of laser diode circuity (E/O) and low noise amplifier (LNA) [35]. The radio protocol stack resides in the CS. Then, an end-to-end logical link between the CS and the MS is established. To communicate with external networks, the CS is playing a role as a gateway to outside networks such as Internet, Mobile Network, public switched telephone network (PSTN) and media resources.

In addition to the high capacity of fiber optics and the wireless access flexibility, in RoF systems, all management algorithms can be carried out in the CS in the centralized way. This centralized way is simpler to allocate bandwidth, plan cells, and increase the efficient use of resources. The next advantage of centralized processing is that the CS can easily update and monitor the status of network load which is dynamic since the mobility of the MS. Based on that information, the CS can implement bandwidth allocation algorithms to improve resource efficiency. The other advantage of the RoF system is its ability to upgrade and maintain network, firmware, management policies at the CS.

However, when operating at the millimeter-wave bands such as 60 GHz, the RoF techniques should consider the major challenge of generation and delivery of the millimeter-wave signals at the AS while keeping the link simple. During the last few years, several methods have been proposed to address this issue [36–39]. The researches proposed in [9, 36–38] mainly focus on improving the performance of RoF transmission of microwave carriers and radio signal modulation formats. However, it is not enough for an RoF system. The RoF system requires a reliable infrastructure supporting multiple wireless accesses and also having a mechanism to adapt dynamically the radio link. The work proposed in [39], which is the extension of the method in [38], the OFM is a promising method to meet the above demands of the RoF system. The Orthogonal frequency-division multiplexing (OFDM) is chosen to design the radio part. The following section introduces the principle of OFM.

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2. Radio over Fiber 60 GHz Indoor Networks Central Office Antenna 2 Controller Internet PSTN Mobile Network Cable TV ... Tranceivers ’n ’ ... n ’ Fiber Distribution ’ Antenna 1 ’ Antenna n n ’n

Figure 2.5: A simple Radio over Fiber system

fsw IM-data MZI radio signals fsc fiber link BPF radio signals fRF = n.fsw ± fsc AS CS

Figure 2.6: The OFM principle scheme

2.2.3 Optical Frequency Multiplication

The OFM is a cost-effective method to generate microwave frequencies and deliver wireless signals to a remote antenna. The OFM principle is based on harmonics generation by Frequency Modulation (FM) to Intensity Modulation (IM) conversion through a periodic band pass filter [39]. The principle of OFM is illustrated in Fig. 2.6. At the CS, a continuous wave laser source ω0 is frequency modulated in the

block FM by a sinusoid with sweep frequency fsw, and IM by the radio signal at low

frequency subcarrier fsc< fsw/2. The output signal is passed through a periodic

band pass filter such as a Mach-Zehnder interferometer (MZI). The obtained signal is transmitted via the fiber link to the antenna site (AS) to be converted into radio signal by a photodetector. After the photodetector, radio frequency components at every harmonic of fsw are obtained fharmonic= n × fsw. At the AS, the radio

signal is along with the generated harmonics at fRF = n × fsw± fscwhere n is the

nthharmonic.

The OFM technique can be deployed with both single-mode (SMF) and multimode (MMF) fiber links [39]. Based on this, a reliable RoF link can be designed. Moreover, the usage of OFM in RoF technology can benefit the following features: increasing

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2.2. RoF technology

Figure 2.7: RF bandwidth capacity [39]

cell capacity allocation, multi-standard support, dynamic radio link adaptation and remote antenna controlling.

Increasing Cell Capacity Allocation

The desired fRF signal can be selected with an adequate bandpass filter. On

the condition that the maximum RF bandwidth, fsw/2, is not exceeded, multiple

wireless signals can be transmitted simultaneously in a sub carrier multiplexing -SCM scheme [39] (Fig. 2.7). Therefore, the obtained radio signals at the AS can be selected at the same or at the different value of harmonic bands. It is possible to increase the cell capacity without the need of installing the additional transceivers (TRX) which are normally costly.

Multi-standard Support

In [39], the feasibility of the multi-standard wireless access support by one OFM link is proved. The desired fRF signal can be selected with an adequate bandpass

filter through a proper selection of fsw and fsc at the CS. By this way, different

wireless standards can be simultaneously transmitted to the antenna.

Dynamic Radio Link Adaptation

Wireless links are affected by several environmental factors such as atmosphere, fading, noise, interference, link distance and obstacles (buildings). In order to guarantee the system performance, the radio link should be dynamically adaptive. In an RoF link, this feature is depicted in two sides: at the CS and at the AS.

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• Dynamic Frequency Selection at the CS. The link adaption can be easily performed from the CS by tuning low frequency sub-carriers.

• Transmit Power Control at the AS. The transmit power can be remotely adjusted at the AS or at the CS. In order to simplify the AS, the transmit power adaptation can be done by the CS following the power regulation procedure. However, the network throughput decreases.

2.3 RoF 60 GHz Indoor Networks

2.3.1 The System Description

As discussed above, the 60 GHz band is the new air interface for wireless broadband system, and RoF techniques employing OFDM present its benefits when applying to extend the radio domain of wireless broadband systems. In order to provide high data rate applications in an indoor environment such as (U)HDTV, On-line Games, VoD, the RoF indoor network operating at 60 GHz is proposed. Beside the typical components of the RoF network, the proposed system consists of two additional components, indoor positioning and movement prediction, as depicted in Fig. 2.8. The description of each components is given below.

Home Communication Controller (HCC)

The HCC plays a role as the CS. It has interfaces with the external networks and resources. The HCC also does all the functions of generating and processing signals. As mentioned before, the management algorithms, network optimization and resource managements are performed by the HCC.

Antennas (AT)

These are similar with the AS discussed in Section 2. These ATs are simplified since all functions of signal processing are transferred into the HCC. In the proposed system, at least one AT is required to cover a room in the building.

Optical distribution network

The optical distribution network is used for transmitting signal between the HCC and the ATs. The length of fiber link is dependent on the Radio over Fiber technique we choose. With the discussed OFM technique, the fiber can be extended to more than 20 km [39].

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2.3. RoF 60 GHz Indoor Networks

Movement Prediction Database

Sensor network

Mobile Networks Internet

PDA _Laptop _Mobile

Home

Communication Controller (HCC)

Optical Distribution Network

Mobile AT1

AT2 AT3

Tablet Computer

Room 1 _{Room 2} Room 3

Video Camera

Figure 2.8: The proposed Radio over Fiber indoor network operating at 60 GHz

Positioning system

In order to predict the movement of the MS, the network should have the historical data of the movements of the MS. This can be done by deploying a positioning system. The positioning system is required to work well in an indoor environment. The positioning system is presented in the section below.

Movement Prediction

To exploit the historical data of the past movements, the prediction model should be carried out at the HCC. Up to date, several prediction models have been proposed. In Chapter 4 of this thesis, the Artificial Intelligent techniques based models are investigated and the Hidden Markov Model is developed to adapt with the proposed system.

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2.3.2 Physical Layer

The RoF technique employed by the proposed system has to transmit radio signals transparently to the ATs. This feature ensures that different modulation formats of the air interface can be delivered into the same link. This leads to the proposed system being support multiple standards simultaneously. The operation of the proposed system is described in Section 2.2.3.

Beside the transparent radio signal transmission, the system should allow other specific procedures inherent to the physical layer of the system. This requirement al-lows the provision of optical resources for bidirectional connectivity to be transparent to radio link adaptation procedures performed by the system.

Another issue the system encountered when operating at high data rate is the inter-symbol interference (ISI). The classic equalization techniques are more complex as the ISI increases. However, employing OFDM with a cyclic prefix mechanism, the system is able to void fading and ISI. To present this statement, an example design of 60 GHz system is given. Assuming that the system is designed to provision for 1 Gbps in a 1 GHz channel. The RoF network is using OFDM and 16 QAM modulation, the symbol duration τ0 is 4 ns. 1024 sub-carriers of the OFDM system make the symbol duration shorter by up to 4 µs. Thus, the guard duration (1/16 of the symbol duration) is 250 ns to protect against the ISI. The cyclic prefix length of 250 ns is much greater than the delay spread of 18 – 20 ns in indoor environments [40].

2.3.3 MAC/LLC Layer

Since the wireless protocol stack is transported transparently from the HCC to the ATs, MAC and link layer control (LLC) may not require any modifications [39]. However, in the proposed system, we should consider the effect of the additional delay introduced by the optical distribution network on the network capacity and the acceptable fiber lengths.

In the system architecture (Fig. 2.8), each antenna has its own identification number (ATi). Since the optical distribution network uses Wavelength-division

multiplexing (WDM), at least one pair of wavelengths for the uplink (λU P l) and

the downlink (λDLl) is fed to each antenna. The antenna information and its

corresponding wavelengths are stored and maintained by the HCC in Table 2.2. In addition, each antenna is usually located in a stable place of a building such as a room or corridor, or common room. Table 2.3 stored in the HCC includes the antenna’s coordinates, and the place it is located in. This table is separated from Table 2.2 due to the reason that wavelengths of each antenna could change and

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each antenna could have more than one pair of wavelengths. Each MS has its own

Table 2.2: Antenna with its corresponding wavelengths

Antenna ID Downlink Uplink ATi λDLl λU P l

ATj λDLk λU P k

Table 2.3: The geographical information table of antennas

Antenna ID X axis Y axis Height Geographical Info.

ATi ATi[x] ATi[y] hi Room l

ATj ATj[x] ATj[y] hj Room m

ATk ATk[x] ATk[y] hk Common Room 1

ATl ATl[x] ATl[y] hl Common Room1

ATm ATm[x] ATm[y] hm Corridor

unique address (M Sq). To communicate with other MSs and to fix the location

of the MS, HCC has to update the other table containing the address of the MS and the corresponding antenna to which the MS is connecting to (Table 2.4). The coordinates of each MS are stored and updated in the database in the server as Fig. 2.8.

2.3.4 Positioning System

The accurate and reliable indoor positioning systems play an important role in the future communications network [41]. The location information of the MS can be used for location-based services including navigation and tracking. It can help to improve the performance of wireless networks such as network planning, network adaptation, and load balancing. Since the transmission between receivers and satellites is not possible in an indoor environment, the most popular positioning system, GPS, is unfeasible for indoor environments. Indoor environments are more complex than outdoor environments because of the presence of various obstacles such as walls, furniture and people. The indoor propagation model could be complex and must include the multi-path effects, specific site parameters such as reflection surfaces and moving objects.

Thus, a number of wireless technologies and location techniques have been devel-oped recently for indoor positioning systems. These wireless technologies include infrared (IR), ultrasound, audible sound, radio-frequency identification (RFID),

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Table 2.4: The address table of an MS and its corresponding antenna

Antenna ID MS address ATi M Sq

ATi M Sp

ATj M So

WLAN, Bluetooth, sensor networks, ultra-wideband (UWB) and magnetic signals. The location techniques can be clarified into three groups as given below.

• The first group is based on the principle of triangulation, using the geometric properties of triangles to estimate the target location. The methods locating the target location by measuring the distance from multiple reference points are lateration methods. These methods do not measure the distance directly. But the distance is derived by using the received signal strengths (RSS), time of arrival (TOA) or time difference of arrival (TDOA), and roundtrip time of flight (RTOF) or received signal phase methods. Other methods in the first group are computing the angles relative to multiple reference points to locate the target location, called direction of arrival (DOA).

• The second group is based on the fingerprint positioning technique. This recognition technique includes two phases: offline phase and online phase. In the offline phase, location data (such as location coordinates, received signal strength) are measured and collected. In the online phase, the current observed signal strength of a target object is compared with the previous collected data to determine the location of the object. The positioning algorithms using in this phase could be probabilistic methods, k-nearest-neighbor, neural networks. • The last group locate the location of a target object using proximity technique. The proximity technique relies on a number of detectors at the known locations. If the observed object is detected, it is considered to be in the proximity area covered by the detector.

Based on these fundamental technologies, a number of indoor positioning systems have been developed by research centers, universities, and companies. These arti-cles [42, 43] have given a survey of them. From the point of view on deployment, there are two main approaches of indoor positioning systems: i) by using the already existing radio frequency infrastructures such as WLAN, Bluetooth and ii) installing specialized indoor positioning systems. The methods in the first category do not require extra infrastructures, but have low accuracy and low degree of precision due

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to signal instability, noise from hardware and environmental factors like humans in motion. The update rate of these methods is in the range of a few seconds. For example, RADAR positioning system [44] was proposed by a Microsoft research group. This system uses the fingerprinting technique. In the offline phase, the RADAR system collects signal strength and signal-to-noise ratio. The alternative method is using the propagation model with wall and floor attenuation factors. In the online phase, the multiple nearest neighbors in signal space (NNSS) location algorithm was proposed. The accuracy of the RADAR system is about 4 m with about 50% probability. Ekahau1 is the commercial location system. The offline phase or site survey is done by a software tool, which demonstrates the network coverage area, signal strength, SNR and the overlapping of the WLAN. A central location engine is used for the online phase. The Ekahau system can achieve the accuracy of 1 m if there are three or more overlapping access points to locate a target object.

In the second category, a new installation of positioning system is required. These can localize the position of the mobile user with high accuracy and a high degree of precision. In addition, the update rate of these systems is short, even achieving real-time responses. The wireless technologies used in the second category can be UWB, Bluetooth, RFID, IR, or wireless sensor networks. For example, the RFID positioning system [45] enables flexible and cheap identification of an individual person or device. In [46], the sensor-based location system is built from a large number of sensors, which are located in the predefined locations. The problem with sensors is a limited processing capacity and battery power. Ubisense2 is a commercial positioning system. The Ubisense system is based on UWB technology to locate a target object in real-time. The performance of the Ubisense system is about 99% precision within 30 cm.

In the proposed system (Fig. 2.8), we assume that the positioning system with a short update rate, high precision and accuracy such as Ubisense is installed to collect the location information periodically. The information should be collected daily, and classification is to be made as weekdays and weekend, working days and vacations. However, this dissertation does not consider this information. Tab. 2.5 is an example of location information format.

1_{Ekahau, http://www.ekahau.com} 2_{Ubisense, http://www.ubisense.net}

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Table 2.5: Data format of the location information

Time Coordinate X Coordinate Y Location SourceID

t1 X1 Y1 Room 1 S1

t2 X2 Y2 Corridor S1

2.4 Conclusion

In this chapter, the Radio over Fiber 60 GHz indoor network has been proposed. At first, the characteristics of the 60 GHz band have been presented. The 60 GHz range offers a wide unlicensed spectrum of 5–7 GHz. It is useful for broadband wireless networks where the demand of high data rate applications such as (U)HDTV or online gaming is high. The 60 GHz band also offers the advantage of security of eavesdropping data since the coverage of one antenna is usually in one room. With its attractions, several standards of 60 GHz have been published. In order to deploy 60 GHz widely, the combination of wireless and optical communication through RoF technique is a promising solution by taking advantages of wireless flexibility and the high capacity of optical communication.

Secondly, the RoF using OFM presented in this chapter can support a fiber length of up to 20 km. The benefits from the selected techniques are simplifying antennas, supporting multiple standards, network capacity and dynamic radio link adaptation. The basic operation of the RoF system is also presented. The OFDM is chosen to design the radio part. This technique can work well in broadband wireless networks operating at a high frequency like 60 GHz. It can eliminate the ISI by applying the cyclic prefix.

However, the limited coverage of 60 GHz antenna and the extra delay caused by the distribution optical network make a handoff difficult in the proposed network which is presented in Chapter 3. In order to solve the issues, the proposed RoF network are employing two additional components: positioning system and movement prediction. The location information is used for multiple network purposes including network planning, managing resource and improving handoff performance.

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Chapter 3

Handoff in Wireless Networks

3.1 Introduction

Handoff is an important aspect in wireless and cellular communication due to the mobility of devices. It is the process that allows a user to move around while keeping an ongoing call or session on a terminal. It does so by changing its current channel in the current cell to a new channel in either the same cell or in a different cell [47]. Handoff is usually transparent to the user, but it directly affects the quality of service. A lot of research has been done on handoffs in cellular networks and WLAN. However, little work has been done on handoff in 60 GHz systems.

Two types of handoffs are distinguished: horizontal handoff and vertical handoff. Horizontal handoff occurs when a MS is moving out of the coverage of a base station (BS) into the coverage of another BS within the same system. Vertical handoff is defined as handoff between BSs that use different wireless networking technologies, e.g., WLAN to and from cellular wireless networks.

As a background, this chapter starts by presenting handoffs in current wireless technologies (in Section 3.2). Next we focus on our main topic: handoff issues in 60 GHz networks (in Section 3.3). Finally, Section 3.4 concludes this chapter.

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3. Handoff in Wireless Networks

3.2 Handoff in Wireless Networks

3.2.1 General

Handoff is a process which maintains continuity of a call or a session of a MS while moving in and out of the coverage area of different cells. It does so by changing the current channel in the current cell into a new channel when the MS moves into a new cell [47]. Fig. 3.1 illustrates a handoff scenario, in which an MS is connected to a BS, BS1. It moves from BS1to BS2 while in a call. Handoff will be performed in

the overlapping area between two BSs where the MS can receive the signal from two BSs. The signal strengths from BS1and BS2are measured continuously. If the

signal strength of BS2is better than the one of BS1and it can provide the MS with

the required resources, a handoff decision is made and now the MS is connected to BS2.

In case, the new BS can not support the required resources of the connection, the handoff is denied and the connection is dropped. The CDP is the possibility of a connection being forced to terminate due to the lack of resources in the target BS. If a new connection access to the target BS is denied, it is called as blocked connection. The CBP is the possibility of a new connection being denied admission into the network. The CDP and the CBP are two fundamental QoS parameters in cellular wireless networks. They offer a good indication of a network’s QoS in terms of mobility. Another important QoS parameter is bandwidth (channel) utilization or an effective use of bandwidth in a network.

In general, a handoff procedure has three phases. The first phase is the mea-surement. The result of this phase is the measurement report with measurement criteria used. The second phase is the handoff decision, which is usually performed by handoff algorithms with algorithm parameters and handoff criteria as inputs. The third phase is the execution in which the new channel will be assigned to the MS and the old connection will be terminated with handoff signaling and radio resource allocation [47].

In the handoff decision phase, if the network makes a handoff decision based on the measurement of the MSs at a number of BSs, it is called Network Controlled Handoff (NCHO). In case the MS makes measurements and the network makes the handoff decision, it is called Mobile Assisted Handoff (MAHO). When each MS completely controls the handoff process, it is Mobile Controlled Handoff (MCHO). From the point of view of a connection, handoffs can be divided into two classes: hard handoff - where the existing connection is broken before making a new one;

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3.2. Handoff in Wireless Networks

and soft handoff - where both the existing connection and the new connections are used while the handoff takes place:

• The hard handoff that occurs in the current cell is called intra-cell handoff, and the hard handoff that occurs when a MS moves into another cell is called inter-cell handoff. This hard handoff is usually used in Frequency division multiple access (FDMA) and Time division multiple access (TDMA) where the MS can be connected with at most one base station at a time.

• One can distinguish between two types of soft handoffs: multi-way soft handoff and the so-called softer handoff, when two BSs exist in two sectors of a sectorized cell [48].

In principle, soft handoff can be used with any radio technology, however the cost may be high and the support for soft handoff may not be good for particular technologies. This is the reason that soft handoff is commonly used only in Code division multiple access (CDMA). Thus, the soft handoffs will not be discussed further in this thesis.

Figure 3.1: Handoff in wireless networks

3.2.2 Vertical Handoff

Two or more different communication systems are interconnected to sustain a seamless connection when a MS moves from one network to another and achieves

Handoff Management in Radio over Fiber 60 GHz Indoor Networks

Handoff Management in

Handoff Management in

Radio over Fiber 60 GHz Indoor Networks

Quang Van BIEN

Contents

Chapter 1

Introduction

1.1

Indoor Wireless Networks

1.1.1

Multimedia Applications

1.1.2

Indoor Wireless Technologies

1.1.3

Radio over Fiber 60 GHz indoor networks

1.2

The Problem Statement

1.3

Summary of Main Contributions

1.4

Thesis Outline

Chapter 2

Radio over Fiber 60 GHz Indoor

Networks

2.1

60 GHz Radio Background

2.1.1

Worldwide Regulation and Standardization

2.1.2

The 60 GHz Band

2.1.3

Potential Applications

2.2

RoF technology

2.2.1

Optical Access Networks

2.2.2

RoF system

2.2.3

Optical Frequency Multiplication

2.3

RoF 60 GHz Indoor Networks

2.3.1

The System Description

2.3.2

Physical Layer

2.3.3

MAC/LLC Layer

2.3.4

Positioning System

2.4

Conclusion

Chapter 3

Handoff in Wireless Networks

3.1

Introduction

3.2

Handoff in Wireless Networks

3.2.1

General

3.2.2

Vertical Handoff