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Department of Science and Technology

Institutionen för teknik och naturvetenskap

Linköping University

Linköpings universitet

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Isolated WiFi Environments

Jacob Carlsson

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LiU-ITN-TEK-A-15/003-SE

Isolated WiFi Environments

Examensarbete utfört i Elektroteknik

vid Tekniska högskolan vid

Linköpings universitet

Jacob Carlsson

Handledare Qin-Zhong Ye

Examinator Shaofang Gong

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Abstract

WiFi is becoming common in households and digital devices needs to support it. At the same time the devices are getting smaller and the Ethernet port may seem superfluous.

When testing these devices the test environment needs to be able to provide WiFi connectivity. The tests may be focused on testing WiFi but it could also be the only network connectivity and thus needs to be very reliable.

With a large number of devices in a small physical area a normal WiFi setup would have a density of devices that is too high for today’s1WiFi standards.

A combination of wired physical medium and physical isolation was consid-ered.

1The current standards considered in this report is 802.11ac, but the one currently used in

house-holds are still 802.11n to a large extent.

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Acknowledgments

I want to thank ARRIS for giving me the opportunity to write this master thesis and for investing in equipment when necessary, something that would not have been possible without financial support.

A big thank you to Jonna Bengtsson at ARRIS for all the help and support you have given me. There has been hundreds of questions about KATT, paperwork, contacting the right people, feedback about reports and written text. You have helped me focusing on the right things to speed up my work flow.

I want to thank Jonas Blick, Magnus Ekhall, Carl Ljungström and Krister Berglund at ARRIS for technical discussions and guidance and Johan Rodin at ARRIS for all the help with network related questions and problems.

I want to thank Shaofang Gong and Qin-Zhong Ye, my examiner and supervisor at Linköping University for help with practical concerns and paperwork as well as technical questions.

I would also like to thank my family Rebecka, Algot and Tage for constantly encouraging me to work hard and for all the great smiles in the mornings.

Linköping, January 2015 Jacob Carlsson

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Contents

Notation 7 1 Introduction 1 1.1 Objective . . . 1 1.2 Scope of work . . . 2 1.3 Method . . . 2 1.4 Discussion of sources . . . 3 1.5 Outline . . . 4 1.6 ARRIS . . . 4 2 Background 5 2.1 Environment . . . 5 2.2 Connected devices . . . 7 2.3 WiFi . . . 7 2.4 Isolation . . . 12 2.5 Considered methods . . . 13 2.6 Tools . . . 14 3 Wired setup 19 3.1 Components . . . 20

3.2 Attenuation between components . . . 21

3.3 Throughput . . . 22 3.4 Reliability . . . 22 4 Encapsulation 23 4.1 Faraday cage . . . 23 4.2 RF-shielding enclosures . . . 25 5 Result 27 5.1 Wired setup . . . 27 5.2 Encapsulation . . . 34 6 Discussion 39 5

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6.1 Wired setup . . . 39 6.2 WiFi technology . . . 39 6.3 Throughput . . . 39 6.4 Isolation . . . 40 6.5 Reliability . . . 41 6.6 Measurements . . . 41 6.7 Adoption in KATT . . . 41 7 Conclusion 43 7.1 Wired setup . . . 43 7.2 Encapsulation . . . 44 7.3 Final solution . . . 44 8 Future Work 45 8.1 Single antenna wired setup . . . 45

8.2 Wireless setup in RF-shielding enclosure . . . 45

8.3 More set-top boxes per AP . . . 46

Bibliography 47

A Considered methods 51

B JRE RF-shielding enclosures datasheets 63

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Notation

Nomenclature

Word Description

client A device that is currently connected to a network (and is not the Access point)

dB Decibel is a logarithmic unit that express a ratio be-tween two values. Often used in electronics

dBm Decibel-milliwats is a power ratio in decibels (dB) of the power divided by 1 mW. A convenient measure of absolute power

WiFi Wireless Fidelity is a wireless network implementing the 802.11 standard

Abbrevations

Abbrevation Description

SMA SubMiniature version A is a connector for RF cables RF Radio Frequency is a rate of oscillation in the range

3 kHz –300 GHz

RSSI Received Signal Strength Indicator is an indication of the signal strength of different networks

KATT KreaTV Automated Test Tools is a framework for au-tomated tests of KreaTV set-top boxes at ARRIS AP Access Point

STB Set-top box

TCP Transmission Control Protocol provides a connection between hosts that are reliable, ordered and error-checked

UDP User Datagram Protocol is a simple protocol that does not guarantee delivery or the received order of packets

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1

Introduction

Providing WiFi connectivity to a large number of devices with high throughput is difficult. When in a small physical space the networks will interfere with each other and the throughput will be constrained.

A solution to this problem has been considered where the networks have been isolated from each other and therefore interference is minimized. The solution is to create a wired network where the antenna connectors have been intercon-nected, this of course means that the network is not wireless any more.

By connecting the devices at the antenna connectors they will work as normal, from the single device’s perspective the network appears as wireless. The devices will be able to use wireless network hardware and software with high throughput in a very limited physical space.

RF-shielding enclosures has been used to further isolate the network, these are specialized enclosures that attenuates radio frequency signals. By encapsulat-ing the network, signals will be attenuated and the entire network will be isolated. The RF-shielding enclosures also attenuates signals from other networks which further isolates the enclosed network.

1.1

Objective

The objective of this work is to:

• Provide WiFi connectivity to a large number of devices • Provide high throughput

• Isolate small networks that will use WiFi but not affect or be affected by other networks

• Fit in a small physical space

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1.2

Scope of work

This work is focused on providing network connectivity using the WiFi standard 802.11ac. The solution will be using of the shelf components to the highest extent to make scaling easier and less time consuming. Using of the shelf components that are tested by the manufacturer will introduce less errors than custom made components.

This is a master thesis work of 30 ECTS1and is limited to 20 weeks of work.

Out of scope Security is out of scope for this work and will not be considered. With that said, WiFi has encryption algorithms that will add data overhead and decrease the throughput. All tests with WiFi will use WPA2-Personal encryption (Wi-Fi Protected Access 2).

1.3

Method

This work has been done with literature studies, especially in WiFi technology, laboratory work and observations.

With literature studies I proposed some possible solutions that were discussed with ARRIS and we agreed to further investigate two of these.

The first is to interconnect all devices antenna connectors with wires to isolate them from other networks, this is described in chapter 3.

To further attenuate the signals that are sent out and signals from other net-works, different types of encapsulation are described in chapter 4. All the pro-posed solutions can be seen in appendix A.

Literature study

To get understanding and ideas a literature study was conducted especially in WiFi and high density networks.

WiFi

WiFi is the technology used in this work and therefore this was studied in depth. The main focus was the physical layer and how it is used.

The limiting factor in this work is that when devices are connected to a net-work, they will remain silent if there is communication on the same channel. This means that the network channel can not be reused in the same physical space. Be-cause all channels are already occupied by other networks it is not possible to use multiple channels to get the desired throughput to a large number of clients. The channel needs to be reused and most desirable the network should be isolated from other networks. The problem is to solve this with a good solution.

1European Credit Transfer and Accumulation System is a standard for comparing higher education

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1.4 Discussion of sources 3

Previous work and ideas

I did not find any previous work in this exact area but I found inspiration from conferenceswhere they have a very high density of devices (large amount of de-vices per area). At conferences the number of dede-vices is very large and the space is often limited. A big difference between conferences and this work is that I am able to modify all equipment and I have more information about all the devices. At conferences the wireless networks needs to support older versions of the WiFi standard and the coverage have to be good.

Microsoft research have designed a wireless data center for 60 GHz WiFi [10]. In their work they use directed antennas to focus the wireless signals to different parts of the system. The main difference in this work is that they use 60 GHz waves as technology, which has a much higher attenuation with distance, which would have been good in this case but something that I was not able to do with 5 GHz waves. The attenuation with distance for 5 GHz can be seen in figure 2.1.

The hardest part of the literature study was to find previous work on this subject and to apply that to the problems in this work. Because this is an in-house solution for larger companies it may not be something that they make publicly accessible.

1.4

Discussion of sources

These are the most influencing resources for this work. They are specifications, books and research done in the WiFi area.

WiFi

Below is the most influencing WiFi sources used in this work.

Matthew Gast

Matthew has written the books 802.11ac: A Survival Guide and 802.11 Wireless Networks: The Definitive Guide which goes through WiFi. Matthew has served as the chair of the security groups at the Wi-Fi Alliance. The books are sold at

oreally.comand has great reviews.

802.11ac WiFi standard

The standard 802.11ac is the latest standard for WiFi by the Wi-Fi Alliance. This is a standard that is used by the manufacturers and the Wi-Fi alliance are the organization that certifies devices.

Research

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Microsoft research

The research project “On the Feasibility of Completely Wireless Datacenters” was conducted at Microsoft research by Cornell University and I think they have the right knowledge and their reputation to account for when publishing some-thing like this. The report contains sources and authors with contact information.

1.5

Outline

1 Introduction Describes problem and motivation

2 Background Background knowledge about WiFi and the environment 3 Wired setup Using wires instead of antennas

4 Encapsulation Isolating the network from other networks 5 Result Result of all measurements and the setup

6 Discussion Discussion of this work 7 Conclusion Conclusions about this work

8 Future Work What could be done to extend this work Appendix Appendix with proposed solutions and datasheets

1.6

ARRIS

ARRIS innovates video and IP-technology for entertainment and communication for people around the world. In Linköping both hardware and software are devel-oped. KreaTV Automated Test Tools (KATT) is a great way to continuously test and improve the set-top boxes.

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2

Background

This chapter provides background theory about wireless networks, the WiFi stan-dard used in this work and other important parts. It also includes a description of the environment and the difficulties with it.

2.1

Environment

The environment for this work is a medium sized room, about 75 m2. Because of the limited size, a wireless network layout would not be able to provide the required throughput.

Figure 2.1 shows the received power from 3 signals sent with different power in dBm1. The attenuation is high but a signal power of -62 dBm will still be received by a WiFi access point, this means that the range of a signal sent with 20 dBm2is interfering with another network at 100 meters [9].

Even at longer distances that signal is still contributing to noise. This long distance means that at 100 meters apart, it will still not be possible to reuse the same channel, more about this in the WiFi section 2.3.

The room is located inside company premises and the network will therefore interfere with and receive noise from other networks. It will not be possible to use all available channels and this will limit the throughput.

There are a large number of clients that needs to access the network, all with high throughput. Because of the physical size of the room the distribution of devices is limited.

1A signal power of 20 dBm is 0.1 Watts. P

dBm= 10 ∗ log10(1 mWPwatt).

220 dBm is in the range of a normal output from an access point. The AP used in this work is

configurable to have an output power of 10 - 20 dBm

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0

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60

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Distance [m]

90

80

70

60

50

40

30

20

10

0

RSSI [dBm]

RSSI of received signal at 5 GHz in air

20 dBm

5 dBm

0 dBm

Figure 2.1: Signal attenuation in free space. The graph shows theoretical values of a 20 dBm signal, a 5 dBm signal and a 0 dBm signal transmitted and the attenuation with distance from the transmission point.

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2.2 Connected devices 7

Figure 2.2: The Wi-Fi CERTIFIED™ logo. Only products that pass the Wi-Fi Alliance® testing can bear the logo [4].

The Wi-Fi CERTIFIED™ logo is a registered trademark of Wi-Fi Alliance®.

2.2

Connected devices

The goal is to connect many devices, hereby called clients or devices to a WiFi net-work. These clients could be different types of devices but in this work they are typically ARRIS VIP1113W set-top boxes, more information about these devices can be seen in section Set-top box on page 11.

2.3

WiFi

WiFi is a wireless network that is certified by the WiFi Alliance and based on the IEEE 802.11 standards [3]. Figure 2.2 shows the Wi-Fi certified logo that only products that pass the Wi-Fi Alliance® certification process can bear.

The original version of IEEE 802.11 was released in 1997 and the current version 2014 is IEEE 802.11ac2013 [9, 2].

WiFi currently uses frequencies of 2.4 GHz and 5 GHz. The initial products were limited to 2 Mbit/s and by 1999 the 802.11b standard had an operating speed of up to 11 Mbit/s while the 802.11a and 802.11n standard operated in the 5 GHz band and had a speed of up to 54 Mbit/s [8, 9, p. 9]. The new standard 802.11ac uses the 5 GHz band and promises a data rate of over 1 Gbit/s3[2, 11]. The 802.11ac standard uses only the 5 GHz band but is backwards compatible with 802.11a/n operating in the 5 GHz band [12, 11].

In this work the standard 802.11ac is used because of the high throughput. The set-top boxes supports the 802.11ac standard and therefore it is not necessary to consider an older standard in this work.

The standard 802.11 The IEEE 802 standard is focused on the two lowest lay-ers in the OSI model (Open Systems Interconnection), the media access control (MAC) layer and physical (PHY) layer, seen in figure 2.3 [8]. 802.11 could be described as “just another link layer for 802.2” [8].

Accessing the medium The 802.11 standard uses a distributed access scheme where all devices are allowed to access the medium (in the WiFi case this means

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Application Presentation Transport Session Network Data link Physical

Figure 2.3: The OSI model with the two lowest layers highlighted

using the air) [8, p. 24]. 802.11 uses the algorithm Carrier Sense Multiple Ac-cess with Collision Avoidance (CSMA/CA) which is build upon the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) algorithm used in pre-vious IEEE 802 standards, but instead of detecting collisions they are avoided [8, p. 24]. The algorithm senses if the medium is available, if not it waits random time (in a predefined interval of microseconds). This is used because collisions waste more transmission capacity than avoiding them [8, p. 24]. When WiFi senses the medium a threshold of -82 dBm is used for detecting signals, if the received signal power is larger than this the device will wait [9].

There are 3 different transmissions possible in 802.11, these are Unicast to a specific device, Multicast to multiple devices and Broadcast to all devices. Uni-cast allows for two additional packets: Request to Send (RTS) and Clear to Send (CTS).

The sender sends a RTS and the responder sends a CTS, this tells all stations that hear the CTS to be quiet for the specified time. These packets are sent to get a duration in which the medium is only available to the device that sent the RTS packet. This makes it possible to send data without collisions.

This is especially useful when there are hidden nodes in the network that will not receive the packets sent from the sender but only those sent from the receiver. An example of a hidden node (client) can be seen in figure 2.4. In this example A wants to send a packet to B but because C is hidden from A it will not receive any packets send from A. This may result in collisions at B if both A and C is sending at the same time. To avoid this A is sending a Request to Send (RTS) that will only be received by B. B will then send a Clear to Send (CTS) that both A and C will receive. C will then wait for the specified time and A is able to send data to B without collisions

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2.3 WiFi 9

A B C

(a) A wants to send to

B but C are unable to receive this communica-tion and thus may send data at the same time as A, resulting in collisions at B.

A B C

(b) B – the receiver –

are able to receive pack-ets and send packpack-ets to both A and C.

A B C

(c) C is able to

communi-cate with B but A is hid-den from C and will not receive any packets that are sent from C

Figure 2.4: These images shows hidden nodes, that are a contributing to collisions.

1

2 3 4 5

6

7 8 9 10

11

12 13

14

20 MHz 5 MHz

Figure 2.5: 802.11n channels in the 2.4 GHz band, channels 1, 6, 11 and 14 can be used without overlap but channel 14 is not allowed everywhere. Redrawn from2.4 GHz Wi-Fi channels (802.11b,g WLAN)

by Michael Gauthier (CC BY-SA 3.0) for the 802.11n standard.

Channels

WiFi uses a range of frequencies that are divided into multiple channels with fixed bandwidth. Channels are used to make it easier for multiple networks to share the available bandwidth. The 802.11ac standard, which uses the 5 GHz band, introduces wider channel widths which enables higher throughput [9].

2.4 GHz and 802.11n

At the 2.4 GHz band in the 802.11n standard a channel bandwidth of 20 MHz is used but has overlaps as seen in figure 2.5. Channels 1, 6 and 11 can be used which would provide a channel layout without overlap. Overlapping channels introduces interference and should be avoided.

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20 MHz 40 MHz 80 MHz 5.2 5.3 5.4 5.5 5.6 5.7 GHz 160 MHz

802.11ac channels in Europe

36 40 44 48 52 56 60 64 100 104 108 112 116 120 124 128 132 136 140

38 46 54 62 102 110 118 126 134

42 58 106 122 138

50 114

36 40 44 48 52 56 60 64 100 104 108 112 116 120 124 128 132 136 140

Figure 2.6: Channels for the 802.11ac standard in Europe. The integers above each subplot are the IEEE channel number.

5 GHz and 802.11ac

The channels in the 5 GHz band are not that easily defined because of regula-tions. Because the frequency spectrum are also used for other technologies than WiFi, countries has approved use of different channels. The european standard EN 301 893 defines the Radio LAN (RLAN) bands to 5 150 MHz – 5 350 MHz and 5 470 MHz – 5 725 MHz [6]. The channels have bandwidths of 20 MHz but the 802.11ac standard also includes 40 MHz, 80 MHz and 160 MHz channel band-widths in the 5 GHz band [9]. The allowed channels in Europe can be seen in figure 2.6.

Access point

An access point (AP) bridges the wired network and the wireless clients [8, p. 16]. A client can only be connected to a single access point at any time. The access point is the center of the network and all traffic will go through it.

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2.3 WiFi 11 Table 2.1: Specification for the ARRIS VAP3400 access point

Specification Value

Model name Arris VAP3400 WiFi version dual band 802.11n/ac

WiFi antennas 4

Antenna usage MIMO

DHCP no

WiFi certified yes

Table 2.2: Specification for the ARRIS VIP1113W set-top box

Specification Value

Model name VIP1113W

WiFi version dual band 802.11n/ac

WiFi antennas 2

Ethernet ports 1

Antenna usage MIMOa

HDMI ports 1

USB ports 1

aMultiple Input Multiple Output enables very high throughput between devices with multiple

antennas

be seen in table 2.1.

Set-top box

A set-top box is an internet enabled media device that is able to stream e.g. TV and movies.

The set-top boxes used in this work are two ARRIS VIP1113W. These are small devices with an ethernet port and a WiFi chip with two antennas. The specification can be seen in table 2.2.

Noise and interference

For WiFi to work the signal needs to be good, this means that the Signal-to-Noise ratio (SNR) needs to be high.

SNR is a measure of the power of the signal compared to the power of noise, SN R = PPsignal

noise. If the signal power is strong and the noise is weak there will be a

very small error in the conversion to data but if this ratio is low there may be a high rate of errors or even impossible to convert the signal to data.

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Figure 2.7: A Faraday cage in operation: the women inside are protected

from the electric arc by the cage. Photograph taken at the Palais de la

Dé-couverte in Paris (Discovery Palace) (CC BY-SA 3.0).

2.4

Isolation

To isolate a WiFi network the radio waves of other networks should not be recog-nizable or add noise to the current network. The current network’s radio waves should not be recognized or add noise to other networks.

In this work I have focused on faraday cages and RF-shielding enclosures to isolate the network. These work by compensating the electromagnetic field created by the network with an internal reverse electromagnetic field that will cancel out the surrounding field.

In figure 2.7 is a faraday cage in operation, the woman does not get electro-cuted because the cage is canceling out the applied electric field.

RF-shielding enclosure The RF-shielding enclosure is a product specifically de-veloped to cancel out RF-fields from electrical equipment for testing purposes. As well as a surrounding faraday cage it also has an absorbing material inside that will cancel out reflections and standing waves. An RF-shielding enclosure also has filtered Input and Output (I/O) connectors, this can be seen in figure 2.8b. Two images of a small RF-shielding enclosure are shown in figure 2.8.

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2.5 Considered methods 13

(a) The inside of a small RF-shielding

enclosure

(b) The outside of a small

RF-shielding enclosure with the connec-tors shown

Figure 2.8: A small RF-shielding enclosure with nothing connected. The enclosure is only accessible via the RF filtered connectors shown in subfigure (b).

2.5

Considered methods

Multiple methods were considered where isolation was the main takeaway to solve the problems in this work. All the considered methods are located in ap-pendix A while this section describes the most important ones.

Directed antennas are used to focus the signal in one direction and could be used to only send to a subset of all devices. This results in a separation in space and isolation between different networks. The directed antennas are only focusing in a specific direction but the distance that the signals could travel will not be shorter. As all the devices would have to use directed antennas the cost and complexity of this system is high.

Using wires to connect the antennas would make the network wired and no longer wireless but as WiFi technology is still used the devices would not notice. The wires would shield the network from other networks resulting in isolation from other networks.

Encapsulating the network with a faraday cage would provide isolation from other networks and make a system that is very easy to understand as you will see the boundaries between different networks clearly.

By using different channels the networks would be separated in frequencies, effectively isolating them from each other. The limited frequency range used for WiFi limits the number of networks and therefore this is not a considerable solution to this work.

If an effective layout of the devices would be possible this would separate the networks in space. As the space for this work is limited this is not possible.

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Algorithm 1An example of measuring throughput from client to server with iperf. This will open a TCP connection and transfer data with as high throughput as possible for 10 seconds.

# On the s e r v e r device ( IP 1 9 2 . 1 6 8 . 1 . 1 0 3 ) i p e r f −s

# On the c l i e n t device i p e r f −c 1 9 2 . 1 6 8 . 1 . 1 0 3

Algorithm 2Use UDP with iperf, this sends UDP packets with 1 Mbit/s for 10 seconds from client to server.

# On the s e r v e r device ( IP 1 9 2 . 1 6 8 . 1 . 1 0 3 ) i p e r f −s −u

# On the c l i e n t device i p e r f −c 1 9 2 . 1 6 8 . 1 . 1 0 3 −u

2.6

Tools

This part shows the most important tools used in this work, what they are capable of and used for.

Iperf

Iperf is a tool to measure throughput between devices in a network, it is a com-mand line tool and so you need access to a console on the devices. To measure the throughput between two devices you set up a iperf server with the com-mand iperf -s [optional flags]. The other device connects to the server with the command iperf -c <server-ip> [optional flags]. An exam-ple can be seen in algorithm 1, this would set up a TCP connection by default and transfer data from the client to the server with the highest throughput possible for 10 seconds.

The tool also gives the opportunity to use UDP which is less reliable, but very useful for testing reliability. Algorithm 2 shows an example of measuring with UDP. This example would send UDP packets with a bandwidth of 1 Mbit/s from client to server for 10 seconds also showing jitter and packet loss.

There are more flags that I have used to really embrace the power of iperf, some of these can be seen in algorithm 3. To view all available flags you can use the command iperf - -help.

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2.6 Tools 15 Algorithm 3Examples of optional flags that uses the power of iperf.

# TCP

# On the s e r v e r devic e ( IP 1 9 2 . 1 6 8 . 1 . 1 0 3 ) i p e r f −s

# On the c l i e n t devic e

# Measure f o r 60 seconds and output data as CSV # One row every 5 seconds

i p e r f −c 1 9 2 . 1 6 8 . 1 . 1 0 3 − t 60 − i 5 −− r e p o r t s t y l e C # UDP

# On the s e r v e r devic e ( IP 1 9 2 . 1 6 8 . 1 . 1 0 3 ) # Setup a s e r v e r with UDP

i p e r f −s −u

# On the c l i e n t devic e

# Measure f o r 30 minutes with a bandwidth of 20 Mbit / s # Output measurements every second

i p e r f −c 1 9 2 . 1 6 8 . 1 . 1 0 3 −u − t 1800 −b 20M − i 1

Output

The output from iperf gives timestamp, throughput, number of transferred bytes and for UDP (User Datagram Protocol) it also gives jitter and lost packets. An example output can can be seen in figure 2.9. In this example the default config-uration is used but with 2 seconds interval between reports. The default config-uration is using a TCP (Transmission Control Protocol) connection and sending data from client to server during 10 seconds.

It is also possible to get Comma Separated Values (CSV) output with the com-mand iperf - -reportstyle C with the output seen in figure 2.9c.

Wifi Analyzer

Wifi Analyzer [1] is an android app that is able to:

1. List all available WiFi networks with Received Signal Strength Indicator (RSSI) in dBm

2. Measure RSSI of all detectable networks over time 3. Show a graph of what channel is used by which network

The tool is useful to quickly get more information about available networks but also to measure RSSI over time for a network.

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(a) Iperf output on server side.

(b) Iperf output on client side.

(c) Iperf output when using CSV output.

Figure 2.9: iperf output when using default configuration with 2 seconds interval between reporting.

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2.6 Tools 17

Figure 2.10: A frequency analyzer showing the frequency spectrum for sig-nals at 5.26 GHz with a span of 40 MHz.

Frequency analyzer

When measuring signal power or analyzing WiFi signals it is not possible to measure the air with a normal oscilloscope as the signals are sharing the same medium. With a frequency analyzer it possible to view signals in the frequency spectrum. This makes it possible to view and measure signal power, bandwidth and a graph of the used frequencies. A picture of a frequency analyzer is shown in figure 2.10.

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3

Wired setup

On each device the antennas are removed and replaced with radio frequency cables. The devices will operate normally but the physical medium (normally this is the air) is replaced by wires. The setup can be seen in figure 3.1, the orange box is the access point connected with 4 U.FL to SMA cables to 4 attenuators. These 4 attenuators are then combined with the 4-way combiner seen as the first blue box. A SMA to SMA cable connects the 4-way combiner to the 8-way splitter splitting the signal to 8 outputs. These are connected with SMA to SMA cables with 8 attenuators. All attenuators are connected with SMA to U.FL cables to the 4 set-top boxes, two cables per set-top box. The picture in figure 3.1b shows only a single set-top box connected and has terminators on all other outputs on the 8-way splitter/combiner.

1113W 1113W 1113W 1113W

AP

8 split

4 comb.

(a) A drawing of the wired network. (b) A camera picture of the setup seen

from above.

Figure 3.1: The wired setup as a drawing and a picture from above.

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(a)U.FL antenna connector as seen in

a AVM Fritz!Box Fon WLAN 7170(CC

BY-SA 3.0).

(b) Male SMA connector, 50 ohm,

manufactured by Huber+Suhner (CC

BY-SA 3.0).

Figure 3.2: An U.FL connector (a) and an SMA connector (b), the U.FL con-nector is only 2 mm in diameter while the SMA concon-nector is about 8 mm in diameter.

Table 3.1: List of components used in this setup Description Model number Quantity

Attenuator 30 dB VAT-30+ 12 Cable 16 inch 086-16SM+ 9 Cable 24 inch 086-24SM+ 4 4 way splitter/combiner ZN4PD1-63-S+ 1 8 way splitter/combiner ZN8PD-642W-S+ 1 Terminator ANNE-50+ 8

U.FL to SMA cable 12

3.1

Components

All the components used in the setup can be seen in table 3.1. These compo-nents were bought fromMini Circuits and complemented with terminators for any open port during testing. The U.FL to SMA cables were bought from Ebay. An U.FL connector is shown in figure 3.2a next to the SMA connector in figure 3.2b.

Slitter/Combiner

There are two splitter/combiners, one 4-way and one 8-way. These splits the signal into 4 or 8 signals or it combines the signals into one. When the signal is split the power of the signal is also divided with the number of outputs. The 4-way splitter/combiner will split the signal into 4 and therefore the signal power will be 14 of the original signal. When multiple signals are combined the signals instead gets added and a 4-way combiner will summarize the signals to 4 times the original signal power. The splitter/combiners also has insertion loss which

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3.2 Attenuation between components 21 further attenuates the signal.

Terminator

A terminator is used to stop the signal and has matched impedance which absorbs the signal, it also has very little reflection.

3.2

Attenuation between components

Normally the air is attenuating the signal and the devices are not built to receive too high power. When wiring the antennas together it is important to attenuate the signal to save the electronics in the devices.

The attenuation between different components in the system are calculated with formula 3.1, 3.2 and 3.3 where A is the attenuation, L is the insertion loss and I is the isolation. Insertion loss is the attenuation of the signal when the component is inserted into the system and isolation is the attenuation between different parts of a component, e.g. between outputs of the splitter/combiners.

AAP−to−settop−box = 2 ∗ (AV AT −30++ LV AT −30+) + (3.1) 3 ∗ L086−16SM++ LZN 4PD1−63−S++ LZN 8PD−642W −S+ AAP−to−AP = 2 ∗ (AV AT −30++ LV AT −30+) + (3.2) 2 ∗ L086−16SM++ IZN 4PD1−63+ Asettop−box−to−settop−box = 2 ∗ (AV AT −30++ LV AT −30+) + (3.3) 2 ∗ L086−16SM++ IZN 8PD−642W +

AAP−to−settop−boxin equation 3.1 shows the attenuation from one connector of the access point through the entire system to one connector at the set-top box. AAP−to−AP in equation 3.2 shows the attenuation from one connector of the ac-cess point to another connector of the acac-cess point. Asettop−box−to−settop−box in equation 3.3 shows the attenuation from one connector of the set-top box to an-other connector of the set-top box.

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3.3

Throughput

The throughput provided by the setup is critical to this work. The goal is to be able to stream 20 Mbit/s video to each set-top box. In WiFi the data will be unicasted to each set-top box and so the access point needs to be able to deliver N ∗ 20 Mbit/s where N is the number of set-top boxes. This is because WiFi will not multicast the data because the modulation of that signal needs to be very low, by unicasting the data the modulation could be as high as possible for each device, leading to higher throughput.

3.4

Reliability

The system needs to be reliable, especially if the set-top boxes are only connected with WiFi. The network may use TCP or UDP traffic and as TCP is more reli-able in design the throughput is most important in this case. With UDP traffic there may be lost packets, jitter (the deviation from true periodicity) and packets received in the wrong order. Therefore the reliability tests are measuring these three properties of UDP traffic.

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4

Encapsulation

The network could further be isolated with encapsulation. Two types of encapsu-lation has been considered in this work:

• Create faraday cage to isolate network • Buy pre made RF-shielding enclosures

4.1

Faraday cage

Faraday cages can be used to isolate the network from other networks or noise. Depending on the background noise and how well the networks are shielded, faraday cages are an option that may isolate the network.

Calculations The wavelength of a 5 GHz signal, as calculated in equation 4.1, is 0.06 m (6 cm). λ = v f = c f = 299792458 5 ∗ 109 = 0.060m (4.1)

Equation 4.2 shows the penetration depth or skin depth, it is the depth in the metal where the power attenuation is exponential [7]. The penetration depth is relative to resistivity ρ, frequency f , and permeability µ.

δs = r

ρ

π ∗ f ∗ µ (4.2)

Using equation 4.2 the values in table 4.1 can be calculated for 2.4 GHz and 5 GHz.

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Table 4.1: Skin depth for different materials at different frequencies[5] Material Resistivity [µΩ ∗ cm] Permeability µr Skin depth at 2.4 GHz [µm] Skin depth at 5 GHz [µm] Aluminum 2.65 1 1.672 1.159 Copper 1.69 1 1.336 0.925 Iron 10.1 500 0.146 0.101

Figure 4.1: A simple faraday cage made with aluminum foil.

If the desired attenuation is known the depth could be calculated relative to the skin depth with equation 4.3 where D is the desired attenuation.

With a desired attenuation of 90 % of the signal power, a total of 2.3δ is needed. For aluminum with skin depth 1.159µm the thickness needed at 5 GHz is 2.3 ∗ 1.159µm = 2.67µm.

e

x

δs = D (4.3)

x = −δ lnD

Aluminum foil cage

This cage is made with one layer standard aluminum foil used in cooking. This foil has no holes and has a thickness of 0.010 mm.

Material

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4.2 RF-shielding enclosures 25

(a) The two RF-shielding enclosures,

the larger one fits the entire network and the smaller one fits only the Ac-cess Point or a VIP1113W device.

(b) The wired network set up in

the larger RF-shielding box with two VIP1113W devices connected. An eth-ernet cable is connected to a DHCP router outside. A laptop is also con-nected to the same network.

Figure 4.2: The RF-shielding enclosures and a network inside. • Grounding cable

• Cardboard box

The cage needs to be created so that no large holes are present. An antenna for measurements needs to be inserted into the cage resulting in at least one opening for a SMA-cable (about 0.4 cm in diameter) is needed. The picture in figure 4.1 shows a faraday cage made with cardboard and covered with aluminum foil.

Microwave oven

Microwave ovens use 2.4 GHz and are therefore made to shield these frequencies. If the holes in the cages are small enough this should theoretically also shield 5 GHz waves.

4.2

RF-shielding enclosures

RF-shielding enclosures are pre made shielding boxes for radio frequencies. For this thesis work the manufacturersJRE testingandRamseywere considered since they seem to be the most recognized. Two RF-shielding enclosures from JRE testingwas ordered, one larger that fits the entire network and one smaller that only fits a single device, these can be seen in figure 4.2a. This makes it possible to test different setups. The datasheets for the RF-shielding enclosures can be seen in appendix B. These has an attenuation of more than 80 dB for frequencies of 5 GHz. The entire network fits in the larger RF-shielding enclosure which has the outside dimensions of 13" H x 17" W x 24" (0.38 m x 0.43 m x 0.61 m).

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Isolation

The isolation is the most important aspect of these enclosures and the goal is that the network should not be visible from outside and the enclosed devices should not be able to find any other network. The wired setup was placed in the larger RF-shielding enclosure as seen in figure 4.2b to be able to measure the isolation from other networks.

The Received Signal Strength Indicator (RSSI) was used to measure the signal strength of WiFi routers. If no network is found from the enclosed devices this is an strong indication of that the RSSI values received are too low or not even recognized. When the entire network is enclosed the devices are still accessible from outside through ethernet and it is possible to query for other networks.

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5

Result

5.1

Wired setup

Measurements for the wired setup are made for isolation, throughput and relia-bility.

Isolation

This wired setup was evaluated and it worked well except it both sends out sig-nals to outside networks and receives sigsig-nals from outside networks. Measure-ments were done with near field probes at the positions specified in figure 5.1a. As seen in figure 5.1b the measured signal power at the antenna connectors (po-sition 1 and 11) were very strong, this is probably where signals from other net-works gets in to the system.

Because the access point has 4 antennas and the set-top boxes has 2 antennas each, there will be 12 possible leakage points to isolate.

The isolation from outside networks can be seen in figure 5.2. This was mea-sured with the wired network setup and a smartphone with the Wifi Analyzer android app. The values are almost equal and the wires does not provide any practical isolation as the signal power of Network 1 needs to be attenuated at least 30 dB for the network to be isolated.

Attenuation between components

The attenuation in the system was measured by connecting one antenna output of the access point with a frequency analyzer and measure the signal power. I used iperf with default settings to send data through the system to get a high signal power. The signal power on one antenna of a set-top box was measured with the same signals sent and the difference in these measurements gives the

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1113W 1113W A P 8 split 4 comb. 1 10 2 3 4 5 6 7 8 9 11

(a) Measuring setup with numbered measuring

points, these are provided in the parenthesis in figure 5.1b.

4 way splitter/combiner (6) 8 way splitter/combiner (7) A single SMA to SMA cable 16 inch after AP (4) Access Point (1) All 4 SMA to SMA cables 16 inch (5) Attenuator after AP (3) Attenuator after box (9) U.fl. to SMA cable from box (10) Wire from AP to attenuators (2) wireless DTV box 1113W (11) Wires from 8 way splitter to attenuators before box (8)

−60 −40 −20 0

dBm

Signal leakage

(b) Signal leakage from different parts of the setup, measured as close

as possible (0–4 mm) to the hardware. Smaller bars means greater power.

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5.1 Wired setup 29

RSSI values of other networks

RSSI v alue [dBm] ● ●● ● ● ●● ●●● ●● ●● ● ●● ●●● ● −100 −80 −60 −40 −20 0

With wires Without wires

Network 1 Network 2

RSSI network 1 RSSI network 2 Without wires [dBm] −45.50 ± 1.8786.83 ± 0.9

With wires [dBm] −50.33 ± 0.8288.17 ± 1.17

Attenuation [dB] 4.83 dB 1.34 dB

Figure 5.2: Measured RSSI values of other networks. The values are compa-rable between wired network and without wires.

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Table 5.1: Values for attenuation in the system

Abbreviation Calculated value [dB] Measured value [dB]

AAP−to−settop−box 72.02 73.8

AAP−to−AP 104.54 no measurementa

Asettop−box−to−settop−box 85.18 no measurement

a

aThis value is to low to measure with the provided equipment

Table 5.2: Values for attenuation A, loss L and isolation I for the compo-nents in the wired network. Datasheets for all compocompo-nents can be seen in appendix C. Component Attenuation/Loss/Isolation [dB] AV AT −30+ 28.72 LV AT −30+ 0.35 L086−16SM+ 1.02 LZN 4PD1−63−S+ 0.7 LZN 8PD−642W −S+ 10.12 IZN 4PD1−63+ 26 IZN 8PD−642W + 25

attenuation AAP−to−settop−box= 73.8dB. This is very close to the theoretical value

AAP−to−settop−box = 72.02dBm calculated with equation 3.3 with values from ta-ble 5.2.

The values for AAP−to−AP and Asettop−box−to−settop−box was not possible to mea-sure as the signal power was to low for the frequency analyzer to pick up.

The calculated values are AAP−to−AP = 104.54dB from equation 3.2 and

Asettop−box−to−settop−box = 85.18dB from equation 3.3. The attenuation between different parts of the system can be seen in table 5.1.

Throughput

In the measurements the AP is using a 20 MHz bandwidth and throughput is mea-sured with the tool iperf and a TCP (Transmission Control Protocol) connection if nothing else is mentioned.

A laptop is used to initiate tests and connect to the set-top boxes. The laptop and access point are connected to a router that has a maximum throughput of 100 Mbit/s which could be a limiting factor in these tests.

Laptop and one set-top box

Figure 5.3 shows the throughput from the laptop to a set-top box. The 100 Mbit/s router may be a limiting factor in the test but the throughput is high in both directions. In this test the access point was set to use 80 MHz bandwidth.

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5.1 Wired setup 31 0 25 50 75 100 0 30 60 90 120 Seconds Mbit/s

Laptop to set−top box Set−top box to laptop

Throughput between laptop and set−top box

Throughput [Mbit/s] From laptop to set-top box 86.62 ± 1.50 From set-top box to laptop 56.69 ± 2.03

Figure 5.3: Measured throughput between a laptop and a set-top box. The throughput is higher from laptop to set-top box than from set-top box to laptop.

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0 25 50 75 100 0 25 50 75 100 Seconds Mbit/s Combined throughput Set−top box 1 Set−top box 2

Throughput from two set−top boxes to laptop

Throughput [Mbit/s] Set-top box 1 28.83 ± 4.33 Set-top box 2 27.54 ± 4.62 Combined throughput 56.38 ± 1.56

Figure 5.4: Measured throughput from two set-top boxes to the laptop.

Laptop and two set-top boxes

The throughput from a two set-top boxes to the same laptop was measured by creating a server on a laptop connected to the AP with the command iperf -s. Both set-top boxes connected to the laptop with the command iperf -c <ip> and measured for 120 seconds. Figure 5.4 shows the throughput which are vary-ing, but the combined throughput is comparable with the throughput from a single set-top box to the laptop seen in figure 5.3. In this test the AP was set to use 80 MHz bandwidth.

The throughput in the reverse direction, from the laptop to two set-top boxes was measured during 120 seconds with iperf by creating two servers (iperf -s), one on each set-top box and then connecting from the laptop to the two set-top boxes simultaneously (in two separate terminals call iperf -c ...). The mea-sured throughput can be seen in figure 5.5, the throughput is stable and varia-tion is small. The combined throughput is about 90 Mbit/s which is high when

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5.1 Wired setup 33 0 25 50 75 100 0 30 60 90 Seconds Mbit/s Combined throughput Set−top box 1 Set−top box 2

Throughput from laptop to two set−top boxes

Throughput [Mbit/s] AP to set-top box 1 42.09 ± 0.39 AP to set-top box 2 47.69 ± 0.61 Combined throughput 89.77 ± 0.72

Figure 5.5: Throughput from laptop to two set-top boxes.

the router limits the throughput to 100 Mbit/s, it is also comparable to the mea-surement in figure 5.3.

Reliability

To measure the reliability the setup was tested by sending UDP packets with 1 Mbit/s for 1 hour in both directions simultaneously. The results shown in ta-ble 5.3 shows that there are some jitter but out of 321 000 packets sent no packets were lost.

When streaming video to the set-top boxes there will mostly be traffic from the laptop (or a server) to each set-top box. The traffic will be using UDP packets and it should be possible to send streams with 20 Mbit/s bandwidth.

This was tested by using iperf and from the laptop making two parallel 20 Mbit/s UDP streams to each set-top box. This would simulate 4 simultaneous

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Table 5.3: Reliability of the wired setup when isolated measured with 1 Mbit/s UDP packets for 1 hour. There are no packets lost out of 321 000 sent packets.

Jitter [ms] Packet loss [%] Laptop to set-top box 0.227 0 Set-top box to laptop 0.102 0

UDP streams with 20 Mbit/s bandwidth through the network. The result can be seen in table 5.6, the throughput is 19.07 Mbit/s, the jitter is 0.73 ms and there are no lost packets.

5.2

Encapsulation

Both faraday cage and RF-shielding enclosures were tested as well as a microwave oven as they shield 2.4 GHz waves very well.

Aluminum foil cage

Figure 5.7 shows the measurements of 2 faraday cages with different number of layers of aluminum foil with a thickness of 0.010 mm. There is no sign of the cages reducing the power significantly.

Microwave oven

The measurements were done by putting a Google Nexus 5 phone (Android phone that has 5 GHz band for WiFi) in a microwave oven and measure the Received Sig-nal Strength Indicator (RSSI) with door open and closed. The measurements can be seen in figure 5.8, the 5 GHz signal is attenuated about 20 dB in a Microwave oven but this is not enough.

RF-shielding enclosure

With the lid open the network with highest RSSI value has RSSI = −54dBm but when the lid is closed no networks can be found by the devices from within the enclosure.

From outside I am able to view all networks with the Wifi Analyzer android app [1]. When closing the lid on the larger RF-shielding enclosure the RSSI value for the enclosed network drops and the network is not even recognizable, this can be seen in figure 5.9. With the lid closed it is not possible to find the network with the Wifi Analyzer android app.

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5.2 Encapsulation 35 0 5 10 15 20 25 0 500 1000 1500 Seconds Mbit/s Set−top box 1 Set−top box 2 Set−top box 3 Set−top box 4

Throughput from laptop to 4 set−top boxes

Mean throughput 19.07 ± 0.02 Mbit/s Mean jitter 0.73 ± 0.02 ms

Lost packets 0

Sent packets 820 135 286

Figure 5.6: Result of 4 parallel measurements from laptop to two set-top boxes (2 parallel to each set-top box).

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Peak power in faraday cage made of aluminum foil P o w er [dBm] ● ● ● ● ● ●● ● ● ● ● ●● ● ● ● ●● ● ●● ● ● ●● ● ● ●● ●●● ●●● ●● ● ● ● ● ●●● −40 −30 −20 −10 0

No cage 1 layer aluminum 2 layers aluminum

Power [dBm] Power [µW ] Attenuation [%] No cage −18.50 ± 3.37 16.7 ± 6.38 0 1 layer aluminum −19.82 ± 4.25 13.4 ± 5.82 20 2 layers aluminum −21.80 ± 3.12 8.08 ± 4.67 52

Figure 5.7: Measurements of faraday cage made of aluminum foil with one and two layers. There are no significant attenuation by any of the faraday cages.

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5.2 Encapsulation 37

(a) Measurements of Received Signal

Strength Indicator (RSSI) in an open microwave at 2.4 GHz

(b) Measurements of Received Signal

Strength Indicator (RSSI) when closing the microwave at 2.4 GHz. The drop in RSSI is when closing the door.

(c) Measurements of Received Signal

Strength Indicator (RSSI) in an open microwave at 5 GHz

(d) Measurements of Received Signal

Strength Indicator (RSSI) in an closed microwave at 5 GHz

Figure 5.8: Measurements of Received Signal Strength Indicator (RSSI) in a microwave for 2.4 GHz and 5 GHz with the WiFiAnalyzer app for Android[1]. The Microwave shields the 2.4 GHz signal but the 5 GHz sig-nal is only attenuated about 20 dB.

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Figure 5.9: Closing the lid on the RF-shielding enclosure. The Received Signal Strength Indicator (RSSI) value are very well shielded.

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6

Discussion

Discussion of the final solution, the considered solutions and other important parts of this work.

6.1

Wired setup

The wired setup seems to work well and are probably very close to the air as physical medium.

I think that multiple spacial streams or beam forming may not work as all the wires are interconnected. This is something that I have not been able to measure.

6.2

WiFi technology

Because of how WiFi works the isolation makes it possible to use any channel and also reuse the same channel for all networks if you will. It is also then possible to use a 80 MHz or 160 MHz bandwidth for every network.

6.3

Throughput

The throughput is high and will be enough to provide 20 Mbit/s to 4 devices and at the same time sending smaller packets in the reverse direction, back to the laptop/server. This is necessary to be able to receive status and log messages from the devices during testing.

The attenuation is currently high in the system, if the attenuation is too high the modulation of the signal will be lower and the throughput lower. This could be solved by using attenuators with lower attenuation, I think 20 dB or 15 dB

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should be enough and that the devices could receive a signal strength that is 30 dB higher (if 15 dB attenuators are used instead of 30 dB).

6.4

Isolation

Three different solutions were tested for network isolation: wires, faraday cages and RF-shielding enclosures. RF-shielding enclosures was definitely the best op-tion with very good isolaop-tion of the network.

Wires

The wired setup has almost no isolation. I think this is because of the strong leakage points shown in figure 5.1. If these could be shielded the total isolation of the wired setup would be higher and encapsulation may not be necessary.

Faraday cages

The faraday cages made of aluminum foil did not give any good result or mea-surements. The measurements changed when rotating the cage. This is probably due to the fact that it is not entirely sealed and that every opening gives signals a way to escape or enter the cage. Also all cables may lead signals from outside into the faraday cage. I was not able to create any better faraday cage and therefore an alternative was needed.

The thickness I used for the aluminum cages should be enough as calculated with the skin depth in equation 4.2. But thicker aluminum foil could maybe shield more.

I did not test to add absorbing foam because I did not find any good provider that I could buy the foam from. I think that this could reduce the reflections in the cage and this is something that is used in the RF-enclosures used in this work.

Microwave

The microwave attenuated less for 5 GHz than 2.4 GHz frequencies, my guess is that the holes used were to large to fully attenuate 5 GHz waves or that connectors into the microwave are filtered for 2.4 GHz and not 5 GHz.

RF-shielding enclosures

The RF-shielding enclosures with 80 dB attenuation of signals provides very good isolation of the network. With WiFi’s threshold of the signal power being larger than -82 dBm, a 80 dB attenuation should remove any WiFi signal from outside as they are in reality always less than 0 dBm.

The RF-shielding enclosures are large and heavy but they do keep the network modular and simple with a single box. As all the connectors need to be filtered it is hard to alter the connectivity options when the enclosure has been ordered. If

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6.5 Reliability 41 changes needs to be made a new connector plate with the configuration wanted needs to be ordered. The RF-shielding enclosures are also expensive.

I ordered the RF-shielding enclosures from JRE instead of Ramsey even though they had similar RF-shielding enclosures. The reason for choosing JRE was that they had a lower price and offered faster manufacture and delivery time.

Cooling

Access point, set-top boxes, transformers and electricity regulators all get hot. The RF-shielding enclosure has ventilation but is otherwise air tight and it may be to hot inside. This is something that I have not tested but that I think will work well if the equipment inside are not blocking the ventilation.

6.5

Reliability

The system are reliable and works like a normal WiFi. The isolation has the benefit that there will be no waiting when other networks sends data on the same channel, and all channels are available to the enclosed network.

6.6

Measurements

When measuring throughput and reliability I have been using the tool iperf which works well. I have only had two set-top boxes to test with and therefore I was not able to test more devices.

When measuring signal strength with the frequency analyzer a problem has been that the access point will not send data without any connected device. This has been solved either by only listening to the beacons sent out automatically or by using only one antenna of the AP for measurements and connecting wirelessly with the laptop to the other 3 antennas.

6.7

Adoption in KATT

The system has been tested to work with ARRIS KreaTV Automated Test Tools (KATT) and it is possible to stream video streams to the set-top boxes without any lost packets. The set-top boxes are also sending log data back without any problems.

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7

Conclusion

In this work two types of techniques has been combined to provide isolation of a WiFi network. The wired setup has high throughput and good reliability but the isolation is low. The RF-shielding enclosure provides very good isolation and the combination of these two techniques creates a good solution to the problems.

With this solution only 4 set-top boxes are connected to the access point, this provides high throughput but the number of set-top boxes is low. As the network is isolated from other network it is possible to place multiple networks side by side to provide high throughput to a large number of devices.

The entire network fits in a single RF-shielding enclosure and the physical space of this is small compared to the environment.

7.1

Wired setup

The wired setup works and communication between different devices has high throughput and is capable of providing 20 Mbit/s UDP streams from the laptop to 4 set-top boxes in parallel. The throughput from laptop to set-top boxes are slightly higher than in the reverse direction.

The network is also reliable with no lost packets during one hour with 1 Mbit/s UDP stream in both directions between the laptop and a set-top box. This shows that the network is reliable with good performance and very low loss.

The wires only isolates slightly and the setup does not have enough isolation from other networks, it is not possible to use only the wired setup as a solution to this master thesis work.

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7.2

Encapsulation

Both faraday cages and RF-shielding enclosures were considered and tested to be used as encapsulation to further isolate the network.

Faraday

The faraday cages made of aluminum foil did not isolate enough and were very unreliable, there were no significant attenuation of the signal.

The test of microwave ovens showed about 20 dB attenuation for 5 GHz but this is not enough for this work. Microwave ovens are also too expensive and de-manding to work with compared to smaller aluminum cages or the RF-shielding enclosures.

RF-shielding enclosure

The RF-shielding enclosures have a high attenuation of 80 dB for 5 GHz waves. This was proven to be enough as the enclosed network is not detectable from outside and the enclosed devices detects no other network than the enclosed network.

Because everything fits within the larger RF-shielding enclosure it is easy to expand the solution with more enclosures, one for each new network.

Using only the larger RF-shielding enclosure was the best option even though it is possible to use both RF-shielding enclosures with a SMA-cable in between.

7.3

Final solution

The final solution is a wired setup where the antennas of each device has been interconnected and this replaces the air as a physical medium. This wired net-work is enclosed by a RF-shielding enclosure to isolate it from other netnet-works. The solution is an isolated network that is not detectable from outside and works with the WiFi standard without modifying any software in the devices.

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8

Future Work

In this chapter there are some ideas that could be useful to evaluate in future work. These are ideas that I have stumbled upon or did not have time to evaluate myself.

8.1

Single antenna wired setup

In the current setup all antennas are connected to the wired setup. This mimics the default behavior and usage of the devices as they are all connected to the air in the normal case. As described in section 6.1 all the WiFi features may not be applicable. Using only one antenna per device may work just as good as connecting all antennas.

With this setup the number of components used will be smaller. The setup could be reduced to only 5 attenuators, 5 U.FL to SMA cables, one 4-way split-ter/combiner, 4 set-top boxes and the access point. This will reduce the cost of the setup.

This could also make it possible to connect 8 set-top boxes instead of 4 if the 8-way splitter is used instead of the 4-way splitter. This system would use 9 attenuators, 9 U.FL to SMA cables, one 8-way splitter/combiner 8 set-top boxes and the access point.

8.2

Wireless setup in RF-shielding enclosure

Because the wires does not isolate the network much they may not be needed. All the wireless devices could fit in the RF-shielding enclosure normally, without the wires and this would make the solution easier and cheaper. There are problems with this idea that could arise, the devices should not be to close and when using

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antennas the signal power sent out is larger so the RF-shielding enclosure may not be able to attenuate it enough for the network to be isolated. All the measure-ments needs to be redone and I have not been able to test this due to the limited time.

8.3

More set-top boxes per AP

In the current measurements the throughput is constrained by the 100 Mbit/s router. If the router is replaced by a faster router and the throughput between devices is enough, more set-top boxes could be added to the system.

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Bibliography

[1] Wifi analyzer. https://play.google.com/store/apps/details?

id=com.farproc.wifi.analyzer. Accessed: 2015-01-05.

[2] Ieee std 802.11ac -2013, 2012.

[3] Wi-Fi Alliance. Wi-fi certified ac. http://www.wi-fi.org/

discover-wi-fi/wi-fi-certified-ac, 10 2014. Accessed:

2014-10-08.

[4] WiFi alliance. Certification. http://www.wi-fi.org/certification,

10 2014. Accessed: 2014-10-08.

[5] Kirt Blattenberger. Skin depth. http://www.rfcafe.com/

references/electrical/skin-depth.htm. Accessed:

2014-10-14.

[6] ETSI. Etsi en 301 893 v1.7.0. http://www.etsi.org/deliver/etsi_ en/301800_301899/301893/01.07.00_40/en_301893v010700o. pdf, 2012.

[7] M M J French. Mobile phone faraday cage. http://arxiv.org/pdf/

1112.5495.pdf, 2009.

[8] Matthew Gast. 802.11 Wireless Networks: The Definitive Guide. O’Reilly Media, 4 2002.

[9] Matthew Gast. 802.11ac: A Survival Guide. O´Reilly, 2013.

[10] Hakim Weatherspoon Ji-Yong Shin, Emin Gün Sirer. On the feasibil-ity of completely wireless datacenters. http://www.cs.cornell.edu/

~jyshin/papers/ancs2012_shin.pdf, 2012.

[11] LitePoint. Ieee 802.11ac: What does it mean for test?http://litepoint.

com/whitepaper/80211ac_Whitepaper.pdf, 2013.

[12] Inc Meru Networks. Understanding the ieee 802.11ac wi-fi standard.

http://www.merunetworks.com/collateral/white-papers/

wp-ieee-802-11ac-understanding-enterprise-wlan-challenges. pdf, 2013.

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Appendix

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A

Considered methods

Here follows methods that may potentially solve the problem. They will be eval-uated and the best solution will hopefully be possible to use.

The methods are chosen to be as simple as possible to make the evaluations specific. They are all using the 802.11ac standard on the 5 GHz band if nothing else is mentioned.

A single access point

A single AP may use the widest 160 MHz channel and the setup will be simple. This method will be used mostly as a comparison when describing other methods.

Pro

1. Simple setup

2. Large bandwidth, could use 160 MHz channel

Against

1. Does not use all available bandwidth 2. Many clients connected to a single AP

(a) Only a limited number of clients may connect to a single AP 3. Throughput will be shared by clients

4. Single point of failure, if AP is down, every client is disconnected

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Channel sharing

Multiple Access Points sharing the same channel (bandwidth). In this simple setup all APs share the same channel.

Pro

1. Large bandwidth, could use a 160 MHz channel

2. No single point of failure, if one AP is down the other APs may still be working, clients could switch to available APs

3. Many connected clients because each AP only connects a small group of clients

Against

1. Throughput will be shared by clients 2. Does not use all available bandwidth

Dual band

Using both the 2.4 MHz band and 5 GHz band enables more bandwidth. The structure may also be used in a way which makes the 2.4 MHz band used for normal data and the 5 GHz band for streaming video.

Pro

1. Very large bandwidth

Against

1. More complex structure (a) Multiple bands

(b) More complex channel selection 2. Noise from current 2.4 GHz usage

Isolated environments using Faraday cages

Faraday cages may be used to create smaller isolated environments where each environment has no influence or noise from surrounding environments. A fara-day cage is shown in figure A.1.

References

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