Chapter 1 Introduction

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Analysis and Planning of 802.11n MIMO wireless network using Multi-Polarized Antenna

This thesis is presented as part of Degree of Bachelors of Science in Electrical Engineering

Blekinge Institute of Technology June 2011

Haotian Wu

Atefeh Dehghan Nayyeri Supervised by J¨orgen Nordberg

July 4, 2011

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Abstract

MIMO (Multi Input Multi Output) technology is widely used in current wireless communication standard. Compared with SISO (Single Input Single Output) technology, MIMO can provide higher data rate and better communication quality. This thesis mainly focus on improving the communication quality of wireless local area network(WLAN) using wireless communication device with MIMO technology and Multi-polarized antenna.

Meanwhile, an WLAN indoor plan example will be studied. The original WLAN indoor plan will be improved by using the device mentioned above. The improvement will be based the the evaluation results.

Keywords: Wireless Communication , MIMO , Multi-polarized antenna , WLAN planning

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Acknowledgement

We would like to express our sincere gratitude to our program manager, Anders Hultgren, for his patient help to study and life, for countless of precious advices he gave us for our professional field and career plan.Special thanks to my supervisor and great teacher Dr.

J¨orgen Nordberg, for his profound knowledge within the field of wireless communication, but also for all his help in improving this thesis.

Special thanks to Shayan Haider, for his great help and advise on buying devices, devices configuration and experient design and for his generous attitude of spending lots of times and effort for this thesis work. His work has made a tremendous contribution to this thesis work.

Finally we’re appreciate our parents’ and our friend Emma Zhao’s courages that make us feel confident and aspiring to work on this thesis work.

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Abbreviations

• AP: Access Point

• CLI: Command-line Interface

• BTH: Blekinge Tekniska Hgskola

• DHCP: Dynamic Host Configuration Protocol

• GUI: Graphical User Interface

• GB: Giga Bytes

• Gbps: Giga bits per second

• ICI: Inter Symbol Interference

• IP: Internet Protocol

• ISI: Inter Channel Interference

• ISM:Industrial, Scientific and Medical

• LOS:Line Of Sight

• MAC: Media Access Control

• Mbps: Mega bits per second

• MIMO:Multi Input Multi Output

• MP antenna:Multi-polarized antenna

• MIMO-MP system: MIMO system with multi-polarized antenna

• OFDM: Orthogonal Frequency Division Multiplexing

• NIC: Network Interface Card

• RF: Radio Frequency

• SISO: Single Input Single Output

• SNR : Signal to Noise Ratio

• SSID: Service Set Identifiers

• STA: Station

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• WDS: Wireless Distribution System

• WEP: Wired Equivalent Privacy

• WLAN: Wireless Local Area Network

• WPA: Wi-Fi Protected Access

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5.2.1 Result and analysis of signal polarization distribution environment test . . . . 25 5.2.2 Result and analysis of Noise environment test . . . . 26 5.2.3 Result and analysis of wireless communication quality test . . . . 27 5.2.4 Result and analysis of Noise resistance ability test . . . . 27 5.2.5 Result and analysis of signal coverage area test . . . . 28

6 New WLAN plan 31

7 Conclusion and Future work 32

7.1 Conclusion . . . . 32 7.2 Future work . . . . 32

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Chapter 1 Introduction

Over the last decade there has been a dramatic growth in the use of wireless communication. Several wireless communication standards and devices have been developed.

It is without doubt that wireless communication is playing a more and more important role in business and normal life. However, not like the wired communication style, the signal form of wireless communication is radio wave travel through open air which means interference can be a major problem. The interference caused by other RF signals causes the limitation of the communication performance, i.e. data rate, signal coverage area, etc.

Many technologies have been developed to improve the performance of wireless communication. These technologies are mainly use special mechanism to avoid interference and collect as more signal power as possible. One of the most popular technologies is called MIMO (Multi Input Multi Output)[1]. Comparing with the regular SISO (Single Input Single Output) system, this technology utilizes multiple antennas on both transmitter and receiver which dramatically increase the transmission data rate and coverage without increase bandwidth and signal power [2]. Current application combines MIMO with other advanced technology (like Orthogonal frequency-division multiplexing technology, also called OFDM) to provide a much better communication service.

In this thesis, on the other hand, the entire approach tries to improve the wireless communication quality based on MIMO device with new type of hardware, which refers to a new type of antenna called multi-polarized antenna (MP antenna)[3]. This thesis work aims to improve the quality of received signal without increase the transmission power and bandwidth by using MP antenna on both transmitter and receiver. This performance improvement will also be implemented in an indoor WLAN (Wireless Local Area Network) plan.

In this thesis, the tasks are test and compare the performance of regular wireless communication antenna and MP antenna. Two wireless routers with build in MIMO technology will be used. The routers are configured to be transmitter and receiver by using a linux firmware called openWRT[4]. The evaluation the performance will be done by measuring certain parameters. Meanwhile, an actual indoor WLAN plan will be studied. A new WLAN plan will be introduced based on the actual WLAN plan and the conclusion of the MP antenna performance evaluation. The device used in the new plan is MIMO access point (AP) with MP antenna.

The organization of this report is as follows. In Chapter 2, the fundamental of antenna will be introduced, some important parameters and feature of different kinds of antennas including MP antenna. In Chapter 3, the overview of wireless communication will be present. In Chapter 4, general feature of openWRT is present. In Chapter5, the measurement methodology and result are shown. In Chapter 6, origin and new WLAN

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plan are present with explaination. Finally, the conclusion of thesis work and further research idea are present in Chapter 7.

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Chapter 2 Antenna Fundamentals

2.1 General introduction

Antenna is a very important element of radio equipment. Antennas are metallic structure that change radio signals in the air in to electricity wave or vice versa, depending on whether it is being used for receiving or for transmitting, respectively. In the other way to describe, they are designed for radiating and receiving electromagnetic energy [5].

Fig.2.1 can explain the radiation for an antenna which shows a voltage source connected to a two conductor transmission line. When the transmission line applies for sinusoidal voltage, an electric field is created which is sinusoidal in nature and this result in the creation of electric lines of force which are tangential to the electric field. The magnitude of the electric field is indicated by the bunching of the electric lines of force.

Figure 2.1: radiation for an antenna

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2.2 Important parameters of antenna

There are several antenna parameters that can be condidered as important: gain, efficiency ,direction ,polarization ,impedance matching ,current and voltage distribution ,resonant antennas ,impedance ,effective area or aperture ,radiation pattern, etc.

In this thesis, only the parameters which are considered important will be introduced.

2.2.1 Antenna Gain

The term Gain describes how much power is transmitted in the direction of peak radiation that of an isotropic source. An antenna with a large aperture has more gain than smaller one. Just as it capture more energy from a passing radio wave; it also radiates more energy in the direction [6].

2.2.2 Directivity of Antenna

The directivity of an antenna is the maximum gain of the antenna compared with its gain averaged in all directions.

Directivity of antenna can be considered as a parameter to evaluate whether an antenna is an onmi-directional antenna or directional antenna. An antenna radiates uniformly at all direction (i.e. an isotropic antenna ) can be considered as zero directionality or have 0dB diectivity [7].

2.2.3 Effective Area of Antenna

Effective area expresses an antenna’s ability to collect an incident radio wave and deliver it as an electronic current at the antenna’s terminals[8]. Effective area can be described (or to say depends on) the antenna’s radiation pattern and directivity.

2.2.4 Radiation Pattern

The radiation pattern is a graphical depiction of the relative field strength transmitted from or received by the antenna. Antenna radiation patterns are taken at one frequency, one polarization, and one place cut(see Fig.2.2) [9]. The patterns are usually presented in polar or rectilinear from with a dB strength scale. Patterns are normalized to the maximum graph value, 0 dB, and directivity is given for the antenna. Radiation pattern is very important to describe an antenna directivity, whether the antenna is directional or non-directional. Radiation pattern can also be presented in 3D figure which gives a 3D horizon for antenna directivity.

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Figure 2.2: Radiation pattern for an antenna [10]

2.2.5 Polarization

Antenna polarization is a very important consideration when choosing and installing an antenna.

The polarization of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth’s surface and is determined by the physical structure of the antenna and by its orientation[11].

Generally there are three types of polarization[11]:

• Linear polarization

• Circular polarization

• Elliptical polarization

In general, most antennas radiate either linear or circular polarization.

A linear polarized antenna radiates wholly in one plane containing the direction of propagation. The polarization of a linear antenna radiates the radio wave which has the same polarization. The general polarization type of a linear polarized antenna is horizontally polarized and vertically polarized[12].

In a circular polarized antenna, the plan of polarization rotates in a circle making one complete revolution during one period of the wave. If the rotation is clock wise looking in the direction of propagation ,the senses is called right-hand-circular(RHC)[11].If the rotation is counter clock wise ,the sense is called left-hand-circular(LHC)[11].

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2.3 Common type of antenna

2.3.1 Directional Antenna

A direction antenna is an antenna which radiates greater power in one or more directions allowing for increased the performance on transmitter and receiver and reduce interference from unwanted radiation in a certain direction[13].

With directional antennas, you can divert the RF energy in a particular direction to farther distances. Then you can cover long ranges, but the effective beam width decrease[14]. These antennas are suited for long range point to point solutions and the polarization for directional antenna is 90-180 degrees. The most common types are the yagi antenna, the log-periodic antenna, and the corner reflector, which are frequently combined and commercially sold as residential TV antenna[13].

2.3.2 Omni-directional Antenna

An omni-directional antenna is an antenna which radiates power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna’s axis. The 3-D radiation pattern can be considered as a shape of donut. Omni-directional antennas are vertically oriented and widely used for non-directional communication (e.g. Mobile phone system radio broadcasting) on the surface of the earth because they radiate equally in all horizontal directions. There will be little radio energy which is aimed in to the sky or down toward the earth wasted. Due to the structure of the antenna, it is very easy to install. Due to the 360 degrees horizontal pattern, it can even be mounted upside down from a ceiling in the indoor environment. Omni-directional antennas are widely used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM radio, Wi-Fi, GPS as well as for base stations that communicate with mobile radio such as police and taxi dispatchers and aircraft communications[15].

In these such antenna, the antenna will not coverage the below area.

This problem can be solved with the design of something called down tilt. With down tilt, the beam widths are manipulated to provide more coverage below the antenna than above the antenna. This solution of down tilt is not possible in an omni-directional antenna because of the nature of its radiation pattern.

The omni-directional antenna is usually a vertically polarized antenna. A low gain omni-directional antenna provides a perfect coverage for an indoor environment. It covers more area the AP or a wireless device in order to increase the probability of receiving the signal in a multi-path environment.

2.3.3 Microstrip Antenna

Microstrip or patch antenna is a kind of antenna which can be printed directly onto a circuit board. Because of this property, microstrip antennas are becoming very widespread within the mobile communication market, especially mobile phone. Patch antennas are low cost, have a low profile and are easily fabricated [16].

Microstrip Antenna can be considered as one kind of directional antenna with linear polarization.

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2.3.4 Multi-polarized antenna

Multi-polarized antenna (MP antenna) use different kind of technology to make the antenna radiates and receives radio wave with different polarization[17].

In this thesis, Trident MP Antenna is used for evaluation. Trident MP Antenna has six build-in linear polarized omni-directional sub-antennas[18]. These sub-antennas has cover almost all different polarization direction. This type of antenna also has build-in spatial diversity to improve the communication quality. This technology will be discussed in next chapter.

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Chapter 3 Overview of wireless communication

3.1 Introduction

In telecommunications, wireless communication can be used to exchange information over different distances. The short distance wireless communication can be within a few meters such as television remote control. The long distances wireless communication can be a radio communication over several kilometers or longer[19]. Wireless communication make the communication possible to be implemented where wired communication can be hardly implemented, such as a long distance communication which is impossible to be processed based on a wired infrastructure. Wireless communication is commonly applied in the telecommunications systems such as radio transmitters and receivers, remote controls, computer networks, network terminals. The information transferred with different form of energy such as radio frequency (RF), infrared light, laser light, visible light, acoustic energy without the use of wires[20].

When it comes to the modern use of wireless communication, one of the most significant fields is wireless networks, which will be repeatedly discussed in this thesis. Wireless network utilize RF (Radio frequency) energy to carry data and transmit it to one or more terminals. The frequency band used in wireless communication is called ISM (industrial, scientific and medical) radio band[21]. The common carrier frequency is 2.4-2.5 GHz and 5.725-5.875 GHz[21]. The digital data will be coded, modulated into analog signal and transmitted over carrier frequency. Wireless technology is used in security systems, cellular telephone (phones and modems), WLAN, Wireless energy transfer, Computer interface devices [19]. In this thesis, most of the discussion will mainly focus on WLAN.

3.2 Significant factor and problem in WLAN communication

Current requirement for WLAN is to perform satisfactory data exchange speed and signal coverage area under limited bandwidth and transmit power. In this case , WLAN should has a satisfactory data rate and signal quality, i.e. signal strength or signal to noise ratio (SNR) and interference resistance ability [22]. Meanwhile, the WLAN should handle multiple user in the same time while still provide satisfactory communication performance.

Since WLAN transmit signal through open air space, the signal can be easily interfered and changed by both natural and artificial matter. Signal power can reduce due to penetration through an obstacle, i.e. shadowing. When Radio wave impinges on a

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rough surface, the reflected energy is diffused in all directions, i.e. scattering. There can be other problem like Inter Channel Interference (ICI), Inter Symbol Interference (ISI) etc, which will not be discussed in this thesis[23][24].

The most interesting problems in WLAN which are under concern in this thesis are multi-path propagation and polarization mismatch. When one signal come across different objects and cause multi-path reflection, causing multi-path propagation. Multi signals will be received at the receiver. Multi-path signals have different phase due to different length of propagation path. These signals will merge at the receiver and cause the power reduction, i.e. fading. However, it is also possible that one signal’s positive peak meets others positive peak at a specific point which make this point has a very high signal strength called hot spot. The worst case, one signal’s positive peak meets another one’s negative peak which causes a null point with no signal power, see Fig.3.1

Figure 3.1: Multi-path propagation of radio waves [26]

Polarization mismatch is caused by reflection, in this case, scattering and multi-path propagation. Due to the reflection, the signal polarization will be shifted which may be different from the polarization of the receivers antenna. In general, for two linearly polarized antennas that are rotated from each other by an angle Phi, the power loss due to this polarization mismatch will be described by the Polarization Loss Factor (PLF),see equation 3.1 [25].

P LF (dB) = 20log(cosφ) (3.1)

Hence, if both antennas have the same polarization, the angle between their radiated E-fields is zero and there is no power loss due to polarization mismatch. If the polarizations of transmission and receiving antenna are perpendicular to each other, then no power will be transferred, see Fig.3.2 [25].

In current days, WLAN devices require more and more mobility. It is hard to configure the antennas polarization in WLAN device to be matched with the transmitter antenna’s polarization. However, that not means the signal will be poor due to polarization mismatch. Since in most of the cases these device are used indoorly, the mixed, scattered multi-propagation signals contains many different polarizations which make it possible to receive signal energy. The variety of signal polarization is called polarization

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Figure 3.2: The polarization mismatch between radio signal and receiver’s antenna [26]

diversity. In thesis, measurement will be taken to evaluate the polarization diversity.

By analyze these measurement results, it is possible to use new type of antenna to collect extra signal energy, i.e. those signals with a mismatched polarization from antenna polarization. In this way, signal quality, i.e. SNR can be optimized.

3.3 MIMO and Spatial diversity

MIMO, also known as Multi-input Multi-output, is a wireless communication technology.

MIMO uses multiple antennas on both transmitter and receiver, which dramatically increases the spectral efficiency, i.e. improves the performance of wireless communication.

The channel capacity is increased proportionally in the number of antennas; meanwhile, no additional power or bandwidth will be applied [27].

As the thesis mentioned in the former section, one of the most significant problems in wireless communication is fading caused by multi-path propagation. The power of the transmitted signal will decrease at the receiver side because of fading. MIMO, however, takes advantages of multi-path propagation. The received multi-path signals can be considered as in independent fading channel (also called independent spatial signature), i.e. possible to be distinguished from each other, if the antennas of receiver are placed far enough compared with signal wave length. MIMO utilizes the independent fading channel to transmit different signals via multiple antennas in same frequency. By using sophisticated signal process technology, it is possible to separate and collect different signals. In general, this technology is called spatial multiplexing, a high speed data stream can be divided into several low speed data stream and send out in the same time over same frequency [1]. In this way, the data rate of the wireless communication is significantly increased.

The most popular wireless communication standard (IEEE 802.11g) can support data rate up to 54Mbps, which cannot meet modern data rate for special service like high definition video stream, data traffic with large number of users at the same time, etc [28]. By adopting MIMO technology, the new wireless communication standard IEEE 802.11n can perform a raw data rate up to 600Mbps with four with the use of four spatial streams (e.g. four antennas) with a channel bandwidth of 40 MHz [29].

Another technology inside MIMO is called spatial diversity [1]. The aim of spatial diversity is to collect different multi-path signal with independent fading properties (if

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the receivers antennas are positioned far enough from each other, then the received signal on each antenna can be considered as independent fading channel). This is also called receive diversity[30]. Several independent observations of the signal (one data bit) are combined at the receiver by combining techniques in order to get a better signal quality[30]. There are three different combination technology, selection combining (SC),equal gain combining (EGC),maximum ratio combining (MRC) [30]. The detail of these technologies will not be discussed in this thesis. In general, take MRC as an example; different multi-path signals are combined after putting different weight and extra phase shifting individually in order to maximize the SNR of the combined signal.

By doing this, the received signal can has a quite high SNR, i.e. better quality. On the other hand, since MIMO utilizes multiple antennas, it is very unlikely that all antennas will be positioned at a null point, which means the received signal are very likely to be better than the signal received in SISO system.

3.4 Significant parameter in WLAN communication evaluation

In this thesis, all approaches will be mainly focused on enhancing the signal quality.

Other than the common thought of signal enhancement implemented by increase transmitting power, extra signal energy will be collected by take advantage of spatial diversity and polarization diversity.

The MP antenna used in this thesis has build in spatial diversity and polarization diversity technology. It is possible to collect more signal energy compared with the regular WLAN antenna since regular antenna has no multiple polarization and multi sub-antenna which can perfectly solve polarization mismatch and multi-path propagation fading problems.

The significant parameters are:

• Signal strength (dBm)

• Noise strength (dBm)

• SNR (dBm)

• Data rate (Mbps)

• Coverage area

SNR can be calculated based on the equation 3.2 [31].

SN R(dBm) = SignalLevel(dBm) − N oiseLevel(dBm) (3.2) The coverage area parameter will be measured and evaluated with data rate over different transmission length.

3.5 WLAN indoor planning

As WLAN become more and more popular, planning WLAN in an indoor environment becomes a very significant issue. Generally, the indoor WLAN planning considers four major factors. They are calculation of the data traffic load, consideration of the signal

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coverage area, minimization of the inter signal interference and consideration of the requirement of mobility. Based on these factors, additional work can be done for buildings structure reconnaissance and security consideration (like user identification in public environment and the communication encryption algorithm, etc) [32]. The four factors will be discussed in the subsection of this section.

3.5.1 Calculation of the data traffic load

Indoor WLAN planning requires a reasonable consideration of the service needs[32]. For example, if a WLAN has users mainly requires e-mail service without any potential increase of data traffic, this WLAN can be designed with relatively low data rate device, like IEEE 802.11b access point. If the network users require service like real time audio- video communication or massive data downloading and uploading, then the devices with higher data rate are necessary, like IEEE 802.11g device.

3.5.2 Consideration of the signal coverage area

As the data rate of the wireless communication devices increases, the signal coverage area will be smaller[32]. The sensitivity of the SNR will be increased along with the higher speed modulation technology (i.e. the data rate will be depends more and more on the SNR). Meanwhile, multi-path propagation causes a significant signal strength fading.

When the radio wave penetrates through the building structure like a wall, shadowing will cause attenuation of the signal strength. Different materials of the building structures cause different degree of shadowing. These issues should be well considered in the indoor WLAN planning.

The current WLAN planning utilizes smarter access point. Different access point can exchange the traffic load information on real time. Each access point can change its coverage area based on the areas traffic load (i.e. if a access point has a higher data traffic load, it can automatically reduce its signal coverage area to provide higher data rate. If the access point senses a rather lower data traffic load, it will enlarge its signal coverage area.) Access points can also control its coverage area to avoid interference between each other.

3.5.3 Minimization of the inter signal interference

Current wireless communication technologies mainly transmit signal with microwave frequency (like Bluetooth device, WLAN device, microwave oven, etc). As more and more devices work in this specific frequency band, interference becomes a big issue[32].

One signal will be considered as noise for other devices. General idea of avoiding inter signal interference is use different channel of wireless channel. For example, different access point use different wireless channel which located far enough from each other, like channel 2,6,11 (i.e. 2 404- 2 428 MHz, 2 426- 2 448MHz, 2 456-2 478MHz) [33]. However, this issue cannot be solved by this countermeasure in some occasion, like microwave ovens will radiates microwave which covers almost all wireless channels.

This thesis, on the other hand, solves this problem in another way. As will be mentioned later, the measurement results of communication quality indicate that MP antenna has a better ability of noise resistance.

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3.5.4 Consideration of the requirement of mobility

Different WLAN has different mobility requirement. In some WLAN, users stay at a rather fixed point. In this environment, users normally do not move when they use WLAN, so this environment does not need continuous wireless network signal coverage.

The mobile device can be disconnected and reconnected again after a few while when being moved. In this condition, access point can be deployed in a low density and the coverage area for each access point in relatively small in order to provide a higher data traffic (users gathers together under an access points coverage area makes it highly possible to generate high data traffic load)[32].

However, in some environments, users need to use mobile device while moving within a relatively large area where one access point cannot provide sufficient service. Then multiple access point are needed. In this way, user will disconnect from one access point and reconnect to another one (i.e. handover) smoothly, which means user can hardly sense the temporary disconnection. This environment needs high density of access point deployed in a specific area while different access point should avoid interference from each other.

In this thesis, the new WLAN plan will not fully reconsider every significant factor mentioned above. Since the BTH building WLAN plan is done by CISCO company, the exsiting WLAN can be regarded as a well considered WLAN plan. The new WLAN plan are generated by modifying the existing WLAN plan based on the advantage of the MIMO-MP system.

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Chapter 4 OpenWRT

4.1 Introduction

OpenWrt is a niche Linux distribution mainly installed on embedded devices, e.g. residential gateways [34]. It is built based on the core code of linux system. OpenWRT generally works in command-line interface (CLI) of ash or bash, but it can also operating in graphical user interface (GUI) such as LuCI or X-Wrt or Gargoyle Router Firmware [34].Like common Linux operation system, openWRT can install program package via opkg command (just like apt-get install command in linux operating system).

OpenWRT generally provides almost every function in a regular routers firmware.

Since linux based programming is open sourced, it is possible to develop custom software for openWRT providing some special functionality without any charges. OpenWrt offers all of the features provided in the stock firmware for residential gateways, such as DHCP services and wireless encryption via WEP(Wired Equivalent Privacy), Wi-Fi Protected Access and WPA2(Wi-Fi Protected Access) [34][35][36][37]. OpenWRT also provide some advanced function that other routers are poorly implemented (e.g. some advanced function only provided in enterprise level production and some function which cannot implemented because of the standard limitation such as transmission power control).

Compared with the CLI operation with GUI operation, CLI can perform all config- urations by typing command, but it is hard and complex when actually doing it. GUI can perform easier configuration for lots of functions, but most of the operation can only perform a basic level configuration, for example, using GUI is much complex to perform a linux shell scripting program . In this thesis, both CLI and GUI are used in order to get all significant parameters readings. The shell scripting code is shown in Appendix III.

4.2 Introduction of installing openWRT in a wireless router

It is not safe to install openWRT into the flash memory soldered on to the circuit board. Flashing the wrong file will destroy the hardware (i.e. brick it), some laboratory procedures are needed (such as using Jtag wire to de-brick the hardware, the detail will not discussed in this thesis). When an openWRT is installed in the wireless router, it is possible to change it back to original configuration, change the version of openWRT [38].

Generally there are three way to install openWRT [38].

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• Using Web Browser Some Web user interface of the original version of router can updgrade the operating system into openWRT directly.

• Running a TFTP server via Ethernet or via serial cable

• Using Kermit protocol to transfer the new image

The actual installing procedure will be introduced in next section.

4.3 Procedure of installing openWRT in this thesis

The precedure used in this thesis is to install openWRT using the TFTP and RS232 method[39][40].

4.3.1 Obtaining Firmware

A stable inmage should be downloaded with factory and SquashFS[41]. Quickest way is to download a precompiled stable image is to look for openwrt-ar71xx-tl-wr1043nd-v1- squashfs-factory.bin at http://downloads.openwrt.org/backfire/10.03.1-rc4/ar71xx/

These images do not have modules for wifi. There is room to easily install missing packages on the jffs2 partition later per opkg update then opkg install kmod-ath9k wpad- mini.

4.3.2 Enabling Serial Access on the Router

Solder a header as shown in the Fig.4.1 or wires with a connector directly. In order to have access to the header we need to fully disassemble the device. The device uses TTL(Transistortransistor logic) @ 3.3V and not a standard RS-232 Serial that oper- ates between 3 and 15V, so do not try to connect it to a common serial adapter: you will certainly fry the serial circuit or even the whole board [42]. There are plenty of USB(Universal Serial Bus) to TTL and RS-232 to TTL available on the market, just be careful with the voltage: the standard is 5V and it may also damage your board [44].

Look for the ones with 3.3V or with both voltages and a way to switch between them.

The TX (transmission) pin of the serial port must linked to the RX (reception) pin of the router and the RX to TX.

4.3.3 Installing the firmware image on the Router

Installing openWRT using TFTP server should follow these steps Requirements:

• terminal program (e.g. minicom) set to 115200 8N1, no flow control

• file named code.bin containing openwrt firmware.

• tftpd server with an address 192.168.0.5 (configurable with setenv command, print- env first if unsure)

The simplest tftp server to use is dnsmasq [43]. Install and run with dnsmasq enable- tftp tftp-root=/code.bindirectory

Commands:

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Figure 4.1: Wireless router circuit board

After you see ”Autobooting in 1 seconds” type ”tpl” and hit enter to get into command promt.

erase 0xbf020000 +7c0000 # 7c0000: size of the firmware (be aware that you may have a different size thus bricking your router)

tftpboot 0x81000000 code.bin

cp.b 0x81000000 0xbf020000 0x7c0000 bootm 0xbf020000

4.3.4 Enabling USB storage and Mounting external Drive

This procedure is mainly used to extract the file which generated by the shell scripting program that contains all the parameters’ readings. This specific file is originally stored in the openWRT file system. The procedure will be introduced step by step.

Type the following command

• opkg update

• opkg install kmod-usb2

• insmod ehci-hcd

Connect your storage device to your PC and partition your storage device. Then for- mat the storage device, ext2 for USB stick and ext3 for USB harddisk are recommended.

Install the following packages via OPKG [45]

• kmod-usb-storage:Kernel support for USB Mass Storage devices [46]

• kmod-usb-storage-extras :Kernel support for some more drivers, such as for SmartMedia card readers

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• block-mount:Scripts used to mount and check block devices (filesystems and swap)

• block-hotplug:Scripts used to automatically check and mount filesystem and/or swap

• kmod-fs-xxx:the filesystem you formated your partition in, in our case kmod-fs- ext4

Connect your storage device to your OpenWrt router, the device and its parti- tions should immediately be available as Device files under /dev/, for example dev/sda, /dev/sda1, /dev/sda2, etc.

Mount the connected filesystem

mkdir -p /mnt/share mount -t ext3 /dev/sdaX /mnt/share -o rw,sync

4.4 WDS (Wireless Distribution System)

A Wireless Distribution System (WDS) Is A System That Enables The Wireless Inter- connection Of Access Points In A Wireless Network Environment [47].

WDS allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client packets across links between access points.

An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet. A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them on to relay or main stations. Connections between clients are made using MAC (Media Access Control) addresses rather than by specifying IP (Internet Protocol) assignments.

All base stations in a Wireless Distribution System must be configured to use the same radio channel, method of encryption (none, WEP, or WPA) and encryption keys.

They can be configured to different service set identifiers (SSID). Wireless Distribution System (WDS) also requires that every base station be configured to forward to others in the system. See Fig.4.2

Figure 4.2: WDS Point to Point

Wireless Distribution System (WDS) may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional

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bridging). It should be noted; however, that throughput in this method is halved for all clients connected wirelessly.

Wireless Distribution System (WDS) can be used to provide two modes of wireless AP-to-AP connectivity:

• Wireless Bridging in which WDS APs communicate only with each other and dont allow wireless clients or Stations (STA) to access them

• Wireless Repeating in which APs communicate with each other and with wireless STAs

4.5 Setting up WDS Bridge between Routers in Open- WRT

Due to its non-standard nature, WDS is often differently implemented in wireless drivers and vendor firmwares making them incompatible to each other. In order to be able to use WDS one should use the same hard- and software on all deployed wireless devices to have the best possible compatibility.

In OpenWrt there are two flavours of WDS available, depending on the wireless chipset and driver in use:

• Broadcom WDS:available on Broadcom wireless chipsets using the proprietary wl.o driver

• AP-to-STA WDS:available for both Madwifi and mac80211 supported wireless devices

The biggest advantage of WDS is the Layer 2 transparency enabling bridging and broadcasting accross the wireless connections - all involved network segments form one common broadcast domain [48][49].

4.5.1 On Access-Point Side

Step 1: edit /etc/config/wireless

add option wds 1 to the existing wifi-iface section Step 2 : disable firewall

/etc/init.d/firewall disable

4.5.2 On Client Side

Step 1: edit /etc/config/wireless

set option mode to sta and add option wds 1 to the wifi-iface section Step 2 : disable firewall

/etc/init.d/firewall disable Step 3 : disable dhcp server Step 4 : disable dnsmasq /etc/init.d/dnsmasq disable

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Chapter 5 Measurement result and Analysis

5.1 Experiment Design

In this thesis, the experimental equipments are two TP-Link TL-WR1043ND wireless routers, six Trident MP Antennas. Two laptops, AirView2-EXT wireless spectrum analyzer.

Before the experiments, certain configuration of the equipments is done. Firstly, re- place the default operating system of TP-Link TL-WR1043ND wireless router by open- WRT operating system. Use openWRT user interface to bridge two router together over the wireless channel, one will be configured as a bridge server and the other one will be configured as bridge server. Two laptop connect to different routers with net cable. The laptop connected to the server router will be configured as an FTP server (use Windows operating system to configure one of the folders as a shared folder). The other laptop will get access to router’s openWRT command line interface via telnet connection. This laptop will run a shell scripting program to get necessary parameter readings from the client router (Signal strength, noise strength and SNR). The program will generate a csv formatted text file. Another Windows based program called DU meter will run on the laptop in the same time to get the data rate from the laptop’s wired network interface card (NIC). In this thesis, the laptop’s wired NIC can perform up to a 1Gbps data rate, which is much higher than the wireless communication data rate. So the data monitored from the wired NIC can be considered as the actual data rate from the wireless link between two wireless routers.

Based on the goals of this thesis work, the following experiments are designed:

• Signal polarization distribution environment test: use AirView2-EXT wireless spectrum analyzer to test the signal polarization distribution on all wireless channels in the indoor environment of BTH building. The spectrum analyzer will measure the signal strength of different polarization.

• Noise environment test: use AirView2-EXT wireless spectrum analyzer to measure the signal strength on all wireless channels in cafeteria BTH when the microwave oven is working to analyze how the noise interferes the wireless communication.

• Wireless communication quality test: two routers will be placed in an indoor environment in BTH building without line of sight (LOS) [50]. The laptop connect to the client router will download files larger than 2 GB from the FTP server (the file size should be large enough to make enough time for monitoring data traffic and get parameter readings). Run the shell scripting program to take parameter

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readings which will be stored in a csv formatted text file. The program will take all significant parameters reading once a second for a minute. DU meter will run at the same time for one minute to get the average data rate. These readings are called one group of readings. This test will run three different subtest, different subtest has different configuration of antennas. The first subtest has vertically polarized omni-directional antenna on both routers. The second subtest has omni- directional antenna mutually perpendicular to each other (this configuration can make three omni-directional antenna work like an MP antenna). The third subtest has three actual MP antennas. Each subtest will take three groups of reading(see Appendix II,picture of antenna configuration).

• Noise resistance ability test: two routers are placed in an indoor environment inside a BTH building with LOS (Since the room with LOS can hardly find a spot without LOS, it is still a multipath propagation environment which makes it sufficient to run tests). The task will be the same to wireless communication quality test. The only difference is that all the tests will run with at least two microwave oven working at the same time.

• Signal coverage area test: two routers are placed in an indoor environment inside a BTH building with LOS (in this way, shadowing will not be taken as an factor in the wireless communication which makes the test simple and the distance between transmitter and receiver is easier to measure). One laptop connected to the server router with net cable and configured as an FTP server. The other laptop download files from the FTP server with wireless NIC. DU meter will run at the same time to take readings of data rate. The antenna configuration is the same as the test mentioned above. The readings will be taken over four different distances.

5.2 Measurement result and analysis

5.2.1 Result and analysis of signal polarization distribution environment test

The readings are taken from cafeteria BTH(see the sructure of the buiding in appendix IV), Fig.5.1 and Fig.5.2 shows the signal distribution on both horizontal polarization and vertical polarization.

Figure 5.1: Signal distribution of horizontal polarization

It can be seen that signals with horizontal and vertical polarization both have substan- tial power. It also can be seen that the signal power in horizontal polarization is a little bit higher than the vertical polarization, that is because the access point in cafeteria are horizontally polarized. Multi-path propagation and scattering are the reasons why signal are shifted from horizontal polarization to vertical polarization. Omni-directional antenna

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Figure 5.2: Signal distribution of vertical polarization

can only receive signal with a certain polarization which means there is a huge amount of signal power with different polarization wasted. Compared with omni-directional antenna, MP antenna can receive signal with almost any type of polarization, which means MP antenna can retrieve more signal power and perform better communication quality.

5.2.2 Result and analysis of Noise environment test

The readings are taken from cafeteria BTH, Fig.5.3 and Fig.5.4 shows the signal power distribution in the wireless channel on both horizontal polarization and vertical polarization

Figure 5.3: Signal distribution of vertical polarization with microwave oven running

Figure 5.4: Signal distribution of vertical polarization with microwave oven running It can be seen that no matter on horizontal polarization or vertical polarization, the microwave power spreads to almost all channel with very high power (even higher than the regular transmission power of WLAN). The conclusion can be made that the wireless communication will be seriously interfered and the communication quality will be affected. Further test mentioned later will explain which parameter will be influenced by high power noise.

Another conclusion made from this test is that in this specific environment, it is better to use channel whose frequency start at 2475MHz or higher frequency, because the microwave can hardly influence that channel.

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5.2.3 Result and analysis of wireless communication quality test

This test is taken in building J second floor.(see the sructure of the buiding and the position to place the two routers in appendix IV) Based on the csv file generated by shell scripting program, the data is analyzed with MATLAB, average values of different parameters are calculated, all these results along with the average data rate calculated by DU meter are shown in table 5.1 ”Parallel” means vertically polarized omni-directional antenna on both routers, ”perpendicular” means omni-directional antenna mutually perpendicular to each other.

Antenna type Data rate Signal strength Noise strength SNR Parallel 15.83 Mbps -41.86 dBm -91 dBm 49.14 dBm Perpendicular 22.15 Mbps -36.5 dBm -92 dBm 55.5 dBm

MP antenna 27.03 Mbps -38.25dBm -91 dBm 52.75 dBm Table 5.1: wireless communication quality test

It can be seen from the result that compared with the result with vertically polarized omni-directional antenna on both routers, the result of omni-directional antenna mutually perpendicular to each other and MP antennas has higher signal strength, SNR and data rate. The conclusion is that when antenna array of MIMO device contains multi-polarized receiving antenna, it can help the system improve its signal strength, SNR and data rate. The noise strength is almost constant in all three subtest which means antenna type do not affect the received noise power.

From the result shown above,it can be seen that noise strength is almost constant.

According to equation 3.2, it is obvious that since the noise is constant, signal strength and SNR always increases or decreases at a same amount. So taking one of them to analyze the communication quality is sufficient. As mentioned before, since high data rate modulation technology are very sensitive to SNR, so further analysis will be mainly based on SNR and data rate. Compared with the measurement result of MP antenna and omni-directional antenna, MP antenna can increase the data rate for 70% and increase SNR for 25.2%.

5.2.4 Result and analysis of Noise resistance ability test

This test is taken in building J second floor, teachers’ rest room.(see the sructure of the buiding and the position to place the two routers in appendix IV) Based on the csv file generated by shell scripting program, the data is analyzed with MATLAB, average values of different parameters are calculated, all these results along with the average data rate calculated by DU meter are shown in table 5.2 ”Parallel” means vertically polarized omni- directional antenna on both routers, ”perpendicular” means omni-directional antenna mutually perpendicular to each other.

Comparing with the measurement result with and without microwave oven working, it can be seen that the noise strength is still constant, but the signal strength significantly decreased cause the decreasing of SNR. Data rate has dropped 70%-84%, SNR dropped 25%. So it can be seen that high noise power can severely affect the SNR and data rate.

Further conclusion is that under high noise power environment, it becomes harder for wireless communication device to retrieve signal power from the environment, causing the drop of signal strength and SNR in which case decrease the data rate.

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Antenna type Data rate Signal strength Noise strength SNR Parallel (no microwave) 63.4 Mbps -15.52 dBm -89 dBm 73.48 dBm MP antenna (no microwave) 86.1 Mbps -14.40 dBm -91 dBm 76.6 dBm

Parallel (microwave) 10.1 Mbps -20.44 dBm -89 dBm 68.56 dBm Perpendicular (microwave) 14.63 Mbps -18.53 dBm -89 dBm 70.47 dBm MP antenna (microwave) 26.2 Mbps -17.85 dBm -91 dBm 73.15 dBm

Table 5.2: Noise resistance ability test

Comparing with the test when microwave ovens were working, it is obvious that MP antenna performs better than the regular omni-directional antenna. MP antenna can retrieve more signal power in which case increase the SNR and data rate. Since the noise level is constant with and without microwave oven working, it can be concluded that MP antenna cannot decrease the received noise strength to increase SNR. MP antenna increases SNR by increasing signal level. Compared with omni-directional antenna, MP antenna has a better noise resistance ability.

5.2.5 Result and analysis of signal coverage area test

This test is taken in building J first floor.(see the sructure of the buiding and the position to place the router in appendix IV) The results are plotted by MATLAB and shown below. Fig.5.5,Fig.5.6 and Fig.5.7 shows the data rate and SNR at different distance with three different antenna configuration. Fig.5.5 shows the result with vertically polarized omni-directional antenna on both routers,Fig.5.6 shows result with omni-directional antenna mutually perpendicular to each other, Fig.5.7 shows results with MP antenna on both routers.

Figure 5.5: Vertically polarized omni-directional antenna on both routers

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Figure 5.6: omni-directional antenna mutually perpendicular to each other It can be seen from the result that as the transmission distance became longer, the data rate and SNR became lower. However, it also can be seen that in some result, as the transmission distance became longer, the data rate, on the other hand, became higher. That may because the structure of the building causing multipath propagation and make the signal strength higher at some specific area than others. From an overview of the whole picture, it is still very obvious that as the transmission distance became longer, the data rate and SNR became lower. Compared with different kind of antenna, under same transmission procedure, MP antenna performs higher data rate in certain transmission distance which also means wireless communication device with MP antenna has larger coverage area under same data rate.

However, this conclusion do not made due to MP antenna can retrieve more signal power, since in this test MP antenna work as transmission antenna other than receiving antenna. A reasonable explanation is that since most of the mobile device moves from place to place, it is hard to just its position and make the polarization of the antenna to match the polarization of received signal. This problem can cause signal attenuation due to polarization mismatch. Because of the multipath propagation in an indoor environment, signal travels in the air with different degree of polarization shifting, but different polarized signal has different power. If a mobile device has an antenna which can receive certain polarized signal with rather low power, it can cause communication problem. But for MP antenna, the power of signal with different polarization is averagely distributed in the environment. It can enlarge the signal power in certain polarization. In this way, no matter how the mobile device are placed and positioned, the received signal power can be both stable and satisfactory.

In this test, the laptop has an wireless NIC with two horizontally polarized omni- directional antenna placed inside the edge of the lid.

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Figure 5.7: MP antenna

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Chapter 6 New WLAN plan

Based the on the analysis of all the result, two new WLAN plans is provided. All access point in the new WLAN plan is MIMO wireless router with MP antennas.

One of the new WLAN plans is based on the WLAN provide by BTH for its G building third floor. The original access point uses IEEE 802.11g standard. See the original plan in Appendix IV. The original plan can perform a well multi-user handling with mobility. In the large lecture room, two access point are deployed to handle large numbers of users get access to Internet at the same time. All access points can increase or decrease their signal coverage area to according to the data traffic load condition.

This kind of WLAN planning can also perform a smooth handover when user moving around in this floor.

Based on the analysis of MIMO-MP system measurement result, it can be considered that the MIMO device (i.e. IEEE 802.11n wireless router) performs higher data rate (i.e. higher data capacity in wireless channel). The new plan is worked out based on the conclusion that MIMO device can handle higher data traffic and more users (here more users can be considered as higher data traffic). Also, MIMO device has larger signal coverage area under same data rate. General experience shows that the IEEE 802.11g access point has ability for signal to penetrate at least one concrete wall, based on the measurement result, MIMO-MP system can have a better signal penetration ability. The new plan made the following modification from the original WLAN plan.

1: Cancel KNAa-HusG-14 access point, move KNAa-HusG-13 to the center of the lecture room.

2:Cancel KNAa-HusG-11 access point, move KNAa-HusG-10 near the wall between to lecture room.

3:Move KNAa-HusG-9 access point to the position near the west wall.

Another reason to reduce the number of access is that based on the original WLAN plan for cafeteria BTH (shown in the Appendix IV), it is possible to handle data traffic for one floor with only one access point in a rather large area compared with a lecture room.

The other WLAN plan is based on the second floor of building J teachers’ office area (see appendix IV). Basically the place and number of access point are not changed, but the device of the access point is replaced by new devices. In this case, the data rate and the signal strength will be largely increased.

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Chapter 7 Conclusion and Future work

7.1 Conclusion

Compared MIMO-MP system with IEEE 802.11g device, MIMO-MP system has higher data rate and larger signal coverage area. It can be a sufficient substitution of IEEE 802.11g device to perform better communication quality with rather low cost. It will become a trend to use this kind of device for future WLAN planning.

7.2 Future work

MIMO-MP system used in this thesis is evaluated based on actual physical test. The parameters used in this thesis are limited. Simulation for MP antenna with MIMO device should be done in order to cover all significant and potential factors that affect communication quality. More test should be run in an ideal environment in order to isolate all factors and examine them one by one.

It can be seen from the test in this thesis that MIMO-MP system will dramatically improve the communication quality when the receiver has used MP antenna. However, the current MP antenna is too large to be utilized in small mobile device like mobile phone, laptop etc. Future MP antenna should be smaller to embedded in small mobile device. The polarization and space diversity technology should be enhanced.

Chapter 1 Introduction

Acknowledgement

Abbreviations

Contents

Chapter 1 Introduction

Chapter 2

Antenna Fundamentals

Chapter 3

Overview of wireless communication

Chapter 4 OpenWRT

Chapter 5

Measurement result and Analysis

Chapter 6

New WLAN plan

Chapter 7

Conclusion and Future work