Performance In A Uganda Deployment

Published Date: 02 Nov 2017

Isaac Mwesigwa

ESO8M10/422

Thesis submitted in partial fulfillment of the requirement for the degree of Master of Information Technology, Uganda Christian University Mukono.

DECLARATION

I Isaac Mwesigwa do hereby declare that this research project report is my original work, and that where references have been made; I have endeavored to acknowledge such intellectual property. To the best of my knowledge, this research work has never been submitted to any University or other Institution of learning for any Academic award.

Isaac Mwesigwa (student)

......………………………………………………

Date ……………………………………………

APPROVAL

The research project report has been submitted to the school of graduate studies for examination with my approval.

Drake. P Mirembe (Supervisor)

…………………………………………………….

Date…………………………………………..

ABSTRACT

The constant increase in demand for high speed internet access and multimedia services has led to providers looking at other ways to deliver their service to both residential and business users. WiMAX was developed to offer wired network results with wireless network versatility. The ability to achieve high-speed wireless network access over a large area with Quality of service guarantees is the fundamentals of the WiMAX protocol.

The research has performed extensive analyses of the physical performance in a fixed WiMAX deployment which has been operative for over a year and where the amount of subscribers constantly increases. The analyses presented in this research focuses on received signal strength and signal to noise ratio. Based on the measured parameters, the research presents a Path Loss model for fixed WiMAX which will hopefully be of great reference value due to the great amount of measurements presented.

Finally, the research’s Path Loss model is compared to other well-known Path Loss models and is found to approach the free space loss model. This is performed by evaluating performance of the 802.16d protocol in both densely and sparsely populated areas of Kampala Metropolitan area (Kampala city and Entebbe).

ACKNOWLEDGEMENT

I would like to thank my supervisor Drake P Mirembe, for the help and advice he offered while attempting this project, as well as brining me back on track when I was beginning to lag with the project. I would like to thank my workmates at Infocom Ltd (Patrick Okui, Jesper Ebong and Duncan Namuhani), MTN and Warid Network Engineers for offering quality advice on the content of the project.

I would also like to thank my classmates (Joseph Nkangi, Mike Kajubi and Sarah Muwanguzi) and my girlfriend who kept telling me to keep going, whenever things didn’t work or reminded me to dedicate more time to the project however much I was occupied in other engagements. Without this unconditional support I feel this project would not have been completed on time. For this I am forever grateful.

LIST OF ACRONYMS

In this report, these acronyms are used.

UDP - User Datagram Protocol

TCP - Transmission Control Protocol

CBR - Constant Bit Rate

FTP – File transfer Protocol

SS - Subscriber Station

BS - Base Station

CPE-Customer Premise Equipment

RSSI- Receive Signal Strength Indicator

UL- Uplink

DL-Downlink

QAM- Quadrature Amplitude Modulation

QPSK - Quadrature Phase Shift Key

BPSK – Binary Phase Shift Key

RNG-REQ - Range Request

RNG-RSP - Range Response

BW-REQ - Bandwidth Request

BW-RSP - Bandwidth Response

UL-MAP - Uplink Map

DL-MAP - Downlink Map

UGS - Unsolicited Grant Service

rTPS - Real Time Polling Service

erTPS - Extended Real Time Polling Service

nrTPS - Non Real Time Polling Service

BE - Best Effort

MAC - Media Access Control

N – Null node a.k.a Sink node

NSP – Network Service Provider

MAN – Metropolitan Area Network

TDD – Time Division Duplexing

FDD – Frequency Division Duplexing

GPC – Grant per connection

GPSS – Grant per subscriber Station

TABLE OF CONTENTS

DECLARATION ii

APPROVAL iii

ABSTRACT iv

ACKNOWLEDGEMENT 1

LIST OF ACRONYMS 2

CHAPTER ONE 8

INTRODUCTION 8

1.1 Background of the study 8

1.2 Problem statement 9

1.3 Objectives 9

1.3.1 Main Objectives 9

1.3.2 Specific Objectives 10

1.3.3 Minimum Requirements 10

1.4 Scope of the study 10

1.5 Significance of the study 10

1.6 Original Schedule 11

CHAPTER TWO 12

LITERATURE REVIEW 12

2.1 Overview 12

2.2 WiMAX Definition 13

2.3 Evolution of WiMAX 14

2.3.1 Evolution in Detail 14

2.3.2 WiMAX Architecture 15

2.4 Manufacturers specified WiMAX performance 21

2.4.1 UDP throughput PtP (using a MACRO BST) 21

2.4.2 UDP Throughput PtMP (13 CPEs) associating with BST 22

2.4.3 UDP Throughput PtMP (highest modulation) 22

2.4.4 FTP Throughput per modulation (15 CPEs) 22

2.4.5 FTP Throughput per number of CPEs 23

CHAPTER THREE 23

METHODOLOGY 23

3.1 Overview 23

3.2 System Description 24

3.3 Experiments and Experiment Design 25

3.3.1 Topology 25

3.4 Implementation and equipment setup 25

3.4.1 Objective 25

3.4.2 Sample field locations chosen 26

3.4.3 Throughput, SNR and Modulation test setup 26

CHAPTER FOUR 29

PRESENTATION OF RESULTS 29

4.1 Kololo Summit results 29

4.2 Entebbe results 30

CHAPTER FIVE 31

DISCUSSION OF RESULTS 31

5.1 Overview 31

5.2 Link Performance 32

5.2.1 Received Signal Strength Indicator (RSSI) 32

5.2.2 Downlink Signal Strength versus Distance 32

5.2.3 Uplink Signal Strength versus Distance 33

5.3 Signal to Noise Ratio (SNR) 34

5.3.1 Downlink Signal to Noise Ratio 35

5.3.2 Uplink Signal to Noise Ratio 35

CHAPTER SIX 37

CONCLUSION AND RECOMMENDATION 37

6.1 Conclusion 37

6.2 Recommendation 37

REFERENCES: 38

LIST OF TABLES

Table 1: QoS classes 19

Table 2: Alvarion specified Base station throughput 21

Table 3: Alvarion specified throughput on a PtMP 22

Table 4: Alvarion specified throughput with highest modulation 22

Table 5: Alvarion specified ftp throughput 22

Table 6: Alvarion specified throughput per number of CPEs 23

Table 7: Kololo summit RF sample test illustration 27

Table 8: Entebbe summit RF sample test illustration 28

Table 9: Kololo summit throughput sample test illustration 28

Table 10: Entebbe throughput sample test illustration 29

LIST OF FIGURES

Figure 1: An example of a WiMAX PHY Layer 16

Figure 2: example of a TDD frame. 18

Figure 3: Local leg throughput test illustration 26

Figure 4: internet throughput test illustration 28

Figure 5. RSSI vs. Distance for DL locations together with the FSL (topmost line), Cost 231 Hata Suburban (middle line) and Cost 231 Hata urban model (bottom line) 32

Figure 6. RSSI vs. Distance for UL locations together with the FSL (topmost line), Cost 231 Hata Suburban (middle line) and Cost 231 Hata urban model (bottom line). 33

Figure 7. Downlink SNR vs. RSSI 35

Figure 8. Uplink RSSI vs. SNR 35

CHAPTER ONE

INTRODUCTION

1.1 Background of the study

For the past few years, demands for high-speed internet access and multimedia service for residential and business customers has increased greatly [1]. This has led to internet service providers looking to other ways in which to deliver their service to the consumer (last mile). This has led to a re-haul in thinking between the traditional methods of wired technology and wireless technology.

Because wireless systems have the capacity to address broad geographic areas without the costly infrastructure required to deploy cable links to individual sites, the technology may prove less expensive to deploy and should lead to more ubiquitous broadband access [3].The forum describes WiMAX as "a standards based technology enabling the delivery of last mile wireless broadband access as an alternative to cable and DSL [2]. Knowing that WiMAX has been developed for this very purpose there is need to test the capabilities of the technology.

This project aims to find out just how robust WiMAX is in terms of scalability. By pushing the protocol to its threshold and seeing how it performs.

1.2 Problem statement

Clients subscribed to a wireless infrastructure cannot optimally access the network due to bottlenecks on the network leading to poor performance on the end user.

A network with minimal interruptions caused by interference, broadcasts, link saturation, BS overload and aging devices is the ultimate goal of any organization so as to provide a stable and/or reliable service to customers

A stable WiMAX performance is a challenge to most companies and this research intends to investigate how robust WiMAX is in terms of scalability by pushing the 802.16d protocol to its threshold and seeing how it performs.

1.3 Objectives

1.3.1 Main Objectives

To evaluate and test the capability and performance of the 802.16 (WiMAX) IEEE wireless protocol under varying scenarios. This Project aims to assess the performance of a single base station and how the scalability affects its performance.

1.3.2 Specific Objectives

Understand how WiMAX works and what can affect its performance.

Set up a WiMAX field tests in various chosen areas to obtain performance results.

1.3.3 Minimum Requirements

A demonstrated understanding of the 802.16 (WiMAX) protocol.

Obtain some performance results through simulation of the protocol

Draw conclusions based on these results.

Compare these results to the literature found in the literature review

1.4 Scope of the study

The study covered an existing WiMAX network and related infrastructure (from server farm, base stations up to the client CPE). The study was expected to take approximately 3 months as shown in the project schedule but due to unavoidable circumstances the researcher requested for an extension of 2 more months.

1.5 Significance of the study

The main contribution of this research is to present measurement results from a real life fixed WiMAX deployment and in depth analysis of the physical performance. Secondly, the research will contribute to the derivation of an analytical Path Loss model based on the measurement results together with performance analysis.

1.6 Original Schedule

CHAPTER TWO

LITERATURE REVIEW

2.1 Overview

This chapter discusses the WiMAX protocol in depth, why there is a need for the protocol. Looks at related literature and ways in which the literature tackles the challenges presented. How best to go about this project looking at past information and relevant observations need to be made in this chapter so that the following chapters can build upon this foundation of knowledge.

Broadband Wireless Access (BWA) is one of the most promising solutions for broadband access. However BWA is still in its early stages of growth with IEEE Project 802 working group 16 working towards building its standards. In this regard, a commercial forum Worldwide Interoperability for Microwave Access (WiMAX) was founded which includes more than 300 member companies.

It is envisioned, that WiMAX will provide the last mile internet access to residential users. This will be particularly useful in regions where wire lined infrastructure does not exist or cannot be setup, such as rural areas and remote mountainous areas for instance. It is interesting to note, that WiMAX proved its importance during the devastating December 2004 Tsunami in Aceh, Indonesia which completely destroyed the existing infrastructure, and thus crucial communication took through WiMAX stations deployed rapidly on urgent basis. For small and medium enterprises, WiMAX will create an economical alternative to expensive leased line solutions. [1] [2]

As broadband internet becomes the standard in homes and business around the world. The demand has never been higher. Originally broadband was delivered by wired connection only. This is meant to implement broadband in homes that did not have the capability, physical changes to the network would have to occur. Streets may have to be dug up, new wires laid etc. This led to a major rethinking in the way that last mile service is provider. The idea that broadband could be delivered with QoS over a wireless protocol was devised, and as such the WiMAX protocol was born.

Over the last 5-6 years there have been many revisions to the WiMAX protocol, adding improvements and making it more robust.

WiMAX is designed to deliver wired network performance over wireless. Wireless MAN’s are created by

WiMAX base stations are metropolitan area networks covering up to 30 miles [14] which means that broadband can be delivered to clients within this radius.

2.2 WiMAX Definition

WiMAX which stands for World Wide interoperability of Microwave Access is a standards-based technology which serves as a wireless extension or alternative to DSL or cable for "broadband" (i.e., faster than 1.5Mbps) access to IP-based networks and the Internet. It utilizes microwave communication in the 2 – 66GHz range to connect WiMAX-enabled fixed, portable, and mobile computers to a "base station" PC which in turn connects to an IP network (e.g., the Mukono University network) and then to the Internet.

Communication can take place over much longer distances than with WiFi (miles vs. hundreds of feet), and by utilizing an array of antennas, each supporting one or more base stations, user PC’s distributed across a very large geographical area (e.g., the entire Town) can all have a link and Internet access without requiring a "wired" DSL or cabled connection. The communication occurs either on licensed frequencies (lower likelihood of interference with other WiMAX service providers in the area) or in an unlicensed part of the 2-66 GHz radio spectrum (perhaps free of cost, but possibly subject to lower radiated power restrictions and/or higher level of interference).

WiMAX is a broadband wireless access system which offers high throughput, great coverage, flexible Quality of Service (QoS) support and extensive security. WiMAX is certified by the WiMAX forum [26], which is a certification mark based on the IEEE 802.16 standard [27] that pass conformity and interoperability tests.

There are two main classes of WiMAX systems called fixed WiMAX and mobile WiMAX. Fixed WiMAX is targeted for providing fixed and nomadic services, while mobile WiMAX will also provide portable and (simple and full) mobile connectivity. The system studied here is a fixed WiMAX system. It uses an air interface based on orthogonal frequency division multiplexing (OFDM), which is very robust against multi-path propagation and frequency selective fading. An adaptive modulation technique is used to enhance performance when the link characteristics vary.

2.3 Evolution of WiMAX

IEEE 802.16 physical layer has evolved much since its first version was completed in October 2001. The first version operated between 10-66 GHz and specified a single carrier for a fixed Point-to-Multipoint (PMP) communication. The second version, 802.16a, extended the frequency band to below 11 GHz. This enabled non line of sight communication by employing the benefits of diffraction which are available only at lower frequencies. In this version, two OFDM based air interfaces; 256-carrier Orthogonal Frequency Division Multiplex (OFDM) and 2048-carrier Orthogonal Frequency Division Multiple Access (OFDMA) were also provided. This version also allowed mesh based topology in addition to the existing PMP communication. This version was followed by 802.16d published in June 2004. It incorporates all the previous versions to provide fixed BWA. Then came 802.16e, concluded in 2005, which supports full mobility at speed up to 70-80 m/s. [2] [6]

2.3.1 Evolution in Detail

IEEE 802.16 Working Group:

In 1998, the IEEE 802.16 working group focused to develop WMAN solution for Line of Sight (LOS) based point to point and point to multipoint wireless broadband systems. It was also decided that the frequency range for IEEE 802.16 will be 10 GHz to 66 GHz. The first standard of WiMAX was completed

in December 2001 which employs single carrier physical (PHY) layer with burst Time Division Multiplexed (TDM) on MAC layer.

IEEE 802.16a:

In January 2003, the working group produced another standard, IEEE 802.16a, after some amendments in the earlier standard including Non-Line of Sight (NLOS) applications in the frequency range of 2 GHz to 11 GHz band. It uses Orthogonal Frequency Division Multiplexing (OFDM) on physical layer with

Orthogonal Frequency Division Multiple Access (OFDMA) on the MAC layer.

IEEE 802.16-2004:

IEEE introduced the new standard, IEEE 802.16-2004, replacing all the previous versions. The main focus is to target fixed applications. It is also called as Fixed WiMAX or IEEE 802.16d.

IEEE 802.16e-2005:

In December 2005, IEEE approved and launched its new standard IEEE 802.16e- 2005. This new standard has come after some amendments in IEEE 802.16-2004 that is the support of mobility. This system gives the concept of nomadic and mobility services to WiMAX technology. It is also referred as Mobile WiMAX.

Moreover, the WiMAX forum defines the subset of mandatory and optional physical and MAC layer features for fixed and mobile WiMAX standards and they are known as System Prole. The system proles based on IEEE 802.16- 2004, OFDM PHY, are called as fixed system proles. The system proles of IEEE 802.16e-2005 scalable OFDMA PHY are known as mobile system profiles. The details of operating frequencies, channel bandwidth, modulation and multiplexing techniques

2.3.2 WiMAX Architecture

The basic architecture is a Base station, which is basically an antenna, which subscriber stations connect to. Subscriber stations will be antenna’s mounted on buildings that will connect to a router inside the building so the delivered broadband can be distributed. Originally both BS and SS were fixed implementations but with the introduction of 802.16e SS now have mobility options. WiMAX has no standard for routing and as such it can only deliver its service. The distribution once it gets to its destination has to be dealt with by another protocol. [23]

802.16 WiMAX protocol can be broken down into layers.

2.3.2.1 PHY Layer

The physical or PHY layer can be broken down into two layers, these are the physical medium dependent which is concerned with the actually transmission medium over which the wireless information is broadcast. The other sub layer is the Transmission convergence layer which deals with merging the physical layer with the MAC Layer [23]

The PHY layer can support bandwidths up to 28 MHz which OFDM efficiency of 3.6 Bytes/Hz can offer bandwidth of over 100Mbp/s for a single base station. [20]

Although this looks very impressive, because as a subscriber station gets further away from the base station the signal to noise ratio increases rapidly with this type of signal. As such adaptive modulation is used to try and counter this. The fact is that it becomes very difficult for a base station to utilize 100% of its bandwidth capabilities [15].

WiMAX also uses adaptive burst profiling to try to deal with this problem, each SS is looked at individually, depending on range, modulation and coding schemes, this can be adjusted frame by frame. [26]

Figure 1: An example of a WiMAX PHY Layer

There are two channels, an Uplink channel and a downlink channel. The downlink channel is a broadcast channel. In that it broadcasts to many different subscriber stations, and it can contain downlink information, grant information, bandwidth request replies, packets sent to individual SS’s. All SS’s receive all bursts that they are robust enough to receive, i.e. they have enough bandwidth to receive all packets, and for example when a SS at a lower modulation scheme will not receive as many bursts as one at a higher modulation scheme. The uplink channel, is distributed in a shared manner by the base station, the base station grants time allocations to each SS in which the SS can send packets to the BS. When a SS connects to a BS it grants it a certain time allocation, this time allocation can then be used by the SS to request more bandwidth and hence more time allocations. [26]

2.3.2.2 MAC Layer

There are two types of WiMAX architectures; point-to-multipoint (PMP) and mesh. PMP consists of a base station (BS) which serves all the subscriber stations (SS) in its range. There is no communication between SSs. They all communicate through the BS. The BS is concerned with the setting up and management of the connections when an SS sends a request. The BS acts as a network gateway.

In case there is communication between SSs as well, then it forms mesh architecture. The mesh architecture allows a connection over several hops and a tree network topology can be formed. The mesh and PMP are incompatible because PMP is only capable of single hop transmission. PMP has a lower signaling overhead than the mesh mode [14], [15]

For data transfer in WiMAX, downlink and uplink sub frames are duplexed using either frequency-division duplex (FDD) or time-division duplex (TDD). [1] It should be noted that WiMAX is a connection oriented network BS schedules the uplink and downlink grants at the start of each frame in order to meet the negotiated QoS requirements. Each SS finds the boundaries of its allocated uplink sub frame by decoding the UL-Map message. The DL-Map message contains information about the downlink grants in the forthcoming sub frame. Both maps are transmitted by the BS at the beginning of each downlink sub frame. This is done for both FDD and TDD modes. [1]

Providing quality of service (QoS) simultaneously to services with different requirements is a much more difficult task in wireless mediums as compared to wired networks because of its highly variable and unpredictable nature in terms of time-dependence as well as location dependence. To cope with such issues, QoS in wireless networks is handled at the medium access control (MAC) layer. [1]

An exciting feature of WiMAX is its support for QOS. It classifies all traffic according to four types:

Unsolicited Grant Services (UGS): because of a constant bit rate requirement, this category needs constant bandwidth allocation.

Real-time Polling Services (rtPS): because of real time variable bit rate requirements, these applications need minimum bandwidth granted and have to request transmission resources by polling. Contention and piggybacking are not allowed.

Non-real-time Polling Services (nrtPS): because of non-real time flows, this category requires traffic polling. Bandwidth requests are allowed when minimum bandwidth requirements are needed, otherwise contention and piggybacking are used.

Best Effort Services (BES): best effort flows can make bandwidth request only with contention and no minimum resources allocation is granted. [16]

2.3.2.3 TDD and FDD Duplexing

The current implementation of WiMAX supports two types of duplexing. Time division duplexing and

Frequency division duplexing. In TDD mode same channel is shared by the uplink and downlinks. Each

frame is separated into downlink and uplink. With the downlink transmitted first then the uplink

transmitted second.

Figure 2: example of a TDD frame.

2.3.2.4 Downlink Sub Frame

The downlink sub frame contains a DL-MAP for the current sub frame, and UL-MAP for the uplink channel. It can also contain DCD and UCD messages. DL-MAP is used to specify parameters that concern the downlink. These include frame duration, frame time and also downlink channel ID. UL-MAP defines specific bandwidth grants to SS’s the channel ID. DCD contains the downlink channel descriptor which describes the physical downlink channel, UCD contains the uplink channel descriptor which does the same for the uplink physical channel. [23]

2.3.2.5 Uplink Sub Frame

The uplink sub frame can contain one of three different types of bursts, these are either bursts that are transmitted within the ranging contention slots, bursts that are transmitted in bandwidth request contention slots or bursts that are transmitted in the assigned slot to specific SS’s. The last is basically data transfer in the granted allocation time. [23]

2.3.2.6 MAC PDU

The MAC protocol data unit, a MAC level data unit that the base station and its subscriber stations transfer between their MAC layers. The MAC PDU can contain a bandwidth request, a packing request, or a fragmentation sub header. A bandwidth request, requests more allocated time from the base station to the SS. A packing request is when two fragments can be packed together. A fragmentation sub header indicates that the packet has been fragmented, it also identifies the location of the fragments. [23]

2.3.2.7 WiMAX QoS

WiMAX 802.16 describes 5 quality of service schedulers that it can use for different traffic types. These schedulers are unique in that they associate with what the SS needs and act in the appropriate manner to what a connection needs. In this way VoIP traffic will receive priority over say web traffic. The following are the QoS classes; [23]

Table 1: QoS classes

QoS Class

Application

QoS Specifications

BE

Best Effort Service

Web browsing, data transfer

Maximum sustained rate

Traffic Priority

nrTPS

Non-real-time Polling Service

File Transfer Protocol

Minimum reserve rate

Traffic Priority

erTPS

Extended real Time Polling Service

Voice with activity detection

Minimum reserve rate

Maximum sustained rate

Traffic Priority

Jitter tolerance

Maximum latency tolerance

UGS

Unsolicited Grant Service

VoIP

Max sustained rate

Max latency tolerance

Jitter tolerance

rTPS

real Time Polling Service

Streaming audio and video

Minimum reserve rate

Maximum sustained rate

Traffic Priority

Maximum latency tolerance

Source [20]

2.3.2.8 Bandwidth Request and Grants

WiMAX deals with requests and grants in two ways. Either grant per connection or grant per subscriber station. GPC type grants work by having the base station schedule each connection individually. As such each connection will only be able to transmit during its transmit time, this time is allocated by the base station. GPSS on the other hand takes all connections from one subscriber station as a set, and allocated all connections a service time, this type of grant means that a scheduler at the subscriber station has to

employed so that it can schedule its own service order. Generally GPC is less saleable than GPSS. [23][26]

2.3.2.9 SS initialization

Channel Acquisition occurs when a SS scans for downlink channels and waits for a downlink control message. Once it has acquired a channel, it waits for a UCD from the base station before it will begin

broadcasting.

Initial Ranging is done by means of a RNG-REQ and RNG-RSP, the SS sends ranging requests of various

power, until it receives a response. Once it receives a response it can extrapolate the distance from the base station. The base station answers with a RNG-RSP which contains power adjustments. Negotiate Basic Capabilities is when a SS sends its capabilities to the BS, this is when modulation, coding

schemes and duplexing are configured.

The next stage is security based and is basic authentication of the SS, a simple key swap is performed.

Registration and IP are then served to the SS from BS. Then the connection is set up. Now the SS can

receive its allocated grants and start requesting bandwidth etc.

2.4 Manufacturers specified WiMAX performance

2.4.1 UDP throughput PtP (using a MACRO BST)

Table 2: Alvarion specified Base station throughput

Modulation

Packet Size

DL

(Mbps)

UL

(Mbps)

UL+DL

(Mbps)

QAM64 ¾

64

3.788

2.337

2.614

1518

3.961

4.030

7.991

QAM64 2/3

64

3.490

2.300

2.626

1518

3.613

3.671

7.018

QAM16 ¾

64

2.547

2.471

2.630

1518

2.710

2.733

5.235

QAM16 ½

64

1.715

1.692

2.619

1518

1.853

1.841

3.428

QPSK ¾

64

1.296

1.311

2.641

1518

1.367

1.378

2.687

QPSK ½

64

0.830

0.830

1.704

1518

0.857

0.857

1.807

BPSK ½

64

0.427

0.412

0.796

1518

0.417

0.394

0.811

2.4.2 UDP Throughput PtMP (13 CPEs) associating with BST

Table 3: Alvarion specified throughput on a PtMP

Modulation

Packet Size

DL

(Mbps)

UL

(Mbps)

UL+DL

(Mbps)

QAM64 ¾

64

4.232

3.700

7.626

1518

4.104

4.092

8.039

QAM64 2/3

64

3.658

3.247

6.639

1518

3.691

3.643

7.067

QAM16 ¾

64

2.662

2.848

5.592

1518

2.732

2.586

5.476

QAM16 ½

64

1.927

1.701

3.621

1518

1.845

1.748

3.424

QPSK ¾

64

1.392

1.334

2.643

1518

1.360

1.408

2.732

QPSK ½

64

0.953

0.879

1.733

1518

0.922

0.898

1.724

BPSK ½

64

0.404

0.417

0.774

1518

0.437

0.412

0.801

2.4.3 UDP Throughput PtMP (highest modulation)

Table 4: Alvarion specified throughput with highest modulation

QAM64 ¾

Packet size (bytes)

Number of

SU’s

64

128

1518

Down

Up

Down

Up

Down

Up

5

4.241

3.221

4.259

3.952

4.371

3.934

13

4.232

3.700

4.224

4.038

4.104

4.092

2.4.4 FTP Throughput per modulation (15 CPEs)

Table 5: Alvarion specified ftp throughput

FTP Traffic (Mbps)

Rate QAM64 ¾

Modulation

DL (Mbps)

UL (Mbps)

DL + UL (Mbps)

QAM64 ¾

3.976

3.572

6.748

QAM64 2/3

3.541

3.114

6.029

QAM16 ¾

2.641

2.363

4.457

QAM16 ½

1.752

1.506

2.963

QPSK ¾

1.305

1.095

2.114

2.4.5 FTP Throughput per number of CPEs

Table 6: Alvarion specified throughput per number of CPEs

FTP Traffic (Mbps)

Rate QAM64 ¾

Channel Spacing 3.5MHz

Number of SUs

1

15

Downlink

3.385

3.976

Uplink

3.115

3.572

Downlink/Uplink

4.511

6.748

Source [26]

CHAPTER THREE

METHODOLOGY

3.1 Overview

In this section, methodology of the experiments that were run will be discussed. When running any experiments it is very important to look at what has been done in the past. What has worked in other projects or journals and what hasn’t worked. To find a platform on which the experiments in this project can build upon.

To effectively evaluate WiMAX performance in relevance to the chosen parameters and performance

metrics, there were 3 possible ways of going about it.

Direct Experiments: This uses physical hardware available to test WiMAX

Mathematical Modeling: A mathematical model of how WiMAX works is created and is used to mathematically calculate outcomes.

Simulation: This uses a computer program that creates a virtual environment by which a network can be

setup in varying ways to test certain criteria. The simulator will then output the results.

So the method chosen for evaluating WiMAX was direct experiment. As it was the most flexible, allowed for greater amount of experiments of varying complexity to be run in a smaller time-scale.

As a fixed WiMAX deployment has been operative for a year, the amount of Base Stations (BS) and subscribers present in the deployment have increased over time. The researcher decided to extract and use the most important parameters from the system, which are Received Signal Strength Indication (RSSI) and Signal to Noise Ratio (SNR), over which extensive analysis was performed. GPS coordinates were also available for each of the subscribers, which gave us the possibility to construct a Path Loss model with great precision due to the large amount of measurement points.

3.2 System Description

The system in use is a fixed WiMAX system operating in the 3.5 GHz frequency band. Totally 10 Base Stations are deployed, where 850 Subscriber Units (SU) are operative. The system utilizes FDD with 3.5 MHz channels in both uplink and downlink.

Each BS sector has a 90° beam width, and 4 licensed frequencies are available for use. Each BS is configured to transmit at a 28 dBm maximum where the BS antenna gain is 14 dBi.

The SUs are fixed antennas, which are located outdoor at the house wall or roof. Automatic Transmission Power Control (ATPC) is enabled at all the SUs where the maximum transmitted power is 20 dBm. SU antenna gain is 18 dBi.

If possible, the SU is setup within Line of Sight (LOS) to the BS, but there are also SUs with Non Line of Sight (NLOS) conditions. The NLOS sites are mostly present in areas close to the BS, whereas LOS becomes more common and also more important at farther distances.

The area of deployment consists of one medium sized town named Entebbe where the population density is low and averagely low buildings and Kampala city with a high population density and 5 floor high buildings.

3.3 Experiments and Experiment Design

3.3.1 Topology

Common to all previous works is the topology. When looking at WiMAX topology there aren’t many variations to consider. Since the fundamentals of the WiMAX protocol is a base station servicing subscriber stations. A single base station node, serving multiple subscriber stations. For example in [9] the topology used is 1 single base station serving 20 Subscriber stations and [11] uses one base station serving 8 subscriber stations. So based on the given evidence, the project will use configurations of the topologies given in the journals.

3.4 Implementation and equipment setup

3.4.1 Objective

Test the performance of a WiMAX network working at 3.5 GHz frequency spectrum, covering long distance and under line-of-sight (LOS) conditions.

3.4.2 Sample field locations chosen

Base station location: Kololo summit and Entebbe

SU location 1, approximately 11km, LOS, away from the base station will be selected as a CPE location with the subscriber unit installed.

SU location 2, approximately 1.5km, LOS, away from the base station will be selected as a CPE location with the subscriber unit installed.

3.4.3 Throughput, SNR and Modulation test setup

TCP and UDP throughput will be carried out in the network at two CPE locations

SU location 1

SU location 2

With the aid of a 3rd party software tool, the throughput, SNR, Modulation and RSSI figures were obtained and summarized as shown in the next sections.

Equipment list:

Subscriber unit (SU) with outdoor unit (ODU)

Indoor unit (IDU)

100BaseT switching Hub

Notebook computer

PC server (linux loaded) at the Base station

Software tools:

I-perf (version 1.7.0 or higher)- used to test local end-to-end tests

Speedtest.net – used to test international traffic

Figure 3: Local leg throughput test illustration

Table 7: Kololo summit RF sample test illustration

SU location

Kololo summit

Direction

LOS

LOS

Estimated distance

11km

1.5km

Modulation type

SNR

RSSI

No. of connections

TCP throughput

8.0Mbit/s

8.3Mbit/s

Round trip delay

35ms-40ms

39ms-47ms

TCP window

48Kbytes

48Kbytes

UDP window

64Kbytes

64Kbytes

Table 8: Entebbe summit RF sample test illustration

SU location

Entebbe

Direction

LOS

LOS

Estimated distance

11km

1.5km

Modulation type

SNR

RSSI

No. of connections

1

1

TCP throughput

8.0Mbit/s

8.3Mbit/s

Round trip delay

26ms-33ms

32ms-40ms

TCP window

48Kbytes

48Kbytes

UDP window

64Kbytes

64Kbytes

Internet Service Test

A client-server network structure was setup at both locations with a LINUX server loaded with HTTP, FTP, DNS, DHCP, POP3 and SMTP services. This simulated the company’s service operations on the WiMAX network.

Figure 4: internet throughput test illustration

Table 9: Kololo summit throughput sample test illustration

Base station

Kololo

Direction

LOS

LOS

Estimated distance

11km

1.5km

Configured PIPE

Local

Internet

Table 10: Entebbe throughput sample test illustration

Base station

Entebbe

Direction

LOS

LOS

Estimated distance

11km

1.5km

Configured PIPE

Local

Internet

CHAPTER FOUR

PRESENTATION OF RESULTS

4.1 Kololo Summit results

The results presented below were collected from one of the locations identified as densely populated.

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

34

23

RSSI

64

70

Local throughput

239

144

Internet throughput

60

29

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

50

76

RSSI

-70

-56

Local throughput

120

100

Internet throughput

100

90

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

35

23

RSSI

-56

-74

Local throughput

230

211

Internet throughput

58

22

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

67

72

RSSI

-64

-68

Local throughput

200

134

Internet throughput

145

101

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

34

25

RSSI

-64

-70

Local throughput

239

144

Internet throughput

150

120

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

18

22

RSSI

-56

-64

Local throughput

200

189

Internet throughput

140

110

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

34

24

RSSI

-64

-74

Local throughput

248

124

Internet throughput

198

200

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

32

30

RSSI

-67

-74

Local throughput

247

242

Internet throughput

152

93

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

32

24

RSSI

-67

-74

Local throughput

249

209

Internet throughput

150

24

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

35

23

RSSI

-58

-73

Local throughput

230

213

Internet throughput

146

49

4.2 Entebbe results

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

35

33

RSSI

-62

-74

Local throughput

256

253

Internet throughput

200

213

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

23

19

RSSI

-85

-73

Local throughput

233

204

Internet throughput

211

219

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

34

35

RSSI

-60

-70

Local throughput

246

250

Internet throughput

198

190

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

31

22

RSSI

-65

-33

Local throughput

231

245

Internet throughput

169

200

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

246

250

RSSI

-60

-70

Local throughput

246

202

Internet throughput

198

190

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

34

33

RSSI

-65

-74

Local throughput

210

235

Internet throughput

183

180

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

27

26

RSSI

-78

-73

Local throughput

250

202

Internet throughput

200

250

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

34

21

RSSI

-70

-69

Local throughput

228

200

Internet throughput

200

187

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

24

29

RSSI

-81

-76

Local throughput

228

220

Internet throughput

200

213

Parameters

Downlink

Uplink

Configured PIPE

256

256

Modulation scheme

QAM643/4

QAM643/4

SNR

30

24

RSSI

-81

-73

Local throughput

240

237

Internet throughput

200

199

CHAPTER FIVE

DISCUSSION OF RESULTS

5.1 Overview

This research used an empirical research method for analysis performed over measurement data extracted from a fixed WiMAX system deployed in real life. Analytical models and conclusions will be based on these collected measurement data presented in the previous section.

A Network Management System (NMS) is used by the researcher for administrating the BSs and SUs. The functionality in the BSs and SUs logs performance attributes. These performance attributes are DL and UL RSSI, DL and UL SNR, transmit (Tx) and receive (Rx) modulation rate and Tx power for the SU which is important due to the use of ATPC.

5.2 Link Performance

5.2.1 Received Signal Strength Indicator (RSSI)

As specified in IEEE 802.16-2004, sect 8.3.9, the WiMAX SUs and BSs have a Received Signal Strength Indicator (RSSI). The Network Monitoring System in use logs the RSSI for all the SUs which are operative during the day. The RSSI related to the distance between the SU and BS gives valuable information related to the power loss in the WiMAX system. The RSSI is measured for both uplink and downlink, and will be analyzed and compared to well-established models in the following subsections.

The well-established models will be Free Space Loss (FSL) and the Cost 231 Hata models for suburban and urban environments.

5.2.2 Downlink Signal Strength versus Distance

The DL RSSI for each subscriber is plotted in Figure 5 together with the well-established models FSL and the Cost 231 Hata models for suburban and urban environments.

Most of the plotted subscribers are expected to perform similar to the FSL since they were installed with LOS conditions to the BS if possible, but this is not always possible when deploying a wireless communication system in cities with obstacles as high buildings. This is illustrated by the divergence in Figure 5.

Figure 5. RSSI vs. Distance for DL locations together with the FSL (topmost line), Cost 231 Hata Suburban (middle line) and Cost 231 Hata urban model (bottom line)

Some of the subscribers very close to the BS perform equal to or worse than the Cost 231 Hata models. This is mainly due to the fact that subscribers close to the BS are more frequently under NLOS conditions than subscribers farther away from the BS. The reason for the greater performance of this system than the Cost 231 Hata models is that this is a fixed system rather than nomadic or mobile as used when constructing the Cost 231 Hata models.

5.2.3 Uplink Signal Strength versus Distance

As for DL RSSI, the UL RSSI values for each subscriber are plotted in Figure 6 together with the models FSL and Cost 231 Hata suburban and urban models.

Figure 6. RSSI vs. Distance for UL locations together with the FSL (topmost line), Cost 231 Hata Suburban (middle line) and Cost 231 Hata urban model (bottom line).

Since Automatic Transmission Power Control (ATPC) is used by the SU, normalization is performed on the RSSI values where the corresponding SU transmission power is below the maximum of 20 dBm. This is done by adding the transmission power back-off in dBm as follows:

RSSIULnorm =RSSIUL + (20 -TxPower) .

The UL RSSI versus distance plot is similar to the DL RSSI versus distance plot with the exception that lower RSSI values are observed. This was expected due to the fact that the SU transmits with 8 dBm less power than the BS.

5.3 Signal to Noise Ratio (SNR)

The Signal to Noise Ratio (SNR) is the power ratio between the signal and the background noise. SNR will give a better indication of the actual system conditions because interference and noise is revealed.

SNR and RSSI are measured at all locations and should be closely correlated, and a plot of RSSI versus SNR should by definition give a linear graph if the interference and background noise is absent. The following subsections analyses SNR for downlink and uplink.

5.3.1 Downlink Signal to Noise Ratio

The DL SNR versus DL RSSI is plotted for each subscriber in Figure 7. The graph flatten off at around -65 dBm RSSI and outwards, which indicates that optimal performance could be achieved if RSSI is above -65 dBm and no interference or background noise is present. The results indicate that the maximum measurable SNR value at the SU is 36 dB.

Figure 7. Downlink SNR vs. RSSI

Many of the subscribers vary from the linearity and the "flatten off" pattern, which indicates that interference may be present.

Another observation is that the curve seems to decrease in SNR at around -52 dBm in RSSI and more, which may be due to saturation in the SU antenna.

5.3.2 Uplink Signal to Noise Ratio

Figure 8 shows the uplink RSSI vs. SNR. A linear increase is observed, and the subscribers that deviate from this line are probably disturbed by interference.

Figure 8. Uplink RSSI vs. SNR

The "flatten off" observation found in the downlink graph (Figure 7) is not present in the uplink, which is because the SU transmits with less power than the BS. The maximum SNR value in the uplink is found at around -68 dBm which is a bit better than for the downlink.

CHAPTER SIX

CONCLUSION AND RECOMMENDATION

6.1 Conclusion

Theoretically, WiMAX technology can provide coverage in both LOS and NLOS conditions. NLOS has many implementation advantages that enable operators to deliver broadband data to a wide range of customers. In this experiment, throughput performance with one connection in short-haul (1.5 km) and long-haul conditions (11 km and above) showed no significant difference. A maximum of 8.4 Mbit/s data rate can be achieved.

It was noted that with the same base station configurations, varying results were obtained both on the signal quality and throughput. This was further proof that sparsely populated areas provide better WiMAX performance than densely populated areas.

6.2 Recommendation