DESIGNING A WiMAX COMMUNICATION NETWORK …ijarcet.org/wp-content/uploads/IJARCET-VOL-5-ISSUE-4-994-1008.pdf · Link budget calculation was used to determine the viability of the

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International Journal of Advanced Research in Computer Engineering & Technology (IJARCET)

Volume 5, Issue 4, April 2016

994

All Rights Reserved © 2016 IJARCET

DESIGNING A WiMAX

COMMUNICATION NETWORK FOR

ACCRA FOR BROADBAND WIRELESS

ACCESS Joseph Kweku Arthur

Faculty of engineering, Ghana Technology University College

PMB 100, Tesano- Accra, Ghana

Abstract –WiMAX, which represents World Interoperability

for Microwave Access, is a major part of broadband wireless

access (BWA) network (IEEE 802.16 standard) provides fixed

and mobile platform for broadband internet access anywhere

atany time. The ever-growing demand for high-speed data

connectivity makes broadband wireless access networks one of

the hottest topics in the field of telecommunications. The

various form of communication networks such as 2G, 3G and

other BWA networks used to deliver data to users have some

degree of limitations in terms of data rate and challenges with

distance. This study aims at designing a broadband

communication network for Accra the capital city of Ghana

using WiMAX technology. The research work introduces

readers to the practical concepts of IEEE802.16e – 2005 thus

mobile WiMAX standard technology. The work also collected

information and used calculations on how to plan the network

and determine the number of Base Stations (BSs) and their

coordinates, azimuth and mechanical tilt to provide sufficient

signal coverage and capacity to the designated area. Link

budget calculation was used to determine the viability of the

design link and the link margin, which shows the stability of

our link. The research work used calculation to determine the

maximum number of subscribers that each specific Mobile

WiMAX site may support.The results and the information

obtained were used to design a reliable network with high data

rates and increase capacity for longer distance. The design

used 19 base stations (BS) to cover an area of 230 sq km. The

capacity of each base station is 300Mbps and can support 256

active subscribers and a user data rate of 1Mbps

Index Terms: WiMAX, BWA, link budget, page

response, end-to-end delay, WiMAX load, WiMAX delay

1 INTRODUCTION

Wireless communication is becoming a major factor

in our daily lives. As one of the most important broadband

wireless technologies, Worldwide Interoperability for

Microwave Access (WiMAX) is anticipated to be a viable

alternative to traditional wired broadband techniques due to

its cost efficiency[1]. Worldwide Interoperability for

Microwave Access (WiMAX) is a certification mark for

products that pass conformity and interoperability tests for

the IEEE 802.16 standards. Products that pass the

conformity tests for WiMAX are capable of forming

wireless connections between them to permit the carrying

of internet packet data. The idea of WiMAX is similar to

Wi-Fi. It is a step much higher than Wi-Fi because it is

focused on offering internet for a whole city. It has a much

higher capacity and longer distances.

The Institute of Electrical and Electronics Engineers

(IEEE) 802.16 standard, widely known as Worldwide

Interoperability for Microwave Access (WiMAX), defines

the Medium Access Control (MAC) and the Physical

(PHY) layer specifications for the broadband wireless

access networks[2]. WiMAX offers an alternative to wired

networks, such as coaxial systems using cable modems,

fiber optics and DSL (Digital Subscriber Line) . The IEEE

802.16 standard is a real revolution in wireless metropolitan

area networks (Wireless MANs) that enables high-speed

access to data, video, and voice services[3]. Worldwide

Interoperability for Microwave Access (WiMAX) is a

technology for point to multipoint wireless networking. The

designing of a WiMAX technology in Accra is expected to

meet the needs of a large variety of users who need high

speed data network. Additionally, its main advantage is fast

deployment, which results in cost savings. WiMAX

installation can be beneficial in very crowded geographical

areas like Accra, and in rural areas where there is no wired

infrastructure.

Initially 802.16a was developed and launched, but it

has been further refined. 802.16d or 802.16-2004 was

released as a refined version of the 802.16a standard aimed

at fixed applications. Another version of the standard,

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802.16e or 802.16-2005 was also released and aimed at the

roaming and mobile markets[2]. Below from the WiMAX

Forum summarizes the 802.16 standards.

Table 1. Summarizes the 802.16 standards [4]

Completion

Date

802.16

Dec

2001

802.16a/802.16R

EVd 802.16a:

Jan 2003

802.16REVd: Q3

2004

802.16e 2005

Spectrum 10 to 66

GHz < 11 GHz < 6 GHz

Channel

Conditions

Line-of-

Sight

only

Non-Line-of-

Sight

Non-Line-of-

Sight

Bit Rate

32 to

134Mbp

s

75Mbps max 20-

MHz

channelization

15Mbps max

5-MHz

channelizatio

n

Modulation

QPSK;

16QAM

;

64QAM

OFDM 256

subcarrier QPSK

16QAM 64QAM

Same as

802.16a

Mobility Fixed Fixed

Pedestrian

mobility

Regional

roaming

Channel

Bandwidths

20, 25

and 28

MHz

Selectable

between 1.25 and

20 MHz

Same as

802.16a with

uplink

subchannels

Typical Cell

Radius

1 to 3

miles

3 to 5 Miles (30

miles max based

on tower height,

antenna gain and

transmit power)

1 to 3 miles

In the wireless domain, WiMAX promises high data

rate over long-range transmission and supports both fixed

and mobile transmission. WiMAX is a standard-based

technology, interoperability of the IEEE 802.16 standard,

officially known as Metropolitan Area Network (Wireless

MAN). WiMAX provides fixed, nomadic, portable and

mobile wireless broadband connectivity[5]. The WiMAX

standard delivers high-speed broadband Internet access

over a wireless connection.

The MAC layer of WiMAX supports Point-to-

Multipoint (PMP) and Mesh Topologies. The wireless

medium access is based on either Time Division Multiple

Access (TDMA) or Frequency Division Multiple Access

(FDMA), with Frequency Division Duplex (FDD) and

Time Division Duplex (TDD) as duplexing techniques.

Multiple PHY layer specifications are supported for Line-

of-Sight (LOS) and Non-Line-of-Sight (NLOS) operational

environments in 10-66 GHz and 2-11 GHz frequency

bands, respectively. Later on the IEEE 802.16e amendment

added mobility support to WiMAX networks. WiMAX is a

3.9G standard or what is called a supper 3G network[6][7].

It is the American version, in attempt to implement a 4G

standard. Long Term Evolution (LTE) on the other hand is

the European attempt to implement 4G standard. LTE, just

like WiMAX fell short of the 4G specifications and it is

also a 3.9G standard. LTE-Advance, (LTE-A) and 802.16m

are the true 4G standard. The deployment of WiMAX will

not only provide services for residential and enterprise, but

it can also benefits from 3G cellular towers and Wi-Fi

hotspots and serve as a backhaul for both of them. The

WiMAX technology will revolutionize the communications

by offering affordable wireless broadband access, which

will lead to the development of many areas nationwide and

bridging the digital divide in Accra and other parts of

Ghana.

The National communication Authority (NCA)

Ghana, has recently issued 3 BWA licenses in the 2500

MHz – 2690 MHz band that could be used for either

WiMAX or LTE data networks. The Authority received

nine (9) applications: five (5) applications for paired

frequency configuration of 2 x 15MHz, and four (4)

applications for unpaired frequency configuration of 1 x

30MHz. At the end of the process, Surfline Limited and

GoldKey Properties Limited each won a license for paired

frequency configuration and G-Kwiknet Limited won a

license for unpaired configuration; each license at a price of

Six Million (US$6,000,000.00) United States Dollars for

the period of 10years[8].

The ever-growing demand for high-speed data

connectivity makes Broadband Wireless Access (BWA)

networks for local and Metropolitan areas one of the hottest

topics in the field of telecommunications. There are various

forms of communication methods, such as 2G, 3G and

other BWA networks such as cable network and WLAN

Wi-Fi that is being used in Ghana, specifically Accra, to

deliver data. These networks have recorded some degree of

limitations such as delay, high cost of deployment and the

challenges with distance. Therefore, the objective of this

research is to design a WiMAX access network for Accra to

fill the gap between the WWANs and WLANs (which

provide very high data rate but short-range coverage)and

the 3G cellular systems (which provide highly mobile long-

range coverage but low data rate) by:

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Designing a reliable wireless network using

WiMAX technology for broadband wireless access

and mobile applications for Accra.

Designing architectures for a proposed fixed and a

mobile WiMAX network for Accra.

Consequently, this research work will try to introduce a

preliminary design of WiMAX network for Ghana and

Accra to be precise.The importance of this research is to

show the technological benefits of WiMAX gives; it greater

system capacity, flexibility and ability to efficiently support

more symmetric links compared to the other wireless

networks.

WiMAX has extensive capabilities to substitute various

world communication infrastructures that are in use at

present. It can substitute the telephone copper wire

networks and cable TV coaxial cable infrastructure in fixed

wireless area and in case of cellular networks; it can

substitute the entire network efficiently. The main factor

here is the cost, which is considerably reduced when

compared to services like the Cable, ADSL and Fiber

Optics.

2 METHODOLOGY

2.1 General Overview of the Design

The research work is aimed at designing a WiMAX

communication network for Accra the capital city of Ghana

for broadband wireless access. As part of the Wireless

network design process, the number of Base Stations (BSs)

and their coordinates, azimuth and mechanical tilt to

provide sufficient signal coverage and capacity to the

designated area will be determined; BS placement within

the area of interest will also be discussed. WiMAX has

theoretical maximum throughput of 75Mbps for frequency

less than 11GHz and a bandwidth of between 1.25MHz to

20MHz with fixed mobility and can be used for NLOS.

This throughput for our network can be achieved by using

64QAM, 16QAM and QPSK modulation but 64QAM can

only be utilized under optimal transmission conditions.

WiMAX supports wide range of modulation algorithms to

enable the efficient use of the bandwidth under all

conditions; LOS and NLOS conditions and its

communication range can be 50km.

2.2 The network design

The WiMAX network design will employ the

WiMAX technology known as the Mobile WiMAX, which

is a rapidly growing broadband wireless access technology

based on IEEE 802.16-2004 and IEEE 802.16e-2005 air-

interface standards. This set of standards specifically

determines the rules and regulations for end-user broadband

access.Mobile WiMAXwas used because it offers the

design, the required speed and most importantly the

distance. Mobile WiMAXhas the capability of mobile units

to hand off between base stations. True mobility is

therefore enabled in addition to what 802.16d-2004 (Fixed

WiMAX), already features. WiMAX is the first solution

conceived to support IP data efficiently and be capable of

providing wireless high-speed data to wide areas,

improving spectrum efficiency over previous technologies.

The geographical area of Accra will be divided into a

number of hexagons, the sites are place in to achieve

maximum optimization. However, there are portions of

Accra that will not have continuous coverage since the

population there are scattered e.gAchimota forest. To

remove the blind spots in the coverage area, the cell

footprints must overlap. The footprint of each cell needs to

be calculated or known for the estimation of the number of

base stations,

Number of required base stations

=𝑆𝑒𝑟𝑣𝑖𝑐𝑒 𝐴𝑟𝑒𝑎 (𝑘𝑚2)

𝐶𝑒𝑙𝑙 𝐹𝑜𝑜𝑡𝑝𝑟𝑖𝑛𝑡 (𝑘𝑚2)or

𝑡𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎 (𝑘𝑚2)

2.598𝑅^2(1)

Where R = radiusof the base stations.

Base on the equation above, we have the number of

base stations =240

2.598 ∗ 3^2=10.26

This means we will require a minimum of 10 or

more base stations in order to cover the overall

geographical area of Accra if a cell radius of 3km is used.

The number of base stations is not determined by the size of

geographical region alone, but also the capacity limitations

of the area understudy. The number of users expected to be

serviced on each base stations is also an important factor.

So the above calculation gives only the minimum number

of base station required, these limitation will be taken care

of when the network coverage simulation is done hence the

number of base station will increase. In thiscase cells in a

three-sector base station will be used, because they are

more preferred for a more precise coverage. Thesector cell

coverage area of a base station with three sectors is defined

by the formula:

𝐴 𝑐𝑒𝑙𝑙 = 2.59𝑅2(2)

Where A cell - Coverage area of a base station and

R- Radius of the cell's base station.

A cell = 2.59 ∗ 2.02 = 10.4km.

Assuming a cell radius of 2kmis used.

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2.3 Environment

The base station will be built on towers and

rooftops. The deployment of the design network will be a

combination of outdoor and indoor units. In the design,

obstacles between two base stationswill be avoided, to

enable Line of Sight (LOS) communication.The Accra

landscape does not have very high mountains and this will

make the design less complex and cost effective. The

subscriber station (SS) will use Non Line of sight (NLOS)

in communicating with the base station. In the city of

Accra, there is no heavy fog in the night and hence our

design networks will not surfer much signal degradation or

fading during the night. The Greater Accra Region has a

total estimated land surface of 3,245 square kilometers and

in terms of population; it is estimated at 4,010,054. But the

capital Accra which is been used as the case study has a

total land size of about 230 to 240 square kilometers and

estimated population of about Two Million (2,000,000) . It

is made up of eleven (11) sub metros.Figure 1 represents an

administrative map of Accra[9].

Figure 1. The Administrative Map of Accra [9]

2.4 Network Topology and Link Type

The physical network layout that was

chosen,depended on the nature of the land topology of

Accra. The wireless network will be configured using these

two logical configurations: Point-to-point links and Point-

to-multipoint links. The topology of a network is one of the

major factors that determines throughput, robustness,

reliability, security and cost. Figure 2 shows the network

topology and link type.

Figure 2. Network Topology and Link Type

2.4.1 Link Budget

A fundamental concept in any communications

system is the link budget, or the summation of all the gains

and the losses in the communication network[10]. There is

the need to calculate the transmit power from the

transmitter required to achieve a signal with a required

Signal to Noise Ratio (SNR) at the receiver for a targeted

Bit Error rate (BER). The overall link margin is given by

the difference in the power received by the receiver and the

receiver sensitivity. The link margin must be positive, and

should be maximized (should be at least 10dB or more for

reliable links).

Figure 3. Link budget illustrations [11]

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P received = Power of the transmitter + Gain of the

transmitting antenna + Gain of the Receiving antenna –

Sum of all losses.

(𝑃𝑟 = 𝑃𝑡𝑥 + 𝐺𝑡𝑥 + 𝐺𝑟𝑥 − 𝐹𝑆𝐿 − 𝐴𝑚)(3)

Now receive power in Watts will be:

𝑃𝑟 = 𝑃𝑡(𝜆

4𝜋𝑑)²𝐺𝑟𝐺𝑡(4)

2.4.1.1 Transmit Power(Tx).

The transmit powers used in this research are

23dBm and 15dBm and it can be express in Watt. This

power was chosenfor the parabolic and the panel antennas

respectively. TX power is often dependent on the

transmission rate. The TX power of the given devices that

was used was specified in the literature provided by the

manufacturer.

2.4.1.2 Antenna Gain

The shape of the antenna determines the antenna

gain. Antenna gain patterns are a function of azimuth and

elevation and have an associated half-power bandwidth.

Antennas are passive devices that create the effect of

amplification by virtue of their physical shape. Antennas

have the same characteristics when receiving and

transmitting. The parabolic antennas that were used has a

gain of 19-24 dBm, and the sectorial antennas have roughly

a 12-15 dBi gain.

2.4.1.3 Minimum Received Signal Level (RSL).

It is simply, the sensitivity of the receiver. The

smallest amount of RSL is always expressed as a negative

dBm (- dBm) and is the least power of signal the radio can

distinguish. The minimum RSL is dependent upon rate of

data; the minimum for this research is in the range of -70 to

-95 dBm.

2.4.1.4 Cable Losses.

Some of the signals energy will be lost in the cables,

the connectors and other devices, going from the radios to

the antennas due to the imperfection in the system and dirt.

These losses are dependent on the type of cable used and on

its length. Signal loss for short coaxial cables including

connectors is quite low, in the range of 2-3 dB. In this

research, a loss per connector value of 0.25dBwas used and

it is estimated that the total losses will be in the region of

2dB.

2.4.1.5 Signal-to-Noise (SNR)

Table shows modulation schemes with their

corresponding SNR requirements

Table 2. Data Rates vs. Minimum SNR

Modulation& Encoding

Scheme

Data Rate

(Mbps)

SNR (dB)

BPSK ½ 6 8

BPSK ¾ 9 9

QPSK ½ 12 11

QPSK ¾ 18 13

16-QAM ½ 24 16

16-QAM ¾ 36 20

16-QAM 2/3 48 24

16-QAM ¾ 54 25

2.4.1.6 Path Loss

These are losses, which occur in the process of

transmitting radio frequency signals from the transmitter to

the receiver and it is dependent on frequency. Therefore, a

lower operating frequency of 2.4GHzwas chosen for the

design, to reduce the path loss, which means the signals can

travel further. In a typical WiMAX link, there are two link

budget calculations: one link from the BS to the SS and the

other link from the SS to the BS. The general path loss can

be express as:

Free Space Path Loss = 20 log (d [meters]) + 20 log (f

[MHz]) + 36.6 dB. [11](5)

At 2.4 GHz, the formula simplifies to:

Free Space Path Loss (FSPL) = 20 log (d [meters]) + 40 dB,

or 100 + 20*log (d)(6)

Where FSPL is expressed in dB and d is in

kilometers and d = distance and f = frequency.

These formulas are used for Line of sight (LOS)

calculation where there are no many obstacles. Another

formula is used for indoor calculation where LOS is

difficult to achieve. At 2.4 GHz, our estimate follows this

formula:

Indoor Path Loss (2.4 GHz) = 55 dB + 0.3 dB / d

[meters](7)

2.4.2 Fresnel Zone

The First Fresnel Zone is an ellipsoid-shaped area

around the Line-of-Sight path between transmitter and

receiver. The Fresnel Zone is an important part of the RF

link design because it defines the area around the LOS that

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must be clear of any obstacle for the maximum power to

reach the receiving antenna. Objects within the Fresnel

Zone such as trees, hilltops and buildings can considerably

attenuate the received signal, even when there is an

unobstructed line of sight (LOS) between the transmitter

(TX) and receiver (RX)[12].

Figure 4. Fresnel Zone.

2.4.3 Frequency Band

The mobile WiMAX network design will operate in

theunlicensed frequency band of 2.4GHz called the

Industrial, Scientific, and Medical (ISM) Band. The 2.4

GHz ISM band has an inherently stronger signal with a

longer range and can travel through walls.The ISM bands

were originally reserved internationally for non-commercial

use of RF electromagnetic fields for industrial, scientific,

and medical purposes. However, this frequencywas chosen

for this work because of its strong signal properties.

2.4.4 Antenna and Advanced Antenna Systems

Two types of antennas were used in this design and

they were chosen base on their gain, transmitand receive

powers, voltage standing wave ratio (VSWR), impedance

and frequency. The sample antenna shown in Figure 5 are

the cross-polarized sector antenna panel type and parabolic

dish antenna. The sector panel antennas are often used

outdoors to cover a sector of a cell while the parabolic can

be used for both between sites and users. They operate

within the frequency range of 2.4 - 2.5GHz band and it has

again of 17.5dBi and 30dBi and offers excellent maximum

front-to-back ratio of greater than 32dB. The antenna has a

nominal impedance of 50 ohms. The polarization of the

antenna is vertical with an azimuth of 60º and elevation of

6º beam widths. The antennas have a very good voltage

standing wave ratio (VSWR) of less than 1.5 and operate at

a power of 200W to 250W. The antenna uses a multiple

input multiple output (MIMO) array modulation scheme.

Spatial multiplexing (SM) or MIMO (Multiple In signal

and Multiple Out signal) are improvements over the

previous solution that uses simultaneous transmit and

receive diversity[1].

(a)

(b)

Figure 5. Typical WiMax Sector Antenna and parabolic

dish Antenna

2.5 Link Budgetcalculations

The table below shows the antenna parameters that

were used in the link budget calculation between two sites.

Table 3. Parameter for panel antenna.

Element Value

Transmit output 15dBm

Cable and connectors for

TX

-1dB

Antenna TX 18dBi

FSL 109.54

Antenna RX 18dBi


RX

-1dB(0.25dB per connector)

Receive Sensibility -85dBm

Total: (margin) 24.46dBm

From metro_3 North to metro_8 link: Distance

(d) = 3km.

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FSPL = 100 + 20*log (d), where FSPL is expressed

in dB and d is in kilometers and d = distance and f =

frequency. Therefore if the distance is 3Km then:

FSPL = 100 + 20 log 3 = 109.54dB then

calculating for the Power received

(Pr = Ptx + Gtx + Grx − FSL − Am)

(Pr = 15 + 18 + 18 − 109.54 − 2 = −60.54dBm

Maximum Channel Noise (MCN) (dBm) = Received

Power (dBm) – SNR (dB)MCN dBm = Pr dBm −

SNR dB = MCN = −60.54 − 25 = −85.45dBm

Link Margin (dB) = Received Power (dBm) -

Receive Sensitivity (dBm)

−60.54 − − 85 = 24.46dBm

At 3km, the link margin will be sufficient to provide

54Mbps data rate and ensure 99% link availability based on

Rayleigh’s Fading Model shown in Table 4.Table 4 shows

the Rayleigh Fading Model, and its relationship with link

availability as a percentage of time.

Table 4. Rayleigh Fading Model

Time Availability (%) Fade Margin (dB)

90 8

99.0 18

99.9 28

99.99 38

99.999 48

Table 5. Parameter for parabolic antenna

Element Value

Transmit output 23dBm


TX

-1dB(0.25dB per connector)

Antenna TX 24dBi

FSL 109.54

Antenna RX 24dBi


RX

-1dB (0.25dB per

connector)

Receive Sensibility -72dBm

Total: (margin) 2896dBm

From Metro_1 to Metro_5 link: Distance (d) =

4km.

Calculating for the Free Space Propagation Loss

(FSPL) = 100 + 20log(d)

FSPL = 100 + 20 log 4 = 112.04dB

Calculating for the Power Received (Pr) = 23 +

24 + 24 − 112.04 − 2 = 43.04dBm

Calculating the Maximum Channel Noise

(MCN) dBm = Pr dBm − SNR dB

MCN dBm = −43.04 dBm − 25 dB = −68.04dBm

Determine the

Link Margin dB = recieve signal(dBm)

− receiver sensitivity(dBm)

LM = −43.04 − (−72) = 28.96dB


54Mbps data rate and ensure 99.9% link availability based

on Rayleigh’s Fading Model shown in Table 4.


4.30km.


(FSPL) = 100 + 20log(d)

FSPL = 100 + 20 log 4.5 = 112.67dB


24 + 24 − 112.67 − 2 = −41.67dBm



MCN dBm = −41.67 dBm − 25 dB = −66.67dBm

Determine the

Link Margin dB = recieve signal(dBm)

− receiver sensitivity(dBm)

LM = −41.67 − (−72) = 30.33dB

At 4.5km, the link margin will be sufficient to

provide 54Mbps data rate and ensure 99% link availability

based on Rayleigh’s Fading Model shown in Table 4.


3.5km


(FSPL) = 100 + 20log(d)

FSPL = 100 + 20 log 3.5 = 110.88dB


24 + 24 − 110.88 − 2 = −41.88dBm



MCN dBm = −41.88 dBm − 25 dB = −66.88dBm

Determine the

Link Margin dB =

recieve signal(dBm) − receiver sensitivity(dBm)

LM = −41.88 − (−72) = 30.12dB

At 3.5km, the link margin will be sufficient to

provide 54Mbps data rate and ensure 99.99% link

availability based on Rayleigh’s Fading Model shown in

Table 4.

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2.50km


(FSPL) = 100 + 20log(d)

FSPL = 100 + 20 log 5 = 113.98dB


24 + 24 − 113.98 − 2 = −44.98dBm



MCN dBm = −44.98 dBm − 25 dB = −69.98dBm

Determine the

Link Margin dB =

recieve signal(dBm) − receiver sensitivity(dBm)

LM = −44.98 − (−72) = 27.02dB


54Mbps data rate and ensure 99% link availability based on

Rayleigh’s Fading Model shown in Table 4

2.6 Plotting of base stations

The names for the different cell sites where chosen

based the structures on the ground and the co-ordinates

(longitude and latitude) were picked from Google map. The

sites were placed to achieve high coverage as shown figure

6a, figure 7b and figure 8c. Asset planning tool was used in

the coverage prediction of the sites. MapInfo and Google

Earth were used to plot the physical location of the sites in

Accra. The path loss formula for the macrocell modelswas

used for the sites. The propagation model used for the

enhancedmacrocell models has a pathloss formula as

follow:

Path Loss (dB) = k1 + k2log(d) + k3(Hms) + k4log(Hms) +

k5log(Heff) + k6log(Heff)log(d) + k7(diffn) + C_Loss. (8)

Where:

d – Distance from the base station to the mobile

station (km).

Hms– Height of the mobile station above ground

(m). This figure may be specified either globally or for

individual clutter categories.

Heff– Effective base station antenna height (m).

Diffn– Diffraction loss calculated using either the

Epstein-Peterson, Bullinton, deygout or Japanese Atlas

knifeedge techniques.

k1 and k2 – Intercept and Slope. These factors

correspond to a constant offset (in dB) and a multiplying

factor for the log of the distance between the base station

and the mobile.

k3 – Mobile Antenna Height Factor. Correction

factor used to take into account the effective mobile

antenna height.

k4 – Multiplying factor for Hms.

k5 – Effective Antenna Height Gain. This is the

multiplying factor for the log of the effective antenna

height.

k6 – multiplying factor for log(Heff)log(d).

k7 – multiplying factor for diffraction loss

calculation.

C_loss– Clutter specification taken into account in

the calculation process.

The propagation model can be tuned by modifying

the k-factors. For improved near and far performance, dual

slope attenuation can be introduced by specifying both near

and far values for k1 &k2 and the crossover point.

(a)

(b)

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(c)

Figure 9. Coverage simulation of the network

3 RESULTS AND ANALYSIS

For the simulation and analysis of the network,

OPNET Modeller version 14.5 with WiMAX Module

capability was used[13]. The network model design

describes the implementation of a mobile WiMAX

network. This network model is shown in Figure 10, where

the whole WiMAX network is implemented on the map of

Accra. Three user profiles were considered, these profiles

are Video, Email, Web Browsing and All profiles. These

users are connected to only one base station. Different

topologiesare built with different user profile.

Figure 10. WiMAX network implementation

As shown in Figure 10, the network model contains

four application servers to provide service to the clients and

one remote client for access in into the system. These

servers are; Web server with an application of Web

browsing (light), the Video Server with an application of

Video Conferencing (Light), an FTP Server with an

application of File Transfer (Light) and email server with

an email application. These severs are connected to a hub

which is a networking device that connects the network

devices together. Between the WiMAX BTS and the hub is

the router, which takes incoming packet, analyses the

packets and then directs them to the appropriate locations.

The links used to connect the nodes are Ethernet 100BaseT

link. In this network the "Physical Layer Enabled", is

enabled. When this attribute is set the simulation accounts

for physical layer effects, (frame-by-frame modellingis also

performed).

In the coverage area of WiMAX BTS (cell) there are

WiMAX Subscriber Stations (SS), these SS are distributed

randomly throughout the cell. The subscriber stations (SS),

which are closer to the base station (BS) have very good

channel condition and have very high modulation scheme

and better coding rate. The Subscriber Stations (SS) which

are far from the Base Station (BS) will use the modulation

scheme that could be set to a medium modulation coding

schemes. The Subscriber Stations (SS) which are very far

from Base Station (BS) i.e. near the edges of the cell may

use a more robust modulation and coding scheme.

3.1 Network Simulation Parameters

3.1.1 Wireless Application Node Configuration

In the network design, the Application Configuration

node is defined by using Application Specifications types.

Here three or four applications are defined (Application

Definition attributes, these applications are File Transfer

(Light Load), Video Conferencing (Light Load) and Voice

over IP Call (PCM Quality)). It is possible that all the three

or four applications Voice, Video and Data are supported

by the Subscriber Stations (SSs).

3.1.2 Wireless Profile node configuration

The "Wireless Profile Config" node is the node

responsible for the creation of user profiles and a profile

describes user activity over a period. A profile consists of

many different applications. These user profiles can then be

specified on different subscriber station (SS) nodes in the

network to generate application layer traffic. The

applications defined in the "Application Config" node are

used by the user nodes to configure their profiles.

Therefore, applications must be created using the

"Application Config" node before using these nodes. The

traffic patterns that the applications must stream can also be

specified as well as their profiles.

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3.1.3 WiMAX Configuration Node. (WiMAX config)

This node is used to store profiles of PHY and

service classes, which can be referenced by all WiMAX

nodes in the network. It defines the profile sets that can be

used by the base station on the UL and the DL for Adaptive

Modulation and Coding. It has the attribute that allows the

configuration of parameters that make up a service class. A

service class groups the QoS requirements of a service

flow. Therefore, the service classifications were done in the

WiMAX config node. The specified duration of the frame

in milliseconds in this design is 5ms.We also used its

attribute to specify duration of an OFDMA symbol. The

duration of the OFDMA symbols is related to the frequency

separation between subcarriers.

3.1.4 WiMAX Base Station (BS) Parameters

The maximum power transmission from the base

station is kept at 23dBm and the again is set to 24dBi. The

base stations (BS) nodes and their associated subscriber

station (SS) nodes are configured with the same PHY

profile and this is referenced with the one configured in

WiMAX config. It is where the minimum and the

maximum receiver sensitivity is set and mobility

configuration are also done here. Error! Reference source

not found.below lists some of the network setting for the

BS and user nodes.

Table 6. Network configuration

Configuration

parameter

Base station Work station

Antenna gain dB 24 dB -1 dB

Transmitted

power

23dBm 0.5 W

PHY profile Wireless

OFDMA

20MHz

Wireless

OFDMA

20MHz

PHY profile type OFDM OFDM

Efficiency mode Physical layer enable

Number of subcarrier 2048

Duplexing technique TDD

Frame duration 5 ms

Channel bandwidth 20 MHz

3.2 Implementation

OPNET Modeller 14.5 was used to simulate the

designed networks to show the way video conferencing

(light), emails, web browsing and all user profiles are used

at the same time on the WiMAX network. Different

scenarios were implemented and their simulated results

were analyzed. The user nodes starts sending data packets

to their destinations through the WiMAX base station.

3.3 Simulation Results and Analysis

The duration of the simulation for all the scenarios

was one hour to eliminate statistical errors. This research

analyses the performance of WiMAX for video

conferencing, web browsing, Email. There are different

QoS parameters that are analysed. They include throughput,

end-to-end delay, packet sent and packet receive, WiMAX

delay, HTTP page response time and WiMAX load. In this

section we will analyse the results by showing the graph for

the WiMAX parameters we have chosen, also the results

with respect to each node are analysed.

3.3.1 WiMAX throughput (bits/sec)

The WiMAX throughput is the successful data that

reached to the desire channel. The rate at which a user or

the network sends or receives data, the data can be shared

out on the logical link or physical link. It can be measured

in bytes/s (Bps) or bits/s (bps) or packet per second.

Figure 11. WiMAXThroughput Vs Simulation time for

video conferencing users

Figure 12.WiMAX Throughput Vs Simulation time for web

browsing users

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Figure 13. WiMAX Throughput Vs Simulation time per

video conferencing users

Figure 14.WiMAX Throughput Vs Simulation time

for all profile users

Figure 15. Throughput Vs Simulation time for SISO and

MIMO for the BS

In figure 15, the throughput of the two systems is compared

and it shows that the performance of MIMO configured

system provides better throughput than SISO system

configuration.

3.3.2 WiMAX Traffic Sent and Receive (bits/sec)

Traffic sent and received is an important outcome

for this network design; traffic sent by the base station (BS)

is near about same, but the traffic received at the BS is so

high. The traffic sent for video conferencing users has an

average of 170kbps per user and the received is 129kbps,

which is less than the traffic sent. . The traffic sent and

traffic received graphs are shown below.

Figure 16. WiMAX Traffic Sent (bits/sec) for video

conferencing user.

Figure 17. WiMAX Traffic Received (bits/sec) for video

conferencing user.

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Figure 18. HTTP traffic Sent (bytes/sec)

Figure 19. WiMAX Traffic sent (bits/sec) for a web

browsing user.

Figure 20. WiMAX Traffic Receive (bits/sec) for a web-

browsing user.

Figure 21. HTTP traffic received (bytes/sec)

3.3.3 Page response

The page response time and the object response

time are parameters that are present only in Data Servers,

such as FTP Servers, this parameter explain the interval

between request send by client or server and the response

which it is getting back from either client or server. From

the Figure 22 we can justify that the average page response time and the object respone time of 0.1359sec and

0.03936sec respectively are good

Figure 22. HTTP Object Response Time (seconds).

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Figure 23. HTTP Object Response Time (seconds).

3.3.4 End-to-End Delay

It was realized from the research that the end-to-end

delay increases with an increase in the number of users that

are connected to the network at a given time. The packet

end-to-end delay is the time required by for a packet to

transfer over a network from basis to end. It was observed

that when the users are less, the value is around 0.5sec.

However, when the users increase the maximum end-to-end

delay is at over 1.5 (sec).

Figure 24. End to End Delay for more users

Figure 25. End-to-End Delay for few user

3.3.5 WiMAX load

In this research, WiMAX load refers to the quantity

of data (traffic) being accepted by the network. It was observed that, the WiMAX load increases with increasing

number of user’s. When the number users are less the

amount of data carried is below 5kbps. However, when the

number of users increase the quantity of load also increases.

When the MIMO system comes in, the response of the site

is instant but when the MIMO is removed, there is a delay.

Figure 26. WiMAX load for more users

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Figure 27. WiMAX load for few users

Figure 28. WiMAX load for MIMO

Figure 29. WiMAX load for non-MIMO

3.3.6 WiMAX Delay (sec)

In terms of WiMAX Delay, it was realized that

when the number of users increase the WiMAX delay

performance decreases. For few users the system has an

average delay of around 0.022sec, but when the users

increase the WiMAX delay recorded the highest of 3.5sec.

Figure 30. WiMAX Delay (sec) for few users

Figure 31. WiMAX Delay (sec) for more users

4 CONCLUSION

The design used 19 base stations (BS) to cover an

area of 230 sq km. The capacity of each base station is

300Mbps and can support 256 active subscribers and a user

data rate of 1Mbps. In the case of the end-to-end delay, it was observed that with 50 video conferencing and web

browsing users per site, the end-to-end delay is 0.5 seconds

and 0.04 seconds respectively. It was also observed that,

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100 video conferencing and web browsing users per site have an end-to-end delay of 1.5 seconds and 0.07 seconds

respectively. As the number of users increase, for the

various profiles, the duration of response also increases.

The network has 99.99% link availability and that will be

sufficient to provide 54Mbps. The average distance covered

by a base station was improved to 15 km in WiMAX.

REFERENCES

[1] L. Korowajczuk, LTE, WiMAX and WLAN

Network Design, Optimization and Performance

Analysis, Wiley, July,2011.

[2] IEEE Std. 802.16e-2005, IEEE Standard for Local

and Metropolitan Area Networks - Part 16: Air

Interface for Fixed Broadband Wireless Access

Systems - Amendment 2: Physical and Medium

Access Control Layers for Combined Fixed and

Mobile Operation in Licensed Bands, IEEE, 2006.

[3] Y. Zhang, MOBILE WiMAX Toward Broadband

Wireless Metropolitan Area Networks..

[4] Sanida Omerovic, “WiMax Overview,” Faculty of

Electrical Engineering, University of Ljubljana,

Slovenia, 2010.

[5] Q. Abluwi, “Introduction to Wimax,” Mesh Mode.

[6] K. Kahn, Evolution of WiMAX: Beyond Fixed

Access Networks, Intel Corporation, January

27,2005.

[7] Kim and Yongchul, “Capacity and Coverage

Analysis for Multihop Relay-Enhanced WiMAX

Networks,” North Corolina State University, North

Corolina, 2011.

[8] National communication Authoruty, Ghana,

“www.nca.org.gh,” NCA, 2013. [Online]. Available:

http://www.nca.org.gh/73/34/News.html?item=291.

[Accessed 18 5 2013].

[9] City of Accra, “Ghana Consultative Citizens' Report

Card,” World Bank, Accra, 2013.

[10] F. Ohrtman, WiMAX Handbook: Building 802.16

Wireless Networks, New York: McGraw-Hill, 2005.

[11] Media Informa Telecoms, “Mobile WiMAX,” 4G

Americas, November 2012. [Online]. Available:

http://www.4gamericas.org/index.cfm?fuseaction=p

age&sectionid=259. [Accessed August 2014].

[12] T. Manning, Microwave Radio Transmission Design

Guide, Artech House, 2009.

[13] OPNET Technologies, “www.opnet.com,” OPNET,

2013. [Online]. Available: http://www.opnet.com.

[Accessed 04 04 2013].

Kweku Arthur is a Lecturer at Ghana Technology University

College, Tesano-Ghana. He obtained

his BSc and MSc degree from St.

Petersburg State University of

Telecommunication. His research

areas are wireless technology and

emerging trends in mobile networking

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