WiMAX Network for Capacity and Coverage Assessment

Wireless Pers Commun (2014) 75:1573–1586DOI 10.1007/s11277-013-1438-8

WiMAX Network for Capacity and Coverage Assessment

Satyendra Sharma · Brahmjit Singh

Published online: 16 October 2013© Springer Science+Business Media New York 2013

Abstract This article represents the system performance and its operation stability of a fixedworldwide interoperability for microwave access network operating with point to multipointtechnology. It provides broadband access in fixed locations for mixed environments in GreaterNoida, UP, India. The Field measurement for its capacity and coverage are recorded simul-taneously to optimize a network by raising customer premises equipment (CPE) antennaheight. This process is not going to alter any technical parameters of a network. CPE antennais a directional antenna facing towards base station to achieve optimum LOS reception. Thenet changes in RSS 10–17 dBm, DTR 512–1.8 Mbps, path loss exponent 0.5–0.9 and stan-dard deviation of 1.2–2.3 were observed by raising CPE antenna height of 2–5 m above theprescribed height. The path loss exponents for different environments are obtained using leastsquares method based on measured data by MatLab statistics tool. Standard deviations ofsignal strength variability with distance are derived. Real coverage of a network is presentedbased upon path loss exponent and standard deviation. Our result suggest that, raising theheight of CPE antenna can reduce transmitted power, there for reducing overall maintenancecost and system interference in future.

Keywords Radio propagation · Received signal strength · Shadow region ·Broadband wireless access · Capacity · Coverage

1 Introduction

Worldwide interoperability for microwave access (WiMAX) is a telecommunication tech-nology which enables wireless transmission of voice and data in many ways, ranging from

S. Sharma (B)Noida Institute of Engineering and Technology, Greater Noida 201306, Indiae-mail: [email protected]

B. SinghNational Institute of Technology, Kurukshetra 136119, Indiae-mail: [email protected]

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1574 S. Sharma, B. Singh

point-to-point (PTP) links to multipoint (PTM) links, the so called broadband wireless access(BWA). The signal propagation path is the path from the WiMAX base station (BS) antennato the CPE antenna depends upon cell coverage areas. The operating network having cell-edge of 15 km and it can deliver 5–7 Mbps to users at 15 km range for fixed location only.It provides more sophisticated services as Internet, TV and high data rate among others at2.62 GHz frequency with channel bandwidth of 10 MHz. The cell coverage depends upon BSantenna height, tilt, RX antenna height, position of obstructions and other factors too [1]. Theinitial step for planning and designing a fixed WiMAX network is the prediction of the qualityof signal strength received by user station. These factors depend on the path loss exponent,shadowing and multipath fading. Study of radio wave propagation in different environmentsis an essential for designing mobile communication systems. The location of tower undermeasurement is in rural area due to adverse radiation effects. The reverse engineering processwas applied for this network to radiate its power from rural area and provide services in urbanarea. In this paper, the field measurements of received signal strength (RSS) in dBm and datatransfer rate (DTR) in Mbps recorded simultaneously at the frequency of 2.62 GHz. Thereceived signal strength from the BS were monitored and recorded every after 100 m to ana-lyze RSS over 8 km distance. The total cell area consist of mixed propagation environmentslike 3 km urban, 2 km industrial, 3 km suburban and 7 km rural areas. The location wheremeasurements were performed falls in between this tower. The rural areas were discarded formeasurement due to minimum subscribers and high signal strength and reported in previouswork. The interference of a network is not included due single operating frequency for all thethree towers in the area and others like GSM, CDMA towers are 10 km away, operating atdifferent frequencies. The nearest BS to provide coverage to Greater Noida city was targetedby CPE antenna to get maximum RSS and DTR. The capacity and coverage are calculated bytaking reference of receiver threshold i.e. −80 dBm to its maximum value, so as to enhancethe capacity of 512 Kbps as minimum required by network. The internet services particularlyin these areas are quite complicated and it is generally agreed that field measurements areessential for assessments of coverage and capacity. The prediction assumes greater signifi-cance in internet service, because it is direct to the subscriber and in urban area it is directlyaffected by buildings and other moving vehicles [2,3]. The main aim to install WiMAX towerby Govt. of India in this zone is to provide internet service at low cost with maximum datatransfer rate in rural zone. To carry out a research work on this topic, meticulous study onoperating network were performed and related data were obtained in Table 2.

1.1 Previous Work Analysis

A large number of experimental studies for received signal strength by tilting antenna havebeen carried out and reported in literature. Authors [4–8] have shown downward tiltingof BS antenna beam can reduce the interference effects in other macro cell and decreasesthe probability of occurrence of unacceptable inter symbol interference due to multipathpropagation. They also reported that upward tilting is useful if radio energy has to be reachedin the upper floor of high rise tower. Sarkar et al. [9] showed that placing the antenna ontop of a tower in case of mobile communication can produce undesirable effects. The signalstrength goes through a series of maxima and minima. If the BS antenna is placed 100 mor higher, the lobe effects are reduced due to the weakening of the image components as aresult of losses in the ground. In another paper, Sarkar et al. [10] advocated the concept ofplacing the transmitting antenna closer to the ground, which requires less transmitter inputpower to achieve higher capacity. They showed that the capacity could be increased by tiltingthe transmitting antenna slightly upward in order to minimize the interference between the

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WiMAX Network for Capacity and Coverage Assessment 1575

fields produced by the antenna and its image. Sharma and Singh [11,12] suggested a suitablepath-loss model by characterizing the environments and calculated coverage area of samenetwork in previous publication. The future plan of previous publications was implicated inthis publication to enhance capacity and coverage by raising CPE antenna height.

Li et al. [13] showed a mechanism for approximating the radio coverage of a real environ-ment is based on data collected by continually monitoring MSs feedback. It is a combinationof clustering of MSs based on RSS perceived on the terrain and a technique that allows theaccuracy of the modeling to be determined.

Galvan-Tejada et al. [14] showed different models for WiMAX under different environ-mental condition to compute path loss at 3.5 GHz for better coverage prediction.

This paper is structured as follows: In Sect. 2, RSS measurements. In Sect. 3, regressionfit analysis. In Sect. 4, impact of CPE antenna height. In Sect. 5, coverage analysis. In Sect. 6,cellular radio environment. In Sect. 7, discussion. In Sect. 8, conclusion.

2 RSS Measurements

The measurements of signal strength and data transfer rate in parallel by test equipments,suggest a new approach in research methodology. It was applied to a WiMAX BS towerinstalled at Bisrakh in Greater Noida, UP, India for providing Internet services in rural sector.Due to its range constraints, a limited coverage in Greater Noida city is possible by operatingnetwork. The next difficulty associated with this network is its rural location with limitedsubscribers. In other way, urban area is facing big difficulties due poor signal strength andlower net speed. In this situation, enhancement of RSS and DTR by some means may adda new life to the network and subscribers. The signal passing through rural → suburban→ industrial and finally reaches to urban areas get retarded by fading environments. Thearea around Greater Noida city is fully vegetation with high rise towers, knowledge parks,shopping complex etc. The BS tower with an antenna height of 40 m is installed in an openarea having cell coverage of 15 km. The measurements were recorded at selected locationsin the area of 10–8 km away from BS by adjusting different height of CPE antenna to getmaximum signal strength. Figure 2 shows the variation of signal strength received at RXwith respect to distance. Figure 3 is a scatter plot of the RSS measurements just to representa clear view of signal at different locations. Each data point is a small scale average overRayleigh fading where the rms value of the envelope is the square root of the mean square.Figure 1 represents a location of towers where RX is the receiver used for monitoring ofDTR i.e. (CPE) along with two Laptops for better accuracy. Pad 10 dB (HP) is an attenuator;RF detector (HP) is radio frequency detector up to 10 GHz along with spectrum analyzer(Micronic 4 GHz) to measure RSS.

Characterizing the environments based on field measurement provide a precise coverageby an operating network. The environment of a network changes continuously due to manmade structure, growing of a plants, lowering or raising of a plane etc. A beam propagating in aparticular direction gets obstructed, which results fading of a signal. It is analyzed by viewingFig. 2 at 1,100–1,500 and 3,100–3,300 m, where signal goes down sharply due to tall buildingof “Denso India Ltd. and Moser bear India Ltd.”. An additional path loss of 10–25 dB wasproduced by these companies structure, in turn data transfer rate also fluctuates, but maintain>2 Mbps. Sudden rise of signal at 3,300–3,500 m is an indication of LOS at ‘DM’ officebeing a single storey building, where antenna was raised almost 7 m to gain maximum signal,latter on signal reduces gradually as distance from RX to BTS increases. Urban area provides

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Fig. 1 BS location and measurement set up

0 1000 2000 3000 4000 5000 6000 7000 8000-90

-80

-70

-60

-50

-40

-30

-20

Distance of MS from BS, mtr

Rec

eive

d S

igna

l Str

engt

h, d

Bm

Fig. 2 Signal strength variability

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102

103

104

-90

-80

-70

-60

-50

-40

-30

-20Scatter Plot of Signal

Distance of MS from BS in log scale, mtr

Rec

eive

d S

igna

l Str

engt

h, d

Bm

Fig. 3 Scatter plot of the signal strength

lots of complication due to multi storey buildings, but height of buildings facilitates a specialadvantage to maintain LOS and stability in signal, if CPE antenna is placed on roof top.

3 Regression Fit Analysis

In this section, linear regression analysis is carried out on the basis of characterizing envi-ronments i.e. urban, suburban and industrial serviced area on the measured data, which is alinear least squares curve fitting procedure [15]. The mean signal strength in dBm at receiveris a function of distance (d) from BS is modeled as

PRSS = K − 10 α log(d) + ξ

PRSS = Received signal strength (dBm)

K = Transmitted Power BS (dB) + Antenna correction factor (43 dBm + 1.4)

α = path loss exponent (1.6−3.5)

d = Distance in meter (100−8,000 m)

ξ = Shadow fading (6 dB). (1)

The statistical analysis of the field measurement data led to single slope characterizationfor RSS against logarithmic scale distance as shown in Fig. 4 Applying regression fit on theentire set of the measurement data, it is observed that the overall path loss exponent α = 3.5and standard deviation of signal strength variability ‘σ’ is equal to 5.75 dB. Figure 2 is theplot of recorded signal strength during the measurement campaign. Shadow fading of 6 dBneeds to be accounted due to additional loss of signal in urban area.

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0 1000 2000 3000 4000 5000 6000 7000 8000-90

-80

-70

-60

-50

-40

-30

-20

-10

Distance, m

Rec

eive

d S

igna

l Str

engt

h,dB

m

Regression Analysis

Fig. 4 Regression analysis

4 Impact of CPE Antenna Height

Customer premises equipment (CPE) antenna is a directional antenna and facing towardsBS to receive even the weakest signal to provide some essential services. Normally, it is acustomer premises equipment provided with separate attachment of directional antenna andconnected with co-axial cable. It’s a major part of fixed WiMAX network, which providesbroadband services. The alignment of CPE antenna with BS antenna beam can change thenetwork performance drastically. The initial operating parameters of a network recorded asreference parameters for RSS and DTR in rural area are −21 dBm with 4.5 Mbps, subur-ban area −27 dBm with 2.8 Mbps, industrial area −55 dBm with 2.5 Mbps and urban area−75 dBm with 512 Kbps, respectively. The path loss exponents were 2.1, 2.8, 4.1 and stan-dard deviation were 9.8, 7.3 and 6.2 at 5, 7 and 10 m height in suburban, industrial and urbanarea respectively. Now the height of CPE antenna is raised to 7, 9 and 12 m, the changesobserved are available in Tables 1, 3, 4 and 5 and Figs. 5, 6 and 7. Raising the height ofCPE antenna beyond 7–12 m, no changes were observed in particular environments. The netchanges in RSS 10–17 dBm, DTR 512 Kbps to 1.8 Mbps, path loss exponent 0.5–0.9 andstandard deviation of 1.2–2.3 were observed by raising CPE antenna height of 2–5 m abovethe prescribed height. As such, there is no regulation of CPE antenna height, but it should belower than BS antenna height. The increase/decrease of few relevant parameters can changethe network capacity/coverage drastically. The urban area is subjected to large variation insignal strength due to fading behavior of environments [16,17]. The demand, utilization andprofit, all these parameters are having direct relation with urban area. The raising of RSSand DTR tends to secure services like video conferencing, multilayer interactive gaming,streaming media, web browsing and instant messaging, media content downloads etc canbe easily provided. But urban area is subjected to location probability. Some of the location

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in urban, where signal strength is less than receiver threshold can be provided with limitedservices i.e. without media content downloads (Table 2).

Table 1 Characteristicsparameters of the propagationenvironment

Environment Path loss exponent(α) (max)

Standard deviation,σ (dB) (max)

Suburban 1.6 8.03

Industrial 2.06 6.65

Urban 3.5 5.75

Table 2 System parameters Equipment made HCL, HUWAI, ICON

Standard used IEEE 802.16-2004

TX power 43 dBm

Antenna 3 Sector

Frequency 2.62 GHz

Ant type Dish type (1 m diameter)

Band width 10 MHz

Sensitivity −80 dBm

Ant. gain 14 dB

Cell range 15 km

Tilt (operating) downward 2◦BS Ant. height 40 m

CPE Ant. height 5–10 m

Wireless MAN OFDM

Tilt facility ±5◦

Table 3 Suburban data Received signal strength(dBm)

Data transfer rate(Mbps)

Antenna (CPE) height(m)

−17 4.2 7

−19 4.1 7

−21 4.0 7

−23 4.0 7

−25 4.0 7

−27 3.8 7

−29 3.8 7

−33 3.8 7

−35 3.2 7

−36 3.1 7

−39 3.0 7

−44 3.0 7

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Table 4 Industrial data Received signal strength(dBm)


Antenna (RX) height(m)

−45 3.5 9

−47 3.2 9

−49 3.0 9

−50 3.0 9

−52 3.0 9

−55 2.8 9

−57 2.8 9

−59 2.6 9

−60 2.6 9

−62 2.5 9

−63 2.5 9

−64 2.5 9

Table 5 Urban area data Received signal strength(dBm)


Antenna (CPE) height(m)

−56 3.0 12

−58 3.0 12

−61 3.0 12

−63 3.1 12

−65 3.1 12

−67 3.0 12

−68 2.8 12

−69 2.8 12

−70 2.2 12

−73 2.0 12

−75 2.3 12

−77 2.0 12

−78 2.564 12

−79 2.228 12

−80 2.064 12

−83 1.032 12

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-44 -39 -36 -35 -33 -29 -27 -25 -23 -21 -19 -170

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Received signal strength,dBm

Dat

a tr

ansf

er r

ate,

Mbp

s

Fig. 5 RSS and DTR in suburban area

-64-63-62 -60-59 -57 -55 -52 -50-49 -47 -450

0.5

1

1.5

2

2.5

3

3.5

Received signal strength, dBm

Dat

a tr

ansf

er r

ate,

Mbp

s

Fig. 6 RSS and DTR in industrial area

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-85 -80 -75 -70 -65 -60 -550

0.5

1

1.5

2

2.5

3

3.5

Received signal strength, dBm

Dat

a tr

ansf

er r

ate,

Mbp

s

Fig. 7 RSS and DTR in urban area

-90 -80 -70 -60 -50 -40 -30 -200.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

Received Signal Strength, dBm

% C

over

age

Urban Area

Fig. 8 Coverage analysis

5 Coverage Analysis

The percentage of coverage area is calculated on receiver threshold i.e. Pmin ≥ −80 dBm,path loss exponent α = 3.5 and standard deviation σ = 5.75 which is maximum for urbanarea after raising CPE antenna to 12 m. Figure 8 indicates almost constant coverage up to−65 dBm and started falling in urban area due to shadow fading. This was the case whenCPE antenna was at 10 m height and α = 4.2 and σ = 6.2. After raising the height of CPE

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antenna to 12 m in urban area, α = 3.5, σ = 5.75 and RSS ≥ −80 dBm were obtained. Nowsignal started increasing and leading towards more than 100 % area coverage. In this case, iftransmitted power is reduced to 38 dBm, the possibility of coverage is 100 %.

C = Q(a) + exp((2−2ab)/b2)Q((2−2 ab)/b)

Q = 1/2 − 1/2 ∗ erf

a = (Pmin − Pr)/ σ and b = 10 × α log10 (e)/ σ

C = Total coverage area

Pr = pt + 10 log10 k − 10 × α log10 (d/do), (2)

where Pr = is the received power at the cell boundary, Pt = Transmitted power, K = Antennacorrection factor, d = Distance from TX to RX, d0 = Reference distance, α= Path loss expo-nent.

The cell coverage area is the expected percentage of area within a cell that has receivedpower above the minimum at a path loss of 174.5 dB, and can be modeled as

PL(dB) = 28.6 + 37.4 log10 (d) , (3)

where PL = Path loss (dB), d = Distance (m).The link budget of a given network can be modeled as

Pr = Pt + Gt + Gr − PL − Cn − Cb , (4)

where Pr = Received signal (dBm), Pt = Transmitted power (43 dBm), Gt = Gain of trans-mitting antenna (14 dB), Gr = Gain of receiving antenna (14 dB), PL = Path loss (174.5 dB),Cn = Connector loss (8 dB), Cb = Cable loss (8 dB).

6 Cellular Radio Environment

Cellular environments differ at different places depends upon various factor like location ofBS, terrain configuration, hills, tower, vegetation etc. The main objective behind field mea-surement campaign is to examine the radio wave propagation at high frequency of 2.62 GHzin mixed environments. The total cell areas under measurement campaign have been dividedinto three categories, (i) suburban (ii) urban (iii) industrial. The urban area is located atWiMAX cell-edge consisted of residential, educational, commercial buildings with wideroads and tall trees. 10 % of urban area is covered with park and green belt. The data mea-sured from these three environments have been analyzed. As a result, path loss exponent andstandard deviation of signal strength variability are obtained as given in Table 1. Parameterobtained in Table 1, indicates that radio signal strength decreases rapidly with increase indistance between RX and BS. In urban area, path loss exponent is maximum (α = 3.5).In suburban area path loss exponent is maximum (α = 1.6), and in industrial area, pathloss exponent is maximum (α = 2.06). Comparing the path loss exponent for above threeconditions, the signal strength attenuates with highest rate in urban area due to tall buildingand commercial tower etc. Further, as per Table 1, the standard deviation of signal strengthincreases with increasing distance. Urban area standard deviation is maximum (σ = 5.75),because total urban area is only 5 km in cell coverage zone.

The above results reinforce the fact that the propagation characteristics are fully dependenton local terrain features and the prevailing environment. Path loss characteristics are definedand acceptable in different user environments, which will yield different path loss models

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in different areas as per Table 1 parameters. In practice, path loss exponent (α) and standarddeviation (σ), statistically describe the path loss model for an arbitrary location having aspecific BS–MS (RX station) separation, and this model may be used in computer simulationto provide received power levels for random locations in cellular communication systemdesign and analysis.

Cellular communication systems are designed scientifically to offer desired service underchanging system parameters, which depends mainly on propagation characteristics of theradio cell environment [17]. WiMAX system is specially designed to provide internet serviceat low cost with high grade of services mostly in rural areas. To achieve consistent qualityof service across varying propagation environmental conditions, receiver may be tuned to itsoptimum value or receiver design parameter need to be adapted [18,19]. Moreover, the fieldstudy may also be useful for planning the cellular network for its optimum coverage [20,21].

Data recorded from different environments shows excellent response of signal in suburban,industrial and urban area for full utilization of services and limited services in few locationsof urban area.

7 Discussion

WiMAX tower a recent technology installed for internet services are divided in two hardwareconcept i.e. BS tower similar to mobile station tower and receiving station (RX) i.e. CPEalong with antenna at 5–10 m mast installed with clients services. The installation of a systemcarried out with different path loss predicting models, which may not be suitable for mixtureof terrain and failed to provide the promised coverage. Previous work reported in manyliteratures indicates that, recording of data during drive test, which may not be accurate forFWA mode of network operation. There for field measurement has to carry out at point topoint by wait and watch process. There for, optimizing this network for its capacity andcoverage together by managing antenna height at customer end (CPE) without altering theBS parameter became a feasible work. Applications of network based on data transfer rateare also reported to enhance the facility and vase maximum profit by said network. Path lossexponent and standard deviation are active parameters to decide the coverage of a networkand were derived from recorded data for different terrains. Due to the tough environments andits varying nature, more and more experimental campaign should be conducted to developsuitable models for this region. The raising of CPE antenna height produced a leading effectsin RSS and DTR, there for, reduction in transmitter power is possible, and in turn it is goingto reduce overall maintenance cost and interference of a network.

8 Conclusion

In this paper, the study shows that variation in propagation environment leads to loss of signalstrength, there for predicted coverage could not be achieved, but it could be optimized byincreasing CPE antenna height. Path loss exponent and standard deviation of signal strengthvariability are determined to provide a range of coverage. The path loss exponent obtainedlie in the range of 1.6–3.5, which provide a rate of change in signal strength. The standarddeviation of signal strength increases with increase in distance and its value can be reducedslightly by taking maximum readings. The net changes in RSS 10–17 dBm, DTR 512 Kbpsto 1.8 Mbps, path loss exponent 0.5–0.9 and standard deviation of 1.2–2.3 were observed byraising CPE antenna height of 2–5 m above the prescribed height. Calculation of coverage

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and capacity over test run were never carried before. The result may be utilized for futurenetwork design, planning and optimization in a particular area.

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http://dx.doi.org/10.1007/s11277-013-1139-3


Author Biographies

Satyendra Sharma has received B.E. and M.Tech. degree in Electron-ics and communication Engineering and VLSI Design from Institutionof Engineers (India), Calcutta and Uttar Pradesh Technical University,Lucknow (India). He has served 20 years in Indian Air Force for instal-lation, operation and maintenance for various Radar and the Communi-cation equipments. Presently, he is working as Associate Professor andheading the department of ECE in Noida Institute of Engineering andTechnology, Greater Noida, UP (India). He has published 17 papers inscientific journal and conferences in the field of wireless communica-tion and VLSI design. He is a life member of ISTE and AMIE.

Brahmjit Singh has completed Bachelor of Engineering in ElectronicsEngineering from Malaviya National Institute of Technology, Jaipur,Master of Engineering with specialization in Microwave and Radarfrom Indian Institute of Technology, Roorkee and Ph.D. degree fromGGS Indraprasth University, Delhi. He is with the department of Elec-tronics and Communication Engineering, National Institute of Tech-nology, Kurukshetra working as Professor having 24 years of teach-ing and research experience. He has held several administrative andacademic positions in NIT Kurukshetra. These include Chairman ECEDepartment, Chairman Computer Engineering Department, Professorin-Charge Centre of Computing and Networking, and Member Plan-ning and Development Board. He has published 75 research papers inInternational/National Journals and conferences, organized several con-ferences and short term courses. His current research interests includeWireless Sensor Networks, Cognitive Radio, Security Algorithm forWireless Networks and Mobility Management in wireless networksand planning and designing of Mobile Cellular Networks. He has been

awarded The Best Research Paper Award on behalf of ‘The Institution of Engineers (India)’. He is the mem-ber of IEEE, Life member of IETE, and Life Member of ISTE.

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WiMAX Network for Capacity and Coverage Assessment