Analysis of Relay Stations in WiMAX Networks - International ...

Khan Mubeen Ahmed et al ,Int.J.Computer Technology & Applications,Vol 3 (4), 1431-1434 

ISSN:2229-6093 

Analysis of Relay Stations in WiMAX Networks 

Khan Mubeen Ahmed, Karada Om Prakash 

Malwa Institute of Technology, Department of Information Technology and Engineering 

makkhan0786@gmail.com 

opkarada@gmail.com 

ABSTRACT 

The demand for broadband services is growing IEEE 

sharply today. The traditional solutions to provide high 

speed broadband access is to use wired access 

technologies such as cable modem, digital subscriber 

line(DSL), Ethernet and fiber optics. It is too difficult 

and expensive for carriers to build and maintain wired 

networks. Broadband Wireless Access (BWA) is flexible, 

efficient, and cost effective solution to overcome the 

problems. Relay station acting a capable role of 

extending the range of Base station for long distances in 

WiMAX networks. Relay station is appropriate to areas 

with partial infrastructure such as rural, mountainous 

and lakes, where it is hard to install many Base stations 

with each having wired connections and it is also 

suitable to those areas where obstacles made the 

coverage limited. In this paper the performance analysis 

of Relay stations has been done in WIMAX networks. 

This paper focuses on increasing number of relay 

stations to the performance of WiMAX networks. 

Keywords: 802.16, Light WiMAX Simulator (LWX), 

Bandwidth Allocation Algorithm (BWA), Relay Station 

1. INTRODUCTION 

Worldwide interoperability for microwave access 

(WiMAX) based on Institute of Electrical and 

Electronics Engineering (IEEE) 802.16 standards, 

enables wireless broadband access anywhere anytime 

and on virtually any device. WiMAX is an ideal 

technology for backhaul applications because it 

eliminates expensive leased line or fiber alternative. It 

can provide broadband access to locations in worlds 

rural and developing areas where broadband is currently 

unavailable. WiMAX has numerous advantages, such as 

improved performance and robustness, end to end 

internet protocol (IP) based networks, secure mobility, 

and broadband speeds for voice, data and video. It is a 

wireless metropolitan area networks (WMAN) 

technology that provides interoperable broadband 

wireless connectivity to fixed, portable, and nomadic 

users within 50 km of service area. It allows the user to 

get broadband connectivity without the need of direct 

line of sight communication to the base station and 

provides total data rate up to 75 Mbps, with the 

sufficient bandwidth to simultaneously support hundreds 

of residential and business areas with a single base 

station. WiMAX is a term coined to describe standard, 

interoperable implementation of IEEE 802.16 wireless 

networks in a way similar to Wi-Fi being interoperable 

of the 802.11 WLAN standards. However, the working 

of WiMAX is very different from Wi-Fi [1][2]. The 

network architecture consists of a base station in the 

center of the city, with the base station communicating 

with all the subscribers or access points. Each sector can 

provide broadband connectivity to dozens of businesses 

and hundreds of homes. The various parameters of IEEE 

802.16 standard in WiMAX are related to the MAC and 

PHY layers. 

Many researchers have offered mechanisms for 

transporting information with Light WiMAX. Most of 

these works focus on IEEE 802.16 bandwidth allocation 

algorithms. The contribution of LWX is in the area 

mainly focused on QoS, OFDMA, and multi hop relay. 

LWX also present a mechanism for dynamic binding for 

user to plug and play different algorithms without 

amendment it and recompiling those algorithms which 

analyze bandwidth allocation. Relay station is one of the 

important research area related to this field which is 

analyzed here. IEEE 802.16j is an enhancement to 

previous IEEE 802.16 standards to provide support for 

relays, thus providing for increased capacity and/or 

coverage, depending on the scenario [3]. The standard 

does not permit changes to SSs, hence the changes 

introduced by the standard focus on communications 

between (enhanced) BS and the new RSs. One issue 

IJCTA | July-August 2012 

Available online@www.ijcta.com 

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which arises in this context is to approach network 

planning a multi-hop radio access network gives rise to 

new problems which have not been addressed in 

previous radio planning approaches. Analysis has been 

done to WiMAX scenario and discusses the benefits of 

relay stations. We propose how RS gives benefit to a set 

of BSs and SSs. 

ISSN:2229-6093 

2. RELAY STATION 

IEEE 802.16j is an improvement to earlier 802.16 

standards to provide support for relays, thus providing 

for increased competence and/or coverage, depending on 

the scenario. The standard does not permit changes to 

SSs, hence the changes introduced by the standard focal 

point on communications between (enhanced) BS and 

the new RSs. One issue which arises in this perspective 

is how to move toward network planning a multi-hop 

radio access network gives rise to new problems which 

have not been addressed in earlier radio planning 

approaches. Here, it is proposed how RS gives benefit to 

a set of BSs and SSs. In this work, the benefit of using 

RS in a network of BS and SS has been anticipated 

Relay based networks has small form 

factor, low outlay relays connected with Base stations. 

Three main benefits provided from relay based 

architecture over single hop architecture are throughput 

improvement, coverage enlargement and operational 

cost. It is expected to increase system capacity by 

deploying RSs in a manner that enables more aggressive 

spatial reuse. The relay technology is expected to 

progress the coverage reliability in geographic areas that 

are severely shadowed from the BS and/or to enlarge the 

range of a BS. Relay based systems have the impend to 

deliver cost gains over traditional single hop wireless 

access systems. Using RSs, an operator could deploy a 

network with wide coverage at a lower cost than using 

only (more) expensive BSs to provide good coverage 

and system capacity. 

3. NETWORK SETUP AND SIMULATION 

STUDY 

The network setup is used to examine the performance 

of Light WiMAX with Relay Station. Scenarios that are 

measured including a Base station Subscriber stations 

and Relay stations. 

I WiMAX WITHRELAY STATION (TOPOLOGY) 

Topology as shown in fig.1 is used to evaluate 

performance analysis of Relay station in Light WiMAX 

[4]. 

Fig. 1 Case_with_RS 

The model topology above contains one BS, one RS 

(increased in simulation) and many SSs. The 

connections from BS to SS are taken downlink is taken 

to analyze the performance. The downlink transmission 

is relayed by BS to SSs via RS. TCP connections are 

created for uplink packet transmission with Ack. There 

are two downlink TCP connections from BS to SSs (one 

TCP connection via RS and another TCP connection 

without RS). 

II. SIMULATION PARAMETERS 

The performance of Relay stations are analyzed in 

WiMAX scenarios by considering following simulation 

parameters given in table I: 

TABLE I Parameters used for simulation 

Parameters 

Routing Protocol 

Transmission Protocol 

Bandwidth Allocation 

Algorithm 

Simulation Time 

Number of Nodes 

III. PERFORMANCE METRICS 

Value 

AODV 

TCP 

Round Robin for Relay 

300 Sec 

1,2,3,……………10 

The three performance metrics are considered to 

evaluate the performance: 

Throughput that measures the amount of raw 

bytes sent by a source. 

Goodput that measures bytes that are 

successfully received. 

Number of dropped packets 



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4. RESULTS 

Throughput/Goodput//Packet 

Drop Rate 

3 

2.5 

2 

1.5 

1 

0.5 

0 


for 1 relay station 

0 5 10 15 

number of nodes 

Throughput 

Goodput 

Packet 

Drop Rate 

Fig. 3 Coverage of Relay station with distance and Throughput 

It is observed from the graph shown in fig. 3 that the 

value of throughput is obtained constant and a very 

small rise in throughput is obtained. Because of higher 

order modulation techniques is used with OFDM 

throughput is obtained smaller with one SS and slight 

increase when nodes increases. Since Multiple bits are 

carried in a single OFDM symbol. A wireless channel 

suffers from delay spread due to the existence of 

multiple propagation paths (especially in NLOS 

conditions). When the data symbol is longer, the delay 

spread is a small and insignificant fraction of the symbol 

length, so the effect due to delay spread is minimized. 

distance and data could be received for more distances 

effectively. Also It is observed from graph shown that as 

the distance increases dropped packets also increases. In 

case of Relay station, it is observed that number of 

dropped packets with relay station are more than without 

relay station and this is due to the fact that when packets 

are send directly then there is less possibility of packets 

to be lost since the signal is transmitting with maximum 

power from base station. As the traffic load increases 

then calls are not serviced properly and are dropped after 

long waiting time [5]. 

It is observed that from fig. 5 below that Dropped 

packets are also increased since high modulation cannot 

be maintained over the entire length of the link or in a 

Non Line of sight environment. For such cases the error 

rates rises and the adaptive modulation feature drops the 

modulation to lower density modulation. 

Throughput/Goodput/Packet 

Drop Rate 

3.5 

3 

2.5 

2 

1.5 

1 

0.5 

0 

-0.5 


0 5 10 15 

ISSN:2229-6093 

Throughput 

Goodput 

Packet Drop 

Rate 

Throughput/Goodput/Packet 

Drop Rate 

3.5 

3 

2.5 

2 

1.5 

1 

0.5 

0 

For 2 relay station 

0 5 10 15 

Number of nodes 

Throughput 

Goodput 

Packet 

Drop Rate 

Fig 4 Coverage of Relay station with distance and Goodput 

It is observed from the graph shown in fig 4 that the 

value of Goodput is obtained minimum when number of 

nodes are lesser for Downlink connection. As number of 

nodes increases data transfer capacity of channel per 

second also increases, hence is obtained highest near to 

base stations. If we add one Relay station then the 

coverage area of base station is enlarged to more 


Fig. 5 Coverage of Relay station with distance and Dropped packet 

The data rates changes through the entire coverage area 

and depends on whether the reception is LOS or NLOS. 

Throughput/Goodput/Packe 

t Drop Rate 

3 

2.5 

2 

1.5 

1 

0.5 

0 

-0.5 


0 5 10 15 


Fig. 6 Coverage of Relay station with Number of nodes and 

Throughput 

Throughput 

Goodput 

Packet 

Drop Rate 



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It is observed from the graph shown in fig 6 that 

throughput per user is increased when number of 

subscriber stations increases. This implies that for full 

utilization of relay station, the use of wider channel is 

necessary. If this condition is satisfied, the system 

capacity may be increased. It is observed that nominal 

bit rate for throughput is obtained 2.61818 Mbps for 4 

users against 2.61974 Mbps up to 10 users without Relay 

station before congestion occurs. It is observed from the 

graph shown in fig 6 that as number of nodes increases 

dropped packets also increases. In case with Relay 

station it is observed that number of dropped packets are 

more due to the fact that when packets are send directly 

then there is less possibility for packets to be lost since 

the signal is transmitting with maximum power from 

base station. As the traffic load increases then calls are 

not serviced properly and are dropped after long waiting 

time [5]. Dropped packets are also observed increased 

since high modulation cannot be maintained over the 

entire length of the link or in a Non Line of sight 

environment. For such cases the error rates will rise and 

the adaptive modulation features will drops the 

modulation to lower density modulation .This means that 

the data rate will drop. 

stations could give performance of many relay stations. 

This whole analysis could also be done with UDP 

protocols and with IPV-6 version. 

6. REFERENCES 

[1] Beyond 3G? Personal Broadband, by Monica Paolini 

,Senza Fili Consulting, august 2006,White Paper The 

Emergance of WiMAX. 

[2] Understanding Wifi and WiMAX com as Metro- 

Access Solution , White paper, Intel 

[3] IEEE 802.16 Work Group. IEEE Standard for local 

and Metropolitan area networks part 16: Air 

Intrerface for broadband wireless access systems. 

May 2009. 

[4] Designing and Implementing an IEEE 802.16 

ISSN:2229-6093 

Network Simulator for Performance Evaluation of 

4. CONCLUSION 

In this paper the performance of relay system is analyzed 

with WiMAX. The simulation results show that adding 

relay station to base stations increases the coverage of 

base station and it is observed that for 1node value of 

throughput, Goodput and packet dropped is obtained 0 

up to 3 nodes for 4 Relay stations then 2.61974, 1.77139 

and0.585336 for Throughput, Goodput and dropped 

packets with 4 Relay stations. Also adding Relay station 

could add more number of nodes to the base stations for 

long distances. When number of nodes increases it is 

observed that throughput is obtained higher with relay 

station. As number of nodes increases value of 

throughput is observed higher with 10 nodes. But as the 

distance increases after 200 meters the value of goodput 

with relay station is obtained higher than without relay 

station. When distance increases it is observed that 

dropped packets are obtained higher than with relay 

station. Similarly for number of nodes also initially 

dropped packets is less but as nodes increases value of 

dropped packets also increases, also dropped packets 

increases with relay stations. 

Bandwidth Allocation algorithm by Yuan-Cheng Lai 

and Yen-Hung Chen 

[5] “Multiuser communications, in IEEE conference on 

About Author: 

communications”, vol. 1 p.331, IEEE 

Washington, DC 1995 

Mubeen Ahmed Khan is Assistant Professor in Malwa 

Institute of Technology Indore. He has done his Masters from 

Rajeev Gandhi Technical University Bhopal in 2012 in 

Computer Science and Engineering, and Bachelor of 

Engineering in Information Technology in 2005. His research 

area includes WiMAX Networks, Ad-Hoc Networks and 

Wireless Networks. 

Om Prakash Karada has done his Engineering from Rajeev 

Gandhi Technical University Bhopal in 2006 in Information 

Technology . Currently doing M-Tech from Rajeev Gnadhi 

Techinical University His research area includes Computer 

Networks, cloud computing and data migration in cloud 

computing. 

5. FUTURE WORK 

Further studies can be carried out about the performance 

of relay station with various bandwidth allocation 

techniques with different Quality of Services parameters. 

WiMAX network by increasing the number of relay 



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