Analysis of Relay Stations in WiMAX Networks

Analysis of Relay Stations in WiMAX Networks

Khan Mubeen Ahmed, Karada Om Prakash

Malwa Institute of Technology, Department of Information Technology and Engineering

[email protected]

[email protected]

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

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

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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.

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 Value

Routing Protocol AODV

Transmission Protocol TCP

Bandwidth Allocation Algorithm

Round Robin for Relay

Simulation Time 300 Sec

Number of Nodes 1,2,3,……………10

III. PERFORMANCE METRICS

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

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.

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

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.

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.

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

Throughput

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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.

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.

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

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

Network Simulator for Performance Evaluation of

Bandwidth Allocation algorithm by Yuan-Cheng Lai

and Yen-Hung Chen

[5] “Multiuser communications, in IEEE conference on

communications”, vol. 1 p.331, IEEE

Washington, DC 1995

About Author:

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.



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Analysis of Relay Stations in WiMAX Networks