Performance Comparison of Non-relay and Relay

2012 IEEE Symposium on Wireless Technology and Applications (ISWTA), September 23-26, 2012, Bandung, Indonesia

Performance Comparison of Non-Relay and Relay Scenario in IEEE 802.16j Network Wan Nurul Izza Wan Darman

Mohd Dani Baba, D. Mohd Ali, Azita Laily Yusof

Fakulti Kejuruteraan Elektrik dan Elektronik Universiti Tun Hussein Onn Malaysia Batu Pahat, Malaysia [email protected]

Fakulti Kejuruteraan Elektrik Universiti Teknologi Mara Shah Alam, Malaysia {mdani074, darma504, azita968}@salam.uitm.edu.my applications have been studied. They evaluate the performance of the network in terms of network throughput, delay and load by using OPNET Modeler and the real time applications are treated as UGS for VoIP and rtPS for MPEG. In [8], performance of WiMAX MMR system to support Multicast/Broadcast service have been done using OPNET Modeler 12.0. However, the developed WiMAX MMR network does not support relay and mobility functions, thus they only imitated the WiMAX relay functions between the BS and the RS. An analytical model to determine the throughput and delay of real-time applications in WiMAX network have been done by [9] where the proposed model helps to investigate throughput and delay in mesh network. A comparison of using relay and MIMO is studied in [10] to evaluate the throughput, coverage extension and spectrum efficiency. However, their work does not mention on the types of traffic generated by the SS. In [11], the system capacity of IEEE 802.16j network using transparent RS have been investigate. In their studies, they evaluate the throughput gains by varying number of RS and relate it with power transmit by the RS.

Abstract— In this paper, we have investigated the use of transparent relay station to improve the throughput of the IEEE 802.16j Mobile Multi-hop Relay (MMR) WiMAX network. Simulations are performed using OPNET Modeler, and only VoIP application is considered. The result shows transparent relay station does improve the throughput of WiMAX network with some coverage extension. Keywords- 802.16j; Wimax; throughput; transparent relay station; OPNET;

I.

INTRODUCTION

IEEE 802.16 standard aims to accommodate users’ demand for multimedia applications are defined in June 2004. In 2005, the standards for mobile user are defined and another amendment was done in 2009 to include support for relay station which enhance coverage and improve network capacity. This standard is known as IEEE 802.16j Mobile Multi-hop Relay (MMR) WiMAX network. With mobility becoming a trend, providing wireless technology with the capability to accommodate broadband access has become quite a challenge. In 2005, the IEEE 802.16 working group has included mobility support [1] to the previous standards and in 2009, the relay task group further developed the IEEE 802.16e standard by specifying the improvement of the MAC layer and OFDMA physical layer for licensed bands to enable relay station (RS) in the IEEE 802.16 system [2]. The amendments are aimed to extend the coverage and improve the throughput of the WiMAX network without having to install expensive Base Station (BS) [3]. Apart from that, RS can also resolve the connectivity issues in single BS configuration [4, 5].

The purpose of this study is to investigate the performance of transparent RS in OPNET Modeler and how it improves the network throughput as well as user throughput. OPNET Modeler is chosen to simulate the scenarios because of the ease of use in designing the network topology and analyzing the data. The rest of the paper is organized as follows. Section II provides some overview on types of RS as defined in IEEE 802.16j standards, the usage scenarios of RS, types of QoS supported by IEEE 802.16. Section III presents the network model under studies. The results and discussion are presented in section IV. Finally section V concludes the paper.

A BS in IEEE 802.16j MMR network must be able to communicate with RSs and support traffic aggregation from multiple RSs but as for the subscriber station (SS), conventional SS should be able to function normally in a multihop mobile configuration [3]. A basic IEEE 802.16 MMR WiMAX network consist of multi-hop relay-BS (MR-BS), one or more RS and the end user devices, the subscriber station (SS) which can be either fixed or mobile nodes [6]. The number of hops between MR-BS and SS is not defined but it must only contain RSs [1, 6].

II.

There are few studies on performance evaluation of IEEE 802.16 network using either network simulator or analytical model. In [7], IEEE 802.16 WiMAX network for real time

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IEEE 802.16J MOBILE MULTI-HOP RELAY NETWORK

Multi-hop relay concepts have been an interest in both the industry and the academia to overcome the problems in single hop network [12,13]. Both [12] and [14] mention the problem with next generation wireless system will face because of the very high operating frequency (>5 GHz) will be the vulnerability of the radio signal especially in non-line-of-sight (NLOS) environment. One of the solutions to overcome this problem that is typically encountered in today’s urban wireless system is to deploy RS which will cost less than the BS.

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According to [12], a relaying system can be categorized as decode-forward or amplify-forward. Both type of system differs in terms of how they operate where a decode-forward RS act quite similar like digital repeaters where as an amplifyforward RS is similar like analog repeaters [12].

B. Quality of Service (QoS) in IEEE 802.16 In wireless networks, QoS is usually managed at the medium access control (MAC) layer to overcome the problem such as unpredictable and highly variable of wireless link [20]. Of the features of the MAC Layer of IEEE 802.16 is it differentiate the service among traffic categories with different requirements [20]. The IEEE 802.16-2009 defines five different class services [2]. Parameters of each scheduling service class are as shown in Table II.

Some properties of relay concept have been discussed in [14] as well as its benefits. RS are anticipated to improve coverage in areas with high shadowing, extend the coverage of a single hop network as well as to increase the network throughput [15].

III. A. Relay Station in IEEE 802.16j MMR Network In [16], it describe the minimal functionality of the air interface between the MR-BS and the RS according to the standard. In an IEEE 802.16j MMR network, the RS are expected to support all licensed band allocated for IEEE 802.16 system, support point-to-multipoint network topology and the RS is perfectly transparent to the SS [16].

OPNET Modeler 16.0 is used to simulate the scenarios because IEEE 802.16j is supported in this version. Two scenarios are simulated where the first scenario is the standard IEEE 802.16 WiMAX network that only has one BS and SSs and the second scenario is the duplicate of the first scenario but with RS. Transparent RS is use in the second scenario because only transparent RS is available in the OPNET Modeler 16.0 module library.

IEEE802.16j Task Group have define two types of relay station can be deployed in IEEE 802.16 network. Types of RS can be deployed are transparent RS or non-transparent RS [2]. Transparent RS is usually used to improve the network capacity because the RSs in this mode do not forward any framing information [17, 18]. Transparent RS only relay data traffic thus the SS which is physically connected to it does not aware the existence of the RS [16]. Non-transparent relay generates their own framing information or forward those provided by the MR-BS depending the scheduling mode and it is used to extend the network coverage [17, 18]. SS will be connected physically and logically to a non-transparent RS that transmit a preamble, broadcast messages and also relay data [16]. Two different modes are defined as the mechanism for bandwidth allocation [2]. The modes are centralized scheduling mode and distributed scheduling mode. An RS operating in distributed mode are capable of scheduling whereas RS operating in centralized mode does not have that ability. Summary of the differences between the types of RS is shown in Table I.

Simulation time for both scenarios is 30 minutes where all generated traffic will be directed to the VoIP server. Table III shows the simulation parameter of the first scenario where as Table IV provides the simulation parameters for the second scenario. VoIP traffic parameters are chosen base on [22] to ease the analysis of the simulation results. In both scenarios, Suburban Path Loss Model presented in [23] are chosen to model the wireless channel. This path loss model is also chosen according to the 802.16 Session #14 documents [24]. Three types of terrain have been categorized by [23]. For maximum path loss category the terrain is describe as hilly terrain with moderate-to-heavy tree densities (Category A). The minimum path loss category is mostly flat terrain with light tree densities (Category C). Intermediate path loss condition is captured in Category B and is described as either mostly flat terrain with moderate-to-heavy tree densities, or hilly terrain with light tree densities. Even OPNET Modeler has the options to set the terrain types, the actual terrain being considered during the simulation is not known. Another limitation of the OPNET Modeler is, the actual coverage area of the BS implemented is not known and is considered only base on the maximum power transmitted by the BS.

The relay task group have also narrowed down the usage of RS into four scenarios [6]. The scenarios are fixed infrastructures, in-building coverage, temporary coverage and on mobile vehicle coverage [6]. Details on the key characteristic of the usage scenarios can be found in [19]. TABLE I.

TABLE II. Class Unsolicited Grant Service (UGS)

COMPARISON OF TRANSPARENT AND NON-TRANSPARENT RELAY STATION Transparent Relay

Non-Transparent Relay

Transmit Frame header Number of hops Coverage extension Throughput enhancement

No

Yes

2 little

2 or more large

Yes

Yes

Scheduling Modes

Centralized

Centralized or distributed

SIMULATIONS

Real-Time Polling Service (rtPS) Enhanced Real-Time Polling Service (ert PS) Non Real-Time Polling Service (nrtPS) Best effort (BE)

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SCHEDULING SERVICE CLASS FEATURES Application VoIP,E1: fixed-size packets on periodic basis

Qos Parameters max rate, latency and jitter

Streaming audio/video

min rate, max rate and latency

VoIP with detection

Min rate, max rate, latency and jitter

activity

FTP Data transfer, Web

Min rate and max rate


TABLE III.

SIMULATION PARAMETERS OF SCENARIO ONE

Parameter

Value

PHY Profile

WirelessOFDMA 20MHz

Max Sustained Traffic Rate (UGS)

96000 bps

Path loss Parameters

Suburban (Erceg)

Terrain Type

Terrain Type A

Efficiency Mode

Mobility and Ranging Enabled

Cell Radius

1 km

Maximum Transmission Power (BS)

0.5 W

Maximum Transmission Power (SS)

0.5 W

Modulation Coding Schemes (MCS)

QPSK 1/2

TABLE IV.

SIMULATION PARAMETERS OF SCENARIO TWO

Parameter PHY Profile Max Sustained Traffic Rate (UGS) Path loss Parameters Terrain Type Efficiency Mode Cell Radius Maximum Transmission Power (BS) Maximum Transmission Power (RS) Maximum Transmission Power (SS) Modulation Coding Schemes (MCS)

Value WirelessOFDMA 20MHz for 802_16j 96000 bps Suburban (Erceg) Terrain Type A Mobility and Ranging Enabled 1 km 0.5W

Figure 2. Scenario two of IEEE 802.16 Network

Fig. 2 shows the second scenario where the same network topology in scenario one was simulated but it deploys RS to serve the SS. Two RS are installed, and it is located 500 m from the BS and only two hops are considered in the simulation because of the limitation of OPNET Modeler where only one RS can be in between the BS and the SS.

0.5W 0.5W QPSK 1/2

IV.

Fig. 1 shows the simulated network topology where RS is not deployed in the cell. Only one cell is considered in the simulation. The BS is connected to the IP Backbone that connects the IEEE 802.16 WiMAX network to the IP cloud where the VoIP Server resides.

RESULTS AND DISCUSSIONS

The results presented in this paper are obtained through simulation of both scenarios in OPNET Modeler. Simulations are done to investigate how RS can improve user throughput of SS which is located far from the BS. Fig. 3 shows the throughput of each SS without RS with respect to the simulation time. Fig. 3, SS1 until SS7 are able to achieve the required throughput by VoIP Applications that uses G.711 as the codec. SS1 until SS7 is located in between 100 m to 700 m from the BS. SS8 which is located 800 m from the BS cannot achieve the required throughput where the maximum achievable throughput is only 87627 bps. From the simulation it shows that SS9 and SS10 which is located 900 m and 1 km respectively from the BS cannot achieve the required throughput. To overcome the problem in scenario one, two RS is installed to act as a repeater as shown in Fig. 2. RS has been installed between the BS and the SS. From previous scenario, the affected SSs that cannot achieve the required throughput are SS8, SS9 and SS10. From the simulation it shows RS improve the throughput of SS8 and SS9. However the throughput for SS10 which is located 1 km from the BS still did not improve and this is still an issue that needs to be further investigated. Fig. 5 shows the improvement of SS8 and SS9 throughput with respect to the simulation time after RS is installed in the network. SS9 only achieve the throughput after a few minutes because SS9 request are relayed by the RS. Fig. 6 shows the

Figure 1. Scenario one of IEEE 802.16 Network

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improvement of the maximum achievable throughput with respect to distance after RS is installed in the network. SSs located in between 100 m to 900 m away from the BS can achieve the required bandwidth specification but not SSs located 1 km away from the BS even though RS is installed to act as a repeater. Table V shows the percentage of improvement for SS8 and SS9 when RS is deployed. Fig. 7 shows the significant improvement on SS9 throughput. By deploying the RS, SS9 is able to achieve up to 96000 bps. This is because the data from SS9 is being relayed by the RS instead of directly connected to the BS like the previous scenario. V.

CONCLUSION

This paper presents how transparent RS in IEEE802.16j MMR network can improve user throughput. The aim of the study is to show how transparent RS can be used to improve user throughput in IEEE802.16 network. The study shows that transparent RS improve SS throughput that is far from the BS and also extend the coverage area of the BS. For future work, multiple service class such as combination of non-real time and real time and SS types can be deployed to resemble real network application. Figure 4. Maximum throughput achieve base on location of SS

ACKNOWLEDGMENT The authors would like to thanks MOHE, UTHM, for sponsoring the studies and UiTM for providing the facilities thus enabling the studies to be conducted.

Figure 5. Throughput of VoIP applications for all SS in scenario two

Figure 3. Throughput of VoIP application for all SS in scenario one

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TABLE V.

COMPARISON OF MAXIMUM THROUGHPUT IN BPS IN NONRELAY AND RELAY SCENARIO

Scenario Without RS

SS8 SS9

87627 bps 0 bps

With RS

96000 bps 96000 bps

Percentage of improvement 8.7 % 100 %

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Figure 6. Maximum throughput achieve base on location of SS with RS deployment

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[13]

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[15] Figure 7. Significant improvements in SS9 throughput [16]

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