Performance Evaluation of Different Modulation Coding for Scheduling Services over VoIP in WIMAX Networks

Transcription

1 Performance Evaluation of Different Modulation Coding for Scheduling Services over VoIP in WIMAX Networks Hussein M. Hathal Al- Mustansiriyah University, College of Engineering, Electrical Engineering Department, Baghdad, Iraq Abstract: WiMAX is a high speed, wireless broadband access technology (including high speed internet and multimedia access) for large coverage area. It presents IP contacting between the base station and subscribers. Voice over Internet Protocol (VoIP) through WiMAX is the most important in telecommunication service. In this paper, simulative discussion for VoIP in WiMAX network have been done considering the effect of Modulation Coding (MC) mechanisms on the Quality of Service(QoS) performance of scheduling types such as; UGS, rtps, and ertps using opnet simulator. The discussion have been done in terms of important QoS parameters like jitter, packet end to end delay and average throughput. The obtained results show that the best type of the MC s that would be enhanced the QoS performance of the WiMAX network is QPSK model with coding rate 1/2. Key Words WiMAX, QoS, UGS, rtps, ertps, QPSK, QAM, modulation coding. 1. Introduction: Wireless networking has the potential to meet the increasing demands for broadband Internet services, video and audio streaming, and to emerge as an alternative to the PSTN for voice service[1]. WiMAX defines five scheduling services for network applications. VoIP represents real time application. therefore, this paper will use real time scheduling services such as Unsolicited Grant Service (UGS) that is designed to support real-time data streams consisting of constant data packets issued at periodic intervals. The BS provides constant data grants at periodic intervals, such as VOIP, without silence suppression. Real-Time Polling Service (rtps) that is designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals. such as MPEG video transmission. Extended Real-Time Polling Service (ertps) that is suitable for variable rate real time applications that have data rate and delay requirements, such as VOIP with silence suppression[2]. Table (1) illustrates real time scheduling services and their QoS requirements provided in the IEEE standard[3]. Table 1: WiMAX Services and QoS requirements QoS service class Application QoS Specifications Minimum reserved rate Maximum sustained rate UGS (Unsolicited Grant Service) VoIP Traffic priority Maximum latency tolerance

2 rtps (Real Time polling Service) ertps (Extended Real Time polling Service) Streaming audio or video; Telemedicine; E-learning VoIP with silence suppression Minimum reserved rate Maximum sustained rate Traffic priority Maximum latency tolerance Minimum reserved rate Maximum sustained rate Traffic priority Maximum latency tolerance Jitter tolerance 1.1Modulation Coding in WIMAX: WiMAX supports different types of modulation and coding schemes. Table(2) summarizes several combinations of modulation and coding rates, which can be allocated selectively to each subscriber, specified by the PHY layer[3]. 1.2 Suburban Area Table 2. Different Modulation and Coding Rates Modulation Because of the impotency of channel parameter, a brief discussion will be shown. Suburban area is based on total empirical data collected at 1.9 GHz in (95) macro cells of suburban areas across some countries. For very large size of cells, base stations will transmits high power and with high antenna height[3]. The equation that represent the suburban calculation is illustrated as follow: rate QPSK 1/2 QPSK 3/4 16-QAM 1/2 16-QAM 3/4 64-QAM 1/2 64-QAM 3/4 where : is the instantaneous attenuation in db. H is the intercept and is given by free space path-loss at the desired frequency over a distance of d= 100m. γ is a Gaussian random variable over the population of macro cells within each terrain category. X f and X h are the correlation factors of the model for the operating frequency and for the MS antenna height, respectively.

3 d= the subscriber distance = reference distance S is represent the surface The paper[4] analyzed various QoS provisions for different application traffics. And they study the effect of Adaptive Modulation Coding (AMC) mechanism on the QoS performance of WiMAX network. They found that significant QoS parameters, i.e., delay, jitter and packet loss are lowest for UGS service flow. The paper[5] made a simulative investigations for VoIP in WiMAX network considering scheduling services in terms of important Quality of Service parameters like jitter, packet end to end delay and Mean Opinion Score. It has been found from the simulation results that UGS service flow has lowest average jitter, least packet end to end delay and satisfactory MOS value. The main aim of [6] is to examine a case of QoS deployment over a cellular WiMAX network. And compares the performance obtained using two different QoS configurations. they are found that ertps scheduling class has the advantage of giving back some of its reserved bandwidth. The paper[7] have made six scenarios. Two types of MAC layer QoS used(ugs and rtps). With application of Voice over IP (VoIP) and MPEG respectively. In each scenario the number of fixed nodes (Fixed Subscriber Stations) and Mobile nodes (Mobile Subscriber Stations) are different. The research should help for deployment of WiMAX system to any country with good QoS to end users or clients. Also observed that QoS has effected with different Applications (Voice over IP Telephony and MPEG). 2. System Model Design : The network topology for the system model is given in figure 1. The simulation model of the studied case is designed for 5-Hexagonal cell network, which contain one mobile subscriber that moves in the range of a base stations. the parameters of simulation are shown in table 3, that illustrate some important parameters such as channel. Three types of scheduling services have been used for simulation. In these types (UGS, rtps, and ertps), the behavior of different Modulation Coding have been analyzed for VoIP using OPNET Modeler (14.5). OPNET is perfect networking simulator to evaluate the performance of a network. QoS achieved is (Jitter, Packet end to end delay, packet drop, and throughput). Figure. 1: System Model Design

4 Simulation time Table 3: Simulation parameters 3 minutes Number of BS 5 Number of MS 1 MS speed scheduling type 50 km/h UGS, rtps, ertps Base frequency(mhz) 5.8 Antenna Gain BS (dbi) 15 Maximum transmission power(w) 0.5 Media of simulation suburban 3. WIMAX Measurements i. Jitter Jitter is the measure of the alteration over time of the latency across a network i.e. the alteration in arrival time of consecutive packets. If two consecutive packets leave the transmitted node with time stamps t1 & t2 and are played back at the received node at time t3 & t4, then: Jitter = (t4 - t3) - (t2 - t1) Negative jitter means that the time difference between the packets at the received node was less than that at the transmitted node[5]. ii. Packet End to End Delay Packet End to End delay is characterized as the amount of time it takes from the speaker's mouth to the listener's ear. The total voice packet delay is calculated as: De2e = Dn + De + Dd + Dc + Dde Where De2e represents the end-to-end delays while Dn, De, Dd, Dc, Dde represent the network, encoding, decoding, compression and decompression delays, respectively[5]. iii. Packet drop Packet drop or packet loss done when one or more packets of data travelling across a computer network fail to reach the receiver. Packet drop is caused by network throng. Packet drop is measured as a percentage of packets lost with respect to packets sent[3]. iv. Throughput Throughput is defined as the traffic load that the channel stream will add to the network. the unit that throughput will be measured is bits/sec. For variable bit rate (VBR), throughput traffic loading has dynamic nature and it is a function of the stage complexity and associated audio content. Variable bit rate (VBR) traffic loads is the peak ranges of throughput [3].

5 4. Results and discussion The jitter case results are illustrated in figure 2. which explain that the modulation coding types has the same jitter results excepting for modulation coding (64QAM) with code rate 3/4, which has positive jitter in ertps scheduling service, while modulation coding (64QAM) with code rate 1/2 has negative jitter in ertps scheduling service. Figure 2: histogram of system jitter For the packet end to end delay, The results are illustrated in figure 3. It is found that modulation coding (64QAM) with coding rate 3/4 for rtps scheduling services has minimum packet end to end delay when compared it with the other modulation coding types, and modulation coding (QPSK) with code rate 3/4 for ertps scheduling services has a maximum value for this type of delay when compared it with the other modulation coding types. These results are better than the results in [8] for the same system environments. Although, the use of free space in [8]. Then that led to delay in data transportation compared to the results of figure 3.

6 Figure 3: histogram of system packet end to end delay Packet drop results are illustrated in figure 4, which explain that the modulation coding (64QAM) with code rate 3/4 has maximum packet drop in UGS scheduling service, and modulation coding (QPSK) with code rate 1/2 has minimum drop in three types of scheduling service. The large value of packet drop for modulation coding (64QAM) with code rate 3/4 is due to the reason that; the QAM modulation is susceptible to noise more than the other modulation coding types[9]. Figure 4: histogram of system packet drop The throughput results are illustrated in figure 5, which explain that the modulation coding (QPSK) with coding rate 1/2 has the maximum throughput in rtps scheduling service. And that modulation coding (64QAM) with code rate 3/4 has minimum throughput in UGS scheduling service. This result is better than the results in [11], since, the increase in the number of user in [11] led to decrease throughput rate for the QPSK model compared with figure 5. Figure 5: histogram of system throughput

7 5. Conclusion In this paper, different modulation coding schemes such as; QPSK and QAM are treated with real types of scheduling services (UGS, rtps, ertps). It is found that the modulation coding type QPSK with coding rate 1/2 has good behavior over the suburban area. therefore, it has the best result compared with other modulation coding types. This result was better than [11] that used ten fixed subscribers with free space channel. For QoS parameter (packet end to end delay), it is found that the modulation coding type 64QAM with coding rate 3/4 has the best results compared with other modulation coding types, but this result led to make modulation coding type 64QAM with coding rate 3/4 has worst result in packet drop parameter. This result was better than [8] that used five mobile subscribers with free space channel. 6. References 1. IEEE Std TM-2004, Part 16: Air interface for fixed broadband wireless access systems, Oct A. H. Rashwan, H. M. El-Badawy and H. H. Ali "Comparative Assessments for Different WiMAX Scheduling Algorithms". Proceedings of the World Congress on Engineering and Computer Science Vol I. WCECS, San Francisco, USA, J. Hamodi, R. Thool, K. Salah, A. Alsagaf and Y. Holba "Performance Study of Mobile TV over Mobile WiMAX Considering Different Modulation and Coding Techniques". scientific research. Int. J. Communications, Network and System Sciences, vol.7, 10-21, V. Grewal, and A. K. Sharma " On Performance Evaluation of Different QoS Mechanisms and AMC scheme for an IEEE based WiMAX Network". International Journal of Computer Applications, Volume 6 No.7, September Priyanka, and J. Malhotra "Performance Evaluation of Scheduling Services for VoIP in WiMAX Networks". International Journal of Computer Applications ( ) Volume 71 No.19, June I. Adhicandra "Measuring Data and VoIP Traffic in WiMAX Networks" Journal of Telecommunications, Volume 2, Issue 1, April R. K. Jha, I. Z. Bholebawa and U. D. Dalal "Location Based Performance of WiMAX Network for QoS with Optimal Base Stations (BS) ". Scientific Research Publisher,Wireless Engineering and Technology, Volume 2, N. Mehta and leena "Performance Analysis of VOIP over WiMAX" International Journal of Science, Engineering and Technology Research (IJSETR), Volume 4, Issue 6, June A. Svensson "An Introduction to Adaptive QAM Modulation Schemes for Known and Predicted Channels" Proceedings of the IEEE. Vol.95, No. 12, December A. Ul Haque, M. Saeed and F. Siddiqui "Comparative Study of BPSK and QPSK for Wireless Networks over NS2" International Journal of Computer Applications. Volume 41 No.19, March E. Onyekachi and E. Elias "Investigating the QoS of Voice over IP using WiMAX Access Networks in a Campus Network" Computer Engineering and Intelligent Systems Vol.4, No.5, 2013.