Modulation Techniques for WiMAX:  A Perspective

 

 

Chandana Patnaik, Sanjay Kumar* and V.K. Patle

School of Studies in Computer Science and IT, Pt. Ravishankar Shukla  University, Raipur, Chhattisgarh, India

 

ABSTRACT:

Today, WiMAX (Worldwide Interoperability for microwave access) is one of the vibrating Broad Band wireless Technologies. Various modules have been considered in WiMAX. In this paper we have considered various Modulation Techniques of WiMax. We have discussed related works done for these modules. Different features of various modules have been given and then comparison of these modules has been done. At last conclusion and future works for these modules have been made.

 

KEYWORDS: WiMAX, Modulation techniques

 

I. INTRODUCTION:

 

WiMAX(Worldwide Interoperability for microwave access) is a promising broadband wireless technology which can offer high speed voice, video and data service upto the service end. WiMAX provides high throughput, large coverage area and minimum delay [1, 2]. The IEEE 802.16 standards offer wireless broadband technology for innovative fixed as well as mobile platform [3].Wimax offers both Line of Sight (LOS) and Non-Line of sight (NLOS) wireless communication [4]. OFDM (Orthogonal Frequency Division Multiplexing) technique is very strong against multipath fading due to which it is widely used in wireless communication systems [5]. OFDM uses adaptive modulation techniques such as (BPSK, QPSK, 16-QAM, 64-QAM, and 256-QAM) on the physical layer of WiMAX.  This module is based on IEEE 802.16 point-to-multipoint (PMP) mode, which means that one BS can serve multiple subscriber stations (SSs) concurrently[5, 6].

 

Basic Data on IEEE 802.16 Standards

 

 


IEEE 802.16 f

Management Information Base.

IEEE 802.16 g

Management Plane Procedures and Services.

IEEE 802.16 h

Improved coexistence Mechanisms for License-Exempt.

IEEE  802.16 i

Mobile Management Information Base. IEEE 802.16j - Multihop Relay Specification

IEEE 802.16 k

Bridging of 802.16.

IEEE 802.16 m

Advanced Air Interface. Data rates of 100 Mbit/s for mobile applications and 1 Gbit/s for fixed applications, cellular, macro and micro cell coverage, with currently no restrictions on the RF bandwidth (which is expected to be 20 MHz or higher).

 

 

II.VARIOUS MODULATION TECHNIQUES:

Superimposition of a weak signal over a strong carrier signal is called modulation. Modulation is needed to carry a signal over large distance. Modulation may be of Analog to Analog, Analog to Digital, Digital to Analog and Digital to Digital. However in WiMAX Digital to Analog modulation is used. In the physical layer modification is done for various modulation techniques. There are three basic types of digital modulation techniques.

§  Amplitude Shift keying(ASK)

§  Frequency Shift Keying(FSK)

§  Phase Shift Keying(PSK)

 

ASK:

In ASK the amplitude of the carrier is changed in response to information and all else is kept fixed.

 

FSK:

In FSK the frequency of the carrier is changed in response to information.

 

PSK:

In PSK we change the phase of the sinusoidal carrier to indicate information. Phase in this context is the starting angle at which sinusoid starts. To transmit 0 shift the phase of sinusoid by 1800. Phase shift represents the change in the state of the information.

 

 

 

·         Various PSK modulation Techniques:

WMAX uses BPSK, QPSK, 16-QAM, 64-QAM and 256-QAM modulation techniques [7].

BPSK:

The phase of the carrier is varied to represent binary ones and zeros which is used to transmit data via changing and modulating of carrier wave is called Phase Shift keying and if the phase shift uses two phases differing by 180 degree to represent binary digits, the modulation is called BPSK.

 

QPSK:

QPSK is also known as quaternary PSK, 4-PSK. Each symbol consists of two bits and signal transmits among the phases that are separated by 90 degrees but used only one bit per channel. The constellation contains four points but the decision make in two bits.

 

QAM:

The modulation equation for QAM is a variation of the one the used for PSK. In PSK all the points lie on a circle and all the points have same amplitude. If we allow the amplitude to change from symbol to symbol then we get the modulation called QAM. QAM signals can be extended to much higher bit rates. 64-QAM and 256-QAM are common in cable modems, satellites and high-speed fixed broad band wireless.

 

16-QAM:

 

.64-QAM:

 

256-QAM:

 

 
III. RELATED WOKS:

Following researches has given their research review as  Md. Ashraful Islam [1]:  The performance of the system under BPSK modulation in 2/3 convolutional code rate is quite satisfactory as compared to other modulation techniques in AWGN channel..With Rayleigh channel, the BER performance is found not to be suitable for transmission. The performance of QPSK and 4-QAM is found better than BPSK modulation for a ½ convolutional code rate with respect to SNR values. In other modulation techniques and there is a little difference exists between BPSK-1/2 and BPSK-2/3 convolutional code rated. Ms. Vaishali Nitnaware[5]:  Throughputs  can be increased by increasing the modulation scheme QPSK, 16-QAM and 64-QAM with respect to simulation time but the delay which is calculated from the difference between the receiving time and sending time can be decreased as QPSK, 16-QAM and 64-QAM. B. Chaitanya[7]: They have used various adaptive modulation techniques  in WiMAX .They have observed that BPSK is more power efficient and need less bandwidth amongst all other modulation techniques used in an OFDM adaptive modulation in Pure AWGN Channel.The 64 and 256QAM modulation requires higher bandwidth and gives an excellent data rates as compared to others. While the QPSK and the 16QAM techniques are in the middle of these two and need higher bandwidth and less power efficient than BPSK. But they required lesser bandwidth and lower data rates than 64QAM. Also, BPSK has the lowest BER while the 64-QAM has highest BER than others. Theyalso suggested that the Cyclic Prefix reduces the Inter Symbol Interference (ISI) that causes the lower BER in the OFDM system but increases the complexity of the system. Model with CP requires high power as compared to the non-CP model. S.Venkatesh[3]: The simulation is performed for fixed WiMAX. QPSK is more tolerant of interference than either 16-QAM or 64-QAM [11]. Implementation of 1/4 cyclic prefix under QPSK modulation technique over SUI- 1,SUI-3 and SUI-4 channels and 1/16 cyclic prefix under QPSK over SUI-2 channel is highly effective comparing to other modulation techniques. Ginni Sharma [12]: They have used Convolution encoder with different code rates (1/2, 2/3, 1/3, 3/4) and with different constraint length for different digital modulations in  AWGN channel. The BER curves were used to compare the performance of different modulation techniques.  Convolutional encoder with rate equals to 1/3 perform better in 4-PSK (QPSK) and BPSK as compared to other code rate. The convolution encoder with code rate equals to 2/3 gives better result compared to other for 16-PSK modulation. BPSK modulation with rate equals to 1/3 gives better result as compared to other modulation i.e QPSK and 16-PSK. D. Satish Kumar [9]: They suggested that  decrease in downlink throughput as the mobile station moves out of coverage area of Base station (BS1), and also the during the Hard hand over process no packets are transferred. The hand over time is 2 sec, after handover the packets are transferred through BS2. M.A. Ismail [10]: They have presented detailed design and implementation of new features to enhance the existing WiMAX module of the ns-3 simulator. The proposed features includes a realistic and scalable physical/channel model, an IP packet classifier, sophisticated uplink and downlink schedulers, support for multicast traffic and pcap packet tracing functionality. We hope that these features will make easier and more realistic the evaluation and design of WiMAX systems.

The new proposed module5 has been ported to the latest

 

Ns-3 development version and is planned to be merged in version 3.7 of ns-3 expected in end of 2009. Our WiMAX module still has some limitations. The fragmentation and de-fragmentation of MAC PDUs is not supported. The optional feature of packet header suppression is not implemented too. However work to support these two functionalities is currently under way. IEEE 802.16e amendment introduces several concepts related to power management. An SS with active connections negotiates with the BS to temporarily turn off its connections to the air interface for a predetermined amount of time and goes into a sleep mode. We plan to implement this functionality for the next release of the module as power saving is crucial for mobile wireless stations.

 

VI. SIMULATORS:

Various simulators are available for Wimax. NS-2, NS-2.29, NS-3, QualNet, OPNET, NCTUNS. [5, 8, 9, 10] . NS-3 supports a realistic and scalable physical model, an IP packet, classifier, efficient uplink and downlink schedulers, support for multicast traffic, and pcap packet tracing functionality. NCTUns supports real-life application program simulation and little more CPU execution time and memory usage due to the overhead resulted from the real-life application supports in NCTUns.

 

V. DISCUSSION AND SUMMARY:

 

Modulation

Techniques

Reyleigh

Channel

AWGN Channel

Modulation

Rate

Throughput

BPSK

4dB<SNR<9dB

7dB<SNR<11dB

 

 

QPSK 1/2

9dB<SNR<15dB

11dB<SNR<17dB

4.99 Mbps

5400 bps

QPSK 3/4

15dB<SNR<18dB

17dB<SNR<19dB

7.48 Mbps

5500 bps

16-QAM 1/2

18dB<SNR<23dB

19dB<SNR<22dB

9.97 Mbps

5600 bps

16-QAM 3/4

23dB<SNR<28dB

22dB<SNR<25dB

14.96 Mbps

5700 bps

64-QAM 1/2

28dB<SNR<40dB

25dB<SNR<29dB

19.95 Mbps

6600 bps

64-QAM 3/4

SNR>40dB

SNR>29dB

22.44 Mbps

6800 bps

 

 

V. CONSLUSION:

According to survey our survey the throughput increases with the increase in code rates in modulation schemes.   Out of the two channels: the Reyleigh channel and AWGN channel, the BER performance in Reyleigh channel was not suitable for transmission.  It is also find that the code rate of BPSK modulation technique was to consume less bandwidth as compared to other modulation techniques in AWGN channel. 64-QAM and 256-QAM modulation requires larger bandwidth but gave quite satisfactory results.

 
VI. REFERENCES:

1.        Md. Ashraful Islam , Riaz Uddin Mondal , Md. Zahid Hasan ,“Performance Evaluation of WiMAX Physical Layer under Adaptive Modulation Techniques and Communication Channels”. (IJCSIS) International Journal of Computer Science and Information Security, Vol. 5, No.1, 2009

2.        Miray Kas, Burcu Yargicoglu, Ibrahim Korpeoglu, and Ezhan Karasan “A Survey on Scheduling in IEEE 802.16    Mesh Mode, IEEE Communications Surveys & Tutorials, VOL. 12, NO. 2, SECOND QUARTER 2010.

3.        S.Venkatesh,V.Palanisamy, K.Baskaran

Comparative Study of SUI Channels in IEEE802.16d using Different Cyclic Prefix”, European Journal of Scientific Research ISSN 1450-216X Vol.48 No.2 (2010), pp.305-314

© EuroJournals Publishing, Inc. 2010

http://www.eurojournals.com/ejsr.htm

4.        M.A Mohamed, F.W Zaki, R.H Mosbeh, “Simulation of WiMAX Physical Layer:IEEE 802.16e”, IJCSIS International Journal of Computer Science and Information Security, Vol. 10, No.11, November 2010.

5.        Ms. Vaishali Nitnaware, Mr. Sudhir B. Lande, Mr. Suresh S. Balpande,“Comparative Study of Various Modulation Techniques used in Point to Multipoint Mode for WiMAX “, Published in International Journal of Advanced Engineering & Applications, Jan. 2010.

6.        Harwinder Singh , Maninder Singh Kamboj “Performance Analysis of QoS in PMP Mode WiMax Networks”, International Journal of Computer Applications (0975 – 8887) Volume 3 No.12, July 2010.

7.        B.Chaitanya, T.Sai Ram Prasad, K.Sruthi and T.Tejaswi, “Adaptive Modulation Techniquesfor WIMAX”, IJCNS) International Journal of Computer and Network Security,Vol. 2, No. 5, May 2010

8.        Shiang-Ming Huang, Ya-Chin Sung, Shie-Yuan ,Wang, Yi-Bing Lin.,NCTUns Simulation Tool for WiMAX Modeling”, WICON 2007, October 22-24, 2007, Austin, Texas, USA

9.        D.Satish Kumar,  Dr.N.Nagarajan  “Simulation of Hard Hand over (HHO) Mechanism in IEEE 802.16j Transparent Mode networks”, International Journal of Computer Applications (0975 – 8887), Volume 14– No.2, January 2011.

10.     M.A. Ismail, G. Piro, L.A. Grieco, T. TurlettiAn Improved IEEE 802.16 WiMAX Module for the NS-3 Simulator”.

11.     Md.Zahid Hasan,Mohammad Reaz Hossain,Md.Ashraful Islam,Riaz Uddin mondal, “Comparative study of Different Guard Time intervals to improve the BER Performance of  Wimax Systems to minimize the Effects of ISI              and ICI under Adaptive modulation techniques over SUI-1 and AWGN Communication Channels” ,IJCSIS,Vol.6,No.2,2009

12.     Ginni Sharma, Sanjeev Kumar, Anita Suman , Parveen Kumar , “Performance Analysis of Convolution Coded WLAN Physical Layer under Different Modulation techniques” Signal Processing: An International Journal (SPIJ), Volume (4): I ssue (4).

 

 

 

Received on 30.12.2010

Modified on 25.01.2011

Accepted on 27.02.2011                                                     

© A&V Publication all right reserved

Research J. Science and Tech.  3(2): March-April. 2011: 85-94