Comparative Study of SUI Channels in IEEE802.16d Using Diff CP

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

Comparative Study of SUI Channels in IEEE802.16d using

Different Cyclic Prefix

S.Venkatesh

Assistant Professor, Department of Electronics and Communication Engineering

Kumaraguru College of Technology, Coimbatore, Tamil Nadu, India

E-mail:[email protected]

V.Palanisamy

Professor and Head, Department of Electronics and Communication Engineering

Info Institute of Engineering, Coimbatore, Tamil Nadu, India

K.Baskaran

Assistant professor (RD), Department of Computer Science Engineering

Government College of Technology, Coimbatore, Tamil Nadu, India

Abstract

WiMAX which represents Worldwide Interoperability for Microwave Access is a

major part of broadband wireless network having IEEE 802.16 standard provides

innovative fixed as well as mobile platform for broadband internet access anywhere in

anytime. The objective of this paper is the comparative study of Stanford University

Interim (SUI) fading channels in IEEE802.16d using different cyclic prefix to improving

BER at different SNR under digital modulation techniques.The simulation is performed for

Fixed WiMAX and the performance measures we presented in this paper are: the bit error

rate (BER) versus the ratio of bit energy to noise power spectral density (Eb/No). The

simulation results of estimated Bit Error Rate displays that the 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.The system parameters used in this paper are based on IEEE 802.16

standards.

Keywords: WiMAX, IEEE802.16, SUI, BER, SNR, Eb/No, QPSK

1. Introduction WiMAX will become the next-generation broadband wireless access technology. Based on Orthogonal

Frequency Division Multiple Access (OFDMA) technology, WiMAX offers better spectral efficiency

as well as overall capacity than the 3G network currently being deployed. It allows communications

which have no direct visibility, coming up as an alternative connection for cable, DSL3, and T1/E1

systems, as well as a possible transport network for Wi-Fi hot-spots, thus becoming a solution to

develop broadband industry platforms. Likewise, products based on WiMAX technology can be

combined with other technologies to over broadband access in many of the possible scenarios of

utilization. It will substitute other broadband technologies competing in the same segment and will

Comparative Study of SUI Channels in IEEE802.16d using Different Cyclic Prefix 306

become an excellent solution for the deployment of the well-known last mile infrastructures in places

where it is very difficult to get with other technologies, such as cable or DSL, and where the costs of

deployment and maintenance of such technologies would not be profitable. In this way, WiMAX will

connect rural areas in developing countries as well as underserved metropolitan areas. It can even be

used to deliver backhaul for carrier structures, enterprise campus, and Wi-Fi hot-spots. It offers a good

solution for these challenges because it provides a cost-effective, rapidly deployable solution [1].

Additionally, WiMAX will represent a serious competitor to third generation cellular systems

as high speed mobile data applications. WiMAX is especially popular in wireless applications because

of its resistance to forms of interference and degradation. In short, WiMAX delivers a wireless signal

much farther with less interference than competing technologies. The first version of the IEEE 802.16

standard operates in the 10–66GHz frequency band and requires lineofsight (LOS) towers. Later the

standard extended its operation through different PHY specification to 2 -11 GHz frequency band

enabling non line of sight (NLOS) connections, which require techniques that efficiently mitigate the

impairment of fading and multipath [1]. Taking the advantage of OFDM technique the PHY is able to

provide robust broadband service in hostile wireless channel.OFDM increases bandwidth and data

capacity by splitting broad channels into multiple narrowband channels each using a different

frequency that can then carry different parts of a message simultaneously. The channels are spaced

very close together but avoid interference because neighboring channels are orthogonal to one another

and thus have no overlap [2].

Generally the signal-to-noise ratio (SNR) requirements of an environment determine the

modulation method to be used in the environment. QPSK is more tolerant of interference than either

16-QAM or 64-QAM [9]. The aim of this paper is the comparative study of different cyclic prefix for

improving BER at different SNR under digital modulation (QPSK, 16-QAM and 64-QAM) techniques

and different communication fading channels Stanford University Interim (SUI-1,SUI-2,SUI-3 and

SUI-4) of an WIMAX system.

2. Simulation Model The simulation model consists of three main components namely transmitter, receiver and channel.

Transmitter and receiver components consist of channel coding and modulation sub-components

whereas channels are modeled as fading channels. This structure corresponds to the physical layer of

the IEEE 802.16 2004 Wireless MAN OFDM air interface. In this setup, we have just implemented the

mandatory features of the specification, while leaving the implementation of optional features for

future work [3].

Figure 1: WiMAX Communication System

Cyclic prefix

Removal

Digital

Modulatio

n

Channel

Encoding

IFFT Cyclic prefix

Insertion

Random data

generation

TRANSIMETTER

Digital

demodulation

Channel

Decoding FFT

RECEIVER

Retrieved

data

307 S.Venkatesh, V.Palanisamy and K.Baskaran

Channel coding part is composed of three steps randomization, Forward Error Correction

(FEC) and interleaving. FEC is done in two phases through the outer Reed Solomon (RS) and inner

Convolutional Code (CC). The complementary operations are applied in the reverse order at channel

decoding in the receiver end. Reed Solomon Encoder that encapsulates the data with coding blocks and

these coding blocks are helpful in dealing with the burst errors. The block formatted (Reed Solomon

encoded) data stream is passed through a convolutional interleaver. Here a code rate can be defined for

convolutional codes as well. If there are k bits per second input to the convolutional encoder and the

output is n bits per second, the code rate is k/n [8].

Figure 2: Channel Encoding

Figure 3: Channel Decoding

The convolutionally encoded bits are interleaved further prior to convert into each of the either

three digital modulation symbols in QPSK, 16-QAM, and 64-QAM modulation and cyclic prefix is

added to the data once the data is converted into time domain and ready to be transmitted. The addition

of cyclic prefix to the data before it is actually transmitted helped the data to cater the problems related

to the multipath propagation and provided a resistance against Inter Symbol Interference [8]. IEEE

802.16 allows the insertion of cyclic prefix of various lengths such 1/4, 1/8, 1/16 and 1/32 is added to

the WiMAX symbol before it is transmitted. The length of the cyclic prefix must be chosen as longer

than the maximum delay spread of the target multipath environment. The transmitted data is then fed

into the SUI-1, SUI-2, SUI-3and SUI-4 channels. At the receiver side, cyclic prefix is removed before

any processing starts.

Table 1: Simulated Coding, Modulation Schemes and Noisy channels

Parameter value

Nominal channel band with 2.5MHz

Cyclic prefix 1/4,1/8,1/16,1/32

Number of used sub carriers 200

Modulation QPSK,16QAM,32QAM

Channels SUI-1,SUI-2,SUI-3,SUI-4

RS Code (255,239,8)

CC Code 1/2


3. Channel Model The performance of the developed communication system, an accurate description of the wireless

channel is required to address its propagation environment. The radio architecture of a communication

system plays very significant role in the modeling of a channel. The wireless channel is characterized

by: Path loss, Multipath delay Spread, Fading characteristics, Doppler spread, Cochannel and adjacent

channel interference [5]. All the model parameters are random in nature and only a statistical

characterization of them is possible, i.e. in terms of the mean and variance value. They are dependent

upon terrain, tree density, antenna height and beamwidth, wind speed.

SUI channel models are an extension of the earlier work by AT&T Wireless and Erceg etal [6].

In this model a set of six channels was selected to address three different terrain types that are typical

of the continental US. This model can be used for simulations, design, and development and testing of

technologies suitable for fixed broadband wireless applications [7]. The parameters for the model were

selected based upon some statistical models. The tables below depict the parametric view of the SUI

channels.

Table 2: Terrain type for SUI channel

Terrain Type

C SUI-1,SUI-2 Mostly flat terrain with light tree densities.

B SUI-3,SUI-4 Hilly terrain with light tree density or flat terrain with

moderate to heavy tree density

A SUI-5,SUI-6 Hilly terrain with moderate to heavy tree density

Table 3: Channel Model parameters

SUI-1 SUI-2 SUI-3 SUI-4

P(Power in each path in dB) [0 -15 -20] [0 -12 -15] [0 -5 -10] [0 -4 -8]

K(Ricen Distribution(linear scale )) [4 0 0] [2 0 0] [1 0 0] [0 0 0]

Tap delay [0.0 0.4 0.9] [0.0 0.4 1.1] [0.0 0.4 0.9] [0.0 0.5 4.0]

Dop(maximum Doppler frequency(Hz)) [0.4 0.3 0.5] [0.2 0.15 0.25] [0.4 0.3 0.5] [0.2 0.15 0.25]

Auto_corr(Coefficient of antenna Correlation) 0.7 0.5 0.4 0.3

Normalized factor of gain (dB) -0.1771 -0.3930 -1.5113 -1.9218

4. Simulation Results In this section we have presented various Bit Error Rate (BER) versus the ratio of bit energy to noise

power spectral density (Eb/No) plots for QPSK, 16QAM and 64QAM modulation using different

cyclic prefix. Figure from 4 to 15 shows the performance on SUI-1, SUI-2, SUI-3 and SUI-4 channel

models respectively. It can be seen from this figures that the lower modulation and coding scheme

provides better performance with less SNR. Simulation results in figure shows the advantage of

considering a 1/2 rated convolutinal coding and Reed-Solomon coding for each of the three digital

modulation schemes.


Figure 4: Comparative study between different cyclic prefix using QPSK modulation under SUI-1

1 2 3 4 5 6 710

-3

10-2

10-1

100

X: 4

Y: 0.02571

BER of the received symbols. ( SUI=1,BW=2.5MHz and modulation of QPSK )

Eb/No

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32

Figure 5: Comparative study between different cyclic prefix using 16QAM modulation under SUI-1

1 2 3 4 5 6 7 8 9 1010

-3

10-2

10-1

100

X: 8

Y: 0.01567

BER of the received symbols. ( SUI=1,BW=2.5MHz and modulation of 16QAM )

Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32


0 2 4 6 8 10 12 1410

-3

10-2

10-1

100

X: 12

Y: 0.003037


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32


Figure 4,5 and 6 shows the Bit Error Rate under QPSK modulation technique over SUI-1

fading channel with 1/4 cyclic prefix for a SNR value of 4dB but in the case of 16QAM and 64 QAM

modulation is found not to be suitable for transmission.


1 2 3 4 5 6 7 8 910

-3

10-2

10-1

100

X: 5

Y: 0.01571

Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32


1 2 3 4 5 6 7 8 9 10 1110

-3

10-2

10-1

100

X: 9

Y: 0.004754


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32


0 5 10 1510

-3

10-2

10-1

100

X: 12

Y: 0.008294


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32






0 5 10 1510

-3

10-2

10-1

100

X: 7

Y: 0.009643


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32

Figure 11: Comparative study between different cyclic prefix using 16 QAM modulation under SUI-3

0 5 10 1510

-3

10-2

10-1

100

X: 9

Y: 0.00669


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32

Figure 12: Comparative study between different cyclic prefix using 64 QAM modulation under SUI-3

0 5 10 1510

-3

10-2

10-1

100

X: 14

Y: 0.004089


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32






0 5 10 1510

-4

10-3

10-2

10-1

100

X: 5

Y: 0.005357


Eb/No(dB)

BE

RCP=1/4

CP=1/8

CP=1/16

CP=1/32


0 5 10 1510

-3

10-2

10-1

100

X: 12

Y: 0.002817


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32


0 5 10 1510

-3

10-2

10-1

100

X: 15

Y: 0.003621


Eb/No(dB)

BE

R

CP=1/4

CP=1/8

CP=1/16

CP=1/32




modulation is found not to be suitable for transmission. In table 4 shows that the Eb/No in dB using

modulation techniques (QPSK, 16QAM and 64QAM) with different cyclic prefix (1/4, 1/8, 1/16, 1/32).

Table 4: Eb/No in dB using modulation techniques with different cyclic prefix

Terrain type SUI-1

C

cyclic prefix 1/4 1/8 1/16 1/32

QPSK 4 5 5 5

16QAM 8 9 8 9

64QAM 13 13 12.2 12

SUI-2

cyclic prefix 1/4 1/8 1/16 1/32

QPSK 7 8 5 6

16QAM 10 9 9 10

64QAM 12 15 13.5 13.5

SUI-3

B

cyclic prefix 1/4 1/8 1/16 1/32

QPSK 7 13.5 8 15

16QAM 13.5 15 9 12

64QAM 14 15 15 15

SUI-4

cyclic prefix 1/4 1/8 1/16 1/32

QPSK 5 15 11.2 13.5

16QAM 15 12 14.2 14.2

64QAM 15 15 15 15

5. Conclusion The comparative study of SUI fading channels in IEEE802.16d using different cyclic prefix to

improving BER at different SNR under digital modulation techniques has been carried out .The

simulation results of estimated Bit Error Rate displays that the 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.

References [1] IEEE std 802.16a 2003(Amendment to IEEE std 802.16 2001), “IEEE standard for Local and

metropolitan area networks part 16:Air Interface for Fixed Broadband Wireless Access System

Amendment 2:Medium Access Control Modulations and Additional Physical Layer

Specifications for 2-11 GHz”, January 2003.

[2] IEEE 802.16 2004, “IEEE Standard for Local and Metropolitan Area Networks Part16: Air

Interface for Fixed Broadband Wireless Access System”, 1 October 2004

[3] IEEE std 802.16e 2005 and IEEE std 802.16 2004(Amendment and Corrigendum to IEEE std

802.16 2004), “IEEE standard for Local and metropolitan area networks part 16:Air Interface

for Fixed and Mobile Broadband Wireless Access System Amendment 2:Physical and Medium

Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands and

Corrigendum”, 1 February 2006.

[4] Mobile WiMAX–Part I: A Technical Overview and Performance

Evaluatio,http://www.wimaxforum.org/technology/downloads/mobile_WiMAX_part1_Overvie

w _and_Performance.pdf

[5] Raj Jain, “Channel model (Tutorial)”, February 2007.


[6] V.Erceg, K.V.S.Hari, M.S.Smith, D.S.Baum et al, “Channel Model for Fixed Wireless

Applications”, IEEE 802.16.3 Task Group Contributions 2001, Feb. 01

[7] Daniel S. Baum, “Simulating the SUI Channel Models”, IEE 802.163c01_53

[8] Simon Haykin, “Digital Communication”, Edition 2006

[9] 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

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Comparative Study of SUI Channels in IEEE802.16d Using Diff CP