Implementation of AMC to Control the SNR for WiMAX Systems ... · Implementation of AMC to Control the SNR for WiMAX Systems Via a Smart Calculator ... ID0 represent the system when

International Transactions on Electrical, Electronics and Communication Engineering,

Vol. 3, No.1, 2013

March Issue 83 ISSN 2249 8923

Implementation of AMC to Control the SNR for WiMAX

Systems Via a Smart Calculator

Albedeir Y. G. Othman1, Mohamed H. M. Nerma

2 and Mohamed A. A. Elmaleeh

3

1Department of Electrical and Electronic Engineering, Umdurman Islamic University, Khartoum, Sudan

2Department of School of Electronic Engineering, Sudan University of Science and Technology, Khartoum, Sudan

3Department of of Electrical and Electronic Engineering, Khartoum, Sudan

Abstract

WiMAX supports a wide range of modulation and coding schemes and allows for the scheme to

adjust on a burst-by-burst basis per link, depending on channel situations. Using the channel

excellence feedback indicator, the mobile can supply the base station with feedback on the downlink

channel excellence. For the uplink, the base station can estimate the channel excellence, based on

the received signal excellence. The base station scheduler can take into account the channel

excellence of each user’s uplink and downlink and assign a modulation and coding scheme that

maximizes the throughput for the available signal to noise ratio (SNR). Adaptive modulation and

coding (AMC) extensively increases the overall system capacity, as it allows real-time exchange

between throughput and robustness on each link. In the downlink, 16 QAM, 64 QAM and QPSK are

mandatory for both fixed and mobile WiMAX; 64 QAM is elective in the uplink. This paper

presented the design of a new device (smart calculator). The device can be used to control the AMC

in WiMAX system according to required bit error rate (BER) and SNR. The graphical user interface

(GUI) for the device and a comprehensive study of using AMC in WiMAX system are also presented

in this work. The results show that the AMC significantly increases the overall system performance,

as it allows real time exchange between throughput and robustness on each link.

Keywords: WiMAX, IEEE Std, 802.16d SISO, OFDM, AMC, CP, SNR, BER, PSD, Space Time Block

Codes, PHY Layer.

1. Introduction

IEEE 802.16 standard for broadband wireless access (BWA) and its related industry association,

worldwide interoperability for microwave access (WiMAX) forum undertake to offer high data rate

over large areas to a large number of users where broadband is unavailable. This is the first industry

wide standard that can be used for fixed wireless access with significantly higher bandwidth than most

cellular networks [1]. Wireless broadband systems have been in use for many years, but the progress of

this standard enables economy of scale that can bring down the cost of equipment, guarantee

interoperability, and reduce investment risk for operators. The first version of the IEEE 802.16

standard operates in the 10–66 GHz frequency band and requires line of sight (LOS) towers. Soon after

the standard extended its operation through different PHY specification to 211 GHz frequency band

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

impairment of fading and multipath [2]. Taking the advantage of orthogonal frequency division

multiplexing (OFDM) technique the physical layer (PHY) is able to provide robust broadband service

in hostile wireless channel.

The OFDM based physical layer of the IEEE 802.16 standard has been standardized in close

cooperation with the European Telecommunications Standards Institute (ETSI) high performance

metropolitan area network (HiperMAN) [3]. Thus, the HiperMAN standard and the OFDM based

physical layer of IEEE 802.16 are nearly matching. Both OFDM based physical layers shall meet the

terms with each other and a global OFDM system should come out [2]. The WiMAX forum certified

products for BWA meet the terms with the both standards. One of the most important problems that are


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challenging in wireless communications is changing the factors that affect the channel and thus reduce

the performance through the impact on throughput and bit error rate (BER) [4]. In fact, a certain area

coverage by the base transceiver station (BTS) in WiMAX system will suffer from different type of

impairments such as the interference and noise that will occur for the transmitted signal [5] and

obviously moving away from the tower will increase the transmission loss. Assume that each ring

represents a certain amount of loss, by using 64QAM modulation with a specific coding, it can be

shown that the bit error rate (BER) inversely proportional to signal to noise ratio (SNR), The same

scenario in the event that device Nomadic but the BER Will vary due to the entry of other factors affect

the SNR [6], [7]. The BER will be improved by increasing the cyclic prefix (CP) length. However,

increasing the CP length leads to decreasing of the throughput [8].

2. System description

This work concentrates on designing a mathematical model using Math WorksTM in

MATLAB ® & SIMULINK® software package. The model simulate particularly, the IEEE®

802.16d, with and without space time block coding (STBC) model was used. The performance

parameters of the proposed system are listed in Table 1. The parameter values are selected to be

within the standard values stated in Literature Review. SISO-WiMAX system model is shown

in Figure1. It conforms to IEEE 802.16 standard model.

Table 1. Performance parameter of the considered system

Parameter Value/ type

Channel bandwidth (MHz): 3.50

Number of OFDM symbols per burst: 2.00

Cyclic prefix factor (G): ¼

Amplifier nonlinearity & Pre-distortion: Enable

Low SNR thresholds for rate control (dB): [6:10:13:16:21:23]

Models a multipath Rician fading channel with: AWGN

K factor: 0.50

Maximum

Doppler shift (Hz):

0.50

Gain vector (dB): [0 -5 -10]

Delay vector (s): [0 0.4 0.9]*e-6

Fading mode: Frequency selective fading

Rate ID without STBC 0 – 6

In this work the AMC will be symbolized according to the type of modulation as follows:

ID0 represent the system when using 1/2 BPSK, ID1 represent the system when using 1/2QPSK,

ID2 represent the system when using 3/4 QPSK, ID3 represent the system when using 1/2 16QAM,

ID4 represent the system when using 3/4 16QAM, ID5 represent the system when using 2/3 64QAM

and ID6 represent the system when using 3/4 64QAM. The proposed device shown was programmed

using basic language through the use of BASCOM. Figure 2 shows the performance of the proposed

device. It can be seen from this figure that the proposed device is used to adjust the WiMAX system in

order to get the highest throughput corresponding to the lowest BER.


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Figure 1. SISO – WiMAX System Model

Figure 2. The Performance of BER and the Throughput of the Proposed Device

3. Results and discussion

The objective of the simulation is to study the scattering plot, power spectrum density (PSD), BER,

the throughput of the considered system and proposed the design of a new device (smart calculator)

that can be used to control the AMC in WiMAX system according to required BER and SNR.

First, the effect of increasing the transmitted power on scatter plot has been studied when using 64-

QAM. Increasing the transmitted power can be used in order to improve the quality of the received

signal. However, this method is not recommended to use in order to avoid the damage occurrence as a

result of increasing the power to high values [9-10]. One more solution is to use the adaptive

modulation and coding [11-12]. Figure 3 shows the scattering plot for 0 dB transmitted power at

different stages of WiMAX system. Figures 3 shows respectively, the scattering plot for the signal

before modification, the signal after AWGN (write in complete form then put the abbreviation)

channel, the signal after nonlinear amplifier, the signal after OFDM and the signal after modification.

Figure 4 shows the scattering plot for 30 dB transmitted power at different stages of WiMAX system.

Figures 4 shows the scattering plot for the signal before modification, the signal after AWGN channel,

Throughput

BE

R

Performance of the

device


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the signal after nonlinear amplifier, the signal after OFDM and the signal after modification

respectively.

(a) Signal before modification. (b) Signal after AWGN channel.

(c) Signal after nonlinear amplifier. (d) Signal after OFDM.

(e) Signal after modification.

Figure 3. Constellation plot for 0 dB transmitted power at different stages of WiMAX system

Second, the effect of increasing the transmitted power on power spectrum density has been studied

and the results were shown in Figure 5 for 0 dB transmitted power at different stages of WiMAX


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system and figure 6 for 30 dB transmitted power at different stages of WiMAX system as stated in

Figure 3 and Figure 4. where, the power spectrum density for the signal before modification, the signal

after AWGN channel, the signal after nonlinear amplifier, the signal after OFDM and the signal after

modification. From the above results it can be seen that the higher transmitted power gives better BER

and PSD results. However, high transmitted power has some drawback in the system such as increase

complexity of analog to digital and digital to analog converters (ADC) / (DAC) and reduces the power

efficiency of the radio frequency (RF) amplifier. There are several techniques have been proposed to

solve the problems related to high transmitted power [13-14].

(a) Signal before modification. (b) Signal after AWGN channel.

(c) Signal after nonlinear amplifier. (d) Signal after OFDM.


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(e) Signal after modification.

Figure 4. Constellation plot for 30 dB transmitted power at different stages of WiMAX system

(a) PSD of the signal before modification. (b) PSD of the signal after AWGN channel.

(c) PSD of the signal after nonlinear amplifier. (b) PSD of the signal after OFDM.

(e) PSD of the signal after modification.

Figure 5. Power spectrum density for 0 dB transmitted power at different stages of WiMAX system

Third, the BER and the throughput performance versus SNR of the considered system have been

studied. The BER is reverse proportional to the SNR i.e. increasing the SNR will reduce the BER. In

contrast, the throughput is proportional to the SNR i.e. increasing the SNR will increase the throughput

[12], [15] and [16]. Figure 6 show the BER versus SNR plots for the considered system. It can be seen


Vol. 3, No.1, 2013


from this figure that the higher SNR values provides better BER result. Figure 7 shows the throughput

versus the SNR. Figure 7 states that the higher SNR values provides good throughput results.

The results in Table 2 and figure 9 discuss the performance of the considered system when applying

the AMC. Table 2 show the average BER results for the considered system when using AMC and

without using AMC (when using 1/2 BPSK (ID0) and when using 3/4 64QAM (ID6)). Table 2 and

figure 9 clearly shows that the use of AMC reduces the BER values and gives better results than using

higher and lower modified in WiMAX system. Figure 9 shows a comparison between the BER results

with and without using AMC (ID0 and ID6). The results in figure 9 show an enormous improvement in

the BER when using AMC. On the other hand, the results show that using ID0 gives better BER results

than using ID6. From these results and results in [17], [18] it can be state that the AMC can be used to

assure the highest transmission speed with a satisfied BER by setting thresholds of channel SNR.

(a) PSD of the signal before modification. (b) PSD of the signal after AWGN channel.

(c) PSD of the signal after nonlinear amplifier. (b) PSD of the signal after OFDM.

(e) PSD of the signal after modification.


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Figure 6. Power spectrum density for 30 dB transmitted power at different stages of WiMAX system

Figure 7. Performance of BER versus SNR

Figure 8. Performance of the throughput versus SNR

Table 2. SNR of the WiMAX with and without using the AMC

SNR 0 1 2 3 BER with AMC 1.181E-01 2.036E-02 1.639E-03 5.176E-04

BER without AMC using ID0 2.403E-01 1.118E-01 2.743E-02 3.019E-03

BER without AMC using ID6 4.988E-01 5.007E-01 4.986E-01 5.007E-01


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Fourth, the design of a new device (smart calculator 1) will be presented in this part. The proposed

device can be used to control the AMC in WiMAX system according to required BER and SNR.

MATLAB has been used to design a GUI in order to represent some important results of using AMC

and OFDM in the considered system. Figure 10 shows the GUI of the proposed device.

The components used in the design are documented in Table 3 and Figure 11 shows the internal

structure and the fundamental parts of the device. Microprocessor ATMEGA16 is used as a processing

unit has been programmed using the BASCOM language. The screen display using liquid crystal

display (LCD) as output unit. The keyboard used as an input unit. The light emitting diode (LED) used

as a sign for the values that determined by the director. The energy source used a five volt rechargeable

battery. The key is used for the device’s operation control. To alert and input stimuli a siren has been

used. Data transfer cables are used for the data transfer between the system units. Finally, number of

capacitors and resistors were also used.

Figure 9. BER Results with and without using the AMC Scheme

Table 3. The equipments used in the design

No. Name of Component

1 Microprocessor ATMEGA16

2 Screen Display LCD

3 Keyboard

4 Light Emitting Diode

5 Battery (5 Volt Rechargeable)

6 Key

7 Siren

8 Capacitors and Resistors

9 Data Transfer Cables


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Figure 12 demonstrates exterior and the actual dimensions of the proposed device. The flow chart in

Figure 13 shows the instructions of using the proposed device. The flowchart gives user instructions

and guides that describe the steps of using the device and the processing of entering the required BER

and the threshold values.

Figure 10. The device in the form of the GUI using MATLAB


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Figure 11. The device’s internal parts

(a)

15 cm

9.5 cm 4 cm

7 cm

Smart Calculator v1

Future Generation

Smart Calculation

Made in SUDAN


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(b)

Figure 12. The device in the form of producer. (a) The device’s label. (b) The device’s dimension.


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Figure 13. Flowchart for instructions of using the proposed device

4. Conclusion

In this study a smart calculator is designed and tested. The calculator can be used to adjust the AMC

in WiMAX system according to the required SNR. The AMC issues for WiMAX system have been

considered. The scattering plot and the PSD were used to investigate the performance of the considered

system when increasing the power of the transmitted signal. The results show that better performance

can be obtained by increasing the power of the transmitted signal. Furthermore, the BER and the

throughput were also used evaluate the system performance in the presence and absence of AMC.

5. References

[1] Ghosh, A.; Wolter, D.R.; Andrews, J.G.; Chen, R., “Broadband wireless access with

WiMax/802.16: current performance benchmarks and future potential”, Communications

Magazine, IEEE, Vol.43, Iss.2, Pages: 129-136, Feb. 2005.

[2] Koffman, I.; Roman, V., ”Broadband wireless access solutions based on OFDM access in IEEE

802.16” Communications Magazine, IEEE, Vol.40, Iss.4, Pages: 96-103, April 2002.

[3] ETSI Broadband Radio Access Networks (BRAN); HIPERMAN; Physical (PHY) Layer. Standard

TS 102177, 2003.

[4] Mohammed H. M. Nerma, Hassan Y. Ahmed, Abdallah M. Monir, Ali M. Mustafa and Munzir M.

Omer, “Inter – Carrier Interference Reduction Technique in OFDM System Based on Self

Cancellation Technique”, International Journal of Engineering and Computer Science, ISSN:

2319-7242, Volume1, Issue 3, PP. 108-113, Dec 2012.


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[5] Mohammed H. M. Nerma and Albedeir Y. G. Othman “Effects of the Cyclic Prefix in SISO and

MISO WiMAX Systems”, International Journal of Engineering and Computer Science, ISSN:

2319-7242, Volume1 Issue 3 PP. 99-107 Dec 2012.

[6] Hadj Zerrouki, “High Throughput of WiMAX MIMO-OFDM Including Adaptive Modulation and

Coding”, International Journal of Computer Science and Information Security, Vol. 7, No. 1, 2010.

[7] Roberto Cristi, “Wireless Communications with Matlab and Simulink: IEEE802.16 (WiMax)

Physical Layer”, August 2009.

[8] Ahmed R. S. Bahai, “Multi-Carrier Digital Communications Theory and Applications of OFDM”,

Second Edition. 2004

[9] Ahmed Bakheit, “Effects of RF/ MW Emitted from Mobile-Phone Base-Stations on Plant Growth

using Chlorophyll a Fluorescence and Vegetative Growth”, international conference, Paris 2012.

[10] Hadj Zerrouki, “High Throughput of WiMAX MIMO-OFDM Including Adaptive Modulation and

Coding”, International Journal of Computer Science and Information Security, Vol. 7, No. 1, 2010.

[11] Mohammed H. M. Nerma and Albedeir Y. G. Othman “Performance Evaluation of SISO/MISO

WiMAX System Using Adaptive Modulation and Coding”, International journal of Research in

Computer Engineering and Electronics, ISSN 2319-376X, Volume: 2 Issue: 1, PP. 99-107,

February 2013.

[12] Mohammad Azizul Hasan, “Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical

Layer”, June 2007.

[13] Mohamed H. M. Nerma, Nidal S. Kamel and Varun Jeoti, “On DTCWT Based OFDM: PAPR

Analysis” in proceeding of 7th International work shop on Multi-Carrier Systems & Solutions

MC-SS 2009, vol. 41, Herrsching, Germany: pp. 207-217, May 2009.

[14] Mohamed H. M. Nerma, Nidal S. Kamel and Varun Jeoti “Investigation of Using Dual Tree

Complex Wavelet Transform to Improve the Performance of OFDM System” Engineering Letters,

Volume 20 Issue 2, Pages 135-142, May 2012.

[15] Dania Marabissi, “Efficient Adaptive Modulation and Coding techniques for WiMAX systems”,

IEEE, 2008.

[16] Ana P´erez-Neira, “Experimental Evaluation of Adaptive Modulation and Coding in MIMO

WiMAX with Limited Feedback”, EURASIP Journal on Advances in Signal Processing, 2007.

[17] Prabhakar Telagarapu, “Analysis of Coding Techniques in WiMAX”, International Journal of

Computer Applications, 2011.

[18] Ronnie P. Milione, “WiMAX/802.16” Digital Communications Conference, 2006.

Authors Profile Albedeir Yaseen Gafer Othman ([email protected]) received his MS.C. degree in

communication engineering from Sudan University of Science and Technology, Sudan in

2012. He has Many of patents in the field of communications and remote control, he has

scientific papers in the field of communications, His research is focused on Wireless

Communication and Optical Fiber in communication. Currently he is working for in

Omdurman Islamic University, Khartoum, Sudan. He is director of management in

technology development organization (TDO), one of the most important founders in Sudan. Mohamed Hussien Mohamed Nerma ([email protected]) received his Ph.D.

degree in communication engineering from Universiti Teknologi PETRONAS, Malaysia in

2010. He is a reviewer and invited reviewer of different international journals and

conferences and and he is also an active member in all assessment and accreditation

activities. His research is focused on Wireless Communication, OFDM (WiMAX, WiFi,

DVB-T, and LTE), Cognitive radio, OFDM and FPGA, Wavelet Based OFDM Systems, and

Optical Fiber Transceivers. Currently he is working for Sudan University of Science and

Engineering, Khartoum, Sudan. He is senior member of IEEE.

mailto:[email protected]


Vol. 3, No.1, 2013


Mohammed Elmaleeh received his BSC degree from University of Gezira (Sudan),

Faculty of Engineering and Technology (Communication and Control). In 1998 Elmaleeh

received his MSc in Electrical Engineering, University of Khartoum, Sudan. From 1994-

1998 he worked as researcher in Sudan Atomic Energy Commission Elmaleeh. In 1999 Mr

Elmaleeh worked as automation engineer at QAPCO, Qatar. In 2009 Elmaleeh received his

PhD degree from University Technology PETRONAS, Malaysia. Currently he works as

Ass. Prof. (Sudan). His research interest includes communication, control and electronic

engineering.

Documents

Implementation of AMC to Control the SNR for WiMAX Systems ... · Implementation of AMC to Control the SNR for WiMAX Systems Via a Smart Calculator ... ID0 represent the system when