ANALYSIS PERFORMANCE OF 256 AND 1024 QAM BY USING REED SOLOMON CODES APPLY IN DIGITAL VIDEO BROADCASTING THROUGH ADDITIVE WHITE GHAUSSIAN NOISE CHANNEL INSTITUT PENGURUSAN PENYELIDIKAN UNIVERSITI TEKNOLOGI MARA 40450 SHAH ALAM, SELANGOR MALAYSIA DISEDIAKAN OLEH : SUZI SEROJA SARNIN NORFISHAH AB WAHAB NOOR HAFIZAH ABDUL AZIZ NOVEMBER 2009
Tarikh : 1 November 2009 No. Fail Projek : 600-RMI/ST/DANA 5/3/Dst (124/2008) Penolong Naib Canselor (Penyelidikan) Institut Pengurusan Penyelidikan Universiti Teknologi MARA 40450 Shah Alam Ybhg. Prof., LAPORAN AKHIR PENYELIDIKAN ANALYSIS PERFORMANCE OF 256 AND 1024 QAM BY USING REED SOLOMON CODES APPLY IN DIGITAL VIDEO BROADCASTING THROUGH ADDITIVE WHITE GHAUSSIAN NOISE CHANNEL Merujuk kepada perkara di atas, bersama-sama ini disertakan 2 (dua) naskah Laporan Akhir Penyelidikan bertajuk Analysis Performance Of 256 and 1024 QAM By Using Reed Solomon Codes apply in Digital Video Broadcasting through Additive White Ghaussian Noise Channels. Sekian, terima kasih. Yang benar, SUZI SEROJA SARNIN Ketua Projek Penyelidikan ii
PROJECT TEAM MEMBERS SUZI SEROJA SARNIN Project Leader NORFISHAH AB WAHAB Project Member.. NOOR HAFIZAH ABDUL AZIZ Project Member.. iii
DECLARATION I hereby pledge this thesis is my original writing except the quotations and summaries that I had clearly quoted the sources. iv
ACKNOWLEDGEMENT First and foremost, I praised God the Almighty for the blessings endowed upon me. My deep sense of gratitude to the group members, madam Norfishah Ab Wahab and miss Noor Hafizah Abdul Aziz for their support and commitment throughout this research. I would also like to thank all of the persons who have directly or indirectly involved and contributed for the success of the project. Finally, my special gratitude is dedicated to my husband, children and family members for their endless support that make this research possible. v
TABLE OF CONTENTS CHAPTER PAGE DECLARATION ACKNOWLEDGEMENT ABSTRACT TABLE OF CONTENTS LIST OF FIGURES LIST OF TABLES LIST OF ABREVIATIONS 1. INTRODUCTION Background Objective Scope of project Thesis Organization 2. LITERATURE RIVIEW Quadrature Phase Shift Keying (QPSK) QPSK Modulator 6
QPSK Bandwidth QPSK Demodulator Minimum Shift Keying (MSK) modulation Cyclic Codes Coding Process (Cyclic Codes) Procedure of Obtaining the Transmitted Polynomial Systematic Encoding of a Cyclic Code Error Correction Additive white Gaussian Noise (AWGN) channel 3. METHODOLOGY 4. RESULTS AND DISCUSSION Flowchart of the simulation Result and analysis from the simulation Input message Encoding process Modulation process Transmission medium Demodulation process Decoding process BER error performance 5. CONCLUSION 7
6. REFERENCES 7. APPENDIX LIST OF FIGURES FIGURE TITLE PAGE 2.1 QPSK modulator block diagram 7 2.2 QPSK scatter diagram 8 2.3 MSK signal 10 2.4 QPSK demodulator block diagram 13 2.5 MSK encoding signal 14 2.6 Encoding circuit 21 2.7 Example of syndrome calculation with an (n-k)-stage shift 8
24 3.1 Cyclic code encoder 27 4.1 Flow chart of simulation 31 4.2(a) QPSK input message 33 4.2(b) MSK input message 33 4.3(a) QPSK encoded signal 35 4.3(b) Output signal QPSK 36 4.4(a) QPSK modulated signal 37 4.4(b) MSK modulated signal 37 4.5(a) QPSK modulated signal added with noise 38 4.5(b) MSK modulated signal added with noise 38 4.6(a) Demodulated signal 39 4.6(b) Demodulated signal 39 4.7 MSK output signal 9
41 4.8(a) QPSK Bit error rate performance 42 4.8(b) MSK Bit error rate performance 43 4.9 Performance of QPSK and MSK Modulation 44 10
LIST OF ABBREVIATIONS AWGN - Additive White Gaussian Noise CRC - Cyclic Redundancy Check ECC - Error Control Coding Ex-OR - Exclusive OR FCS - Frame Check Sequence FEC - Forward Error Correction FSK - Frequency Shift Keying MSK - Minimum Shift Keying QPSK - Quadrature Phase Shift Keying MOD-2 - Modulo-2 PISO - Parallel in Serial Out 11
PSK - Phase Shift Keying S/N - Signal to Noise SISO - Serial In Serial Out Tb - Bit Period Ts - Time Symbol 12
ABSTRACT This project is highlight about the performance of 256-Quadrature Amplitude Modulation (QAM) and 1024-QAM applying in Digital Video Broadcasting (DVB) through Additive White Gaussian Noise (AWGN) channel. Besides, this project using Reed-Solomon (R-S) code as the decode/encode technique in order to act as a forward error correcting code. Furthermore, this project is basically deal with one transmit antenna and one receive antenna at the transmission part and receiving part respectively. There are some comparison will be made between the 256-QAM and 1024-QAM purposefully to get the best performance when applying in DVB through AWGN channel in which both of them is using the same forward error correcting code (Reed- Solomon code) technique. Basically, the best performance is determined in term of Bit Error Rate (BER) and Signal Energy to Noise Power Density Ratio (E b /N o ). It is observed that as the constellation order of QAM increase the performance will be degraded. Thus, 256-QAM will give the best performances either in term of E b /N o or BER. In the mean time, both of the QAM (256-QAM and 1024-QAM) also being compared in term of the symbol-error correcting capability that is known as t in which it is observed that the performance is graded in response to the increasing of the value of t. During this project, all the simulation process that presented the performances of both of the QAM is done by using software that is known as MATLAB version 7.6.0. 13
ANALYSIS PERFORMANCE OF 256 AND 1024 QAM BY USING REED SOLOMON CODES APPLY IN DIGITAL VIDEO BROADCASTING THROUGH ADDITIVE WHITE GHAUSSIAN NOISE CHANNEL DISEDIAKAN OLEH : SUZI SEROJA SARNIN NORFISHAH AB WAHAB NOOR HAFIZAH ABDUL AZIZ NOVEMBER 2009
CHAPTER 1 INTRODUCTION 1.1 BACKGROUND It is well known that the QAM has been widely used as a modulation technique for digital communication system due to its simple detection [1] and the ability to achieve high rate transmission without increasing the bandwidth [2]. In response to this fact, QAM become a suitable modulation technique in order to fulfill the requirement that needs high speed transmission in DVB. However, there is a need for efficient process or techniques of implementation of QAM to make sure that QAM can operate in maximum or optimize performance. This is because by moving to a higher-order constellation, it is possible to transmit more bits per symbol but on the other hands, if the mean energy of the constellation is remain the same thus more susceptible to noise and other corruption [3]. The fact that increasing the order of the QAM constellation will degrade the QAM performance will be study in this project. In digital communication, one of the most important technical issues that might be occurred which are synchronization problem and the forward error correction used in this project which is R-S code has a unique advantage that suited to modify this problem. This is because this R-S code has the ability to recover the synchronization problem since this code is self-synchronizable [4]. Owing to this reasons, the R-S code has been choose in order to study the performance of QAM apply in DVB. Nevertheless, the R-S code is affected with its Symbol-Error Correcting Capability (t) in which the R- S code will perform better in higher value of t. This fact also will be discuss during this 1
project in order to study the performance of both 256-QAM and 1024-QAM apply in DVB through AWGN channel for various value of t. Since, this project is study the performance of QAM in DVB, it is necessary to find the most suitable channel that use to propagate the signal. Basically, channel is fall into three types which are fading channels, channels in which the noise stems from the others and AWGN channel. As the author compared all the three type of channels, the best suite channel for DVB is AWGN channel. This is because in the practical world is that AWGN never infinite in bandwidth. Thus, the destruction process is successfully safe since the receiver or measuring instrument has finite bandwidth [5]. 1.2 OBJECTIVE This project has several objectives such as to analysis and simulates the performance between 256-QAM and 1024-QAM using Reed-Solomon code applying in DVB through AWGN channel. Besides, this project also purposefully to compare both constellation order of QAM (256-QAM and 1024-QAM) in order to yield the best performances when applying in DVB in term of BER as well as E b /N o. Furthermore, the performance of Reed-Solomon code also being highlight in term of symbol-error correcting capability (t) for both of the constellation order of QAM. Lastly, this project also guides me to have the ability in using the MATLAB 7.6.0. 1.3 SCOPE OF PROJECT This project focusing on the analysis performance of 256 QAM as well as 1024 QAM when applying in DVB. AWGN channel and Reed Solomon code have been choose in this project in which the Reed-Solomon code is act as the decode/encode technique or also can be describe as forward error correction and on the other hands, AWGN is act as the medium for signal propagation. Basically, this project makes a comparison between both of the constellation order of QAM (256-QAM and 1024-QAM) in order to find which one of them can yield the best performance in DVB through AWGN channel. 2
Besides, the performance comparison for both constellation order of QAM also being done in term of symbol-error correcting capability (t) as the value of t will determined the capability of Reed-Solomon code to correct error. All the comparison during this project is represented using the graph of BER versus E b /N o as the performance for both order of QAM applying in DVB is analyze in term of BER and E b /N o using MATLAB version 7.6.0. 1.4 PROBLEM STATEMENT Modulation and demodulation process is the important process that involved in this project in which modulation process is modulated the information signal with carrier signal in order to make the signal compatible to the transmission channel. On the other hands, demodulation process is the reverse process of the modulation process since it is responsible to convert the modulated signal back to the original information signal (remove the carrier signal from the information signal). Thus, it is important to determine what type of modulation that is suitable applying in DVB. Since QAM has ability due to its simple detection and the ability to achieve high rate transmission without increasing the bandwidth, QAM become a suitable modulation technique in order to fulfill the requirement that needs high speed transmission in DVB. This is because QAM allowing two digital carrier signals to get transmitted on the same bandwidth that will give QAM an advantage of conservation of bandwidth. Furthermore, with QAM, amplitude and phase shift keying are combined so that can optimized the distance between the point in the constellation diagrams and will reduced the probability of one point to misinterpreted with neighbour point as compared to other digital modulation technique. All of these facts lead to make the QAM being chosen as the modulation technique for this project. The synchronization problem which is one of the most important technical issues in digital communication required the best coding/decoding technique in order to make the information or signal successfully received at the receiving part. Since the Reed- Solomon code have an ability to provide self-synchronization, this type of code being 3
selected to act as the code/decode technique or also can be known as the forward error correcting code. In the mean time, the Reed-Solomon is a powerful class of code and extremely flexible in use since Reed-Solomon code is a good choice for a variety of channel condition as has low redundancy overhead. Besides, with Reed-Solomon code, one code can be use both to detect and correct errors in which depends to the redundant message being added. Furthermore, the other problem that causes the author to study in this project is about the most suite channel for yield the good performance of DVB. This is because it is difficult to eliminate of all the noise of the received signal at the receiver part in order to get the original input signal. As a result, the author is decided to study about the best channel in DVB. Basically, channel is fall into three types which are fading channels, channels in which the noise stems from the others and AWGN channel. As the author compared all the three type of channels, the best suite channel for DVB is AWGN channel. This is because in the practical world is that AWGN never infinite in bandwidth. Thus, the destruction process is successfully safe since the receiver or measuring instrument has finite bandwidth. 1.5 THESIS ORGANIZATION This thesis has been divided into five chapters. Chapter 1 covers the introduction of this thesis, the objective of this project, the scope of work and the thesis organization. In Chapter 2, the basic theory has been discussed and this basic theory included Quadrature Amplitude Modulation (QAM), Reed-Solomon (R-S) code, Additive White Gaussian Noise (AWGN) channel and Digital Video Broadcasting (DVB). Chapter 3 presents the methodology of this project and also contains the explanation about the simulation steps that being used during this project using MATLAB version 7.6.0. Then, Chapter 4 is focusing on the result obtained and all of the result has been discussed in this chapter. Finally, Chapter 5 is provide the conclusion for the whole project and also provide the idea for future development in order to improve the project in future 4
CHAPTER 2 LITERATURE REVIEW 2.1 MODULATION AND DEMODULATION Modulation and demodulation process are the important processes that involved in this project and both of them play a specific utility applying at different part in this project s process in which modulation is takes place at transmission part and the demodulation is requires at the receiving part. In order to propagate the information signal over standard transmission media, it is necessary to modulate the information signal onto higher frequency analog signal called a carrier. Thus, the modulation process can be define as a process of impressing low frequency information signals onto a high frequency carrier signal due to make the signal compatible to the transmission channel [6]. On the other hands, the demodulation process is the reverse process of the modulation process since it is responsible to convert the modulated carrier signal back to the original signal (remove the information signal from the carrier signal). Furthermore, in digital communication, there are several types of modulation process might be involves. For instance: Amplitude Shift Keying (ASK) amplitude of the carrier is modulated. Frequency Shift Keying (FSK) frequency of the carrier is modulated. Phase Shift Keying (PSK) phase of the carrier is modulated. Quadrature Amplitude Modulation (QAM) amplitude and phase are modulated.
All of these types of digital communication as their own pros and contras and QAM have been chosen as the modulation technique for this project as it has the ability that fulfilled the DVB requirement. In respond to this, the theoritical part of QAM has been further discussed later. 2.2 QUADRATURE AMPLITUDE MODULATION (QAM) As a modulation technique in this project, QAM modulated the information signal due to make it compatible to the channel then lead to successfully being transmitted to the receiver. QAM is a modulation scheme which conveys data by changing or modulating the amplitude and the phase of two carrier waves as QAM process involves two input signal that is classified as in phase component, I-channel and quadrature component Q- channel [2]. The process of QAM can best be described using QAM block diagram [6]: Figure 2.1: (a) QAM Modulator; (b) QAM Demodulator According to the QAM block diagram, the input signal is divided into two channels (Ichannel and Q-channel) as being state before in which both of them will added together at linear summer in order to produce the QAM output. Basically, the balance modulator is act as a multiplier that multiplied one channel by sine wave (I-channel) and the other channel is multiplied by a cosine wave (Q-channel). Actually, the sine and cosine wave is the carrier signal that being produced by carrier oscillator but one of them undergoes 90 o phase shifter that make them differ by 90 o out of phase. Owing to this reason that
cause both of the channel (I-channel and Q-channel) also 90 o out of phases and lead to bandwidth conservation (higher data rate without require increasing of bandwidth) as one of the advantage for QAM. Then, when the signal is captured at the receiver, the filter at the QAM demodulator will removes the high frequency terms leaving only the independently modulated signal (independently of the quadrature component for I- channel and independently of the in phase component for Q-channel) [7]. Digital signal is being represented using constellation diagram. Similarly with QAM that also represented using constellation diagram that purposefully to graphically represent the quality of the signal as well as the distortion of the digital signal. There are many types of constellation diagram which is depending on the constellation order of QAM,. For instance, Square constellation is created when the order of QAM is a power of 4. Besides, the Cross constellation diagram can be constructed when the order of QAM is not equal to the power of 4. This statement can be summarized as [8]: Square Constellation M = 4 n (2.1) Where n =1, 2, 3, Figure 2.2: Square Constellation Diagram Cross Constellation M 4 n (2.2)
Where n =1, 2, 3, Figure 2.3: Cross Constellation Diagram However, it also can be other type of QAM constellation diagram: Figure 2.4: Constellation Diagram Of 8-QAM In digital telecommunication, the data is usually binary and the number of points in the grid is usually a power of two (2, 4, 8, ). Thus, the Square Quadrature Amplitude Modulation is produce and widely used as a modulation technique that has the number of bits per symbol is even. This modulation technique is suitable for this project since involves 256-QAM and 1024-QAM that have the number of bit is equal to eight and ten respectively (even). On the other hands, for the odd number of bits per symbol, the most suitable modulation technique is Cross Quadrature Amplitude Modulation [7]. Furthermore, the QAM technique is being development in order to improve its performance. As a result, the new technique of QAM is yield such as Triangular Quadrature Amplitude Modulation [1] and Rectangular Quadrature Amplitude Modulation [2]. During this project, there are two constellation orders of QAM that has been studied which are 256-QAM and also 1024-QAM.
In mathematically, QAM represented as [9]: ; ; (2.3) Where ε is represent the signal energy, is equal to the signal amplitude for the information conveyed by the cosine of the carrier and the signal amplitude for the information conveyed by the sine of the carrier is denoted as 2.2.1 256-QAM 256-QAM is one type of QAM that constructed with 256 as the constellation order (M=256). Beside, the bit rate of input data of 256-QAM is denoted as. This statement can best be described using the 256-QAM block diagram below: Figure 2.5: 256-QAM Block Diagram at Transmission Part Referring to the 256-QAM block diagram at the transmission part, it is shows that he input data is divided into two channels which are I-channel and Q-channel and both of them consists of bit rate that is equal to the original input data divided by eight. Then, both of the channel is undergoes 2-to-16 level converter in order to produce 16 level PAM signal. Next, I-channel is multiplied with the carrier signal that is denoted as sin
w c t. On the other hands, Q-channel also multiplied with carrier signal but the carrier signal is undergoes 90 o phase shifter first that make the carrier signal is in cosine function (cos w c t) and lead both channel are 90 o out of phase. Lastly, the linear summer will add both of them in order to yield the QAM output. 256-QAM has a capability to transmit only smaller data rate as the 256-QAM constructed with number of bits is equal to eight. By mathematically: (2.4) Where is represent the constellation order of QAM and is equal to the number of bits. In respond to this, 256-QAM has less susceptible to noise. This is because the error performance of QAM depends primarily on the minimum distance among points in its constellation [5] and this distance is determined by the constellation order of QAM as higher order will yield minimum distance of points in the constellation diagram. Its can be proved using formula [5]: (2.5) Where represent the nearest-neighbour distance in the constellation, is the number of distinct pairs at the distance and is represent the number of points in the constellation. Thus, the probability of error is decline as the point distance in the constellation is increase since the probability for one point to misinterpret to the neighbour point is reduced. Oppositely for large value of M, it causes in decreasing value of point distance in the constellation, hence the probability for one point to misinterpret to others is