Performance analysis of x-frequency shift keying based communication systems for power line and visible light communications channels

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(2) Performance analysis of x-frequency shift keying based communication systems for power line and visible light communications channels by. G ABRIEL M ELCHIADE M OUGOUE YAMGA A dissertation submitted to the Faculty of Engineering and the Built Environment in the fulfillment of the requirements for the degree of. M AGISTER I NGENERIAE in. E LECTRICAL AND E LECTRONIC E NGINEERING S CIENCE at the. U NIVERSITY OF J OHANNESBURG. Supervisor: P ROF. K HMAIES O UAHADA September 2018.

(3) Dedication I dedicate this work entirely to my Family MOUGOUE without which I could not achieve my dreams. A special dedication to my Mother Mrs. Mougoue Cécile for her prayers and encouragements. A lovely dedication to my wife Mrs. Mougoue Gaelle who accepted to share the rest of her life with me during this academic journey. An everlasting dedication to my sister Simone and my Father Mr. Mougoue Barthélémy for believing in me though they did not live long enough to see the fruit of their labour in me.. i.

(4) Acknowledgements I use this work as an opportunity to express my sincere gratitude to all those who supported me throughout my studies and particularly in the completion of my MEng. I am particularly thankful for their constructive criticism, guidance and presence from start to completion of my Masters Degree. In this light, I will always be grateful to Prof. Khmaies Ouahada, Dr. Alain Richard Ndjiongue and the University of Johannesburg. I would also like to thank my friends and fellow colleagues for their support in times of need, and ideas shared throughout this journey. Above all, I thank the Almighty God for His eternal Hand in my Life, His protection and for keeping me Healthy during this course. Hence, taking me to another level in my life.. ii.

(5) Abstract Power line communications (PLC) and visible light communications (VLC) are two emerging telecommunication technologies which may be seriously considered in the near future. This is due to the fact that both technologies present a channel or antennas, normally used for other purposes. The power wires which constitute the PLC channel are primarily exploited for electrical energy transmission, and the light bulbs which are VLC transmitting antennas are sources of illumination. PLC and VLC technologies also present four meaningful similarities: (i) Impulsive noise is the most destructive PLC noise, it is modelled using Poisson distribution. Similarly, the VLC channel is dominated by shot noise, also modelled using the same statistical distribution. (ii) Multiple reflections of the transmitted signal characterise the PLC channel. This is similar to the multipath propagation of VLC, which is due to multiple reflections that light rays undergo in the transmission environment. (iii) PLC technology presents economic advantages owing to the fact that it uses ubiquitous power wires already installed. This is the case of VLC technology, which uses the omnipresent light bulbs, naturally used for illumination. (iv) Both power wires and light bulbs are physically connected; light bulbs are powered through power wires. These similarities, added to the fact that both PLC and VLC are naturally connected to each other (light sources receive electrical energy from the electrical cable), are advantages related to cost effectiveness which is of a great importance in engineering. Among the applications of these two communication technologies, some are low data rate based. Generally, these low data rate applications require a modulation technique different from those exploited in high data applications. Lots of low data rate modulation schemes are used in communication engineering, they include on-off keying (OOK), pulse position modulation (PPM) and its variances, and frequency shift keying (FSK), to mention only iii.

(6) three. FSK is been a trial over the PLC channel. It was reported that its spread variance spread-FSK (S-FSK) has a better performance over the PLC environment. VLC technology, relatively new when compared to PLC, has not yet experienced a deep development on FSK. We deeply analyse the performance of FSK over PLC and VLC environments and propose a compared performance. We firstly analyse the performance of FSK and its variances over the PLC channel to confirm the best performance of S-FSK against narrowband interference. Secondly, we look at the performance of FSK over the VLC environment. The application of FSK in VLC is not straight forward as the channel requires a positive signal. After conversion of the conventional FSK to a VLK version, we analyse its performance for both additive white gaussian noise (AWGN) and fading VLC channels. All these results are finally compared to each other.. GM. M OUGOUE YAMGA. iv.

(7) Publications 1. G.M Mougoue Yamga, A. R. Ndjiongue, K. Ouahada, ”Performance Analysis of M-FSK Modulation in PLC and VLC Communication Systems” submitted in IEEE ACCESS, 2018. 2. G.M Mougoue Yamga, A. R. Ndjiongue, K. Ouahada, ”FSK-Based Modulation Scheme for VLC and PLC communication Systems” in 2nd African Winter School on Information Theory and Communications 2015, At Kruger, South Africa. 3. G.M Mougoue Yamga, A. R. Ndjiongue, K. Ouahada, ”Low complexity clipped Frequency Shift Keying (FSK) for Visible Light Communications” submitted in IEEE 7th International Conference on Adaptive Science & Technology (ICAST), 2018.. v.

(8) Contents List of Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ix. List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. x. List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. 1.1 1.1 1.2 1.2 1.3 1.4 1.5. CHAPTER 2: LITERATURE REVIEW . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 FSK In The PLC Channel . . . . . . . . . . . . . . . . . . . 2.2.0.1 Combined Modulation and Coding used 2.3 FSK In The VLC Channel . . . . . . . . . . . . . . . . . . . 2.4 Fading VLC channel . . . . . . . . . . . . . . . . . . . . . 2.5 Similar Work . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. 2.1 2.1 2.2 2.3 2.5 2.6 2.6 2.7. CHAPTER 3: PLC AND VLC CHANNELS . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Power Line Communication . . . . . . . . . . . . . . 3.2.1 PLC Cables . . . . . . . . . . . . . . . . . . . . 3.2.1.1 High voltage Cables . . . . . . . . . . 3.2.1.2 Low Voltage Cables . . . . . . . . . . 3.2.1.3 Power Line Network . . . . . . . . . 3.2.1.4 Frequency of Transmission . . . . . . 3.2.2 Nature of the Channel . . . . . . . . . . . . . . 3.2.2.1 Attenuation . . . . . . . . . . . . . . . 3.2.2.2 Noise . . . . . . . . . . . . . . . . . . 3.2.2.2.1 Coloured broad-band noise 3.2.2.2.2 Impulsive noise . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. 3.1 3.1 3.2 3.2 3.2 3.3 3.4 3.5 3.5 3.6 3.7 3.8 3.8. CHAPTER 1: INTRODUCTION 1.1 Introduction . . . . . . . . . 1.2 Problem Statement . . . . . 1.3 Objectives . . . . . . . . . . 1.4 Methodology and Tools . . 1.5 Expected Outcome . . . . . 1.6 Overview of the document .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . . . . . . . .. . . . . . . . . . . . . .. vi.

(9) CONTENTS. CONTENTS. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . .. . 3.9 . 3.9 . 3.12 . 3.13 . 3.15 . 3.16 . 3.16 . 3.17 . 3.18 . 3.19 . 3.19 . 3.22 . 3.22 . 3.22 . 3.22 . 3.22 . 3.24. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . 4.1 . 4.1 . 4.3 . 4.4 . 4.4 . 4.7 . 4.9 . 4.10 . 4.12 . 4.14. CHAPTER 5: DESIGN OVERVIEW . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 FSK version for PLC Channel . . . . . . . . . . . . . . . . . . 5.2.1 Simulation system overview . . . . . . . . . . . . . . 5.2.1.1 Advantages of FSK in PLC communications 5.3 FSK version for VLC Channel . . . . . . . . . . . . . . . . . . 5.3.0.2 Advantages of this system . . . . . . . . . . 5.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . 5.1 . 5.1 . 5.2 . 5.2 . 5.4 . 5.4 . 5.10 . 5.10. CHAPTER 6: ANALYTICAL RESULTS . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . 6.2 General FSK analysis . . . . . . . . . . . . . . . . . . 6.3 Transmission in the PLC channel . . . . . . . . . . . 6.3.1 Some Usage and Applications of FSK in PLC 6.4 Transmission in the VLC channel . . . . . . . . . . . 6.4.1 Applications in VLC communications . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . 6.1 . 6.1 . 6.1 . 6.5 . 6.10 . 6.11 . 6.13. 3.3. 3.4. 3.5. 3.6. 3.2.2.2.3 Narrow band interference Visible Light Communications . . . . . . . . . . . . 3.3.1 System description . . . . . . . . . . . . . . . 3.3.1.1 The LED . . . . . . . . . . . . . . . The VLC Channel . . . . . . . . . . . . . . . . . . . . 3.4.1 Single VLC Channel . . . . . . . . . . . . . . 3.4.1.1 LOS VLC Link . . . . . . . . . . . . 3.4.1.2 NLOS VLC link . . . . . . . . . . . 3.4.2 VLC systems with Multiple channels . . . . AWGN and Other Noise Types . . . . . . . . . . . . 3.5.1 Additive White Gaussian Noise . . . . . . . 3.5.2 Other Noise . . . . . . . . . . . . . . . . . . . 3.5.2.1 Coloured broad-band noise . . . . 3.5.2.2 Impulsive noise . . . . . . . . . . . 3.5.2.3 Narrowband interference . . . . . . 3.5.2.4 Shot and thermal noise . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . .. CHAPTER 4: FSK MODULATION . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . 4.2 Frequency of Transmission . . . . . . . . . . . . 4.3 Types of Frequency Shift Keying Modulations 4.3.1 Binary FSK Modulation . . . . . . . . . 4.3.2 Binary FSK Demodulation . . . . . . . . 4.4 M-FSK Modulation . . . . . . . . . . . . . . . . 4.4.1 Performance Measures . . . . . . . . . . 4.5 S-FSK Modulation . . . . . . . . . . . . . . . . . 4.6 Conclusion . . . . . . . . . . . . . . . . . . . . .. GM. M OUGOUE YAMGA. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. vii.

(10) 6.5 6.6. Performance comparisons in both channels . . . . . . . . . . . . . . . . . . . 6.14 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.15. CHAPTER 7: HARDWARE IMPLEMENTATION AND RESULTS 7.1 PLC systems Implementation . . . . . . . . . . . . . . . . . . . 7.1.1 Physical PLC system . . . . . . . . . . . . . . . . . . . . 7.1.2 PLC Results . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 VLC systems Design and Implementation . . . . . . . . . . . . 7.2.1 Physical VLC system . . . . . . . . . . . . . . . . . . . . 7.2.2 VLC Results . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . . . . . . . .. . 7.1 . 7.1 . 7.7 . 7.8 . 7.11 . 7.13 . 7.15 . 7.16. CHAPTER 8: CONCLUSIONS AND FUTURE WORK . . . . . . . . . . . . . . . 8.1 8.1 Achievements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 8.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. I. Applicable design diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. a. viii.

(11) List of Abbreviations AWGN ASK AFSK BAFSK BFSK BER BBPLC FFT FSK HF IAs IFFT LED LTI LOS LAN MFSK MAC NBPLC NLOS OOK PSD PD PLC RF RSC SNR S-FSK SOCPBFSK SS SDOs VLC. Additive White Gaussian Noise Amplitude Shift Keying Asymmetric frequency shift keying Binary asymmetric frequency shift keying Binary FSK Bit error rate Broad-Band power line communications Fast fourier transform Frequency shift keying High frequency Information appliances Inverse fast Fourier transform Light emitting diode Linear time-invariant Line-of-sight local area network M-ary FSK Media Access Control Narrow-Band power line communications Non-line-of-sight On-Off-Keying Power spectral density Photo detector Power Line Communications Radio Frequency Recursive systematic convolutional Signal to noise ratio Spread frequency shift keying Spread orthogonal continuous phase binary frequency shift keying Spread spectrum Standards of organization Visible light communications. ix.

(12) List of Figures Figure 1.1: Methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Figure 2.1: Non Coherent Demodulator. . . . . . . . . . . . . . . . . . . . . . . . 2.4 Figure 2.2: Simulation results from sub optimum S-FSK receiver performing FSK or ASK [1]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Figure 3.1: PLC channel power line: Middle phase coupled to ground [14]. . . Figure 3.2: Time and frequency dependence attenuation at low frequency in PLC cables [19]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 3.3: Two-port network for PLC Channel. . . . . . . . . . . . . . . . . . . Figure 3.4: (a) Topology Without ground bonding; (b) topology with ground bonding; (c) Effects of bonding on transfer function [19]. . . . . . . Figure 3.5: Noise Scenarios in PLC. . . . . . . . . . . . . . . . . . . . . . . . . . Figure 3.6: Illustration of the VLC concept. . . . . . . . . . . . . . . . . . . . . . Figure 3.7: VLC System Block Diagram. . . . . . . . . . . . . . . . . . . . . . . Figure 3.8: Line-of-sight VLC link. . . . . . . . . . . . . . . . . . . . . . . . . . . Figure 3.9: Effect of AWGN on a transmitted signal. . . . . . . . . . . . . . . .. . 3.3 . 3.6 . 3.6 . 3.8 . 3.10 . 3.11 . 3.15 . 3.17 . 3.20. Figure 4.1: Coherent Binary FSK signal generator. . . . . . . . . . . . . . . . . . . 4.5 Figure 4.2: FSK Signal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Figure 4.3: Coherent BFSK detector. . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9 Figure 5.1: NRZ representation of signals in electrical and optical systems. . . . 5.2 Figure 5.2: General PLC Communication system. . . . . . . . . . . . . . . . . . . 5.3 Figure 5.3: General VLC Communication system highlighting the two electrical domains and one optical domain. . . . . . . . . . . . . . . . . . . 5.4 Figure 5.4: Example of FSK transmission in VLC channel obtained by simulation. 5.6 Figure 5.5: Binary asymmetric frequency shift keying (BAFSK)generated from the normal binary frequency shift keying. . . . . . . . . . . . . . . . . 5.6 Figure 5.6: Asymmetric frequency shift keying waveform. . . . . . . . . . . . . . 5.7 Figure 5.7: Example of transmission in Normal FSK obtained by simulation. . . 5.9 Figure 6.1: Binary FSK transmission PLC channel. . . . . . . . . . . . . . . . . . 6.2 Figure 6.2: Bit error rate probability of coherent M-ary FSK over the AWGN channel (PLC and VLC general performance analysis). . . . . . . . . 6.2 Figure 6.3: Symbol error rate probability of coherent M-ary FSK over the AWGN channel (PLC and VLC general performance analysis). . . . . . . . . 6.3. x.

(13) LIST OF FIGURES. LIST OF FIGURES. Figure 6.4: Bit error rate probability of non-coherent M-ary FSK over the AWGN channel (PLC and VLC general performance analysis). . . . . . . . . 6.3 Figure 6.5: Bit error rate probability comparison between coherent and noncoherent binary FSK over the AWGN channel (PLC and VLC general performance analysis). . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Figure 6.6: Two states Class A Middleton model. . . . . . . . . . . . . . . . . . . 6.6 Figure 6.7: Symbol error rate probability of a 16FSK over both AWGN and impulsive noise, PLC channel, for A = 0.01 and multiple Γ (PLC channel only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Figure 6.8: Symbol error rate probability of a 16FSK over both AWGN and impulsive noise, PLC channel, for A = 0.03 and multiple Γ (PLC channel only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.7 Figure 6.9: Bit error rate probability of a binary S-FSK over both AWGN and impulsive noise, PLC channel, for A = 0.01 and multiple Γ (PLC channel only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 Figure 6.10: Bit error rate probability of a binary S-FSK over both AWGN and impulsive noise, PLC channel, for A = 0.03 and multiple Γ (PLC channel only). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.9 Figure 6.11: Binary FSK transmission VLC channel. . . . . . . . . . . . . . . . . . 6.11 Figure 6.12: Bit error rate probability of a 2FSK over a fading channel using the Chi-square channel model (VLC channel only) . . . . . . . . . . . . . 6.12 Figure 6.13: Bit error rate probability of a binary S-FSK over an AWGN channel. 6.13 Figure 7.1: Figure 7.2: Figure 7.3: Figure 7.4: Figure 7.5: Figure 7.6: Figure 7.7: Figure 7.8: Figure 7.9: Figure 7.10: Figure 7.11: Figure 7.12: Figure 7.13: Figure 7.14: Figure 7.15:. Schematic of final PLC design. . . . . . . . . . . . Mode of Operation of the coupling circuit. . . . . Circuit diagram of Coupling circuit. . . . . . . . . FSK tracking bandwidth. . . . . . . . . . . . . . . Communication System . . . . . . . . . . . . . . . Transmitting unit. . . . . . . . . . . . . . . . . . . . Receiving unit. . . . . . . . . . . . . . . . . . . . . Modulator and demodulator circuits. . . . . . . . FSK signal generated. . . . . . . . . . . . . . . . . Spectra Of signal in channel and channel noise. . Schematic of final VLC design. . . . . . . . . . . . VLC communication system. . . . . . . . . . . . . VLC transmitter layout. . . . . . . . . . . . . . . . FSK signal generated during VLC transmission. . Output voltage in (V) versus optical power (mW).. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .. . 7.2 . 7.4 . 7.4 . 7.6 . 7.7 . 7.7 . 7.8 . 7.8 . 7.9 . 7.9 . 7.11 . 7.13 . 7.14 . 7.14 . 7.15. Figure A.1: Figure A.2: Figure A.3: Figure A.4:. XR-2206 Chip block diagram. . . . . . FSK Generator circuit using XR-2206. XR-2211 block diagram. . . . . . . . . FSK Decoder circuit for XR-2211. . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. GM. M OUGOUE YAMGA. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. . . . .. a b c d. xi.

(14) List of Tables Table 2.1: Code Book for M=4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Table 4.1: Frequency allocation standards over PLC channel . . . . . . . . . . . . 4.4 Table 6.1: Detail Analysis of 2FSK versus S-FSK . . . . . . . . . . . . . . . . . . . 6.9 Table 6.2: Implementation results . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.15 Table 7.1: Implementation results . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.10 Table 7.2: Implementation results . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.16 Table A.1: Pin description for XR-2206 . . . . . . . . . . . . . . . . . . . . . . . . . Table A.2: Pin description for XR-2211 . . . . . . . . . . . . . . . . . . . . . . . . .. b c. xii.

(15) Chapter 1 Introduction 1.1. I NTRODUCTION. Over the last decade, telecommunication engineering has experienced major improvements driven by the challenges faced with transmission of data and the need to develop low cost transmission systems to suit the demand of the increasing users. This has led to the development of communication systems based on pre-existing technologies such as power line communications (PLC) and visible light communications (VLC). During the last two decades, lots of interests have been given to the development of new modulation schemes to overcome these challenges. Many studies have been done over the past decades on the investigation of modulation schemes over the power line channel amongst which FSK has been investigated [2]. When compared to PLC, VLC technology is quite new. Modulation schemes such as wavelength multiplexing, orthogonal frequency division multiplexing (OFDM) and its versions suitable to the optical channel which are direct current (DC)-offset (DCO)-OFDM and asymmetric clipped optical (ACO)-OFDM, to mention only two. On-off-keying (OOK) has also previously been used to modulate data over this channel [3]. In this dissertation, the focus will be on the investigation of frequency shift keying (FSK) modulation scheme over power line and visible light communications systems.. 1.1.

(16) CHAPTER 1: INTRODUCTION. 1.2. 1.2. PROBLEM STATEMENT. P ROBLEM S TATEMENT. The nature of the channel remains a major problem in communication systems. Thus choosing an appropriate modulation scheme is of utmost importance. Therefore in this dissertation, the investigation of FSK modulation over PLC and VLC channels will be done. Digital modulation will be taken into consideration and a given signal will be transmitted over each channel. In this regard, it is worth mentioning factors influencing the choice of digital modulation schemes such as bandwidth and transmission power. Ideally, in terms of communication, PLC is a very harsh environment when compared to VLC. The idea here is to do proper study with respect to these two channels in order to be able to rate them in terms of the quality of signal transmission. In communication, a certain information rate needs to be maintained in order to guarantee proper transmission of the message. This can be controlled by the knowledge of the bit error rate (BER). The amount by which the signal power needs to be increased to maintain this BER often depends on the modulation scheme in play. Likewise, bandwidth capacity is a function of the signal to noise ratio (SNR). It therefore follows that for an optimum BER, the corresponding SNR can be used to devise the required band width for proper transmission. From the results obtained in each scenario, having the above factors in mind and exploiting the FSK scheme, we should be able to tell with confidence in which of both PLC and VLC channels the signal will be transmitted with more noise immunity.. 1.3. O BJECTIVES. This will entail simulating, designing and implementing both PLC and VLC communication channels whereby signal transmission will be done using FSK modulation technique. Analysis of the quality in signal transmission will be done in each channel type taking into consideration M-ary FSK (M-FSK) in both channels and spread frequency shift keying (S-FSK) in the PLC channel only. Analysis of the respective FSK modulation schemes GM. M OUGOUE YAMGA. 1.2.

(17) CHAPTER 1: INTRODUCTION. 1.4. METHODOLOGY AND TOOLS. for each channels will be done following the indicated noise types as detailed below: 1. General performance in additive white gaussian noise channel: An analysis of coherent and non-coherent M-FSK modulation will be done considering AWGN in both channels whereby bit error rate probability curve will be used to present the results. 2. Performance analysis in PLC channel only: The aim here will be to rate the performanceM-FSK and S-FSK modulation schemes when subjected to both AWGN and impulsive noise. A cross performance will also be done to rate each M-FSK modulation level considered in this dissertation versus S-FSK. 3. Performance analysis in VLC channel only: Strictly to VLC channel, M-FSK will be analyzed when the transmitted signal is subjected to a fading channel using the Chi-square channel model. 4. Hardware implementation: To finalize, FSK transmission systems in both channels will be implemented. The respective analysis in the quality of the signal transmitted will be done and results will also be presented.. 1.4. M ETHODOLOGY AND T OOLS. The Methodology which will be used to carry out this investigation will follow the protocol elaborated below: 1. The requirements to meet the target for this project will be investigated and hence proper selection will follow thereof. 2. Literature review will be done in order to understand other concepts which have some similarities with the project at hand. This will be done by studying previous work which are related to the subject matter. 3. From the literature review, a clear idea on how to simulate, design and implement signal transmission using FSK modulation in both PLC and VLC communication GM. M OUGOUE YAMGA. 1.3.

(18) CHAPTER 1: INTRODUCTION. 1.5. EXPECTED OUTCOME. Figure 1.1: Methodology. channels will be obtained. The simulations will be done using MatLAB. Results obtained will be interpreted following research evidence from related work. 4. With all the above steps been satisfied, concluding remarks will be done on the results obtained. A flow chart summarizing the entire approach used in this project is shown in Fig.1.1.. 1.5. E XPECTED O UTCOME. This project in a sense will end up with something new in the field of communications. As it stands, lots of works are proposed in the literature, but not much work has been done on the VLC channels in particular and a comparison with PLC considering FSK modulation will provide a proper guidance for possible implementations in real life. The analysis will technically give an idea on what frequencies to consider when implementing, the bandwidth on which the system works perfectly and the noise tolerance for each scheme based on the BER versus SNR curve. GM. M OUGOUE YAMGA. 1.4.

(19) CHAPTER 1: INTRODUCTION. 1.6. OVERVIEW OF THE DOCUMENT. The results obtained in the actual hardware implementations will be the key in the advancement of any large scale application of this technology since the main objective is to use such research work in the advancement of technology.. 1.6. O VERVIEW OF THE DOCUMENT. The rest of this work will be split into chapters each dedicated to specific contents which will sum up to a proper methodology to go through this research efficiently. • Chapter 2: This focuses on the literature review giving in-depth understanding of the necessary knowledge needed in this research. • Chapter 3: The two channels to be investigated in this work will be studied properly in this chapter and their particularities will be highlighted hence giving a good guide in the design process. • Chapter 4: This presents frequency shift keying and its various forms. Being the modulation of interest in this study, technical aspects in relation to this are covered in this chapter. • Chapter 5: The in-depth designs which will be followed in both simulations and hardware implementations are presented in this chapter. • Chapter 6: This handles simulation results and analysis of results obtained in each channel. It further does a comparison of performances between the two channels. • Chapter 7: This chapter presents the various hardware implementations done and the results obtained in each case. Similar to the simulations, the performances between both channels are compared and conclusions are made. • Chapter 8: Conclusive remarks are made here based on the findings from the project and suggestions for future optimizations are made as well.. GM. M OUGOUE YAMGA. 1.5.

(20) Chapter 2 Literature Review This chapter focusses on reviewing the literature related to the topic treated in this dissertation. It gives a quick view of FSK for both PLC and VLC channels. Works that present some similarities with that in this dissertation are also reviewed.. 2.1. I NTRODUCTION. Frequency shift keying modulation technique involves the transmission of digital information through discrete frequency changes of the carrier. An in depth description of this technique will be touched in Chapter 4. However, it is worth mentioning the simplest form of FSK which is 2-ary FSK or binary FSK (BFSK). Here the frequency of the carrier signal is varied to represent binary 1 and 0. The study of this technique over the PLC and VLC channels can lead to the development of new systems based on the findings done in this dissertation. However, revisiting previous work in the same line of thoughts is good as this will give us a better idea on what to expect in terms of results. Indeed previous work has been done in both channels as detailed in the following subsections.. 2.1.

(21) CHAPTER 2: LITERATURE REVIEW. 2.2. 2.2. FSK IN THE PLC CHANNEL. FSK I N T HE PLC C HANNEL. FSK modulation has been studied over the PLC channel in various research works. One of such studies is elaborated in [2] where it was demonstrated that combining M-ary FSK modulation and coding can provide for a constant envelope modulation signal, frequency spreading. This was seen to help avoiding bad parts of the frequency spectrum, and time spreading to facilitate correction of frequency disturbances and impulse noise simultaneously. The low frequency range region of 150 kHz was the point of focus in this study. This presents a channel characterized by attenuation, permanent frequency disturbances and impulsive noise which needs special attention. The goal here was to demonstrate how combining M-ary FSK modulation and coding could provide a constant envelope modulation signal, frequency spreading in order to avoid bad parts of the frequency spectrum, and time spreading hence facilitating correction of frequency disturbances and impulse noise simultaneously. A simplistic equation representing the M-ary modulation is given by s si ( t ) =. 2ES i−1 cos(2π f i t); f i = f 0 + , 1 ≤ i ≤ M. TS Ts. (2-1). where i = 1,2,..., M and ES is the signal energy per modulated symbol. The signals represented by this equation are orthogonal in nature whereby the frequencies are spaced by 1 Ts Hz. in order to avoid abrupt frequency switching between the frequencies.. Demodulation here was done by modifying the demodulator in such a way that the envelopes detected were used in the decoding processes of a special class of error control codes, called permutation codes. Combining this to M-FSK for modulation over the PLC channel gave rise to a constant modulator output envelope including frequency and time diversity.. GM. M OUGOUE YAMGA. 2.2.

(22) CHAPTER 2: LITERATURE REVIEW. 2.2. FSK IN THE PLC CHANNEL. Table 2.1: Code Book for M=4. Message 1 2 3 4. 2.2.0.1. dmin = 4 Code word 1,2,3,4 2,1,4,3 3,4,1,2 4,3,2,1. Message 1 2 3 4 5 6. dmin = 3 Code word 1,2,3,4 1,3,4,2 2,1,4,3 2,4,3,1 3,1,2,4 3,4,1,2. Message 7 8 9 10 11 12. dmin = 3 Code word 4,2,1,3 4,3,2,1 1,4,2,3 2,3,1,4 3,2,4,1 4,1,3,2. Combined Modulation and Coding used. The sample code book used in this technique is shown in Table 2.1. Table 2.1 presents the code book used in this study where dmin in each case represents the Hamming distance between any two code words respectively 3 and 4. Considering message 3 with Hamming distance 4, it is seen that the transmission is done in time, in series of frequencies of ( f 3 , f 4 , f 1 , f 2 ). It was shown here that the required bandwidth and symbol duration time of permutation for the M-FSK is given by B = M.. M b.M , Ts = , log2 |C | B. (2-2). where • b :is the information transmission rate in bits per second. • |C |: number of code words in code Demodulation here was done using a non-coherent demodulator as shown on Fig. 2.1. As shown above, 2M correlators are used in this demodulator with 2 per signal waveform. M envelopes are computed by the sub-optimum non-coherent demodulator. The output of this computation is an estimate of the transmitted frequency which corresponds to the largest envelope. An optimum decision derived from the knowledge of the SNR per sub-channel for a particular frequency. The output rk is normalized with respect to the noise variance (σk2 ) and its probability density function of the normalized output (yk = GM. M OUGOUE YAMGA. 2.3.

(23) CHAPTER 2: LITERATURE REVIEW. 2.2. FSK IN THE PLC CHANNEL. Figure 2.1: Non Coherent Demodulator. rk /σk ) is given by ∆k,j = p(yk |frequency k transmitted). = yke. (−. y2 +2Ek /σ2 k k ) I ( yk 0 2. q. 2Ek /σk2 ). ∆k,j = p(yk |frequency k not transmitted). = yke. −. y2 k 2. (2-3). (2-4). ,. where Ek and σk2 respectively denote the symbol energy and noise variance for given PLC channel K and I0 is the modified Basel function of zero order. The outcome of this study was a new modulation and coding scheme which could handle frequency disturbances such as narrow band noise in the PLC channel. This made used of M-FSK modulation in conjunction with permutation codes. As communication technique over the PLC channel, FSK was presented in [4] as a good solution for low cost transmission over the PLC channel at a low data rate. This study also revealed that in the PLC channel, when using FSK technique the signal spectrum is attenuated more than 40 dB (3-6 MHz range) including parts that are not flat for FSK transmission. It is also seen that combining M-ary FSK modulation and coding provides a constant envelope modulation signal, frequency spreading which helps avoids bad parts of the frequency spectrum. It also provides time spreading thus facilitating correction of frequency. GM. M OUGOUE YAMGA. 2.4.

(24) CHAPTER 2: LITERATURE REVIEW. 2.3. FSK IN THE VLC CHANNEL. disturbances and impulse noise. This in all can make signal transmission over the power line robust and more reliable.. 2.3. FSK I N T HE VLC C HANNEL. Unlike the PLC channel, communication in the VLC channel is still an evolving one and much is yet to be done in this field. However, a few FSK oriented work has been done in this channel. To the best of the author’s knowledge, only few achievements have been reported on the investigation of FSK over the VLC channel. They are given in [5–8]. Some discuss a combination of FSK and OOK [9, 10], while some of the work done involved an integrated system between PLC and VLC system as presented in [11]. In [5], a demonstration of a visible light verbal exchange system upon eight meters fair space transmission using off-the-shelf LEDs with an audio interface on a clever phone is given. The transmitted signal is produced in an FSK modulation format. The profitable empirical accomplishment validates the probability regarding the proposed rule between future Wi-Fi communication networks. This work is a practical demonstration of FSK in VLC applications using smart devices. A more fundamental work comparing FSK and many other modulations schemes for VLC is depicted in [6]. This work is more close to that of [7], where the use of visible light as a means of data communication, to implement a wireless visible light communication (VLC) system that can transmit and receive data with a range of more than 3 cm based on varying modulation techniques, which are Phase Shift Keying (PSK), FSK and, Amplitude Shift Keying (ASK). FSK and PWM are also used in [8] to achieve transmission. In [9] and [10], frequency shift ON-OFF keying are exploited to achieve transmission in a VLC system using camera receivers in which mark and space frequencies that are harmonics of the camera frame rate are exploited in the processing of the subsampled aliased frequencies to decode the message.. GM. M OUGOUE YAMGA. 2.5.

(25) CHAPTER 2: LITERATURE REVIEW. 2.4. 2.4. FADING VLC CHANNEL. FADING VLC CHANNEL. The Gaussian distribution is largely exploited in telecommunication engineering in the analysis of the system performance. However, the true channel is in general different from a Gaussian distribution. This statement remains valid for VLC technology. It is clear and justified that the main sources of noise in VLC, which are shot and thermal noises, are well described by a normal distribution. Nevertheless, after the photodetector, the noise model close to the real word may not be Gaussian. It is then required to analyse FSK over the VLC channel based on both Gaussian and a distribution representing a fading channel. In general several distributions have a fading aspect. They are the Log-normal distribution, the Nakagami distribution and the Chi-square distribution to mention only a few. The later, added to the Gaussian distribution, will be exploited in this work to assess the performance of the FSK.. 2.5. S IMILAR W ORK. A similar study was performed in [1] on S-FSK which proved to be a low cost approach for spread spectrum modulation. It was highlighted here that the quality of transmission depends on the carrying frequency and not the receiver. This claim was characteristic of NB-PLC which operated based on Amplitude Shift Keying (ASK) and M-FSK with M16. This study revealed spread spectrum techniques to be more expensive for low cost applications despite their satisfactory performances. S-FSK on the other hand was found to combine both advantages presented by classical spread spectrum and FSK modulations. Hence it is suitable for low cost applications. The maximum likely-hood was applied in this results and the results obtained for each modulation scheme is shown on Fig.2.2 [1]. The solid lines represent S-FSK and the dotted lines ASK. It can be seen that at x = 20 dB there is no significant difference in the performance of the two schemes. A slight difference occurs in their error at x = 10 dB, while a marked difference in their error rate is seen at x = 0 dB. Based on this, it could be concluded that S-FSK was seen to be the better modulation scheme. GM. M OUGOUE YAMGA. 2.6.

(26) CHAPTER 2: LITERATURE REVIEW. 2.6. CONCLUSION. Figure 2.2: Simulation results from sub optimum S-FSK receiver performing FSK or ASK [1]. In [12], low data rate transmission over PLC and VLC channel was done using spread orthogonal continuous phase binary frequency shift keying (SOCPBFSK) combined with OOK. Orthogonal continuous phase binary FSK (OCPBFSK) is a binary version of orthogonal continuous phase FSK whose carrier signal is given by the equation. n −1 πhan (t − nT ) c FSK (t) = A FSK cos[2π f c t + ( ) + πh ∑ ai ], nT ≤ t ≤ (n + 1) T. T i =0. (2-5). This system was analysed using the eye diagram and it could be inferred from the eye diagram that little distortion was observed at the received signal in a dark environment. When the system was subjected to sunlight entering the room, the eye was observed to close indicating a high rate of noise.. 2.6. C ONCLUSION. This chapter presented an overview of previous work done on FSK with respect to PLC and VLC channels. It also highlighted previous investigation of S-FSK in the PLC channel. The analysis was strictly dedicated to M-FSK in one case and S-FSK in the other. No cross. GM. M OUGOUE YAMGA. 2.7.

(27) CHAPTER 2: LITERATURE REVIEW. 2.6. CONCLUSION. comparison was done between the two schemes. This work goes further in considering impulsive noise for both types over the PLC channel and performs a cross comparison between both schemes in this channel. In the VLC channel, the previous work focused mostly on the combination of FSK modulation with other schemes. This dissertation only considers FSK in the VLC channel and investigates M-FSK performance in a fading channel using the Chi-square channel model. The next chapter will be based on a proper analysis of the PLC and VLC channels and will highlight key points to be taken into consideration for this study.. GM. M OUGOUE YAMGA. 2.8.

(28) Chapter 3 Power Line And Visible Light Communications Channels In this chapter, a quick but sufficient presentation of both PLC and VLC channels is given. PLC channel parameters such as the nature of the channel, the voltage level, the cables used, the transmission frequencies and the noise scenario are discussed. On the VLC channel, the description of the transmission system is proposed with noise sources and their impact on the overall quality of service. Finally, an introductory word is given on the integration of PLC and VLC channels.. 3.1. I NTRODUCTION. Telecommunication has witnessed many changes in the quest of quality in information transfer. Added to this, competition in the market has also led to the development of new systems which can make use of other existing technologies and thus reducing cost in infrastructure. Such systems include power line communications and visible light communications which make use of power line cables and light emitting diodes (LEDs) respectively as channels. This in a sense optimizes present technologies to suit communication needs. In this chapter, proper study of PLC, VLC and FSK modulation from previous work or publications will be done in order to have a better idea on how to come up with suitable communications based on the FSK technique and utilizing either of these chan3.1.

(29) CHAPTER 3: PLC AND VLC CHANNELS. 3.2. POWER LINE COMMUNICATION. nels. This will serve as guidance for the best solution possible.. 3.2. P OWER L INE C OMMUNICATION. To begin with, PLC is a technology developed over power line cables. Thus making use of these cables to transmit data without obstructing their intended function in conveying electrical energy. This technology has been grouped under Narrow band which operates at frequency ranges of 3-500 kHz with data rates up to 100s of kps and Broadband PLC which operates at higher frequencies generally above 200 MHz with data rates up to 100 s of Mbps [13]. To better understand how signal transmission over these cables can be done, we need to investigate various aspects of the line such as the nature of the cable, frequency of transmission, voltage, attenuation and noise.. 3.2.1. PLC C ABLES. Two categories of cables can be identified here, mainly high and low voltage cables which serve as communication medium when devices are connected to them. It is of interest to have an idea of the basics of each cable type in order to understand the type of communications channel they can present.. 3.2.1.1. High voltage Cables. This is a multi conductor system made up of three or more phase conductors which are shielded by wires. Besides the fact that they serve as transmission lines for high voltage current over long distances, these conductors also serve as medium for the transmission of signals. Their phase difference has led to the usage of different coupling schemes for connecting communication devices to them [14]. Fig.3.1 shows the PLC channel with coupling of the middle phase to ground [14]. This illustrates the path taken by the signal from the transmitter, coupling devices both on the transmitting and receiving sides.. GM. M OUGOUE YAMGA. 3.2.

(30) CHAPTER 3: PLC AND VLC CHANNELS. 3.2. POWER LINE COMMUNICATION. Figure 3.1: PLC channel power line: Middle phase coupled to ground [14].. 3.2.1.2. Low Voltage Cables. These cables in contrary to high voltage cables deal with low voltage electrical wiring on smaller distances. As it is, these cables are meant and designed for electrical transmission thus their intended use for communication is been impaired by harsh conditions characterized by extreme noise making it unsuitable for high speed communications. Nevertheless, with the advancement of communications technologies and modulation schemes these cables can support communication networks at speeds similar to those present in wired local area networks (LANs) [15]. In the quest of using power cables for signal transmission, adaptive devices have been developed most of which are transceivers thus permitting sending and reception of data via an entry point to the electrical network. These cables constitutes the indoor PLC network. This network being mostly restricted to wirings in homes or small business areas, it can be visualized as a wired structure with many devices connected to it. Hence, indoor PLC mainly constitutes of a series of interconnected transmission lines which are terminated with loads of different varieties [16]. Typically, in a family home, connected devices such as fridges and other electric appliances constitute these loads. They are the main cause of broadband noise introduced in this indoor channel. In summary, it is worth mentioning that for indoor power networks the voltage to current relation is linear time-invariant (LTI) for some devices. For such devices, when. GM. M OUGOUE YAMGA. 3.3.

(31) CHAPTER 3: PLC AND VLC CHANNELS. 3.2. POWER LINE COMMUNICATION. modelling this channel their load can be characterized by an impedance which is usually frequency dependent. We also have device whose behaviours are not LTI, hence for such devices the noise generated is stationary and can be characterized by a power spectral density (PSD) [16].. 3.2.1.3. Power Line Network. The PLC cables as discussed constructively build up the PLC network. These networks assume various topologies based on their length, number of branches and equipment such as capacitor banks [17]. It is therefore seen that PLC operates in a network which was not initially meant for data transmission and this ignored all communications requirements. Added to this, the material for electric wiring differs in the sense that there are those used for electric distribution lines and others used for home wiring. This sums up to incoherence in terms of communication requirements and the noise produced in such networks is almost unavoidable since people need to connect each time to this network to power appliances and for various needs. In communications, the layered model is used to define the functional aspects. Amongst these layers, the technology centred around PLC is found in the physical and media access control (MAC) layers whereby the physical layer consists of modulation methods and synchronization which can be applied to power lines [17]. Modulation methods and synchronization constitute the physical layer and some of the methods applicable for PLC modems include FSK modulation which is the technique considered in this dissertation. To conclude with this section, the power line network operates on a standard meant for electrical wiring and thus it consists of different conductor types and cross section joins almost at random. This gives rise to a wide variety of characteristic impedances over the network. This also results in a high variation in the network terminal impedance based on the frequency of communication since the load pattern varies in proportion to consumer needs. This results in mismatch effects causing deep notches at certain frequencies [18]. Typically, the attenuation on the power line in a home network is between 20 and 60 dB.. GM. M OUGOUE YAMGA. 3.4.

(32) CHAPTER 3: PLC AND VLC CHANNELS. 3.2.1.4. 3.2. POWER LINE COMMUNICATION. Frequency of Transmission. This dissertation is centered on FSK modulation. From its name, it is clear that the parameter of interest here is frequency. The channel presented by PLC exhibits different properties at different frequencies. This is because the essential parameter determining impact of reflections is the relationship between the wavelength (λ) of the injected radio signal and the geometric line length [15]. The length of cables play a lot when it comes to noise, the presence of parasitic components in the form of high inductance leads to high signal attenuation. Power lines which are very lengthy exhibit frequency selective fading with sharp notches which comes as a result of strong echoes caused by low attenuations unlike those observed in higher frequency ranges. The relationship between time and frequency dependent attenuation in low frequency ranges is depicted by Fig.3.2 [19]. The results shown here are also relevant for frequency ranges of up to 500 kHz, which is a range within which the study done in this dissertation falls since it also accounts for the power line intelligent metering evolution (PRIME) and G3-PLC standards [20]. The ideal will be to be able to transmit using modulations schemes capable of resisting frequency selective attenuations. From the graph, it can be seen that at 60 dB there is maximum attenuation. This stems from attenuation resulting from time and frequency coupled to signal path length. Deep notches are observed around 50 kHz while at higher frequencies there is a decrease in attenuation thus deviating from expected increase in cable loss when frequency increases. This can be explained by the fact that in high frequency (HF) ranges, the access impedance of a line is dominated by the line’s characteristic impedance. From this analogy, it is seen that the load of Information appliances (IAs) are dominant at low frequencies thus the radio frequency (RF) properties of the lines are meaningless when compared to that resulting from the IAs.. 3.2.2. N ATURE OF THE C HANNEL. Being a technology developed over an existing one meant for electrical energy distribution, this makes it quite difficult to transmit signals without experiencing much noise and attenuation. GM. M OUGOUE YAMGA. 3.5.

(33) CHAPTER 3: PLC AND VLC CHANNELS. 3.2. POWER LINE COMMUNICATION. Figure 3.2: Time and frequency dependence attenuation at low frequency in PLC cables [19].. Figure 3.3: Two-port network for PLC Channel.. 3.2.2.1. Attenuation. This is seen in Power Line by making reference to frequency selectivity of the channel. The messagesignal sent over the channel is attenuated at certain frequencies due to the impedance mismatch in parallel conductors. Power cables used for indoor wiring usually comprise of three to four conductors which are all confined in an outer Jacket. Attenuation and mismatch can be visualized by considering the transfer function of a two port network given in Fig.3.3. This transfer function is then given as [21], H=. UL Us. Zc = , AZc + B + CZc + DZs GM. M OUGOUE YAMGA. (3-1). 3.6.

(34) CHAPTER 3: PLC AND VLC CHANNELS. 3.2. POWER LINE COMMUNICATION. where Zc is the characteristic impedance given by: s Zc =. R + jωL , G + jωc. (3-2). where: • R is the series resistance; • L is the series Inductance; • G is the shunt conductance; • C is the shunt capacitance. Mismatches responsible for attenuation in PLC can be explained by considering Fig.3.4 [19]. Fig.3.4 (a) shows a two conductor topology comprised of hot and return wires. With its far end terminated with a mismatched resistor. The attenuation experienced here has no notches with increasing frequencies. When the same topology is made up of three cables whereby the third cable is the ground which is bounded to the return as shown of Fig.3.4 (b), this results in notches as indicated on Fig.3.4 (c). As shown on Fig.3.4 (c) when the cable was bounded, resonant attenuation was experienced around 3.27 MHz and 9.9 MHz which plays a major effect on the transfer function since the characteristic impedance Zc is frequency dependent due to its inductive and capacitive nature.. 3.2.2.2. Noise. The PLC channel is characterized by some intrinsic noise which either arise due to the electrical energy it transmits or when there is a load on the system. The net result is interference with the transmitted signal. It should be noted that most often, the noise in PLC is unavoidable since it stems from its original intended functions. Some of these noises are: Coloured Broad- band noise, Impulsive noise, and narrow-band interference [22]. Unlike other communication channels, additive white Gaussian noise is not present in the Power line channels in the frequency range spanning from hundreds of kHz up. GM. M OUGOUE YAMGA. 3.7.

(35) CHAPTER 3: PLC AND VLC CHANNELS. 3.2. POWER LINE COMMUNICATION. Figure 3.4: (a) Topology Without ground bonding; (b) topology with ground bonding; (c) Effects of bonding on transfer function [19]. to 20 MHz [22], [23]. For clarity sake, we will briefly define each type of noise involved. Some of the major noise present in PLC are elucidated briefly as follows: 3.2.2.2.1. Coloured broad-band noise. This results from daily appliances such as computers, microwaves and shavers to name a few. Their disturbing effects can be pronounced up to frequency ranges of about 30 MHz. They have low power spectral density which increases around low frequencies. 3.2.2.2.2. Impulsive noise. This is subdivided into two main categories namely: periodic and non-periodic. The periodic type is further divided into synchronous and asynchronous with respect to the mains frequency. Synchronous impulsive noise arise from rectifiers within DC power supplier and exhibit a repetitive sequence based on multiples of the mains frequency. GM. M OUGOUE YAMGA. 3.8.

(36) CHAPTER 3: PLC AND VLC CHANNELS. 3.3. VISIBLE LIGHT COMMUNICATIONS. Similarly, the asynchronous type of impulsive noise results from switching power supply and has a repetition rate in the range of 50 - 200 kHz. Concisely, impulsive noise are characterized by short ”onoff” duration caused by sources such as switches. The sum of these noise can be assumed as a cyclic additive Gaussian noise whose mean is zero [24]. The time frequency dependent of noise n(t) can be represented by the equation below: σ2 (t, f ) = σ2 (t) a( f ), where σ2 ( t ) =. (3-3). 3. ∑ Ai |sin(2πTAC t + θi )|ni ,. (3-4). i =1. and a( f ) = R. e− a f f 0 +W − a f e df f0. .. (3-5). From the above equations, TAC is the cyclic duration of the mains AC which is usually 1 50. or. 1 60 .. a( f ) denotes the noise PSD normalized by the total noise power in the frequency. range f 0 to f 0 + W. 3.2.2.2.3. Narrow band interference. This is made up of modulated sinusoidal signals caused by broadcasting stations which typically operates in the frequency range of 1-22 MHz [22]. Fig.3.5 gives a visual summary of the different types of noise we can experience over the PLC channel [22].. 3.3. V ISIBLE L IGHT C OMMUNICATIONS. It is worth mentioning optical wireless communication (OWC) when talking about visible light communication. OWC is a technology which involves the transmission of information filled with optical radiation via a free space channel [25]. In the same way, VLC is based on optical devices which are LEDs. Just as is the case with PLC which is based on an existing technology, this communication system takes advantage of the illumination. GM. M OUGOUE YAMGA. 3.9.

(37) CHAPTER 3: PLC AND VLC CHANNELS. 3.3. VISIBLE LIGHT COMMUNICATIONS. Figure 3.5: Noise Scenarios in PLC. capability of LEDs to transmit data by modulating the visible light spectrum. Unlike fluorescent lamps, it was easier to develop VLC using LEDs because their current densities is easily modulated. This is one of the most recent technologies in the field of communications. The transmission channel here is simply the visible light spectrum. Though this is a new concept in the communications field, its first demonstration actually dates back as far as 1870 s when Alexander Graham Bell transmitted an audio signal using a mirror which was made to vibrate using a person’s voice. This system was not very successful because it depended on sunlight [25]. Thus in recent technology, this has been replicated using LED. This operates under the principle of solid state lighting which is the generation of light through solid state electroluminescent. Since their creation, the luminous efficiency of LED’s has improved from o.1 lmW to over 230 lmW having a lifetime of about 100,000 h. In modern times, the first VLC transmission system started at Nakagawa Laboratory in Keio University, Japan in 2003. The switching of phosphorescent white LEDs on and off rapidly permits the transmission at data rates of up to 40 Mbps. With the same technique, higher data rates of about 100 Mbps can be achieved with RGB color LEDs. This concept makes it suitable for applications using modulations schemes such as FSK. Fig.3.6 represents the VLC concept and also highlights key components of the entire system [25].. GM. M OUGOUE YAMGA. 3.10.

(38) CHAPTER 3: PLC AND VLC CHANNELS. 3.3. VISIBLE LIGHT COMMUNICATIONS. Figure 3.6: Illustration of the VLC concept.. GM. M OUGOUE YAMGA. 3.11.

(39) CHAPTER 3: PLC AND VLC CHANNELS. 3.3.1. 3.3. VISIBLE LIGHT COMMUNICATIONS. S YSTEM DESCRIPTION. Initially, visible light was seen to be capable of transmitting and receiving data in early 1870 when Alexander Graham Bell used a mirror made to vibrate at a person’s voice in order to transmit audio signal [25]. The dependence of Bell’s system on sunlight was a major draw back since it is not always certain to have sunlight whenever needed. This however has been overcome with the development of LEDs whereby their lighting capacity has been exploited for data transmission resulting in the dual usage of the device. In terms of data transmission, we therefore see that LEDs plays the major role here thus we will have a closer look at the LED from a technical angle. The VLC system is summarized in Fig.3.7. LEDs short response time during on-off switch periods unlike incandescent and gas lamps makes it easier to control the dimming level. Thus modulation of the driver current at high frequencies switches LEDs on and off such that it is not perceivable to the human eye. In this way, light emitted by LEDs assumes a repetitive high frequency with low average power pulse stream. It therefore follows that the average luminous flux emitted by an LED is linearly proportional to the relative width of the dimming signal The parameter used to express the LEDs brightness is the luminous intensity. This is the luminous flux per angle given by the equation I=. dΦ , dΩ. (3-6). where φ = Luminous flux and Ω = Spatial angle. The spatial angle Ω is calculated from the flux energy as follows [26]: Ω = Km. Z 780 380. V (λ)φe (λ)dλ,. (3-7). where V (λ) = standard luminous curve and Km = maximum visibility which is ∼ 683 lmW at 555nm wavelength. It then follows that the transmitted optical power Pt is given GM. M OUGOUE YAMGA. 3.12.

(40) CHAPTER 3: PLC AND VLC CHANNELS. by: Pt = Km. 3.3. VISIBLE LIGHT COMMUNICATIONS. Z Λmax Z 2π Λmin. 0. φe dθdλ,. (3-8). where the values of Λmin and Λmax are obtained from the photodiode sensitivity curve.. 3.3.1.1. The LED. The acronym stands for light-emitting diode and it is a device which emits both visible and infrared red radiation when current passes through it. Structurally, they are made of semiconductors, which are mixed with phosphors, and substances capable of absorbing electromagnetic radiations and emitting them as visible light. Upon application of an electric current through the LED, the semiconductors emit infrared radiation, which are absorbed by the phosphors and then re-emitted as visible light which is then used for various applications amongst which we have the present day VLC. The LED, in a normal state, has an empty conduction band. This is populated by electrons when a forward current is injected through its junction. This causes the emission of light when these electrons recombine with the holes and hence cause the emission of photons [27]. Hence LED produce light by the mechanism of stimulated emission. LEDs have a linewidth corresponding to a range of photon energy of 1-3.5 KT, where K is Boltman’s constant and T represents the absolute temperature. This makes it easy for the LEDs to support many optical modes and therefore has facilitated its use as a multi-mode source as we shall see later on in this work. From a research perspective, a few factors have favoured the use of LEDs in their choice for communication systems. Though these have favoured the growth in their use for optical fibre communication, these factors are also relevant in VLC since this also relies on the transmission of information via light. These factors include [27]: 1. Simple fabrication: There are no mirror facets and their geometry is not striped. 2. Cost effective: LEDs construction is relatively simple, this favors massive production and easy maintenance of the system. 3. Reliability: LEDS are not susceptible to catastrophic degradation and are less sensiGM. M OUGOUE YAMGA. 3.13.

(41) CHAPTER 3: PLC AND VLC CHANNELS. 3.3. VISIBLE LIGHT COMMUNICATIONS. tive to gradual degradation as well. Finally, they are also immune to self-pulsation and modal noise problems. 4. Generally less temperature dependent LEDs are not threshold devices. Thus, raising temperatures do not increase the current threshold above their operating point and hence halt them. 5. Simpler drive circuitry: This comes as a result of lower drive currents with reduced temperature dependence. This makes it unnecessary to include temperature compensation circuits. 6. Linearity: LEDs have a linear light output against the current characteristics. This is advantageous as well in the sense that they can be used for analog modulation Structurally, there are six major types of LEDs amongst which two have been of major use. In essence, the light emitted by LEDs are generated through solid state electroluminescence from which we have the term solid state lighting. With the evolution in time, the luminous of LEDs has improved from 0.1 lmW to over 230 lmW and with a life time of about 100,000 h. With the above ideology in place, the whole idea about VLC communication is as summarized in Fig.3.6. Such systems communicate by switching the LEDs on and off rapidly and thus sending data at rates up to 40 Mbps. This is basically the OOK technique. OOK is a binary modulation scheme whereby a signal is defined over two voltage levels with one of its voltages being null. In simple terms, OOK is an amplitude shift keying modulation (ASK). In OOK modulation technique, the amplitude of the carrier is keyed between the two possible voltage values used to denote the symbols 1 and 0. Hence OOK signal can be represented by:.  √  E for binary 1 b b(t) =  0 for binary 0. (3-9). where: b(t) is the bit signal and Eb is the energy per bit. GM. M OUGOUE YAMGA. 3.14.

(42) CHAPTER 3: PLC AND VLC CHANNELS. 3.4. THE VLC CHANNEL. Figure 3.7: VLC System Block Diagram. In FSK modulation, the same concept is applied the difference being that instances of on and off can be attributed to different frequencies respectively. As it is for now, the major drawback of OOK in VLC technology is flickering which is not good for human eyes. Hence, the need for research in this technique considering other modulation forms such as FSK. Fig.3.7 is the block diagram of a VLC system. This system just as other optical communication systems best work using Line Of Sight as the link between the transmitter and receiver. Though in real life this appears to be straight forward, Fig.3.7 details the components of such systems.. 3.4. T HE VLC C HANNEL. The channel presented by LED is of two main types: The single VLC channel and the multi-VLC channel. As other communication channels, it provides the path necessary for the transmission of a signal from transmitter to receiver. It is also subjected to adverse conditions such as attenuation, interference and noise. These factors differ from channel to channel as we see later on with the example of the VLC Channel. GM. M OUGOUE YAMGA. 3.15.

(43) CHAPTER 3: PLC AND VLC CHANNELS. 3.4.1. 3.4. THE VLC CHANNEL. S INGLE VLC C HANNEL. As can be understood from its name, it is a channel which is made up of a single transmitter (LED) and a single receiver photo detector (PD). This constructively forms a transmission system whose capacity can be defined by [28]: CSISO = log2 (1 +. g2 Pt ), σ2 B. (3-10). where: • Pt : Transmitter Power, • B : Transmission Bandwidth, • σ2 : Total noise variance in AWGN channel, • g: Channel gain , •. g2 Pt σ2 B. is the SNR characterizing this channel.. The transmission here can assume two types of models based on the type of link which could be Line-of-sight (LOS) or non-line-of-sight (NLOS) link.. 3.4.1.1. LOS VLC Link. This is a situation wherein there is a direct a link free of obstacles between the LED (transmitter) and the PD (receiver). Two subtypes can be identified here as depicted by Fig.3.8 [29]. We can see the direct line-of-sight (dLOS) characterized by a 0° incidence where β = 0 and the non-direct LOS (ndLOS) in which the angle of incidence is not zero (β 6= 0). For such a system, the transmission equation can be re-written as: ri = HLOS si + ωi ,. (3-11). where HLOS = channel response and ωi is the AWGN which accounts for the noise during transmission. The model shown in Fig.3.8 is a diffuse model whereby in simple terms GM. M OUGOUE YAMGA. 3.16.

(44) CHAPTER 3: PLC AND VLC CHANNELS. 3.4. THE VLC CHANNEL. Figure 3.8: Line-of-sight VLC link. the angle α is considered to be zero thus the receiver is always pointing vertically in the direction of the transmitter. From this the path loss performance of the system can be calculated as [30]: L≈. gt ( β ) Ar , R θmax D2 0 2πgt (θ )sinθdθ. (3-12). where Ar is the receiver area. In such a system, the received optical power is the net sum of the optical power of all LED chips within the system.. 3.4.1.2. NLOS VLC link. In this system there can be single or multiple reflections encountered by the light rays from the transmitter before they reach the receiver. This results from obstacles which falls within the transmission path. The channel impulse response is likened to an infinite sum of light rays and can be represented as [31]: ∞. HNLOS =. ∑ h(k) ,. (3-13). k=o. where h(k) is the impulse response of rays undergoing the k(th) path. In a similar way, the transmission equation for such a system can be written as: ri = HNLOS Si + ωi = ρHLOS si + ωi. GM. M OUGOUE YAMGA. (3-14). 3.17.

(45) CHAPTER 3: PLC AND VLC CHANNELS. 3.4. THE VLC CHANNEL. Where ρ is the coefficient of multiplication which comes into play when looking at a line of sight transfer matrix in the case of multi-carrier VLC system explained in the next section.. 3.4.2. VLC SYSTEMS WITH M ULTIPLE CHANNELS. The aggregation of LEDs can be used in order to achieve a Multi-carrier communication system in VLC systems. The base idea is the use of more than one colour LED through which the message can be sent conveniently. In such a system, there are finite numbers n and z of LEDs used as antennas and PDs used as detectors. The transfer matrix is therefore represented as: . h h  1,1 1,2  h2,1 h2,2 Hmulti =   .. ..  . .  hz,1 hz,2. . . . h1,n. .   . . . h2,n   ..  , ... .   . . . hz,n. (3-15). where • hi,i : Front-end gain between the ith LED and the corresponding PD, and • hi,j : Crosstalk gain between the ith LED and the jth PD. In the absence of crosstalk, Hmulti becomes a diagonal matrix with hi,i entries. For such a system, the channel capacity is given by:. Cmulti = γCCISO ,. (3-16). where γ = min(n, z) and CCISO is detailed in [28].. GM. M OUGOUE YAMGA. 3.18.

(46) CHAPTER 3: PLC AND VLC CHANNELS. 3.5. AWGN AND OTHER NOISE TYPES. Among the multi-wavelength LEDs, the most used is RGB - LEDs. The channel transfer matrix for a single case RGB-LED transmitter is given by: . hrr. hrg. hrb. .     H3×3 = h gr h gg h gb  .   hbr hbg hbb. (3-17). The LOS link between a single LED and its corresponding PD is given by the diagonal entries (hrr , h gg , hbb ). Cross-talks between channels is represented by the remaining entries.. 3.5. AWGN AND O THER N OISE T YPES. The whole idea about conducting research investigating performances of modulation schemes in communications is due to the presence of noise in its various forms. Channels in the real world experience different types but for the sake of this dissertation we will focus more on Additive White Gaussian Noise (AWGN) since this was considered in simulations to account for noise in both channel types.. 3.5.1. A DDITIVE W HITE G AUSSIAN N OISE. This is a channel model which is used universally to analyze modulation schemes. It serves to account for the various types of noise which can be experienced in real life systems. This explains why I have chosen this to carry out my investigation. Fig.3.11 represents an example of a signal before and after addition of AWGN. Here, the channel’s amplitude frequency response is flat with unlimited and infinite bandwidth with a linear phase response for all frequencies which permits the modulated signal to pass through without expressing amplitude, phase or frequency distortions [32]. For a given signal transmitted through a channel subjected to additive white Gaussian noise, the signal at reception is given by the equation below: Yi = Xi + Zi ,. GM. M OUGOUE YAMGA. (3-18). 3.19.

(47) CHAPTER 3: PLC AND VLC CHANNELS. 3.5. AWGN AND OTHER NOISE TYPES. Figure 3.9: Effect of AWGN on a transmitted signal. where: • Yi is the received signal, • Xi is the modulated signal, and • Zi is zero-mean Gaussian. This channel model is different from others in that, the output can take continuous values. This makes it good for practical communication channels. Assuming constrains on an input power, for a given input in codeword say x1 , x2 , ..., xn . The average power constrained is obtained as [33]. 1 n 2 xi ≤ P. n i∑ =1. (3-19). The probability of error when considering binary transmission can be established by con√ √ sidering sending either + P or − P over the channel. At reception, detection by the receiver is done by looking at the signal’s amplitude based on a threshold test summarised. GM. M OUGOUE YAMGA. 3.20.

(48) CHAPTER 3: PLC AND VLC CHANNELS. 3.5. AWGN AND OTHER NOISE TYPES. as follows: 1 Pe = P(Y < 0| X 2 √ √ 1 = + P ) + P (Y > 0 | X = − P ) 2 √ √ √ 1 1 = P( Z < − P| X = + P) + P( Z > P| X 2 2 √ = − P) √ = P( Z > P). =. Z √P ∞. √. √. 1 2πN. (3-20). − x2. e 2N dx. = Q( PN ) √ = 1 − Φ( PN ), where: 1 Q( x ) = √ 2π. Z ∞. 1 Φ( x ) = √ 2π. Z x. x. 2. e− x 2 dx,. (3-21). and −∞. 2. e− x t dx.. (3-22). The capacity of the Gaussian channel with power constraint P and noise variance N is derived as follows: I ( X; Y ) = h(Y ) − h(Y | X ). = h (Y ) − h ( X + Z | X ) = h(Y ) − h( ZX ) = h (Y ) − h ( Z ). (3-23). 1 1 log2πeN ≤ log2πe( P + N ) − 2 2en 1 = log(1 + PN ). 2 This sums up to the equation 1 P C = log(1 + ) bits per transmission. 2 N GM. M OUGOUE YAMGA. (3-24) 3.21.

(49) CHAPTER 3: PLC AND VLC CHANNELS. 3.5.2. 3.5. AWGN AND OTHER NOISE TYPES. O THER N OISE. In communications, real world applications such as the power line channel face various types of noise. Though this is not part of the scope of this research, I will brief on some of these noise [22].. 3.5.2.1. Coloured broad-band noise. This is noise caused by common home appliances such as computers and hair dryers. This disturbing effects can be pronounced up to frequency ranges of about 30 MHz. Their power spectral density is low in nature and increases around low frequencies.. 3.5.2.2. Impulsive noise. This however falls into two main categories which are periodic and non-periodic. The periodic impulsive noise is equally divided into synchronous and asynchronous with respect to the mains frequency. The synchronous results from rectifiers within DC power supplier and exhibit a repetitive sequence based on multiples of the mains frequency. On the other hand, the asynchronous results from switching power supply and has a repetition rate in the range of 50-200 kHz. To wrap up, impulsive noise are characterized by short ”onoff” durations caused by sources such as switches.. 3.5.2.3. Narrowband interference. Narrow band interference noise is made up of modulated sinusoidal signals caused by broadcasting stations which typically operates in the frequency range of 1-22 MHz.. 3.5.2.4. Shot and thermal noise. Similarly to the PLC channel, the VLC channel has its own noise and this depends on the environment hosting the VLC system. For instance, the outdoor VLC channel is very noisy due to the presence of sunlight and street lights. Indoor VLC communication on. GM. M OUGOUE YAMGA. 3.22.

(50) CHAPTER 3: PLC AND VLC CHANNELS. 3.5. AWGN AND OTHER NOISE TYPES. the other hand suffers due to the presence of unwanted light from bulbs, television sets and movements within the confined region which cannot be avoided at times. Several noise sources are present over the VLC environment. Shot and thermal noise are the most important noise in VLC. Shot noise, induced by both desired and unwanted signals is well described by BoseEinstein statistics when it is generated by a coherent light. If it is engendered by a thermal light, it is best represented by Poisson statistics. Note that both Bose-Einstein and Poisson distributions have the same expectation and exhibit a Gaussian fit for large values of interacting photons. Two shot noise scenarios are identified over the VLC environment. The second shot noise scenario is related to the light due to the transmitted message itself. The receiver circuitry generates thermal noise. This happens regardless of the voltage source used to power the circuit. It is modelled using a central limit theorem. Finally, shot and thermal noise are modelled using a normal distribution, therefore, the AWGN model may be used in outdoor VLC channel modelling. However, after a square law detector, the noise maybe modelled using the Chi-square statistic, which corresponds to a scenario where non-Gaussian components of noise are dominant. Hence, to use the Gaussian model, it is recommended to use biased PDs to increase thermal noise (more Gaussian components) and improve signal detection. Biasing PDs is already adopted in the literature. The total noise affecting the VLC channel can be expressed as [34] Ntotal =. q. 2 2 Nshot + Nthermal .. (3-25). Thermal and shot noise are Gaussian in nature and signal independent. Hence the total noise affecting this channel can be modelled as Gaussian noise [34]. It should also be mentioned that the distance plays a major role in the signal degradation as this fades away with increasing distance. Added to this, whether conditions such as rain, fog and wind which could carry dust particles could affect VLC transmission negatively.. GM. M OUGOUE YAMGA. 3.23.

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