Li-Fi modulation and networked Li-Fi attocell concept Tutorial

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1 Li-Fi modulation and networked Li-Fi attocell concept Tutorial Professor Harald Haas

2 Contributions by Svilen Dimitrov, Thilo Fath, Irina Stefan, Dobroslav Tsonev, Stefan Videv, Wasiu Popoola, Enrique Poves, Harald Burchardt, Sinan Sinanovic Nikola Serafimovski, Abdelhamid Younis, Mostafa Afgani, Cheng Chen, Yichen Li, John Fakidis, 2

3 Wireless data is growing exponentially YouTube In 2011, ~ 140 views for every person on earth (over 1 Trillion views More video is uploaded to YouTube in one month than the 3 major US networks created in 60 years 72 hours of video are uploaded to YouTube every minute 25% of global YouTube views come from mobile devices Source - Internet video traffic is growing at 48% CAGR Source - Cisco Visual Networking Index: Forecast and Methodology,

4 leading to RF Spectrum Shortage Global Mobile Data Traffic 4

5 How fix the problem? 1. Identify new spectrum, and/or 2. Enhance spectrum reuse (smaller cells) 5

6 The electromagnetic spectrum 6.

7 Li-Fi

8 Optical Attocell Concept 8

9 Link-Level Communication System 9

10 Communication Scenarios 12

11 State-of-the-Art: Wi-Fi Wi-Fi Router Location 13

12 State-of-the-Art: Wi-Fi Wi-Fi Router Location 14

13 15

14 Optical Attocell Network 16

15 Data rates per device Space per desk 4 m employees per floor Assume a uniform distribution of employees 20m x 20m floor = 400 m 2 Area can be covered by a single Wi-Fi AP Each Li-Fi AP can cover around 4 m 2 Wi-Fi data rate 600 Mbps Li-Fi data rate 20 Mbps 17

16 Interference Scenario desired signal user, k I. Stefan, et al., VTC -Spring, 20

17 Optimisation Framework 21

18 Rx FOV 85 - without lighting constraint 22

19 Rx FOV 85 - with lighting constraint 23

20 Rx FOV 45 - without lighting constraint 24

21 Rx FOV 45 - with lighting constraint 25

22 26

23 Digital Modulation 27

24 Key differences to RF System Information Signal RF carried on electric field complex valued bipolar Incoherent Optical carried on optical intensity real valued unipolar non-negative 28 December 23,

25 Non-linear Characteristic 29

26 Optical channel 30

27 Coherence Bandwidth of Channel 31

28 Path loss bi-directional reflectance distribution function (BRDF) 32

29 Path loss, cont d Optical path gain Electrical path gain Path loss Detector area distance 33 Irradiance

30 Example: Aircraft cabin / LOS 34

31 Example: Aircraft cabin / NLOS 35

32 Modulation Techniques 36

33 Transceiver building blocks 37

34 Pulsed Modulation On-OFF Keying On Intensity Finite slope limits achievable data rates Thres. Off Time 38 December 23,

35 Single Carrier Binary 39

36 Single Carrier Multi-level 40

37 PPM: BER Performance Spectal Efficiency: 41

38 PAM: BER performance Spectal Efficiency: 42

39 OFDM-based OWC System 43 December 23,

40 OFDM 44

41 DCO-OFDM and ACO-OFDM Symbol Structures DCO-OFDM xn 2 1 xn 2 x N 2 1 x 1 ACO-OFDM xn 2 1 xn 2 x N 2 1 x 1 45

42 ACO-OFDM Time Domain Signal 46

43 QAM vs. CAP QAM CAP Not feasible if C is much greater than the symbol frequency A. H. Abdolhamid, et al. A Comparison of QAM/CAP Architectures,

44 OFDM Generation (Time Domain) After the IFFT, the signal follows a zero-mean Gaussian distribution in the time domain: Time-domain signal Probability density function 6 Scatter plot 4 2 Quadrature In-Phase 48 December 23,

45 Multi-carrier Multi-level 49

46 DC Bias and Signal Power β DC σ 50

47 UPVLC Results (assuming single colour µled) 51

48 Bussgang Theorem X is a zero-mean Gaussian random variable with variance σ and g(x) is an arbitrary transform on X, which could be linear or nonlinear. The Bussgang theorem: gx KX EXY 0 n Y n Then: E N new b new o N o 2 old K Eb Var Y n K E E 2 2 Y E g X n Y Eg X n Var E 2 Y E Y EY 2 n X g 2 X n K 2 n 2 52 December 23,

49 Redefintion of the Distortion Any arbitrary distortion function g(x) can be represented with a set of intervals I and a number of continuous polynomials which describe the function in those intervals. Then g(x) becomes: g I nk j x ck, j x Ux xmin, k Ux xmax, k k 1 j0 where n k is the order of the polynomial in interval k, and U(x) is the unit step function: U x 0, x 0 1, x 0 53 December 23,

50 Examples 3-bit DAC: g x 3Ux 1.5 Ux 1Ux Ux 1.5 1Ux 1.5 Ux 3Ux Ux 1.5 Clipping and LED current-to-light conversion: g x 3Ux 3 Ux 2 1x 7x 5 U x 1 1Ux Ux 1 Ux 3 54 December 23,

51 The equations from the Bussgang analysis become: December 23, 55 Closed Form Solutions I k n j t j k k j j k k t x x t c K max, min, 1, 2 d,0,,, D d 1 I k n j t j k k j j k k t x x t c X g max, min,, d,0,,, D d E I k n j t n m m j k k m j m k j k k k t x x t c c X g max, min,,, 2 d,0,,, D d E Tsonev, et al., JLT,

52 Channel Capacity: Optimisation Frameworks 56

53 Results 57

54 Spectral Efficiencies 58

55 Spectral Efficiencies, cont d 59

56 Implications on Dimming 60

57 Optical Output Power 62

58 Spectral Efficiency of OFDM 63

59 Theoretical Capacity limits, cont d For 10 db dynamic range: (1): with optimisation, DC bias power not included (2): without optimisation, DC bias power not included (3): with optimisation, DC bias power included (4): without optimisation, DC bias power included 22 July

60 Spatial Modulation: How does it work? Spectral Efficiency: Im Signal Constellation Im 01(00) 00 (Tx0) 10(00) 00(00) 11(00) Re Im 01 (Tx1) 01(11) Re 11 (Tx3) 10 (Tx2) 10(11) 00(11) 11(11) Re Spatial Constellation 66 The University of Edinburgh 12/23/

61 Spatial Modulation OFDM 67

62 Thank You! 68

Pulse Shaping in Unipolar OFDMbased Modulation Schemes

Pulse Shaping in Unipolar OFDMbased Modulation Schemes Dobroslav Tsonev, Sinan Sinanović and Harald Haas Institute of Digital Communications The University of Edinburgh, UK d.tsonev@ed.ac.uk s.sinanovic@ed.ac.uk