## Performance of a novel LED lamp arrangement to reduce SNR fluctuation for multi-user visible light communication systems |

Optics Express, Vol. 20, Issue 4, pp. 4564-4573 (2012)

http://dx.doi.org/10.1364/OE.20.004564

Acrobat PDF (1897 KB)

### Abstract

This paper investigates the performance of our recently proposed LED lamp arrangement to reduce the SNR fluctuation from different locations in the room for multi-user visible light communications. The LED lamp arrangement consists of 4 LED lamps positioned in the corners and 12 LED lamps spread evenly on a circle. Our studies show that the SNR fluctuation under such a LED lamp arrangement is reduced from 14.5 dB to 0.9 dB, which guarantees that users can obtain almost identical communication quality, regardless of their locations. After time domain zero-forcing (ZF) equalization, the BER performances and channel capacities of 100-Mbit/s and 200-Mbit/s bipolar on-off-keying (OOK) signal with most significant inter-symbol interference (ISI) are very close to that of the channel without any ISI caused by this LED lamp arrangement.

© 2012 OSA

## 1. Introduction

8. M. Zhang, Y. Zhang, X. Yuan, and J. Zhang, “Mathematic models for a ray tracing method and its applications in wireless optical communications,” Opt. Express **18**(17), 18431–18437 (2010). [CrossRef] [PubMed]

5. T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron. **50**(1), 100–107 (2004). [CrossRef]

^{−4}, ZF equalization provides 3.2-dB and 5.4-dB power reduction for 100-Mbit/s and 200-Mbit/s bipolar OOK signal, respectively, where the Monte-Carlo simulation and theoretical results match with each other very well. In addition, the maximum channel capacity improvements by ZF equalization are 0.17 bits/symbol for 100-Mbit/s bipolar OOK signal when the total LED power is 2 W and 0.16 bits/symbol for 200-Mbit/s bipolar OOK signal when the total LED power is 4 W. Both the BER performance and channel capacity after applying ZF equalization are very close to that of the channel without ISI. Therefore, the new LED arrangement and ZF equalization provide similar communication qualities to all users, no matter where they locate in the room.

## 2. Principle and optimum parameters

7. J. M. Kahn and J. R. Barry, “Wireless infrared communications,” Proc. IEEE **85**(2), 265–298 (1997). [CrossRef]

*φ*is the angle of irradiance from the LED,

*m*is the order of Lambertian emission defined by the LED’s semi-angle at half power

*φ*

_{1/2}, which is

*m*= ln(1/2) / ln(cos(

*φ*

_{1/2})). Hence the channel direct current (DC) gain is described by [5

5. T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron. **50**(1), 100–107 (2004). [CrossRef]

7. J. M. Kahn and J. R. Barry, “Wireless infrared communications,” Proc. IEEE **85**(2), 265–298 (1997). [CrossRef]

*d*is the distance between LED and the photo-detector,

*A*is the physical area of photo-detector, and

*θ*is the angle of incidence. Note that in this paper all the LEDs point vertically to the plane where the photo-detector is located.

*p*(

*t*) =

*P*(1 +

_{t}*M**

_{I}*f*(

*t*));

*P*is the launched power of LED Lamp;

_{t}*M*is the modulation index [12

_{I}12. I. Neokosmidis, T. Kamalakis, J. Walewski, B. Inan, and T. Sphicopoulos, “Impact of nonlinear LED transfer function on discrete multitone modulation: analytical approach,” J. Lightwave Technol. **27**(22), 4970–4978 (2009). [CrossRef]

*f*(

*t*) is the modulating bipolar OOK signal. The average received optical power is

*s*(

*t*) =

*R**

*P**

_{r}*M**

_{I}*f*(

*t*), where

*R*is the responsivity of the photo-detector. Hence, the SNR of the output detected electrical signal is given by [7

7. J. M. Kahn and J. R. Barry, “Wireless infrared communications,” Proc. IEEE **85**(2), 265–298 (1997). [CrossRef]

*P*is the power of noise which is defined in [5

_{noise}5. T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron. **50**(1), 100–107 (2004). [CrossRef]

*var*(

*SNR*) represents the variance of SNR. The higher the Q-factor is, the more uniformly the SNR distributes in the room. The SNR distribution is shown in Fig. 1(a) , where the fluctuation of SNR is 14.5 dB, while the Q-factor of SNR distribution is only 0.5 dB, which means that the value of SNR varies substantially in the room, i.e., communication quality is associated closely with user’s location. The user in the corner will obtain less than 1/10 (10 dB) of the SNR in the center of the room. Note that in the calculation of SNR distribution we do not consider the reflection of walls or the ISI, which will be involved in the analysis of BER performance in Section 3.

*P*, i.e.,where

_{r}*E*(∙) represents the mean value and

*Pr*

_{j}is the received power at position

*j*, which is described by

## 3. BER performance under 4 cornered-LED lamps and 12 circled-LED lamps arrangement

**85**(2), 265–298 (1997). [CrossRef]

### 3.1 100-Mbit/s bipolar OOK signal

*T*is 10 ns ( = 1/100M).

*k*received bits are denoted by

*n*is the additive white Gaussian noise (AWGN) with power spectral density of

*N*

_{0}/2. Then, the conditional error probability when the present received bit is ‘1’, i.e., amplitude is

*k*received bits that

*k*received bits could either be ‘1’ or ‘0’. Note that bit ‘0’ is mapped to ‘-1’ for bipolar OOK signal.

*k*received bits occurs. For example, when all the previous

*k*received bits and present received bit are ‘1’, the conditional error probability in (9) is

^{−4}, the total LED power is 6.2 W without applying ZF equalization; while the total LED power reduces to 3.0 W after applying ZF equalization. Therefore, ZF equalization provides 3.2-dB ( = 10*log

_{10}(6.2/3.0)) power reduction. In addition, the BER performance with ZF equalization (red curve) is almost the same as that without ISI (blue curve), i.e., only the present received bit

^{−3}when forward-error correction (FEC) is applied [15

15. R. Essiambre, G. Kramer, P. Winzer, G. Foschini, and B. Goebel, “Capacity limits of optical fiber networks,” J. Lightwave Technol. **28**(4), 662–701 (2010). [CrossRef]

### 3.2 200-Mbit/s bipolar OOK signal

^{−4}, a total LED power of 23.9 W is required without applying ZF equalization; while the power is reduced to 6.9 W when ZF equalization is applied. Therefore, ZF equalization provides 5.4-dB ( = 10*log

_{10}(23.9/6.9)) power reduction. The BER performance of 200-Mbit/s bipolar OOK signal without applying ZF equalization is much worse than that of 100-Mbit/s bipolar OOK signal. Because on the one hand the ISI is more severe, on the other hand the power of noise is determined by the data rate [5

**50**(1), 100–107 (2004). [CrossRef]

## 4. Channel capacity under 4 cornered-LEDs and 12 circled-LEDs arrangement

12. I. Neokosmidis, T. Kamalakis, J. Walewski, B. Inan, and T. Sphicopoulos, “Impact of nonlinear LED transfer function on discrete multitone modulation: analytical approach,” J. Lightwave Technol. **27**(22), 4970–4978 (2009). [CrossRef]

*x*is the discrete-input symbol in the set of

*X*,

*y*, and

*y*when the input symbol is

*x*. For bipolar OOK signal,

## 5. Conclusion

^{−4}. In addition, the maximum improvements of channel capacity by ZF equalization are 0.17 bits/symbol and 0.16 bits/symbol for 100-Mbit/s and 200-Mbit/s bipolar OOK signal, respectively. The BER performance and channel capacity after applying ZF equalization are very close to that of the channel without ISI. Therefore, the new LED lamp arrangement combined with time domain ZF equalization provide similar communication qualities to all users at different locations in a room.

## Acknowledgment

## References and links

1. | S. Hann, J.-H. Kim, S.-Y. Jung, and C.-S. Park, “White LED ceiling lights positioning systems for optical wireless indoor applications,” Proc. ECOC, 1–3 (2010). |

2. | H. Elgala, R. Mesleh, H. Haas, and B. Pricope, “OFDM visible light wireless communication based on white LEDs,” Proc. VTC, 2185–2189 (2007). |

3. | O. Bouchet, P. Porcon, M. Wolf, L. Grobe, J. W. Walewski, S. Nerreter, K. Langer, L. Fernandez, J. Vucic, T. Kamalakis, G. Ntogari, and E. Gueutier, “Visible-light communication system enabling 73Mb/s data streaming,” GLOBECOM Workshops , 1042–1046 (2010). [CrossRef] |

4. | K. Langer, J. Vucic, C. Kottke, L. Fernandez, K. Habe, A. Paraskevopoulos, M. Wendl, and V. Markov, “Exploring the potentials of optical-wireless communication using white LEDs,”in 13 |

5. | T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron. |

6. | L. Zeng, D. O’Brien, H. Le-Minh, K. Lee, D. Jung, and Y. Oh, “Improvement of data rate by using equalization in an indoor visible light communication system,” in |

7. | J. M. Kahn and J. R. Barry, “Wireless infrared communications,” Proc. IEEE |

8. | M. Zhang, Y. Zhang, X. Yuan, and J. Zhang, “Mathematic models for a ray tracing method and its applications in wireless optical communications,” Opt. Express |

9. | Z. Wang, C. Yu, W-D. Zhong, and J. Chen, “A novel LED arrangement to reduce SNR fluctuation for multi-user in visible light communication systems,” accepted by |

10. | J. Proakis, |

11. | A. Goldsmith, |

12. | I. Neokosmidis, T. Kamalakis, J. Walewski, B. Inan, and T. Sphicopoulos, “Impact of nonlinear LED transfer function on discrete multitone modulation: analytical approach,” J. Lightwave Technol. |

13. | |

14. | |

15. | R. Essiambre, G. Kramer, P. Winzer, G. Foschini, and B. Goebel, “Capacity limits of optical fiber networks,” J. Lightwave Technol. |

**OCIS Codes**

(060.4080) Fiber optics and optical communications : Modulation

(060.4510) Fiber optics and optical communications : Optical communications

(200.4560) Optics in computing : Optical data processing

(230.3670) Optical devices : Light-emitting diodes

**ToC Category:**

Fiber Optics and Optical Communications

**History**

Original Manuscript: October 18, 2011

Revised Manuscript: December 29, 2011

Manuscript Accepted: January 18, 2012

Published: February 9, 2012

**Citation**

Zixiong Wang, Changyuan Yu, Wen-De Zhong, Jian Chen, and Wei Chen, "Performance of a novel LED lamp arrangement to reduce SNR fluctuation for multi-user visible light communication systems," Opt. Express **20**, 4564-4573 (2012)

http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-4-4564

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### References

- S. Hann, J.-H. Kim, S.-Y. Jung, and C.-S. Park, “White LED ceiling lights positioning systems for optical wireless indoor applications,” Proc. ECOC, 1–3 (2010).
- H. Elgala, R. Mesleh, H. Haas, and B. Pricope, “OFDM visible light wireless communication based on white LEDs,” Proc. VTC, 2185–2189 (2007).
- O. Bouchet, P. Porcon, M. Wolf, L. Grobe, J. W. Walewski, S. Nerreter, K. Langer, L. Fernandez, J. Vucic, T. Kamalakis, G. Ntogari, and E. Gueutier, “Visible-light communication system enabling 73Mb/s data streaming,” GLOBECOM Workshops, 1042–1046 (2010). [CrossRef]
- K. Langer, J. Vucic, C. Kottke, L. Fernandez, K. Habe, A. Paraskevopoulos, M. Wendl, and V. Markov, “Exploring the potentials of optical-wireless communication using white LEDs,”in 13th Annual Conference on Transparent Optical Networks (ICTON), 1–5 (2011).
- T. Komine and M. Nakagawa, “Fundamental analysis for visible-light communication system using LED lights,” IEEE Trans. Consum. Electron.50(1), 100–107 (2004). [CrossRef]
- L. Zeng, D. O’Brien, H. Le-Minh, K. Lee, D. Jung, and Y. Oh, “Improvement of data rate by using equalization in an indoor visible light communication system,” in International Conference on Circuits and Systems for Communications, 678–682 (2008).
- J. M. Kahn and J. R. Barry, “Wireless infrared communications,” Proc. IEEE85(2), 265–298 (1997). [CrossRef]
- M. Zhang, Y. Zhang, X. Yuan, and J. Zhang, “Mathematic models for a ray tracing method and its applications in wireless optical communications,” Opt. Express18(17), 18431–18437 (2010). [CrossRef] [PubMed]
- Z. Wang, C. Yu, W-D. Zhong, and J. Chen, “A novel LED arrangement to reduce SNR fluctuation for multi-user in visible light communication systems,” accepted by International Conference on Information, Communication and Signal Processing, (2011).
- J. Proakis, Digital Communications (McGraw-Hill, 2008).
- A. Goldsmith, Wireless Communications (Cambridge University, 2005).
- I. Neokosmidis, T. Kamalakis, J. Walewski, B. Inan, and T. Sphicopoulos, “Impact of nonlinear LED transfer function on discrete multitone modulation: analytical approach,” J. Lightwave Technol.27(22), 4970–4978 (2009). [CrossRef]
- http://en.wikipedia.org/wiki/Lumen_(unit)
- http://en.wikipedia.org/wiki/Illuminance
- R. Essiambre, G. Kramer, P. Winzer, G. Foschini, and B. Goebel, “Capacity limits of optical fiber networks,” J. Lightwave Technol.28(4), 662–701 (2010). [CrossRef]

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