Wireless Communications with LEDs

Wireless Communications with LEDs

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Description: VISIBLE LIGHT COMMUNICATIONS - Adaptive Equalization System for Visible Light Wireless Communication Utilizing Multiple White LED Lighting Equipment. Efficient Resource Allocation for Rapid Link Recovery and Visibility in Visible-Light Local Area Networks. Experimental Evaluation of Video Transmission Through LED Illumination Devices.

 
Author: Toshihiko Komine (Fellow) | Visits: 2208 | Page Views: 3700
Domain:  High Tech Category: Displays Subcategory: LED 
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Contents:
VISIBLE LIGHT COMMUNICATIONS
R00922137 R00922112

OUTLINE
� Adaptive Equalization System for Visible Light Wireless Communication Utilizing Multiple White LED Lighting Equipment.
Toshihiko Komine,, Jun Hwan Lee, Shinichiro Haruyama, and Masao Nakagawa [IEEE Transactions on Wireless Communications, Vol. 8, No. 6, June 2009]

� Efficient Resource Allocation for Rapid Link Recovery and Visibility in Visible-Light Local Area Networks.
Woo-Chan Kim, Chi-Sung Bae, Soo-Yong Jeon, Sung-Yeop Pyun, and Dong-Ho Cho [IEEE Transactions on Consumer Electronics, Vol. 56, No. 2, May 2010]

� Experimental Evaluation of Video Transmission Through LED Illumination Devices.
J. Rufo, J. Rabadan, F. Delgado, C. Quintana, and R. Perez-Jimenez [IEEE Transactions on Consumer Electronics, Vol. 56, No. 3, August 2010]

2

Adaptive Equalization System for Visible Light Wireless Communication Utilizing

Multiple White LED Lighting Equipment
Toshihiko Komine, Jun Hwan Lee, Shinichiro Haruyama, and Masao Nakagawa

[IEEE Transactions on Wireless Communications, Vol. 8, No. 6, June 2009]

3

ADVANTAGES OF VLC
� The robustness against EM interference. � Safety for human eye. � Security against undesired network access. � Can be used in several areas where there are limitations to the use of RF signals.

4

INTRODUCTION
� We tend to install many lighting sources on a ceiling in order to illuminate the room as evenly as possible. � But the optical path difference between the multiple sources triggers intersymbol interference (ISI), which significantly degrades system performance. � This paper overcomes the ISI problem by proposing an adaptive equalization system.

5

ILLUMINANCE DISTRIBUTION BASED ON LIGHTING ENGINEERING
� The horizontal illuminance E =
=

� The LOS horizontal illuminance E0 =
� Higher order terms(n > 0) En =





-



C(1,4)

D(4,4)

5[M]

A(1,1) 5[M]

B(4,1)

6

AVERAGE RECEIVED OPTICAL POWER
� The average received optical power Pr =
=

� The LOS average received optical power Pr0 =

(0)

, H(0) = , > � Higher order terms(n > 0) Prn =
-



7

OPTICAL WIRELESS CHANNEL MODEL
� We define X(t) as the transmitted optical signal. X(t) = 0 or 1

� The optical wireless channel model used here is expressed as follows

Y(t) = RX(t) h(t) + N(t)
RR is the O/E convergence efficiency at photodiode. h(t)impulse response, here we define the impulse response as the sum of received signals from lighting sources and walls when an impulse is input to HUB in the ceiling. N(t)additive white Gaussian noise ( AWGN ).

8

PROPAGATION DELAY BY MULTIPLE LIGHTING EQUIPMENTS

9

PROPAGATION DELAY BY MULTIPLE LIGHTING EQUIPMENTS
� The root mean square (RMS) delay spread ( ) is a remarkably accurate predictor of ISI induced SNR penalty. � =
-

-

-







� =

- -

10

ADAPTIVE EQUALIZATION
� Decision Feedback Equalizer

The basic idea behind DFE is that once an information symbol has been detected and decided upon, the ISI that it induces on future symbols can be estimated and eliminated before detecting the subsequent symbols.

11

ADAPTIVE EQUALIZATION
� Decision Feedback Equalizer

k =

=0

- +

=1 -

Feedforward filter

Feedback filter

12

ADAPTIVE EQUALIZATION
� Least Mean Square Algorithm

� Here, we define the input signal to the equalizer as vector = [ -1 -2 ... - ]
� The weight vector can be written as = [0 1 2 ... ] � The error signal = -


� The mean square error | |2 = [ ]

13

ADAPTIVE EQUALIZATION
� Least Mean Square Algorithm
(n) = (n)

() = () - (n)
(n+1) = (n) + (n) (n)


nthe sequence of iterations Nthe number of delay stages in the equalizer the step size

14

BER PERFORMANCE

15

BER PERFORMANCE
� We define the outage area rate as the ratio of the area where BER is larger than 10-6 to the total service area.

16

TRAINING SEQUENCE INTERVAL

17

INFLUENCE OF SHADOWING

18

INFLUENCE OF SHADOWING
� Outage Call Duration Rate

C

D

A

B

the ratio of the total duration when the BER exceeds 10-6 to the total call duration.
� The mean density of pedestrians

is included a concept of time.
For example, five pedestrians exist during 5s per 100s each. Here, the floor size 5�5 2 . The mean density of pedestrians is (5[pedestrian]�5[s]/100[s]) = 0.01[-2 ] (5[m]�5[m])

19

CONCLUSION
� The DFE with LMS algorithm effectively mitigates the influence caused by ISI. � The system with adaptive equalization is robust against shadowing and could accommodate more calls.

20

Efficient Resource Allocation for Rapid Link Recovery
and Visibility in Visible-Light Local Area Networks
Woo-Chan Kim,Chi-Sung Bae,Soo-Yong Jeon,Sung-Yeop Pyun,Dong-Ho Cho [IEEE Transactions on Consumer Electronics, Vol. 56, No. 2, May 2010]

21

INTRODUCTION
� Rapid Link Recovery

Let a user know about link failure as quickly as possible
The link failure problem may be solved by realigning the transmission signal towards the receiver. � Visibility in Visible-Light Local Area Networks Three schemes for supporting visibility without reducing system performance in a visible-light local area network.

22

INTRODUCTION
In the new MAC protocol for VLC, we define three service modes � The VL (Visible-light Local Area Network) mode � The BI (Broadcast Information) mode � The PI (Peripheral Interface) mode

23

MAC PROTOCOL FOR THE VLAN
� The VLAN system is synchronous and time-slotted � The VLAN system supports both full and half duplex modes. Because the straightness of visible-light.

24

MAC PROTOCOL FOR THE VLAN
The first uplink slot is used as a contention slot (C-slot).

The C-slot consists of several mini-slots.
An MN that attempts initial access to an AP randomly selects a mini-slot and transmits signals at the mini-slot.

Since usage information for each mini-slot is included in the
FH, the MNs can make proper use of the mini-slot without confusion.

25

RAPID LINK RECOVERY SCHEME
Link failure � Temporary blockages

� Poor orientation
AP provides a rapid link recovery service in the case of link failure

26

VISIBILITY SUPPORTING SCHEME
In three case, visibility is necessary

� MN attempts an initial access
� To re-establish the VLC link, when the VLC link has become disconnected due to poor orientation � VLC link disconnected due to obstacles. Users cannot see the uplink signal if they use too few timeslots MN should transmit extra signals other than the data signal, "point-shot signals", which consists of a signal

"1" for visibility and contains no other information.

27

VISIBILITY SUPPORTING SCHEME

28

VISIBILITY SUPPORTING SCHEME

29

VISIBILITY SUPPORTING SCHEME

30

SIMULATION RESULTS
The performance of the rapid link recovery scheme:

Assumption
� 10 uplink slots � 20 mini-slots

� 3 to 5 MNs arrive simultaneously at a frequency ranging from every 10 seconds to every 2 minutes
� 10 ms frame length � 5 minutes average communication time

31

SIMULATION RESULTS
The performance of the rapid link recovery scheme:

Collision probability of the initial access

32

SIMULATION RESULTS
The performance of the rapid link recovery scheme:

Drop probability

33

SIMULATION RESULTS
The performance of the rapid link recovery scheme:

Channel utilization

34

SIMULATION RESULTS
Performance of the visibility supporting schemes

Assumption
� Reorientation rate at 1/60 � The link recovery time at 3 seconds

� MN stops data transmission if it recognizes 5 consecutive errors in the semi-reserved point-shot scheme.

35

SIMULATION RESULTS
Performance of the visibility supporting schemes

36

SIMULATION RESULTS
Performance of the visibility supporting schemes

37

CONCLUSION
� Rapid link recovery scheme increases the collision probability of an initial access. However, the increased collision probability does not reduce channel utilization or system throughput as shown in the results. � To support visibility, We conclude that the semi-reserved pointshot scheme represents the best approach.

38

Experimental Evaluation of Video Transmission Through LED Illumination Devices
J. Rufo, J. Rabadan, F. Delgado, C. Quintana, and R. Perez-Jimenez [IEEE Transactions on Consumer Electronics, Vol. 56, No. 3, August 2010]

39

GOAL
Describe the implementation of a prototype An optical wireless system based on visible white LED lamps, which allows a video broadcasting to reach a bit rate of 2 Mbps

40

SCENARIO

41

CONSTRAINT
� Should be able to transmit while maintaining the same optical emitted power, even when the lamp is off 4 state switch for the lamp off, off with data, on with data, on � The uplink channel for commands, for acknowledging the transmission, or for providing the network with the required measured parameters Low/medium speed infrared channels, with which visible ones do not interfere.

42

LEDS
Natural white light contains all the colours in visible light spectrum. In LED, a quasi-white light source Red/Green/Blue (RGB) Yellow-phosphor/Blue (YB) LEDs Low power consumption High illumination efficiency Low production cost. The narrow modulation bandwidth caused by the slow

temporal response of phosphor emission compared
with the blue LED raise and fall times

43

MODULATIONS
VLC use IM/DD for data transmission and reception

Provide Sufficient lighting
Data communication Work even when lamp is switched off

2 Modulation
Pulse Width Modulation(PWM) Pulse-Position Modulation (PPM) Because of its capability to avoid the effects of symbol interference produced by the phosphor LEDs

44

MODULATION TECHNIQUES
2 operating modes for data transmission

� LED lamps are turned off-emit "Positive" pulse
Use short light pulses �ideally under eye sensitivity�

� LED lamps are switch on-emit "Negative" pulse
Cutting the light flux during a short interval 85% optical power for the "turn on" mode 15% for the "turn off" one

45

MODULATION TECHNIQUES
Drawback

The necessity of a complex synchronism system to ensure correct detection
Use Constant Rate-Differential Pulse Position Modulation (CR-DPPM) Symbol information is contained in the distance between two adjacent pulses, so detection is achieved counting clock samples between rising edges

46

47

PROCESS
The video server can take a MPEG-TS (Transport Stream) codified video file and send the frames into UDP packets in constant bit rate mode (2 Mbps in this case). Emitter mode The FPGA extracts the payload and delivers the data to the VLC communications stage.

Reception mode The FPGA takes serial data from the optical receptor and rebuilds the UDP packets.
These packets are sent to the receiver computer by means of an Ethernet connection, where the video client collects the packets and reproduces the video.

48

OPTICAL TRANSCEIVER

49

TRANSMITTER
� The implemented scheme makes use of several gates, each of them driving a group of 5 parallel connected LEDs. � This configuration improves the current control and reduces the capacitive charge introduced by the LEDs

50

RECEIVER
� Two PIN photodiodes, with 15 MHz bandwidth, 0.45 A/W optical sensitivity at a 660 nm wavelength and an active area of 66 2 .

51

UPLINK
� The uplink implements a 115 kbps infrared link, at a wavelength of 950 nm. The driver scheme is similar to that used at the downlink

52

RESULT1
� To transmit compressed video MPEG-TS codified file with a MPEG2 video compression bit rate of 200 Kbps and 64 Kbps audio rate, using video streaming software.

53

RESULT1
� Transmitted several video fragments of 108 length

� Zero errors werefound on them
� Estimate that error probability should be below 10-8 on a 4 meters link in the previous conditions.

54

RESULT2
In two operative conditions:

� Absence or presence of artificial lighting.
� Using 30 second video segments

The average of lost frames
� Absence of artificial lighting:0.116% � Presence of artificial lighting :0.175%

55

RESULT3
Using a similar LED lamp emitting simultaneously but with different amplitudes, placed side by side with the VLC emitter

56

CONCLUSION
� It is now able to transmit encrypted video at a baud rate up to 2 Mb/s. The same structure allows audio or raw data transmission without loss of generality. � Link distance over 3 meters the received SNR is over 40 dB, with a bit error rate extremely low

57

CONCLUSION
Future work

� test other lamps in order to achieve real-time video transmission or even symmetrical 10 Mbps Ethernet transmission
Application

� Areas where there are limitations to the use of RF signals
(hospitals, industrial and nuclear facilities, etc.). � It can be used also for in-house applications when WiFi channels are saturated � Need interference-free (or secure) transmissions.

58

END
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