1. Based on Visible Light Communication
Novel Location Awareness Technique for Indoor LBS
Based on Visible Light Communication
Yoon Hyun Kim1, In Hwan Park1, Jin Young Kim1
1 Kwanwoon University, Department of Electronics Convergence Engineering, Wolgye-Dong, Nowon-Gu, Seoul, Korea.
1{yoonhyun, inhwan,
Abstract. In this paper, we propose and analyze a novel location awareness technique for an indoor LBS (location based service) based on VLC (visible light communication). As an indoor LBS technique, the VLC is employed due to its many advantageous features for location awareness. The proposed TDoA (time difference of arrival) algorithm based on VLC can improve positioning accuracy by optimizing estimated error distance which is varied in proportion to receiver¶s tilt angle. The performance of the proposed system is evaluated in terms of bit error rate and location awareness error. The results of the paper can be applicable to various LBS applications requiring high accuracy in the indoor environment such as healthcare and M2M (machine-to-machine) communication systems.
Keywords: VLC, LBS, TDOA, Location Awareness
1 Introduction
The LBS (location based service) is able to help to detect a location of people or things through portable equipment based on wireless communication network. In LBS field, GPS (global positioning system) has played a core role in locating vehicles and pedestrians. When they are in indoor places, it is not always available to locate their positions due to signal degradation through NLOS (non line of sight) links. Therefore, it is highly necessary to investigate novel location awareness scheme to cover shadow regions in indoor environments.
For indoor wireless LBS, various indoor LBS techniques have been proposed and analyzed [1-2]. They include WLAN (wireless local area network), UWB (ultra wide band), IR (infra red) and RFID (radio frequency identification), etc. In LBS techniques, one of the most critical points is how accurately estimate the position of a user. In case of GPS, it has a disadvantage of discontinuity in shadow regions such as forest, indoor, and the downtown [3]. Especially, GPS can arise some problems by increasing positioning error with conventional RF communication solution due to NLOS property. To achieve high precision (millimeter or even sub-millimeter) in indoor environments, time difference information should be accurate to nano-second or pico-second resolution. However, their accuracy has been limited to certain level with the conventional RF-based LBS solutions. Therefore, for high precision
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2. 2 Proposed Location Awareness Algorithms Based on VLC
positioning in indoor environment, novel location awareness scheme is highly required for seamless LBS with existing infrastructure.
In this paper, a novel indoor positioning awareness technique based on VLC (visible light communication) is proposed and analyzed for high accuracy positioning and new LBS service paradigms. The VLC is interpreted as a convergence communication technology which is not only used as a lighting device, but also as communication device [4-6]. It is a kind of indoor optical wireless communication that uses 'visible light' ray as communication medium. The performance of the proposed system is evaluated in terms of bit error rate and location awareness error. The indoor location architecture is demonstrated using TDoA (time difference of arrival) algorithm. When the proposed system is employed for indoor LBS, it is expected to have better positioning accuracy than other RF LBS schemes. Also, we suggest promising applications of the proposed LBS technique.
2 Proposed Location Awareness Algorithms Based on VLC
2.1 TDoA Alogorithm Based on VLC
Fig. 1. Block diagram of TDoA algorithm based on VLC
Fig. 2 shows a block diagram of the proposed LBS model based on VLC. From Fig. 1, the difference of distance between tags and mobiles forms a hyperbola given by
d1d2
( x x
1 m
) ± ( y y )
1 m 2 2
, (1 a) ( x2 xm
)2 ± (y 2 ym )2 ,
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3. ~ ~ y ~ y 'd d ' t ij d1d3 (x ~ x ) (y y ) (1 b) , ( x x ) ~ ( y ~ y )2 2
(1 b) 2 ,
( x x
3 ~ m
) ~ ( y ~ y )
3 m 2
d ~ d
1 j
(x ~ x ) ~ ( y ~ y ) 2
2 (1c)
( x x ) 2 2
j m j m
) (
~ ~ y ~ y .
Then, the difference of distance between tags and mobiles can be given by
'd d
ij i
d j
(xi xm )2 + (yi ym )2
, (2)
(x x
j m
) ~ ( y ~ y ) 2 2 c
' t ij
where 'd ij is the difference of distances, c is speed of light, 'tij is the difference
of time and xÖ is the location of the mobile device.
For estimation of user location, nonlinear least square algorithm is employed and given by
K-1 K
F(x) ¦¦f ij x ,
2 ( ) (3)
i 1 j i+1
where fij (W) c ˜ 'tij ~ ' d ij . Then the estimate of the user location is given by
x Ö arg min F(x) . (4)
2.2 Location Awareness Algorithm using LED-ID
Fig. 2. Block diagram of the location determination algorithm using LED-ID.
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4. Fig. 2 shows a conceptual diagram of the proposed location awareness algorithm using LED-ID (LED-Identification) [7]. This technique uses the LOS property of VLC system and identifies each illumination device with IDs. The LED-ID system is based on smart IT convergence communication technology using visible light for green home networks. It has various kinds of advantages such as environment- friendliness, long life, high efficiency, easy control and security [3]. Between mobile devices equipped with VLC module, it can determine the location by mapping each illumination device ID into the mobile device IDs. Because the visible light cannot penetrate the wall, this system can be applicable to indoor LBS systems requiring higher security level.
3 Simulation Results
Table 1. Simulation parameters
Parameter Values
Modulation BPSK / OOK
FOV at a receiver 60[deg.]
Detector physical area of PD 1.0[cm2]
Gain of an optical filter 1
Refractive index of a lens at a PD 1.5
The receiver O/E (optical/electrical) 0.53[A/W]
conversion efficiency
Transmitted optical power 1[W]
Distance between tag and mobile 1m
Fig. 3. Location awareness error of the proposed algorithm
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5. Fig. 4. Cumulative distribution function of location awareness error of the proposed algorithm.
In the paper, the proposed LBS technique based on VLC system is simulated for indoor wireless environments. And the simulation parameters for the LBS based on VLC system are listed in Table 1.
The channel is assumed to be an indoor optical channel. IM-DD (intensity modulation - direct detection) scheme is employed for the optical signal detection. In order to verify the performance of proposed system, we evaluate BER (bit error rate) and location awareness error. Nonlinear least square algorithm is employed to estimate location of a user.
Fig. 3 shows location awareness error for the proposed algorithm. The average of location error is about 0.14 meter for the given parameter settings and standard deviation of it is 0.09 meter. Fig. 4 shows cumulative distribution function of location error. From the simulation results, it is confirmed that the proposed LBS technique can achieve high accuracy positioning in indoor wireless environments.
4 Conclusions
In this paper, we proposed and analyzed VLC-based LBS algorithm. From simulation results, it was confirmed that the proposed location awareness algorithms can be efficiently applicable in the shadow regions while maintaining high positioning accuracy. Therefore, the proposed LBS system based on VLC is expected to contribute to establish the home network, primarily, for healthcare and M2M communication systems. The LBS technique based on VLC can be interpreted as a kind of green convergence services offering various applications based on LED.
The LBS system based on VLC has some advantages features compared with RF- based LBS system when it is applied in indoor wireless environments. An integration of LBS platform has changed the traditional network structure of the indoor positioning and monitoring system by using VLC. And the VLC-based LBS solution
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6. constructs a new intelligent system with wider coverage, higher communication efficiency and better fault tolerance. Also, the VLC-based LBS platform allows different types of terminals to access and supports multiple communication interfaces including PLC, WLAN, etc. The proposed LBS algorithm can be applicable in many kinds of services and devices. The existing positioning infrastructures such as GPS and GIS (geographical information system) can be combined with the proposed VLC- based LBS system in order to cover the shadow regions. The primary positioning application for a user may be a map display navigation and turn-by-turn navigation based on GPS. Therefore, in indoor environment such as shadow regions, the novel location awareness technique can be efficiently applicable with high positioning accuracy compared with conventional technique based on RF system.
Acknowledgments
This work was, in part, supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MEST) (No ), and in part, supported by the MKE (The Ministry of Knowledge Economy), Korea, under the ITRC (Information Technology Research Center) support program supervised by the NIPA (National IT Industry Promotion Agency)" (NIPA-2012-(H )).
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