Using specific and adaptive arrangement of grid-type pilot in channel estimation for white-lightLED-based OFDM visible light communication system

doi:10.1016/j.optcom.2014.09.080

Optics Communications

Volume 338, 1 March 2015, Pages 7-10

https://doi.org/10.1016/j.optcom.2014.09.080 Get rights and content

Abstract

Orthogonal frequency division multiplexing (OFDM) is a promising candidate for light emitting diode (LED)-based optical wireless communication (OWC); however, precise channel estimation is required for synchronization and equalization. In this work, we study and discover that the channel response of the white-lightLED-based OWC was smooth and stable. Hence we propose and demonstrate using a specific and adaptive arrangement of grid-type pilot scheme to estimate the LED OWC channel response. Experimental results show that our scheme can achieve better transmission performance and with some transmission capacity enhancement when compared with the method using training-symbol scheme (also called block-type pilot scheme).

Introduction

Recently, Optical wireless communication (OWC) has attracted significant attention for providing broadband access connections to both fixed and mobile users in places where the deployment of optical fiber is difficult [1], [2], [3], [4], [5], [6]. Besides, white-light light emitting diode (LED) is gradually replacing the traditional lamps for lighting applications. The combination of the LED lamp with OWC can provide lighting and communication (visible light communication (VLC)) simultaneously [7], [8]. The LED-based OWC provides many transmission advantages, such as license free and electromagnetic-interference (EMI) free. It can be used in the radio-frequency (RF) forbidden areas, such as hospital and airplane. Hence, it is regarded as one of the promising access solutions in the future. In the literatures, besides, conventional non-return-to-zero (NRZ) modulation [9], [10], [11], several modulation schemes can be applied for the LED-based OWC [12], [13], [14], [15], [16], [17], [18], [19], [20], and they have their merits. For example, Ref. [12] proposed using superposed pulse amplitude modulation to improve the non-linearity response of the LED; and Ref. [13] proposed using Manchester coding to mitigate optical background noises; however, this scheme requires twice the modulation bandwidth. Pulse position modulation [14], [15], [16] can be used for LED-based VLC. Among these modulation schemes, orthogonal-frequency division multiplexing (OFDM) [19], [20] is a highly spectral efficient modulation scheme that is suitable for the LED-based OWC since the direct modulation bandwidth of the white-light LED is about 1 MHz [21]. Hence, by using spectral efficient OFDM modulation format, the data rate of white-light LED OWC can be enhanced. Besides, according to our previous studies, OFDM can also mitigate the background optical noises, such as that generated from fluorescent lamp and AC-LED [20]; as well as providing an adaptive scheme for maintaining the performance of the in-homewhite-LED [4]. Besides, we have also demonstrated a practical real-timewhite-lightphosphor-LED OWC system for video communication using OFDM format at a transmission distance of 2 m [21].

Although OFDM is a promising candidate for LED-based OWC, it can provide transmission advantages only if we have the precise channel estimation. The channel estimation can be achieved mainly by two schemes. The popular scheme is using training symbol (also called block-type pilot scheme). In our previous works, training symbol method is used for the channel estimation. The idea of training symbol is to use known subcarriers inserted in a symbol to estimate the channel response. Then the parameters obtained from the channel estimation are used at the receiver (Rx) for signal equalization [4], [20]. The other channel estimation scheme can by performed by using grid-type pilot scheme. Using grid-type pilot for channel estimation has been used for the RF communication [22]. In this work, we propose and demonstrate using a specific and adaptive arrangement of grid-type pilot to estimate the LED OWC channel response owing to the stable channel of LED. The arrangement of the gird-type pilot can be adaptively changed depends on different channel environments. Experimental results show that our scheme can achieve better transmission performance with some transmission capacity enhancement when compared with the method using training-symbol (block-type pilot), while the proposed scheme does not increase the system complexity much.

Section snippets

Proposed architecture and experiment

The two types of channel estimation schemes: training symbol and grid-type pilot are shown in Fig. 1(a) and (b) respectively. The training-symbol channel estimation (block-type pilot) is a typical method for OFDM OWC system to achieve precise synchronization and equalization. The basic ideal for training-symbol estimation is that we insert known subcarriers in one or more OFDM symbols and send from the transmitter (Tx) to the Rx. After the channel, the data change is analyzed at the Rx side;

Results and discussion

Fig. 2(a) and (b) shows the SNR of the proposed OWC transmission against different OFDM subcarriers at distance 40 cm and 60 cm respectively. We can observe that the response is stable but SNR is not enough to achieve FEC limit at high frequency domain. Hence, we adaptively switch-off some subcarriers at high frequencies. There are total 64 OFDM subcarriers occupying 8 MHz bandwidth. We purposely switch-off the direct-current (DC) (subcarrier #0) and 10 subcarriers with the highest frequency

Conclusion

OFDM is a promising candidate for LED-based OWC; however, precise channel estimation is required. In this work, we studied and discovered that the channel response of the white-lightLED-based OWC was smooth and stable. Hence we proposed and demonstrated using a specific and adaptive arrangement of grid-type pilot scheme to estimate the LED OWC channel response. Although similar estimation technique used in RF is applied, we evaluate and characterize using a specific and adaptive arrangement of

Acknowledgement

This work was supported by the Ministry of Science and Technology, Taiwan, ROC, MOST-103-2218-E-035-011-MY3, MOST-103-2221-E-009-030-MY3, MOST-101-2628-E-009-007-MY3, Aim for the Top University Plan, Taiwan, and Ministry of Education, Taiwan.

References (22)

D. Lee et al.
Visible light wireless communications based on predistorted OFDM,
Opt. Comm.
(2012)
P. Das et al.
Performance improvement of color space based VLC modulation schemes under color and intensity variation
Opt. Comm.
(2013)
C.W. Chow et al.
Adaptive scheme for maintaining the performance of the in-home white-LED visible light wireless communications using OFDM
Opt. Comm.
(2013)
K. Cuia et al.
Performance of indoor optical femtocell by visible light communication
Opt. Comm.
(2013)
C.–Y. Chen et al.
Bidirectional 16-QAM OFDM in-building network over SMF and free-space VLC transport
Opt. Lett.
(2013)
W.–Y. Lin et al.
10 m/500 Mbps WDM visible light communication systems
Opt. Express
(2012)
Z. Wang et al.
Performance of dimming control scheme in visible light communication system
Opt. Express
(2012)
Z. Wang et al.
Performance of a novel LED lamp arrangement to reduce SNR fluctuation for multi-user visible light communication systems
Opt. Express
(2012)
H. Le Minh et al.
100-Mb/s NRZ visible light communications using a postequalized white LED
IEEE Photon. Technol. Lett.
(2009)
Y.F. Liu et al.
Alternating-signal-biased system design and demonstration for visible light communication
IEEE Photon. J.
(2013)

Y.F. Liu et al.

Demonstration of bi-directional LED visible light communication using TDD traffic with mitigation of reflection interference

Opt. Express

(2012)

Cited by (20)

Blind channel estimation for DCO-OFDM based vehicular visible light communication
2023, Physical Communication
Blind channel estimation (CE) methods for OFDM based RF communication provide high-rate transmission by eliminating pilot overhead in conventional pilot-based methods, at the cost of lower accuracy. However, there is no work on the blind CE for OFDM based visible light communication (VLC) systems. In this paper, we propose a novel blind CE method for vehicular VLC with the goal of improving CE accuracy based on the exploitation of the channel statistics derived, by utilizing extensive amount of data collected for different communication angles, distances, and ambient light conditions. First, the normalized channel frequency response (CFR) of the V2LC channel is demonstrated to be invariant of inter-vehicular distance, relative transmitter/receiver zenith angle and ambient light. Then, this channel characteristic is exploited in the blind CE to improve its accuracy with two-step estimation of normalization factor. Extensive simulations at different vehicle speeds show that the proposed method outperforms the pilot-based and superimposed training-based CE methods in terms of spectral efficiency both for all modulation schemes and at all relative speeds. The proposed blind channel estimation (CE) method provides 9.77% increase in the spectral efficiency, compared to the second best method, superimposed training-based CE, at 20 dB signal-to-noise ratio (SNR) and 160 km/h relative speed, for 64-Quadrature Amplitude Modulation (QAM) Direct Current-Biased Optical Orthogonal Frequency Division Multiplexing (DCO-OFDM). Moreover, the real-time performance of the proposed blind CE is demonstrated for a realistic vehicle mobility scenario extracted from SUMO.
Adaptive least squares channel estimation for visible light communications based on tap detection
2020, Optics Communications
Citation Excerpt :
In comparison with RF scenarios, there has been limited considerations on channel estimation for VLC systems. The principles of conventional channel estimation algorithms, for example pilot-aided channel estimation algorithms, are applicable to VLC scenarios [12,13]. Some estimation algorithms for optical channels [14–16] have been developed, where maximum likelihood sequence detection (MLSD) [17] was adopted for mitigating inter-symbol interference (ISI).
Visible light communication (VLC) is one of the promising technologies for future wireless communications and has attracted increasing research interest in recent years. In this paper, we propose an adaptive least squares (LS) channel estimation algorithm for VLC systems using the direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM) scheme. The proposed algorithm is obtained by employing the tap detection that provides the maximum probability of correctly separating non-zero and zero-value channel taps, yielding significantly improved estimation performance. We prove that the Cramér–Rao lower bound of the proposed algorithm is lower than that of the conventional LS algorithm. Finally, numerical results demonstrate that the proposed algorithm achieves better performance in terms of the received constellation, mean squared error (MSE) and bit error rate (BER).
Pilot-based parametric channel estimation algorithm for DCO-OFDM-based visual light communications
2017, Optics Communications
Citation Excerpt :
To ensure stable and efficient transmissions of OFDM-based VLC systems, channel state information (CSI) must be estimated. One algorithm is exploiting the pilots which can be generated by block-type and scattered schemes [1,3,4]. Another algorithm is based on the preamble which is a kind of block-type pilot symbol.
Due to wide modulation bandwidth in optical communication, multipath channels may be non-sparse and deteriorate communication performance heavily. Traditional compressive sensing-based channel estimation algorithm cannot be employed in this kind of situation. In this paper, we propose a practical parametric channel estimation algorithm for orthogonal frequency division multiplexing (OFDM)-based visual light communication (VLC) systems based on modified zero correlation code (ZCC) pair that has the impulse-like correlation property. Simulation results show that the proposed algorithm achieves better performances than existing least squares (LS)-based algorithm in both bit error ratio (BER) and frequency response estimation.
Performance enhancement technique of visible light communications using passive photovoltaic cell
2017, Optics Communications
Citation Excerpt :
As the light emitting diode (LED) has a lifespan and electrical efficiency several times greater than traditional lighting sources, such as incandescent and fluorescent lamps, it is expected that the LED lamp market will continue to grow and eventually replace the traditional lighting market. Besides, LED can be used as the optical transmitter (Tx) for the visible light communication (VLC) [1–6]. Unlike laser based VLC systems [7–10], the LED based VLC can use the exiting illumination infrastructure to provide lighting and communication simultaneously.
The light emitting diode (LED) based visible light communication (VLC) system can provide lighting and communication simultaneously. It has attracted much attenuation recently. As the photovoltaic cell (also known as solar cell) is physically flexible, low cost, and easily available, it could be a good choice for the VLC receiver (Rx). Furthermore, besides acting as the VLC Rx, the solar cell can convert VLC signal into electricity for charging up the Rx devices. Hence, it could be a promising candidate for the future internet-of-thing (IoT) networks. However, using solar cell as VLC Rx is challenging, since the response of the solar cell is highly limited and it will limit the VLC data rate. In this work, we propose and demonstrate for the first time using pre-distortion Manchester coding (MC) signal to enhance the signal performance of solar cell Rx based VLC. The proposed scheme can significantly mitigate the slow response, as well as the direct-current (DC) wandering effect of the solar cell; hence 50 times increase in data rate can be experimentally achieved.
A Wheeled Robot Chain Control System for Underground Facilities Inspection Using Visible Light Communication and Solar Panel Receivers
2022, IEEE/ASME Transactions on Mechatronics
The Interplay between Block Design Theory and Channel Estimation in Visible Light System
2021, IEEE Transactions on Information Theory

View all citing articles on Scopus

View full text

Using specific and adaptive arrangement of grid-type pilot in channel estimation for white-lightLED-based OFDM visible light communication system

Abstract

Introduction

Section snippets

Proposed architecture and experiment

Results and discussion

Conclusion

Acknowledgement

Opt. Comm.

Opt. Comm.

Opt. Comm.

Performance of indoor optical femtocell by visible light communication

Opt. Comm.

Bidirectional 16-QAM OFDM in-building network over SMF and free-space VLC transport

Opt. Lett.

10 m/500 Mbps WDM visible light communication systems

Opt. Express

Performance of dimming control scheme in visible light communication system

Opt. Express

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

Opt. Express

100-Mb/s NRZ visible light communications using a postequalized white LED

IEEE Photon. Technol. Lett.

Alternating-signal-biased system design and demonstration for visible light communication

IEEE Photon. J.

Demonstration of bi-directional LED visible light communication using TDD traffic with mitigation of reflection interference

Opt. Express