Fast and Efficient Adaptation Techniques for Visible Light Communication Systems

Ahmed Taha Hussein; Mohammed T. Alresheedi; Jaafar M. H. Elmirghani

doi:10.1364/JOCN.8.000382

Journal of Optical Communications and Networking
Vol. 8,
Issue 6,
pp. 382-397
(2016)
•https://doi.org/10.1364/JOCN.8.000382

Fast and Efficient Adaptation Techniques for Visible Light Communication Systems

Ahmed Taha Hussein, Mohammed T. Alresheedi, and Jaafar M. H. Elmirghani

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Ahmed Taha Hussein, Mohammed T. Alresheedi, and Jaafar M. H. Elmirghani, "Fast and Efficient Adaptation Techniques for Visible Light Communication Systems," J. Opt. Commun. Netw. 8, 382-397 (2016)

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Abstract

Beam steering visible light communication (VLC) systems have been shown to offer performance enhancements over traditional VLC systems. However, an increase in the computational cost is incurred. In this paper, we introduce fast computer-generated holograms to speed up the adaptation process. The new, fast, and efficient fully adaptive VLC system can improve the receiver signal-to-noise ratio (SNR) and reduce the required time to estimate the position of the VLC receiver. It can also adapt to environmental changes, providing a robust link against signal blockage and shadowing. In addition, an angle diversity receiver and a delay adaptation technique are used to reduce the effect of intersymbol interference and multipath dispersion. Significant enhancements in the SNR with VLC channel bandwidths of more than 26 GHz are obtained, resulting in a compact impulse response and a VLC system that is able to achieve higher data rates (25 Gbps) with full mobility in the considered realistic indoor environment.

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Parameters	Configurations
Length	8 m
Width	4 m
Height	3 m
$ρ$ -ceiling	0.8 [18]
$ρ$ - $x z$ wall	0.8 [18]
$ρ$ - $y z$ wall	0.8 [18]
$ρ$ - $x z$ op-wall	0.8 [18]
$ρ$ - $y z$ op-wall	0.8 [18]
$ρ$ -floor	0.3 [18]
Bounces	1 2
Number of elements	32,000 2000
$d A$	$5 cm \times 5 cm$ $20 cm \times 20 cm$ [29,30]
Transmitters
Number of transmitters	8
Locations	(1,1,3), (1,3,3), (1,5,3),(1,7,3)
( $x, y, z$ )	(3,1,3), (3,3,3), (3,5,3), (3,7,3)
Elevation	90°
Azimuth	0°
Number of RGB-LDs in each transmitter unit	9 $(3 \times 3)$
Semi-angle at half power	70°
Center luminous intensity	162 cd [24]
Transmitted optical power of a RGB-LD	2 W [24]

	Inputs: $N = 8$ ; (Number of RGB-LD light units)
	$j = 3$ ; (Number of branches in ADR)
	$p (.)$ is a rectangular pulse over $[0, T b]$ , $T b = 1 / B$ ( $B$ is the bit rate).
1.	for $S = 1 ∶ j$ ;
2.	for $R = 1 ∶ N$ ;
3.	Calculate and sum the received powers within a time bin (0.01 ns duration)
4.	Produce the impulse response $h_{j} (t)$
5.	Calculate the pulse response $h_{j} (t) \otimes P (t - T b)$ and then calculate $(P S_{1} - P S_{0})$
6.	Compute ${SNR}_{j} = {(\frac{R (P_{S 1} - P_{S 0})}{σ_{t}})}^{2}$
7.	end for
8.	${SNR}_{N} = \max ({SNR}_{j})$
9.	end for
10.	${SNR}_{\max} = \max ({SNR}_{N})$
11.	Select RGB-LD unit that yields ${SNR}_{\max}$

	Inputs: $θ_{x}^{start} = - 70 °$ and $θ_{x}^{end} = 70 °$ (the lower and higher holograms scan ranges along the $x$ -axis).
	$θ_{y}^{start} = - 70 °$ and $θ_{y}^{end} = 70 °$ (the lower and higher holograms scan ranges along the $y$ -axis).
	$θ_{steps} = 26.56 °$ (initial value, step size 100 cm)
1.	for $i = 0 ∶ 26.56 ∶ 140$ ;
2.	for $l = 0 ∶ 26.56 ∶ 140$ ;
3.	$θ_{x} = i$ ; $θ_{y} = l$ ; (Transmission angles in $x$ - and $y$ -axes)
4.	Produce a hologram with a direction associated with $θ_{x}$ and $θ_{y}$ .
5.	for $S = 1 ∶ j$ ;
6.	Calculate and sum the received powers within a time bin (0.01 ns duration)
7.	Produce the impulse response $h_{j} (t)$
8.	Calculate the pulse response $h_{j} (t) \otimes P (t - T b)$ and then calculate $(P S_{1} - P S_{0})$
9.	Compute ${SNR}_{j} = {(\frac{R (P_{S 1} - P_{S 0})}{σ_{t}})}^{2}$ ;
10.	end for
11.	$SNR (i, l) = \max ({SNR}_{j})$ ;
12.	$detector (i, l) = find ({SNR}_{j}) == (\max ({SNR}_{j}))$ ;
13.	end for
14.	end for
15.	${SNR}_{\max} = \max SNR (i, l)$ ;
16.	[ $θ_{x - suboptimum}$ , $θ_{y - suboptimum}] = find (SNR (i, l)) == ({SNR}_{\max})$ ; (identify suboptimum hologram).
17.	If $\| θ_{x - suboptimum} \| \leq (\| θ_{x}^{end} \| - \| θ_{x}^{start} \|) / 2$ (reset new scan range in the $x$ -axis)
18.	$θ_{x}^{end} = θ_{x - suboptimum}$ ;
19.	Else
20.	$θ_{x}^{start} = θ_{x - suboptimum}$ ;
21.	end If
22.	If $\| θ_{y - suboptimum} \|$ $\| θ_{y}^{end} \| - \| θ_{y}^{start} \|) / 2$ (reset new scan range in the $y$ -axis)
23.	$θ_{y}^{end} = θ_{y - suboptimum}$ ;
24.	Else
25.	$θ_{y}^{start} = θ_{y - suboptimum}$ ;
26.	end If
27.	$θ_{x}^{optimum} = θ_{x - suboptimum}$ ; $θ_{y}^{optimum} = θ_{y - suboptimum}$ ; (identify optimum hologram).

1.	for $S = 1 ∶ j$ ;
2.	for $R = 1 ∶ N$ ;
3.	Compute the impulse response observed by the desired branch.
4.	$μ_{{NLD}_{S}} = \frac{Σ_{i} t_{i} P_{r i}^{2}}{Σ_{i} P_{r i}^{2}}$ ; (compute mean delay associated with each signal from each RGB-LD unit)
5.	end for
6.	end for
7.	$μ_{\max} = \max (μ_{{NLD}_{S}})$ ;
8.	for $R = 1 ∶ N$ ;
9.	$Δ t_N_{L D} = μ_{\max} - μ_{{NLD}_{S}}$ ; (Calculate the time delay)
10.	Compute the impulse response $h_{NLD} (t)$ observed by the desired branch.
11.	Introduce time delay as $h_{NLD} (t - Δ t_N_{LD})$ ; (shift the impulse response)
12.	end for
13.	Produce the optimized impulse response $h_{optimized} (t)$
14.	Calculate the pulse response $h_{optimized} (t) \otimes P (t - T b)$ and then calculate $(P S_{1} - P S_{0})$
15.	Compute the delay spread, 3 dB channel and SNR optimized.

	3 dB Channel Bandwidth [GHz]
	Receiver Locations Along the $y$ -Axis, $Y$ [m]
System	1	2	3	4	5	6	7
DAT ADR	8.7	8.3	8.7	8.3	8.7	8.3	8.7
Fully adaptive ADR	29.5	26	29.5	26	29.5	26	29.5

	BER
	Receiver Locations Along the $y$ -Axis, $y$ [m]
System	1	2	3	4
Room A–fully adaptive VLC	$1.6 \times 10^{- 9}$	$2.9 \times 10^{- 6}$	$1.6 \times 10^{- 9}$	$2.9 \times 10^{- 6}$
Room B–fully adaptive VLC	$4.4 \times 10^{- 9}$	$4.1 \times 10^{- 6}$	$4.4 \times 10^{- 9}$	$4.1 \times 10^{- 6}$

Abstract

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Figures (17)

Tables (7)

Equations (12)

Journal of Optical Communications and Networking