Adaptive WHTS-Assisted SDMA-OFDM Scheme for Fair Resource Allocation in Multi-User Visible Light Communications

Oswaldo González; Marcos F. Guerra-Medina; Inocencio R. Martín; Francisco Delgado; Rafael Pérez-Jiménez

doi:10.1364/JOCN.8.000427

Journal of Optical Communications and Networking
Vol. 8,
Issue 6,
pp. 427-440
(2016)
•https://doi.org/10.1364/JOCN.8.000427

Adaptive WHTS-Assisted SDMA-OFDM Scheme for Fair Resource Allocation in Multi-User Visible Light Communications

Oswaldo González, Marcos F. Guerra-Medina, Inocencio R. Martín, Francisco Delgado, and Rafael Pérez-Jiménez

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Oswaldo González, Marcos F. Guerra-Medina, Inocencio R. Martín, Francisco Delgado, and Rafael Pérez-Jiménez, "Adaptive WHTS-Assisted SDMA-OFDM Scheme for Fair Resource Allocation in Multi-User Visible Light Communications," J. Opt. Commun. Netw. 8, 427-440 (2016)

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Abstract

This paper proposes applying Walsh–Hadamard transform spreading (WHTS) in conjunction with space-division multiple access (SDMA) in an orthogonal frequency-division multiplexing (OFDM) system to provide enhanced multi-user downlink capability in visible light communication (VLC) scenarios. VLC environments are characterized by strong interference from the emissions of adjacent lamps. Thus, SDMA-OFDM schemes can be applied to enable multi-user capability while ensuring a highly efficient use of the limited available bandwidth. However, these SDMA-OFDM systems can only provide multiple access for a small number of users whenever there is enough channel diversity to separate the users’ information. This is the case, for example, when each single user is associated with a specific emitting lamp and angle-diversity receiving techniques are applied. However, to accommodate a greater number of users requires a user’s distribution in the frequency domain. In this sense, the proposed Walsh–Hadamard transform spreading scheme provides a fair assignment of the available subcarriers among the different users leading to an identical throughput and bit error rate (BER) for users allocated to the same emitting lamp. This BER is also controllable by means of an adaptive throughput mechanism. The numerical results show that the proposed adaptive WHTS-assisted SDMA-OFDM system in a full-user scenario presents a similar performance to that of an adaptive SDMA-OFDM system irrespective of the number of users per lamp, while providing enhanced multi-user capability. Finally, an adaptive algorithm for resource allocation is evaluated, demonstrating a high degree of satisfaction (regarding demanded data rates) when large numbers of users are simultaneously served.

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Parameter	Value
Room size ( $length \times width \times height$ ):	$7.5 m \times 5.5 m \times 3.5 m$
Number of LED arrays:	6 ( $3 \times 2$ )
Number of LEDs per array:	900 ( $30 \times 30$ )
Dimensions of each LED array:	$0.6 m \times 0.6 m$
Positions of LED arrays (central point) $(x, y, z)$ :	array 1: (1.50,1.50,3.50)
	array 2: (3.75,1.50,3.50)
	array 3: (6.00,1.50,3.50)
	array 4: (1.50,4.00,3.50)
	array 5: (3.75,4.00,3.50)
	array 6: (6.00,4.00,3.50)
LED Lambertian order ( $n$ ):	1
LED transmission bandwidth:	$\sim 15 MHz$
Receiver plane height:	0.75 m
Imaging lens f-number ( $f_{#}$ ):	1
Lens diameter ( $D$ ):	2 cm
Detector physical area ( $A$ ):	$36 {cm}^{2}$
Number of pixels or receiving channels ( $P$ ):	16 ( $4 \times 4$ )
Pixel physical area ( $A_{r}$ ):	$2.25 {cm}^{2}$

Parameter	Value
Total number of subcarriers ( $N$ ):	64
Number of information subcarriers ( $S_{I}$ ):	48
Available modulation modes:	(“no transmission,” BPSK, QPSK, 16-QAM, 64-QAM)
Maximum number of bits per subcarrier ( $b_{\max}$ ):	6 (64-QAM)
OFDM symbol period ( $T_{S}$ ):	4 μs
Cyclic prefix extension ( $N_{E}$ ):	8
Maximum aggregate throughput ( $R_{\max}$ ):	$432 Mbit / s$
Number of training sequences ( $N_{TS}$ ):	20

Parameter	Value
Number of lamps ( $L$ ):	6
WHT block size ( $K$ ):	4
Number of simultaneous users ( $U = L \times K$ ):	24
Relative average user’s throughput ( ${\bar{R}}_{u} / R_{u, \max}$ ):	{0.5, 0.8, 1.0}
Simulation time ( $t_{sim}$ )	1 s
Number of allocation periods ( $N_{A}$ ):	1000
Number of data symbols between allocation periods ( $N_{D}$ ):	250
Number of simulations per case ( $N_{R}$ ):	100
Target bit error rate ( $P_{e}$ ):	$10^{- 3}$

Parameter	Value
Room size ( $length \times width \times height$ ):	$7.5 m \times 5.5 m \times 3.5 m$
Number of LED arrays:	6 ( $3 \times 2$ )
Number of LEDs per array:	900 ( $30 \times 30$ )
Dimensions of each LED array:	$0.6 m \times 0.6 m$
Positions of LED arrays (central point) $(x, y, z)$ :	array 1: (1.50,1.50,3.50)
	array 2: (3.75,1.50,3.50)
	array 3: (6.00,1.50,3.50)
	array 4: (1.50,4.00,3.50)
	array 5: (3.75,4.00,3.50)
	array 6: (6.00,4.00,3.50)
LED Lambertian order ( $n$ ):	1
LED transmission bandwidth:	$\sim 15 MHz$
Receiver plane height:	0.75 m
Imaging lens f-number ( $f_{#}$ ):	1
Lens diameter ( $D$ ):	2 cm
Detector physical area ( $A$ ):	$36 {cm}^{2}$
Number of pixels or receiving channels ( $P$ ):	16 ( $4 \times 4$ )
Pixel physical area ( $A_{r}$ ):	$2.25 {cm}^{2}$

Parameter	Value
Total number of subcarriers ( $N$ ):	64
Number of information subcarriers ( $S_{I}$ ):	48
Available modulation modes:	(“no transmission,” BPSK, QPSK, 16-QAM, 64-QAM)
Maximum number of bits per subcarrier ( $b_{\max}$ ):	6 (64-QAM)
OFDM symbol period ( $T_{S}$ ):	4 μs
Cyclic prefix extension ( $N_{E}$ ):	8
Maximum aggregate throughput ( $R_{\max}$ ):	$432 Mbit / s$
Number of training sequences ( $N_{TS}$ ):	20

Abstract

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Equations (25)

Journal of Optical Communications and Networking