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A Novel VLC Attocell Network Structure Using Superimposed Optical-OFDM
... The large variation of the SNR in a room can significantly reduce the overall attocell performance as studied in [16]. This large SNR difference is caused not only because of distance between the VLC-AP and the UD, but also due to non-normal incidence of the light from the AP to the device (the effect of NLoS). ...
Visible Light Communication (IEEE 802.15.7) implements a centralized topology using a visible-light personal network coordinator (VPNC) for network access and data sharing. A VPNC is a user-device (UD) that is dynamically selected based on several parameters ranking its ability as the most capable device in the attocell network. Theoretical performance bounds of attocell networks based on the use of a coordinator have not been significantly explored in the literature. We investigate how various UD capabilities such as device lifetime, network stability, optical power receiving ability and coverage area to accommodate the maximum possible number of associated devices, can contribute towards the enhancement of the IEEE Std 802.15.7 VPNC selection criteria, and develop an enhanced process with new information elements (IEs) added to the VPNC selection criteria. The selection process is extended to use a greedy approach. Simulation results, supported by theoretical modelling, verify a 61% reduction in VPNC handovers, a 30% improved throughput and up to 40% reduction in power consumption when compared with the VPAN (Visible-light Personal Area Network) standard. The proposed enhancement features backward compatibility to the current standard.
... A coordination of multiple VLC attocells is performed through power line communication (PLC). Other examples include the works by H. Kazemi et al. [21], H. Alshaer et al. [22] or Z. Li et al. [23]. They all demonstrated the networking of multiple attocells using novel methods with various advantages. ...
Multi-band carrierless amplitude and phase modulation and subcarrier multiplexing (SCM) are combined to produce a novel multi-users access scheme for visible light communications (VLC). To demonstrate this scheme, an experimental and realistic scenario is set-up by using a low-cost commercial office white light-emitting diode (LED) downlight. Furthermore, subcarrier spacings are added to reduce the inter-channel interferences and the parameters of the pulse shaping filters are optimized. The distance between the transmitter and the receiver is fixed at 2.15 m. After the optimization, the experiment setup achieves a spectral efficiency of 5.08 b/s/Hz after subcarrier spacing and with very light post-processing. A total of 20 users can be provided with the multi-users access scheme with a sum data rate of 162.5 Mb/s. The receiving attocell is measured at 4.56 m
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. To the best of our knowledge, the resulting work presents the highest range, and one of the highest spectral efficiencies for a phosphorous white LED (ph-LED)-based VLC system, thanks to subcarrier spacing. With SCM, it is also the first ph-LED-based VLC multi-users system.
In this letter, we present a novel hybrid intensity modulation and direct detection communication system, which integrates asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and on-off keying (OOK) modulation schemes. First, the negative ACO-OFDM is proposed based on the conventional ACO-OFDM system to accommodate the on case with direct current in the OOK modulation, while the ACO-OFDM can match the off case in the OOK modulation. Therefore, the novel hybrid system combines the ACO-OFDM and OOK modulation schemes, while the signals can be recovered at the receiver to support the different qualities of service with high spectral efficiency and can be adapted to various receivers with different complexities. Simulation results are reported for the visible light channel and show that both the ACO-OFDM and OOK signals can be well recovered.
In this paper, an indoor visible light communication (VLC) cellular network, referred to as an optical attocell network, is analysed at system level. A line-of-sight (LOS) ray-tracing model is used to characterise the light propagation and its effect on the performance of an intensity modulation (IM) and direct detection (DD) communication system. Orthogonal frequency division multiple access (OFDMA) based on direct-current optical orthogonal frequency division multiplexing (DCO-OFDM) is used as a multi-user access scheme. The signal-to-interference-plus-noise ratio (SINR) for a user with a random location in an optical attocell is studied. An analytical approach to calculate the statistics of the SINR is presented and verified by Monte Carlo simulations. Moreover, average spectral efficiency is also studied in order to estimate the downlink wireless capacity of the optical attocell network. The spectral efficiency of the system has been found to be strongly dependent on the radius of an optical attocell and on the half-power semi-angle of the light transmission profile. Guidelines for the configuration of the relevant attocell parameters are provided. An optical attocell with an average spectral efficiency of 5.9 bits/s/Hz is demonstrated for an appropriate set of attocell parameters.
In this paper a fractional frequency reuse (FFR) technique is considered in a direct-current optical orthogonal frequency-division multiplexing-based optical attocell network. An optical attocell network is proposed as a special type of visible light communication system that has the complete function of a cellular network. The cellular network is composed of many cells of extremely small size - the optical attocells. Two FFR schemes, strict fractional frequency reuse and soft frequency reuse, are considered. The signal-to-interference-plus-noise ratio (SINR) statistics and the spectral efficiency of the optical cellular system with FFR are analyzed. The performance of the systems with full frequency reuse and FFR is evaluated and compared. The results show that the FFR scheme can effectively achieve interference mitigation in an optical attocell network. The cell edge user SINR and spectral efficiency are significantly improved. Additionally, FFR provides improvements in average spectral efficiency. The effects of important parameters such as cell radius are also studied.
The European second generation digital video broadcasting standard introduces a P1 symbol. This P1 symbol facilitates the coarse synchronization and carries 7-bit transmission parameter signaling (TPS), including the fast Fourier transform size, single-input/single-output and multiple-input/single-output transmission modes, etc. However, this P1 symbol suffers from obvious performance loss over fading channels. In this paper, an improved preamble scheme is proposed, where a pair of optimal m sequences are inserted into the frequency domain. One sequence is used for carrier frequency offset (CFO) estimation, and the other carries TPS to inform the receiver about the transmission configuration parameters. Compared with the conventional preamble scheme, the proposed preamble improves CFO estimation performance and the signaling capacity. Meanwhile, without additional overhead, the proposed scheme exploits more active pilots than the conventional schemes. In this way, it can facilitate the channel estimation, improve the frame synchronization accuracy as well as enhance its robustness to frequency selective fading channels.
Visible light communication (VLC) using the light-emitting diode (LED) will become an appealing alternative to the radio frequency communication technology for indoor wireless broadband broadcasting. However, the LED lamps should access to the backbone information network and this requirement is not easily satisfied. Power line communication (PLC) systems utilize the ubiquitous power line network to power the LED lamps while serving as the backbone network for the VLC systems naturally. In this paper, we propose a novel and cost-effective indoor broadband broadcasting system based on the deep integration of PLC and VLC. The proposed scheme significantly reduces the complexity of the VLC network protocol, and requires much less modification to the current infrastructure, while providing better signal coverage. A two-lamp network demo is implemented and the performance evaluation for the proposed scheme is carried out in the laboratory. The proposed scheme is an appealing solution for the indoor family broadcasting, and could be well extended to the scenarios including the hospitals, shopping malls, stadiums, music halls, and etc.
Inter-cell interference is the critical issue not only in cellular systems but also in visible light communication (VLC) systems. In this paper, an inter-cell interference mitigation using soft frequency reuse (SFR) for VLC is presented. Our proposed scheme aims to decrease inter-cell interference and get higher signal-to interference-and-noise ratio (SINR) to all users in the cell range. To differentiate with cellular system, which is used power to divide the range of cell into cell-center and cell-edge, we use two fields of view (FOVs) to divide illumination cell into cell-center and cell-edge. We show bit error ratio (BER) and SINR in our simulation for different FOVs. Simulation results show that the proposed scheme can reduce the inter-cell interference depended on the cell-center FOV of LEDs.
We examine systems of fixed-channel reuse for base stations in an
indoor infrared wireless communication system. The following techniques
are compared: time-division multiple access (TDMA) using on-off keying
(OOK) or pulse-position modulation (PPM); frequency-division multiple
access (FDMA) using binary phase-shift keying (BPSK) or quadrature
phase-shift keying (QPSK); code-division multiple access (CDMA) using
OOK with direct-sequence spreading by m-sequences or optical orthogonal
codes (OOCs). We define a parameter γ, which equals the
signal-to-noise ratio (SNR) for unit optical path gain and is
proportional to the square of the transmitted average optical power.
Using measured pathloss data, it is found that in a system using
hexagonal cells and a reuse factor of three, for cell radii above 3 m,
TDMA with OOK or 2-PPM, and CDMA using OOCs all require approximately
the same γ to achieve a worst-case bit-error rate (BER) of
10<sup>-9</sup> within a cell. Using TDMA with 4-PPM results in a 6-dB
decrease in the required value of γ. CDMA using m-sequences
requires an increase in γ of 5 dB over TDMA using OOK, and FDMA
with BPSK requires an increase of 12 dB. For a given reuse factor N in
the noise-limited regime, the required value of γ decreases in
inverse proportion to N<sup>2</sup> for TDMA schemes and inversely with
N for FDMA and CDMA schemes. For cell radii below 3 m, cochannel
interference dominates the systems using TDMA, FDMA, and CDMA with an
OOC, resulting in an irreducible BER above 10<sup>-9</sup> at cell radii
below 1.5 m. Only CDMA with m-sequences does not develop an irreducible
BER, making it the only choice for cell radii below 1.5 m
In this paper, three forms of orthogonal frequency division multiplexing (OFDM) designed for intensity modulated/direct detection (IM/DD) optical systems are compared. These are asymmetrically clipped optical OFDM (ACO-OFDM), DC biased optical OFDM (DCO-OFDM) and asymmetrically clipped DC biased optical OFDM (ADO-OFDM). ADO-OFDM is a new technique that combines aspects of ACO-OFDM and DCO-OFDM by simultaneously transmitting ACO-OFDM on the odd subcarriers and DCO-OFDM on the even subcarriers. The odd subcarriers are demodulated as in a conventional ACO-OFDM receiver and the even subcarriers are demodulated using a form of interference cancellation. ADO-OFDM is shown to be more optically power efficient than conventional ACO-OFDM and DCO-OFDM, for some bit rate/normalized bandwidths. It is also shown that by varying the proportion of optical power on the ACO-OFDM component, the DC bias level of DCO-OFDM and the constellations sent on the odd and even subcarriers, the optical power efficiency of ADO-OFDM can be changed.
It is necessary in visible light communication where different information from adjacent cells is distinguishable without inter-cell interference for indoor localization-based services and positioning systems. In order to mitigate inter-cell interference, a carrier allocation- visible light communication system, adopting various carriers among the system's respective cells, is suggested. The effects of inter-cell interference for a single channel and the proposed systems are investigated by experimentation with simultaneous transmissions of QPSK signals.
In this paper, we present a new form of orthogonal frequency division multiplexing (OFDM) for intensity modulated direct detection (IM/DD) systems. This new form of OFDM uses asymmetrically clipped optical OFDM (ACO-OFDM) on the odd frequency subcarriers and DC biased optical OFDM (DCO-OFDM) on the even subcarriers. By using a form of interference cancellation both the ACO-OFDM and the DCO-OFDM signals can be recovered at the receiver. It is shown that the DCO-OFDM component causes no interference on the odd frequency subcarriers so the receiver processing for the ACO-OFDM signal is identical to a conventional ACO-OFDM system. The ACO-OFDM signal causes clipping noise which falls on the even subcarriers. However, this interference can be estimated and cancelled at the receiver. The cancellation process results in a 3 dB noise penalty in the DCO-OFDM component. Simulation results are presented for an additive white Gaussian noise channel and it is shown that the new technique can achieve better optical power performance than the conventional schemes.
A new technique for using orthogonal frequency division multiplexing (OFDM) in optical systems is presented. Clipped OFDM is derived from a bipolar OFDM waveform by setting the negative values to zero. It has an optical efficiency 8 dB better than DC biased OFDM. If only the odd OFDM subcarriers are modulated, the clipping noise is orthogonal to the wanted signal.
White LED offers advantageous properties such as high brightness, reliability, lower power consumption and long lifetime. White LEDs are expected to serve in the next generation of lamps. An indoor visible-light communication system utilizing white LED lights has been proposed from our laboratory. In the proposed system, these devices are used not only for illuminating rooms but also for an optical wireless communication system. Generally, plural lights are installed in our room. So, their optical path difference must be considered. In this paper, we discuss about the influence of interference and reflection. Based on numerical analyses, we show that the system is expected to be the indoor communication of the next generation.
The use of infrared radiation as a medium for high-speed
short-range wireless digital communication is discussed. Available
infrared links and local-area networks are described. Advantages and
drawbacks of the infrared medium are compared to those of radio and
microwave media. The physical characteristics of infrared channels using
intensity modulation with direct detection (IM/DD) are presented
including path losses and multipath responses. Natural and artificial
ambient infrared noise sources are characterized. Strategies for designs
of transmitter and receivers that maximize link signal-to-noise ratio
(SNR) are described. Several modification formats are discussed in
detail, including on-off keying (OOK) pulse-position modulation (PPM),
and subcarrier modulation. The performance of these techniques in the
presence of multipath distortion is quantified. Techniques for
multiplexing the transmissions of different users are reviewed. The
performance of an experimental 50-Mb/s on-off-keyed diffuse infrared
link is described
this paper, unless otherwise noted, "infrared" refers to the near-infrared band between about 780 nm and 950 nm