Exploiting the increasingly wide use of light emitting diodes (LEDs) lighting, in this paper we propose a reversed indoor positioning system (IPS) based on LED visible light communication (VLC) in order to improve indoor positioning accuracy. Unlike other VLC positioning systems, we employ two annular receivers with multi-photodiodes installed on the ceiling to locate the persons who carry LEDs. The basic idea is using multi-photodiodes to calculate the angle while using the received signal strength (RSS) method to calculate the distance. The experiment results show that the effective positioning range of the proposed system is 1.8 m when the distance between two receivers is 1.2 m. Moreover, a positioning error less than 0.2 m can be achieved under the condition that the radius of the PIN circle is between 0.16 m and 0.2 m, and the distance of the transmitter-receiver plane is less than 1.8 m, which will be effective in practice.

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We report a novel indoor positioning scheme based on MIMO LED VLC system applying space diversity receiver. The simulation results show that the BER performance can be significantly improved by using MIMO-MRC algorithm. IntroductionVisible light communication (VLC) is expected to provide multi-gigable bit mobile data transmission, and has been intensively studied in the reseach community [1][2]. A number of papers have described the use of LEDs for localization [3][4][5]. The performance variation at the receiver is one of important issues for VLC. In a typical lighting application a number of LEDs will be used to achieve the required intensity, and parallel transmission of data, with groups of sources transmitting independent data is an intuitively attractive approach. Such multiple-input-multipleoutput (MIMO) techniques are widely applied in the VLC positioning system [4][5][6][7]. Moreover, Multipath propagation is a key feature of VLC communication [8]. There are some interference between the positioning signals emitted by neighboring LEDs in the contemporary MIMO-VLC system [9]. In order to achieve highaccuracy positioning for VLC system, MIMO-maximum ratio combining (MRC) algorithm is a feasible option.In this paper, we proposed a novel indoor positioning scheme based on LED VLC system. In order to obtain more accurate positioning signals, the MIMO-MRC algorithm was used in the proposed system. 2×2 MIMO was used in this positioning system, and the MRC algorithm was used for merge the received positioning signals form two receivers. On the analogy of the conclusions, a plurality of LED emitter array can be improved in the positioning system. This paper is organized as follows. Section 2 introduces the principle and system setup. The simulation and results are presented and discussed in Section 3 before we conclude this paper in Section4. Principle and system setupThe schematic of VLC positioning system is shown in Fig.1 (a). In the transmitter, different positioning signals are loaded on the LEDs. Quadrature amplitude modulation (QAM) technique used in the positioning system would be helpful in which the desired waveform is modulated onto the instantaneous power of the carrier. On the other hand, QAM demodulation algorithm is the requirement proportional to the received data in receivers. The positioning signals are multiplied with parameters which represent the distribution of the illuminance. The positioning signal from LED1 is considered as valid signal and the signal from LED2 is presented as noise. Besides, in our channel model, we add two different channel noises, respectively. At the receiving end, we obtain the weighting sum of received signals using MRC algorithm, then, it demodulates the restoration of the original positioning signal.

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Peak-over-average power ratio (PAPR) control utilizing precoding technique based on square rootgeneralized raised cosine function is proposed and verified experimentally through a visible light communication system employing phosphor-based white light-emitting diodes for the first time. The simulation results show that the improved precoding matrix can further reduce PAPR by nearly 1 dB compared with existing precoding matrix based on square root raised cosine function and significantly achieve 3.5 dB improvement in contrast to original signals without precoding. The experimental result also proves that the bit error rate performance can be effectively improved by 1.62 dB at the same bandwidth and 0.76 dB at the same raw data rate in terms of quality factor when proposed precoding technique is applied, which clearly demonstrates its benefit and feasibility.