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The pilot-assisted peak-to-average power ratio (PAPR) reduction technique proposed for optical orthogonal frequency division multiplexing (OFDM) communication systems is evaluated empirically and theoretically in this letter. The PAPR reduction is achieved by rotating the phase of data symbols with $P$ iterations of randomly generated pilot symbol sequence. The results of our hardware implementation and analysis show a close agreement to that of computer simulations. In comparison with basic OFDM, where no PAPR reduction technique is implemented, experimental PAPR reduction gain of pilot-assisted OFDM at a complementary cumulative distribution function of $10^{-3}$ with $P=5$ is $\sim 2$ dB. This gain is $\sim 0.2$ dB less than that of analytical results. The experimental results also show that the pilot-assisted technique does not cause any significant deterioration of the bit error performance.

This paper describes the simulation results and hardware implementation of an inexpensive, low-complexity LED based indoor positioning system. Localization by multiple LEDs estimation model (MLEM) approximates position of a mobile receiver by the acquisition of positional information from LED transmitters. Multiple LED orientation can either be with or without overlap. Receivers in a no-overlap LED orientation experience only single access while multiple access receivers are designed for orientations with overlaps. Single and multiple access systems were developed and implemented by the use of low cost ATMEG 328 microcontroller. Since multiple LEDs transmit data at the same wavelength and are asynchronous, overlap in multiple access system causes interference. The possibility of this interference is reduced by packet based pulse duration multiplexing (PDM) and a low duty cycle transmission protocol. By the use of MLEM, root mean square error in position estimation is reduced to about 1 percent of the length an indoor location. Experimental results show that overlap increases positional accuracy over a wider coverage region and that the multiple access system allows for a more reliable positioning.

In this paper, we present a study of the combined use of pilot-assisted (PA) electrical PAPR reduction technique and O-OFDM utilising G light emitting diode (LED) groups. In comparison with basic O-OFDM with G = 16, simulation results show that PA technique is capable of reducing G to 3 in order to achieve the same PAPR of approximately 11 dB using P = 5 at complementary cumulative distribution function (CCDF) of 10−3. The PAPR reduction gain using PA technique is achieved with less hardware complexity, but at the expense of increased computational complexity at the transmitter without sacrificing the bit error rate (BER) performance of the system.

Spatial summation in optical orthogonal frequency division multiplexing (O-OFDM) provides opportunity of simultaneously transmitting narrowband visible light communications (VLC) signals using G light emitting diode (LED) groups. However, the number of transmit chains increases as the number of LED groups G increases. The limited dynamic range of these LEDs reinforces the need to reduce peak-to-average-power-ratio (PAPR) of O-OFDM signal in the VLC system. In this paper, we present study of the pilot-assisted (PA) PAPR reduction technique in O-OFDM using multiple LEDs. The PA technique is based on data symbol phase rotation with P iterations of pilot symbol to achieve PAPR reduction. Results show tradeoff between multiple LEDs hardware complexity and the PA technique to achieve desirable PAPR reduction. In comparison with basic O-OFDM with G = 12, simulation results show that PA technique is capable of reducing G by about half to achieve same PAPR of approximately 12 dB using P = 2 at a complementary cumulative distribution function (CCDF) of 10−3. Using the PA technique, further PAPR reduction can be achieved with the combination of increased P and G.

One of the evolved technologies which has the prospect of providing huge data rate is visible light communication (VLC). Use of optical orthogonal frequency-division multiplexing (OFDM) has been demonstrated as one of the viable schemes in achieving high data rate in VLC system. However, the limitation of optical OFDM still remains the high peak-to-average power ratio (PAPR) which results in signal distortion and increase in error rate. In this paper, we describe a technique that can mitigate high PAPR in optical OFDM using pilot symbol in the indoor VLC environment. The pilot assisted OFDM system gives 2.4 dB PAPR reduction for a 4-QAM. There is indication from the simulation results that not only can the technique reduce high PAPR but it also offers good bit error rate (BER) performance. For the BER performance of 64-QAM, the pilot symbol estimation error leads to about 0.6 dB degradation at BER of 10−3.