LED nonlinearity mitigation in LACO-OFDM optical communications based on adaptive predistortion and postdistortion techniques.

The preinstalled white light emitting diodes (WLEDs) inside buildings can be exploited as an optical source in visible light communications (VLC) motivated by high optical efficiency and low cost. One of the main challenges for VLC is LED nonlinear distortion, which has a detrimental effect on system performance. Estimation and compensation of the LED nonlinear behavior can be accomplished using predistortion or postdistortion techniques. Three compensation techniques are adopted to mitigate the effect of LED nonlinearity on layered asymmetrically clipped optical, orthogonal frequency division multiplexing. Their performance and efficiency are discussed and compared with the aid of error vector magnitude and bit error rate (BER) in an additive white Gaussian noise channel. The obtained results reveal that polynomial-based predistorters and postdistorters can overcome the LED nonlinear behavior with extra SNR of only 0.25 dB at BER of 10-3. Furthermore, the look-up-table-based predistorter can provide the same BER with lower SNR penalty than the previous two systems.

Exploring the effect of LED nonlinearity on the performance of layered ACO-OFDM.

Visible light communication (VLC) depends on light emitting diodes (LEDs) for data transmission. This is one of the strengths of VLC motivated by high optical efficiency and low cost. However, LEDs impose nonlinear effects on the transmitted signal and limit overall system performance, especially in the case of multicarrier modulation systems. This paper extends to the layered asymmetrically clipped optical, orthogonal frequency division multiplexing (LACO-OFDM) and investigates the impact of LED nonlinearity on system performance. The effect of the second-order nonlinear distortion in addition to the clipping noise is presented and analyzed at different power values assuming different strengths of nonlinearity. With a variable number of layers, the system performance is explored considering a nonlinear LED model. Finally, the impact of nonlinearity is investigated in the case of ACO-OFDM for the sake of comparison, bearing in mind that ACO-OFDM represents the first layer of LACO-OFDM.

An optimized design for motivated broadband LPDA antenna.

This paper presents a super wideband and high-gain log periodic dipole array (LPDA) antenna. The overall structure of the antenna was constructed using microwave studio computer simulation technology. The optimal sizes of the planned antenna are 39 × 10× 0.254 mm3. The engineered antenna arrangement is implemented on an RT5880 substrate as a dielectric medium. The LPDA is arranged in four arms that are equally spaced on both lines. The main 50Ω feeder line is partially grounded at the back of the substrate. A combination of circular director units is being studied and tuned in a regular pattern at a predefined distance from the antenna. An improvement in gain of 3 dBi is the response of the director units. The Conformist LPDA is adjusted to achieve a wide range of millimeter wave bands ranging from 40 to over 70 GHz. The antenna resonates at 60 GHz, where the maximum realized gain of 14.97 dBi is attained. The antenna was tested for utilization in the V-band involving wireless personal area network (WPAN) applications recommended by IEEE 802.11ad and IEEE 802.15.3c. The outcomes of the constructed antenna elements' tests and simulations agree fairly well. The proposed layout works better than previous efforts in this field.