Search

Mutual interference is a crucial issue for the visible light communication (VLC) systems to be addressed, including both co-channel interference (CCI) and inter-carrier interference (ICI). In this paper, to solve the CCI problem, a novel optical attocell network is introduced, which can be regarded as a hybrid network based on both single frequency network and multi-frequency network. Meanwhile, to eliminate the ICI, a pre-distorted enhanced asymmetrically clipped DC biased optical orthogonal frequency division multiplexing (PEADO-OFDM) approach is designed. In addition, the corresponding properties of PEADO-OFDM are analyzed, and different modulation schemes are employed for downlink and uplink in the same ADO-OFDM modulation framework to reduce the complexity of user processing. Simulation results indicate that the proposed PEADO-OFDM scheme outperforms the conventional ADO-OFDM approach in terms of bit error rate, while the processing latency and computational complexity are greatly reduced at the receiver.

In this paper, an adaptive modulation scheme for visible light communication (VLC) system based on partially pre-distorted layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) is proposed. The clipping noise that falls on the higher layers in the conventional LACO-OFDM results in inter layer interference, which can be eliminated by the operation of pre-distortion at the expense of extra power consumption. The proposed partially pre-distorted scheme makes a tradeoff between error propagation and power cost to suit different transmission environments. The probability distribution functions of the conventional and pre-distorted LACO-OFDM schemes are analyzed and compared and the layers that should be pre-distorted in the proposed scheme is decided adaptively by maximizing the achievable rate. The computational complexity of the proposed scheme is also investigated, which is acceptable compared with the previous schemes. Simulation results show that the proposed scheme has a superior bit error rate performance compared with the conventional and pre-distorted LACO-OFDM schemes.

Orthogonal Frequency Division Multiplexing (OFDM) is one of the key modulations for current and novel broadband communications standards. For example, Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) is an excellent choice for the ECMA-368 Ultra Wide-band (UWB) wireless communication standard. Nevertheless, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals reduces the power efficiency of the key element in mobile devices, the High Power Amplifier (HPA), due to non-linear distortion, known as the non-linear saturation of the HPA. In order to deal with this limiting problem, a new and efficient pre-distorter scheme using a Neural Networks (NN) is proposed and also implemented on Field Programmable Gate Array (FPGA). This solution based on the pre-distortion concept of HPA non-linearities offers a good trade-off between complexity and performance. Some tests and validation have been conducted on the two types of HPA: Travelling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA). The results show that the proposed pre-distorter design presents low complexity and low error rate. Indeed, the implemented architecture uses 10% of DSP (Digital Signal Processing) blocks and 1% of LUTs (Look up Table) in case of SSPA, whereas it only uses 1% of LUTs in case of TWTA. In addition, it allows us to conclude that advanced machine learning techniques can be efficiently implemented in hardware with the adequate design. This work was partly funded by projects TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/ AEI/FEDER, UE) and MFOC (Madrid Flight on Chip—Innovation Cooperative Projects Comunidad of Madrid—HUBS 2018/MadridFlightOnChip).

Organic photo-detector (OPD) is lightweight and physically flexible. It can transform plastic or glass into smart surfaces. Visible light communication (VLC) is considered as one of the promising technologies for the future wireless communications. VLC combines the advantages of lighting and communication simultaneously. Besides, it can be deployed using existing lighting infrastructure; hence little extra cost is needed to provide this wireless communication. As the OPD has a large optical detection area, it would be interesting to employ the OPD as VLC receiver (Rx). If the OPD can be used in the VLC systems, it can benefit the Internet-of-Thing (IoT) networks by providing efficient human-to-machine and machine-to-machine communications. However, implementing VLC using OPD Rx is challenging. Due to the slow charging and discharging processes of the OPD, the optical-to-electrical response speed is limited. Besides, the OPD requires external bias to be operated. Here, we propose and demonstrate using pre-distortion scheme for pulse-amplitude-modulation (PAM) signal to a self-powered PCBM:P3HT OPD to enhance the VLC transmission performance. The operation of the self-powered PCBM:P3HT OPD is discussed. Both experiments using PAM-2 and PAM-4 (with and without pre-distortion) are evaluated. The performance, requirement and capability limitations of the pre-distortion schemes are also analyzed and discussed by using numerical simulations.

In this paper, a low-complexity symbol-based equalizer that performs non-linear distortion cancellation is proposed for application at the user terminal in the DVB-S2X satellite forward link. The channel is comprehensively modeled, including the non-linear travelling wave tube amplifier characteristics, the input-multiplexing and output-multiplexing filter responses at the satellite transponder, and the phase noise at the user terminal, according to the very-small aperture terminal reference scenario. Two detectors in the cancellation loop are considered, comparing the packet-error rate (PER) performance of simple maximum likelihood demodulation with hard decision to soft information exchange with low-density parity-check decoder, and showing only marginal improvement with the latter solution. The PER performance is compared against a number of pre-distortion techniques at the transmitter, such as dynamic data pre-distortion, successive data pre-distortion, and static data pre-distortion. The novel receiver demonstrates superior performance even with one iteration of distortion cancellation, while the joint application of successive data pre-distortion and iterative symbol-based equalization shows up to 4.95-dB energy efficiency gain for 32-level amplitude and phase-shift keying (32-APSK). The computational complexity is also evaluated. The improved receiver is particularly suitable for application with higher order modulation, a wide-band carrier, and low roll-off factors.

In this paper, we propose and experimentally demonstrate an optical self-interference cancellation (OSIC) system with baseband predistortion for wideband over-the-air in-band full-duplex (IBFD) communication. The key factors of OSIC bandwidth limitation are analyzed, and the solution toward it is proposed for the first time. Experimental results show that, by traditional OSIC under over-the-air condition, only narrow even zero band is with enough cancellation depth to satisfy IBFD. But with our proposed baseband predistortion scheme, deep OSIC depth is achieved over the whole 1 GHz/5 GHz baseband within the total 7–25 GHz available band of horn antennas. The employment of baseband predistortion obviously broadens the cancellation bandwidth of an EML-based OSIC system. The largest OSIC bandwidth for over-the-air IBFD communication is demonstrated so far.

This paper describes a 15.6-18.2GHz fractional-N bang-bang digital PLL fabricated in 28nm CMOS. To compensate for the nonlinearity of the digital-to-time converter and reduce the level of fractional spurs, two alternative predistortion techniques are introduced. The adoption of those algorithms operating continuously in background is demonstrated to reduce the level of the in-band fractional spur at 300kHz from −20dBc to −57dBc and −63dBc, respectively. The fabricated PLL achieves FoM of −237.2dB.

This paper describes a novel scheme for the fusion of spectrum sensing information in cooperative spectrum sensing for cognitive radio applications. The scheme combines a spectrum-efficient, pre-distortion-based fusion strategy with an energy-efficient censoring-based fusion strategy to achieve the combined effect of reduction in bandwidth and power consumption during the transmissions of the local decisions to the fusion center. Expressions for computing the key performance metrics of the spectrum sensing of the proposed scheme are derived and validated by means of computer simulations. An extensive analysis of the overall energy efficiency is made, along with comparisons with reference strategies proposed in the literature. It is demonstrated that the proposed fusion scheme can outperform the energy efficiency attained by these reference strategies. Moreover, it attains approximately the same global decision performance of the best among these strategies.