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Lookup table (LUT) is an efficient digital predistortion technique for mitigating the pattern dependent distortion in the field of underwater wireless optical communication (UWOC) system. However, the complexity of LUT grows geometrically when applied with high-order QAM modulation formats with multi-pattern length sequences. The complexity reduction of LUT is essential for practical applications. In this paper, we study the patterning effects of LUT predistortion and propose to reduce the LUT complexity by pruning its table entries aided with multi-modulus weighted strategy. The size of LUT has been reduced significantly in experiments, which shows that the complexity of the proposed MMW-RLUT only accounts for 17.6%, 9.8%, 4.9% and 14% of full-size LUT for 64QAM, normal 32QAM, square geometrical shaping (SGS) 32QAM and 16QAM modulated UWOC system, without degradation of performance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An adaptive compression method in intermediate frequency band digitized radio over fiber is proposed for mobile fronthaul, aiming at reducing the transmission rates. The proposed method uses radio channel state information parameters to control fronthaul compression. The simulation results demonstrate the ability of the proposed method on reducing the quantization error, allowing the use of lower (4-bits) quantizer resolution for 64-QAM modulated signals, providing 2:1 compression rate with near zero EVM. In addition, our proposed method surpasses $\mu $ -law and $A$ -law compression techniques and performs in shorter times than 5G latency target (1 ms). Finally, the performance of uncompressed and compressed signal is assessed experimentally in 20 km of fiber transmission. [ABSTRACT FROM AUTHOR]

In this article, analysis of a linearised travelling tube amplifier (TWT) using multi-tone signal under the digital modulation schemes is presented. The pre-distortion lineariser circuit based on the Schottky diodes is used to compensate for the nonlinear behaviour of the TWT amplifier in the noisy channel. The stability of the TWTA in combination with the lineariser has also been investigated through simulations. The 4-QAM and QPSK modulators are utilised and applied before linearised TWTA and capture results. The data passing through the linearised TWTA is analysed by using advanced design system (ADS). Constellation and eye diagrams are obtained from different modulation schemes and compared with each other in the same environment. Finally, the bit-error-rate (BER) performance of the system is evaluated using Monte Carlo estimation for three different values of input-back-off (IBO). It is shown that the performance is improved by applying the proposed signal pre-distortion lineariser. [ABSTRACT FROM AUTHOR]

This letter discusses the implementation of microwave backscatter links in CMOS technology which are similar to existing systems at mid-UHF for RFID, but intended for use at the 5.8 GHz ISM band for supporting future low-power WLAN applications. In order for backscatter links to operate in highly channelized environments we introduce a pulse-shaping technique to reduce out-of-band emissions as well as a symbol pre-distortion technique to improve the constellation spacing. Both techniques are introduced into a 65 nm prototype backscatter modulator chip and are shown to operate with QPSK modulation at 54 Mb/s (typical of WLAN standards). The backscatter modulator chip was shown to consume 1.61 mW of power. [ABSTRACT FROM PUBLISHER]