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Modern communication networks require improved signal quality and spectrum efficiency. Modern wireless communication relies heavily on the multiple input multiple output (MIMO) technology to improve spectrum efficiency and achieve faster data rates. However, the performance of MIMO systems is significantly hampered by non-linear distortions in power amplifiers (PA), especially under dynamic operating conditions. Traditional methods to reduce these distortions often lack the adaptability required for effective optimization. The proposed dynamic nonlinear distortion adaptive optimization analysis (DNDAOA) therefore introduces an adaptive approach that dynamically adjusts the pre-distortion signals using real-time feedback mechanisms. DNDAOA effectively reduces non-linear distortions and thus improves the performance of MIMO systems. Simulation results show that DNDAOA significantly increases spectrum efficiency, reduces error rates, and improves signal quality. This method is widely used in areas such as wireless telecommunications, internet of things (IoT), autonomous vehicles, and smart infrastructure, driving advances in connectivity, reliability, and data integrity. [ABSTRACT FROM AUTHOR]

In this study, we proposed a pre-distorted driver of a power amplifier in which the driver stage can serve as a pre-distorter of the power stage. In order to secure the linearity of the power amplifier, AM-PM distortions according to the input power of the common-source (CS) and two stacked-FET structures were analyzed and compared with the simulated results. Based on the analyzed AM-PM distortions of the two structure, it was verified that the driver stage with CS structure can act as a pre-distorter of the power stage with the two stacked-FET structure by optimizing the bias voltages of the two structures. The Ka-band power amplifier was designed with a 65-nm CMOS process to verify the feasibility of the proposed pre-distorted driver stage. At 28 GHz, the measured P1dB, saturated output power (P $_{\mathrm {SAT}}$ ), and peak power-added efficiency (PAE) were 18.6 dBm, 19.7 dBm, and 32.9%, respectively. The measured small signal gain was 24.1 dB. When 5G-NR modulation signals (64-QAM, 100-Msym/s, 9.7-dB PAPR) were used, under conditions where the EVM was less than –25 dB, the measured output power and ACLR were 13.3 dBm and –29.4 dBc, respectively.

Modern wireless communication systems use orthogonal frequency division multiplexing (OFDM), a multi-carrier modulation method that resists multipath channels and provides bandwidth efficiency. OFDM is generally used with a Multiple-Input Multiple-Output (MIMO) system to boost diversity gain and channel capacity. MIMO-OFDM has several advantages, but its high PAPR value is a drawback. A non-linear high-power amplifier (HPA) can distort signals with high PAPR values. This issue can be resolved by employing predistortion, which compensates for nonlinear HPA. In addition to PD, channel coding can be used to improve the quality of systems with high PAPR values by adding redundant bits to the bits to be sent. In this paper, we report the experimental evaluations of the joint channel coding and pre-distortion (PD) technique on a 2x2 MIMO OFDM system using USRP hardware. The experiments are conducted in two scenarios: line-of-sight (LOS) and nonline-of-sight (NLOS) scenarios. The channel coding used in this scenario is convolutional code with code rates of 1/2, 2/3, and 3/4. From the results of the experiment, it can be seen that the system that uses PD combined with the convolution code produces better performance in the LOS and NLOS scenarios compared to the system without PD. In the LOS scenario, the use of PD can improve the SNR value of code rates 1/2, 2/3, and 3/4 by approximately 58.74%, 75.97%, and 96.20%. In the NLOS scenario, the use of PD can improve the SNR value of code rates 1/2, 2/3, and 3/4 by about 60.71%, 73.59%, and 71.84%. The measurement of the LOS scenario gives a better SNR value than the NLOS scenario, with a maximum SNR value of 30.86 dB, while the maximum SNR value of the NLOS scenario is 30.23 dB. This happened because the LOS scenario suffered minimal multipath fading compared to the NLOS scenario

One of the major problems faced in digital communication systems is Inter-Symbol Interference (ISI), induced by the propagation channel in the single carrier based systems. Classic digital equalization techniques based on pilot training sequences become tedious in the presence of nonlinear power amplifiers. The existing techniques for digital pre-distortion need a high transmitter computation complexity and those for the post-distortion require pilot overhead. In this review, we focus on fully generic blind processing for both channel equalization and power amplifier post-distortion. We propose a receiver based on two complex-valued neural networks (CV-NN). The first CV-NN is dedicated to generic blind equalization (GBE) to mitigate ISI. The second one is used for generic blind post-distortion compensation (GBPDC) of the power amplifier nonlinearity (PANL). The GBE and the GBPDC have no prior information about the transmission channel, the used constellation, and the PA model. For the first CV-NN, we consider an updated probability density fitting (PDF) based criteria, corresponding to many assumed possible constellations, that are used jointly with an automatic modulation classification (AMC) based on the k-nearest neighbors (KNN) algorithm. For the second CV-NN, we use the final updated PDF criterion resulting from the first CV-NN training process. Numerical results show that our generic blind Deep learning-based signal receiver formed with the two CV-NNs is effective in alleviating the two coupled signal distortions: the ISI and the PANL. Compared with the state-of-the-art methods, banking on a supervised post-distortion compensation and channel equalization, the proposed generic blind DL-based scheme exhibits good detection performance.

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 article, we propose a CMOS active balun targeting high linearity up to high voltage swing and over wide bandwidth for direct RF sampling applications. All the blocks of this active balun are derived using a common highly linear building block (HLBB). The HLBB is designed using an inverter with strong source degeneration. To increase the linearity of this HLBB further, its nonlinearity mechanisms are analyzed in detail. A bootstrapping technique is included in the HLBB to reduce the dominant nonlinearity. Furthermore, a pre-distortion technique cancels most of the non-linearity of the output driving stages. All the linearization techniques proposed are robust to process, voltage, and temperature (PVT) changes. The measured results of the active balun realized on-chip in a 22-nm FDSOI CMOS shows $ < -$ 44-dBc third harmonic distortion (HD3) up to 1.5- $\text{V}_{\textrm {p-p}}$ output swing over 0.01–5.4 GHz. The measured gain and phase errors of the balun action are less than 0.5 dB and $\pm 5{^\circ }$ , respectively. The chip is powered from a 5-V supply and dissipates 925 mW. [ABSTRACT FROM AUTHOR]

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.

This paper presents a new high-efficiency two-way Doherty Power Amplifier (DPA) with a modified output matching structure for Wideband Code Division Multiple Access (W-CDMA) low-to-medium power base station applications. A blended design is proposed using the symmetrical topology of equal rated power amplifying devices with unequal output impedances for the carrier and peaking amplifier to achieve enhanced efficiency and desired linearity in 1900 MHz band. The proposed output circuit modifications encompass the usage of parasitic capacitor compensation technique for the carrier amplifier, optimum offset line along with the Doherty combiner to achieve high efficiency over 6 to 10 dB extended range of back-off operation. The measured results of the DPA demonstrate a Power Added Efficiency (PAE) of more than 49.9% at +34 dBm W-CDMA signal power, which is between 8 and 8.5 dB back-off from the peak power level of 42.2 dBm. The DPA has a large signal power gain of 13 dB at 1960 MHz. Further, the PAE is 39.5% and linearised Adjacent Channel Power Ratio (ACPR) is −46.2 dBc, both at 10 dB back-off from peak power. In these back-off power levels, this implementation provides significant efficiency improvement using symmetrical devices and with excellent linearity. [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.

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.

A 10-GHz sub-sampling phase-locked loop (PLL) (SSPLL) with wideband low-noise frequency modulation for frequency-modulated continuous-wave (FMCW) radar applications is presented. It uses a low-power charge-integrating digital-to-analog converter (QDAC) to tune the voltage-controlled oscillator (VCO) in a two-point modulation architecture. A full background calibration engine corrects for the nonlinearities in the QDAC modulation path. Implemented in a 28-nm CMOS process, the SSPLL consumes 11.7 mW (of which less-than 0.5 mW from the QDAC) to generate a 23.6-MHz/ $\mu \text{s}$ sawtooth chirp-slope with 28-kHz rms-frequency-error for 1.21-GHz chirp-bandwidth. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Semiconductor optical amplifier (SOA) is regarded as a promising candidate to amplify the optical signal in next-generation access network, especially for O-band signal transmission. However, the SOA-based system suffers from the pattern-dependent effect due to its gain saturation. Compared to digital signal processing (DSP) at receiver, DSP in the transmitter can reduce implementation complexity, which is attractive for the multi-user system. In this paper, we propose three methods to mitigate the pattern-dependent effect in SOA and compare their performance based on: 1) look-up-table (LUT) considering pattern-dependent effect, 2) pre-distortion without considering pattern-dependent effect, 3) probabilistic shaping (PS). The performance of three mitigation methods is investigated in an intensity modulation with direct detection (IM/DD) 4-ary pulse-amplitude-modulation (PAM-4) transmission system at O-band. Our research results show that all these schemes can improve the receiver dynamic range of PAM-4 signals at 50 Gbit/s and 100 Gbit/s. Moreover, PS and LUT can also improve the receiver dynamic range of 75-Gbit/s PAM-8 signals. [ABSTRACT FROM AUTHOR]

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.

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]

This paper describes a 23-GHz digital bang–bang phase-locked loop (PLL) fabricated in 65-nm CMOS for millimeter-wave frequency-modulated continuous-wave radars. The presented circuit aims to generate a fast sawtooth chirp signal that grants significant advantages with respect to the more conventional triangular waveform. Such a signal, however, features a very large bandwidth that requires the adoption of a two-point injection scheme. This paper, after intuitively discussing how the nonlinearity of the digitally controlled oscillator affects the accuracy of frequency modulation, presents a novel automatic pre-distortion engine, operating fully in background, which linearizes the tuning characteristic. The 19.7-mA fractional-N PLL having an rms jitter of 213 fs and an in-band fractional spur of −58 dBc is capable of synthesizing fast chirps with 173-MHz/ $\mu \text{s}$ maximum slope and an idle time of less than 200 ns after an abrupt frequency step with no over or undershoot. [ABSTRACT FROM AUTHOR]

Computational intelligent systems are becoming an increasingly attractive solution for power amplifier (PA) behavioural modelling, due to their excellent approximation capability. This paper utilizes an adaptive fuzzy logic system (AFLS) for the modelling of the highly nonlinear MIMIX CFH2162-P3 PA. Moreover, PA’s inverse model based also on AFLS has been developed in order to act as a pre-distorter unit. Driving an LTE 1.4 MHz 64 QAM signal at 880 MHz as centre frequency at PA’s input, very good modelling performance was achieved, for both PA’s forward and inverse dynamics. A comparative study of AFLS and neural networks (NN) has been carried out to establish AFLS as an effective, robust and easy-to-implement baseband model, which is suitable for inverse modelling of PAs and capable to be used as an effective digital pre-distorter. Pre-distortion system based on AFLS achieved distortion suppression of 84.2%, compared to the 48.4% gained using the NN-based equivalent scheme. [ABSTRACT FROM AUTHOR]

Digital signal processing (DSP) with both linear equalization and nonlinear compensations are studied in this paper for the single-carrier 400G system based on 65-GBaud 16-quadrature amplitude modulation (QAM) signals. The 16-QAM signals are generated and pre-processed with pre-equalization (Pre-EQ) and Look-up-Table (LUT) based pre-distortion (Pre-DT) at the transmitter (Tx)-side. The implementation principle of training-based equalization and pre-distortion are presented here in this paper with experimental studies. At the receiver (Rx)-side, fiber-nonlinearity compensation based on digital backward propagation (DBP) are also utilized to further improve the transmission performances. With joint LUT-based Pre-DT and DBP-based post-compensation to mitigate the opto-electronic components and fiber nonlinearity impairments, we demonstrate the unrepeatered transmission of 1.6Tb/s based on 4-lane 400G single-carrier PDM-16QAM over 205-km SSMF without distributed amplifier. [ABSTRACT FROM AUTHOR]

We present high-speed single-channel discrete multitone (DMT) operations of directly modulated 850-nm vertical-cavity surface-emitting lasers (VCSEL). Successful transmission of 135 Gb/s over 10 m of OM4 multi-mode fiber (MMF) and 114 Gb/s over 550 m is demonstrated below the 7 % overhead hard-decision forward error correction (FEC) bit error rate (BER) limit. At higher BER limits, i.e. 20%overhead soft-decision FEC, which are of arising interest for these high-speed short-range links, data rates of up to 161 Gb/s are presented. This is enabled by high-bandwidth low-noise VCSEL, which operate in quasi-single mode to overcome the mode dispersion limitations of the MMF. The applied modulation format is DMT in combination with a Volterrafilter- based pre-distortion approach, which pre-compensates the linear and nonlinear behavior of the transmission system, primarily the digital-analog converter, the VCSEL, the MMF, and the photoreceiver. Furthermore, a detailed investigation of the predistortion is given by experimental means, showing that the optimum amount of pre-distortion depends on the applied components and the signal bandwidth. This makes it challenging to predict the optimum; however, a pure electrical pre-distortion offers already a fair gain in performance. [ABSTRACT FROM AUTHOR]

This work proposes a novel pre-distortion technique for the quantization noise cancellation of fractional-N frequency synthesizers. The proposed technique utilizes the coordinate rotation digital computer (CORDIC) algorithm to pre-distort the baseband signal of a wireless system with the quantization noise. The pre-distorted signal then modulates the noisy output signal of the fractional-N frequency synthesizer. The transmitter (Tx) modulation quality is thereby improved. In the receiver (Rx) mode, the phase noise of the Rx carrier signal can also be improved by modulation with a pre-distorted sinusoidal signal rather than a baseband signal. Experimental results demonstrate that the novel pre-distortion technique effectively improves the modulation quality of a Tx by an error vector magnitude (EVM) of about 10 % under a 13 Mbps QPSK modulation. The carrier in-band and out-band phase noise of the fractional-N frequency synthesizer is improved by approximately 6 dB and 10 dB, respectively.

This paper presents a sub-2-dB Noise Figure (NF) wideband differential Common Gate (CG) Low Noise Amplifier (LNA) in 0.18 µm CMOS technology. The circuit benefits from several new techniques to improve the overall performance. A new current bleeding scheme is proposed in which not only enhances the gain of the circuit but also improves transconductance and noise performance simultaneously. In addition, double positive feedback is employed with only an auxiliary NMOS transistor to break the trade-off between noise and input matching condition of the CG structure. Moreover, the added transistor is biased in moderate inversion region to form pre-distortion performance and sink third order nonlinearity of main transistors at the input. Thus, low noise figure is obtained simultaneous with good linearity. Post-layout simulation results in TSMC 0.18 µm RF-CMOS show a voltage gain of 20.1 dB with a −3 dB bandwidth of 0.38–2.7 GHz, while S 11 is below −10 dB over the frequency band. The minimum NF equals to 1.88 dB and an average NF of 2.04 dB is achieved over the frequency band. Third Input Intercept Point (IIP3) of the proposed circuit is +6 dBm. The circuit occupies an area of 0.055 mm 2 while consuming 2.55 mA from a 1.2-V supply voltage. [ABSTRACT FROM AUTHOR]

This paper presents an Ultra Wide-Band (UWB) high linear low noise amplifier. The linearity of Common Gate (CG) structure is improved based on pre-distortion technique. An auxiliary transistor is used at the input to sink the nonlinear terms of source current, resulting linearity improvement. Furthermore, an inductor is used in the gate of the main amplifying transistor, which efficiently improves gain, input matching and noise performance at higher frequencies. Detailed mathematical analysis show the effectiveness of both linearity improvement and bandwidth extension techniques. Post-layout simulation results of the proposed LNA in TSMC 0.18 µm RF-CMOS process show a gain of 13.7 dB with −3 dB bandwidth of 0.8–10.4 GHz and minimum noise figure (NF) of 3 dB. Input Third Intercept Point (IIP3) of 10.3–13 dBm is achieved which shows 8 dB improvement compared to conventional common gate structure. The core circuit occupies an area of 0.19 mm 2 including bond pads, while consuming 4 mA from a 1.8-V supply. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

In this paper, a nonlinear autoregressive with exogenous inputs (NARX) digital pre-distortion scheme to linearize power amplifiers is proposed. The proposed NARX digital pre-distortion gives better accuracy and spectral leakage suppression compared with other commonly used Volterra-based techniques. The stability criterion of the NARX digital pre-distortion is derived from the frequency domain analysis. Simulation is carried out with a 20 MHz single carrier long-term evolution signal and two-carrier long-term evolution signal and instantaneous to average ratio of 6.2 dB at 0.01% complementary cumulative distribution function (CCDF). The results of simulation analysis show a slight improvement in adjacent channel leakage ratio performance with 30% reduction in the number of floating point operations compared with conventional pre-distortion techniques. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A digital polar transmitter is introduced using 9-b thermometer-coded uniform cells for wideband signal. By analyzing amplitude and phase paths impairment which causes both in-band and out-of-band distortions, a 960-MHz delay tuner is designed for precise amplitude and phase alignment. Furthermore, two digital pre-distortion algorithms for digital power amplifier (DPA) are implemented and compared. Importantly, an on-chip dc–dc converter is included for direct battery connection and output power control. Boosted cascode gate bias improves PA efficiency at low power region. The proposed design is fabricated using a 55-nm RF CMOS technology. This DPA including digital amplitude modulation (AM) filtering achieves peak power of +21.9 dBm with 41% drain efficiency in continuous-wave measurements. It achieves EVM of 2.9% with 20-MHz IEEE 802.11ac compliance of 256-QAM OFDM signal, and also achieves EVM of 4.5% (CC0)/4.8% (CC1) with 40-MHz LTE-A carrier aggregation compliance of 64-QAM OFDM signal. [ABSTRACT FROM AUTHOR]

A novel technique to improve the linearity of Low Noise Amplifier (LNA) based on pre-distortion in the input matching circuit is proposed. The linearization technique is applied to a Capacitive Cross Coupled Common Gate (CCC-CG) structure. An auxiliary transistor operating in weak inversion region is used to adjust the input matching circuit nonlinearity. It has been shown that the nonlinearity of input matching circuit can efficiently compensate the nonlinearity of transconductance ( G m ) of the amplifier, and improves the third Input Intercept Point (IIP3). Furthermore, the added transistor is used in a feedback path which provides a noise canceling scheme. Thus, linearity improvement is achieved in addition to low Noise Figure (NF). Post-layout simulation results in TSMC 0.18 µm CMOS technology, show a gain of 18.55 dB with an upper −3 dB frequency of 2.96 GHz, the minimum NF equals to 2.63 dB and IIP3 of 11 dBm, while consuming 2.77 mA from a 1.5 V supply. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We propose a pre-distortion scheme in transmitter DSP to reduce the peak-to-average power ratio (PAPR) in multi-intermediate-frequency (IF)-over-fiber mobile fronthaul (MFH). In optical spectral efficient MFH, multiple modulated sub-bands are transmitted with different IFs serving multi-in multi-out and carrier aggregation in 5G. By applying phase pre-distortion on sub-bands in the transmitter DSP, we reduce the PAPR by more than 2.2 dB with 1% complementary cumulative distribution function value in MFH for 5G mobile networks and significantly increase the transmitted signal power and quality without modifying the system linearity and resolution. The proposed scheme generates small latency. It is DSP efficient and compatible with current mobile devices, without additional noise. With 32 sub-bands served, we demonstrated a 2-dB sensitivity improvement experimentally by applying the proposed scheme. [ABSTRACT FROM PUBLISHER]

This paper presents a V-band two-stage power amplifier integrated circuit using TSMC 65 nm CMOS process. The simple input, output, and inter-stage matching networks based on passive components are integrated. By compensating for power gain characteristics using a pre-distortion technique, the linearity of the power amplifier was improved. The implemented two-stage power amplifier showed a power gain of 10.4 dB, a saturated output power of 9.7 dBm, and an efficiency of 20.8 % with a supply voltage of 1 V at the frequency band of 58.8 GHz. [ABSTRACT FROM AUTHOR]

A nonlinear pre-distorter (NLPD) at the transmitter, and a maximum-a-posteriori probability (MAP) detector, time-domain Volterra nonlinear equalizer (VNLE), or sparse-VNLE at the receiver are compared for compensation of the pattern-dependent distortion that can occur in high baud rate transmitters and receivers. Experimental results are presented for a 1.206-Tb/s dual-polarization 16-ary quadrature-amplitude-modulation (16-QAM) superchannel signal with three subcarriers. The NLPD with iterative calculation of the pre-distortion provides the best performance in back-to-back systems and transmission systems followed by the MAP detector, VNLE, and sparse-VNLE. At the FEC threshold of 1.9\times 10^-2 , the NLPD provides an increase in the transmission distance of 300 km compared with the sparse-VNLE, VNLE, and MAP detector. For transmission over 1500 km of SMF, the VNLE and MAP detector exhibit additional optical signal-to-noise ratio margins of 0.16 and 0.47 dB relative to the sparse-VNLE. Compared with the VNLE, the sparse-VNLE exhibits a 55% reduction in number of kernel coefficients. [ABSTRACT FROM PUBLISHER]

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.

Power amplifier (PA) plays a key role in transceivers for mobile communication systems and the improvement of the linearity of the PA becomes an objective of first importance. This paper proposes a novel linearization method for PA based on the Legendre wavelet possessing rich properties, so as to this technique combines the advantages of piecewise linear functions and orthogonal polynomials for pre-distortion linearization. Pre-distorter (PD) has been identified and power spectrum also has been compared based on the data of the PA characteristics for WCDMA and OFDM signals, respectively. The computational results demonstrate that a quite significant improvement in linearity is achieved and the PD is stable and effective. The most attractive aspects of the presented method is that the Legendre wavelet bases can approximate static nonlinearity of the PA with different level of resolution and lower order piecewise polynomials than that of other polynomials. [ABSTRACT FROM AUTHOR]

OFDM technology has become the core technology of DTMB system. The high Doherty power amplifier can effectively improve the peak-average power ratio of OFDM system, but with poor linear performance. This paper starts with improving linear performance of Doherty power amplifier, analyzes the nonlinear model of power amplifier, presents a construction method of nonlinear performance model of Doherty power amplifier, gets the corresponding nonlinear performance curve, and then presents a design of pre-distorter which can improve system linear performance. The nonlinear performance curve is used to do the simulation. The result shows that the system linear performance is improved greatly. [ABSTRACT FROM AUTHOR]

This work proposes a novel pre-distortion technique for the quantization noise cancellation of fractional-N frequency synthesizers. The proposed technique utilizes the coordinate rotation digital computer (CORDIC) algorithm to pre-distort the baseband signal of a wireless system with the quantization noise. The pre-distorted signal then modulates the noisy output signal of the fractional-N frequency synthesizer. The transmitter (Tx) modulation quality is thereby improved. In the receiver (Rx) mode, the phase noise of the Rx carrier signal can also be improved by modulation with a pre-distorted sinusoidal signal rather than a baseband signal. Experimental results demonstrate that the novel pre-distortion technique effectively improves the modulation quality of a Tx by an error vector magnitude (EVM) of about 10 % under a 13 Mbps QPSK modulation. The carrier in-band and out-band phase noise of the fractional-N frequency synthesizer is improved by approximately 6 dB and 10 dB, respectively. [ABSTRACT FROM AUTHOR]

Data-dependent channel cross-modulation (XM) in multiband radio-over-fiber (RoF) systems have been investigated and illustrated for the first time. Nonlinear XM behaviors induced by a Mach-Zehnder modulator (MZM), including the intra-band XM between in-phase (I) and quadrature (Q) components of vector signals, as well as the inter-band XM between multiple bands of scalar/vector signals, have been studied by a closed-form theoretical analysis, and validated by experimental measurements. Consistent results have been obtained by both theoretical and experimental investigations. It was demonstrated that scalar signals only suffer from inter-band XM; whereas vector signals suffer from both intra- and inter-band XMs. Intra-band XM induces constellation compression distortion to vector signals, while inter-band XM induces eye-diagram degradation to scalar signals, and constellation scaling distortion to vector signals. To mitigate the signal distortions induced by data-dependent XM, arcsine pre-distortion technique was implemented to compensate the nonlinear response of MZM. Effective cancellations of both intra- and inter-band XM were achieved. [ABSTRACT FROM PUBLISHER]

A phase-delay cold-FET pre-distortion linearizer technique is proposed to improve the gain compensation ability compared with the conventional cold-FET pre-distortion linearizer. The gain expansion analysis of the power amplifier (PA) cascading with a pre-distortion linearizer and the comparison with the conventional linearizer and the proposed phase-delay linearizer are provided in this paper. To demonstrate the feasibility of this concept, a single-ended V-band cascode PA with the 90^\circ phase-delay linearizer and a differential K-band common-source PA with the 180^\circ phase-delay linearizer are developed to verify the characteristics. The V-band PA implemented in 90-nm CMOS process exhibits the output 1-dB compression power (OP1~dB) of 13.7 dBm and the power-added efficiency (PAE) at OP1~dB of 14.3%. The K-band PA implemented in 0.18- \mum CMOS process demonstrates 17.5-dBm OP1~dB and 13.6% PAE at OP1~dB. [ABSTRACT FROM AUTHOR]

The paper proposes a new formulation of a minimum mean square error pre-distortion scheme for multiple-input single-output impulsive ultra-wideband in multiple user environment. For the performance evaluation, scenarios CM1 and CM3 of the IEEE 802.15.3a channel model are considered. Results show that such a scheme has a good trade-off between intersymbol interference and multiple access interference reduction and signal-to-noise ratio preservation, performing better than time reversal and zero forcing pre-distortion schemes. [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]

Abstract: In this paper a novel all-optical scheme is proposed to reduce fiber nonlinear distortions in high-speed dense wavelength division multiplexed (DWDM) optical fiber communication systems by applying time-domain fractional Fourier transform (FRFT) based on the time–space duality theory. The modulated optical pulses will be pre-distorted by an FRFT module before being launched into fiber links. It has been validated that the pre-distorted signal performs better fiber nonlinearity tolerance compared to that without pre-distortion. Simulation results show that the received bit error rate (BER) is improved by several orders of magnitude for a 40Gbit/s carrier-suppressed return-to-zero on-off keying (CSRZ-OOK) DWDM system, which can be used in a current 40Gbit/s system easily to improve the nonlinearity effect tolerance. [Copyright &y& Elsevier]

Abstract: An optical waveform pre-distortion method is proposed in reducing the temporal broadening of pulse based on the optical implementation of time domain fractional Fourier transform (FRFT). Moreover, a new analysis of the dispersion and self-phase modulation effects is investigated. The simulation results show that prechirp coefficient and proper fractional orders of FRFT can be beneficial in mitigating pulse broadening. [ABSTRACT FROM AUTHOR]

For adaptive improvement of linearity above a 12 dB PAPR for 64QAM WiMAX, a complementary feedback loop in a differential amplifier is adopted as a pre-distorter that is realized using an NMOS cell operating in the triode region in order to compensate the gm3, the third order transconductance, of the differential amplifier. The power amplifier has been implemented in 0.18 μm CMOS technology, and the chip size is 870 μm × 1050 μm. The proposed PA obtains the 42% efficiency at P1dB while improving the IMD by more than 10 dB above 15 dBm output power levels. It shows a gain of as much as 14.5 dB, and a return loss below -12 dB for 2.3–2.4 GHz operation. Finally, the fabricated PA complies with the spurious emission of WiMAX standards up to 22 dBm. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52:833–836, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25062 [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]

This paper deals with the system and circuit-level aspects of an ultra-low-power robust wireless node for an asymmetric wireless link. A single building block TX front-end for a frequency hopping spread spectrum (FHSS) transmitter implemented in silicon-on-anything (SOA) bipolar technology is presented. It is realized with a directly modulated RF cascoded Colpitts power voltage-controlled oscillator (VCO), a frequency locked loop for center frequency calibration, and a digital pre-distortion algorithm for accurate frequency bins synthesis. The TX front-end draws only 1 mA at -18 dBm output power. By combining digital system techniques for frequency hopping and merging the VCO and the power amplifier (PA), a robust solution is obtained for indoor ultra-low-power wireless links. The proposed pre-distortion concept allows reduction of the hardware complexity, while the combination of a cascode output buffer and a common-collector Colpitts VCO allows us to reduce the complete FHSS front-end to a single building block that directly drives the antenna through a balun. A dedicated digital algorithm on the receiver side reduces the center frequency offset from a maximum value of 8.2 MHz to less than 8 ppm avoiding the use of any crystal on the transmitter side. Precision in the hopping synthesis is obtained by employing a ST-DFT based demodulator with differential encoding and an offset sending technique. The novel FHSS-predistortion concept has been verified by realizing a full wireless link that achieves a bit error rate better than 1.1% at -25 dBm output power while transmitting across an 8 meters indoor non-line-of-sight (NLOS) path. [ABSTRACT FROM AUTHOR]