Design and implementation of adaptive baseband predistorter for OFDM nonlinear transmitter. Simulation and measurement of OFDM transmitter in presence of RF high power amplifier nonlinear distortion and the development of adaptive digital predistorters based on Hammerstein approach.

The objective of this research work is to investigate, design and measurement of a digital predistortion linearizer that is able to compensate the dynamic nonlinear distortion of a High Power Amplifier (PA). The effectiveness of the proposed baseband predistorter (PD) on the performance of a WLAN OFDM transmitter utilizing a nonlinear PA with memory effect is observed and discussed. For this purpose, a 10W Class-A/B power amplifier with a gain of 22 dB, operated over the 3.5 GHz frequency band was designed and implemented. The proposed baseband PD is independent of the operating RF frequency and can be used in multiband applications. Its operation is based on the Hammerstein system, taking into account PA memory effect compensation, and demonstrates a noticeable improvement compared to memoryless predistorters. Different types of modelling procedures and linearizers were introduced and investigated, in which accurate behavioural models of Radio Frequency (RF) PAs exhibiting linear and nonlinear memory effects were presented and considered, based on the Wiener approach employing a linear parametric estimation technique. Three new linear methods of parameter estimation were investigated, with the aim of reducing the complexity of the required filtering process in linear memory compensation. Moreover, an improved wiener model is represented to include the nonlinear memory effect in the system. The validity of the PA modelling approaches and predistortion techniques for compensation of nonlinearities of a PA were verified by several tests and measurements. The approaches presented, based on the Wiener system, have the capacity to deal with the existing trade-off between accuracy and convergence speed compared to more computationally complex behavioural modelling algorithms considering memory effects, such as those based on Volterra series and Neural Networks. In addition, nonlinear and linear crosstalks introduced by the power amplifier nonlinear behaviour and antennas mutual coupling due to the compact size of a MIMO OFDM transmitter have been investigated

Optimum Design of Doherty RFPA for Mobile WiMAX Base Stations

YesRF power amplifiers in mobile WiMAX transceivers operate in an inherently nonlinear manner. It is possible to amplify the signal in the linear region, and avoid distortion, using output power back-off; however, this approach may suffer significant reduction in efficiency and power output. This paper investigates the use of Doherty techniques instead of back-off, to simultaneously achieve good efficiency and acceptable linearity. A 3.5 GHz Doherty RFPA has been designed and optimized using a large signal model simulation of the active device, and performance analysis under different drive levels. However, the Doherty EVM is generally poor for mobile WiMAX. Linearity may be improved by further digital pre-distortion, and a simple pre-distortion method using forward and reverse AM-AM and AM-PM modeling. Measurements on the realized amplifier show that this approach satisfies the EVM requirements for WiMAX base stations. It exhibits a PAE over 60%, and increases the maximum linear output power to 43 dBm, whilst improving the EVM

Improvements in Multicarrier Modulation Systems using a Wavelet OFDM Scheme

yesThis paper investigates the performance of wavelet OFDM signals over a wireless communications link. The scheme is shown to be generally similar to Fourier based OFDM, but with some additional features, and improved characteristics. The sensitivity of both schemes to the nonlinear amplification in the transmitter is compared by monitoring the time domain output data and the adjacent channel power ratio (ACPR) performance

Improved QC-STBC OFDM system using null interfeence elimination

YesThe quasi-orthogonal space time block coding (QO-STBC) over orthogonal frequency division multiplexing (OFDM) is investigated. Traditionally, QO-STBC does not achieve full diversity since the detection matrix of QO-STBC scheme is not a diagonal matrix. In STBC, the decoding matrix is a diagonal matrix which enables linear decoding whereas the decoding matrix in traditional QO-STBC does not enable linear decoding. In this paper it is shown that there are some interfering terms in terms of non-diagonal elements that result from the decoding process which limit the linear decoding. As a result, interference from the application of the QO-STBC decoding matrix depletes the performance of the scheme such that full diversity is not attained. A method of eliminating this interference in QO-STBC is investigated by nulling the interfering terms towards full diversity for an OFDM system. It was found that the interference reduction technique permits circa 2dB BER performance gain in QO-STBC. The theoretical and simulation results are presented, for both traditional QO-STBC and interference-free QO-STBC applying OFD

Probability Distribution of Rician K-Factor in Urban, Suburban and Rural Areas Using Real World Captured Data

YesThe Rician K-factor of the vehicle-to-vehicle (V2V) wireless propagation channel is estimated using a moment-based method on the envelope of measured pulse data. The measurements were carried out under vehicle-to-vehicle wireless communication channel condition with car rooftop antenna heights at one end of the link and very low antenna height at the other end. Data captured from typical urban, suburban and rural areas are analyzed and the K-factor probability density function is generated for each scenario to give an insight into the V2V channel behavior. For all three areas, the majority of K values are found to be within the range of -10 to +10 dB. The K-factor distributions are close to normal with mean values of 1.8, 2.6 and 3 dB respectively for urban, suburban and rural area

MIMO Discrete Wavelet Transform for the Next Generation Wireless Systems

Study is presented into the performance of Fast Fourier Transform (FFT) and Discrete Wavelet Transform (DWT) and MIMO-DWT with transmit beamforming. Feedback loop has been used between the equalizer at the transmitter to the receiver which provided the channel state information which was then used to construct a steering matrix for the transmission sequence such that the received signals at the transmitter can be combined constructively in order to provide a reliable and improved system for next generation wireless systems. As convolution in time domain equals multiplication in frequency domain no such counterpart exist for the symbols in space, means linear convolution and Intersymbol Interference (ISI) generation so both zero forcing (ZF) and minimum mean squared error (MMSE) equalizations have been employed. The results show superior performance improvement and in addition allow keeping the processing, power and implementation cost at the transmitter which has less constraints and the results also show that both equalization algorithms perform alike in wavelets and the ISI is spread equally between different wavelet domains

An evaluation of coded wavelet for multicarrier modulation with OFDM

NoOrthogonal frequency division multiplexing (OFDM) is pronounced in wireless communication systems. Methods for improving the performance of the OFDM-based systems are mostly sought. A method of doing this involves error correction coding and another, a better multicarrier modulation kernel. In this work, convolutional error correction coding with interleaving is introduced in wavelet multicarrier modulation OFDM system (wavelet-OFDM) to improve the performance of multicarrier systems as the signal traverses the multipath and noisy transmission channels. This is compared with FFT-based multicarrier modulation (FFT-OFDM). Results show that coded wavelet-OFDM saves more than a half of the transmit power than the uncoded wavelet. Also it will be shown that, the interleaved and non-interleaved coded wavelet-OFDM well outperform interleaved coded and non-interleaved coded FFT-OFDM systems respectively

Miniaturized tunable conical helix antenna

NoA miniaturized conical helix antenna is presented, which displays vertical polarization with electrically small dimensions of 10mm×10mm×45mm. The resonance of the antenna is made tunable by adding a variable digital MEMS capacitor load at the bottom of the helix, giving a tuning range of 316 MHz to 400 MHz. The antenna demonstrates considerable impedance matching bandwidth and gain over the entire tuning frequency band. Most importantly, the antenna is capable of compact, flexible and easy integration into a wireless device package or for platform installation.Datong of Seven Technology Group, for their support under the KTP project grant No. 008734

Comparison of three vertical refractivity profiles in the Gulf region

In this paper, a set of local radiosonde meteorological data, from 1990 to 2005, have been used to statistically analyze the refractivity gradient, DeltaN, at the lowest 65 m, 100 m and 1 km of the atmosphere above the surface of the Earth in the Gulf region. These three levels are the reference atmospheric layers in which the refractivity gradients have been evaluated by the ITU-R Recommendations P.453-10 and P.452-12The vertical variations of the refractivity profile aredisplayed through the cumulative distributions of the refractivity gradients at the targeted levels. The obtained results are compared for the three layers and also compared with the estimated values in the ITU maps and tables when available. Index Terms – Atmospheric refraction, Refractivity gradient

Fractional Fourier Transform modulation for multiple input multiple output multicarrier systems

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