Tahereh Sadeghpour

Linear and nonlinear crosstalk in MIMO OFDM transceivers

This paper studies the effect of nonlinear and linear crosstalk in a MIMO (multiple in, multiple out) transceiver. These effects are mainly due to the power amplifier (PA) nonlinear behaviour and mutual coupling of antennas in the MIMO transmitter. The effects of the crosstalk interference on the signal performance are studied based on the measured error vector magnitude (EVM) at the transmitting antennas. The simulation and measurement results show that PA nonlinearity and RF crosstalk need to be considered in the design process.

Modeling and Linearization Method for Nonlinear Power Amplifier with Memory Effect for Wideband Application

This paper represents a new adaptive method to model the nonlinearity of power amplifiers(PAs) with memory effects based on Wiener approach and also adaptive predistorter to counterbalance the AM/AM and AM/PM nonlinear effects of the transmitter power amplifier is proposed by Hammerstein approach. Finally we consider the effectiveness of proposed method on performance of OFDM signal as the wideband system by reduction of distortion. It is confirmed by computer simulation that proposed approach produces a faster convergence speed than the previous adaptive predistortion technique.

A compact size reconfigurable PIFA antenna for use in mobile handset

A planar inverted-F type reconfigurable antenna with slot is presented. The antenna can cover frequency bands which include Digital Cellular Service (DCS: 1710–1880 MHz), Personal Communication Service (PCS: 1850–1990 MHz), and Universal Mobile Telecommunications System (UMTS: 1900–2200 MHz). Initially, the reconfigurability of the proposed antenna is achieved by attaching lumped capacitor over the slit of the radiator with values range from 1.5–4pf. The measured and simulated results reveal that the fabricated proposed antenna is capable of obtaining tunable frequency ratio from 1850MHz to 2200MHz with overall size of 21×13.5×5 mm3 that makes it suitable for handset applications and can be easily integrated inside commercial mobile handsets.

Reconfigurable antenna design approach for mobile applications and a technique for harmonics suppression

A design procedure for reconfigurable mobile antenna module is presented. A tuneable antenna, including a varactor diode placed at specific position over the radiating slot, was fabricated and tested over several targeted frequency bands (centred at 1.7, 1.8, 1.9 and 2.04 GHz) and their harmonics. A limitation of the tuneable antenna is its non-linear behaviour at the transmitter. A method to measure the radiated power from an active antenna (AA) at fundamental and harmonic frequencies is introduced to suppress the harmonic radiations of the active antenna. The experimental results on the received power show a very good capability for harmonic suppression.

Envelope correlation formula for (N, N) MIMO antenna array including power losses

The scattering parameter formulation for the envelope correlation in an (N, N) MIMO antenna array has been modified to take the intrinsic antenna power losses into account. This method of calculation provides a major simplification over the use of antenna radiation field patterns. Its accuracy is illustrated in three examples, which also show that the locations of the correlation minima are sensitive to the intrinsic losses.

Optimum Design of Doherty RFPA for Mobile WiMAX Base Stations

RF 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.

Modeling of Nonlinear Power Amplifier with Memory Effect for Wideband Application

This paper is concerned with a new time-domain modeling topology for signals which is applied to wideband power amplifiers. The memory effect will be shown using two-tone intermodulation distortion (IMD) measurement with different tone frequency spacing and power levels. The model is developed by using a memoryless nonlinearity followed by a dynamic LTI system (Hammerstein model) to consider the memory effects associated with wideband signals. For this purpose an Nth-order FIR filter is used. It is shown that the accuracy of wideband signal simulations can be improved by optimizing the model parameters based on time-domain measurements of wideband signals.

Broadband Omnidirectional and Miniature Fold-up Discone Antenna in VHF/UHF Band

Abstract In this article, a novel miniature broadband omnidirectional antenna is proposed. This antenna is suitable to use in vehicles, especially in unmanned aerial vehicles, since it will be folded in order to reduce its size when the unmanned aerial vehicle lands. A special kind of wire discone antenna is chosen to achieve all desired goals. Passive broadband impedance matching at the input of the antenna improves the voltage standing-wave ratio. A telescopic fiberglass axis is used in the antenna structure in order to reduce size and increase wind resistance. The assessment of the novel structure in implementing the antenna is confirmed by experimental measurements. The measurement results reveal the preference of the new techniques over the existing approaches, showing voltage standing-wave ratio better than 2.1 and gain between −5.9 and 2 dBi in a total band of 30–500 MHz.

Hammerstein predistorter for high power RF amplifiers in OFDM transmitters

OFDM (Orthogonal Frequency-Division Multiplexing) is a wideband digital modulation scheme which is critically dependent on linearity in the hardware system, due to its reliance on Fourier Transformation and its inherently high peak-to-average power ratio (PAPR), and minimization of nonlinearity is thus a priority. In this paper the effectiveness of a predistortion based on the Hammerstein model dealing with the nonlinear response is investigated by measurement of Error Vector Magnitude (EVM) in AWGN channel and Adjacent Channel Power Ratio (ACPR). Accuracy of prediction of Power Amplifier (PA) nonlinearity with memory effect and baseband predistorter is investigated by the experimental results.

Improvements in Multicarrier Modulation Systems Using a Wavelet OFDM Scheme

This 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.