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This paper proposes a novel crossover digital predistorter (CO-DPD) model to compensate for crosstalk and nonlinearity in multiple-input multiple-output (MIMO) radio systems. Crosstalk can take place before or after the power amplifiers, designated herein as nonlinear and linear crosstalk, respectively. This paper demonstrates that, contrary to linear crosstalk, nonlinear crosstalk significantly affects the performance of the digital predistortion algorithm; and, it cannot be embedded and compensated for by the conventional channel matrix inversion algorithm at the receiver side of MIMO links. Based on a parametric study of system-level simulations and measurements, it was found that for a -20-dB nonlinear crosstalk level, the use of a memory multi-branch polynomial predistorter, along with the channel matrix inversion algorithm, bounds the adjacent channel power ratio (ACPR) for a wideband code division multiple access (WCDMA) signal to -46 dbc and the error vector magnitude (EVM) for a world interoperability for microwave access (WIMAX) signal to -43 dB in MIMO links. The proposed CO-DPD was investigated and analyzed for the MIMO transmitter with N = 2, where N is the number of RF front-ends. Its performance was evaluated through measurements, the experimental results obtained show that, in the presence of -20-dB nonlinear crosstalk, the proposed CO-DPD improve the ACPR of the WCDMA signal by 13 dB to -56.81 dBc from those obtained using a conventional digital predistorter. The same improvement was observed in the EVM measurement of the WIMAX signal, where the EVM decreases from -21.22 dB for the conventional DPD to -49.71 dB for the proposed CO-DPD. Index Terms--Antenna crosstalk, digital predistortion (DPD), multiple input multiple output (MIMO), power amplifier (PA), RF crosstalk, wideband code division multiple access (WCDMA), world interoperability for microwave access (WIMAX).

This paper analyzes the power losses in distributed multiharmonic matching networks and proposes a methodology to minimize these losses, which are critical in designing harmonic controlled or switching mode power amplifiers (PAs). The effect of the harmonic output matching topology on PA performance is studied. An analytical evaluation is developed to show the effect of the harmonic network topology on the conduction losses in the fundamental matching network. This analysis is validated through the comparison of two different matching network topologies in the design of an inverse class F PA with a carrier frequency of around 1 GHz. A 0.2-dB improvement in the losses is achieved, allowing for an improvement of the output power and gain and for an increase in the power-added efficiency by 4%, reaching 81%. Index Terms--Class F, efficiency, harmonic matching network, inverse class F, switching mode power amplifier (PAL

This paper proposes a new architecture of delta-sigma (DS) modulator suitable for RF digital transmitter design. This novel architecture considerably reduces the speed requirements of the digital signal processing block. The novelty lies in the implementation of a specific fully digital up-conversion in combination with a low-pass DS modulator to produce high-frequency digital-like signals, which can be used to drive highly efficient switching-mode power amplifiers. The proposed architecture is suitable for reconfigurable all-digital, multistandard and multiband wireless transmitters. The novel transmitter architecture has been validated using simulation and implemented on a field-programmable gate array development board for two different signals, code division multiple access and orthogonal frequency division multiplex. Index Terms--Field-programmable gate array (FPGA), low-pass (LP) delta-sigma (DS), RF transmitter.

This paper proposes a new amplifier architecture based on the outphasing technique intended for the efficiency enhancement of linear amplification with nonlinear components (LINC) transmitters. The proposed mode-multiplexing linear amplification with nonlinear components (MM-LINC) scheme operates according to the LINC concept for input signal magnitude drive levels below a certain threshold and as a balanced amplifier beyond this threshold. The setting of this threshold level influences the performance of the amplifier in terms of average power-added efficiency and linearity. A 2-W up-link transmitter prototype for worldwide interoperability for microwave access (WiMAX) applications was designed using this new architecture and optimized for a WiMAX signal with an ll.3-dB peak-to-average power ratio. The experimental results revealed a significant increase in power-added efficiency, from 6% for a LINC transmitter to 21% for the MM-LINC amplifier, while maintaining an error vector magnitude value under 8 %, which is compliant with the standard requirement. Index Terms--Linear amplification with nonlinear components (LINC), outphasing, power amplifiers (PAs), worldwide interoperability for microwave access (WiMAX) transmitters.

In this paper, an active load-pull-based large-signal modeling approach suitable for designing and optimizing Doherty amplifiers is proposed. The optimization of the drive dependant dynamic loads seen by both carrier and peaking amplifier's transistors was carried out using a large-signal load-pull-based behavior model built into CAD software. The latter was also used to optimize the biasing conditions of the peaking and carrier amplifier transistors. The simulation versus measurement results demonstrated the strong ability of the constructed model to predict the nonlinear behavior of 16 watts peak-envelope power designed Doherty amplifier in terms of power added efficiency, AM/AM, and AM/PM distortions. In addition, a complex digital predistortion technique was used to significantly enhance the linearity of the Doherty amplifier and to preserve an ACPR level better than 50 dBc under a WCDMA signal while attaining a power added efficiency of about 44% at the same time. Index Terms--High efficiency Doherty amplifier, load-pull, baseband predistortion, WCDMA.

In this paper, a system-level RF/digital signal processing (DSP) design approach of power-efficient orthogonal frequency-division multiplexing (OFDM) transmitters is proposed. A DSP-based low-IF architecture, which allows a significant enhancement of their power and spectrum efficiencies, is proposed. The cascade of the peak-to-average power ratio (PAPR) reduction technique, predistortion technique, and the in-phase and quadrature modulation led to impressive improvement in the power efficiency and effective linear output power of the OFDM transmitter. Measurement results carried out on an IEEE 802.11a transmitter designed and built for this experiment are presented in terms of error vector magnitude (EVM), adjacent channel leakage ratio, and power efficiency. The power stage of this transmitter uses a heterojunction bipolar InGaP transistor operating in a deeply class AB. The cascade of the PAPR reduction and baseband predistortion processing modules results in the reduction of the power backoff operation point by approximately 10 dB accompanied by a relative increase in the wireless local area network transmitter power efficiency by roughly 400% while meeting the emission mask spectrum and EVM levels demanded by the 802.11a standard. Index Terms--Peak-to-average power ratio (PAPR) reduction, power-amplifier linearization, predistortion, wireless local area network (WLAN).