Due to the increasing demands for large capacity and high performance wireless transmitters, multi-band/multi-standard transmitter architectures play an important role in modern communication. Thus, advances in the design techniques of radio frequency (RF) power amplifiers (PAs) have promoted it to use single multi-band PA and RF components in order to concurrently process multiple input signals located in different frequency bands.
In this dissertation, different RF imperfections are investigated and compensated for in multi-band wireless communications systems. Thus, a comprehensive analysis and different digital signal processing (DSP) solutions are proposed for distortion mitigation of different RF impairments in dual-band and tri-band transmitters.
A novel Feedforward Hammerstein model/DPD is proposed for the accurate characterization of the dynamic, nonlinear behavior of RF PAs. Indeed, the performance of different DPD linearizers is affected by the imperfections of the up-converters in the transmission path and down-converters in the feedback path. Therefore, a complexity-reduced compound DPD is proposed for the compensation of the impairments stemming from the quadrature modulators and PA nonlinearity in single-band transmitters.
This study is extended for multi-band transmitters and the nonlinear distortion in case of dual-band transmitters is analyzed. Indeed, the problem of modulator imperfections is more highlighted in multi-band transmitters. Therefore, a dual-input truncated Volterra DPD is proposed for the joint mitigation of dual-band PA distortion in the presence of modulator imperfections.
A theoretical analysis of the nonlinear distortion in the concurrent tri-band PA has been given, and a three-dimensional (3-D) DPD is presented for the linearization of tri-band PA. The analysis is further extended in order to include the effects of the phase distortion in tri-band transmitters. Indeed, the transmitter wideband phase variation effects will affect the transmission quality and needs to be compensated for. Therefore, a novel 3-D phase-aligned DPD is proposed that takes into account both the compound amplitude and phase variation effects in a concurrent tri-band transmitter.
Finally, in order to reduce the computational complexity of multi-band DPDs, a novel multi-branch DPD is proposed for the linearization of dual-band transmitters. The proposed model is based on a distributed polynomial basis function with a radial pruning approach.