LINC based amplifier architectures for power efficient wireless transmitters

Nowadays, high speed and high data rates based wireless applications are largely widespread. These applications require wireless communication systems with broadband and high spectral efficiency in addition to cost and compatibility effectiveness. Different modulation and power amplification techniques are being studied and explored for these applications as the wireless communication systems are continuously in development, as the need for cost-effective, spectrum-efficient, ubiquitous, always-on and interoperable wireless systems.;The increasing consumer demand for higher speed mobile data services and the mobile network operators need for ways to cut costs accelerated by the adoption of the new futuristic 4G standard. The 4G technologies promise a wireless access which is fast and ubiquitous broadband. Once the radio IC chips are cheap enough, the new technology will not just be used in handsets and laptops, but also in devices such as digital cameras and electricity meters, which are unconnected today.;Based on the beforehand discussion this research project is aimed at developing new efficient RF power amplifying techniques for these emerging wireless systems. The efficiency of power amplifier is one of the most critical factors affecting the overall system performance due to the power dissipation in the amplification stage. The existing techniques used to improve amplifier efficiency result in a loss of linearity, which is unacceptable for the new wireless communication systems employing advanced spectrally-efficient modulation techniques. The new complex modulated signals, like OFDM, main disadvantage is that the signal peak may rise up to N times (N can be higher than 10) the average power, which will force the amplifier to work in the nonlinear region, causing inter-modulation distortions and an increase in Bit Error Rate (BER) or work with a large back up to keep the linearity, but in this case the power efficiency degrades considerably.;To remedy this compromise between efficiency and linearity, an efficient amplification technique is proposed in this thesis. It is based on a system-level solution to provide high efficiency while maintaining linearity of the signal.;In this research project a study for new transmitter architectures with emphasis on topologies that can meet today's linearity and high efficiency requirements was carried out. Due to the conventional LINC efficiency degradation problems owing to the combiner losses, a new system level modified LINC solution is proposed. This new solution introduces a new topology intended for efficiency of the power amplification front end in wireless communication transmitters. Instead of combining them at the transmitter the two RF amplified branch signals are transmitted and then combined at the receiver. Accordingly, the LINC based transmitter efficiency is improved, and the overall system power efficiency is enhanced, while the linearity of the modulated signals is maintained. This new architecture has the advantage of using two nonlinear amplifiers working in saturation in their high efficiency operation region, and also adds flexibility at the system level to compensate for the signal distortions due to the channel and LINC branches imbalances.;The main contributions of this thesis are listed as follows: An addition of an extra filtering step in the processing, taking place in the signal separation unit of the LINC transmitter, results in an improved LINC amplifier system performance from the perspective of linearity and robustness to branch mismatches in terms of gain and phase unbalance.;Furthermore, two novel system level topologies 2X1 and 2X2 LINC amplification solutions for the wireless communication systems are also introduced. These two LINC new architectures are intended to replace the conventional LINC transmitter to reduce degradation of the average efficiency when high peak to average signal is transmitted. Simulation results show improved efficiency and immunity to branch signals imbalance, while maintaining the required linearity and quality of signal.