Walid Khairy Mohamed Ahmed

Performance analysis of a novel real-time closed-loop technique for non-linearity correction of power amplifiers

In this paper we discuss performance results of a novel real-time closed-loop power amplifier (PA) linearization technique that has originally been proposed by Ahmed and Li. The novel approach performs on-the-fly prediction and measurement of the PA AM/AM and AM/PM non-linearity, stores such non-linear characteristics and calculates their inverse functions in order to pre-distort the base-band amplitude and phase signals modulating the PA such that the combination, or the resultant, of the pre-distorter and the PA leads to a linear behavior at the output of the PA. We present a model of our predictor based approach and evaluate its performance for an GSM/EDGE application. The key performance metrics we evaluate have been based on the GSM/EDGE requirements, such as the Error Vector Magnitude (EVM), Switching Transients (ST), Adjacent Channel Power Ratio (ACPR), transmit time mask, modulation spectrum and PAE.

High efficiency digital polar transmitter for cellular handsets

In this paper, the architecture of a digital polar transmitter system for cellular multi-mode handset is presented with hardware implementation emphasis on 2/2.5G systems (GSM/EDGE). The most prominent feature of this architecture is its ability to employ a highly nonlinear PA, this highly efficient. This is accomplished via our novel real-time nonlinear closed-loop predictive calibration for correcting the PAs nonlinearity. In addition, our architecture makes it possible to eliminate or minimize the need for extensive factory calibration since our predictive realtime auto-calibration scheme does not require much prior knowledge of the system characteristics.