Performance Evaluation of Noisy Nonlinear QAM and QPSK Systems in the Presence of the Signal Predistortion Linearizer
Pedram Hajipour1, Ali Forotanpour2, Leila Mohammadi3

1Pedram Hajipour, CTI, Research Institute for ICT, Tehran, Iran.
2Ali Forotanpour, CTI, University, Research Institute for ICT, Tehran, Iran.
3Leila Mohammadi, CTI, Research Institute for ICT, Tehran, Iran.
Manuscript received on August 12, 2011. | Revised Manuscript received on August 17, 2011. | Manuscript published on September 05, 2011. | PP: 82-86 | Volume-1 Issue-4, September 2011. | Retrieval Number: D089071411/2011©BEIESP
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Abstract: In this paper, the design and simulation process of a TWTA amplifier which is linearized with a signal predistortion method is presented. The aim of the linearizer circuit which is based on the schottky diodes is to compensation-linearity behavior of the amplifier in a noisy channel. The linearizer circuit is optimized to give the best AM-to-AM and AM-to-PM characteristics. In addition, the stability of the TWTA with combination of the proposed linearizer is investigated through computer simulations. The data is modulated by a 4-QAM and QPSK modulator, separately and is applied to the linearized TWTA. The received data after passing through the linearized TWTA is analyzed by using advanced design system (ADS) and the constellation and eye diagrams are obtained. Finally the BER performance of the system is evaluated using Monte Carlo estimation for three different values of input-back-off (IBO). It is also shown that decreasing the IBO degrades the performance. The results of the modulations are compared with together.
Keywords: TWTA, Predistortion, QAM, QPSK, BER.