OFDM Modulation And B3g Research And Implementation Of Pre - Distortion Technique

Orthogonal Frequency Division Multiplexing (OFDM) is a wide-band wireless communication technique. One of the major drawbacks is a very high peak to average power ratio (PAPR) of OFDM signals because all signal components can add up in phase. A serious problem of large PAPR presents when energy-efficient nonlinear power amplifiers (HPA) used such as spectrum spread and signals distortion. This paper focuses on the algorithm research and hardware implementation on FPGA platform with as less as possible logic resource to this issure.In order to achieve better performance, the paper introduces signal aberration based on the large PAR analysis and its effect on OFDM system. One of the technologies practically used is limitr, which is simple but leads to some shortage in performance. Another one generally used in signal aberration is predistortion. This technology can be used in base-band, intermedia-band or RF and the base-band predistortion have some advantages for its cost-effective and adaptive.In algorithm design,the theory of adaptive filter applied to nonlinear estimation of HPA is solvable but hard to realize for its rigid restriction. The LMS-based algorithm proposed by Widrow that achieves MMSE by updating samples one after another is introduced based on this problem. Based on LMS-algorithm, the paper presents some methods using curve-fit that are also hard to implement for large scale of calculation. Compared to those complex techniques, the look-up table is widely used. In order to simplify the hardware implementation, this paper adopts two 1-D look-up tables instead of one 2-D look-up table to store the amplitude and phase respectively and uses the supposed signal instead of adaptive filter. The performance is better in this way such as the solving of constellation problem, the out of band gain 2dB, the higher convergence rate and the lower BER of system.In FPGA design, this paper accomplishes the realization of OFDM modulation and frame making modules, as well as other relative modules including baseband interface and DAC interface. Because of the limitation of hardware platform, the system only introduces a limitr instead of adaptive predistorter, but the paper presents a draft-design about the latter. All of these have been proved available in the Beyond 3G experimental system.