Adaptive polynomial predistorters for M‐QAM transmission using non‐linear power amplifiers

Abstract

In this paper, adaptive baseband polynomial predistortion techniques are introduced to counter-balance the AM/AM and AM/PM non-linear effects of the transmit power amplifier. The proposed polynomial predistortion scheme is based on polar coordinate representation. Both LMS and RLS concepts are used to derive the adaptive algorithms. An enhanced LMS-based algorithm with fast convergence and low complexity is proposed. For very fast convergence, a cascaded RLS-based adaptive polynomial predistorter structure is introduced. The performance of the proposed schemes in terms of intermodulation distortion, spectral regrowth, and convergence rate are examined. The obtained results show that the polynomial predistortion schemes can be used in M-QAM transmitters with power amplifiers operating near saturation to achieve a highest power efficiency.

Power amplifier linearisation scheme to mitigate superfluous radiations and suppress adjacent channel interference

“…The important term in (17) is P [| x ( n )| 2 ]/( r ( n ) S 0 [| r ( n )| 2 ]) called gain factor. Gain factor is a constant between zero and one, where higher values give faster convergence, but lower performance and lower values yield higher performance, but slower convergence [10, 11]. In the CGC scheme, the parameter α represents the gain factor which is not constant because of the memory effects modelling in CGC scheme.…”

“…In addition, most of the proposed techniques lack feasibility. Authors in [10, 11] proposed a pre‐distortion technique applied in code division multiple access (CDMA) applications; however, the drawback was its high complexity. In this paper, design of a high power amplifier for CDMA applications is carried out.…”