Yang Zhixing

Effects of PAPR reduction on HPA predistortion

There have been many papers concerning about the peak to average power ratio (PAPR) reduction and high power amplifier (HPA) linearization techniques for wireless OFDM communication systems. Few papers, however, make deep analysis on the relation between these two techniques. Based on Salehs memoryless traveling wave tube amplifier (TWTA) model, computer simulations and analysis in this paper demonstrates that, especially when the HPA is working near or in the saturation region, a predistorter ceases to be in effect. In such cases, PAPR reduction techniques may be resorted to help to improve the adjacent channel interference (ACI), BER performances and HPA efficiency.

Improved LUT Technique for HPA Nonlinear Pre-Distortion in OFDM Systems

In this paper, we focus on the Look-up Table (LUT) technique for the compensation of HPA nonlinear distortion. An improved LUT method is proposed with better performance compared with conventional LUT technique in terms of convergence speeds, BER and total degradation (TD). It can get over 8 dB gain in out-of-band spectrum re-growth suppression and about 0.3 dB BER performance gain than conventional LUT technique with the same iteration times. Also, we propose an actual application of HPA with pre-distorter in OFDM transmitter.

Design and FPGA implementation of high-speed square-root-raised-cosine FIR filters

A series of square-root-raised-cosine (SRRC) FIR filter with CSD coefficients were designed according to the local search algorithm based upon minimax error criteria. The simulation results of a baseband system show that two 13-tap SRRC FIR filters with a roll-off factor 0.6 only introduced about 6% peak distortion in the eye pattern. A bit-level pipeline architecture was used to realize the high sampling rate FIR filter. An additional tap with fixed input of 10 was added to the final stage of the filter to avoid carry ripple. Consequently, the critical path consists of only a single one-bit full adder and a pipeline register. The filter was implemented in an alteras FPGA: EP20K60EFC144-1 and the timing analyses results show that the sampling rate could be over 200 MHz.

Multiuser synchronization in noncoherent asynchronous CDMA

The influence of multiple access interference (MAI) on noncoherent code tracking loops is analyzed and in order to acquire the reliable synchronization, a new scheme is proposed which can eliminate the steady-state phase error and reduce the rms tracking jitter considerably.