A BER Simulation Study of Digital Phase Modulation in Nonlinear Bandpass Channels

• Main Authors: Yi-ru Chen, 陳怡如
• Other Authors: Hsin-hsyong Yang
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/90504129264953858653

碩士 === 國立高雄第一科技大學 === 電腦與通訊工程所 === 97 === In this thesis, we study the bit error rate (BER) performance of quadrature phase shift keying (QPSK) signals in nonlinear bandpass channels. The channel interference considered basically coming from signals through bandpass filter (BPF) , nonlinear high power amplifier (HPA) , additive white Gaussian noise (AWGN) and adjacent channel interference (ACI) . We allow the QPSK to be transmitted in different operating points of the nonlinear power amplifier, and the BER is simulated for different ACI’s. In [2] , Rapp found that as HPA operated in the optimum operating point for non-constant envelope modulation like quadrature phase shift keying (QPSK) , the performance is no worse than the truly constant envelope modulation. Nevertheless, signals cannot be operated in the optimal operation point all the time, e.x. CDMA systems deploy adaptive power control. Therefore, this work investigates QPSK signals in similar environment but allows the signal to be operated in different operating point. The BER is than averaged for the same signal to noise ratio (SNR) for different operating point. The BER performance is a simulated for quadrature phase shift keying (QPSK) through HPA and ACI in nonlinear bandpass channels. The degradation of QPSK is calculated by considering output backoff (OBO) and compared with theoretical value. It is concluded that as the HPA is operated ±2dB near the optimal point with adjacent channel interference using normalized channel spacing from 0.6 to 1.2, the results shown that the degradation is between 2.35 to 1.09 dB. Also, when channel spacing is over 1.0, the degradation is about 1.0 dB.