Impact Analysis And Compensation Of Power Amplifier Nonliearity For 60GHz Communication Systems

With the increasing demand for the high rate short-range wireless communication, the technology of 60 GHz communication becomes the new hot spot rapidly. Since the research of 60 GHz is in the development stage, the emphasis of the power amplifier in 60 GHz is on the designing and implementation of hardware circuits. Nowadays, there is little literature about the power amplifier model based on the draft standard of newly proposed IEEE 802.11 ad, nor is about the digital compensation in the baseband. Hence, this text will focus on these two points.Before the formal analysis, according to the standard of IEEE 802.11 ad, a systematic simulation model which is based on SCBT is constructed and a detailed introduction about the design of the channel and the physical layer is made.In theory, the nonlinear characteristics will bring about distortion in and out of the band. Distortion in the band will cause inter-modulation components and thus it may reduce the performance of the system.Distortion out of band will cause spectral regrowth which is to interfere with adjacent channels.Based on the amplifier model and the simulated system, this paper will make an analysis about how the nonlinearity of the amplifier influence the 60 GHz system in different modulations on the aspects of the signal and the system respectively. The results of the simulation show that the influence of nonlinearity is very little on QPSK, but it is great on 16 QAM. Thus in order to ensure the performance of communication, QPSK is recommended. When average output power back-off is large, that is, the influence of the nonlinearity is very little, 16 QAM can also be used if only the systematic SNR can be improved.For the loss caused by the amplifier nonlinearity, it needs to be compensated by efficient methods of linearization. Taken the low complexity into consideration, the compensation method is realized by polynomial based digital predistorter.Based on the nonlinear amplifier model of 60 GHz, the performance of power spectrum suppression before and after predistortion can be simulated by constructing the memoryless polynomial based predistorter where the polynomial coefficients are estimated by the RLS adaptive algorithm.The results show that after predistortion, the output spectrum of the amplifer is nearly identical with the original input signal. In addition, 7-odder memoryless polynomial based digital predistortion can effectively compensate the performance loss caused by the amplifier nonlinearity. This proves the validity of the memoryless polynomial predistortion method theoretically. Lastly, in order to avoid the strict requirement to the AD sampling of feedback link, a design of offline compensation is proposed to adapt to single carrier modulation.