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Study On Key Techniques For Broadband High Efficient And Linear RF Front-end

Posted on:2016-08-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:W S PanFull Text:PDF
GTID:1108330473956087Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
With the dramatic increase of wireless data services, wireless communication technologies have been improved significantly in recent years. In order to transmit non-constant envelope wideband radio frequency(RF) signals, and achieve green wireless communications, the RF front-end is consequently required to have wide bandwidth, high linearity, and high efficiency.This thesis, aims at improving the efficiency, bandwidth and linearity of the RF front-end, respectively. The main contributions of the thesis are listed as follows.1. A novel design of the high-efficiency broadband Doherty power amplifier(DPA) with load modulation is proposed. Due to the wide bandwidth of the DPA, the load modulation performances of the DPA degrade, and the power-added efficiency(PAE) drops over the wide bandwidth. To solve this problem, a new design method based on the broadband asymmetric DPA is proposed, which optimizes the wideband impedance matching networks. It is observed by experiments that, within the frequency range from 2.50 GHz to 2.7GHz, the proposed asymmetric DPA can provide an efficiency higher than 42% with an instantaneous bandwidth(IBW) of 100 MHz at 7 d B back-off from saturation.2. A peak-to-average power ratio(PAPR) reduction method with peak cancellation is proposed for broadband signals. As the optimal iterative amplitude clipping and filtering(OICF) involves the convex optimization, its computational complexity will increase cubically with the number of subcarriers. To reduce the computational complexity, a new peak cancellation scheme for PAPR reduction is proposed. The cancelling pulse is filtered before the peak cancellation by a zero-phase digital filter to mitigate the out-of-band radiation, and the original signal is then subtracted by the filtered signal to reduce the PAPR. Analytical and simulation results reveal that, the computational com--plexity of the proposed method is proportional to the number of subcarriers, with a PAPR reduction performance loss of only 0.06 d B compared with OICF.3. A digital predistortion(DPD) linearization method based on precisely solving the reverse function of the PA model is introduced. The conventional indirect learning DPD method uses a training function to represent the predistortion transfer function, which results in linearization performance degradation. To overcome this degradation, a new PA model learning method is proposed, which calculates the DPD function by solving the reverse function of the PA transfer function using observations. Analytical and simulation results demonstrate that the proposed method outperforms the conventional one by 4 d B.4. A new DPD method is proposed to reduce the feedback bandwidth. The effects of the feedback bandwidth on the DPD linearization performance are analyzed first. To reduce the feedback bandwidth, a band-pass filter with known parameters is inserted in the feedback channel, and a deconvolution operation is applied to the band-limited signal to recover the full-band feedback signal, then the recovered signal is used in the DPD function derivation. Analytical and simulation results show that the proposed method can reduce the feedback bandwidth from 5 times to 2 times the bandwidth of the input signal, with an ACPR performance loss of only 5.6 d B.5. A LTE-Advanced RF evaluation platform is implemented to validate the above key techniques. It is demonstrated that, from 2.50 GHz to 2.70 GHz with an instantaneous bandwidth of 100 MHz, the output power level of the proposed RF front end is larger than 40 d Bm. The efficiency of the DPA is higher than 42% with an ACPR of lower than –45 d Bc.The research results in this thesis can be applied to satellite communications, microwave relay systems, and military common data links(CDL), as well as broadband wireless local area networks(WLAN) and next-generation mobile communications(NGMN).
Keywords/Search Tags:Broadband high-efficiency power amplifier, Doherty power amplifier, Peak-to-average power ratio reduction, Narrow bandwidth feedback, Broadband digital predistortion
PDF Full Text Request
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