Key Technology Research On Broadcasting Uplink System

With the development of next-generation digital TV broadcasting,uplink broadcasting system specialized for interactive services has been supported by ATSC3.0(Advanced Television Systems Committee)standard-setting committee.The terrestrial digital TV standards all use OFDM technology to resist the frequency selective fading caused by multipath distortion.Since the modulation order of the second generation system increases to 16K/32K,the problem of increasing the peak to average power ratio(PAPR)is more serious.Thus,reducing PAPR in system which means reducing the linear distortion of power amplifier,is of great significance in the digital broadcasting uplink system.To compare the SC-FDM architecture of digital TV uplink system with OFDM architecture of existing standard,this paper first constructs mathematic models of PAPR problem in SC-FDM system.Then this paper analyzes that PAPR is lower in SC-FDM compared with OFDM and also shows the influence of system parameters on PAPR theoretically.At the same time,this paper investigates the existing schemes to reduce PAPR,including Clipping method,Selective Mapping method(SLM),Tone Reservation(TR),and Active Constellation Extension(ACE).Through comparing PAPR performanc and complexity,TR method is selected in the main research direction to reduce PAPR.Then,traditional TR techniques including OTOP(One Tone One Peak),OKOP(One Kernel One Peak),gradient Gradient and SCR(Signal to Clipping noise Ratio)schemes are researched comparing with the Active Set scheme.The shortage of traditional algorithms are analyzed from convergence,iteration number,complexity and so on.Since the Active Set scheme first only considers real baseband signal,the improved algorithm based on complex baseband signal has the problem of quadratic constraint.Therefore,polygon fitting is designed for the proposed algorithm which makes Active Set scheme implemented for hardware.In addition,two key issues of TR scheme are discussed:the numbers and the place of reserved tones.Considering TR numbers,the concept of effective signal energy is first defined in this paper.It combines the extra energy consumption caused by reserved carriers and PAPR performance enhancement.So the problem of optimal TR numbers is studied by modeling the effective signal energy from theory.Furthermore,for the problem of optimal carrier position,the original objective function is the minimum sub-peak of the time-domain kernel.Then variance of kernel signal instead of sub-peak is proposed to reduce the computational complexity of the search process.Finally,a nonuniform frequency-domain kernel scheme is designed to improve current constant-envelope scheme.The closed-form derivable formula of minimum variance is given,and the nonuniform scheme is simulated to verify better PAPR performance.After researching the theoretical analysis and scheme optimization of TR,system is simulated and implemented using hardware board based on Xilinx Virtex6.The PAPR performance of SC-FDM system with Tone Reservation is verified,which provides theoretical support and feasible solutions verification for PAPR key techniques in broadcasting uplink system.