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Research And Implementation Of Fast Fourier Transform (FFT) Processor In TDS - OFDM System

Posted on:2015-07-07Degree:MasterType:Thesis
Country:ChinaCandidate:D G WangFull Text:PDF
GTID:2208330464963304Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
In modern wireless communication system, in order to take full advantage of limited spectrum resources, OFDM has become the main technique in broadband wireless communication system and has been adopted by many wireless communication standards. The Chinese DMBT standard adopts TDS-OFDM system which is different from the conventional OFDM.TDS-OFDM system uses PN sequence to fill guard intervals among OFDM symbols, making the spectrum efficientcy higher because there is no need of pilot signal assertion in frequency domain. TDS-OFDM selects 3780 as its number of subcarriers, and uses 3780 points FFT/IFFT processor to complish multi-carrier modulation and demodulation. As one of the key module in the system, research work of algorithm, structure, and hardware implementation aiming at 3780 points FFT processor is provided with great theoretical and pratical significance.In this thesis, detailed research work on main FFT algorithms and their hardware architectures has been accomplished. The decomposition process of diffierent algorithm has been analyzed and deduced. Their arithmetic complexity and applying scope are compared. In the aspect of hardware structure of FFT processor, two main implementation method, memory-based structure and piplelined structure have been discussed and compared.Based on the study of existing 3780 points FFT processors, thorough research work and several modifications have been carried out as follows:1. At algorithmic level, the Colley-Tukey and Good-Thomas mixed-radix algorithm are applied simultaneously. By decomposing the prime factor first and doing cascaded decomposition, less twiddle factor storages are required. At architectural level, based on the multi-bank memory strategy of general mixed-radix algorithm, a conflict-free memory allocation scheme and address generation mechanism which is suitable for the 3780 point FFT is obtained.2. In order to meet the continuous flow requirement of real-time processing, this thesis proposed a novel input/output address mapping method. By changing the computation order of last three stages, in-place computation as well as continuous flow processing can be achieved efficiently.3. A novel architecture of FFT processing element is proposed, which reuses two streams of 3-point, one 4-point, one 5-point and one 7-point WFTA butterfly structure. This method reduces the computation cycles of FFT by improving the degree of data parallelism, meanwhile, it lowers the hardware cost of the computation unit.4. Modification has been made on the subject of twiddle factor multiplication. A novel modified high-radix CORDIC algorithm is proposed. It reduces the iteration number of conventional CORDIC algorithm, and keeps the scaling factor as a constant. The designed twiddle factor multiplication unit consumes less hardware resources and memory storage in comparison with the scheme composed of general complex multipliers.On the basis of above modifications and research work, this thesis proposes an efficient memory-based implementation scheme of 3780 point FFT processor. Detailed design methods of system architecture and key modules have been discussed. Compared with the existing methods, this architecture has the advantage of less hardware cost, memory storage and computation cycles.This thesis has established floating-point and fixed-point reference model of 3780 points FFT based on Matlab, use Verilog HDL to complish RTL-level hardware design, and built FPGA hardware simulation and verification platform in order to do functional verification and performance evaluation. Simulation results show that the designed 3780 points FFT processor perfectly meets the requirements of TDS-OFDM system. At the end, synthesis and layout design have been finished based on TSMC 65nm process and final layout result are obtained.
Keywords/Search Tags:TDS-OFDM, DMBT mixed-radix algorithm, FFT, WFTA, CORDIC
PDF Full Text Request
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