• ETRI Journal
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• v.44 no.3
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• pp.379-388
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• 2022

This study proposes a novel low-complexity algorithm for computing inverse fast Fourier transform (IFFT)/fast Fourier transform (FFT) operations in binary phase shift keying-modulated orthogonal frequency division multiplexing (OFDM) communication systems without requiring any twiddle factor multiplications. The peak-to-average power ratio (PAPR) reduction capacity of an efficient PAPR reduction technique, that is, H-SLM method, is evaluated using the proposed IFFT algorithm without any complex multiplications, and the impact of oversampling factor for the accurate calculation of PAPR is analyzed. The power spectral density of an OFDM signal generated using the proposed multiplierless IFFT algorithm is also examined. Moreover, the bit-error-rate performance of the H-SLM technique with the proposed IFFT/FFT algorithm is compared with the classical methods. Simulation results show that the proposed IFFT/FFT algorithm used in the H-SLM method requires no complex multiplications, thereby minimizing power consumption as well as the area of IFFT/FFT processors used in OFDM communication systems.

• The Journal of the Acoustical Society of Korea
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• v.26 no.5
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• pp.214-219
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• 2007

This paper proposes a new IFFT(Inverse Fast Fourier Transform) algorithm, which is proper for IMDCT(Inverse Modified Discrete Cosine Transform) of MPEG-2 AAC(Advanced Audio Coding) decoder. The $2^n$(N-point) type IMDCT is the most powerful among many IMDCT algorithms, however it includes IFFT that requires many calculation cycles. The IFFT used in $2^n$(N-point) type IMDCT employ the bit-reverse data arrangement of inputs and N/4-point complex IFFT to reduce the calculation cycles. We devised a new data arrangement method of IFFT input and $N/4^{n+1}$-type IFFT and thus we can reduce multiplication cycles, addition cycles, and ROM size.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.11
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• pp.11-18
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• 2007

FFT(Fast Fourier Transform) processor is one of the key components in the implementation of OFDM systems such as WiBro, DAB and UWB systems. Most of the researches on the implementation of FFT processors have focused on reducing the complexities of multipliers, memory and control circuits. In this paper, to reduce the memory size required for IFFT(Inverse Fast Fourier Transform), we propose a new IFFT design method based on a mapping method. By simulations, it is shown that the reposed IFFT design method achieves more than 60% area reduction and much SQNR(Signal-to-Quantization-Noise Ratio) gain compared with previous IFFT circuits.

• Journal of Communications and Networks
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• v.8 no.1
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• pp.38-48
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• 2006

A synchronous multicarrier (MC) code-division multiple access (CDMA) system using inverse fast Fourier transform (IFFT) and fast Fourier transform (FFT) for the downlink mobile communication system operating in a frequency selective Rayleigh fading channel is analyzed. Both carrier frequency offset and timing offset are considered in the analysis. Bit error rate performance of the system with both equal gain combining and maximum ratio combining are obtained. The performance is compared to that of the conventional system using correlation receiver. It is shown that when subcarrier number is large, the system using IFFT/FFT has nearly the same performance as the conventional one, while when the sub carrier number is small, the system using IFFT/FFT will suffer slightly worse performance in the presence of carrier frequency offset.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.3
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• pp.570-576
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• 2004

In this paper, we design the IFFT/FFT (Inverse fast Fourier Transform/Fast Fourier Transform) modules for IEEE 802.11a-1999, which is a standard of the High-speed Wireless LAN using the OFDM (Orthogonal Frequency Division Multiplexing). The designed IFFT/FFT is the 64-point FFT to be compatible with IEEE 802.11a and the pipelined architecture which needs neither serial-to-parallel nor parallel-to-serial converter. We compare four types of IFFT/FFT modules for the hardware complexity and operation : R22SDF (Radix-2 Single-path Delay feedback), the R2SDF (Radix-2 Single-path Delay feedback), R2SDF (Radix-4 Single-path Delay Feedback), and R4SDC (Radix-4 Single-path Delay Commutator). In order to minimize the error, we design the IFFT/FFT module to operate with additional decimal parts after butterfly operation. In case of the R22SDF, the IFFT/FFT module has 44,747 gate counts excluding RAMs and the minimized error rate as compared with other types. And we know that the R22SDF has a small hardware structure as compared with other types.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.3
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• pp.294-303
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• 2008

ISAR(Inverse Synthetic Aperture Radar) images represent the 2-D(two-dimensional) spatial distribution of RCS (Radar Cross Section) of an object, and they can be applied to the problem of target identification. A traditional approach to ISAR imaging is to use a 2-D IFFT(Inverse Fast Fourier Transform). However, the 2-D IFFT results in low resolution ISAR images especially when the measured frequency bandwidth and angular region are limited. In order to improve the resolution capability of the Fourier transform, various high-resolution spectral estimation approaches have been applied to obtain ISAR images, such as AR(Auto Regressive), MUSIC(Multiple Signal Classification) or Modified MUSIC algorithms. In this study, these high-resolution spectral estimators as well as 2-D IFFT approach are combined with a recently developed ISAR image classification algorithm, and their performances are carefully analyzed and compared in the framework of radar target recognition.

• Journal of Internet Computing and Services
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• v.13 no.2
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• pp.13-20
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• 2012

SLM (Selected Mapping) is an efficient PAPR (Peak-to-Average Power Ratio) reduction scheme without transmitted signal distortion in OFDM (Orthogonal Frequency Division Multiplexing) systems. However, enormous IFFTs (Inverse Fast Fourier Transforms) are needed to generate sufficient candidate OFDM signals, which cause the SLM to become quite complex. In this paper, we propose a new SLM scheme that replaces the IFFT operations with a conversion of the first candidate OFDM signal. The proposed scheme significantly reduces computational complexity, while it shows almost the same PAPR performance as the conventional SLM scheme.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.3
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• pp.184-191
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• 2018

Orthogonal frequency division multiplexing(OFDM) is a multicarrier modulation(MCM) system that enables high-speed communications using multiple carriers and has advantages of power and spectral efficiency. Therefore, this study aims to complement the existing shortcomings and to design an efficient MCM system. The proposed system uses the inverse discrete wavelet transform(IDWT) operation instead of the inverse fast Fourier transform(IFFT) operation. The bit error rate(BER), spectral efficiency, and peak-to-average power ratio(PAPR) performance were compared with the conventional OFDM system through the OFDM system design based on wavelet transform. Our results showed that the conventional OFDM and Wavelet-OFDM exhibited the same BER performance, and that the Wavelet-OFDM using the discrete Meyer wavelet had the same spectral efficiency as the conventional OFDM. In addition, all systems of Wavelet-OFDM based on various wavelets confirm a PAPR performance lower than that of conventional OFDM.

• Proceedings of the IEEK Conference
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• 2007.07a
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• pp.261-262
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• 2007

This paper proposes a new IFFT(Inverse Fast Fourier Transform) algorithm, which is proper for IMDCT(Inverse Modified Discrete Cosine Transform) of MPEG-2 AAC(Advanced Audio Coding) decoder. The IFFT used in $2^N$-point IMDCT employ the bit-reverse data arrangement of inputs and N/4-IFFT to reduce the calculation cycles. We devised a new data arrangement algorithm of IFFT input and N/$4^{n+1}$-IFFT and can reduce multiplication cycles, addition cycles, and ROM size.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.7A
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• pp.1005-1015
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• 1999

This paper is concerned with an improvement on IFFT (inverse fast Fourier transform) and FFT based baseband digital implementation algorithm for BPSK (binary phase shift keying)-modulated MC-CDMA (multicarrier-code division multiple access) systems, that is functionally equivalent to the conventional implementation algorithm, while reducing computational complexity and bandwidth requirement. We also derive an equalizer structure for the proposed implementation algorithm. The proposed algorithm is based on a variant of FFT algorithm that utilizes a N/2-point FFT/IFFT for simultaneous transformation and reconstruction of two N/2-point real signals. The computer simulations under additive white Gaussian noise channels and frequency selective fading channels using equal gain combiner and maximal ratio combiner diversities, demonstrate the performance of the proposed algorithm.