Hikaru Kawasaki

N-continuous symbol padding OFDM for sidelobe suppression

N-continuous orthogonal frequency division multiplexing (OFDM) is a modulation technique that has a lower sidelobe than the original OFDM as a result of the continuous connection with its higher-order derivatives between the OFDM symbols. However, N-continuous OFDM requires an iterative algorithm for removing correction symbols from received signals at the receiver. In this paper, a method called N-continuous symbol padding is proposed, which inserts N-continuous OFDM correction symbols only into the guard interval and seamlessly connects each OFDM symbol, thereby suppressing the sidelobes. It has been demonstrated by numerical experiments that the N-continuous symbol padding method provides power spectral density and SER characteristics equal to or better than those of the conventional method, without using an iterative algorithm. This method is particularly effective for a system with a small number of subcarriers.

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The modulation technique of N-continuous orthogonal frequency division multiplexing (OFDM) has lower sidelobes than those of the original OFDM as a result of the continuous connection with higher-order derivatives between the OFDM symbols. Compared with the other sidelobe suppression schemes, for example, cancellation carrier insertion, and windowing, N-continuous OFDM does not require an extended guard interval nor the insertion of a wide guard band or cancellation carriers. However, N-continuous OFDM requires an iterative algorithm to remove the correction symbols from received symbols at the receiver and the large power of the correction symbols in the high-frequency area results in unavailable bandwidth. Here, we propose an extension of the N-continuous OFDM precoder matrix that flattens the bias power caused by the correction symbols in all frequency areas. Numerical experiments show that the proposed method improves the error rate performance without degrading the sidelobe suppression performance. The proposed method can also reduce the unavailable bandwidth.

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N-continuous orthogonal frequency division multiplexing is a modulation technique that achieves a lower-sidelobe transmission signal. However, the calculation (precoding) method requires a wide dynamic range arithmetic. This study considered two decompositions of the precoder matrix for a low-end field-programmable gate array (FPGA) without DSP blocks. Results of numerical experiments and a test design confirm that the singular value decomposition is suitable for FPGA implementation.

-Continuous OFDM Precoder Matrix for Improving Error Rate

N-continuous symbol padding orthogonal frequency division multiplexing (NCSP-OFDM) is a modulation technique for sidelobe suppression, which adds the correction symbol only into the guard interval to enable the seamless connection of OFDM symbols. NCSP-OFDM requires the calculation of an inverse matrix per channel estimation, and so its computational complexity is large. This paper considers low-complexity receivers of the NCSP-OFDM. Numerical experiments are conducted to evaluate its performance compared with conventional NCSP-OFDM receiver.

Matrix decomposition suitable for FPGA implementation of N-continuous OFDM

Spectrum sculpting (SS) is a precoding scheme for sidelobe suppression of orthogonal frequency division multiplexing (OFDM) signals and can shape a spectrum with deep notches at chosen frequencies. However, the SS method will degrade the error rate as the number of notched frequencies increases. Orthogonal precoding of the SS has both a notched spectrum and an ideal error rate, but the computational complexity of the precoder matrix is very large. This paper proposes a matrix decomposition of the precoder matrix of the orthogonal precoding to reduce the computational complexity. Numerical experiments show that the proposed method can drastically reduce the computational complexity.

A study on low-complexity receiver of NCSP-OFDM for sidelobe suppression

Both N-continuous OFDM and N-continuous symbol padding OFDM (NCSP-OFDM) are modulation techniques that achieve a low sidelobe transmission signal. This study compares the timing synchronization performance of these modulation techniques by using a simple non-data-aided algorithm. The experimental results indicate that the timing metric curve of N-continuous OFDM becomes flat near the ideal timing to detect an OFDM symbol. On the other hand, the curve of NCSP-OFDM exhibits a sharp peak, although its time has the gap against the ideal timing. We propose a gap-corrected ML estimation of time offset. From the results of numerical experiment, we find that the proposed estimation improves the timing synchronization performance of NCSP-OFDM as compared with that of N-continuous OFDM.