• Journal of information and communication convergence engineering
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• v.20 no.1
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• pp.1-7
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• 2022

Herein, a new space-time block coding technique is proposed for a MIMO 2 × 2 multiple-input multiple output (MIMO) system to minimize the bit error rate (BER) in Rayleigh fading channels with reduced decoding complexity using ZF and MMSE linear detection techniques. The main objective is to improve the service quality of wireless communication systems and optimize the number of antennas used in base stations and terminals. The idea is to exploit the correlation product technique between both information symbols to transmit per space-time block code and their own orthogonal Walsh-Hadamard sequences to ensure orthogonality between both symbol vectors and create a full-rate orthogonal STBC code. Using 16 quadrature amplitude modulation and the quasi-static Rayleigh channel model in the MATLAB environment, the simulation results show that the proposed space-time block code performs better than the Alamouti code in terms of BER performance in the 2 × 2 MIMO system for both cases of linear decoding ZF and MMSE.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.12
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• pp.66-74
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• 2001

In this paper, we proposed the new structure of the Rake Finger using Walsh Switch, the shared accumulator, and the pipeline FWHT(Fast Walsh Hadamard Transform) algorithm for reducing the signal processing complexity resulting from the increase of the number of data correlators. The function simulation of the proposed architecture is performed by Synopsys tool and the timing simulation is performed by Compass tool. The number of computational operation in the proposed data correlators is 160 additions and the conventional ones is 512 additions when the number of walsh code channels is 4. As a result, it is reduced about 3.2 times other than the number of computational operation of the conventional ones. Also, the result shows that the data processing time of the proposed Rake Finger architecture is 90,496[ns] and the conventional ones is 110,696[ns]. It is 18.3% faster than the data processing time of the conventional Rake Finger architecture.

• Korean Journal of Optics and Photonics
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• v.19 no.4
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• pp.262-269
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• 2008

In this paper, we propose an image watermark method using multiple decoding keys. The advantages of this method are that the multiple original images are reconstructed by using multiple decoding keys in the same watermark image, and that the quality of reconstructed images is clearly enhanced based on the idea of Walsh code without any side lobe components in the decoding process. The zero-padded original images, multiplied with random-phase pattern to each other, are Fourier transformed. Encoded images are then obtained by taking the real-valued data from these Fourier transformed images. The embedding images are obtained by the product of independent Walsh codes, and these spreaded phase-encoded images which are multiplied with new random-phase images. Also we obtain the decoding keys by multiplying these random-phase images with the same Walsh code images used in the embedding images. A watermark image is then made from the linear superposition of the weighted embedding images and a cover image, which is multiplied with a new independent Walsh code. The original image is simply reconstructed by the inverse-Fourier transform of the despreaded image of the multiplication between the watermark image and the decoding key. Computer simulations demonstrate the efficiency of the proposed watermark method with multiple decoding keys and a good robustness to the external attacks such as cropping and compression.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.7
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• pp.12-22
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• 2012

The main drawback of the multi-code spread spectrum communication system, which spreads data bits stream by the multiplexed orthogonal codes, is the need for the highly linear amplifier. Several constant amplitude precoding schemes have been proposed for the Walsh code or the extended $m$-sequence based multi-code spread spectrum systems. In the constant amplitude spread spectrum systems the accompany code is transmitted together with orthogonal codes to maintain the transmitter output in a constant level. In this paper we propose the use of the accompany in the receiver to improve the BER performance. The proposed receiver has the capability to correct the code detection error(up to one code error). We carried out simulations to verify the validity of the proposed algorithm. BER performance improvement was noticed compared with the conventional receiver.

• Journal of Digital Convergence
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• v.12 no.8
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• pp.249-255
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• 2014

In this paper, we proposed to reduce the interference in the visible light Communication with multi-LEDs for improving the performance of BER and satisfied the QoS. LED is not only lighting device, but also transmitting device in the VLC. Our proposed system is aim to decrease the interference in the multi-LEDs. In addition, it occurred the ISI and CCI by transmitter to receiver different distance. To solve this problem, we proposed the multi-LEDs system using walsh code to reduce ISI and CCI. In addition, our proposed system is able to improve the performance of BER and satisfied the Qos to desire users.

• Journal of Satellite, Information and Communications
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• v.7 no.3
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• pp.26-29
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• 2012

In this paper, we propose a Single Carrier Frequency Division Multiple Access(SC-FDMA) scheme with greatly enhanced tolerance of timing offset among the users. The type of the proposed scheme is similar to code spread Multiple Carrier Direct Spread Code Division Multiple Access(MC DS CDMA). The proposed scheme performs partial Discrete Fourier Transform(DFT) in order to solve high Peak to Average Power Ratio(PAPR) of the MC DS CDMA before Inverse Fast Fourier Transform(IFFT). Exploiting the property Properly Scrambled Walsh-Hadamard(PSW) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed scheme achieves Multiple Access Interference free performance with the timing offset up to ${\pm}1$ OFDM symbol duration with low PAPR. In contrast, the other existing schemes in comparison undergo severe performance degradation even with small timing offset in multipath fading channel.

• Proceedings of the Optical Society of Korea Conference
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• 2005.02a
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• pp.312-313
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• 2005

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.21 no.6
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• pp.43-48
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• 2021

We propose 2-channel filter bank method instead of FFT method to decrease sub-channel interference for using of efficient frequency resource in MC-CDMA method. Since a prototype filter of filter bank having wavelet characteristic is designed having more less side-lobe, the nearest co-channel interference and inter symbol interference are decreased efficiently. Since the spreading signal of suggesting MC-CDMA system is being demanded for less chip rate and is not being considering for autocorrelation characteristic, the Walsh code can be used as a optimal orthogonal signal set. We consider bit error rate and signal to noise ratio to estimate the performance of suggested system on condition that white noise channel and arbitrary sinusoidal jammer are existing. As a result of comparing to traditional FFT-based MC-CDMA simulation result, our suggested system has shown better performance than traditional MC-CDMA method on the side of minimizing interference effect.

• Journal of the Korea Society of Computer and Information
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• v.7 no.3
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• pp.135-142
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• 2002

In this paper, we proposed the new structure of the Rake Finger using Walsh Switch, the shared accumulator and the pipeline FWHT algorithm for reducing the signal processing complexity resulting from the increase of the number of data correlators. The number of computational operation in the proposed data correlators is 160 additions when the number of walsh code channels is 4. As a result, it is reduced about 3.2 times other than the number of computational operation of the conventional ones. Also, the result shows that the data processing time of the proposed Rake Finger architecture is 90,496〔ns〕 and the conventional ones is 110,696〔ns〕. It is 18.3% faster than the data processing time of the conventional Rake Finger architecture.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.29-32
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• 2000

In this paper, we present an extension of the multi-code CDMA (code division multiple access) systems based on bi-orthogonal modulation by employing a convolutional encoder and an interleaver before serial-to-parallel conversion in the modulator. Bandwidth expansion by the convolutional encoder can be compensated for by the bi-orthogonal modulation, and the interleaver in the system scrambles the convolutionally encoded data bits so that, after serial-to-parallel conversion, each code channel conveys those bits far apart in time. The result is that the proposed system with several order of magnitude less implementational complexity, achieves quite close performance of the conventional systems comprised of Walsh modulation and multiple convolutional encoders and interleavers in all the code channels.