• Journal of Communications and Networks
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• 제14권3호
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• pp.280-285
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• 2012

We propose self-encoded spread spectrum with two different iterative detection methods in multi-channel communication. The centralized iterative detection outperforms the iterative detection distributed over multiple channels. The results show that self-encoded spread spectrum with the centralized iterative detection is an excellent candidate for cognitive radio network.

• Journal of Communications and Networks
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• 제15권3호
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• pp.258-265
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• 2013

In this study, we investigate the multi-carrier spread spectrum (MCSS) communication system which adopts the self-encoded spread spectrum in a downlink synchronous channel. It is very difficult to completely eliminate the frequency offset in practical channel scenarios. We demonstrate that the self-encoded MCSS (SE-MCSS) with iterative despreading manifests a remarkable immunity to residual frequency offset. The SE-MCSS can be an excellent candidate for the future generation of wireless services.

• Journal of Communications and Networks
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• 제15권3호
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• pp.276-282
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• 2013

Self-encoded spread spectrum (SESS) is a novel modulation technique that acquires its spreading code from a random information source, rather than using the traditional pseudo-random noise (PN) codes. In this paper, we present our study of the SESS system performance under pulsed-noise jamming and show that iterative detection can significantly improve the bit error rate (BER) performance. The jamming performance of the SESS with correlation detection is verified to be similar to that of the conventional direct sequence spread spectrum (DSSS) system. On the other hand, the time diversity detection of the SESS can completely mitigate the effect of jamming by exploiting the inherent temporal diversity of the SESS system. Furthermore, iterative detection with multiple iterations can not only eliminate the jamming completely but also achieve a gain of approximately 1 dB at $10^{-3}$ BER as compared with the binary phase shift keying (BPSK) system under additive white gaussian noise (AWGN) by effectively combining the correlation and time diversity detections.

• Journal of Communications and Networks
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• 제8권3호
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• pp.267-274
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• 2006

Self-spreading (SSP) is a spread spectrum technique where the spreading sequence is generated from data bits. Although SSP allows communications with low probability of interception by unintended receivers, despreading by the intended receiver is prone to error propagation. In this paper, we propose both a new transmitter and a new receiver based on SSP with the aim to a) reduce error propagation and b) increase the concealment of the transmission. We first describe a new technique for the generation of SSP spreading sequence, which generalizes SSPs of existing literature. We include also coding at the transmitter, in order to further reduce the effects of error propagation at the receiver. For the receiver, we propose a turbo architecture based on the exchange of information between a soft despreader and a soft-input soft-output decoder. We design the despreader in order to fully exploit the information provided by the decoder. Lastly, we propose a chip decoder that extracts the information on data bits contained in the spreading sequence from the received signal. The performance of the proposed scheme is evaluated and compared with existing spread-spectrum systems.

• Journal of Communications and Networks
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• 제6권1호
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• pp.9-18
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• 2004

Self-encoded multiple access (SEMA) is a unique realization of random spread spectrum. As the term implies, the spreading code is obtained from the random digital information source instead of the traditional pseudo noise (PN) code generators. The time-varying random codes can provide additional security in wireless communications. Multi-rate transmissions or multi-level grade of services are also easily implementable in SEMA. In this paper, we analyze the performance of SEMA in additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. Differential encoding eliminates the BER effect of error propagations due to receiver detection errors. The performance of SEMA approaches the random spread spectrum discussed in literature at high signal to noise ratios. For performance improvement, we employ multiuser detection and Turbo coding. We consider a downlink synchronous system such as base station to mobile communication though the analysis can be extended to uplink communications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권2호
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• pp.253-270
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• 2013

To achieve accurate localization information, complex algorithms that have high computational complexity are usually implemented. In addition, many of these algorithms have been developed to overcome several limitations, e.g., obstruction interference in multi-path and non-line-of-sight (NLOS) environments. However, localization systems those have complex design experience latency when operating multiple mobile nodes occupying various channels and try to compensate for inaccurate distance values. To operate multiple mobile nodes concurrently, we propose a localization system with both low complexity and high accuracy and that is based on a chirp spread spectrum (CSS) radio. The proposed localization system is composed of accurate ranging values that are analyzed by simple linear regression that utilizes a Big-$O(n^2)$ of only a few data points and an algorithm with a self-calibration feature. The performance of the proposed localization system is verified by means of actual experiments. The results show a mean error of about 1 m and multiple mobile node operation in a $100{\times}35m^2$ environment under NLOS condition.

• 동력기계공학회지
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• 제19권2호
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• pp.33-39
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• 2015

In conducting indoor positioning by code division multiple access using spread spectrum ultrasonic waves, it is required to detect signals under the influence of near-far problem occurred by difference on signal power, caused by distance between transmitter and receiver. For discussing robustness to the problem, we verified measuring accuracy on distance from an experiment on a real space with a hardware device where our proposed method is mounted. The proposed method performs automatic signal detection by setting threshold level dynamically. As an experimental result, measurable distance were improved by the proposed method, and measurement errors were up to 50mm in distances from 1000mm to 6000mm; therefore, enough accuracy to realize self-localization or navigation for autonomous mobile robot or human was obtained.

• Journal of Communications and Networks
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• 제9권1호
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• pp.50-55
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• 2007

We propose to apply chip interleaving and iterative detection to self-encoded multiple access (SEMA) communications. In SEMA, the spreading code is obtained from user bit information itself without using a pseudo noise code generator. The proposed scheme exploits the inherent diversity in self encoded spread spectrum signals. Chip interleaving not only increases the diversity gain, but also enhances the performance of iterative detection. We employ user-mask and interference cancellation to decouple self-encoded multiuser signals. This paper describes the proposed scheme and analyzes its performance. The analytical and simulation results show that the proposed system can achieve a 3 dB power gain and possess a diversity gain that can yield a significant performance improvement in both Rayleigh and multipath fading channels.

• 동력기계공학회지
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• 제17권5호
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• pp.100-111
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• 2013

Indoor real-time positioning for multiple targets is required to realize human-robot symbiosis. This study firstly presents positioning accuracy on an autonomous mobile robot controlled by 3-D coordinates that is obtained by a real-time indoor positioning system with spread spectrum (SS) ultrasonic signals communicated by code-division multiple access. Although many positioning systems have been investigated, the positioning system with the SS ultrasonic signals can measure identified multiple 3-D positions in every 70 ms with noise tolerance and error within 100 mm. This system is also robust to occlusion and environmental changes. However, thus far, the positioning errors in an autonomous mobile robot, controlled by these systems using the SS ultrasonic signals, have not been evaluated as an experimental study. Therefore, a positioning experiment for trajectory control is conducted using an autonomous mobile robot and our positioning system. The effectiveness of this positioning method for robot self-localization is shown, from this experiment, because the average control error between the target position and the robot's position at 29 mm is obtained.

• 한국정보통신학회논문지
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• 제20권8호
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• pp.1422-1430
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• 2016

전송되는 정보들의 가로채기 확률을 감소시키기 위한 피감청 기술 중 대표적인 대역확산통신 기법을 적용함으로써 통신 성능에 미치는 영향을 분석하고, 이를 통해 최적의 은밀 수중음향통신 시스템의 모델을 제안한다. 대역확산 통신 된 신호의 레벨이 낮아져 주변의 배경소음과 같은 레벨로 전송하기 때문에 피탐지 확률이 감소하고 은밀성의 특징을 갖게 된다. 본 논문에서는 BCJR(Bahl, Cocke, Jelinek, Raviv) 복호방법과 대역 확산 기법 중 직접 수열 대역 확산 기법을 적용하였으며, 은밀 수중 통신에서 고려되는 송수신 모델은 크게 두 가지로 나뉘는데, 경판정 기반의 송수신 모델과 반복기반의 터보 등화 모델의 성능을 시뮬레이션과 호수 실험을 통해 성능을 비교 분석하였다.