• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2C
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• pp.192-199
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• 2008

In ultra-wideband (UWB) systems, conventionally, the synchronization is to align time phases of a locally generated template and any of multipath components to within an allowable range. However, the synchronization with a low-power multipath component could incur significant performance degradation in receiver operation (e.g., detection) after the synchronization. On the other hand, the synchronization with a high-power multipath component can improve the performance in receiver operation after the synchronization. Generally, the first one among multipath components has the largest power. Thus, the synchronization with the first path component can make better performance than that with low-power component in receiver operation after the synchronization, Based on which, we first propose an optimal decision rule based on a maximum likelihood (ML) approach, and then, develope a simpler suboptimal decision rule for selecting the first path component. Simulation results show that the system has good demodulation performance, which uses new synchronization definition and the proposed decision rules have better performance than that of the conventional decision rule in UWB multipath channels. Between macroblocks in the previous and the current frame. On video samples with high motion and scene change cases, experimental results show that (1) the proposed algorithm adapts the encoded bitstream to limited channel capacity, while existing algorithms abruptly excess the limit bit rate; (2) the proposed algorithm improves picture quality with $0.4{\sim}0.9$dB in average.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.7
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• pp.22-31
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• 2008

Cognitive radio should imply a proper sensing technique for detecting the presence of licensed users to identify the unused spectrum holes. Besides this, this information should also be used to opportunistically provide communication among secondary users. At the same time the performance of the primary user should not be declined by the secondary users. The detection of licensed users may be significantly difficult for shadowing effect. To prevail over this problem cooperative spectrum sensing, In which the combined observation information gained by multiple secondary users is employed to achieve higher performance of detection, has been inspected. However, the primary challenge of cooperative sensing lays in its ability to detect the presence of licensed user quickly and accurately. In this paper, we have used UltraWideBand (UWB) to detect the presence of licensed users and transmit the sensing information among the nodes of the network. UWB has the capability of transmitting data at a very high rate. It is unique in co-existence capability with narrow band systems. Here, we have shown that the detection probability of licensed user is improved by means of transmitting the spectrum sensing information via UWB. We also have analyzed the throughput of the proposed technique and compared the result with existing sensing method.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.5
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• pp.1316-1332
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• 2012

Formation flying is an important technology that enables high cost-effective organization of outer space aircrafts. The ad-hoc wireless network based on direct-sequence ultra-wideband (DS-UWB) techniques is seen as an effective means of establishing wireless communication links between aircrafts. In this paper, based on the theory of matched filter and error bits correction, a hybrid detection algorithm is proposed for realizing multiuser detection (MUD) when the DS-UWB technique is used in the ad-hoc wireless network. The matched filter is used to generate a candidate code set which may contain several error bits. The error bits are then recognized and corrected by an novel error-bit corrector, which consists of two steps: code mapping and clustering. In the former step, based on the modified optimum MUD decision function, a novel mapping function is presented that maps the output candidate codes into a feature space for differentiating the right and wrong codes. In the latter step, the codes are clustered into the right and wrong sets by using the K-means clustering approach. Additionally, in order to prevent some right codes being wrongly classified, a sign judgment method is proposed that reduces the bit error rate (BER) of the system. Compared with the traditional detection approaches, e.g., matched filter, minimum mean square error (MMSE) and decorrelation receiver (DEC), the proposed algorithm can considerably improve the BER performance of the system because of its high probability of recognizing wrong codes. Simulation results show that the proposed algorithm can almost achieve the BER performance of the optimum MUD (OMD). Furthermore, compared with OMD, the proposed algorithm has lower computational complexity, and its BER performance is less sensitive to the number of users.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1151-1158
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• 2014

In this paper, a concatenated frame algorighm for improving transmission efficiency in WiMedia protocol is studied. And an efficient transmission scheme to reduce the degradation of network performance by the loss of mini-frame is proposed in this paper. The proposed scheme can reduce total energy consumption and improve the transmission efficiency since it only retransmits mini-frame in which error is occurred. The simulation results show that proposed protocol can enhance the throughput performance and improve energy efficiency by minimizing the retransmission of mini-frame.

• Proceedings of the IEEK Conference
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• 2002.07b
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• pp.1350-1353
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• 2002

A new form of spread spectrum technique called the ultra wideband impulse radio (UWB-IR) system has drawn much attention for future high speed wireless communication services. In this paper, a new type of time hopping sequences constructed from multiple distinct m-sequences of the same order, is proposed for multiple access in the UWB-IR systems. Simulation results reveal that the proposed time hopping sequences achieve comparable or even better bit error rate performance than the ideal random sequences, and can be effectively applied in various multiple access situations.

• Journal of Korea Multimedia Society
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• v.15 no.4
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• pp.516-525
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• 2012

In this paper, an efficient technique for enhancing the QoS of multimedia service for an WiMedia network applying distributed cooperative medium access (D-MAC) protocol is proposed. D-MAC protocol has been proposed to support high-rate Wireless Personal Area Networks (HR-WPANs) by the WiMedia Alliance. Unlike the centralized IEEE 802.15.3 MAC, the D-MAC UWB specified by WiMedia supports all devices to be self-organized and removes the SOP (Simultaneous Operating Piconet) problem, i.e., packet collisions between overlapped piconets in the centralized IEEE 802.15.3 MAC. However the WiMedia D-MAC can't prevent reduce the throughput degradation occurred by mobile nodes with low data rate. Therefore, a distributed cooperative MAC protocol for multi-hop UWB network is proposed in this paper. The proposed technique can intelligently select the transmission path with higher data rate to provide real-time multimedia services with minimum delay, thus enhances QoS of multimedia service.

• Journal of Advanced Navigation Technology
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• v.23 no.6
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• pp.584-588
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• 2019

Wireless body area network (WBAN) is a networking technology that enables early detection of abnormal health conditions, real-time medical monitoring, and telemedicine support systems. The internet of things (IoT) for healthcare, which has become an issue recently, is one of the most promising areas for improving the quality of human life. It must meet the high QoS requirements of the medical communication system like any other communication system. Therefore, the bit error rate (BER) threshold was chosen to accommodate the QoS requirements of the WBAN communication system. In this paper, we calculated BER performance of WBAN channel using IR-UWB PPM modulation and analyzed link budget and system margin of WBAN according to various system parameters.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.1A
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• pp.1-12
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• 2002

Ultra Wideband (UWB) system uses wide band signal, which power spectral density likes as a noise floor, so UWB system can be used high speed communication without interfering with other communication system. As this system doesn't use radio frequency carrier. Its structure would be very simple and consume very low power. For the first time, we adopted Rayleigh monopulse multiple access system. And under the AWGN, we analysis and compare error probability, the number of user and data rate of the two methods that pulse position modulation and antipodal. In the result, We concluded that the antipodal method had much better probability of error, the number of user and data rate than PPM.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5A
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• pp.467-474
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• 2007

MB-OFDM (Multiband-orthogonal frequency division multiplexing) UWB (ultra wide band) system uses DCM (dual carrier modulation) scheme to achieve high-data rate transmission. The basic idea of DCM is that to transmit the 4 bits more reliably two 16-QAM (quadrature amplitude modulation) symbols are used and the two 16-QAM sysmbols are allocated to each subcarrier of OFDM with maximum-distance. In the case of using the DCM, if one 16-QAM symbol is broken by deep fadding channel, a receiver can detect the transmitted signal by using another 16-QAM symbol. In the conventional ML(maximum likelihood) decision scheme, since the receiver does not use the CSI (channel state information), loss in diversity can not be reduced. In this paper, we propose improved soft-decision scheme with CSI for higher performance of MB-OFDM UWB systemn.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2011.10a
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• pp.109-113
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• 2011

In intelligent subway systems, UWB-based WiMedia D-MAC Protocol can be considered to send and receive multimedia data which requires high data rate. However, network devices which do not exist within 10 meters, the limited communication rage, can not communicate with each other because WiMedia does not support multi-hop communications. In this paper, we developed the algorithm to select a relaying device for multi-hop routing on WiMedia networks. In the first step, each device acquires information of neighbors through beacon and decides whether it is a normal or relaying device using the acquired information. In the next step, all devices can create the 2-hop routing table using the information received via relaying devices and the whole routing table for all devices on networks, eventually.