• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.3
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• pp.523-541
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• 2011

In current IEEE 802.11 wireless LAN, every unicast transmission requires an ACK from the receiver for reliability, though it consumes energy and bandwidth. There have been studies to remove or reduce ACK overhead, especially for energy efficiency. However none of them are practically used now. This paper introduces a noble method of selective unacknowledged transmission, where skipping an ACK is dynamically decided frame by frame. Utilizing the fact that a multicast frame is transmitted without accompanying an ACK in 802.11, the basic unacknowledged transmission is achieved simply by transforming the destination address of a frame to a multicast address. Since removing ACK is inherently more efficient but less strict, its practical profit is dependent on traffic characteristics of a frame as well as network error conditions. To figure out the selective conditions, energy and performance implications of unacknowledged transmission have been explored. Extensive experiments show that energy consumption is almost always reduced, but performance may be dropped especially when TCP exchanges long data with a long distance node through a poor wireless link. An experiment with a well-known traffic model shows that selective unacknowledged transmission gives energy saving with comparable performance.

• Proceedings of the KIEE Conference
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• 2003.07e
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• pp.62-69
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• 2003

In recent years, data transmission using power lines has been much highlighted. Power line is known to be cost-effective communication medium because the entire cable infrastructure has been already established and it is entirely connected with any home. Recently, the target of researches is to communicate data reliably over power lines at the speed of at least 1Mbits/s over the frequency range from 1MHz to 10MHz. OFDM communication system has been used for the high speed data transmission. Next, the conventional and adaptive OFDM systems for high speed data transmission over power line channel are investigated. The performance of AOFDM(adaptive OFDM) over the frequency selective channel with impulsive and narrow-band noise are studied to be a nice solution for high speed data transmission over power lines. The simulation results show that data the rates of the AOFDM are improved about 47% more than the ones of the conventional OFDM over the frequency response of case 4. In the results, the data rate has been much improved by the proposed adaptive algorithm in the frequency selective channel.

• The Journal of the Acoustical Society of Korea
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• v.6 no.1
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• pp.5-14
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• 1987

In this paper, the transmission characteristics of a frequency-hopped spread spectrum communication system operating in the presence of both time and frequency-selective fading channel is presented. The receiver is a binary noncoherent matched-filter FFH-SS system with square-law combiner. The probability of error to the variations of the parameters such as signal-to-noise ratio, selectivity of a channel, and power ratio is derived with the use of diversity concept without considering the data rate. The analysis of the data for probability of error shoves that the performance of FFH-SS system in time-selective fading channel is better than in frequency-selective fading channel.

• Journal of Korea Multimedia Society
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• v.20 no.8
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• pp.1312-1320
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• 2017

Recently, vector map data is developed and used in many domains widely. In the most cases, vector map data contains confidential information which must be kept away from unauthorized users. Moreover, the production process of vector maps is considerably complex and consumes a lot of money and human resources. Therefore, the secured storage and transmission are necessary to prevent the illegal copying and distribution from hacker. This paper presents a selective encryption algorithm using geometric objects in frequency domain for vector map data. In the proposed algorithm, polyline and polygon data in vector map is the target of the selective encryption process. Experimental results verified that proposed algorithm is effectively and adaptive the requirements of security.

• International Journal of Fuzzy Logic and Intelligent Systems
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• v.8 no.1
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• pp.11-17
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• 2008

Typical wireless sensor networks used in structural monitoring are continuous types wherein data transmission is progressive at all time that may include irrelevant and insignificant data and information. Continuous types of wireless monitoring systems often pose problems of handling large-sized data that may deteriorate the performance of the system. The proposed method is to suggest an event-triggered monitoring system that captures and transmits relevant data only. An error signal generated by the Principal Components Analysis (PCA) is utilized as an index for event detection and selective data transmission. With this new monitoring scheme, the remote server is relieved of unwanted data by receiving only relevant information from the wireless sensor networks. The performance of the proposed scheme was verified with simulation studies.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.894-897
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• 2008

This paper analyzes the throughput performance of a selective repeat (SR)/automatic repeat request (ARQ) scheme to transmit packet data in burst home network channel. To combat the high degree of error caused by transmission of home network data a robust error control scheme is a necessity. Basically, error control schemes can be divided in two categories: ARQ schemes and forward error correction (FEC) schemes. ARQ schemes are often used for reliable data transmission. The performance of packet transmission using SR-ARQ schemes for bursty channels is analyzed and simple analytical expressions of its throughput are presented. Theoretic analysis and numerical results indicate that a small number of packet sizes can get good performance in bursty home network channel.

• Journal of electromagnetic engineering and science
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• v.6 no.4
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• pp.203-208
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• 2006

Channel estimation and data detection for OFDM systems over time- and frequency-selective channels are investigated. Relying on the complex exponential basis expansion channel model, a pilot-embedded channel estimation scheme with low computational complexity and spectral efficiency is proposed. A periodic pilot sequence is superimposed at a low power on information bearing sequence at the transmitter before modulation and transmission. The channel state information(CSI) can be estimated using the first-order statistics of the received data. In order to enhance the performance of channel estimation, we recover the transmitted data which can be exploited to estimate CSI iteratively. Simulation results show that the proposed method is suitable for doubly-selective channel estimation for the OFDM systems and the performance of the proposed method can be better than that of the Wiener filter method under some conditions. Through simulations, we also analyze the factors which can affect the system performances.

• The KIPS Transactions:PartC
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• v.10C no.7
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• pp.891-898
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• 2003

This paper analyzes and proposes a scheme that improves the performance of the RTP that is developed to support the end-to-end transmission function and QoS monitor function for real-time multimedia data transmission. Although the existing RTP module supports real-time transmission, it has some problems in guaranteeing QoS parameters. To solve this problem, we propose a new Selective Repeat Adaptive Rate Control (SRARC). The SRARC can support QoS by referring to the data transmission status from the client and then classifying the network status into three levels. It selectively transmits multimedia data and dynamically controls transmission rates based on such information as bandwidth, packet loss rate, and latency that can be calculated in data transfer phase. To verify the SRARC, we implement it in real local area networks and compare the QoS parameters of the SRARC with those of the SR and RTP By the experimental results, the SRARC shows better performance in the aspects of bandwidth usage rate, packet loss rates, and transmission delays than the existing RTP schemes.

• ETRI Journal
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• v.37 no.2
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• pp.338-347
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• 2015

The multi-carrier transmission signal in Multi-Carrier Code Division Multiple Access (MC-CDMA) has a high peak-to-average power ratio (PAPR), which results in nonlinear distortion and deteriorative system performance. An n-tuple selective mapping method is proposed to reduce the PAPR, in this paper. This method generates $2^n$ sequences of an original data sequence by adding n-tuple of n PAPR control bits to it followed by an interleaver and error-control code (ECC) to reduce its PAPR. The convolutional, Golay, and Hamming codes are used as ECCs in the proposed scheme. The proposed method uses different numbers of the n PAPR control bits to accomplish a noteworthy PAPR reduction and also avoids the need for a side-information transmission. The simulation results authenticate the effectiveness of the proposed method.

• Journal of Communications and Networks
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• v.8 no.2
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• pp.212-219
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• 2006

In this paper, a new turbo codes-based hybrid automatic repeat request (TC-HARQ) scheme with segment selective repeat (SSR) is proposed. The main strategy is, upon retransmission, to repeat the data that are most important for the next round of decoding based on the distribution of residual errors after current decoding. The performance in terms of reliability and throughput is analyzed. To adapt to correlated fading channels where an inter-leaver is always employed before transmission, we further modify the SSR strategy so that data having experienced correlated deep fading are selected for retransmission. Finally, this proposed scheme is applied to the wideband code division multiple access (WCDMA) system under frequency selective fading channels. Simulation results demonstrate that in all single and multiple user cases, SSR-based TC-HARQ leads to significant throughput improvement with similar bit error rate (BER) performance as compared to type-I TC-HARQ.