• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.4 no.6
• /
• pp.989-1005
• /
• 2010

Cooperative diversity is a technique with which a virtual multiple antenna array is established among the single antenna users of the wireless network to realize space diversity. Signal space diversity (SSD) is a bandwidth-efficient diversity technique, which uses constellation rotation and interleaving techniques to achieve diversity gain. A new cooperative diversity scheme with rotated constellations (RCCD) is proposed in this paper. In this scheme, data are modulated by using a rotated constellation, and the source and the relays transmit different components of the modulated symbols. Since any one of the components contains full information of the symbols, the destination can obtain multiple signals conveying the same information from different users. In this way, space diversity is achieved. The RCCD scheme inherits the advantage of SSD - being bandwidth-efficient but without the delay problem of SSD brought by interleaving. The symbol error rate of the RCCD scheme is analyzed and simulated. The analysis and simulation results show that the RCCD scheme can achieve full diversity order of two when the inter-user channel is good enough, and, with the same bandwidth efficiency, has a better performance than amplify-and-forward and detect-and-forward methods.

• Proceedings of the Korea Society for Simulation Conference
• /
• 1998.03a
• /
• pp.27-31
• /
• 1998

The growing usage of multimedia communication applications with specific bandwidth and real-time delivery requirements has created the needs for quality of service(QoS). In response to the growing demand for an integrated services, the Reservation Protocol(RSVP) has been designed to exchange resource reservation among routers in the internet. RSVP protocol provides the quality of service for real-time applications but the network efficiency is reduced because of the limited bandwidth. In order to use network resources efficiently. We compare the resource efficiency of traditional reservation methods with that of the proposed method and evaluate the performance of the internet phone.

• Proceedings of the KIEE Conference
• /
• 2008.10c
• /
• pp.199-201
• /
• 2008

In this paper, We studied optimum service model of passenger car monitoring system at limited wireless bandwidth subway and railway. High bandwidth is better if we need more services. But, high bandwidth requires more cost at tunnel of subway. More bandwidth make receive sensitivity to bad. We deduced best bandwidth of subway wireless transmission system reflecting the cost of installation and efficiency of system. Consequently, we decide efficient service model of passenger car monitoring system.

• Journal of Advanced Navigation Technology
• /
• v.18 no.5
• /
• pp.415-420
• /
• 2014

Another crucial issue is a providing secondary user(SU) with the its guaranteed quality of service(QoS) in cognitive radio systems, from the SU view to be allowed to opportunistically utilize the primary user(PU) spectrum on non-interfering. In this paper, we propose a bandwidth reallocation scheme for reducing SU dropping rate through renegotiation of requested channel numbers when available bandwidth is not enough for accepting the spectrum handoff SUs. We categorize SU calls into two types : the first priority and the second priority SU, and the first SU' service is supported by bandwidth reservation based on ARMA prediction model for PU arrivals, while the second SU's bandwidth demands for spectrum handoff is to be reallocated through their renegotiation. Simulation results show that our scheme can improve SU dropping rate and system resource utilization efficiency by bandwidth reallocation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.12B
• /
• pp.2275-2282
• /
• 1999

In ATM networks, bandwidth allocation using available bandwidth is important to control ABR traffic efficiently. However, it is difficult to dynamically assign bandwidth on bursty traffic, because the tracking of the existing available bandwidth information uses statistical value. In this paper, we propose a output-bufferd ATM switch using Per-VC queueing scheme with timer and Controller. The controller determines whether each VC is in congestion state or not, and the timer can assign dynamically as determining the available bandwidth for the Present period by Backlogged time and total link capacity, and then transmitting the determined bandwidth to source. Instead of using statistical parameters, the proposed scheme can improve link efficiency as allocating the bandwidth of the next period, by use of measured bandwidth during the current period.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.45 no.8
• /
• pp.8-14
• /
• 2008

In this paper, the effects of ground size on the characteristics such as input resistance, fractional bandwidth, and radiation efficiency of epsilon negative (ENG) zeroth order resonance (ZOR) antennas were investigated theoratically. Two types of ENG ZOR antennas were studied: mushroom ENG ZOR antenna with via and via-free defected ground structure (DGS) ENG ZOR antenna. It was confirmed that the ground size had more effects on the characteristics of a Via-free ZOR antenna than those of mushroom ZOR antenna with via. The via-free antenna could radiate properly with the required size of ground plane since the size of ground plane should exceed some critical value for DGS to suitably operate. As a height of substrate of mushroom ZOR antenna with via increased, the fractional bandwidth and radiation efficiency were improved. On the other hand, as a height of via-free ZOR antenna increased, the fractional bandwidth and radiation efficiency were degraded. Finally, a via-free ZOR antenna had an advantage of compactness even though its fractional bandwidth is narrow and its radiation efficiency is poor, compared with thoses of mushroom ZOR antenna with via.

• Communications for Statistical Applications and Methods
• /
• v.10 no.2
• /
• pp.607-617
• /
• 2003

This paper offers a practical comparison of efficiency between local likelihood approach and conventional kernel approach in density estimation. The local likelihood estimation procedure maximizes a kernel smoothed log-likelihood function with respect to a polynomial approximation of the log likelihood function. We use two types of data driven bandwidths for each method and compare the mean integrated squares for several densities. Numerical results reveal that local log-linear approach with simple plug-in bandwidth shows better performance comparing to the standard kernel approach in heavy tailed distribution. For normal mixture density cases, standard kernel estimator with the bandwidth in Sheather and Jones(1991) dominates the others in moderately large sample size.

• ETRI Journal
• /
• v.37 no.5
• /
• pp.940-944
• /
• 2015

We present a frame synchronization algorithm for lowdensity parity-check (LDPC) coded burst transmissions, which combines a conventional pilots-assisted frame synchronization algorithm and a code-aided algorithm based on the mean magnitude of the soft outputs from the LDPC decoder. With moderate computational complexity, the proposed algorithm is more efficient in bandwidth than conventional pilots-assisted algorithms. When compared with other code-aided algorithms, the proposed algorithm offers a better trade-off between complexity and performance. Simulation results in the case of an 8-PSK system with (1944, 972) LDPC code show that the proposed algorithm can achieve a performance equivalent to that of the perfect frame synchronization, with a bandwidth efficiency loss of 0.06 dB due to the use of pilot symbols.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.8
• /
• pp.119-124
• /
• 2004

In this paper, we are designed and fabricated circular polarization microstrip patch antenna of 5［GH］z bandwidth for the wireless LAN and the ISM. We are proposed new structure that removed the section which intersected at a right angle and were composed to four separated slots. The antenna of proposed structure could solve parasitic elements from intersected in a right angle and weak coupling efficiency from asymmetry between feed line and a slot. The proposed cross slots antenna is easily impedance matching and increased impedance bandwidth. Also this is increased efficiency and a bandwidth of antenna and reduce back lobe of radiation pattern. We designed 2${\times}$2 array antenna of 5［GHz］ band. It took impedance bandwidth 280［MHz］(VSWR < 1.5) and gam 12.5［dBi］

• Journal of Broadcast Engineering
• /
• v.13 no.1
• /
• pp.119-127
• /
• 2008

Transmission of video over Internet or wireless network requires coded stream capable of adapting to dynamic network conditions instantly. To meet this requirement, various scalable video coding schemes have been developed, among which the Scalable Video Coding (SVC) extension of the H.264/AVC is the most recent one. In comparison with the scalable profiles of previous video coding standards, the SVC achieves significant improvement on coding efficiency performance. For adapting to dynamic network bandwidth, the SVC employs inter-layer switching between different temporal, spatial or/and fidelity layers, which is currently supported with instantaneous decoding refresh (IDR) access unit. However, for real-time adaptability, the SVC has to frequently employ the IDR picture, which dramatically decreases the coding efficiency. Therefore, an extension of SP picture from the AVC to the SVC for an efficient inter-layer switching is investigated and presented in this paper. Simulations regarding the adaptability to dynamic network bandwidth are implemented. Results of experiment show that the SP picture added SVC provides an average 1.2 dB PSNR enhancement over the current SVC while providing similar adaptive functionality.