Hyuckjae Lee

Query tree-based reservation for efficient RFID tag anti-collision

Since the tree based RFID tag anti-collision protocol achieves 100% read rate, and the slotted ALOHA based tag anti-collision protocol allows simple implementation and good performance in small amount of tags, we consider how to take the advantages of each algorithm. This paper presents query tree based reservation for efficient RFID tag anti-collision. According to the simulation results, the proposed protocol requires less time consumption for tag identification than the present tag anti-collision protocols implemented in EPC Class 0, Class 1, and Class 1 Gen. 2

Bounds on Secrecy Capacity Over Correlated Ergodic Fading Channels at High SNR

We investigate the secrecy capacity of an ergodic fading wiretap channel when the main and eavesdropper channels are correlated. Assuming that the transmitter knows the full channel state information (CSI) (i.e., the channel gains from the transmitter to the legitimate receiver and eavesdropper), we quantify the loss of the secrecy capacity due to the correlation and investigate the asymptotic behavior of the secrecy capacity in the high signal-to-noise ratio (SNR) regime. While the ergodic capacity of fading channels grows logarithmically with SNR in general, we have found that the secrecy capacity converges to an upper-bound (a closed-form expression is derived) that will be shown to be a function of two channel parameters; the correlation coefficient and the ratio of the main to eavesdropper channel gains. From this, we are able to see how the two channel parameters affect the secrecy capacity and conclude that the excessively large signal power does not help to improve the secrecy capacity and the loss due to the correlation could be significant especially when the ratio of the main to eavesdropper channel gains is low.

Modulation and Pre-Equalization Method to Minimize Time Delay in Equalization Digital On-Channel Repeater

This paper presents novel modulation and pre-equalization methods to minimize a signal processing time delay in the equalization digital on-channel repeater (EDOCR) for the ATSC terrestrial digital TV system. The proposed modulation method uses equi-ripple (ER) filter for vestigial side bands (VSB) pulse shaping instead of conventional square root raised cosine (SRRC) filter. And the proposed pre-equalization method calculates pre-equalizer filter coefficients by comparing a baseband signal as a reference signal and a demodulated repeater output signal, and then creates new VSB pulse shaping filter coefficients by the convolution of the ER filter and the pre-equalizer filter coefficients. The new VSB pulse shaping filter minimizes the time delay of EDOCR by adjusting the number of its pre-taps and also compensates the linear distortions due to the use of the ER filter and mask filter.

L12 (Al,Cr)3Ti-based two-phase intermetallic compounds-II. Application to coating materials on TiAl

Abstract Ti-48Al specimens were coated with Al-21Ti-23Cr film by RF magnetron sputtering. Ti-48Al specimen coated at 200 W, 0.8 Pa and 573 K showed the best oxidation-resistant property in the isothermal oxidation test. Al-21Ti-23Cr film was amorphous after deposition, but crystallized and formed a protective AlzO, layer on the surface during oxidation. The oxidation behavior of the coated specimens has been investigated through isothermal oxidation tests at 1073 K, 1173 K and 1273 K for 100 h. The isothermal oxidation curves showed that the parabolic stage continued up to 100 h at all tested temperature ranges, and the excellent oxidation resistance is attributable to the formation of a protective AlzO3 layer on the surface of the Al-21Ti-23Cr film. After the oxidation test at 1273K, the matrix of the Al-21Ti-23Cr film had transformed into the TiAlCr phase due to the depletion of Al during oxidation and the diffusion of Ti from the substrate, and the extent of mass gain of the specimen increased compared with that of specimens tested at lower temperatures.

Secure Type-Based Multiple Access

We consider data confidentiality in a distributed detection scenario with a type-based multiple-access (TBMA) protocol where a large set of sensors sends local measurements to an ally fusion center (FC) over an insecure wireless medium called the main channel. Then, the ally FC makes a final decision to the physical environment. Although many wireless sensor networks are mission-specific and need data confidentiality due to the broadcast nature of wireless transmission, it can be easily wiretapped by unauthorized enemy FCs through eavesdropping channels. We propose a novel TBMA protocol called secure TBMA which provides data confidentiality by taking advantage of inherent properties of wireless channels, namely randomness and independence of the main and eavesdropping channels. In particular, the secure TBMA activates sensors having strong and weak main channel gains and makes the sensors follow different reporting rules based on the magnitudes of their channel gains. The reporting rules are carefully designed to confuse the enemy FC. The proposed secure TBMA delivers unconditional/perfect secrecy and does not assume any superiority of the ally FC over the enemy FC in terms of computational capability, secret key, and so on. For Rayleigh fading channels, we analyze the performance of the secure TBMA at both enemy and ally FCs by investigating conditions for perfect secrecy and an error exponent of detection error probability, respectively. On the one hand, the analysis at the enemy FC provides a design criterion of the reporting rules to achieve perfect secrecy. On the other hand, the analysis of the error exponent carried out with a Gaussian approximation shows that perfect secrecy is achievable at a marginal cost in detection error performance. All our claims are also verified with simulation results which have good matches with the analysis.

Scanning-Based Pre-Processing for En hanced Tag Anti-Collision Protocols

RFID is a generic term for technologies which use RF waves to identify, track, or categorize any object. One of the research areas in RFID systems is a tag anti-collision protocol; how to reduce identification time with a given number of tags in the field of an RFID reader. There are two types of tag anti-collision protocols for RFID systems: tree based algorithms and slotted aloha based algorithms. This paper proposes a method for enhancing the performance of the present RFID tag anti-collision protocols by scanning the positions of collided bits and once accessing few memories at tags to inform the positions. Since any of the present RFID tag anti-collision protocols with the scanning-based pre-processing can ignore the overhead from no collided bits, the analytic results show that scanning-based pre-processing elicits lower time consumption for tag identification from the present schemes

On multiuser secrecy rate in flat fading channel

We consider a physical layer security based on the wiretap channel for wireless communication systems in which there are one transmitter and multiple receivers/users who report their channel state information (CSI) to the transmitter. This scenario is practically useful since it models the forward link of cellular systems where the systems can take advantage of the multiuser diversity. We are curious about the role of the multiuser diversity in the secure communication under the wiretap channel framework. Although it is well known that fixed transmit power is not optimal when CSI is available to the transmitter, to get useful insights, we consider a fixed transmit power case. In return, we can have some of important performance measures such as outage probability, average secrecy rate, failure rate, and average wait time in closed forms. The analysis interestingly shows that the multiuser diversity becomes always disadvantageous for the secure communications. We substantiate our claims with the analytic results and numerical evaluations.

An efficient transmission of traffic and traveler information using digital multimedia broadcasting network

This paper introduces an efficient transmission of traffic and traveler information through digital multimedia broadcasting system, which is a multimedia and mobility empowered version of European digital audio broadcasting system. By introducing Korean characteristic traffic information into the transport protocol expert group messages, we could get highly efficient traffic and traveler information system that could be used in Korea as well as in European countries Keywords-component; traffic and traveler information, digital multimedia broadcasting, digital audio broadcasting

Optimization of multi-cluster multi-group based cooperative sensing in cognitive radio networks

In cognitive radio (CR) networks, there are two parameters associated with spectrum sensing: probability of detection (PoD) and probability of false alarm (PoF). The higher the PoD, the better the primary users (PUs) are protected. On the other hand, the lower the PoF, the more the throughput of secondary users (SUs) can be achieved. When the cooperative spectrum sensing is used, the performance of these two parameters depends heavily on the fusion scheme. In this paper, the multi-cluster multi-group based cooperative spectrum sensing scheme is proposed. By using k-out-of-N fusion rule, we obtain the optimal number of groups which minimizes the error rate of a cluster. Computer simulations show that the significant improvement of the total error rate in CR networks can be achieved when optimized parameters from the k-out-of-N fusion rule are used.

Code-Division Multiplexing Based MIMO Channel Sounder with Loosely Synchronous Codes and Kasami Codes

In this paper, the code-division multiplexing (CDM) based MIMO channel sounder with loosely synchronous (LS) codes and Kasami codes is presented for real time measurement of MIMO radio channel. Since this scheme has drawback of reduced dynamic range depending on the number of transmit antennas, it is important that low correlation codes should be utilized to get reliable performance. This paper adopts two efficient codes, LS codes and Kasami codes, of which performances are investigated through Monte-Carlo simulation in 2 x 8 and 4 x 8 MIMO channel environment, respectively. Basically, LS codes are noise-limited and Kasami codes are interference-limited in relation with cross-correlation characteristic. According to the simulation, LS codes are the best in 2 x 8 MIMO channel measurement and modified LS codes approach to this performance of LS codes in both 2 x 8 and 4 x 8 MIMO channel measurement. Kasami codes achieve somewhat less performance than the others, but are not nearly affected by the number of transmit antennas. Thus, Kasami codes are effective when transmit antennas are more than 4.