Ji Hwan Choi

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

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

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.

Fast spectrum sensing algorithm for 802.22 WRAN Systems

As the wireless communication services grow quickly, the seriousness of spectrum scarcity has been on the rise gradually. Recently, the FCC (Federal Communications Commission) announced very interesting reports. It pointed out that more than 70 % of radio spectrums are underutilized in certain times or geographic locations. This means that spectrum scarcity is not due to fundamental lack of spectrum but wasteful static spectrum allocations. In this context, IEEE 802.22 WG (working group) was organized in November 2004. Since it is originated by the secondary spectrum usage approach, its critical technology is spectrum sensing not to interfere with licensed users. Thus, in this paper, we propose the fast spectrum sensing algorithm based on the discrete wavelet packet transform focusing on the coarse detection. By simulations and complexity analysis, we verify our algorithm