Wooju Lee

Resource alloation for orthogonal and co-channel femtocells in a hierarchical cell structure

This paper focuses on the frequency allocation (FA) schemes between a macro-cell base station (MBS) and femtocells in a hiearachical cell structure. We present two simple methods among the many cases of FA schemes. One is a co-channel FA scheme in which frequency band is shared between MBS and femtocells. The other is an orthogonal FA scheme in which the frequency is separately allocated between MBS and femtocells. Through a computer simulation, we demonstrate the orthogonal FA scheme has a coverage extension compared with co-channel FA scheme as well as MBS without femtocells.

Frequency Allocation Scheme for Interference Avoidance in Cellular System with Fixed Relay

The introduction of fixed relays is expected to be inevitable as 4G wireless communications coverage is expanded and data processing ratios enhanced, and for reducing costs of base station extension and backhaul communication network holding. Additional interference is an unwanted concomitant of adding many fixed relays to the existing cellular system without an efficient frequency allocation scheme. We propose an efficient frequency allocation scheme for avoiding co-channel interference between cells/sectors when installing fixed relays on cellular systems. The proposed frequency allocation scheme can minimize the co-channel interference between cells/sectors by not sharing a frequency band among neighboring fixed relays, or between the base station and fixed relays, and instead using different frequency bands in sectors.

Performance Analysis of Maximum Data Rate for Telemetry Links in Space Communications for Lunar Explorations

Telemetry link requires high data rate to transmit the multimedia data for lunar explorations in space communications. In this paper, we analyze a data rate with the modulation and channel coding schemes based on Consultative Committee for Space Data Systems (CCSDS) in S, X, Ku and Ka bands, respectively. Then, we suggests modulation and channel coding schemes to meet the link margins and have a maximum data rate for lunar explorations in telemetry links.

Design and Performance Analysis of Downlink in Space Communications System for Lunar Exploration

This paper designs a data link between a Lunar Orbiter (LO) and an Earth Station (ES), and analyzes the downlink performance of a space communications system for lunar exploration, conforming to the recommendations by the Consultative Committee for Space Data Systems (CCSDS). The results provided in the paper can be useful references for the design of reliable communication link for the Korean lunar exploration in the near future.

Adaptive Coding and Modulation Scheme for Ka Band Space Communications

Department of Electronics and Communications Engineering Hanyang University, Seoul 133-791, KoreaRain attenuation can cause a serious problem that an availability of space communication link on Ka band becomes low. To reduce the effect of rain attenuation on the error performance of space communications in Ka band, an adaptive coding and modulation (ACM) scheme is required. In this paper, to achieve a reliable telemetry data transmission, we propose an adaptive coding and modulation level using turbo code recommended by the consultative committee for space data systems (CCSDS) and various modulation methods (QPSK, 8PSK, 4+12 APSK, and 4+12+16 APSK) adopted in the digital video broadcasting-satellite2 (DVB-S2).

An Improved Estimation of Integer Frequency Offset in OFDM Systems Using ML Method

In this paper, we propose a simple maximum likelihood (ML) estimation method with one training symbol for the integral part of the carrier frequency offset between the transmitter and the receiver in orthogonal frequency division multiplexing (OFDM) systems. The carrier frequency offset is obtained by using the information of the training symbol. The performance of each estimator is compared through Monte Carlo simulation, and we show that proposed estimator performs better than the conventional one

Frequency Allocation Scheme to Maximize Cell Capacity in a Cellular System with Cooperative Relay

When deploying the fixed relay stations (RSs) in a cellular system, additional co-channel interferences occur necessarily. To avoid the co-channel interferences, an effective frequency allocation (FA) scheme is essentially required. Cooperative relay can achieve the diversity gain as well as coverage extension of the cellular system. FA schemes with non-cooperative relay have been widely studied, but little research has been done for those with cooperative relay. Since cooperative relay is that RS and base station (BS) simultaneously transmit the same signal using the same time and frequency resources, FA scheme with cooperative relay has different FA patterns compared with that for non-cooperative relay. In this paper, we propose an improved FA scheme with cooperative relay in the system. The proposed scheme can maximize the cell capacity through minimizing co-channel interferences and achieving the cooperative source diversity gain. Through a computer simulation, we demonstrate the proposed FA scheme with cooperative relay can increase average cell, user, and edge user throughputs compared with those for conventional systems under the IEEE 802.16j environment.

FPGA Design and Implementation of UDCM for the WiBro System

In this paper, we implement the UDCM (up down conversion module) for the WiBro base station equipment RAS (radio access station). It performs the digital IF (intermediate frequency) signal processing between a channel card and the radio equipments (REs). The UDCM embed on digital optic interface unit of RAS. Converting the frequency into 10 MHz or baseband is the main function. It filters the spurious within channel bandwidth for downlink (DL) /uplink (UL). Also to support the communication with the other chips or peripherals, we design the interface modules and controller. As the UDCM is optimized on the Virtex5 families, it can save the dedicated FPGA resources and lowers the development costs. Its functionality is verified using simulation tools on the RTL (register transfer level) for the predefined test vector. After setting the timing constraints for the interface signals and timing verification, the UDCM downloaded into main unit. Finally, this digital unit is connected to a channel card and REs to ensure the expected performance for its reference simulation results by capturing I/Q, synchronization signals.

Decoupling matrix with rate one Quasi-Orthogonal STBC for eight transmit antennas

In this paper, we propose a numerical formulation of decoupling matrix with rate one quasi-orthogonal space-time block code (QOSTBC) for eight transmit antennas. Tirkkonen et al. provided zero-forcing decoupling matrix for eliminating inter-symbol interference (ISI) in QOSTBC with 4 transmit antennas. We expand zero-forcing decoupling matrix with 8 transmit antennas, and also MMSE decoupling matrix with 4, 8 transmit antennas. Simulation results were provided to demonstrate that some SNR gains can be achieved by using decoupling matrix.

Implementation of DSRC System with Wireless Link Between RSE and Local Server

Telematics can provide various multimedia services in wireless access systems. One method of wireless access in telematics is DSRC (dedicated short range communication) which supports a wireless channel between RSE (road side equipment) and QBE (on board equipment). In this DSRC system, a wire path such as ADSL (asymmetric digital subscriber line) connects the RSE to a local server. However, the wire itself presents some technical problems, such as high installation costs, difficulty of maintenance and repair, and so on. We propose replacing the wire path with a wireless link between the RSE and local server, and test the performance through experiments