Han-Lim Lee

Radio-Over-Fiber System for TDD-Based OFDMA Wireless Communication Systems

We report on a fiber-optic transport system for next-generation wireless-communication systems utilizing 4 times 4 multiple-input multiple-output (MIMO) orthogonal-frequency-division-multiple-access (OFDMA) technology. Our system supports time-division-duplex (TDD)-based wireless signals operating at 3.775 GHz. To accommodate the TDD-based MIMO signals over a single strand of optical fiber, we utilize nine-channel coarse wavelength-division-multiplexed optical channels: one for link delay measurement and TDD control signal transmission, four for downlink, and the others for uplink. The system first measures the propagation delay between the central base station (CBS) and the remote antenna (RA) and sends the result to delay modules to compensate for the delay added by the transmission link. This procedure makes the CBS and RA emit the downstream signals simultaneously into the air and, consequently, helps avoid the performance degradation caused by the propagation delay of the radio-over-fiber system. The system then sends the MIMO signals together with TDD control signals to the RA. Our experimental demonstration is carried out with 1-Gb/s OFDMA signals having pilot, control, and data channels. For downstream, the error vector magnitudes (EVMs) are measured to be < -30 dB after a 3.9-km transmission over conventional single-mode fiber when the antenna output power is set to be 24 dBm. For upstream, the best EVMs are measured to be < -35 dB. Both the downstream and upstream performance is limited by the shot and thermal noise of the receiver when the signal power is low, whereas nonlinear distortions of electrical amplifiers start to degrade the system performance as the signal power increases. We also measure the crosstalk between channels. It is measured to be less than -42 dB for all channels, which is found to be caused by board-to-board interference at the RA.

Integrated Planar Monopole Antenna With Microstrip Resonators Having Band-Notched Characteristics

Novel integrated planar monopole antennas with various microstrip resonators are presented. The proposed integrated antennas consist of wideband planar monopole antennas and electromagnetically coupled microstrip resonators producing band-notched characteristics. Various types of microstrip resonators such as open-circuited line resonator, short-circuited line resonator, closed-loop resonator and open-loop resonator are described. The proposed designs are suitable for wideband antennas with narrowband interferer rejection characteristic or multi-band antennas.

A novel way to improve the dispersion-limited transmission distance of electroabsorption modulated lasers

We propose and demonstrate a way to improve the dispersion-limited reach of electroabsorption modulated lasers (EMLs). We generate continuous-phase frequency-shift keying/amplitude-shift keying (ASK) signals with the EML by applying a small current modulation to the laser diode (LD) on top of electroabsorption-modulated ASK signals. The amount of frequency deviation induced by the current modulation is adjusted to have the EML output signals experience /spl pi/ phase shift at every space. The experimental demonstration shows that with the proposed scheme we can increase the dispersion-limited transmission distance of the EML-based transmitter by 25%-75%, and it can be further improved by employing an LD with flat frequency-modulation response.

Switchable Distance-Based Impedance Matching Networks for a Tunable HF System

Distance-based impedance matching networks for a tunable high frequency (HF) system are presented in this paper for the improved performance. The transmitting antenna for a HF system with an operating frequency of 13.56MHz consists of a two-turn loop and three channel impedance matching networks corresponding to the distance of the receiving antenna. Each impedance matching network maximizes the system performance such as uniform power e-ciency and reading range at speciflc distance between a transmitting and a receiving antenna. By controlling the distance-based matching networks, the power e-ciency of the proposed antenna improves by up to 89% compared to the conventional antenna system with the flxed matching (FM) condition for distances, and the reliable reading range according to the impedance matching conditions is also increased. The proposed technique is applicable for near fleld communication (NFC), radio frequency identiflcation (RFID), or wireless power transfer (WPT) devices.

Uniform magnetic field distribution of a spatially structured resonant coil for wireless power transfer

A spatially structured resonant coil with uniform magnetic field distribution for wireless power transfer is presented. The characteristics of the proposed resonant coil are verified by the theoretical analysis, simulation results, and experimental measurements. Due to the uniform magnetic field distribution, the overall transfer efficiency between the transmitting and receiving resonant coils can be improved up to 44% compared to the conventional coil regardless of the location of the receiving coil at the transfer distance.

A Novel Method for Providing Precise Time Synchronization in a Distributed Control System Using Boundary Clock

We propose and demonstrate a method to provide precise time synchronization in distributed control systems using a boundary clock scheme. The major drawback of the boundary clock scheme is the exponential accumulation of time synchronization error as the number of hops increases. To make the error accumulation linearly increase with the number of hops, we first separate the frequency compensation interval (FCI) and the offset and frequency compensation interval (OFCI) and then separately optimize each interval. To demonstrate the performance of this method, we implemented test benches using Ethernet-linked distributed control systems. We measured the peak-to-peak jitter performance along with the maximum time interval error to assess the short- and long-term stability after several hops in distributed control systems. Our method enables the peak-to-peak jitter to be maintained under 107 ns after seven hops. The experimental results show that the performance of time synchronization is dominated by fast jitter rather than frequency error and wander, and the proposed scheme can be used to improve the time synchronization performance in IEEE 1588-compliant control systems using boundary clock.

On the use of 2.5-Gb/s Mach-Zehnder modulators to generate 10-Gb/s optical duobinary signals

We demonstrate the generation of 10-Gb/s optical duobinary signals from 2.5-Gb/s Mach-Zehnder (MZ) modulators without using duobinary encoders. The absence of the duobinary encoder not only permits the monolithic integration of electrical components but also reduces the required bandwidth of MZ modulators as low as 3 GHz. However, it might induce pattern-length dependency to the signals. Our demonstration, performed with four 2.5-Gb/s MZ modulators obtained from two different vendors, shows that the receiver sensitivity of better than -33.8 dBm is achieved at a pseudorandom bit sequence length of 2/sup 31/-1 when dispersion of 1200 /spl sim/ 1700 ps/nm is applied to the signals. This is 1.6 dB poorer than using an 8.5-GHz bandwidth MZ modulator along with a 3.0-GHz Bessel filter. Therefore, this scheme can be used to implement cost-effective 10-Gb/s optical duobinary transmitters without significant performance degradation.

Reconfigurable 1

This letter presents a reconfigurable 1 × 4 power divider operated at 2.45 GHz. The proposed circuit has four power transmission states and is designed mathematically to satisfy matching conditions for each state. The experimental results for the transmission losses for each state are 1.2 dB ~ 1.9 dB while the isolations for non-path ports are greater than 25 dB and the reflection coefficients for each power transmission state are less than -20 dB at the target frequency.

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A new balanced Doppler radar front-end architecture with Tx leakage canceller for antenna impedance variation and antenna mutual coupling is proposed. Consisting of two quadrature hybrids, two ring hybrids and 4-port feed antenna system, the proposed balanced structure achieves high transmit/receive (Tx/Rx) isolation stable to antenna impedance variation and antenna mutual coupling. The proposed 4-port feed antenna is configured by dual fed 2 × 1 patch array having 6.97 dBi and 5.65 dBi of measured Tx and Rx peak gain, respectively. In addition, the proposed architecture undergoes no power loss in both transmit and receive paths, and obtains the measured Tx/Rx isolation of more than 45 dB stable at 24 GHz regardless of the load variation. The proposed architecture that can determine the speed as low as 0.5 mm/s (0.078 Hz Doppler shift) is theoretically and experimentally analyzed for high isolation despite of antenna mismatch.

4 Power Divider With Switched Impedance Matching Circuits

This paper reports on a fiber-optic system for in-building wireless communication/broadcast systems developed in Samsung Electronics. Our system delivers the third generation mobile system, satellite-digital multimedia broadcast, and wireless local access network services over a single strand of single-mode fiber or multi-mode fiber. We present the design issue and experimental results of the radio-over-fiber link.