Chang-Jun Ahn

Sorter-Based Arithmetic Circuits for Sigma-Delta Domain Signal Processing—Part I: Addition, Approximate Transcendental Functions, and Log-Domain Operations

We construct arithmetic modules for signal processing with sigma-delta modulated signal form which has advantage in signal quality over other pulsed signal forms. In the first part of this paper, adders and exponential function modules are presented first and secondly. By utilizing the two modules, several transcendental functions including hyperbolic and logarithmic functions are constructed. The exponential functions and logarithmic functions provide log-domain arithmetic operations including multiplication, division, and power functions. Only two bit-manipulations, bit-permutation with sorting networks and bit-reversal with NOT gates, have built up all the arithmetic operations on any form of sigma-delta modulated signals. These modules, together with algebraic functions to be presented in the second part of this paper, organize an extensive module library for the sigma-delta domain signal processing.

Mobile Phone Camera-Based Indoor Visible Light Communications With Rotation Compensation

Downlink visible light communication (VLC) using a mobile phone camera is presented. The proposed scheme consists of an 8 × 8 light-emitting diode (LED) array for data transmission and eight white LEDs for an adequate level of illumination. The white LEDs are also used to acquire camera focus and light metering. Moreover, an efficient rotation compensation feature is provided in the form of a special header frame called keyframe to allow multiple users to receive the data simultaneously at 90°, 180°, and 270° orientations. Unlike conventional LED allocation methods for the rotation compensation, this keyframe-based method improves the data rate significantly. The experimental results demonstrate that the data rate achieves up to 1280 bps, whereas the theoretical simulations exhibit a potential data rate of up to 5120 bps using the identical LED array. The proposed scheme can be considered to be an efficient short-range camera-based VLC in an indoor environment with advanced features such as illumination, relatively high data rate, and robust camera rotation compensation for multiuser access.

Ultra-wideband surface acoustic wave resonator employing Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals

Theoretical analysis showed that high performance surface acoustic wave (SAW) resonator with an extremely large electromechanical coupling factor K2 could be realized on Y cut X propagating Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (YX-PIN-PMN-PT) substrate. A one-port SAW resonator was designed, fabricated, and characterized on Cu-grating/YX-PIN-PMN-PT substrate structure. The experimental results demonstrate that very large K2 of 57.3% is realizable. Such an extremely large K2 makes PIN-PMN-PT single crystal great potential for realizing wideband SAW filters and tunable SAW filters. The influence of inhomogeneity and instability of the domain structure on the fabricated resonators has been discussed thoroughly for further improvement of the devices.

Sorter-Based Arithmetic Circuits for Sigma-Delta Domain Signal Processing—Part II: Multiplication and Algebraic Functions

We construct arithmetic modules for signal processing with sigma-delta modulated signal form which has advantage in signal quality over other pulsed signal forms. In the second part of this paper, multi-input multipliers are presented first. Secondly, dividers and square root function modules with the multiplier on their internal feedback path are constructed. Combined use of the multipliers, dividers, and the square root functions creates various algebraic functions including polynomial and rational functions. Only two bit-manipulations, bit-permutation with sorting networks and bit-reversal with NOT gates, have built up all the algebraic operations on any form of SD modulated signals. These modules, together with transcendental functions presented in the first part of this paper, organize an extensive module library for the sigma-delta domain signal processing. The multiplier output contains noise components which originate from quantization. The noise power can decrease in exchange for circuit complexity. A time-division multiplexing technique based on N-tone sigma-delta modulation is applied to the multipliers for reducing the complexity. Signal processing circuits built of nanometer-scale quantum effect devices must be equipped with fault tolerance of transient device error. By computer simulation of a multiplier built of single-electron tunneling devices, we found that the multiplier decreased its output SNDR from 43 to 27 dB at an OSR of 28 as the device error rate increased from 0 to 10-3. However, the multiplier was never functionally failed during the simulation.

RF Energy Harvesting and Charging Circuits for Low Power Mobile Devices

The electrical power generated by RF energy harvesting techniques is small, depending on techniques it is enough to drive low power consumption devices. Therefore, it is possible to increase the battery life and to reduce the environmental pollution. In this paper, we focus on the RF energy harvesting and design the rectenna with a 4×4 patch antenna of 2.13 GHz for low power mobile devices. The rectenna element is a microstrip patch antenna with PTFT board of 10 dielectric constant and 1.6 mm thick that has a gain of 5.8dBi. A step-up converter is adopted the Texas Instruments TPS61220. The step-up converter is operated with load at 0.7V to 5.5V. If the output current is 1.7mA, the conversion efficiency shows 80.9%. From the evaluated results of RF energy harvesting system, the low power mobile devices such as Zigbee when we set the distance of 12m can be operated

High Q surface acoustic wave resonators in 2–3 GHz range using ScAlN/single crystalline diamond structure

This paper describes application of the ScAIN/single crystalline diamond (SCD) structure to wideband surface acoustic wave (SAW) devices operating in 2-3 GHz range. First, it is shown theoretically that large velocity V and large electromechanical coupling factor K2 are simultaneously achievable for the Sezawa mode existing in the structure. Next, a SAW delay line is fabricated on the structure, and it is shown experimentally that the structure offers large V and K2 as theoretically expected, and the structure possesses very small SAW attenuation even in 3 GHz range. Finally, one-port SAW resonators are fabricated on the structure, and it is shown that wideband and high Q SAW devices are realizable in a few GHz range using the structure.

Frequency symbol spreading based adaptive subcarrier block selection for OFDMA system

In a wireless network, the signals transmitted from one sender to different users have independent channel fluctuation characteristics. The diversity that exists between users is called multiuser diversity and can be exploited by the sender to enhance the capacity of wireless network. In multiuser diversity OFDMA system, exploiting channel fluctuation diversity is in essence done by selecting the user with the strong subcarrier channels. The individual subcarrier selection for each user can achieve the best system performance but high signaling overhead and high system complexity are required. On the other hand, the adaptive subcarrier block method achieves worse BER than that of individual subcarrier selection. This is because the selected block contains the poor channel subcarriers. To overcome this problem, in this paper, we propose an adaptive subcarrier block selection with frequency symbol spreading for an OFDMA system.

Path-selection based adaptive guard interval for TFI-OFDM system

TFI-OFDM system can achieve an accurate channel identification property with small pilot symbols. However, when the guard interval is longer than the maximum delay spread, the fixed guard interval is inefficient. To mitigate this problem, in this paper, we propose the path-selection based adaptive guard interval for TFI-OFDM system. In the proposed system, the paths that exceeded the threshold which was set to a noise variance, were selected. Moreover, due to the selected large delay path, the proposed system can control the guard interval adaptively. From the simulation results, the proposed adaptive guard interval TFI-OFDM can achieve 7.2% and 3.2% throughput enhancement to compare with the conventional fixed guard interval TFI-OFDM under the 15path and vehicular A channels, respectively.

Achievable throughput enhancement based on modified carrier interferometry for MIMO/OFDM

In MIMO systems, channel estimation is important to distinguish the transmitted signals from multiple transmit antennas. When MIMO systems are introduced in cellular systems, we have to measure the received power from all the connectable base station (BS), as well as to distinguish all the channel state information (CSI) for the combination of transmitter and receiver antenna elements. One of the most typical channel estimation schemes for MIMO in a cellular system is to employ a code division multiplexing (CDM) scheme in which a unique spreading code is assigned to distinguish both BS and MS antenna elements. However, by increasing the number of transmit antenna elements, large spreading codes and pilot symbols are required to estimate an accurate CSI. To reduce this problem, in this paper, we propose a high time resolution carrier interferometry (HTRCI) for MIMO/OFDM to achieve an accurate CSI without increasing the number of pilot symbols.

Reverse link performance improvement for an wideband OFDM using Alamouti coded heterogeneous polarization antennas

The combination of OFDM and multiple antennas in either the transmitter or receiver is attractive to increase a diversity gain. However, multiple antennas system requires an antenna separation of 510 /spl lambda/ to keep the correlation coefficient below 0.7 for the space diversity, so this may be difficult to implement in a mobile station with high mobility. Recently, the polarization transmit diversity is considered in a mobile station. However, polarization transmit diversity requires twice transmit powers to compare with the conventional transmit diversity, since only vertically polar antenna cannot receive the horizontal signal components. In this paper, we express the cross correlation of each polarization antenna and the cross polarization discrimination (XPD) of multiple polarization antennas with simple model, and we propose a wideband OFDM using Alamouti coded heterogeneous polarization antennas for reducing the previous problem. From the simulated results, the proposed system shows better BER performance than that of the conventional STBC/OFDM.