Hyeong-Sook Park

A design and performance analysis of OFDMA modulator based on IEEE 802.16a standard

This paper presents the implementation and performance of the OFDMA modulator based on the IEEE 802.16a standard. We present the bit-word length for subblocks of modulator to support the acceptable performance and lower complexity. To show the signal quality of transmit signal, the error vector magnitude (EVM) of designed modulator is simulated under ideal demodulation process. We also analyze the peak average power ratio (PAPR) characteristics of transmitted signal, which is almost same for any modulation schemes and the number of subchannels, but the probability distribution of transmitted signal varies depending on the number of subchannels.

SISO polarized flat fading channel modeling for dual-polarized antenna systems

The next-generation wireless systems are expected to support data rates of more than 100 Mbps in the outdoor environment. In order to support such large payloads, the polarized antenna can be employed as one of candidate technologies. Recently, the third generation partnership standards bodies (3GPP/3GPP2) have defined a cross-polarized channel model in SCM-E for MIMO systems, but this model is quite complex and too many parameters are included. The SCM-E channel model generates only single channel output for each time instant, therefore it is not so appropriate to apply the SCM-E channel model directly to MIMO spatial multiplexing or receive combining systems. In this paper, we provide practical but simple dual-polarized channel models, which take into account both cross-polarization discrimination (XPD) and Rician K-factor. We verify the proposed channel model by observing the XPD and correlation values among polarized channels. In addition, BER & PER performances and system throughput using MRC and EGC combining at Rx side are simulated in this paper. The simulation results show the dramatically increased system throughput by the adoption of dual-polarized antenna.

Design of Synchronization in OFDMA/TDD based Wibro System

The issues of time and frequency synchronization in OFDM system are quite essential to preserve the orthogonality among subcarriers, not to produce ICI. This paper deals with the efficient design of time and frequency synchronization in 802.16e and WiBro system which uses preamble sequence. We present the implementation issues and proper algorithm of the synchronization blocks such as coarse and fine timing synchronization, and fractional and integer frequency offset compensation. A technique to mitigate the false alarms of frame timing acquisition is proposed, which is added to the verification process using the results of cell search. Also, we present the frequency offset compensation process that compensates separate estimation result of fractional and integer frequency offset.

Noise Power and SNR Estimation Based on the Preamble in Tri-Sectored OFDM Systems

This paper describes the signal-to-noise ratio (SNR) estimation based on the preamble in tri-sectored OFDM systems. Several SNR estimators from previous literature suffer degradation in several important fading channel models. This paper proposes an estimation method that takes advantage of the fact that the preamble sequence symbols are assigned to every third subcarrier for each BS sector. Typically the closer the MS is to the BS, the more corrupted the noise power estimate is due to the higher signal power term in the estimator. The proposed method lowers the noise estimate by exploiting the differences in the powers of the orthogonal preambles received from the three spatially separated BS sectors. The simulation results show that the performance of our estimator improves as the power received from the two non-serving sectors decreases relative to the received power of the serving sector.

On the Design of Wideband CDMA User Equipment (UE) Modem

This paper describes the details of the implementation issues on wideband CDMA UE Modem, concentrating on the receiving side. Employed top-down design methodology and corresponding work efforts on each task are stated to demonstrate the effectiveness of the methodology.

A design of QAM modulator for multicode WCDMA

A QAM modulator using multiple four-output FIR filters based on look-up table (LUT) is proposed for downlink of wideband CDMA systems, and its functions are verified by stand-alone tests by means of the test equipment that achieves the functions of a QAM receiver system. Because a modulator employs the multicode modulation and M-QAM unlike QPSK modulation, the FIR filter for pulse shaping requires the multi-bit input word. So we propose the filter structure with multi-bit input word, which consists of multiple four-output FIR filter and bit-weighted accumulators. It is easy to extend the filter structure as increase of input bit word without higher clock frequency. We measure the spectrum of the implemented modulator by using a spectrum analyzer. Also, the demodulated signal constellation is obtained in the case of 16, 64 and 256-QAM as increase of multicode number.

The implementation of modulator using FPGA technology for W-CDMA WLL

This paper describes the design and implementation of the modulator in subscriber unit for wideband code division multiple access (CDMA) wireless local loop (WLL) testbed with 5 MHz bandwidth using Field Programmable Gate Array (FPGA) technology. The modulator presented in this paper provides two main functions: it carries out the complete digital modulation process for the reverse link and deinterleaves the forward-link symbols received from the symbol combiner of the demodulating unit. Also, the spectral degradation due to quantization error of filter coefficients and truncation of filter output is simulated. Filter output signals obtained from this implemented modulator are also included.

Precise estimation of noise power and SNR from OFDM signals

This paper describes the signal to noise ratio (SNR) estimation method for OFDM system. While many prior researches on SNR estimation uses training sequences subcarriers to measure noise power, our proposed method measures noise power from unused subcarriers of training sequences since most of OFDM systems leave some subcarriers in training sequences unused for various purposes. This method proved simple and accurate compared to other conventional methods and showed satisfactory accuracy even when only a few unused subcarriers are available.

Indoor field experiment results on spatial multiplexing MIMO using dual-polarized antennas

This paper describes the performance of MIMO (multiple Input Multiple Output) system using dual-polarized antenna in a IEEE 802.16m. The use of dual-polarized antennas in MIMO systems has emerged as a cost-and space-effective alternative, where two spatially separated uni-polarized antennas can be replaced by a single antenna element employing orthogonal polarizations. Several papers show mainly polarization diversity in multiple antenna system so far. In this paper, we show the simulation results of spatial multiplexing(SM) and space frequency block codes (SFBC) MIMO employing dual-polarized antenna. Also, we measure the PER (packet error rate) of downlink signal in implemented SM and SFBC MIMO system which is employing dual-polarized antenna under the indoor field environment. Dual-polarized antenna system achieved the similar trend PER (packet error rate) curve with uni-polarized one. That means that multiplexing gain is obtained from polarized antennas system having space and cost effective.

SNR Estimation in OFDMA/TDD Based WiBro System

This paper presents the signal-to-noise ratio (SNR) estimations for OFDM based system. In this paper, we examine simple SNR estimators, DASS (difference of adjacent subcarrier signal) estimator and EVM (error vector magnitude) estimator, which can be easily implemented into hardware. Moreover, we examine the effect factors which degrade the performance of SNR estimation in practical environment. The effect factors might be timing offset and frequency offset of received signal, and overlapping window length of transmitter. These factors have an impact upon SNR estimation at high SNR region. Thus, we propose the differential-DASS to improve the estimation performance according to the change of time and frequency offset at high SNR region.