Myung Don Kim

Experimental Multipath-Cluster Characteristics of 28-GHz Propagation Channel

In this paper, a channel measurement campaign is introduced, which utilizes direction-scan-sounding to capture the spatial characteristics of 28-GHz wave propagation channels with 500-MHz sounding bandwidth in office environments. Both line-of-sight and non-line-of-sight scenarios were considered. Measurements were performed by fixing a transmit pyramidal horn antenna, and rotating another one in the receiver site at 10° steps in azimuth. The antenna outputs are viewed as array signals, and a space-alternating generalized expectation-maximization (SAGE) algorithm is applied to estimate delay and angular parameters of multipath components. Benefiting from high resolution achieved by using the SAGE and deembedding of antenna radiation pattern and system responses, more multipath clusters with less spreads in delay and azimuth are found per channel compared with existing works on 28-GHz propagation. The statistics of channel parameters extracted here constitute a preliminary stochastic multipath-cluster spatial channel model.

Selective temporal error concealment algorithm for H.264/AVC

The paper presents a new selective temporal error concealment algorithm (STEC) for error-corrupted H.264/AVC video bitstreams over the cdma2000 (or UMTS) air interface. The proposed algorithm performs selective temporal error concealment depending on whether a lost MB (macroblock) is in the background or foreground. It is shown that under the FMO coding mode of H.264/AVC, the proposed algorithm provides PSNR gain up to 1.18dB compared to the algorithm built into the H.264/AVC test model. In addition, the proposed STEC has an average PSNR improvement of 0.33dB compared with that under the N slice coding mode.

Measurement Results at 3.7 GHz in Urban Macrocell Environment

This paper presents the BECS (Band Exploration and Channel Sounding) 2005 system which was developed in ETRI to measure a MIMO wireless channel characteristics at 3.7 GHz carrier frequency and 100 MHz bandwidth. We present propagation analysis results for so called typical urban macrocell scenario in Korea. Propagation characteristics between LOS and NLOS scenarios have been compared, and we introduce small scale channel characteristics, i.e. root-mean-square (RMS) delay spread, rms angular spread, for stochastic geometry based channel model.

Distribution of Eigenvalues for 2x2 MIMO Channel Capacity Based on Indoor Measurements

Based on the non line-of-sight (NLOS) indoor measurements performed in the corridors on the third floor of the Electronics and Telecommunications Research Institute (ETRI) building in Daejeon city, Republic of Korea, we investigated the distribution of the eigenvalues of HH*, where H denotes a 2×2 multiple-input multiple-output (MIMO) channel matrix. Using the observation that the distribution of the measured eigenvalues matches well with the Gamma distribution, we propose a model of eigenvalues as Gamma distributed random variables that prominently feature both transmitting and receiving correlations. Using the model with positive integer k_i, i=1, 2, which is the shape parameter of a Gamma distribution, we derive the closed-form ergodic capacity of the 2×2 MIMO channel. Validation results show that the proposed model enables the evaluation of the outage and ergodic capacities of the correlated 2×2 MIMO channel in the NLOS indoor corridor environment.

Millimeter-wave channel model parameters for urban microcellular environment based on 28 and 38 GHz measurements

To meet the increasing demand for 5G high datarate communications, millimeter-wave frequency bands are expected to be utilized. However, the existing channel models are not applicable to predict channel behaviors in these frequency bands. In this paper we investigate millimeter-wave channel model parameters including path loss exponents, delay and angular spread, and clustering parameters based on measurements collected in urban microcell environments at 28 and 38 GHz. Our measurement data were obtained with a wideband millimeter-wave channel sounder equipped not only an omnidirectional antenna and but also a steerable direction antenna. The measurement campaigns were held in Dunsan District area in Daejeon City, Korea, which is a typical downtown area surrounded with high-rise buildings. From our analysis, fitting results indicate that a path loss exponent of LoS is close to the free space path loss exponent of 2. In NLoS, the path loss exponent is about 3 at both frequencies. Furthermore, we observe that delay and angular spread, and clustering parameters at 28 GHz are similar to those at 38 GHz. We believe that these analysis results will facilitate developing millimeter-wave band 5G wireless systems.

Time-Division Multiplexing Based MIMO Channel Sounder Using Loosely Synchronous Codes

In this paper, we propose the time-division multiplexing (TDM) based MIMO channel sounding technique using loosely synchronous (LS) codes for real time measurement of MIMO radio channel. Since LS codes have perfect autocorrelation and cross-correlation functions within certain vicinity of the zero shifts, the proposed technique can substantially reduce multipath channel interference. When cumulative distribution functions (CDFs) of absolute root mean square (RMS) delay spread error are considered, simulation results show that the proposed technique outperforms the conventional TDM based MIMO channel sounding technique. Moreover, in the MIMO channel environment where a mobile station moves with various speeds, the proposed technique is more efficient than the conventional TDM based MIMO channel sounding technique, because the proposed technique obtains about twice the measurement data of the conventional TDM based MIMO channel sounding technique at given time slots.

Error-resilient performance evaluation of MPEG-4 and H.264

Recent advances in video coding technology have resulted in rapid growth of application in mobile communication. With this explosive growth, reliable transmission and error resilient technique become increasingly necessary to offer high quality multimedia service. This paper discusses the error resilient performances of the MPEG-4 simple profile under the H.324/M and the H.264 baseline under the IP packet networks. MPEG-4 simple profile has error resilient tools such as resynchronization marker insertion, data partitioning, and reversible VLC. H.264 baseline has the flexible macroblock ordering scheme, and others. The objective and subjective quality of decoded video is measured under various random bit and burst error conditions.

Performance Analysis of Spatially Correlated MIMO-OFDM Beamforming Systems with the Maximum Eigenvalue Model from Measured MIMO Channels

The performance of MIMO-OFDM beamforming systems with maximal ratio combining receivers is considered based on the extensive wideband 2 × 8 (i.e., 2 transmitting and 8 receiving antennas) MIMO channel measurement data in non line-of-sight urban macrocell environments. Using the experimental observation that the probability density function (PDF) of the measured maximum eigenvalue for H† mHm, where Hm and superscript † denote a MIMO channel frequency response matrix and conjugation and transposition, respectively, matches the Gamma distribution well, we propose the maximum eigenvalue model as Gamma distributed random variables whose parameters are both transmitting and receiving correlations and the number of receiving antennas. Using the model, the performances of MIMO-OFDM beamforming systems, such as the PDF of the output signal-to-noise ratio, outage probability, symbol error rate, and achievable diversity order, are analyzed to demonstrate the effect of spatial correlation in the realistic 2 × n (downlink) and n × 2 (uplink) MIMO channels.

Directional path loss characteristics of large indoor environments with 28 GHz measurements

For 5G communications, millimeter-wave frequency bands are considered strong candidates for new spectra. However, propagation studies in these bands are still in their initial stages. Using 28 GHz measurements collected in railway and airport passenger terminals, this paper investigates path loss characteristics of large indoor environments. In particular, we conducted measurement campaigns in passenger terminals at Seoul Railway Station and Incheon International Airport, which are representative of commercial areas with a dense population. By employing steerable directional antennas, we characterize path loss not only with respect to distance but also with respect to antenna orientation. Directional path loss exhibits near free space propagation characteristics for LOS conditions (path loss exponent is about 2.15-2.17) and a path loss exponent of about 2.68-3.03 for NLOS conditions. From the dependency on antenna orientation, we found the range of azimuthal orientations satisfying a certain power level from the peaks. Consequently, this information provides a tool for determination of the amount of power deviation due to beam mis-alignment.

An autocorrelation model for shadow fading in rural macro environments

We propose an autocorrelation model of SF (shadow fading) in LOS (line-of-sight) rural macro environments. The proposed model is based on the empirical autocorrelations obtained from wideband MIMO (multiple input multiple output) channel measurements at 2.38 and 3.705 GHz. It was found that the SF depends on frequency and so do the empirical autocorrelations. The proposed model provides good matches to empirical autocorrelations in the individual measurement routes.