Jae Joon Park

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.

3G-class space-time array transceiver for high data rate service WCDMA smart antenna system

This paper specially considers a new space-time (S-T) array transceiver for 3G-class high data rate service WCDMA system (460.8 kbps image data services) employing an optimum beamformer-channel estimator. To attain significant performance improvement, decision-directed MMSE (MMSE/DD) weight calculation algorithm based on channel estimation schemes is developed as an alternative to the conventional beamformer-RAKE schemes. Appropriate S-T array processing transceiver structure is derived and incorporated into system performance analysis to investigate the effect of channel estimations and decision-directed feedback on the overall performance of proposed MMSE/DD S-T array transceiver-based 3.6861 Mcps WCDMA smart basestation system. It is shown that highly improved S-T array design is possible and system employing the proposed smart basestation transceiver structure can sustain significant co-channel interference and multipath fading suppression capability while maintaining low bit error performance at the mobile high data rate service applications.

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.

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.

Distribution of eigenvalues for 2×N MIMO channel capacity based on urban microcell measurements

In this paper, we investigate the distribution of eigenvalues of HH† where the H and superscript † denote the MIMO (multiple input multiple output) channel matrix measured in urban microcell and conjugation and transposition. Our channel sounding system is the BECS (band exploration and channel sounding) 2006, which works at a carrier frequency of 3.705 GHz with 100 MHz bandwidth. From the measured data, It is observed that the distribution of eigenvalues of HH† almost fits with Gamma distribution. We derive simple expressions of mean and variance of eigenvalues, which are functions of the absolute values of Tx (transmit) and Rx (receive) antenna correlation coefficients and the number of Rx antennas. Using the expressions of mean and variance, we then model the eigenvalues as Gamma distributed random variables for 2×N (i.e., 2 Tx and N Rx antennas) MIMO channel capacity. Monte Carlo simulations are used to generate eigenvalue realizations according to the model. The results are compared with the measure data and good agreements are found.

Modeling of Eigenvalues for MIMO Channel Capacity Based on Outdoor Measurements

This paper aims at modeling of eigenvalues for 2×N (i.e., 2 transmit and N receive antennas) channel capacity based on non line-of-sight (NLOS) wideband outdoor measurements. Our channel sounding system is the Band Exploration and Channel Sounding System (BECS) 2005, which works at a carrier frequency of 3.7 GHz with 100 MHz bandwidth. From the measured data, we investigate transmit antenna correlation coefficient (TxACC), receive antenna correlation coefficient (RxACC), channel capacity and eigenvalues of HH * where H and (*) are channel frequency response matrix and conjugate transpose. Based on eigenvalue characteristics, we derive mean and variance of eigenvalue which are a function of the absolute value of TxACC, |TxACC|, the absolute value of RxACC, |RxACC|, and the number of Rx antennas, and then model eigenvalues for 2×N channel capacity. Monte Carlo simulations are used to generate eigenvalue realizations according to the model. The results are compared with the measure data and good agreements are found. Keywords-antenna correlation; capacity; CDF; channel sounder;

Uplink Packet Synchronization of OFDMA Systems

In order to support high rate data transmission, orthogonal frequency division multiplexing (OFDM) technology uses broadband consisting of a large number of narrow band orthogonal subcarriers. To apply the OFDM technology to outdoor mobile applications, the limitation of the transmission power of mobile station (MS) and the detrimental effect due to the granularity of bandwidth assignment have to be taken account. Some of the current standards are introducing the orthogonal frequency division multiple access (OFDMA) to take advantage of enhanced spectral efficiency by the fine granularity of bandwidth assignment and the coverage extension by power concentration gain in the uplink. This paper analyzes the uplink packet synchronization of current OFDMA standard and proposes a new uplink packet synchronization method, which makes implementation simple and improves system throughput.