Hyun Kyu Chung

Range-dependent path-loss model in residential areas for the VHF and UHF bands

Implementation digital fixed wireless systems, such as digital FM, high definition TV (HDTV) and wireless local loop (WILL), require a high level of accuracy of propagation prediction in the VHF and UHF bands. This paper presents a theoretical model that predicts the average path loss from an elevated base station to subscriber antennas at rooftop level in residential areas for frequencies in the approximate band from 30 MHz up to 3 GHz. In addition, the model gives the standard deviation of the path loss at the average rooftop level and the height gain for subscriber antennas above or below the average rooftop level. The approach used here generalizes that of Walfisch and Bertoni (1988), who developed a theoretical model of UHF propagation in urban environments. The rows of buildings in residential areas are modeled as a series of dielectric screens having random heights and uniform spacing. Propagation takes place over and through the dielectric screens, and ground reflections are included. The fields at the plane of each screen are obtained in terms of repeated numerical evaluation of the physical optics (PO) integral. Results obtained for the variation of the range dependence on frequency and row spacing are consistent with those previously found for high frequencies by assuming the screens to be totally absorbing. Using the results at different heights of receiving antenna allows computation of the height gain. The predictions are in agreement with the International Telecommunication Union Radio Communication (ITRU-R) recommendations in the VHF and UHF bands.

An efficient synchronization signal structure for OFDM-based cellular systems

OFDM has been a widely accepted technology in high rate and multimedia data service systems such as long term evolution (LTE) in the 3rd generation partnership project (3GPP). In this paper, we investigate a synchronization signal structure and corresponding cell search algorithm in the LTE system where two, primary and secondary synchronization signals are employed. We focus on the secondary synchronization signal which possesses two layered scrambling sequences in addition to basic sequences. These scrambling sequences minimize performance degradation in cell search, but incur a high complexity to a mobile station receiver. In this paper, we propose a new secondary synchronization signal structure which does not require additional scrambling sequences while maintaining almost the same performance as the current LTE scheme. We evaluate the performance of the proposed scheme under various channel environments by examining the impacts of multipath fading, frequency offset, and vehicular speed. We also compare the complexity of the proposed scheme with the LTE scheme.

MIMO channel sounder implementation and effects of sounder impairment on statistics of multipath delay spread

This paper introduces the Band Exploration and Channel Sounding System (BECS) as a prototype of 2x8 MIMO wireless channel sounder, which is under developing in ETRI to explore wideband channel and frequency characteristics at 2.6 GHz. Engineering parameters for the BECS implementation are presented and the sounder system response is obtained and analyzed using the hardware channel simulator, Elektrobit PROPsim ® . The impact of imperfect system response on rms delay spread is analyzed using the 3GPP Spatial Channel Model (SCM). Based on Monte-Carlo simulations generating multiple ensembles of the wireless channel, it is found that rms delay spreads measured by the sounder do not depend on the sounder impairment such as the bell-shaped system response induced from RRC filter, and the equalized matched filter technique can improve the delay resolution against the imperfect system response

An Iterative Decoding Technique for Cooperative STBC-OFDM Systems with Multiple Carrier Frequency Offsets

In this paper, an iterative decoding technique for cooperative space-time block coded orthogonal frequency division multiplexing (STBC-OFDM) systems is proposed to mitigate the intercarrier interference (ICI) caused by multiple carrier frequency offsets (CFOs) in cooperative transmission. The proposed iterative decoding technique is shown to mitigate the noise enhancement effect on the STBC-OFDM signals caused by multiple CFOs, and be effective in reducing ICI especially when the system has a large FFT size and a large multiple CFOs.

Opportunistic Beamforming Communication With Throughput Analysis Using Asymptotic Approach

The opportunistic beamforming system (OBS) is currently receiving much attention in the field of downlink beamforming due to its simple random beamforming, low feedback complexity, and same throughput scaling obtained with perfect channel-state information using dirty paper coding at the transmitter. In this paper, we focus on its closed-form throughput evaluation over Rayleigh fading channels, based on the asymptotic theory of extreme order statistics. First, the throughput of a single-beam OBS is investigated, and an analytical solution tighter than the previously reported one is derived. Then, the asymptotic throughput bounds on a multibeam OBS are presented, and also, our analytical expression is shown to be very tight with the simulation results even with fewer users. After that, we argue that the reported conclusion that the single-beam OBS is much preferable to the multibeam OBS in the high-signal-to-noise-ratio (SNR) regime is inaccurate, but that, instead, it is satisfied only when the number of users is very small, due to its limited multiuser diversity gain. Finally, we show that four transmit beams is the most preferable in the multibeam OBS with a large number of users and moderate SNR, which arrives at the tradeoff between increasing spatial multiplexing gain and disappearing multiuser diversity gain.

Novel Multi-User MIMO Scheme Based on Successive Interference Cancellation

Multiple Input Multiple Output (MIMO) technology using multiple transmit and receive antennas is considered one of essential elements for wireless communication systems in order to achieve the required spectral efficiency and high data rates. In this paper, we propose new multi-user preceding MIMO schemes named successive interference cancellation (SIC) based Per User and Stream Rate Control (S-PUSRC), and modified S-PUSRC, which are characterized by SIC based multiple stream reception and the feedback of decoding order for efficient multi-user scheduling. Additionally, a number of simulation results are presented.

Code-Division Multiplexing Based MIMO Channel Sounder with Loosely Synchronous Codes and Kasami Codes

In this paper, the code-division multiplexing (CDM) based MIMO channel sounder with loosely synchronous (LS) codes and Kasami codes is presented for real time measurement of MIMO radio channel. Since this scheme has drawback of reduced dynamic range depending on the number of transmit antennas, it is important that low correlation codes should be utilized to get reliable performance. This paper adopts two efficient codes, LS codes and Kasami codes, of which performances are investigated through Monte-Carlo simulation in 2 x 8 and 4 x 8 MIMO channel environment, respectively. Basically, LS codes are noise-limited and Kasami codes are interference-limited in relation with cross-correlation characteristic. According to the simulation, LS codes are the best in 2 x 8 MIMO channel measurement and modified LS codes approach to this performance of LS codes in both 2 x 8 and 4 x 8 MIMO channel measurement. Kasami codes achieve somewhat less performance than the others, but are not nearly affected by the number of transmit antennas. Thus, Kasami codes are effective when transmit antennas are more than 4.

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.

Sounding Method for Proportional Fair Scheduling in OFDMA/FDD Uplink

Sounding provides a BS with knowledge of the channel state information of a user in an orthogonal frequency division multiple access (OFDMA) full duplex division (FDD) uplink. In this paper, we propose a novel sounding subband allocation algorithm for the proportional fair (PF) scheduler. Simulation results show that our proposed sounding method enables the PF scheduler to achieve the throughput gain and guarantee fairness at the same time.

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.