Seung Chan Bang

Sequence hopping cell search scheme for OFDM cellular systems

OFDM has been a widely accepted technology in high rate and multimedia data service systems, such as 3G Long Term Evolution (3G LTE) system in the 3rd Generation Partnership Project (3GPP). In this paper, we propose a new cell search scheme based on the frequency domain sequence hopping of synchronization channel symbols. The assigned hopping pattern provides frame boundary information as well as cell identification (cell ID) to a mobile station (MS). The proposed synchronization channel structure allows MS to acquire OFDM symbol/frame timing, cell ID and frequency offset estimates in the initial cell search stage. The cell search in MS is composed of 2 steps; OFDM symbol synchronization step, frequency offset correction and cell ID/frame boundary detection step. We evaluate the performance of proposed scheme under various channel environments. The impacts of multipath fading, vehicular speed and frequency offset on the performance are investigated. We also compare the performance of proposed scheme with 3G LTE cell search scheme.

Performance studies of rate matching for WCDMA mobile receiver

The use of the rate matching algorithm in a WCDMA system for the downlink channel is studied. The rate matching algorithm is an important part of the WCDMA system to support the multirate and multi-service feature. To support this feature, the rate matching algorithm has two main tasks. The first task is to match the instantaneous rate of the physical channel. The other task is to to minimize unnecessary increase in the required channel coded bit energy to satisfy different QoS. By a simulation performance study, the effect of rate matching in the WCDMA system is presented.

Transmit Diversity and Multiplexing Methods for 3G-LTE Downlink Control Channels

In order to provide a smooth migration toward 4G, studies on 3G long-term Evolution (3G-LTE) have been announced recently in third generation partnership project (3GPP) [1] and standardization work is under way. This paper investigates multiplexing method combined with transmit antenna diversity for the downlink control channels in 3G- LTE. Four schemes, such as FDM-STBC, CDM-STBC, FDM- SFBC and CDM-SFBC, are investigated for the downlink control channels, in particular, for one bit type control channels. Through computer simulation, the receiver performance of these candidate schemes are analyzed under multi-path fading channel environments. The effects of channel estimation, Doppler shift and the number of users on the performance are investigated. It is shown that the CDM-SFBC outperforms other schemes. We believe that results will provide beneficial information to design the 3G-LTE downlink control channels.

Open-Loop Transmit Diversity for Broadcast Channel Transmission in E-UTRA

This paper proposes applying precoding vector switching (PVS) transmit diversity scheme for primary broadcast channel (P-BCH) and secondary synchronization channel (S- SCH) in OFDM-based E-UTRA systems. The S-SCH is used as phase reference for P-BCH demodulation, which results in making no blind detection of the number of transmit antennas. Performance comparison is made with space frequency block coding (SFBC) using common reference signal (RS) as phase reference.

Massive MIMO test-bed design for next-generation long term evolution (LTE) mobile systems in the frequency division duplex (FDD) mode.

A massive MIMO test-bed under design is introduced as the pilot for next-generation long term evolution (LTE) mobile systems in the frequency division duplex (FDD) mode. In the design stage, computer simulations are performed and in a given conditions the results demonstrate that the test-bed algorithms possibly fulfill the capacity requirements of the fifth generation cellular system, which is one thousand times of that of the legacy LTE system. However, the complexity of the test-bed is not significantly increased with the adoption of new concepts like user grouping and beamforming, which enables the base station (BS) to use both smaller numbers of transmit pilot patterns and smaller amounts of channel state information feedback.

Model based antenna array calibration for digital beamforming systems

Model based calibration algorithm is presented to remove the antenna array errors for the digital beamforming system. It results in a reduced sidelobe in the array beam pattern and can be used to predict the element patterns from the array manifold measured at a small number of directions. The performance of the presented algorithm was shown by electromagnetic simulation and experiment results.

Channel estimation methods adequate to space time transmit diversity receiver in the W-CDMA IMT-2000 system

This paper presents some channel estimation methods adequate for the space time transmit diversity (STTD) receiver that coherently demodulates signals from each path of two transmit antennas. The STTD mode receiver estimates the channel information of each antenna path from the received common pilot channel (CPICH) signals with known orthogonal patterns transmitted by two antennas at the base station. The conventional channel estimation methods using a pilot filter result in serious inter-antenna interference caused by imperfect orthogonal processing of signals between the two antennas. Another drawback is the inter-symbol interference caused by lack of orthogonality between two symbols Which is the basic premise of the STTD decoding algorithm. This paper analyzes the effects of the inter-symbol interference and proposes some robust channel estimation methods to reduce the effects of the inter-symbol interference; This paper also compares the performance of the proposed channel estimation methods in various fading channel environments through the effective signal to interference ratio (SIR) and the bit error rate (BER).

Performance of a fast forward power control using power control bits for the reverse power control as power measurement

In this paper, we propose a fast forward power control in which the power control bits in the forward link used for the reverse link power control are utilized to measure the estimate of forward power. In a DS-CDMA system, there are generally power control bits transmitted in the forward link for fast reverse power control and they are transmitted usually with a fixed rate. Even if they have polarity, the SNR of a power control bit is equivalent to that of a pilot bit. This means that they can play an equivalent role to the pilot symbols in the sense of power measurement. In some systems, the position of a power control bit in a power control group is usually randomized to average out the interference. Then the power measurement by power control bits is performed quasi-periodically while the power measurement by pilot symbols or periodic power control bits can be made periodically. Computer simulation shows that the performance degradation by this quasi-periodicity is small to validate the proposed fast forward power control scheme.

Performance analysis of uplink power control in W-CDMA system for high data rate transmission

For IMT-2000, W-CDMA system adopts the SIR based power control on uplink and downlink. This paper analyzed the uplink power control performance for high data rate transmission on the system and suggest the efficient SIR estimation method for uplink power control.

A maximum-likelihood technique for preamble search in a CDMA reverse link

The performance of a maximum-likelihood code acquisition technique is analyzed for slotted-mode preamble search in a CDMA reverse link. The probabilities of detection, miss, and false alarm are derived analytically for a frequency-selective Rayleigh fading channel by taking into account the fading characteristics of a received signal for both single and dual antenna cases. Numerical examples illustrate the effects of post-detection integration, fading rate, and antenna diversity on the code acquisition performance.