Goohyun Park

Level crossing rate estimation with Doppler adaptive noise suppression technique in frequency domain

The maximum Doppler frequency, or, equivalently, the mobile speed, is very useful information for optimizing the performance of many wireless communication systems. The paper proposes an improved method for estimating the maximum Doppler frequency based on the level crossing rate (LCR) estimator. To reduce the effect of additive noise, the proposed algorithm uses a novel Doppler adaptive noise suppression (DANS) process in the frequency domain. The proposed DANS process does not require additional channel information such as signal-to-noise ratio (SNR).

A modified covariance-based mobile velocity estimation method for Rician fading channels

This paper contains our proposal for a novel velocity estimation method based on the auto-covariance of the received signal and that of the squared envelope. This modified covariance-based (MCOV) estimator exhibits unbiased characteristics in a Rician fading environment. Moreover, it requires no other channel information, such as Rician factors or the angle of arrival (AoA). The authors also propose a scaling technique which can improve the performance of the MCOV method in a Rayleigh fading environment. When coupled with the scaling technique, the new method demonstrates robust performance in both the Rayleigh and Rician fading environments.

SNR-independent methods for estimating maximum Doppler frequency

In this letter, we propose two maximum Doppler frequency estimators that are based on the level crossing rate (LCR) and the covariance function (COV). To eliminate the effect of additive noise, we analyze the conditions for the estimators independent of the signal-to-noise ratio (SNR) and implement the conditions with a simple downsampling process. The proposed methods achieve good SNR-independent performance.

A modified covariance-based velocity estimation method for Rician fading channel

In wireless mobile communication systems, the mobile velocity or, equivalently, the maximum Doppler frequency, is very useful information to optimize the system performance. A novel velocity estimation method, based on the autocovariance of the received signal and that of the squared envelope, is proposed. The proposed estimator provides unbiased characteristics. Moreover, the proposed method does not need any other channel information such as Rician factor and angle of arrival (AoA). The performance of the proposed estimator is verified by tracking simulation in realistic cellular mobile communication scenarios.

A new maximum Doppler frequency estimation algorithm in frequency domain

A novel maximum Doppler spread estimation algorithm for mobile communication systems is proposed. The proposed algorithm uses a fast Fourier transform (FFT) of received pilot signals, which are related with the maximum Doppler frequency f/sub D/. The proposed algorithm does not need to know any other channel information such as signal to noise ratio(SNR) because of using only the distribution of a fading channel power spectrum. Especially, the proposed algorithm shows good performance over wide a Doppler frequency in low SNR (< 10dB).

An implementation method of a turbo-code decoder using a block-wise MAP algorithm

The several implementation methods of the MAP decoder are proposed. By using the novel time-shared process of a pipe-lined structure, the restriction of recursion process on the state metric can be efficiently conquered, and the complexity of the MAP decoder can be reduced to the order of a SOYA (soft output Viterbi algorithm) decoder. An efficient structure for the controller is also proposed for the cdma-2000 system. The designed MAP decoder using a block-wire MAP algorithm has been implemented in only one 20,000 gate circuit. It has been validated by VHDL, which has been compared with the results of the initial simulation (C programs). The designed decoder has A 300 kbps decoding processing ability with 8 times iterations on a FPGA circuit, and just has a deviation of about 01-0.2 dB over the ideal MAP decoder; even if all hardware environments were considered.

An MPI mitigation technique for high order data modulations in the presence of intracell interference

Increasing throughput using high order data modulations in downlink WCDMA systems requires the elimination of the multipath interference (MPI). Linear chip equalizers using zero forcing (ZF) and minimum mean square error (MMSE) were proposed in downlink. A multipath interference canceller (MPIC) using weighted multi-stage parallel interference cancellation (PIC) was introduced in high speed downlink packet access (HSDPA) systems. We propose a multipath interference mitigation algorithm which removes the MPI in the presence of intracell interference. The proposed algorithm employs a linear tentative decision device with null zone in order to eliminate the MPI for intracell interference. As the intracell interference power increases, the proposed algorithm exhibits better performance compared with the RAKE and the MPIC.

A block-wise MAP decoder using a probability ratio for branch metrics

In this paper, we propose several methods for the block-wise MAP decoder for turbo codes. The novelties of this method are a branch metric obtained from the logarithm of the probability ratio and a pipelined and time-shared structure. The proposed block-wise method can reduce the excessive memory requirement and the decoding delay without increasing the complexity. In the simulation, the effects of quantization, the limits of input signals and the approximation of Max operation are considered.

A velocity-adaptive channel estimation scheme using the simple zero-forcing technique in the frequency domain

We propose a velocity-adaptive channel estimation scheme using a simple zero-forcing technique in the frequency domain. The proposed scheme is derived by approximating the frequency response of the Wiener filter as a rectangular shape. Channel estimation is performed by removing frequency components that are higher than the maximum Doppler frequency in the received signal. Simulation results show that the proposed scheme outperforms conventional schemes for a wide range of mobile velocities (3-300 km/h).

Robust velocity estimation for non-isotropic and AWGN channel

The maximum Doppler frequency, or equivalently, the mobile speed is very useful information to improve the performance of future wireless communication systems. In practical systems, however, the accuracy of the maximum Doppler frequency estimation is decreased by additive noise. Moreover, the information of signal-to-noise ratio (SNR) is not easily obtainable. Previously, several methods have been proposed to reduce the distortion due to the additive noise. However, these methods are not suitable for the non-isotropic fading channels and cause the distortion of the estimation values. In this paper, we propose the SNR-independent velocity estimation method for the nonisotropic channel which uses the covariance values of received signal. The proposed method provides accurate estimatation values without SNR information. In addition, it shows robust performance in the non-isotropic fading channels.