Jeong-Wook Seo

An Enhanced DFT-Based Channel Estimation Using Virtual Interpolation with Guard Bands Prediction for OFDM

In this paper, we investigate the conventional windowed DFT-based channel estimation for OFDM systems with guard bands. The conventional method suffers from the edge effect and the pilot position mismatch. In order to solve the problems, we propose an enhanced DFT-based channel estimation using virtual interpolation with guard bands prediction, where linear minimum mean square error (LMMSE) smoothing/prediction and circular frequency shifting are employed. This technique can efficiently mitigate the edge effect caused by the DFT of the truncated channel impulse response and compensate the pilot position mismatch that pilot symbols are not allocated at the first and the last subcarriers in a useful band. Simulation results show that the proposed method has about 5 dB SNR gain at BER=10-3 compared to the conventional method and is as good as the frequency-domain LMMSE method

Analysis of Pilot-Aided Channel Estimation with Optimal Leakage Suppression for OFDM Systems

This letter analyzes the effect of the leakage on the mean square error (MSE) performance of the pilot-aided channel estimator using discrete Fourier transform (DFT)-based interpolation in orthogonal frequency division multiplexing (OFDM) systems with virtual carriers. The optimal linear estimator for leakage suppression is derived to minimize the MSE. Numerical results show that the pilot-aided channel estimator with optimal leakage suppression improves the MSE performance significantly over the conventional one.

Successive Interference Cancellation for STBC-OFDM systems in a fast fading channel

A time-varying multipath channel causes co-channel interference (CCI) as well as inter-carrier interference (ICI) in a space-time block coded orthogonal frequency-division multiplexing (STBC-OFDM) system using two transmit antennas and an conventional simplified decoding scheme (SDS). In this paper, we derive the power of the CCI as a function of normalized channel variation rate. Also, we propose a successive interference cancellation (SIC) technique to improve the performance of the STBC-OFDM by considering the CCI mechanism. The proposed SIC technique can compensate the CCI to some extend with slightly increased complexity compared to the SDS.

DFT-based Channel Estimation Using CIR Adaptation in OFDM Systems

It is well known that discrete Fourier transform (DFT)-based channel estimators provides good performance with low complexity. Since its performance is influenced by estimated channel taps to lessen the noise effects, it is necessary to estimate the number of the channel taps and their time-domain position. Therefore, this paper proposes a modified DFT-based channel estimator with channel impulse response (CIR) adaptation which can simply find the significant channel path delays. The CIR adaptation uses scaling coefficients and threshold level which are generated by Monte-Carlo simulation. Simulation results show that the proposed method has a similar performance of the frequency-domain linear minimum mean squared error (LMMSE) method. Moreover, its performance is rather better than that of the LMMSE method under symbol timing offset (STO).

Performance evaluation of V2X communications in practical small-scale fading models

This paper investigates the simulation performances of vehicle-to-anything (V2X) communications based on the IEEE 802.11p wireless access in vehicular environments (WAVE) system in practical small-scale fading models. The main contributions of this paper are as follows. First, we modify the experimental fading models reported by Georgia Institute of Technology to be applied to the computer simulation of V2X communications. Second, an enhanced linear minimum mean square error smoothing-aided decision directed (LSA-DD) channel estimator is proposed to track the time variation of fading channels and mitigate noise enhancement.

Iterative Detection and ICI Cancellation for MISO-mode DVB-T2 System with Dual Carrier Frequency Offsets

In the DVB-T2 system with a multiple-input single-output (MISO) transmission mode, Alamouti coded orthogonal frequency division multiplexing (OFDM) signals are transmitted simultaneously from two spatially separated transmitters in a single frequency network (SFN). In such systems, each transmit-receive link may have a distinct carrier frequency offset (CFO) due to the Doppler shift and/or frequency mismatch between the local oscillators. Thus, the received signal experiences dual CFOs. This not only causes dual phase errors in desired data but also introduces inter-carrier interference (ICI), which cannot be removed completely by simply performing a CFO compensation. To overcome this problem, this paper proposes an iterative detection with dual phase errors compensation technique. In addition, we propose a successive-iterative ICI cancellation technique. This technique successively eliminates ICI in the initial iteration by exploiting pre-detected data pairs. Then, in subsequent iterations, it performs a fine interference cancellation using a priori information, iteratively fed back from the channel decoder. In contrast to previous works, the proposed techniques do not require estimates of dual CFOs. Their performances are evaluated via a full DVB-T2 simulator. Simulation results show that the DVB-T2 receiver equipped with the proposed dual phase errors compensation and the successive-iterative ICI cancellation techniques achieves almost the same performance as ideal dual CFOs-free systems, even for large dual CFOs.

An efficient feedback scheme using compressive sensing for MIMO broadcast channel with random beamforming

In this paper we proposes an efficient feedback scheme using compressive sensing (CS) for MIMO broadcast channel(BC) with random beamforming(RBF). Feedback resources are opportunististically accessed by strong users whose SINR is larger than threshold. Strong users transmit same feedback information on feedback channel and they are indentified by BS using CS. There is reduction of the feedback overhead via CS. Besides, we can achieve sum-rate throughput as full feedback. To exploit CS, feedback signal must be sparse. However, because there exist a trade-off between the sparsity and multiplexing gain, we must know how to decide K-sparsity and threshold. Therefore, we drive relation between K-spasity and threshold. These are suitable to ‘actual’ BC feedback channel with CS.

Iterative Joint Detection, ICI Cancelation and Estimation of Multiple CFOs and Channels for DVB-T2 in MISO Transmission Mode

When DVB-T2 uses the option of (distributed) multiple-input single-output transmission mode, a pair of Alamouti-encoded orthogonal frequency division multiplex signals is transmitted simultaneously from two spatially separated transmitters in a single frequency network. Since both transmitters have their own local oscillators, two distinct carrier frequency offsets (CFOs), one for each transmitter-receiver link, occur in the received signal due to the frequency mismatch between the local oscillators. Unfortunately, the multiple CFOs cannot be compensated simultaneously by merely adjusting the carrier frequency at the receiver side, so intercarrier interference (ICI) always exists. In this paper, we present an iterative receiver design to combat multiple CFOs for DVB-T2 application. To estimate both multiple CFOs and channels jointly without sacrificing the spectral efficiency, the joint maximum likelihood (ML) estimation based on the soft information from the channel decoder is used. The proposed receiver performs the iterative joint processing of the data detection, ICI cancelation, and joint ML estimation of the multiple CFOs and channels by exchanging the soft information. We also show that the complexity of the joint ML estimation can be reduced significantly by transforming a huge matrix pseudo-inversion into two sub-matrix pseudo-inversions. The performances are evaluated via a full DVB-T2 simulator. The numerical results show that the mean-squared error performance of the joint ML estimation is closely matched with the Cramér-Rao bound. Furthermore, the resulting bit error rate performance is enhanced in a progressive manner and is able to approach the ideal CFOs-free performance within a few iterations.

An MMSE-based compressive domain interference cancellator for wideband systems

Compressive sensing enables us to reduce the sampling rate below the Shannon Nyquist sampling rate. Unfortunately, in wideband systems, compressive sensing based signal processing often includes the undesired signals. In a previous work, ZF based method was proposed for interference cancellation. However, ZF based method do not consider the effect of noise. Moreover this method causes the degradation of desired signal. In this paper, we propose an interference cancellation method in compressive domain based on MMSE algorithm. The simulation results manifest that the proposed method improves the performance of reconstruction error rate.

A Composite LMMSE Channel Estimator for Spectrum-Efficient OFDM Transmit Diversity

In this paper, we propose a subcarrier allocation method and a composite linear minimum mean square error (LMMSE) channel estimator to increase spectrum efficiency in orthogonal frequency division multiplexing (OFDM) transmit diversity. The pilot symbols for OFDM transmit (Alamouti) diversity are exclusively allocated in two OFDM symbols in different antennas, which causes serious degradation of spectrum efficiency. To reduce the number of pilot symbols, our subcarrier allocation method uses repetition-coded data symbols, and the proposed channel estimator maintains good bit error rate (BER) performance.