Heung Ki Baik

Shannon Capacity and Symbol Error Rate of Space-Time Block Codes in MIMO Rayleigh Channels With Channel estimation Error

Space-time block coding (STBC) is an attractive solution for improving quality in wireless links. In this paper, we analyze the impact of channel estimation error on the ergodic capacity and symbol error rate (SER) for space-time block coded multiple-input multiple-output (MIMO) systems. We derive a closed-form capacity expression over MIMO Rayleigh channels with channel estimation error. Moreover, we derive an exact closed-form SER for general PAM/PSK/QAM with channel estimation error. We show that, as expected, channel estimation error introduces the capacity loss and diversity gain loss. Furthermore, as the number of transmit and receive antennas increases, the sensitivity of the STBC system to channel estimation error increases. Simulation results demonstrate the accuracy of our analysis.

Decision feedback detection for space-time block coding over time-selective fading channels

Most existing space-time coding (STC) schemes have been developed for flat fading channels. To obtain antenna diversity gain, they rely on channel state information (CSl) required at the receiver through channel estimation techniques. This paper proposes a new decision feedback decoding scheme for Alamouti-based space-time block coding (STBC) transmission over time-selective fading channels. In wireless channels, time-selective fading effects arise mainly due to Doppler shift and carrier frequency offset. Modelling the time-selective fading channels as the first-order Gauss-Markov processes, we use recursive algorithms such as Kalman filtering, LMS and RLS algorithms for channel tracking. The proposed scheme consists of the symbol decoding stage and channel tracking algorithms. Computer simulations confirm that the proposed scheme shows the better performance and robustness to time-selectivity.

Phase noise suppression algorithm for OFDM-based 60 GHz WLANs

In this paper, we investigate the OFDM-based wireless local area networks (WLANs) operating in the 60 GHz frequency band. The performance of OFDM system is severely degraded by the local oscillator phase noise, which causes both common phase error (CPE) and inter-carrier interference (ICI). We analyze the impact of phase noise on OFDM systems. Moreover, in order to reduce the phase noise problem, we consider the phase noise suppression (PNS) algorithm. Some numerical results are presented to illustrate the effectiveness of the PNS algorithm for OFDM-based 60 GHz WLANs.

Training-based channel estimation and equalization for space-time block-coded systems over frequency-selective fading channels

Channel estimation for a space-time block coded transmission system is considered. By assuming that the channel frequency response is quasi-static, we develop channel estimation based on the use of a space-time block coded (STBC) training block. The optimality criterion for training sequence design is derived and the design tradeoffs associated with the choice of training length are discussed. A novel equalization and detection algorithm for the Alamouti scheme is developed, which is derived from the max-log maximum a posteriori (MAP) algorithm for conventional single-antenna systems. Zero-forcing (ZF) and minimum mean square error (MMSE) equalization are derived for the suboptimal detection algorithm. Numerical results are provided to demonstrate the performance of the proposed channel estimation and equalization algorithm for space-time block coded transmission systems.

Blind adaptive channel equalization using multichannel linear prediction-based cross-correlation vector estimation

Blind equalization of transmission channel is important in communication areas and signal processing applications because it does not need training sequences, nor does it require a priori channel information. In this paper, an adaptive blind MMSE channel equalization technique based on second-order statistics is investigated. We present an adaptive blind MMSE channel equalization using multichannel linear prediction error method for estimating cross-correlation vector. They can be implemented as RLS or LMS algorithms to recursively update the cross-correlation vector. Once cross-correlation vector is available, it can be used for MMSE channel equalization. Unlike many known subspace methods, our proposed algorithms do not require channel order estimation. Therefore, our algorithms are robust to channel order mismatch. Performance of our algorithms and comparison with existing algorithms are shown for real measured digital microwave channel.

Asymptotic Performance and Exact Symbol Error Probability Analysis of Orthogonal STBC in Spatially Correlated Rayleigh MIMO Channel

Space-time block coding is an attractive solution for improving quality in wireless links. In general, the multiple-input multiple-output (MIMO) channel is correlated by an amount that depends on the propagation environment as well as the polarization of the antenna elements and the spacing between them. In this paper, asymptotic performance and exact symbol error probability (SEP) of orthogonal space-time block code (STBC) are considered in spatially correlated Rayleigh fading MIMO channel. We derive the moment generating function (MGF) of effective signal-to-noise ration (SNR) after combining scheme at the receiver. Using the MGF of effective SNR, we calculate the probability density function (pdf) of the effective SNR and derive exact closed-form SEP expressions of PAM/PSK/QAM with M-ary signaling. We prove that the diversity order is given by the product of the rank of the transmit and receive correlation matrix. Moreover, we quantify the loss in coding gain due to the spatial correlation. Simulation results demonstrate that our analysis provides accuracy.

Symbol Error Probability for Space-Time Block Codes Over Spatially Correlated Rayleigh Fading Channels

In general, multi-input multi-output (MIMO) channel is correlated by an amount that depends on the propagation environment as well as the polarization of the antenna elements and the spacing between them. In this paper, an exact error probability of orthogonal space-time block codes is considered in spatially correlated Rayleigh fading channels. We derive a general formula for the symbol error probability (SEP) of orthogonal space-time block codes for general PSK/PAM/QAM over spatially correlated Rayleigh fading channels.

A study on the real-time photoacoustic tomography system for functional imaging and the monitoring of kidney inflammation in rats

Photoacoustic tomography (PAT) is a promising medical imaging modality by reason of its particularity. It combines optical imaging contrast with the spatial resolution of ultrasound imaging, and it can distinguish changes in biological features in an image. For these reasons, many studies are in progress to apply the technique for diagnosis. However, realtime PAT systems are necessary to confirm biological reactions induced by external stimulation immediately. Thus, we have developed a real-time PAT system using a linear array transducer and a custom-developed data acquisition board (DAQ). To evaluate the feasibility and performance of our proposed system, a phantom test was also performed. As a result of those experiments, the proposed system shows satisfactory performance, and its usefulness has been confirmed. We monitored the degradation of a rat’s kidney inducing inflammation, using our developed real-time PAT.

Real-time, High-resolution Diagnosis for Osteoarthritis in the Rat Using Common-Path Fourier-Domain Optical Coherence Tomography

The need for an inexpensive, real-time, high-resolution diagnosis for osteoarthritis (OA) is profound. After inducing OA in rats, we monitored the degradation of the articular cartilage by experimentally using in-house developed common-path Fourier-domain optical coherence tomography (CP-FDOCT). To observe the progression of OA, we injected monosodium iodoacetate (MIA) into the left knee joint. The histological images showed patterns that are similar to OCT images. These results illustrated the potential of CP-FDOCT for use in the noninvasive diagnosis of this particular grade of OA.

Monitoring of the degradation in the rat's articular cartilage inducing osteoarthritis using common-path Fourier-domain optical coherence tomography

The objective of this experiment is to evaluate the utility and limitations of optical coherence tomography (OCT) for real-time, high-resolution structural analysis. We monitored the degradation of the rat’s articular cartilage inducing osteoarthritis (OA) and the change of the rat’s articular cartilage recovery by treatment medication, using our developed common-path Fourier-domain (CP-FD) OCT. Also, we have done a comparative analysis the rat’s articular cartilage and OA grade. To observe the progression of OA, we induced OA by injecting the monosodium iodoacetate (MIA) into the right knee joint. After the injection of MIA, we sacrificed the rats at intervals of 3 days and obtained OCT and histological images. OCT and histological images showed the OA progress of similar pattern. These results illustrated the potential for non-invasive diagnosis about the grade of OA using CP-FD OCT.