Hoojin Lee

The performance of space-time block codes from coordinate interleaved orthogonal designs over nakagami-m fading channels

Space-time block codes (STBCs) from coordinate interleaved orthogonal designs (CIODs) offer several advantages including full-diversity and single-symbol decodability. In an effort to assess their performance in quasi-static frequency nonselective i.i.d. Nakagami-m fading channels, we analyze the error rate, outage capacity, and information outage probability. First, based on an accurate closed-form formula for the average symbol pairwise error rate (SPER), we derive tight union upper and lower bounds on the symbol-error rate (SER). Second, we apply Gaussian and Gamma approximations to provide closed form expressions for the outage capacity. Third, using high signal-to-noise ratio (SNR) and moment-matching approximation techniques, we also derive accurate closed-form approximations for the information outage probability (IOP). Finally, we show that STBCs from CIODs provide full-diversity by deriving SER based and IOP-based asymptotic and instantaneous diversity orders. Monte-Carlo simulations show that the analytical results agree with simulation experiments.

Combined ML and DFE Decoding for Coded Double STBC-OFDM System

An efficient combined maximum likelihood (ML) and decision feedback equalization (DFE) decoding method is proposed for a coded double space-time block code orthogonal frequency division multiplexing (DSTBC-OFDM) system. For the missing bit log likelihood ratios (LLRs) in the DFE part, our proposed detector effectively exploits Gaussian approximated LLRs with reference to the colored noise covariance matrix. Simulation results demonstrate that the proposed method can achieve comparable performance to the coded full ML detectors with deterministic and lower complexity.

Low-complexity ZF detector for D-STTD systems in time-selective fading channels

By combining transmit diversity and spatial mul- tiplexing schemes, a double space-time transmit diversity (D- STTD) system achieves both diversity gain and increased data rate. However, the performance degradation of the D-STTD system is caused by channel time-selectivity due to the high Doppler spread effect in wireless mobile fading channels. To overcome this problem, we propose a computationally efficient zero-forcing (ZF) detection scheme. The detector exploits two effective filtering processes with no matrix inversion. Therefore, it offers the same performance as existing ZF methods, but at less receiver complexity. We compare the complexity of the proposed detection scheme with those of the known ZF schemes and demonstrate its validity by simulation.

QR-decomposition-based linear and decision-feedback detections for D-STTD systems over time-selective fading channels

In this paper, we propose QR-decomposition-based unordered/ordered decorrelating decision-feedback detection (D-DFD) schemes with linear or D-DFD symbol estimators for a double space-time transmit diversity (D-STTD) system. The time-selective fading mobile channel severely degrades the performance of conventional detectors, since the time-selectivity of the fading channel destroys the orthogonality of the space-time codeword. Moreover, the complexity of the known symbol-by-symbol detectors is too high to be implemented, due to the multiple channel inversions. In contrast, through the block-by-block QR-decomposition, our proposed methods can decorrelate the two STTD units while preserving the Alamouti-like codeword structure and exploit this structure to efficiently estimate the symbols corrupted by the severe time-selective fading channels

Performance Evaluation of Space-Time Block Codes from Coordinate Interleaved Orthogonal Designs in Shadowed Fading Channels

In this correspondence, we evaluate the symbol error rate (SER) and information outage probability (IOP) of space-time block codes (STBCs) from coordinate interleaved orthogonal designs (CIODs) in the composite channel of lognormal shadowing and Rayleigh fading. By applying the Gauss-Hermite quadrature integration, we derive an accurate closed-form approximation for the symbol pairwise error rate (SPER) and corresponding tight upper and lower bounds on the SER of STBCs from CIODs. An accurate closed-form approximate formula for the IOP is also derived by formulating the composite squared lognormal/chi-square probability density function and exploiting the high-signal-to-noise-ratio (SNR) approximation technique. Furthermore, we investigate the achievability of full diversity in Rayleigh fading channels with shadowing effects. Finally, various Monte Carlo simulations are performed to validate our theoretical results.

Performance Analysis of a Dual-Hop Relay With STBC-CIOD over Rayleigh Fading Channels

In this paper, a symbol error rate (SER) study is presented for the dual-hop relay networks employing space-time block code (STBC) from coordinate interleaved orthogonal design (STBC-CIOD), where a relay with either a decode-and-forward (DF) or an amplify-and-forward (AF) protocol is equipped with multiple antennas. More specifically, we provide the union upper and lower bounds on the average SER by deriving an accurate closed-form formula for the corresponding symbol pairwise error rate (SPER). In addition, the asymptotic diversity order is analyzed. The theoretically derived bounds are in good agreement with the simulation results.

Joint Frame/Frequency Synchronization and Channel Estimation for Single-Carrier FDE 60 GHz WPAN System

It is well-known that the OFDM scheme has some tolerance for symbol/frame timing errors (i.e. valid starting position of FFT window). Such tolerance exist for SC-FDE. However, frame timing offset affects the receiver performance due to deviation in frequency domain channel estimation result when fractional channel estimation vector is applied in time domain. To achieve optimized receive performance at all times, symbol/frame timing must be estimated precisely in accordance to the exact starting position of the channel estimation sequence block. In this paper, we propose an efficient frame/frequency synchronization along with channel estimation technique suitable for implementation of SC-FDE based 60GHz WPAN physical layer systems employing a Frank-Zadoff preamble structure. The proposed method is designed for parallel processing, and is robust against carrier frequency offset in moderately dispersive multipath-fading LOS+NLOS channels.

Effect of Generalized-K Fading on the Performance of Symmetric Coordinate Interleaved Orthogonal Designs

In this letter, an efficient method of evaluating the performance of space-time block codes (STBCs) from symmetrically structured coordinate interleaved orthogonal designs (CIODs) is presented over generalized-K MIMO fading channels. By effectively approximating the moment generating function (MGF), we derive approximate closed-form expressions for the symbol pairwise error rate (SPER) and corresponding tight approximate symbol error rate (SER) of STBCs from symmetric CIODs. Finally, various Monte-Carlo simulations are performed to validate our theoretical results.

Design of Novel Orthogonal Space-Time-Frequency Block Codes for OFDM systems Over Fading Channel Environments

In this paper, we propose a novel orthogonal space- time-frequency block codes using Alamouti scheme for OFDM systems (STFBC-OFDM) employing two transmit antennas. Space-time block coded OFDM (STBC-OFDM) systems and space-frequency block coded OFDM (SFBC-OFDM) systems face problems in time-selective fading (i.e., time-varying channel) and frequency-selective fading environments, respectively. In the proposed STFBC-OFDM, the Alamouti code is applied over two successive OFDM symbols and neighboring subcarriers simultaneously with scaling factor to reduce the performance degradation from channel selectivities. Although the repetition of coding decreases the code rate, a SNR gain obtained by scaling can nearly compensate for the loss of code rate. The simulation results show that the proposed STFBC-OFDM outperforms STBC-OFDM in time-selective fading channels and SFBC-OFDM in frequency-selective fading channels.

Efficient OFDM symbol estimation algorithm over time-frequency-selective fading channels

In orthogonal frequency division multiplexing (OFDM) systems, time-frequency-selective, equivalently time-variant multipath fading destroys subcarrier orthogonality, resulting in intercarrier interference (ICI). OFDM systems with guard interval (GI) can prevent intersymbol interference (ISI) caused by frequency-selective fading, but do not combat ICI caused by time-selective fading. To mitigate the effects of ICI, several estimation methods have been proposed. These conventional algorithms are highly complex in general due to the large-sized matrix inversion. In this paper, we propose an efficient OFDM symbol estimation scheme, called iterative sequential neighbor search (ISNS) algorithm, which achieves an enhanced performance with a moderate complexity compared with the conventional methods. The validity of the proposed estimation scheme is demonstrated by computer simulations.