Yu-Kuan Chang

Iterative multiuser detection for LDPC MIMO SC-FDMA communication systems

In order to provide high quality services, current communication systems require high-data transmission rate and good error performance. Because single-carrier frequency division multiple access SC-FDMA is with the desirable characteristics of orthogonal frequency division multiple access and the low peak-to-average power ratio of single-carrier transmission schemes, it has been adopted as the uplink transmission scheme in 3GPP long-term evolution to approach the demand for data transmission rates and error performance. By combining multiple-input multiple-output MIMO techniques with the SC-FDMA modulation scheme, MIMO SC-FDMA systems can achieve high data rates over broadband wireless channels. In this paper, we propose the iterative multiuser detection scheme for the low-density parity-check-coded MIMO SC-FDMA communication systems. On the basis of the property of space-frequency block coding, we develop the frequency domain minimum mean-squared error and zero-forcing equalisers with multiuser interference cancellation technique on each subcarrier to recover the transmitted symbols. Some simulation examples for uplink scenario are given to demonstrate the effectiveness of the proposed schemes. Copyright

A New SAGE-Based Receiver for MC-CDMA Communication Systems

Abstract Multicarrier code division multiple access (MC-CDMA) systems have arrested a lot of attention, owing to the simple implementation and powerful resistance to frequency-selective channels and the CDMA with the suitability for multiuser systems. Although MC-CDMA systems spread symbols using orthogonal codes to ensure orthogonality, orthogonality may be destroyed at the receiver due to frequency selective fading and then results in multiple access interference (MAI) and inter-carrier interference (ICI). The space-alternating generalized expectation–maximization (SAGE) algorithm is with high convergence speed and performs maximum-likelihood estimation/detection of the transmitted signals. For MC-CDMA systems, existing SAGE algorithm is used to cancel the ICI (Panayirci et al. in IEEE Trans Signal Process 58(8): 4225–4238, 2010), or to cancel the MAI (Panayirci et al. in 16th IST Mobile and Wireless Communications Summit, 2007). In this paper, the proposed interference cancellation scheme not only performs MAI cancellation but also performs ICI cancellation for the MC-CDMA systems. Some simulation examples are given to show the effectiveness and comparisons of the proposed receiver.

A low-complexity turbo MUD for MU-MIMO SC-FDMA systems

In order to provide high-quality services, current communication systems require high data-transmission rate and good error performance. Single carrier-frequency division multiple access SC-FDMA has been adopted as the uplink transmission standard in fourth generation cellular network to enable the power efficiency transmission in mobile station. Multi-user multiple-input multiple-output MU-MIMO technologies are adopted in many standards to enhance the data rate and the link robustness. By combining MU-MIMO techniques with the SC-FDMA modulation scheme, MU-MIMO SC-FDMA systems can achieve high data rates over broadband wireless channels. For MU-MIMO SC-FDMA systems, possible detection techniques include zero-forcing detection, minimum mean squared error detection and maximum likelihood detection MLD. Among these schemes, MLD is optimal, but its complexity grows exponentially with the number of symbols detected. As a result, there are demands for near MLD schemes that provide similar performance with less complexity. In this paper, we consider the MU-MIMO SC-FDMA communication and propose a low-complexity and high-performance turbo receiver for the systems. Some simulation examples for uplink scenario are given to demonstrate the effectiveness of the proposed scheme. Copyright

Frequency-Domain Iterative SDFE for MIMO-OFDM Systems

Abstract This paper proposes a frequency-domain iterative soft decision feedback equalization (SDFE) scheme for multiple-input–multiple-output orthogonal frequency division multiplexing communication systems in multi-path fading channels. Error propagation can seriously affect the performance of the adaptive decision feedback equalization. We propose an iterative SDFE to not only combat error propagation but also be suitable for multilevel modulation systems. Under a Gaussian approximation of the a priori information and the SDFE output, the output of an equivalent AWGN channel and expressions for the a posteriori log likelihood ratio (LLR) and the extrinsic LLR are derived for multilevel modulation. In addition, we also investigate the iterative receivers by employing irregular low-density parity check codes (LDPC) and turbo codes. The performance of the LDPC-coded iterative receiver is better than that of the turbo-coded iterative receiver. Some simulation examples are given to show the effectiveness and comparisons of the proposed receiver.

Channel parameters estimation for multiuser MIMO MC-CDMA systems

This paper investigates the channel estimation method for multiuser multiple input/multiple output (MIMO) multi-carrier code division multiple access (MC-CDMA) communication systems. For the asynchronous uplink transmission situation, the receiver needs to estimate the channel parameters, including the multi-path gain coefficient, the carrier phase offset and the transmission time delay, to demodulate the received signals. Based on the knowledge of the spreading sequences, the proposed parameter estimation method employs the least mean-squared error (LMSE) criterion to the required parameters for the multiuser MIMO MC-CDMA systems. Some simulation examples for uplink scenario are given to demonstrate the effectiveness of the proposed methods.

MIMO receivers for SFBC SC-FDMA communication systems

Single carrier-frequency division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth generation cellular network to enable the power efficiency transmission in mobile station. Since multiuser multiple-input multiple-output (MU-MIMO) is a promising technology to fully exploit the channel capacity in mobile radio network, this paper investigates the uplink transmission of SC-FDMA systems with orthogonal space frequency block codes (SFBC). Two linear multiuser MIMO (MV-MIMO) receivers, orthogonal SFBC (OSFBC) and minimum mean square error (MMSE), are derived for the scenarios with limited number of users or adequate receive antennas at base station.

Pipelined turbo multiuser detection and Kalman channel estimation for MU-MIMO SC-FDMA systems

Single carrier-frequency division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth generation cellular network to enable the power efficiency transmission in mobile station. Since multiuser multiple-input multiple-output (MU-MIMO) is a promising technology to fully exploit the channel capacity in mobile radio network, this paper investigates the uplink transmission of SC-FDMA systems with orthogonal space frequency block codes (SFBC). It is necessary to joint consider the channel estimation, multiuser detection and turbo equalization for MU-MIMO SC-FDMA system. The pipelined turbo equalizer architecture has the feature that multiple soft-decisions become available at various processing stage. These multiple decisions from different pipeline stage have varying levels of reliability and can be used to track the variation of the channels. A critical issue in turbo receiver design is long processing latency due to inherent iterative processing of information. Pipeline architecture reduces the latency and improves processing throughput in turbo receivers and thus is the prevailing choice of the implementation architecture. The optimum channel estimator is a Kalman-based channel estimator for MU-MIMO SC-FDMA systems. In this paper, we use the pipelined structure to design the iterative channel tracking, multiuser detection and turbo equalization which with low latency, reasonable computation complexity and good channel tracking capability. Some simulation examples for uplink scenario are given to demonstrate the effectiveness of the proposed schemes.

Blind receiver for MIMO SC-FDMA communications

Because SC-FDMA (Single Carrier Frequency Division Multiple Access) is with the desirable characteristics of OFDMA and the low PAPR (Peak-to-Average Power Ratio) of single-carrier transmission schemes, it has been adopted as the uplink transmission scheme in 3GPP LTE to approach the demand for data transmission rates and error performance. By combining multiple-input multiple-output (MIMO) techniques with the SC-FDMA modulation scheme, MIMO SC-FDMA systems can achieve high data rates over broadband wireless channels. In this paper, we propose the iterative multiuser detection scheme for the low-density parity-check (LDPC) coded MIMO SC-FDMA communication systems. Some simulation examples for uplink scenario are given to demonstrate the effectiveness of the proposed schemes.