Hayoung Yang

Analysis of a pipelined successive interference cancellation scheme for a DS/CDMA system

The bit error rate (BER) expression for a proposed pipelined successive interference cancellation (PSIC) scheme in a direct sequence/code division multiple access (DS/CDMA) system is derived analytically. The proposed PSIC scheme is a pipelined modification of a successive interference cancellation (SIC) scheme. The numerical results show that the proposed PSIC scheme outperforms the SIC scheme in viewpoints of the BER and the decoding delay performances.

Performance of space-time trellis codes in frequency selective WCDMA systems

The paper considers the performance of space-time trellis codes (STTC) in WCDMA forward links and its receiver structures. The performance of a RAKE matched filter over frequency selective multiuser multiple-input multiple-output (MIMO) channels is first investigated. Then we present an minimum mean-squared error (MMSE) detector which suppresses the interference in STTC WCDMA systems generated from multipath, multiuser, and multiple antenna propagation. The bit error rate performance of the MMSE detector is analyzed for STTC WCDMA systems. To obtain further performance improvement, a more efficient interference cancellation algorithm, an iterative MMSE detector, is considered. The iterative receiver performs soft interference cancellation for each user and each antenna based on a combination of the MMSE criterion and the turbo processing principle. It is shown that these space-time detectors have potential to provide significant capacity enhancements over the conventional temporal single-user receiver.

Iterative decoding of serially concatenated convolutional codes applying the SOVA

In numerous researches, the soft output Viterbi algorithm (SOVA) has been used for the iterative decoding of a parallel concatenated convolutional code (PCCC) instead of the maximum a posteriori (MAP) decoding algorithm having a suboptimal bounds to the maximum likelihood (ML) performance. The authors propose a modified SOVA for the iterative decoding of a serially concatenated convolutional code (SCCC). The most important reason for using the SOVA is that it can achieve real-time decoding without noticeable information losses. Another advantage is that the SOVA requires less structural modification of the conventional decoder than other iterative decoding algorithms such as maximum a posteriori (MAP). The simulation results show that the proposed SCCC decoding scheme using the SOVA is superior to the non-iterative SCCC. However, when compared with the scheme using the MAP algorithm, the performance gain is lower, as expected.

An adaptive channel precoded space-time transmitter for 3GPP TDD system

An adaptive channel precoded transmitter for space-time block coding based transmit diversity (STTD) is developed for a 3GPP WCDMA TDD system. Since all the functions of precoding are implemented in the base station, the channel equalization process can be left out in the mobile station. This results in the minimization of hardware complexity of the portable unit. Simulation results show that the adaptive channel precoded transmitter gives a close performance to the conventional Rake combiner.

Turbo code and star 16-QAM for DS/SSMA communications

In this paper, we propose a turbo coding scheme for spread spectrum with bandwidth efficiency. The scheme has a good performance on Gaussian channels and Rayleigh fading channels. We also show that the turbo code is powerful in multi-user environments. In our research, the turbo coded direct-sequence spread spectrum multiple access (DS/SSMA) system with differentially encoded star 16-QAM modulation is investigated in both aspects of error control performance and bandwidth efficiency. The results show that the coding system has a good error performance and spectral efficiency of 2 bits/s/Hz with star 16-QAM.

An iterative adaptive receiver design using the multi-layer RLS algorithm with applications to layered space time coded systems

Layered space-time (LST) architectures can support efficient signal processing in multiple-input multiple-output (MIMO) systems. Current applications to LST systems are based on pilot-aid transmissions, with the problem of reducing spectral efficiency. In this paper, the new adaptive algorithm called multilayer recursive least square (RLS) is applied to an iterative receiver structure in LST systems. A multi-layer RLS algorithm is an efficient method to provide accurate interference cancellation and fast convergence. This multi-layer RLS adaptive iterative receiver considers joint detection/decoding and channel estimation to avoid the periodic insertion of pilot-tones and hence improves spectral efficiency. The proposed iterative adaptive receiver is compared with a lower bound non-adaptive MMSE receiver where the channel state information (CSI) is assumed to be perfectly known a priori at the receiver. The proposed receiver structure is suitable for MIMO systems in slow time variant channels. Simulation results are supplied to demonstrate the excellent performance of the proposed multi-layer RLS adaptive receiver over a conventional linear RLS receiver.

Space-time block coding based transmit diversity using an adaptive channel precoder for WCDMA system

An adaptive channel precoded transmitter for space-time block coding based transmit diversity (STTD) is developed for a 3GPP WCDMA TDD system. Since all the functions of precoding are implemented in the base station, the channel equalization process can be left out in the mobile station. This results in the minimization of hardware complexity of the portable unit. Simulation results show that the adaptive channel precoded transmitter gives a close performance to the conventional RAKE combiner.

Combination of multiple turbo codes and multiple antennas for direct-sequence CDMA systems

A combined multiple turbo codes and multiple antenna diversity scheme for synchronous DS/CDMA systems over fading mobile radio channels is considered to improve the BER performance. In spite of the multiple structures no time delay and a lesser amount of computation can be achieved by a modified parallel mode decoding process and a reduced MAP algorithm using a code trellis structure. The performance of the proposed combining scheme is studied by means of simulation for a QPSK DS/CDMA system on a non-frequency selective Rayleigh fading channel.

An optimal and adaptive transmit power allocation scheme for mimo system

The water-filling principle, which maxi- mizes the capacity of MIMO wireless communication system by strategically allocating power to transmit antennas, results in a high bit error rate (BER) perfor- mance in the sub-channels with small eigenmodes. An adaptive transmission strategy is developed to pro- vide a tradeoff between the system capacity and the instantaneous BER performance with the constant to- tal transmit power.

A reduced rank constrained adaptive space-time interference canceller for multiuser multirate WCDMA systems

This paper concentrates on developing a complexity reduced adaptive space-time interference canceller for multiuser WCDMA forward link. Through exploring the multiuser interference and utilizing the space-time diversity, a sub-optimum diversity receiver, called a reduced-rank constrained adaptive space-time interference canceller (R-CASTIC), is proposed. The proposed scheme mitigates the disadvantages of the full-rank multiple antenna system, such as computational complexity and increased difficulty to accurately tune the algorithm. R-CASTIC performs similar to the full-rank receiver within 1 dB at the BER of 10/sup -3/ in less than 60% of total cell capacity, with only an eighth of the complexity of a full-rank receiver.