Luo Han-wen

Radar detection for 802.11a systems in 5 GHz band

In order to coexist with radar in the 5 GHz frequency band, dynamic frequency selection (DFS) mechanisms are imperative for 802.11a systems, which require detection of radar signals. Firstly, characters of radar signals are summarized, and several known radar detection algorithms are surveyed. By utilizing characters of radar signals, some other candidate algorithms based on matched filtering technique, frequency domain and time-frequency analysis are presented. Through the analysis of above algorithms, a simple and prospective method based on power detection in time domain is given, and some considerations for applying the method are illustrated as well.

Genetic algorithm based multiuser detection for CDMA systems

Genetic algorithms (GAs) are applied to suboptimal joint multiuser detection in bit-synchronous code division multiple access (CDMA) systems, whereas GAs have been employed for solving many optimization problems in numerous fields. The major advantage of the proposed GAs multiuser detector is that it provides a good compromise between the performance and computational complexity, that in contrast to the case of the optimal maximum-likelihood multiuser detector has a computational complexity that is exponentially increasing with the number of users. Computer simulation results show that GAs multiuser detector has powerful properties both in bit error probability and near-far resistance comparison of the conventional detector and some other multiuser detector.

Neural networks based parallel Viterbi decoder by hybrid design

A hybrid scheme integrating analog and digital methods is presented to design a Viterbi decoder based on neural networks. Due to its fully parallel architecture, neural networks based Viterbi decoder is significantly faster than the purely digital decoder. The fully parallel structure is obtained by implementing the branch metric calculation and add-compare-select (ACS) using the neural networks while the register exchange using parallel digital circuits. The hybrid Viterbi decoder is more suitable for VLSI implementation.

AGC and IF amplifier circuits design

Effective and fast analog AGC improves receiver operational performance. According to the theory of AGC, this paper develops AGC and IF amplifier circuits that can be applied in a receiver of a base station in 3G (third generation) mobile communications. The paper introduces the structure figure of the design circuit, and the unit circuit design. Experimental results are given. The experimental results have shown that the designed AGC and IF amplifier circuits in the receiver can satisfy the technical specification of the receiver of the base station in 3G mobile communications systems.

VLSI design and implementation of WCDMA channel decoder

We present a memory and driving clock efficient design scheme to achieve WCDMA high-speed channel decoder module (including a de-interleaving and de-multiplexing processing unit, a turbo decoder, a Viterbi decoder, etc.) on a single Xilinx XVC1000E FPGA chip. Using a modified MAP algorithm, say parallel sliding window logarithmic maximum a posteriori (PSW-log-MAP), the on-chip turbo decoder can decode an information bit by only an average of two clocks per iteration. On the other hand, a high-parallel pipeline Viterbi algorithm is adopted to realize the 256-state convolutional code decoding. The final decoder with an 8/sub i/ chip-clock (30.72 MHz) driving can concurrently process a data rate up to 2.5/spl sim/5 Mbps of turbo coded sequences and a data rate over 400 kbps of convolutional codes under a reasonable BER performance. If the de-interleaving and de-multiplexing processing unit is excluded, there is no external memory needed. Test results show that the decoding performance of these two type channel decoders is only 0.2-0.25 dB or less loss compared to float simulations.

3D positioning system using magnetic field

A method to determine the 3D position using harmless magnetic field is proposed as a solution to the problem of positioning the medical instruments such as endoscope inside the patients body. The intension expression of magnetic induction produced by a single loop coil is derived and the mathematical model of 3D positioning system with a mode of magnetic field is established. Then a practical 3D positioning system is developed to implement real-time 6 degrees of freedom measurement by a 3D magnetic sensor attached to the endoscope and 5 degrees measurement by a single magnetic sensor.

A simple channel estimator for space-time coded OFDM systems in rapid fading channels"

A simple channel estimator for space-time coded orthogonal frequency division multiplexing (OFDM) systems in rapid fading channels is proposed. The channels at the training bauds are estimated using the EM (expectation-maximization) algorithm, while the channels at the data bauds are estimated based on the method for modelling the time-varying channel as the linear combination of several time-invariant “Doppler channels”. Computer simulations showed that this estimator outperforms the decision-directed tracking in rapid fading channels and that the performance of this method can be improved by iteration.

A novel MMSE based codebook construction for MIMO precoded spatial multiplexing with limited feedback

This paper deals with the design and performance analysis of the transmission precoder optimization for multiple-input multiple-output (MIMO) systems with limited feedback of channel state information (CSI). We assume that the receiver can get perfect channel knowledge by channel estimation while the transmitter only has partial channel knowledge from limited feedback. We present a minimum mean square error (MMSE) criterion based codebook construction algorithm for MIMO precoded spatial multiplexing systems under a specific average power constraint. The optimal transmitter structure is employed in this paper. Simulation results show that the MMSE criteria based codebook construction algorithm with hybrid design of power allocation and precoding can achieve better performance than that of equal power allocation based codebook of previous research.

Extended Kalman filtering-based channel estimation for space-time coded MIMO-OFDM systems

A space-time coded multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system is considered as a solution to the future wideband wireless communication system. This paper proposes an extended Kalman filtering-based (EKF-based) channel estimation method for space-time coded MIMO-OFDM systems. The proposed method can exploit pilot symbols and an extended Kalman filter to estimate channel without any prior knowledge of channel statistics. In comparison with the least square (LS) and the least mean square (LMS) methods, the EKF-based approach has a better performance in theory. Computer simulations demonstrate the proposed method outperforms the LS and LMS methods. Therefore it can offer dramatic system performance improvement at a modest cost of computational complexity.

Channel estimation for MIMO-OFDM systems in rapid fading channels

A channel estimation approach for orthogonal frequency division multiplexing with multiple-input and multiple-output (MIMO-OFDM) in rapid fading channels is proposed. This approach combines the advantages of an optimal training sequence based least-square (OLS) algorithm and an expectation-maximization (EM) algorithm. The channels at the training blocks are estimated using an estimator based on the OLS algorithm. To compensate for the fast Rayleigh fading at the data blocks, a time domain based Gaussian interpolation filter is presented. Furthermore, an EM algorithm is introduced to improve the performance of channel estimation by a few iterations. Simulations show that this channel estimation approach can effectively track rapid channel variation.