Xu Youyun

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.

A relay node selection technique for opportunistic routing in mobile Ad Hoc networks

In this paper, we propose a new relay node selection algorithm: relay node selection Considering Future Path(CFP) for opportunistic routings in mobile Ad Hoc networks, aiming to provide enhanced performance of successful delivery ratio. CFP based on the shortest distance algorithm and it not only considers the current distance towards the destination but also considers the future hops and estimates whether through the current node can a packet arrive at the destination. CFP can enhance the performance of successful delivery ratio by solving the potential problem of no forwarding relays in the shortest distance algorithm. Simulation results show that contrast against the shortest distance algorithm in opportunistic routing protocol GeRaF, CFP has better performance on both delivery ratio and goodput.

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.

An improvement on opportunistic spectrum access MAC protocol

Radio spectrum resource is a finite resource and of fundamental importance for wireless communication. But the utilization of the spectrum became unbalanced, some spectrum is crowd with users and some is inefficiently used. The concept of cognitive radio is a good solution for this problem. One of the tasks to realize this technology is to design an efficient MAC protocol. OSA-MAC is one of the practical MAC protocol used for opportunistic spectrum access in cognitive wireless network. However, in this protocol after contention for channel, secondary users still have to use back off mechanism when transmitting data. As a result, the throughput and the channel utilization is low in OSA-MAC. We make some improvement on OSA-MAC protocol. In our protocol, the transmission process is divided into time slots. New competition mechanism is used for each secondary user who has data to send to access the channel. Using this mechanism, collision is avoided when transmission and channel utilization is increased. In the end of the paper, we make some analysis and comparison between the two protocols.

A reordered first fit algorithm based novel storage scheme for parallel turbo decoder

In this paper we discuss a novel storage scheme for simultaneous memory access in parallel turbo decoder. The new scheme employs vertex coloring in graph theory. Compared to a similar method that also uses unnatural order in storage, our scheme requires 25 more memory blocks but allows a simpler configuration for variable sizes of code lengths that can be implemented on-chip. Experiment shows that for a moderate to high decoding throughput (40∼100 Mbps), the hardware cost is still affordable for 3GPP’s (3rd generation partnership project) interleaver.

Novel time-frequency differential space-time modulation for multi-antenna OFDM systems

Abstract Differential space-time (DST) modulation has been proposed recently for multiple-antenna systems over Rayleigh fading channels, where neither the transmitter nor the receiver knows the fading coefficients. Among existing schemes, differential modulation is always performed in the time domain and suffers performance degradations in frequency-selective fading channels. In order to combat the fast time and frequency-selective fading, a novel time-frequency differential space-time (TF-DST) modulation scheme, which adopts differential modulation in both time and frequency domains, is proposed for multi-antenna orthogonal frequency division multiplexing (OFDM) system. A corresponding suboptimal yet low-complexity non-coherent detection approach is also proposed. Simulation results demonstrate that the proposed system is robust for time and frequency-selective Rayleigh fading channels.