Xuejun Sha

A multi-level orthogonal sequences design and implementation method

In this paper, a multi-level orthogonal sequences design method is proposed based on the solution of optimization problem using genetic algorithm. The orthogonality performance of the orthogonal sequences designed here is good, which can effectively reduce multiple access interference (MAI). Compared with the traditional Gold sequences, this design approach can achieve better system performance in both synchronous and asynchronous systems. Especially in the asynchronous system, MAI is smaller and the method in this paper has advantage of the system BER performance. In addition, the sequence length is not strictly limited by the number of users, and a higher bit rate can be obtained.

A new multiple-access method based on FRACTIONAL FOURIER TRANSFORM

This paper introduces a new multiple-access technique named Frequency Band Width Division Multiple-Access (FBW-DMA). The proposed method processes signal in Fractional Fourier Transform (FrFT) domain to avoid some crucial problems in CDMA, such as high requirement of synchronization and suffering from single-frequency interference generated by other systems. By using chirp signals with different frequency band widths as carriers at the transmitter, the received signal is transformed into corresponding FrFT domain, then the narrow band matching coherent demodulation is used. Simulation results indicate that the proposed FBW-DMA achieves better Bit Error Rate (BER) performances compared with CDMA when serious single-frequency interferences exist, and the BER is lower one or two orders of magnitude.

The analysis of the discrete fractional Fourier transform algorithms

The discrete formal FRFT is difficult to obtained by the directly sampling the continuous FRFT because the kernel function of the continuous fractional Fourier transform (FRFT) exhibits drastic oscillation and the oscillation amplitude has the distinct difference from the different order of the FRFT. Discrete FRFT has been intensively investigated recently and many definitions of the discrete FRFT have emerged. Firstly, the multiplicity of discrete FRFT is presented and the discrete FRFT are classified in term of its definition mode. Some of discrete FRFT are demonstrated which kind of the continuous FRFT they correspond to. Secondly, the problem of the discrete FRFT is analyzed and digital simulations are presented to verify the conclusion.

Base station cooperation based on location-aided in cellular system

Base station cooperation will bring a certain delay due to a series of signaling information exchange, cooperation strategy on base station based on location-aided is proposed in this paper. Future location information is provided by moving speed and direction to predict track of user. Signal strength and adjacent cell load combining with location information will be constraints to selecting cooperative base station. User can execute signaling interaction in advance with network before signal strength down to an intolerable to reduce delay to increase satisfaction of users. Meanwhile, Quality of signal in edge of cell is improved due to base station cooperation and handover requests decrease in the process of user mobility. Then unnecessary handover is avoided. Comparing with no location-aided, pseudo cooperative request and cooperative setting updating will be reduced. It was shown that base station cooperation based on location-aided we provided can reduce system overhead and increase system capacity.

Fractional fourier domain communication system (FrFDCS): Analytic, modeling and simulation results

A proposed fractional Fourier domain communication system (FrFDCS) using transform domain processing is demonstrated as having enhanced interference avoidance capability under adverse environmental conditions. The basic idea for this system is to synthesize an intelligent adaptive waveform in the fractional Fourier domain at both the transmitter and receiver for avoiding spectral crowded regions. This approach offers better bit error performance in contrast to other conventional interference mitigation techniques which process the signal at the receiver only. Moreover, since this smart waveform is able to search “spectrum hole” and adapt to electromagnetic environment, it could be a potential candidate in cognitive radio technology. The FrFDCS and its response to interferences are modeled and simulation results are obtained. Compared to similar systems such as the transform domain communication system (TDCS), the results indicate that the proposed FrFDCS is a viable option for interference avoidance communications.

Narrowband interference suppression method in Cognitive Ultra-wide Band Radio

This paper investigates a novel narrowband interference (NBI) suppression method in Cognitive Ultra-wide Band (CUWB) Radio system. UWB signals and NBI are separated by Fractional Fourier Transform (FRFT) domain filters, and therefore an estimation of NBI can be obtained by utilizing inverse FRFT. The simulation results show that the UWB pulse waveform designed by Semi-definite Programming (SDP), which is a weighted sum of chirp functions, meets the emission mask established by the Federal Communications Commission (FCC), and the use of chirp function ensures that the FRFT domain duration of UWB pulse waveform is very short. Therefore the NBI parameters (e.g. center frequency, bandwidth, energy) are more convenient to be obtained by the estimated NBI. The UWB signal will not have a detrimental effect on the performance of the narrowband system by suppressing the UWB signal in the NBI band.

Analysis of relay handoff algorithms in cooperative diversity systems using absolute and relative measurements of energy gain

Multi-user cooperative diversity is a recently proposed technique, which can improve the performance of wireless communication systems operating in fading environments. Choosing a good partner is important in cooperation and some partner selection methods have been proposed. However, there is no research has mentioned how often partners should be reassigned. In this paper, we propose a handoff scheme between relays. In the proposed scheme, handoff is performed when the energy gain of the working relay drops below a threshold and the energy gain of the best relay exceed the energy gain of the working relay by a certain hysteresis level. Simulation results are given to show the performance of the newly proposed scheme.

Implementation of coded cooperation using a kind of convolutional codes

User cooperative communication can bring spatial diversity, and improve cell boundary uplink quality. This paper gives a kind of convolutional codes suitable for user cooperation with lower complexity than Turbo codes and LDPC codes, and can guarantee good inter-user communication quality when cooperation succeeds, and also good uplink communication quality when cooperation defeats. Simulation results show that when we use 50% cooperation, under the condition that the two users have similar uplink quality and perfect inter-user channel, at BER=10−3, this kind of coded cooperation can provide almost 11 dB performance gains, compared with non-cooperation. Moreover, performance of user cooperation using this kind of convolutional codes is better than that using rate-compatible punctured convolutional codes.

Partner selection strategy for users with high speed in cooperative diversity systems

Cooperative diversity has been adopted to form virtual antenna arrays in order to obtain spatial diversity gains. Various partner selection methods in cooperative diversity systems were proposed and analyzed. However, these methods are not effective for users with high speed, such as users in cars on high way. A novel partner selection strategy is presented in this paper by dividing users into three groups according to their moving speeds and directions if there are any high speed users in a certain cell. The partners for cooperation are selected from the same group with the source user. Simulation results show that the selection strategy can increase duration of cooperation, as well as decrease the partner handoff times and probability of unsuccessful partner selection.

Novel nearly tridiagonal commuting matrix and fractionalizations of generalized DFT matrix

Based on discrete Hermite-Gaussian-like functions, a discrete fractional Fourier transform (DFRFT), which provides sample approximations of the continuous fractional Fourier transform, was defined and investigated recently. In this paper, we propose a novel nearly tridiagonal matrix, which commutes with the generalized discrete Fourier transform (GDFT) matrix. It doesnt has repeated eigenvalue. We can determine a unique orthonormal eigenvector set based on block diagonalization of new commuting matrix. The eigenvectors of the new nearly tridiagonal matrix are shown to be GDFT eigenvectors, which are more similar to the continuous Hermite-Gaussian functions than those developed before. The fractional transform of GDFT (GDFRFT) is defined through eigendecomposition. The new version of GDFRFT produce their transform outputs closer to the samples of the continuous fractional Fourier transform through numerical comparison.