Wu Xuanli

Pulse shaping method to compensate for antenna distortion in ultra-wideband communications

In the ultra-wideband (UWB) communication systems, a critical spectral mask is released to restrict the allowable interference to other wireless devices by the Federal Communications Commission (FCC), and then some pulse shaping methods have been presented to fulfil the mask. However, most pulse shaping methods do not consider the antenna distortion which cannot be neglected in the UWB communication systems compared with the conventional systems. To this end, an orthogonal wavelet based pulse shaping method is proposed in this paper to integrate compensation of antenna distortion into pulse shaping. Simulation results show that the novel pulse shaping method can be used to achieve compensation for antenna distortion, optimization of transmission power spectrum, and simplification of the algorithm, as well as simple implementation of the pulse generator.

Performance Comparison with Different Pulse Waveforms in Ultra-wideband Based Wireless Sensor Networks

Recently approved IEEE 802.15.4a standard defines an ultra-wideband (UWB) based physical layer technique, and performance analysis of UWB systems shows that the pulse waveform will affect the received SINR when multipath interference, multiple access interference and additive white Gaussian noise are considered. In order to obtain an optimal pulse waveform in UWB based wireless sensor networks, the normalized SNR is firstly proposed without the effect of pulse waveform, and then three pulse waveforms are analyzed and compared in different channels. Finally, the critical value of normalized SNR for different pulse waveforms is drawn with different transmission data rates and user numbers. Results show that the performance of UWB systems is affected by power efficiency and correlation property of transmitted pulse waveform together. And the pulse with high power efficiency shows better performance in low SNR, and the pulse with good correlation property shows better performance in high SNR.

Power Control for Self-Organizing Network in LTE-Advanced System

Self-organizing network is used for regional communications, which makes up for the coverage of mobile communication system. In LTE-Advanced network, such network forms by proximity communications and utilizes the limited bandwidth efficiently. However, the system frequencies shared by the terminals in self-organizing network belong to cellular terminals, the resource reusing leads to interference. Meanwhile, due to the mobility of devices and the dynamic topology of self-organizing network, the level of interference becomes more unpredictable. In this paper, we proposed to establish a probabilistic statistical model that randomizer the spectrum allocation problem for self-organizing terminals. Through the model, we simplify the power control algorithm with convex optimization method. Simulation shows that our proposed distributed admission and power control (DAPC) algorithm can improve the Signal to Interference plus Noise Ratio of users mostly 5-10 dB. Even the network changes during the communication process, this algorithm also province that the interference is acceptable.

Load balancing in the integration of WLAN and cellular network based on fuzzy logic algorithm

Recently, the integration of WLAN network and cellular network is one of the most important research contents in wireless communications, and load balancing is the main technique and research highlight of such network. Compared with game theory, policy algorithm, gray analyses, fuzzy logic algorithm fits for the problem of multiple in multiple out in load balancing and enhance system robustness as well. Hence, in this paper, fuzzy logic algorithm is used to solve the load balancing problem, considering the following aspects: the bandwidth of the WLAN and cellular network that can still be used, the speed of the terminals and the changeable download rate. Simulation results show that fuzzy logic algorithm can allocate the bandwidth flexibly and achieve the goal of load balancing in WLAN and cellular heterogeneous network.

A mobile relay selection strategy in cooperative spectrum sharing framework

In spectrum sharing networks with relay cooperation, primary users can benefit from the assistance of secondary users while secondary users accessing the primary bandwidth to transmit their signals. Reasonable relay selection strategy can improve the performances of both primary and secondary users in terms of higher transmission data rate and lower outage probability, and at the same time, frequent relay switching can be avoided. In this paper, we propose a relay selection strategy considering both relay mobility and the required transmission data rate of primary user. The metrics of relay selection combine the relay activation duration and the transmission data rate of the secondary users through the mobility prediction of relay nodes. Simulation results show that the proposed strategy can select the best relay with lower primary outage probability and longer relay activation duration compared with existing schemes, and the transmission data rate of secondary user can also be improved so that the total number of transmit information bits can be increased.In spectrum sharing networks with relay cooperation, primary users can benefit from the assistance of secondary users while secondary users accessing the primary bandwidth to transmit their signals. Reasonable relay selection strategy can improve the performances of both primary and secondary users in terms of higher transmission data rate and lower outage probability, and at the same time, frequent relay switching can be avoided. In this paper, we propose a relay selection strategy considering both relay mobility and the required transmission data rate of primary user. The metrics of relay selection combine the relay activation duration and the transmission data rate of the secondary users through the mobility prediction of relay nodes. Simulation results show that the proposed strategy can select the best relay with lower primary outage probability and longer relay activation duration compared with existing schemes, and the transmission data rate of secondary user can also be improved so that the total number of transmit information bits can be increased.

Narrow-Band Waveform Design in Cooperative Spectrum Sensing

In order to use the idle spectrum effectively and improve the spectrum efficiency, cognitive radio technology has attracted extensive attention. On account of low detection probability and low spectrum efficiency of previous spectrum sensing framework, a relay-based cooperative spectrum sensing framework is proposed and multiple narrow-band waveforms are required for different users which could be separated easily in the fractional Fourier transform domain. Aiming at this problem, this paper proposes a narrow-band waveform design method, and considering the energy concentration property of chirp signals in fractional Fourier transform domain, we adopt chirp signal as basic function to design narrow-band waveforms and CVX toolbox is used to solve the problem. Simulation results show that the de-signed two waveforms can be separated effectively and hence the detection probability of the cognitive framework could be increased. Moreover, the designed waveforms have relatively high power efficiency so that the transmission performance of cognitive users can be improved as well.

The Analysis of Detection Algorithms in UWB Spatial Multiplexing System

In order to satisfy the requirement for higher data rates, the UWB spatial multiplexing system that combines MB-OFDM UWB and V-BLAST scheme is presented in this paper. And then, various detection algorithms are studied and simulated in this system for the sake of a better performance. Simulation results show that MMSE-BLAST is an appropriate one among the conventional suboptimal algorithms, and the accuracy of the first detected layer determines the degree of error propagation. At last, a modified algorithm with the combination of ML and MMSE-BLAST is employed to reduce error propagation in the UWB channel with rich multipath.

Semi-Definite Programming Based Pulse Shaping Algorithm in IEEE 802.15.4a

In order to increase the peak transmission data rate of Zigbee and expand its application scenario, IEEE 802.15.4a standard has been proposed in 2007, and ultra-wideband (UWB) technique has been selected as one of its physical layer standard. The performance of wireless sensor networks (WSN) will be affected by the pulse waveform transmitted in the channel, hence, in this paper, the Chinese regulation for UWB devices is firstly given, and then, a semi-definite programming based pulse shaping algorithm to comply with such regulation is proposed. Simulation results show that the proposed algorithm can comply with the given regulation with high power efficiency, which can increase the signal to noise ratio (SNR) in the receiver end.

A double-ridged horn antenna applied to ultra-wideband radar for human being detection

In this paper, a double-ridged horn antenna applied to ultra-wideband radar for human being detection is designed. First, the principle of ultra-wideband (UWB) radar for human being detection is analyzed. Then, the proposed double-ridged horn antenna is simulated through CST MICROWAVE STUDIO® software. And the influences of antenna structural parameters on antenna pass band are discussed and analyzed. The working frequency is 0.86~2.37GHz with reflection coefficient less than -10dB (relative bandwidth 93.5%). And the antenna gain is 9.6-12.0dBi in the pass band. So the proposed antenna has characteristics of ultra-wide band, high gain, and strong directional radiation. And it is suitable to be the transmitting antenna of UWB radar to send ultra-short electric pulses.

Multipath interference analysis of IR-UWB systems in indoor office LOS environment

Bit error rate (BER) performance of impulse radio Ultra-Wideband (UWB) systems in the presence of intra-symbol interference, inter-symbol interference, multiuser interference and addictive white Gaussian noise (AWGN) is presented in this paper. By analyzing the indoor office LOS channel model defined by IEEE 802.15.4a Task Group and deducing the variance for intra-symbol interference (IASI), inter-symbol interference (ISI) and multiuser interference (MUI), the system BER expression is obtained and verified by MATLAB simulations. Through comparing the simulation results with and without intra-symbol interference, the conclusion that intra-symbol interference cannot be neglected is drawn-moreover, such interference will significantly decrease performance of UWB based wireless sensor networks (WSN). Then, the BER performance of UWB systems in multiuser environment is also analyzed and analysis results show that multiuser interference will further worsen the transmission performance of UWB systems.