Xuanli Wu

Internet of Vehicles for E-Health Applications in View of EMI on Medical Sensors

Wireless technologies are pervasive to support ubiquitous healthcare applications. However, RF transmission in wireless technologies can lead to electromagnetic interference (EMI) on medical sensors under a healthcare scenario, and a high level of EMI may lead to a critical malfunction of medical sensors. In view of EMI to medical sensors, we propose a joint power and rate control algorithm under game theoretic framework to schedule data transmission at each of wireless sensors. The objective of such a game is to maximize the utility of each wireless user subject to the EMI constraints for medical sensors. We show that the proposed game has a unique Nash equilibrium and our joint power and rate control algorithm would converge to the Nash equilibrium. Numerical results illustrate that the proposed algorithm can achieve robust performance against the variations of mobile hospital environments.

Secondary Spectrum Access Based on Cooperative OFDM Relaying

In this paper, we propose an opportunistic spectrum sharing protocol that exploits the situation when the primary system experiences weak channel conditions. Specifically, when the outage rate of the primary systeme falls below the target rate, the secondary system tries to help the primary system achieve its target rate by acting as a decode-and-forward relay for the primary system, and allocating a fraction of its subcarriers to forward the primary signal. As a reward, the secondary system gains spectrum access by using the remaining subcarriers to transmit its own signal. We study the joint optimization of the set of subcarriers used for cooperation and the secondary subcarrier power allocation such that the transmission rate of the secondary system is maximized, while guaranteeing the primary system to achieve its target rate. Simulation results demonstrate that both primary and secondary systems can benefit from the proposed secondary spectrum access scheme.

Performance Analysis of Cooperative Ultra-wideband Communication System

The combination of ultra-wideband technique and cooperative technique can improve the performance of ultra-wideband communications effectively and reduce the power consumption. In order to improve the system performance as well as reduce the hardware cost, a cooperative ultra-wideband system model using transmitted reference receiver and decode-and-forward (DF) relay protocol is proposed, and normalized SNR is introduced to analyze different system BER performances. Simulation results show that the cooperative scheme functions about 10dB better under LOS channel than that under NLOS channel by means of normalized SNR, and system BER performance would be improved with the growth of the number of relay nodes.

Cooperative Spectrum Sensing under Imperfect Channel Estimation

Recently proposed cooperative spectrum sensing method suggests that Cognitive Radio (CR) users can detect the primary users at low SNR with less time and higher accuracy through user cooperation. However, previous works assume CR users can acquire fully channel state information by pilot symbols, which is impractical. In this paper, the performance with imperfect channel estimation in cooperative spectrum sensing method is analyzed and the trade-offs between false alarm probability and leakage alarm probability on the decision of threshold under imperfect channel estimation is presented. Simulation results show that the imperfect channel estimation would reduce the benefits obtained from cooperation. When estimation error grows to 0.3 there would be a 0.11 loss in detection probability and the false alarm probability, which is important to CR system, would increase from 0.1 to 0.4.

Safeguarding Physical Layer Security Using Weighted Fractional Fourier Transform

In this paper, weighted fractional Fourier transform (WFRFT) is employed to safeguard the physical layer (PHY) security of wireless communications. By leveraging the features of WFRFT, we propose a PHY security modulation scheme, which significantly degrades the equivalent signal-to-noise ratio (SNR) of the unauthorized receiver while imposing no impact on the legitimate receiver. With the proposed scheme, a robust nonzero secrecy capacity can be guaranteed. Moreover, the proposed scheme can conceal the actual modulation paradigms to prevent malicious signal detection, due to the variation in signal characteristics. A higher order statistics (HOS) based classifier is used to investigate the anti- recognition performance. Meanwhile, the secrecy performance of the proposed scheme is evaluated in terms of both secrecy capacity and average bit error rate (BER) by numerical simulations. Finally, as a proof-of-concept, an all-digital field programmable gate array (FPGA) based prototype system is developed to validate the practicability of the proposed scheme.

Relay-Based Cooperative Spectrum Sensing Framework Under Imperfect Channel Estimation

To reduce interference to primary user and improve channel capacity with an acceptable detection probability in cognitive radio networks, we propose a relay-based cooperative spectrum sensing framework. Different from conventionally cognitive radio network, where spectrum sensing and signal transmission are performed separately, the proposed framework integrates spectrum sensing into signal transmission by assigning different signal types to primary user and cognitive users, i.e., sinusoidal signal and chirp signals for primary user and cognitive users, respectively. Thanks to the energy concentration property of chirp signals in the fractional Fourier transform (FrFT) domain, the separation of primary user and cognitive users can be realized easily. In this proposed framework, interference to primary user can be reduced because of the simplified time slot structure, and channel capacity can also be improved by removing the separate spectrum sensing process. Moreover, by using the energy accumulation of the primary user in the signal transmission process, the detection probability of the proposed framework can also be improved even with channel estimation error and signal separation error.

Modified Hermite Function Based Pulse Shaping Algorithm for Ultra-Wideband Communications

In recently years, with the release of spectral mask by the Federal Communications Commission (FCC), ultra-wideband (UWB) communications by means of impulse-radio (IR) are gaining increasing interest. In order to optimize transmission power spectrum, judicious pulse shaping is required. This paper proposed a modified Hermite function based pulse shaping algorithm and the simulation results show that pulses obtained with the proposed pulse shaping algorithm can optimize transmission power spectrum, reduce system complexity and minimize the pulse duration in the time domain

A Localization Based Routing Protocol for Dynamic Underwater Sensor Networks

Owing to the rapid development of underwater applications, the research on underwater wireless sensor networks (UWSNs) is becoming more and more significant. Low bandwidth, high latency, limited energy and node float mobility are basic challenges for underwater sensor networks. Most of the theories for terrestrial sensor networks can not be applied to underwater sensor networks. In this paper, we focus on the localization and routing issues for dynamic UWSNs. Location based routing protocols can suit the dynamic situation of UWSNs well. However, most research assumes that the nodes know their locations, which may be not appropriate for some applications. This paper combines these two aspects together to design a localization based routing protocol for dynamic UWSNs. The simulation results show our method can effectively route data from the source nodes to the sink nodes in a dynamic environment.

QoS oriented heterogeneous traffic scheduling in LTE downlink

In this paper, Rate-Level-Based Scheduling (RLBS) Algorithm is proposed to support the heterogeneous traffic in downlink of Long Time Evolution (LTE) system. The proposed scheduling algorithm aims to minimize the packet loss ratio of real-time traffic while guaranteeing Quality of Service (QoS) requirements. We compares the performance of the proposed scheduling algorithm with Modified Largest Weighted Delay First (M-LWDF) algorithm, Exponential PF (EXP/PF) algorithm and Z-Based QoS Scheduler (ZBQoS) algorithm. Simulation shows that compared with other algorithms, the proposed scheduling algorithm can achieve a good tradeoff between satisfaction of QoS requirement and fairness, meanwhile, it can can satisfy the requirement of Guaranteed Bit Rate (GBR) traffic preferably and improve the Packet Loss Ratio (PLR) performance significantly.

Fractional Fourier transform based transmitted reference scheme for UWB communications

In this paper, we propose a receiving system for impulse radio ultra-wideband (IR-UWB) communications, in which the data and reference pulses are combined as one signal to transmit, and the received signal can be divided into the data and reference pulses in the receiver end using the energy concentration property of Chirp pulses in fractional Fourier transform (FrFT) domain. A detailed theoretical analysis of the proposed system is given, and the formulation of bit error rate (BER) is obtained. Then according to the BER formulation, system performance of the proposed receiving system is compared with existing STR, DTR and ATR systems, considering timing-variance of IR-UWB channels as well as timing jitter at the transmitter. Results show that the proposed receiving system outperforms existing systems in most situations.