As for safety applications of vehicular Ad-hoc network (VANET), many valuable broadcast protocols have been proposed nowadays, most of which are based on either senders or receivers. In fact, sender-based protocols would fall into invalidation due to high mobility of network, while receiver-based ones would generate extra delay. Combining both the advantages of the two schemes, this paper proposes an efficient and reliable broadcast protocol based on quality of forwarding (ERBPQF) of candidate nodes. In ERBPQF, a double-phase relay scheme is presented to reach fast message dissemination in the first phase and to ensure high packet delivery ratio (PDR) in the second phase. Then, considering signal fading, channel contention, queuing delay, broadcast interference and high mobility of vehicles, a new metric called quality of forwarding (QoF) for relay selection is further proposed. The simulation results show that the delay and dissemination efficiency (DE) of ERBPQF outperforms slotted-1 protocol, accompanying with the achievement of more than 95% PDR.

In vehicular Ad-hoc networks (VANETs), beacon message is designed for the purpose of periodically broadcasting the status information (velocity, direction, etc.), which enable neighbor awareness and support some safety applications. However, under high density scenarios, fixed rate beaconing can cause severe congestion and lower the deliver rate of beacons and other kinds of messages. In this paper, we describe beaconing rate control approach with an one-dimensional Markov model, and based on this, an optimized beacon rate control scheme is proposed which aims to mitigate the congestion and maximize the deliver efficiency of beaconing. Analytical and simulation results show that our proposed scheme can achieve higher adaptability and beaconing efficiency compared with other schemes in various environments.

As the vehicles gain the extensive popularity and increasing demand, traffic accident is one of the most serious problems faced by modern transportation system. Hereinto, crashes between cars and pedestrians cause plenty of injuries and even death. Diverting attention from walking to smartphones is one of the main reasons for pedestrians getting injured by vehicles. However, the traditional measures protecting pedestrians from the vehicles heavily rely on the sound warning method, which do not capable for pedestrians focusing on the smartphones. As the smartphones become ubiquitous and intelligent, they have the capacity to provide alert for the pedestrians with the help of vehicle-to-pedestrian (V2P) communication. In this paper, an efficient vehicle-to-X (V2X) communication system is designed for the vehicle and pedestrian communication to guarantee the safety of people. It achieves the IEEE 802.11p and the WiFi protocols meanwhile on the on-board unit (OBU) designed for vehicles. Extensive evaluation shows that the OBU can provide the reliable communication for vehicle-to-vehicle (V2V) and V2P in terms of packet delivery rate and average delay. Furthermore, two safety applications have been developed to protect the safety of vehicles and pedestrians based on the data transferred from the OBU. The first application is designed to show the driving information and provide the collision forewarning alert on the tablet within the vehicle. The second application is developed for the smartphone to provide forewarning alert information to the smartphone-distracted vulnerable pedestrians. Smartphone states are appreciable to provide the adaptive alert modes. Experimental results show that these applications are capable of alerting the intersection accidents, and the pedestrians can get the adaptive alerts according to smartphone usage contexts.

With the wide application of radio frequency identification (RFID) technology, its security privacy issues are becoming more and more prominent. A RFID mutual-authentication protocol with synchronous updated-keys based on Hash function is proposed to tackle those problems in this paper. An updated mechanism of the dynamic tag keys is introduced and a self-synchronized scheme is designed in the protocol, which has achieved the second verification for the tags. The security of the protocol is verified and analyzed by the Burrows-Abadi-Needham (BAN) logic and the attack models, moreover it has been compared with the existing schemes of security properties and its storage and computational performance. The results show that the proposed protocol has the ability to considerably reduce the amount of computation between tags and back-end database, and enhance the search efficiency of the whole system without the additional cost of the tags. It can satisfy safe requirements of RFID system effectively, also improve the authentication efficiency. The proposed protocol is more suitable for the low cost RFID system.

This paper proposes the first lattice-based sequential aggregate signature (SAS) scheme with lazy verification that is provably secure in the random oracle model. As opposed to large integer factoring and discrete logarithm based systems, the security of the construction relies on worst-case lattice problem, namely, under the small integer solution (SIS) assumption. Generally speaking, SAS schemes enable any group of signers ordered in a chain to sequentially combine their signatures such that the size of the aggregate signature is much smaller than the total size of all individual signatures. Unlike prior such proposals, the new scheme does not require a signer to retrieve the keys of other signers and verify the aggregate-so-far before adding its own signature, and the signer can add its own signature to an unverified aggregate and forward it along immediately, postponing verification until load permits or the necessary public keys are obtained. Indeed, the new scheme does not even require a signer to know the public keys of other signers.

Recently Li et al. proposed special partially entangled states serving as quantum channel in quantum controlled teleportation, while there are some limitations in their scheme. Based on that, we present a possible improvement in this paper. We construct a novel three-particle partially entangled state which is suitable for perfect controlled teleportation. A simple quantum circuit is designed to obtain this state. We evaluate quantum controlled teleportation from three points of view: teleportation fidelity, success probability and the controller’s power. Detailed calculations and simulation analyses show that the constructed state is a suitable channel for controlled teleportation of arbitrary qubits, unit teleportation fidelity and 100% success probability can be achieved. Meanwhile, as long as channel’s entanglement degree equals to or greater than 3/4, the controller’s power can be guaranteed.

Axially displaced elliptical (ADE) antenna is an evolved version of Gregorian antenna, bearing advantages of minimized blockage and relatively uniform field distribution. However, the analysis of the electrical performance of this type of antenna is a difficulty to be addressed properly. To enable the simulation of such type of reflector antenna, a hybrid method is derived for predicting the farfield of ADE antennas. Closed formulae are firstly derived for the calculation of the near field of ADE antennas based on vector analysis and the law of energy conservation. These formulae avoid time-consuming surface current integration and the current singularity on the vertex of the sub-reflector. In addition, the nature of vector analysis makes the hybrid method be capable of predicting vector electric field precisely. Furthermore, since these formulae are in explicit manner, no ray tracing process is required. The farfield is then predicted using Huygens equivalent method, assuring the accuracy in the farfield. Compared to published experimental results in the literature, the proposed method agrees well with the measurement in the main beam region. In comparison to physical optic method, the computational efficiency is much improved.

A novel tri-band bandpass filter (BPF) is proposed by using cross-coupled stepped impedance resonators (SIRs), which can operate at 2.4 GHz, 3.5 GHz and 5.25 GHz respectively. In engineering application, it is suitable for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX). In addition, the passband of this filter can be easily controlled by changing the electrical parameters of the resonators. So it is helpful to the selection of passband in engineering applications. For in-depth analysis, the equivalent circuit of the filter is also proposed. At last, it shows that the measured results agree well with the simulated results. The insertion loss of the filter within each passband is less than 1.9 dB, meanwhile two transmission zeros are obtained which can be able to meet the engineering requirements.

A novel printed microstrip-fed ladder patch monopole antenna is presented for ultrawide band (UWB) application. The antenna consists of rectangular patch elements ladder arrayed at the both sides of the microstrip-fed line on a printed circuit board (PCB) and a rectangular ground plane. The antenna parameters of ladder number N, the rectangular patches geometry of ladder elements, the ladder step length and the length of ground plane are studied to obtain optimized antenna performances. The successfully designed, implemented and measured antenna has a compact size of 12 mm×12 mm and operation frequency band from 3.1 GHz to 10.6 GHz with voltage standing wave ratio (VSWR) less than 2. Using the ladder patch array in microstrip monopole antenna design makes antennas flexible in terms of controlling resonances, bandwidth, stable radiation patterns, and constant group delay.

Given the flaws in traditional cascading design of the filtering antennas, a kind of filtering antenna based on the defected ground structure (DGS) is proposed. It adopts the method of co-design to integrate the filter and the antenna into one substrate, resulting in a miniaturized size of 34 mm×30 mm. In the design, the structure with dumbbell shape is etched on the ground of dual-band antenna, aiming for the low-pass property of the filtering antenna. The simulated results show that the filtering antenna’s co-design can effectively enlarge the bandwidth of the pass-band and suppress the bandwidth of T-patch, whose pass-band can cover the bandwidths of wireless local area network (WLAN) 2.4 GHz, wideband code division multiple access (WCDMA) 2.1 GHz, long term evolution (LTE) 2.3/ 2.5/ 2.6/ 2.8 GHz etc. In addition, the filtering antenna’s physical module is fabricated and measured, whose test results are basically consistent with the ones of simulation. Moreover, the filtering antenna with liner polarization has a good radiation pattern of omni-direction, and can be applied to the terminals of wireless mobile system.

The enhanced eigenvalue decomposition (EEVD) based channel estimation algorithm, which could solve the pilot contamination problem in massive multiple-input and multiple-output (Massive MIMO) channel estimation when the number of antennas at base stations (NABT) tends to infinity, is proposed in this paper. The algorithm is based on the close relationship between covariance matrix of received pilot signal and the channel fast fading coefficient matrix, i.e. the latter is the eigenvector matrix of the former when NABT tends to infinity. Therefore, we can get a set of normalized base vectors from the eigenvalue decomposition (EVD) of sample covariance matrix in practical Massive MIMO networks. By multiplying the received pilot signal with conjugate transpose of normalized base vector matrix, the channel matrix is projected to a lower dimensional matrix, and the intra-cell and inter-cell interference can be eliminated completely when NABT tends to infinity. Thus, we only need to estimate the lower dimensional projected matrix during the channel estimation. Simulation results show that the mean square error (MSE) performance of channel estimation is improved with approximately two orders of magnitude when the signal-to-noise ratio (SNR) is 40 dB, compared with EVD based channel estimation algorithm. And the signal-to-interference ratio (SIR) is improved greatly as well. The increment of SIR becomes larger and larger as SNR increasing.

Filter bank multi-carrier (FBMC) with offset quadrature amplitude modulation (OQAM) has been regarded as one of the candidates for next generation broadband wireless communication systems. Being a multi-carrier technique, FBMC suffers from the inherent drawback of high peak-to-average power ratio (PAPR). And it has been turned out that conventional PAPR reduction schemes for orthogonal frequency division multiplexing (OFDM) systems are ineffective for FBMC-OQAM systems, due to the overlapping structure of FBMC-OQAM signals. In this paper, we propose an efficient PAPR reduction scheme based on a two-step optimization structure, named pretreated partial transmit sequence (P-PTS). The first step uses a multiple overlapping symbols joint optimization scheme that the phase rotation sequences for current symbol is determined and optimized according to previous overlapped symbols. And in the second step, it employs a novel segment PAPR reduction scheme based on PTS technique. Simulation results indicate that the proposed P-PTS scheme can achieve better PAPR reduction performance than conventional methods with lower computational complexity and the complexity can be traded off more flexibly with PAPR reduction performance.

An orthogonal frequency division multiplexing (OFDM) is one of the effective techniques used in wireless communication. In OFDM systems, channel impairments due to multipath dispersive spreading can cause deep fades in wireless channels. Thus, the OFDM receiver requires channel state information when coherent detection is involved. Therefore, to overcome the impact of channel fades good channel estimation (CE) methods are needed in OFDM systems. And one of these CE methods is a semi-blind CE. However, the semi-blind method requires a large number of processing operations. In order to avoid the high computing complexity of the existing method, scaled least square (SLS) technique is applied to improve the performance of the semi-blind channel estimator which require less knowledge of the channel second-order statistics and have better performance than the least square (LS) which used in semi-blind CE. Simulation results shows, this proposed method of semi-blind CE has the capacity of elevating CE performance in multiple-input multiple-output (MIMO) OFDM systems.

The unforeseen mobile data explosion poses a major challenge to the performance of today’s cellular networks, and cellular networks are in urgent need of novel solutions to handle such voluminous mobile data. Obviously, data offloading through third-party WiFi access points (APs) can effectively alleviate the data load in the cellular networks with a low operational and capital expenditure. In this paper, we propose and analyze an adaptive WiFi-offloading algorithm based on attractor selection in heterogeneous wireless networks. In the proposed WiFi-offloading algorithm, the WiFi system throughput and cellular throughput in the coverage area of WiFi, are mapped into the activity of the attractor, which is the reflector of the current network environment. When the current attractor activity is low, the network is dominated by the noise. Then, the noise triggers the controller to select adaptive attractor, an optimal WiFi-offloading ratio , to adapt to the dynamic network environment. And users offload the specific portion of traffic to the WiFi networks with the ratio of , which improves the throughput of heterogeneous wireless networks and alleviates the load of cellular networks. Through simulation, we show that the proposed WiFi-offloading algorithm outperforms the existing ones with 21% higher heterogeneous network throughput in a dense traffic environment.