Earticle

Cognitive radio enabled vehicular networks (CR-VNETs) is a new communication paradigm that enables moving vehicles to identify spectrum opportunities along busy streets and freeways. This detected spectrum may possibly lie in licensed frequency bands, and can be used for emergency communications, such as by primary responders during crises events. Spectrum sensing ensures that this spectrum is not currently occupied by licensed users, who have priority access rights. However, as the vehicles are in motion, the spectrum sensing at a given location must be completed with minimum delay, a challenge for classical energy and feature based detection schemes. This paper presents a new distributed compressive sampling technique that allows individual vehicles to report partial information to a centralized base station (BS), with an overhead of only few bytes. Thus, we tradeoff reporting time with processing complexity at the BS, which is tasked with re-constructing the overall spectrum utilization from these portions. Simulation results reveal significant improvements in detection time and accuracy, making our approach suitable for CR-VNETs.

For mobile ad-hoc networks (MANETs), caching data is important and useful. By exercising cache cooperation between mobile nodes, cooperative caching schemes can improve data accessibility and system performance. Seeing that the cache hit ratios tend to degrade due to high node mobility, restricted battery energy and limited wireless bandwidth in a MANET, we introduce a new cooperative caching scheme, the Regionally Maintained Cooperative Caching (RMCC) scheme, to solve the problem. RMCC allows one node in a region to cache a data item while the other nodes in the same region to cache the path to the node when to acquire the same item. Such a design helps generate more cache space and wider cached data variety for nodes in one region, and as a result attains higher cache hit ratios as well as lower data access latency. Experimental evaluation shows that the proposed RMCC outperforms other schemes in terms of cache hit ratios, in-cache ratios and amounts of required file packets.

Recently, more and more researches have been focused on proposing dynamic identity based remote authentication scheme for multi-server environment. In 2011, Lee, Lin and Chang proposed an improved scheme to remedy the weaknesses of Hsiang-Shih's scheme. However, we observe that Lee-Lin-Chang's scheme is still vulnerable to stolen smart card attack and malicious server attack. Besides, the password change phase of Lee-Lin-Chang's scheme is neither efficient enough nor convenient to users. In this paper, we propose an improved scheme to remove the aforementioned weaknesses and simultaneously not to decrease other security features. In the proposed scheme, there is no useful information can be obtained from the values stored in smart cards. Thus the stolen smart card attack can be blocked. To avoid malicious server attack, we move the user authentication process from service providing servers to the registration center, which can ensure each server has a different secret key. Through comparing with several schemes proposed recently, we demonstrate our proposed scheme is more secure and efficient. Therefore, the proposed scheme is more practicable.

A simple and cost-effective design of centralized light source wavelength division multiplexing passive optical network (WDM-PON) is proposed, which supports simultaneous transmission of point-to-point data and broadcast services. 10 Gbit/s differential quadrature phase shift keying (DQPSK) downstream data and superimposed 2.5 Gbit/s inverse return-to-zero (IRZ) broadcast service are simultaneously transmitted from optical line terminal (OLT) in downstream channels without pulse carving, whereas a 2.5 Gbit/s on-off keying (OOK) data signal is used for upstream signal using re-modulation of downstream signal power, no additional laser is used at optical network unit (ONU). Simulation results show that downstream transmissions of 10 DQPSK point-to-point channels with IRZ broadcast service and upstream transmission of 10 OOK channels, using 100 GHz channel spacing and high extinction ratio (ER), can be successfully achieved over a distance of 20 km with low transmission power penalties and improved receiver sensitivity. It is also evident from results that proposed simple technique has good tolerance against transmission nonlinearities and can be implemented as a cost-effective solution in future WDM-PON networks.

A modified U-shaped patch antenna for triband applications with improved bandwidth and isolation characteristics is presented in this paper. The proposed antenna resonates at triband of 8 GHz, 9.73 GHz and 11.1 GHz frequencies for VSWR ≤ 1.4, with an improved impedance bandwidth of 42.3%. A 2×2 MIMO is developed by using the proposed antenna with a reduced mutual coupling of -40 dB. The simulation results of return loss, mutual coupling, VSWR and gain are presented. The proposed antenna is a good choice for MIMO systems operating for several Wideband applications.

Satellite network, especially low earth orbit (LEO) satellite network, which has advantages of global coverage and short round-trip time (RTT), has played an increasingly important role in the future generation of global communication network. Due to fast velocity, frequent handover and time-varying topology, designing effective routing algorithm for LEO satellite network has always been challenging. An Agent-based distributed Routing Algorithm with Traffic Prediction (TPARA) is proposed in this paper. TPARA algorithm, which fully takes traffic density of the surface of the Earth into account, consists of two parts: traffic prediction and routing decision. In the former, not only the heterogeneity of traffic on the ground is considered, but upcoming traffic from terrestrial terminals is predicted using an improved Kalman filtering as well. In the latter, mobile agents (MAs) are used to explore satellite network and collect routing information. The ultimate routing decision is determined by both current status and future status of satellite network. Simulation results show that, compared with the classical algorithm of ACO, TPARA not only has shorter delay, but alleviates congestion as well.

In this paper, a comprehensive BER performance simulative study has been made on secure color image transmission in a SC-FDMA wireless communication system. The system implements a modified form of Chaos-based image encryption scheme under utilization of three channel equalization techniques (MMSE, ZF and Q-Less QR Decomposition) and three digital modulation schemes (QPSK, DQPSK and QAM).In comparative study, it is noticeable from simulation results that the ½-rated convolutionally encoded system combined with both transmit and receive diversity in Rayleigh multipath fading channel outperforms in QAM and ZF schemes.

This paper provides a clusterhead review of clusterhead selection algorithm in Mobile Ad Hoc Networks (MANETs) and proposes a Stable Clusterhead Selection Algorithm for ad hoc networks (SCSA). The algorithm constructs a stable clusterhead with the help of reducing the number of clusterhead reconstruction. It selects the nodes which have the stability to be the clusterheaders. The results of simulation show that, with the proposed SCSA clusterhead selection algorithm, the average number of clusterheads, the frequency of clusterhead changes, the frequency of cluster member changes, and cluster lifetime can be improved in most of cases. It is an available approach to clusterhead decision.