A mobile ad hoc network (MANET) is the cooperative engagement of a collection of wireless mobile nodes without the aid of any established infrastructure or centralized administration. The conventional security solutions to provide key management through accessing trusted authorities or centralized servers are infeasible for this new environment since mobile ad hoc networks are characterized by the absence of any infrastructure, frequent mobility, and wireless links. In this paper, we propose an on‐demand, fully localized, and hop‐by‐hop public key management scheme for MANETs. It can be performed by generating public/private key pairs by nodes themselves, issuing certificates to neighboring nodes, holding these certificates in their certificate repositories, and providing authentication service adaptive quickly to the dynamic topology of the network without relying on any servers. Also, our scheme can be performed successfully as long as there is a physical communication line between two nodes, and it is accustomed well to the on‐demand routing for MANETs. Copyright © 2006 John Wiley & Sons, Ltd.
Past researches on sensor network routing have been focused on efficiency and effectiveness of data dissemination. Few of them consider security issues during the design time of routing protocols. Security is very important for many sensor network applications. Studies and experiences have shown that considering security during design time is the best way to provide security for sensor network routing. In this paper, we propose an efficient key management scheme and a novel secure routing protocol—Secure cell relay (SCR) for sensor networks. We also present an effective key setup scheme for sensor nodes deployed in the later stage. We analyze the security of SCR under various attacks and show that SCR is very effective in defending against several sophisticated attacks, including selective forwarding, sinkhole, wormhole, Sybil, hello flooding, and clone attacks. SCR is an energy‐efficient routing protocol with acceptable security overhead. Our simulations demonstrate that with all the security primitives, SCR still has lower energy consumption and higher delivery ratio than a popular routing protocol—directed diffusion. Copyright © 2006 John Wiley & Sons, Ltd.
SUMMARYThis paper proposes a non-matrix inversion based algorithm to implement decorrelating detection (DD), namely quasi-decorrelating detector (QDD), which uses truncated matrix power expansion instead of inverted correlation matrix to overcome the problems associated with the inversion transformation in DD, such as noise enhancement, computational complexity and matrix singularity etc. Two alternative QDD implementation schemes are presented in this paper; one is to use multi-stage feed-forward filters and the other is to use an nth order single matrix filter (neither involves matrix inversion). In addition to significantly reduced computational complexity, if compared with DD, the QDD algorithm offers a unique flexibility to trade among multiple access interference (MAI) suppression, near-far resistance and noise enhancement according to varying system set-ups. The obtained results show that the QDD outperforms decorrelator in either additive white Gaussian noise (AWGN) or multi-path channel, if the number of feed-forward stages is chosen properly. This paper also studies the impact of correlation statistics of spreading codes on the QDD's performance with the help of a performance-determining factor derived in this paper, which offers a codeselection guideline for the optimal performance of the QDD algorithm.
SUMMARYBandwidth efficiency of all digital modulations is associated closely with baseband pulse shaping waveforms (PSW's) before carrier modulation. Traditional PSW designing approaches usually work in a way such that the design of PSW's in the time domain hardly reveals a direct connection with their spectral characteristics. In other words, designing process of the PSW's offers too little degree-of-freedom to control spectral properties of the resultant signals. This paper will present a methodology, based on which several new PSW synthesising approaches, including time-domain convolution (TDC), steepest sidelobe roll-off (SSR) and zero-point insertion (ZPI) methods, will be proposed to design different PSW's with controllable spectral characteristics, such as sidelobe roll-off rate, main lobe width and null positions in their power spectral density functions. In particular, the SSR and ZPI methods are based on a truncated cosine function series, which can be further generalised to use other seed functions. The results show that the approaches can help us to generate a PSW database containing a wide collection of promising PSW's to suit for diverse wireless applications, such as traditional digital modems as well as emerging ultra-wideband systems.
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