Current Issue : October - December Volume : 2012 Issue Number : 4 Articles : 7 Articles
We introduce an improved image transmission scheme over wireless channels with flat Rayleigh fading. The proposed scheme\r\njointly optimizes bit power and modulation level to maximize the peak signal-to-noise ratio (PSNR) of the reconstructed image\r\nand hence improves the perceptual quality of the received image. In this optimization process, the significance of bits with regard to\r\nthe overall quality of the image is exploited. The optimality of the proposed algorithm is demonstrated using the Lagrange method\r\nand verified through an iterative offline exhaustive search algorithm. For practical implementation, a look-up table is used at the\r\ntransmitter for assigning the bit power and modulation level to each bit stream according to the received signal-to-noise ratio\r\n(SNR) observed at the receiver. The proposed scheme has low complexity since the look-up table is computed offline, only once,\r\nand used for any image which makes it suitable for devices with limited processing capability. Analytical and simulation results\r\nshow that the proposed scheme with jointly optimized bit power and variable modulation level provides an improvement in PSNR\r\nof about 10 to 20 dB over fixed power fixed modulation (16-QAM). A further reduction in complexity is achieved by using the\r\naverage signal-to-noise ratio rather than the instantaneous SNR in selecting the system parameters....
Conventional proactive routing protocols, due to their inherent nature based on shortest paths, select longer links which are\r\namenable to rapid breakages as nodes move around. In this paper, we propose a novel adaptive probabilistic approach to handle\r\nrouting information in dense mobile ad hoc networks in a way to improve the proactive routing pertinence as a function of\r\nnetwork dynamics. We first propose a new proactive routing framework based on probabilistic decisions and a generic model to\r\ncompute the existence probabilities of nodes and links. Then, we present a distributed algorithm to collect the cartography of the\r\nnetwork. This cartography is used to instantiate the existence probabilities. Conducted simulations show that our proposal yields\r\nsubstantially better routing validity. Nonetheless, it amounts to much longer routes. We proposed then a bounding technique to\r\nadapt and overcome this side effect and defined two probabilistic proactive routing variants. Conducted simulations show that our\r\nproposed bounded probabilistic proactive routing schemes outperform conventional routing protocols and yield up to 66 percent\r\nincrease in throughput....
Wireless Ad hoc Network consists of nodes which have fixed topology and almost all the nodes in such network is energy constrained. So, it is a necessity for this kind of networks to have an topology such that the energy utilization will be maximum and therefore the longevity of the network will be increased. In this paper, we have proposed such an approach named as BPC (Beaconed Powered Clusters) for wireless ad hoc network for the power efficient routing in multi-hop wireless routes....
It is not only for test and measurement of great importance to synchronize clocks of networked devices to timely coordinate data\r\nacquisition. In this context the seek for high accuracy in Ethernet-based clock synchronization has been significantly supported\r\nby enhancements to the Network Time Protocol (NTP) and the introduction of the Precision Time Protocol (PTP). The latter\r\nwas even applied to instrumentation and measurement applications through the introduction of LXI. These protocols are usually\r\nimplemented in software; however, the synchronization accuracy can only substantially be improved by hardware which supports\r\ndrawing of precise event timestamps. Especially, the quality of the timestamps for ingress and egress synchronization packets has a\r\nmajor influence on the achievable performance of a distributed measurement or control system. This paper analyzes the influence\r\nof jitter sources remaining despite hardware support and proposes enhanced methods for up to now unmatched timestamping\r\naccuracy in Ethernet-based synchronization protocols. The methods shown in this paper reach sub-nanosecond accuracy, which\r\nis proven in theory and practice....
Telecom infrastructures are facing unprecedented challenges, with increasing demands on network capacity. Today, network\r\noperators must determine how to expand the existing access network infrastructure into networks capable of satisfying the userââ?¬â?¢s\r\nrequirements. Thus, in this context, providers need to identify the technological solutions that enable them to profitably serve\r\ncustomers and support future needs. However, the identification of the ââ?¬Å?bestââ?¬Â solution is a difficult task. Although the cost of\r\nbandwidth in the active layer has reduced significantly (and continually) in recent years, the cost of the civil worksââ?¬â?such as\r\ndigging and trenchingââ?¬â?represents a major barrier for operators to deploy NGA infrastructure. Duct is a critical part of the nextgeneration\r\naccess networks, and its sharing would reduce or eliminate this capital cost and this barrier to entry. The aim of this\r\npaper is to provide a better understanding of the economics of broadband access networks technologies (wireline and wireless),\r\ntheir role in the deployment of several services in different regions, and the development of competition in the access networks....
Optimal resource allocation for cooperative cognitive radio networks with opportunistic access to the licensed spectrumis studied.\r\nResource allocation is based on minimizing the symbol error rate at the receiver. Both the cases of all-participate relaying and\r\nselective relaying are considered. The objective function is derived and the constraints are detailed for both scenarios. It is then\r\nshown that the objective functions and the constraints are nonlinear and nonconvex functions of the parameters of interest, that\r\nis, source and relay powers, symbol time, and sensing time. Therefore, it is difficult to obtain closed-form solutions for the optimal\r\nresource allocation. The optimization problem is then solved using numerical techniques. Numerical results show that the allparticipate\r\nsystem provides better performance than its selection counterpart, at the cost of greater resources....
: OFDM is a modulation technique for multicarrier path that provides high spectral efficiency, low implementation complexity, non – linear distortion. High peak – to – average power ratio (PAPR) of the system is the main limitation of it. PAPR increases the complexity of the signal converter and reduces the efficiency of the radio – frequency (RF) power amplifier. If some Regulatory and application constraints are implemented to reduce the peak transmitted power then it reduces the range of multi carrier transmission. This limits the spectral growth, battery life and the transmitter power amplifier is no longer confined to linear region in which it should operate. In this paper we have used the clipping and filtering method to reduce the PAPR....
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