waashk/dblp huggingface dataset:
adaptive time synchronization for wireless sensor networks with self-calibration. time synchronization is important for wireless sensor networks because it facilitates cooperation among nodes and helps raise power efficiency. time synchronization protocols like tpsn, rbs and ftsp have provided great schemes to fulfill fast synchronization with efficiency. in some applications, nodes might hope to sleep for a long time without timestamp exchanges with other nodes. in that case, accurate time drift prediction is quite necessary. for that purpose, firstly, we propose a time synchronization scheme, which fully utilizes the broadcast nature. the scheme achieves time synchronization with fewer timestamps compared with rbs and tpsn. secondly, we introduce a method to find relative time drift rate on the fly. thirdly, we introduce a scheme to predict time drift rates of the next few hours. we also analyze a few factors that deteriorate frequency drift or time drift rate. the diurnal periodical environment trend, instead of mathematical extrapolation, is used for time drift rates prediction of the next few hours.
probability-based combination for cooperative spectrum sensing in cognitive radio networks. to take advantage of time-varying spectrum opportunities, a cognitive radio (cr) network monitors the dynamic usage of the licensed band through cooperative spectrum sensing. in this paper, we propose a probability-based scheme for combination of spectrum sensing information collected from several cr users. different from conventional cooperative spectrum sensing schemes that assume synchronous local sensing information, our scheme enables combination of both synchronous and asynchronous sensing information by utilizing the statistics of licensed band occupancy. in our scheme, the amount of information from each cr user is flexible and a simplified implementation is also feasible under a symmetrical case. simulation results demonstrate that our scheme is robust and superior in terms of detection performance.
measuring indoor mobile wireless link quality. this paper investigates methods for link quality measurement of an indoor, time-varying wireless link. link quality estimates are used for a number of higher-layer functions, including rate adaptation, routing, and topology control. the objective is to rapidly and efficiently estimate the current reliability of an rf link in terms of its packet success probability in the presence of a time-varying channel. we compare various approaches to estimating the current packet success rate (psr), including packet counting and several methods employing physical layer signal-to-noise ratio (snr) measurements. among the snr-based estimators, we consider those using a simple moving average, an exponential moving average, and a yule-walker predictor of the current snr. the analysis shows that the snr-based estimators are more efficient than packet counting methods in terms of the number of measurements needed, are more accurate when link quality variability increases, and are more flexible in terms of predicting the psr for various bit rates and packet sizes. an important requirement, however, of the snr-based estimators is a priori knowledge of the snr-psr relationship, which is environment- and radio-dependent. an efficient methodology for obtaining this mapping is presented.
decomposition for low-complexity near-optimal routing in multi-hop wireless networks. network flow models serve as a popular mathematical framework for the analysis and optimization of multi-hop wireless networks. they also serve to provide the understanding necessary to derive effective distributed protocols. however, the high computational complexity of realistic models restrict the translation of theoretical insights into distributed protocols. in this paper, we consider an np-hard, mixed integer linear programming based routing model that computes single-path routes in a wireless network. we propose an efficient, polynomial time algorithm that applies domain specific heuristics to reduce the complexity. we employ a decomposition based approach to break the monolithic problem into several sub-problems that cooperate to find near-optimal routes. the sub-problem structure is chosen such that it captures the optimal route discovery process between a source and destination; this is a design principle that can be directly used in distributed routing protocols. we show that the resulting formulation achieves orders of magnitude improvement in the run-time. simulation results show that the routes derived from the model are effective even in practical wireless networks with commonly used protocol stack.
joint bandwidth reservation and admission control in ieee 802.16e based networks. the ieee 802.16e is a compatible and reasonable technology to solve the last mile access problem. since the multiple services in the system are connection-oriented, it is crucial to provide effective admission control and resource allocation mechanisms to guarantee the quality of service (qos) of the system. in this paper, we investigate the joint bandwidth reservation and admission control in the ieee 802.16e networks. foremost, we consider two system models: model without buffer and model with buffer. then two optimization problems are formulated for the two models separately. to solve the two min-max optimization problems, we propose a bandwidth reservation algorithm. in addition, the bandwidth reservation thus obtained can be used with admission control jointly. our aim is to enhance fairness while satisfying qos requirement. numerical results are presented to demonstrate the performance of the proposed scheme in terms of maximal call blocking probability and fairness.
a blind channel estimation algorithm for space-time coded mc-cdma receivers. in this paper we proposed a linearly constrained minimum variance receiver for a space-time coded multicarrier (mc) cdma system in frequency selective fading channels. it is shown that in the proposed receiver the channel can be blindly estimated as the eigenvector that corresponds to the maximum eigenvalue of an autocorrelation matrix, and then, efficient algorithms for subspace tracking can be used. computer simulations shows that the proposed channel estimation algorithm achieves performance comparable to traditional algorithms with less computational cost.
power allocations for adaptive distributed mimo multi-hop networks. distributed mimo multi-hop relaying is one of the most promising technologies that permits cost-effective improvement of coverage, data rate and end-to-end (e2e) user experience by utilizing distributed low-complexity space-time codes to overcome path losses and deep fades of wireless channels. however, an efficient transmission scheme and resource management are required to exploit these advantages. specifically, low-complexity adaptive schemes and power control strategies should be designed, thereby achieving robust and cost-efficient e2e communications. in this paper an adaptive transmission scheme is presented, where one relay stops forwarding the message if it is in outage and other nodes adapt to a new space-time code. for this adaptive scheme, optimal as well as sub-optimal closed-form power allocation solutions are derived which minimize the total transmission power while satisfying a given e2e outage probability. the significant power savings due to the proposed approaches in comparison to a non-adaptive scheme is demonstrated by numerical results.
signal detection in distributed cooperative cellular systems without perfect synchronisation. in this paper, an asynchronous cooperative cellular system is investigated on the uplink. we propose a signal detector which involves successive interference cancellation (sic) and parallel interference cancellation (pic) to suppress the impact of interference caused by co-channel users and imperfect synchronisation. simulation results show that the proposed scheme provides significant performance improvement with low computational complexity.
weighted size-aware packet distribution for multipath live streaming. we focus on the problem of packet distribution for live media streaming over multipath networks. after proposing multipath live streaming model and an in-depth analysis of it, we suggest that traffic load should be allocated to paths in proportion to the paths' available bandwidths, considering complicated network status changing as well as burst of media sending rate, that can minimize the bandwidth overload probability. moreover, weighted size-aware packet distribution algorithm is proposed to avoid the actual traffic deviation from expected due to variance of packet sizes. simulation results show that the proposed algorithm outperforms other traditional algorithms, especially on reducing late packets, which has negative impact on real-time requirement.
relay-assisted routing in cognitive radio networks. cognitive radio has been proposed in recent years to promote spectrum efficiency by exploiting the existence of spectrum holes. the heterogeneity of both spectrum availability and traffic demand among secondary users has brought significant challenge for efficient spectrum allocation in cognitive radio networks. observing that spectrum resource can be better matched to traffic demand of secondary users with the help of relay nodes, in this paper we propose to utilize cooperative relays to assist the transmission and improve spectrum efficiency. different from traditional cooperative communication within a single channel, in our scheme a relay node may be selected for a link to bridge the link's source and destination using its different common channels with those two nodes. with these new logical links composed of both direct link and relay link, new routing protocols are needed so that end-to-end performance can be better improved. therefore, we define a new link cost, relay-aware link cost, which considers several aspects including channel availability, channel condition, channel utilization and potential relays. based on this link cost, a relay-assisted routing (rar) protocol is proposed which includes routing discovery and local adjustment. simulation results demonstrate the effectiveness of the proposed routing scheme.
performance analysis of optimal joint beamforming in multi-keyhole mimo channels. this paper presents an analytical performance analysis for a multi-keyhole multiple-input multiple-output (mimo) fading channel. our main contribution is a set of new statistical results for the maximum eigenvalue of the random multikeyhole channel matrix, which includes closed-form expressions for the cumulative distribution function and probability density function, as well as asymptotic expansions. based on the results, we analyze the outage performance of the optimal joint beamforming system in multi-keyhole mimo channels. our results illustrate that the outage performance of the multi-keyhole channels is generally worse than that of rich-scattering mimo rayleigh channels.
the interference-multiple-access channel. we introduce the interference-multiple-access channel, which is a discrete memoryless channel with two transmitters and two receivers, similar to the interference channel. one receiver is required to decode the information encoded at one transmitter, the other receiver is required to decode the messages from both transmitters. we provide an inner bound on the capacity region of this channel, as well as an outer bound for a special class of such channels. for this class, we also quantify the gap between inner and outer bound and show that the bounds match for a semi-deterministic channel, providing a complete characterization. for the gaussian case, we show that the gap is at most 1 bit, yielding an approximate characterization.
throughput-gain analysis of network coding in multi-channel multi-radio wireless networks. wireless network coding (nc) has emerged as a promising technology that improves network throughput and spectrum efficiency. how large can the coding gain be? in this paper, we study the network throughput gains of two types of wireless nc schemes, the conventional wireless nc and the analog nc, respectively, over the traditional non-nc scheme in multi-hop, multi-channel, and multi-radio wireless networks. in particular, we propose an analytical framework, which can exploit the best coding opportunities among all the possible realistic ones, for deriving the network throughput gains of the wireless nc schemes. by solving the problem of maximizing the network throughput subject to the fairness requirements under our proposed framework, we quantitatively analyze the network throughput gains of these two types of wireless nc schemes under various wireless network topologies.
cooperative content dissemination in intermittently connected networks. over the last few years, the popularity of multimedia content sharing among the internet users has promoted a new kind of networking where the content dissemination is determined by the interests of users rather than pre-specified destinations. development of wireless mobile devices has further enhanced the trend of content exchange among the mobile users. however, such mobile nodes based content dissemination may suffer the underlying intermittent connectivity due to the inherent limitations such as short radio transmission range, sporadic node densities and constrained power. to this effect, some solutions have been proposed in the literature that exploit the mobility and storage space of the nodes to distribute contents even if a route never exists. in all these mechanisms, whenever two mobile nodes encounter each other, each node only focuses on making independent disseminating decisions to improve the overall performance. however, even though each node can get its own optimized decisions, it may not be an optimized decision between the two encountering nodes. with this in mind, this paper presents a cooperative content dissemination framework (ccdf) with an analytical model to select and store the contents that maximizes the overall content delivery probability in the future. simulation results demonstrate the enhanced delivery performance offered by the proposed ccdf over existing schemes.
distributed usage control architecture for business coalitions. the dynamic environment of business coalition (bc) requires a flexible access control approach to deal with user management and policy writing. however, the traditional approach applied to bc assigns to access control a burden, mainly to the service provider, thus requiring ad hoc schemes to mitigate the lack of controls developed to bc needs. we present a brokered access control architecture, based on uconabc, to obtain an integrated usage control management for bc. the broker intermediates contract establishment between service provider and consumer, and derives from it the policies to regulate the usage at service-level. the consumer defines user-level policies to control the usage of the contracted services. we developed a web services based prototype to evaluate the feasibility of our proposal. the proposed architecture enables distribution of duties and integration of usage control management in a loosely coupled fashion, providing the flexibility desired in bc environments.
a body surface coordinator for implanted biosensor networks. biomedical sensors can be implanted and networked in the human body for health monitor, diagnosis, treatment or as a prosthetic device. life time and heat generated by implant due to communication and circuitry power consumption are big concerns. this paper presents a new network architecture for long range communications in the implanted sensor networks. we measured the on-body propagation around body surface and in-body propagation through tissue in the frequency ranges of 403mhz and 2.45ghz. we have found that the in-body path loss is more than that of on-body. to exploit the path loss difference, we propose to introduce a body surface coordinator which has more resources to the implanted sensor networks. instead of only routing data among implants, the coordinator on the body surface can forward data from one implant to another over long distance more safely and efficiently.
improving performance of tcp-based applications over dvb-rcs links. dvb-rcs links, as well as most of vsat systems, to improve tcp performance usually consider a pep solution. the satlabs group of the european space agency issued i-pep, selecting scps-tp as transport protocol, which supports two congestion control schemes: tcp vegas (default) and van jacobson's slow start and congestion avoidance. in both cases the most popular tcp-based applications, i.e. web browsing and e-mail, achieve very poor performance especially when dama schemes run at the mac layer. in this frame, tcp noordwijk has been specifically designed to optimize performance of short tcp-based data transfers over dvb-rcs dama links, meeting the requirement to be compatible with i-pep specifications. this paper presents an overview of tcp-based application criticalities over dvb-rcs links and shows how tcp noordwijk improves performance.
evaluate reliability of wireless sensor networks with obdd. reliability evaluation of wireless sensor networks (wsn) is a critical step in wsn design. to evaluate the reliability of wsn, an algorithm named cobdd is presented in this paper. cobdd executes recursive construction of the ordered binary decision diagram (obdd) only once, and therefore save much running time when wsn is subject to large number of common causes. furthermore, it constructs obdd with node expansion and decrease redundant computations from isomorphic subnetworks. experiments show that cobdd is an efficient algorithm for the reliability evaluation of wsn.
distributed multi-user scheduling for improving throughput of wireless lan. carrier sense multi-access (csma) is a typical method to share the common channel in a wireless lan (wlan). it works fairly well in times of light traffic. however as the number of nodes in a wlan increases quickly, severe collision greatly degrades network performance. in this paper we propose a distributed multi-user scheduling (dmus) scheme to solve this problem, taking time-variant link quality and rate adaptation into account. instead of all nodes, only nodes with high instantaneous link quality are allowed to contend for the channel. by setting a suitable snr threshold, at any instance only a small percentage of nodes join the contention. as a result, collision is mitigated, fairness is retained by independent fading, and the total throughput is increased since transmissions are finished at higher rates. simulation results show when there are 40 nodes in a wlan, the dmus scheme improves total throughput by up to 49.6% compared with the contention-free scheme, and by up to 194.6% compared with the csma/ca scheme.
selection cooperation with transparent amplify-and-forward relaying in mimo relay channels. in this paper, we consider a single-relay cooperative scenario, where the source, relay, and destination terminals are equipped with multiple transmit and receive antennas. we focus on the so-called transparent amplify-and-forward (t-aaf) for mimo relay channels, in which the relay requires neither channel state information (csi) nor synchronization of symbols or carrier. specifically, we propose and analyze new selection schemes where the relay, based on the received signal energies, select the "best" received signals on the s → r hop and retransmits them to the destination terminal with either repetitive or selective transmission. through the derivation of pairwise error probability (pep) expressions and asymptotic order of diversity (aod) analysis, we demonstrate that the proposed selection schemes maintain full diversity order. furthermore, we show that selective transmission on r → d hop has better performance, better throughput, and significantly better energy efficiency than repetitive transmission.
highly integrated fractional-n synthesizer for locatable wireless sensor nodes. local positioning systems significantly enhance the value of wireless sensor networks (wsn). this paper presents an integrated synthesizer for localization using frequency modulated continuous wave (fmcw) radar. the synthesizer is based on a fractional-n phase-locked loop (pll) architecture. all components of the pll are carefully designed with respect to their power consumption, and the digital parts are implemented in current-mode logic (cml). the complete synthesizer was manufactured in a 0.18µm sige bicmos process from ibm, and it consumes only 100mw, achieves a phase noise better than -117 dbc/hz and has a silicon area of 1.15mm2. due to its high integration level and its optimized design, the synthesizer achieves low power consumption and low phase noise that make it suitable for precise localization in mobile sensor nodes. localization measurements in indoor environments with multi-path propagation showed mean distance errors about 10 cm.
deterministic combining for fading channels. for a communication system employing receive diversity in flat rician fading, we consider linear combining receivers with deterministic weights. two receiver structures are proposed: (1) a modified maximum likelihood receiver in which detection is performed by maximizing the likelihood function of the combined received signal, (2) a deterministic maximal-ratio combining (mrc) receiver which uses the same structure as that of an mrc receiver with deterministic weights. the deterministic weight vector is chosen such that it minimizes the union bound on the symbol error probability. the error performance of the receivers is compared with that of the square-law combining and the equal-gain combining receivers.
transmission capacity of two-way communication in wireless ad hoc networks. wireless ad hoc networks require bidirectional data transmission to support two-way traffic and control functions like packet acknowledgement. most prior work on the capacity of wireless ad hoc networks, however, has focused only on one-way communication. in this paper we develop the concept of transmission capacity of two-way communication in wireless ad hoc networks. the transmission capacity has been used extensively to analyze one-way ad hoc networks - in this paper we provide a generalization that incorporates the concept of a two-way outage. we derive an upper bound and an approximation for the two-way transmission capacity, which are shown to be relatively tight for small outage probability constraints. we also quantify how the two-way success requirement reduces network capacity. our numerical and simulation results show that for certain two-way networks the capacity loss is considerable.
implementing secure p2p-ons. name services for the internet of things (specifically, the epcglobal network) are distributed systems that serve the following fundamental lookup function: given an identifier for a real-world object, e.g., an electronic product code (epc), they return a list of internet addresses of services, which offer additional information about this object. without name services acting as a broker between items and their information sources, the internet of things could not achieve the flexibility and global scalability necessary to live up to its vision. the currently specified object naming service (ons) for the epcglobal network has severe security drawbacks in its architecture and design. in this paper, we present the implementation of a peer-to-peer name service architecture based on distributed hash tables (dht) on the research platform planetlab. this alternative ons architecture named oida, if deployed as an infrastructure network, offers enhanced overall multilateral security compared to ons, combined with potentially better functionality, scalability, and roughly equivalent performance.