waashk/dblp huggingface dataset:
cost and target-based scheduling for switch power control. in this paper we propose two advanced algorithms which allow for both differentiated quality-of-service (qos) and power conservation in input-queued packet switches. these algorithms are based on two core ideas: first, we assume that the switch can operate in a number of operational speed modes; a higher speed mode serves more packets per time slot at the cost of higher power consumption. second, each virtual output queue may tolerate a certain low backlog which is called a target in this setting. thus, one can control power by adjusting the speed mode and qos by setting the targets appropriately. we first survey previous work to provide the necessary background behind our approach. we then describe our algorithms and evaluate their performance experimentally through simulation. our preliminary results show that these new procedures offer significant performance gains compared to existing approaches.
evaluation of sip signaling and qos for voip over satellite networks. in satellite networks, voice over ip performance is degraded by long delays and low bandwidth. both call setup time and quality of service (qos) for voice calls are affected. separate studies have been undertaken for these performance metrics. in this paper, we have carried out experiments using different voice codecs to evaluate sip call setup time and qos parameters together. the experiments are performed on the satellite network testbed at centre for communication systems research (ccsr) at university of surrey. the results present a comparison of different codecs, highlighting their performance.
polynomial eigen-beamformer in time domain for mimo-ofdm systems. co-space interference (csi) mitigation is one of the main challenging issues in multiple input multiple output (mimo) systems. using beamformer in both transmit and receive sides is an approach to mitigate the csi. in the mimo systems employing orthogonal frequency division multiplexing (ofdm) technique, frequency domain or time domain beamforming can be used. in this paper, we propose a new time domain broadband beamforming (tbbf) for mimo-ofdm systems based on a svd type of block circular channel matrix. tbbf is attained by polynomial eigen-beamformer when the right and the left polynomial eigenvectors are utilized at the transmitter and the receiver sides, respectively. the new proposed tbbf is able to completely mitigate the csi due to shaping the multiple beams in orthogonal directions. performance of the proposed polynomial eigen-based tbbf is evaluated by computer simulations and compared with the previously proposed tbbf scheme based on the sbr2 algorithm. the results show that the proposed time domain beamforming method outperforms the sbr2-based scheme.
pilot matrix design for interim channel estimation in two-hop mimo af relay systems. in this paper, we are concerned with a two-hop multi-input-multi-output (mimo) amplify-and-forward (af) relay system consisting of a source node (sn), a relay node (rn), and a destination node (dn). since the simple rn in this system is unaware of the structure of its received signal and incapable of performing complicated signal processing, the interim channels over the sn-rn and the rn-dn hops can not be estimated directly. therefore, we develop a novel interim channel estimation approach in this paper. furthermore, we find necessary and sufficient conditions for the pilot amplifying matrix sequence at the rn to ensure successful interim channel estimation at the dn, and present rules to design low-complexity pilot amplifying matrices meeting these conditions.
interference-aware channel assignments with seamless multi-channel monitoring in wireless mesh networks. the wireless mesh networks (wmns) are statically deployed on heterogeneous areas and are operating in open wireless media, and thus it coexists with other networks operating on the same frequency with the same or different radio access technology (rat). the wmns experience two types of interferences according to the source of interference. coexisted networks with wmn induce the interference called external interference and nodes in wmn experience interference each other, which is called internal interference. most of existing protocols strive for dealing with internal interference. but the increased external interferences can degrade the performance of wmn significantly. to resolve this coexistence problem, we propose three channel assignment schemes for hybrid multi-channel protocol (hmcp) by capturing the states of each channel and selecting its operating channel. we also devise a seamless multi-channel monitoring method to recognize channel states without performance degradation. intensive simulation results demonstrate that our proposed channel assignment schemes outperform existing hmcp's channel assignment scheme in terms of aggregate throughput, delay, and fairness.
prioritized flow optimization with generalized routing for scalable multirate multicasting. this paper addresses the performance optimization for scalable video coding and multicast over networks. multi-path video streaming, network coding based routing, and network flow control are jointly optimized to maximize a network utility function defined over heterogeneous receivers. importantly, contextual priors of scalable video layers are imposed on the flow routing optimization problem, seeking to guarantee the transmission cost for each layer in an incremental order and find jointly optimal multicast paths and associated rates. through a primal decomposition and the primal-dual approach, a decentralized algorithm with two-level optimization update is developed to solve the target convex optimization problem. numerical and simulation results validate the convergence and network performance of the proposed algorithm.
evaluation of link protection schemes in physically impaired optical networks. link protection schemes for wdm-based optical networks have been extensively researched. most work to date has ignored the physical layer impairments (plis) that could be dominant in transparent optical networks with long links. in this paper, we first evaluate the performance of two link protection schemes - namely, p-cycles and generalized loopback - when plis are considered. our evaluation shows that a choice of p-cycles that merely tries to optimize the wavelength usage can be more susceptible to failures in a realistic environment. in particular, we show that the hamiltonian p-cycle is not the optimal choice for p-cycle selection in all-optical networks. this is mainly due to the interference caused by the long lightpaths that appear in the network after a failure occurs. we show that although a selection of smaller p-cycles can cause higher blocking probability, it is less vulnerable to failures. we also compare the performance of p-cycles to the generalized loopback link cover approach in these environments. finally, we apply a cross-layer routing and wavelength assignment algorithm to these schemes that significantly enhances performance in physically impaired optical networks.
exploiting the operating point in sensing-based opportunistic spectrum access scenarios. spectrum sensing is one key enabler towards opportunistic spectrum access in cognitive radio networks. such scenarios allow cognitive users (a.k.a. secondary users) to access some licensed spectrum band as long as they do not interfere with the licensed (or primary) users. the main goal is to achieve an efficient and utmost access to the otherwise underutilized spectrum resources while still guaranteeing primary users a non-harmful operation. spectrum sensing can be then used by secondary users to detect spectrum holes that may be accessed in a non-interfering manner. however, spectrum sensing may be subject to errors in the form of false-alarm and misdetection. false-alarm causes spectrum under-use while misdetection leads to spectrum interference between primary and secondary users. unfortunately, these two magnitudes pose a trade-off on the sensing mechanism: low misdetection is achieved at the expense of high false alarm and vice versa. consequently, an adequate operating point of the sensing mechanism should be determined. in this work we evaluate the impact of false-alarm and misdetection errors on the performance of a spectrum sensing scenario.we use a discrete time markov chain (dtmc) model and we determine the suitable operating point for the sensing mechanism under different traffic load conditions such that some quality of service is attained by both primary and secondary users. performance results reveal that by effectively choosing the operation point bearing in mind the traffic load levels will lead to enhanced perceived quality of service of both primary and secondary users.
capacity analysis and experimental study with multiple interfaces and multiple channels in 802.11 mesh networks. a key challenge in multihop wireless network is to provision for sufficient network capacity to meet user requirements. the contributions of this paper are two-fold: (a) we analyses wireless bandwidth, the ratio between the number of channels and the number of interfaces, the ratio between the number of gateways and the number of mesh routers, and the impact on the capacity of mesh backbone, and present the asymptotic upper bound of the average throughput of mesh routers (b) based on insights from capacity analysis, we built tju meshnet testbed and develop a multi-interface routing protocol (mirp). we implement the proposed protocol in our testbed to demonstrate the feasibility in practice.
repeater-assisted capacity enhancement (race) for mimo links in a line-of-sight environment. a single on-frequency, full duplex wireless repeater is considered for enhancing the capacity of a long-distance 2×2 multiple-input multiple-output (mimo) wireless link with a dominant line-of-sight (los) component. such links might be used for high-speed communication between buildings or towers. for practical reasons, the aperture sizes of the transmit (tx) and receive (rx) arrays may be limited, which tends to make the rank of the long-distance mimo channel matrix close to unity. the paper shows that the addition of just one repeater can bring the channel to full rank, approximately doubling the capacity of the link. typical values of repeater isolation are assumed. for small tx and rx array element spacings, there is considerable robustness in optimal repeater location. even with some multipath, most of the capacity improvement is retained.
adaptive bandwidth control to handle long-duration large flows. we describe a method of adaptively controlling bandwidth allocation to flows for reducing the file transfer time of short flows without decreasing throughput of long-duration large flows. according to the rapid increase in internet traffic volume, effective traffic engineering is increasingly required. specifically, the traffic of long-duration large flows due to the use of peer-to-peer applications, for example, is a problem. most conventional qos controls allocate a fair-share bandwidth to each flow regardless of its duration. thus, a long-duration large flow (such as a p2p flow) is allocated the same bandwidth as a short-duration flow (such as data from a web page) in which the user is more sensitive to response time, i.e., file transfer time. as a result, long-duration large flows consume bandwidth over a long period and increase response times of short-duration flows, and conventional qos methods do nothing to prevent this. in this paper, we therefore investigate a different approach, that is, a new form of bandwidth control that enables us to achieve better performance when handling short-duration flows while maintaining performance when handling long-duration flows. the basic idea is to tag packets of long-duration large flows according to traffic conditions and to give temporarily higher priority to nontagged packets during network congestion. we also show the effectiveness of our method through simulation.
design of survivable hybrid wireless-optical broadband-access network. the hybrid wireless-optical broadband-access network (woban) is a promising architecture for access networks. although the front-end wireless mesh networks in a woban are self-healing, the back-end passive optical networks (pons) do not have survivability due to their tree topology. we propose a costeffective protection method for woban that deals with network element failures in the optical part of woban. we define the maximum protection with minimum cost (mpmc) problem and show that the problem can be converted to the minimum cost maximum flow (mcmf) problem. we also present an ilp model for the mcmf problem. numerical results are reported for applying our algorithm to obtain the optimal solutions for different instances of the mpmc problem.
spatial-temporal event correlation. temporal event correlation deals with removing temporally redundant events to produce synthesized events, simplifying downstream processing. in situation management applications and location-based services, it is necessary to incorporate spatial constraints into the correlation process. this requirement is difficult to meet because the traditional algorithms for spatial processing are not well-suited to spatial dynamics occurring in these applications. in this paper we formalize spatial-temporal event correlation compared to the functionality of temporal correlation, present an architecture for efficient implementation, analytically analyze the architecture's performance relative to two other designs, and describe a system design for efficiently supporting situation management applications and location-based services.
hybridcast: a hybrid probabilistic/deterministic approach for adjustable broadcast reliability in mobile wireless ad hoc networks. broadcast is a crucial yet expensive building block for many applications in bandwidth-scarce mobile wireless ad hoc networks. we propose a hybrid deterministic/probabilistic, decentralized broadcast protocol with adjustable broadcast reliability and overhead. the paper first proposes a purely probabilistic, topology-aware broadcast algorithm. the probabilistic broadcast adjusts each node's broadcast forwarding probability locally such that the average broadcast reliability requirement is met. an extension of the probabilistic broadcast to tolerate node mobility and packet loss is then presented. furthermore, the paper augments the proposed probabilistic broadcast scheme with an existing deterministic broadcast protocol in order to reduce excessive broadcast overhead. the proposed hybrid protocol, called hybridcast, combines good characteristics of probabilistic broadcasts, such as adjustable reliability and resilience to mobility, with good characteristics of deterministic broadcasts, such as few retransmissions and low packet collisions. the simulation results show that the proposed protocol can achieve the system's reliability requirement with good tolerance to mobility and packet losses while incurring low broadcast overhead.
interference cancellation in distributed space-time coded wireless relay networks. this paper considers the interference cancellation (ic) problem in multi-user wireless relay networks. first, it is shown that using distributed space-time coding (dstc), the multiple antenna ic scheme previously proposed for systems with direct transmissions can be applied to relay networks. the ml decoding after full ic can be performed symbol by symbol. then, by allowing ic at relays, a new degree of freedom in relay network design is discovered. with this new idea, the required number of antennas at the receiver for full ic can be reduced and a balance between diversity and delay can be obtained.
robust pim-sm multicasting using anycast rp in wireless ad hoc networks. due to its bandwidth efficiency, multicast makes a group-centric communication more viable in wireless ad hoc networks with limited radio resources. pim-sm, a de facto standard multicast protocol known for its high scalability, is a good fit for a large-scale ad hoc network. however, it does not provide a robust multicast communication under rp outage and host mobility. in this paper, we propose a robust way of configuring pim-sm using anycast rp in wireless ad hoc networks. we analyze the impact of cardinality and locations of anycast rps on the network performance under node mobility. based on these observations, we find metrics for near-optimal cardinality of anycast rps and propose a novel rp selection scheme. the proposed scheme is proven to make pim-sm robust against mobility while satisfying qos requirements and maintaining the scalability of pim-sm.
evidences behind skype outage. skype is one of the most successful voip application in the current internet spectrum. one of the most peculiar characteristics of skype is that it relies on a p2p infrastructure for the exchange of signaling information amongst active peers. during august 2007, an unexpected outage hit the skype overlay, yielding to a service blackout that lasted for more than two days: this paper aims at throwing light to this event. leveraging on the use of an accurate skype classification engine, we carry on an experimental study of skype signaling during the outage. in particular, we focus on the signaling traffic before, during and after the outage, in the attempt to quantify interesting properties of the event. while it is very difficult to gather clear insights concerning the root causes of the breakdown itself, the collected measurement allow nevertheless to quantify several interesting aspects of the outage: for instance, measurements show that the outage caused, on average, a 3-fold increase of signaling traffic and a 10-fold increase of number of contacted peers, topping to more than 11 million connections for the most active node in our network - which immediately gives the feeling of the extent of the phenomenon.
capex-aware design of survivable dwdm mesh networks. this paper reviews the basic architecture and component costs of opaque, transparent, and semitransparent dwdm networks and looks at the network design problem from a capital expenditure (capex) point of view. given are a fiber topology and a demand matrix with different bit rates. required is the least-cost optical equipment for that topology together with the routing and potential muxponder-based aggregation of all demands such that they can be supported by the newly designed network. we look at the problem for networks without resilience requirements and for survivable networks using 1+1 protection against single fiber cuts. we model this problem for the three types of optical networks by integer linear programs (ilps) in a canonical way.
deference mechanisms significantly increase the mac delay of slotted csma/ca. slotted csma/ca is an algorithm proposed by ieee 802.15.4 in order to deal with the contention of energy constrained nodes. slotted csma/ca is used during a limited time interval, included in a superframe. two specific mechanisms defer the transmissions that would occur towards the end of the contention period. multiple models of the average delay or throughput of slotted csma/ca have been proposed recently, but they do not take into account the deference mechanisms. in this paper, we show that the deference mechanisms occurring at the end of the superframe have a significant impact on the performance of slotted csma/ca. we prove this by giving the distribution of the delay in a simple scenario, obtained by simulation. then, we compute the average delay tmac of traversing the mac layer, as the mac parameters or the frame size vary. we show that for either reactive wpans and energy-efficient wpans, the impact of the deference mechanisms is important.
sphere packing optimization and exit chart analysis for multi-dimensional qam signaling. we investigate on multi-dimensional qam constellations optimized by sphere packing with the known densest lattices. we propose a greedy design method assisted by the sphere detection. it is demonstrated that the optimized constellations can significantly increase the squared minimum distance in comparison to the conventional qam constellations. in addition, we analyze the optimized qams through the use of an extrinsic information transfer (exit) chart for iterative decoding.
femtocell coverage optimization using switched multi-element antennas. femtocells are low-cost, low-power cellular base stations that are deployed by the end user to supplement macrocellular coverage and provide high data rates in the customer's premises. in femtocell deployments, leakage of the pilot signal to the outside of a house can result in a highly increased signalling load to the core network as a result of the higher number of mobility events caused by passing users. in this paper, a low cost multi-element antenna solution is proposed to reduce the core network mobility signalling over previously published results using a single antenna only. antenna gain pattern measurements of a prototype with two patches and two inverted f antennas are presented and a corresponding feeder network is discussed. self-optimization methods are proposed that jointly select an appropriate antenna pattern and optimize the pilot power. this allows to better match the femtocell coverage to the shape of each individual house and results in an improvement of both indoor coverage and core network signalling resulting from mobility events.
statistical analysis of multiple access interference in asynchronous uwb impulse radio. optimal component and system design requires knowledge of the statistics underlying the system. to date, the determination of the probability distributions characterizing the multiple access interference in ultra-wide bandwidth wireless systems is an unsolved problem. the statistical characteristics of the multiple access interference in ultra-wide bandwidth wireless systems are studied. expressions for the probability density functions of the distribution due to asynchronous multiple access interference and additive white gaussian noise are derived for both additive white gaussian noise and multipath fading ultra-wide bandwidth environments. the accuracies of the derived expressions for the probability density functions are assessed and confirmed by simulation results.
on the performance of ofdm in zero-if receivers impaired by tx leakage. transmitter leakage has a significant impact on the system performance in mobile devices using zero-if receivers. in this contribution, the statistical properties of the tx leakage impact in zero-if receivers are derived, in the context of uplink and downlink ofdm transmission. in order to design suitable algorithms for the digital compensation of tx leakage in ofdm communication systems, an accurate modeling of the corresponding performance loss is required.we therefore provide a statistical description of tx leakage effects on ofdm signals, which is used to compute bit error rates and mutual information.
on the log-normal fading networks: power control and spatial reuse. in this paper, we consider two fundamental problems in log-normal fading networks. one is the energy efficiency. the other is the characterization of the internode interferences and spacial reuse. we first introduce a power efficiency factor as a new parameter to measure the transmit efficiency and obtain an optimal transmit power allocation of the concurrent transmitters in such fading environment. the internode interference caused by the simultaneous transmissions within a local area is then analyzed. the analysis will also be extended to the whole network within unlimited region where the interference accumulative impact is taken into account. by doing so, we set up a direct link between the interference double disc model with the statistical accumulative interference model and derive the optimal spatial reuse distance to guarantee the network efficiency. finally, we propose a concurrent access strategy, ocmac (opportunistic concurrent mac), which can efficiently mitigate the internode interference through the node coordination before the simultaneous transmissions while keeping a relatively low transmit power and high spatial reuse efficiency.