Real global-scale quantum communications and quantum key distribution systems cannot be implemented by the current fiber and free-space links. These links have high attenuation, low polarization-preserving capability or extreme sensitivity to the environment. A potential solution to the problem is the space-earth quantum channels. These channels have no absorption since the signal states are propagated in empty space, however a small fraction of these channels is in the atmosphere, which causes slight depolarizing effect. Furthermore, the relative motion of the ground station and the satellite causes a rotation in the polarization of the quantum states. In the current approaches to compensate for these types of polarization errors, high computational costs and extra physical apparatuses are required. Here we introduce a novel approach which breaks with the traditional views of currently developed quantum-error correction schemes. The proposed solution can be applied to fix the polarization errors which are critical in space-earth quantum communication systems. The channel coding scheme provides capacity-achieving communication over slightly depolarizing space-earth channels.

Continuous monitoring of performance is a necessary tool for the maintenance and improvement of service quality. This applies to the rapidly developing 3D multimedia applications, where acceptability and user experience are the ultimate determinants of value. Satisfying demands in order to achieve high level Quality of Experience is challenging due to Quality of Service requirements and sensitivity of 3D services, especially in case of multi-access devices capable to benefit from wired, wireless and mobile network technologies. Feedback procedures relying on human evaluators are considered to be one of the most important industrial inputs of QoE monitoring. Distortions regarding this input necessitate additional attention due to their ability of making measurement results considerably inaccurate and misleading. This paper aims to observe and analyze the effect of specific environmental information, which is commonly public to the evaluators. The performed series of measurements demonstrates how the awareness of the type of connection can make constant objective quality to result in a rather varying subjective quality. It is also revealed how cognitive dissonance played a role during the evaluation of streaming services on a portable 3D terminal. In order to support understanding evaluator behavior, measurement subjects were distinguished by Level of Comprehension, based on prior technical knowledge and experience.

ABSTRACT This paper analyzes the information‐theoretical security of the of Differential Phase Shift (DPS) Quantum Key Distribution (QKD) protocol, using efficient computational information geometric algorithms. The protocol was introduced for practical reasons, since the earlier QKD schemes were too complicated to implement in practice. The DPS QKD protocol can be an integrated part of current network security applications; hence its practical implementation is much easier with the current optical devices and optical networks. The proposed algorithm could be a very valuable tool to answer the still open questions related to the security bounds of the DPS QKD protocol. Copyright © 2012 John Wiley & Sons, Ltd.

In wireless smart metering optimization for energy efficiency is indispensable, because in case of systems without external power supply, battery life is a key factor regarding the usability of the whole system. Sensor networks are less sensitive for delay, this is why aggregation of packets is possible. The aim of this paper is to determine analytically the amount of meter records to aggregate in one packet, regarding the SNR which characterizes the quality of the channel, so that the energy usage is optimal. The introduced formulas, help determining scheduling parameters in wireless smart metering systems. The calculations are presented on a real world scenario and system using GFSK modulation.

The authors take a look at the existing 3G systems in service and investigate the capabilities of 4G, and while the theoretical throughput of these cellular systems is expected to be high, the future promises to offer more technological improvements and innovations.

The Myth: Sixty years of research following Shannon's pioneering paper has led to telecommunications solutions operating arbitrarily close to the channel capacity—“flawless telepresence” with zero error is available to anyone, anywhere, anytime across the globe.

The bandwidth of cellular mobile systems is remarkably growing with emerging new network technologies. LTE is a key step towards future high speed cellular networks, but large bandwidth on its own does not fulfill the QoS requirements of real- time multimedia connections. It is more important to guarantee the amount of network resources required by real-time VoIP and video connections. In this paper, we introduce a Ring based Call Admission Control (CAC) Scheme which enables the prediction of the future position of the users thus enhancing CAC decisions. We examined the required number of rings for optimal prediction using analytical methods. Furthermore we present a vector based extension of the newly proposed algorithm.

In order to fulfill the users' requirements, today's mobile devices are equipped with multiple interfaces to make the connection possible to different type of networks. To select dynamically the best interface according to different network attributes, such as delay, bandwidth, cost, etc. must be taken into account. Grey Relational Analysis (GRA) is a promising algorithmic approach that can realize dynamic interface selection with multiple alternatives (interfaces) and attributes; however, similarly to some other decision methods, GRA also suffers from rank reversal phenomenon. In this paper alternative solutions are introduced to reduce and eliminate the probability of rank inconsistency, caused by the addition or deletion of an interface. The proposed methods are analyzed analytically and by simulations. Our results confirm that the proposed normalization methods significantly reduce, while one of it eliminates the rank reversal phenomenon.

Retransmission based error recovery is not always applicable for multimedia applications; however it can be used if the transmission characteristics and network conditions are examined before. Retransmissions can be carried out only if there is no congestion in the network and the network delay is low enough to receive the retransmitted packet before the playout. These two attributes are depending and one can be estimated from the other. In this paper we introduce a TFRC and RTT threshold interdependence model to determinate network delay thresholds for the retransmission decision algorithm. Using the calculated sending rate of the TFRC (TCP Friendly Rate Control) to estimate the congestion level in the network, we can set up a threshold of disabling/enabling the retransmissions. Our goal was to determinate a matching RTT threshold to gain similar retransmission behavior as using the sending rate threshold. We found that using our threshold estimating model, the number of retransmitted packets was similar, using the TFRC-based sending rate threshold and the RTT retransmission threshold.

Radio frequency identification technology is becoming ubiquitous and as an unfortunate side effect, more and more authentication solutions come to light that have plenty of security issues to deal with.

Since tags have very limited memory and very low computational capacity a so-called lightweight authentication is needed. The earlier suggested algorithms do not satisfy all of the security requirements. In this paper we introduce our SLAP protocol which meets all the security requirements. Our solution provides an efficient mutual authentication method by which a given tag and the back-end can authenticate each other easily, quickly and securely even if large amount of tags are stored in the database. The protocol can defy the well-known attacks and does not demand high computational capacity.

In this paper we introduce some example algorithms that can work with the Client-based Mobility Frame System presented recently by us. In this solution all the logic and structure is transferred from the network to the Mobile Node and thus each individuum can use the resources in a personalized and efficient way. In the present work modeling and detailed discussion on the parameters of the algorithms is given and comparison to existing mobility approaches and protocols is done. We prepared a simulation to test our protocol and to back up the proposals we provide the reader with simulation results. We stress that one the most important benefit of our findings is that all the MNs can run different management strategies and can optimize mobility for themselves.

The efficient dimensioning of cellular wireless access networks depends highly on the accuracy of the underlying mathematical models of user distribution and traffic estimations. The optimal placement/deployment of e.g. UMTS, IEEE 802.16 WiMAX base stations or IEEE 802.11 WLAN access points is based on user distribution and traffic characteristics in the service area. In this paper we focus on the tradeoff between the accuracy and the complexity of the mathematical models used to describe user movements in the network. We propose a novel Markov chain based model capable of utilizing user's movement history thus providing more accurate results than other models in the literature. The new model is applicable in real-life scenarios, because it relies on information effectively available in cellular networks (e.g. handover history). The complexity of the proposed model is analyzed, and the accuracy is justified by means of simulation.

Retransmission-based error recovery is the simplest technique to minimize the overall packet loss ratio in order to increase the quality of the applications. Multimedia applications are becoming increasingly popular in IP networks, while in mobile environment the limited bandwidth and the higher error rate arise in spite of its popularity. Retransmission can be also used for loss recovery in media applications, but the number of retransmissions is limited by the playout buffer and the recent network delay.

Multimedia applications are becoming increasingly popular in IP networks, while in mobile environment the limited bandwidth and the higher error rate arise in spite of its popularity. The wireless network characteristics make the deployment of these applications more challenging. Retransmission-based error recovery is considered inappropriate for multimedia applications, because of its latency. However, this solution can be attractive because it requires minimal network bandwidth and processing cost as well as improvement of the video quality. Despite its latency, retransmission can be used successfully in many cases, especially if playout buffering is employed. In this paper we propose a source controlled and playout time oriented retransmission scheme for multimedia streaming. Due to source controlling the receiver do not need to send additional retransmission request messages. The other advantage of transmitter controlled decision algorithm is that all the needed information is available at the source due to DCCP transport protocol. Therefore no additional network measurements and probe messages are needed. The results show that our scheme reduces traffic overhead generated by retransmission and hardly degrades the number of unsuccessfully retransmitted packets at all.

Many information processing and computing problems can be traced back to find the extreme value of a database or a function. Unfortunately, classical solutions suffer from high computational complexity if the database is unsorted or, equivalently, the function has many local minimum/maximum points. Proposed quantum computing-based solutions involve the repeated application of Grower's searching algorithm. In this paper, we introduce a new technique exploiting the parallel processing capabilities of quantum computing in a different way. We derive a special case of quantum counting - we call it quantum existence testing - which allows adapting the classical logarithmic search algorithm so that it is suitable for structured databases to unstructured ones. The paper analyzes the required number of database queries, the corresponding computational complexity, and the probability of error and their relationship

In a wireless mobile network, two major problems arise: the poor performance of the wireless layer and the effect of user mobility. The problems related to limited available radio bandwidth and radio channel errors seem to be solved by CDMA technique applied in 3G mobile systems. Terminal mobility causes problems in call admission control because the number of active mobile terminals in a cell is a random variable. In this paper we introduce a new method to predict the number of terminals in each cell. Based on this information a more effective CAC algorithm can be applied in order to ensure user's satisfaction.

3G and 4G mobile systems are based on CDMA technology. In order to increase the efficiency of CDMA receivers a large amount of effort is invested to develop suitable multi-user detector techniques. However, at this moment there are only suboptimal solutions available because of the rather high complexity of optimal detectors. One of the possible receiver technologies can be the quantum assisted computing devices which allows high level parallelism in computation. The first commercial devices are estimated by 2004, which meets the advent of 3G and 4G systems. We introduce a novel quantum computation based quantum multi-user detection (QMUD), employing Grover's (see Bell Labs, April 1999)search algorithm, which provides optimal solution. The proposed algorithm is robust to any kind of noise/suboptimal solutions.

Nowadays state of the art WLAN support one-hop ad-hoc functionality. However, real home automation or disaster rescue systems require much more sophisticated ad-hoc capabilities. Therefore the investigation of open questions of multi-hop ad-hoc networks becomes more and more important. The problems to solve can be categorized into two major topics: medium access control (MAC) and routing. In this paper we introduce a novel concept called distributed cell reservation scheme (DCRS) which works over the MAC protocols designed for operation in a one-hop environment and allows efficient MAC in multi-hop scenarios. We define the basic criteria for MAC protocols required by DCRS. Based on a large number of simulations we evaluate and compare the new solution using the well-known CSMA/CA and EY-NPMA as basic MAC protocols for DCRS.

Abstract Multiuser/multisubchannel detection schemes based on a recurrent neural network (RNN) structure are a promising alternative to conventional detection schemes, both in terms of performance and complexity. This paper gives an overview of different approaches that make use of the results of RNN research for multiuser/multisubchannel detection. The detectors' results are compared with the results of conventional detection schemes in simulations of the uplink of a DS‐CDMA packet transmission system. Copyright © 2002 John Wiley & Sons, Ltd.