Bandwidth Asymmetry Research Articles

ERFR-CTC: Exploiting Residual Frequency Resources in Physical-Level Cross-Technology Communication

In Internet of Things (IoT), physical-level cross-technology communication (CTC) enables IoT gateways to communicate with heterogeneous nodes economically. However, because of bandwidth asymmetry between heterogeneous technologies, many residual frequency resources are often not fully utilized. Without modification on hardware, in this article, we consider the coexistence of ultralow power (ULP) and WiFi nodes, and propose ERFR-CTC that enables an IoT gateway to fully exploit residual frequency resources without adding additional cost. With ERFR-CTC, the gateway can simultaneously communicate with ULP and WiFi nodes only via a single WiFi network interface card (NIC), which is not only economic but also very efficient. In particular, ERFR-CTC enables ULP nodes to correctly demodulate ULP signals without being interfered by WiFi signals. We then develop theoretical models to quantify available residual frequency resources and analyze the system throughput. Finally, extensive simulations verify that our model is very accurate and show that ERFR-CTC can increase the system throughput by up to 51.4%.

An Improved TCP Vegas Model for the Space Networks of the Bandwidth Asymmetry

An Improved TCP Vegas Model for the Space Networks of the Bandwidth Asymmetry

An Improved TCP Vegas Model for Space Networks of the Bandwidth Asymmetry

An Improved TCP Vegas Model for Space Networks of the Bandwidth Asymmetry

Theory of the spin-filtering effect in ferromagnet/ferromagnetic insulator/superconductor junctions

Although it is well known that the ferromagnetic insulator at the interface of the superconducting junctions works as a spin-filter, its detailed mechanism has not yet been clarified. Here we present a simple factor inducing the spin-filtering effect in ferromagnet/ferromagnetic insulator/superconductor junctions by applying the extended Blonder-Thinkham-Klapwijk theory. From the factor, one can see easily how the spin-filtering effect is induced by the ferromagnetic insulator. Furthermore, it is also shown that the spin-filtering effect can be caused only by ferromagnet without ferromagnetic insulator. As an interesting application, we study the spin-filtering effect for a chiral p-wave superconductor. In ferromagnet/insulator/chiral p-wave superconductor junction, we find that the zero-bias conductance peak is shifted in opposite bias-voltage directions for Stoner model and spin bandwidth asymmetry ferromagents. It is also shown that the additional shift by ferromagnetic insulator may be useful for identifying the dominant mechanism of the Stoner and spin bandwidth asymmetry mixed ferromagnet.

Impact of Frame Duration and Modulation Coding Schemes With WiMAX Bandwidth Asymmetry in Transmission Control Protocol Variants

WiMAX stands for Worldwide Interoperability for Microwave Access which is based on IEEE 802.16 specification and is considered as de facto standard for the broadband wireless data transfer over the internet. The different values of various WiMAX parameters for different TCP variants may affect the performance of the network. This article compares the performance of different TCP variants with bandwidth asymmetry, frame duration, and modulation coding schemes, along with the operating parameter namely number of wireless nodes. During the simulation study the performance was evaluated only for one-way data transfer. The finding suggests that the TCP New Reno performed better than other variants included in the simulation study for the comparison. The performance was measured on the basis of throughput, goodput and packets dropped.

FRUDP: A Reliable Data Transport Protocol for Aeronautical Ad Hoc Networks

In this paper, we cope with the reliable and efficient data transfer problem in aeronautical ad hoc networks (AANETs). AANETs are different from terrestrial ad hoc networks and these distinctions feature AANETs with large propagation delay, highly dynamic network topology, and high error probability, which pose many new challenges for data transfer in such environments. In this paper, we propose a protocol, called FRUDP, which combines reliable UDP and fountain code to achieve reliable and efficient data transfer in AANETs. It employs Raptor codes to recover from data losses to mitigate retransmission caused by high channel losses in AANETs. A code rate determining algorithm is developed to estimate the redundancy on the fly by taking into full consideration the time-varying aeronautical network conditions. Moreover, the improved selective negative acknowledgment scheme is utilized to solve the bandwidth asymmetry problem in AANETs and a congestion control scheme is deployed to decouple congestion decisions from packet losses in order to avoid the erroneous congestion decisions due to frequent link handoffs. The proposed FRUDP is fully implemented directly on top of UDP in Linux and examined over a variety of emulation network environments. The experimental results show that FRUDP is suitable for reliable and efficient data transfer service in AANETs.

POEM: Minimizing Energy Consumption for WiFi Tethering Service

Despite the rapidly increasing number of public WiFi hotspots, their coverage is still limited to indoor and office/business environments. WiFi tethering is thus a useful and economic means of providing on-the-go mobile users’ Internet connection. One of the main problems of WiFi tethering is the excessive power consumption of mobile access points (APs), or tethered smartphones. Since the power-saving mechanism, defined and deployed in the IEEE 802.11 standard, is intended for clients only, the WiFi interface of a mobile AP never enters the sleep mode. In this paper, we propose a simple but effective system, called power-efficient mobile (POEM), which reduces energy consumption of a mobile AP by allowing its WiFi interface to sleep even during data transfer. The POEM exploits the inherent bandwidth asymmetry between the WiFi and the WWAN interfaces of a mobile AP by buffering the data packets received via the WWAN interface at the mobile AP, thereby allowing the WiFi interface to enter the sleep mode. Compared with the other power-saving solutions for WiFi tethering, the POEM is able to handle various types of applications, such as video steaming and file download, designed to support legacy clients (i.e., clients without POEM), and is also efficient in reducing the clients’ energy consumption. We have implemented and conducted an extensive evaluation of the POEM’s effectiveness in an android/linux-based test bed. Our experimental results show that the POEM can allow the WiFi interface of a mobile AP to sleep for up to 90% of the total transfer time without significantly affecting system throughput or end-to-end delay.

Satellite-TCP: A Flow Control Algorithm for Satellite Network

Objective: In this world of advanced technology, satellite communication is the basis for all data communications. TCP was designed to be flexible and robust but it cannot perform efficiently over the satellite links with long delay. The major objective of our work is to propose a novel flow control algorithm for satellite network to prevent the heavy degradation in the network performance due to long propagation delay, high bit error rate and bandwidth asymmetry. Methods: A strong flow control mechanism is necessary to eliminate the network performance degradation due to the satellite link characteristics like long propagation delay, high bit error rate and bandwidth asymmetry. Satellite-TCP is a flow control mechanism based on the negative acknowledgement strategy and connection splitting. The satellite link utilization is monitored and the active connections are assigned with the window values. The window values were considered as it can easily reflect the available bandwidth in the satellite links. Findings: The major problems affecting the performance in satellite links are long propagation delay, high bit error rate and bandwidth asymmetry. The proposed Flow Control Algorithm called Satellite-TCP is based on controlling the flow of Negative Acknowledgement packets (NACK), according to the level of congestion at the network. The two main modules in the proposed system include an enhanced TCP flow control mechanism and a data loss recovery mechanism. Among this the flow control is based on link utilization measurements and throughput calculation techniques. Data loss recovery strategy is based on Negative Acknowledgements coming from the receiver side. In this way, we can decrease the amount of packet loss in the network and even eliminate the packet loss, sometimes. Satellite-TCP adopts a window growth strategy to accelerate the speed of increase in the size of congestion window. The flow control mechanism not only enhanced the throughput of forward link but also greatly reduced the bandwidth occupancy rate in back-ward link in the satellite network. This in turn increases the overall performance of the satellite link. Improvements: If we add a priority based strategy to the new flow control mechanism, it can judge the network performance according to the data loss. Moreover we are expecting that, if we add a priority bit based strategy to the new flow control mechanism, it will help to distinguish the specific reasons for data loss and can take corresponding flow control strategies. While considering the throughput and loss rate, Satellite –TCP is showing excellent performance in the case of forward link but it performs poor in the case of backward link. So we are planning to extend our work in such a way that it will perform well in the case of backward link also.

A New Transmission Control Protocol for Satellite Networks

According to technical statistics, current TCP protocols with approximately 80% Internet applications run on perform very well on wired networks. However, due to the effects of long propagation delay, great band- width asymmetry, high sporadic Bit Error Rate (BER) and etc., TCP performance degrades obviously on the satellite communication networks. To avoid the problems, TP-S, a novel transport control protocol, is introduced for satellite IP networks. Firstly, in order to increase the increment speed of Congestion Window (cwnd) at the beginning of data transmission, the traditional Slow Start strategy is replaced by a new strategy, known as Super Start. Secondly, a new packet lost discriminated scheme based on IP packets alternately sending with different priority is used in the protocol to decouple congestion decision from errors. Thirdly, bandwidth asymmetry problem is avoided by adopting Modified NACK (M-NACK) in receiving ends, which is sent periodically. In addition, the sending strategy in routers is also modified along with others changes to support the protocol. Finally, the simulation experiments show that the new protocol can not only significantly enhance throughput performance, but also reduce sharply bandwidth used in the reverse path as compared with traditional TCP protocols and those protocols, which are recently proposed for satellite IP networks.

Josephson effect in S/F/S junctions: Spin bandwidth asymmetry versus Stoner exchange

We analyze the dc Josephson effect in a ballistic superconductor/ferromagnet/superconductor junction by means of the Bogoliubov--de Gennes equations in the quasiclassical Andreev approximation. We consider the possibility of ferromagnetism originating from a mass renormalization of carriers of opposite spin, i.e., a spin bandwidth asymmetry. We provide a general formula for Andreev levels that is valid for arbitrary interface transparency, exchange interaction, and bandwidth asymmetry, and we analyze the current-phase relation, free energy, and critical current in the short junction regime. We compare the phase diagrams and the critical current magnitudes of two identical junctions differing only in the mechanism by which the midlayer becomes magnetic. We show that a larger number of $0\ensuremath{-}\ensuremath{\pi}$ transitions caused by a change in junction width or polarization magnitude is expected when ferromagnetism is driven by spin bandwidth asymmetry compared to Stoner magnetism. Moreover, we show that these features can be present also for ferromagnets of the Stoner type having only a partial bandwidth asymmetry.

Intrinsic limitations to the quality of pulsed spontaneous parametric downconversion sources for quantum information applications

Spontaneous parametric downconversion (SPDC) sources are an essential element of quantum communication and quantum information processing systems. Their quality can be hampered by spectral, temporal, or spatial distinguishability of the two photons of a generated pair. Even when such defects have been corrected, the ultimate quality of the SPDC source is limited by the intrinsic multiple pair generation. In this paper, the effect of transmission, filtering and detection losses and asymmetrical spectral bandwidths in the photon pair paths on the visibility of the two-photon interference delivered by the SPDC source and its useful pair rate are investigated. In this investigation, two subcases are distinguished: deterministic and statistical splittings of the generated pairs, whatever the coherence of the multiple pairs. We show that the visibility is strongly degraded by a spectral bandwidth asymmetry, while the losses mainly affect the measured coincidence probability. The deterministic splitting configuration is shown to be generally more advantageous, although statistical splitting may present some advantages in applications with a narrow bandwidth requirement, such as those involving quantum memories. Moreover, while pump-induced optical noise only produces small visibility reductions, dark counts of the single-photon detectors are shown to limit the maximum possible visibility, particularly in the case of high-loss photon pair sources. Because our model quantifies the intrinsic limitations due to double pair emission in a simple way, the results presented can be used to optimize the design of SPDC sources and choose the optimum trade-offs between several key parameters such as visibility, generation probabilities, and spectral bandwidth, in particular for small bandwidth SPDC sources in the perspective of quantum networking and computing applications.

Charge and spin transport through a ferromagnet/insulator/unconventional superconductor junction

We analyze the charge and spin transport through a ballistic ferromagnet/insulator/superconductor junction by means of the Bogoliubov-de Gennes equations. For the ferromagnetic side we assume that ferromagnetism may be driven by an unequal mass renormalization of oppositely polarized carriers, i.e. a spin bandwidth asymmetry, and/or by a rigid splitting of up-and down-spin electron bands, as in a standard Stoner ferromagnet, whereas the superconducting side is assumed to exhibit a d-wave symmetry of the order parameter, which can be pure or accompanied by a minority component breaking time-reversal symmetry. Several remarkable features in the charge conductance arise in this kind of junction, providing useful information about the mechanism of ferromagnetism in the ferromagnetic electrode, as well as of the order parameter symmetry in the superconducting one. In particular, we show that when a time-reversal symmetry breaking superconductor is considered, the use of the two kinds of ferromagnet mentioned above represents a valuable tool to discriminate between the different superconducting mixed states. We also explain how this junction may mimic a switch able to turn on and off a spin current, leaving the charge conductance unchanged, and we show that for a wide range of insulating barrier strengths, a spin bandwidth asymmetry ferromagnet may support a spin current larger than a standard Stoner one.

Does a ferromagnet with spin-dependent masses produce a spin-filtering effect in aferromagnetic/insulator/superconductor junction?

We analyze charge transport through a ballistic ferromagnet/insulator/superconductorjunction by means of the Bogoliubov–de Gennes equations. We take into account thepossibility that ferromagnetism in the first electrode may be driven by a massrenormalization of oppositely polarized carriers, i.e. by a spin bandwidth asymmetry, ratherthan by a rigid splitting of up- and down-spin electron bands as in a standard Stonerferromagnet. By evaluating the averaged charge conductance for both an s- and adx2 − y2-wave order parameter for the S side, we show that the mass mismatch in the ferromagneticelectrode may mimic a spin active barrier. Indeed, in the s-wave case we show that undersuitable conditions the spin-dependent conductance of minority carriers below the energy gapΔ0 can be larger than for majority carriers, and lower aboveΔ0. On the otherhand, for a dx2 − y2-wave superconductor similar spin-dependent effects give rise to an asymmetric peaksplitting in the conductance. These results suggest that the junction may work as aspin-filtering device.

A New Transmission Control Protocol for Satellite Networks

According to technical statistics, current TCP protocols with approximately 80% Internet applications run on perform very well on wired networks. However, due to the effects of long propagation delay, great bandwidth asymmetry, high sporadic Bit Error Rate (BER) and etc., TCP performance degrades obviously on the satellite communication networks. To avoid the problems, TP-S, a novel transport control protocol, is introduced for satellite IP networks. Firstly, in order to increase the increment speed of Congestion Window (cwnd) at the beginning of data transmission, the traditional Slow Start strategy is replaced by a new strategy, known as Super Start. Secondly, a new packet lost discriminated scheme based on IP packets alternately sending with different priority is used in the protocol to decouple congestion decision from errors. Thirdly, bandwidth asymmetry problem is avoided by adopting Modified NACK (M-NACK) in receiving ends, which is sent periodically. In addition, the sending strategy in routers is also modified along with other’s changes to support the protocol. Finally, the simulation experiments show that the new protocol can not only significantly enhance throughput performance, but also reduce sharply bandwidth used in the reverse path as compared with traditional TCP protocols and those protocols, which are recently proposed for satellite IP networks.

Stability and throughput of FAST transfer control protocol traffic in bi-directional connections

FAST TCP is a promising new transfer control protocol developed for high-speed long-latency networks, whose performance has previously only been studied for data traffic sent in one direction. In this study, the authors propose a mathematical model for bi-directional connections using the FAST TCP protocol, which captures the asymmetric bandwidth dynamics in duplex dumbbell networks, prevalent in ADSL, satellite and other high-speed technologies. Using this model, the authors obtain a powerful result that the queue delays observed by opposite FAST TCP flows only have a time difference in a dumbbell network. Furthermore, the authors establish the conditions under which the bi-directional FAST TCP flows achieve stability, and on this basis the throughput rates of the forward and backward flows at steady-state are deduced. The authors find that, in the case of bandwidth asymmetry and one flow in each direction, in equilibrium the throughput of the bi-directional FAST TCP flows can only achieve the smaller link capacity of the duplex links, and the link with larger capacity is not fully occupied. These theoretical findings are corroborated by NS2 simulations.

TP-Satellite: A New Transport Protocol for Satellite IP Networks

As a result of the exponential growth of the worldwide Internet, satellite systems are used to support broadband Internet access. Existing TCP protocols perform very well for Internet access on wired networks. However, in the case of satellite channels, due to the effects of high bandwidth asymmetry, long propagation delay, high sporadic bit error rate (BER) and burst errors, TCP performance degrades significantly. In this paper, a new end-to-end transport protocol, TP-Satellite, is proposed for satellite IP networks. TP-Satellite replaces the traditional slow start algorithm with a novel super start algorithm. In order to distinguish congestion events from link errors, a new scheme is introduced, which is based on alternate transmission of different class priority packets. Bandwidth asymmetry problems are addressed by the adoption of a modified negative acknowledgement (M-NACK) strategy, which periodically sends M-NACK packets. Simulation results show that TP-Satellite enhances the throughput performance on the forward path, reduces the bandwidth used in the reverse path, and offers a fair share of network resources.

Bandwidth Reallocation for Bandwidth Asymmetry Wireless Networks Based on Distributed Multiservice Admission Control

This paper addresses when and how to adjust bandwidth allocation on uplink and downlink in a multi-service mobile wireless network under dynamic traffic load conditions. Our design objective is to improve system bandwidth utilization while satisfying call level QoS requirements of various call classes. We first develop a new threshold-based multi-service admission control scheme (DMS-AC) as the study base for bandwidth re-allocation. When the traffic load brought by some specific classes under dynamic traffic conditions in a system exceeds the control range of DMS-AC, the QoS of some call classes may not be guaranteed. In such a situation, bandwidth re-allocation process is activated and the admission control scheme will try to meet the QoS requirements under the adjusted bandwidth allocation. We explore the relationship between admission thresholds and bandwidth allocation by identifying certain constraints for verifying the feasibility of the adjusted bandwidth allocation. We conduct extensive simulation experiments to validate the effectiveness of the proposed bandwidth re-allocation scheme. Numerical results show that when traffic pattern with certain bandwidth asymmetry between uplink and downlink changes, the system can re-allocate the bandwidth on uplink and downlink adaptively and at the same time improve the system performance significantly.

Coexistence of strong pairing correlations and itinerant ferromagnetism arising from spin asymmetric bandwidths: A reduced BCS model study

We investigate the conditions for the occurrence of the coexisting phases that exhibit singlet superconductivity and itinerant ferromagnetism arising from spin asymmetric bandwidths. The exact solution for a reduced BCS pairing model with spin dependent bandwidths is used to determine the ground-state diagram as a function of the coupling parameter, the total density, and the topology of the single-particle spectrum. A spin-polarized superconducting state is obtained in the regime of large pair couplings with a strong bandwidth asymmetry. The analysis reveals that, for such a type of ferromagnetism, small (large) values of the density of states at energies close to the edges of the band enhance (hinder) the tendency toward a coexistence of strong pairing correlations and finite spin polarizations.

Proximity effect between an unconventional superconductor and a ferromagnet with spin bandwidth asymmetry

We study the proximity effect within a junction made of an unconventional superconductor (US) and a ferromagnet $(F)$ in the clean limit with high barrier transparency. Superconductivity in the US side is described by an extended Hubbard model with intersite attractive interaction, while metallic ferromagnetism in the $F$ side is assumed to be originated by a relative change in the bandwidths of electrons with opposite spin. The effect of this mass-split mechanism is analyzed in conjunction with the usual Stoner-like one, where one band is rigidly shifted with respect to the other, due to the presence of a constant exchange field. Starting from the numerical solution of the Bogoliubov-de Gennes equations, we show that the two above mentioned mechanisms for ferromagnetism lead to different features as concerns the formation at the interface of dominant and subdominant superconducting components, as well as their propagation in the ferromagnetic side. This considerably affects the opening of gaplike structures in the local density of states for majority and minority spin electrons, leading to distinct effects as one moves toward the half-metallic regime, where the density of the minority carriers becomes vanishing.

Optimizing Admission Control for Multiservice Wireless Networks With Bandwidth Asymmetry Between Uplink and Downlink

Next-generation wireless networks need to support multiclass services with asymmetric bandwidth allocation between uplink and downlink to match the asymmetric traffic load brought by some data services. For the design of call admission control (CAC) policy in such networks, how to decrease the average system cost is a key issue. In this paper, we study the optimal admission policy for minimizing the system cost. We consider the CAC problem as a decision process. By modeling the admission control problem into a Markov decision process (MDP) and analyzing the corresponding value function, we obtain some monotonicity properties of the optimal policy. These properties suggest that the optimal admission control policy for the bandwidth asymmetry wireless networks should have a threshold structure and the threshold specified for a class of calls may change with the system state. Due to the prohibitively high complexity for computing the thresholds in a system with large state-space, we propose a heuristic CAC policy called call-rate-based dynamic threshold (CRDT) policy to approximate the theoretical optimal policy based on the insights we obtain from the modeling and the analytical study on the properties of the optimal policy. The CRDT policy is efficient and can be easily implemented. The numerical results show that the performance of average system cost of the proposed CRDT policy is close to that of the optimal policy from the MDP model and is better than that of some known existing CAC schemes, including those performing well in bandwidth asymmetry wireless networks