This paper presents a history of the IPFIX working group, from initial chartering through development and testing, re-chartering and further development, and looking ahead to future developments. As a standardised way of exporting information about traffic flows, IPFIX has attracted a growing number of implementors, who have continued to develop it in useful ways without changing its underlying architecture. This makes it a good example of how to develop a new technology. Further, it demonstrates widespread recognition of the importance of network measurement in the development, deployment and production stages of networks and the applications that depend on them.

抄録全体を表示

Packet pacing is a well-known technique for reducing the short-time-scale burstiness of traffic, and software-based packet pacing has been categorized into two approaches: the timer interrupt-based approach and the gap packet-based approach. The former was originally hard to implement for Gigabit class networks because it requires the operating system to handle too frequent periodic timer interrupts, thus incurring a large overhead. On the other hand, a gap packet-based packet pacing mechanism achieves precise pacing without depending on the timer resolution. However, in order to guarantee the accuracy of rate control, the system must be able to transmit packets at the wire rate. In this paper, we propose a high-resolution timer-based packet pacing mechanism that determines the transmission timing of packets by using a sub-microsecond resolution timer. The high-resolution timer is a light-weight mechanism compared to the traditional low-resolution periodic timer. With recent progress in hardware protocol offload technologies and multicore-aware network protocol stacks, we believe high-resolution timer-based packet pacing has become practical. Our experimental results show that the proposed mechanism can work on a wider range of systems without degrading the accuracy of rate control. However, a higher CPU load is observed when the number of traffic classes increases, compared to a gap packet-based pacing mechanism.

抄録全体を表示

This paper proposes ladder-logic programming model for sensor actuator networks. We also demonstrate optimized operations of them with central controller-based device management (CCDM) architecture. A wireless sensor actuator network consists of distributed wireless nodes, and implementing data streams and data processors onto these wireless nodes has been challenging. System programmers have to describe their instructions by a programming language, and data processors must be placed so that it optimizes, for example, total network traffic. The ladder-logic model enables the programming of them, and CCDM makes various types of optimizations feasible, including the optimization of network traffic, delivery latency, load-balancing and fault-tolerance even though these algorithms are not lightweight. In this paper, we focus on traffic reduction case, and propose two moderately complex algorithms. The experiment has shown that CCDM achieves optimizations even with such moderately complex algorithms.

抄録全体を表示

In future mobile networks, the ever-increasing loads imposed by mobile Internet traffic will force the network architecture to be changed from hierarchical to flat structure. Most of the existing mobility protocols are based on a centralized mobility anchor, which will process all control and data traffic. In the flat network architecture, however, the centralized mobility scheme has some limitations, such as unwanted traffic flowing into the core network, service degradation by a single point of failure, and increased operational costs, etc. This paper proposes mobility schemes for distributed mobility control in the flat network architecture. Based on the Proxy Mobile IPv6 (PMIP), which is a well-known mobility protocol, we propose the three mobility schemes: Signal-driven PMIP (S-PMIP), Data-driven Distributed PMIP (DD-PMIP), and Signal-driven Distributed PMIP (SD-PMIP). By numerical analysis, we show that the proposed distributed mobility schemes can give better performance than the existing centralized scheme in terms of the binding update and packet delivery costs, and that SD-PMIP provides the best performance among the proposed distributed schemes.

抄録全体を表示

In existing systems of mobile routers, the frequency band is shared in uplinks from wireless terminals to mobile routers, and carrier sense multiple access with collision avoidance (CSMA/CA) is generally used as the medium access control protocol. To use the frequency band effectively, adaptive control is one promising approach. In this paper, a decentralized access control protocol in which mobile routers adaptively select the minimum contention window size is proposed. However, because of their mobility, which is one of the main difference between mobile routers and fixed access points, individual local area networks (LANs) consisting of the mobile routers and wireless terminals randomly interact with each other, and such random interactions can cause instability. To analyze the stability of the proposed control, evolutionary game theory is introduced because a system with random interactions between numerous decision-making entities can be analyzed by using evolutionary game theory. Using evolutionary game theory, the condition for existence of a convergence point is obtained. In addition, to implement the decentralized access control, a learning rule is proposed. In the proposed learning rule, each mobile router selects a strategy based on the result of past trials. From the simulation result, it is confirmed that the decentralized access control converges to a point closed to the stable state derived through evolutionary game theory.

抄録全体を表示

The VoIP-based Internet Phonesystem is now seen as one of the killer applications in the high speed and broadband internet environment. Given the wide-spread use of the Internet Phone, it is necessary to provide security services for guaranteeing users' privacy. However, providing security service in Internet Phone has the possibility of incurring additional overheads such as call setup delay time. In this paper, we present a one-way key agreement model based on VoIP in order to reduce call setup time as well as protecting user privacy. The proposed approach decreases the delay time of the call setup in comparison with the previous models because our model enables the key generation in caller side without waiting the response from the receiver.

抄録全体を表示

Detecting distributed anomalies rapidly and accurately is critical for efficient backbone network management. In this letter, we propose a novel anomaly detection method that uses router connection relationships to detect distributed anomalies in the backbone Internet. The proposed method unveils the underlying relationships among abnormal traffic behavior through closed frequent graph mining, which makes the detection effective and scalable.

抄録全体を表示

In this letter, we propose a simple but effective buffer management scheme to achieve fair bandwidth sharing with a FIFO scheduling algorithm, that is, Dynamic Detection and Expulsion (DDE). The DDE scheme dynamically detects buffer occupancy and then precisely expels resided packets on demand through simple comparisons. Simulation results under various traffic conditions show that DDE can arrive at more robust and better fairness, and lower implementation complexity than that of a well-known Pushout (PO) scheme.

抄録全体を表示

The processor-sharing (PS) rule arises as a natural paradigm in a variety of practical situations, including time-shared computer systems. Although there has been much work on Poisson-input queueing analysis for the PS rule, there have been few results for renewal-input GI/G/1 (PS) systems. We consider the GI/G/1 (PS) system to provide develop a two-moment approximation for the mean performance measures. We derive the relationship between the mean unfinished work and the conditional mean sojourn time for the GI/G/1 (PS) system. Using this relationship, we derive approximate formulas for the mean conditional sojourn time, mean sojourn time, and the mean number of customers in the GI/G/1 (PS) system. Numerical examples are presented to compare the approximation with exact and simulated results. We show that the proposed approximate formulas have good accuracy.

抄録全体を表示

Wireless Sensor Networks (WSNs) are gradually moving toward the adoption of clustered heterogeneous designs, incorporating a mixture of variety kinds of sensor nodes with different radio coverage and battery capacity. Compared with homogeneous networks, heterogeneous networks are able to reduce the initial cost of the network or prolong the network lifetime. The architecture and routing protocol for this type of heterogeneous WSN should be energy aware in order to prolong the lifetime of the network. However, most of the existing clustering methods consider only initial energy of the sensor nodes and ignore the non-uniform energy drainage caused by many-to-one traffic near sink and/or cluster heads in heterogeneous network environment. In this paper, we propose a new clustering method for WSN with heterogeneous node types which selects cluster heads considering not only the transmission power and residual energy of each node but also those of its adjacent nodes. Simulation experiments show that the proposed method increases network lifetime by 80% and 60% more than that of the CC and HEED, respectively.

抄録全体を表示

We analyze subjective assessments by comparative evaluations of bulk data transmission by using two psychological methods (the method of successive categories and the constant method). From the results of the first experiment, the thresholds at which participants downloading a data file began to feel dissatisfaction with service degradation are 15.7Mbps and 11.6Mbps obtained by the two different methods when the throughput without the service degradation is approximately 22Mbps. In the second experiment, we investigate the threshold of user satisfaction for various network environments. The threshold is 63% of the throughput of the user's usual network environment. Moreover, from the viewpoint of download time, users feel dissatisfaction with the quality when download time becomes 1.5 times longer. These values can be used to more effectively allocate network resources and thereby achieve higher service quality.

抄録全体を表示

Detecting spreaders, or scan sources, helps intrusion detection systems (IDS) identify potential attackers. The existing work can only detect aggressive spreaders that scan a large number of distinct destinations in a short period of time. However, stealthy spreaders may perform scanning deliberately at a low rate. We observe that these spreaders can easily evade the detection because current IDS's have serious limitations. Being lightweight, the proposed scheme can detect scan sources in high speed networking while residing in SRAM. By theoretical analysis and experiments on real Internet traffic traces, we demonstrate that the proposed scheme detects stealthy spreaders successfully.

抄録全体を表示

We present a new multi-path routing methodology, MLB-routing, that is based on the multinomial logit model, which is well known in the random utility field. The key concept of the study is to set multiple paths from the origin to the destination, and distribute packets in accordance with multinomial logit type probability. Since MLB-routing is pure multi-path routing, it reduces the convergence on some links and increases bandwidth utilization in the network. Unlike existing multi-path routing schemes, which pre-set alternate paths, the proposed method can dynamically distribute packets to every possible path and thus is more efficient. Furthermore, it should be mentioned that this methodology can be implemented as either a link-state protocol or a distance-vector protocol. Therefore, it well supports the existing Internet. Simulations show that this methodology raises network utilization and significantly reduces end-to-end delay and jitter.

抄録全体を表示

Antipodal Fermi antenna (APFA) that uses an antipodal feeding section is proposed and its fundamental characteristics are presented. It is shown that the cross polarization level is decreased by 5-10dB by the presence of the corrugation. It is also found that high gain, low VSWR and low side lobes and low back lobes are obtained. The mechanism of operation principles is discussed by using FDTD analysis. It is found that the corrugation transforms the current of parallel line mode to the current of traveling wave radiation mode and the effective aperture is enlarged which yields high gain characteristics.

抄録全体を表示

This paper presents the initial results of a study of an asymptotic method for calculating the received intensity of multi-path millimeter waves transmitted over an undulating surface. First, an integral expression of the received intensity is derived using a physical optics approximation. Then its zero-th order asymptotic expression is derived, using the Pearcey integral, for the case where the phase function appearing in the integrand can be approximated by a quartic polynomial. A numerical examination made at 59.5GHz showed that the asymptotic method is in good agreement with the physical optics method, even in cases where the geometrical optics method deviates significantly from the physical optics method, and that the range of applicability of the asymptotic method has its upper bound somewhere around a transmission distance to surface undulation wavelength ratio of 2.

抄録全体を表示

A thin electromagnetic band-gap (EBG) absorber is employed to capture the 2-d image of radio-frequency (RF) power distribution. The EBG absorber consists of an array of mushroom unit cells formed on a thin dielectric substrate with a metal backplane, and lumped resistors interconnecting the surface patches of the mushrooms. Around the resonance frequency at which the EBG structure acts as a high-impedance surface, the RF power incident on the surface is absorbed by the lumped resistors which are matched with the incident wave impedance. By detecting directly the amounts of power consumed by the individual resistors, an “RF power imager” can be constructed which captures the 2-d distribution of the RF power illuminating the EBG surface, where polarization discrimination is possible. The resonance (i.e., absorption) frequency is made tunable by adding varactor diodes in parallel with the lumped resistors. The EBG absorber tunable in the frequency range of 700MHz-2.7GHz is designed and fabricated, and its performance is evaluated by an equivalent-circuit analysis, simulation and measurement. It is shown that the small resistance of the varactors have a considerable effect on the absorption performance. RF power distributions radiated from a dipole antenna are successfully measured by a matrix of sensitive power detectors installed on the backside of the absorber. Using such an RF power imager, the power distributions of even impulsive RF signals and/or noises can be captured and visualized in situ and in real-time, while the electromagnetic environment is almost undisturbed by the EBG absorber.

抄録全体を表示

In this paper, we propose precoding and power allocation strategies for full-duplex multiple input multiple output (MIMO) relays. The precoding scheme for full-duplex MIMO relays is derived based on the block diagonalization (BD) method to suppress the self-interference in the full-duplex relaying so that each relay station (RS) can receive multiple data streams from the base station (BS), while forwarding the decoded data streams to mobile stations (MS's) simultaneously. We also develop the optimal power allocation scheme for full-duplex MIMO relays. Numerical results verify that the proposed scheme provides substantial performance improvement compared with the conventional half-duplex relay (HDR), if sufficient physical isolation between the transmit and receive antennas is ensured such that the proposed full-duplex MIMO relays operate in a tolerable self-interference range.

抄録全体を表示

This paper proposes a new resource allocation algorithm for uplink OFDMA-based cooperative relay networks, assuming multiple user nodes, multiple relay nodes and a single destination. The aim is to maximise the total sum of the users' data rates, while guaranteeing fairness among them with different QoS requirements. Assuming perfect channel state information (CSI) at the resource allocation controller, the optimisation problem is formulated such that each user is assigned a weight factor based on its QoS requirements. The ones with higher weights are given higher priorities to select their resources (relay stations and subcarriers) first. Once the required QoS is achieved for all users, the weight factor for all users is reduced to a small uniform value. The remaining resources are then allocated to the users with higher instantaneous rates in order of magnitude. The results show that the proposed algorithm outperforms the greedy and static algorithms in terms of outage probability and fairness, and at the same time outperforms Jeong's algorithm by 58% in terms of total sum rate, with an average 74% reduction in system complexity.

抄録全体を表示

In this article, we study different methods to enhance the capacity of Voice-over-IP (VoIP) in Evolved UTRAN (E-UTRAN) downlink. According to previous E-UTRAN system level simulation results, VoIP capacity with dynamic scheduling and semi-persistent scheduling is limited by available Physical Downlink Control CHannel (PDCCH) resources and Physical Downlink Shared CHannel (PDSCH) resources respectively. The different behavior of these two packet scheduling schemes and specific bottleneck on capacity lead us to formulate two distinctly different performance enhancement strategies, which are the main focus of this paper. For dynamic scheduling, we propose a bi-directional power control algorithm to rationalize PDCCH resource allocation, thus greatly improving VoIP capacity. For semi-persistent scheduling, we introduce Adaptive Transmission Bandwidth (ATB) to rationalize PDSCH resource allocation and further apply dynamic packet bundling in highly-loaded network, thus improving VoIP capacity in a considerable manner. The proposed enhancement methods are validated through large-scale system level simulations and the obtained system simulation results further confirm effectiveness of these enhancement methods.

抄録全体を表示

This paper proposes a low-complexity signal detection algorithm for spatially correlated multiple-input multiple-output (MIMO) channels. The proposed algorithm sets a minimum mean-square error (MMSE) detection result to the starting point, and searches for signal candidates in multi-dimensions of the noise enhancement from which the MMSE detection suffers. The multi-dimensional search is needed because the number of dominant directions of the noise enhancement is likely to be more than one over the correlated MIMO channels. To reduce the computational complexity of the multi-dimensional search, the proposed algorithm limits the number of signal candidates to O(N_T) where N_T is the number of transmit antennas and O() is big O notation. Specifically, the signal candidates, which are unquantized, are obtained as the solution of a minimization problem under a constraint that a stream of the candidates should be equal to a constellation point. Finally, the detected signal is selected from hard decisions of both the MMSE detection result and unquantized signal candidates on the basis of the log likelihood function. For reducing the complexity of this process, the proposed algorithm decreases the number of calculations of the log likelihood functions for the quantized signal candidates. Computer simulations under a correlated MIMO channel condition demonstrate that the proposed scheme provides an excellent trade-off between BER performance and complexity, and that it is superior to conventional one-dimensional search algorithms in BER performance while requiring less complexity than the conventional algorithms.

抄録全体を表示

This paper proposes a resource allocation method based on TCP (Transmission Control Protocol) throughput for base station diversity systems. A goal of this study is to achieve high throughput wireless Internet access by utilizing multiple wireless links effectively.The conventional work showed that base station diversity techniques can improve TCP performance. However, the improvement depends on the wireless environment of the wireless terminal.The proposed resource allocation method allocates wireless links to a wireless terminal based on its estimated TCP throughput and current traffic of each base station. Our method can take account of some network protocols such as TCP and UDP (User Datagram Protocol) by measuring the current traffic of each base station. In addition, wireless links are preferentially assigned to the wireless terminal that has the largest performance improvement per wireless link. Therefore, the proposal provides better overall system performance than the previous technique.

抄録全体を表示

UWB (Ultra Wide-Band) pulse radar is promising for surveillance systems because it has an outstanding high range-resolution. To realize an accurate UWB radar imaging system, we propose a new approach that employs multipath echoes from a target in an indoor environment. Using multipath echoes, the proposed system can accurately estimate images, even for targets in a shadow region where the targets are out of sight of the antenna. We apply a simple interferometry technique using the multiple mirror image antennas generated by multipath propagation. We find that this simple method also produces many undesired false image points. To tackle this issue, we also propose an effective false image reduction algorithm to obtain a clear image. Numerical simulations verify that most of the false image points are removed and the target shape is accurately estimated.

抄録全体を表示

In this letter, we propose a multi-stage decoding scheme with post-processing for low-density parity-check (LDPC) codes, which remedies the rapid performance degradation in the high signal-to-noise ratio (SNR) range known as error floor. In the proposed scheme, the unsuccessfully decoded words of the previous decoding stage are re-decoded by manipulating the received log-likelihood ratios (LLRs) of the properly selected variable nodes. Two effective criteria for selecting the probably erroneous variable nodes are also presented. Numerical results show that the proposed scheme can correct most of the unsuccessfully decoded words of the first stage having oscillatory behavior, which are regarded as a main cause of the error floor.

抄録全体を表示

Reducing the energy consumption of wireless communication systems with new technologies and solutions continues to be an important concern in developing future standards. In this paper, we study the routing strategies in multi-hop relaying networks. For a 2-way assignment routing method, an efficient feedback scheme is presented to minimize the power consumption over the whole system. Compared with the full channel information in traditional feedback scheme, only the backward accumulated feedback metrics are required. If the proposed routing calculation is used, there is no performance loss. When the number of the hops and the relays is large, the new scheme achieves a significant feedback overhead reduction. Moreover, we show a proof for the optimality of the presented routing strategy based on mathematical induction.

抄録全体を表示

Femtocell is considered a promising solution for indoor service enhancement in IEEE 802.16e cellular systems. However, the scanning scheme of IEEE 802.16e is not suitable for direct use in scanning femtocells in terms of efficiency and scan duration. In this paper, we propose an efficient scanning scheme for femtocells in IEEE 802.16e systems. The proposed scheme can achieve a lower scanning overhead by reducing the number of femtocells needed to be scanned. Numerical results show that the proposed scanning scheme can reduce the control message overhead and the scan duration.

抄録全体を表示

Per-flow traffic measurement is essential for network management; billing, traffic engineering, mitigating denial of service attacks, to mention just a few. In this field, the fundamental problem is that the size of expensive SRAM is too small to hold traffic data from high-speed networks. In this paper, we propose a new method for per-flow traffic measurement, which is based on the virtual vector that was originally designed for the problem of spread estimation. We modify the original virtual vector and show that this simple change yields a highly effective per-flow traffic estimator. Experiments show that our proposed scheme outperforms the state-of-the-art method in terms of both processing time and space requirement.

抄録全体を表示

The past decade has seen a surge of research activities in the fields of mobile computing and wireless communication. In particular, recent technological advances have made portable devices, such as PDA, laptops, and wireless modems to be very compact and affordable. To effectively operate portable devices, energy efficiency and Quality of Service (QoS) provisioning are two primary concerns. Dynamic Voltage Scaling (DVS) is a common method for energy conservation for portable devices. However, due to the amount of data that needs to be dynamically handled in varying time periods, it is difficult to apply conventional DVS techniques to QoS sensitive multimedia applications. In this paper, a new adaptive DVS algorithm is proposed for QoS assurance and energy efficiency. Based on the repeated learning model, the proposed algorithm dynamically schedules multimedia service requests to strike the appropriate performance balance between contradictory requirements. Experimental results clearly indicate the performance of the proposed algorithm over that of existing schemes.

抄録全体を表示

In this paper, Transmission Control Protocol/Internet Protocol (TCP/IP) over Stream Control Transmission Protocol (SCTP)/IP parallel transmission system is proposed to realize large TCP/IP throughput. The proposed system enables SCTP/IP connection between switches by protocol stacking. The proposed system is implemented on a software switch to evaluate its performance. The evaluation result indicates that proposed system can achieve 90% throughput compared with serial transmission when the delay difference among parallel routes is 20msec.

抄録全体を表示

A compact antenna capable of generating two wide operating bands to cover the GSM850/900 (824-960MHz) and GSM1800/1900/UMTS (1710-2170MHz) systems is presented. The antenna occupies just 81.5(L)×7(W)×0.5(H)mm³ on the top edge of the supporting metal frame of the display panel, and is therefore easily embedded in the ultra-thin laptop computers as an internal antenna. The antenna is implemented using a ceramic substrate and consists of multi-branch strips. Based on the principle of the inverted-F antenna, our design yields two operating bands covering 816-983MHz and 1703-2196MHz can be achieved with good radiation performance for our design. The proposed antenna is thus suitable to be installed in the ultra-thin laptop computers for Wireless Wide Area Network applications.

抄録全体を表示

We study a joint optimal design of the receive equalizer and relaying architecture in terms of the weighted sum of mean square errors for the multi-user multiple-input multiple-output (MIMO) relaying system. We show that the optimal relaying architecture depends on the weight factors and that conventional diagonal relaying is a special case of the proposed relaying architecture. Interestingly, for unequal weights, it turns out that the optimal relaying is different from the existing diagonal relaying schemes. By simulation, we show that the proposed joint design improves the weighted sum of mean square error (MSE) over the existing MIMO relaying schemes.

抄録全体を表示

This paper introduces a random selection cooperation scheme that takes the Decode-and-Forward (DF) approach to solve the unfairness problem in selection cooperation. Compared to previous work which obtained fairness but introduced performance loss, the proposed scheme guarantees fairness without performance loss. Its essence is to randomly select from the relays that can ensure the successful communication between the source and the destination, rather than to select the best relay. Both a theoretical analysis and simulation results confirm that the proposed scheme could achieve fairness and introduce no performance loss. We also discuss the conditions under which the proposed scheme is practical to implement.

抄録全体を表示

A new transmission scheme for OFDM systems that uses the odd discrete Fourier transform to provide frequency diversity gain is proposed. Odd DFT allows the transmission of data subcarriers in frequencies that are centred between those employed by the traditional DFT. This fact is exploited to transmit data subcarriers on the group of frequencies that gives better performance using either traditional DFT or odd DFT. As an example, by using this approach a diversity gain up to 5.3dB at a BER of 10^-4 in a typical indoor channel model can be achieved.

抄録全体を表示

In this letter, a study on the end-to-end outage performance of dual-hop non-regenerative relaying in the presence of co-channel interference is presented. We assume that both the desired and the interfering signals are subjected to Nakagami-m fading. Exact analytical expressions, as well as tight lower bounds of the end-to-end outage probability, are derived. An asymptotic expression for the outage probability at high values of Signal-to-Interference Ratio is also presented. Furthermore, we also propose the optimal power allocation for high values of Signal-to-Interference Ratio. Extensive numerically evaluation and computer simulation results are presented to verify the validity and the accuracy of the proposed analysis.

抄録全体を表示

In this letter, we derive another exact bit error rate (BER) for decode-and-forward (DF) relay systems over Rayleigh fading channels. At first, our focus is on fixed-DF (FDF) relay schemes in which the probability density function (PDF) is derived based on error-events at relay nodes. Some insight into how erroneous detection and transmission at relay nodes affect both the combined signal-to-noise ratio (SNR) and the averaged BER is obtained, and cooperative diversity is observed from the closed-form BER expression. In addition, the developed analytical method is extended to adaptive-DF (ADF) schemes and the exact BER expressions are derived. Simulation results are finally presented to validate the analysis.

抄録全体を表示

In this letter, we investigate the Nth-best user selection scheme for amplify-and-forward cooperative systems over Rayleigh fading channels. We deduce the probability density function, the cumulative density function, and the moment generating function of the end-to-end signal-to-noise ratio of the system. Then, the respective closed-form expressions of the average symbol error probability and the outage probability at the destination are derived. The diversity order obtained in the scheme increases with user number but becomes less as the selection sequence number N increases. Simulation results verify the analytical results.

抄録全体を表示

In this paper, a new power control scheme is proposed to maximize the network throughput with fairness provisioning. Based on the Stackelberg game model, the proposed scheme consists of two control mechanisms; user-level and system-level mechanisms. Control decisions in each mechanism act cooperatively and collaborate with each other to satisfy efficiency and fairness requirements. Simulation results demonstrate that the proposed scheme has excellent network performance, while other schemes cannot offer such an attractive performance balance.

抄録全体を表示

In this letter, we propose two low complexity algorithms for least square (LS) and minimum mean square error (MMSE) based multi-cell joint channel estimation (MJCE). The algorithm for LS-MJCE achieves the same complexity and mean square error (MSE) performance as the previously proposed most efficient algorithm, while the algorithm for MMSE-MJCE is superior to the conventional ones, in terms of either complexity or MSE performance.

抄録全体を表示

Multiple-attribute based handoff schemes suffer from instability because of the dynamic nature of attributes and the distribution of handoff procedure over candidate networks, resulting in frequent handoffs that degrade the efficiency of resource management. To alleviate such instability, a service-history based scheme was proposed but it has several improper design decisions, e.g. it considers the history factors too optimistically and employs fixed weights that are likely to distort handoff decisions. This letter proposes to improve handoff performance by considering network state along with the service history. It takes into account the network utilization to avoid the optimistic dependency on the history and adaptively determines the weight to the service history in order to adjust its effect on the handoff decision. Simulation results show that the proposed scheme optimizes the number of handoff and the dropping probability when compared with existing schemes.

抄録全体を表示

In this letter, we focus on the spectrum sharing cognitive radio system, wherein a single-input multi-output cognitive fading channel is considered. Subject to the joint average interference constraint and peak interference constraint at the primary receiver, the outage capacity of the cognitive channel involving joint beamforming and power control is analyzed. We derive the optimal beamforming and power control strategy and deduce the closed-form expression for the outage capacity under Rayleigh fading model, the functional regions of two kinds of interference constraints are discussed as well. Furthermore, considering zero-outage transmission, we investigate the delay-limited capacity and introduce a new concept called the zero-outage average interference wall. Extensive simulations corroborate our theoretical results.

抄録全体を表示