Due to the requirement of establishing several independent links, multi-device multi-path beamforming (BF) training becomes rather time-consuming in 60-GHz millimeterwave communications. To reduce training overhead, a novel BF training scheme is proposed in this paper. The scheme includes a simultaneous training strategy for multiple devices and multiple paths, and a corresponding multi-path beam-pair detection algorithm. The training pilot of the source device is broadcasted to all destination devices. Subsequently, in each destination device, the proposed detection is separately conducted to detect significant-path-related beam pairs from the channel responses, via exploiting the time resolvability and space sparsity of physical paths. Finally, the training results are successively fed back to the source device. The proposed scheme achieves simultaneous training of multiple devices and multiple paths, and obtains significant reduction of overhead. Comprehensive simulations are presented to verify the effectiveness of this scheme.

Owing to the requirement of power‐hungry ultra‐high‐speed analogue‐to‐digital converters (ADCs), 60 GHz wireless local area network systems face the challenge of high energy consumption in idle listening (IL). To cope with this problem, a 1 bit‐sampling IL (1BS‐IL) scheme is proposed in this paper. This scheme includes a mixed 1/ M ‐bit‐sampling receiver, and a corresponding packet detection algorithm termed 1BS generalised likelihood ratio test (1BS‐GLRT). The receiver enables packet detection in IL with a 1 bit ADC, which considerably lowers down the energy consumption; besides, the 1BS‐GLRT algorithm guarantees promising performance on packet detection. Once detecting the arrival of a packet, the receiver switches to an original multi‐bit sampling precision, that is, M ‐bit, ADC to demodulate the packet, which maintains the demodulation performance. Comparisons show that 1BS‐IL not only significantly reduces energy consumption, but also achieves competitive detection performance.

Groups of people with mobile phones using short-range connections such as WiFi and Bluetooth to propagate messages can be modeled as, with regard to regular absence of end-to-end connection, mobile social networks (MSNs), which can be exploited to offload a significant amount of mobile content from the overloaded infrastructure networks such as 3G. The study of content transmission delay for the applications of mobile content dissemination in MSNs is an important problem, because to enhance the network capacity, the traffic is offloaded at the cost of inducing longer delay. In contrast to existing works, which ignore the factors of contact duration limits and large content size, we present a contact duration aware framework to model the content dissemination process in MSNs, give an explicit expression for the average content dissemination delay, and reveals its relationship with various system parameters of content size, users' selfishness, number of involved subscribers, infecting ratio, and so on. We apply our proposed model to real-life traces to assess its reliability by comparing the theoretical results with measured statistics and present extensive upshots to evaluate the influence of various parameters on system performance. The results demonstrate the accuracy of our proposed framework and reveal that system parameters of content size, system infecting ratio and intragroup transmission are the most important factors to influence the content dissemination delay.

Various network optimization and management goals in cloud data centers can be achieved by re-mapping VMs to the substrate servers. Live VM migration is used to implement such re-mapping by moving VMs from the initial servers to the target ones. For efficiency and usability considerations, these migration tasks are expected to be completed as soon as possible, which can be achieved by planning multiple VMs to be migrated simultaneously. However, the available resources of computation and bandwidth limits the number of VMs that can be migrated at the same time. Besides, the available resources change with the progress of migration process, which makes VM migration planning a challenge problem. Considering both resources constraints and the dependence between the migration plan and the total migration time, in this paper, we investigate the problem of virtual machine migration planning to minimize the total migration time. We formulate VM migration planning as an optimization problem considering both computation and bandwidth constraints. Our formulation is based on a step-by-step migration scheme, where multiple VMs can be migrated simultaneously as long as the resource constraints are satisfied. The solution of the optimization problem outputs the migration plan which achieves the minimum time to finish the migration task. Moreover, we verify the effectiveness of the optimal migration plan through extensive simulations and comparison with the best algorithm in existing works.

With the emerging demands for extensive mobile applications, Device-to-Device (D2D) communication is viewed as an important technology for the next-generation cellular communication and mobile networks to increase spectral efficiency and enhance network capacity. Existing works usually study D2D communications under a network consisting of four nodes. In this paper, we jointly investigate the problems of optimal system resource allocation and mode selection for large scale networks. Specifically, by formulating a max-flow optimization problem that maximizes the system throughput through any possible of transmission modes with the decisions of resource allocations, we obtain the optimal system performance. Under realistic scenario driven simulations, we demonstrate the efficiency of our proposed scheme for combined mode selection and resource allocation.

Due to the requirement of power-hungry multi-Gsps analog-to-digital converters (ADCs), 60-GHz wireless local-area network (WLAN) systems face the challenge of high power consumption in idle listening (IL). To cope with this problem, a 1-bit-sampling IL (1BS-IL) scheme is proposed in this paper. This scheme includes a mixed 1/M-bit-sampling receiver, and a corresponding packet detection algorithm termed 1-bit-sampling generalized likelihood ratio test (1BS-GLRT). The receiver enables packet detection in IL with a 1-bit ADC, which considerably lowers down the power consumption; besides, the 1BS-GLRT algorithm guarantees promising performance on packet detection. Once detecting the arrival of a packet, the receiver switches to an original sampling precision (i.e., M-bit) ADC to demodulate the packet, which maintains the demodulation performance. Comparisons show that 1BS-IL not only significantly reduces power consumption, but also achieves competitive detection performance.

Multicast services are highly desirable in 60-GHz millimeter-wave communications, but multicast beamforming remains a challenge due to special structure of high frequency system. To solve this problem, a transmit and receive multicast beamforming scheme has been proposed in this paper. Unlike conventional multicast models in LTE/EMBMS, every device in proposed system is equipped with a multi-antenna array, which helps enhance beam directivity and reduce interference. Two stages are put forward to generate transmit and receive beams for multicasting. Performance evaluations have shown that the total throughput of the network has been improved largely by using the proposed scheme compared with unicast beamforming. Additionally, the designed algorithm has a minor performance loss compared with previous quasi-optimal algorithm, but with much lower complexity, which makes it advantageous for practical use.

Due to human blockage and device mobility, 60GHz wireless local-area network (WLAN) faces the challenge of communication-link outage. To cope with this problem, a double-link beam tracking scheme is proposed in this paper. This scheme includes a search strategy of transmission and alternative links, and an in-packet double-link tracking and switching method. The transmission and alternative links are simultaneously tracked against device mobility, through probing neighboring beams; once the human blockage is detected in transmission link, the system can thus switch to the alternative link directly. Besides, the proposed scheme finds the finish of human blockage quickly through in-packet double-link tracking, and enables the system to communication in the maximal received-power link. The comparison between the proposed scheme and the IEEE 802.11ad scheme is conducted. The comparison shows that the proposed scheme significantly reduces the probability of outage, and achieves an improved throughput.

Wireless Virtualization enables multiple concurrent virtual networks running on shared wireless substrate resource, which makes networks more flexible, efficient and customizable. Efficiently allocating physical wireless spectrum to multiple virtual networks to enhance the resource utilization is a fundamental challenge. Different from previous works focusing on only one physical wireless network, we study the problem under the multiple physical networks scenario, which makes the problem more general and practical. Furthermore, after analyzing the fluctuation feature in wireless virtualization, we introduce an opportunistic spectrum sharing method to increase spectrum allocation efficiency. First, we formulate the problem of opportunistic spectrum sharing with multiple physical wireless networks and prove it as an NP-Hard problem. Then, we propose a genetic algorithm and heuristic algorithm to solve the problem. Simulations show that opportunistic spectrum sharing conspicuously improves the performance of spectrum utilization and confirm the advantage of our proposed algorithms.

Estimation of the multipath channel in 60‐GHz communications is challenging, because the channel may be sparse or dense during beam training. Specifically, because of the variation of the number of non‐zero taps, it is hard for common estimators to obtain robust and prominent performance. In order to address this problem, the authors propose a sparse/dense channel estimation with non‐zero tap detection (SDCE‐NTD). The estimation is conducted in a three‐stage fashion, including initial estimation with the unstructured least‐square (LS) algorithm, non‐zero‐tap detection with the generalised likelihood ratio test approach, and posterior estimation with the structured LS algorithm. The false‐alarm and detection probability of the tap detector, as well as the mean square error (MSE) of SDCE‐NTD, are derived and confirmed via simulations. Comparisons are conducted between SDCE‐NTD and the common estimators in the beam training scenarios, where both dense and sparse channels exist. Results show that SDCE‐NTD reveals a significant gain in terms of MSE over both the conventional LS algorithm, which does not exploit the sparse nature of the channel, and the matching pursuit algorithm, which endeavours to exploit the sparsity. In addition, it is also demonstrated that the proposed estimator can approach the lower bound with high signal‐to‐noise ratio.

To cope with explosive vehicular traffic and ever-increasing application demands in the vehicular cellular network, opportunistic vehicular networks are used to disseminate mobile data by high-capacity device-to-device communication, which offloads significant traffic from the cellular network. In the current opportunistic vehicular data transmission, coding-based schemes are proposed to address the challenge of opportunistic contact. However, whether coding techniques can be beneficial in the context of vehicular mobile data offloading is still an open question. In this paper, we establish a mathematical framework to study the problem of coding-based mobile data offloading under realistic network assumptions, where 1) mobile data items are heterogeneous in terms of size; 2) mobile users have different interests to different data; and 3) the storage of offloading participants is limited. We formulate the problem as a users' interest satisfaction maximization problem with multiple linear constraints of limited storage. Then, we propose an efficient scheme to solve the problem, by providing a solution that decides when the coding should be used and how to allocate the network resources in terms of contact rate and offloading helpers' storage. Finally, we show the effectiveness of our algorithm through extensive simulations using two real vehicular traces.

As malware attacks become more frequently in mobile networks, deploying an efficient defense system to protect against infection and to help the infected nodes to recover is important to prevent serious spreading and outbreaks. The technical challenges are that mobile devices are heterogeneous in terms of operating systems, the malware infects the targeted system in any opportunistic fashion via local and global connectivity, while the to-be-deployed defense system on the other hand would be usually resource limited. In this paper, we investigate the problem of how to optimally distribute the content-based signatures of malware, which helps to detect the corresponding malware and disable further propagation, to minimize the number of infected nodes. We model the defense system with realistic assumptions addressing all the above challenges that have not been addressed in previous analytical work. Based on the framework of optimizing the system welfare utility, which is the weighted summation of individual utility depending on the final number of infected nodes through the signature allocation, we propose an encounter-based distributed algorithm based on Metropolis sampler. Through theoretical analysis and simulations with both synthetic and realistic mobility traces, we show that the distributed algorithm achieves the optimal solution, and performs efficiently in realistic environments.

Vehicular networks have been attracting increasing attention recently from both the industry and research communities. One of the challenges in this area is understanding vehicular mobility, which is vital for developing accurate and realistic mobility models to aid the vehicular communication and network design and evaluation. Most of the existing works mainly focus on designing microscopic level models that describe the individual mobility behaviors. In this paper, we explore the use of Markov jump process to model the macroscopic level vehicular mobility. Our proposed simple model can accurately describe the vehicular mobility and, moreover, it can predict various measures of network-level performance, such as the vehicular distribution, and vehicular-level performance, such as average sojourn time in each area and the number of sojourned areas in the networks. Model validation based on two large scale urban city vehicular motion traces confirms that this simple model can accurately predict a number of system metrics crucial for vehicular network performance evaluation. Furthermore, we propose two applications to illustrate that the proposed model is effective in analysis of system-level performance and dimensioning for vehicular networks.

Owing to the uncertainty of transmission opportunities between mobile nodes, the routing in delay tolerant networks (DTNs) exploits the mechanism of store-carry-and-forward. In this routing mechanism, mobility plays an important role, and we need to control the mobility of nodes around the network to help with carrying messages from the source to the destination. This is a difficult problem because the nodes in the network may move arbitrarily and it is difficult for us to determine when the nodes should move faster to help the data transmission while considering the complicated energy consumption in such a network. At the same time, for most DTNs, the system energy is limited, and energy efficient algorithms are crucial to maximizing the message delivery probability while reducing the delivery cost. In this paper, we investigate the problem of energy efficient mobility speed control in epidemic routing of DTN. We model the message dissemination process under variable mobility speed by a continuous-time Markov model. With this model, we then formulate the optimization problem of the optimal mobility control for epidemic routing and obtain the optimal policy from the solution of this optimization problem. Furthermore, extensive numerical results demonstrate that the proposed optimal policy significantly outperforms the static policy with constant speed, in terms of energy saving. Copyright © 2012 John Wiley & Sons, Ltd.

In this paper, a novel lower-power multigigabit Viterbi decoder architecture is proposed for 60 GHz wireless personal-area network (WPAN) systems. Since add-compare-select (ACS) computation is the main bottleneck in decoding speed of Viterbi decoders, a balanced add-select-register-compare (BASIC) architecture is put forward to reduce critical path of ACS with low complexity. This work develops an 8-parallel BASIC Viterbi decoder for IEEE 802.15.3c standard to accomplish high-throughput and low-power goals. Based on synthesized results in 0.13 μm CMOS technology, the proposed decoder achieves up to 4 Gb/s throughput with energy efficiency 0.104 nJ/bit at 1.2 V.

Opportunistic contact between moving vehicles is one of the key features in vehicular delay tolerant networks (VDTNs) that critically influences the design of routing schemes and the network throughput. Due to prohibitive costs to collect enough realistic contact recodes, to the best of our knowledge, little experiment work has been conducted to study the opportunistic contact patterns in large scale urban vehicular mobility environment. In this work, we carry out an extensive experiment involving tens of thousands of operational taxis in Beijing city. Based on studying this newly collected Beijing trace and the existing Shanghai trace, we find some invariant characteristics of the opportunistic contacts for large scale urban VDTN. Specifically, in terms of contact duration, we find that there exists a characteristic time point, up to which and including at least 80% of the distribution, the contact duration obeys an exponential distribution, while beyond which it decays as a power law one. This property is in sharp contrast to the recent empirical data studies based on human mobility, where the contact duration exhibits a power law distribution. In terms of contact interval, we find that its distribution can be modelled by a three-segmented distribution, and there exists a characteristic time point, up to which the contact interval obeys a power law distribution, while beyond which it decays as an exponential one. Our observations thus reveal fundamental patterns for large scale vehicular mobility, and further provide useful guidelines for the design of new urban VDTN' routing protocols and their performance evaluation.

Roadside Units (RSUs), which enable the vehicles-to-infrastructure communication, are deployed along the roadside to handle the growing communication demands as the number of vehicles increases. How to optimally deploy the RSUs and efficiently use them to enhance the vehicular network performance are important problems in the RSU-aided opportunistic networks. In order to solving these problems, we need to understand fundamental laws and properties of the opportunistic contacts. Due to the prohibitive costs to collect enough realistic contact records, to the best of our knowledge, little experiment work has been conducted to study the communication contact patterns in RSU-aided opportunistic networks. In this work, we carry out an extensive experiment involving tens of thousands of operational taxis in Beijing city. Based on this newly collected Beijing trace and the existing Shanghai trace, we find some invariant characters for the communication contacts for large scale RSU-aided vehicular opportunistic networks. In terms of inter-contact time between the RSUs and vehicles, we find it obeys exponential distribution, while in terms of contact rate, it follows Poisson distribution. Our observations reveal fundamental patterns for large scale vehicular mobility, and further provide useful guidelines for the design of new routing protocols and their performance evaluation for RSU-aided vehicular opportunistic networks.

Data plane programmability is regarded as an essential feature of future Internet. However, the flexibility of programmability has not been carefully considered. We present GrainFlow, a hardware-based packet processing platform supporting customization on every header bit's processing and adapting to packet header length variation. We evaluate GrainFlow on a Virtex-5 FPGA board. Experiment results show that users can flexibly redefine the data plane with only 10-20 rules and data plane forwarding rate can achieve wire-speed with acceptable latency increase.

A significant concern for cloud operators is to provide global network performance isolation for concurrent tenants. To address this, we propose M2cloud, a software defined framework providing scalable network control for multi-site data centers (DCs). M2cloud employs two-level controllers with decoupled functions, providing each tenant with flexible virtualization support in both intra- and inter-DC networks.

With the rapid growth of the demands for mobile data, wireless network faces several challenges, such as lack of efficient interconnection among heterogeneous wireless networks, and shortage of customized QoS guarantees between services. The fundamental reason for these challenges is that the radio access network (RAN) is closed and ossified. We propose OpenRAN, an architecture for software-defined RAN via virtualization. It achieves complete virtualization and programmability vertically, and benefits the convergence of heterogeneous network horizontally. It provides open, controllable, flexible and evolvable wireless networks.

Beamforming is necessary in 60GHz millimeter-wave communications in order to compensate for high path loss. A complete beamforming algorithm includes codebook design and beam training. The existing beamforming protocol of IEEE 802.15.3c standard has following flaws: (1) Not all three beamforming pattern types (quasi-omni pattern, sector and beam) have their own codebooks; (2) Almost every beam points to two directions, one of which is expected but the other one is unwanted; (3) Setup time of beam training is long. This paper proposes a codebook design and corresponding training procedure based on circular antenna array with a two-layer-structure. It allows every pattern type to own its corresponding codebook and highly directional antenna radiation pattern. The training setup time is reduced to around half of 3c training time. Performance evaluations also manifest that the proposed algorithm leads to less antenna gain loss and more robust performance than the 3c standard.

60 GHz communication supporting multigigabit data rate is a popular choice of industry for next generation short distance wireless communications. However, multi-Gsps ADC becomes a challenge in 60 GHz systems which have ultra wide Nyquist bandwidth. To reduce sampling rate of ADC in the estimation stage, we propose a joint signal-to-noise ratio (SNR) and channel estimation algorithm using compressed sensing (CS) theory. In 60 GHz systems, CS encoding and decoding strategies are optimized to maximize benefits from the design of pilots and estimators. For pilot design, m-sequence rather than conventional Bernoulli random sequence is selected owning to a better average restricted isometry property; for estimator design, a quasi-optimal channel and noise power estimation is put forward underlying signal subspace provided by CS algorithm. Simulation results show that the proposed algorithm reduces the sampling rate of ADC to 9.1% Nyquist bandwidth of 60 GHz communication. Moreover, the algorithm with this compressed sampling efficiently outperforms classical least square algorithm with Nyquist sampling as SNR exceeds 7 dB.

Modeling complicated vehicular mobility behavior and the associated network connectivity in large scale vehicular ad hoc network has been a challenging problem for the past several years. In this paper, we carry out extensive experiments involving thousands of operational taxies in Shanghai and Beijing cities. Studying the taxi traces on the vehicular connectivity, we observe that the vehicle isolation probability exhibits an exponential decay with the increase of transmission range. This observation is in sharp contrast to the most widely used system models such as Random Way Point and Random Walk, where the vehicle isolation probability changes with transmission range as exp(-λR2), where R is the transmission range. We propose a simple theoretical model to explain the exponential decay of vehicle isolation. Validation of our model is carried through comparisons between the synthetic trace and the real trace, and the results show that our mobility model has a good approximation to the real scenario. Our results give insights on the behavior of connectivity, thus providing fundamental guidelines on design of new vehicular mobility models, new data forwarding protocols and their performance analysis.

Contact duration between moving vehicles is one of the key metrics in vehicular ad hoc networks (VANETs), that critically influences the design of routing schemes and network throughput. Due to prohibitive costs to collect enough realistic contact records, little experimental work has been conducted to study the contact duration in urban VANETs. In this work, we carry out an extensive experiment involving tens of thousands of operational taxis in Beijing city. Based on studying this newly collected Beijing trace and the existing Shanghai trace, we find an invariant characteristic that there exists a characteristic time point, up to which the contact duration obeys an exponential distribution that includes at least 80% of the whole distribution, while beyond which it decays as a power law one. This property is in sharp contrast to the recent empirical data studies based on human mobility, where the contact duration exhibits a power law distribution. Our observations thus provide fundamental guidelines for the design of new urban VANETs' routing protocols and their performance evaluation.

The signal constellation of 60 GHz millimeter wave (mmWave) communications is distorted by power amplifier (PA) nonlinearity seriously and the bit error rate (BER) performance declines, due to the huge bandwidth and high equivalent isotropic radiated power (EIRP), especially for quadrature amplitude modulation (QAM) signals. This paper aims at non-data-aided (NDA) distorted constellation (DC) estimation and demodulation to deal with PA nonlinearity. An estimation algorithm of expectation-maximization (EM) is proposed and the corresponding Cramer-Rao lower bounds (CRLBs) are calculated, then the estimated DC is used as reference for demodulation. Simulation results indicate that the means of the estimation results are unbiased and the mean square errors (MSEs) reach the CRLBs under easy requirements on signal-to-noise ratio (SNR) and output power back-off (OBO). Additionally, with PA nonlinearity, the BER performance of the presented DC demodulation is close to that of the ideal PA case, and much superior to that of the traditional standard constellation (SC) demodulation.

1/2 network capacity is often believed to be the limit of worst-case throughput for mesh networks. However, this paper provides a new worst-case throughput bound, which is higher than 1/2 network capacity, for odd radix two-dimensional mesh networks. In addition, we propose a routing algorithm called U2TURN that can achieve this worst-case throughput bound for odd radix meshes. For even radix meshes, we prove that U2TURN achieves the optimal worst-case throughput, namely, half of network capacity. U2TURN considers all routing paths with at most 2 turns and distributes the traffic loads uniformly in both X and Y dimensions. Theoretical analysis and simulation results show that U2TURN outperforms existing routing algorithms in worst-case throughput. Moreover, U2TURN achieves good average-throughput at the expense of approximately 1.5× minimal average hop count. For asymmetric meshes, we further propose an algorithm called “U2TURN-A” and provide theoretical analysis for different algorithms. Both theoretical analysis and simulation show that U2TURN and U2TURN-A outperform existing algorithms VAL, DOR and O1TURN in both worst-case and average throughput for asymmetric meshes.

Vehicular Delay Tolerant Networks (VDTN) are used to distribute a large amount of mobile data by high-capacity device-to-device communication. Given a number of available vehicles in VDTN, the current vehicular data sharing models always utilize all of them to achieve the best effect, failing to balance the performance gained and cost of employing them. Taking the cost into account, we study the problem of the optimal number of vehicles to be deployed in the data sharing system, which considers using erasure codes to further increase the system efficiency if possible. By establishing the system goal which consists both the effectiveness and the cost of the vehicular network mathematically, we formulate the above problem as a utility function minimization problem. Finally, we solve the problem by theoretical derivation, and demonstrate the efficiency of the obtained solution through simulations using real vehicular traces of Beijing and Shanghai.

Network virtualization provides an alternative for wireless testbed to support multiple experiments simultaneously, as its properties of isolation, customization and efficiency are able to improve network resources utilization significantly. However, complex radio environment makes the employment of virtualization in wireless networks become a difficult problem, in which strict isolation across different experiments is hard to maintain. What is more, present radio experimental systems mostly exploit only Time Division Multiplexing, which may cause resources waste when the scale of experiments is relatively small. In this paper, we propose a time-space combined resources allocation scheme by taking advantage of both Time Division Multiplexing and Space Division Multiplexing. In this scheme, we first select a new time slot and some unscheduled experiments. Then we adopt Space Division Multiplexing to fit in as many experiments as possible in a time slot while ensuring required isolation across them. Extensive simulation shows that our scheme improves experimental resources utilization effectively, while each experiment in the same time slot have enough bandwidth among all nodes and the fairness of resources utility is also ensured.

Currently, Delay Tolerant Networking (DTN) research community urgently needs a credible and flexible platform to setup large scale DTN networks to accurately evaluate the performance of algorithms and protocols. In this work, we present such an emulation testbed. By using network virtualization and OpenFlow technologies to generate virtual DTN nodes and to simulate the opportunistic links controlled by mobility scenarios, our designed testbed is a realistic DTN protocol evaluation environment composing realistic networks and applications, which provide high credibility, flexible controlling, and supporting for large scale experiments.

Contact interval between moving vehicles is one of the key metrics in vehicular ad hoc networks (VANETs), which is important to routing schemes and network capacity. In this work, by carrying out an extensive experiment involving tens of thousands of operational taxis in Beijing city, we find an invariant character that the contact interval can be modeled by a three-segmented distribution, and there exists a characteristic time point, up to which the contact interval obeys a power law distribution, while beyond which it decays as an exponential one. This property is in sharp contrast to the recent empirical data studies based on Shanghai vehicular mobility, where the contact interval exhibits only exponential distribution.

Groups of people with mobile phones using short range connections like WiFi and Bluetooth to propagate messages can be modeled as, with regard to regular absence of end-to-end connection, Delay Tolerant Networks (DTNs). The study of message transmission speed in such kind of networks has attracted increasing attention in recent years. In this paper, we present a realistic framework to model the message propagation process, and give a detailed expression of average information dissemination delay based on message size, users' selfishness, number of involved subscribers and other related parameters. We apply our model to real-life traces to assess its reliability by comparing the theoretical results with measured statistics, and present extensive upshots to evaluate the influence of various parameters on system performance.

The nonlinear distortion caused by power amplifier (PA) nonlinearity distorts the constellation and degrades the bit error rate (BER) performance of 60 GHz millimeter wave (mmWave) wireless local area network (WLAN) easily, due to the huge bandwidth and high equivalent isotropic radiated power (EIRP), especially for quadrature amplitude modulation (QAM) signals. This paper aims at data-aided (DA) distorted constellation (DC) estimation and demodulation to resist PA nonlinearity. A maximum likelihood (ML) estimation algorithm is proposed, and the corresponding Cramer-Rao lower bounds (CRLBs) are computed. Furthermore, we implement the demodulation based on the DC rather than the standard constellation (SC). Simulation results indicate that the means of the estimated parameters are unbiased and the mean square errors (MSEs) approach the CRLBs. Meanwhile, the proposed DC demodulation with PA nonlinearity achieves BER performance close to the ideal PA case, and evidently outperforms the traditional SC demodulation especially in the high-code-rate or uncoded case.

We study the performance of collaborative vehicular content dissemination, where the content is distributed within the network by vehicle-to-vehicle opportunistic communications and the vehicle nodes are equipped with directional antennas. Through analysing a large real-world vehicle trace, we adopt an accurate mobility model of Levy-walk to set up the realistic vehicular network simulation environment. Using a fluid approximation, we derive a theoretical model to depict the system performance of content dissemination time. The accuracy of the proposed analysis is confirmed by simulation results, which also show that the directional antenna performs better than the omni-directional antenna in our considered scenario, especially when the antenna beam is well scheduled with small beamwidth and high beam steering rate.

Some new medical applications, such as wireless endoscopy system for the diagnoses of whole human digestive tract and real-time endoscopic image monitoring, demand high speed transmission in wireless body sensor network (WBSN). This paper proposes a heterogeneous high speed wireless body sensor network based on ZIGBEE and single carrier ultra wideband (SC-UWB). Our system can choose high speed mode or low speed mode automatically according to the type of data source. Several measures are taken to miniaturize the nodes, lower the system complexity and reduce power consumption, offering system users great mobility and flexibility. We develop and validate a prototype WBSN, supporting four real-time high speed video streams and six low speed sensor data. The performance of the developed system is experimentally evaluated using prototype WBSN, and the ASIC has been designed and fabricated in the standard 0.18im CMOS technology, occupying a die area of 3.0mm * 3.0mm and consuming a dynamic power of 43.4280mw.

Network community needs a flexible platform for network experiment of new architectures, algorithms and protocols in the process of network innovation. However, building such a platform faces lots of challenges due to complicate requirements. In this paper, we present ExpoNet, a platform for rapid concurrent experiment of network innovation on the virtualized programmable infrastructure. ExpoNet integrates both software- and hardware-based router virtualization technologies to provide a flexible approach to configure and customize both the control plane and data plane while satisfying various experiment requirements. We implement ExpoNet, and design a management system to efficiently provide the users with convenient interface to access the platform. Based on its implementation, we present a live network experiment of Network Tomography, which infers the network inner performance according to the observed results of outside nodes. The experiment design and related results show the flexibility and effectiveness of our ExpoNet.

Due to the uncertainty of transmission opportunities between mobile nodes, Delay Tolerant Networks (DTNs) exploits the opportunistic forwarding mechanism. This mechanism requires nodes to forward messages in a cooperative and selfish way. However, in the real word, most of the nodes exhibit selfish behaviors such as individual and social selfishness. At the same time, the energy is usually limited in such networks. In this paper, we investigate how the selfish behaviors affect the performance of two-hop relaying multicast in energy-constrained DTN. We model the message delivery process under selfish behaviors and system energy constraint by a three- dimensional continuous time Markov chain. In terms of multicast performance, we investigate the average message transmission delay and transmission cost. Numerical results show that different selfish behaviors may have opposite impacts on different performance metrics in the energy-constrained DTN.

Mobility plays an important role in the message transmission of Disruption Tolerant Networks (DTNs), and we need to control the mobility of nodes around the network to efficiently carry and relay messages around the network. This is a challenging problem since the nodes in the network may move arbitrarily and it is hard for us to determine how the nodes should move, faster or slower, to help with the data transmission. Moreover, in such network, the energy is usually limited, and we need to consider its complicated energy consumption. In this paper, we investigate the problem of energy-constrained mobility velocity control in epidemic routing of DTN. We first model the message dissemination process under variable mobility velocity by a continuous-time Markov model, then formulate the optimal mobility control problem, and finally obtain the optimal threshold policy from the solution of this optimization problem. Furthermore, extensive numerical results demonstrate that the proposed optimal threshold policy significantly outperforms the static policy with constant velocity, in terms of energy saving.

This paper presents channel measurements for wireless body area network (WBAN) and provides performance evaluation using the model derived from measurement and the model in the final document of the IEEE802.15.6 channel modeling subcommittee. We measure the radio propagation from 3.0GHz to 5.0GHz which falls in ultra-wideband (UWB) frequency range in an anechoic chamber and give out a static model. 10 positions for medical entertainment and sports application are chosen to conduct measurement on a fat body, a normal body and a thin body in order to compare different path loss of different types of body for Chinese people. Moreover, we compare the bit error ratio (BER) of a single carrier UWB (SC-UWB) system which employs different receiving policies such as rake, equalizer and channel coding. The results show that slimmer people cause less path loss in the valid distance from 100mm to 1000mm. The measured model we derived has less multi-path effect than that of the model in the final report given by IEEE802.15.6 channel modeling subcommittee. Even though, rake receiver, equalizer and channel coding are needed to get a satisfying system performance.

In order to provide communication services in Delay Tolerant Networks (DTNs) where it lacks of end-to-end paths between the communication sources and destinations, a variety of routing schemes have been proposed. Consequently it is significant to accurately evaluate their performance to show their advantages and inferiority. At the same time, the energy is very limited in a large number of DTNs, such as sparse mobile sensor networks and emergency ad hoc networks, and it impacts the routing performance significantly. However, current related works ignore the influence of the energy constraint on the routing. In this paper, we investigate the performance of routing schemes for the energy-constrained DTNs. First, we model the two-hop relaying, epidemic routing and K-hop forwarding with energy constraint based on a two-dimensional continuous time Markov chain. Then, we obtain the system performance of message delivery delay and delivery cost by explicit expressions. By both simulation and numerical results, we demonstrate the accuracy of our proposed model and reveal that the energy constraint can actually avoid the message storms which are harmful to the systems in term of delivery cost and transmission contention.

In Delay Tolerant Networks (DTNs), there exists only intermittent connectivity between communication sources and destinations. In order to provide successful communication services for these challenged networks, a variety of relaying and routing algorithms have been proposed with the assumption that nodes are homogeneous in terms of contact rate and delivery cost. However, various applications of DTN have shown that mobile nodes can be divided into different classes in terms of their energy requirements and communication ability, and real application data have revealed the heterogeneous contact rates between node pairs. In this paper, we design an optimal relaying scheme for DTNs, which takes into account nodes' heterogeneous contact rates and delivery costs when selecting relays to minimise the delivery cost while satisfying the required message delivery probability. Extensive results based on real traces demonstrate that our relaying scheme requires the least delivery cost and achieves the largest maximum delivery probability, compared with the schemes that neglect nodes' heterogeneity.

The applications of dynamic content updates for a group of users, for example weather report and traffic congestion broadcast, have been shown to benefit significantly from Delay Tolerant Networks (DTN) communication mechanisms such as opportunistic contact and user sharing. In this paper, we study the dynamic content updates over energy-constrained DTN, and focus on its asymptotic properties about stability and scalability on the time and network size dimensions respectively. By introducing a continuous time Markov framework, we characterize the content dissemination system by both the source update & node sharing process and energy constraint. Based on this framework, we prove the system is stable when the time t approaches to infty, and the convergence rate is exponential. At the same time, by simulation we find that the content's average stable age decreases as Θ(√N) as the number of users N increases. Moreover, through extensive numerical results, we demonstrate the correctness of the theoretically obtained properties of stability.

We present TUNIE, a network platform for rapid concurrent experiment of network innovation on virtualized programmable infrastructure. TUNIE integrates both software-and hardware-based router virtualization technologies to provide a flexible approach to configure and customize both the control plane and data plane, and at the same time satisfied various experiment designing requirements. We implement TUNIE, and deploy it in Tsinghua University. Early experiment of algorithm evaluation verifies the efficiency TUNIE.

We collect data trace from taxis with GPS devices installed to study some important metrics of vehicle mobile networks. Such study may contribute to the future intelligent transportation systems and wireless communication protocols or algorithms designs. To our knowledge, only a few works in this area have been done before since such experiment is usually a huge cost. We took experiments on operative taxis in Beijing, who sent the geographical informations to the console automatically. In this paper, we focus on two of the most important metrics called flight length and pause time distribution in vehicle networks. Through analyzing our own trace datas as well as those collected by Shanghai Jiaotong University, we draw a conclusion that vehicle moving pattern actually shares some resemblances with the previous achievements on Levy-walk nature in human walk. In another word, cars run like human. Index Terms—Flight length; pause time; truncated pareto; Vehicle networks

In the Wireless Body Area Network (WBAN), the wireless channel is complex and distinctive because of the irregular shape of human body. The channel modeling methods and results are different from those in traditional narrow-band communication environments. In this paper, we present channel models for WBAN in Ultra wide band (UWB) frequency range 3-9 GHz. The channels are modeled statistically and the channel model parameters are derived from actual measured data in an office environment. An interesting common result is that different shape people have significantly differences in multipath parameters. Taking into account the characteristics of body shape, we provide a new classified small-scale channel model which has three kind of channel models: sparse, medium and dense multipath channel models. These models can be applied to different scenarios and improve the system design. We evaluated these models by delays and average number of mUltipaths with the measured data. Results prove the effectiveness of our models.

As malware attacks become more frequent in mobile networks, deploying an efficient defense system to protect against infection and to help the infected nodes to recover is important to contain serious spreading and outbreaks. The technical challenges are that mobile devices are heterogeneous in terms of operating systems, and the malware can infect the targeted system in any opportunistic fashion via local and global connectivity, while the to-be-deployed defense system on the other hand would be usually resource limited. In this paper, we investigate the problem of optimal distribution of content-based signatures of malware to minimize the number of infected nodes, which can help to detect the corresponding malware and to disable further propagation. We model the defense system with realistic assumptions addressing all the above challenges, which have not been addressed in previous analytical work. Based on the proposed framework of optimizing the system welfare utility through the signature allocation, we provide an encounter-based distributed algorithm based on Metropolis sampler. Through extensive simulations with both synthetic and real mobility traces, we show that the distributed algorithm achieves the optimal solution, and performs efficiently in realistic environments.

With the development of mobile networks, terminals' locations become increasingly valuable for both the whole system performance and terminals' applications or services. As knowing the knowledge of terminals' location information in advance would provide extern preparation time to accelerate response to terminals' requirements, location prediction plays a quite important role. Since most of the mobile terminals are human-carried devices, terminals' location prediction is actually the persons' location prediction. On the other hand, the research on social networks has experienced a fast development and provided a new kind of view on prediction. In our paper, we propose a location prediction scheme based on the idea of social correlation which is a kind of link between different terminals weighted by statistic results of history information.We also model topologies as sequences of snapshots to guide prediction. Few limits on the format of history location information record makes sure a strong adaptiveness of our scheme to various application's requirements.

Due to the lack of end-to-end paths between the communication sources and destinations, the routing of Delay Tolerant Networks (DTN) exploits the store-carry-and-forward mechanism. In this new routing mechanism, how to efficiently integrate forwarding and replication mechanisms is significant for achieving high message delivery ratio while requiring low delivery cost. In this paper, by using famous social properties such as communities and centrality, we design a routing scheme efficiently Integrating Forwarding and Replication (IFR), which allow node to replicate messages in the same community and to forward messages outside the community according to delivery weight obtained from node centrality. Realistic traces based simulations show that our scheme IFR is efficient in improving the message delivery performance on the tradeoff between the delivery success ratio and total delivery cost.

In order to provide communication service in the Intermittently Connected Mobile Networks (ICMN) where there is only intermittent connectivity between mobile nodes, a variety of epidemic-style routing algorithms have been proposed to achieve high message delivery probability. However, current works do not address the realistic environment that a message is split into multi frames to be transmitted. In this paper, we investigate the problem of optimal multi-frame message transmission for the ICMN. First, we formulate the optimization problem by introducing a continuous time Markov framework. Then, we theoretically derive the optimal policies for the message transmission by solving the formulated problem. Finally, we investigate the performance of the proposed optimal policies through extensive numerical results. We conclude that our optimal policies give the best performance in the multi-frame message transmission.

Traditional Delay-Locked-Loop (DLL) method can be hardly used in high-rate Direct-Sequence Ultra-Wideband (DS-UWB) systems due to dense multipath environment, low spreading factor and high-frequency clock. Most of the existing researches on tracking in UWB scenario focus on low-rate Impulse-Radio UWB (IR-UWB). In this paper, a non-Numerical Controlled Oscillator (NCO) periodical-pilot-assisted tracking method is proposed for practical high-rate DS-UWB systems. Analytical expressions of Equivalent Probability Density Function (EPDF) of timing error in locked state, Mean Square Error (MSE, or termed timing jitter) and Mean Time to Lose Lock (MTLL) are derived. Numerical results are presented, and then confirmed by means of extensive computer simulation results. These results corroborate our theoretical analysis, and show performance superiority of the proposed method over traditional DLL. Additionally, this proposed method has been used and justified in our practical DS-UWB system.

Running multiple virtual networks over a shared physical network is a promising way to support diverse applications, consequently network virtualization is viewed as the keystone of the next-generation architecture. However, decoupling the role of traditional ISPs into Infrastructure Providers (InPs) and Service Providers (SPs), also brings some new challenges to us. For example, how to fairly and efficiently share the sacred physical resources of InPs among multiple SPs is a key problem. The interaction between InPs and SPs, such as cooperation and competition, makes this topic even more complicated. In this paper, we develop a novel approach to encourage efficient behavior in solving the interaction between InPs and SPs by introducing economic incentives, in the form of Game Theory. Based on the non-cooperative game model, a bandwidth allocation scheme in the network virtualization environment is established, using the concept of the Nash Equilibrium. Then we propose an iterative algorithm to find the Nash Equilibrium and solve the bandwidth allocation problem. Finally, we demonstrate the convergence and the effectiveness of our scheme in the experiments.

Tracking constitutes a major challenge in Ultra-Wideband (UWB)communications due to dense multipath environment and low power consumption. Most of the existing studies on tracking fall within low rate Impulse Radio UWB (IR-UWB) scope, with the assumption that Inter-Frame Interference (IFI) or Inter-Symbol Interference (ISI) is absent. In this paper, we settle on high rate Direct-Sequence UWB (DS-UWB) systems, in which ISI is inevitable. A Periodical-Pilot-Assisted Tracking Loop with RAKE combining, which we termed PPATL, is proposed for high rate DS-UWB scenario. The proposed tracking loop can effectively combat ISI and capture multipath energy. Analytical expressions of Probability Density Function (PDF) of timing error in locked state, Mean Square Error (MSE, or termed timing jitter) and Mean Time to Lose Lock (MTLL) are derived. Numerical results are presented and then confirmed by means of extensive computer simulation results. These results corroborate our theoretical analysis. Additionally, this proposed PPATL has been used and justified in our realistic DS-UWB system.

Due to the uncertainty of transmission opportunities between mobile nodes, Delay Tolerant Networks (DTN) routing exploits the opportunistic forwarding mechanism. Optimal policies for opportunistic forwarding are crucial to maximizing the message delivery probability while reducing the forwarding cost. In this paper, we investigate the optimal opportunistic forwarding policies for the energy- constrained DTN by introducing a continuous time Markov framework to model the message dissemination. Based on this framework, we obtain the optimal static and dynamic policies by theoretical analysis and proof. Through extensive numerical results, we conclude that the performance of the optimal dynamic policy is better than that of the static policy. Among the dynamic policies, we find that the negative power function based optimal policy provides the best performance.

Topology information plays an important role in network management. The existing methods for topology inference based on end-to-end measurements need a threshold for general topologies, which is difficult to select to ensure the inference accuracy. In this paper, we propose a sort-based approach, named SBA, to infer the general topologies without using a threshold. First, a sort-based clustering algorithm, named SBC-AL, is proposed to cluster a group of nodes in which every node has at least one sibling. In the SBA, the nodes are classified into disjoint groups by a fan-out decrement mechanism. Then the SBA uses the SBC-AL to cluster the nodes group by group from the bottom up to infer the topology. We prove that the SBA is consistent and suitable for general topologies. The simulation results show that the SBA has a good performance in both accuracy and efficiency.

Many acquisition schemes have been proposed and investigated for Ultra-Wideband (UWB) systems, however, most of them setup for low duty-cycle Impulse Radio UWB (IR-UWB) signals, with the assumption that the pulse repetition time is greater than the maximum excess delay of channels, so that intra- and inter-frame interference can be bypassed. This assumption limits the transmission rate and cannot hold in high-rate Direct-Sequence UWB (DS-UWB) systems. In this paper, we propose a two-step data-aided acquisition scheme for high-rate DS-UWB systems. The first step is to quickly acquire an arbitrary train sequence; a two-stage correlation architecture is employed to combat Inter-Symbol Interference (ISI) and collect multipath energy, so as to speed up acquisition. Correspondingly, the second step is to search for the first arriving path with a maximum gap based search method (also new proposed), so as to improve Bit Error Rate (BER) performance. Closed-form expressions of Mean Acquisition Time (MAT), Overall Acquisition Probability (OAP) and False Alarm Rate (FAR) are derived. Based on them, parameter selections that minimize MAT and maximize OAP are discussed under certain FAR constrain. Simulations corroborate our theoretical results.

Resilience issue in Ethernet is becoming even more important when Ethernet is becoming more pervasive. The authors propose a local recovery scheme, named Ethernet ultra-fast switching (EUFS), to address this issue. EUFS is based on the multiple spanning tree protocol, which is the basics of both load balancing and fast recovery mechanisms in large-scale Ethernet networks. For each node, the authors construct a pair of protection trees rooted at this node. Normally, the traffic is forwarded along the working trees. When a link or node fails, the immediate upstream node switches the traffic, which intends to pass through the failed link or node, from the working trees to one of the protection trees rooted at itself. EUFS has the following features. First, it achieves an ultra-fast recovery from any single failure in two-connected networks. Second, it supports backward compatibility, because switches implementing EUFS can inter-operate with the legacy Ethernet switches.

Network tomography has been widely used recently to obtain the network internal characteristics by end-to-end measurement. In this study, the authors consider the problem of estimating link loss rates using network tomography. The existing work based on maximum likelihood estimator (MLE) uses iterative approximation to make the inference, which requires a long execution time for large scale network. To overcome this limitation, the authors propose a fast path-based approach (FPA) by explicit estimation to infer the loss rate of links. Instead of estimating the link loss rates directly, the authors first estimate the path loss rates that are used to derive the link loss rates. In addition, the path loss rates are inferred by a new estimator which is an explicit function of loss observations. The authors evaluate the accuracy of this approach through the analysis of the loss rate estimator and simulation. The estimator is proved to be consistent and have the same asymptotic variance as that of the MLE. The simulation results show that the estimated loss rates using the FPA correctly converge to the real loss rates.

Proxy mobile IPv6 (PMIPv6), a network-based IP mobility solution, is a promising approach for mobility management in all-IP wireless networks. How to enhance its handoff-related performance, such as handoff delay and signaling cost, is an important issue. Current solutions rely on approaches such as fast handoff, routing optimization and paging extension. However, the case of many correlated mobile nodes (MNs) moving together and taking handoffs at the same time has not been considered. In this paper, we propose a group-based handoff scheme for correlated MNs to enhance the performance of PMIPv6. We first propose a correlated MNs detection algorithm to detect MNs as groups. Based on this algorithm, we propose a group-based handoff procedure, and discuss its benefits and limitations. Furthermore, we evaluate the performance of PMIPv6 and our proposal through the analysis and simulation. The results show that the proposed scheme is very efficient in reducing both the handoff delay and signaling cost.

Delay Tolerant Networks (DTNs) are able to provide communication services in challenged networks where the end-to-end path between the source and destination does not exist. In order to increase the probability of delivery, DTN routing mechanisms may require nodes in the network to store and carry messages in their local buffer and replicate many copies. When the limited buffer is consumed, choosing the appropriate messages to drop is critical to maximizing the system performance. Current methods for this are sub-optimal or assume unrealistic conditions. In this paper, we propose an adaptive optimal buffer management scheme for DTN in the situations where the bandwidth is limited and messages vary in size. In our proposal, the mobility model is adjusted according to the nodes' historical meeting information, and the message dropping policies are designed to optimize certain network performance goals, such as maximizing the average delivery rate or minimizing the average delivery delay. Furthermore, we theoretically prove that the designed message dropping policies are optimal to achieve the best system performance.

Network-on-Chip (NoC) design methodology is considered as an important trend for large System-on-Chip design because of the bandwidth and power constraints in traditional synchronous bus architecture. In the design of packet-based NoC, packetizing mechanism has great effect on communication performance, area, and energy consumption of NoC. In this paper, we carry out detailed simulation to evaluate several kinds of packetizing mechanisms of NoC based on topology of Ring and Spidergon. Simulation results show that Condition-Waiting adaptive packetizing mechanism (CW-APM) is the best trade-off packetizing mechanism in NoC design.

Proxy Mobile IPv6 (PMIPv6), a network-based local mobility management solution, is being actively discussed and standardized by IETF recently. Compared with the host-based mobility protocols such as mobile IPv6, PMIPv6 separates mobile node from the involvement of handover procedure and promises easier deployment and better handover performance. The system performance analysis of PMIPv6 is significant to its design and deployment. However, current related work is either restricted to a single performance metric or not considered in a realistic network environment. In this paper, we propose an analytical framework based on IP-based cellular networks. Based on the framework, we investigate the performance of PMIPv6 with respect to various metrics, including signaling cost, handover delay and packet loss, and compare it with host-based mobility management protocols, such as Mobile IPv6, FMIPv6 and HMIPv6. The simulation results demonstrate the salient performance of PMIPv6.

Proxy mobile IPv6 (PMIPv6) is being actively standardized by IETF, and its salient features, such as supporting unmodified mobile node (MN), expedite the real deployment of IP mobility management. However, current research and development mainly focus on its unicast mechanism. In this paper, we propose two multicast listener mobility mechanisms for PMIPv6, named LMA-MLM and MAG-MLM, by drawing a lesson from the designing of Mobile IP (MIP) based multicast solutions. Moreover, we present qualitative and quantitative comparison between MlP-based solutions and our proposals. Although the research of PMIPv6-based multicast mobility is at an early stage yet, it is strongly expected to be a promising candidate solution for multicast mobility in the wireless mobile IP networks.

The accuracy of interconnect delay estimations can be improved by the method presented in this paper, in which the first two moments are obtained with ABCD matrix and a stable model to incorporate effects of transport delay into the delay estimate is developed. Simulation results show that the method share the same accuracy with traditional methods when rise time delay is much longer than transport delay and more accurate when the two are of the same order.

In this paper, a hierarchical cluster-based irregular topology customization method is proposed for Networks-on-Chip (NoC). This method contains three steps: (1) partitioning IPs into many hierarchical clusters; (2) generating a core network; (3) deleting redundant edge routers. Results show that the irregular topologies generated by our hierarchical cluster-based method consume less power when satisfying the bandwidth and port number constraints. Compared with the previous method, our method can save about 15.41% of power averagely for all benchmark applications. Particularly, for MPEG 4 decoder, our method can save 31.62% of power.

Network tomography has been widely used recently as an method to infer the network internal link-level characteristics by end-to-end measurement. In this paper, we consider the problem of estimating link loss rates using network tomography. The existing methods make the inference based on the whole tree of network, which is very complex for large scale network. To overcome this limitation, we propose a low complexity inference approach named LCIA. In the LCIA, we deploy monitors at internal nodes to reduce the complexity of inferring the link loss rates. It mainly consists of two steps. The first step is to deploy monitors at specific internal nodes to divide the original tree into several sub-trees with minimum depth. The second step is to infer the link loss rates of sub-trees by a new estimator which is an explicit function of loss measurements. The LCIA has the following features. First, it greatly reduces the inference complexity as the inference on the sub-trees is much simpler. Second, it improves the accuracy of the estimated results since the variance of loss estimator on sub-trees with lower depth is smaller than that on the original tree. The analytical and simulation results demonstrate that the LCIA outperforms the existing methods both on computation complexity and inference accuracy.

Monitoring traffic pattern is always an important approach to improve the performance of computer networks. In recent years, peer-to-peer (P2P) service gradually dominates the Internet traffic against traditional client-server (C-S) service such as Web. The changed situation of networks is mainly in two aspects. One is that popular P2P file-sharing applications require both board downstream and upstream bandwidth, which conflicts to asymmetry structure of the C-S service oriented networks, and another is that the topology of P2P overlay networks is varying with peers joining and leaving. The dramatic shift of Internet traffic may cause different patterns from that observed in early years. This leads a new round of Internet measurement, which requires effective monitoring of network-wide traffic within the region of ISP or autonomous system. Unfortunately, few of technologies can capture well the dynamics of C-S and P2P traffic in a macroscopic level. In this paper, we propose a method based on random matrix theory (RMT) for the detection of networkwide traffic pattern. Using only a few observation points, our method can monitor the macroscopic effect of the Internet traffic. We show that such macroscopic-level monitoring can be used to capture shifts in spatial-temporal patterns caused by P2P and C-S traffic, and inform where and when P2P and C-S traffic possibly arise in transit networks.

Localization is one of the fundamental problems in many wireless sensor networks applications. They require sensor nodes to obtain their absolute or relative geographical position. Although many localization algorithms have been proposed recently, most of them require the node to equip special range-determining or angel-determining hardware in order to obtain the position related information. In this paper, we propose a concentric beacons localization algorithm which is a range-free approach. Four anchors are set in the four corners of the square target region, and emit localizing beacons at different power levels, with the information of their position and the estimated range of the beacon. The nodes in this region receive these beacons and compute their positions correspondingly. In region of different scale, we propose two alternative schemes. The One for small scale has lower calculation complexity, and the other has better stability on large scale applications. Simulation results show the estimation error is less than 0.4 times the beacon interval.

We propose a fair and simple high-performance scheduling algorithm for combined input-crosspoint-queued switches, which is called tracking fair quota allocation (TFQA). Our algorithm is based on low-cost round-Robin scheme, which prioritizes the ports lagging behind our fair quota allocation scheme. Simulation shows that our algorithm could maintain over 99% throughput and achieve relatively low mean delay under almost all typical test traffic patterns, outperforming all known algorithms with the same implementation complexity, especially under heavy load scenarios. Moreover, our algorithm could provide max-min fairness under inadmissible traffic, better than many other typical algorithms proposed before.

Emulating Output Queued (OQ) Switch with sustainable implementation cost and low fixed delay is always preferable in designing high performance routers. The Switch-Memory-Switch (SMS) router, also called Distributed Shared Memory (DSM) Switch, provides a possible way towards practically emulating OQ in backbone switches. However, the architectures and algorithms for SMS switches ever proposed are either unpractical or only supporting First-Come-First-Serve (FCFS) scheduling policy, which cannot support QoS and is unfair for light traffic flow. Our improved SMS architecture and algorithm aim at emulating Push-In-First-Out (PIFO) OQ. We employ a randomly-dispatching first stage and resolve memory access conflictions on the second stage of the switch through a probabilistic matching method, at the cost of fixed delay and sufficiently low cell loss probability (PCLP). The relative fixed delay of our algorithms for an NXN switch is composed of two parts: N and (-3/2log2PCLP), which result from the pipelined scheduling process and probabilistic method, respectively. Moreover, both the total memory and fabric bandwidth of our architecture implemented on crossbar could be lowered to only 2NR, where R is line rate, counting read and write separately.

This article presents a novel universal all-digital clock-smoothing technique - counting-prognostication. Operation principles, performance analysis, and comparisons are given. Analysis and measurement results show that this technique can efficiently smooth jitter and wander for a wide pull-in range and pull-out range, and jitter accumulation is small. A cycle-varying counting-prognostication method, which decreases pull-in time, is also suggested.

High-speed broadband digital communication networks rely on digital multiplexing technology where clock synchronization, including processing, transmission, and recovery of the clock, is the critical technique. This paper interprets the process of clock synchronization in multiplexing systems as quantizing and coding the information of clock synchronization, interprets clock justification as timing sigma-delta modulation (TΔ-ΣM), and interprets the jitter of justification as quantization error. As a result, decreasing the quantization error is equivalent to decreasing the jitter of justification. Using this theory, the paper studies the existing jitter-reducing techniques in transmitters and receivers, presents some techniques that can decrease the quantization error (justification jitter) in digital multiplexing systems, and presents a new method of clock recovery.