In the evolution of wireless networks such as wireless sensor networks, mobile ad-hoc networks, and delay/disruption tolerant networks, the Store-Carry-Forward (SCF) message relaying paradigm has been commonly featured and studied with much attention. SCF networking is essential for offsetting the deficiencies of intermittent and range limited communication environments because it allows moving wireless communication nodes to act as “mobile relay nodes”. Such relay nodes can store/carry/process messages, wait for a better opportunity for transmission, and finally forward the messages to other nodes. This paper starts with a short overview of SCF routing and then examines two SCF networking scenarios. The first one deals with large content delivery across multiple islands using existing infrastructural transportation networks (e.g., cars and ferries) in which mobility is uncontrollable from an SCF viewpoint. Simulations show how a simple coding technique can improve flooding-based SCF. The other scenario looks at a prototype system of unmanned aerial vehicle (UAV) for high-quality video surveillance from the sky in which mobility is partially controllable from an SCF viewpoint. Three requisite techniques in this scenario are highlighted - fast link setup, millimeter wave communications, and use of multiple links. Through these examples, we discuss the benefits and issues of the practical use of SCF networking-based systems.
After the East Japan great earthquake on March 11, 2011, many Japanese coastal resident areas were isolated from other because of destruction of information infrastructure, disconnection of communication network and excessive traffic congestion. The undelivered disaster information influenced the speed of evacuation, rescue of injured residents, and sending life-support materials to evacuation shelters. From the experience of such disaster, more robust and resilient networks are strongly required, particularly for preparation of large scale disasters. In this paper, in order to respond to those problems, we introduce Delay Tolerant Network (DTN) for disaster information transmission application in challenged network environment. Message delivery by transport vehicles such as cars between disaster-response headquarter and evacuation shelters in challenged network environment is considered. A improved message delivery method combined with DTN protocols and cognitive wireless network is explained. The computer simulation for the actual rural area in Japan is made to evaluate the performance and effectiveness of proposed method.
We propose a home base-aware store-carry-forward routing scheme using location-dependent utilities of nodes, which adopts different message forwarding strategies depending on location where nodes encounter. Our routing scheme first attempts to deliver messages to its home base, the area with the highest potential for the presence of the destination node in the near future. Once a message copy reaches its home base, message dissemination is limited within the home base, and nodes with message copies wait for encountering the destination node. To realize our routing scheme, we use two different utilities of nodes depending on location: Outside the home base of a message, nodes approaching to the home base have high utility values, while within the home base, nodes staying the home base have high utility values. By using these utilities properly, nodes with message copies will catch the destination node “by ambush” in the home base of the destination node. Through simulation experiments, we demonstrate the effectiveness of our routing scheme.
In ad hoc networks, broadcast forwarding protocols called OR (opportunistic routing) have been proposed to gain path diversity for higher packet delivery rates and shorter end-to-end delays. In general backoff-based OR protocols, each receiver autonomously makes a forwarding decision by using certain metrics to determine if a random backoff time is to be applied. However, each forwarder candidate must wait for the expiration of the backoff timer before forwarding a packet. Moreover, they cannot gain path diversity if the forwarding path includes local sparse areas, and this degrades performance as it strongly depends on the terminal density. In this paper, we propose a novel OR protocol called PRIOR (prioritized forwarding for opportunistic routing). In PRIOR, a terminal, called a prioritized forwarder and which forwards packets without using a backoff time, is selected from among the neighbours. In addition, PRIOR uses lightweight hop-by-hop retransmission control to mitigate the effect of terminal density. Moreover, we introduce an enhancement to PRIOR to reduce unnecessary forwarding by using an explicit acknowledgement. We evaluate PRIOR in comparison with conventional protocols in computer simulations.
We propose a QoS scheme for ad hoc networks by combining TDMA and IEEE 802.11 DCF, and present performance evaluation results of the scheme. In the proposed scheme, the channel time is composed of two different periods, specifically TDMA period and DCF period. The TDMA period provides contention free transmission opportunities for QoS flows, and the DCF period provides contention-based access for best effort or low priority flows. We evaluate the proposed scheme for various numbers of TCP flows and different CBR data rates with QualNet simulator. Simulation results show that the protocol is able to provide an efficient solution for QoS control in ad hoc networks.
The self-organizing nature of ad hoc networks is a good aspect in that terminals are not dependent on any infrastructure, that is, networks can be formed with decentralized and autonomous manner according to communication demand. However, this characteristic might affect the performance in terms of stability, reliability and so forth. Moreover, ad hoc networks face a scalability problem, which arise when the number of terminals in a network increases or a physical network domain expands, due to the network capacity limitation caused by the decentralized and the autonomous manner. Regarding this problem, some hierarchical and cluster-based routings have been proposed to effectively manage the networks. In this paper, we apply the concept of hierarchical routing and clustering to opportunistic routing, which can forward packets without using any pre-established path to achieve a path diversity gain with greater reachability. The simulation results show that the proposed method can achieve 11% higher reliability with a reasonable end-to-end delay in dense environments and 30% higher in large-scale networks.
The Mobile IPv6 protocol (MIPv6) allows a single Mobile Node (MN) to keep the same IPv6 address independently of its network of attachment. Network Mobility protocol (NEMO) is an extension of MIPv6. NEMO is concerned with managing the mobility of an entire network, so it's used for devices or vehicles which move to another point of attachment to the Internet. Proxy Mobile IPv6 (PMIPv6) has been developed for local mobility management whereas MIPv6 and NEMO address global mobility for both hosts and routers. This paper proposes a distributed mobility solution based on NEMO for heterogeneous mobile IP networks, so called Host-based and Network-based Distributed Mobility Management for NEMO (HND-NEMO), where different types of IP mobility management are operating. Our solution utilizes both network-based and host-based mechanisms. Multiple Home Agents (HAs) are deployed, and the mobility anchors are closer to the edge of the network in order to provide optimal routing and lower delays. We show that our solution provides smooth mobility in global domains, local domains, and no mobility service domains, in terms of handover latency, signaling and packet delivery costs, and end to end delay.
The λ-tunable WDM/TDM-PON is a promising candidate for next-generation optical access networks since it can provide load balancing between optical subscriber units, power savings, high reliability, and pay-as-you-grow capability. In a λ-tunable WDM/TDM-PON system, the degradation of communication quality caused by wavelength switching should be minimized. The system should also preferably be able to change wavelengths of multi ONUs simultaneously to make wavelength reallocation speed high. The system should also be able to accommodate ONUs whose wavelength tuning times are different. The challenge to meet all three requirements is to suppress latency degradation and frame loss when wavelengths of multi-type ONU are switched simultaneously in WDM/TDM-PON systems. We proposed an OLT architecture and a wavelength switching method that cooperates with traffic control to suppress frame loss and latency degradation by multi-ONU wavelength switching. However, there have been no reports on the impact on latency of downstream and upstream traffic when wavelengths of multi-ONU are simultaneously switched in λ-tunable WDM/TDM-PON. In this paper, we evaluate and analyze the impact of wavelength switching on latency in 40 Gbps WDM/TDM-PON systems. An experiment results show that latency degradation and frame loss are suppressed. Dynamic wavelength allocation operation with 8-ONUs-simulateous wavelength switching in 512-ONUs WDM/TDM-PON system is demonstrated.
This paper investigates the data persistence problem with compressive sensing (CS) in wireless sensor networks (WSNs) where the sensed readings should be temporarily stored among the entire network in a distributed manner until gathered by a mobile sink. Since there is an energy-performance tradeoff, conventional CS-based schemes only focus on reducing the energy consumption or improving the CS construction performance. In this paper, we propose an efficient Compressive Sensing based Data Persistence (CSDP) scheme to achieve the optimum balance between energy consumption and reconstruction performance. Unlike most existing CS-based schemes which require packets visiting the entire network to reach the equilibrium distribution, in our proposed scheme information exchange is only performed among neighboring nodes. Therefore, such an approach will result in a non-uniform distribution of measurements, and the CS measurement matrix depends heavily on the node degree. The CS reconstruction performance and energy consumption are analyzed. Simulation results confirm that the proposed CSDP scheme consumes the least energy and computational overheads compared with other representative schemes, while almost without sacrificing the CS reconstruction performance.
Service chaining (SC) is a method for realizing a service by transferring flows among several service functions (SFs) that process packets. A route among SFs is called a service path (SP). Service chaining is being developed to reduce costs, increase flexibility, and shorten time-to-market. SC technologies are expected to be applied to carrier networks so that large communication carriers benefit from them. We assume that SPs process the traffic of services that treat all users in the same way such as an Internet access service for home users. An SP processes flows from several users. We do not assume that each SP is assigned to a user. Because a carrier network accommodates many users, each service will be heavily utilized. Therefore, it is assumed that the amount of traffic of a service is larger than the resource of an SF apparatus. Several SPs are required to process the traffic. SPs are supposed to meet two requirements. One is guaranteeing minimum bandwidth. The other is reducing the number of SF apparatuses, i.e., high resource utilization. Resource utilization depends on the combination of the resource quantities of SF apparatuses. Network operators have to determine the bandwidth of each SP within the range from the minimum bandwidth to the resource quantities of SF apparatuses to maximize resource utilization. Methods for determining the bandwidth of each SP have not been proposed for meeting the two requirements. Therefore, we propose a resource allocation method for this purpose. The proposed method determines the bandwidth of each SP on the basis of the combination of the resource quantities of SF apparatuses for guaranteeing the minimum bandwidth and maximizing resource utilization and allocates necessary resources to each SP. We also evaluate the proposed method and confirm that it can guarantee the minimum bandwidth of SPs and achieve high resource utilization regardless of the combination of the resource quantities of SF apparatuses. Although SF apparatuses are generally produced without considering the combinations of resource quantities of SF apparatuses in SPs, the proposed method can provide more options for selecting SF apparatuses.
It is expected that a large number of different objects, such as sensor devices and consumer electronics, will be connected to future networks. For such networks, we propose a name resolution method for directly specifying a condition on a set of attribute-value pairs of real-world information without needing prior knowledge of the uniquely assigned name of a target object, e.g., a URL. For name resolution, we need an algorithm to find the target object(s) satisfying a query condition on multiple attributes. To address the problem that multi-attribute searching algorithms may not work well when the number of attributes (i.e., dimensions) d increases, which is related to the curse of dimensionality, we also propose a probabilistic searching algorithm to reduce searching time at the expense of a small probability of false positives. With this algorithm, we choose permutation pattern(s) of d attributes to use the first K (K « d) ones to search objects so that they contain relevant attributes with a high probability. We argue that our algorithm can identify the target objects at a false positive rate less than 10-6 and a few percentages of tree-searching cost compared with a naive d-dimensional searching under a certain condition.
This paper proposes a recommendation-based bandwidth calendaring system for packet transport networks. The system provides a user-portal interface with which users can directly reserve packet transport resources. In this regard, the system recommends multi-grade (e.g., multi-price) reservation plans. By adjusting grades of plans in accordance with network resource utilization, this system provides not only reservation flexibility for users but also efficient utilization of network resources. For recommending multi-grade plans, pre-computation of resource allocation is required for every time slot. Because the number of time slots is huge, we also propose an algorithm for fast computation of resource allocation based on time-slot aggregation. Our evaluation suggests that our algorithm can produce a sub-optimal solution within quasi-real time for a large-scale network. We also show that our recommendation-based system can increase the service-provider-revenue in peaky traffic demand environments.
With the proliferation of hand-held devices in recent years, mobile video streaming has become an extremely popular application. However, Internet video streaming to mobile devices faces several problems, such as unstable connections, long latency, high jitter, etc. We present a system, OptVid, which enhances the user's experiences of video streaming service on cellular networks. OptVid takes the user's profile and provides seamless adaptive bitrate streaming by leveraging the video transcoding solution. It provides very agile bitrate adaptation, especially in the mobile scenario where the wireless channel is not stable. We prototype video transcoding on a WiMAX testbed to bridge the gap between the wireless channel capacity and the video quality. Our evaluations reveal that OptVid provides better user experience than conventional schemes in terms of PSNR, video stalls, and buffering time. OptVid does not require any additional storage since it transcodes videos on-the-fly upon receiving requests and delivers them directly to the client.
We introduce the notion of hierarchical aggregate entropy and apply it to identify DNS client hosts that wastefully consume server resources. Entropy of DNS query traffic can capture client query patterns, e.g., the concentration of queries to a specific domain or dispersion to a large domain name space. However, entropy alone cannot capture the spatial structure of the traffic. That is, even if queries disperse to various domains but concentrate in the same upper domain, entropy among domain names provides no information on the upper domain structure, which is an important characteristic of DNS traffic. On the other hand, entropies of aggregated upper domains do not have detailed information on individual domains. To overcome this difficulty, we introduce the notion of hierarchical aggregate entropy, where queries are recursively aggregated into upper domains along the DNS domain tree, and their entropies are calculated. Thus, this method enables us to analyze the spatial characteristics of DNS traffic in a multi-resolution manner. We calculate the hierarchical aggregate entropies for actual DNS heavy-hitters and observed that the entropies of normal heavy-hitters were concentrated in a specific range. On the basis of this observation, we adopt the support vector machine method to identify the range and to classify DNS heavy-hitters as anomalous or normal. It is shown that with hierarchical aggregate entropy can halve the classification error compared to non-hierarchical entropies.
We propose a new configuration for phased array antennas. The proposal uses radiation pattern reconfigurable antennas as the antenna element to improve the gain on the scanning angle and to suppress the grating lobes of sparse phased array antennas. This configuration can reduce the element number because the desired gain of the total array can be achieved by using fewer elements. We demonstrate the concept by designing a radiation pattern reconfigurable Yagi-Uda antenna. PIN diode switches are added to the parasitic elements to change director and reflector. The switches of multiple array elements are concurrently controlled by just a single one-pair line. This control structure is simple and can be applied to large-scale arrays. The proposed antenna yields an element gain that almost matches the theoretical limit across about half the coverage, even if the element spacing is enlarged to 1λ. If the switch states are interchanged, the gain in the mirror direction can be increased. We design a 48-element array and compare its gain against those of normal dipole antennas. We also fabricate the proposed antenna and demonstrate radiation pattern switching.
An alignment control system using beam-tilting 1-D arrays for a 120-GHz-band corporate-feed 2-D waveguide-slot array antenna is presented. The 2-D waveguide-slot array antenna transmits data, and the 1-D arrays are used to determine array alignment. We design two types of 1-D array antenna and fabricate a corporate-feed 2-D waveguide-slot array antenna surrounded by four beam-tilting 1-D arrays. We then construct an alignment control system and evaluate the performance of the control. We find that the angular accuracy of the antenna alignment control was within ±1deg.
This paper proposes novel simplified maximum likelihood detection for XOR physical layer network coding (XOR-PNC) in bi-directional wireless relay systems with Quaternary phase shift keying (QPSK). The proposed detection applies unitary precoding to achieve superior performance without computationally prohibitive exhaustive search. The performance of the XOR employing the proposed simplified MLD with the precoding is analyzed in relay systems with orthogonal frequency division multiplexing (OFDM). The performance of the XOR-PNC with the proposed techniques is also evaluated by computer simulation. The XOR-PNC with the proposed techniques achieves about 7dB better performance than the amplify-and-forward physical layer network coding in the 5-path fading channel at BER=10-4. It is also shown that the XOR-PNC with the proposed techniques achieves better performance than that without precoding.
Non-orthogonal multiple access (NOMA) enables multiple mobile devices to share the same frequency band. In a conventional NOMA scheme, the receiver of a far user detects its desired signal without canceling the signal for a near user. However, the signal for the near user acts as interference and degrades the accuracy of likelihood values for the far user. In this paper, a joint maximum likelihood detection scheme for the far user of the NOMA downlink is proposed. The proposed scheme takes the interference signal into account in calculating the likelihood values. Numerical results obtained through computer simulation show that the proposed scheme improves the performance by from 0.2dB to 3.1dB for power allocation coefficients of 0.2 to 0.4 at a bit error rate (BER) of 10-2 relative to the conventional scheme.
In this paper, we investigate the problem of maximizing the weighted sum outage rate in multiuser multiple-input single-output (MISO) interference channels, where the transmitters have no knowledge of the exact values of channel coefficients, only the statistical information. Unfortunately, this problem is nonconvex and very difficult to deal with. We propose a new, provably convergent iterative algorithm where in each iteration, the original problem is approximated as second-order cone programming (SOCP) by introducing slack variables and using convex approximation. Simulation results show that the proposed SOCP algorithm converges in a few steps, and yields a better performance gain with a lower computational complexity than existing algorithms.