In past, dependable networks meant minimizing network outages or the impact of the outages. However, over the decade, major network services have shifted from telephone and data transmission to Internet and to mobile communication, where higher layer services with a variety of contents are provided. Reviewing these backgrounds of network development, the importance of the dependability of higher layer network services are pointed out. Then, the main aspects to realize the dependability are given for lower, middle and higher layer network services. In addition, some particular issues for dependable networks are described.

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As a variety of digital services are provided through networks, more and more efforts are made to ensure dependability of software behavior implementing services. Formal methods and tools have been considered as promising means to support dependability in complex software systems during the development. On the other hand, there have been serious doubts on practical applicability of formal methods. This paper overviews the present state of formal methods and discusses their applicability, especially focusing on two representative methods (SPIN and B Method) and their recent industrial applications. This paper also discusses applications of formal methods to dependable networked software.

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This paper introduces a methodology for engineering best-effort P2P algorithms into dependable P2P-based network control mechanism. The proposed method is built upon an iterative approach consisting of improving the original P2P algorithm by appropriate mechanisms and of thorough performance assessment with respect to dependability measures. The potential of the methodology is outlined by the example of timely routing control for vertical handover in B3G wireless networks. In detail, the well-known Pastry and CAN algorithms are enhanced to include locality. By showing how to combine algorithmic enhancements with performance indicators, this case study paves the way for future engineering of dependable network control mechanisms through P2P algorithms.

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In this paper, we study the end-to-end TCP performance over a path deploying a High-Availability cluster, whose characteristics are highlighted by the failover procedure to remove single-point failure. This paper proposes an approach, called High-Availability Local Recovery (HALR), to enhance TCP performance in the face of a cluster failover. To minimize the latency of retransmission, HALR saves TCP packets selectively and resends them locally after the failover is finished. For better understanding, we further develop simple analytic models to predict the TCP performance in the aspect of flow latency under a range of failover times and the effects of HALR. Using simulation results, we validate our models and show that HALR improves the TCP performance significantly over a failover event as compared with the original TCP. Typically, HALR reduces the flow latency from 4.1sec to less than 1.9sec when the failover time equals to 500ms. The simulation by real packet trace further demonstrates that the memory requirement of the proposed solution is not a concern for modern network equipments.

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Many content distribution systems such as CDN and P2P file sharing have been developed. In these systems, file-type contents require downloads to be completed before they can be played and they have no value before the download finishes. Therefore, a user's satisfaction depends on the length of the service latency. That is, the length of time from when the user issued a request until the user received an entire file. Reducing the sum of that time is necessary for the whole delivery system to satisfy users and maintain dependability on system performance. We discuss a hop-by-hop file delivery system suitable for delivering file contents whereby the sum of service latency is reduced by using the request conditions. Moreover, we propose a file delivery scheduling algorithm for a one-link model given that the content request frequency is unknown. The algorithm is based on a local optimal strategy. We performed a characteristic analysis by computer simulation. The results showed that our algorithm performs at nearly the theoretical efficiency limit of the hop-by-hop system when the request frequency distribution of each content has a deviation.

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Bolstering survivable backbone networks against multiple failures is becoming a common concern among telecom companies that need to continue services even when disasters occur. This paper presents a multiple-failure recovery scheme that considers the operation and management of optical paths. The presented scheme employs scheme escalation from pre-planned restoration to full rerouting. First, the survivability of this scheme against multiple failures is evaluated considering operational constraints such as route selection, resource allocation, and the recovery order of failed paths. The evaluation results show that scheme escalation provides a high level of survivability even under operational constraints, and this paper quantitatively clarifies the impact of these various operational constraints. In addition, the fundamental functions of the scheme escalation are implemented in the Generalized Multi-Protocol Label Switching control plane and verified in an optical-cross-connect-based network.

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Traffic Engineering (TE) is important for improving QoS in forwarding paths by efficient use of network resources. In fact, MPLS allows several detour paths to be (pre-)established for some source-destination pair as well as its primary path of minimum hops. Thus, we focus on a two-phase path management scheme using these two kinds of paths. In the first phase, each primary path is allocated to a flow on a specific source-destination pair if the path is not congested, i.e., if its utilization is less than some predetermined threshold; otherwise, as the second phase, one of the detour paths is allocated randomly if the path is available. Therefore, in this paper, we analytically evaluate this path management scheme by extending the M/M/c/c queueing system, and through some numerical results we investigate the impact of a threshold on the flow-blocking probability. Through some numerical results, we discuss the adequacy of the path management scheme for MPLS-TE.

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When an IP Multicast network is constructed on a switch-based network, many IP Multicast packet broadcasts are generated, and these broadcasts cause trouble for all of the other kinds of communication. To solve this problem, implementing IGMP Snooping on various switches has been proposed. However, some switches have insufficient IP Multicast packet-handling capability. This problem is also mentioned in RFC4541. In this paper, we propose the IGMP Snooping Activator (ISA) mechanism as a way to solve the IP Multicast packet-handling problem. The ISA transmits dummy IGMP Queries to maintain the IP Multicast network, and it joins the flooding IP Multicast group to activate IGMP Snooping in switches that are unable to handle IP Multicast packets. The experimental evaluation shows the effectiveness of our proposed method: the network load decreases because of the method's effective restraint of IP Multicast packet flooding.

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Mobile IPv6 and Network Mobility (NEMO) have been standardized as IP extensions. While these technologies are planned to be adopted by several communities, such as the vehicle, aviation, and cellular industries, Mobile IPv6 has serious deployment issues such as scalability, protocol resilience, and redundancy. In these technologies, a special router called a home agent is introduced to support the movement of mobile nodes. This home agent introduces overlapping, inefficient routes, and becomes a single point of failure and a performance bottleneck. In this paper, a new concept for scalable and dependable mobility management scheme is proposed. Multiple home agents serve the same set of mobile nodes. The Home Agent Reliability protocol and Home Agent migration are introduced to achieve this concept. We also propose an overlay network named a Global Mobile eXchange (GMX) that efficiently handles data traffic from and to mobile nodes, and operates home agents as would an Internet eXchange Point (IXP).

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A cell planning and resource allocation scheme called EBRD (Enhanced Bandwidth and Region Division) is presented for improving channel capacity and for maintaining a proper QoS (Quality of Service) over the downlink OFDMA (Orthogonal Frequency Division Multiple Access) system. Through an optimal combination of sectorization and frequency overlay, the EBRD scheme improves both channel capacity and outage probability. In order to analyze the performance of the proposed algorithm, the outage probability is obtained as a closed numerical form. In the simulation, the EBRD scheme outperforms 3-sectorization in terms of throughput and outage probability.

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Orthogonal Frequency Division Multiple Access (OFDMA) is the technique for the next generation wireless networks, whose enhanced capacity is to serve a combination of traffic with diverse QoS requirements. To realize this, the resource allocation scheme has to be carefully designed so that the instantaneous channel condition, QoS provision, and the network utilization are integrated. In this paper, we propose the resource allocation scheme for downlink traffic of 2 classes; guaranteed and non-guaranteed, having different traffic contracts. We provide guaranteed throughput for the guaranteed class by considering the cost incurred from serving this class. Then, we formulate the assignment problem with the objective of minimizing this cost. For the non-guaranteed class, we aim to maximize network utilization and to maintain throughput fairness, by employing Proportional Fairness (PF) utility function and emphasizing on the portion of network resource that the user received and the individual user's queue length. We use a heuristic approach to schedule users' data into the downlink subframe by exploiting multi-user multi-channel diversity to utilize system's bandwidth efficiently. Intensive simulation shows that our scheme differentiates classes of traffic and provides satisfied throughput, lower packet drop rate, and lower queuing delay to the guaranteed class, comparing with those of the non-guaranteed class. Furthermore, the results also show that the scheme is fair to users in the same class in both throughput and service time.

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QoS (Quality of Service) control in WLAN (IEEE802.11 Wireless LAN) is becoming increasingly important because WLAN is widely deployed as an access network and also plays a key role in providing seamless QoS communication between wired networks and wireless terminals. Although previous research has attempted to increase total throughput or available bandwidth in WLAN, few studies have treated individual TCP/UDP flow QoS. EDCA in IEEE802.11e might provide prioritized QoS functions that would partially address this problem. However, in uplink flow, which is defined as data moving from a terminal toward an Access Point, EDCA has limitations. These manifest themselves both across classes and in differentiated QoS control between terminals in the same class. Furthermore, 802.11e requires modification of terminals as well as other alterations proposed by other researchers. Instead of 802.11e or other modifications of 802.11, we propose an approach to controlling QoS that requires no terminal modifications or installation of additional software/hardware. The proposed idea is MAC-frame Receiving-Opportunity Control (ROC), in which a MAC (Media Access Control) frame is completely delivered only if it has sufficiently high priority; otherwise either the MAC frame is discarded or an Acknowledge (ACK) to the frame is not sent. The frame that was discarded is forced to accept a back-off waiting time for retransmission, consistent with 802.11DCF. This results in QoS degradation for low priority flows and eventually results in QoS improvements for high priority flows. Performance evaluation shows that the ROC causes some performance degradation in total WLAN throughput but can achieve not only QoS priority control but also arbitrary throughput performance. In particular, the ROC (in the MAC layer) can also permit different throughputs for high priority and low priority flows, conditioned on control processes in other layers. These may include rate adaptation (in the MAC layer) and TCP congestion control (in the TCP layer).

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Multicast communication over mobile ad hoc networks has become popular. However, dependable and scalable multicast routing is required for mobile ad hoc networks even though network size and node mobility continue to increase. Therefore, this paper proposes a new hierarchical multicast routing scheme for such ad hoc networks. The proposed scheme introduces the inter-cluster group mesh structure based on our previous autonomous clustering proposal. In the proposed scheme, data packets are delivered from the source node to the multicast members through multiple routes over the inter-cluster group mesh structure. Simulations show that the proposed scheme is scalable with regard to network size and strong against node mobility; it can provide dependable multicast communication on large mobile ad hoc networks.

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Most routing protocols in MANET use IP addresses as one of the most important routing information. To implement the routing protocol of MANET, the IP assignment in MANET should be solved. Allocating IP addresses is one of current key issues in the MANET, due to the absence of a centralized agent server. Previous methods require a large address space or can not use all the IP addresses of the given IP address space. For that reason, many IP addresses remain unused. To resolve this, we propose an IP address assignment protocol that uses the contiguous IP address assignment strategy without unused IP addresses. Simulations perform on ns-2 and confirm the viability of our protocol.

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For many sensor network applications such as military, homeland security, it is necessary for users (sinks) to access sensor networks while they are moving. However, sink mobility brings new challenges to secure routing in large-scale sensor networks. Mobile sinks have to constantly propagate their current location to all nodes, and these nodes need to exchange messages with each other so that the sensor network can establish and maintain a secure multi-hop path between a source node and a mobile sink. This causes significant computation and communication overhead for sensor nodes. Previous studies on sink mobility have mainly focused on efficiency and effectiveness of data dissemination without security consideration. In this paper, we propose a secure and energy-efficient data dissemination protocol — Secure COodination-based Data dissEmination (SCODE) — for mobile sinks in sensor networks. We take advantages of coordination networks (grid structure) based on Geographical Adaptive Fidelity (GAF) protocol to construct a secure and efficient routing path between sources and sinks. Our security analysis demonstrates that the proposed protocol can defend against common attacks in sensor network routing such as replay attacks, selective forwarding attacks, sinkhole and wormhole, Sybil attacks, HELLO flood attacks. Our performance evaluation both in mathematical analysis and simulation shows that the SCODE significantly reduces communication overhead and energy consumption while the latency is similar compared with the existing routing protocols, and it always delivers more than 90 percentage of packets successfully.

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This paper presents the baseband receiver design and implementation for the ultra-wideband (UWB) wireless personal area networks (WPAN). In particular, the receiver algorithms, which include frame detection, timing/frequency synchronization, and channel estimation, are designed and implemented. Simulation results demonstrate that the receiver has a packet error rate of less than 8% when E_b/N₀ =4.7dB, link margin =10.7dB, and data rate =200Mb/s. The proposed design has been designed using 0.13μm single-poly eight-metal CMOS process. The overall power dissipation is 132mW at a 132MHz system clock, while the core area is 5.62mm².

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This paper presents the formulation for the evaluation of external coupling in the alternating-phase feed single-layer slotted waveguide array antenna with baffles by using the Spectrum of Two-Dimensional Solutions (S2DS) method. A one-dimensional slot array is extracted from the array by assuming the periodicity in transversal direction and introducing the perfect electric conductors in the external region. The uniform excitation over the finite array is synthesized iteratively to demonstrate the fast and accurate results by S2DS. A unit design model with the baffles is introduced to determine the initial parameters of the slot pair which accelerate the iteration. Experiment at 25.3GHz demonstrates good uniformity of the aperture field distribution as well as the effects of the baffles. The directivity is 32.7dB which corresponds to the aperture efficiency 90.5% and the reflection is below -15.0dB over 1.3GHz.

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The expansion and diversification of wireless systems are proceeding rapidly, and the wireless communication environment will become a hybrid environment composed of multiple wireless systems. On the other hand, the resources of wireless systems are finite. Therefore, there is increasing concern that the growing use ofwireless systems will exhaust the finite wireless resources. Cognitive radio has been proposed as a solution to this problem. Cognitive radio aims to optimize the utilization of wireless resources by combining multiple wireless interfaces. Therefore, the future wireless access networks will be composed of multiple wireless systems. In this paper, we propose a packet distribution for communications using multiple IEEE802.11 wireless interfaces. The proposed method optimizes the utilization efficiency of multiple IEEE802.11 wireless interfaces based on a link cost which shows the load of the wireless link, and it improves delay and throughput in the access network. Furthermore, we show its impact on TCP.

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Obtaining current traffic matrices is essential to traffic engineering (TE) methods. Because it is difficult to monitor traffic matrices, several methods for estimating them from link loads have been proposed. The models used in these methods, however, are incorrect for some real networks. Thus, methods improving the accuracy of estimation by changing routes also have been proposed. However, existing methods for estimating the traffic matrix by changing routes can only capture long-term variations and cannot obtain current traffic matrices accurately. In this paper, we propose a method for estimating current traffic matrices that uses route changes introduced by a TE method. In this method, we first estimate the long-term variations of traffic by using the link loads monitored at previous times. Then, we adjust the estimated long-term variations so as to fit the current link loads. In addition, when the traffic variation trends change and the estimated long-term variations fail to match the current traffic, our method detects mismatch. Then, so as to capture the current traffic variations, the method re-estimates the long-term variations after removing monitored data corresponding to the end-to-end traffic causing the mismatches. We evaluate our method through simulation. The results show that our method can estimate current traffic matrices accurately even when some end-to-end traffic changes suddenly.

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For successful data collection in wireless sensor networks, it is important to ensure that the required delivery ratio is maintained while keeping a fair rate for every sensor. Furthermore, emerging high-rate applications might require complete reliability and the transfer of large volume of data, where persistent congestion might occur. These requirements demand a complete but efficient solution for data transport in sensor networks which reliably transports data from many sources to one or more sinks, avoids congestion and maintains fairness. In this paper, we propose congestion-aware and rate-controlled reliable transport (CRRT), an efficient and low-overhead data transport mechanism for sensor networks. CRRT uses efficient MAC retransmission to increase one-hop reliability and end-to-end retransmission for loss recovery. It also controls the total rate of the sources centrally, avoids the congestion in the bottleneck based on congestion notifications from intermediate nodes and centrally assigns the rate to the sources based on rate assignment policy of the applications. Performance of CRRT is evaluated in NS-2 and simulation results demonstrate the effectiveness of CRRT.

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IPv4 private addresses are commonly used in local area networks (LANs). With the increasing popularity of virtual private networks (VPNs), it has become common that a user connects to multiple LANs at the same time. However, private address ranges for LANs frequently overlap. In such cases, existing systems do not allow the user to access the resources on all LANs at the same time. In this paper, we propose name-based address mapping for VPNs, a novel method that allows connecting to hosts through multiple VPNs at the same time, even when the address ranges of the VPNs overlap. In name-based address mapping, rather than using the IP addresses used on the LANs (the real addresses), we assign a unique virtual address to each remote host based on its domain name. The local host uses the virtual addresses to communicate with remote hosts. We have implemented name-based address mapping for layer 3 OpenVPN connections on Linux and measured its performance. The communication overhead of our system is less than 1.5% for throughput and less than 0.2ms for each name resolution.

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This paper addresses the problem of joint transceiver design for Tomlinson-Harashima Precoding (THP) in the multiuser multiple-input-multiple-output (MIMO) downlink under both perfect and imperfect channel state information at the transmitter (CSIT). For the case of perfect CSIT, we differ from the previous work by performing stream-wise (both inter-user and intra-user) interference pre-cancelation at the transmitter. A minimum total mean square error (MT-MSE) criterion is used to formulate our optimization problem. By some convex analysis of the problem, we obtain the necessary conditions for the optimal solution. An iterative algorithm is proposed to handle this problem and its convergence is proved. Then we extend our designed algorithm to the robust version by minimizing the conditional expectation of the T-MSE under imperfect CSIT. Simulation results are given to verify the efficacy of our proposed schemes and to show their superiorities over existing MMSE-based THP schemes.

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Orthogonal frequency division multiplexing (OFDM), which uses a number of narrowband orthogonal sub-carriers, is a promising transmission technique. Also multi-carrier code division multi-access (MC-CDMA), which combines OFDM and frequency-domain spreading, has been attracting much attention as a future broadband wireless access. It was shown that MC-CDMA has lower channel capacity than OFDM, due to inter-code interference (ICI) resulting from orthogonality distortion caused by frequency-selective fading. Recently, many ICI cancellers have been proposed to mitigate the effect of ICI. In this paper, we derive a channel capacity expression for MC-CDMA assuming perfect ICI cancellation taking into account both frequency diversity gain and space diversity gain and compare it to that of OFDM. Furthermore, we derive a channel capacity expression for the case of imperfect ICI cancellation to discuss the impact of the residual ICI.

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This paper proposes Twin Turbo (T2) MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing). The advanced iterative decoder, called the T2 decoder, decreases the transmission error rate compared to conventional turbo decoders because it uses the correlation information among the bits mapped on an identical symbol of multi-level modulation and updates the channel reliability. When T2 is applied to a MIMO-OFDM, the required symbol energy to noise power density ratio (E_s/N₀) can be reduced more effectively than when T2 is applied to SISO (Single Input Single Output). This is because T2 can use the correlation among the bits not only mapped on an identical symbol but also transmitted from different antennas. Moreover, T2 achieves good performance in a correlated MIMO channel because the average minimum squared Euclidean distances between symbol replica candidates consisting of signals transmitted from multiple transmitter antennas are reduced. Computer simulations verify that the required E_s/N₀ of T2 MIMO-OFDM using 16QAM is 1.9dB lower than that of a conventional turbo decoder when the correlation coefficients of transmitter and receiver antennas are 0.8. A computational complexity analysis clarifies the relation between the increase in computational complexity and the reduction in the required E_s/N₀.

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This paper presents a high performance and hardware efficient packet detection structure, which employs a cross correlator for the M-sample time delayed correlation operation and a signal power calculator using the received input samples less than or equal to a zero-padded suffix of length M. We investigate the detailed characteristics of the proposed packet detector. In this paper, the performance of a class of packet detection algorithms in the ultra-wideband (UWB) channel environments is also studied. The best packet detection algorithm for the multi-band orthogonal frequency division multiplexing (MB-OFDM) UWB transmission is determined through analysis and extensive simulations. The results of analysis show that the proposed packet detection structure has advantages in the hardware complexity as well as performance when compared with the existing packet detection structures. In order to effectively conduct the packet detection before the automatic gain control (AGC) mode, we investigate the effects of both a frequency offset and the initial gain level of a variable gain amplifier (VGA) on the performance of the packet detection. We also suggest a VGA gain control technique to enhance the performance of packet detection.

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One of the promising wireless access techniques for the next generation mobile communications systems is multi-carrier code division multiple access (MC-CDMA). MC-CDMA can provide good transmission performance owing to the frequency diversity effect in a severe frequency-selective fading channel. However, the bit error rate (BER) performance of coded MC-CDMA is inferior to that of orthogonal frequency division multiplexing (OFDM) due to the residual inter-code interference (ICI) after frequency-domain equalization (FDE). Recently, we proposed a frequency-domain soft interference cancellation (FDSIC) to reduce the residual ICI and confirmed by computer simulation that the MC-CDMA with FDSIC provides better BER performance than OFDM. However, ideal channel estimation was assumed. In this paper, we propose adaptive decision-feedback channel estimation (ADFCE) and evaluate by computer simulation the average BER and throughput performances of turbo-coded MC-CDMA with FDSIC. We show that even if a practical channel estimation is used, MC-CDMA with FDSIC can still provide better performance than OFDM.

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Multiple-input multiple- output (MIMO) and orthogonal frequency division multiplexing (OFDM) are two key techniques for broadband wireless mobile communications and channel state information (CSI) is critical for the realization and performance of MIMO-OFDM systems in doubly-selective fading channels. Channel estimation based on two-dimensional discrete-time Fourier transform interpolation (2D-DFTI) is a promising solution to obtain accurate CSI for MIMO-OFDM systems in theory because of both its robustness and high computational efficiency, however, its performance will degrade significantly in practical MIMO-OFDM systems due to the two-dimensional Gibbs phenomenon caused by virtual subcarriers and burst transmission. In this paper, we propose a novel channel estimation method based on the two-dimensional enhanced DFT interpolation (2D-EDFTI), i.e., the frequency-domain EDFTI (FD-EDFTI) concatenated with the time-domain EDFTI (TD-EDFTI), for practical burst-mode MIMO-OFDM systems with virtual subcarriers, which can increase the channel estimation accuracy effectively by mitigating the Gibbs phenomenon in frequency-domain and time-domain, respectively, while keeping good robustness and high computational efficiency. In addition to computer simulations, we further implement the 2D-EDFTI channel estimator into our real-time FPGA testbed of 4 × 4 MIMO-OFDM transmission via spatial multiplexing, together with different MIMO detectors. Both computer simulations and RF experiments demonstrate the superior performance of 2D-EDFTI channel estimation in doubly-selective fading channels, therefore, high-throughput MIMO-OFDM transmission based on different MIMO detection algorithms can always be well supported. Also, it can be applied to other MIMO-OFDM transmission schemes straightforwardly.

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This paper proposes a Inter-symbol Interference (ISI) suppressing method For Orthogonal Frequency Division Multiplexing (OFDM) system. In the environments where the delay spread exceeds the guard interval, the occurrence of ISI results in a degradation of system performance. A receiving method based on the Equivalent Transmission Path (ETP) model is proposed for Single-Input Multiple-Output (SIMO) OFDM system. Compared to the receiving scheme using Maximal Ratio Combining (MRC) method, the proposed one shows better performance in suppressing errors due to ISI. The paper also points out that the ETP-based model can be used for detecting the desired signal in the multi-user OFDM system. Simulation results of the system performance show the effectiveness of the proposed method over the conventional OFDM system in suppressing ISI.

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As the IEEE 802.16e Wireless Metropolitan Access Network (WMAN) supports the mobility of a mobile station (MS), increasing MS power efficiency has become an important issue. In this paper, we analyze the sleep-mode operation for an efficient power saving mechanism for delay-guaranteed services in the IEEE 802.16e WMAN and observe the effects of the operating parameters related to this operation. For the analysis we use the M/GI/1/K queueing system with multiple vacations, exhaustive services and setup times. In the analysis, we consider the power consumption during the wake-mode period as well as the sleep-mode period. As a performance measure for the power consumption, we propose the power consumption per unit time per effective arrival which considers the power consumption and the packet blocking probability simultaneously. In addition, since we consider delay-guaranteed services, the average packet response delay is also considered as a performance measure. Based on the performance measures, we obtain the optimal sleep-mode operation which minimizes the power consumption per unit time per effective arrival with a given delay requirement. Numerical studies are also provided to investigate the system performance and to show how to achieve our objective.

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We propose a velocity-based bicasting handover scheme for the efficient utilization of backhaul network resources in fourth-generation mobile systems. The original bicasting handover scheme adopts the mechanism of holding the data of a mobile station (MS) in all potential target base stations in advance, before the actual handover execution of the MS. The scheme minimizes the packet transmission delay caused by handover and achieves the goal of seamless connectivity, however, it results in an aggressive consumption of the backhaul network resources. Moreover, as the scheme gets widely adopted for high data rate real-time services and the demand for these services grows, the amount of the resources consumed due to the bicasting will increase tremendously. In this paper, we present a new bicasting handover scheme that reduces the data bicasting time, thereby improving the backhaul network resource utilization. Our scheme exploits the velocity parameter of MS and introduces a novel concept of bicasting threshold determined for the specific mobile speed groups. Simulations prove the efficiency of our scheme over the original one in overcoming the aggressive resource consumption at the backhaul network.

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A novel timing synchronizing scheme is proposed for use in inter-vehicle communication (IVC) with an autonomous distributed intelligent transport system (ITS). The scheme determines the timing of packet signal transmission in the IVC network and employs the guard interval (GI) timing in the orthogonal frequency divisional multiplexing (OFDM) signal currently used for terrestrial broadcasts in the Japanese digital television system (ISDB-T). This signal is used because it is expected that the automotive market will demand the capability for cars to receive terrestrial digital TV broadcasts in the near future. The use of broadcasts by automobiles presupposes that the on-board receivers are capable of accurately detecting the GI timing data in an extremely low carrier-to-noise ratio (CNR) condition regardless of a severe multipath environment which will introduce broad scatter in signal arrival times. Therefore, we analyzed actual broadcast signals received in a moving vehicle in a field experiment and showed that the GI timing signal is detected with the desired accuracy even in the case of extremely low-CNR environments. Some considerations were also given about how to use these findings.

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This letter presents a necessary and sufficient condition for a class of quasi-cyclic low-density parity-check (QC LDPC) codes without girth four. Girth-four property of a class of QC LDPC codes is investigated. Good QC LDPC codes without girth four can be constructed by selecting proper shifting factors according to the proposed theorems. Examples are provided to verify the theorems. The simulation results show that the QC LDPC codes without girth four achieve a better BER performance compared with that of randomly constructed LDPC codes.

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A single chip NFC transceiver with Dual Antenna structure supporting not only NFC active and passive mode but also 13.56MHz RFID reader and tag mode is designed and fabricated. The proposed NFC transceiver can operate as a RFID tag even without external power supply thanks to a dual antenna structure for initiator and target. The area increment due to additional target antenna is negligible because the target antenna is constructed by using a shielding layer of the initiator antenna.

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IEEE 802.11 MAC is the most commonly used protocol in multi-hop ad-hoc networks which need no infrastructure. In multi-hop ad-hoc networks based on IEEE 802.11, since nodes try transmitting their packets at every possible slot, there is a high packet loss probability. This degrades network performance attributes such as throughput and fairness. In this paper, we focus on achieving the maximum throughput of the given network topology by adding extra backoff time to random backoff time based on IEEE 802.11. Specifically, the optimal load rate is obtained with constraints of Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA) mechanism.

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An information-theoretic, optimal framework is developed for tracking the residents in a Context-aware Heterogenous Smart Environment. The resident-tracking problem is formulated in terms of weighted entropy. The framework provides an optimal, online learning and prediction of users movement, location as well as most probable path segments from the symbolic domain. Successful prediction helps in on-demand operations of automated indoor devices along the users future paths and locations, thus providing the necessary comfort at a near-optimal cost. Simulation results corroborate the high prediction success, thereby providing resident-comfort while reducing energy consumption and manual operations.

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This letter proposes a novel method of large-scale IP traffic matrix (TM) estimation, called algebraic reconstruction technique inference (ARTI), which is based on the partial flow measurement and Fratar model. In contrast to previous methods, ARTI can accurately capture the spatio-temporal correlations of TM. Moreover, ARTI is computationally simple since it uses the algebraic reconstruction technique. We use the real data from the Abilene network to validate ARTI. Simulation results show that ARTI can accurately estimate large-scale IP TM and track its dynamics.

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Software defined radio (SDR) technology has been widely applied for its powerful universality and flexibility in the past decade. To address the issue of bandpass sampling of multiband signals, a novel and efficient method of finding the minimum valid sampling frequency is proposed. Since there are frequency deviations due to the channel effect and hardware instability in actual systems, we also consider the guard-bands between downconverted signal spectra in determining the minimum sampling frequency. In addition, the case that the spectra within the sampled bandwidth are located in inverse placement can be avoided by our proposed method, which will reduce the complexity of the succeeding digital signal process significantly. Simulation results illustrate that the proper minimum sampling frequency can be determined rapidly and accurately.

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A modified Schnorr-Euchner sphere decoding (SE-SD) algorithm to search for the receive minimum distance is presented. In the proposed algorithm, the visit to negative symmetric vectors of already spanned vectors is avoided by using a biased spanning, and the redundant processes to visit the all-zero vector are also eliminated. A numerical experiment shows that the modified SE-SD algorithm is much more efficient than the conventional algorithm in terms of average computational complexity.

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In this paper, we propose and analyze a multi-level acknowledgement scheme for hybrid ARQ (H-ARQ) systems, which modifies the general ACK/NAK signals to represent multilevel information. For instance, the other signals except the ACK/NAK signals may be used for scheduling of retransmission in the H-ARQ scheme, which results in increasing the resolution of the uplink channel estimation signals. Simulation results demonstrate that when the retransmission interval is set to the optimal length, the proposed H-ARQ scheme shows a 0.5-2dB gain with properly selected parameters.

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We investigate the symbol error rate (SER) of the cooperative transmission with the decode-and-forward relay protocol under Rayleigh fading channels. The technique of orthogonal space-time block coding (OSTBC) is applied at the links source-relay, source-destination and relay-destination. A closed-form SER expression is derived. Simulation results demonstrate the theoretical solutions.

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In this letter, a novel power allocation scheme is proposed to improve the outage performance of an amplify-and-forward (AF) cooperative communication network with multiple potential relays under the assumption that only mean channel gains are available at the transmitters. In this scheme, power allocation is studied jointly with a relay selection algorithm which has low computational complexity. Simulation results demonstrate the performance improvement of the proposed scheme in terms of outage behavior.

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This paper develops a methodology for resizing image resolutions in an arbitrary orthogonal block transform domain. To accomplish this, we represent the procedures resizing images in an orthogonal transform domain in the form of matrix multiplications from which the matrix scaling the image resolutions is produce. The experiments showed that the proposed method produces reliable performance without increasing the computational complexity, compared to conventional methods when applied to various transforms.

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To address the low performance for channel scanning in the DVB-T system, we propose an enhanced front-end algorithm in this paper. The proposed algorithm consists of Auto Scan and Normal Scan, which is a part of the tuning algorithm for front-end (tuner) drivers in the DVB-T receiver. The key idea is that the frequency offset is saved when performing Auto Scan in order to reduce the channel change time for Normal Scan. In addition, the results of a performance evaluation demonstrate that our enhanced front-end algorithm improves the performance of channel scanning significantly, as compared to the generic front-end algorithm.

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This letter proposes a computationally efficient way of jointly estimating the residual frequency offset (RFO) and sampling frequency offset (SFO) by using a continual pilot (CP) defined in OFDM-based DVB-T system. In order to devise an unbiased joint frequency estimator in the current DVB-T system, a CP subset is selected to offset the effects of RFO and SFO simultaneously.

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