Building video‐on‐demand servers

We have designed and implemented a controllable software architecture for a VideoonDemand (VOD) server. With the proposed software architecture, many system design issues can be investigated. For example, we studied several disk striping schemes in the storage subsystem and examined the impact of the disk striping schemes on the utilization of system resources. In the processing component, we observed that additional concurrent video streams can be supported by using efficient memory interleaving. Buffering with a large memory space in the processing subsystem is a common technique to alleviate the latency variance of accessing different system components. By employing userlevel control and scheduling, the variance can be decreased thereby reducing the resulting buffer space needed for each video stream. In the network subsystem, we adopted a serverdriven approach for investigating MPEG2 video delivery over Asynchronous Transfer Mode (ATM) networks. The VOD server controls the pace of video transmission and reduces the complexity of the client. Since the client has limited buffer space (due to cost considerations), we have reduced the buffer requirement by regulating the transmission based on timing information embedded in the MPEG2 streams. Our research and experimental results are based on a VOD server which is currently under construction. The prototype server is based on an SGI sharedmemory multiprocessor with a mass storage system consisting of RAID3 disk arrays. Using 30 RAID3 disk arrays, preliminary experimental results show that the prototype server can potentially support more than 360 highquality video streams with careful design and coordination of the different system components.     

Evaluating scheduling in integrated‐services networks using a semi‐fluid‐flow model

An integratedservices network carries diverse traffic, which leads to diverse performance objectives. For example, voice and video packets typically have performance objectives based on the fraction of packets that will be delivered within a given delay bound, while data packets often have objectives based on mean delay. Greater loads can be supported in networks in which a voice or video packet is given priority over data packets if and only if the former is in danger of missing its deadline. Algorithms that allow this include CostBased Scheduling, occupancybased algorithms, the Priority Token Bank, and to a lesser extent, the Leaky Bucket. This paper presents an approach to evaluating performance with these algorithms in the realistic case where data arrivals are highly bursty, but voice and video packets are not. Mean queueing delay for data bursts is determined analytically in some important scenarios, and an efficient simulation approach based on the same model is described for cases where analysis is not currently possible. The model is a semifluidflow model in which voice or video packets are assumed to arrive as a continuous fluid flow, whereas data packets arrive in large bursts at discrete instants in time.     

Trade‐off analysis of forward link capacity in IS‐95‐based CDMA cellular systems

This paper provides an analytic method to determine how many paging channels can be simultaneously used with traffic channels in the same CDMA forward link. So far, since one or two paging channels are enough to convey control messages from bases to mobiles, little considerations have been given to the paging channel configuration. CDMA network operators, however, recently plan to provide optional services which highly utilize the paging channel. Thus, more paging channels are required for the latest situation. Since the total number of channels that can be used in the forward link is limited by the interfering cellular environments, less traffic channels should be used if additional paging channels are required. It is the objective of this paper to examine the capacity of forward link in terms of paging and traffic channels so as to determine the impact of introducing value‐added services via paging channels. Different capacity regions are presented for various cellular environments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Quality‐of‐service guarantees architecture with weighted fair shaping

Weighted Fair Queuing (WFQ), conducted for each flow at ATM nodes, is effective for ensuring fairness among differently behaving flows, and for preventing incremental delay as cells are transmitted through multiple nodes. Implemented thus in accordance with rates assigned to flows and actual cell transmission conditions, WFQ is known as “shaping”. This paper proposes a new installable algorithm that dynamically adapts WFQ to each of multiple flows. The Quality‐of‐Service (QoS) guaranteed by this algorithm is also explained. This revised version was published online in June 2006 with corrections to the Cover Date.     

Low‐noise,low‐voltage,low‐power IF gain controlled amplifiers for wireless communication

Circuit solutions of various types of gain controlled IF amplifiers with digital and analog gain control are described. Advantages and disadvantages of the different solutions are shown. Requirements for lowpower, lowvoltage, low noise, high gain and linearity at high IFfrequencies from the system point of view are worked out. Solutions will be presented to optain optimum performance by technology and circuit design technique for digital wireless telephone systems used for GSM and PCN systems.     

Novel optimal real‐time admission control and buffer management for the Video‐On‐Demand (VOD) service

In order to meet the Quality of Service (QoS) requirements of the VOD service, and, on the other hand, to maximize the system throughput (revenue), it is essential that the video call request admission control algorithm be carefully designed. In this paper, in addition to the Single Segment (SS) admission control first described in [7], we propose two new types of admission control schemes called Segmental Re‐tuned (SR) admission control and Multiple Segment (MS) admission control for variable‐bit‐rate video streams under various video server architectures. The basic approach to the algorithm development is first to formulate each problem as a mathematical problem and then to identify special structures and properties for such formulations so that optimal real‐time algorithms can be developed. In computational experiments, it is shown that the proposed algorithms for the considered video server architectures, compared with the traditional admission control scheme based upon the peak frame size, typically achieve over 175–200% improvement in the system throughput. In addition, the new proposed MS scheme performs 5–25% better than SS and SR schemes. This revised version was published online in June 2006 with corrections to the Cover Date.     

A spread‐slotted random‐access protocol with multi‐priority for personal and mobile communication networks carrying integrated traffic

This paper describes and analyzes a medium access protocol for wireless personal communication networks serving integrated traffic. A multipriority mechanism, which is implemented and controlled explicitly by the users and without any involvement from the network is incorporated into the protocol. We examine the proposed protocol under reservation and nonreservation policies and evaluate its performance when handling integrated voice and data traffic. The proposed protocol is suitable to be used in Personal Communication Systems aiming to provide integrated (voice/data) services.     

An unslotted multichannel channel‐access protocol for distributed direct‐sequence networks

A multichannel reservation-based channel-access protocol is investigated in this paper. The available system bandwidth is divided into distinct frequency channels. Under the protocol, one channel (the control channel) is used to exchange reservation messages and the remaining channels (the traffic channels) are used for information-bearing traffic. The performance of this scheme is compared to that of a single-channel reservation-based protocol. A simple contention-based slotted-Aloha protocol is also considered. Performance results take into account the effects of multiple-access interference on acquisition and packet errors. Results show that the reservation-based approach is advantageous under conditions of high traffic. In addition, a pacing mechanism that mitigates multiple-access interference and promotes fairness is described, and results are presented that demonstrate its effectiveness. This revised version was published online in June 2006 with corrections to the Cover Date.     

Contactless vital signs monitoring based on few‐mode and multi‐core fibers

Few-mode and multi-core fibers are proposed and demonstrated for contactless vital signs monitoring in this paper.In-line optical fiber interferometers using few-mode and multi-core fibers are designed and offset splicing is utilized for mode excitation.Extinction ratio and insertion loss are analyzed experimentally under different offset distances.The fabricated in-line interferometers are packaged under the mattress to realize contactless vital signs signals collection.By using filtering techniques,both respiration and heartbeat signals can be recovered successfully,and respiration as well as heartbeat ratio are obtained.Mode excitation and interference are theoretically analyzed in few-mode fiber while curvature sensing experiments using multi-core fiber interferometer are performed to verify its excellent performance on vital signs monitoring.The successful demonstration on contactless vital signs monitoring makes few-mode and multi-core fibers promising candidates for healthcare applications.     

A deadlock model for a multi‐service medium access protocol employing multi‐slot N‐ary stack algorithm (msSTART)

Many modern multi‐service medium access protocols (MACs) use a collision based capacity request signaling channel as part of a hybrid TDMA frame structure. Multi‐slot Stack Random Access Algorithm (msSTART) is proposed for use in IEEE 802.14 hybrid fiber/coaxial network and will be highly relevant for the S‐MAC development of evolving WATM MAC specifications. This paper studies the performance of msSTART as an example of a Q‐ary tree contention resolution algorithm (CRA) in the wireless environment using the novel Basic Deadlock model. We contrast approximate results for msSTART performance obtained by simulation under extreme inter‐station correlation with analytical results for the more popular p‐persistence CRA used in several testbed WATM implementations. Using three signaling channel schemes designed to provide support for increased system stability, to implement priority in the wireless MAC, and maximise efficiency, we provide comparative results for evaluation of msSTART and p‐persistence ALOHA under what the IEEE 802.14 working group has termed the “disaster scenario”. We find that of the three schemes evaluated the full Contention Mini‐Slot (CMS) sharing scheme employing multiple CMSs per data region extends the protocol's useable load region the furthest. We conclude that Q‐ary tree contention resolution algorithms (in particular msSTART) are best adapted to the wireless environment, providing less case sensitive performance. This revised version was published online in July 2006 with corrections to the Cover Date.     

A logarithmic lower bound for time‐spread multiple‐access (TSMA) protocols

Time‐Spread Multiple‐Access (TSMA) protocols are scheduled access protocols for mobile multi‐hop radio networks that guarantee deterministic access to the shared channel regardless of the possibility of radio interference. In scheduled access methods, time is considered to be slotted and time slots are cyclically organized into frames. In general, the shorter the frame, the more efficient the protocol. An Ω(log log n) lower bound is known on the minimum length of the frame of TSMA protocols in networks with n nodes. In this note we improve that lower bound by characterizing the multiple access to the radio channel as a combinatorial problem. The proposed characterization allows us to prove that no TSMA protocols can successfully schedule the transmissions of the nodes of a multi‐hop radio network in frames with less than log n time slots. This revised version was published online in August 2006 with corrections to the Cover Date.     

Energy‐efficient selective cache invalidation

In a mobile environment, users of portable computers can query databases over the wireless communication channels. To reduce contention on the limited bandwidth of the wireless channels, frequently accessed data are cached at the mobile clients. However, maintenance of the cache consistency is complicated by the mobile clients' frequent disconnection to conserve energy. One promising approach in the literature is for the server to periodically broadcast invalidation reports from which clients can salvage their cache content that are still valid. This mechanism is, however, not energy efficient as clients are expected to examine the entire invalidation report. In this paper, we reexamine the cache coherency problem and propose three novel cache coherency schemes. While these schemes are based on periodic broadcast of invalidation reports, they allow clients to selectively tune to the portions of the invalidation report that are of interest to them. This allows the clients to minimize the power consumption when invalidating their cache content. We conducted extensive studies based on a simulation model. Our study shows that the proposed schemes are not only effective in salvaging the cache content that are still valid (and hence result in lower access time), but are also efficient in energy utilization. While none of the proposed algorithms is superior in both the access time and energy efficiency, one of the schemes, Selective Cache Invalidation, provides the best overall performance.     

A low‐complexity multiuser detector for up‐link CDMA QPSK mobile radio communications

This paper deals with a multiuser detector based on a new decorrelating approach for asynchronous uplink DS/CDMA communications in which the QPSK modulation scheme is used in transmission. It is shown here that the receiver proposed is near–far resistant and exhibits a low complexity which allows realtime operation. Performance is expressed in terms of bit error rate (BER) which has been derived by simulations under the assumption of a slowly frequencyselective Rayleigh fading channel.     

A new approach to the design and analysis of peer‐to‐peer mobile networks

This paper introduces a new model and methodological approach for dealing with the probabilistic nature of mobile networks based on the theory of random graphs. Probabilistic dependence between the random links prevents the direct application of the theory of random graphs to communication networks. The new model, termed Random Network Model, generalizes conventional random graph models to allow for the inclusion of link dependencies in a mobile network. The new Random Network Model is obtained through the superposition of Kolmogorov complexity and random graph theory, making in this way random graph theory applicable to mobile networks. To the best of the authors' knowledge, it is the first application of random graphs to the field of mobile networks and a first general modeling framework for dealing with adhoc network mobility. The application of this methodology makes it possible to derive results with proven properties. The theory is demonstrated by addressing the issue of the establishment of a connected virtual backbone among mobile clusterheads in a peertopeer mobile wireless network. Using the Random Network Model, we show that it is possible to construct a randomized distributed algorithm which provides connectivity with high probability, requiring exponentially fewer connections (peertopeer logical links) per clusterhead than the number of connections needed for an algorithm with a worst case deterministic guarantee.     

Virtual tree‐based multicast routing with a distributed numbering algorithm for WM‐ATM handover

The flexibility offered by the ATM transport mechanism and its potential capabilities, together with its compatibility with the B‐ISDN, makes ATM the prime candidate for the support of multimedia services over the wireless medium. However, technical issues remain to be resolved in relation to the feasibility of ATM for the support of mobility over the radio interface. This paper examines network issues in supporting handover in a wireless ATM network. In particular, analysis has been performed for a virtual tree-based network architecture. Results have shown that by using multicast transmission and by using a distributed numbering algorithm, the potential problems of cell-loss and cell-duplication have been eliminated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Multiservices MAC‐protocol for wireless ATM

ATM is the future networking technology in the area of broadband networks. Using fiber optical cabling offers high bandwidth and low error rates. It is supposed to support different kinds of services, e.g., file transfer, videoconferencing, and speech transmissions. To support seamless end-to-end quality of service in a mobile environment a suitable extension to the fixed network part is necessary. In a wireless ATM environment the medium access protocol takes a prominent position. It is responsible for an efficient and fair media access on the shared radio resource. Due to the limited available bandwidth and the much higher error rates on the radio link special provisions must be provided. The compliance of traffic contracts for connections with different quality of services is the aim of our proposed protocol. This is the base of true end-to-end services with quality of service assurance in wireless ATM. This revised version was published online in June 2006 with corrections to the Cover Date.     

Controlling plasmon‐exciton interactions through photothermal reshaping

We investigated the plasmon-exciton interactions in an individual gold nanorod(GNR)with monolayer MoS2 at room temperature with the single-particle spectroscopy technique.To control the plasmon-exciton interaction,we tuned the local surface plasmon resonance of an individual GNR in-situ by employing the photothermal reshaping effect.The scattering spectra of the GNR-MoS2 hybrids exhibited two dips at the frequencies of the A and B excitons of monolayer MoS2,which were caused by the plasmon-induced resonance energy transfer effect.The resonance energy transfer rate increased when the surface plasmon resonance of the nanorod matched well with the exciton transition energy.Also,we demonstrated that the plasmon-enhanced fluorescence process dominated the photoluminescence of the GNR-MoS2 hybrid.These results provide a flexible way to control the plasmon-exciton interaction in an all-solid-state operating system at room temperature.     

Time‐varying modeling of a nonstationary signal

In this paper, a method for modeling a nonstationary signal using timevarying parameters by considering that the signal is generated by a linear, timevarying (LTV) system with a stationary white noise input is presented. This method is based on the Wold–Cramer (WC) representation of a nonstationary signal. Because the relationship between the generalized transfer function of an LTV system and the timevarying coefficients of the difference equation of a discretetime system is not addressed so far in the literature, therefore, in this paper a solution to this problem is proposed. A simple relationship between the system generalized transfer function and the timevarying parameters of the system is derived, then an MLS algorithm is developed to solve for the system timevarying parameters. Computer simulation illustrating the effectiveness of our algorithm is presented.     

A public‐key based secure Mobile IP

The need of scaleable key management support for Mobile IP, especially the routeoptimized Mobile IP, is well known. In this paper, we present the design and the implementation of a public key management system that can be used with IETF basic and route optimized Mobile IP. The system, known as the Mobile IP Security (MoIPS) system, was built upon a DNS based X.509 Public Key Infrastructure and the innovation in cross certification and zeromessage key generation. The system can supply cryptographic keys for authenticating Mobile IPv.4 location management messages and establishing IPSec tunnels for Mobile IP redirected packets. It can also be used to augment firewall traversal of Mobile IP datagrams. A FreeBSD UNIX implementation of the MoIPS prototype is available for noncommercial uses.     

Demand re‐registration for PCS database restoration

In a Personal Communications Services (PCS) network, mobility databases such as Home Location Register (HLR) and Visitor Location Register (VLR) are utilized to support mobility management for Mobile Stations (MSs). If the location databases fail, the location information loss or corruption will seriously degrade the service offered to the subscribers. In this paper, we propose a new VLR failure recovery scheme called demand reregistration. In this scheme, the VLR broadcasts a reregistration request to all MSs after the VLR failure. When an MS receives the reregistration request, it sends a registration message to the VLR to recover the location record. Since all MSs will reregister after receiving the broadcasting request, traffic jam (and thus collisions) may occur. If a collision occurs, then the involved MSs must resend the registration messages. This paper studies the performance of demand reregistration by investigating how effectively the reregistration can recover the location record for an MS before the first MS call termination occurs. Our results indicate that demand reregistration can effectively recover VLR failure.