Scheduling and bandwidth allocation for the distribution of archived video in VOD systems

Providing costeffective videoondemand (VOD) services necessitates reducing the required bandwidth for transporting video over highspeed networks. In this paper, we investigate efficient schemes for transporting archived MPEGcoded video over a VOD distribution network. A video stream is characterized by a timevarying traffic envelope, which provides an upper bound on the bit rate. Using such envelopes, we show that video streams can be scheduled for transmission over the network such that the perstream allocated bandwidth is significantly less than the source peak rate. In a previous work [13], we investigated stream scheduling and bandwidth allocation using global traffic envelopes and homogeneous streams. In this paper, we generalize the scheduling scheme in [13] to include the heterogeneous case. We then investigate the allocation problem under windowbased traffic envelopes, which provide tight bounds on the bit rate. Using such envelopes, we introduce three streamscheduling schemes for multiplexing video connections at a server. The performance of these schemes is evaluated under static and dynamic scenarios. Our results indicate a significant reduction in the perstream allocated bandwidth when stream scheduling is used. While this reduction is obtained through statistical multiplexing, the transported streams are guaranteed stringent, deterministic quality of service (i.e., zero loss rate and small, bounded delay). In contrast to video smoothing, our approach requires virtually no buffer at the settop box since frames are delivered at their playback rate.     

Consistency management in Deno

We describe a new replicatedobject protocol designed for use in mobile and weaklyconnected environments. The protocol differs from previous protocols in combining epidemic information propagation with voting, and in using fixed perobject currencies for voting. The advantage of epidemic protocols is that data movement only requires pairwise communication. Hence, there is no need for a majority quorum to be available and simultaneously connected at any single time. The protocols increase availability by using voting, rather than primarycopy or primarycommit schemes. Finally, the use of perobject currencies allows voting to take place in an entirely decentralized fashion, without any server having complete knowledge of group membership. We show that currency allocation can be used to implement diverse policies. For example, uniform currency distributions emulate traditional voting schemes, while allocating all currency to a single server emulates a primarycopy scheme. We present simulation results showing both schemes, as well as the performance advantages of using currency proxies to temporarily reallocate currency during planned disconnections. Furthermore, we discuss an initial design of the underlying replicatedobject system and present a basic API.     

Assigning codes in wireless networks: bounds and scaling properties

In the Code Division Multiple Access (CDMA) framework, collisions that can occur in wireless networks are eliminated by assigning orthogonal codes to stations, a problem equivalent to that of coloring graphs associated to the physical network. In this paper we present new upper and lower bounds for two versions of the problem (hidden and primary collision avoidance – HPCA – or hidden collision avoidance only – HCA). In particular, optimal assignments for special topologies and heuristics for general topologies are proposed. The schemes show better average results with respect to existing alternatives. Furthermore, the gaps between the upper bound given by the heuristic solution, the lower bound obtained from the maximumclique problem, and the optimal solution obtained by branch and bound are investigated in the different settings. A scaling law is then proposed to explain the relations between the number of codes needed in Euclidean networks with different station densities and connection distances. The substantial difference between the two versions HPCA and HCA of the problem is investigated by studying the probabilistic distribution of connections as a function of the distance, and the asymptotic size of the maximum cliques.     

Noise considerations for mixed‐signal RF IC transceivers

This paper discusses design tradeoffs for mixedsignal radio frequency integrated circuit (RF IC) transceivers for wireless applications in terms of noise, signal power, receiver linearity, and gain. During air wave transmission, the signal is corrupted by channel noise, adjacent interfering users, image signals, and multipath fading. Furthermore, the receiver corrupts the incoming signal due to RF circuit nonlinearity (intermodulation), electronic device noise, and digital switching noise. This tutorial paper gives an overview of the design tradeoffs needed to minimize RF noise in an integrated wireless transceiver. Fundamental device noise and the coupling of switching noise from digital circuits to sensitive analog sections and their impact on RF circuits such as frequency synthesizers are examined. Methods to minimize mixedsignal noise coupling and to model substrate noise effects are presented.     

Adaptive multicast routing in multirate loss networks

In this paper, we study two versions of the multicast routing problem in multirate loss networks: complete and partial. In the complete version of the multicast routing problem, the identities of all destination nodes are available to the multicast routing algorithm at once. Conversely, in the partial version of the multicast problem, the identities of the destination nodes are revealed to the routing algorithm one by one. Although the complete version of the multicast routing problem, also known as the Steiner tree problem, has been well studied in the literature, less attention has been paid for the definition of link costs and evaluating the performance of multicast routing algorithm from the network revenue point of view. Therefore, in this paper, we first propose two approaches, namely, the Markov Decision Processbased (MDPbased) and Least Loaded Routingbased (LLRbased) approaches, for defining link costs. Several heuristic multicast routing algorithms are then proposed for both fully connected networks and sparsely connected networks. We have also proposed a new performance metric, referred to as fractional reward loss, for evaluating the performance of multicast routing algorithms. Our simulation results indicate that algorithms based on partial destination information yield worse performance than those based on complete information. We also found that, for fully connected networks, algorithms that use LLRbased link costs yield very competitive performance as compared to those that use MDP approach. However, for sparsely connected networks, LLRbased algorithms yield significantly worse performance as compared to the MDPbased algorithms.     

Floor acquisition multiple access (FAMA) in single‐channel wireless networks

The FAMANCS protocol is introduced for wireless LANs and adhoc networks that are based on a single channel and asynchronous transmissions (i.e., no time slotting). FAMANCS (for floor acquisition multiple access with nonpersistent carrier sensing) guarantees that a single sender is able to send data packets free of collisions to a given receiver at any given time. FAMANCS is based on a threeway handshake between sender and receiver in which the sender uses nonpersistent carrier sensing to transmit a requesttosend (RTS) and the receiver sends a cleartosend (CTS) that lasts much longer than the RTS to serve as a busy tone that forces all hidden nodes to back off long enough to allow a collisionfree data packet to arrive at the receiver. It is shown that carrier sensing is needed to support collisionfree transmissions in the presence of hidden terminals when nodes transmit RTSs asynchronously. The throughput of FAMANCS is analyzed for singlechannel networks with and without hidden terminals; the analysis shows that FAMANCS performs better than ALOHA, CSMA, and all prior proposals based on collision avoidance dialogues (e.g., MACA, MACAW, and IEEE 802.11 DFWMAC) in the presence of hidden terminals. Simulation experiments are used to confirm the analytical results.     

The effects of asymmetry on TCP performance

In this paper, we study the effects of network asymmetry on endtoend TCP performance and suggest techniques to improve it. The networks investigated in this study include a wireless cable modem network and a packet radio network, both of which can form an important part of a mobile ad hoc network. In recent literature (e.g., [18]), asymmetry has been considered in terms of a mismatch in bandwidths in the two directions of a data transfer. We generalize this notion of bandwidth asymmetry to other aspects of asymmetry, such as latency and mediaaccess, and packet error rate, which are common in widearea wireless networks. Using a combination of experiments on real networks and simulation, we analyze TCP performance in such networks where the throughput achieved is not solely a function of the link and traffic characteristics in the direction of data transfer (the forward direction), but depends significantly on the reverse direction as well. We focus on bandwidth and latency asymmetries, and propose and evaluate several techniques to improve endtoend performance. These include techniques to decrease the rate of acknowledgments on the constrained reverse channel (ack congestion control and ack filtering), techniques to reduce source burstiness when acknowledgments are infrequent (TCP sender adaptation), and algorithms at the reverse bottleneck router to schedule data and acks differently from FIFO (acksfirst scheduling).     

NETMAN: The design of a collaborative wearable computer system

This paper presents a wearable groupware system designed to enhance the communication and cooperation of highly mobile network technicians. It provides technicians in the field with the capabilities for realtime audioconferencing, transmission of video images back to the office, and contextsensitive access to a shared notebook. An infrared locationtracking device allows for the automatic retrieval of notebook entries depending on the user's current location.     

Simulation‐based performance evaluation of routing protocols for mobile ad hoc networks

In this paper we evaluate several routing protocols for mobile, wireless, ad hoc networks via packetlevel simulations. The ad hoc networks are multihop wireless networks with dynamically changing network connectivity owing to mobility. The protocol suite includes several routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector, used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, endtoend delay, and routing load for a given traffic and mobility model. Both small (30 nodes) and medium sized (60 nodes) networks are used. It is observed that the new generation of ondemand routing protocols use much lower routing load, especially with small number of peertopeer conversations. However, the traditional link state and distance vector protocols provide, in general, better packet delivery and endtoend delay performance.     

Dynamic capacity allocation and hybrid multiplexing techniques for ATM wireless LANs

We consider digital wireless multimedia LANs and timevarying traffic rates. To deal effectively with the dynamics of the timevarying traffic rates, a Traffic Monitoring Algorithm (TMA) is deployed to dynamically allocate channel capacities to the heterogeneous traffics. The TMA is implemented as a higher level protocol that dictates the capacity boundaries within two distinct framed transmission techniques: a Framed Time DomainBased (FTDB) technique and a Framed CDMA (FCDMA) technique. The performance of the TMA in the presence of the FTDB technique is compared to its performance in the presence of the FCDMA technique for some traffic scenarios. The performance metrics used for the TMAFTDB and TMAFCDMA combinations are channel capacity utilization factors, traffic rejection rates, and traffic delays. It is found that the TMAFTDB is superior to the TMAFCDMA when the speed of the transmission links is relatively low and the lengths of the transmitted messages are relatively short. As the speed of the transmission links and the length of the transmitted messages increase, the TMAFCDMA eventually outperforms the TMAFTDB.     

Performance evaluation of optimum combining and maximal ratio combining in the presence of co‐channel interference and channel correlation for wireless communication systems

Antenna diversity is an important technique to combat fading and reduce cochannel interference (CCI). In this paper, we present an analytical approach to derive bit error rate (BER) for Optimum Combining (OC) and Maximal Ratio Combining (MRC) in the presence of CCI. The paper has two parts. In the first part, the analysis of BER for OC with two cochannel interferers and MRC with an arbitrary number of interferers is presented for Marray antenna systems under the assumption that the channels of users are independent of each other. In the second part, the analysis of BER for OC and MRC in the presence of one dominant cochannel interferer is presented for dual antenna systems by assuming that the channels of the desired user or cochannel interferer are correlated. For DPSK signal, an exact BER expression is derived. The work presented here also yields an upper bound for BPSK or QAM signal based on the results of Foschini and Salz (1983).     

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.     

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.     

MA‐WATM: A new approach towards an adaptive wireless ATM network

In a cellular multimedia network like wireless ATM (WATM), self control seems primordial. Our new approach is based on the application of DAI (distributed artificial intelligence) techniques in order to build a selfadaptive network within random nonuniform traffic conditions. Attempting to achieve a high network capacity in terms of resource allocation and air interface BER (bit error rate), we propose to apply intelligent agent features to enhance the architecture of WATM systems. In fact, the intelligent platform MAWATM (multiagent wireless ATM) is used to provide a flexible integration of the multiagent technique in wireless entities, BSs (base stations), MSs (mobile stations) and MSCs (mobile switching centers). Two applications are investigated and explored by simulations in order to bear out the feasibility of the multiagent approach.     

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.     

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.     

Personal Imaging and lookpainting as tools for personal documentary and investigative photojournalism

A means and apparatus for covert capture of extremely highresolution photorealistic images is presented. The apparatus embodies a new form of userinterface – instead of the traditional point and click metaphor which was thought to be the simplest photography had to offer, what is proposed is a look metaphor in which images are generated through the natural process of looking around, in a manner that does not require conscious thought or effort. These lookpaintings become photographic/videographic memories that may, at times, exceed the quality attainable with even large and cumbersome professional photographic film cameras, yet they may be captured through a device that resembles ordinary sunglasses. The method is based on longterm psychophysical adaptation using a covert sunglassbased realitymediating apparatus, together with two new results in image processing. The first new result is a means of estimating the true projective coordinate transformation between successive pairs of images, and the second is that of estimating, to within a single unknown scalar constant, the quantity of light arriving at the image plane. Furthermore, what is captured is more than just a picture. The resulting environment map may be explored by one or more remote participants who may also correspond and interact with the wearer during the actual shooting process, giving rise to computer supported collaborative (collective) photography, videography, shared photographic/videographic memory, etc.     

A general purpose proxy filtering mechanism applied to the mobile environment

Host mobility complicates the standard networking model in unexpected ways. It increases network heterogeneity, causing difficulty within applications that expect a high or constant amount of network bandwidth. Mobility increases cost when a user switches from a relatively inexpensive high bandwidth network to a low bandwidth paybycall or paybybyte network. Mobility may also reduce security when a user moves from a safe network onto a foreign one. This situation can be improved by introducing a proxy between the mobile client and its peer. The purpose of this intermediary is to process data moving between the client and peer. The type of processing performed depends on the desired result: the proxy can hide network heterogeneity via data filtering, reduce cost by using compression, and increase security through the use of secure protocols between the client and proxy. This paper presents a general purpose proxy system and how it has been applied to the mobile environment. The overall architecture is described, examples of its use given, and a study on its feasibility and performance is presented.     

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.     

Upper bounds for blocking probabilities in large multi‐rate loss networks

In this paper, we consider large loss networks with fixed routing and multirate traffic. We use singlelink formulae and standard results on multidimensional Gaussian distributions to obtain upper bounds for blocking probabilities of new calls under light up to critical loading conditions. This is the loading regime of interest for many practical applications such as admission control in ATM networks. The main advantage of our approach is that the complexity does not scale with the size of the system, making it numerically attractive. Comparison with simulation results show that we get good upper bounds. We conclude by discussing the correlation between links in a network.