On the design of feedback controllers to achieve prescribed initial value constraints

The problem of designing a stabilizing compensator for a control system to achieve prescribed initial value constraints ⁽ⁱ⁾(0⁺)=y_i is considered. Indeed, modulo certain technical conditions, such a compensator exists if and only if y_i=0;i= 0,1,...,rp +rt –2; whererp is the relative degree of the plant andrt is the relative degree of the system input. This theorem is derived and a complete parameterization of the set of compensators that achieve the prescribed design constraints is formulated.This research was supported in part by NSF Grant No. 921106.     

Immittance-type tabular stability test for 2-D LSI systems based on a zero location test for 1-D complex polynomials

A new algebraic test is developed to determine whether or not a two-variable (2-D) characteristic polynomial of a recursive linear shift invariant (LSI, discrete-time) system is stable (i.e., it does not vanish in the closed exterior of the unit bi-circle). The method is based on the original form of a unit-circle zero location test for one variable (1-D) polynomials with complex coefficients proposed by the author. The test requires the construction of a table, in the form of a sequence of centrosymmetric matrices or 2-D polynomials, that is obtained using a certain three-term recursion, and examination of the zero location with respect to the unit circle of a few associated 1-D polynomials. The minimal set necessary and sufficient conditions for 2-D stability involves one 1-D polynomial whose zeros must reside inside the unit circle (which may be examined before the table is constructed), and one symmetric 1-D polynomial (which becomes available after completing the table) that is required not to have zeros on the unit circle. A larger set of intermediate necessary conditions for stability (which may be examined during the table's construction) are also given. The test compares favorably with Jury's recently improved 2-D stability test in terms of complexity and munerical stability.     

The discrete Einstein relation

In this paper the connection between massM, resistance and commute time for random walks on graphs is further explored, and the relation=2M · is proved. An extension of the result is made to multigraphs, which are an extension of the graph concept where a black box is treated like an edge.     

Recursive estimation of two-dimensional processes with application to image processing

A low order quarter-plane-causal recursive model is presented to represent the class of 2-D stationary Gaussian processes with power spectra matrices factorable into a quarter-plane-causal and anti-causal parts. This model is used to develop a technique for obtaining optimal 2-D recursive estimators. The approach taken here is similar to Attasi's [8], with no commutability condition imposed on the model. Circumventing this condition allows the modeling of the 2-D processes to be achieved with fewer parameters, and enables one to find the solutions to the problems of blur and color noise which are inherent in most image degraded images. Some simulated examples illustrate these points.This research was supported in part by the U.S. Army Research Grant DAAG29-79-C-0054 and the National Science Foundation Grant ECS-8011911.     

Tree multicast strategies in mobile,multihop wireless networks

Tree multicast is a well established concept in wired networks. Two versions, persource tree multicast (e.g., DVMRP) and shared tree multicast (e.g., Core Based Tree), account for the majority of the wireline implementations. In this paper, we extend the tree multicast concept to wireless, mobile, multihop networks for applications ranging from ad hoc networking to disaster recovery and battlefield. The main challenge in wireless, mobile networks is the rapidly changing environment. We address this issue in our design by: (a) using soft state (b) assigning different roles to nodes depending on their mobility (2level mobility model); (c) proposing an adaptive scheme which combines shared tree and persource tree benefits, and (d) dynamically relocating the shared tree Rendezvous Point (RP). A detailed wireless simulation model is used to evaluate various multicast schemes. The results show that persource trees perform better in heavy loads because of the more efficient traffic distribution; while shared trees are more robust to mobility and are more scalable to large network sizes. The adaptive tree multicast scheme, a hybrid between shared tree and persource tree, combines the advantages of both and performs consistently well across all load and mobility scenarios. The main contributions of this study are: the use of a 2level mobility model to improve the stability of the shared tree, the development of a hybrid, adaptive persource and shared tree scheme, and the dynamic relocation of the RP in the shared tree.     

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.     

On the structure of the privacy hierarchy

An N argument function f(x ₁,...,x _N ) is called t-private if a protocol for computing f exists so that no coalition of at most t parties can infer any additional information from the execution, other than the value of the function. The motivation of this work is to understand what levels of privacy are attainable. So far, only two levels of privacy are known for N argument functions which are defined over finite domains: functions that are N-private and functions that are (N – 1)/2-private but not N/2-private.In this work we show that the privacy hierarchy for N-argument functions which are defined over finite domains, has exactly (N + 1)/2 levels. We prove this by constructing, for any N/2 t N – 2, an N-argument function which is t-private but not (t + 1)-private.This research was supported by US-Israel Binational Science Foundation Grant 88-00282.     

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.     

On the analysis of two-dimensional discrete singular systems

In contrast to 1-D systems, the 2-D systems have no natural notion of causality. An artificial restriction traditionally imposed to allow recursive solution of these systems is that of recursibility. In this paper we study 2-Dsingular systems, taking advantage of the nonoriented or noncausal nature of these systems to provide a solution even if the requirement of recursibility does not hold. It is shown thatnonrecursible masks may be described using singular 2-D systems. The analysis approach relies on thefundamental matrix.Research supported by the US Fulbright Foundation in Greece and NSF Grant ECS-8805932.     

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.     

2-D harmonic retrieval using higher-order statistics

We consider the problem of estimating the harmonics of a noisy 2-D signal. The observed data is modeled as a 2-D sinusoidal signal, with either random or deterministic phases, plus additive Gaussian noise ofunknown covariance. Our method utilizes recently defined higher-order statistics, referred to as mixed-cumulants, which permit a formulation that is applicable to both the random and deterministic case. In particular, we first estimate the frequencies in each dimension using an overdetermined Yule-Walker type approach. Then, the 1-D frequencies are paired using a matching criterion. To support our theory, we examine the performance of the proposed method via simulations.     

Predictive Caching Strategy for On-Demand Routing Protocols in Wireless Ad Hoc Networks

Route caching strategy is important in on-demand routing protocols in wireless ad hoc networks. While high routing overhead usually has a significant performance impact in low bandwidth wireless networks, a good route caching strategy can reduce routing overheads by making use of the available route information more efficiently. In this paper, we first study the effects of two cache schemes, link cache and path cache, on the performance of on-demand routing protocols through simulations based on the Dynamic Source Routing (DSR) protocol. Since the path cache DSR has been extensively studied, we focus in this paper on the link cache DSR in combination with timer-based stale link expiry mechanisms. The effects of different link lifetime values on the performance of routing protocol in terms of routing overhead, packet delivery ratio and packet latency are investigated. A caching strategy incorporating adaptive link timeout is then proposed, which aims at tracking the optimal link lifetime under various node mobility levels by adaptively adjusting the link lifetime based on the real link lifetime statistics. The performance of the proposed strategy is then compared with the conventional path cache DSR. The results show that without a timeout mechanism, a link cache scheme may suffer severe performance degradation due to the use of broken routes, while the proposed adaptive link cache strategy achieves significantly improved performance by reducing the routing overhead when the network traffic load is high.     

Economics of “design for test” to remain competitive in the 90s

This article emphasizes the criticality of maximizing value adders and minimizing the costs of design for test (DFT) in order to remain competitive in ASIC manufacturing in the 90s.     

Mobile ATM buffer capacity analysis

This paper extends a stochastic theory for buffer fill distribution for multiple on and off sources to a mobile environment. Queue fill distribution is described by a set of differential equations assuming sources alternate asynchronously between exponentially distributed periods in on and off states. This paper includes the probabilities that mobile sources have links to a given queue. The sources represent mobile user nodes, and the queue represents the capacity of a switch. This paper presents a method of analysis which uses mobile parameters such as speed, call rates per unit area, cell area, and call duration and determines queue fill distribution at the ATM cell level. The analytic results are compared with simulation results.This paper is partially funded by ARPA contract number J-FBI-94-223.The Mathematica code for this paper can be found on http://www.tisl.ukans.edu/sbush.     

On the Capacity of IEEE 802.11 DCF with Capture in Multipath-Faded Channels

In this paper, we estimated the influence of capture effect over the capacity of IEEE 802.11b DCF within a single picocell. The channel utilization is examined analytically by introducing two capture models based on Rayleigh-distributed envelopes of the captured and the interfering frames divided into two local-mean power classes. Simulations in a pure Rician-faded channel depict the conditions under which both Rayleigh-faded capture models can be used to accurately predict the peak network capacity. Unlike the RTS/CTS handshake access mode, Basic access mode is significantly sensitive to the capture ratio, i.e., the receiver design. The packet size threshold over which it is convenient to switch from Basic to RTS/CTS handshake access scheme is also sensitive to the capture effect.     

A necessary and sufficient condition for right coprime factorization of nonlinear feedback systems

In this short note, we establish a simple, yet precise, necessary and sufficient condition for the right coprime factorization of a nonlinear feedback control system. As a consequence, we also obtain similar conditions for the stable right coprime factorizations of the nonlinear feedback control system.     

Solutions for H∞ Filtering of Two-Dimensional Systems

Thispaper deals with the H filtering problemfor linear discrete-time two-dimensional (2-D) systems describedby the Roesser model. It firstly establishes a version of thebounded real lemma to give a sufficient condition for quantificationof the H noise attenuation for 2-D systems.Based on the bounded real lemma, the H filteringproblem is investigated for filters of an observer-based structureor a general state equation form and the solutions are obtainedin terms of Riccati inequalities or linear matrix inequalities.The design approach is illustrated by an example of a stationaryfield in image processing.     

Mobility Management for Hierarchical Wireless Networks

In this paper, we consider the mobility management in large, hierarchically organized multihop wireless networks. The examples of such networks range from battlefield networks, emergency disaster relief and law enforcement etc. We present a novel network addressing architecture to accommodate mobility using a Home Agent concept akin to mobile IP. We distinguish between the physical routing hierarchy (dictated by geographical relationships between nodes) and logical hierarchy of subnets in which the members move as a group (e.g., company, brigade, battalion in the battlefield). The performance of the mobility management scheme is investigated through simulation.     

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.