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.     

Using a WLFSR to Embed Test Pattern Pairs in Minimum Time

We propose a methodology for reducing the number of test cycles needed by a Weighted LFSR (WLFSR) to reproduce a 2P × W test matrix T of P pattern pairs. The methodology introduces a very small number of extra cells into the WLFSR and uses appropriate combinational mapping logic in order to make the time be equal to that required by a (W + )-bit WLFSR to generate vectors containing the W bits of the first pattern for each pair plus the extra bits. We present an algorithm that makes the value of be less than or equal to log₂, where is the size of the maximum subset of pairs in T with identical first patterns. This is a significant improvement over the time E _P,W · P required by a trivial approach that uses a WLFSR with W cells to generate the first patterns of the pairs and a P × W ROM to store the second patterns of the pairs. Experimental results on the application of the methodology to the embedding of test matrices for path delay faults are particularly encouraging, even for very large numbers of test pattern pairs that are necessary for provably high fault coverage.     

The dangers of simplistic delay models

The identification of sensitizable paths and the determination of path delays play key roles in many delay fault testing schemes. In this paper we examine a range of gate delay models with respect to their impact on identifying both sensitizable paths and maximum circuit delays in combinational logic circuits. We provide recommendations on the minimum acceptable model for identifying critical paths, and a minimum acceptable model for determining maximum circuit delays. In particular, we recommend against the use of delay models which fail to distinguish between rise and fall delays. Such models, including the commonly-used unit-delay model, are shown to significantly misrepresent circuit delay behaviour, particularly with respect to critical paths and long false paths.This research is supported by the Natural Sciences and Engineering Research Council of Canada.     

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.     

Detection of Defects Using Fault Model Oriented Test Sequences

This paper analyzes the possibilities and limitations of defect detection using fault model oriented test sequences. The analysis is conducted through the example of a short defect considering the static voltage test technique. Firstly, the problem of defect excitation and effect propagation is studied. It is shown that the effect can be either a defective effect or a defect-free effect depending on the value of unpredictable parameters. The concept of Analog Detectability Interval (ADI) is used to represent the range of the unpredictable parameters creating a defective effect. It is demonstrated that the ADIs are pattern dependent. New concepts (Global ADI, Covered ADI) are then proposed to optimize the defect detection taking into account the unpredictable parameters. Finally, the ability of a fault oriented test sequence to detect defect is discussed. In particular, it is shown that the test sequence generated to target the stuck-at faults can reasonably guarantee short defect detection till a limit given by the Analog Detectability Intervals.     

A New Approach to Realize Variable Gain Amplifiers

A new methodology to develop variable gain amplifiers is developed. The methodology is based on a feedback loop to generate the exponential characteristic, which is required for VGA circuits. The proposed idea is very suitable for applications that require very low power consumption, and as an application, a new current mode variable gain amplifier will be shown. The gain is adapted via a current signal ranges from –7.5 A to +6.5 A. Pspice simulations based on Mietec 0.5 m CMOS technology show that the gain can be varied over a range of 29.5 dB, with bandwidth of 3 MHz at maximum gain value. The circuit operates between ±1.5 V and consumes an average amount of power less than 495 W.     

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.     

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).     

Microsystems Engineering: A Great Stride Forward in Microelectronics Technology

The development of new-generation technological and engineering concepts by the example of microsystems technology and microsystems engineering approaches is considered.     

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.     

Design and Analysis of an Efficient Communication Strategy for Hierarchical and Highly Changing Ad-hoc Mobile Networks

In this work we introduce two practical and interesting models of ad-hoc mobile networks: (a) hierarchical ad-hoc networks, comprised of dense subnetworks of mobile users interconnected by a very fast yet limited backbone infrastructure, (b) highly changing ad-hoc networks, where the deployment area changes in a highly dynamic way and is unknown to the protocol. In such networks, we study the problem of basic communication, i.e., sending messages from a sender node to a receiver node. For highly changing networks, we investigate an efficient communication protocol exploiting the coordinated motion of a small part of an ad-hoc mobile network (the runners support) to achieve fast communication. This protocol instead of using a fixed sized support for the whole duration of the protocol, employs a support of some initial (small) size which adapts (given some time which can be made fast enough) to the actual levels of traffic and the (unknown and possibly rapidly changing) network area, by changing its size in order to converge to an optimal size, thus satisfying certain Quality of Service criteria. Using random walks theory, we show that such an adaptive approach is, for this class of ad-hoc mobile networks, significantly more efficient than a simple non-adaptive implementation of the basic runners support idea, introduced in [9,10]. For hierarchical ad-hoc networks, we establish communication by using a runners support in each lower level of the hierarchy (i.e., in each dense subnetwork), while the fast backbone provides interconnections at the upper level (i.e., between the various subnetworks). We analyze the time efficiency of this hierarchical approach. This analysis indicates that the hierarchical implementation of the support approach significantly outperforms a simple implementation of it in hierarchical ad-hoc networks. Finally, we discuss a possible combination of the two approaches above (the hierarchical and the adaptive ones) that can be useful in ad-hoc networks that are both hierarchical and highly changing. Indeed, in such cases the hierarchical nature of these networks further supports the possibility of adaptation.     

Optical-LSP Establishment and a QoS Maintenance Scheme Based on Differentiated Optical QoS Classes in OVPNs

A virtual private network (VPN) over Internet has the benefit of being cost-effective and flexible. However, it has difficulties providing sufficient QoS and adequate transmission capacity for high bandwidth services. Given the increasing demand for high bandwidth Internet and the demand for QoS assurances in a VPN over Internet, IP/generalized multi-protocol label switching (GMPLS) based on a control plane combined with a high-bandwidth, dense-wavelength division multiplexing (DWDM) optical network is seen as a very favorable approach for realizing the future optical VPN (OVPN) over IP/GMPLS over DWDM. Within this architecture, providing QoS guaranteed multimedia services with a differentiated QoS guaranteed protocol framework with QoS recovery is one of the key issues to implement. Therefore, we suggest in this paper optical-label switched path (O-LSP) establishment and its QoS maintenance scheme based on differentiated optical QoS-service (DOQoS) classes. They are the key components for this DOQoS framework in assuring end-to-end QoS in an OVPN over IP/GMPLS over DWDM architecture.     

An adaptive algorithm for optimizing the packet size used in wireless ARQ protocols

We develop an algorithm that allows an ARQ protocol to dynamically optimize the packet size based on estimates of the channel biterrorrate. Our algorithm is particularly useful for wireless and satellite channels where the biterrorrates tend to be relatively high and time variable. Our algorithm uses the acknowledgment history to make estimates of the channel biterrorrate, based on which the optimal packet size can be chosen. We develop a Markov chain model for the analysis of the system, under static channel conditions, and show that the algorithm can achieve close to optimal performance using a history of just 10,000 bits. We also use the Gilbert–Elliott twostate Markov channel to model dynamic channel conditions. We show, through simulation, that the algorithm performs well even under rapidly changing channel conditions. Finally, we discuss a maximum likelihood approach for choosing the packet size, which performs almost optimally but is much easier to implement.     

Comments on “Aliasing Properties of Circular MISRs”

The analysis of aliasing probability presented in a recent article, Aliasing Properties of Circular MISRs [1], is based on an error model that cannot adequately represent real circuits. We show why conclusions presented in [1] should not be used in practice, substantiating our claim with experimental results.This work was supported in part by grants from the Natural Sciences and Engineering Research Council of Canada and in part by the British Columbia Advanced Systems Institute     

A scalable wireless virtual LAN

This paper presents a Wireless Virtual Local Area Network (WVLAN) to support mobility in IPoverATM local area networks. Mobility is handled by a joint ATMlayer handoff for connection rerouting and MAClayer handoff for location tracking, such that the effects of mobility are localized and transparent to the higherlayer protocols. Different functions, such as Address Resolution Protocol (ARP), mobile location, and ATM connection admission are combined to reduce protocol overhead and frontend delay for connectionless packet transmission in connectionoriented ATM networks. The proposed WVLAN, through the use of ATM technology, provides a scalable wireless virtual LAN solution for IP mobile hosts.     

Order selection statistical test for nonstationary AR models

A new statistical test for selecting the order of a nonstationary AR modelyk is presented based on the predictive least-squares principle. This test is of the same order as the accumulated cost function _n = _k=1 ⁿ ( _k ^* – _k )²;i.e., ^* wherey _k ^* is the predictive least-square estimate. It is constructed to show how many times the integrated AR processy _k is differenced in order to obtain a stationary AR process given that the exact order of the process is unknown.     

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.     

Scan test architectures for digital board testers

Boundary scan is a method of implementing test access to the terminals of a component, cluster, or board. Although substituting boundary scan access for direct tester access to these terminals does not alter the concept of digital testing, the replacement of parallel test vectors by serial data streams requires tester support for serial data.This article first considers the problems posed by boundary scan sequences, which are long and contain meaningful vector data, constant data, and irrelevant, or don't care bits, arbitrarily interspersed. We use the model of meaningful data within a frame of constant or irrelevant bits as a means of handling vector data efficiently, and we propose the sequencing and control features of the general-purpose digital tester as an efficient way to implement these frames. Using a specific example, we show that the performance achieved and the data storage resources required compare favorably to approaches based on special-purpose framing hardware.     

Gaussian radial basis functions and inner product spaces

An approximation result is given concerning Gaussian radial basis functions in a general inner product space. Applications are described concerning the classification of the elements of disjoint sets of signals, and also the approximation of continuous real functions defined on all of ⁿ using radial basis function (RBF) networks. More specifically, it is shown that an important large class of classification problems involving signals can be solved using a structure consisting of only a generalized RBF network followed by a quantizer. It is also shown that Gaussian radial basis functions defined on ⁿ can uniformly approximate arbitrarily well over all of ⁿ any continuous real functionalf on ⁿ that meets the condition that |f(x)|0 as x.     

Biasing a differential pair in low-voltage analog circuits: a systematic approach

This paper deals with a systematic approach to the common mode and the differential mode biasing of a differential transistor pair. Four different variants will be shown, two of these variants show practical importance; a practical circuit of one of these variants turns out to be the traditional long-tailed pair. This variant is mainly suited, if the input signal operates at voltage level, whereas another variant has great advantages if operation at current level occurs. Besides, the latter variant turns out to be very favorable in circuits operating with a single low supply voltage. Two practical circuits based on this variant are given.