Search

The state of the art in resistance-based memory technology is presented. Recently memory technology has been focused on convergence towards ubiquitous memories which are non-volatile, have random access, and have fast programming times. This chapter is focused on electrically induced resistive change memories (including the resistive switching materials and mechanism) and other applications. Resistive random access memory (RRAM) has the simplest structure of new memory technologies, in fact the resistance change phenomenon can be observed in a metal–insulator–metal structure. Also, the switching speed has been reported to be about 10 ns and the resistance change effect scales down to cell sizes of 10 × 10 nm2 [1, 2]. First, we review classification of resistance memory and materials: unipolar, bipolar, ionic, and electronic effect memory. The second section deals with structure of cell stack architecture, which is a very important merit of resistance memories in particular, RRAM cell scaling and RRAM integration. In the final section the superior intrinsic scaling characteristics of RRAM compared to charge-based devices, and multilevel cell (MLC) RRAM, are discussed. Finally, we conclude with some comments on the outlook, future works, and research necessary for realization of RRAM technology.

The random access control (MAC) technique of standard WLANs is called the distributed coordination function (DCF) [3]. DCF is a carrier sense multiple access based on collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. This exponential backoff makes the system more complex, and fairness [3−13] among the stations is a major concern. This chapter shows one possible evolution of WLANs where exponential backoff is not employed. In the new techniques herein users transmit randomly but adapt themselves to traffic conditions, thus improving throughput and delay while guarantying fairness. Users in the first technique are controlled by a table which is derived from traffic measurements (table driven). In the second, users’ transmission activities are function of their buffer contents.

Static random access memory (SRAM) has been embedded in almost all of VLSI chips and has played a key role in the wide variety of applications required to enhance the performances of high speed, high density, low power, low voltage, low cost, time to market. Embedded SRAM has had a long reign in upper memory hierarchy than any other memories such as dynamic random access memory (DRAM). This is largely because SRAM is able to provide the highest random access speed performance among various embedded memory technologies. In addition, SRAM is fully compatible with CMOS logic process technology and operating voltage, enabling a seamless integration with logic circuits. Meanwhile, the device miniaturization driven by the technology scaling into nanometer regime has made it more challenging to maintain a sufficient SRAM cell stability margin while continuing to increase a random access speed as the transistor threshold voltage mismatching becomes significant. This also makes it more difficult to scale the operating voltage (V DD) while keeping the compatibility with logic’s. This chapter intends to provide an overview on the state-of-the-art SRAM circuit design technologies to address the key SRAM challenges in nanometer-scale technologies in terms of the read/write stability margins, cell current, and leakages.

A variety of magnetic random access memory (MRAM) technologies have been explored over a period of many decades. Their advantages include an unlimited number of read-write cycles, random access to any address, radiation-hardness, and non-volatility (namely, the state of the memory does not require periodic refreshing and is maintained even when power is removed from the memory).

In Chapter 6, we described a number of TDMA based multiple accesss schemes proposed and developed over the years. [119, 289]. These schemes span from fully random access schemes such as ALOHA to hybrid reservation DAMA schemes at the other end of the spectrum. However, they are not adequate enough to support the future broadband applications over satellite ATM networks.

List of Figures. List of Tables. Preface. Contributing Authors. 1: The Role of Satellite Networks in the 21st Century Son K. Dao. 1. Introduction. 2. Internet over Satellite Architecture. 3. Common Applications. 4. Visions for the Future. 5. Challenges. 2: Satellite Constellation Networks L. Wood. 1. Introduction. 2. Benefits of Going to LEO. 3. Describing the Symptoms. 4. Geometry, Topology and Delay. 5. Delay. 6. Handover. 7. Networking Design. 8. Simulators. 9. Summary. 3: Medium Access Control Protocols for Satellite Communications S.V. Krishnamurthy, et al. 1. Introduction. 2. Polling Based Access Protocols. 3. Fixed Assignment Multiple Access (FAMA) Protocols. 4. Random Access Protocols. 5. Demand Assignment Multiple Access (DAMA) Protocols. 6. Hybrid Protocols. 4: Direct Broadcast Satellites and Asymmetric Routing Yongguang Zhang. 1. Introduction. 2. Problems with Dynamic, Asymmetric Routing. 3. Tunneling: A Practical Solution. 4. Demonstration of Tunneling Approach. 5. RFC 3077: The IETF Standard. 6. Limitations and Long-Term Solutions. 5: Using Satellite Links in the Delivery of Terrestrial Multicast Trasffic K.C. Almeroth. 1. Introduction. 2. Overview of Multicast Deployment. 3. Satellite Delivery of Multicast. 4. Integrating Satellite and Terrestrial Networks. 5. Using Satellite Paths for Multicast Sessions. 6. When to Use Satellites? 6: TCP Performance over Satellite Channels T.R. Henderson. 1. Introduction. 2. Overview of Multicast Deployment. 3. Satellite Delivery of Multicast. 4. Integrating Satellite and Terrestial Networks. 5. Using Satellite Paths for Multicast Sessions. 6. When to Use Satellites. 7: TCP Performance Enhancement Proxy Yongguang Zhang. 1. Introduction. 2. The Motivation. 3. The Practical Solution. 4. The Big Argument. 5. The Show Stopper. 6. Conclusion. 8: Performance Evaluation of TCP Splitting over Satellite Mingyan Liu. 1. Introduction. 2. Model-based Analysis. 3. Discussion. 4. The Experiment System. 5. Measurement-based Analysis. 6. Implications on System design. 7. Conclusion. 9: Scheduling Data Broadcast Shu Jiang, N.H. Vaidya. 1.Introduction. 2. The Basic Model. 3. Theoretical Results. 4. On-line Scheduling Algorithm. 5. Performance Evaluation. 6. Conclusions. 10: Information Dissemination Applications E.C. Shek, et al. 1.Introduction. 2. IIDS Architecture. 3. Mobile User Profiling. 4. Dynamic User Profile Clustering and Aggregation. 5. Data Dissemination Techniques. 6. Implementation and Demonstration. 7. Conclusions. Index.

There is a novel approach for realising distributed manufacturing systems based on an object-oriented database which entirely runs in the random access memories (RAM) of the involved distributed computers. This is a very advantageous way to reduce costs for the design, implementation, operation and maintenance of a Supply Chain Management system. The example of an automotive parts’ supplier shows the capability and benefits of the new concept especially if the manufacturing is performed by different companies in different countries. The object-oriented database fits seamlessly into the Internet/Intranet approach and provides chances to realise virtual enterprises with minimum efforts and expenditures. Hence, this system is not only interesting for big companies but also for small and medium.

Consider a binary i.i.d. sequence that consists of K=2/sup J/ blocks of length T. We are looking for a universal compaction method that allows us to decode a certain block by looking only at certain segments in the code sequence. We have investigated a hierarchical method that encodes the source sequence into a code sequence that consists of 2/sup J+1/ variable-length segments. For decoding a certain block only J+2 segments need to be accessed. During decoding it is always clear where the next segment that needs to be accessed appears in the code sequence. The cumulative individual redundancy that is achieved by this method, is optimal in the sense that 1/2 log/sub 2/ N behavior is obtained where N=2/sup J/T. An additional increase of at most one bit per code-segment is possible however.

It is known that the average length of a CRP, i.e. Collision Resolution Period, in a random access algorithm is proportional to the mutual information between the packet’s arrival time and the set of all partitions of those arrival times that result in a resolution. Considering an ideal adaptive antenna, we can generalize this result for a two dimensional splitting algorithm in which resolutions of conflict are performed jointly in time and space. As a by-product of this result, the effectiveness of a multi-dimensional splitting algorithm is understood from an information theoretic view point.

Suppose in a random multiple access system, all the packets are transmitted in a single channel. The receiver can at most receive one packet at a time. Given the upper limit of expected system energy expenditure E within a period of time T and the peak power limit P max that a packet can use, at most how many packets can be received correctly within the time period T ? We find that the use of a single power level is optimal under a condition on the decodability threshold.

In this paper we analyse the performance of an Adaptive Random-Reservation Medium Access Control (MAC) protocol which can support all ATM service classes while providing the required Quality of Service (QoS). Our study focuses on parameter optimisation of the multiple access schemes for ATM over a GEO satellite with on-board processing capabilities, considering various traffic mixes of Constant Bit Rate (CBR), real-time Variable Bit Rate (rt VBR), non-real-time VBR (nrt VBR) and Unspecified Bit Rate (UBR). It is shown that maximum throughput can be achieved by using this access scheme. A TDMA access protocol combining both Random Access and Demand Assignment Multiple Access (DAMA) is particularly suited for a scenario with a high number of terminals and very bursty UBR traffic (e.g. web browsing). UBR sources with short burst length access the slots remaining after the reservation procedure by random access which drastically reduces the slot access delay, at the expense of lower utilisation.

This paper presents a simulation study comparing different mechanisms used in the upstream channel of ATM access networks. In request polling, status information from the access stations is transmitted periodically in minislots dedicated to each access station. In request contention,the access stations use a contention based multiple access scheme with a multi-slot stack contention resolution algorithm for random access to the minislots. In addition, in both cases request information is piggy-backed to upstream ATM cells.

From the Publisher: Thin Film Ferroelectric Materials and Devices is a compilation of current research and development in two very important ferroelectric device technologies, namely ferroelectrics for Dynamic Random Access Memories (DRAM's) and Non-Volatile Ferroelectric Random Access Memories (NV-FRAM's). Given the rapid pace of development and the broad scope of the general topic of ferroelectric materials, readers will benefit from such a focused presentation. Thin Film Ferroelectric Materials and Devices will be of great value to materials and device scientists, device and process engineers, students, and postdoctoral associates. Furthermore, this compilation will serve as a concise introduction for new entrants to this exciting field.

Medium access control (MAC) protocols have proposed since 1970’s for wireless communications networks. Idle Signal Multiple Access (ISMA) [1] and Reserved Idle Signal Multiple Access (R-ISMA) [2] were proposed as the examples of those MAC protocols. However, these protocols suffer from the system instability due to the random access mechanism. The instability problem can be found in most of MAC protocols using simple random access such as an ALOHA type with a fixed transmission probability.

The future success of the personal communications service depends on its ability to accommodate efficiently integrated traffic and service a variety of applications and communication sources with different quality of service requirements. For doing so, efficient algorithms are needed to support integrated services in the personal and mobile communications environment. In the present work, we propose a Spread Slotted Random Access protocol with a multi-priority service mechanism incorporated in its structure. The priority mechanism is implemented and controlled explicitly by the users and without any involvement from the network. This makes the allocation of priority transparent to the network infrastructure and adds to the simplicity and practical value of the proposed scheme. We examine the proposed protocol under reservation and non-reservation policies and evaluate it for integrated and data traffic. Our results show that the protocol is able to achieve high levels of utilization and is capable to accommodate relatively large volumes of integrated traffic.

This paper propose a Medium Access Control (MAC) protocol for wireless data networks. The main feature of this protocol is the combination of Polling and Slotted ALOHA contention in the multiaccess environment to insure stability and robustness. The frame structure in Advanced TDMA is used to guarantee that polling or random access are allocated with timeslots in every frame. The performance of such protocol is evaluated using simulation and Transient Fluid Approximation (TFA). It is shown that the protocol is adaptive to varying access rates when the system is near or in the overload region.

Networks with random access protocols offer a fair access to all users, they also show a robustness towards node failures. These features make them an attractive solution for computer applications. A vast amount of present day networks work under this scheme, being Ethernet one of the most significant technological contributions in this area. Collision Resolution Protocols are a special kind of random access schemes, offering the advantage that stability of the network is guaranteed, provided that the average packet input rate does not exceed a given limit.

This paper treats fundamental properties of real computers. Unsolvable problems (the halting problem is a well-known example) are known to exist on theoretical computers such as Turing machines, random access machines, etc. This leads to a corresponding question regarding real computers: are there problems concerning computations performed on a real computer and important from viewpoint of its user which are at the same time unsolvable by the computer? We give affirmative answer here showing e.g., that the halting problem concerning a real computer and a collection of real programs satisfying a weak closure property is unsolvable by the computer. Unsolvability of another problem dealing with approximation of results of computations performed by programs from given collection is proved as well.