It is shown that, particularly for terrestrial cellular telephony, the interference-suppression feature of CDMA (code division multiple access) can result in a many-fold increase in capacity over analog and even over competing digital techniques. A single-cell system, such as a hubbed satellite network, is addressed, and the basic expression for capacity is developed. The corresponding expressions for a multiple-cell system are derived. and the distribution on the number of users supportable per cell is determined. It is concluded that properly augmented and power-controlled multiple-cell CDMA promises a quantum increase in current cellular capacity. >

On the capacity of a cellular CDMA system

The Smart Grid, regarded as the next generation power grid, uses two-way flows of electricity and information to create a widely distributed automated energy delivery network. In this article, we survey the literature till 2011 on the enabling technologies for the Smart Grid. We explore three major systems, namely the smart infrastructure system, the smart management system, and the smart protection system. We also propose possible future directions in each system. colorred{Specifically, for the smart infrastructure system, we explore the smart energy subsystem, the smart information subsystem, and the smart communication subsystem.} For the smart management system, we explore various management objectives, such as improving energy efficiency, profiling demand, maximizing utility, reducing cost, and controlling emission. We also explore various management methods to achieve these objectives. For the smart protection system, we explore various failure protection mechanisms which improve the reliability of the Smart Grid, and explore the security and privacy issues in the Smart Grid.

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Smart Grid — The New and Improved Power Grid: A Survey

Smart Grid - The New and Improved Power Grid:

Much has been written about theory and practice in the law, and the tension between practitioners and theorists. Judges do not cite theoretical articles often; they rarely "apply" theories to particular cases. These arguments are not revisited. Instead the Essay explores the working and interaction of theory and practice, practitioners and theorists. The Essay starts with a story about solving a legal issue using our intellectual tools - theory, practice, and their progenies: experience and "gut." Next the Essay elaborates on the nature of theory, practice, experience and "gut." The third part of the Essay discusses theories that are helpful to practitioners and those that are less helpful. The Essay concludes that practitioners theorize, and theorists practice. They use these intellectual tools differently because the goals and orientations of theorists and practitioners, and the constraints under which they act, differ. Theory, practice, experience and "gut" help us think, remember, decide and create. They complement each other like the two sides of the same coin: distinct but inseparable.

Of Theory and Practice

Mobile ad hoc networks (MANETs) represent complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self-organize into arbitrary and temporary, ‘‘ad-hoc’’ network topologies, allowing people and devices to seamlessly internetwork in areas with no pre-existing communication infrastructure, e.g., disaster recovery environments. Ad hoc networking concept is not a new one, having been around in various forms for over 20 years. Traditionally, tactical networks have been the only communication networking application that followed the ad hoc paradigm. Recently, the introduction of new technologies such as the Bluetooth, IEEE 802.11 and Hyperlan are helping enable eventual commercial MANET deployments outside the military domain. These recent evolutions have been generating a renewed and growing interest in the research and development of MANET. This paper attempts to provide a comprehensive overview of this dynamic field. It first explains the important role that mobile ad hoc networks play in the evolution of future wireless technologies. Then, it reviews the latest research activities in these areas, including a summary of MANETs characteristics, capabilities, applications, and design constraints. The paper concludes by presenting a set of challenges and problems requiring further research in the future. � 2003 Elsevier B.V. All rights reserved.

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Mobile ad hoc networking: imperatives and challenges

A new global positioning system (GPS)-based routing protocol for ad hoc networks, called zone-based hierarchical link state (ZHLS) routing protocol, is proposed. In this protocol, the network is divided into nonoverlapping zones. Each node only knows the node connectivity within its zone and the zone connectivity of the whole network. The link state routing is performed on two levels: focal node and global zone levels. Unlike other hierarchical protocols, there is no cluster head in this protocol. The zone level topological information is distributed to all nodes. This "peer-to-peer" manner mitigates traffic bottleneck, avoids single point of failure, and simplifies mobility management. Since only zone ID and node ID of a destination are needed for routing, the route from a source to a destination is adaptable to changing topology. The zone ID of the destination is found by sending one location request to every zone. Simulation results show that our location search scheme generates less overhead than the schemes based on flooding. The results also confirm that the communication overhead for creating and maintaining the topology in the proposed protocol is smaller than that in the flat LSR protocol. This new routing protocol provides a flexible, efficient, and effective approach to accommodate the changing topology in a wireless network environment.

A peer-to-peer zone-based two-level link state routing for mobile ad hoc networks

Spread spectrum techniques and collision avoidance multiple access protocols are combined to form a new set of medium access protocols for mobile wireless ad hoc networks. The request-to-send and clear-to-send message dialogue solves the "hidden terminal" and the "exposed terminal" problems and speeds up the retransmission. The spreading code assignment avoids disruption of any ongoing transmission by an intruder. Simulation results confirm that a higher channel throughput is achieved by the new protocols even in a dense network.

Spread spectrum medium access protocol with collision avoidance in mobile ad-hoc wireless network

Multiple ray paths are resolved using high-resolution digital signal processing algorithms. The Cramer-Rao (CR) bound is used as a benchmark where a combination of the singular value decomposition method and the eigen-matrix pencil method is proven to be most successful. The conventional complex channel model for wireless propagation is extended to include the frequency-dependent feature of rays which can be used to classify the ray arrivals and provide physical insight of the channel. A novel complex-time model is used to approximate the suggested model. This approach is important to various applications such as equalizers, RAKE receivers, etc., in wireless communication systems. Five key features (noise immunity, robustness, resolution, accuracy, and physical insight) of the proposed algorithm are studied using numerical examples.

Multipath resolving with frequency dependence for wide-band wireless channel modeling

Design criteria and analysis procedures for a practical OFDM underwater communications system are presented. A new broadband underwater channel model with Doppler time scaling effect is developed. A two-dimensional MMSE scheme using time and frequency pilots is employed for channel estimation. Doppler frequency shift is estimated using cyclic prefix and is compensated by a digital sampling rate conversion procedure. Numerical simulations demonstrate that the OFDM technique is robust with respect to frequency selectivity and time selectivity.

Parameter study of OFDM underwater communications system

A “peer-to-peer” hierarchical routing protocol—also referred to as Zone-based Hierarchical Link State Routing protocol (or “ZHLS”)—which incorporates location information into a novel “peer-to-peer” hierarchical routing approach. The network may be divided into non-overlapping zones. Aggregating nodes into zones conceals the detail of the network topology. Initially, each node knows its own position and therefore zone ID through a position determination unit, such as a Global Positioning System (GPS). After the network is established, each node knows the low level (node level) topology about node connectivity within its zone and the high level (zone level) topology about zone connectivity of the whole network. A packet may be forwarded by specifying the hierarchical address—zone ID and node ID—of a destination node in the packet header.

I-Tai Lu

Papers

A peer-to-peer zone-based two-level link state routing for mobile ad hoc networks

Spread spectrum medium access protocol with collision avoidance in mobile ad-hoc wireless network

Multipath resolving with frequency dependence for wide-band wireless channel modeling

Parameter study of OFDM underwater communications system

Methods and apparatus for routing in a mobile ad hoc network