The use of real time channel borrowing in digital cellular asynchronous hybrid FDMA/TDMA systems is considered. These systems, which are exemplified by North American digital cellular (IS-54), are asynchronous in the sense that time slots in different cells are not aligned. CBWL (channel borrowing without locking) techniques can be applied but (without cell-to-cell synchronization) borrowing individual time slots from adjacent cells would violate co-channel interference constraints. Instead, frequency carriers can be borrowed. In IS-54, a carrier supports three TDMA slots. So if only one TDMA slot is needed in the borrowing cell, two TDMA slots are unnecessarily transferred. We devised an appropriate carrier borrowing scheme and an analytical model to determine the traffic performance of TDMA/CBWL. Fast carrier returning is used to increase channel utilization by returning borrowed carriers as soon as possible. An efficient computational method that uses macro-states, decomposition, combinatorial analysis and the convolution algorithm is devised to find blocking probabilities. The results show that in comparison with FCA, the new CBWL scheme can significantly improve system performance of asynchronous TDMA cellular systems that use FDMA/TDMA multiplexing. 相似文献
This paper proposes a distributed borrowing addressing (DIBA) scheme to solve problems of failure in address assignments resulting from limited tree depth and width when the distributed address assignment mechanism is used in a ZigBee/IEEE 802.15.4 wireless sensor network. DIBA is a method of borrowing addresses from neighbor nodes for newly entering nodes and assigning the borrowed addresses. Its network or sensing coverage can increase with almost the same overhead as the existing method. DIBA is a simple and lightweight means of addressing and routing, making it suitable for wireless sensor networks. Simulations showed that DIBA is a distributed addressing scheme with consistently excellent performance. 相似文献
In the third generation cellular networks and beyond, a wide variety of different services are/will be provided by the operators. Out of QoS reasons, it is preferable to assign higher priority to certain connection types. These include calls carrying delay-sensitive services and already ongoing calls. In this paper, a prioritization method combining bandwidth borrowing and reservation, called BBR, will be presented. BBR monitors the rate-adaptiveness of the ongoing calls in a cell. Simultaneously, advanced movement predictions are applied to estimate the arrival rate to each cell. If it is determined that the use of bandwidth borrowing (temporarily reducing the data rate of other connections in the same cell) is not sufficient to support the high priority calls that are expected to arrive, a portion of the assigned bandwidth to the cell is exclusively reserved for these calls to prevent call dropping. The scheme enables the operator to increase the average user satisfaction in the network. This is achieved by defining appropriate penalty functions for the events of blocking, dropping and bandwidth reduction of a call. 相似文献
The study of the history of new words in theNewOED described in this paper was undertaken in 1986-87, and is based on the material then available. Since then, theNewOED has been finished, and PAT, the inquiry system developed at the University of Waterloo for the investigation of theNewOED data base, has been much altered and improved. Nevertheless, this report should prove useful in indicating the potentiality for analyzing the computerizedNewOED and some of the problems. This project is a study of the ways in which new words are created in English at various periods of time. A chronological dictionary 's created listing words introduced into the language over 50 year increments. These words are then classified by the processes used in forming them to show, in proportional terms, if certain processes are more common at some times than at others.H. M. Logan, Associate Professor, Department of English, University of Waterloo, Waterloo, Ontario, Canada, has written The Dialect of the Middle English Life of St. Katherine (Mouton, 1973), making use of the computer in a study of medieval dialectology. He has also written articles on computer stylistics and literary analysis inCHum, ALLC Journal, Language and Style, College Literature, and on the dictionary inDictionaries. 相似文献
Triazole‐phosphine‐copper complexes (TAP−Cu) have been synthesized and applied as tunable and efficient catalysts for the selective synthesis of fluoro‐substituted 2‐aryl‐1H ‐benzo[d]imidazole and 1‐benzyl‐2‐aryl‐1H ‐benzo[d]imidazole derivatives from simple alcohols in only one step. TAP−Cu exhibited excellent and tunable catalytic activity for both dehydrogenation and borrowing hydrogen reactions with more than 80 examples being demonstrated for the first time. It was observed that the ligand played a critical role in catalyst activity. Mechanistic studies and deuterium labeling experiments indicated that the reactions proceeded by an initial and reversible alcohol dehydrogenation resulting in a copper hydride intermediate. This was also supported by the direct observation of a diagnostic copper hydride signal by solid‐state infrared spectroscopy. The TAP−Cu‐H complex showed absorptions at 912 cm−1 that could be assigned to copper−hydride stretches. Furthermore, the direct trapping of an intermediate bisimine was also successfully performed.
