NEC

About: NEC is a company organization based out in Tokyo, Japan. It is known for research contribution in the topics: Signal & Layer (electronics). The organization has 33269 authors who have published 57670 publications receiving 835952 citations. The organization is also known as: NEC Corporation & NEC Electronics Corporation.

The Impact of Autocorrelation on Queuing Systems

Abstract: The performance of single-server queues with independent interarrival intervals and service demands is well understood, and often analytically tractable. In particular, the M/M/1 queue has been thoroughly studied, due to its analytical tractability. Little is known, though, when autocorrelation is introduced into interarrival times or service demands, resulting in loss of analytical tractability. Even the simple case of an M/M/1 queue with autocorrelations does not appear to be well understood. Such autocorrelations do, in fact, abound in real-life systems, and worse, simplifying independence assumptions can lead to very poor estimates of performance measures. This paper reports the results of a simulation study of the impact of autocorrelation on performance in an FIFO queue. The study used two computer methods for generating autocorrelated random sequences, with different autocorrelation characteristics. The simulation results show that the injection of autocorrelation into interarrival times, and to a lesser extent into service demands, can have a dramatic impact on performance measures. From a performance viewpoint, these effects are generally deleterious, and their magnitude depends on the method used to generate the autocorrelated process. The paper discusses these empirical results and makes some recommendations to practitioners of performance analysis of queuing systems.

Phased array antenna apparatus

Abstract: A phased array antenna apparatus includes a plurality of radiation elements, a power supply unit, a power distributor, a feed probe, a plurality of electromagnetic coupling units, and a plurality of phase shifters. The radiation elements are aligned and arranged to be electromagnetically driven. The power supply units supply power to the radiation elements. The power distributor has a pair of conductive plates arranged to be parallel to each other and acts as a radial waveguide distributing the power supplied from the power supply unit to the radiation elements. The feed probe is arranged on one of the conductive plates to radiate an electromagnetic wave into the radial waveguide in accordance with the power supplied from the power supply unit. The electromagnetic coupling units are arranged on the other conductive plate in correspondence with the radiation elements to extract the electromagnetic wave radiated from the feed probe and propagating through the radial waveguide by electromagnetic coupling. The phase shifters control a phase of the electromagnetic wave extracted by the electromagnetic coupling units and supply the electromagnetic wave to the radiation elements.

A 2.5 ns clock access 250 MHz 256 Mb SDRAM with a synchronous mirror delay

Abstract: A 256-Mb SDRAM (245.7 mm/sup 2/) has been developed using (1) a high cell occupation ratio (60.2%) array design for chip size reduction and a high yield, (2) a prefetched pipeline scheme (PPS) using a first-in first-out (FIFO) buffer with parallel serial converter for 250-MHz clock frequency operation, and (3) a synchronous mirror delay (SMD) circuit for 2.5-ns clock access and low standby current.