Connor-Winfield

<p>His leadership enabled National Semiconductor to become the leader in its industry peer group for lowest logistics and purchasing costs per dollar product shipped and per dollar of material purchased,” said chief executive Rodgers. Woodward will be charged with making Cypress's manufacturing just as efficient.”</p>

Cell phone makers may have overestimated the dimensions and requirements of the high-end market, agreed Norman Brodeur, marketing manager with M/A-Com (Lowell, Mass). The true consumers of novelty handsets would be teenagers, for whom the phones would have to be ultracheap with, say, leopardskin faceplates, he suggested. Japanese teens, for example, do not consume high-data-rate services, opting for horoscopes and crude text messages, he said.

Wireless penalty

Fixed-wireless signals can punch though walls with no penalty. This fallacy comes from the blurring of the distinction between fixed and mobile wireless. Certainly, mobile wireless telephony works inside buildings-why should fixed wireless require outdoor antennas? The answer lies in the differences between the two services: Wireless telephony deals with the path loss inherent in indoor operation by building in a large margin of signal-to-noise ratio, providing a very small bandwidth within a fairly small cell, of which there are hundreds in many large cities.

RN60D4320FRSL_Vishay Dale_Through Hole Resistors

An indoor” fixed-wireless system would have to make similar compromises: try to push up the data rate to something competitive with DSL, keep the cell size quite small and use peak power transmissions from the customer premise equipment (CPE) that may bump up against FCC RF-intensity safety limits. Within this set of trade-offs, it is possible to architect a system. Whether such a system's cost and performance are economically viable for large-scale operation remains to be proven.

Every subscriber needs nonline-of-sight (NLOS) operation.

Reading recent articles and press releases on broadband fixed wireless, you will soon gain the impression that nonline-of-sight operation is absolutely necessary, indeed the holy grail of this technology. True, serving 100 percent of potential subscribers in an area will require technology that does not depend on line of sight to the hub. What is overlooked is that techniques to overcome NLOS problems are far from cost-free. Not only do such technologies become more complex to minimize multipath, but also they need an increased signal level to overcome path loss, which is inevitable in NLOS situations. Technologies that minimize multipath and provide a large margin of signal level to overcome path loss will inevitably cost more, especially in the price of the customer premises equipment. (Low CPE price is the real holy grail of BWA.)

RN60D4320FRSL_Vishay Dale_Through Hole Resistors

Line-of-sight hubs

Also overlooked is that a large fraction of subscribers will have line of sight to a hub station. This is true when the hub is a supercell, with a tall tower in the middle of the service area, and more true if a service area is covered by a number of smaller cells. A subscriber who can't see hub A may have clear line of sight to hub B or C.

RN60D4320FRSL_Vishay Dale_Through Hole Resistors

TDD is more spectrally efficient than FDD. On the face of it, this seems self-evident. Time-domain duplexing, in which the outbound and return data time share the same slice of spectrum, seems to be inherently more spectrum-economical than frequency-domain duplexing, where different RF channels are used for the BWA downstream and upstream signals.

In FDD you have to provide a guardband between transmit and receive, thus giving up spectral efficiency, while in TDD you must allocate a guard time between transmit and receive and thereby lose spectral efficiency. TDD is more spectrally efficient in the special case where only a single narrow channel is allocated, and duplex filters providing spectral efficiency are difficult to make. For MMDS and LMDS, where the allocated spectrum is larger than a single user demands, FDD is more efficient because a spectrum pair can be allocated with sufficient guardband and the guardband can be used in another cell.

We are still a very long way from a spintronics device,” said LaBella. It is very easy to align the electrons' spin in a ferromagnet, and polarised electrons will travel as far as 1005m in GaAs and maintain polarisation. But it has been very difficult to get polarised electrons from the ferromagnet to the semiconductor without losing coherence.”

The Arkansas team has addressed this problem by using the tip of a scanning tunnelling microscope as the source of the electrons, injecting them directly into the GaAs lattice.

Because it tunnels through a vacuum, the spin is maintained,” said LaBella. This suggests maybe a tunnelling junction is the way to go.”

The electrons are drawn from a single crystal nickel wire with all the electrons in the spin-down state. The use of up and down spin in semiconductors offers the possibility of significantly smaller and faster devices. It should also be possible to develop higher order multifunctional devices.

But the efficiency of injection is highly dependent on the smoothness of the GaAs surface. A nanoscale step undermines the entire process.

Bidirectional parts

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