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Chapter: Mobile Networks : Pervasive Computing

Device Technology

Hardware and Battery, Displays, Memory, Processors.



Hardware and Battery

Today, lithium ion (Li ion) batteries can be found in all sorts of electronic equipment. These batteries are lighter and have better energy density, resulting in more power delivered. The weight of a NiCad battery for a five-year-old mobile phone is often higher than the total weight of a modern mobile phone, including the Li ion battery. While the latter does have a lower capacity, it still offers longer talk time because of the reduced power requirements of modern devices.


Table. 1 gives an estimate of the expected standby and talk time for a mobile phone when used with typical batteries available today. The data is taken from the specification of three batteries of comparable size. The latest in battery technology is the emergence of lithium polymer cells, which use a gel material for the electrolyte. The batteries are made from a few thin and flexible layers, and do not require a leak-proof casing. This means the batteries can be made in almost any shape or size.

Expected lifetime for NiCad, NiMH, and Li ion batteries




·        LCDs are already replacing the bulky cathode ray tubes.

·        Larger and more readable

·        Dramatic weight, size, and power consumption benefits of LCD technology outweigh their relatively high cost.

·        Today's PDAs usually feature dual-scan (DSTN) displays that control individual display elements via passive matrix addressing.

·        This technology consumes considerably less power than the thin-film transistor (TFT) active matrix technology.

·        This latter technology is more expensive, but is capable of significantly superior display performance and thus is generally used in portable computers.

·        Better and thinner displays will be available in the future based on the light-emitting organic diode (OLED) or light-emitting polymer (LEP) technologies.

·        OLED technology was invented about 15 years ago.


 It only recently became commercially attractive when the initial problems with the expected life and efficiency were solved.


Instead of crystalline semiconductor material, organic compounds are used.


·        The simplified manufacturing process of smaller structures and a rich selection of organic compounds enable OLEDs to be built in almost any size and colour.


·        This will eventually allow manufacturers to create extremely thin displays that are flexible enough to be bent and shaped as required.


·        Other new display technologies, such as chip-on-glass (CoG) and liquid- crystal-on-glass (LCoG), integrate the picture elements with transistors on a layer of glass.


·        This allows manufacturing of extremely small displays, with a pixel size of only 10 micrometers.


·        In contrast to regular small displays like those on the back of a camcorder, the microdisplays usually require some form of magnification.


·        They can be found, for example, in projection systems and in head-mounted displays used with wearable computers.




Memory is becoming cheaper, while the demand from applications is growing.


Development is driven in part by smart phones, digital cameras, MP3 players and PDAs.




 For these mobile devices, the currently available technologies and their associated costs have reached a point where it is now feasible to integrate several megabytes of memory into a mobile device with an acceptable form factor.


 On PCs, permanent data can be stored on hard disk drives.


 For mobile devices, this is often not an option because neither the space nor the power supply is available.


 Recently, extremely small removable disk drives like the IBM Microdrive became available.


 Their capacity ranges between 340 MB and 1 GB, and is sufficient to store, for example, several hundred pictures when used in a digital camera.



Other devices such as smart phones and PDAs store their operating system


code and application data in non-volatile Flash memory and battery-backed random-access memory (RAM) instead.


These semiconductor -based technologies require less power and offer faster access than disk drives.


The typical capacity of built-in memory in mobile devices ranges from 2 to 16 MB.


Expansion slots allow additional memory modules to be plugged into the device, which in turn allow data exchange and replace removable media such as diskettes and CD-ROM for a PC.



 During the last couple of years, the clock rate of microprocessors and the processing power available from them has increased steadily.


 Rapid improvements in the CMOS manufacturing process have created ever-smaller structures and delivered higher and higher numbers of transistors per chip.


  At the same time, the processor core voltage was lowered from the industry standard 3.3 V in 1995 to 1.35 V in 2000.


  This means lower heat emissions, which in turn paves the way for new improvements like larger on-die caches.


  This, together with advances in packaging technologies, delivers the modern Central Processing Units (CPUs) found in mobile computers and PDAs today.



Intel's Speed Step technology


·         Recent processors include improvements in power management.


·         These processors are capable of changing their internal clock frequencies and core voltage to adapt to changes in power supply.


·         Newer designs are even capable of switching parts of the CPU on or off depending on whether the current calculations require them to be available.


·         One such design is the Speed Step technology from Intel.


·         While the system is connected to an external power supply, the full clock rate and core voltage are available to the processor, resulting in the maximum performance.


·         When running on batteries, the clock rate and core voltage of the processor are reduced, resulting in significant power savings.



·        The transition between both modes is very fast and completely transparent to the user.


·        During the boot cycle, the Crusoe processor loads its software into a section of the main memory.


·        Frequently used code parts are optimized during run-time and kept in a separate cache.


·        A technology called LongRun promises to reduce the power consumption even more by reducing the processor's voltage on the fly when the processor is idle.


·        The big advantage of this approach is that the Crusoe processor can be used to emulate almost any other processor and uses only a few watts, even with high clock rates.

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