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Programming

Mobile Handheld Devices : DATA SYNCHRONIZATION

3/22/2012 11:26:21 AM
Where multiple applications hold the same sets of data, such as addresses, and a change in the state of one of the shared objects is implemented in one application, this change needs to be propagated to the other applications that share that data. The process of sending, receiving, and updating data between multiple systems is called data synchronization. One example is when a user keeps a phonebook on both his or her desktop PC and a handheld device. Using data synchronization technology, the user can synchronize the phonebooks on both machines constantly and thus does not need to worry about any inconsistencies between the two phonebooks. Synchronization connects handheld devices to desktop computers, notebooks, and peripherals in order to transfer or synchronize data. Traditional synchronization uses serial cables to connect handheld devices and other computing equipment, as shown in Figure 2, but nowadays many handheld devices use either an infrared (IR) port or Bluetooth technology to send information to other devices without needing to use cables. Table 1 gives a comparison of these three synchronization methods.
Table 1. A comparison among the three synchronization methods
 Serial CablesInfrared PortBluetooth Wireless Technology
PriceLowMediumHigh
Transmission DistanceAbout 1 meter (the cable length)Up to 1 meterLess than 100 meters
Transmission RateUp to 100 Kbits/sUp to 16 Mbits/sSeveral Mbits/s
Wireless?NoYesYes

Figure 1. A series cable connecting an HP iPAQ and a PC

Serial Cables

The traditional method of synchronization uses serial cables to connect handheld devices and other computing equipment, as shown in Figure 1. For example, cables are generally provided with a digital camera so that the camera can be connected to a personal computer and images downloaded onto the computer hard disk. Some cameras also include an audio visual cable to enable images to be displayed on a television. Both utilize Universal Serial Bus (USB) technology, a protocol for transferring data to and from digital devices, and many digital cameras and memory card readers connect directly to the USB port on a computer. USB card readers are typically faster than cameras or readers that connect to the serial port, but slower than those that connect via FireWire. USB is a highly versatile connectivity specification developed by Intel and other technology industry leaders and is arguably the most successful interconnect in computing history. Originally released in 1995 at 12 Mbps, USB today operates at 480 Mbps and can be found in over 2 billion PC, CE, and mobile devices. In addition to high performance and ubiquity, USB enjoys strong consumer brand recognition and a reputation for ease-of-use.

Figure 2. An infrared port on an HP iPAQ device

Infrared Port

IrDA Data (Infrared Data Association, 2003), a standard formulated by the Infrared Data Association to ensure the quality and interoperability of infrared hardware, is designed for data transfer over distances of up to one meter, acting as a point-to-point cable replacement. Figure 2 shows an infrared port on a Compaq device.

Bluetooth Wireless Technology

Bluetooth wireless technology is a short-range communications technology intended to replace the cables connecting portable and/or fixed devices while maintaining high levels of security. It is designed to simplify communications among handheld devices, printers, computers, and other devices based on short-range radio technology. The Bluetooth specification defines a uniform structure for a wide range of devices to connect and communicate with each other. It has achieved global acceptance such that any Bluetooth enabled device, almost everywhere in the world, can connect to any other nearby Bluetooth enabled devices. The Bluetooth 2.1 specifications consist of two documents:

Figure 3. Devices communicating with a notebook using Bluetooth

  • the Core, which provides design specifications, and

  • the Profile, which provides interoperability guidelines.

Figure 3 shows a PDA and a smartphone communicating with a notebook using Bluetooth

Bluetooth enabled electronic devices connect and communicate wirelessly through short-range, ad hoc networks known as piconets. Each device can simultaneously communicate with up to seven other devices within a single piconet and can belong to several piconets simultaneously. Piconets are established dynamically and automatically as Bluetooth enabled devices enter and leave radio proximity. A fundamental Bluetooth wireless technology strength is the ability to simultaneously handle both data and voice transmissions, enabling users to use a hands-free headset for voice calls, print out documents, send faxes, and synchronize their PDA, laptop, and mobile phone applications. It has the following features:

  • Core specification versions:

    • Version 2.0 + Enhanced Data Rate (EDR), adopted November, 2004

    • Version 1.2, adopted November, 2003

  • Spectrum: Bluetooth technology operates in the unlicensed industrial, scientific and medical (ISM) band at 2.4 to 2.485 GHz, using a spread spectrum, frequency hopping, full-duplex signal at a nominal rate of 1600 hops/sec. The 2.4 GHz ISM band is available and unlicensed in most countries.

  • Interference: Bluetooth technology's adaptive frequency hopping (AFH) capability was designed to reduce interference between wireless technologies sharing the 2.4 GHz spectrum. AFH works within the spectrum to take advantage of the available frequency by detecting other devices operating in the same spectrum and avoiding the frequencies they are using. This adaptive hopping allows for more efficient transmission within the spectrum, providing users with greater performance even if simultaneously using other technologies. The signal hops among 79 frequencies at 1 MHz intervals to give a high degree of interference immunity.

  • Range: The operating range depends on the device class:

    • Class 3 radios, which have a range of up to 1 meter or 3 feet

    • Class 2 radios, which are most commonly found in mobile devices, have a range of 10 meters or 30 feet

    • Class 1 radios, which are used primarily in industrial environments, have a range of 100 meters or 300 feet

  • Power: The most commonly used radio is Class 2, which uses 2.5 mW of power. Bluetooth technology is designed to have very low power consumption. This is reinforced in the specification by allowing radios to be powered down when inactive.

  • Data rate: 1 Mbps for Version 1.2; Up to 3 Mbps supported for Version 2.0 + EDR

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