MOBILE COMPUTING
Distinction between "wireless" and "mobile."
Wireless refers to the method of transferring information between computing devices, such as a personal data assistant (PDA), and a data source, such as an agency database server, without a physical connection. Not all wireless communications technologies are mobile. For example, lasers are used in wireless data transfer between buildings, but cannot be used in mobile communications at this time.
Mobile simply describes a computing device that is not restricted to a desktop. A mobile device may be a PDA, a "smart" cell phone or Web phone, a laptop computer, or any one of numerous other devices that allow the user to complete computing tasks without being tethered, or connected, to a network. Mobile computing does not necessarily require wireless communication. In fact, it may not require communication between devices at all.
.. Mobile devices
Here we have seven different types of mobile devices:
Laptop computers
PDA’s and handheld PCs
Pagers
Smart phones and cellular phones
Task devices, such as bar code scanners
Blue tooth
Bridge
.. Challenges in mobile computing
Wireless and mobile environments bring different challenges to users and service providers when compared to fixed, wired networks. Physical constraints become much more important, such as device weight, battery power, screen size, portability, quality of radio transmission, error rates. The major challenges in mobile computing are described including: low bandwidth, high error rate, power restrictions, security, limited capabilities, disconnection and problems due to client mobility.
.. Low Bandwidth
Wireless networks deliver lower bandwidth than wired networks. As a result, mobile applications have to be carefully designed to control the bandwidth consumption. Software techniques required to improve effective bandwidth usage include data compression logging requests to combine multiple short ones, lazy write back, difference-based updates, caching, prefetching, usage of proxy, priority scheduling, etc.
.. High Error Rate
The network quality varies as the mobile computer moves across the heterogeneous network connections. The wireless environment exhibits higher error rates, which results in retransmission and affects the Quality of Service. By minimizing the usage of wireless transmission, the data is less exposed to transmission errors. In addition, error correction schemes can be employed to improve performance. However, these schemes also add to the communication overhead and reduce the usable bandwidth.
.. Power Limitations
Mobile computers are concerned with the limited power supply, an issue that does not appear in distributed wired environment. Hardware improvements on batteries can help to lengthen the life of a charge and reduce battery weight. In addition, efficient software operations can help to lower the power consumption. Examples include: shifting the processing to a fixed host, aggressively caching and prefetching data to reduce disk traffic, and transmitting less data while receiving more
.. Security
Security and privacy are of specific concerns in wireless communication because of the ease of connecting to the wireless link anonymously. Common problems are impersonation, denial of service and tapping. The main technique used is encryption. In personal profiles of users are used to restrict access to the mobile units.
.. Merits
