SPEC-India

Multiplexing is a term used to describe how a signal can be divided among multiple users. This spectrum sharing allows wireless operators to maximize the use of their spectrum to accommodate a large number of users over fewer channels. For digital systems, three main multiplexing techniques are being used for wide area networks: frequency division, time division, and code division. A fourth method, called orthogonal frequency division, is the most complex of all of these methods. It is commonly used in high-speed local area networks, as discussed earlier in this chapter, but is starting to grow in popularity for wide area networks as well.

1. Frequency-division multiplexing (FDM). Numerous signals are combined on a single channel. Each signal on the channel is assigned unique frequency for communication. The caller and the receiver tune to the same frequency to communicate. This is similar to how radio stations work. Each has its own frequency band over which it broadcasts. To listen to a particular channel, you tune the receiver to that particular frequency. For person-to-person communication, this is a very inefficient use of spectrum, hence is only used by analog wireless networks.
2. Time-division multiplexing (TDM). As with FDM, numerous signals are combined on a single channel, but with TDM they are divided into separate time slots. The time segments are assigned to an individual user and are rotated at regular intervals. The receiver interprets the appropriate time slot (channel) to receive the information. This technique allows for variation in the number of signals sent along the line, and constantly adjusts the time intervals to maximize bandwidth. Many of the current second-generation wireless systems are based on time-division multiplexing as it provides efficient use of spectrum with minimal interference.
3. Code-division multiplexing (CDM). Rather than dividing the signal using frequency or time, CDM attaches a code to each signal, and sends them all over the same broad spectrum. This results in very high spectrum efficiency and low levels of interference by other signals. Even though all of the signals are being broadcast at once, a receiver will only accept the signals with the right code. This technique is used in several second-generation wireless networks and is the basis for nearly all third-generation networks.

Advantages

The following are the key advantages of wireless Internet (thin client) architecture:

1.  Minimal to zero software deployment. This allows applications to be deployed without any additional client-side configuration. Updates to these applications are also straightforward since only the server has to be updated.
2.  Extends Internet computing model. Many corporate applications are based on the Internet model. Wireless Internet is a natural extension to these applications.
3.  Familiar user interface. Many users are familiar with a browser interface to their applications. Providing a similar interface on mobile devices allows them to be productive immediately; there is no learning curve.
4.  Enterprise integration. If an existing Internet application is being extended, the application logic and enterprise integration layers may already be taken care of. This is a tremendous benefit, as enterprise integration often proves to be the most resource-intensive part of a mobile application.
5.  Security. All of the data is stored on the server behind corporate firewalls. No data is stored on the client.

Disadvantages

Wireless Internet architectures have some disadvantages as well, namely:

1.  Wireless connectivity. To access any data, all of which resides on the server, you need wireless connectivity. This can be problematic when users are moving between multiple locations. The exception is when browsers have content-caching capabilities. That said, even when caching is available, there is still a very limited amount of data and logic available to perform transactions.
2.  Simple user interface. Many microbrowsers have limited capabilities for graphics or other “rich” components. Graphics are also often avoided to minimize the amount of data being downloaded over potentially slow wireless networks.
3.  Application performance. For each request being transferred over a wireless network, performance can be an issue. This is due partially to network throughput and partially to network latency.
4.  Application testing. Controlling, predicting, and testing the behavior of the application is difficult on the full range of microbrowsers. When emulation software is used to simulate devices, it is not always an accurate representation of the end-user experience since it is not executing over a wireless network.
5.  Availability. If a server-side problem occurs, all users will be brought to a halt.
6.  Security. Total control of the environment is not available in most cases, because a wireless gateway exists that may lead to security concerns.
7.  Cost. Wireless airtime fees can become an issue if the mobile user has to constantly be connected to use the application. On circuit-switched networks, where fees are charged based on the time connected, not the data transferred, charges are incurred even when a user is reading Web content or filling in a form.

A wireless technology that enables short-range wireless data connections between devices. The name came from: Harald Bluetooth, a Viking and king of Denmark from the years 940 to 981, was renown for his ability to help people communicate. During his reign, he united Denmark and Norway.

Bluetooth wireless technology is a worldwide specification for low-cost radio that provides links between mobile computers, mobile phones, other portable handheld devices, and connectivity to the Internet. There is a written specification developed, published and promoted by the Bluetooth Special Interest Group (SIG). This SIG includes Agere, Ericsson, IBM, Intel, Microsoft, Motorola, Nokia and Toshiba, and hundreds of Associate and Adopter member companies. In mid 2002, the Bluetooth SIG established its global headquarters in Overland Park, Kansas, USA.

The Bluetooth wireless technology is essentially designed to replace cables between cell phones, laptops, and other computing and communication devices within a 10-meter range. When Bluetooth wireless technology connects devices to each other, they become paired. An example of such device pairings includes:

1. Your wireless headset connecting to the cell phone in your pocket
2. Your PDA automatically synchronizes with your computer when you walk into the office.

And this is only the tip of the iceberg. Bluetooth Technology is poised to expand into areas such as industrial automation, gaming and delivery tracking. It is not too far off from when you will use a Bluetooth pen to write on an image board located in a different office. 

Bluetooth has already managed to immerse itself into the automotive industry. Your mobile phone headset will be wirelessly connected to the car’s in-built audio system enabling completely hands-free

BREW is an application development platform created by Qualcomm for mobile phones. It was originally developed for CDMA handsets, but has since been ported to other air interfaces including GSM/GPRS. BREW is a software platform that can download and run small programs for playing games, sending messages, sharing photos, etc. The main advantage of BREW platforms is that the application developers can easily port their applications between all Qualcomm devices. BREW runs between the application and the wireless device’s chip operating system so as to enable a programmer to develop applications without needing to code for system interface or understand wireless applications