Two-Unit Configuration
Two-unit connections require two pieces of equipment to work together, such as a PDA and a cell phone, as shown in Figure. One unit provides the wireless connectivity for the other unit to use. These devices can communicate with each other in a variety of ways:
Cable connection. This involves having a physical cable connecting the cell phone and mobile device. The phone must have wireless data support as well as an interface cable to the device of choice.
Infrared connection. This involves lining up the Infrared ports on the cell phone and mobile device for communication. A direct line of sight is required for this solution to work. In addition, only selected phones have infrared support available.
Bluetooth connection. Bluetooth may be the best option for two-unit connectivity. It allows a mobile phone to provide connectivity through a personal area network (PAN) up to a range of about 10 meters. A direct line of sight is not required, so it is possible to have the cell phone in a different location from the mobile device. This will become an increasingly popular option as more Bluetooth-enabled devices are released.
Figure : Two-unit configuration.
The advantage of the two-unit configuration is that you can choose each device based on its own functionality, and you do not have to sacrifice features for wireless capabilities. The configuration also provides a great degree of flexibility. If one device becomes outdated or malfunctions, it can be replaced without having to replace the entire system. This is especially appealing when the data device is a laptop or PDA that may not need to be replaced as frequently. In addition, the cell phone can potentially provide the wireless communication for several other devices.
The downside to this configuration is its complexity. Both the cell phone and the mobile device have to be configured properly for this to work. When Bluetooth is not available, the cable or Infrared connections can become cumbersome.
This setup is recommended only where occasional wireless connectivity is required. When frequent access is necessary, it is worthwhile to investigate some of the other options available.
Detachable Configuration
A detachable configuration involves using a plug-in module or clip-on attachment to a mobile device to provide wireless connectivity. These additional modules can provide connectivity to a variety of wireless networks with little configuration. For the plug-in modules, either CompactFlash or PCMCIA cards can be used. This obviously requires a device that has a slot for this type of peripheral. For devices that do not have integrated CompactFlash or PCMCIA slots, external jackets are often available. These jackets (often called sleds) provide the support for CompactFlash or PCMCIA cards.
Note Some of the wireless modems on the market also include support for voice calls. An example of this is the Sierra AirCard 555, which provides CDMA2000 1x wireless data as well as voice capabilities.
The benefit of using these interfaces is that multiple wireless modems are available, providing connectivity to several wireless networks including WLANs, WANs, and PANs. You can then switch interface cards as you move into different wireless environments. Cards are also available that support connecting to multiple network protocols in one unit.
In some cases, the only available option is a clip-on modem. This is similar to the external jacket, except that the modem is incorporated directly to the unit. These modules are often purchased in conjunction with a wireless service plan since they only provide access to a single wireless protocol, most commonly a wireless WAN.
The majority of the PDAs available now use a detachable configuration for wireless connectivity. It allows users to select the PDA and wireless component separately, but at the same time have them integrate well together. The disadvantage is that the wireless modem uses the open expansion slot so other peripherals cannot be used at the same time.
Integrated Configuration
An emerging trend is to enclose wireless connectivity within the mobile device. This has always been the case for voice-oriented devices such as cell phones and smart phones, but is a new concept for many handheld devices. This configuration has many advantages, as it alleviates complexity and provides tight integration between the mobile OS and wireless modem. Applications for these devices can be designed to take advantage of the wireless modem, knowing that it is always going to be present. Troubleshooting is also simplified, since there is only one manufacturer involved in the solution.
On the downside, some flexibility is lost. The user is now limited to the wireless net-work type that has been integrated into the device. In addition, it may become more difficult for developers to calculate the amount of power an application requires, as they will have a hard time differentiating between the power that the application requires and that of the wireless modem.
For users who will be using wireless communication frequently or who are looking for a very intuitive, user-friendly experience, integrated configurations are ideal. Devices are available for a variety of wireless networks. Many ruggedized devices with integrated wireless LAN access have been on the market for some time, while integrated public WAN devices are just now being deployed on a large scale. As devices continue to evolve, it may become practical to carry a single device for both data and voice communication.
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