Wireless Data Communications Technologies

The use of wireless technologies has been found to be very useful over the years as a way of remaining in touch, reducing the costs of communications, or increasing productivity. There are a variety of wireless technologies in use today and one major distinction is how large of a geographic area they cover:

• Wide Area Networks (WANs) such as satellite transmissions allow for sending information over a broad geographic area and is very cost effective when many people need to receive the same information. A good example of this is business data such as the stock market.

• Metropolitan Area Networks (MANs) covers the area around a city. Service dispatching and mobile professionals use this technology.

• Local Area Networks (LANs) allow computers within a building to communicate with each other. Avoiding the installation of wiring and the use within notebook computers are two applications of this technology.

• Personal Area Networks (PANs) are designed for applications of less than 10 meters. Peripherals for computers and device control are applications of PAN.

The use of the frequencies for any of these wireless applications is controlled by the Federal Communications Commission in the US and other such bodies in their respective countries. These national groups come together every few years at the World Administrative Radio Council (WARC) to work out details that allow similar usage of frequencies for various applications.

In general, the LAN and PAN frequencies have been set aside and a user does not have to pay for a license. WAN and MAN frequencies are set aside and allocated to companies that are allow these companies to invest in the infrastructure and then recover the cost of their investments.

For all radio transmission devices, there are very stringent rules that govern the equipment that operate in their respective bands. These rules ensure that devices will not interfere with other services in different bands. The important characteristics for creating a device for an application are:

• Frequency - Different bands are assigned for a particular purpose. For example the AM and FM radio bands, TV channels, cell phone and satellite transmissions allow manufactures to make devices that are useful throughout the world.

• Bandwidth - This translates into the peak speeds for a device.

• Power - Determines how far the signal will go.

• Modulation - determines the efficiency of signal verses how robust the signal will be in the presence of interference.
  

LAN/PAN Technology

There are a variety of wireless technologies that may be used in the home and business environment. The major applicable standards are shown below.

Table 1. List of Wireless LAN/PAN Technologies

Note: CDMA=Code Division Multiple Access, FEC=Forward Error Correction Code, FH = Frequency Hopping, OFDM=Orthogonal Frequency Division Multiplexing, OQPSK=Offset Quadrature Phase Shift Keying, QoS=Quality of Service

The most popular of these technologies for the home market is the IEEE 802.11b standard. It does not currently support QoS but efforts are underway to complete this. Its cost and data rate (11 Mb/s) is sufficient for current customer needs. Its major drawback is that it operates in the 2.4 GHz band and thus must share the spectrum microwave ovens and new generation digital phones. For many environments it is "good enough" but high-density housing may see service problems.

Devices based on the IEEE 802.11a will started to appear recently but are not widely deployed. This standard makes use of the much "cleaner" 5.1 GHz band and allows for much higher data rates (54 Mb/s). Another standard is under development (IEEE 802.11g) that will probably delay the acceptance of the 802.11a market. It is also 54 Mb/s but is in the same band as 802.11b. Its promise is to have a dual-functioning mode to allow the 802.11b products to work and then allow migration to the higher data rates. It cannot operate in both modes simultaneously but current unit projections are for 3 times more (g) products than (a) products for the next few years.

For the European market, the HiPerLAN 2 standard is likely to be more prevalent than the IEEE 802.11 standard. For the rest of the world, it remains to be seen whether the IEEE or HiPerLAN standard will be more widely deployed.

The Bluetooth standard is geared more towards the PC market to replace USB cabling. It is meant to be a short distance communications. Variants of this technology include light control and other inexpensive devices requiring low bandwidth.

MAN Technology

As in the LAN/PAN applications, there are a variety of technologies addressing data communications. Third Generation (3G) cell phones are using the cell phone frequencies to transmit voice as well as data. Short Messaging Service (SMS) has found a niche in "chat" types of messaging for teenagers.
PDAs are using dedicated networks to carry business traffic that improve the productivity of the work force. These networks tend to be somewhat expensive to use and may be replaced by more cost effective and higher speed systems.

There is also a new class of devices that will be emerging based on usage of the 5.1 GHz band. This band is divided into three areas for use in short distance multimedia applications, non-time critical applications, and community networks. These same frequencies can be used in the LAN environment and since they are unlicensed, companies may begin to deploy services using this spectrum for MAN applications.

WAN Technology

Satellite technology is very good at providing wireless coverage in sparsely populated areas where the cost of putting in fixed wiring is prohibitive. It also shines for sending data cheaply to thousands of receivers simultaneously.

Hughes Satellite is deploying a system for Internet access. Their initial system used a downlink from the satellite for data and the reverse channel used the phone line. Their latest system, "Direct Duo", uses a wireless reverse path.

The performance of such a system is not as good as other broadband systems because of the long delays of going up 24,000 miles and down 24,000 miles. While not as cost effective as a cable modem or ADSL, this type of system allows those in more isolated areas to participate in higher speed Internet access.

In Summary:

• There are several types of wireless technologies and they are distinguished by the geographic coverage area of the technology.

• The major features of wireless technologies are the frequency, bandwidth, power, and modulation.

• There are similar spectrum usage rules across national boundaries and some frequencies are free to use and others are reserved for specific license holders (i.e. companies).