Some of the most common acronyms used in the discussion of wireless are those that describe the air interface method of a wireless network. The air interface technology specifies the method for transmitting information over the air between base stations and mobile units. Most air interface technologies are specified in standards that are agreed upon by multinational bodies comprising representatives in the wireless industry. Some air interface methods, however, remain proprietary with certain companies and details of their operation may or may not be publicly accessible.

The list of wireless air interface protocols that follows represents the most common standards in use around the world today. They are organized roughly in terms of the generations (1G, 2G, and 3G) of development and include various derivations or alternate terms used to describe them:

— Dave Mock is a writer and consultant covering wireless technologies and markets. Contact him at [email protected] or visit www.davemock.com for further information.

The first generation of wireless air interface standards, implemented in the late 1970s and early 1980s, were largely analog in nature. Basically, that means that the transmission of voice was simply done by modulating a carrier wave.

These systems operated with relatively high-powered signals (compared to current systems) and the range of transmission from mobile unit to base station could be several miles. Due to their simple analog nature, these systems were not very secure, making them prone to fraud and eavesdropping. They also had limited capacity, as a paired frequency channel was dedicated to a single call (see FDMA description below).

First-generation wireless systems also were limited to voice services. No provision was made in the air interface to send or receive any meaningful amounts of data, so services such as messaging and Caller ID are not provided for in these air interface protocols. Here are the more popular protocols, many of which are still in use:

The second-generation air interface technologies introduced digital techniques to enhance the efficiency of transmission and therefore increase network capacity. Many of these methods increased the capacity several times over analog systems by digitizing the voice signal before it is sent over the air. Voice packets from individual conversations could then be packed more tightly into channels to boost system capacity. They first began being deployed in the early 1990s, often times alongside analog systems still in operation.

To increase capacity, many of these air interface protocols employ the concept of multiple access (or multiplexing). Individual calls can be multiplexed in time (time division), in frequency (frequency division), or by codes (code division) to “stack” multiple callers in a frequency band that, using analog technology, could handle far fewer callers. Here’s a brief description of each technology:

In addition to their digital techniques for transmitting voice, most of these air interface protocols also have provisions for sending limited amounts of data. This enables features such as paging, messaging, and Internet browsing. The digital nature of transmission also makes these protocols more secure and much harder to tap into illegally.

Below are several advanced 2G wireless standards that exist now or will be deployed soon. Keep in mind that these standards are each based on one of the three technologies above. Confusion arises because many of the standards are simply referred to by the technology they use, as in the case of TDMA and CDMA. It’s actually more accurate to refer to them as IS-136 and IS-95 respectively.

Most of the third-generation wireless technologies employed in networks will maximize capacity through the use of code division techniques in the air interface. Significant variations exist among the different standards, though, in terms of synchronization, spectrum use, and coding techniques. There’s still a lot of work going on to solidify the various standards, and some still have technical issues that need to be worked out before widespread use is possible.