Three Wireless Generations

As previously mentioned, cellular technologies are divided into three generations: first, second, and third, abbreviated respectively as 1G, 2G, and 3G. In the past, various standard bodies and international consortia defined these terms rather vaguely and sometimes inconsistently. In response to this situation, publications and even academia are now renaming some of the technologies at the boundaries of "G" definition, adding a "decimal point" to their generation designation, such as 2.5G for example. Luckily, the discussions around this and other terminology issues in general are not entirely relevant to the main purpose of this book (and the majority of technical publications for that matter). While recognizing this problem, we do not attempt to solve it. In this book we applied current "xG.y" taxonomy as consistently as possible with as many standard definitions as we could get our hands on. Clear understanding of this classification will become important in later chapters. Table 3.1 summarizes the basic features, nomenclature, and properties of cellular systems comprising the cellular generations.

First-generation cellular wireless systems provide analog speech transmission based on Frequency Division Multiple Access (FDMA) with core networking based on time-division multiplexing (TDM). Examples of 1G include Advanced Mobile Phone System (AMPS), used throughout the United States, and Nordic Mobile Telephone system (NMT), which is still deployed in many Western European countries. Typically, 1G technologies were deployed within a single county or group of countries, were not standardized by international standard bodies, and were not intended for international use.

In contrast with the first generation, 2G technologies were designed for international deployment. Greater emphasis was placed on compatibility, sophisticated roaming ability, and the use of digitally encoded speech transmission over the air. This last feature is actually a requirement for a cellular system to be classified as 2G. Popular examples of 2G systems are Global System for Mobile Communications (GSM) and cdmaOne (based on the TIA [IS95] standard). 2G core networking technology may rely on circuit as well as packet data (more on this in Chapter 4).

A cellular system can be classified as a 3G system if it complies with a number of requirements set forth by the ITU:

• It must operate in one of the spectrum frequencies allocated for 3G services.

• It must provide an array of new data services to the user, including multimedia, independently from the air interface technology.

• It must support mobile data transmission at 144 Kbps for high mobility users (vehicular speed), 384 Kbps for pedestrians, and stationary data transmission at up to 2 Mbps (at least in theory).

• It must enable packet data services (that is, data services not based on a circuit connection to a data network, but on a native packet-based bearer service).

• It must adhere to a principle of independence of the core network from the radio access interface.

Some 2G systems are evolving toward at least partial compliance with these requirements. This is having an undesirable side effect: It is wreaking havoc with the "generations" terminology. For example, GSM with circuit data support is classified as a pure 2G system. When augmented with General Packet Radio Service (GPRS), it becomes compliant with many 3G requirements. This leaves it in a neither 2G nor 3G "between generations" class; as a result, GPRS-augmented GSM system is now referred to as a 2.5G system, while in actuality still belonging to a 2G class, at least from a radio transmission technology perspective.

Figure 3.1 summarizes this discussion by illustrating main cellular systems and their migration paths classified in three generations.

Figure 3.1: Cellular systems migration paths.