Cellular Network History
First Generation
Motorola DynaTAC
First generation cellular wireless standards modulated voice over an analog signal. The first commercially available cellular network was launched by Nippon Telegraph Corporation in 1979 in Japan. Using 23 base stations, the network had the ability to cover the Tokyo metropolitan area’s 20 million inhabitants. By 1984, the network had been expanded to cover the majority of the island to become the first nation-wide cellular network. The first cellular network in America was launched in Chicago in 1983 by Ameritech. It used the first handheld mobile phone, the Motorola DynaTAC.
Second Generation
The second generation advancement in mobile telecommunications occurred in 1991 when phone conversations began to be encoded digitally on the Oy Radiolinja Ab network in Finland. The use of digital signals between wireless phones and radio towers increased the capacity of the telecommunications systems, providing the ability to compress and multiplex voice data more effectively. The digital signals required less radio power from the wireless handsets, paving the way for reductions in size and cost. The switch to digital, along with its associated efficiencies, opened the door for mobile data services, beginning with Short Message Service (SMS) text messaging.While 2G was designed to provide primarily voice services, 2.5G, also known as General Packet Radio Service, acted as an intermediate link between the second and third generation mobile telephone technologies. This packet-oriented system provided moderate data speeds of 56-114 Kbit/s through its deployment of unused time division multiple access channels. The focus on mobile data transfer revolutionized the way customers were charged for mobile services, as traditional circuit switched networks billed clients per minute of connection time, while 2.5G charged per megabyte of data that was transferred. The use of packet switching extended cellular wireless technology by enabling continuous Internet access, multimedia messaging service (MMS), push-to-talk over cellular, instant messaging, and point-to-point inter-networking over IP. SMS transmission speed increased from approximately six to 10 messages per minute to about 30 messages per minute.
Third Generation
The introduction of 3G mobile telecommunications technology features the simultaneous use of voice and data services. In order to provide concurrent voice and data, 3G deploys both circuit switched and packet switched network nodes running in parallel. Classified under the International Mobile Telecommunications-2000 family of standards, 3G systems offers download speeds of up to 14 Mbit/s, and uploads at a rate of 5.8 Mbit/s. The IMT-2000 standardization is not a specific technology, but rather a set of minimum requirements for a cellular network technology to be considered 3G. The requirements for the IMT-2000 are set by the International Telecommunication Union (ITU).
3G's increase in data rates has spurred the development of software services previously not available on mobile phones. Applications include mobile television, location-based services, video conferencing, and video on demand. Gemma Tedesco, a senior analyst at In-Stat, estimates that use of 3G technologies will continue for at least the next 10 years, acting as a transition technology while 4G networks are built.
Fourth Generation
The fourth generation of cellular wireless technology implements an all-IP packet switched network, eliminating the use of circuit switching. 4G networks treat voice calls just like any other type of streaming media, transferring voice via packet switching over LAN and WAN networks using Voice over IP (VoIP). 4G networks support IP telephony, ultra-broadband Internet access, and streamed multimedia, as well as advances in mobile gaming. Due to the technology’s reliance on packet switching and the impending exhaustion of IPv4 addresses, 4G devices must support the IPv6 address space. In June 2009, Verizon Wireless announced that any 4G devices on its network will be required to support IPv6.
There are currently two primary 4G technologies: Long Term Evolution Advanced from 3rd Generation Partnership Project (3GGP), and the IEEE’s WiMAX. In order to be considered 4G, network technologies must meet the requirements of the IMT-Advanced standard, as defined by ITU. Major requirements of the standard include at least 40 MHz of scalable bandwidth, 100 Mbit/s for high mobility access devices such mobile handsets, and 1 Gbit/s for low mobility access devices such as local wireless. Although there are two competing 4G implementations, each focuses on using the available radio spectrum more efficiently. This involves replacing the code division multiple access (CDMA) and time division multiple access (TDMA) methods for multiplexing data transmission, and instead using orthogonal frequency division multiple access (OFDMA) schemes. OFDMA digital modulation splits its signal into multiple narrowband frequency channels, allowing simultaneous transmission by multiple users, as shown in the figure below. It is more resistant to interference than CDMA, which simultaneously transmits several signals along the same channel. OFDMA has the additional benefit of being less complex than CDMA. Unlike TDMA, which divides several channels into time slots with users taking turns transmitting, OFDMA can simultaneously transmits data from multiple users. It also has the advantage of a shorter, constant delay between slots.
Orthoganal Frequency DIvision Multiple Access
