The real breakthrough came with the UMTS (Universal Mobile Telecommunications System) and CDMA (Code Division Multiple Access) systems. Until now our mobile networks were largely based on Circuit Switching techniques, but the evolution to UMTS embraced Packet Switching with Internet Protocol to provide fast data up to 2Mbps for mobile computer and cell phone users.
The evolution continued with the advent of two technologies:
HSDPA - High-Speed Downlink Packet Access, which was sometimes labelled as 3.5G gave us the potential for up to 21Mbps downlink transfer speeds. True multimedia transmissions could now be accessed from the Internet via our mobile devices.
HSUPA - High-Speed Uplink Packet Access, which provided for uplink speeds of up to 5.8Mbps.
The two together are often just referred to as High Speed Packet Access, building on the WCDMA (Wideband Code Division Multiple Access) technologies. The result was an increase in peak data rates, both uplink and downlink that allowed for true multimedia capabilities.
So what is LTE (Long Term Evolution)? It is a Next Generation mobile broadband technology, promising fast data rates of 100Mbps and beyond utilising existing 3g technology to effectively turn our mobile computing devices and phones into true IP nodes. The demand for data has been growing at an exponential rate and the mobile operators have been competing in order to provide the best mobile broadband services cost effectively.
The history of LTE goes back as far as 2004 when discussions by members of the 3GPP (3rd Generation Partnership Project) to define and develop and upgrade existing systems to a packet only system capable of providing true broadband services from mobile devices. In order for voice and video to be viable in packet form then round trip times on any system must be kept within certain limits (30 milliseconds) and access times below 300 milliseconds. Uplink and Downlink speeds must also improve. Network capacity issues must also be addressed.
In order to achieve the high data rates, maintain low error rates and to keep power consumption of mobile devices within practical limits an upgrade to what is known as the LTE Air Interface had to be undertaken. Two technologies for the uplink and downlink were chosen as follows:
OFDMA (Orthogonal Frequency Division Multiple Access) was chosen for the downlink to provide the multi user access to the networks. OFDMA utilises both frequency and time domain by allocating resources to end users based on a frequency / time slots. The use of multiple antennas through the use of MIMO (Multiple Input Multiple Output) helps to maintain the low date rates necessary. 3G WCDMA networks were based on 5Mhz wide channels, while LTE uses 20Mhz wide channels to accommodate the higher date rates.
SC-FDMA (Single Carrier - FDMA) is the choice for the uplink channels from mobile devices to the network. Power efficiency is achieved where PAPR (Peak to Peak Average Power Ratio) greatly benefits devices in the uplink wireless transmission.
Additional elements are added to the UTRAN (UMTS Terrestrial Radio Access Network) for LTE, the most notable are:
SAE (System Architecture Evolution) Gateway is actually comprised 2 separate gateways, the first of which is the Serving SAE Gateway which serves as the main contact point the the network and the PDM (Public Data Network) SAE Gateway provides the interface to the external IP networks.
MME (Mobility Management Entity) provides a number of key functions in the LTE core network such as registration, paging, authentication and mobility.
An element in the LTE network which has a compatible element in the UTRAN is eNodeB, otherwise known as the Base Station, which provides resource management and two important functions for the data stream of IP Header compression and security of the user data stream through the use of encryption.
NB. Other network elements / nodes are omitted from this post.
Evolution continues with LTE-A (Long Term Evolution - Advanced) which provides uplink data rates up to 500Mbps and 1Gpbs downlink rates, compared to 75Mbps and 150Mbps for LTE. This requires wider channels of 40Mhz for the uplink and 100Mhz for the downlink with 3 times the capacity of LTE.