Once a new telecommunications standard begins to roll out, the industry will quickly begin hyping the next standard. Such is the case with Long Term Evolution (LTE), which began to take over headlines during third-generation (3G) network buildouts. While LTE is widely touted as a fourth-generation (4G) standard, however, it does not meet all of the 4G requirements. Because of the industry's confusion over what truly constitutes 4G, it has been tricky for standards bodies to proceed with their efforts regarding this next-generation technology.
As summarized by Moray Rumney, Technology Advisor at Agilent Technologies, "In recent months, the usage of the term 4G' has become more widespread. it is being used by the industry to describe not just the IMT-advanced technologies of LTE-advanced and WirelessMAN-advanced (IEEE 802.16m/WiMAX Release 2), but also other technologies like WiMAX, LTE, and HSPA+, which were previously referred to as 3.5G or 3.9G. The International Telecommunications Union (ITU) has accepted this usage of 4G and sent out a communication saying, IMT-Advanced is considered as 4G.' Yet it is recognized that this term, while undefined, may also be applied to the forerunners of these technologies: LTE and WiMAX and other evolved 3G technologies providing a substantial level of improvement in performance."
In 2009, the Third-Generation Partnership Project (3GPP) submitted LTE-Advanced to the ITU as a contender for 4G IMT-Advanced. The ITU had previously defined the requirements for 4G cellular technology in the IMT-Advanced standard. LTE-A was accepted this past fall and work is currently being done on Release 10. In terms of performance, LTE has a peak data rate of 300 Mb/s on the downlink and 75 Mb/s on the uplink while LTE-A provides data rates to 1 Gb/s on the downlink and 500 Mb/s on the uplink. At high mobility, such data rates will reach 100 Mb/s (versus 1 Gb/s at low mobility).
In addition, LTE offers peak spectrum efficiency of 15 b/s/Hz on the downlink and 3.75 b/s/Hz on the uplink with transmit bandwidth to 20 MHz. By comparison, LTE-A provides 30 b/s/Hz peak downlink efficiency and 15 b/s/Hz uplink efficiency with transmit bandwidth reaching 100 MHz. Peak spectrum efficiency for IMT-Advanced is 15 and 6.75 b/s/Hz, respectively, for the downlink and uplink. it covers transmit bandwidth to 40 mHz. The standards also differ in spatial-multiplexing approaches. LTE and IMT-Advanced use multiple-input multiple-output (MIMO) antenna schemes to 4x4 on the downlink while LTE-A ranges to 8x8 configurations.
No matter how they achieve these rates and what their performance may be, all of these technologies are technically permitted to be called "4G." Yet most of them can be thought of as steps on the way to the WiMAX wireless-MAN standard and IMT-Advanced. Despite any differences, they all have been created to provide the higher peak data rates needed to support advanced services and applications. Of course, by the time these technologies are actually rolled out, the industry will have moved on to talking about 5G.