In March 1998, the International Telecommunications Union-Radio communications sector (ITU-R) specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced (IMT-Advanced) specification, setting peak speed requirements for 4G service at 100 megabits per second (Mbit/s)(=12.5 megabytes per second) for high mobility communication (such as from trains and cars) and 1 gigabit per second (Gbit/s) for low mobility communication (such as pedestrians and stationary users).

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Although originally marketed as 4G technology, LTE (Long Term Evolution) didn't satisfy the technical requirements that the ITU-R outlined, meaning that many early tariffs sold as 4G weren't actually 4G. LTE supports much less than the 1 Gbit/s peak bit rate, they are not fully IMT-Advanced compliant, but are often branded and considered 4G by service providers, due to marketing pressures and the significant advancements that LTE brought to original 3G technologies.

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Mobile WiMAX Release 2 (also known as WirelessMAN-Advanced or IEEE 802.16m) and LTE Advanced (LTE-A) are IMT-Advanced compliant backwards compatible versions of the above two systems, standardized during the spring 2011, and promising speeds in the order of 1 Gbit/s. Services were expected in 2013.

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As opposed to earlier generations, a 4G system does not support traditional circuit-switched telephony service, but instead relies on all-Internet Protocol (IP) based communication such as IP telephony. The spread spectrum radio technology used in 3G systems is abandoned in all 4G candidate systems and replaced by OFDMA multi-carrier transmission and other frequency-domain equalization (FDE) schemes, making it possible to transfer very high bit rates despite extensive multi-path radio propagation (echoes). The peak bit rate is further improved by smart antenna arrays for multiple-input multiple-output (MIMO) communications: a practical technique for sending and receiving more than one data signal on the same channel at the same time by using more than one antenna. MIMO paved the way for LTE-A, which is considered “true 4G”.

 

The following key features can be observed in all suggested 4G technologies:

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• Physical layer transmission techniques are as follows

  • MIMO: To attain ultra-high spectral efficiency by means of spatial processing including multi-antenna and multi-user MIMO

  • Frequency-domain-equalization, for example multi-carrier modulation (OFDM) in the downlink or single-carrier frequency-domain-equalization (SC-FDE) in the uplink: To exploit the frequency selective channel property without complex equalization

  • Frequency-domain statistical multiplexing, for example (OFDMA) or (single-carrier FDMA) (SC-FDMA, a.k.a. linearly precoded OFDMA, LP-OFDMA) in the uplink: Variable bit rate by assigning different sub-channels to different users based on the channel conditions

  • Turbo principle error-correcting codes: To minimize the required SNR at the reception side

• Channel-dependent scheduling: To use the time-varying channel

• Link adaptation: Adaptive modulation and error-correcting codes

• Mobile IP utilized for mobility

• IP-based femtocells (home nodes connected to fixed Internet broadband infrastructure)

 

As opposed to earlier generations, 4G systems do not support circuit switched telephony. IEEE 802.20, UMB and OFDM standard lack soft-handover support, also known as cooperative relaying.

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