Technologies - 4G LTE
4G LTE (Long Term Evolution) networks are the fourth generation of broadband cellular network technology, and have been available in the UK since 2012. Over the past 8 years, 4G has enabled superior speeds and greater capacity, allowing for new types of application and services. The preceding 3G networks have been relegated to a fallback option should 4G be unavailable.
A 4G system must provide capabilities defined by ITU in IMT Advanced. Potential and current applications include amended mobile web access, IP telephony, gaming services, high-definition mobile TV, video conferencing, and 3D television.
4G is powered by multiple frequency bands, providing different characteristics.
The 2.6GHz and 800MHz bands were auctioned off by Ofcom in February 2013. 2.6GHz provides higher data capacity compared to the other two bands, but sacrificing performance over long distances. It is therefore ideal for cities and other compact, densely populated areas but not so good for rural locations.
The 800MHz band was previously used to provide analogue terrestrial TV, but has been freed up since the switchover to digital television. While it doesn't provide the same data capacity as the 2.6GHz band, the 800MHz frequency can easily travel over long distances, making it better able to provide broadband speeds to rural areas where telephone exchanges can't reach. Lower frequencies are also better when used indoors, due to their ability to penetrate walls.
1800MHz is also used by some providers, and is a good middle ground between the trade off in the properties described above.
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).
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.
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.
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:
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
Mobile IP utilized for mobility
IP-based femtocells (home nodes connected to fixed Internet broadband infrastructure)