A 4G LTE network can be classed based on the state of its evolution within the LTE standard. As a continuously developing technology, the LTE standard has undergone several releases by it's developer 3GPP.
LTE was introduced in December 2008 when, after several years of development, Release 8 of the specification was finalised. In comparison to legacy 2G and 3G networks, the objective of LTE was to provide high spectral efficiency, high peak data rates, short round trip time, and flexibility in frequency and bandwidth.
The new all-IP standard was based on OFDMA (Orthogonal Frequency Division Multiple Access) and in combination with higher order modulation (up to 64QAM), large bandwidths (up to 20 MHz) and spatial multiplexing in the downlink (up to 4X4) high data rates can be achieved. The highest theoretical peak data rate on the transport channel is 75 Mbps in the uplink, and in the downlink, using spatial multiplexing, the rate can be as high as 300 Mbps.
As a summary, the first LTE release (Rel. 8) supported the following:
- 20 MHz channel sizes
- 4X4 MIMO spatial multiplexing
- 64QAM Modulation Downlink
- 16QAM Modulation Uplink
- 300 Mbps DL (Peak)
- 75 Mbps UL (Peak)
3GPP continued development of the LTE standard, finalising Release 10 in September 2011. LTE-Advanced, or LTE-A focused on improving network capacity. The key new functionalities introduced were Carrier Aggregation (CA), enhanced use of multi-antenna techniques, and support for Relay Nodes (RN). LTE-A is often informally referred to as a "4.5G" network.
As a summary LTE Release 10, which we now call LTE-Advanced, provided the following technological enhancements:
- Increased peak data rate, DL 3 Gbps, UL 1.5 Gbps
- Higher spectral efficiency, from 16 bps/Hz with 4X4 MIMO to 30 bps/Hz with 8X8 MIMO
- Increased number of simultaneously active subscribers
- Improved performance at cell edges, e.g. for DL 2X2 MIMO at least 2.40 bps/Hz/cell
- Up to 5C carrier aggregation (100 MHz total bandwidth)
- LTE Supplemental Downlink (SDL)
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Development continued for the next five years until March 2016 with the finalisation of Release 13, known as LTE-Advanced Pro. The major advances achieved with the completion of Release 13 include: MTC enhancements, public safety features – such as D2D and ProSe - small cell dual-connectivity and architecture, carrier aggregation enhancements, interworking with Wi-Fi, licensed assisted access (at 5 GHz), 3D/FD-MIMO, indoor positioning, single cell-point to multi-point and work on latency reduction. LTE-A Pro networks are often called "4.9G" or "Gigabit LTE" networks.
The key distinguishing enhancements were:
- 256QAM modulation in downlink (Release 12) and uplink (Release 13)
- LTE-U technologies, such as LTE Licence Assisted Access (LAA) leveraging the 5 GHz band
- Massive MIMO, such as 64T64R and 128T128R antenna technologies
- Beginning of IoT features such as LTE Cat-1
- Ultra low frequency bands: B31 (450 MHz) (Rel. 12)
3GPP Rel. 14 was made public in September 2017, which included further enhancements, most notably the formalisation of LTE IoT technologies NB-IoT and eMTC (LTE-M), and further bands in the 600 MHz digital dividend. It is unlikely that these features will be branded, instead they will remain classed as Rel. 14 (and above) until such a time when they are to be added to the 5G NR standard.