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The Past, Present, and Future of LTE

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(Tower Bridge, London, UK - Hsi-Pin Ma)

LTE Evolution - The Long Run To 5G


LTE Standardization and Deployment


- The Main Main Targets for the LTE

LTE (Long Term Evolution) has been playing a key role in the adoption of 4G (fourth Generation) since it was commercially launched in early 2010. In a matter of a few years, LTE has been successfully deployed around the world driving the entire wireless ecosystem to connect over 1 in 4 mobile users worldwide, a trend that is continuing to grow tremendously. 

Many Mobile Network Operators (MNO) have heavily invested in the LTE network rollouts across the world for the transition from the 2G/3G (second/third Generation) to 4G. This deployment has been an instrumental step to enhance the Mobile Broadband (MBB) proposition and improved coverage, as well as for offering more attractively priced data tariffs, greater availability and affordability of higher speed devices. 

The main targets for LTE are increased data rates, improved spectrum efficiency, improved coverage, reduced latency and packet-optimized system that support multiple Radio Access Technologies. LTE networks run on many bands and across a wide range of frequencies. LTE networks use bandwidths between 1.4 to 20 Mhz. LTE provides downlink peak rates of at least 100 Mbit/s, 50 Mbit/s in the uplink and RAN (Radio Access Network) round-trip times of less than 10 ms. 

LTE increases the capacity and speed using a different radio interface together with core network improvements. The evolved architecture comprises E-UTRAN (Evolved UTRAN) on the access side and EPC (Evolved Packet Core) on the core side. 


- LTE Standards

LTE is a packet switch IP technology based on OFDMA digital modulation scheme to supports channels bandwidth up to 20MHz and antenna techniques with Multiple-Input-Multiple-Output (MIMO), such that multiple data streams are delivered and received on a given frequency time by multiple antennas. For an example, 4x2 MIMO where 4 antennas are transmitting, on network side, and 2 are receiving, on User Equipment (UE).

System Architecture Evolution (SAE) is the core network architecture of 3GPP's LTE wireless communication standard. The SAE has a flat, all-IP architecture with separation of control plane and user plane traffic. 

LTE standards are in matured state now. The 3GPP developed the LTE standard in its Release 8 document series. Releases 9, 10 and 11 bring new features and enhancements, such as: carrier aggregation, enhanced downlink control channel, advanced MIMO technique and more. Release 12 delivered more enhancements, such as: FDD/TDD carrier aggregation, massive MIMO and beamforming or enhanced small cells and heterogeneous networks.  


- LTE Architecture and Components

A standard LTE system architecture consists of an Evolved UMTS Terrestrial Radio Access Network, more commonly known as E-UTRAN, and the System Architecture Evolution, also known as SAE. SAE is the core network architecture of 3GPP's LTE wireless communication standard. SAE's main component is the Evolved Packet Core, also known as an EPC.

The standards for EPC operation were specified by an industry trade group called the Third Generation Partnership Project (3GPP) in early 2009. EPC is the core component of Service Architecture Evolution (SAE), 3GPP's flat LTE architecture.


- LTE Evolved Packet Core (EPC)

Evolved Packet Core (EPC) is a framework for providing converged voice and data on a 4G Long-Term Evolution (LTE) network. 2G and 3G network architectures process and switch voice and data through two separate sub-domains: circuit-switched (CS) for voice and packet-switched (PS) for data. Evolved Packet Core unifies voice and data on an Internet Protocol (IP ) service architecture and voice is treated as just another IP application. This allows operators to deploy and operate one packet network for 2G, 3G, WLAN, WiMAX, LTE and fixed access (Ethernet, DSL, cable and fiber). 


- Frequency Bands

LTE networks run on many bands and across a wide range of frequencies. LTE networks use bandwidths between 1.4 to 20 Mhz. 

LTE uses either Frequency Division Duplex (FDD) or Time Division Duplex (TDD). While FDD makes use of separate bands to transmit uplink and downlink data, TDD uses time slots on the same frequency for both uplink and downlink. FDD and TDD LTE networks have been deployed on all continents. LTE’s performance can reach download rates of up to 299.6 Mbit/s and upload rates of up to 75.4 Mbit/s. It’s RAN latency is lower than 5ms latency for small IP packets in optimal conditions, and has a 2 up to 4 times improved spectral efficiency than previous communications technologies. 


- Modulation Schemes

LTE uses the following inner modulation schemes: 

  • Downlink: QPSK, 16-QAM, 64-QAM, 256-QAM (Release 12) 
  • Uplink: QPSK, 16-QAM, 64-QAM (depending on the UE)

A lower QAM is more robust against noise and interference, while a higher QAM offers a higher data rate. 

- Carrier Aggregation

Carrier Aggregation (CA) is a technology that combines two or more carriers into one data channel to enhance the data capacity of a network. It is possible to combine carriers in the same or different frequency bands. The easiest way to aggregate carriers is to take two or more contiguous channels within the same frequency band (intra-band, contiguous). It is also possible to combine two or more non-contiguous channels within the same band (intra-band, non-contiguous). The most challenging form is to aggregate two or more carriers from different frequency bands (intra-band; non-contiguous).  

CA technology is implemented in most modern mobile communication systems, like LTE and WiMax. In IEEE 802.11 (Wi-Fi) it is possible to combine two contiguous channels into one big data channels. In IEEE 802.11 terminology this is called channel bonding. Using existing spectrum, CA helps mobile network operators (MNOs) provide increased uplink and downlink data rates. CA has been crucial in increasing user throughput in 4G and it will be just as important for 5G. 

For 4G, CA allows MNOs to increase bandwidth and utilize fragmented frequency resources to provide higher data rates for user equipment. It improves peak data rates up to 2 Gbps as well as optimizes user throughput at low load. CA in 5G new radio (NR) will provide multi-connectivity with asymmetric upload and download, providing even more bandwidth, to a single user; up to 700 MHz is available in millimeter wave frequencies. In the sub-7 GHz band, up to 400 MHz of instantaneous bandwidth can be achieved using four 100 MHz channel.



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