Overview §

• LTE was designed by 3GPP (Third Generation Partnership Project)
• LTE is known in full as 3GPP Long-Term Evolution
• LTE evolved from UMTS (Universal Mobile Telecommunications System), which in turn evolved into GSM (Global System for Mobile Communications)

Radio Access Network §

• The RAN (Radio Access Network) handles the core network’s radio communications with the user
  • e.g. GERAN (GSM EDGE RAN), UTRAN (UMTS RAN)
• Each mobile and base station transmits on a certain radio frequency, the “carrier frequency”
  • A certain amount of frequency around the carrier is occupied, known as “bandwidth”
  • e.g. if carrier frequency = 1960MHz and bandwidth = 10MHz, then frequency range = 1955MHz to 1965MHz
• FDD (Frequency Division Duplex) = base station transmits on one carrier frequency, mobiles on another
• TDD (Time Division Duplex) = base stations and mobiles transmit on same carrier frequency, but at different times

Generations 1G to 3G §

• 1G (first generation)
  • ~1980s
  • Similar to traditional analogue radio
  • Large cells, inefficient use of spectrum, bulky devices
  • Almost exclusively used by business users
• 2G (second generation)
  • ~1990s
  • Used digital technology
  • Originally just for voice, but SMS (Short Message Service) added later
  • Most popular 2G service was GSM
  • Also notable was IS-95 (aka cdmaOne), which was dominant in the USA
• “2.5G”
  • Introduced GPRS (General Packet Radio Service) to support data in GSM
  • Similarly, IS-95 was developed into IS-95B
  • To keep up with increasing internet speeds, EDGE (Enhanced Data Rates for GSM Evolution) was developed
• 3G
  • ~2000s
  • Used different techniques for radio transmission/reception vs. 2G, which increased peak data rates
  • However, early systems were excessively hyped and performance did not meet expectations
• “3.5G”
  • 2005
  • 3G began to take off properly
  • Air interface included extra optimisations that targeted data applications, at the expense of greater variability in data rate and arrival time
    • e.g. HSPA (High-Speed Packet Access)
  • UTMS is dominant 3G system
  • UMTS air interface has two slightly different implementations:
    • WCDMA (Wideband Code Divison Multiple Access)
      • Dominant implementation world-wide
      • Uses FDD
      • Bandwidth of 5MHz
    • TD-SCDMA (Time Division Synchronous Code Division Multiple Access)
      • Developed by and deployed in China
      • Purpose was to minimize dependence upon Western technology and avoid royalty payments
      • Uses TDD
      • Bandwidth of 1.6MHz

Introducing LTE §

• SAE (System Architecture Evolution) covers the core network
• LTE (Long-Term Evolution) covers the air interface
• Officially, EPS (Evolved Packet System) refers to the whole system
  • However, LTE has become the colloquial name for the whole system, and is regularly used that way even by 3GPP

Requirements for LTE §

• Initial requirements
  • Peak data rate of 100Mbps downlink and 50Mbps uplink
• Eventual requirements
  • Peak data rate of 300Mbps downlink and 75Mbps uplink
• For comparison, WCDMA requirements
  • Peak data rate of 14bps downlink and 5.7Mbps uplink

Requirements for 4G §

• The ITU (International Telecommunication Union) helped drive the development of 3G by publishing a set of requirements for 3G mobile communication systems
  • Published as IMT-2000 (International Mobile Telecommunications)
• In 2008, the ITU published a set of requirements for 4G named IMT-Advanced
  • Required peak data rata of 600Mbps on downlink, 270Mbps on uplink, bandwidth of 40MHz
  • These requirements exceed the capabilities of LTE!

Requirements for LTE-Advanced §

• Initial requirements
  • Peak data rate of 1000Mbps downlink and 500Mbps uplink
• Eventual requirements
  • Peak data rate of 3000Mbps downlink and 1500Mbps uplink, bandwidth of 100MHz (split across five separate components of 20MHz)
• LTE-Advanced is backwards compatible with LTE

The Meaning of 4G §

• Originally, the ITU intended that the term 4G should only be used by systems that met the requirements of IMT-Advanced
• LTE did not meet these requirements, so engineers took to calling it “3.9G”
• However, marketing communities described LTE as “4G”
• In December 2010, the ITU gave approval to use “4G” to describe LTE, and any other system with “substantially better” performance than early 3G systems
  • However, they did not define what “substantially better” means!

References §

• Cox, C. (2014), An Introduction to LTE: LTE, LTE-Advanced, SAE, VoLTE and 4G Mobile Communications (2nd ed.). Wiley. https://doi.org/10.1002/9781118818046