Sam Hooke

Notes on history of LTE and 4G

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
  • 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 §