LTE-U: Update from 3GPP

LTE-unlicensed or LTE-U was once again a major topic of discussion at the 3GPP RAN plenary meeting last week. Although no Study/Work Items were approved regarding the usage of LTE in unlicensed spectrum, a half-day workshop is planned for sharing ideas on LTE-U. It will be held after RAN #64 meeting on 13.06.2014.

An earlier workshop on the same topic was organised in Jan 2014, attended by 40-odd companies. A summary of that workshop is available in RP-140060. The key points are given below.

Possible use cases / scenarios Main discussion focused on Operator-deployed small cells

  • Indoor and outdoor hotspot
  • Primary cell on licensed spectrum aggregated with secondary cell on unlicensed spectrum
  • Dual connectivity and stand-alone operation were discussed as well

Other scenarios such as user-deployed small cells, Wireless backhaul were also discussed. Potential Technical Requirements

  • Multi-technology coexistence and fairness – Especially LTE – WiFi
  • Multi-operator coexistence and fairness – Especially LTE – LTE
  • In-device coexistence
  • Regulatory requirements, e.g., radar protection

Possible bands Main discussion focused on 5GHz band, considering:

  • Middle (5.4GHz) and upper part (5.8GHz)
  • DL-only and/or UL and DL
  • The need for a (almost) global band was discussed

It was expressed that LTE in unlicensed should be designed to work in (almost) any un-licensed band, e.g. not tailored to a specific band. Other bands (e.g., 3.5GHz in US, TVWS) were also discussed. Potential Technical Features The following new and existing features were discussed

  • FDD-TDD Carrier Aggregation, cross-carrier scheduling
  • Listen-before-talk, carrier sensing, RTS-CTS, Setting 802.11 NAV by sending CTS
  • Small cell on/off and discovery, subframe muting
  • Dynamic frequency/carrier selection
  • Transmit power control
  • Flexible/dynamic duplex
  • CA of more than 100MHz, larger channel BW
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