Category Archives: 5G

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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LTE-A in Unlicensed Band (LTE-U)

Qualcomm has recently floated the idea of deploying LTE in unlicensed bands, particularly focusing on the 5GHz band, which is currently used mostly for WiFi. According to a document (RP-131635) submitted to the upcoming 3GPP plenary meeting, the proposal is to deploy LTE as Supplemental Downlink (SDL) in 5725-5850 MHz in USA, with the PCell (Primary Cell) always operating on a carrier in a licensed band. Verizon has also submitted a Work Item Proposal (RP-131680) to to introduce the new band for SDL usage. There’s also a Study Item proposal from Ericsson (RP-131788) is the rapporteur to study the modifications necessary to the LTE radio.

These documents can be downloaded from the 3GPP FTP site.

In addition, there’s a presentation from Qualcomm on the same topic.

LTE Release 12: Small Cell Enhancements – Higher Layer Aspects

One of the 3GPP Rel-12 Study Items focuses on Small Cell Enhancements.from the perspective of higher layers. There are 3 scenarios under consideration:

Scenario 1:  Macro and small cells on the same carrier frequency, connected via non-ideal backhaul.

Scenario 2: Macro and small cells on different carrier frequencies, connected via non-ideal backhaul.

Scenario 3: Only small cells on one or more carrier frequencies, connected via non-ideal backhaul.

The challenges posed by these scenarios are summarized in the table below.

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To address these challenges, 3GPP’s RAN Working Group 2, is currently working towards a set of solutions, with the following design goals in mind:

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The idea of ‘dual connectivity’ has more or less been accepted as the way forward. This term refers to operation where a given UE consumes radio resources provided by at least two different network points connected with non-ideal backhaul. Each eNB involved in dual connectivity for a UE may assume different roles and these roles do not necessarily depend on the eNB’s power class and can vary among UEs.

Within the dual-connectivity framework, there are two potential solutions being discussed:

Inter-node radio resource aggregation: This solution is aimed at improving per-user throughput by aggregating radio resources in more than one eNB for user plane data transmission.ImageRRC Diversity: This solution is targeted at improving mobility robustness by transmitting handover related RRC signalling could from/to a potential target cell. The RRC diversity scheme could also be applied for handovers from the macro to pico cells, between macro or between pico cells.

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Further details of these solutions can be found in TR36.842.

5G – The new buzzword

Now that the hype over 4G has somewhat reduced, 5G is slowly becoming the new thing. Lots of claims are being thrown around by vendors and silicon companies, staking claim to having achieved to having found the new holy grail, aka 5G. On one hand we have WiFi chip manufacturers referring to 802.11ac as ‘5G WiFi’ (ever heard of 3G/4G WiFi?) while there are the likes of Samsung who has tagged a new mm-wave based transmission scheme as 5G.

Real work on defining 5G (or the nearest equivalent) requirements has just started in ITU Working Party 5D. If IMT-Advanced was the equivalent of 4G, IMT-2020 technologies are expected to be branded as 5G. At the next meeting of 5D to be held in a few weeks time, various organizations will present their vision of 5G, in terms of technical requirements. Hence, the flurry of whitepapers from vendors:

5G radio access – research and vision (Ericsson)

On the road to 5G (NSN)

Various global telecom standards bodies like 3GPP, IEEE have been asked by ITU to submit their inputs for IMT-2020 requirements. Within 3GPP, there’s an ITU-R Ad-Hoc Group which is currently discussing this topic and preparing an input (Liaison Statement in 3GPP jargon). More details about that in the next blog.