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.
In LTE Rel-1o, the concept of Primary Cell (PCell) and Secondary Cell (SCell) was introduced to support Carrier Aggregation. The PCell is more or less like the serving cell in the non-CA case. The functions provided by the PCell are summarized below (see Section 7.5 of 3GPP TS36.300 for more details).
– Provides Security inputs
– Provides NAS mobility functions
– Have always Uplink and Downlink resources: Carrier frequency (FDD) or UL/DL subframes (TDD)
– Used for PUCCH transmission
– Used for RRC connection re-establishment
– Used for Radio Link Monitoring
– Can be changed only by Handover
– Cannot be deactivated
– Cannot be cross scheduled
– Semi-persistent resources can only be configured for the PCell
– UE acquires system information of PCell from the Physical Broadcast Channel (PBCH)
While current LTE deployments are mostly based on Rel. 8/9, work is ongoing in 3GPP on Release 12. The July issue of IEEE Communications Magazine has a nice article which provides an overview of the key features being developed in Release 12. It can be viewed online via the IEEE Digital Library at http://digital.comsoc.org/publication/ieee-communications-magazine.
Carrier Aggregation (CA) is one of the key technologies in LTE-Advanced (Rel. 10 and beyond). In simple terms, CA allows multiple radio channels to be bonded together to create bigger bandwidth pipes. The channels may belong to the same or different spectrum bands. Release 10 supports both intra-band contiguous and inter-band CA in the FDD downlink but only intra-band CA for TDD downlink. Only intra-band CA is supported in both FDD & TDD uplink. More details regarding CA are available in the following Agilent presentation.
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:
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.