LTE Carrier Aggregation - What's Going On...

Recently I reviewed the 3GPP Standards site to check in on the status of LTE Carrier Aggregation.  I found a gold mine of information.

First a few definitions:  Carrier Aggregation allows a wireless carrier to band together different blocks of their spectrum to form a larger pipe for LTE.  This can be accomplished in two ways:  Inter-band and Intra-band.

Inter-band combines spectrum from two different bands.  The spectrum in each band to be combined must be contiguous within that band.  Intra-band combines spectrum from two non-contiguous areas of the same band.

Here is a link to an article from 3GPP that explains Carrier Aggregation.

Below is a table summarizing the relevant 3GPP working group descriptions for Carrier Aggregation.

First of all, the current network release for all carriers is Release 9.  T-Mobile, Sprint, and Clearwire have announced that they are deploying Release 9 equipment that is software up-gradable to Release 10 (LTE Advance).  From the chart, it does not appear that there are any carrier configurations planned until Release 11.  Release 10 appears to be a late 2013 commercial appearance and Release 11 will likely be very late 2014 or mid-2015.  For Carrier Aggregation to work it must be enabled and configured at the cell site base station and a compatible handset must be available.  The handsets will transmit and receive their LTE data on two different spectrum bands for the Inter-band solution.  All handsets currently only operate in one mode, 700MHz, Cellular, PCS, AWS, or 2.5GHz.

Highlights by Carrier:
Canada:  Rogers Wireless will have support for inter-band aggregation between their AWS spectrum  and the paired blocks of 2.5GHz spectrum.

AT&T: Inter-band support in Release 11 for their Cellular and 700MHz spectrum, inter-band support to combine their AWS and Cellular spectrum, as well as configuration to support combining  their PCS and 700MHz spectrum.  All of the 700MHz band plans only include their 700B/C holdings. No 700MHz inter-operability.

USCellular: Inter-band support in Release 11 for Cellular and 700MHz (A/B/C).  No support for PCS or AWS spectrum combinations

Clearwire: Intra-band support for the entire 2.5GHz band.  China Mobile is also supporting this with an inter-band aggregation between 2.5GHz and their TDD 1.9GHz spectrum.

Sprint:  Support in Release 12 for combining (intra-band)their holding across the PCS spectrum, including their G spectrum but not the un-auctioned H spectrum.  No band support for their iDEN band or the 2.5GHz band.

T-Mobile:  Support in Release 12 for intra-band in the AWS band and inter-band between AWS and PCS.

Verizon:  Ericsson appears to be supporting Verizon's need to combine (inter-band) between AWS and 700MHz C.  Not support for Verizon's Cellular or PCS holdings.

Dish:  Release 12 support to combine their S band (AWS4) spectrum (inter-band) with the 700 MHz E holdings.   This is the only aggregation scenerio for the US that combines FDD operation (AWS4) with TDD operation (700MHz E).

Carrier Plans for VoLTE

In listening to the wireless carrier earnings calls for 4Q2012, many of the analysts are interested in the timing for offering VoLTE.  VoLTE stands for Voice over LTE, in other words, Carrier VoIP.  It is unclear whether the carriers are looking at this as a launch of a handset supporting only VoLTE or whether it is essentially a dual-mode handset providing VoLTE where the quality is acceptable and traditional 2G or 3G voice everywhere else.

There is no doubt that 4G speeds enable VoLTE and all of the other VoIP over-the-top (OTT) providers like Skype, OOMA, and GoogleTalk.  Carriers will have the ability to better control their customer experience with their VoLTE service since they can change the QOS settings because they can identify the data as a voice call.

I believe that Verizon has essentially stamped a date for their networks being 100% VoLTE for voice as the same 2021 data for shutting down CDMA.  This is a reason time frame for networks to mature so they are capable of supporting VoIP seamlessly across the carriers footprint.

A key consideration that is not openly discussed, is the fact that the traditional wireless carriers that began as wireless voice providers have only overlaid their 4G data networks on top of a network that was originally designed for voice.  This is important because capacity is impacted differently on a voice network than a data network.  A voice user, whether 100ft or 4 miles from a site, essentially consumes the same amount of voice capacity.  A data user, 100ft from the site, is capable of transmitting his data with a high efficient data modulation scheme, which reduces the capacity burden on the cell site.  A user, 4 miles from the site, will receive his data using a more robust modulation scheme with a significant cost to the site's capacity.   In this example the first user transmits his data on a train that has 64 cars for data, while the user 4 miles from the site only has 4 cars to carry his data.

How does this affect VoIP and the launch of VoLTE?  With the diagram above I have indicated the areas of each cell site that will have high, medium, and low capacity based upon their voice network design.  These are the areas that VoIP voice quality will suffer due to lack of coverage or capacity.  With each carrier only offering LTE on one channel, the option to add additional spectrum to solve the capacity issue is not available.  Carriers are pursuing small cell solutions to meet this capacity need but it will require extensive time to mature the networks to support VoLTE and VoIP on a standalone basis.