3GPP standardization is well ahead of real life deployments and it has to be, as developing and testing the ever more complicated features takes time. Currently, Release 8 of the specifications has made it into the real world, with HSPA+ Dual Carrier deployments and first LTE networks now in commercial use. So from a radio access, speed and capacity point of view, what's in store between this and what will Release 11, that is currently under development, put on top of it?
A detailed resource listing the new features of each Release can be found here. If you have a look you'll immediately see that my list below is but a tiny fraction of what has been done in each release. My focus for this post, however, is very narrow and only looks at how the capacity of the macro base stations is enhanced as we go forward.
In Release 9, HSDPA gets enhanced by adding MIMO to Release 8's combination of Dual Carrier + 64-QAM, pushing theoretical peek data rates from 42.2 MBit/s to 84.4 MBit/s. To make things more flexible, the two 5 MHz carriers can now be in different frequency bands. In the uplink direction, dual carrier operation is introduced (while having been present in the downlink since Release 8), thus pushing theoretical uplink data rates beyond 20 MBit/s.
With Release 10, 3 and 4-carrier HSDPA is specified in up to two different frequency bands. Like the already existing dual-carrier feature, aggregating carriers has little impact on overall capacity of the network but offers higher peak data rates to individual users. On the LTE side, carrier aggregation beyond the initial 20 MHz is introduced and the number of antennas for MIMO in the downlink direction is increased from 4 to 8. Again, this is well beyond what is used in life networks today with up to two independent streams in the case of LTE. In the uplink direction, up to 4 antennas are now specified to increase data rates under ideal conditions.
From a raw maximum throughput point of view it seems that a limit has been reached. It is unlikely anything more than 64-QAM modulation makes sense and 8 MIMO data streams will keep engineers busy for a long time to figure out how to put such a high number of antennas on roof tops and crammed into small devices.
But ultra high data rates are not everything when it comes to overall maco network capacity. A major issue is interference between cells, especially for users that are at a location where they get a strong signal from more than one cell. Here, higher order modulation and MIMO is not much help.
Therefore, one of the major topics in 3GPP Release 11 in this respect is Coordinated Multi-Point (CoMP) transmission. Nomor's current LTE newsletter shows this quite clearly by giving an overview of currently active work items in the different RAN working groups.
Here's an abbreviated list of the objectives of CoMP from the current version of the work item description (RP-111117):
- Specify the support of intra- and inter-cell CoMP
- Joint transmission
- Coordinated scheduling/beamforming
And, in case that has sparked your interest, further details can be found in the study item 3GPP TR 36.819 that preceded the current work item.
Coming back to the title of the post "the air is getting thin", it's interesting to observe that after years of specifying how to get ever faster data rates, significant work is now done around improving data rates in places far away from a good signal. Not only will this help individual users to get a higher data rate in such places, but network capacity in general is increased by spending less time transmitting and repeating lost data slowly with a very low modulation and coding scheme. It will take a few years before we see this in practice but I think chances are high that the result of this work item will see the light of day.