LTE Rel-10 : eICIC in detail

In my last post, some of the key techniques in LTE-A is summarized. Now I'd like to look into the detail of eICIC, which is currently a very active topic in 3GPP.

An index of latest eICIC studies within 3GPP can be found in R1-104238, which listed a set of references. In particular, I found the R1-103822 from NSN has a very good summary.

In general, there are two scenarios (except relay) need consideration:

A) Macro + Pico case

In this case, the UE is free to camp on a Macro or Pico cell which offers the best RSRP. It was concluded that co-channel deployment of macro + pico cases works without any explicit interference management mechanism. There is no need for introducing any new specifications (such as resources partitioning in time or frequency domain).

B) Macro + CSG Femto case

In this case, it is observed that so called macro-cell coverage holes can be experienced by macro-UEs being close to CSG HeNBs. This is because although the HeNB offers better signal quality, but UEs are not allowed to connect due to HeNB's close-access mode. This issue is primarily observed in the downlink. There are a few candidate solutions:

1. Apply power control for the HeNBs (reducing the Tx power for some HeNB)
2. Introducing resource partitioning between Macro eNBs and CSG HeNBs
3. Relaxing the CSG contraint, so Macro-UEs get temporily access to HeNB.

There are many variants for the 1st option. One simple example is to have HeNB measure its RSRP towards the strongest co-channel deployed macro-eNB, and reduce its Tx power accordingly. Others are more complex, may require signalling between different network elements.

For the 2nd option, i.e. resource partitioning, there are mainly two types. One is to partition the resources on frequency domain, e.g. certain carriers/sub-carriers are only reserved to Macro-eNB, the other is to partition the resources on time domain, for e.g. shift the HeNB's downlink frames by at least 3 OFDM symbols to avoid HeNB's CCH overlapping with MeNB's CCH. The time domain solution requires synchronization between Macro eNB and HeNB, which could be a challenge.

I am not sure if the 3rd option had been discussed in 3GPP (as I am not a 3GPP delegate).

by July 2010, the RAN WG1 #61bis meeting has concluded (which nothing concluded actually) on Macro-Femto case:

· Consider power control and time domain solution as baseline solutions

· Frequency domain solution is not precluded