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

LTA-Advanced related technologies

3GPP release 10 is to introduce some LTE-A features. LTE-A can archieve >1Gbps data rate by 4-by-4 MIMO, on ~70MHz system bandwidth.

The spectrum efficiency for LTE Rel-8 satisfies IMT-Advanced requirements in the downlink, however, in the uplink, SE needs to double to satisfy IMT-Advanced requirements.

LTE-A related Rel-10 work items:

• Carrier Aggregation (CA)
• Enhanced downlink multiple antenna transmission
• Uplink multiple antenna transmission
• Relay
• Enhanced ICIC for non-CA deployments of Heterogeneous networks (eICIC)

1) Carrier Aggregation (CA)
Entire system BW up to 100MHz, composed of component carriers
Each component carrier can be configured in a backward compatible way
Support both contiguous and non-contiguous spectrum


2) Enhanced downlink multiple antenna transmission
Up to 8 layers transmission, increased from 4 layers in Rel-8/9
Additional RS signal specified
MU-MIMO (max 4 layers, 2 per user)
Dynamic switching between SU and MU-MIMO


3) Uplink multiple antenna transmission
UL transmit diversity for PUCCH
SU-MIMO up to 4-streams

4) Relay
For places where wired backhaul is not avialable or very expensive
"type 1" - inband relay, RN (Relay Node) appears to be a Rel-8/9 eNB.
"type 1a" - outband relay, backhaul use a different frequency from access link

5) eICIC
For Micro-Pico scenario,
DL - No Problem for control channel, reuse Rel8/9 ICIC for data channel
UL - Reuse ICIC for data channel, reuse power control in Rel8/9

For Micro-Femto scenario,
Consider power control and time domain solution as baseline solutions.
At least one common TDD and FDD solution whenever possible