E-DCH serving cell

12 Oct 2014   Category: Radioaccess

Kind of busy these days. I will simply share some basic knowledge from my personal wiki. The first one is about the definition of E-DCH serving cell.

Once you read about all kinds of technical materials, like 3GPP technical specification or those feature documentations within your company. You might probably have met several specific terms related to E-DCH serving cell, which are not explicitly explained. Therefore you would confuse about them. Let me get it straight.

Actually, most of them come from 3GPP TS25.321 subclause 3.1.

• Serving E-DCH cell: Cell from which the UE receives Absolute Grants from the Node-B scheduler. A UE has one Serving E-DCH cell.
• E-DCH active set: The set of cells which carry the E-DCH for one UE. For FDD, in CELL_FACH state and Idle mode, the E-DCH active set consists of the Serving E-DCH cell only. There are at most 4 cells within one E-DCH active set for a certain UE.
• Non-serving E-DCH RL or Non-serving RL: Cell which belongs to the E-DCH active set but does not belong to the Serving E-DCH RLS and from which the UE can receive one Relative Grant. The UE can have zero, one or several Non-serving E-DCH RL(s).
• Serving E-DCH RLS or Serving RLS: Set of cells which contains at least the Serving E-DCH cell and from which the UE can receive and combine one Relative Grant. The UE has only one Serving E-DCH RLS. For FDD, in CELL_FACH state and Idle mode, the Serving E-DCH RLS or Serving RLS contains the Serving E-DCH cell only, from which the UE can receive one Relative Grant.

For better understanding, I draw a picture to illustrate.

As you can see from above picture, cell 2 of Node B 1 is the Serving E-DCH cell for this UE. Cell 2 and cell 3 from Node B 1 and cell 1 from Node B2 consist of E-DCH active set. While Serving E-DCH RLS includes cell 2 and cell 3 of Node B 1. And Cell 1 of Node B 2 is Non-serving E-DCH RL.

Please note, the presumption for Serving E-DCH RLS in above picture is cell 2 and cell 3 are controlled and scheduled by the same scheduler. Or they share the same source for E-RGCH decision. Otherwise they cannot be called as a Serving E-DCH cell.

And you can find that:

1. Serving E-DCH cell could send E-AGCH and all three kinds of E-RGCH, i.e. UP, Hold, and DOWN;
2. The cells in Serving E-DCH RLS other than Serving E-DCH cell could only send E-RGCH with all three possible decisions: UP/HOLD/DOWN;
3. Non-serving E-DCH RL could only send E-RGCH with two kinds of E-RGCH: HOLD/DOWN;

Why there is no UP for Non-serving E-DCH RL? Think about it. Basically E-RGCH from non-serving E-DCH RL is major for power overload control and not in charge of UE scheduling, which means non-serving E-DCH RL only send E-RGCH once the total cell power is exceeded certain threshold. Then it would send E-RGCH DOWN to those non-serving UEs in order to decrease the interference from other cells.

All above definition are from UE point of view. However there is also a term from cell perspective. That is Non-serving UE. Generally non-serving UE is the user equipment whose serving cell is not this cell. Talk to above picture, we can say this UE is non-serving UE for cell 3 of Node B 1 as well as cell 1 of Node B 2.

This is just my personal understanding. Please correct me if I am wrong. I’d be really appreciated.