The enhanced Physical Downlink Control Channel (ePDCCH) in Long Term Evolution Advanced (LTE A) networks by means of Intercell Interference Coordination (ICIC). Given the flexible design of the ePDCCH, based on frequency division multiplexing, static ICIC techniques such as Soft Frequency Reuse (SFR) can be applied and hence, performance degradations at cell edges can be avoided in contrast to its antecesor, the Physical Downlink Control Channel (PDCCH) in LTE.
The standardization of the E-PDCCH was necessary to support new features like CoMP, downlink MIMO and the considered introduction of a new carrier type with 3GPP Release 12 all with the intention to support the following goals:
- Support of increased control channel capacity.
- Support of frequency-domain ICIC.
- Achieve improved spatial reuse of control channel resources.
- Support beamforming and/or diversity.
- Operate on a new carrier type and in MBSFN subframes.
- Coexist on the same carrier as legacy Rel-8 and Rel-10 devices.
You can find more info here 3GPP TS 36.213 - subclauses 9.1.4, and here some more about transmission mode 3GPP TS 36.211 - subclauses 6.8A.1
Foregoing ahead before next question will be asked..
According to the requirement for LTE-Advanced to be backwards compatible to legacy LTE, when using the standard legacy carrier (radio frame structure), both the PDCCH and E-PDCCH shall coexist. This is due to the fact that the carrier need to support all the Rel. 8, Rel. 10 and Rel. 11 UEs. Because of the Rel. 8 UE, that does not recognize E-PDCCH, in order to serve them, the PDCCH need to be there. UE searches for the configured PDCCHs, i.e. if configured, it may use only PDCCH, or PDCCH (e.g. for SI reading, i.e. common search space) together with E-PDCCH (for dedicated resource scheduling – i.e. dedicated search space). For Rel. 11 the E-PDCCH is configured to be used for dedicated search space only (i.e. there’s no E-PDCCH including common search space – types of messages).
Taking a step further into the future, there are concepts for Rel. 12 and beyond to define a new carrier type (i.e. Lean Carrier), that would not include legacy Control Region with PDCCH, but only E-PDCCH with both common and dedicated search spaces. This concept is however under discussion.