eICIC (enhanced Inter-cell interference coordination)

  eICIC (enhanced Inter-cell interference coordination)

·         eICIC introduced in 3GPP release 10

·         eICIC introduced to deal interference issues in Heterogeneous Networks (HetNet)

·         eICIC mitigates interference on traffic and control channels

·         eICIC uses power, frequency and also time domain to mitigate intra frequency interference in heterogeneous networks

ICIC technology evolution

In time domain approach, a subframe can take MBSFN subframe approach.

    MBSFN subframe

·         MBSFN subframes and almost blank subframes that we mentioned previously could be used to reduce interference to the co-channel PDCCH in the other cell layer.

·         The macrocell and picocell can configure their MBSFN and almost blank subframes in a cooperative manner in the time domain. For MBSFN, the macrocell configures subframe N as an MBSFN subframe with only one OFDM symbol used for the control region, while the picocell configures this subframe as a normal subframe.

·         Thus, only one OFDM symbol in the control region at the picocell would suffer the improved compared with the situation where all of the three OFDM symbols are the Victims.

·          The almost blank subframe (ABS) refers to the subframe that carries only the CRS in the whole subframe region. Similar to the previous MBSFN, the interference of the control channel could be alleviated. For example, we assume that the eNBI sends the ABS pattern and the RNTP, UL HII (high interference indicator), and UL 01 (overload indicator) to the eNB2.
·         We also assume that the DL subframe n is configured as an ABS. The ABS may have no other signals that are transmitted in ABSs except the CRS.

·          If the primary synchronization signal (PSS), secondary synchronization signal (SSS), physical broadcast channel (PBCH), system information block (SIB) 1, paging, and the positioning reference signal (PRS) coincide with an ABS.

·         They will be transmitted in the ABS. In CoMP scenarios, an aggressor cell informs a victim cell of certain ABSs in a time-domain manner, and based on this information the victim cell can perform appropriate user scheduling with RRC signalling to UEs for related RRM and CSI measurements .

 HII(High Interference indicator in ABS)

·         In the DL subframe, which is configured as an ABS by eNBI, eNB2 can do PDSCH scheduling without being concerned with the interference from eNBI regardless of the RNTP message.

·          It is worth mentioning that the performance of the victim PDCCH and PDSCH could be improved further if the UE is enabled with the capability to detect and cancel the neighbour cell's CRS.

·         Interference from the macro, and the PDCCH performance at the picocell could be another method of decreasing the interference is power reduction or muting on the portion of symbols of the macrocell that overlapped the control region of the picocell by scheduling and power control.

·          From the previous discussion we can see that Rel-8 and Rel-9 frequency domain ICIC and LTE-A time domain ICIC can coexist.

·         Each eNB can send both Rel-8 and Rel-9 and LTE-A ICIC messages to its neighbouring cell. Further, possible LTE-A eICIC methods include space domain coordination, network power control, network interference cancellation, network coding, network MIMO, and net-work beam-forming, which means an aggressor cell informs a victim cell of certain kinds of network information in a space, time, code, or frequency domain manner, so as to be utilized at a victim cell for appropriate avoidance schemes.