Monday, June 11, 2012

ICIC and eICIC

Background

  • LTE is designed for frequency reuse 1 (To maximize spectrum efficiency), which means that all the neighbor cells are using same frequency channels and therefore there is no cell-planning to deal with the interference issues
  • There is a high probability that a resource block scheduled to cell edge user, is also being transmitted by neighbor cell, resulting in high interference, eventually low throughput or call drops (see figure) 
  • Traffic channel can sustain upto 10% of BLER in low SINR but control channels cannot. Neighbor interference can result in radio link failures at cell edge.
  • Heterogeneous networks require some sort of interference mitigation, since pico-cells/femto cells and macro-cells are overlapping in many scenarios


ICIC (Inter-cell interference coordination)

  • Inter-cell interference coordination is introduced in 3GPP release 8
  • ICIC is introduced to deal with interference issues at cell-edge
  • ICIC mitigates interference on traffic channels only
  • ICIC uses power and frequency domain to mitigate cell-edge interference from neighbor cells 
  • One scheme of ICIC is where neighbor eNBs use different sets of resource blocks through out the cell at given time i.e. no two neighbor eNBs will use same resource assignments for their UEs. This greatly improves cell-edge SINR. The disadvantage is decrease in throughput throughout the cell, since full resources blocks are not being utilized.
  • In the second scheme, all eNBs utilize complete range of resource blocks for centrally located users but for cell-edge users, no two neighbor eNBs uses the same set of resource blocks at give time
  • In the third scheme (probably the preferred scheme), all the neighbor eNBs use different power schemes across the spectrum while resource block assignment can be according to second scheme explained above. For example, eNB can use power boost for cell edge users with specific set of resources (not used by neighbors), while keeping low signal power for center users with availability of all resource blocks (see the figure)
  • X2 interface is used to share the information between the eNBs

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
  • eICIC introduces concept of "Almost blank subframe" (ABS). ABS subframes do not send any traffic channels and are mostly control channel frames with very low power. If macro cell configure ABS subframes then UEs connected to pico/femto cells can send their data during such ABS frames and avoid interference from macro cell (see the figure)
  • ABS configuration is shared via OAM or x2 interface

9 comments:

  1. may below is also useful to us,..

    teletopix.blogspot.com

    ReplyDelete
  2. While I accept the principle and necessity to implement the ICIC scheme outlined above, I question the practicality. To implement ICIC means all the neighboring eNBs are time-synchronized, at least to half of the normal cyclic prefix duration of (about 2.4 micro-seconds). CDMA mandates the use of GPS timing receiver to coordinate the PN offset assignment, but since 3G WCDMA, the use of GPS time coordination has been eliminated. I do not think the LTE cells are time-coordinated. I doubt the x2 interface linking neighboring cells can achieve the time synchronization up to micro-seconds, considering all those embedded SW/HW and even signal propagation delays. I could be wrong. Someone please enlighten me. Thanks.

    Renshou Dai
    Sage Instruments

    ReplyDelete
  3. I don't think eNBs needs to time synchronized in the case of FDD systems. Increase in the noise level dues no synchronization is not high.

    ReplyDelete
    Replies
    1. Hello Adnan, great blog.

      If my understanding is correct, eICIC consists of basetsations coordinating their transmissions in the time domain to reduce interference and consequent degradation of throughout, particularly at the edges of the cells so you would expect that timing would be critical.
      Unfortunately, there is no agreement in 3GPP what level of sync accuracy is required.
      I wonder if anyone has a view on this on any test data that confirms the impact of timing on throughput.

      Delete
  4. Hi Adnan, your blog is a very useful reference for me. I'd like to use one of your diagrams in an upcoming market research report....could you please reply to let me know if this is ok?

    Joe Madden
    Principal Analyst
    Mobile Experts

    ReplyDelete
    Replies
    1. Hi Joe,
      Yes you can use it. But please kindly mention the source
      Thanks

      Adnan Basir

      Delete
  5. Hello, my name is Milena and I'm student of Universidad Del Cauca in Popayán, Colombia. I whish find a sofware allow me to simulate a HetNet link to system level in different scenarios, varying of femtocell densyti. My e-mail is: milemile12009@hotmail.com and accept suggestions.
    P.D: This is for my work career grade. Tks

    ReplyDelete
  6. Yes it is true eNBs has to be critically time sync in order to support eICIC. May be X2 interface has to have optical fibre as the layer-2.

    ReplyDelete
  7. Hello all, thanks for this blog !

    I have a question about the follwoing:

    If macro cell configure ABS subframes then UEs connected to pico/femto cells can send their data during such ABS frames and avoid interference from macro cell.

    1. What about the UE2 which is connected to MACRO cell? it should be also impacted by the ABS generation.
    2. Is UE2 configured with the right measurement ABS for the patterns (eg. csi-MeasSubframeSet) ?
    3. Is UE2 impacted by creating of CRE (in idle and connected states)?
    4. Is UE2 sends CQI at two different offsets as configured by RRC?

    Thanks in advance for your clarifications.

    Mr: HAMICHI (ALCATEL-LUCENT)


    ReplyDelete