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`R1-050629
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`3GPP TSG RAN WG1 Ad Hoc on LTE
`Sophia Antipolis, France, June 20th -21st 2005
`
`Agenda Item:
`Source:
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`
`Title:
`
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`Document for:
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`1. Introduction
`For delivering a uniform user experience across the cell area, it was mentioned in [1],
`that "cell edge bit rate” should be increased whilst maintaining the same site locations as
`deployed today. Nevertheless, inter-cell interference is the main reason of “cell edge bit
`rate” limitation. In last meeting, several contributions [2~4] on Inter-cell interference
`mitigation or suppression were proposed and discussed. This document categorizes all
`proposed solutions into two classes, and gives a simple comparison.
`
`4.1
`Huawei
`Inter-cell Interference Mitigation
`Discussion & Decision
`
`2. Background
`To reduce or suppress the inter-cell interference, some mechanisms could be imposed
`to scheduler when UE is located at cell edge. Currently, solutions proposed in RAN1 can
`be classed into two classes.
`
`Class 1: Interference reduction by frequency allocation
`
`Generally speaking, all subcarriers are divided into two groups in each cell. One group
`can be called as major subcarriers group, and these subcarriers can be used for UE
`located near the cell edge and common channels that should cover all area of the cell.
`The other subcarriers compose minor subcarriers group, which is only used for cell
`center users. UE with minor subcarriers could be strongly interfered by some major
`subcarriers from other cells. If it occurs, Node B/UE can stop using these subcarriers
`and shift to other minor subcarriers with low interference. By proper O&M configuration
`(Network planning), the major subcarriers should not be overlapped among several
`neighbouring cells.
`
`Minor Subcarrier
`
`Major Subcarrier
`
`Figure 1 Subcarriers Allocation
`
`f
`
`f
`
`Ericsson v. IV II LLC
`Ex. 1008 / Page 1 of 3
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`

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`Figure 1 is uplink frequency allocation example; Major subcarriers group can be
`localized or distributed. Here Major subcarriers are indicated with blue colour, while
`minor subcarriers are indicated with red colour.
`
`Using this kind of frequency allocation, when one UE is located near cell edge, in
`downlink, it is easy to achieve a good SIR for signal from serving cell because TX
`power for the same subcarriers in adjacent cells is small. In uplink, similarly, serving
`cell can receive a high SIR for the signal from this UE since the interference UEs with
`the same subcarriers in adjacent cells is far away from this UE.
`
`Class 2: Interference reduction by cell coordination
`
`In this solution, interference reduction is realized by real-time coordination among all
`involved cells to avoid that two cell edge UEs in neighbouring cells use the same
`subcarriers.
`
`One example, assuming one UE with subcarrier f0 located Cell1 center from the
`beginning, when this UE move to the cell boundary between Cell1 and Cell2, after
`sense the interference from Cell2 and report to Cell1, then the serving cell (Cell1) of
`this UE shall coordinate with Cell2 to avoid use this sub-carrier f0 at the Cell2 edge or
`suppress the Tx power for the UE with f0 in Cell2. By this kind of real-time coordination,
`the inter-cell interference can be reduced.
`
`3. Discussion & Comparison
`In fact, both classes implicitly make frequency reuse factor larger than one at cell edge
`(that is the real reason why interference can be reduced). Solution1 is semi-static
`method by subcarriers (frequency) allocation, while solution2 is a dynamic method by
`real-time cell coordination.
`
`Class 1:
`
`+ Simple to be utilized
`+ No interface among involved cells
`…
`- Not easy to modify the major frequency distributions among adjacent cells
`
`Class 2:
`
`+ Flexible, no frequency planning is required
`…
`- Interface between Node B is necessary for coordination
`- When subcarriers can be scheduled, much more coordination are required, it can
`hardly work
`(Here is the reason: If adaptive subcarrier allocation technique is employed, Node
`B will select the DL&UL subcarriers for UE according to UE’s channel quality. In
`other words, subcarriers of one UE perhaps vary frequently. Once subcarriers
`changes, serving cell of UE has to inform all involved cell about newest subcarriers
`of this UE, otherwise these subcarriers could be allocate to other UE in adjacent
`
`Ex. 1008 / Page 2 of 3
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`

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`cells, especially for DL subcarriers. In this case, the number of required
`coordination could be intolerable.
`4. Conclusion
`This document addresses two main solutions for inter-cell interference mitigation for
`E-UTRA. We consider that solution 2 can hardly work in case adaptive subcarrier
`selection used. So we propose solutions in class1 can be the way for inter cell
`interference mitigation, and also we don’t preclude other solutions based on interference
`randomisation/averaging mechanism.
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`
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`5. Reference
`[1] 3GPP TR 25.913 V2.0.0, “Requirements for Evolved UTRA and UTRAN”
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`[2] 3GPP R1-050407, “Soft Frequency Reuse Scheme for UTRAN LTE”, Huawei
`
`[3] 3GPP R1-050507, “Interference Coordination in new OFDM DL interface”, Alcatel
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`[4] 3GPP R1-050476, “EUTRA uplink scheduling and frequency reuse”, Siemens
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`
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`Ex. 1008 / Page 3 of 3
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