Rationale. Problem Statement Universal or aggressive frequency reuse in upcoming OFDMA systems including TGm causes very severe inter-cell interference especially in the cell boundaries and limits system capacity. What should we do?
Universal or aggressive frequency reuse in upcoming OFDMA systems including TGm causes very severe inter-cell interference especially in the cell boundaries and limits system capacity.
In order to improve system performance not only PHY/MAC layer but also Inter-BS coordination to mitigate inter-cell interference should be specified in SDD.
11.x Interference Management
11.x.1 Inter-cell Coordination
[FFR, power control, and Multi-cell MIMO are the key factors to mitigate inter-cell interference. Inter-BS coordination is indispensible to support these functionalities. These functionalities can be used separately or jointly]
11.x.2 Logical Control Channels
[DL and UL control channels for resource allocation and for carrying required measurements may be necessary.]
11.x.3 Interference Randomization
[Allocating subcarriers into a subchannel, the adjacent cells permute them differently in order to guarantee minimum subcarrier-hit probability. But when applying FFR where some of the subcarriers are not used to reduce inter-cell interference, the subcarrier permutation may not be necessary. With the absence of permutation in FFR, there is no subcarrier hit and therefore no inter-cell interference between neighbors. But with the permutation, there still exists inter-cell interference due to the subcarrier-hit.]
11.x.4.1 Hard FFR
[Some of the subcarriers can not be used to mitigate inter-cell interference.]
11.x.4.2 Soft FFR
[To mitigate inter-cell interference the power of some of the subcarriers can be adjusted (reduced) rather than not used. Uplink power control considering the neighbor cells’ overload condition falls into soft FFR.]
11.x.5 Multi-cell MIMO
[Network coordinated BF, precoding, or interference nulling shall be supported to mitigate inter-cell interference. A multi-cell MIMO zone can be configured in a frame to support multi-cell MIMO transmission.]
 IEEE 802.16m-07/002r4, “TGm System Requirements Document (SRD)”
 IEEE 802.16m-08/004r2, “TGm Evaluation Methodology Document”
 IEEE 802.16m-08/003r3, “Draft IEEE 802.16m System Description Document”
 IEEE C802.16m-08/017, “Frame Structure to Support Inter-cell Interference Mitigation for Downlink Traffic Channel using Co-MIMO and FFR”
 IEEE C802.16m-08/374r1, “Network Coordinated Beamforming”