Inter-cell interference mitigation
To address the problem of inter-cell interference in a heterogeneous network, several methods and systems are disclosed for determining interference caused by an aggressor mobile node, and transmitting at appropriate times and with transmit power that does not cause interference. Methods disclosed include using X2 communications, such as HII and RNTP messages, switching to an alternative radio access technology, sniffing at the eNodeB to obtain information, coordinating with a cloud coordination server, and using CFI information to avoid interfering with communications on the PDCCH.
1. A method for reducing downlink interference at a first base station, the first base station being a micro cell, comprising:
obtaining, at a cloud coordination server from the first base station, neighboring radio power information for a second base station via a measurement report message from a mobile device attached to the first base station, the second base station being a macro cell;
sending a message from the cloud coordination server to assign, at the first base station, a transmit power for the mobile device based on the neighboring radio power information;
obtaining, at the cloud coordination server from the first base station, a format indicator of a neighboring control channel used by the second base station;
sending a second message from the cloud coordination to assign the first base station, at least one control channel parameter, the control channel parameter comprising a control channel symbol location, a control channel modulation code scheme, or a control channel aggregation level, for a user channel at the mobile device and based on the neighboring control channel format indicator;
sending the assigned transmit power and assigning the at least one control channel parameter to the mobile device;
assigning the control channel symbol location for the downlink channel to avoid symbol locations indicated as being in use in the neighboring control channel; and
sniffing a Control Format Indicator (CFI) of the macro cell to avoid interfering with a Physical Control Format Indicator Channel (PCFICH).
2. The method of claim 1 , further comprising receiving a relative power bitmap from a macro base station, wherein the macro base station is an interfering base station.
3. The method of claim 1 , further comprising comparing interference at the mobile device to a predetermined power threshold to assess a handover to a different radio access technology.
4. The method of claim 1 , further comprising performing real-time sniffing to determine the format indicator used by the second base station.
5. The method of claim 1 , further comprising determining the control format used by the second base station from a received X2 message.
6. The method of claim 1 , further comprising receiving a sub-band quality message from the mobile device and assigning the at least one control channel parameter based on the sub-band quality message, for a downlink channel.
7. The method of claim 1 , further comprising increasing a degree of coding via adjusting the control channel modulation code scheme, wherein the control channel symbol location used by the second base station includes at least a first three symbols in a control channel sub-frame.
8. The method of claim 1 , wherein the first base station, in coordination with the cloud coordination server, determines whether mobile devices connected to the mobile base station may be switched to a Wi-Fi connection.
9. The method of claim 1 , wherein the format indicator is a control format indicator (CFI) and the user channel is a physical downlink control channel (PDCCH).
10. A method for reducing downlink interference at a second base station, comprising:
obtaining, at a cloud coordination server from a first base station, radio power information of the second base station received from a mobile device via a measurement report message;
sending a message from the cloud coordination server to assign, at the first base station, a transmit power for a mobile device based on the radio power information of the second base station;
obtaining, at the cloud coordination server from the first base station, a format indicator of a neighboring control channel used by the second base station;
sending a second message from the cloud coordination server as a base station control plane signaling message to assign, at the first base station, at least one control channel parameter, the control channel parameter comprising a control channel symbol location, a control channel modulation code scheme, or a control channel aggregation level, for a user data channel at the mobile device and based on the neighboring control channel format indicator;
assigning the control channel symbol location for the downlink channel to avoid symbol locations indicated as being in use in the neighboring control channel;
sniffing a Control Format Indicator (CFI) of the macro cell to avoid interfering with a Physical Control Format Indicator Channel (PCFICH); and
reducing the transmit power for the mobile device at the first base station, wherein the first base station is a micro cell and the second base station is a macro cell.
11. The method of claim 1 , further comprising increasing a PDCCH control channel element (CCE) aggregation level at the first base station based on the neighboring radio power information, thereby reducing output power of the mobile device, and setting a control format indicator (CFI) at the first base station to the format indicator of the neighboring control channel used by the second base station.