Detecting and reporting physical-layer cell identifier collisions in wireless networks
Physical-Layer Cell Identifier (PCID) collisions may occur in a wireless network when two neighboring evolved Node Bs (eNBs) having different Global Cell Identifiers (GCID) select identical PCIDs. Evolved Node Bs may uniquely identify themselves by transmitting on a broadcast channel, such as a Physical Broadcast Channel (PBCH), a pattern of bits corresponding to the eNB's GCID. Individual User Equipments (UEs) may recognize the PCID collision by decoding the PBCH payload to identify different GCID-modulated payloads from two eNBs involved in the PCID collision. Alternatively, UEs may detect PCID collisions in the wireless network by monitoring Primary Synchronization Signals (PSS) and Secondary Synchronization Signals (SSS) on the PBCH for identical signals separated by a relatively large time offset. After detecting a PCID collision, the UEs may attempt by best effort to report the PCID collision, may report to a fallback eNB, or the UEs may use special resources on an uplink channel.
1. A method of communicating in a wireless network, the method comprising:
receiving, at a user equipment (UE), wireless signals from at least two base stations;
determining whether a Physical-Layer Cell Identifier (PCID) collision exists, from the wireless signals, based at least in part on:
performing a first channel estimate corresponding to a data transmission in the wireless signals using a pilot signal;
performing a second channel estimate for the data transmission in the wireless signals using a data modulation portion; and
determining whether PCID collision exists based at least in part on the first and second channel estimates; and
reporting the PCID collision to at least one neighboring base station based at least in part on the determination that the PCID collision exists.
2. The method of claim 1 , further comprising reporting the PCID collision to at least one other base station.
3. The method of claim 1 , in which the reporting comprises reporting a global cell identifier involved in the PCID collision.
4. The method of claim 1 , further comprising reporting the PCID collision on a reserved uplink resource.
5. The method of claim 1 , in which the determining further comprises determining the at least two base stations have the common physical-layer cell identifier when receiving a plurality of system information blocks (SIBs) corresponding to the common physical-layer cell identifier.
6. The method of claim 5 , in which the determining further comprises determining the at least two base stations have the common physical-layer cell identifier when receiving a plurality of physical downlink control channels (PDCCHs) for the SIBs corresponding to the common physical-layer cell identifier.
7. The method of claim 1 , in which the determining further comprises receiving a plurality of Physical Broadcast Channels (PBCHs) corresponding to the common physical-layer cell identifier, the PBCHs having different payloads.
8. The method of claim 7 , in which the plurality of different payloads comprise a first payload and a second payload based on a Global Cell Identifier (GCID).
9. The method of claim 7 , in which the determining further comprises:
decoding a first payload corresponding to a first cell identifier;
performing interference cancellation by removing a signal corresponding to the first payload from a received signal;
triggering a second decoding for the first cell identifier; and
determining the PCID collision further based at least in part on decoding of a second payload differing from the first payload after canceling the first payload from the received signal being successful.
10. The method of claim 9 , in which the interference cancellation comprises pilot and data cancellation.
11. The method of claim 10 , in which the pilot cancellation makes use of channel estimates of a data signal.
12. The method of claim 1 , in which the pilot signal comprises one of a Common Reference Signal (CRS) and a user equipment reference signal (UE-RS).
13. The method of claim 1 , in which a first base station of the at least two base stations is a non-serving base station and a second base station of the at least two base stations is a serving base station.
14. An apparatus for wireless communication, comprising:
means for receiving wireless signals from at least two base stations;
means for determining whether a Physical-Layer Cell Identifier (PCID) collision exists, from the wireless signals, based at least in part on:
performing a first channel estimate corresponding to a data transmission in the wireless signals using a pilot signal;
performing a second channel estimate for the data transmission in the wireless signals using a data modulation portion; and
determining whether PCID collision exists based at least in part on the first and second channel estimates; and
means for reporting the PCID collision to at least one neighboring base station based at least in part on the determination that the PCID collision exists.
15. A non-transitory computer-readable medium having non-transitory program codes which, when executed by a processor, cause the processor to:
receive, at a user equipment (UE), wireless signals from at least two base stations;
determine whether a Physical-Layer Cell Identifier (PCID) collision exists, from the wireless signals, based at least in part on:
performing a first channel estimate corresponding to a data transmission in the wireless signals using a pilot signal;
performing a second channel estimate for the data transmission in the wireless signals using a data modulation portion; and
determining whether PCID collision exists based at least in part on the first and second channel estimates; and
report the PCID collision to at least one neighboring base station based at least in part on the determination that the PCID collision exists.
16. An apparatus for wireless communication, comprising:
a memory; and
at least one processor coupled to the memory, the at least one processor being configured:
to receive wireless signals from at least two base stations; and
to determine whether a Physical-Layer Cell Identifier (PCID) collision exists, from the wireless signals, based at least in part on:
performing a first channel estimate corresponding to a data transmission in the wireless signals using a pilot signal;
performing a second channel estimate for the data transmission in the wireless signals using a data modulation portion; and
determining whether PCID collision exists based at least in part on the first and second channel estimates; and
to report the PCID collision to at least one neighboring base station based at least in part on the determination that the PCID collision exists.
17. The apparatus of claim 16 , in which the at least one processor is further configured to report the PCID collision to at least one other base station.
18. The apparatus of claim 16 , in which the reporting comprises reporting a global cell identifier involved in the PCID collision.
19. The apparatus of claim 16 , in which the at least one processor is further configured to report the PCID collision on a reserved uplink resource.
20. The apparatus of claim 16 , in which the at least one processor being configured to determine comprises the at least one processor configured to determine whether the at least two base stations have the common physical-layer cell identifier when receiving a plurality of system information blocks (SIBs) corresponding to the common physical-layer cell identifier.
21. The apparatus of claim 20 , in which the at least one processor being configured to determine comprises the at least one processor configured to determine whether the at least two base stations have the common physical-layer cell identifier when receiving a plurality of physical downlink control channels (PDCCHs) for the SIBs corresponding to the common physical-layer cell identifier.
22. The apparatus of claim 16 , in which the at least one processor being configured to determine further comprises the at least one processor configured to receive a plurality of Physical Broadcast Channels (PBCHs) corresponding to the common physical-layer cell identifier, the PBCHs having different payloads.
23. The apparatus of claim 22 , in which the plurality of different payloads comprise a first payload and a second payload based on a Global Cell Identifier (GCID).
24. The apparatus of claim 16 , in which the at least one processor being configured to determine further comprises the at least one processor configured:
to decode a first payload corresponding to a first cell identifier;
to perform interference cancellation by removing a signal corresponding to the first payload from a received signal;
to trigger a second decoding for the first cell identifier; and
to determine the PCID collision further based at least in part on decoding of a second payload differing from the first payload after canceling the first payload from the received signal being successful.
25. The apparatus of claim 24 , in which the interference cancellation comprises pilot and data cancellation.
26. The apparatus of claim 24 , in which the pilot cancellation makes use of channel estimates of a data signal.
27. The apparatus of claim 16 , in which the pilot signal comprises one of a Common Reference Signal (CRS) and a user equipment reference signal (UE-RS).
28. A method of communicating in a wireless network, the method comprising:
receiving, at an evolved NodeB (eNB), wireless signals from a plurality of user equipments (UEs), the wireless signals including a pilot signal from each UE corresponding to a common Physical-Layer Cell Identifier (PCID), and a data message from a first UE of the plurality of UEs being different from a data message from a second UE of the plurality of UEs;
performing a first channel estimate corresponding to a data transmission using a pilot signal from one of the plurality of UEs;
performing a second channel estimate for the data transmission using a data modulation portion; and
declaring a PCID collision when the first channel estimate differs from the second channel estimate beyond a threshold difference.
29. The method of claim 28 , further comprising detecting whether the at least one of the first UE or the second UE was scheduled by the eNB, wherein
declaring the PCID collision is based at least in part on determining that the at least one of the first UE or the second UE was not scheduled by the eNB.
30. An apparatus for wireless communication, comprising:
means for receiving, at an evolved NodeB (eNB), wireless signals from a plurality of user equipments (UEs), the wireless signals including a pilot signal from each UE corresponding to a common Physical-Layer Cell Identifier (PCID), and a data message from a first UE of the plurality of UEs being different from a data message from a second UE of the plurality of UEs;
means for performing a first channel estimate corresponding to a data transmission using a pilot signal from one of the plurality of UEs;
means for performing a second channel estimate for the data transmission using a data modulation portion; and
means for declaring a PCID collision when the first channel estimate differs from the second channel estimate beyond a threshold difference.
31. A non-transitory computer-readable medium having non-transitory program codes, which when executed by a processor, cause the processor to:
receive, at an evolved NodeB (eNB), wireless signals from a plurality of user equipments (UEs), the wireless signals including a pilot signal from each UE corresponding to a common Physical-Layer Cell Identifier (PCID), and a data message from a first UE of the plurality of UEs being different from a data message from a second UE of the plurality of UEs;
perform a first channel estimate corresponding to a data transmission using a pilot signal from one of the plurality of UEs;
perform a second channel estimate for the data transmission using a data modulation portion; and
declare a PCID collision when the first channel estimate differs from the second channel estimate beyond a threshold difference.
32. An apparatus for wireless communication, comprising:
a memory; and
at least one processor coupled to the memory, the at least one processor being configured:
to receive, at an evolved NodeB (eNB), wireless signals from a plurality of user equipments (UEs), the wireless signals including a pilot signal from each UE corresponding to a common Physical-Layer Cell Identifier (PCID), and a data message from a first UE of the plurality of UEs being different from a data message from a second UE of the plurality of UEs;
to perform a first channel estimate corresponding to a data transmission using a pilot signal from one of the plurality of UEs;
to perform a second channel estimate for the data transmission using a data modulation portion; and
to declare a PCID collision when the first channel estimate differs from the second channel estimate beyond a threshold difference.
33. The apparatus of claim 32 , in which the at least one processor is further configured to determine whether the at least one of the first UE or the second UE was scheduled by the eNB; and
wherein the at least one processor is configured to declare the PCID collision based further at least in part on determining that the at least one of the first UE or the second UE was not scheduled by the eNB.