Method and Arrangement, Cell ID Collision Detection

• US 20110159901A1
• Filed: 08/27/2008
• Published: 06/30/2011
• Est. Priority Date: 08/27/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Gunnarsson, Fredrik, Frenger, Pal
• Granted Patent: US 8,626,213 B2
• Time in Patent Office: Days
• US Class Current: 455/502
• CPC Class Codes: H04L 5/0033 each allocating device acting autonomously, i.e. without negotiation with other allocating devices
• CPC Class Codes: H04L 5/005 of common pilots, i.e. pilots destined for multiple users or terminals
• CPC Class Codes: H04L 5/0073 Allocation arrangements that take into account other cell interferences for intercell interference mitigation or co-ordination in orthogonal multiplex systems H04J11/005
• CPC Class Codes: H04L 5/0078 Timing of allocation
• CPC Class Codes: H04L 5/0082 at predetermined intervals
• CPC Class Codes: H04W 16/12 Fixed resource partitioning
• CPC Class Codes: H04W 24/02 Arrangements for optimising operational condition
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 8/26 Network addressing or numbering for mobility support

Abstract

The present invention relates to methods, a communication network node and a user equipment for detecting collision of physical cell identities in a communication network system comprising radio base stations each serving at least one cell through which user equipments are moving. Reference signals comprising reference symbols corresponding to a physical cell identity are sent from said radio base stations to said user equipments over a radio interface. Transmission gaps of reference symbols are inserted in the reference signal in order to perform a physical cell identity collision test. The user equipments are arranged to detect if any other radio base station is sending reference symbols corresponding to the same physical cell identity during the transmission gaps. Thereby a physical cell identity collision is detected. The reference symbol transmission gaps are fractionally distributed within said reference signal such that at least some of said reference symbols are unaffected by said reference symbol transmission gaps.

Claims

1-22. -22. (canceled)

23. A method in a communication network node for detecting a collision between physical cell identities in a communication network system, the communication network system comprising radio base stations, each radio base station configured to serve at least one cell and send a reference signal to user equipments in that at least one cell over a radio interface, the reference signal comprising reference symbols corresponding to a physical cell identity of said at least one cell, the method comprising performing a physical cell identity collision test by fractionally distributing reference symbol transmission gaps within a reference signal to be sent in a cell by a radio base station, wherein during reference symbol transmission gaps some reference symbols are not sent, to enable user equipments in that cell to detect if another radio base station is sending reference symbols corresponding to the same physical cell identity, while other reference symbols remain unaffected by said reference symbol transmission gaps

24. The method according to claim 23, wherein distributing said reference symbol transmission gaps comprises distributing the reference symbol transmission gaps according to a fractional time and frequency pattern.

25. The method according to claim 23, further comprising starting transmission of a physical cell identity collision detection signal containing said reference symbol transmission gaps.

26. The method according to claim 23, wherein said reference signal comprises resource block pairs, each resource block pair comprising a first resource block containing a control region and a data region, and a second resource block comprising a data region, and wherein during reference symbol transmission gaps at least some of those reference symbols that remain unaffected are included in said control region.

27. The method according to claim 23, wherein said reference signal comprises resource block pairs, each resource block pair comprising a first resource block containing a control region and a data region, and a second resource block comprising a data region, wherein a physical broadcast channel is transmitted in some of said resource blocks, and wherein during reference symbol transmission gaps at least some of those reference symbols that remain unaffected are included in resource blocks that transmit said physical broadcast channel.

28. The method according to claim 23, further comprising increasing a transmitted power of those reference symbols that are sent during a reference symbol transmission gap, as compared to when those reference symbols are sent outside of a reference symbol transmission gap, in order to keep a total transmitted reference signal power constant.

29. The method according to claim 23, further comprising deciding to perform said physical cell identity collision test based on at least one of the following:

a timer;

an amount of traffic in said cell;

handover failure reports received from neighboring cells;

proposals from another communication network node;

handover failure statistics;

or an amount of inter-frequency or inter-RAT (radio access technology) handovers is above a threshold value.

30. The method according to claim 23, wherein a timing of when said physical cell identity collision test is initiated is pseudo-random or follows a pre-determined time pattern.

31. The method according to claim 23, further comprising notifying said user equipments when said physical cell identity collision test is performed.

32. The method according to claim 23, further comprising, if a physical cell identity collision is detected, changing said conflicting physical cell identity to a new physical cell identity.

33. A method in a user equipment for detecting a collision of physical cell identities in a communication network system, the communication network system comprising radio base stations, each radio base station configured to serve at least one cell and send a reference signal to user equipments in that at least one cell over a radio interface, the reference signal comprising reference symbols corresponding to a physical cell identity of said at least one cell, and wherein the method comprises:

receiving a notification from a communication network node that a physical cell identity collision test is to be performed, for detecting a collision with the physical cell identity of a serving cell;

searching for the physical cell identity of the serving cell during reference symbol transmission gaps fractionally distributed within a reference signal received by the user equipment from the serving cell, wherein during reference symbol transmission gaps some reference symbols are not sent while other reference symbols remain unaffected by said reference symbol transmission gaps; and

if a physical cell identity collision is detected, whereby the physical cell identity of the serving cell is found during said reference symbol transmission gaps, sending an alarm to said communication network node.

34. A communication network node for detecting a collision of physical cell identities in a communication network system, the communication network system comprising radio base stations, each radio base station configured to serve at least one cell and send a reference signal to user equipments in that at least one cell over a radio interface, the reference signal comprising reference symbols corresponding to a physical cell identity of said at least one cell, the communication network node comprising a distributing unit configured to perform a physical cell identity collision test by fractionally distributing reference symbol transmission gaps within a reference signal to be sent in a cell by a radio base station, wherein during reference symbol transmission gaps some reference symbols are not sent, to enable user equipments in that cell to detect if another radio base station is sending reference symbols corresponding to the same physical cell identity, while other reference symbols remain unaffected by said reference symbol transmission gaps.

35. The communication network node according to claim 34, wherein said distributing unit is configured to distribute reference symbol transmission gaps according to a fractional time and frequency pattern.

36. The communication network node according to claim 34, further configured to start transmission of a physical cell identity collision detection signal containing said reference symbol transmission gaps.

37. The communication network node according to claim 34, wherein said reference signal consists of resource block pairs, each resource block pair comprising a first resource block containing a control region and a data region, and a second resource block containing a data region, and wherein the communication network node further comprises a signaling unit configured to include at least some of those reference symbols that remain unaffected in said control region during reference symbol transmission gaps.

38. The communication network node according to claim 37, wherein a physical broadcast channel is transmitted in some of said resource blocks, and wherein said signaling unit is further configured to include, during reference symbol transmission gaps, at least some of those reference symbols that remain unaffected in resource blocks that transmit said physical broadcast channel.

39. The communication network node according to claim 34, further comprising a power regulating unit configured to increase a transmitted power of those reference symbols that are sent during a reference symbol transmission gap, as compared to when those reference symbols are sent outside of a reference symbol transmission gap, in order to keep a total transmitted reference signal power constant.

40. The communication network node according to claim 34, further comprising a decision unit configured to decide when to perform said physical cell identity collision test based on at least one of the following:

a timer;

an amount of traffic in said cell;

handover failure reports received from neighboring cells;

proposals from another communication network node;

handover failure statistics;

or, an amount of inter-frequency or inter-RAT (radio access technology) handovers is above a threshold value.

41. The communication network node according to claim 34, wherein a timing of when said physical cell identity collision test is initiated is pseudo-random or follows a pre-determined time pattern.

42. The communication network node according to claim 34, configured to notify said user equipments when said physical cell identity collision test is performed.

43. The communication network node according to claim 34, further comprising an identity handling unit configured, if a physical cell identity collision is detected, to change said conflicting physical cell identity to a new physical cell identity.

44. A user equipment configured to detect a collision of physical cell identities in a communication network system, the communication network system comprising radio base stations, each radio base station configured to serve at least one cell and to send a reference signal to user equipments in that at least one cell over a radio interface, wherein a reference signal comprises reference symbols corresponding to a physical cell identity of said at least one cell, and wherein the user equipment comprises:

a receiver configured to receive a notification from a communication network node that a physical cell identity collision test is to be performed, for detecting a collision with the physical cell identity of a serving cell;

a monitoring unit configured to search for the physical cell identity of the serving cell during reference symbol transmission gaps fractionally distributed within a reference signal received by the user equipment from the serving cell, wherein during reference symbol transmission gaps some reference symbols are not sent while other reference symbols remain unaffected by said reference symbol transmission gaps; and

a transmitter configured to send an alarm to said communication network node if a physical cell identity collision is detected, whereby the physical cell identity of the serving cell is found during said reference symbol transmission gaps.