TRACKING LOOP DESIGN FOR UNICAST AND MULTICAST/BROADCAST SIGNALS

• US 20120314591A1
• Filed: 09/21/2011
• Published: 12/13/2012
• Est. Priority Date: 06/10/2011
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Walker, Gordon Kent, Wang, Jun, Liu, Zhengwei, ZHANG, XIAOXIA
• Granted Patent: US 8,995,291 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04B 7/068 using space frequency diversity space-frequency coding H04L1/0606
• CPC Class Codes: H04L 12/189 in combination with wireless systems selective distribution or broadcast in wireless communication networks H04W4/06
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/266 Fine or fractional frequency offset determination and synchronisation
• CPC Class Codes: H04L 27/2665 Fine synchronisation, e.g. by positioning the FFT window
• CPC Class Codes: H04L 27/2675 Pilot or known symbols

Abstract

A method, an apparatus, and a computer program product for wireless communication are provided. In a first configuration, the apparatus maintains a first set of tracking loops associated with unicast signals and a second set of tracking loops associated with multicast/broadcast signals. In addition, the apparatus decoding at least one of a received unicast signal based on the first set of tracking loops or a received multicast/broadcast signal based on the second set of tracking loops. In a second configuration, the apparatus maintains a TTL and a FTL associated with unicast signals based only on received unicast signals. In addition, the apparatus receives a multicast/broadcast signal and decodes the received multicast/broadcast signal based on the TTL and the FTL maintained based only on the received unicast signals.

Claims

1. A method of wireless communication, comprising:

maintaining a first set of tracking loops associated with unicast signals;

maintaining a second set of tracking loops associated with multicast/broadcast signals; and

decoding at least one of a received unicast signal based on the first set of tracking loops or a received multicast/broadcast signal based on the second set of tracking loops.

2. The method of claim 1, wherein the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the method further comprises:

maintaining the TTL by determining a downlink timing for receiving the unicast signals, determining a timing offset with respect to the downlink timing for the received unicast signal, and adjusting the downlink timing based on the timing offset; and

maintaining the FTL by determining a carrier frequency for receiving the unicast signals, determining a frequency offset with respect to the carrier frequency for the received unicast signal, and adjusting a sampling frequency based on the frequency offset.

3. The method of claim 2, wherein the timing offset and the frequency offset are determined based on at least one of cell-specific reference signals (CRS), channel state information reference signals (CSI-RS), or user equipment specific reference signals (UE-RS) within the received unicast signal.

4. The method of claim 1, wherein the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the method further comprises:

maintaining the TTL by determining a downlink timing for receiving the multicast/broadcast signals, determining a timing offset with respect to the downlink timing for the received multicast/broadcast signal, and adjusting the downlink timing based on the timing offset; and

maintaining the FTL by determining a carrier frequency for receiving the multicast/broadcast signals, determining a frequency offset with respect to the carrier frequency for the received multicast/broadcast signal, and adjusting a sampling frequency based on the frequency offset.

5. The method of claim 4, wherein the timing offset and the frequency offset are determined based on multi-media broadcast over single frequency network (MBSFN) reference signals within the received multicast/broadcast signal.

6. The method of claim 4, wherein the received multicast/broadcast signal is received from a plurality of multi-media broadcast over single frequency network (MBSFN) areas, the timing offset is a composite timing offset of the received multicast/broadcast signal from each of the MBSFN areas, and the frequency offset is a composite frequency offset of the received multicast/broadcast signal from each of the MBSFN areas.

7. The method of claim 1, wherein the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each carrier on which the unicast signals are received.

8. The method of claim 1, wherein the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each carrier on which the multicast/broadcast signals are received.

9. The method of claim 1, wherein the received multicast/broadcast signal is received from a plurality of multi-media broadcast over single frequency network (MBSFN) areas, and the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each of the MBSFN areas.

10. The method of claim 9, wherein the method further comprises maintaining the TTL and the FTL for each MBSFN area based on MBSFN reference signals within the multicast/broadcast signals from the MBSFN area.

11. The method of claim 1, wherein the unicast signals comprise unicast control information and unicast data, the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the method further comprises maintaining the TTL and the FTL for both the unicast control information and the unicast data.

12. The method of claim 11, wherein the unicast control information is received in both MBSFN subframes and non-MBSFN subframes.

13. The method of claim 1, wherein the unicast signals comprise unicast control information and unicast data, the first set of tracking loops comprise a first time tracking loop (TTL), a first frequency tracking loop (FTL), a second TTL, and a second FTL, and the method further comprises:

maintaining the first TTL and the first FTL for the unicast control information; and

maintaining the second TTL and the second FTL for the unicast data.

14. The method of claim 13, wherein the first TTL and the first FTL are maintained based on at least one of cell-specific reference signals (CRS) or channel state information reference signals (CSI-RS) within the unicast control information, and the second TTL and the second FTL are maintained based on user equipment specific reference signals (UE-RS) within the unicast data.

15. The method of claim 1, wherein the first set of tracking loops are maintained based on the unicast signals received from a set of cells, and the first set of tracking loops comprises:

at least one time tracking loop (TTL) for tracking a timing offset of unicast signals received from at least one cell with respect to a downlink timing, and

at least one frequency tracking loop (FTL) for tracking a frequency offset of unicast signals received from at least one cell with respect to a carrier frequency on which the unicast signals are received,

wherein when the at least one cell comprises a plurality of cells, the timing offset is a composite timing offset of the unicast signals received from each cell in the plurality of cells and the frequency offset is a composite frequency offset of the unicast signals received from each cell in the plurality of cells.

16. The method of claim 1, wherein the second set of tracking loops are maintained based on the multicast/broadcast signals received from at least one cell, and the second set of tracking loops comprises:

at least one time tracking loop (TTL) for tracking a timing offset of multicast/broadcast signals received from the at least one cell with respect to a downlink timing, and

at least one frequency tracking loop (FTL) for tracking a frequency offset of multicast/broadcast signals received from the at least one cell with respect to a carrier frequency on which the multicast/broadcast signals are received,

wherein when the at least one cell comprises a plurality of cells, the timing offset is a composite timing offset of the multicast/broadcast signals received from each cell in the plurality of cells and the frequency offset is a composite frequency offset of the multicast/broadcast signals received from each cell in the plurality of cells.

17. The method of claim 1, wherein the first set of tracking loops comprise a first time tracking loop (TTL) and a first frequency tracking loop (FTL), the second set of tracking loops comprise a second TTL and a second FTL, and the method further comprises:

determining a first downlink timing and a first carrier frequency for receiving unicast signals and a second downlink timing and a second carrier frequency for receiving multicast/broadcast signals;

determining a first timing offset with respect to the first downlink timing for receiving the unicast signals, a first frequency offset with respect to the first carrier frequency for receiving the unicast signals, a second timing offset with respect to the second downlink timing for receiving the multicast/broadcast signals, and a second frequency offset with respect to the second carrier frequency for receiving the multicast/broadcast signals;

decoding at least one of the received unicast signal based on the first timing offset and the first frequency offset or the received multicast/broadcast signal based on the second timing offset and the second frequency offset; and

adjusting the first downlink timing, a first sampling frequency, the second downlink timing, and a second sampling frequency by adjusting the first downlink timing within the first TTL, adjusting the first sampling frequency within the first FTL, adjusting the second downlink timing within the second TTL, and adjusting the second sampling frequency within the second FTL.

18. A method of wireless communication, comprising:

maintaining a time tracking loop (TTL) and a frequency tracking loop (FTL) associated with unicast signals based only on received unicast signals;

receiving a multicast/broadcast signal; and

decoding the received multicast/broadcast signal based on the TTL and the FTL maintained based only on the received unicast signals.

19. The method of claim 18, wherein the maintaining the TTL and the FTL comprises:

maintaining the TTL by determining a downlink timing for receiving the unicast signals, determining a timing offset with respect to the downlink timing for the received unicast signal, and adjusting the downlink timing based on the timing offset; and

maintaining the FTL by determining a carrier frequency for receiving the unicast signals, determining a frequency offset with respect to the carrier frequency for the received unicast signal, and adjusting a sampling frequency based on the frequency offset.

20. The method of claim 19, wherein the timing offset and the frequency offset are determined based on at least one of cell-specific reference signals (CRS), channel state information reference signals (CSI-RS), or user equipment specific reference signals (UE-RS) within the received unicast signals.

21. An apparatus for wireless communication, comprising:

means for maintaining a first set of tracking loops associated with unicast signals;

means for maintaining a second set of tracking loops associated with multicast/broadcast signals; and

means for decoding at least one of a received unicast signal based on the first set of tracking loops or a received multicast/broadcast signal based on the second set of tracking loops.

22. The apparatus of claim 21, wherein the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the apparatus further comprises:

means for maintaining the TTL by determining a downlink timing for receiving the unicast signals, means for determining a timing offset with respect to the downlink timing for the received unicast signal, and means for adjusting the downlink timing based on the timing offset; and

means for maintaining the FTL by determining a carrier frequency for receiving the unicast signals, means for determining a frequency offset with respect to the carrier frequency for the received unicast signal, and means for adjusting a sampling frequency based on the frequency offset.

23. The apparatus of claim 22, wherein the timing offset and the frequency offset are determined based on at least one of cell-specific reference signals (CRS), channel state information reference signals (CSI-RS), or user equipment specific reference signals (UE-RS) within the received unicast signal.

24. The apparatus of claim 21, wherein the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the apparatus further comprises:

means for maintaining the TTL by determining a downlink timing for receiving the multicast/broadcast signals, means for determining a timing offset with respect to the downlink timing for the received multicast/broadcast signal, and means for adjusting the downlink timing based on the timing offset; and

means for maintaining the FTL by determining a carrier frequency for receiving the multicast/broadcast signals, means for determining a frequency offset with respect to the carrier frequency for the received multicast/broadcast signal, and means for adjusting a sampling frequency based on the frequency offset.

25. The apparatus of claim 24, wherein the timing offset and the frequency offset are determined based on multi-media broadcast over single frequency network (MBSFN) reference signals within the received multicast/broadcast signal.

26. The apparatus of claim 24, wherein the received multicast/broadcast signal is received from a plurality of multi-media broadcast over single frequency network (MBSFN) areas, the timing offset is a composite timing offset of the received multicast/broadcast signal from each of the MBSFN areas, and the frequency offset is a composite frequency offset of the received multicast/broadcast signal from each of the MBSFN areas.

27. The apparatus of claim 21, wherein the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each carrier on which the unicast signals are received.

28. The apparatus of claim 21, wherein the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each carrier on which the multicast/broadcast signals are received.

29. The apparatus of claim 21, wherein the received multicast/broadcast signal is received from a plurality of multi-media broadcast over single frequency network (MBSFN) areas, and the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each of the MBSFN areas.

30. The apparatus of claim 29, wherein the apparatus further comprises means for maintaining the TTL and the FTL for each MBSFN area based on MBSFN reference signals within the multicast/broadcast signals from the MBSFN area.

31. The apparatus of claim 21, wherein the unicast signals comprise unicast control information and unicast data, the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the apparatus further comprises means for maintaining the TTL and the FTL for both the unicast control information and the unicast data.

32. The apparatus of claim 31, wherein the unicast control information is received in both MBSFN subframes and non-MBSFN subframes.

33. The apparatus of claim 21, wherein the unicast signals comprise unicast control information and unicast data, the first set of tracking loops comprise a first time tracking loop (TTL), a first frequency tracking loop (FTL), a second TTL, and a second FTL, and the apparatus further comprises:

means for maintaining the first TTL and the first FTL for the unicast control information; and

means for maintaining the second TTL and the second FTL for the unicast data.

34. The apparatus of claim 33, wherein the first TTL and the first FTL are maintained based on at least one of cell-specific reference signals (CRS) or channel state information reference signals (CSI-RS) within the unicast control information, and the second TTL and the second FTL are maintained based on user equipment specific reference signals (UE-RS) within the unicast data.

35. The apparatus of claim 21, wherein the first set of tracking loops are maintained based on the unicast signals received from a set of cells, and the first set of tracking loops comprises:

at least one time tracking loop (TTL) for tracking a timing offset of unicast signals received from at least one cell with respect to a downlink timing, and

at least one frequency tracking loop (FTL) for tracking a frequency offset of unicast signals received from at least one cell with respect to a carrier frequency on which the unicast signals are received,

wherein when the at least one cell comprises a plurality of cells, the timing offset is a composite timing offset of the unicast signals received from each cell in the plurality of cells and the frequency offset is a composite frequency offset of the unicast signals received from each cell in the plurality of cells.

36. The apparatus of claim 21, wherein the second set of tracking loops are maintained based on the multicast/broadcast signals received from at least one cell, and the second set of tracking loops comprises:

at least one time tracking loop (TTL) for tracking a timing offset of multicast/broadcast signals received from the at least one cell with respect to a downlink timing, and

at least one frequency tracking loop (FTL) for tracking a frequency offset of multicast/broadcast signals received from the at least one cell with respect to a carrier frequency on which the multicast/broadcast signals are received,

wherein when the at least one cell comprises a plurality of cells, the timing offset is a composite timing offset of the multicast/broadcast signals received from each cell in the plurality of cells and the frequency offset is a composite frequency offset of the multicast/broadcast signals received from each cell in the plurality of cells.

37. The apparatus of claim 21, wherein the first set of tracking loops comprise a first time tracking loop (TTL) and a first frequency tracking loop (FTL), the second set of tracking loops comprise a second TTL and a second FTL, and the apparatus further comprises:

means for determining a first downlink timing and a first carrier frequency for receiving unicast signals and a second downlink timing and a second carrier frequency for receiving multicast/broadcast signals;

means for determining a first timing offset with respect to the first downlink timing for receiving the unicast signals, a first frequency offset with respect to the first carrier frequency for receiving the unicast signals, a second timing offset with respect to the second downlink timing for receiving the multicast/broadcast signals, and a second frequency offset with respect to the second carrier frequency for receiving the multicast/broadcast signals;

means for decoding at least one of the received unicast signal based on the first timing offset and the first frequency offset or the received multicast/broadcast signal based on the second timing offset and the second frequency offset; and

means for adjusting the first downlink timing, a first sampling frequency, the second downlink timing, and a second sampling frequency by adjusting the first downlink timing within the first TTL, adjusting the first sampling frequency within the first FTL, adjusting the second downlink timing within the second TTL, and adjusting the second sampling frequency within the second FTL.

38. An apparatus for wireless communication, comprising:

means for maintaining a time tracking loop (TTL) and a frequency tracking loop (FTL) associated with unicast signals based only on received unicast signals;

means for receiving a multicast/broadcast signal; and

means for decoding the received multicast/broadcast signal based on the TTL and the FTL maintained based only on the received unicast signals.

39. The apparatus of claim 38, wherein the means for maintaining the TTL and the FTL is configured to:

maintain the TTL by determining a downlink timing for receiving the unicast signals, determining a timing offset with respect to the downlink timing for the received unicast signal, and adjusting the downlink timing based on the timing offset; and

maintain the FTL by determining a carrier frequency for receiving the unicast signals, determining a frequency offset with respect to the carrier frequency for the received unicast signal, and adjusting a sampling frequency based on the frequency offset.

40. The apparatus of claim 39, wherein the timing offset and the frequency offset are determined based on at least one of cell-specific reference signals (CRS), channel state information reference signals (CSI-RS), or user equipment specific reference signals (UE-RS) within the received unicast signals.

41. An apparatus for wireless communication, comprising:

a processing system configured to;

maintain a first set of tracking loops associated with unicast signals;

maintain a second set of tracking loops associated with multicast/broadcast signals; and

decode at least one of a received unicast signal based on the first set of tracking loops or a received multicast/broadcast signal based on the second set of tracking loops.

42. The apparatus of claim 41, wherein the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the processing system is further configured to:

maintain the TTL by determining a downlink timing for receiving the unicast signals, determine a timing offset with respect to the downlink timing for the received unicast signal, and adjust the downlink timing based on the timing offset; and

maintain the FTL by determining a carrier frequency for receiving the unicast signals, determine a frequency offset with respect to the carrier frequency for the received unicast signal, and adjust a sampling frequency based on the frequency offset.

43. The apparatus of claim 42, wherein the timing offset and the frequency offset are determined based on at least one of cell-specific reference signals (CRS), channel state information reference signals (CSI-RS), or user equipment specific reference signals (UE-RS) within the received unicast signal.

44. The apparatus of claim 41, wherein the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the processing system is further configured to:

maintain the TTL by determining a downlink timing for receiving the multicast/broadcast signals, determine a timing offset with respect to the downlink timing for the received multicast/broadcast signal, and adjust the downlink timing based on the timing offset; and

maintain the FTL by determining a carrier frequency for receiving the multicast/broadcast signals, determine a frequency offset with respect to the carrier frequency for the received multicast/broadcast signal, and adjust a sampling frequency based on the frequency offset.

45. The apparatus of claim 44, wherein the timing offset and the frequency offset are determined based on multi-media broadcast over single frequency network (MBSFN) reference signals within the received multicast/broadcast signal.

46. The apparatus of claim 44, wherein the received multicast/broadcast signal is received from a plurality of multi-media broadcast over single frequency network (MBSFN) areas, the timing offset is a composite timing offset of the received multicast/broadcast signal from each of the MBSFN areas, and the frequency offset is a composite frequency offset of the received multicast/broadcast signal from each of the MBSFN areas.

47. The apparatus of claim 41, wherein the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each carrier on which the unicast signals are received.

48. The apparatus of claim 41, wherein the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each carrier on which the multicast/broadcast signals are received.

49. The apparatus of claim 41, wherein the received multicast/broadcast signal is received from a plurality of multi-media broadcast over single frequency network (MBSFN) areas, and the second set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL) for each of the MBSFN areas.

50. The apparatus of claim 49, wherein the processing system is further configured to maintain the TTL and the FTL for each MBSFN area based on MBSFN reference signals within the multicast/broadcast signals from the MBSFN area.

51. The apparatus of claim 41, wherein the unicast signals comprise unicast control information and unicast data, the first set of tracking loops comprise a time tracking loop (TTL) and a frequency tracking loop (FTL), and the processing system is further configured to maintain the TTL and the FTL for both the unicast control information and the unicast data.

52. The apparatus of claim 51, wherein the unicast control information is received in both MBSFN subframes and non-MBSFN subframes.

53. The apparatus of claim 41, wherein the unicast signals comprise unicast control information and unicast data, the first set of tracking loops comprise a first time tracking loop (TTL), a first frequency tracking loop (FTL), a second TTL, and a second FTL, and the processing system is further configured to:

maintain the first TTL and the first FTL for the unicast control information; and

maintain the second TTL and the second FTL for the unicast data.

54. The apparatus of claim 53, wherein the first TTL and the first FTL are maintained based on at least one of cell-specific reference signals (CRS) or channel state information reference signals (CSI-RS) within the unicast control information, and the second TTL and the second FTL are maintained based on user equipment specific reference signals (UE-RS) within the unicast data.

55. The apparatus of claim 41, wherein the first set of tracking loops are maintained based on the unicast signals received from a set of cells, and the first set of tracking loops comprises:

at least one time tracking loop (TTL) for tracking a timing offset of unicast signals received from at least one cell with respect to a downlink timing, and

at least one frequency tracking loop (FTL) for tracking a frequency offset of unicast signals received from at least one cell with respect to a carrier frequency on which the unicast signals are received,

wherein when the at least one cell comprises a plurality of cells, the timing offset is a composite timing offset of the unicast signals received from each cell in the plurality of cells and the frequency offset is a composite frequency offset of the unicast signals received from each cell in the plurality of cells.

56. The apparatus of claim 41, wherein the second set of tracking loops are maintained based on the multicast/broadcast signals received from at least one cell, and the second set of tracking loops comprises:

at least one time tracking loop (TTL) for tracking a timing offset of multicast/broadcast signals received from the at least one cell with respect to a downlink timing, and

at least one frequency tracking loop (FTL) for tracking a frequency offset of multicast/broadcast signals received from the at least one cell with respect to a carrier frequency on which the multicast/broadcast signals are received,

wherein when the at least one cell comprises a plurality of cells, the timing offset is a composite timing offset of the multicast/broadcast signals received from each cell in the plurality of cells and the frequency offset is a composite frequency offset of the multicast/broadcast signals received from each cell in the plurality of cells.

57. The apparatus of claim 41, wherein the first set of tracking loops comprise a first time tracking loop (TTL) and a first frequency tracking loop (FTL), the second set of tracking loops comprise a second TTL and a second FTL, and the processing system is further configured to:

determine a first downlink timing and a first carrier frequency for receiving unicast signals and a second downlink timing and a second carrier frequency for receiving multicast/broadcast signals;

determine a first timing offset with respect to the first downlink timing for receiving the unicast signals, a first frequency offset with respect to the first carrier frequency for receiving the unicast signals, a second timing offset with respect to the second downlink timing for receiving the multicast/broadcast signals, and a second frequency offset with respect to the second carrier frequency for receiving the multicast/broadcast signals;

decode at least one of the received unicast signal based on the first timing offset and the first frequency offset or the received multicast/broadcast signal based on the second timing offset and the second frequency offset; and

adjust the first downlink timing, a first sampling frequency, the second downlink timing, and a second sampling frequency by adjusting the first downlink timing within the first TTL, adjusting the first sampling frequency within the first FTL, adjusting the second downlink timing within the second TTL, and adjusting the second sampling frequency within the second FTL.

58. An apparatus for wireless communication, comprising:

a processing system configured to;

maintain a time tracking loop (TTL) and a frequency tracking loop (FTL) associated with unicast signals based only on received unicast signals;

receive a multicast/broadcast signal; and

decode the received multicast/broadcast signal based on the TTL and the FTL maintained based only on the received unicast signals.

59. The apparatus of claim 58, wherein to maintain the TTL and the FTL, the processing system is configured to:

maintain the TTL by determining a downlink timing for receiving the unicast signals, determining a timing offset with respect to the downlink timing for the received unicast signal, and adjusting the downlink timing based on the timing offset; and

maintain the FTL by determining a carrier frequency for receiving the unicast signals, determining a frequency offset with respect to the carrier frequency for the received unicast signal, and adjusting a sampling frequency based on the frequency offset.

60. The apparatus of claim 59, wherein the timing offset and the frequency offset are determined based on at least one of cell-specific reference signals (CRS), channel state information reference signals (CSI-RS), or user equipment specific reference signals (UE-RS) within the received unicast signals.

61. A computer program product, comprising:

a computer-readable medium comprising code for;

maintaining a first set of tracking loops associated with unicast signals;

maintaining a second set of tracking loops associated with multicast/broadcast signals; and

decoding at least one of a received unicast signal based on the first set of tracking loops or a received multicast/broadcast signal based on the second set of tracking loops.

62. A computer program product, comprising:

a computer-readable medium comprising code for;

maintaining a time tracking loop (TTL) and a frequency tracking loop (FTL) associated with unicast signals based only on received unicast signals;

receiving a multicast/broadcast signal; and

decoding the received multicast/broadcast signal based on the TTL and the FTL maintained based only on the received unicast signals.