Fast cell search and accurate synchronization in wireless communications

• US 20060062196A1
• Filed: 08/16/2005
• Published: 03/23/2006
• Est. Priority Date: 08/16/2004
• Status: Active Grant

• Current Assignee: ZTE Corporation
• Original Assignee: ZTE Corporation
• Inventors: Zhang, Wenzhong, Yang, Yunsong, Wang, Jing, Fang, Yonggang, Cai, Sean, Hou, Jason
• Granted Patent: US 7,496,113 B2
• Time in Patent Office: Days
• US Class Current: 370/345
• CPC Class Codes: H04B 1/70735 Code identification H04B1/7083 takes precedence
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 27/2613 Structure of the reference signals
• CPC Class Codes: H04L 27/26132 using repetition
• CPC Class Codes: H04L 27/26136 Pilot sequence conveying additional information
• CPC Class Codes: H04L 27/2655 Synchronisation arrangements
• CPC Class Codes: H04L 27/2656 Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2692 with preamble design, i.e. with negotiation of the synchronisation sequence with transmitter or sequence linked to the algorithm used at the receiver
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/0037 Inter-user or inter-terminal allocation
• CPC Class Codes: H04L 5/0048 Allocation of pilot signals, i.e. of signals known to the receiver
• CPC Class Codes: H04L 5/0091 Signaling for the administration of the divided path

Abstract

Techniques for fast cell search, selection and reselection for wireless communication systems such as OFDM or OFDMA communication systems. In various implementations of the described techniques, downlink subframes from base stations to mobile stations are designed to include information in form of preambles or post-ambles in one or more downlink subframes to facilitate cell search at receiving mobile stations at high speeds. The described preambles and post-ambles may also be used to improve the accuracy of signal synchronization in time and frequency.

Claims

1. A method for wireless communications, comprising:

using a cell identification sequence as a leading symbol of and as at least part of a preamble of every downlink subframe in time of a downlink signal from a base station to a mobile station, wherein the cell identification sequence is one of a set of cell identification sequences and is designated to identify a base station and a cell sector of the base station;

including at least one data symbol, at a position subsequent to the cell identification sequence in time, in every downlink subframe of the downlink signal; and

including in every other L frames of the downlink signal, at a position subsequent to the cell identification sequence in time, a symbol comprising a plurality of copies of a sequence placed sequentially in time,

wherein L is an integer greater than 0 and the sequence is common to at least a portion of base stations with which the mobile station is capable of communicating.

2. A method as in claim 1, wherein the sequence is common to all of the base stations.

3. A method as in claim 1, wherein the base stations are divided into a plurality of different groups and each group has a plurality of base stations, and wherein the sequence is common to one group of the base stations and varies from one group to another.

4. A method as in claim 1, wherein the symbol further comprises, at a position in time subsequent to the plurality of copies of the sequence, a plurality of copies of a long sequence, wherein the long sequence is longer in time than the sequence.

5. A method as in claim 4, wherein the base stations are divided into a plurality of different groups and each group has a plurality of base stations, and wherein the long sequence is a group identification sequence and is common to one group of the base stations.

6. A method as in claim 4, wherein the symbol further comprises a cyclic prefix positioned in time prior to the plurality of copies of the sequence, wherein the cyclic prefix is a copy of a last segment of the sequence.

7. A method as in claim 1, wherein the symbol further comprises a cyclic prefix positioned in time prior to the plurality of copies of the sequence, wherein the cyclic prefix is a copy of a last segment of the sequence.

8. A method as in claim 1, wherein the symbol is placed in time after the leading symbol and before the at least one data symbol.

9. A method as in claim 1, wherein the symbol is placed in time at an end of the subframe as a post-amble.

10. A method as in claim 1, further comprising:

including a second symbol at a position in time subsequent to the symbol with the plurality of copies of the sequence, a plurality of copies of a long sequence, wherein the long sequence is longer in time than the sequence,

wherein the sequence comprises a group identification sequence to identify a group of base stations among a plurality of different groups, and

wherein the long sequence comprises a subgroup identification sequence to identify a subgroup of base stations among each group of base stations.

11. A method as in claim 10, further comprising:

dividing the sequence into a plurality of short subsequences;

assigning, in frequency, the short subsequences to different subcarriers as different short subsequence carrier sets;

dividing the long sequence into a plurality of long subsequences;

assigning, in frequency, the long subsequences to different subcarriers as different long subsequence carrier sets; and

assigning the different short and long subsequence carrier sets to two or more different antennas in the base station for downlink transmission.

12. A method for wireless communications, comprising:

controlling a mobile station to detect a downlink signal received from a base station, wherein the downlink signal comprises a cell identification sequence as a leading symbol of and as at least part of a preamble of every downlink subframe in time, at least one data symbol, at a position subsequent to the cell identification sequence in time, in every downlink subframe of the downlink signal, and, in every other L frames of the downlink signal, at a position subsequent to the cell identification sequence in time, a symbol comprising a plurality of copies of a sequence placed sequentially in time, wherein L is an integer greater than 0 and the sequence is common to at least a portion of base stations with which the mobile station is capable of communicating,

wherein the cell identification sequence is one of a set of cell identification sequences and is designated to identify a base station and a cell sector of the base station;

controlling the mobile station to perform synchronization in time and frequency based on the sequence; and

controlling the mobile station to perform a correlation between the cell identification sequencer and the set of cell identification sequences to identify the cell sector and the base station.

13. A method as in claim 12, wherein the symbol further comprises, at a position in time subsequent to the plurality of copies of the sequence, a plurality of copies of a long sequence, wherein the long sequence is longer in time than the sequence, and

the method further comprising:

controlling the mobile station to process the plurality of copies of the sequence in the symbol for coarse synchronization in time and frequency; and

controlling the mobile station to process the plurality of copies of the long sequence in the symbol for fine synchronization in time and frequency.

14. A method as in claim 12, wherein the symbol further comprises, at a position in time subsequent to the plurality of copies of the sequence, a plurality of copies of a long sequence, wherein the long sequence is longer in time than the sequence and is a group identification sequence and is common to one group of the base stations among different groups of the base stations,

the method further comprising:

controlling the mobile station to process the plurality of copies of the long sequence in the symbol and to identify a group to which the base station emitting the downlink signal belongs; and

controlling the mobile station to perform correlations between the cell identification sequence in the downlink signal with only a portion of the set of cell identification sequences for the identified group, without performing correlations between the cell identification sequence in the downlink signal and cell identification sequences for groups other than the identified group.

15. A method as in claim 12, wherein the downlink signal further comprises a second symbol being at a position in time subsequent to the symbol with the plurality of copies of the sequence and comprising a plurality of copies of a long sequence,

wherein the long sequence is longer in time than the sequence, wherein the sequence comprises a group identification sequence to identify a group of base stations among a plurality of different groups, and

wherein the long sequence comprises a subgroup identification sequence to identify a subgroup of base stations among each group of base stations,

the method further comprising:

controlling the mobile station to process the plurality of copies of the sequence in the symbol and to identify a group to which the base station emitting the downlink signal belongs;

controlling the mobile station to process the plurality of copies of the long sequence in the second symbol and to identify a subgroup within the identified group; and

controlling the mobile station to perform correlations between the cell identification sequence in the downlink signal with only a portion of the set of cell identification sequences for the identified subgroup, without performing correlations between the cell identification sequence in the downlink signal and cell identification sequences for subgroups other than the identified subgroup and for groups other than the identified group.

16. A method as in claim 12, wherein the downlink signal further comprises a second symbol being at a position in time subsequent to the symbol with the plurality of copies of the sequence and comprising a plurality of copies of a long sequence, wherein the long sequence is longer in time than the sequence,

wherein the sequence comprises a group identification sequence to identify a group of base stations among a plurality of different groups, and

wherein the long sequence comprises a subgroup identification sequence to identify a subgroup of base stations among each group of base stations,

the method further comprising:

controlling a mobile station which receives the downlink signal to process the plurality of copies of the long sequence in the second symbol and to identify a subgroup to which the base station emitting the downlink signal belongs; and

controlling the mobile station to perform correlations between the cell identification sequence in the downlink signal with only a portion of the set of cell identification sequences for the identified subgroup for all groups, without performing correlations between the cell identification sequence in the downlink signal and cell identification sequences for subgroups other than the identified subgroup.

17. A method for wireless communications, comprising:

using one group identification sequence as part of a downlink subframe from a base station to a mobile station to identify a group of base stations, wherein different group identification sequences are respectively assigned to different groups of base stations and different base stations in one group have a common group identification sequence; and

including in the downlink subframe a cell identification sequence to identify a specific base station and a cell sector of the base station in the group identified by the one group identification sequence in the downlink subframe.

18. A method as in claim 17, wherein the one group identification sequence and the cell identification sequence in the downlink subframe are included as part of a preamble of the downlink subframe.

19. A method as in claim 18, further comprising:

including a plurality of identical short preambles sequentially in time in a first section of the preamble and a plurality of identical long preambles in a second section of the preamble subsequent to the first section, wherein each long preamble includes the one group identification sequence and is longer in time than each short preamble and is common for base stations in one group.

20. A method as in claim 19, wherein there are four short preambles and two long preambles in the preamble, wherein a length of each short preamble in time is one half of a length of each long preamble.

21. A method as in claim 19, further comprising including a cyclic prefix at a beginning portion of the preamble in time, wherein the cyclic prefix is a copy of a last segment of a short preamble following the cyclic prefix in time.

22. A method as in claim 19, further comprising:

placing the plurality of short preambles and the plurality of long preambles within one OFDM symbol in the downlink subframe.

23. A method as in claim 22, further comprising:

including a first cyclic prefix at a beginning portion of the one OFDM symbol, wherein the first cyclic prefix is a copy of a last segment of a short preamble following the first cyclic prefix in time.

24. A method as in claim 19, wherein the short preambles are common to all base stations.

25. A method as in claim 19, further comprising:

dividing each short preamble into a plurality of short subsequences;

assigning, in frequency, the short subsequences to different subcarriers as different short subsequence carrier sets;

dividing each long preamble into a plurality of long subsequences;

assigning, in frequency, the long subsequences to different subcarriers as different long subsequence carrier sets; and

assigning the different short and long subsequence carrier sets to two or more different antennas in the base station for downlink transmission.

26. A method as in claim 18, wherein the cell identification sequence is placed at a beginning portion of the preamble in time.

27. A method as in claim 18, wherein the one group identification sequence is placed before the cell identification sequence within the preamble in time.

28. A method as in claim 17, further comprising:

including a long preamble symbol in the downlink subframe as part of a preamble for the downlink subframe, wherein the long preamble symbol includes a plurality of identical sequential long preambles;

including the one cell identification sequence as part of the preamble for the downlink subframe; and

placing a second downlink subframe immediately ahead of the downlink subframe in time to include a second preamble which includes a copy of the one cell identification sequence and a short preamble symbol which includes a plurality of identical sequential short preambles, wherein each short preamble is shorter than each long preamble.

29. A method as in claim 28, wherein the one cell identification sequence is at a beginning portion of the preamble in time and the long preamble symbol is placed immediately after the one cell identification sequence in time, and wherein the copy of the one cell identification sequence is at a beginning portion of the second preamble in time and the short preamble symbol is placed immediately after the copy of the one cell identification sequence in the second preamble in time.

30. A method as in claim 29, further comprising:

including a first cyclic prefix immediately before the leading long preamble in the preamble of the downlink subframe, wherein the first cyclic prefix is a copy of a last segment of the leading short preamble in time; and

including a second cyclic prefix immediately before the leading short preamble in the second preamble of the second downlink subframe, wherein the second cyclic prefix is a copy of a last segment of the leading short preamble in time.

31. A method as in claim 28, wherein the long preamble symbol is at a beginning portion of the preamble in time and the one cell identification sequence is placed immediately after the long preamble symbol in time, and wherein the short preamble symbol is at a beginning portion of the second preamble in time and the copy of the one cell identification sequence is placed immediately after the short preamble symbol in the second preamble in time.

32. A method as in claim 31, further comprising:

including a first cyclic prefix immediately before the leading long preamble in the preamble of the downlink subframe, wherein the first cyclic prefix is a copy of a last segment of the leading short preamble in time; and

including a second cyclic prefix immediately before the leading short preamble in the second preamble of the second downlink subframe, wherein the second cyclic prefix is a copy of a last segment of the leading short preamble in time.

33. A method as in claim 28, further comprising:

dividing each short preamble into a plurality of short subsequences;

assigning, in frequency, the short subsequences to different subcarriers as different short subsequence carrier sets;

dividing each long preamble into a plurality of long subsequences;

assigning, in frequency, the long subsequences to different subcarriers as different long subsequence carrier sets; and

assigning the different short and long subsequence carrier sets to two or more different antennas in the base station for downlink transmission.

34. A method as in claim 18, further comprising:

including a long preamble symbol in the downlink subframe as part of the preamble for the downlink subframe, wherein the long preamble symbol includes a plurality of identical sequential long preambles each comprising a subgroup identification sequence to identify one of a plurality of subgroups within one group;

including the one cell identification sequence as part of the preamble for the downlink subframe; and

including a short preamble symbol as part of the preamble for the downlink subframe, wherein the short preamble symbol is equal in length in time to the long preamble symbol and includes a plurality of identical sequential short preambles, wherein each short preamble is shorter than each long preamble and includes the one group identification sequence.

35. A method as in claim 34, wherein the short preamble symbol is placed in time before the long preamble symbol which is placed in time before the one cell identification sequence.

36. A method as in claim 34, wherein the short preamble symbol is placed in time before the long preamble symbol and the one cell identification sequence is placed in time before the short preamble symbol.

37. A method as in claim 34, further comprising:

dividing each short preamble into a plurality of short subsequences;

assigning, in frequency, the short subsequences to different subcarriers as different short subsequence carrier sets;

dividing each long preamble into a plurality of long subsequences;

assigning, in frequency, the long subsequences to different subcarriers as different long subsequence carrier sets; and

assigning the different short and long subsequence carrier sets to two or more different antennas in the base station for downlink transmission.

38. A method as in claim 17, wherein the one group identification sequence is included as part of a post-amble at the end in time of the downlink subframe, and the cell identification sequence is included as part of a preamble at the beginning in time of the downlink subframe.

39. A method as in claim 38, further comprising:

including a plurality of identical short post-ambles sequentially in a first section of the post-amble in time and a plurality of identical long post-ambles in a second section of the post-amble subsequent to the first section, wherein each short post-amble includes the one group identification sequence and is shorter in time than each long post-amble and is common for base stations in one group, and wherein each long post-amble includes a subgroup identification sequence to identify one of a plurality of subgroups within one group.

40. A method as in claim 39, wherein there are four short post-ambles and two long post-ambles in the post-amble, wherein a length of each short post-amble in time is one half of a length of each long post-amble.

41. A method as in claim 39, further comprising including a cyclic prefix at a beginning portion of the post-amble in time, wherein the cyclic prefix is a copy of a last segment of a short post-amble following the cyclic prefix in time.

42. A method as in claim 39, further comprising:

placing the plurality of short post-ambles in a first OFDM symbol within the downlink subframe; and

placing the plurality of long post-ambles in a second, different OFDM symbol within the downlink subframe.

43. A method as in claim 39, further comprising:

including a first cyclic prefix at a beginning portion of the first OFDM symbol, wherein the first cyclic prefix is a copy of a last segment of a short post-amble following the first cyclic prefix in time.

44. A method as in claim 43, further comprising:

including a second cyclic prefix at a beginning portion of the second OFDM symbol, wherein the second cyclic prefix is a copy of a last segment of a long post-amble following the second cyclic prefix in time.

45. A method as in claim 39, further comprising:

dividing each short preamble into a plurality of short subsequences;

assigning, in frequency, the short subsequences to different subcarriers as different short subsequence carrier sets;

dividing each long preamble into a plurality of long subsequences;

assigning, in frequency, the long subsequences to different subcarriers as different long subsequence carrier sets; and

assigning the different short and long subsequence carrier sets to two or more different antennas in the base station for downlink transmission.

46. A method as in claim 38, wherein the cell identification sequence is placed in time at a beginning portion of the post-amble.

47. A method as in claim 17, further comprising:

including a long post-amble symbol in the downlink subframe as part of a post-amble for the downlink subframe, wherein the long post-amble symbol includes a plurality of identical sequential long post-ambles each comprising a subgroup identification sequence to identify one of a plurality of subgroups within one group;

including the one cell identification sequence as part of a preamble at the beginning of the downlink subframe; and

placing a second downlink subframe immediately ahead of the downlink subframe in time to include (1) a second preamble which includes a copy of the one cell identification sequence at the beginning of the second downlink subframe and (2) a second post-amble at the end of the second downlink subframe to include a plurality of identical sequential short post-ambles as a short post-amble symbol, wherein each short post-amble is shorter than each long post-amble and includes the one group identification sequence.

48. A method as in claim 47, wherein the short post-amble symbol includes eight identical and sequential short post-ambles and the long short post-amble symbol includes four identical and sequential long post-ambles, wherein a length of each short post-amble in time is one half of a length of each long post-amble.

49. A method as in claim 47, further comprising:

dividing each short preamble into a plurality of short subsequences;

assigning, in frequency, the short subsequences to different subcarriers as different short subsequence carrier sets;

dividing each long preamble into a plurality of long subsequences;

assigning, in frequency, the long subsequences to different subcarriers as different long subsequence carrier sets; and

assigning the different short and long subsequence carrier sets to two or more different antennas in the base station for downlink transmission.

50. A method as in claim 17, further comprising:

including a long post-amble symbol in the downlink subframe as part of a post-amble at the end in time of the downlink subframe, wherein the long post-amble symbol includes a plurality of identical sequential long post-ambles each comprising a subgroup identification sequence to identify one of a plurality of subgroups within one group;

including a short post-amble symbol as part of the post-amble for the downlink subframe, wherein the short post-amble symbol is equal in length in time to the long post-amble symbol and includes a plurality of identical sequential short post-ambles, wherein each short post-amble is shorter than each long post-amble and includes the one group identification sequence; and

including the one cell identification sequence as part of a preamble at the beginning in time of the downlink subframe.

51. A method as in claim 50, wherein the short post-amble symbol is placed in time before the long post-amble symbol.

52. A method as in claim 50, further comprising:

dividing each short preamble into a plurality of short subsequences;

assigning, in frequency, the short subsequences to different subcarriers as different short subsequence carrier sets;

dividing each long preamble into a plurality of long subsequences;

assigning, in frequency, the long subsequences to different subcarriers as different long subsequence carrier sets; and

assigning the different short and long subsequence carrier sets to two or more different antennas in the base station for downlink transmission.

53. A method as in claim 17, further comprising

including a subgroup identification sequence in the downlink subframe to identify a subgroup of base stations within each group,

wherein different subgroup identification sequences are respectively assigned to different subgroups of base stations.

54. A method as in claim 17, wherein the one group identification sequence is in every other L frames of sequential downlink subframes in a downlink signal, wherein L is an integer greater than 0.