Synchronization techniques for a wireless system

• US 7,133,354 B2
• Filed: 08/13/2003
• Issued: 11/07/2006
• Est. Priority Date: 08/26/2002
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Li, Junyi, Lane, Frank A.
• Primary Examiner(s): Lee, Andrew C.
• Application Number:
  US10/641,335
• Publication Number:
  US 20040095904A1
• Time in Patent Office: 1,182 Days
• Field of Search: None
• US Class Current: 370/208
• CPC Class Codes: H04B 7/12 Frequency diversity
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04W 52/34 TPC management, i.e. sharing limited amount of power among users or channels or data types, e.g. cell loading
• CPC Class Codes: H04W 52/343 taking into account loading or congestion level
• CPC Class Codes: H04W 52/42 in systems with time, space, frequency or polarisation diversity

Abstract

Power control methods and apparatus for use in a sectorized cell of an OFDM communications system are described. Each sector of a cell uses the same frequencies and transmission times and is synchronized with the other sectors in the cell in terms of tone frequencies used at any given time and symbol transmission times. Tones are allocated to channels in each cell in the same manner so that each channel in a sector has a corresponding channel in another sector. Power differences between channels in different sectors are maintained to be within a pre-selected power difference. Different channels in a cell are assigned different power levels. Wireless terminals are assigned to channels based on channel feedback information. Wireless terminals with poor channel conditions are allocated to higher power channels than wireless terminals with good channel conditions. Lower power channels often include more tones per symbol time than high power channels.

Claims

1. A communication method for use in a base station of a cell, the base station transmitting symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the method comprising:

operating each sector to use a set of tones to transmit orthogonal frequency division multiplexed symbols, each orthogonal frequency division multiplexed symbol having a symbol transmission start time, and controlling each sector to simultaneously use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times.

2. The communications method of claim 1, wherein each of said orthogonal frequency division multiplexed symbols include a cyclic prefix having a cyclic prefix length,

wherein said substantially the same symbol transmission start times are such that the difference between the symbol transmission start times of any two adjacent sectors are at most the amount of time used to transmit the cyclic prefix.

3. A communication method for use in a base station of a cell, the base station transmitting symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the method comprising:

operating each sector to use a set of tones to transmit orthogonal frequency division multiplexed symbols, each orthogonal frequency division multiplexed symbol having a symbol transmission start time;

controlling each sector to use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times;

using a set of hopping sequences to allocate tones to a first set of communication channels in a first sector of said cell; and

using said set of hopping sequences to allocate tones to a corresponding set of communication channels in each of the other sectors of said cell, each hopping sequence having a start time, the start time of each hopping sequence in said set of hopping sequences being the same in each of said sectors.

4. The method of claim 3, further comprising:

scrambling symbols to be transmitted prior to transmitting said symbols using said transmitted symbols, a different scrambling sequence being used in each sector of said cell.

5. The method of claim 3, wherein the communication channels in each of said sectors are partitioned into segments, segments of corresponding channels in each of the sectors of the cell having the same segment partitions and having segment start times which are substantially the same, such that for a segment of a channel in one sector there is another segment of the corresponding channel where the two segments use the same set of hopping sequences and the same segment start times.

6. The method of claim 5, wherein the segment start times for segments of the same channel in different cells differ by no more than the time used to transmit a cyclic prefix.

12. The method of claim 3, wherein the set of communication channels to which tones are allocated, in each sector includes at least one pilot channel and at least one of a control channel and a data channel, the method further comprising.:

discarding a symbol corresponding to said at least one of said control and data channels when said pilot channel and said at least one of said control and data channels are allocated the same tone at a given orthogonal frequency division multiplexed symbol transmission period.

7. A communication method for use in a base station of a cell, the base station transmitting symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the method comprising:

operating each sector to use a set of tones to transmit orthogonal frequency division multiplexed symbols, each orthogonal frequency division multiplexed symbol having a symbol transmission start time;

controlling each sector to use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times; and

transmitting a portion of pilot tones in each sector of the cell according to a pilot tone hopping sequence, the same pilot tone hopping sequence being used in each sector but with a different fixed tone offset being used in each of the sectors of a cell.

8. The method of claim 7, wherein said pilot tone hopping sequence is a slope hopping sequence.

9. The method of claim 8, wherein adjacent cells use different slope values for determining the slope hopping sequences to be used.

10. A communication method for use in a base station of a cell, the base station transmitting symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the method comprising:

operating each sector to use a set of tones to transmit orthogonal frequency division multiplexed symbols, each orthogonal frequency division multiplexed symbol having a symbol transmission start time;

controlling each sector to use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times;

transmitting pilot tones in each sector of the cell according to a set of pilot tone hopping sequences, the same set of pilot cone hopping sequences being used in each sector but with different fixed tone offsets being used in each of the sectors of the cell; and

wherein pilot tone hopping sequences in a set of pilot tone hopping sequences corresponding to a sector are offset from each other by a corresponding preselected set of offsets, the corresponding preselected set of offsets being the same in each sector of the cell.

11. The method of claim 10, wherein the set of pilot tone hopping sequences being used in any two adjacent sectors of the cell are not identical due to the use of different fixed tone offsets in the adjacent sectors.

13. A control system for use in a base station of a cell, the base station transmitting modulation symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the system comprising:

a transmitter assembly for transmitting signals into multiple sectors of said cell; and

means for controlling the transmitter to transmit orthogonal frequency division multiplexed symbols into each sector of the cell, each orthogonal frequency division multiplexed symbol having a symbol transmission start time, and for controlling each sector to simultaneously use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times.

14. The control system of claim 13,

wherein each of said orthogonal frequency division multiplexed symbols include a cyclic prefix;

and

wherein said substantially the same symbol transmission start times are such that the difference between the symbol transmission start times of any two adjacent sectors are at most the amount of time used to transmit the cyclic prefix.

15. A control system for use in a base station of a cell, the base station transmitting modulation symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the system comprising:

a transmitter assembly for transmitting signals into multiple sectors of said cell;

means for controlling the transmitter to transmit orthogonal frequency division multiplexed symbols into each sector of the cell, each orthogonal frequency division multiplexed symbol having a symbol transmission start time, and for controlling each sector to use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times;

means for generating a set of hopping sequences used to allocate tones to a first set of communication channels in a first sector of said cell; and

means for allocating tones to a corresponding set of communication channels in each of the other sectors of said cell according to said set of hopping sequences, each hopping sequence having a start time, the start time of each hopping sequence in said set of hopping sequences being the same in each of said sectors.

16. The control system of claim 15, further comprising:

a scrambler in each sector of said cell for scrambling symbols to be transmitted prior to transmitting said modulated symbols using orthogonal frequency divisional multiplexed symbols, a different scrambling sequence being used in each sector of said cell.

17. The control system of claim 15, wherein the communication channels in each of said sectors are partitioned into segments, segments of corresponding channels in each of the sectors of the cell having the same segment partitions and having segment start times which are substantially the same, such that for a segment of a channel in one sector there is another segment of the corresponding channel where the two segments use the same set of hopping sequences and the same segment start times.

18. The control system of claim 17, wherein the segment start times for segments of the same channel in different cells differ by no more than the time used to transmit a cyclic prefix.

24. The system of claim 15, wherein the set of communication channels to which tones are allocated in each sector includes at least one pilot channel and at least one of a control channel and a data channel, the system further comprising:

means for discarding a symbol corresponding to said at least one of said control and data channels when said pilot channel and said at least one of said control and data channels are allocated the same tone at a given orthogonal frequency division multiplexed symbol transmission period.

19. A control system for use in a base station of a cell, the base station transmitting modulation symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the system comprising:

a transmitter assembly for transmitting signals into multiple sectors of said cell;

means for controlling the transmitter to transmit orthogonal frequency division multiplexed symbols into each sector of the cell, each orthogonal frequency division multiplexed symbol having a symbol transmission start time, and for controlling each sector to use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times; and

means for generating pilot tones in each sector of the cell according to a pilot tone hopping sequence, the same pilot tone hopping sequence being used in each sector but with a different fixed tone offset being used in each of the sectors of a cell.

20. The system of claim 19, wherein said pilot tone hopping sequence is a slope hopping sequence.

21. The system of claim 20, wherein adjacent cells use different slope values for determining the slope hopping sequences to be used.

22. A control system for use in a base station of a cell, the base station transmitting modulation symbols into multiple sectors of said cell using orthogonal frequency division multiplexed symbols, the system comprising:

a transmitter assembly for transmitting signals into multiple sectors of said cell;

means for controlling the transmitter to transmit orthogonal frequency division multiplexed symbols into each sector of the cell, each orthogonal frequency division multiplexed symbol having a symbol transmission start time, and for controlling each sector to use the same set of tones, the same duration of each symbol transmission period, and substantially the same symbol start times; and

means for transmitting pilot tones in each sector of the cell according to a set of pilot tone hopping sequences, the same set of pilot tone hopping sequences being used in each sector but with different fixed tone offsets being used in each of the sectors of the cell, pilot tone hopping sequences in a set of pilot tone hopping sequences corresponding to a sector being offset from each other by a corresponding preselected set of offsets, the corresponding preselected set of offsets being the same in each sector of the cell.

23. The system of claim 22, wherein the set of pilot tone hopping sequences being used in any two adjacent sectors of the cell are not identical due to the use of different fixed tone offsets in the adjacent sectors.