Orthogonal frequency division multiplexing based spread spectrum multiple access

• US 6,711,120 B1
• Filed: 03/11/1999
• Issued: 03/23/2004
• Est. Priority Date: 03/11/1999
• Status: Expired due to Term

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Flarion Technologies Inc (Qualcomm, Inc.)
• Inventors: Laroia, Rajiv, Li, Junyi, Vanderveen, Michaela Catalina
• Primary Examiner(s): Olms, Douglas
• Assistant Examiner(s): NGUYEN, BRIAN D
• Application Number:
  US09/266,370
• Time in Patent Office: 1,839 Days
• Field of Search: 370/204, 370/203, 370/208, 370/209, 370/210, 370/319, 370/328, 370/344, 370/329, 370/330, 370/341, 370/343, 370/335, 370/336, 370/337, 370/479, 370/480, 375/130, 375/346, 375/355, 375/356
• US Class Current: 370/204
• CPC Class Codes: H04L 5/026 using code division

Abstract

An orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access system using offsetting between cells, and in particular, the use of tone offsetting and time offsetting, is disclosed. More specifically, frequencies that define the tone set of one cell is offset from the frequencies that define the tone set of at least one adjacent cell. In other words, if a first base station is using tones F₁, F₂, . . . , F_N within a frequency band, then a second base station adjacent to the first base station uses tones F₁+Δf, F₂+Δf . . . , F_N+Δf within the same frequency band. Furthermore, the symbol timing of the base-station of one cell may be offset from the symbol timing of the base-station of an adjacent cell. Thus, if a first base station starts successive symbols at times T1, T2, and T3, then a second base station adjacent to the first base station starts its respective corresponding successive symbols at times T1+Δt, T2+Δt, and T3+Δt. For example, in a cellular system with hexagonally shaped cells, the tone sets of two adjacent cells are offset by ⅓ of the spacing between adjacent tones, and the symbol timings of two adjacent cells are offset by ⅓ of a symbol period. Advantageously, the intercell interference is more uniformly distributed among users in a cell.

Claims

1. A method for operating a cellular orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system in which each base station establishes its own tone set within the same frequency band, comprising the steps of:

in a first base station corresponding to a first cell, assigning a first set of orthogonal tones, said first set of orthogonal tones being for use in communicating between said first base station and mobile units served by said first base station; and

in a second base station corresponding to a second cell, located adjacent said first cell, assigning a second set of orthogonal tones, said second set of orthogonal tones being for use in communicating between said second base station and mobile units served by said second base station;

wherein said second set of orthogonal tones are placed within the same frequency band as are said first set of orthogonal tones, tones in said second set of orthogonal tones being positioned in said same frequency band at the same points but being offset by a fixed frequency offset which is smaller than the frequency separation between adjacent tones in said first set of orthogonal tones.

2. The method of claim 1, further comprising:

in said first base station, assigning a first symbol start time;

in said second base station, assigning a second symbol start time that is offset from said first symbol start time but occurs within the duration of time between said first symbol start time at which point a first symbol beings being transmitted by the first base station and the end of the transmission of said first symbol.

3. The method of claim 1, wherein the first and second base stations are located in physically adjacent cells.

4. The method of claim 3, wherein said offset is ⅓

the spacing between adjacent tones included in said first set of orthogonal tones.

5. A method for operating a cellular orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system in which each base station establishes its own tone set within the same frequency band, comprising the steps of:

in a first base station corresponding to a first cell, assigning a first set of orthogonal tones, F₁, F₂, . . . , F_N, where N is the number of tones assigned in said first set of orthogonal tones, said first set of orthogonal tones being for use in communicating between said first base station and mobile units served by said first base station; and

in a second base station corresponding to a second cell, located adjacent to said first cell, assigning a second set of orthogonal F₁+Δ

f, F₂+Δ

f, . . . F_N+Δ

f, said second set of orthogonal tones being for use in communicating between said second base station and mobile units served by said second base station, Δ

f being a fixed frequency offset which is less than the frequency spacing between two adjacent tones in said first set of orthogonal tones.

6. The method of claim 5, wherein the first and second base stations are located in physically adjacent cells.

7. A method for operating a cellular orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system in which each base station establishes its own tone set within the same frequency band, comprising the steps of:

in a first base station corresponding to a first cell, assigning a first set of parameters for communication between said first base station and mobile units served by said first base station; and

in a second base station corresponding to a second cell, located adjacent to said first cell, assigning a second set of parameters for use in communication between said second base station and mobile units served by said second base station;

wherein parameters of said second set of parameters are offset from corresponding parameters of said first set of parameters, by a fixed amount corresponding to a frequency spacing which is less than the spacing between adjacent tones transmitted by said first base station.

8. The method of claim 7 wherein said offset is uniform for all members of said first and second set of parameters.

9. The method of claim 7 wherein said first and second set of parameters are tones used for OFDM communication by said first and second base stations, respectively.

10. The method of claim 7 further comprising:

operating said first and second base stations to transmit sequences of symbols, the second base station using symbol start times which are offset from the symbol start times used by said first base station by a fraction of a symbol transmission time period.

11. A method for operating a cellular orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system in which each base station establishes its own symbol start time, comprising the steps of:

in a first base station corresponding to a first cell, assigning a start time for each successive symbol;

in a second base station corresponding to a second cell, located adjacent to said first cell, assigning a start time for each successive symbol that is offset from said start time of a corresponding in time symbol in said first base station but that is offset by Δ

t which is a fixed time offset that is greater than zero and less than one symbol duration.

12. A communications method comprising:

operating a first base station, corresponding to a first cell, to transmit a first sequence of data symbols; and

operating a second base station, corresponding to a second cell located adjacent said first cell, to transmit a second sequence of data symbols, the second base station transmitting symbols in said second sequence at a fixed time offset from the time at which the first base station transmits data symbols in the first sequence, the fixed time offset being less than the duration of a single symbol.

13. The communications method of claim 12, wherein the fixed time offset is ⅓

a symbol duration.

14. A communications method comprising:

operating a first base station, corresponding to a first cell, to transmit a first sequence of data symbols; and

operating a second base station, corresponding to a second cell, to transmit a second sequence of data symbols, the second base station transmitting symbols in said second sequence at a fixed time offset from the time at which the first base station transmits data symbols in the first sequence, the fixed time offset being less than the duration of a single symbol;

operating the first base station to transmit said data symbols using a first set of tones; and

operating the second base station to transmit said data symbols using a second set of tones, the first and second sets of tones each including the same number of tones, each tone in the second set of tones having a frequency which differs from the frequency of a corresponding tone in the first set of tones by a fixed frequency offset, the fixed frequency offset being less than the frequency spacing between adjacent tones in said first set of tones.

15. A communications system comprising:

a first base station, corresponding to a first cell, said first base station including means for means for assigning a first set of tones, F₁, F₂, . . . , F_N, where N is the number of tones assigned in said first set of tones, said first set of tones being for use in communicating between said first base station and mobile units served by said first base station; and

a second base station, corresponding to a second cell located adjacent said first cell, said second base station including means for assigning a second set of tones F₁+Δ

f, F₂+Δ

f, . . . F_N+Δ

f, said second set of orthogonal tones being for use in communicating between said second base station and mobile units served by said second base station and Δ

f is a fixed frequency offset which is less than the frequency spacing between two adjacent tones in said first set of tones.

16. The communications system of claim 15, wherein the communications system further includes:

a first communications cell including said first base station; and

a second communications cell including said second base, the second communications cell being physically adjacent said first communications cell.

17. The communications system of claim 16,

wherein the first base station further includes means for transmitting symbols using said first set of tones at first symbol transmission start times;

and

wherein the second base station further includes means for transmitting symbols using said second set of tones at second symbol transmission start times, the second symbol transmission start times having values corresponding to the first transmission start times plus a fixed time offset, the fixed time offset being shorter than a symbol duration.

18. The communications system of claim 17, wherein the tones in the first and second sets of tones are orthogonal tones.

19. A multiple access communications system, comprising:

a first communications cell including a first base station, the first base station including means for assigning a start time for each of a first plurality of successive symbols; and

a second communications cell adjacent said first communications cell, the second communications cell including a second base station the second base station including means for assigning a start time for each of a second plurality of successive symbols, the start time of each symbol in the second plurality of successive symbols being offset from said start time of a corresponding, in time, symbol in said first plurality of successive symbols by a fixed time offset Δ

t which is greater than zero and less than one symbol duration.

20. The communication system of claim 19, wherein the first and second base stations further include means for transmitting orthogonal frequency division multiplexed signals.