Base station identification in orthogonal frequency division multiplexing ...

1. Apparatus for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system including at least two adjacent base stations, each one of the adjacent base stations transmitting pilot tones according to one of a plurality of different pilot tone hopping sequences over at least a portion of a pilot sequence transmission time period, said portion including multiple symbol time periods, at least one of the different pilot tone hopping sequences including at least two pilot tones per symbol time period which are separated from one another by at least one tone during said portion of said pilot sequence transmission time period, in each of the different pilot tone hopping sequences the number of pilot tones used in each successive symbol time periods in said portion of said pilot sequence transmission period being the same but the tones used in a symbol time period by any one of the different pilot tone hopping sequences changing in frequency from one symbol time period to the next symbol time period by a frequency shift corresponding to a fixed number of tones, adjacent base stations using different frequency shifts to generate pilot tone hopping sequences with different pilot tone slopes which can be determined from the frequency shift of the pilot tones used in consecutive symbol time periods, the apparatus comprising:

a receiver for receiving one or more of said plurality of different pilot tone hopping sequences having different pilot tone slopes; and

a detector, responsive to said one or more received pilot tone hopping sequences, said detector including an energy accumulator for generating an accumulated energy measurement for each individual one of the plurality of pilot tone hoping sequences having different slopes over a period including multiple symbol time periods, said detector detecting a received pilot tone hopping sequence having the maximum accumulated energy over said period including multiple symbol time periods.

2. The invention as defined in claim 1 wherein each of said one or more received pilot tone hopping sequences is a Latin Squares based pilot tone hopping sequence.

3. The invention as defined in claim 1 wherein said receiver yields a baseband version of a received signal and further includes a unit for generating a fast Fourier transform version of said baseband signal, and wherein said detector is supplied with said fast Fourier transform version of said baseband signal to detect, based on accumulated energy measurements, the received pilot tone sequence having the maximum accumulated energy.

4. The invention as defined in claim 3 wherein said receiver further includes a quantizer for quantizing the results of said fast Fourier transform.

5. The invention as defined in claim 3 wherein said detector is a maximum energy detector.

6. The invention as defined in claim 5, wherein different initial frequency shifts are possible for different pilot tone hopping sequences having the same slope; and wherein said maximum energy detector determines a slope and an initial frequency shift for pilot tones in the detected pilot tone hopping sequence having the maximum accumulated energy.

7. The method of claim 1, wherein frequency spacing between pilot tones which occur in a symbol time period in each of said plurality of tone hopping sequences is fixed and is the same for all of said plurality of pilot tone hopping sequences.

8. Apparatus for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system comprising:

a receiver for receiving one or more pilot tone hopping sequences each including pilot tones, said pilot tones each being generated at a prescribed frequency and time instants in a prescribed time-frequency grid; and

a maximum energy detector, responsive to said one or more received pilot tone hopping sequences, for detecting the received pilot tone hopping sequence having the strongest power,

said maximum energy detector including a slope-shift accumulator for accumulating energy along each possible slope and initial frequency shift of said one or more received pilot tone hopping sequences and generating an accumulated energy signal, a frequency shift accumulator supplied with said accumulated energy signal for accumulating energy along pilot frequency shifts of said one or more received pilot tone hopping sequences, and a maximum detector supplied with an output from said frequency shift accumulator for estimating a slope and initial frequency shift of the strongest received pilot tone hopping sequence as a slope and initial frequency shift corresponding to the strongest accumulated energy.

9. The invention as defined in claim 8 wherein said accumulated energy is represented by the signal J0(s, b0), where J 0 ⁡ ( s , b 0 ) = ∑ t = 0 N sy - 1 ⁢ ⁢  Y ⁡ ( t , st + b 0 ⁡ ( mod ⁢ N ) )  2 ,

and s is the slope of the pilot signal, b0 is an initial frequency shift of the pilot signal, Y(t,n) is the fast Fourier transform data, t=0, . . . , Nsy−1, n=st+b0 (mod N), and n=0, . . . N−1.

10. The invention as defined in claim 8 wherein said frequency shift accumulator accumulates energy along pilot frequency shifts of said one or more received pilot tone hopping sequences in accordance with J ⁡ ( s , b 0 ) = ∑ j = 1 N p ⁢ ⁢ J 0 ⁡ ( s , b 0 + n j ) ,

where s is the slope of the pilot signal, b0 is an initial frequency shift of the pilot signal and nj are frequency offsets.

11. The invention as defined in claim 8 wherein said maximum detector estimates said slope and initial frequency shift of the strongest received pilot tone hopping sequence in accordance with s ^ , b ^ 0 = arg ⁢ ⁢ max s , b 0 ⁢ J ⁡ ( s , b 0 ) ,

where ŝ is the estimate of the slope, {circumflex over (b)}0 is the estimate of the initial frequency shift, and where the maximum is taken over sεS and b0=0, . . . ,N−1.

12. Apparatus for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system comprising:

a receiver for receiving one or more pilot tone hopping sequences each including pilot tones, said pilot tones each being generated at a prescribed frequency and time instants in a prescribed time-frequency grid; and

a maximum energy detector, responsive to said one or more received pilot tone hopping sequences, for detecting the received pilot tone hopping sequence having the strongest power, said maximum energy detector including a frequency shift detector for estimating at a given time frequency shift of the received pilot tone hopping sequence having strongest energy and an estimated maximum energy value, and a slope and frequency shift solver, responsive to said estimated frequency shift and said estimated maximum energy value, for generating estimates of an estimated slope and an estimated initial frequency shift of the strongest received pilot signal.

13. The invention as defined in claim 12 wherein said estimated frequency shift at time t is obtained in accordance with n(t)=st+b0(mod N), where s is the pilot signal slope, t is a symbol time and n(t) is a frequency shift estimate.

14. The invention as defined in claim 13 wherein said estimated maximum energy value is obtained in accordance with [ E ⁡ ( t ) , n ⁡ ( t ) ] = max n ⁢ ∑ j = 1 N p ⁢ ⁢  Y ⁡ ( t , n + n j ⁡ ( mod ⁢ ⁢ N ) )  2 ,

where E(t) is the maximum energy value, Y(t,n) is the fast Fourier transform data, j=1, . . . , Np and nj are frequency offsets.

15. The invention as defined in claim 14 wherein said slope is estimated in accordance with s ^ = arg ⁢ ⁢ max s ∈ ⁢ S ⁢ ∑ l = 1 N sy - 1 ⁢ E ⁡ ( t ) ⁢ 1 { n ⁡ ( t ) - n ⁡ ( t - 1 ) = s } ,

where both n(t) and n(t−1) satisfy n(t)=st+b0 (mod N).

16. The invention as defined in claim 14 wherein said frequency shift is estimated in accordance with b 0 = arg ⁢ ⁢ max b 0 = 0 , … , N - 1 ⁢ ∑ t = 1 N sy - 1 ⁢ E ⁡ ( t ) ⁢ 1 { n ⁡ ( t ) = st + b 0 } .

17. The invention as defined in claim 12 wherein said maximum energy detector detects said slope in accordance with determining the time, t0εT, and slope, s0εS, such that the set of times t on the line n(t)=n(t0)+s0(t−t0), has the largest total pilot signal energy.

18. A method for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system including at least two adjacent base stations, each one of the adjacent base stations transmitting pilot tones according to one of a plurality of different pilot tone hopping sequences, in each of the different pilot tone hopping sequences over at least a portion of a pilot sequence transmission time period, said portion including multiple symbol time periods, the number of pilot tones used in each successive symbol time period in said portion of said pilot sequence transmission time period being the same but the tones used in a symbol time period by any one of the different pilot tone hopping sequences changing in frequency from one symbol time period to the next symbol time period by a frequency shift corresponding to a fixed number of tones, adjacent base stations using different frequency shifts to generate pilot tone hoping sequences with different pilot tone slopes which can be determined from the frequency shift of the pilot tones used in consecutive symbol time periods, the method comprising the steps of:

receiving one or more of said plurality of different pilot tone hopping sequences having different pilot tone hopping slopes; and

in response to said one or more received pilot tone hopping sequences:

generating an accumulated energy measurement for each individual one of the plurality of pilot tone hoping sequences having different pilot tone hopping slopes over a period including multiple symbol time periods; and

detecting a received pilot tone hopping sequence having the maximum accumulated energy over said period including multiple symbol time periods.

19. The method as defined in claim 18 wherein each of said one or more received pilot tone hopping sequences is a Latin Squares based pilot tone hopping sequence.

20. The method as defined in claim 18 wherein said step of receiving yields a baseband version of a received signal and further including a step of generating a fast Fourier transform version of said baseband signal, and wherein said step of detecting is responsive to said fast Fourier transform version of said baseband signal for detecting the received pilot tone sequence having the maximum accumulated energy.

21. The method as defined in claim 20 wherein said step of receiving further includes a step of quantizing the results of said fast Fourier transform.

22. The method as defined in claim 20 wherein said step of detecting detects a maximum energy.

23. The method as defined in claim 22 wherein said step of detecting said maximum energy includes a step of determining a slope and initial frequency shift of pilot tones in a detected pilot tone hopping sequence having the maximum accumulated energy.

24. A method for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system comprising the steps of:

receiving one or more pilot tone hopping sequences each including pilot tones, said pilot tones each being generated at a prescribed frequency and time instants in a prescribed time-frequency grid; and

in response to said one or more received pilot tone hopping sequences, detecting the received pilot tone hopping sequence having the maximum energy, said step of detecting said maximum energy including the steps of accumulating energy along each possible slope and initial frequency shift of said one or more received pilot tone hopping sequences and generating an accumulated energy signal, in response to said accumulated energy signal, accumulating energy along pilot frequency shifts of said one or more received pilot tone hopping sequences, and in response to an output from said step of frequency shift accumulating, estimating a slope and initial frequency shift of the strongest received pilot tone hopping sequence as a slope and initial frequency shift corresponding to the strongest accumulated energy.

25. The method as defined in claim 24 wherein said accumulated energy is represented by the signal J0(s,b0), where J 0 ⁡ ( s , b 0 ) = ∑ t = 0 N sy - 1 ⁢  Y ( t , st + b 0 ( mod ⁢ ⁢ N ) )  2 ,

and s is the slope of the pilot signal, b0 is an initial frequency shift of the pilot signal, Y(t,n) is the fast Fourier transform data, t=0, . . . , Nsy−1, n=st+b0(mod N), and n=0, . . . N−1.

26. The method as defined in claim 24 wherein said step of frequency shift accumulating includes a step of accumulating energy along pilot frequency shifts of said one or more received pilot tone hopping sequences in accordance with J ⁡ ( s , b 0 ) = ∑ j = 1 N p ⁢ J 0 ⁡ ( s , b 0 + n j ) ,

where s is the slope of the pilot signal, b0 is an initial frequency shift of the pilot signal and nj are frequency offsets.

27. The method as defined in claim 24 wherein said step of maximum energy detecting includes a step of estimating said slope and initial frequency shift of the strongest received pilot tone hopping sequence in accordance with s ^ , b ^ 0 = arg ⁢ ⁢ max s , b 0 ⁢ J ⁡ ( s , b 0 ) ,

where ŝ is the estimate of the slope, {circumflex over (b)}0 is the estimate of the initial frequency shift, and where the maximum is taken over sεS and b0=0, . . . ,N−1.

28. A method for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system comprising the steps of:

receiving one or more pilot tone hopping sequences each including pilot tones, said pilot tones each being generated at a prescribed frequency and time instants in a prescribed time-frequency grid; and

in response to said one or more received pilot tone hopping sequences, detecting the received pilot tone hopping sequence having maximum energy, said step of detecting the received pilot tone hopping sequence having maximum energy including a step of estimating, at a given time, a frequency shift of the received pilot tone hopping sequence having maximum energy and estimating a maximum energy value, and in response to said estimated frequency shift and said estimated maximum energy value, generating estimates of an estimated slope and an estimated initial frequency shift of the strongest received pilot signal.

29. The method as defined in claim 28 wherein said estimated frequency shift at time t is obtained in accordance with n(t)=st+b0(mod N), where s is the pilot signal slope, t is a symbol time and n(t) is a frequency shift estimate.

30. The method as defined in claim 29 wherein said estimated maximum energy value is obtained in accordance with [ E ⁡ ( t ) , n ⁡ ( t ) ] = max n ⁢ ∑ j = 1 N p ⁢  Y ( t , n + n j ( mod ⁢ ⁢ N ) )  2 ,

where E(t) is the maximum energy value, Y(t,n) is the fast Fourier transform data, j=1, . . . , Np and nj are frequency offsets.

31. The method as defined in claim 30 wherein said slope is estimated in accordance with s ^ = arg ⁢ ⁢ max s ∈ S ⁢ ∑ t = 1 N sy - 1 ⁢ E ⁡ ( t ) ⁢ 1 { n ⁡ ( t ) - n ⁡ ( t - 1 ) = s } ,

where both n(t) and n(t−1) satisfy n(t)=st+b0(mod N).

32. The method as defined in claim 30 wherein said frequency shift is estimated in accordance with b ^ 0 = arg ⁢ ⁢ max b 0 = 0 ⁢ ⁢ … ⁢ ⁢ N - 1 ⁢ ∑ t = 0 N sy - 1 ⁢ E ⁡ ( t ) ⁢ 1 { n ⁡ ( t ) = st + b 0 } .

33. The method as defined in claim 28 wherein said step of maximum energy detecting includes a step of finding the time, t0εT, and slope, s0εS, such that the set of times t on the line n(t)=n(t0)+s0(t−t0), has the largest total pilot signal energy.

34. Apparatus for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system including at least two adjacent base stations, each one of the adjacent base stations transmitting pilot tones according to one of a plurality of different pilot tone hopping sequences over at least a portion of a pilot sequence transmission time period, said portion including multiple symbol time periods, at least one of the different pilot tone hopping sequences including at least two pilot tones per symbol time period which are separated from one another by at least one tone during said portion of said pilot sequence transmission time period, in each of the different pilot tone hopping sequences the number of pilot tones used in each successive symbol time period in said portion of said pilot sequence transmission time period being the same but the tones used in a symbol time period by any one of the different pilot tone hopping sequences changing in frequency from one symbol time period to the next symbol time period by a frequency shift corresponding to a fixed number of tones, adjacent base stations using different frequency shifts to generate pilot tone hopping sequences with different pilot tone slopes which can be determined from the frequency shift of the pilot tones used in consecutive symbol time periods, the apparatus comprising:

means for receiving one or more of said different pilot tone hopping sequences each including pilot tones; and

means, responsive to said one or more received pilot tone hopping sequences, for generating an accumulated energy measurement for each individual one of the plurality of different pilot tone hoping sequences having different pilot tone slopes; and

detector means for detecting a received pilot tone hopping sequence having the maximum accumulated energy over a period including multiple symbol time periods.

35. The invention as defined in claim 34 wherein each of said one or more received pilot tone hopping sequences is a Latin Squares based pilot tone hopping sequence.

36. The invention as defined in claim 34 wherein said means for receiving yields a baseband version of a received signal and further including means for generating a fast Fourier transform version of said baseband signal, and wherein said means for detecting is responsive to said fast Fourier transform version of said baseband signal for determining a received pilot tone sequence having the maximum energy.

37. The invention as defined in claim 36 wherein said means for generating said fast Fourier transform includes means for quantizing the results of said fast Fourier transform.

38. The invention as defined in claim 36 wherein means for detecting detects a maximum energy.

39. The invention as defined in claim 38 wherein said means for detecting said maximum energy includes means for determining a slope and an initial frequency shift of pilot tones in a detected pilot tone hopping sequence having the maximum energy.

40. Apparatus for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system comprising the steps of:

means for receiving one or more pilot tone hopping sequences each including pilot tones, said pilot tones each being generated at a prescribed frequency and time instants in a prescribed time-frequency grid; and

means, responsive to said one or more received pilot tone hopping sequences, for detecting the received pilot tone hopping sequence having maximum energy, said means for detecting said maximum energy including means for accumulating energy along each possible slope and initial frequency shift of said one or more received pilot tone hopping sequences, means for generating an accumulated energy signal, means, responsive to said accumulated energy signal, for accumulating energy along pilot frequency shifts of said one or more received pilot tone hopping sequences, and means, responsive to an output from said means for frequency shift accumulating, for estimating a slope and an initial frequency shift of the strongest received pilot tone hopping sequence as the slope and the initial frequency shift corresponding to the strongest accumulated energy.

41. The invention as defined in claim 40 wherein said accumulated energy is represented by the signal J0(s1b0), where J 0 ⁡ ( s , b 0 ) = ∑ t = 0 N sy - 1 ⁢  Y ⁢ ( t , st + b 0 ( mod ⁢ ⁢ N ) )  2 ,

and s is the slope of the pilot signal, b0 is an initial frequency shift of the pilot signal, Y(t,n) is the fast Fourier transform data, t=0, . . . Nsy−1, n=st+b0(mod N), and n=0, . . . N−1.

42. The invention as defined in claim 40 wherein said means for frequency shift accumulating includes means for accumulating energy along pilot frequency shifts of said one or more received pilot tone hopping sequences in accordance with J ⁡ ( s , b 0 ) = ∑ j = 1 N p ⁢ J 0 ⁡ ( s , b 0 + n j ) ,

where s is the slope of the pilot signal, b0 is an initial frequency shift of the pilot signal and nj are frequency offsets.

43. The invention as defined in claim 40 wherein said means for maximum energy detecting includes means for estimating said slope and initial frequency shift of the strongest received pilot tone hopping sequence in accordance with s ^ , b ^ 0 = arg ⁢ ⁢ max s , b 0 ⁢ J ⁡ ( s , b 0 ) ,

where ŝ is the estimate of the slope, {circumflex over (b)}0 is the estimate of the initial frequency shift, and where the maximum is taken over sεS and b0=0, . . . ,N−1.

44. Apparatus for use in a mobile user unit in an orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system comprising the steps of:

means for receiving one or more pilot tone hopping sequences each including pilot tones, said pilot tones each being generated at a prescribed frequency and time instants in a prescribed time-frequency grid; and

means, responsive to said one or more received pilot tone hopping sequences, for detecting the received pilot tone hopping sequence having maximum energy, said means for detecting said maximum energy including means for estimating at a given time a frequency shift of the received pilot tone hopping sequence having maximum energy and for estimating a maximum energy value, and means, responsive to said estimated frequency shift and said estimated maximum energy value, for generating estimates of an estimated slope and an estimated initial frequency shift of the strongest received pilot signal.

45. The invention as defined in claim 44 wherein said estimated frequency shift at time t is obtained in accordance with n(t)=st+b0(mod N), where s is the pilot signal slope, t is a symbol time and n(t) is a frequency shift estimate.

46. The invention as defined in claim 45 wherein said estimated maximum energy value is obtained in accordance with [ E ⁡ ( t ) , n ⁡ ( t ) ] = max n ⁢ ∑ j = 1 N p ⁢  Y ( t , n + n j ( mod ⁢ ⁢ N ) )  2 ,

where E(t) is the maximum energy value, Y(t,n) is the fast Fourier transform data, j=1, . . . , Np and nj are frequency offsets.

47. The invention as defined in claim 46 wherein said slope is estimated in accordance with s ^ = arg ⁢ ⁢ max s ∈ S ⁢ ∑ t = 1 N sy - 1 ⁢ E ⁡ ( t ) ⁢ 1 { n ⁡ ( t ) - n ⁡ ( t - 1 ) = s } ,

where both n(t) and n(t−1) satisfy

n(t)=st+b0(mod N).

48. The invention as defined in claim 46 wherein said frequency shift is estimated in accordance with b ^ 0 = arg ⁢ ⁢ max b 0 = 0 ⁢ ⁢ … ⁢ ⁢ N - 1 ⁢ ∑ t = 0 N sy - 1 ⁢ E ⁡ ( t ) ⁢ 1 { n ⁡ ( t ) = st + b 0 } .

49. The invention as defined in claim 44 wherein said means for detecting maximum energy includes means for finding the time, t0εT, and slope, s0εS, such that the set of times t on the line n(t)=n(t0)+s0(t−t0), has the largest total pilot signal energy.

50. An orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless system comprising:

at least two adjacent base stations, each one of the adjacent base stations transmitting pilot tones according to one of a plurality of different pilot tone hopping sequences over at least a portion of a pilot sequence transmission time period, said portion including multiple symbol time periods, at least one of the different pilot tone hopping sequences including at least two pilot tones per symbol time period which are separated from one another by at least one tone during said portion of said pilot sequence transmission time period, in each of the different pilot tone hopping sequences the number of pilot tones used in each successive symbol time period in said portion of said pilot sequence transmission period being the same but the tones used in a symbol time period by any one of the different pilot tone hopping sequences changing in frequency from one symbol time period to the next symbol time period by a frequency shift corresponding to a fixed number of tones, adjacent base stations using different frequency shifts to generate pilot tone hopping sequences with different pilot tone slopes which can be determined from the frequency shift of the pilot tones used in consecutive symbol time periods; and

a mobile communications device including:

i) a receiver for receiving one or more of said plurality of different pilot tone hopping sequences; and

ii) means for determining the pilot tone slope of a received pilot tone hopping sequence.

51. An orthogonal frequency division multiplexing (OFDM) based spread spectrum multiple access wireless communications method, comprising:

at least two adjacent bases stations which transmit pilot tones according to different ones of a plurality of different pilot tone hopping sequences over at least a portion of a pilot sequence transmission time period, said portion including multiple symbol time periods, at least one of the different pilot tone hopping sequences including at least two pilot tones per symbol time period which are separated from one another by at least one tone during said portion of said pilot sequence transmission time period, in each of the different pilot tone hopping sequences the number of pilot tones used in each successive symbol time period in said portion of said pilot sequence transmission period being the same but the tones used in a symbol time period by any one of the different pilot tone hopping sequences changing in frequency from one symbol time period to the next symbol time period by a frequency shift corresponding to a fixed number of tones, each of the adjacent base stations using different frequency shifts to generate the transmitted pilot tone hopping sequences resulting in different pilot tone slopes which can be determined from the frequency shift of the pilot tones transmitted in consecutive symbol time periods.

52. The method of claim 51, wherein frequency spacing between pilot tones which occur in a symbol time period in each of said plurality of tone hopping sequences is fixed and is the same for all of said plurality of pilot tone hopping sequences.