Multipath propagation delay determining means using periodically inserted pilot symbols

• US 6,731,622 B1
• Filed: 05/26/1999
• Issued: 05/04/2004
• Est. Priority Date: 05/01/1998
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Frank, Georg, Maurer, Alexander, Schulist, Mathias, Popovic, Branislav, Granzow, Wolfgang
• Primary Examiner(s): Trost, William
• Assistant Examiner(s): D AGOSTA, STEPHEN M
• Application Number:
  US09/320,638
• Time in Patent Office: 1,805 Days
• Field of Search: 370/335, 370/342, 370/350, 455/63.1, 455/67.13, 455/65, 455/501, 455/504, 455/506
• US Class Current: 370/342
• CPC Class Codes: G01S 5/0218 Multipath in signal reception
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/70754 Setting of search window, i.e. range of code offsets to be searched H04B1/70758 takes precedence
• CPC Class Codes: H04B 1/70755 Setting of lock conditions, e.g. threshold
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/7113 Determination of path profile
• CPC Class Codes: H04B 1/7117 Selection, re-selection, allocation or re-allocation of paths to fingers, e.g. timing offset control of allocated fingers
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 48/08 Access restriction or access information delivery, e.g. discovery data delivery signalling during connection H04W76/00

Abstract

The invention relates to a multipath propagation delay determining means (STU, FIGS. 6, 7) for determining a power delay spectrum (DPS) of a CDMA signal transmission between a CDMA base station (BS) and a CDMA mobile station (MS) on a plurality of propagation paths (P1, P2) within a cell (CL) of a CDMA communication system, comprising an A/D conversion means (A/D) for converting an analog CDMA multipath signal (S₁, S₂) received from at least one antenna (Ant1, Ant2) within said cell (CL) into a digital CDMA multipath signal (S₁, S₂) consisting of consecutive radio frames (RF1 . . . RFn) including consecutive time slots (TS1 . . . TSm) with complex pilot symbols (PSi) and data symbols (Pdi), a demultiplexing means (PI-DEMUX) for extracting complex pilot symbols (PSi) and data symbols (PDi) from at least two consecutive time slots (TSk−1, TSk, TSk+1) of each radio frame (RFn) and for storing them consecutively in a memory means (BUF) thereof; and a searching means (S1 . . . SL) for determining a power delay profile (DPS, DPS1, DPS2, FIG. 14) of said each antenna (Ant.1, Ant.2) on the basis of said extracted and stored complex pilot symbols and said data symbols (PSi, PDi).

Claims

1. An apparatus for determining a power delay spectrum of a code division multiple access (CDMA) signal transmission between a CDMA base station and a CDMA mobile station on a plurality of propagation paths within a cell of a CDMA communication system, comprising:

an analog-to-digital (A/D) converter for converting an analog CDMA multipath signal received from at least one antenna within said cell into a digital CDMA multipath signal;

wherein said A/D converter is adapted for converting said analog CDMA multipath signal into a digital CDMA multipath signal having consecutive radio frames including consecutive time slots with spread complex pilot symbols and spread data symbols;

a demultiplexer for extracting spread complex pilot symbols and spread data symbols from at least two consecutive time slots of each radio frame and for storing the extracted spread complex pilot symbols consecutively in a memory thereof; and

at least one search processor for determining a power delay spectrum of each of the at least one antenna on the basis of said extracted and stored spread complex pilot symbols and said spread data symbols.

2. The apparatus according to claim 1, further comprising:

a despreading sequence generator for generating a predetermined despreading sequence;

a despreader for despreading each of said complex pilot symbols with said despreading sequence to output complex despread pilot values for each time slot; and

an averaging unit for averaging said despread complex pilot values, comprising;

a coherent accumulator for coherently adding the real and imaginary parts of corresponding despread complex pilot symbols of at least two consecutive time slots into one complex power delay spectrum sample value;

an absolute value determiner for outputting one real power delay spectrum sample value by determining the absolute value of said one complex power delay spectrum sample value; and

a phase controller for successively shifting the phase between said despreading sequence generated by said despreading generator and said extracted and stored pilot symbols and said data symbols a predetermined number of times, wherein said absolute value determiner outputs as a real power delay spectrum a predetermined number of real power delay spectrum sample values dependent on the phase shift.

3. The apparatus of claim 1, wherein the apparatus is part of a system comprising at least one of the CDMA base station and the CDMA mobile station.

4. The apparatus according to claim 2, wherein:

said despreader, said coherent accumulator, and said absolute value determiner determine at each phase shift a plurality of real power delay spectrum sample values each value being based on the coherent addition of corresponding despread complex pilot symbols in at least two respective consecutive time slots, wherein the at least two consecutive time slots used for one value are different to those used for another value; and

a non-coherent accumulator is provided for non-coherently adding the corresponding real power delay spectrum sample values to output one real power delay spectrum sample value.

5. The apparatus according to claim 1, further comprising a path selection unit for determining from said real power delay spectrum the delay times of a predetermined number of propagation paths of said multipath transmission.

6. The apparatus according to claim 3, further comprising a tracking and control unit for adapting a search window used in the at least one search processor and for updating the power delay spectrum and the delay times according to at least one of position and distance variations between said mobile station and said base station.

7. The apparatus according to claim 3, wherein:

said CDMA cell served by said CDMA base station is subdivided into a predetermined number of sectors, each comprising at least one antenna, and said A/D converter converts all of said antenna signals into a corresponding digital CDMA multipath signal; and

a selector is provided for applying said digital CDMA multipath signals to said at least one search processor in response to an application control sequence output by a controller.

8. The apparatus according to claim 7, wherein each sector contains two antennas and said selector applies the converted digital CDMA multipath signals from each sector respectively to one search processor of said at least one search processor.

9. The apparatus according to claim 7, wherein the number of sectors equals the number of the at least one search processor.

10. The apparatus according to claim 7, wherein the number of sectors is not equal to the number of the at least one search processor.

11. The apparatus according to claim 1, wherein said demultiplexer comprises a switch, said memory and a sink, wherein a controller controls said switch in response to a frame clock control signal to consecutively transfer said extracted complex pilot symbols and data symbols into said memory and transfers other data symbols of said time slots into said sink.

12. The apparatus according to claim 2, wherein said despreader comprising a complex correlator having a multiplier and an integrator.

13. The apparatus according to claim 12, wherein said multiplier comprises a first, second, third and fourth multiplier and a first and second adder, wherein the first multiplier multiplies the real part of each pilot symbol with the real part of a symbol of said despreading sequence, said second multiplier multiplies the imaginary part of said pilot symbol with the real part of a symbol from said despreading sequence, said third multiplier multiplies the imaginary part of each pilot symbol with the imaginary part of said symbol of said despreading sequence, said fourth multiplier multiplies the real part of each pilot symbol with the imaginary part of said symbol of said despreading sequence, said first adder adds the outputs from the first and third multiplier and said second adder adds the outputs of said second and said fourth multipliers, wherein said integrator comprises a first and second summation unit which respectively add the values output from said first and second adder over a predetermined number of pilot chips, wherein said first and second summation unit respectively output the real and the imaginary part of said complex despread pilot values.

14. The apparatus according to claim 5, wherein said path selection unit comprises:

a peak detection/removal unit for detecting a predetermined number of peaks in said power delay spectrum and for setting zero or removing at least those samples of said real power delay spectrum corresponding to the detected peaks and a predetermined number of additional samples left and right to said maximum;

a noise estimator for averaging the real power delay spectrum having the peak samples and said additional samples set to zero or removed to determine an effective noise value; and

a path estimator for selecting delay times of the determined peaks which exceed a threshold formed by multiplying the effective noise value with a threshold factor.

15. The apparatus according to claim 8, wherein said path selection unit further comprises:

an adder to sum up a first and second real power delay spectrum of the two antennas per sector, wherein the peak detection/removal unit detects and zeros peaks in said added real power delay spectrum; and

first and second path verification units for comparing the multiplied threshold determined by said path estimator respectively with said first and second real power delay spectrum of each antenna at the determined delay values wherein only such peaks in the first and second power delay spectrum are detected which are equal or above the multiplied threshold.

16. The apparatus according to claim 15, further comprising a maximum detection unit for receiving the candidate peaks from the respective path verification units from a plurality of search processors of the at least one search processor, each serving one or more sectors and for ordering a predetermined number of highest peaks as well as their delay times output by the path verification units of the respective plurality of search processors in a descending order and for determining a selection information for each delay time indicating to which sector the respective delay times belong.

17. The apparatus according to claim 2, wherein said radio frames each comprise sixteen time slots, wherein a plurality of real power delay spectra are calculated non-coherently.

18. The apparatus according to claim 6, wherein said tracking and control unit receives said selection information values and said delay times and selects a predetermined number of delay times and corresponding selection information.

19. The apparatus according to claim 18, wherein said tracking and control unit uses a predetermined sector scanning rule for the currently active and non-active sectors as indicated by said selection information for instructing said selector to apply the respective antenna signals from the respective sectors to said at least one search processor according to said predetermined sector scanning rule.

20. The apparatus according to claim 19, wherein said tracking and control unit determines, on the basis of the number of time slots in each radio frame, the number of total sectors, the number of the at least one search processor, a predetermined update period for active sectors and the number of currently active and non-active sectors as indicated by said selection information, a predetermined number of coherent and non-coherent calculations of the real power delay spectrum and the update period for non-active sectors, said sector scanning rule indicating which sector is to be scanned at each respective time slot of each radio frame.

21. The apparatus according to claim 19, wherein said tracking and control unit evaluates changes in the respective real power delay spectra over time in each active and non-active sector with respect to each other in order to determine the moving direction and the sector of the cell in which said mobile station moves.

22. The apparatus according to claim 19, wherein said tracking and control unit selects a new sector scanning rule whenever a status of a scanned sector changes from active to non-active or vice versa.

23. The apparatus according to claim 3, wherein the apparatus is part of a system comprising at least one of the CDMA base station and the CDMA mobile station, and wherein the apparatus is connected to a RAKE receiver thereof.

24. A path selection apparatus for determining delay times of a code division multiple access (CDMA) signal transmission between a CDMA base station and a CDMA mobile station on a plurality of propagation paths within a CDMA cell subdivided into a predetermined number of sectors respectively with two diversity reception antennas, said delay times are delay times associated with one of said sectors, said path selection apparatus including:

an adder to sum up a first and second real power delay spectrum of the two antennas per sector into an added power delay spectrum;

a peak detection/removal unit for detecting a predetermined number of peaks in said added power delay spectrum and for removing or setting to zero at least those samples of said added real power delay spectrum corresponding to the detected peaks;

a noise estimator for averaging said added real power delay spectrum having the peak samples removed or set to zero to determine an effective noise value;

a path estimator for selecting delay times of those determined peaks which exceed a threshold formed by multiplying the effective noise value with a threshold factor;

a first and second path verification units for comparing the multiplied threshold determined by said path estimator respectively with said first and second real power delay spectrum of each antenna at the determined delay times wherein only such delay times are detected whose peaks in the first and second power delay spectrum are equal or above the multiplied threshold.

25. The apparatus according to claim 24, wherein said path selection apparatus further comprises:

a maximum detection unit for receiving the candidate peaks from the respective path verification units from a plurality of search processors, each serving one or more sectors and for ordering a predetermined number of highest peaks as well as their delay times output by the path verification units of the respective search processor of the at least one search processor in a descending order and for determining a selection information for each delay time indicating to which sector the respective delay times belong.

26. A searching and tracking unit for determining at least one of the location and the moving direction of a code division multiple access (CDMA) CDMA mobile station of a CDMA signal transmission between a CDMA base station and a CDMA mobile station on a plurality of propagation paths within a CDMA cell subdivided into a predetermined number of sectors respectively with two reception antennas on the basis of a determination of delay times, including:

a plurality of search processors for determining real power delay spectra of the multipath transmission in each sector;

a path selection unit for determining from said real power delay spectra the delay times of a predetermined number of strongest propagation paths of said multipath transmission and respective selection information indicating the active sectors to which said delay times belong;

a tracking and control unit for determining on the basis of said delay times and said selection information of the active and non-active sectors, a sector scanning rule to instruct the selector to apply particular antenna signals to said plurality of search processors at particular timings in the respective time slots of the radio frames and for evaluating the real power delay spectra respectively obtained when applying the particular antenna signals to the plurality of search processors to determine at least one of the location and the moving direction of the mobile station within the CDMA cell.

27. The apparatus according to claim 26, wherein said tracking and control unit receives said selection information values and said delay times and selects a predetermined number of delay times and corresponding selection information.

28. The apparatus according to claim 26, wherein said tracking and control unit determines, on the basis of the number of time slots in each radio frame, the number of total sectors, the number of the plurality of search processors, a predetermined update period for active sectors, and the number of currently active and non-active sectors as indicated by said selection information, a predetermined number of coherent and non-coherent calculations of the real power delay spectrum and the update period for non-active sectors, said sector scanning rule indicating which sector is to be scanned at each respective time slot of each radio frame.

29. The apparatus according to claim 26, wherein said tracking and control unit selects a new sector scanning rule whenever a status of a scanned sector changes from active to non-active or vice versa.

30. A method of determining a power delay spectrum of a code division multiple access (CDMA) signal transmission between a CDMA base station and a CDMA mobile station on a plurality of propagation paths within a cell of a CDMA communication system, the method comprising:

converting an analog CDMA multipath signal received from at least one antenna within said cell into a digital CDMA multipath signal, the digital CDMA multipath signal having consecutive radio frames including consecutive time slots with spread complex pilot symbols and spread data symbols;

extracting spread complex pilot symbols and spread data symbols from at least two consecutive time slots of each radio frame;

storing the extracted spread complex pilot symbols consecutively in a memory; and

determining a power delay spectrum of each of the at least one antenna on the basis of said extracted and stored spread complex pilot symbols and said spread data symbols.

31. The method according to claim 30, further comprising:

generating a predetermined despreading sequence;

despreading each of said complex pilot symbols with said despreading sequence to output complex despread pilot values for each time slot; and

averaging said despread complex pilot values, the step of averaging comprising;

coherently adding the real and imaginary parts of corresponding despread complex pilot symbols of at least two consecutive time slots into one complex power delay spectrum sample value;

outputting one real power delay spectrum sample value by determining the absolute value of said one complex power delay spectrum sample value; and

successively shifting the phase between said despreading sequence and said extracted and stored pilot symbols and said data symbols a predetermined number of times; and

outputting as a real power delay spectrum a predetermined number of real power delay spectrum sample values dependent on the phase shift.

32. The method of claim 30, wherein the method is performed by at least one of the CDMA base station and the CDMA mobile station.

33. The method according to claim 31, comprising:

determining at each phase shift a plurality of real power delay spectrum sample values, each value being based on the coherent addition of corresponding despread complex pilot symbols in at least two respective consecutive time slots, wherein the at least two consecutive time slots used for one value are different to those used for another value; and

non-coherently adding the corresponding real power delay spectrum sample values to output one real power delay spectrum sample value.

34. The method according to claim 30, further comprising determining from said real power delay spectrum the delay times of a predetermined number of propagation paths of said multipath transmission.

35. The method according to claim 32, further comprising adapting a search window and updating the power delay spectrum and the delay times according to at least one of position and distance variations between said mobile station and said base station.

36. A path selection method for determining delay times of a code division multiple access (CDMA) signal transmission between a CDMA base station and a CDMA mobile station on a plurality of propagation paths within a CDMA cell subdivided into a predetermined number of sectors respectively with two diversity reception antennas, said delay times are delay times associated with one of said sectors, said path selection method including:

summing up a first and second real power delay spectrum of the two antennas per sector into an added power delay spectrum;

detecting a predetermined number of peaks in said added power delay spectrum and removing or setting to zero at least those samples of said added real power delay spectrum corresponding to the detected peaks;

averaging said added real power delay spectrum having the peak samples removed or set to zero to determine an effective noise value;

selecting delay times of those determined peaks which exceed a threshold formed by multiplying the effective noise value with a threshold factor;

comparing the multiplied threshold with said first and second real power delay spectrum of each antenna at the determined delay times; and

wherein only delay times having peaks in the first and second power delay spectrum that are equal or above the multiplied threshold are detected.

37. The method according to claim 36, wherein said path selection method further comprises receiving the candidate peaks, ordering a predetermined number of highest peaks as well as their delay times output in a descending order, and determining a selection information for each delay time indicating to which sector the respective delay times belong.

38. A method of determining at least one of the location and the moving direction of a code division multiple access (CDMA) mobile station of a CDMA signal transmission between a CDMA base station and a CDMA mobile station on a plurality of propagation paths within a CDMA cell subdivided into a predetermined number of sectors respectively with two reception antennas on the basis of a determination of delay times, the method including:

determining real power delay spectra of the multipath transmission in each sector;

determining from said real power delay spectra the delay times of a predetermined number of strongest propagation paths of said multipath transmission and respective selection information indicating the active sectors to which said delay times belong; and

determining, on the basis of said delay times and said selection information of the active and non-active sectors, a sector scanning rule used in connection with application of particular antenna signals at particular timings in the respective time slots of the radio frames and evaluating the real power delay spectra respectively obtained when applying the particular antenna signals to determine at least one of the location and the moving direction of the mobile station within the CDMA cell.

39. The method according to claim 38, wherein said step of determining a sector scanning rule comprises receiving said selection information and said delay times and selecting a predetermined number of delay times and corresponding selection information.

40. The method according to claim 38, wherein said step of determining a sector scanning rule comprises determining, on the basis of the number of time slots in each radio frame, the number of total sectors, a predetermined update period for active sectors, and the number of currently active and non-active sectors as indicated by said selection information, a predetermined number of coherent and non-coherent calculations of the real power delay spectrum and the update period for non-active sectors, said sector scanning rule indicating which sector is to be scanned at each respective time slot of each radio frame.

41. The method according to claim 38, wherein said step of determining a sector scanning rule comprises selecting a new sector scanning rule whenever a status of a scanned sector changes from active to non-active or vice versa.