Time tracking loop for diversity pilots

• US 20030142729A1
• Filed: 01/31/2002
• Published: 07/31/2003
• Est. Priority Date: 01/31/2002
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Subrahmanya, Parvathanathan, Clark, Kevin J.
• Granted Patent: US 7,006,557 B2
• Time in Patent Office: Days
• US Class Current: 375/147
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Techniques for time tracking diversity pilots are disclosed. In one aspect, an early and a late energy calculation is made on each incoming symbol using a first pilot sequence for despreading. The difference between the two energies is used to drive a tracking loop, which generates a time reference for producing a first pilot estimate and a second pilot estimate, the two estimates used for demodulating data. In another aspect, the early and late energies are made including a plurality of incoming symbols, the number of which corresponds to the number of symbols in a run of positive or negative values in an orthogonalizing sequence. The orthogonalizing sequence is used to generate a second pilot sequence from a first pilot sequence, the resulting second pilot sequence being orthogonal to the first. These aspects have the benefit of simplifying the hardware or processing steps required for transmit diversity time tracking, resulting in cost savings, power savings, simplicity of design, and the like.

Claims

1. A time tracking apparatus, operable with a base station configured for transmit diversity, transmitting a first pilot sequence on a first antenna and a second pilot sequence on a second antenna, the second sequence generated by multiplying each symbol of the first pilot sequence by a value from an orthogonalizing sequence, the symbols consisting of a first pre-determined number of chips, comprising:

a first timing offset for receiving input samples and for generating an early sequence of samples corresponding to a pre-determined offset before a timing reference;

a second timing offset for receiving input samples and for generating a late sequence of samples corresponding to a pre-determined offset after a timing reference;

a first despreader for despreading the early sequence of samples with the first pilot sequence;

a second despreader for despreading the late sequence of samples with the first pilot sequence;

a first accumulator for accumulating despread samples from the first despreader for a second pre-determined number of chips to produce a first accumulation;

a second accumulator for accumulating despread samples from the second despreader for the second pre-determined number of chips to produce a second accumulation;

a first magnitude squarer for generating a first squared magnitude from the first accumulation;

a second magnitude squarer for generating a second squared magnitude from a second accumulation;

a subtractor for generating the difference between the first and second squared magnitudes;

a tracking loop for generating the timing reference in response to the difference; and

a pilot decover for estimating the first and second pilots from the input samples in accordance with the timing reference,

2. The apparatus of claim 1, wherein the second pre-determined number of chips equals the first pre-determined number of chips.

3. The apparatus of claim 2, wherein the first pre-determined number of chips is 256.

4. The apparatus of claim 1, wherein the first and second timing offsets are one timing offset.

5. The apparatus of claim 1, wherein the pre-determined offset is one half chip.

6. The apparatus of claim 1, wherein:

the orthogonalizing sequence comprises alternating runs of positive values with runs of negative values, the runs being a pre-determined number of values;

the second pre-determined number of chips equals the first predetermined number of chips multiplied by the pre-determined number of values in a run; and

the first and second accumulators align the accumulation with the runs.

7. The apparatus of claim 6, wherein the first pre-determined number of chips is 256.

8. The apparatus of claim 6, wherein the pre-determined number of values is 2.

9. The apparatus of claim 1, further comprising a data demodulator for demodulating a first and second data stream with the first and second estimated pilots.

10. The apparatus of claim 9, further comprising a data de-multiplexor for de-multiplexing the demodulated first and second data streams to produce output symbols.

11. A method of time tracking a plurality of pilot sequences, a first pilot sequence transmitted from a first antenna, each of the remaining plurality of pilot sequences transmitted on a corresponding plurality of antennas, each remaining pilot sequence generated by multiplying each symbol of the first pilot sequence by a value from an orthogonalizing sequence of a plurality of orthogonalizing sequences, the symbols consisting of a first pre-determined number of chips, comprising:

calculating a difference between the energy in a correlation of the first pilot sequence with an early received sequence of input samples and the energy in a correlation of the first pilot sequence with a late received sequence of input samples, the correlations for a pre-determined length, the early and late sequences referenced to a timing reference;

updating a tracking loop with the difference to produce the timing reference; and

estimating the plurality of pilot sequences in accordance with the timing reference.

12. The method of claim 11, wherein the pre-determined number of chips is 256.

13. The method of claim 11, wherein the pre-determined length is one symbol.

14. The method of claim 11, wherein:

the orthogonalizing sequence comprises alternating runs of positive values with runs of negative values, the runs being a pre-determined number of values;

the pre-determined length equals the pre-determined number of chips multiplied by the pre-determined number of values in a run; and

the correlation is aligned with the runs.

15. An apparatus, operable with a base station configured for transmit diversity, transmitting a first pilot sequence on a first antenna, transmitting each of the remaining plurality of pilot sequences transmitted on a corresponding plurality of antennas, each remaining pilot sequence generated by multiplying each symbol of the first pilot sequence by a value from an orthogonalizing sequence of a plurality of orthogonalizing sequences, the symbols consisting of a first pre-determined number of chips, comprising:

means for calculating a difference between the energy in a correlation of the first pilot sequence with an early received sequence of input samples and the energy in a correlation of the first pilot sequence with a late received sequence of input samples, the correlations for a pre-determined length, the early and late sequences referenced to a timing reference;

means for updating a tracking loop with the difference to produce the timing reference; and

means for estimating the plurality of pilot sequences in accordance with the timing reference.

16. The apparatus of claim 15, wherein the pre-determined length is one symbol.

17. The apparatus of claim 15, wherein:

the orthogonalizing sequence comprises alternating runs of positive values with runs of negative values, the runs being a pre-determined number of values;

the pre-determined length equals the pre-determined number of chips multiplied by the pre-determined number of values in a run; and

the correlation is aligned with the runs.

18. Processor readable media operable to perform the following steps:

calculating a difference between the energy in a correlation of a first pilot with an early received sequence of input samples and the energy in a correlation of the first pilot sequence with a late received sequence of input samples, the correlations for a pre-determined length, the early and late sequences referenced to a timing reference;

updating a tracking loop with the difference to produce the timing reference; and

estimating a plurality of pilot sequences in accordance with the timing reference, the plurality of pilot sequences including the first pilot sequence, and a plurality of pilot sequences generated by multiplying symbols of the first pilot sequence by a plurality of orthogonalizing sequences.

19. The processor readable media of claim 18, wherein the pre-determined length is one symbol.

20. The processor readable media of claim 18, wherein:

the orthogonalizing sequences comprise alternating runs of positive values with runs of negative values, the runs being a pre-determined number of values;

the pre-determined length equals the pre-determined number of chips multiplied by the pre-determined number of values in a run; and

the correlation is aligned with the runs.

21. A mobile station, operable with a base station configured for transmit diversity, transmitting a first pilot sequence on a first antenna and a second pilot sequence on a second antenna, the second sequence generated by multiplying each symbol of the first pilot sequence by a value from an orthogonalizing sequence, the symbols consisting of a first pre-determined number of chips, comprising:

a first timing offset for receiving input samples and for generating an early sequence of samples corresponding to a pre-determined offset before a timing reference;

a second timing offset for receiving input samples and for generating a late sequence of samples corresponding to a pre-determined offset after a timing reference;

a first despreader for despreading the early sequence of samples with the first pilot sequence;

a second despreader for despreading the late sequence of samples with the first pilot sequence;

a first accumulator for accumulating despread samples from the first despreader for a second pre-determined number of chips to produce a first accumulation;

a second accumulator for accumulating despread samples from the second despreader for the second pre-determined number of chips to produce a second accumulation;

a first magnitude squarer for generating a first squared magnitude from the first accumulation;

a second magnitude squarer for generating a second squared magnitude from a second accumulation;

a subtractor for generating the difference between the first and second squared magnitudes;

a tracking loop for generating the timing reference in response to the difference; and

a pilot decover for estimating the first and second pilots from the input samples in accordance with the timing reference.

22. A mobile station, operable with a base station configured for transmit diversity, transmitting a first pilot sequence on a first antenna, transmitting each of the remaining plurality of pilot sequences transmitted on a corresponding plurality of antennas, each remaining pilot sequence generated by multiplying each symbol of the first pilot sequence by a value from an orthogonalizing sequence of a plurality of orthogonalizing sequences, the symbols consisting of a first pre-determined number of chips, comprising:

means for calculating a difference between the energy in a correlation of the first pilot sequence with an early received sequence of input samples and the energy in a correlation of the first pilot sequence with a late received sequence of input samples, the correlations for a pre-determined length, the early and late sequences referenced to a timing reference;

means for updating a tracking loop with the difference to produce the timing reference; and

means for estimating the plurality of pilot sequences in accordance with the timing reference.

23. A wireless communication system including a mobile station, operable with a base station configured for transmit diversity, transmitting a first pilot sequence on a first antenna, transmitting each of the remaining plurality of pilot sequences transmitted on a corresponding plurality of antennas, each remaining pilot sequence generated by multiplying each symbol of the first pilot sequence by a value from an orthogonalizing sequence of a plurality of orthogonalizing sequences, the symbols consisting of a first pre-determined number of chips, comprising:

means for calculating a difference between the energy in a correlation of the first pilot sequence with an early received sequence of input samples and the energy in a correlation of the first pilot sequence with a late received sequence of input samples, the correlations for a pre-determined length, the early and late sequences referenced to a timing reference;

means for updating a tracking loop with the difference to produce the timing reference; and

means for estimating the plurality of pilot sequences in accordance with the timing reference.