Apparatus and method for estimating a plurality of channels

• US 7,327,812 B2
• Filed: 01/19/2005
• Issued: 02/05/2008
• Est. Priority Date: 03/27/2003
• Status: Expired due to Fees

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: DoCoMo Communications Laboratories Europe GmbH (Government of Japan)
• Inventors: Auer, Gunther
• Primary Examiner(s): Ghebretinsae; Temesghen
• Application Number:
  US11/038,674
• Publication Number:
  US 20050147025A1
• Time in Patent Office: 1,112 Days
• Field of Search: 375/130, 375/147, 375/267, 375/347, 370/203, 370/342, 455/101
• US Class Current: 375/347
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 7/0684 using different training sequences per antenna
• CPC Class Codes: H04L 1/0618 Space-time coding
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0226 sounding signals per se
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

An apparatus for estimating a plurality of channels from a plurality of distinct transmitting points, wherein an input signal includes a super position of signals based on a first pilot sequence transmittable from a first transmitting point and on a second pilot sequence transmittable from a second transmitting point, the first pilot sequence and the second pilot sequence having a phase shift to each other, comprises a transformer, which is operative to translate phase shifts between the first and the second pilot sequence into a delay, so that a first group of a set of discrete values of the transformed signal includes channel information of a first channel and that a second group of a set of discrete values includes channel information of a second channel, a selector for selecting the first group from the set of discrete values and for selecting the second group from the set of discrete values to obtain selected groups, and means for determining channel information for the plurality of channels based on the selected groups. The selection of groups at the output of the transformer for obtaining channel information for the channel allows the construction of a simplified receiver.

Claims

1. Apparatus for estimating a plurality of channels from a plurality of distinct transmitting points to a receiving point, wherein an input signal includes a superposition of a first signal based on a first pilot sequence transmittable from a first transmitting point and a second signal based on a second pilot sequence transmittable from a second transmitting point, the first pilot sequence and the second pilot sequence being orthogonal to each other within a predetermined orthogonality range and having a phase shift to each other, comprising:

a transformer for transforming the input signal into a transformed signal having a set of discrete values, the transformer being operative to translate the phase shift between the first and the second pilot sequence into a delay, so that a first group of the set of the discrete values includes channel information of a first channel from the first transmitting point to the receiving point and that a second group of the set of discrete values includes channel information of a second channel from the second transmitting point to the receiving point;

a selector for selecting the first group from the set of discrete values and for selecting the second group from the set of discrete values to obtain selected groups; and

a processor for determining channel information for the plurality of channels based on the selected groups.

2. Apparatus in accordance with claim 1, wherein the input signal includes, in a superimposed manner, a third signal based on a third pilot sequence transmittable from a third transmitting point, the third pilot sequence being orthogonal to the first and the second pilot sequences within the orthogonality range, and having a further phase shift to the first pilot sequence, the transformer being further operative to translate the further phase shift into a further delay, so that a third group of the set of discrete values includes channel information of a third channel from the third transmitting point to the receiving point;

and

wherein the selector is operative to further select the third group from the set of discrete values to obtain a selected third group.

3. Apparatus in accordance with claim 1, wherein each group consists of an equal number of successive discrete values of the set of discrete values.

4. Apparatus in accordance with claim 1, wherein the transformer is operative to perform a Fourier transform or a fast Fourier transform or a discrete Fourier transform or an inverse Fourier transform or an inverse fast Fourier transform or an inverse discrete Fourier transform on the input signal.

5. Apparatus in accordance with claim 1, wherein the set of discrete values includes a total number of discrete values, the number being obtained by the transformer.

6. Apparatus in accordance with claim 5, in which the plurality of transmitting points has a total number of transmitting points, wherein the selector is operative to select, as a group, a number of successive discrete values, the number being equal to the total number of discrete values divided by the total number of transmitting points.

7. Apparatus in accordance with claim 6, in which the selector is operative to select the groups such that a first discrete value of the set of discrete values is a first discrete value in the first group and a first discrete value of the second group of discrete values is a discrete value in the set of discrete values succeeding a discrete value having a highest order of the values selected to obtain the first group.

8. Apparatus in accordance with claim 1, in which the input signal is a set of successive input signal values, and in which the transformer is operative to transform the set of successive input signal values into the set of discrete values, wherein a total number of discrete values of the set of discrete values is equal to a total number of input signal values in the set of input signal values.

9. Apparatus in accordance with claim 1, in which the transformer is operative to perform a transform algorithm, and in which the set of discrete values is generated by a single execution of the transform algorithm by the transformer.

10. Apparatus in accordance with claim 9, in which the transform algorithm being performed by the transformer is a Fourier transform or a fast Fourier transform or a discrete Fourier transform or an inverse Fourier transform or an inverse fast Fourier transform or an inverse discrete Fourier transform algorithm applied to the total number of input signal values.

11. Apparatus in accordance with claim 1, wherein the pilot sequences include a complex amplitude sequence and phase information, wherein the complex amplitude sequence is the same for the pilot sequences, comprising:

a multiplier being operative to multiply a received signal by a complex-conjugated version of the amplitude sequence to obtain the input signal.

12. Apparatus in accordance with claim 11, wherein the received signal is a set of successive discrete received signal values and wherein the complex conjugated version of the amplitude sequence is a set of successive discrete complex conjugated amplitude signal values, and

wherein the multiplier is operative to perform a single complex multiplication for a value of the set of successive discrete signal values and a corresponding value of the set of successive discrete complex conjugated amplitude signal values, so that after a number of single multiplications the set of successive discrete input values is obtained.

13. Apparatus in accordance with claim 1, in which the processor for determining channel information is operative to receive the selected groups and to output the selected groups, each group of the selected groups including channel information of a particular channel.

14. Apparatus in accordance with claim 13, wherein the processor for determining channel information is operative to determine the channel information by outputting the selected groups, each group including channel impulse responses of a particular channel as channel information.

15. Apparatus in accordance with claim 13, wherein the processor for determining channel information includes a time/frequency converter for obtaining a channel transfer function as the channel information.

16. Apparatus in accordance with claim 1, wherein a group of the selected groups and a further group of the selected groups include channel information of a channel and channel information of a further channel in a super imposed manner, wherein the processor for determining channel information is operative to determine the channel information of the channel and the channel information of the further channel based on the group and on the further group.

17. Apparatus in accordance with claim 16, wherein a group of the selected groups includes a superposition of the channel information of a channel being multiplied by a phase shift factor and of a further channel information of a further channel being multiplied by a further phase shift factor, and

wherein a further group of the selected groups includes a superposition of the channel information of the channel being multiplied by the complex conjugated phase shift factor and of the further channel information of the further channel being multiplied by the complex-conjugated further phase shift factor, the phase shift factor and the further phase shift factor being caused by the pilot sequences, wherein

the processor for determining channel information is operative to determine the channel information of the channel and the channel information of the further channel using the group and the further group.

18. Apparatus in accordance with claim 17, wherein the processor for determining channel information is operative to determine the channel information and the further channel information using phase shift operations and addition and/or subtraction operations applied to the group and to the further group.

19. Apparatus in accordance with claim 17, wherein the phase shift factor is a function of a phase shift of 180 degrees divided by the total number of transmitting points.

20. Apparatus in accordance with claim 1, wherein a channel information is corrupted by a distortion signal, the processor for determining further comprising an estimator being operative to estimate the channel information from the corrupted channel information.

21. Apparatus in accordance with claim 20, wherein the estimator is operative to perform a minimum mean squared error estimation or a maximum a posteriori estimation or a maximum likelihood estimation for providing an estimated channel information.

22. Apparatus in accordance with claim 1, in which the pilot sequences are used to modulate a discrete carrier in a multi carrier modulation scheme at a predetermined time instant, the apparatus further comprising:

a controller for detecting the input signal in a received signal and for enabling the transformer, the selector or the processor for determining only when the input signal is detected in the received signal.

23. Apparatus in accordance with claim 1, in which the pilot sequences are used to modulate the same pilot carrier in a multi carrier modulation scheme at distinct transmitting time instants, the apparatus further comprising:

a controller for detecting a pilot carrier in a received signal including successive multi carrier modulated symbols and for collecting values of the pilot carrier at time instants corresponding to transmitting instants to obtain the input signal, wherein the channel information obtained by processing the input signal using the transformer, the selector and the processor for determining includes information on a multi carrier channel from transmitting points to receiving point defined by the pilot carrier over time.

24. Apparatus in accordance with claim 1, wherein the apparatus further comprises a single processor for windowing the input signal to obtain a windowed input signal to be used as the input signal for the transformer.

25. Method for estimating a plurality of channels from a plurality of distinct transmitting points to a receiving point, wherein an input signal includes a superposition of a first signal based on a first pilot sequence transmittable from a first transmitting point and a second signal based on a second pilot sequence transmittable from a second transmitting point, the first pilot sequence and the second pilot sequence being orthogonal to each other within a predetermined orthogonality range and having a phase shift to each other, comprising the following steps:

transforming the input signal into a transformed signal having a set of discrete values by translating the phase shift between the first and the second pilot sequence into a delay, so that a first group of the set of discrete values includes channel information of a first channel from the first transmitting point to the receiving point and that a second group of the set of discrete values includes channel information of a second channel from the second transmitting point to the receiving point;

selecting the first group from the set of discrete values and selecting the second group from the set of discrete values to obtain selected groups;

determining channel information for the plurality of channels on the basis of the selected groups.