Method for sequentially transmitting a downlink signal from a communication station that has an antenna array to achieve an omnidirectional radiation

• US 6,185,440 B1
• Filed: 02/09/1998
• Issued: 02/06/2001
• Est. Priority Date: 12/10/1997
• Status: Expired due to Term

• Current Assignee: Intel Corporation
• Original Assignee: ArrayComm LLC (Ygomi LLC)
• Inventors: Uhlik, Christopher R., Boyd, Stephen, Yun, Louis C., Goldburg, Marc H., Barratt, Craig H., Parish, David M.
• Primary Examiner(s): Urban, Edward F.
• Assistant Examiner(s): Gesesse, Tilahun
• Application Number:
  US09/020,619
• Time in Patent Office: 1,093 Days
• Field of Search: 455/562, 455/561, 455/103, 455/105, 455/107, 455/129, 370/334, 375/135, 375/146
• US Class Current: 455/562.1
• CPC Class Codes: H01Q 1/246 specially adapted for base stations
• CPC Class Codes: H01Q 3/26 varying the relative phase or relative amplitude of energisation between two or more active radiating elements; varying the distribution of energy across a radiating aperture H01Q3/12, H01Q3/22, H01Q3/24 take precedence
• CPC Class Codes: H04B 7/0697 using spatial multiplexing
• CPC Class Codes: H04W 16/28 using beam steering

Abstract

This invention relates to a method and apparatus for transmitting a downlink signal from a communication station to one or more subscriber units to achieve a desired radiation level over a desired sector (e.g., everywhere), the communication station including an array of antenna elements and one or more signal processors programmed (in the case of programmable signal processors) to weight the downlink signal according to one of a sequence of complex valued weight vectors. The method includes sequentially repeating transmitting the downlink signal, each repetition with a different weight vector from the sequence until all weight vectors in the sequence have been transmitted with. The sequence is designed for achieving the desired radiation level during at least one of the repetitions. In this way, every user in the desired region is transmitted to in the time period.

Claims

1. A method for transmitting a downlink signal from a communication station to one or more subscriber units, the communication station including an array of antenna elements, each antenna element coupled to an associated transmit apparatus having an input and an output, the coupling of each antenna element being to the output of its associated transmit apparatus, the associated transmit apparatus inputs coupled to a signal processor, the method comprising:

for each particular signal processing procedure of a set of different signal processing procedures, each of the signal processing procedures being for processing the downlink signal to form a plurality of processed downlink antenna signals, each of the signal processing procedures including weighting the downlink signal in phase and amplitude according to a corresponding weight vector, each processed downlink antenna signal having an intended antenna element in the array, repeating the steps of;

(a) processing the downlink signal according to the particular signal processing procedure to form a particular plurality of processed downlink antenna signals;

(b) transmitting the downlink signal by passing each processed downlink antenna signal of the particular plurality of processed downlink antenna signals to its intended antenna element through the intended antenna element'"'"'s associated transmit apparatus

the set of different signal processing procedures designed to achieve a desirable radiation level at any location in the complete range of azimuths of the antenna array during at least one of the repetitions of step (b) of transmitting,

each corresponding weight vector used for weighting in each different processing procedure being a different weight vector of a sequence of different weight vectors, the weighting according to each corresponding weight vector producing the plurality of processed downlink antenna signals, the sequence of weight vectors designed to achieve a desirable radiation level at any location in a desired sector during at least one of the repetitions of step (b) of transmitting.

2. The method according to claim 1 wherein the weight vectors of the sequence of weight vectors are pre-stored in a memory.

3. The method according to claim 1, wherein the weight vectors of the sequence of weight vectors are computed from a set of one or more prototype weight vectors, the set of prototype weight vectors being pre-stored in a memory.

4. The method according to claim 1 wherein the weight vectors of the sequence of weight vectors each have elements that have the same amplitude and have random phase.

5. The method according to claim 1 wherein the elements of each of the weight vectors of the sequence of weight vectors have equal magnitude.

6. The method according to claim 1 wherein the number of weight vectors in the sequence of weight vectors is the same as the number of antennas, the number of antennas denoted by m, and the weight vectors of the sequence of weight vectors are orthogonal.

7. The method according to claim 6 wherein the elements of each of the weight vectors of the sequence of weight vectors have equal magnitude.

8. The method according to claim 6 wherein the weight vectors of the sequence of weight vectors are formed from the rows of a complex valued m-dimensional Walsh-Hadamard matrix.

9. The method according to claim 6 wherein the weight vectors of the sequence of weight vectors are formed from the rows of a real valued m-dimensional Hadamard matrix.

10. The method according to claim 6 wherein the weight vectors of the sequence of weight vectors are formed from the basis vectors of a m-dimensional discrete Fourier transform (DFT).

11. The method according to claim 6 wherein each of the weight vectors of the sequence of different weight vectors is designed to provide a particular desirable radiation pattern within a sub-sector of the overall desired sector, all the sub-sectors covering the overall desired sector, each weight vectors minimizing a cost function of possible weight vectors which includes an expression of the variation from the particular desirable radiation pattern of the radiation pattern within the particular sub-sector resulting from transmitting using the weight vector.

12. The method according to claim 11 wherein the antenna array has elements which are substantially uniformly distributed, a prototype weight vector for one sub-sector is designed, and the other weight vectors of the sequence are shifted versions of the prototype obtained by shifting the prototype weight vector by an amount determined by the angular shift of the sub-sector from the prototype weight vector sub-sector.

13. The method according to claim 11 wherein the antenna array has elements which are substantially uniformly distributed, a prototype weight vector for one sub-sector is designed, and the other weight vectors of the sequence are shifted versions of the prototype obtained by shifting the prototype weight vector by an amount determined by the angular shift of the sub-sector from the prototype weight vector sub-sector.

14. The method according to claim 13 wherein the set of representative weight vectors included in the sequence has fewer weight vectors than the number of known subscriber units.

15. The method according to claim 14 wherein the representative weight vectors are determined from the weight vectors designed for transmission to the known subscriber units, the determining of the representative weight vectors from the designed-for-subscriber-unit weight vectors using a vector quantization clustering method.

16. The method of claim 15 wherein the clustering method includes:

(i) assigning an initial set of weight vectors as a current set of representative weight vectors;

(ii) combining each designed-for-subscriber-unit weight vector with its nearest representative weight vector in the current set, nearest according to some association criterion;

(iii) determining an average measure of the distance between each representative weight vector in the current set and all the weight vectors combined with that representative vector;

(iv) replacing each representative weight vector in the current set with a core weight vector for all the weight vectors that have been combined with that representative weight vector;

(v) iteratively repeating steps (ii), (iii) and (iv) until the magnitude of the difference between the average measure in the present iteration and the average distance in the previous iteration is less than a threshold,

the set of representative weight vectors being the current set when the magnitude of the difference is less than the threshold.

17. The method of claim 16 wherein the association criterion for nearness is the Euclidean distance and the core weight vector is the geometric centroid of all the weight vectors that have been combined with the representative weight vector of the current set of representative weight vectors during that iteration.

18. The method of claim 16 wherein the average measure is the average square of the distance.

19. The method of claim 16 wherein the association criterion used for nearness is the maximal cosine angle and the core weight vector is the principal singular vector obtained from carrying out the singular value decomposition on all the weight vectors that have been combined with the representative weight vector of the present set of representative weight vectors during that iteration.

20. The method of claim 16 wherein the initial set of weight vectors are the unit amplitude weight vectors aimed at different uniformly spaced angles in the desired sector.

21. The method of claim 13 wherein the set of representative weight vectors forms a first sub-sequence of the sequence of weight vectors and the sequence of weight vectors further comprises a second sub-sequence of weight vectors.

22. The method of claim 13 wherein the second sub-sequence comprises a particular weight vector designed to provide a particular desirable radiation pattern in the desired sector, the particular weight vectors minimizing a cost function of possible weight vectors which includes an expression of the variation from the particular desirable radiation pattern of the radiation pattern within the sector resulting from transmitting using the weight vector.

23. The method of claim 22 wherein the particular desirable radiation pattern is a near omnidirectional pattern.

24. The method of claim 22 wherein the second sub-sequence is a set of orthogonal weight vectors.

25. The method according to claim 1 wherein the sequence of weight vectors includes weight vectors designed for transmission to the known subscriber units of the communication station, the designed weight vectors determined from transmit spatial signatures of the known subscriber units of the communication station.

26. A method for transmitting a downlink signal from a communication station to one or more subscriber units, the communication station including an array of antenna elements, each antenna element coupled to an associated transmit apparatus having an input and an output, the coupling of each antenna element being to the output of its associated transmit apparatus, the associated transmit apparatus inputs coupled to a signal processor, the method comprising:

for each particular signal processing procedure of a set of different signal processing procedures, each of the signal processing procedures being for processing the downlink signal to form a plurality of processed downlink antenna signals, each of the signal processing procedures including weighting the downlink signal in phase and amplitude according to a corresponding weight vector, each processed downlink antenna signal having an intended antenna element in the array, repeating the steps of;

(a) processing the downlink signal according to the particular signal processing procedure to form a particular plurality of processed downlink antenna signals;

(b) transmitting the downlink signal by passing each processed downlink antenna signal of the particular plurality of processed downlink antenna signals to its intended antenna element through the intended antenna element'"'"'s associated transmit apparatus

the set of different signal processing procedures designed to achieve a desirable radiation level at any location in the complete range of azimuths of the antenna array during at least one of the repetitions of step (b) of transmitting,

each different procedure of the set of different signal processing procedures also comprising a set of post-processing procedures of a corresponding sequence of different sets of post-processing procedures,

the corresponding weight vectors being essentially identical for each set of procedures of the sequence of different sets of signal processing procedures, and

the repetition of step (a) comprising

(i) weighting the downlink signal according to the corresponding weight vector to form a plurality of downlink antenna signals, and

(ii) applying a different post-processing procedure of one of the sets of post-processing procedures to each of the downlink antenna signals of the plurality of downlink antenna signals to form each processed downlink antenna signals of the particular plurality of processed downlink antenna signals.

27. The method of claim 26 wherein each set of post-processing procedures of the corresponding sequence of different sets of post-processing procedures comprises applying a different set of phase shifts.

28. The method of claim 27 wherein the phase shifts in each different set are random relative to each other.

29. The method of claim 26 wherein each set of post-processing procedures of the corresponding sequence of different sets of post-processing procedures comprises applying a different set of time delays.

30. The method of claim 26 wherein each post-processing procedure of the corresponding set of different post-processing procedures comprises applying a different frequency offset.