Method for identifying pre-candidate cells for a mobile unit operating with a switched beam antenna in a wireless communication system, and corresponding system

• US 7,308,264 B2
• Filed: 02/04/2005
• Issued: 12/11/2007
• Est. Priority Date: 02/05/2004
• Status: Expired due to Fees

• Current Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Original Assignee: Interdigital Technology Corporation (InterDigital, Inc.)
• Inventors: Iacono, Ana Lucia, Stern-Berkowitz, Janet, Zangi, Kambiz Casey
• Primary Examiner(s): Trost; William
• Assistant Examiner(s): EWART, JAMES D
• Application Number:
  US11/051,138
• Publication Number:
  US 20050176469A1
• Time in Patent Office: 1,040 Days
• Field of Search: 455/62, 455/63.4, 455/101, 455/269, 455/436, 455/442, 455/443, 455/450, 455/550.1, 455/562.1, 455/575.7, 4552771-2781, 342/81, 342/154, 342/354, 342/367, 342/368, 343/757, 343/777, 343/824
• US Class Current: 455/442
• CPC Class Codes: H04W 16/28 using beam steering
• CPC Class Codes: H04W 36/00835 Determination of neighbour cell lists
• CPC Class Codes: H04W 88/02 Terminal devices

Abstract

Measurements for identifying pre-candidate cells are made by a wireless transmit/receive unit (WTRU) operating with a switched beam antenna in a wireless communication system. The switched beam antenna is a smart antenna generating a plurality of directional beams and an omni-directional beam. The WTRU measures signals from cells not in an active set of cells to define a pre-candidate set of cells. Measured signals from cells in the pre-candidate set of cells are compared to a threshold, and the corresponding cells are moved from the pre-candidate set of cells to a candidate set of cells based upon the comparison to the threshold. A measurement report is then sent to the network.

Claims

1. A method for operating a wireless transmit/receive unit (WTRU) in a wireless communication system comprising a plurality of cells, the WTRU comprising a switched beam antenna for generating antenna beams including a plurality of directional beams and an omni-directional beam, the method comprising:

Using a selected antenna beam for exchanging data with a cell in an active set of cells;

receiving signals from cells not in the active set of cells using the selected antenna beam;

measuring the received signals from each cell not in the active set of cells for the selected antenna beam;

comparing the measured signals to an add pre-candidate set threshold, and adding the corresponding cells to a pre-candidate set of cells based upon the comparison;

ranking the cells in the pre-candidate set of cells based upon a level of their measured signals;

receiving signals from N of the top-ranked cells in the pre-candidate set of cells using the omni-directional beam and the selected antenna beam, with N being greater than or equal to 1;

measuring the received signals from each of the N cells for the omni-directional beam and the selected antenna beam;

comparing the measured signals to an add candidate set threshold, and moving the corresponding cells from the pre-candidate set of cells to the candidate set of cells based upon the comparison to the add candidate set threshold; and

sending a measurement report to the network.

2. A method according to claim 1 further comprising:

receiving signals from the cells in the candidate set of cells using the omni-directional beam;

measuring the received signals from each cell for the omni-directional beam; and

comparing the measured signals to an add active set threshold, and sending a measurement report to the network based upon the comparison to the add candidate set threshold.

3. A method according to claim 1 wherein the add candidate set threshold is greater than the add pre-candidate set threshold.

4. A method according to claim 1 wherein the add pre-candidate set threshold is set by the WTRU.

5. A method according to claim 1 wherein the selected antenna beam comprises a directional beam;

and further comprising dropping cells in the pre-candidate set of cells based upon;

receiving signals from the pre-candidate set of cells using the selected directional beam;

measuring the received signals from each cell for the selected directional beam;

comparing the measured signals to a drop pre-candidate set threshold; and

dropping the corresponding cells from the pre-candidate set of cells based upon the comparison to the drop pre-candidate set threshold.

6. A method according to claim 1 wherein the selected antenna beam comprises a directional beam;

and further comprising dropping cells in the candidate set of cells based upon;

receiving signals from cells in the candidate set of cells using the omni-directional beam and the selected directional beam;

measuring the received signals from each cell in the candidate set of cells for the omni-directional and the selected directional beam;

comparing the measured signals from each cell for the omni-directional beam to a drop candidate set threshold; and

dropping the corresponding cells from the candidate set of cells based upon the comparison to the drop candidate set threshold, and sending a measurement report to the network.

7. A method according to claim 6 further comprising adding the cells dropped from the candidate set of cells to the pre-candidate set of cells based upon a comparison of the measured signals from each dropped cell for the selected directional beam to the add pre-candidate threshold.

8. A method according to claim 1 wherein the selected antenna beam comprises a directional beam;

and further comprising;

receiving signals from cells in the active set of cells using the omni-directional beam and the selected directional beam;

measuring the received signals from each cell in the active set of cells for the omni-directional and the selected directional beam;

comparing the measured signals from each cell for the selected directional beam to a drop active set threshold and to the add candidate set threshold; and

sending a measurement report to the network for the corresponding cells from the active set of cells based upon the comparison to the drop active set threshold and the add candidate set threshold.

9. A method according to claim 1 wherein the selected antenna beam comprises a directional beam;

and further comprising;

receiving signals from cells in the active set of cells using the omni-directional beam and the selected directional beam;

measuring the received signals from each cell in the active set of cells for the omni-directional and the selected directional beam;

comparing the measured signals from each cell for the selected directional beam to a drop active set threshold, and comparing the measured signals from each cell for the omni-directional beam to each other; and

sending a measurement report to the network for the corresponding cells in the active set of cells based upon a comparison to the drop active set threshold, and based upon a comparison to a threshold corresponding to a level of the strongest measured signal for the omni-directional beam less a predetermined level.

10. A method according to claim 1 wherein the wireless communication system comprises a code division multiple access (CDMA) system.

11. A method according to claim 1 wherein the received signals being measured comprise a pilot signal.

12. A method according to claim 1 wherein the measuring comprises measuring at least one of a signal to interference ratio (SIR), a signal to noise ratio, and a signal strength of the received signals.

13. A method according to claim 1 further comprising sending a measurement report to the network when a measured signal from a cell in the active set of cells for the selected antenna beam falls below a threshold.

14. A method according to claim 1 wherein the selected antenna beam comprises a directional beam;

and wherein the measurement reports for cells in the active set of cells are sent to the network based upon;

receiving signals from cells in the active set of cells using the omni-directional beam and the selected directional beam;

measuring the received signals from each cell in the active set of cells for the omni-directional and the selected directional beam;

comparing the measured signals from each cell for the selected directional beam to a drop active set threshold, and comparing the measured signals from each cell for the omni-directional beam to each other; and

reporting to the network measurements of the corresponding cells in the active set of cells based upon a comparison to the drop active set threshold, and based upon a comparison to a threshold corresponding to a level of the strongest measured signal for the omni-directional beam less a predetermined level.

15. A method according to claim 1 wherein the selected antenna beam comprises a directional beam;

and further comprising;

receiving signals from cells in the active set of cells using the omni-directional beam and the selected directional beam;

measuring the received signals from each cell in the active set of cells for the omni-directional and the selected directional beam;

comparing the measured signals from each cell for the selected directional beam to the add pre-candidate set threshold; and

sending a measurement report to the network for the corresponding cells in the active set of cells based upon a comparison to the add pre-candidate set threshold if the add pre-candidate set threshold is less than a drop active set threshold.

16. A method according to claim 1 wherein the comparing further comprises comparing to a threshold, before sending the measurement report, with the threshold being based upon at least one of a condition that holds true for a predetermined number of measurements, and a percentage of measurements within a predetermined number of measurements.

17. A wireless communication system comprising:

an active set of cells;

a non-active set of cells; and

a wireless transmit/receive unit (WTRU) comprising

a switched beam antenna for generating antenna beams including a plurality of directional beams and an omni-directional beam, an antenna beam being selected for exchanging data with one or more cells in the active set of cells,

a transceiver connected to said switched beam antenna for receiving signals from cells-not in the active set of cells using the selected antenna beam,

a measuring unit connected to said transceiver for measuring the received signals from each cell not in the active set of cells for the selected antenna beam, and

a controller for comparing the measured signals to an add pre-candidate set threshold, and adding the corresponding cells to a pre-candidate set of cells based upon the comparison, and ranking the cells in the pre-candidate set of cells based upon a level of their measured signals,

said transceiver also receiving signals from N of the top-ranked cells in the pre-candidate set of cells using the omni-directional beam and the selected antenna beam, with N being greater than or equal to 1,

said measuring unit also measuring the received signals from each of the N cells for the omni-directional beam and the selected antenna beam, and

said controller also comparing the measured signals to an add candidate set threshold, and moving the corresponding cells from the pre-candidate set of cells to the candidate set of cells based upon the comparison to the add candidate set threshold, and sending a measurement report to the network.

18. A wireless communication system according to claim 17 wherein said transceiver receives signals from the cells in the candidate set of cells using the omni-directional beam;

wherein said measuring unit measures the received signals from each cell for the omni-directional beam, and wherein said controller compares the measured signals to an add active set threshold, and sends a measurement report to the network based upon the comparison to the add active set threshold.

19. A wireless communication system according to claim 17 wherein the add candidate set threshold is greater than the add pre-candidate set threshold.

20. A wireless communication system according to claim 17 wherein the add pre-candidate set threshold is set by the WTRU.

21. A wireless communication system according to claim 17 wherein the selected antenna beam comprises a directional beam;

and wherein cells are dropped from the pre-candidate set of cells based upon;

said transceiver receiving signals from the pre-candidate set of cells using the selected directional beam;

said measuring unit measuring the received signals from each cell for the selected directional beam; and

said controller comparing the measured signals to a drop pre-candidate set threshold, and dropping the corresponding cells from the pre-candidate set of cells based upon the comparison to the drop pre-candidate set threshold.

22. A wireless communication system according to claim 17 wherein the selected antenna beam comprises a directional beam;

and wherein cells are dropped from the candidate set of cells based upon;

said transceiver receiving signals from cells in the candidate set of cells using the omni-directional beam and the selected directional beam;

said measuring unit measuring the received signals from each cell in the candidate set of cells for the omni-directional and the selected directional beam; and

said controller comparing the measured signals from each cell for the omni-directional beam to a drop candidate set threshold, and dropping the corresponding cells from the candidate set of cells based upon the comparison to the drop candidate set threshold.

23. A wireless communication system according to claim 22 wherein the WTRU adds the cells dropped from the candidate set of cells to the pre-candidate set of cells based upon a comparison by said controller of the measured signals from each dropped cell for the selected directional beam to the add pre-candidate threshold.

24. A wireless communication system according to claim 17 wherein the selected antenna beam comprises a directional beam and wherein the measurement reports for cells in the active set of cells are sent to the network based upon:

said transceiver receiving signals from cells in the active set of cells using the omni-directional beam and the selected directional beam;

said measuring unit measuring the received signals from each cell in the active set of cells for the omni-directional and the selected directional beam; and

said controller comparing the measured signals from each cell for the selected directional beam to a drop active set threshold and to the add candidate set threshold, and sending a measurement report to the network based upon the comparison to the drop active set threshold and the add candidate set threshold.

25. A wireless communication system according to claim 17 wherein the selected antenna beam comprises a directional beam;

and wherein the measurement reports for cells in the active set of cells are sent to the network based upon;

said transceiver receiving signals from cells in the active set of cells using the omni-directional beam and the selected directional beam;

said measuring unit measuring the received signals from each cell in the active set of cells for the omni-directional and the selected directional beam;

said controller comparing the measured signals from each cell for the selected directional beam to a drop active set threshold, and comparing the measured signals from each cell for the omni-directional beam to each other, reporting to the network measurements of the corresponding cells in the active set of cells based upon a comparison to the drop active set threshold, and based upon a comparison to a threshold corresponding to a level of the strongest measured signal for the omni-directional beam less a predetermined level.

26. A wireless communication system according to claim 17 wherein the selected antenna beam comprises a directional beam;

and wherein the measurement reports for cells in the active set of cells are sent to the network based upon;

said transceiver receiving signals from cells in the active set of cells using the omni-directional beam and the selected directional beam;

said measurement unit measuring the received signals from each cell in the active set of cells for the omni-directional and the selected directional beam; and

said controller comparing the measured signals from each cell for the selected directional beam to the add pre-candidate set threshold, and sending a measurement report to the network for the corresponding cells in the active set of cells based upon a comparison to the add pre-candidate set threshold if the add pre-candidate set threshold is less than a drop active set threshold.

27. A wireless communication system according to claim 17 wherein the comparing further comprises comparing to a threshold, before sending the measurement report, with the threshold being based upon at least one of a condition that holds true for a predetermined number of measurements, and a percentage of measurements within a predetermined number of measurements.