Method & apparatus for W-CDMA handoff searching

• US 20030039228A1
• Filed: 08/22/2001
• Published: 02/27/2003
• Est. Priority Date: 08/22/2001
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Rao, Subramanya P.N., Subrahmanya, Parvathanathan, Shiu, Da-Shan
• Granted Patent: US 6,744,747 B2
• Time in Patent Office: Days
• US Class Current: 370/331
• CPC Class Codes: H04B 1/7083 Cell search, e.g. using a three-step approach
• CPC Class Codes: H04B 2201/70701 featuring pilot assisted reception
• CPC Class Codes: H04B 2201/70702 Intercell-related aspects
• CPC Class Codes: H04W 36/00 Hand-off or reselection arrangements
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

Techniques for improved handoff searching in asynchronous systems, such as W-CDMA, are disclosed. In one aspect, a two-step search procedure is used when a list of neighbor codes is known. In the first step, a received signal is correlated with a slot timing code to locate on or more pilots and the slot boundaries associated therewith. In the second step, the received signal is correlated with each of the list of codes at the slot boundaries identified with pilots in the first step to identify the pilot code and the frame timing associated with each pilot. Various other aspects of the invention are also presented. These aspects have the benefit of decreasing search time, which translates to increased acquisition speed, higher quality signal transmission, increased data throughput, decreased power, and improved overall system capacity.

Claims

1. A method for searching comprising:

correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith; and

correlating the received signal with each of a list of codes for each of the pilots to identify the pilot code and the frame timing associated with each pilot.

2. The method of claim 1, wherein the step of correlating the incoming data stream with the slot timing code further comprises correlating the received signal with the slot timing code for a specified duration to calculate a received energy for each slot hypothesis.

3. The method of claim 2, further comprising selecting one or more slot hypotheses with the greatest received energy as the one or more located pilots.

4. The method of claim 2, wherein the slot code is a primary synchronization code (PSC).

5. The method of claim 1, wherein the list of codes is a neighbor list, received from a base station

6. The method of claim 1, wherein the step of correlating the received signal with the list of codes comprises:

performing a pilot test for each pilot, the pilot test comprising;

performing a code test for each code of the list of codes, the code test comprising;

performing a slot test for each slot corresponding to the pilot, the slot test comprising correlating the received signal with the code for a duration at an offset corresponding to the slot to generate an energy value.

7. The method of claim 6, further comprising comparing each energy value to a threshold to determine if the code corresponds to the pilot.

8. The method of claim 7, further comprising:

using the code corresponding to an energy which exceeds the threshold as a scrambling code for demodulation; and

using the slot boundary corresponding to the energy which exceeds the threshold as the frame boundary for the scrambling code.

9. The method of claim 6, wherein the slot test further comprises:

testing a window of offset hypotheses around the slot boundary, wherein for each offset hypothesis the received signal is correlated with the code for a duration to generate an energy value.

10. The method of claim 9, further comprising peak detecting the energy values corresponding to the offset hypotheses to locate one or more peaks.

11. The method of claim 10, further comprising comparing each of the peaks to a threshold to determine if the code corresponds to the pilot.

12. The method of claim 11, further comprising:

for each peak which exceeds the threshold, using the corresponding code as a scrambling code for demodulation; and

for each peak which exceeds the threshold, using the corresponding slot boundary as the frame boundary for the scrambling code.

13. The method of claim 11, further comprising terminating the step of testing the window of offset hypotheses around the slot when a pre-determined number of peaks are detected above the threshold.

14. The method of claim 11, further comprising terminating the code test for the pilot when one or more peaks are detected above the threshold during the slot test.

15. The method of claim 11, further comprising terminating the pilot test of a pilot when one or more peaks are detected above the threshold during the code test.

16. The method of claim 11, further comprising removing the code from the list of codes for subsequent pilot tests when one or more peaks are detected above the threshold during the code test.

17. A searcher for handoff searching, comprising:

a first correlator for correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith; and

a second correlator for correlating the received signal with each of a list of codes for each of the pilots to identify the pilot code and the frame timing associated with each pilot.

18. The searcher of claim 17, wherein the first correlator and the second correlator are the same correlator.

19. A subscriber unit, for use in a CDMA system, including a searcher for handoff searching, comprising:

correlator means for correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith; and

correlator means for correlating the received signal with each of a list of codes for each of the pilots to identify the pilot code and the frame timing associated with each pilot.

20. A W-CDMA system including a searcher for handoff searching, comprising:

correlator means for correlating a received signal with a slot timing code to locate one or more pilots and slot boundaries associated therewith; and

correlator means for correlating the received signal with each of a list of codes for each of the pilots to identify the pilot code and the frame timing associated with each pilot.