Methods and apparatus for selecting between multiple carriers based on signal energy measurements

• US 20050233746A1
• Filed: 10/14/2004
• Published: 10/20/2005
• Est. Priority Date: 04/15/2004
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Li, Junyi, Lane, Frank A.
• Granted Patent: US 7,453,912 B2
• Time in Patent Office: Days
• US Class Current: 455/436
• CPC Class Codes: H04B 1/005 adapting radio receivers, transmitters andtransceivers for operation on two or more bands, i.e. frequency ranges
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/406 with more than one transmission mode, e.g. analog and digital modes
• CPC Class Codes: H04B 17/327 Received signal code power [RSCP]
• CPC Class Codes: H04B 17/382 for resource allocation, admission control or handover
• CPC Class Codes: H04L 1/20 using signal quality detector
• CPC Class Codes: H04L 27/261 Details of reference signals
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 36/302 due to low signal strength
• CPC Class Codes: H04W 48/08 Access restriction or access information delivery, e.g. discovery data delivery signalling during connection H04W76/00
• CPC Class Codes: H04W 72/02 Selection of wireless resources by user or terminal
• CPC Class Codes: H04W 72/0453 Resources in frequency domain, e.g. a carrier in FDMA

Abstract

Carrier frequency selection and handoff initiation methods in wireless communications systems employing multiple carrier frequencies are described. Although the receiver is tuned to a single band, based on the relative energy of one or more beacon signal components corresponding to the currently used carrier and one or more beacon signal components corresponding to an alternative carrier, a carrier selection and a handoff determination is made. Mobile nodes can use a single RF chain with a controllable RF filter to receive and process a signal within a first selected carrier band including components from different transmitters, e.g., a first signal component identified with the first currently selected band and a second signal component identified with a second alternative band. The signal components, e.g., beacon signal components from different transmitters may be obtained from a signal which corresponds to multiple symbol transmission time periods. Separate signal energy measurements are performed on the first and second signal components. The signal component energy is compared, and a determination is made as to whether a handoff should be initiated.

Claims

1. A communications method for use in a wireless terminal in an OFDM communication system, the method comprising:

receiving a first signal in a first frequency band, said first signal including a plurality of signal tones, each signal tone corresponding to a different frequency;

performing a time to frequency conversion on said received signal to generate a set of signal components corresponding to different signal tones in the first frequency band;

determining the energy of each of a plurality of different signal components which correspond to different signal tones within said first frequency band to generate a set of per signal tone energy values, each per signal tone energy value corresponding to a different frequency;

detecting, from the per tone energy value of said signal components, a signal component corresponding to a beacon signal; and

determining, based on the frequency of the signal component detected to correspond to a beacon signal, a carrier frequency corresponding to said beacon signal.

2. The communications method of claim 1,

wherein said carrier frequency corresponding to said beacon signal is different from a current carrier frequency used to communicate with a current network point of attachment;

and

wherein said carrier frequency corresponding to said beacon signal is located in a second frequency band which is used, to transmit user data, by a network point of attachment which transmitted said detected beacon signal component, said detected beacon signal component being located outside said second frequency band.

3. The method of claim 1, further comprising:

making a handoff decision as a function of the amount of energy included in at least one beacon signal component received from the current network point of attachment and the amount of energy included in the detected beacon signal component, said detected beacon signal component having been transmitted by a network point of attachment which is different from the current point of network attachment.

4. The method of claim 1, wherein detecting from the per tone signal energy value of said signal components a signal component correspond to a beacon signal includes:

comparing the determined energy of each of said plurality of different signal components to a threshold energy level which is greater than the average per tone signal energy of said received signal.

5. The method of claim 4, wherein said threshold energy level is at least N times the average per tone signal energy of said received first signal in said first frequency band, where N is a positive value greater than 5.

6. The method of claim 4, wherein said threshold energy level is at least N times the average per tone signal energy of said received first signal in said first frequency band, where N is a positive value greater than 20.

7. The method of claim 4, wherein said threshold energy level is at least N times the average per tone signal energy of said received first signal in said first frequency band, where N is a positive value greater than 99.

8. The method of claim 4, wherein said threshold energy level is at least N times the average per tone signal energy of said received first signal in said first frequency band, where N is a positive value greater than 150.

9. The communications method of claim 4, wherein said step of performing a time to frequency conversion is performed using one of a discrete Fourier transform (DFT) and a fast Fourier transform (FFT).

10. The method of claim 6, further comprising:

in response to detecting the presence of a signal component corresponding to a beacon signal determining at least one of a sector ID and a cell ID, based on the frequency of the signal component exceeding said threshold.

11. The method of claim 10, wherein said received symbol is received during a first period of time which is a symbol transmission time period.

12. The method of claim 11, further comprising the step of:

detecting OFDM symbols included in said first received signal on tones which do not have energy levels exceeding said threshold.

13. The method of claim 4, wherein said threshold is a dynamically generated threshold, the method further comprising:

generating said threshold from at least one received signal.

14. The method of claim 13, wherein said at least one received signal includes a plurality of tones, the step of generating said threshold includes:

determining the per tone energy of said at least one received signal.

15. The method of claim 14, where said per tone energy corresponds to the total energy of said at least one received signal divided by the number of different tones included in said at least one received signal, each tone corresponding to a different frequency.

16. The method of claim 13, wherein said at least one received signal is a signal received in an OFDM symbol transmission time preceding said first time period in which said first signal is received.

17. The method of claim 13, wherein said at least one received signal is said first received signal.

18. The method of claim 4, further comprising:

storing information on the determined energy and frequency of a first signal component in said received signal which was determined to have a signal component energy level exceeding said threshold energy level.

19. The method of claim 18, wherein said first signal component is received from a base station sector transmitter corresponding to a base station sector in which said wireless terminal performing said receiving step is located.

20. The method of claim 18, wherein said first signal is received in a first period of time, the method further comprising:

receiving a second signal in a second period of time, said second signal including a plurality of signal tones, each signal tone in said second signal corresponding to a different frequency;

performing a time to frequency conversion on said received second signal to generate a second set of signal components corresponding to different signal tones in the first frequency band;

determining the energy of each of a plurality of different signal components in said second set of signal components to generate a second set of per signal tone energy values, each per signal tone energy value in said second set of per signal tone energy values corresponding to a different frequency;

comparing the determined energy of each of said plurality of different signal components to said threshed energy level; and

generating a second indicator signal indicating the presence of a second beacon signal when said comparing step determines that said threshold energy level is exceeded.

21. The method of claim 19, further comprising:

determining which base station sector to use as a network point of attachment based on a comparison of the determined energy of the first signal component and the determined energy of the signal component in said second signal determined have an energy level exceeding said threshold energy level.

22. The method of claim 1, wherein the current network attachment point is a first sector of a cell and wherein said detected beacon signal is transmitted by a different sector of said cell.

23. The method of claim 1, wherein the current network attachment point is a first sector of a cell and wherein said detected beacon signal is transmitted by a different sector of a different cell.

24. The method of claim 1, wherein the current network attachment point is a first module corresponding to a first carrier used in a first sector of a cell and wherein said detected beacon signal is transmitted by a second module corresponding to a second carrier used in said first sector of said cell, said second module serving as a second network attachment point in said first sector of said cell.

25. A wireless terminal for use in a communication system, the wireless terminal comprising:

means for receiving a signal in a first period of time, said signal including a plurality of signal tones, each signal tone corresponding to a different frequency;

means for performing a time to frequency conversion on said received signal to generate a set of signal components corresponding to different signal tones in a first frequency band;

means for determining the energy of each of a plurality of different signal components which correspond to different frequencies within said first frequency band to generate a set of per signal tone energy values, each per signal tone energy value corresponding to a different frequency;

means for comparing the determined energy of each of said plurality of different signal components to a threshed energy level which is greater than the average per signal tone energy of said received signal to detect a signal component corresponding to a beacon signal; and

means for determining if a handoff should be initiated to a network attachment point which transmitted a detected beacon signal and which uses a carrier frequency to transmit user data that is different from a carrier frequency in use by said wireless terminal to communicate with a current point of network attachment.

26. The wireless terminal of claim 25, wherein said threshold energy level is at least N times the average per signal tone energy of said received signal in said first frequency band, where N is a positive value greater than 5.

27. The wireless terminal of claim 25, wherein said threshold energy level is at least N times the average signal energy of said received signal in said first frequency band, where N is a positive value greater than 150.

28. The wireless terminal of claim 25, wherein said means for performing a time to frequency conversion is performed using one of a discrete Fourier transform (DFT) and a fast Fourier transform (FFT).

29. The wireless terminal of claim 28, further comprising:

means for determining at least one of a sector ID and a cell ID based on the frequency of the signal component exceeding said threshold.

30. The wireless terminal of claim 29, wherein said first period of time is an OFDM symbol transmission time period.

31. The wireless terminal of claim 30, further comprising:

a symbol detection module detecting symbols included in said received signal on tones which do not have energy levels exceeding said threshold.

32. The wireless terminal of claim 25, wherein said threshold is a dynamically generated threshold, the wireless terminal comprising:

a threshold generation module coupled to said means for performing a time to frequency conversion.

33. The wireless terminal of claim 25, further comprising:

means for storing information on the determined energy and frequency of a first signal component received during said first period of time which was determined to have a signal component energy level exceeding said threshold energy level.

34. The wireless terminal of claim 33, wherein said first signal component is received from a base station sector transmitter corresponding to a base station sector in which said wireless terminal performing said receiving step is located.

35. The wireless terminal of claim 33,

wherein the majority of the energy included in said first signal component is received from a base station sector corresponding to a base station sector located adjacent the base station sector in which the wireless terminal receiving the first signal component is located.

36. The wireless terminal of claim 33, further comprising:

means for receiving a second signal in a second period of time, said second signal including a plurality of signal tones, each signal tone in said second signal corresponding to a different frequency;

means for performing a time to frequency conversion on said received second signal to generate a second set of signal components corresponding to different signal tones in the first frequency band;

means for determining the energy of each of a plurality of different signal components in said second set of signal components to generate a second set of per signal tone energy values, each per signal tone energy value in said second set of per signal tone energy values corresponding to a different frequency;

means for comparing the determined energy of each of said plurality of different signal components to said threshed energy level; and

means for determining if a handoff should be initiated.

37. The wireless terminal of claim 34, further comprising:

means for determining which base station sector to use as a network point of attachment based on a comparison of the determined energy of the first signal component and the determined energy of the signal component in said second signal determined have an energy level exceeding said threshold energy level.