Methods for generating and transmitting frequency hopped signals

• US 20050025220A1
• Filed: 07/08/2003
• Published: 02/03/2005
• Est. Priority Date: 07/08/2003
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Laroia, Rajiv, Li, Junyi
• Granted Patent: US 7,639,728 B2
• Time in Patent Office: Days
• US Class Current: 375/132
• CPC Class Codes: H04B 1/7136 Arrangements for generation of hop frequencies, e.g. using a bank of frequency sources, using continuous tuning or using a transform
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

Methods and apparatus for generating and transmitting frequency division multiplexed signals are described. The methods are well suited for use where a device uses a small subset, M, of a larger set of N subcarrier frequencies at any given time. Each transmitted FDM signal is generated by combining a plurality of individual analog subcarrier signals whose frequency may change, e.g., be hopped as a function of time. Each generated analog subcarrier signal is amplified, e.g., power amplified, and filtered prior to being combined with other analog subcarrier signals. Filters are used to compensate for or correct signal distortions and/or reduce interference between subcarriers. Fixed frequency filters are used in an exemplary frequency hopping OFDM system. In another embodiment, the filters are programmable and change, e.g., in terms of center frequency, to match the selected subcarrier frequency as frequency hopping occurs. The bandwidth of the programmable filters may remain constant.

Claims

1. A frequency hopping communications device for transmitting signals on a plurality of M subcarrier signals in parallel, each of said M subcarrier signals corresponding to a different one of M subcarrier signal frequencies, said M subcarrier signal frequencies being a subset of N subcarrier frequencies on which said communications device may transmit signals over time, where M<

N, said frequency hopping communications device including;

a frequency control circuit for controlling which of the N subcarrier frequencies are used by said device for the transmission of signals;

a plurality of M separate subcarrier signals paths operating in parallel, each of the M subcarrier signal paths including a programmable signal generator coupled to said frequency control circuit, a power amplification circuit and a filter circuit, said programmable signal generator for generating a subcarrier signal having a subcarrier frequency corresponding to said subcarrier signal path to which said signal generator corresponds; and

a combining circuit for combining analog subcarrier signals corresponding to different subcarrier signal paths prior to transmission.

2. The device of claim 1, wherein each of the M signal filter circuits, that each correspond to a different one of said M signal paths, is a fixed filter, at least one of the M fixed filters having a passband bandwidth at least equal to Y times the average frequency spacing between the N frequencies that said device can use as the N subcarrier frequencies, where Y is a positive number greater than 1.

3. The method of claim 2, wherein Y≧

N divided by M.

4. The method of claim 2, wherein Y is at least as large as N.

5. The method of claim 2, wherein each of said M signal filter circuits are identical fixed filters each having a passband bandwidth covering the full set of N subcarrier signal frequencies which may be used by said device.

6. The method of claim 5, wherein the M subcarrier signals are OFDM subcarrier signals and where the N subcarrier frequencies are evenly spaced frequencies.

7. The device of claim 2, wherein the fixed filter included on each of said M signal paths is positioned in series with said corresponding power amplification circuit either before or after the corresponding power amplification circuit.

8. The device of claim 7,

wherein the programmable signal generator included in each subcarrier signal path generates an analog subcarrier signal;

and

wherein said power amplification circuit and said filter circuit included in each subcarrier signal path are analog circuits.

9. The device of claim 1, wherein each of the M signal filter circuits, that each correspond to a different one of said M signal paths, is a programmable filter.

10. The device of claim 9, wherein each of the M programmable filters has a passband corresponding to the subcarrier signal frequency of the subcarrier signal generated by the programmable signal generator circuit included on the same subcarrier signal path as the programmable filter.

11. The device of claim 10, wherein the programmable filters have a passband which has a bandwidth sufficient to pass said subcarrier signal but reject the nearest neighboring one, in frequency, of said N subcarrier signals.

12. The device of claim 9, wherein said device further transmits information using at least one additional preselected subcarrier frequency, the device further comprising:

an additional subcarrier signal path including an amplifier and fixed filter for amplifying and filtering a subcarrier signal corresponding to said additional preselected subcarrier frequency.

13. The device of claim 12, where said additional subcarrier frequency corresponds to a control channel used to transmit control information.

14. A frequency hopping communication method for use in a communications system wherein a device can transmit information using M subcarrier signals at a time, each of the M subcarrier signals corresponding to a different subcarrier frequency, where M is less than N and where N is the total number of different subcarrier frequencies said device can use over time, the method comprising:

i) operating M programmable signal generators to generate said M subcarrier signals;

ii) separately processing each of the M subcarrier signals to produce M processed subcarrier signals, the processing of each of said M subcarrier signals including a amplification operation and a filtering operation, said separate processing thus including M separate filtering operations; and

iii) combining the M processed subcarrier signals to generate a frequency division multiplexed transmission signal;

iv) controlling at least one of said M programmable signal generators to change the frequency of the subcarrier signal generated by said at least one programmable signal generator; and

v) repeating steps (i), (ii), and (iii).

15. The method of claim 14, wherein said M subcarrier signals are analog signals and wherein said filtering operation is an analog filtering operation.

16. The method of claim 14, wherein said M separate filtering operations are performed using M separate fixed filters, at least one of the M fixed filters having a bandwidth at least equal to Y times the average frequency spacing between the N frequencies that said device can use as the N subcarrier frequencies, where Y is a positive number greater than 1.

17. The method of claim 16, wherein Y≧

N divided by M.

18. The method of claim 16, wherein Y is equal to or greater than N.

19. The method of claim 15, wherein said M separate filtering operations are performed using identical fixed filters each having a bandwidth covering the full set of N subcarrier signal frequencies which may be used by said device.

20. The method of claim 19, wherein the N subcarrier signals are OFDM subcarrier signals.

21. The method of claim 14, wherein said M separate filtering operations are performed using M separate programmable filters, the frequency of each of each of the M programmable filters corresponding to the frequency of the subcarrier signal being filtered.

22. The method of claim 14, further comprising:

changing the amount of power amplification performed on one of the M subcarrier signals when the frequency of said subcarrier signal is changed.

23. The method of claim 16, wherein controlling at least one of said M programmable signal generators to change the frequency of the subcarrier signal includes:

operating said M programmable generators to switch from generating a first set of M subcarrier signals corresponding to a first set of M uniformly spaced subcarrier frequencies to generating a second set of M subcarrier signals corresponding to a second set of M uniformly spaced subcarrier frequencies, a first subcarrier frequency in said first set of M subcarrier frequencies being separated from a first subcarrier frequency in said second set of M subcarrier frequencies by a frequency spacing that is less than Y times the frequency spacing between subcarrier signals in said first and second sets of M subcarrier signals.