Bandwidth efficient QAM on a TDM-FDM system for wireless communications

• US 6,856,652 B2
• Filed: 05/24/2001
• Issued: 02/15/2005
• Est. Priority Date: 11/11/1998
• Status: Expired due to Term

• Current Assignee: Benhov GmbH, LLC (Intellectual Ventures LLC)
• Original Assignee: Cyntrust Communications, Inc.
• Inventors: Kluesing, Alvin Dale, West, Randall J., McCarty, Robert Joseph Jr.
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US09/865,912
• Publication Number:
  US 20010031015A1
• Time in Patent Office: 1,363 Days
• Field of Search: 375/260, 375/261, 375/267, 375/295, 375/298, 375/299, 370/208, 370/209, 370/210, 370/437, 370/458, 370/395.41
• US Class Current: 375/260
• CPC Class Codes: H04L 27/36 Modulator circuits; Transmitter circuits
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26
• CPC Class Codes: H04W 52/362 Aspects of the step size
• CPC Class Codes: H04W 52/367 Power values between minimum and maximum limits, e.g. dynamic range

Abstract

Efficient usage of available spectrum is increased by logically dividing government licensed frequency channels into sub-channels, each of which can individually transmit a signal between a base unit and terminal. The sub-channels are each offset from the center of the frequency channel by a unique offset amount to avoid interference. Power control, sub-channel interference cancellation, and frequency control are employed to minimize the effects of out-of-band sub-channel signals on adjacent sub-channels. Any given sub-channel can be dynamically configured to transmit voice or data signals. Further spectral efficiency is realized using time division multiplexing on some or all of the sub-channels.

Claims

1. A method of accommodating pre-defined channels of differing bandwidths without substantial retrofitting of communication system components, each pre-defined channel having a center frequency, comprising:

when broad pre-defined channels are available, transmitting N independent communication signals to N mobile units over a single broad pre-defined channel, each independent communication signal being broadcast at a pre-defined offset from the center frequency of the broad pre-defined channel;

when only narrow pre-defined channels are available, each narrow pre-defined channel having 1/M bandwidth of the broad pre-defined channel, transmitting N/M independent signals to N/M mobile units over each of M narrow pre-defined channels, each of the N/M independent signals being broadcast at a pre-defined offset from the center frequency of the narrow pre-defined channels;

wherein the pre-defined offsets from the center frequency of the narrow pre-defined channels is a sub-set of the pre-defined offsets from the center frequency of the broad pre-defined channel.

2. The method of claim 1 wherein a mobile unit can be configured to accommodate a narrow pre-defined frequency channel by tuning the mobile unit to a new center frequency, but not changing the pre-defined offset from the center frequency.

3. The method of claim 1 wherein a mobile unit can be configured to accommodate a narrow pre-defined frequency by changing the pre-defined offset from the center frequency to which the mobile unit is tuned.

4. The method of claim 1 wherein N is four and M is two.

5. The method of claim 1 further comprising, time division multiplexing each sub-channel into two or more time slots.

6. The method of claim 1 wherein N is an integer multiple of M.

7. The method of claim 1 wherein a board pre-defined channel is 25 kHz.

8. The method of claim 7 wherein a narrow pre-defined channel is 6.24 kHz.

9. A radio system capable of accommodating pre-defined frequency channels of differing bandwidths, each pre-defined frequency channel having a center frequency, comprising:

a data source providing at least N independent communication signals;

a transmitter coupled to the data source and configured to transmit N independent communication signals to N mobile units over N sub-channels of a broad pre-defined frequency channel when available;

each of the N sub-channels having a frequency offset from the center frequency of the broad pre-defined frequency channel, but falling entirely within the bandwidth of the broad pre-defined frequency channel, and no two of the N sub-channels having the same frequency offset;

the transmitter being configured to transmit M independent signals to M mobile units over a each of a N/M narrow pre-defined frequency channels when a broad pre-defined frequency channel is unavailable, wherein N is an integer multiple of M;

each of the M sub-channels for each of the plurality of narrow pre-defined frequency channels having a frequency offset from the center frequency of the narrow pre-defined frequency channel, but falling entirely within the bandwidth of the narrow pre-defined frequency channel;

wherein the frequency offsets for the sub-channels of the narrow pre-defined frequency channels comprise a subset of the frequency offsets for the broad pre-defined frequency channel.

10. The radio system of claim 9 further comprising:

N mobile units, each mobile unit configured to receive one of the N independent communication signals by being tuned to a particular pre-defined frequency channel and a particular frequency offset.

11. The radio system of claim 10 wherein a mobile unit can be configured to accommodate a narrow pre-defined frequency channel by re-tuning either the center frequency or the offset frequency.

12. The radio system of claim 9 wherein each sub-channel is time division multiplexed.

13. The radio system of claim 9 wherein N is four and M is two.

14. The radio system of claim 9 wherein the offset frequencies comprise plus or minus 2.4 kHz and plus or minus 7.2 kHz.

15. The radio system of claim 9 wherein the pre-defined frequency channels are assigned by a governmental authority.

16. The radio system of claim 9 wherein the N/M narrow pre-defied frequency channels occupy contiguous bandwidth.

17. The radio system of claim 9 wherein the data source is a public telephone network.

18. The radio system of claim 11 wherein the mobile unit is configured via control signals broadcast by the base unit.