Signal combining scheme for wireless transmission systems having multiple modulation schemes

• US 6,580,705 B1
• Filed: 10/28/1999
• Issued: 06/17/2003
• Est. Priority Date: 10/28/1999
• Status: Expired due to Term

• Current Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Zheng, Dunmin, Sayeed, Zulfiquar, Riazi, Habib
• Primary Examiner(s): Nguyen, Lee
• Assistant Examiner(s): LE, DANH C
• Application Number:
  US09/428,732
• Time in Patent Office: 1,328 Days
• Field of Search: 370/209, 370/204, 370/208, 370/329, 370/330, 370/350, 370/344, 455/101, 455/102, 455/103, 375/130
• US Class Current: 370/347
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

In a wireless transmission system that transmits the same information in parallel using two or more different types of modulation schemes, such as a satellite-based digital audio transmission system transmitting two TDM signals and a single OFDM signal, a receiver processes the differently modulated signals to generate separate demodulated signals that are then combined to form a single combined signal for further processing (e.g., decoding). In one embodiment, the receiver applies a maximal ratio combining (MRC) technique to generate a single optimal ratio combined signal from the differently modulated signals. By combining the differently modulated signals using an MRC technique, the adverse affects of noise related to inter-symbol interference in the individual signals can be reduced and the complexity of hardware in the receiver can be reduced.

Claims

1. A transmitter, comprising:

(a) an encoder to add redundancy to a data sequence;

(b) an interleaver connected to the encoder to output encoded symbols as interleaved symbols in data frames;

(c) an inserter connected to the interleaver to insert synch bits into data frames to generate synchronized data, of which copies of the synchronized data undergo further processing;

(d) a first modulator for modulating a first copy of the synchronized data to generate a signal having a first modulation scheme; and

(e) a second modulator for modulating a second copy of the synchronized data to generate a signal having a second modulation scheme.

2. The transmitter of claim 1, wherein:

the first modulator is a DQSPK modulator and the first modulation scheme is OFDM.

3. The transmitter of claim 1, wherein:

the second modulator is a QSPK modulator and the second modulation scheme is TDM.

4. The transmitter of claim 1, further comprising a third modulator for modulating a third copy of the synchronized data to a generate a time-delayed signal having a third modulation scheme.

5. The transmitter of claim 4, wherein:

the third modulator is a DQSPK modulator and the third modulation scheme is TDM, wherein the time-delayed signal is delayed by a delay buffer configured with the third modulator to a known delay value.

6. The transmitter of claim 1, wherein:

the first modulator is adapted to generate an OFDM signal; and

the second modulator is adapted to generate a TDM signal.

7. The transmitter of claim 6, wherein:

the first modulator performs DQPSK modulation followed by a differential modulation over frequency; and

the second modulator performs QPSK modulation.

8. The transmitter of claim 1, further comprising a third modulator for modulating a third copy of the synchronized data to a generate a signal having a third modulation scheme.

9. The transmitter of claim 8, wherein:

the first modulator is adapted to generate an OFDM signal;

the second modulator is adapted to generate a first TDM signal;

the third modulator is adapted to generate a second TDM signal.

10. The transmitter of claim 9, wherein the OFDM signal and the second TDM signal are time-delayed relative to the first TDM signal.

11. The transmitter of claim 10, wherein:

the first modulator comprises a delay buffer followed by a DQPSK modulator followed by a frequency interleaver and difference modulator, followed by an inverse fast Fourier transform (IFFT), followed by a guard interval block;

the second modulator comprises a QPSK modulator followed by an equalizer training sequence inserter followed by an intermediate frequency (IF) modulator; and

the third modulator comprises a delay buffer followed by a QPSK modulator followed by an equalizer training sequence inserter followed by an IF modulator.

12. The transmitter of claim 9, wherein:

the first modulator performs DQPSK modulation followed by a differential modulation over frequency;

the second modulator performs QPSK modulation; and

the third modulator performs QPSK modulation.

13. A transmitter, comprising:

(a) an encoder adapted to encode input data;

(b) an interleaver adapted to generate interleaved data from encoded data generated by the encoder;

(c) an inserter adapted to insert synch bits into the interleaved data to generate synchronized data;

(d) a first modulator adapted to modulate a first copy of the synchronized data using a first modulation scheme to generate a first modulated signal; and

(e) a second modulator adapted to modulate a second copy of the synchronized data using a second modulation scheme to generate a second modulated signal.

14. The transmitter of claim 13, wherein:

the first modulator is adapted to generate an OFDM signal; and

the second modulator is adapted to generate a TDM signal.

15. The transmitter of claim 14, wherein:

the first modulator performs DQPSK modulation followed by a differential modulation over frequency; and

the second modulator performs QPSK modulation.

16. The transmitter of claim 13, further comprising a third modulator for modulating a third copy of the synchronized data to a generate a signal having a third modulation scheme.

17. The transmitter of claim 16, wherein:

the first modulator is adapted to generate an OFDM signal;

the second modulator is adapted to generate a first TDM signal;

the third modulator is adapted to generate a second TDM signal.

18. The transmitter of claim 17, wherein the OFDM signal and the second TDM signal are time-delayed relative to the first TDM signal.

19. The transmitter of claim 18, wherein:

the first modulator comprises a delay buffer followed by a DQPSK modulator followed by a frequency interleaver and difference modulator, followed by an inverse fast Fourier transform (IFFT), followed by a guard interval block;

the second modulator comprises a QPSK modulator followed by an equalizer training sequence inserter followed by an intermediate frequency (IF) modulator; and

the third modulator comprises a delay buffer followed by a QPSK modulator followed by an equalizer training sequence inserter followed by an IF modulator.

20. The transmitter of claim 17, wherein:

the first modulator performs DQPSK modulation followed by a differential modulation over frequency;

the second modulator performs QPSK modulation; and

the third modulator performs QPSK modulation.