Method and apparatus for identifying an orthogonal frequency division multiplexing (OFDM) terrestrial repeater using inactive sub-carriers

• US 20040151255A1
• Filed: 01/23/2004
• Published: 08/05/2004
• Est. Priority Date: 09/17/1999
• Status: Active Grant

• Current Assignee: RPX Corporation
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Zheng, Dunmin, Sayeed, Zulfiquar, Riazi, Habib
• Granted Patent: US 7,359,312 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04H 60/54 where broadcast information is generated
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems

Abstract

A terrestrial repeater is disclosed for use in a satellite transmission system that may also include a plurality of satellites. The terrestrial repeaters are implemented as OFDM transmitters to minimize the channel impairments caused by multi-path propagation. The OFDM terrestrial repeaters differentially encode the transmitted signal over frequency, as opposed to time, in order to avoid channel phase distortion. The OFDM receiver allocates two unmodulated sub-carriers as pilot bins and thereby provides two sub-carriers as a reference within each OFDM symbol. At the OFDM receiver, the two unmodulated pilot bins contain no phase information and provide a reference for the differential demodulation performed by the OFDM receiver. The OFDM transmitter operates in two modes, namely, a normal mode and a transmitter identifier information (TII) mode. The TII mode contains all of the functions of the normal mode, and also transmits a repeater identification signal with the customer data, using the inactive OFDM sub-carriers (bins). In a normal mode, the OFDM transmitter optionally fills unused (inactive) sub-carriers with zeroes and in a TII mode, the OFDM transmitter uses at least some of the unused (inactive) sub-carriers to transmit the transmitter identifier information (TII). The predefined TII value is mapped onto a set of complex symbols. The TII signal facilitates the receiver test equipment in associating the received signal with the terrestrial repeater(s) that generate the TII signal.

Claims

1. A method of transmitting an identifying signal in an orthogonal frequency division multiplexing system, comprising the steps of:

modulating said signal;

transforming said modulated signal to create an OFDM signal having a plurality of sub-carriers; and

transmitting an identifying signal on inactive sub-carriers, wherein said identifying signal identifies a transmitter.

2. The method of claim 1, wherein said modulation step further comprises the step of differentially modulating said signal in the frequency domain.

3. The method of claim 1, wherein said inactive sub-carriers will be modulated in accordance with a predefined transmitter identifier information value.

4. The method of claim 1, wherein said inactive sub-carriers carrying said identifying signal are transmitted at a reduced power.

5. The method of claim 1, further comprising the step of mapping said identifying value onto a set of complex symbols.

6. The method of claim 1, wherein said inactive sub-carriers carrying said identifying signal are transmitted with each OFDM symbol.

7. The method of claim 1, wherein said transforming step implements a Fast Fourier Transform.

8. The method of claim 1, wherein said transforming step implements an orthogonal transform.

9. An orthogonal frequency division multiplexing transmitter for transmitting an OFDM signal, comprising:

an encoder for modulating said OFDM signal;

a transformer for creating said OFDM signal having a plurality of sub-carriers; and

means for inserting an identifying signal on inactive sub-carriers, wherein said identifying signal identifies a transmitter.

10. The transmitter of claim 9, wherein said encoder differentially modulates said signal in the frequency domain.

11. The transmitter of claim 9, wherein said inactive sub-carriers will be modulated in accordance with a predefined transmitter identifier information value.

12. The transmitter of claim 9, wherein said inactive sub-carriers carrying said identifying signal are transmitted at a reduced power.

13. The transmitter of claim 9, wherein said identifying value is mapped onto a set of complex symbols.

14. The transmitter of claim 9, wherein said inactive sub-carriers carrying said identifying signal are transmitted with each OFDM symbol.

15. The transmitter of claim 9, wherein said transformer a Fast Fourier Transform.

16. The transmitter of claim 9, wherein said transformer implements an orthogonal transform.

17. A method of receiving an identifying signal in an orthogonal frequency division multiplexing system, comprising the steps of:

transforming said received signal to recover an OFDM signal in the frequency domain having a plurality of sub-carriers;

decoding said OFDM signal; and

processing an identifying signal received on inactive sub-carriers, wherein said identifying signal identifies a transmitter.

18. The method of claim 17, wherein said decoding step further comprises the step of differentially demodulating said signal in the frequency domain.

19. The method of claim 17, wherein said inactive sub-carriers will be demodulated in accordance with a predefined transmitter identifier information value.

20. The method of claim 17, wherein said inactive sub-carriers carrying said identifying signal are received at a reduced power.

21. The method of claim 17, wherein said inactive sub-carriers carrying said identifying signal are received with each OFDM symbol.

22. The method of claim 17, wherein said transforming step implements a Fast Fourier Transform.

23. The method of claim 17, wherein said transforming step implements an orthogonal transform.

24. An orthogonal frequency division multiplexing receiver for receiving an OFDM signal, comprising:

a transformer for transforming said received signal to recover an OFDM signal in the frequency domain having a plurality of sub-carriers;

a decoder for demodulating said OFDM signal; and

means for processing an identifying signal received on inactive sub-carriers, wherein said identifying signal identifies a transmitter.

25. The receiver of claim 24, wherein said decoder differentially demodulates said signal in the frequency domain.

26. The receiver of claim 24, wherein said inactive sub-carriers will be demodulated in accordance with a predefined transmitter identifier information value.

27. The receiver of claim 24, wherein said inactive sub-carriers carrying said identifying signal are received at a reduced power.

28. The receiver of claim 24, wherein said inactive sub-carriers carrying said identifying signal are received with each OFDM symbol.

29. The receiver of claim 24, wherein said transformer implements a Fast Fourier Transform.

30. The receiver of claim 24, wherein said transformer implements an orthogonal transform.