Method and apparatus for mobile platform reception and synchronization in direct digital satellite broadcast system

• US 6,956,814 B1
• Filed: 08/18/2000
• Issued: 10/18/2005
• Est. Priority Date: 02/29/2000
• Status: Expired due to Fees

• Current Assignee: WorldSpace Systems Corp. (WorldSpace, Inc.)
• Original Assignee: Worldspace, LLC
• Inventors: Campanella, S. Joseph
• Primary Examiner(s): HSU, ALPUS
• Application Number:
  US09/640,686
• Time in Patent Office: 1,887 Days
• Field of Search: 370/204, 370/210, 370312-314, 370/316, 370/319, 370/321, 370/324, 370/326, 370/350, 370465-467, 370/503, 370/516, 375/260, 375/267, 375/346, 375/347, 375/362, 375/371, 455/436, 455/12.1, 455/13.2, 455/23, 455/61, 455/63.1, 455/65
• US Class Current: 370/210
• CPC Class Codes: H04B 7/18534 for enhancing link reliablility, e.g. satellites diversity
• CPC Class Codes: H04J 3/0602 Systems characterised by the synchronising information used
• CPC Class Codes: H04L 27/2602 Signal structure

Abstract

A satellite system employing time diversity and a single frequency network of terrestrial re-radiation stations is provided wherein each terrestrial re-radiation station inserts a delay into a terrestrial signal. The delay allows the time of arrival of the early time diversity signal at the center of terrestrial coverage to coincide with the arrival of the corresponding late time diversity signal, thereby improving hand-off between terrestrial and satellite signals at a receiver. The delay also adjusts for distance differences between each terrestrial re-radiation station and the satellite and between each station and the center of the terrestrial coverage region. This adjustment optimizes the TDM-MCM reception by synchronizing at the center of the SFN the phase of the MCM signals re-radiated from the re-radiating stations of the SFN. The delay also compensates for the processing delay encountered when converting a satellite LOS TDM stream into a multicarrier modulated stream for transporting the satellite LOS TDM stream to user receivers and for the diversity delay between the early and late signals.

Claims

1. A method of synchronizing a selected number of time division multiplexed or TDM symbols in a TDM data stream to an equal number of the subcarriers of a time division multiplexed/multicarrier modulated or TDM-MCM symbol in a TDM-MCM waveform comprising the steps of:

locating one of a master frame preamble (MFP) code and a distributed synchronization sequence in said TDM data stream, said TDM data stream having at least one TDM frame comprising said one of a MFP code and a distributed synchronization sequence and a plurality of said symbols, said one of a MFP code and a distributed synchronization sequence being useful to locate said TDM frame within said TDM data stream;

generating an array using said symbols in said TDM frame, said array comprising a first number of columns and a second number of rows; and

generating TDM-MCM symbols corresponding in number to said first number using an Inverse Fast Fourier Transform (IFFT) with said array, each of said TDM- MCM symbols having said second number of said subcarriers for respective ones of said TDM symbols in corresponding said rows, said first number of said TDM-MCM symbols corresponding to a TDM-MCM symbol frame.

2. A method as claimed in claim 1, wherein said generating step comprises the step of filling said array by providing the earliest arriving of TDM symbols in said TDM frame into the earliest generated one of said rows of said array, and continuing to sequentially fill said rows until the last of said rows is filled with the last of said TDM symbols in said TDM frame.

3. A method as claimed in claim 1, wherein said TDM data stream comprises a plurality of TDM frames, said TDM-MCM symbol frame having essentially the same duration as said TDM frame.

4. A method as claimed in claim 1, wherein said generating step comprises the step of synchronizing said TDM-MCM symbols in said TDM-MCM symbol frame to within a fraction of one of said symbols in said TDM data stream.

5. A method as claimed in claim 4, wherein the number of said TDM-MCM symbols in said TDM-MCM symbol frame is an integer number.

6. A method as claimed in claim 1, further comprising the step of providing each said TDM-MCM symbol in said TDM-MCM frame with a guard interval, the TDM-MCM symbol period corresponding to said second number divided by the number of said TDM symbols per second, said guard interval being less than said TDM-MCM symbol period.

7. A method as claimed in claim 1, further comprising the step of providing each said TDM-MCM symbol frame in said TDM-MCM waveform with a synchronization word.

8. A method as claimed in claim 1, further comprising the steps of:

providing each said TDM-MCM symbol in said TDM-MCM frame with a guard interval, the TDM-MCM symbol period corresponding to said second number divided by the number of said TDM symbols per second, said guard interval being less than said TDM-MCM symbol period;

providing each said TDM-MCM symbol frame in said TDM-MCM waveform with a synchronization word; and

compressing each said MCM-TDM symbol to compensate for the insertion of said guard interval and said synchronization word in each said TDM-MCM symbol frame such that said TDM-MCM symbols having said guard interval and a time allocation corresponding to said synchronization word for the corresponding said TDM-MCM frame occupy one TDM frame period.

9. A method as claimed in claim 1, wherein said IFFT employs a number of coefficients that is greater than said second number of said symbols.

10. A method as claimed in claim 1, wherein said TDM data stream comprises a plurality of TDM frames, said generating step further comprising the step of assigning said symbols in respective said TDM frames in said TDM data stream to said subcarriers of said TDM-MCM symbols in corresponding said TDM- MCM frames.

11. An apparatus for use at a terrestrial re-radiation station comprising:

a receiving device for receiving a time division multiplexed or TDM data stream comprising symbols, each of said symbols corresponding to a selected number of bits in said data stream; and

a processing device connected to said receiving device and operable to locate one of a master frame preamble (MFP) code and a distributed synchronization sequence in said TDM data stream, said TDM data stream having at least one TDM frame comprising said one of a MFP code and a distributed synchronization sequence and a plurality of said bits, said one of a MFP code and a distributed synchronization sequence being useful to locate said TDM frame within said TDM data stream;

wherein said processing device transforms said symbols in said TDM data stream into respective subcarriers to generate a time division multiplexed/multicarrier modulated or TDM-MCM waveform comprising TDM-MCM symbols, each of said TDM-MCM symbols having a selected number of subcarriers, said processing device employing said one of a MFP code and a distributed synchronization sequence to synchronize said symbols in said TDM data stream with corresponding ones of said subcarriers in respective said TDM-MCM symbols.

12. An apparatus as claimed in claim 11, wherein said processing device employs an inverse fast Fourier transform (IFFT) to transform said symbols in said TDM data stream into respective said subcarriers.

13. An apparatus as claimed in claim 12, wherein a TDM-MCM frame comprises a selected number of said TDM-MCM symbols, said processing device being operable to generate an integer number of said TDM-MCM symbols for said TDM frame in said TDM data stream.

14. An apparatus as claimed in claim 13, wherein said processing device is operable to provide each said TDM-MCM symbol frame with the same said symbols in a corresponding said TDM frame.

15. An apparatus as claimed in claim 14, wherein said processing device is operable to assign said symbols in the corresponding said TDM frame to respective carriers of said TDM-MCM symbols in said TDM-MCM symbol frame.

16. An apparatus as claimed in claim 15, wherein said apparatus is employed at a terrestrial re-radiation station that is operable to receive said TDM data stream and transform to said symbols therein into respective subcarriers to generate TDM-MCM frames comprising TDM-MCM symbols, said processing device being operable to assign said symbols in respective said TDM frames in said TDM data stream to said subcarriers of said TDM-MCM symbols in corresponding said TDM-MCM frames.

17. A system for use at a terrestrial re-radiation station comprising:

a receiver for receiving a time division multiplexed or TDM data stream from a satellite;

a transcoder connected to said receiver for transforming said TDM data stream into a multicarrier modulated (MCM) waveform to create a time division multiplexed/multicarrier modulated or TDM-MCM signal that is robust to terrestrial path transmission multipath and blockage vagaries and interferences; and

a transmitter connected to said transcoder for transmitting said TDM-MCM signal;

wherein a plurality of said systems are located at respective terrestrial re- radiation stations in a single frequency network, said systems operating substantially simultaneously using timing coordination and synchronization with respect to one another to achieve substantially seamless reception of said TDM-MCM signal over the area associated with said single frequency network.

18. A system as claimed in claim 17, wherein said terrestrial re-radiation stations are geographically located to serve a city and its surrounding suburban regions.