SYNCHRONIZATION AND SEGMENT TYPE DETECTION METHOD FOR DATA TRANSMISSION VIA AN AUDIO COMMUNICATION SYSTEM

• US 20080273644A1
• Filed: 05/03/2007
• Published: 11/06/2008
• Est. Priority Date: 05/03/2007
• Status: Active Grant

• Current Assignee: General Motors LLC (General Motors Company)
• Original Assignee: General Motors LLC (General Motors Company)
• Inventors: Surti, Iqbal, Chesnutt, Elizabeth, Madhavan, Sethu, Yin, Jijun
• Granted Patent: US 7,912,149 B2
• Time in Patent Office: Days
• US Class Current: 375/370
• CPC Class Codes: H04L 7/08 the synchronisation signals recurring cyclically

Abstract

A system and method for asynchronous data communication over a cellular communications network that allows the transmission of different types of data frames over a voice channel using a vocoder. The data frames include a synchronization signal and data segment, with the synchronization signal being selected in accordance with an attribute of the data segment so that, upon receipt of the data frame, the synchronization signal can be used by the demodulating modem to determine not only where the data segment begins, but also to identify what type of data segment is in the received data frame. The synchronization signals used have low cross-correlation and an auto-correlation function that approximates a unit impulse function to provide reliable transmission through the vocoder.

Claims

1. A method of asynchronous data transmission over an audio communication system, comprising the steps of:

generating a data frame containing a data segment using the steps of;

selecting a synchronization signal based on an attribute of the data segment; and

prefixing the data segment with the selected synchronization signal;

encoding the data frame using a vocoder; and

sending the encoded data frame over a wireless communication system.

2. The method set forth in claim 1, wherein the selecting step further comprises selecting one of a plurality of a non-modulated signature signals based on the attribute.

3. The method set forth in claim 2, wherein each of the signature signals comprises a single sampled sequence that is different from the other sequence(s).

4. The method set forth in claim 2, wherein each of the signature signals comprises a two-part sampled sequence that includes a synchronization sequence common to all of the signature signals and a segment type identifier sequence that is unique to each signature signal.

5. The method set forth in claim 2, wherein the selecting step further comprises selecting one of a plurality of a signature signals based on the attribute, wherein each of the signature signals has low cross-correlation.

6. The method set forth in claim 5, further comprising the step of storing the signature signals in a digital memory, wherein the selecting step comprises retrieving a selected signature signal from the digital memory.

7. The method set forth in claim 5, wherein the signature signals include first and second modified maximum length sequences.

8. The method set forth in claim 1, further comprising the step of generating the synchronization signal as an upsampled modified maximum length sequence.

9. The method set forth in claim 8, wherein the step of generating the modified maximum length sequence further comprises the steps of:

providing an MLS;

deleting one bit from the MLS such that the resulting sequence has a zero mean; and

adding a zero at each end of the sequence.

10. The method set forth in claim 1, wherein the attribute is indicative of one of the following:

the length of the data segment, a type of data encryption, the type of encoding used by the vocoder, a type of modulation used to encode data in the data segment, or a type of error correction used in the data segment.

11. A method of asynchronous data communication over an audio communication system, comprising the steps of:

generating a data frame containing a data segment using the steps of;

selecting a synchronization signal based on an attribute of the data segment; and

prefixing the data segment with the selected synchronization signal;

sending the data frame over a wireless communication system having a first vocoder that encodes the data frame prior to transmission and a second vocoder that decodes the encoded data frame after receipt of the transmission;

identifying the selected synchronization signal from the decoded data frame; and

determining the attribute based on the identified synchronization signal.

12. The method set forth in claim 11, wherein the selecting step further comprises selecting one of a plurality of a non-modulated signature signals based on the attribute.

13. The method set forth in claim 12, wherein each of the signature signals comprises a single sampled sequence that is different from the other sequence(s).

14. The method set forth in claim 12, wherein each of the signature signals comprises a two-part sampled sequence that includes a synchronization sequence common to all of the signature signals and a segment type identifier sequence that is unique to each signature signal.

15. The method set forth in claim 12, wherein the selecting step further comprises selecting one of a plurality of a signature signals based on the attribute, wherein each of the signature signals has low cross-correlation.

16. The method set forth in claim 11, wherein the identifying step further comprises correlating the synchronization signal to one of a plurality of different known synchronization signals by processing the decoded data frame using a plurality of filters.

17. The method set forth in claim 11, wherein the data frame comprises a data payload frame having a data payload in the data segment, and wherein the method further comprises the steps of sending back over the wireless communication system an acknowledgement frame that comprises a second synchronization signal and a second data segment, wherein the second synchronization signal is different than the synchronization signal contained in the data payload frame.

18. The method set forth in claim 17, wherein the determining step further comprises determining if the data frame is a data payload frame or an acknowledgement frame based on the synchronization signal.

19. The method set forth in claim 11, wherein the attribute is indicative of one of the following:

the length of the data segment, a type of data encryption, the type of encoding used by the vocoders, a type of modulation used to encode data in the data segment, or a type of error correction used in the data segment.

20. A method of asynchronous data communication over an audio communication system, comprising the steps of:

generating a data frame comprising a first synchronization signal followed by a first data segment that includes a frame ID, payload, and error correction;

transmitting the data frame over a wireless audio communication system using vocoders to encode the data frame prior to wireless transmission and decode the data frame after the wireless transmission;

determining the location and length of the first data segment in the decoded data frame based on the first synchronization signal;

extracting the frame ID and payload from the first data segment;

generating an acknowledgement frame comprising a second synchronization signal followed by a second data segment containing the frame ID and having a second length that is different than the length of the first data segment;

transmitting the acknowledgement frame back over the wireless audio communication system using vocoders to encode the acknowledgement frame prior to wireless transmission and decode the acknowledgement frame after the wireless transmission; and

determining the location and length of the second data segment in the received acknowledgement frame based on the second synchronization signal; and

extracting the frame ID from the second data segment.