ADAPTIVE CODING AND MODULATION FOR BROADBAND DATA TRANSMISSION

• US 20070116151A1
• Filed: 10/30/2006
• Published: 05/24/2007
• Est. Priority Date: 10/28/2005
• Status: Active Grant

• Current Assignee: ViaSat Incorporated
• Original Assignee: ViaSat Incorporated
• Inventors: Thesling, William
• Granted Patent: US 7,680,040 B2
• Time in Patent Office: Days
• US Class Current: 375/326
• CPC Class Codes: H04B 7/18543 for adaptation of transmission parameters, e.g. power control for detecting or preventing errors in the information received H04L1/00
• CPC Class Codes: H04B 7/18582 Arrangements for data linking, i.e. for data framing, for error recovery, for multiple access
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0007 by modifying the frame length
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0016 involving special memory structures, e.g. look-up tables
• CPC Class Codes: H04L 1/0021 in which the algorithm uses adaptive thresholds
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/0083 Formatting with frames or packets; Protocol or part of protocol for error control
• CPC Class Codes: H04L 2001/0093 Point-to-multipoint
• CPC Class Codes: H04L 27/0008 arrangements for allowing a transmitter or receiver to use more than one type of modulation negotiating modulation type for two-way transmission paths H04L5/1453
• CPC Class Codes: H04L 47/6215 Individual queue per QOS, rate or priority
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601
• CPC Class Codes: H04W 28/10 Flow control between communication endpoints
• CPC Class Codes: H04W 72/1221 based on age of data to be sent
• CPC Class Codes: H04W 72/542 using measured or perceived quality
• CPC Class Codes: H04W 80/00 Wireless network protocols or protocol adaptations to wireless operation
• CPC Class Codes: H04W 84/06 Airborne or Satellite Networks space-based or airborne stations H04B7/185

Abstract

A process is described to build physical layer frames with a modcode adapted to the signal quality of a destination terminal. Data packets assigned to the same modcode may be sent in the same frame, although packets associated with higher modcodes may be used to complete a frame before switching to the applicable higher modcode for construction of subsequent frames. After an interval, the order of progression is restarted with an out of order packet above a threshold age. Flow control filtering mechanisms and a variable reliability margin may be used to adapt dynamically to the current data traffic conditions.

Claims

1. A method of implementing adaptive coding and modulation in a broadcast signal, the method comprising:

associating a first modcode with a first signal quality range;

associating a second modcode of a higher order than the first modcode with a second signal quality range of better quality than the first signal quality range;

receiving a first data packet destined for a first link within the first signal quality range and a second data packet destined for a second link within the second signal quality range;

encapsulating the first data packet and at least a part of the second data packet in a first frame; and

transmitting the first frame in the broadcast signal according to the first modcode.

2. The method of claim 1, further comprising:

varying at least one of the first signal quality range and the second signal quality range to modify a reliability margin for data packets destined for a link within the varied signal quality range.

3. The method of claim 2, wherein the varying step comprises:

varying at least one of the first signal quality range and the second signal quality range based at least in part on latency associated with the transmitting step.

4. The method of claim 1,

fragmenting the second data packet into a first fragment and a second fragment;

transmitting the first fragment in the first frame; and

transmitting the second fragment in a second frame according to the second modcode.

5. The method of claim 1, wherein the encapsulating step further comprises:

applying a policy of encapsulating data packets associated with different modcodes in one frame to be transmitted according to a lowest order modcode of the different modcodes, the policy applied when there are no other remaining data packets associated with the lowest order modcode.

6. The method of claim 5, wherein the policy comprises:

determining a length of a prospective pad for the at least one data packet associated with a first modcode;

determining that no data packet associated with the first modcode remains to fill the prospective pad; and

filling the prospective pad with the data packet associated with the second modcode.

7. The method of claim 1, further comprising:

transmitting additional frames in the broadcast signal according to a defined order of progression; and

interrupting the defined order of progression upon expiration of a timer to transmit, in a second frame, a packet exceeding a threshold age.

8. The method of claim 7, further comprising:

varying the period of the timer based at least in part on a delay associated with transmitting the additional frames.

9. The method of claim 1, wherein,

the associating the first modcode with the first data packet comprises placing the first data packet in a first packet forwarding queue associated with the first signal quality range;

and

the associating the second modcode with the second data packet comprises placing the second data packet in a second packet forwarding queue associated with the second signal quality range.

10. The method of claim 1, further comprising:

inserting, in a linked list, a first element corresponding to the first data packet and associated first signal quality;

inserting, in the linked list, a second element corresponding to the second data packet and associated second signal quality; and

iterating through the linked list to identify a set of data packets for encapsulation and transmission based at least in part on a signal quality associated with each element of the linked list.

11. The method of claim 1, wherein the adaptive coding and modulation is implemented in accordance with a DVB-S2 standard.

12. The method of claim 1, wherein signal quality comprises at least one of a signal to noise ratio, an estimated signal to noise ratio, a bit error rate, a receive power level, and another communication link quality indicator.

13. A device for implementing adaptive modcodes, the device comprising:

a sorting unit configured to;

associate a first modcode with a first packet to be received on a first link defined by a signal quality in a first signal quality range;

associate a higher order second modcode with a second packet to be received on a second link defined by a signal quality in a second signal quality range of better quality than the first signal quality range;

an encapsulation unit, coupled with the sorting unit, and configured to encapsulate the first packet and second packet in a first frame; and

a modulation and coding unit, coupled with the encapsulation unit, and configured to encode and map the frame according to the first modcode.

14. The device of claim 13, wherein,

the sorting unit is further configured to vary at least one of the first signal quality range and the second signal quality range to modify a reliability margin for a transmitted data packet destined for a link within the varied signal quality range.

15. The device of claim 13, wherein,

the sorting unit is further configured to vary at least one of the first signal quality range and the second signal quality range based at least in part on latency associated with the transmitting step.

16. The device of claim 13, wherein,

the encapsulation unit is further configured to:

fragment the second data packet into a first fragment and a second fragment;

encapsulate the first fragment in the first frame; and

encapsulate the second fragment in a second frame to be transmitted according to the second modcode.

17. The device of claim 13, wherein,

the sorting unit is configured to group data packets associated with different modcodes for encapsulation in one frame to be transmitted according to a lowest order modcode of the different modcodes, the grouping to occur when there are no other remaining data packets associated with the lowest order modcode.

18. The device of claim 13, further comprising a transmitter configured to:

transmit additional frames in the broadcast signal according to a defined order of progression; and

interrupt the defined order of progression upon expiration of a timer to transmit, in a second frame, a packet exceeding a threshold age.

19. The device of claim 18, wherein,

the transmitter is further configured to vary the period of timer based at least in part on a latency associated with transmitting the additional frames.

20. A method of controlling the flow of data traffic for a broadcast signal implementing adaptive coding and modulation, the method comprising:

dynamically assigning a modcode of a plurality of modcodes to each of a plurality of data packets based at least in part on a signal quality of a link on which each respective packet is destined;

associating a timestamp with each of the plurality of data packets;

transmitting a subset of the plurality of data packets according to a defined order of progression; and

interrupting the defined order of progression upon expiration of a timer to transmit an out of order packet with a timestamp exceeding a first threshold age, wherein the out of order packet comprises one of the plurality of packets not included in the subset.

21. The method of claim 20, wherein the first threshold age comprises the timestamp of the second oldest of the plurality of data packets not included in the subset.

22. The method of claim 20, further comprising:

blocking additional data packets when the out of order packet exceeds a second threshold age.

23. The method of claim 22, further comprising:

allowing only data packets associated with a threshold quality or class of service to enter while blocking the additional packets.

24. The method of claim 20, further comprising:

restarting the defined order of progression from the out of order packet.

25. The method of claim 20, further comprising:

varying the period of timer based at least in part on a delay associated with transmitting from the packet forwarding queues.

26. The method of claim 20, wherein the transmitting according to the defined order of progression comprises:

transmitting each data packet associated with a first modcode of the plurality of modcodes; and

incrementing to a next higher order second modcode of the plurality of modcodes to transmit a data packet associated with an oldest timestamp of the plurality of data packets associated with the second modcode.

27. The method of claim 26, wherein the transmitting according to the defined order of progression further comprises:

transmitting at least one data packet associated with a first modcode and the data packet associated with the second modcode in a single frame according the first modcode.

29. The method of claim 20, further comprising:

utilizing a counter to associate an order with the plurality of data packets; and

holding transmission of a data packet of the plurality of data packets when the packet is out of the order specified by the counter.

30. The method of claim 20, further comprising:

varying a signal quality range associated with one or more of the plurality of modcodes to modify a reliability margin for at least a subset of the plurality of data packets destined for a link within the varied signal quality range.

31. The method of claim 20, wherein the transmitting according to the defined order of progression comprises:

fragmenting an internet protocol data packet of the plurality of data packets into first fragment and second fragment, each fragment associated with a first modcode of the plurality of modcodes;

transmitting the first fragment according to a second modcode of the plurality of modcodes; and

transmitting the second fragment according to the first modcode, the first modcode of higher order than the second modcode.

32. The method of claim 31, wherein the first fragment is sized to fill a length of prospective pad for a frame to be transmitted according to the second modcode.

33. The method of claim 20, wherein the dynamically assigning the modcode step comprises:

placing selected data packets of the plurality of data packet into selective ones of a plurality of packet forwarding queues each associated with different signal quality ranges.

34. The method of claim 20, further comprising:

inserting, into a linked list, a plurality of elements each corresponding to one or more of the plurality of data packets and an associated signal quality; and

iterating through the linked list to identify a set of data packets for encapsulation and transmission based at least in part on a signal quality associated with each element of the linked list.

35. The method of claim 20, wherein the adaptive coding and modulation is implemented in accordance with a DVB-S2 standard.

36. The method of claim 20, wherein the signal quality comprises at least one of a signal to noise ratio, an estimated signal to noise ratio, a bit error rate, a receive power level, and another communication link quality indicator.

28. The method of claim 28, wherein the transmitting according to the defined order of progression further comprises:

determining a length of a prospective pad for the at least one data packet associated with a first modcode;

determining that no data packet associated with the first modcode remains to fill the prospective pad; and

filling the prospective pad with the data packet associated with the second modcode.

37. A device for controlling the flow of data traffic for a broadcast signal implementing adaptive coding and modulation, the device comprising:

a sorting unit configured to dynamically assign a different modcode to each of a plurality of packets based at least in part on a signal quality of a link on which each respective packet is to be received;

a transmitting unit, coupled with the sorting unit, and configured to;

transmit a subset of the plurality of packets according to a defined order of progression; and

interrupt the defined order of progression upon expiration of a timer to transmit an out of order packet exceeding a threshold age, wherein the out of order packet comprises one of the plurality of packets not included in the subset.

38. The device of claim 37, wherein,

the sorting unit is further configured to block additional data packets when the out of order packet exceeds a second threshold age.

39. The device of claim 38, wherein,

the sorting unit is further configured to allow data packets associated with a threshold quality or class of service to enter.

40. The device of claim 37, wherein,

the transmitting unit is further configured to restarting the defined order of progression from the out of order packet.

41. The device of claim 37, wherein,

the transmitting unit is further configured to varying the period of the timer based at least in part on a latency associated with transmitting from the packet forwarding queues.

42. The device of claim 37, wherein,

the transmitting unit is further configured to:

transmit each data packet associated with a first modcode of the plurality of modcodes before incrementing to a next higher order second modcode of the plurality of modcodes; and

transmit a data packet with an oldest timestamp associated with the second modcode.

43. The device of claim 42, wherein,

the transmitting unit is further configured to transmit at least one data packet associated with the first modcode and the data packet associated with the second modcode in a single frame according to the first modcode.

44. The device of claim 37, wherein,

the sorting unit is configured to vary a signal quality range associated with one or more of the plurality of modcodes to modify a reliability margin for at least a subset of the plurality of data packets destined for a link within the varied signal quality range.