Encoded transmission
View Patent ↗Significant improvement in Raptor codes and punctured LDPC codes are obtainable by use of the invention. In both a transmission scheme for Raptor-encoded or LDPC-encoded information, a dynamic adjustment approach is employed. A fraction of a codeword or information frame is transmitted. A feedback signal is sent from the receiver to the transmitter indicating either 1) successful decoding, or 2) failure to decode and/or a feedback signal indicative of a statistical measure of transmission channel quality. If decoding fails, a further portion of the codeword or frame is sent. The intensity and/or size of the fraction is adjusted based on the feedback signal. In one embodiment, a specific range for probabilities employed in the encoding process for Raptor codes provides the ability to increase transmission throughput. Further it has been found that the advantageous Raptor codes are useful in noise conditions where even the improved punctured LDPC codes of the invention begin to degrade.
1. A method, comprising:
encoding data words of a sequence according to a Raptor-encoding scheme;
transmitting the encoded data words from a transmitter to a receiver such that each encoded data word is transmitted between the same transmitter and receiver; and
receiving feedback signals from the receiver at the transmitter, said feedback being indicative of a statistical measure of transmission channel quality; and
wherein the transmitting is performed at an information transmission rate and a power level, the transmitting being performed such that the information transmission rate or the power level is dynamically responsive to the received feedback signals such that throughput is within 30% of the Shannon limit.
2. The method of claim 1 , wherein the transmitting includes increasing the information transmission rate in response to one of the feedback signals indicating an increase in the SNR or a decrease is the symbol erasure rate and decreasing the information transmission rate in response to one of the feedback signals indicating a decrease in the SNR or an increase in the symbol erasure rate.
3. The method of claim 1 , wherein the transmitting includes decreasing the power level in response to one of the feedback signals indicating an increase in the SNR or a decrease in the symbol erasure rate and increasing the power level in response to one of the feedback signals indicating a decrease in the SNR or an increase in the symbol erasure rate.
4. The method of claim 1 , wherein the encoding further comprises encoding the data words according to a low-density parity-encoding scheme.
5. The method of claim 1 , wherein said statistical measure comprises either a signal-to-noise ratio at the receiver or a bit erasure rate at the receiver.
6. The method of claim 1 , further comprising:
receiving at the transmitter acknowledgement signals from the receiver, each acknowledgement signal indicating that a corresponding set of the encoded data words has been decoded; and
wherein the transmitting of another set of the encoded data words is performed in response to receiving at the transmitter one of the acknowledgement signals indicating that a previously transmitted set of the Raptor encoded data words has been decoded at the receiver.
7. The method of claim 1 for transmitting a Raptor encoded LDPC code signal wherein during the j th transmission interval associated with a bit frame the signal intensity and the number of bits sent is within 25% of a value derivable from the formula:
R
j
(
1
-
γ
(
j
)
)
>
c
0
Π
Ω
-
∑
i
=
1
j
-
1
R
i
(
1
-
γ
(
i
)
)
with
Π
Ω
=
θ
min
P
(
θ
)
θ
and
P
(
θ
)
=
∑
d
Ω
d
∑
j
=
1
j
odd
d
(
d
j
)
θ
j
(
1
-
θ
)
d
-
j
where R j is the number of summed bits transmitted in said jth interval, γ(j) is the Bhattacharyya noise on the channel during said jth interval, c 0 is the ensemble spectrum parameter, p(θ) is the probability of obtaining a 1 for said transmission in said Raptor code for an underlying codeword of fractional weight θ and Ω d is a probability associated with choice of d bits to include in said sum.
8. The method of claim 7 wherein said Raptor encoded signal is transmitted over a communication channel when said channel is too noisy to allow transmission of LDPC encoded messages.
9. A method, comprising:
encoding data words of a sequence according to LDPC encoding scheme;
transmitting the encoded data words from a transmitter to a receiver such that said encoded data word is transmitted between the same transmitter and receiver; and receiving a feedback signal at the transmitter from the receiver, said feedback signal being indicative of a statistical measure of transmission channel quality erasure rate; and
wherein the transmitting is performed at an information transmission rate and a power level, the transmitting being performed such that the information transmission rate or the power level is dynamically responsive to the received feedback signals such that throughput is within 30% of the Shannon limit.
10. The method of claim 9 wherein the transmitting includes increasing the information transmission rate in response to one of the feedback signals indicating an increase in the SNR or decrease in the symbol erasure rate and decreasing the information transmission rate in response to one of the feedback signals indicating a decrease in the SNR or increase of the symbol erasure rate.
11. The method of claim 9 , wherein the transmitting includes decreasing the power level in response to one of the feedback signals indicating an increase in the SNR or decrease in the symbol erasure rate and increasing the power level in response to one of the feedback signals indicating a decrease in the SNR or increase in the symbol erasure rate.
12. The method of claim 9 , wherein the encoding further comprises encoding the data words according to a low-density parity-encoding scheme.
13. The method of claim 9 , wherein said statistical measure comprises either a signal-to-noise ratio at the receiver or a bit erasure rate at the receiver.
14. The method of claim 9 , further comprising:
receiving at the transmitter acknowledgement signals from the receiver, each acknowledgement signal indicating that a corresponding set of the encoded data words has been decoded; and
wherein the transmitting of another set of the encoded data words is performed in response to receiving at the transmitter one of the acknowledgement signals indicating that a previously transmitted set of the Raptor encoded data words has been decoded at the receiver.
15. The method of claim 9 , wherein the intensity of said signal during a j th interval of a series of transmission time intervals and the fraction of bits of said LDPC encoded signal that is transmitted during the j th interval of said series of intervals comprise values that are within ±25% of such values derivable from the formula:
α
j
>
1
-
ⅇ
-
C
0
-
∑
i
=
1
j
-
1
α
(
i
)
(
1
-
γ
(
i
)
)
where α j is the fraction of bits sent in said j th interval, c 0 is the ensemble spectrum and γ(j) is the Bhattacharyya noise after the J th transmission interval.
16. A method, comprising:
encoding some of the data words of a sequence according to a Raptor-encoding scheme;
encoding others of the data words of the same sequence according to a punctured turbo or a punctured LDPC encoding scheme;
transmitting the encoded data words from a transmitter to a receiver such that each encoded data word is transmitted between the same transmitter and receiver;
receiving feedback signals from the receiver at the transmitter, each feedback signal being indicative of either a signal-to-noise ratio (SNR) at the receiver or a symbol erasure rate at the receiver; and
wherein the transmitting includes switching between transmitting of the punctured turbo or LDPC encoded data words and transmitting of the Raptor-encoded data words in a manner that is dynamically responsive to the received feedback signals.
17. The method of claim 16 , wherein the switching includes transmitting the Raptor-encoded ones of the data words in response to the feedback signals and indicating that a SNR at the receiver is below preselected threshold or indicating that an erasure rate at the receiver is above a preselected threshold.
18. The method of claim 16 , wherein the switching includes transmitting the punctured LDPC encoded ones of the data words in response to the feedback signals indicating that a SNR at the receiver is above a preselected threshold or indicating that an erasure rate at the receiver is below a preselected threshold.
19. A method of transmitting a message comprising propagating a signal carrying said message so that said signal is capable of being received and decoded wherein said signal comprises LDPC or Turbo codewords encoded by forming individual encoded bits by choosing d bits in number from said codewords and summing said d bits to form said individual encoded bits wherein for said summing the number, d, of bits chosen is in accordance with a probability assigned to the value, d, wherein said probability, Ω d , is within A) ±30% for values of 0.05 or less and within B) ±10% for values of greater than 0.05, said probability, derivable from the formula
K
≤
-
Ω
′
(
1
-
X
)
log
X
with
Ω
′
(
X
)
=
∑
d
=
1
D
d
Ω
d
X
(
d
-
1
)
where X is a fraction on average in the interval from p to 1 inclusive and p is the maximum number of bit erasures detectable from said LDPC code during said decoding.
20. The method of claim 19 wherein said values of Ω d are derived using linear programming.
21. The method of claim 19 wherein said derivable value is obtained by a choice of at least 100 values of X.
22. The method of claim 21 wherein at least 1000 values of X are employed.