Method and apparatus for frame rate determination without decoding in a spread spectrum receiver
View Patent ↗A spread spectrum receiver ( 124 ) for receiving and decoding a data frame having one of a plurality of coding rates is coupled to a rate determination device ( 132 ). The rate determination device ( 132 ) is coupled to receive a data frame coded at one of the plurality of coding rates and to receive symbol data from the receiver ( 124 ). The rate determination device ( 132 ) is adapted to determine a probability based at least upon an rate-based symbol repetition constraints within the data frame, wherein the probability is an indication of the rate at which the data frame is encoded.
1. A spread spectrum receiver for receiving and decoding a data frame having one of a plurality of coding rates, the spread spectrum receiver comprising:
a rate determination device coupled to receive a data frame coded at one of the plurality of coding rates and to receive symbol data from the receiver, the rate determination device being adapted to determine a probability based at least upon rate-based symbol repetition constraints within the data frame, wherein the probability is an indication of the rate at which the data frame is encoded, wherein the probability comprises a log likelihood ratio based at least upon the rate-based symbol repetition constraints within the data frame and
wherein the log likelihood ratio indicative of the rate is the maximum of the group of log likelihood ratios comprising:
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where y i represents a sequence of received symbols, r i represents the coding rates, Δ represents a reliability that pairs of symbols or partial sums have a same sign or opposite signs, and γ represents a ratio of mean and variance of v i a decoder, decoding the received data frame according to the determined frame rate.
2. The spread spectrum receiver of claim 1 , comprising a decision rule based upon the probability.
3. The spread spectrum receiver of claim 2 , wherein the decision rule comprises:
i) if Ψ 4 ≦η 1 , rate=r 4 ;
ii) if Ψ 3 ≦η 1 and Ψ 4 >η 1 , rate=r 3 ;
iii) if Ψ 2 ≦η 1 and Ψ 3 >η 1 and Ψ 4 >η 1 , rate=r 2 ;
iv) if Ψ 2 >η 1 and Ψ 3 >η 1 and Ψ 4 >η 1 , rate=r 1 , and
wherein Ψ measures a reliability that pairs of symbols or partial sums have a same sign or opposite signs and η represents a threshold.
4. The spread spectrum receiver of claim 2 , wherein the decision rule comprises:
i) if Ω 4 ≦η 2 , rate=r 4 ;
ii) if Ω 3 ≦η 2 and Ω 4 >η 2 , rate=r 3 ;
iii) if Ω 2 ≦η 2 and Ω 3 >η 2 and Ω 4 >η 2 , rate=r 2 ;
iv) if Ω 2 >η 2 and Ω 3 >η 2 and Ω 4 >η 2 , rate=r 1 , and
wherein Ω measures a reliability that pairs of symbols or partial sums have a same sign or opposite signs and η represents a threshold.
5. The spread spectrum receiver of claim 2 , wherein the decision rule comprises:
rate=r i , where
i=arg max{Λ i 3 , iε{1, 2, 3, 4}},
with
Λ
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,
Λ 2 3 =a 2 (( s 1,2 2 +s 3,4 2 +s 5,6 2 +s 7,8 2 )−8δ 2 ),
Λ 3 3 =a 3 (( s 3,4 2 +s 5,8 2 )−8δ 2 ),
Λ 4 3 =a 4 ( s 1,8 2 −8δ 2 ),
and δ is at least an estimate of the interference variance at the output of the RAKE combiner and wherein Λ measures a reliability that pairs of symbols or partial sums have a same sign or opposite signs and s j,k represent partial sums and j,k denote the first and last symbols of the span of symbols included in the partial sum.
6. The spread spectrum receiver of claim 1 , comprising a plurality of rate determination algorithms, the rate determination device operable to select one of the plurality of rate determination algorithms based upon a channel characteristic.
7. The spread spectrum receiver of claim 6 , wherein the channel characteristic comprises one of the group of characteristics comprising: signal-to-noise ratio (SNR), symbol energy-to-to-noise ratio (E s N 0 ), bit energy-to-noise ratio (E b /N 0 ), characteristics of the channel fading process such as fading rate, and rate set.
8. In a spread spectrum receiver for receiving and decoding a data frame having one of a plurality of coding rates, a method for decoding received data frames comprising:
determining a probability based upon rate-based symbol repetition constraints within a received data frame;
determining a frame rate based upon the probability; and
decoding the received data frame according to the determined frame rate, wherein the step of determining a probability comprises determining a log likelihood ratio based at least upon the rate-based symbol repetition constraints within the data frame and
wherein the log likelihood ratio indicative of the rate is the maximum of the group of log likelihood ratios comprising:
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1
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≈
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log
2
-
2
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(
Δ
1
+
Δ
2
)
log
p
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y
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4
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p
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1
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≈
7
log
2
-
2
γ
(
Δ
1
+
Δ
2
+
Δ
3
)
where v i represents a sequence of received symbols, r i represents the coding rates, Δ represents a reliability that pairs of symbols or partial sums have a same sign or opposite signs, and γ represents a ratio of mean and variance of y i .
9. The method of claim 8 , wherein the step of determining the frame rate comprises applying a decision rule based upon the probability.
10. The method of claim 9 , wherein the decision rule comprises:
i) if Ψ 4 ≦η 1 , rate=r 4 ;
ii) if Ψ 3 ≦η 1 and Ψ 4 >η 1 , rate=r 3 ;
iii) if Ψ 2 ≦η 1 and Ψ 3 >η 1 and Ψ 4 >η 1 , rate=r 2 ;
iv) if Ψ 2 >η 1 and Ψ 3 >η 1 and Ψ 4 >η 1 , rate=r 1 , and
wherein Ψ measures a reliability that pairs of symbols or partial sums have a same sign or opposite signs and η represents a threshold.
11. The method of claim 9 , wherein the decision rule comprises:
i) if Ω 4 ≦η 2 , rate=r 4 ;
ii) if Ω 3 ≦η 2 and Ω 4 >η 2 , rate=r 3 ;
iii) if Ω 2 ≦η 2 and Ω 3 >η 2 and Ω 4 >η 2 , rate=r 2 ;
iv) if Ω 2 >η 2 and Ω 3 >η 2 and Ω 4 >η 2 , rate=r 1 , and
wherein Ω measures a reliability that pairs of symbols or partial sums have a same sign or opposite signs and η represents a threshold.
12. The spread spectrum receiver of claim 9 , wherein the decision rule comprises:
rate=r i , where
i=arg max{Λ i 3 , i ε{1,2,3,4}},
with
Λ
1
3
=
a
1
(
(
∑
i
=
1
8
y
i
2
)
-
8
δ
2
)
,
Λ 2 3 =a 2 (( s 1,2 2 +s 3,4 2 +s 5,6 2 +s 7,8 2 )−8δ 2 ),
Λ 3 3 =a 3 (( s 1,4 2 +s 5,8 2 )−8δ 2 ),
Λ 4 3 =a 4 ( s 1,8 2 −8δ 2 ),
and δ is at least an estimate of the interference variance at the output of the RAKE combiner and wherein Λ measures a reliability that pairs of symbols or partial sums have a same sign or opposite signs and s j,k represent partial sums and j,k denote the first and last symbols of the span of symbols included in the partial sum.
13. The method of claim 8 , comprising the step of selecting from a plurality of rate determination algorithms a rate determination algorithm to be used to determine the frame rate based upon a channel characteristic.
14. The method of claim 13 , wherein the channel characteristic comprises one of the group of chatacteristics comprising: signal-to-noise ratio (SNR), symbol energy-to-noise ratio (E s /N 0 ), bit energy-to-noise ratio (E b /N 0 ), characteristics of the channel fading process such as fading rate, and rate set.
15. A spread spectrum receiver for receiving and decoding a data frame having one of a plurality of coding rates comprising:
means for determining a probability based upon rate-base symbol repetition constraints within a received data frame;
means for determining a frame rate based upon the probability; and
means for decoding the received data frame according to the determined frame rate wherein determining a probability comprises determining a log likelihood ratio based at least upon the rate-based symbol repetition constraints within the data frame and wherein the log likelihood ratio indicative of the rate is the maximum of the group of log likelihood ratios comprising:
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y
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2
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Δ
1
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4
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p
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≈
7
log
2
-
2
γ
(
Δ
1
+
Δ
2
+
Δ
3
)
where y i represents a sequence of received symbols, r i represents the coding rates, Δ represents a reliability that pairs of symbols or partial sums have a same sign or opposite signs, and γ represents a ratio of mean and variance and y i .
16. The spread spectrum receiver of claim 15 , comprising means for selecting from a plurality of rate determination algorithms a rate determination algorithm to be used to determine the frame rate based upon a channel characteristic.