`Uniform Random lnterleavers
`
`Henry Pfister and Paul H. Siegel
`Signal Transmission and Recording (STAR) Lab
`University of California, San Diego
`
`{hpfister, psiege|}@ucsd.edu
`
`Allerton Conference
`
`September 22-24 , 1999
`
`0
`
`Apple 1005
`Apple 1005
`
`1
`
`
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`The Sena] Concatcnation of Rate—l Codes Through Uniform Random Interleavers
`
`Outline
`
`o Union Bounds and Code Performance
`
`0 Serial Concatenation and Repeat-Accumulate (RA) Codes
`
`o Serial Concatenation of Rate-1 Codes
`
`o Repeat-Accumulate-Accumulate (RAA) Codes
`
`a Summary
`
`
`
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`The Serial Concatenation of Rate—1 Codes Through Uniform Random Interleavers
`Union Bounds on Performance
`
`o Rate 7" = 19/72, linear block code C’
`
`o Input Output Weight Enumerator Function (IOWEF) :
`
`Awah Cg # codewords, input weight 10, output weight h
`
`o Union bound on word error probability PW
`(binary-input, memoryless channel, maximum-likelihood decoding):
`
`PW S 22:1 25:1 Aw,hZh
`
`o z is channel dependent; e.g., for Gaussian channel, 2 : e""(Eb/N0).
`
`o For ensembles, replace AWL by average IOWEF Awfi
`
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`2
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`The Sefial Concatenation of Rate—1 Codes Through Uniform Random Interleavers
`
`Serial Concatenation through a Uniform lnterleaver
`
`aih
`
`o Let C1, C; be (711, /:1), (n2, kg) linear block codes with n1 : I22,
`and IOWEFS Affh, A,ff>h.
`
`o Let C be the (n2, kl) code obtained by serial concatenation of C1 and 02
`through a uniform interleaver of size 711, with average IOWEF AW1 :
`
`711
`AM : Z An)
`,h
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`4
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`The Serial Concatenation of Rate-1 Codes Through Uniform Random Interleavers
`
`Repeat-Accumulate (RA) Codes
`(Divsalar, et al., Al|erton’98)
`
`qN
`Repeat
`. —>
`%—> .
`b1t q tunes
`
`P
`
`qN
`
`qN
`——>
`
`1/(1+D)
`Rate-=1
`
`o Repeat input block $15132 ~
`
`-
`
`- a:N a total of q times.
`
`o Permute with random interleaver P of size n = qN.
`
`o Accumulate over block:
`
`vn=u1+---+un
`
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`The Serial Concatenation of Rate—l Codes Through Uniform Random Interleavers
`
`A Simple Example
`
`o Rate-1, (n, k) = (3, 3) Accumulate code:
`
`lnputweightw
`
`Output Bits Outputweighth
`
`
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`The Serial Concatenation of Rate—1 Codes Through Uniform Random Interleavers
`RA Weight Enumerator
`(Divsalar, et aI., A|lerton’98)
`
`o (qN, N) Repeat Code
`
`(1)
`AW:
`
`0
`if
`h;éq'w
`(95) if h:q1u
`
`(n, n) Accumulate Code (cf. "Oberg and Siegel, A||erton’98)
`
`< {:75} )( M723 31)
`
`0 (qN, N) RA Code
`
`N
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`qN—h
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`hA1
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`gm : ifw,h > 0
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`qw
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`Signal Transmz'ssz'0n and Recording Grnup, Universily 0_fCalzf0r71ia, San Diego
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`The Serial Concatenation of Rate—1 Codes Through Uniform Random Interleavers
`
`RA Coding Theorem
`(Divsalar, et al., Allerton’98)
`
`0 Theorem: For q 2 3 , there exists ~yq > 0 such that, for any Eb/No > *yq, as the
`block length N becomes large,
`
`P5?/B = o<N‘*>,
`
`wherefiz — [9-§3].HencePW—>OasN—+oo.
`
`o Example 7,] estimates (from Viterbi—Viterbi Bound):
`
`V3 2,» 1.112 dB
`
`
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`Signal Trmzsnzission and Recording Group, University of California, San Diego
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`7
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`The Serial Concatenation of Ratc—1 Codes Through Uniform Random lnterleavcrs
`
`Performance of RA Codes
`
`o RA codes, 7“ = % and 7° :
`
`with iterative decoding.
`
`
`
`WER for Rate 1/q HA Codes (20 iterations)
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`The Sena] Concatenation of Rate—1 Codes Through Uniform Random Interleavers
`
`Serial Concatenation
`
`0 Consider an encoder architecture of the following form:
`
`*+ AnyC°d6
`R316 K1
`
`UIC
`Rate 1
`
`UIC _+
`Rate 1
`
`o UIC represents a Uniform Interleaver in cascade with a rate-1 Code (e.g., an
`(n, n) Accumulate Code).
`
`c We want to characterize the average IOWEF when the code is concatenated with
`m UlC’s.
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`The Serial Concatenation of Rate—1 Codes Through Unifoim Random interleave/rs
`
`Serial Concatenation with U |C’s
`
`e Let IOWEF for rate-1, (n, 72,) code be A = [A- -],
`1,]
`
`0 < z',j < n.
`_
`_
`
`o Define IOW Transition Probabilities (IOWTP): P : [PM],
`
`0 < z',j 3 n7
`
`o Rate-1, (n, k) : (3, 3) Accumulate code:
`
`.
`.
`[PW] Z [P’"(h : 9'” Z Z” Z
`
`1
`0
`0
`0
`0 03 03’ 03
`0
`0.6 03
`0
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`0
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`The Serial Concatenation of Rate—1 Codes Through Uniform Random Interleavcrs
`
`Serial Concatenation with U|C’s
`
`—. Any C0“
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`
`
`
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`UIC H_.
`Rate 1
`
`UIC _%.
`Rate 1
`
`o Outer (n, is) code C’, IOWEF CW1.
`
`o Cascade of m, rate—1 (n, n) U|C’s, each with IOWTP P : [PM].
`
`o Average IOWEF AWL of serial concatenation:
`
`Aw,h : Z Cw,h1 [P7n]h1,h
`/11:0
`
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`The Serial Concatenation of Rate—1 Codes Through Uniform Random lnterleavers
`
`Perron-Frobenius Theory
`
`0 Theorem: An irreducible stochastic matrix P has a unique stationary distribution
`71'S.t. 7'l'P:’7Tal'ldZ7l'Z' = 1.
`
`o Theorem: An irreducible aperiodic (primitive) stochastic matrix P with unique
`stationary distribution 71' satisfies:
`
`lim Pm :
`7'rL:>OO
`
`o A linear rate-1 code is primitive if P+ : [Pm], 2', j 75 O,
`
`is a primitive matrix.
`
`
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`
`Signal Transmission and Recording Group, I,/niversiry of California, San Diego
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`12
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`The Sefial Concatenation of Ratc—1 Codes Through Uniform Random Interleavcrs
`
`A Simple Example (cont.)
`
`o Rate-1, (n, k:) : (3, 3) Accumulate Code:
`
`1
`
`0
`
`0
`
`0
`
`< 0
`
`r
`g
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`%
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`% )
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`Signal Transmission and Recording Group, University 0fC{1lIf0rn.ia, San Diego
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`14
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`15
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`The Serial Concatenation of Rate—1 Codes Through Uniform Random Interleavers
`
`Stationary Distributions and Rate-1 Codes
`
`0 Proposition: Consider the SC of m primitive rate-1 codes through uniform
`interleavers. For non—zero input weights and as m —> 00, the output weight
`distribution is independent of the input weight distribution and is
`
`7rh=
`
`(Z)
`2n—1’
`
`for h7EO.
`
`o The ensemble averaged OWEF for any rate 7’ < 1 code SC with m —+ 00
`primitive rate-1 codes is
`
`2’I"fL __ 1
`
`“Z3751” (Z)
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`
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`Signal Transmission and Recording Group, Un.iver.vity nfCalif0rm'a, San Diego
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`14
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`The Serial Concatenation of Rate-l Codes Through Uniform Random Interleavers
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`Iterated Rate-1 Codes Make Good Codes
`
`o Proposition: For a code randomly chosen from an ensemble with average OWE
`A—h,
`
`El. —-1
`
`(of. Gallager, 1963)
`
`Il
`13
`
`o For length n, rate 7" < 1,and e > 0, let d*(n, r, e) be the largest value of d
`satisfying
`
`d— 1
`
`n
`
`2 h
`
`I120
`
`2”
`— TTL _
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`Szgnal Trcmsmzsston and Recordmg Group, Umverszty of Calzforma, San Diego
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`The Serial Concatenation of Rate—1 Codes Through Uniform Random Interleavers
`Iterated Rate-1 Codes Make Good Codes
`
`0 Proposition: For the ensemble of length-n codes obtained by serial
`concatenation of a rate-r linear block code with m —> oo primitive rate-1 linear
`codes through uniform random interleavers,
`
`P7‘(dmz-n < d*(n, 1", 6)) 3 e.
`
`0 Corollary: Let e = (2(1"’)” — 1)(2""” — 1)/(2” — 1). Then,
`
`where d*is the largest value of d satisfying
`
`<
`
`S E < 1,
`
`d—1
`n
`2<h)g2
`
`h=0
`
`(1)
`n—r‘_n~
`
`-2
`
`k
`
`(i.e., at least one code satisfies the Gilbert-Varshamov Bound).
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`The Serial Concatenation of Rate—l Codes Through Uniform Random Interleavers
`
`Bounds for CA” Codes
`
`o Rate r<1, outer code C.
`
`0 Serial concatenation with m uniformly interleaved Accumulate codes.
`
`o Compute largest value d* satisfying
`
`d—1 j 1
`2 Ah < —.
`h=1
`2
`
`o Then, by the bound,
`
`*
`1
`PT(d7rLin < d ) < 57
`(i.e., at least half the codes satisfy dmm > d*).
`
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`17
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`The Serial Concatenation of Rate-1 Codes Through Uniform Random Interleavers
`
`Numerical Results
`
`o CAT” bounds for Repeat-2 and Repeat-4 codes, 1 3 m 3 4.
`
`Minimum distance guaranteed for half of the codes by our bound
`_I
`.
`— >+ - Repeat by 2 m=1
`— ><-
`V Repeat by 2 m=2
`— >+ » Repeat by 2 m=3
`200- ~ * Repeat by 2 m=4
`—><— GV Bound rate 1/2
`4 —- Repeat by 4 m=1
`'
`7 Repeat by 4 m=2
`—: Repeatby4m=3
`~“ ~ Repeat by4 m=4
`GV Bound rate 1/4
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`The Serial Concatenation of Rate-1 Codes Through Uniform Random Interleavers
`
`Numerical Results
`
`0 For (8,4) Hamming and rate 7/8 parity-check codes, 1 3 m 3 4.
`
`120
`
`100
`
`80
`
`(
`- Hamming 8,4) m=1
`- Hamming (8,4) m=2
`— Hamming (8,4) m=3
`~ Hamming (8,4) m=4
`GV Bound rate 1/2
`Rate 7/8 Parity m=1
`a Rate 7/8 Parity m=2
`Rate 7/8 Parity m=3
`7 Rate 7/8 Parity m=4
`
`GV Bound rate 7/8
` :5;"’l;7: 1 ~32
`
`Minimum distance guaranteed for half of the codes by our bound
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`
`The Serial Concatenation of Rate—I Codes Through Uniform Random Interleavcrs
`Rate 1/2, RAA Codes
`
`N
`
`qN
`
`qN
`
`qN
`
`qN
`
`qN
`
`Repeat
`bit q timfis
`
`P
`
`1/(1+D)
`Rate=l
`
`P
`
`1/(1+D)
`Rate=l
`
`o For rate 7" = 1/2 RA code, analysis and simulations suggest that there is no
`word-error-probability interleaving gain.
`
`9 For rate r : 1/2 RAA code, analysis and simulations suggest that there is...
`
` —.—
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`Signal Transmission. and Recording Group, University of California, San Diego
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`20
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`21
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`
`The Serial Concatcnation of Rate—1 Codes Through Uniform Random Interleavcrs
`
`Rate 1/2, RA vs. RAA
`
`o Word-error-probability PW , from computer simulation.
`Comparison of Word Error rate for RA and RAA Codes
`__ z __ ’* _ _x
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`><- ~ ><
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`e—o Acc2 K=256
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`21
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`22
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`23
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`The Serial Concatcnation of Rate—l Codes Through Uniform Random Interleavcrs
`
`Summary
`
`c We investigated a new class of codes based upon serial concatenation of a rate-r
`code with m 3 1, uniformly interleaved rate-1 codes.
`
`0 We analyzed the output weight enumerator function TL for finite m, as well as
`asymptotically for m —> oo.
`
`o We evaluated the “goodness” of these ensembles in terms of the
`Gilbert-Varshamov Bound.
`
`c We compared 7" : 1/2 RAA codes to RA codes.
`
`Question: For 7“ = 1/2, RAA codes, is there a y such that , for Eb/N0 > 7,
`PW —> O as N —> oo ?
`
`
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