Modulation Techniques for Mobile Systems

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?µ?µa ???a????? ?/? ?a? ?????f??????
???ast???? ?pe?e??as?a? S?µ?t?? ?a?
???ep??????????
????t? ???t?a ?p??????????
????? ? ???ep????????a?? T?µata ?e??????
??d???p???s?? ????? ? ?e??pt?s? t?? F????
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?e?????? ??d???p???s?? F????

• ??d???p???s? ????? ? p????f???a µ?a? d?a???t??
  p???? ??d???p??e?ta? µe s??p? t?? ??????µ???
  d?ad??? a?apa??stas?. ??s? t?? d?ad??as?a? a?t??
  ap????pteta? ? p?e??????sa p????f???a.
• ? ??d???p???s? ????? ap??e?e? (lossless)
  ?p??e?ta? st? ?eµe???d? pe?????sµ? ?t? µ?a p???
  µe e?t??p?a ? µp??e? ?a ??d???p????e? µe µ?de????
  p??a??t?ta sf??µat?? ef?s?? ? ???µ?? p??
  p????pte? e??a? R gt H, ?a? a?t?st??fa, e?? R lt
  H t?te, a?e???t?ta ap? t?? p???p????t?ta t??
  ??d??a ?a p?????e? µ? µ?de???? p??a??t?ta
  sf??µat?? , (1? Te???µa t?? Shannon).
• ??as???? te?????? lossless, ?e????? s??p??
• - ???????µ?? t?? Shannon
• - ???????µ?? t?? Lempel Ziv
• - ???????µ?? t?? Huffman
• ??d???p???s? a?a??????? p???? ??e?
  a?ap?fe??ta ap??e?e? (lossy) p?? ?fe????ta? st?
  d?a???t?p???s? t?? t?µ?? (?ßa?t?sµ??). ? st????
  st?? pe??pt?s? a?t? e??a? ? e?a??st?p???s? a?t??
  t?? ap??e??? ?a? e? s??e?e?a ? s?µp?es? µe
  e?e???µe?e? ?a? p??? ap??e?e? (Rate-Distortion
  Theory)

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?e?????? ??d???p???s?? F????

• ??d???p???s? F???? ?d?a?te?a ???s?µ?
  d?ad??as?a a? a?a????st??µe ?t? µe???? µ???? t??
  d?a?????µe??? p????f???a? e??a? f??? ?a? ?t? µ?s?
  t?? s?µp?es?? t?? µp??e? ?a ep?te???e? s?µa?t???
  µe??s? t?? apa?t??µe??? e????? ????? (µ???? ?a?
  4-5 f????, ????? a?s??t? ?p?ß??µ?s? t??
  p???t?ta?).
• Ge???? ?at??????p???s? t?? te??????
• 1) Waveform Coding
• - Temporal
• - Spectral (Transform)
• 2) Model-based Coding
• ?a??µ??a ?at??????p???s? ?s??e? ?a? se ?????
  t?p?? a?a??????? p????,
• p.?. e????a ? video (? f?s??? s???? e??a?
  s?ed?? p??ta a?a??????)

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?e?????? ??d???p???s?? F????
?e?a????? ?at??????p???s? t?? d?af???? te??????
??d???p???s??
5
?e?????? ??d???p???s?? F????
?????aµµa ßa?µ?d?? e??? ??d???p???t? ADPCM (CT2
cordless telephone system)
?? s?st?µa e??a? p??sa?µ?st??? (p??ß??pt?? ?a?
?ßa?t?st??) ?a? ?ts? e??a? se ??s? ?a
pa?a??????e? t?? stat?st???? a??a??? t?? s?µat??
e?s?d?? S(k)
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?e?????? ??d???p???s?? F????
??a???µµata ßa?µ?d?? ?p?-??????? ??d???p???t? ?a?
ap???d???p???t?

• ?? s?µa f???? ?????eta? se ???e? s????t?t??, p??
  ?ßa?t????ta? ?a? ??d???p?????ta? ?e????st?
• St?? ???e? p?? e??a? pe??ss?te?? s?µa?t???? ??a
  t?? a????p??? a??? a?at??e?ta? pe??ss?te?a bits
• ???s? t?? filter banks QMF ??a a????s? t??
  a?ad?p??s?? f?sµat??

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?e?????? ??d???p???s?? F????
??p???? d?a????sµ?? ?p?-?????

• Adaptive Transform Coding (ADC)
• ??d???p???s? tµ?µ?t?? f???? st? ped?? s????t?t??
  
• S?????? ???s?µ?p??e?ta? ? ??a???t??
  ?etas??µat?sµ?? S???µ?t???? (DCT) t?? ?p???? ??
  s??se?? a????s?? ?a? s???es?? fa????ta? pa?a??t?
  ( g(0)1, g(k)21/2 )

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?e?????? ??d???p???s?? F????
???t??? pa?a????? f????
?e ded?µ??? t? ßas??? f???t??? ?d?, apa?te?ta?
ep?p???? ? e?t?µ?s? t?? e??? pa?aµ?t??? - ??
t? f???µa e??a? e?f??? (voiced) ? ?f???
(unvoiced) - - Teµe???d?? s????t?ta
(pitch) - ??s? ?s??? t?? f???µat??
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?e?????? ??d???p???s?? F????
??d???p???t?? f???? (Vocoders) t?p?? LPC (Linear
Predictive Coding)
??a? LPC Vocoder µ??te??p??e? t? f???t??? ?d? ??
??a ??aµµ??? s?st?µa t?p?? all-pole µe s????t?s?
µetaf????
???sd????sµ?? t?? s??te?est?? t?? LPC Vocoder
To t????? de??µa ???feta? ?? ??aµµ????
s??d?asµ?? p??????µ???? de??µ?t??
minS e2n w.r.t. ak ? R a r (R
Toeplitz) (Levinson-Durbin Algorithm)
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?e?????? ??d???p???s?? F????
?????aµµa ßa?µ?d?? e??? ??d???p???t? LPC
?pa?t??µe?? p????f???a st?? d??t? -
S??te?est?? LPC (?ßa?t?sµ????) -
Voiced/unvoiced decision - Pitch period
- Gain gt ?e?????? e?t?µ?s??/a????e?s?? ??a t??
pa?ap??? pa?aµ?t????
? d?ad??as?a LPC ??µ??e? t? ADPCM µe t? ßas???
d?af??? ?t? a?t? ?a ap?st???eta? t? ?ßa?t?sµ???
sf??µa ap?st?????ta? ??p??a ?a?a?t???st??? t??
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?e?????? ??d???p???s?? F????
???f??e? e?a??a?t???? µ???d?? d?µ??????a? t??
s?µat?? d???e?s?? st?? ap???d???p???t? LPC
LPC Vocoder MPE-LPC (Multipulse
Excitation) ???s? p????? pa?µ?? a?? pe???d? µe
µetaßa???µe?a p??t? ?a? ??se?? CELP (Code
Excited LP) ???s? e??? p???a????sµ???? codebook
µe s?µata d???e?s??
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?e?????? ??d???p???s?? F????
?????aµµa ßa?µ?d?? t?? d?ad??as?a? code book
search t?? s?st?µat?? ??d???p???s?? CELP (Code
Excited Linear Predictive)
?? ßas???? d?ad??as?e? st?? ??d???p???t? CELP
- ?p?????sµ?? t?? d?? p??ß?ept?? (LTP,
STP) ap? t? e??st?te tµ?µa f????
(Long Term Short
Term Prediction) - ???es? t??
ß??t?st?? d???e?s?? (ap? t? codebook). ??
a?t??e?µe???? sf??µa a?a?atas?e???
(error) ?f?stata? pe?a?t??? µetas??µat?sµ?
s?µf??a µe t?? a?t???pt???
µ??a??sµ? µa? (perceptual masking)
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?e?????? ??d???p???s?? F????

?????aµµa ßa?µ?d?? t?? s?st?µat?? ??d???p???s??
RELP (Residual
Excited Linear Predictive)
To s?st?µa ??d???p???s?? RELP ßas??eta?
??s?ast??? st?? ?d?a ?????? µe a?t? t??
s?st?µat?? ADPCM µe ep?p???? st???e?a t??
e?s?µ?t?s? ?a?a?t???st???? t?? t?????t??
de??µat?? (v/u, gain, pitch) . S??µat??eta? t?
s?µa sf??µat?? (residual) t? ?p??? ?ßa?t??eta?
?a? µetad?deta?.
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?e?????? ??d???p???s?? F????
?????aµµa ßa?µ?d?? t?? ??d???p???t? f???? t??
s?st?µat?? GSM ( Regular Pulse Excited - Long
Term Prediction RPE-LTP )
To s?st?µa RPE-LTP s??d???e? ta p?e??e?t?µata
t?? RELP ?a? t?? MPE-LTP. ??s?ast??? e??a?
s?st?µa t?p?? RELP p?? ??e? e?s?µat?se? t?
d?ad??as?a LTP.
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?e?????? ??d???p???s?? F????
?????aµµa ßa?µ?d?? t?? ap???d???p???t? f???? t??
s?st?µat?? GSM
- H a????s? STP (st?? ??d???p???t?) d??e? t???
?e??µe???? reflection coefficients ?a? ??? t???
?d???? t??? s??te?est?? p??ß?e???. ???a?
µa??µat??? ?s?d??aµ? pa?aµet??p???s?. - St?
s????e?a ap? t??? r.c. ?p????????ta? ??
s??te?est?? L.A.R. (logarithmic area ratios)
µ?s? e??? ap??? µ?-??aµµ???? µetas??µat?sµ??. ??
s??te?est?? p?? p????pt??? ????? ?a??te?e?
?d??t?te? ?ß??t?s??.
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?e?????? ??d???p???s?? F????
?e?????? ??d???p???s?? p?? ???s?µ?p?????ta? se
d??f??a s?st?µata ????t?? ep??????????
???t?p? ??p?? ?p??es?a? ??d???p???t?? F???? Bit Rate (kbps)
GSM Cellular RPE-LTP 13
CD-900 Cellular SBC 16
USDC (IS-54) Cellular VSELP 8
IS-95 Cellular CELP 1.2, 2.4, 4.8, 9.6
IS-95 PCS PCS CELP 14.4
PDC Cellular VSELP 4.5, 6.7, 11.2
CT2 Cordless ADPCM 32
DECT Cordless ADPCM 32
PHS Cordless ADPCM 32
DCS-1800 PCS RPE-LTP 13
PACS PCS ADPCM 32

• S?st?µata 3?? ?e???? Adaptive Multirate (AMR)
  speech codec
• ?? s?st?µa ep?t??pe? s?µp?es? se d?af??et?????
  ???µ??? a?????a µe t?? s?????e?. St?? p????a t??
  s?st?µat?? e??a? ? te????? ACELP (Algebraic CELP)
  p?? e??a? ?at? ß?s? ? CELP µe d?af??et???
  coodbook design and search.

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?e?????? ??d???p???s?? F????
????????s? t?? ap?d?s?? d?af???? te??????
??d???p???s?? µe ß?s? t?? de??t? MOS (Mean
Opinion Score)