ece 4074
play

ECE- 4074 W eb Si te http: //w w w . csc. gatech. edu/~copel - PowerPoint PPT Presentation

Mar 15, 2024 •311 likes •430 views

ECE- 4074 W eb Si te http: //w w w . csc. gatech. edu/~copel and/4074 Pr of . John A . Copel and j ohn. copel and@ ece. gatech. edu 404 894- 5177 O f f i ce: GCA TT 579 F or of f i ce vi si t, em ai l or

  1. ECE- 4074 W eb Si te http: //w w w . csc. gatech. edu/~copel and/4074 Pr of . John A . Copel and j ohn. copel and@ ece. gatech. edu 404 894- 5177 O f f i ce: GCA TT 579 F or of f i ce vi si t, em ai l or cal l m e or dr op by dur i ng of f i ce hour s posted on the W eb Si te • Fr am i ng • Rati os as Deci bel s • Char acter i sti c I m pedance • Scr am bl i ng A ppendi ces 3A - 3C, pp 115- 120 EE4074. 03 v8

  2. Char acter i sti c I m pedance A uni f or m tr ansm i ssi on l i ne w i l l conduct an el ectr i cal pul se • i n one di r ecti on at a constant speed ( usual l y ~ 2E8 m /s) • w i thout r ef l ecti on i f the end i s ter m i nated w i th R = Zo Tr ansm i tter Tr ansm i ssi on Li ne, Zo = R R + - V ol tage Di stance

  3. Deci bel s = 10 * l og (Rati o) Loss Loss Gai n Loss Gai n f actor f actor f actor f actor f actor = . 05 = 100 = . 02 = 40 = . 01 - 13 dB = 20 dB = - 17 dB =16 dB = - 20 dB Ci r cui t Gai n = Ci r cui t Gai n = . 05 - 13 dB . 05 = 10**- 1. 3 x 100 +20 dB 100 = 10**+2. 0 x . 02 - 17 dB . 02 = 10**- 1. 7 x 40 +16 dB 40 = 10**+1. 6 x . 01 - 20 dB . 01 = 10 **- 2. 0 0. 04 - 14 dB

  4. Deci bel Rel ati onshi ps Rati o dB Q ui ck Cal cul ati on 1 0 1 = 10**0 1. 25 1 1. 25 = 5/4 = 7- 6 dB 2 3 (5/4)**3 = 125/64 4 6 2*2 = 3+3 dB 5 7 10/2 = 10- 3 dB 8 9 2*2*2 = 3+3+3 dB 10 10 10**1 100 20 10**2 1000 30 10**3 1/R - D w her e R - > D l og(1/x) = - l og(x) 1+0. 25*f f f < 1 (f r acti on) M em or i ze the r ati os cor r espondi ng to 1, 3, and 10 dB, and you can qui ckl y cal cul ate the r ati o f or any dB.

  5. Bi t- O r i ent Fr am i ng 10010111111001101000011001010110110001101000110111110011 A str eam of 0' s and 1' s ar e r ecei ved. W e know i t i s text data (char acter s encoded as 8- bi t codes). W her e ar e the f i r st bi ts of a code? O ne techni que i s to use a speci al 8- bi t "f l ag" code (byte or octet) that contai ns si x "1"s i n a r ow (01111110). 1001 01111110 01001000 01000101 01001100 01001100 01001111 10011 Start H E L L O Flag Dat a Flag The "f l ags" "f r am e" the "data". Thi s type of str uctur e i s cal l ed a "packet", "cel l " or "f r am e" dependi ng on the pr otocol .

  6. Bi t Stuf f i ng To pr event a f l ag- l i ke sequence appear i ng i n the data, the f ol l ow i ng r ul e i s appl i ed w hen the f r am e i s f or m ed: • A f ter f i ve "1"s i n a r ow , an extr a zer o i s "stuf f ed" i nto the bi t str eam (w hether the next bi t i s a "1" or a "zer o"). W hen data i s taken out of a f r am e at the r ecei vi ng end, the f ol l ow i ng r ul e r estor es the data: • w henever f i ve "1"s i n a r ow appear , the next bi t i s di scar ded. Data: 0110111110110001011111100101000000 Framed Data: 0111111001101111100110001011111010010100000001111110

  7. Encodi ng Rul e V i ol ati on Fr am i ng I n som e system s, the tr ansm i tter w i l l send a si gnal that vi ol ates an encodi ng r ul e to si gnal the star t of a f r am e. Exam pl es: M an- chester Encodi ng Bi t str eam 0 x 1 1 0 1 A l ter nate M ar k- I nver si on A M I 0 1 X 1 0 1 Bi t str eam

  8. Char acter - O r i ented Fr am i ng Som e char acter - or i ented pr otocol s need to di vi de a str eam of char acter s (octets, bytes) i nto f r am es. Thr ee codes ar e used to bui l d f r am es w hi ch ar e desi gnated: • "Data Li nk Escape" or DLE • "Star t Tr ansm i ssi on" or STX • "End Tr ansm i ssi on" or ETX The r ul es ar e: • Fr am es ar e star ted w i th the tw o- octets: DLE STX • Fr am es ar e ended w i th the tw o octets: DLE ETX Si nce al l 256 possi bl e 8- bi t codes can appear i n the data, w henever a DLE octet appear s, a second DLE i s stuf f ed i nto the char acter str eam af ter i t. Data: A B DLE C D STX F ETX G H Framed Data: DLE STX A B DLE DLE C D STX F ETX G H DLE ETX

  9. Char acter - O r i ented Fr am e Decode Decodi ng r ul e: w henever a DLE char acter appear s i n the i ncom i ng char acter str eam , i t i s i nter pr eted i n com bi nati on w i th the next char acter accor di ng to thi s tabl e: • DLE STX = Star t of Fr am e (di scar d, star t savi ng data) • DLE DLE = Repl ace w i th si ngl e DLE • DLE ETX = End of Fr am e (di scar d, pass data to hi gher l evel ) • DLE [anythi ng el se] = codi ng er r or . Framed Data: DLE STX A B DLE DLE STX D E F ETX G H DLE ETX Data: A B DLE STX D E F ETX G H

  10. Scram bl ers Ther e ar e pr obl em s w hen l ong str i ngs of onl y "0"s or onl y "1"s ar e tr ansm i tted. To pr event thi s a scr am bl er can be used at the tr ansm i tter , and a m atchi ng descr am bl er at the r ecei ver . A (m ) ⊕ 3) ⊕ Scr am bl er : B(m ) = B(m - B(m - 5) e ⊕ • w her i n the "excl usi ve or " • A (m ) i s the m ' th bi t i nput • B(m ) i s the m ' th bi t output. B(m ) ⊕ 3) ⊕ Descr am bl er : C(m ) = B(m - B(m - 5) • B(m ) i s the m ' th bi t i nput p. 147- 149 • C(m ) i s the m ' th bi t output.

  11. Shi f t Regi ster Scr am bl er s A (m ) ⊕ 3) ⊕ Scr am bl er : B(m ) = B(m - B(m - 5) B(m ) ⊕ 3) ⊕ Descr am bl er : C(m ) = B(m - B(m - 5) B(m - 5) B(m - 4) B(m - 3) B(m - 2) B(m - 1) A (m ) B(m ) C(m ) B(m ) ⊕ 3) ⊕ C(m ) = B(m - B(m - 5) {A (m ) ⊕ 3) ⊕ 5)} ⊕ 3) ⊕ C(m ) = B(m - B(m - B(m - B(m - 5) X ⊕ Y ⊕ C(m ) = A (m ) si nce X = 0, 0 = Y

More recommend