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Chuong 2

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CHNG 2 : TN HIEU NG TRUYEN 2.1. Nh旦探ng kha湛i nie辰m chung ve t鱈n hie辰u 単旦担淡ng truyen : * 旦担淡ng no叩i tr旦誰c tie叩p kho但ng qua thie叩t b嘆 trung gian na淡o tr旦淡 nh旦探ng bo辰 khue叩ch 単a誰i hoa谷c repeater du淡ng 単e奪 ta棚ng 単o辰 ma誰nh cu短a t鱈n hie辰u. 旦担淡ng no叩i tr旦誰c tie叩p 単ie奪m 単ie奪m va淡 単a 単ie奪m 単a 単ie奪m du淡ng cho ca短 mo但i tr旦担淡ng truyen da達n 単嘆nh h旦担湛ng va淡 kho但ng 単嘆nh h旦担湛ng. * Theo quan 単ie奪m th担淡i gian ta co湛 t鱈n hie辰u 単ieu ho淡a : s(t) = A sin (2f0t + ) +A : bie但n 単o辰 (V) 1 +f0 : tan so叩 la淡 so叩 chu ky淡 cu短a t鱈n hie辰u xa短y ra trong 1 gia但y : f0 = (Hz) T 0 + 0 : go湛c pha (2 radians = 360 ) * Theo quan 単ie奪m cu短a tan so叩 : pho奪 cu短a t鱈n hie辰u lie但n tu誰c la淡 nh旦探ng va誰ch pho奪 r担淡i ra誰c, co淡n pho奪 cu短a t鱈n hie辰u r担淡i ra誰c (xung) la淡 pho奪 lie但n tu誰c. 1 1 * o叩i v担湛i da探y xung vuo但ng 1010 単o辰 ro辰ng cu短a 1 xung la淡 T= ne但n to叩c 2 2f 単o辰 truyen se探 la淡 2f (bps). * Mo辰t t鱈n hie辰u tre但n 単旦担淡ng truyen se探 ch嘆u a短nh h旦担短ng sau : - B嘆 suy gia短m va淡 da達n 単e叩n me湛o da誰ng - B嘆 la淡m cha辰m (tre達) - B嘆 nhie達u. 2.2. Mo但i tr旦担淡ng truyen : 2.2.1. H旦探u tuye叩n : gom da但y song ha淡nh, ca湛p 単ong tru誰c, ca湛p quang. * Da但y song ha淡nh co淡n go誰i la淡 ca谷p da但y xoa辿n th旦担淡ng du淡ng trong ca湛c he辰 tho叩ng 単ie辰n thoa誰i nh旦 vo淡ng no辰i bo辰, 単旦担淡ng trung ke叩 va淡 trong ma誰ng ma湛y t鱈nh no辰i bo辰. 旦担淡ng da但y song ha淡nh co湛 the奪 truyen cho t鱈n hie辰u analog cu探ng nh旦 t鱈n hie辰u so叩. * Ca湛p 単ong tru誰c : co湛 the奪 truyen t鱈n hie辰u analog v担湛i khoa短ng ca湛ch va淡i km va淡 fmax = 400 MHz hoa谷c truyen t鱈n hie辰u so叩 v担湛i khoa短ng ca湛ch 1,6 km 単a誰t to叩c 単o辰 500 Mbps. Pha誰m vi 旦湛ng du誰ng cu短a ca湛p 単ong tru誰c ro辰ng h担n da但y song ha淡nh, 単旦担誰c s旦短 du誰ng ca短 cho 単旦担淡ng tivi ca湛p. * S担誰i quang ch脱 truyen 単旦担誰c t鱈n hie辰u so叩, ng旦担淡i ta hay du淡ng ASK. S担誰i quang 単旦担誰c du淡ng do ba棚ng tho但ng ro辰ng, k鱈ch th旦担湛c nho短, tro誰ng l旦担誰ng nhe誰, suy gia短m 鱈t,
ca湛ch ly 単ie辰n t旦淡 va淡 khoa短ng ca湛ch la谷p la誰i l担湛n. S担誰i quang du淡ng nhieu trong ma誰ng 単ie辰n thoa誰i tha淡nh pho叩, truyen 単ie辰n thoa誰i khoa短ng ca湛ch xa va淡 ma誰ng LAN. 2.2.2. Vo但 tuye叩n : gom radio, vi ba ma谷t 単a叩t, vi ba ve辰 tinh. * So湛ng radio truyen kho但ng 単嘆nh h旦担湛ng tre但n tang 単ie辰n ly, th旦担淡ng du淡ng trong ca湛c he辰 tho叩ng pha湛t thanh (AM, FM), pha湛t h狸nh (VHF, UHF) hoa谷c he辰 tho叩ng radio go湛i trong ma誰ng truyen so叩 lie辰u. * Vi ba ma谷t 単a叩t truyen 単嘆nh h旦担湛ng chu淡m tia ve h旦担湛ng can thie叩t v担湛i pha誰m vi tan so叩 2 歎 40 GHz. Vi ba ma谷t 単a叩t co湛 the奪 truyen ca短 t鱈n hie辰u t旦担ng t旦誰 va淡 so叩 担短 khoa短ng ca湛ch xa v担湛i cha叩t l旦担誰ng cao. Vi ba ma谷t 単a叩t 単旦担誰c du淡ng cho ca湛c 単旦担淡ng no叩i 単ie奪m 単ie奪m gi旦探a ca湛c to淡a nha淡, cung ca叩p d旦探 lie辰u 単嘆a ph旦担ng va淡 thay the叩 ca湛p 単ong tru誰c trong truyen h狸nh ca湛p va淡 tie叩ng no湛i. * Vi ba ve辰 tinh : Ve辰 tinh tho但ng tin la淡 mo辰t tra誰m chuye奪n tie叩p. No湛 du淡ng 単e奪 no叩i hai hoa谷c nhieu bo辰 thu pha湛t c担 ba短n va淡 単旦担誰c coi la淡 tra誰m ma谷t 単a叩t. Bo辰 thu cu短a ve辰 tinh truyen tre但n mo辰t ba棚ng tan (単旦担淡ng le但n), khue叩ch 単a誰i hoa谷c repeater va淡 chuye奪n no湛 sang ba棚ng tan kha湛c(単旦担淡ng xuo叩ng). Ve辰 tinh t旦誰 quay quanh no湛 v担湛i to叩c 単o辰 35784 km. Co湛 hai loa誰i tie但u chua奪n : 0 - Ba棚ng tan 4/6 GHz v担湛i go湛c nga奪ng 4 . 0 _ Ba棚ng tan 12/16 GHz v担湛i go湛c nga奪ng 3 . Ve辰 tinh 単旦担誰c s旦短 du誰ng 単e奪 pha但n pho叩i truyen h狸nh, truyen 単ie辰n thoa誰i khoa短ng ca湛ch xa va淡 ma誰ng th旦担ng ma誰i t旦 nha但n. 2.3. Ky探 thua辰t so叩 cho t鱈n hie辰u analog : 2.3.1. PAM : ieu bie但n xung : * Trong he辰 tho叩ng PAM kho但ng co湛 thie叩t b嘆 ma探 ho湛a va淡 gia短i ma探. Ng旦担淡i ta ch脱 truyen mo辰t da探y xung co湛 bie但n 単o辰 単旦担誰c 単ieu che叩 b担短i t鱈n hie辰u analog tho但ng tin can truyen va淡 tan so叩 da探y xung 単a湛p 旦湛ng tan so叩 la叩y ma達u 単e叩n bo辰 pha辰n thu. bo辰 pha辰n thu se探 phu誰c hoi la誰i tho但ng tin can truyen. * 嘆nh ly湛 la叩y ma達u : t鱈n hie辰u analog 単旦担誰c ta誰o la誰i khi va淡 ch脱 khi tan so叩 la叩y ma達u (fs) l担湛n h担n hoa谷c ba竪ng hai lan tan so叩 cao nha叩t cu短a t鱈n hie辰u 単au va淡o (fa). fs 2fa + fa : tan so叩 c旦誰c 単a誰i cu短a t鱈n hie辰u 単au va淡o. + fs : tan so叩 la叩y ma達u.
V鱈 du誰 : T鱈n hie辰u thoa誰i co湛 ba棚ng tho但ng : 300 Hz 歎 3400Hz fa = 3400 Hz fs 2.3400 = 6800 Hz fs = 8000 Hz 2.3.2. PCM : ieu co叩t (code - ma探) xung (ieu xung co叩t) Va Bo辰 n bie叩 va淡 A o Lo誰 tho但g c n L旦担誰 g t旦短 a n ho湛 Ma探 tha叩p 単o奪song i ho湛 a song sang f La叩 ma達 y u PCM 0 0 f no叩tie叩 i p b r nfs 単旦担淡g n b bw = r no叩 i Va 2 Lo誰 tho但g c n Bo辰 n bie叩 ra A 単o奪no叩 i i tha叩p Gia短ma探 i PCM f tie叩 sang p 0 0 f song song H 狸nh 2.1 . H e辰 ng tho但g tin so叩 M tho叩 n PC PCM la淡 t鱈n hie辰u PAM sau khi 単a探 l旦担誰ng t旦短 ho湛a. Nh旦ng trong PAM gi旦探a hai th担淡i gian la叩y ma達u ta ch脱 can truyen mo辰t xung la叩y ma達u th狸 trong PCM ta can truyen n xung. 1 b f = 2T = 2 = BW r So湛g PCM no叩 tie叩 n i p b 1 : 単o辰 ro辰ng cu短a bit (s) 0 1 0 1 0 1 Tb = 0 1 br Tb 2Tb au ra br cu短a bo辰 pha湛t co湛 n bit no叩i tie叩p PCM : br nfs 2nfa (bps) V鱈 du誰 : v担湛i PCM 8 bit trong he辰 tho叩ng 単ie辰n thoa誰i : + Ba棚ng tho但ng cu短a voice : 300 Hz 歎 3400 Hz fa = 3400 Hz + Tan so叩 la叩y ma達u : fs 2fa = 6800 Hz cho誰n fs = 8 KHz 3 + To叩c 単o辰 cu短a mo辰t ke但nh PCM : br nfs = 8.8.10 = 64 Kbps br 64.10 3 + Ba棚ng tho但ng cu短a mo辰t ke但nh PCM : BW = = = 32 KHz. 2 2 1 + Ne叩u trong mo辰t chu ky淡 la叩y ma達u Ts = f = 125 袖s (go誰i la淡 mo辰t s khung) ta sa辿p xe叩p N ke但nh, th狸 to叩c 単o辰 truyen mo辰t khung se探 ta棚ng le但n : R = N. br
BW = NBW 3 V鱈 du誰 : + PCM 30 co湛 N = 32 R = 32.64.10 = 2048 Kbps BW = 32.32.10 = 1024 3 KHz 3 + PCM _ 24 co湛 N = 32 R = 24.64.10 = 1536 Kbps BW = 24.32.10 = 768 KHz 3 2.3.3. PCM-24 : la淡 chua奪n cu短a Ba辿c My探 va淡 Nha辰t : Ca叩u tru湛c PCM - 24 gom : + Ca湛c 単a khung (multiframe) co湛 12 khung (12 x 125 袖s = 1,5 ms); mo達i khung co湛 24 ke但nh gom 193 bit chie叩m 125 袖s [(24x8) + 1= 193 bit)]. Bit 単ong bo辰 go誰i la淡 bit S, ca湛c bit S cu短a khung le短 lan l旦担誰t la淡 101010 va淡 ca湛c bit S cu短a khung cha端n lan l旦担誰t la淡 001110. Frame 1 Frame 2 Frame 3 ... Frame 11 Frame 12 Ke但h 1 Ke但h 2 Ke但h 3 n n n ... Ke但h 24 n Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit S 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 Frame 1 2 3 4 5 6 7 8 9 10 11 12 S - bit 1 0 1 0 1 0 0 0 1 1 1 0 2.3.4. PCM-30 : la淡 chua奪n cu短a cha但u A但u. Ca叩u tru湛c PCM-30 gom : + Ca湛c 単a khung co湛 16 khung (16 x 125 袖s = 2 ms); mo達i khung co湛 32 ke但nh gom 256 bit (8 x 32 = 256 bit). Ke但nh 0 la淡 ke但nh 単ong bo辰, ke但nh 16 la淡 ke但nh ba湛o hie辰u. Frame 0 Frame 1 Frame 2 ... Frame 14 Frame 15 Ke但h 0 Ke但h 1 n n ... Ke但h 15 Ke但h 16 Ke但h 17 n n n ... Ke但h 31 n 15 ke但h thoa誰 n i 15 ke但h thoa誰 n i ke但h 1 ke但h 16 n n Bit 1 2 3 4 5 6 7 8 Ra 1 0 0 1 1 0 1 1 : T鱈n hie辰 単og bo辰 u n 1 2 3 4 5 6 7 8 MC 1 1 D N 1 1 1 1 : Tho但g ba湛 lo達 n o i 0 1 1 1 1 1 1 1 ke但h ba湛 hie辰 16 n o u D = 1 : Tho但g ba湛 lo達kha奪 ca叩 n o i n p D = 0 : kho但g co湛 i kha奪 ca叩 n lo達 n p + 4 bit 1,2,3,4 ba湛 hie辰 cho 16 ke但h 単a (0-15) o u n u N = 1 : kho但g co湛 i kho但g kha奪 ca叩 n lo達 n n p + 4 bit 5,6,7,8 ba湛 hie辰 cho 16 ke但h sau (16-31) o u n N = 0 : co湛 i kho但g kha奪 ca叩 lo達 n n p
* ieu che叩 PCM 単a誰t cha叩t l旦担誰ng cao nh旦ng 単o淡i ho短i ba棚ng tho但ng l担湛n. e奪 gia短m ba棚ng tho但ng 単i mo辰t n旦短a ng旦担淡i ta du淡ng 単ieu che叩 Delta, nh旦ng khi 単o湛 nhie達u l旦担誰ng t旦短 se探 l担湛n va淡 me湛o do qua湛 ta短i s旦担淡n cu探ng l担湛n. ieu che叩 PCM vi pha但n la淡 単ieu che叩 ke叩t h担誰p gi旦探a Delta va淡 PCM. Khi 単o湛 cha叩t l旦担誰ng t鱈n hie辰u va達n 単a短m ba短o, ma淡 ba棚ng tho但ng va達n gia短m mo辰t n旦短a va淡 me湛o do qua湛 ta短i s旦担淡n ch脱 co淡n 3% kho但ng 単a湛ng ke奪. ieu che叩 PCM gom 8 bits, co淡n 単ieu che叩 PCM vi pha但n ch脱 can 4 bits.

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Chuong 2

  • 1. CHNG 2 : TN HIEU NG TRUYEN 2.1. Nh旦探ng kha湛i nie辰m chung ve t鱈n hie辰u 単旦担淡ng truyen : * 旦担淡ng no叩i tr旦誰c tie叩p kho但ng qua thie叩t b嘆 trung gian na淡o tr旦淡 nh旦探ng bo辰 khue叩ch 単a誰i hoa谷c repeater du淡ng 単e奪 ta棚ng 単o辰 ma誰nh cu短a t鱈n hie辰u. 旦担淡ng no叩i tr旦誰c tie叩p 単ie奪m 単ie奪m va淡 単a 単ie奪m 単a 単ie奪m du淡ng cho ca短 mo但i tr旦担淡ng truyen da達n 単嘆nh h旦担湛ng va淡 kho但ng 単嘆nh h旦担湛ng. * Theo quan 単ie奪m th担淡i gian ta co湛 t鱈n hie辰u 単ieu ho淡a : s(t) = A sin (2f0t + ) +A : bie但n 単o辰 (V) 1 +f0 : tan so叩 la淡 so叩 chu ky淡 cu短a t鱈n hie辰u xa短y ra trong 1 gia但y : f0 = (Hz) T 0 + 0 : go湛c pha (2 radians = 360 ) * Theo quan 単ie奪m cu短a tan so叩 : pho奪 cu短a t鱈n hie辰u lie但n tu誰c la淡 nh旦探ng va誰ch pho奪 r担淡i ra誰c, co淡n pho奪 cu短a t鱈n hie辰u r担淡i ra誰c (xung) la淡 pho奪 lie但n tu誰c. 1 1 * o叩i v担湛i da探y xung vuo但ng 1010 単o辰 ro辰ng cu短a 1 xung la淡 T= ne但n to叩c 2 2f 単o辰 truyen se探 la淡 2f (bps). * Mo辰t t鱈n hie辰u tre但n 単旦担淡ng truyen se探 ch嘆u a短nh h旦担短ng sau : - B嘆 suy gia短m va淡 da達n 単e叩n me湛o da誰ng - B嘆 la淡m cha辰m (tre達) - B嘆 nhie達u. 2.2. Mo但i tr旦担淡ng truyen : 2.2.1. H旦探u tuye叩n : gom da但y song ha淡nh, ca湛p 単ong tru誰c, ca湛p quang. * Da但y song ha淡nh co淡n go誰i la淡 ca谷p da但y xoa辿n th旦担淡ng du淡ng trong ca湛c he辰 tho叩ng 単ie辰n thoa誰i nh旦 vo淡ng no辰i bo辰, 単旦担淡ng trung ke叩 va淡 trong ma誰ng ma湛y t鱈nh no辰i bo辰. 旦担淡ng da但y song ha淡nh co湛 the奪 truyen cho t鱈n hie辰u analog cu探ng nh旦 t鱈n hie辰u so叩. * Ca湛p 単ong tru誰c : co湛 the奪 truyen t鱈n hie辰u analog v担湛i khoa短ng ca湛ch va淡i km va淡 fmax = 400 MHz hoa谷c truyen t鱈n hie辰u so叩 v担湛i khoa短ng ca湛ch 1,6 km 単a誰t to叩c 単o辰 500 Mbps. Pha誰m vi 旦湛ng du誰ng cu短a ca湛p 単ong tru誰c ro辰ng h担n da但y song ha淡nh, 単旦担誰c s旦短 du誰ng ca短 cho 単旦担淡ng tivi ca湛p. * S担誰i quang ch脱 truyen 単旦担誰c t鱈n hie辰u so叩, ng旦担淡i ta hay du淡ng ASK. S担誰i quang 単旦担誰c du淡ng do ba棚ng tho但ng ro辰ng, k鱈ch th旦担湛c nho短, tro誰ng l旦担誰ng nhe誰, suy gia短m 鱈t,
  • 2. ca湛ch ly 単ie辰n t旦淡 va淡 khoa短ng ca湛ch la谷p la誰i l担湛n. S担誰i quang du淡ng nhieu trong ma誰ng 単ie辰n thoa誰i tha淡nh pho叩, truyen 単ie辰n thoa誰i khoa短ng ca湛ch xa va淡 ma誰ng LAN. 2.2.2. Vo但 tuye叩n : gom radio, vi ba ma谷t 単a叩t, vi ba ve辰 tinh. * So湛ng radio truyen kho但ng 単嘆nh h旦担湛ng tre但n tang 単ie辰n ly, th旦担淡ng du淡ng trong ca湛c he辰 tho叩ng pha湛t thanh (AM, FM), pha湛t h狸nh (VHF, UHF) hoa谷c he辰 tho叩ng radio go湛i trong ma誰ng truyen so叩 lie辰u. * Vi ba ma谷t 単a叩t truyen 単嘆nh h旦担湛ng chu淡m tia ve h旦担湛ng can thie叩t v担湛i pha誰m vi tan so叩 2 歎 40 GHz. Vi ba ma谷t 単a叩t co湛 the奪 truyen ca短 t鱈n hie辰u t旦担ng t旦誰 va淡 so叩 担短 khoa短ng ca湛ch xa v担湛i cha叩t l旦担誰ng cao. Vi ba ma谷t 単a叩t 単旦担誰c du淡ng cho ca湛c 単旦担淡ng no叩i 単ie奪m 単ie奪m gi旦探a ca湛c to淡a nha淡, cung ca叩p d旦探 lie辰u 単嘆a ph旦担ng va淡 thay the叩 ca湛p 単ong tru誰c trong truyen h狸nh ca湛p va淡 tie叩ng no湛i. * Vi ba ve辰 tinh : Ve辰 tinh tho但ng tin la淡 mo辰t tra誰m chuye奪n tie叩p. No湛 du淡ng 単e奪 no叩i hai hoa谷c nhieu bo辰 thu pha湛t c担 ba短n va淡 単旦担誰c coi la淡 tra誰m ma谷t 単a叩t. Bo辰 thu cu短a ve辰 tinh truyen tre但n mo辰t ba棚ng tan (単旦担淡ng le但n), khue叩ch 単a誰i hoa谷c repeater va淡 chuye奪n no湛 sang ba棚ng tan kha湛c(単旦担淡ng xuo叩ng). Ve辰 tinh t旦誰 quay quanh no湛 v担湛i to叩c 単o辰 35784 km. Co湛 hai loa誰i tie但u chua奪n : 0 - Ba棚ng tan 4/6 GHz v担湛i go湛c nga奪ng 4 . 0 _ Ba棚ng tan 12/16 GHz v担湛i go湛c nga奪ng 3 . Ve辰 tinh 単旦担誰c s旦短 du誰ng 単e奪 pha但n pho叩i truyen h狸nh, truyen 単ie辰n thoa誰i khoa短ng ca湛ch xa va淡 ma誰ng th旦担ng ma誰i t旦 nha但n. 2.3. Ky探 thua辰t so叩 cho t鱈n hie辰u analog : 2.3.1. PAM : ieu bie但n xung : * Trong he辰 tho叩ng PAM kho但ng co湛 thie叩t b嘆 ma探 ho湛a va淡 gia短i ma探. Ng旦担淡i ta ch脱 truyen mo辰t da探y xung co湛 bie但n 単o辰 単旦担誰c 単ieu che叩 b担短i t鱈n hie辰u analog tho但ng tin can truyen va淡 tan so叩 da探y xung 単a湛p 旦湛ng tan so叩 la叩y ma達u 単e叩n bo辰 pha辰n thu. bo辰 pha辰n thu se探 phu誰c hoi la誰i tho但ng tin can truyen. * 嘆nh ly湛 la叩y ma達u : t鱈n hie辰u analog 単旦担誰c ta誰o la誰i khi va淡 ch脱 khi tan so叩 la叩y ma達u (fs) l担湛n h担n hoa谷c ba竪ng hai lan tan so叩 cao nha叩t cu短a t鱈n hie辰u 単au va淡o (fa). fs 2fa + fa : tan so叩 c旦誰c 単a誰i cu短a t鱈n hie辰u 単au va淡o. + fs : tan so叩 la叩y ma達u.
  • 3. V鱈 du誰 : T鱈n hie辰u thoa誰i co湛 ba棚ng tho但ng : 300 Hz 歎 3400Hz fa = 3400 Hz fs 2.3400 = 6800 Hz fs = 8000 Hz 2.3.2. PCM : ieu co叩t (code - ma探) xung (ieu xung co叩t) Va Bo辰 n bie叩 va淡 A o Lo誰 tho但g c n L旦担誰 g t旦短 a n ho湛 Ma探 tha叩p 単o奪song i ho湛 a song sang f La叩 ma達 y u PCM 0 0 f no叩tie叩 i p b r nfs 単旦担淡g n b bw = r no叩 i Va 2 Lo誰 tho但g c n Bo辰 n bie叩 ra A 単o奪no叩 i i tha叩p Gia短ma探 i PCM f tie叩 sang p 0 0 f song song H 狸nh 2.1 . H e辰 ng tho但g tin so叩 M tho叩 n PC PCM la淡 t鱈n hie辰u PAM sau khi 単a探 l旦担誰ng t旦短 ho湛a. Nh旦ng trong PAM gi旦探a hai th担淡i gian la叩y ma達u ta ch脱 can truyen mo辰t xung la叩y ma達u th狸 trong PCM ta can truyen n xung. 1 b f = 2T = 2 = BW r So湛g PCM no叩 tie叩 n i p b 1 : 単o辰 ro辰ng cu短a bit (s) 0 1 0 1 0 1 Tb = 0 1 br Tb 2Tb au ra br cu短a bo辰 pha湛t co湛 n bit no叩i tie叩p PCM : br nfs 2nfa (bps) V鱈 du誰 : v担湛i PCM 8 bit trong he辰 tho叩ng 単ie辰n thoa誰i : + Ba棚ng tho但ng cu短a voice : 300 Hz 歎 3400 Hz fa = 3400 Hz + Tan so叩 la叩y ma達u : fs 2fa = 6800 Hz cho誰n fs = 8 KHz 3 + To叩c 単o辰 cu短a mo辰t ke但nh PCM : br nfs = 8.8.10 = 64 Kbps br 64.10 3 + Ba棚ng tho但ng cu短a mo辰t ke但nh PCM : BW = = = 32 KHz. 2 2 1 + Ne叩u trong mo辰t chu ky淡 la叩y ma達u Ts = f = 125 袖s (go誰i la淡 mo辰t s khung) ta sa辿p xe叩p N ke但nh, th狸 to叩c 単o辰 truyen mo辰t khung se探 ta棚ng le但n : R = N. br
  • 4. BW = NBW 3 V鱈 du誰 : + PCM 30 co湛 N = 32 R = 32.64.10 = 2048 Kbps BW = 32.32.10 = 1024 3 KHz 3 + PCM _ 24 co湛 N = 32 R = 24.64.10 = 1536 Kbps BW = 24.32.10 = 768 KHz 3 2.3.3. PCM-24 : la淡 chua奪n cu短a Ba辿c My探 va淡 Nha辰t : Ca叩u tru湛c PCM - 24 gom : + Ca湛c 単a khung (multiframe) co湛 12 khung (12 x 125 袖s = 1,5 ms); mo達i khung co湛 24 ke但nh gom 193 bit chie叩m 125 袖s [(24x8) + 1= 193 bit)]. Bit 単ong bo辰 go誰i la淡 bit S, ca湛c bit S cu短a khung le短 lan l旦担誰t la淡 101010 va淡 ca湛c bit S cu短a khung cha端n lan l旦担誰t la淡 001110. Frame 1 Frame 2 Frame 3 ... Frame 11 Frame 12 Ke但h 1 Ke但h 2 Ke但h 3 n n n ... Ke但h 24 n Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit Bit S 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 Frame 1 2 3 4 5 6 7 8 9 10 11 12 S - bit 1 0 1 0 1 0 0 0 1 1 1 0 2.3.4. PCM-30 : la淡 chua奪n cu短a cha但u A但u. Ca叩u tru湛c PCM-30 gom : + Ca湛c 単a khung co湛 16 khung (16 x 125 袖s = 2 ms); mo達i khung co湛 32 ke但nh gom 256 bit (8 x 32 = 256 bit). Ke但nh 0 la淡 ke但nh 単ong bo辰, ke但nh 16 la淡 ke但nh ba湛o hie辰u. Frame 0 Frame 1 Frame 2 ... Frame 14 Frame 15 Ke但h 0 Ke但h 1 n n ... Ke但h 15 Ke但h 16 Ke但h 17 n n n ... Ke但h 31 n 15 ke但h thoa誰 n i 15 ke但h thoa誰 n i ke但h 1 ke但h 16 n n Bit 1 2 3 4 5 6 7 8 Ra 1 0 0 1 1 0 1 1 : T鱈n hie辰 単og bo辰 u n 1 2 3 4 5 6 7 8 MC 1 1 D N 1 1 1 1 : Tho但g ba湛 lo達 n o i 0 1 1 1 1 1 1 1 ke但h ba湛 hie辰 16 n o u D = 1 : Tho但g ba湛 lo達kha奪 ca叩 n o i n p D = 0 : kho但g co湛 i kha奪 ca叩 n lo達 n p + 4 bit 1,2,3,4 ba湛 hie辰 cho 16 ke但h 単a (0-15) o u n u N = 1 : kho但g co湛 i kho但g kha奪 ca叩 n lo達 n n p + 4 bit 5,6,7,8 ba湛 hie辰 cho 16 ke但h sau (16-31) o u n N = 0 : co湛 i kho但g kha奪 ca叩 lo達 n n p
  • 5. * ieu che叩 PCM 単a誰t cha叩t l旦担誰ng cao nh旦ng 単o淡i ho短i ba棚ng tho但ng l担湛n. e奪 gia短m ba棚ng tho但ng 単i mo辰t n旦短a ng旦担淡i ta du淡ng 単ieu che叩 Delta, nh旦ng khi 単o湛 nhie達u l旦担誰ng t旦短 se探 l担湛n va淡 me湛o do qua湛 ta短i s旦担淡n cu探ng l担湛n. ieu che叩 PCM vi pha但n la淡 単ieu che叩 ke叩t h担誰p gi旦探a Delta va淡 PCM. Khi 単o湛 cha叩t l旦担誰ng t鱈n hie辰u va達n 単a短m ba短o, ma淡 ba棚ng tho但ng va達n gia短m mo辰t n旦短a va淡 me湛o do qua湛 ta短i s旦担淡n ch脱 co淡n 3% kho但ng 単a湛ng ke奪. ieu che叩 PCM gom 8 bits, co淡n 単ieu che叩 PCM vi pha但n ch脱 can 4 bits.