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Page 1 Amplitude Modulation : DSB-SC : u (t) = m(t) cos 2p t Power P = Conventioanal AM : u (t) = [1 + m(t)] Cos 2p t . as long as |m(t)| = 1 demodulation is simple . Practically m(t) = a m (t) . Modulation index a = ( ) ( ) , m (t) = ( ) | ( )| Power = + SSB-AM : ? Square law Detector SNR = ( ) Square law modulator ? = 2a / a ? amplitude Sensitivity Envelope Detector R C (i/p) < < 1 / R C (o/P) >> 1/ R C << 1/? = Frequency & Phase Modulation : Angle Modulation :- u (t) = Cos (2p t + Ø (t) ) Ø (t) ( ) ? 2p m(t) . dt ? phase & frequency deviation constant ? max phase deviation ?Ø = max | m(t) | ? max requency deviation ? = max |m(t) | Bandwidth : Effective Bandwidth = 2 (ß + 1) ? 98% power Noise in Analog Modulation :- ? (SNR) = = = R = m(t) cos 2p ? = / 2 Page 2 Amplitude Modulation : DSB-SC : u (t) = m(t) cos 2p t Power P = Conventioanal AM : u (t) = [1 + m(t)] Cos 2p t . as long as |m(t)| = 1 demodulation is simple . Practically m(t) = a m (t) . Modulation index a = ( ) ( ) , m (t) = ( ) | ( )| Power = + SSB-AM : ? Square law Detector SNR = ( ) Square law modulator ? = 2a / a ? amplitude Sensitivity Envelope Detector R C (i/p) < < 1 / R C (o/P) >> 1/ R C << 1/? = Frequency & Phase Modulation : Angle Modulation :- u (t) = Cos (2p t + Ø (t) ) Ø (t) ( ) ? 2p m(t) . dt ? phase & frequency deviation constant ? max phase deviation ?Ø = max | m(t) | ? max requency deviation ? = max |m(t) | Bandwidth : Effective Bandwidth = 2 (ß + 1) ? 98% power Noise in Analog Modulation :- ? (SNR) = = = R = m(t) cos 2p ? = / 2 ? (SNR) = / / = = = = = (SNR) ? (SNR) = / / = = = = (SNR) . = . = ? ? = Noise in Angle Modulation :- = PCM :- ? Min. no of samples required for reconstruction = 2? = ; ? = Bandwidth of msg signal . ? Total bits required = v bps . v ? bits / sample ? Bandwidth = R /2 = v / 2 = v . ? ? SNR = 1.76 + 6.02 v ? As Number of bits increased SNR increased by 6 dB/bit . Band width also increases. Delta Modulation :- ? By increasing step size slope over load distortion eliminated [ Signal raised sharply ] ? By Reducing step size Grannualar distortion eliminated . [ Signal varies slowly ] Digital Communication Matched filter: ? impulse response a(t) = ( T – t) . P(t) ? i/p ? Matched filter o/p will be max at multiples of ‘T’ . So, sampling @ multiples of ‘T’ will give max SNR (2 nd point ) ? matched filter is always causal a(t) = 0 for t < 0 ? Spectrum of o/p signal of matched filter with the matched signal as i/p ie, except for a delay factor ; proportional to energy spectral density of i/p. Ø ( ) = (f) Ø(f) = Ø(f) Ø*(f) e Ø ( ) = |Ø( )| e Page 3 Amplitude Modulation : DSB-SC : u (t) = m(t) cos 2p t Power P = Conventioanal AM : u (t) = [1 + m(t)] Cos 2p t . as long as |m(t)| = 1 demodulation is simple . Practically m(t) = a m (t) . Modulation index a = ( ) ( ) , m (t) = ( ) | ( )| Power = + SSB-AM : ? Square law Detector SNR = ( ) Square law modulator ? = 2a / a ? amplitude Sensitivity Envelope Detector R C (i/p) < < 1 / R C (o/P) >> 1/ R C << 1/? = Frequency & Phase Modulation : Angle Modulation :- u (t) = Cos (2p t + Ø (t) ) Ø (t) ( ) ? 2p m(t) . dt ? phase & frequency deviation constant ? max phase deviation ?Ø = max | m(t) | ? max requency deviation ? = max |m(t) | Bandwidth : Effective Bandwidth = 2 (ß + 1) ? 98% power Noise in Analog Modulation :- ? (SNR) = = = R = m(t) cos 2p ? = / 2 ? (SNR) = / / = = = = = (SNR) ? (SNR) = / / = = = = (SNR) . = . = ? ? = Noise in Angle Modulation :- = PCM :- ? Min. no of samples required for reconstruction = 2? = ; ? = Bandwidth of msg signal . ? Total bits required = v bps . v ? bits / sample ? Bandwidth = R /2 = v / 2 = v . ? ? SNR = 1.76 + 6.02 v ? As Number of bits increased SNR increased by 6 dB/bit . Band width also increases. Delta Modulation :- ? By increasing step size slope over load distortion eliminated [ Signal raised sharply ] ? By Reducing step size Grannualar distortion eliminated . [ Signal varies slowly ] Digital Communication Matched filter: ? impulse response a(t) = ( T – t) . P(t) ? i/p ? Matched filter o/p will be max at multiples of ‘T’ . So, sampling @ multiples of ‘T’ will give max SNR (2 nd point ) ? matched filter is always causal a(t) = 0 for t < 0 ? Spectrum of o/p signal of matched filter with the matched signal as i/p ie, except for a delay factor ; proportional to energy spectral density of i/p. Ø ( ) = (f) Ø(f) = Ø(f) Ø*(f) e Ø ( ) = |Ø( )| e ? o/p signal of matched filter is proportional to shifted version of auto correlation fine of i/p signal Ø (t) = R Ø (t – T) At t = T Ø (T) = R Ø (0) ? which proves 2 nd point Cauchy-Schwartz in equality :- |g (t) g (t) dt| = g (t) dt |g (t)| dt If g (t) = c g (t) then equality holds otherwise ‘<’ holds Raised Cosine pulses : P(t) = ( ) ( ) . ( ) P(f) = | | = cos | | =| | = | | ? Bamdwidth of Raised cosine filter = ? Bit rate = a ? roll o actor ? signal time period ? For Binary PSK = Q = Q = erfc . ? 4 PSK = 2Q 1 FSK:- For BPSK = Q = Q = erfc ? All signals have same energy (Const energy modulation ) ? Energy & min distance both can be kept constant while increasing no. of points . But Bandwidth Compramised. ? PPM is called as Dual of FSK . ? For DPSK = e / Page 4 Amplitude Modulation : DSB-SC : u (t) = m(t) cos 2p t Power P = Conventioanal AM : u (t) = [1 + m(t)] Cos 2p t . as long as |m(t)| = 1 demodulation is simple . Practically m(t) = a m (t) . Modulation index a = ( ) ( ) , m (t) = ( ) | ( )| Power = + SSB-AM : ? Square law Detector SNR = ( ) Square law modulator ? = 2a / a ? amplitude Sensitivity Envelope Detector R C (i/p) < < 1 / R C (o/P) >> 1/ R C << 1/? = Frequency & Phase Modulation : Angle Modulation :- u (t) = Cos (2p t + Ø (t) ) Ø (t) ( ) ? 2p m(t) . dt ? phase & frequency deviation constant ? max phase deviation ?Ø = max | m(t) | ? max requency deviation ? = max |m(t) | Bandwidth : Effective Bandwidth = 2 (ß + 1) ? 98% power Noise in Analog Modulation :- ? (SNR) = = = R = m(t) cos 2p ? = / 2 ? (SNR) = / / = = = = = (SNR) ? (SNR) = / / = = = = (SNR) . = . = ? ? = Noise in Angle Modulation :- = PCM :- ? Min. no of samples required for reconstruction = 2? = ; ? = Bandwidth of msg signal . ? Total bits required = v bps . v ? bits / sample ? Bandwidth = R /2 = v / 2 = v . ? ? SNR = 1.76 + 6.02 v ? As Number of bits increased SNR increased by 6 dB/bit . Band width also increases. Delta Modulation :- ? By increasing step size slope over load distortion eliminated [ Signal raised sharply ] ? By Reducing step size Grannualar distortion eliminated . [ Signal varies slowly ] Digital Communication Matched filter: ? impulse response a(t) = ( T – t) . P(t) ? i/p ? Matched filter o/p will be max at multiples of ‘T’ . So, sampling @ multiples of ‘T’ will give max SNR (2 nd point ) ? matched filter is always causal a(t) = 0 for t < 0 ? Spectrum of o/p signal of matched filter with the matched signal as i/p ie, except for a delay factor ; proportional to energy spectral density of i/p. Ø ( ) = (f) Ø(f) = Ø(f) Ø*(f) e Ø ( ) = |Ø( )| e ? o/p signal of matched filter is proportional to shifted version of auto correlation fine of i/p signal Ø (t) = R Ø (t – T) At t = T Ø (T) = R Ø (0) ? which proves 2 nd point Cauchy-Schwartz in equality :- |g (t) g (t) dt| = g (t) dt |g (t)| dt If g (t) = c g (t) then equality holds otherwise ‘<’ holds Raised Cosine pulses : P(t) = ( ) ( ) . ( ) P(f) = | | = cos | | =| | = | | ? Bamdwidth of Raised cosine filter = ? Bit rate = a ? roll o actor ? signal time period ? For Binary PSK = Q = Q = erfc . ? 4 PSK = 2Q 1 FSK:- For BPSK = Q = Q = erfc ? All signals have same energy (Const energy modulation ) ? Energy & min distance both can be kept constant while increasing no. of points . But Bandwidth Compramised. ? PPM is called as Dual of FSK . ? For DPSK = e / ? Orthogonal signals require factor of ‘2’ more energy to achieve same as anti podal signals ? Orthogonal signals are 3 dB poorer than antipodal signals. The 3dB difference is due to distance b/w 2 points. ? For non coherent FSK = e / ? FPSK & 4 QAM both have comparable performance . ? 32 QAM has 7 dB advantage over 32 PSK. ? Bandwidth of Mary PSK = = ; S = ? Bandwidth of Mary FSK = = ; S = ? Bandwidth efficiency S = . . ? Symbol time = log ? Band rate = Page 5 Amplitude Modulation : DSB-SC : u (t) = m(t) cos 2p t Power P = Conventioanal AM : u (t) = [1 + m(t)] Cos 2p t . as long as |m(t)| = 1 demodulation is simple . Practically m(t) = a m (t) . Modulation index a = ( ) ( ) , m (t) = ( ) | ( )| Power = + SSB-AM : ? Square law Detector SNR = ( ) Square law modulator ? = 2a / a ? amplitude Sensitivity Envelope Detector R C (i/p) < < 1 / R C (o/P) >> 1/ R C << 1/? = Frequency & Phase Modulation : Angle Modulation :- u (t) = Cos (2p t + Ø (t) ) Ø (t) ( ) ? 2p m(t) . dt ? phase & frequency deviation constant ? max phase deviation ?Ø = max | m(t) | ? max requency deviation ? = max |m(t) | Bandwidth : Effective Bandwidth = 2 (ß + 1) ? 98% power Noise in Analog Modulation :- ? (SNR) = = = R = m(t) cos 2p ? = / 2 ? (SNR) = / / = = = = = (SNR) ? (SNR) = / / = = = = (SNR) . = . = ? ? = Noise in Angle Modulation :- = PCM :- ? Min. no of samples required for reconstruction = 2? = ; ? = Bandwidth of msg signal . ? Total bits required = v bps . v ? bits / sample ? Bandwidth = R /2 = v / 2 = v . ? ? SNR = 1.76 + 6.02 v ? As Number of bits increased SNR increased by 6 dB/bit . Band width also increases. Delta Modulation :- ? By increasing step size slope over load distortion eliminated [ Signal raised sharply ] ? By Reducing step size Grannualar distortion eliminated . [ Signal varies slowly ] Digital Communication Matched filter: ? impulse response a(t) = ( T – t) . P(t) ? i/p ? Matched filter o/p will be max at multiples of ‘T’ . So, sampling @ multiples of ‘T’ will give max SNR (2 nd point ) ? matched filter is always causal a(t) = 0 for t < 0 ? Spectrum of o/p signal of matched filter with the matched signal as i/p ie, except for a delay factor ; proportional to energy spectral density of i/p. Ø ( ) = (f) Ø(f) = Ø(f) Ø*(f) e Ø ( ) = |Ø( )| e ? o/p signal of matched filter is proportional to shifted version of auto correlation fine of i/p signal Ø (t) = R Ø (t – T) At t = T Ø (T) = R Ø (0) ? which proves 2 nd point Cauchy-Schwartz in equality :- |g (t) g (t) dt| = g (t) dt |g (t)| dt If g (t) = c g (t) then equality holds otherwise ‘<’ holds Raised Cosine pulses : P(t) = ( ) ( ) . ( ) P(f) = | | = cos | | =| | = | | ? Bamdwidth of Raised cosine filter = ? Bit rate = a ? roll o actor ? signal time period ? For Binary PSK = Q = Q = erfc . ? 4 PSK = 2Q 1 FSK:- For BPSK = Q = Q = erfc ? All signals have same energy (Const energy modulation ) ? Energy & min distance both can be kept constant while increasing no. of points . But Bandwidth Compramised. ? PPM is called as Dual of FSK . ? For DPSK = e / ? Orthogonal signals require factor of ‘2’ more energy to achieve same as anti podal signals ? Orthogonal signals are 3 dB poorer than antipodal signals. The 3dB difference is due to distance b/w 2 points. ? For non coherent FSK = e / ? FPSK & 4 QAM both have comparable performance . ? 32 QAM has 7 dB advantage over 32 PSK. ? Bandwidth of Mary PSK = = ; S = ? Bandwidth of Mary FSK = = ; S = ? Bandwidth efficiency S = . . ? Symbol time = log ? Band rate = ? Energy of a signal |x(t)| dt = | [ ]| ? Power of a signal P = lim ? |x(t)| dt = lim ? |x[n]| ? x (t) ? ; x (t) ? x (t) + x (t) ? + iff x (t) & x (t) orthogonal ? Shifting & Time scaling won’t effect power . Frequency content doesn’t effect power. ? if power = 8 ? neither energy nor power signal Power = 0 ? Energy signal Power = K ? power signal ? Energy of power signal = 8 ; Power of energy signal = 0 ? Generally Periodic & random signals ? Power signals Aperiodic & deterministic ? Energy signals Precedence rule for scaling & Shifting : x(at + b) ? (1) shift x(t) by ‘b’ ? x(t + b) (2) Scale x(t + b) by ‘a’ ? x(at + b) x( a ( t + b/a)) ? (1) scale x(t) by a ? x(at) (2) shift x(at) by b/a ? x (a (t+b/a)). ? x(at +b) = y(t) ? x(t) = y ? Step response s(t) = h(t) * u(t) = h(t)dt S’ (t) = h(t) S[n] = [ ] h[n] = s[n] – s[n-1] ? e u(t) * e u(t) = [ e - e ] u(t) . ? Rect (t / 2 ) * Rect(t / 2 ) = 2 min ( , ) trapezoid ( , ) ? Rect (t / 2T) * Rect (t / 2T) = 2T tri(t / T) Hilbert Transform Pairs : e / dx = s 2p ; x e / dx = s 2p s > 0 Laplace Transform :-Read More
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