Digital Baseband Modulation & Waveform coding Techniques<br />Or<br />Source Coding Techniques<br />V. S. Hendre  Departme...
UNIT-I:  Digital Baseband Modulation Techniques and Waveform Coding Techniques<br />Base band system, Formatting textual d...
INTRODUCTION<br />Formatting: is to insure that the message is compatible with Digital Signal Processing<br />Transmit For...
INTRODUCTION<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />4<br />Formatting<br />Character Coding<br />Sampling...
Baseband Systems<br />5<br />Signal Source / information source<br />Signal Sampling circuit<br />Source quantiser encoder...
6<br />Digital info.<br />Format<br />Textual <br />info.<br />source<br />Pulse<br />modulate<br />Transmit<br />Encode<b...
Formatting Textual Data  (Character Coding)<br />Original or baseband data is either textual or analog.<br />If data is al...
ASCII Format (7 bit)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />8<br />
EBCDIC Format <br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />9<br />
Messages, Characters & Symbols <br />Textual message is first encoded in digital form by using ASCII or EBCDIC format.<br ...
Ex: Messages, Characters & Symbols <br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />11<br />
Formatting Analog Information <br />If information is in Analog form then we can not be character encoded it as in textual...
Sampling for Low Pass Signals<br />Sampling is the process of taking a periodic sample of the waveform to be transmitted.<...
Sampling for Low Pass Signals<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />14<br />
Proof for Sampling Theorem<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />15<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />16<br />V (volt)<br />f (Hz)<br />fs<br />2fs<br />3fs<br />fm(max)<br ...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />17<br />V (volt)<br />Guardband<br />f (Hz)<br />fs<br />2fs<br />fm(ma...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />18<br />V (volt)<br />Aliasing distortion<br />f (Hz)<br />2fs<br />fs<...
Sampling<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />19<br />Aliasing effect in Time Domain<br />
Sampling<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />20<br />Sampling Rate: Practical Consideration<br />Voice...
Sampling<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />21<br />Sampling Rate: Practical Consideration<br />Voice...
Why Over Sample?<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />22<br /><ul><li> Oversampling is the most economi...
 This is so because signal processing performed with high performance analog equipment is typically much more costly than ...
Why Over Sample?<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />23<br />With Oversampling<br />1. The signal is p...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />24<br />Communication<br />System<br />Continuous Wave<br />Digital Wav...
Analog Pulse Modulation (APM)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />25<br />In APM, the carrier signal i...
Waveforms for PAM, PWM and PPM<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />26<br />Modulating signal<br />carr...
Pulse Amplitude Modulation (PAM)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />27<br />It is very similar to AM<...
Pulse Width Modulation (PWM)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />28<br />The technique of varying the ...
Pulse Position Modulation (PPM)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />29<br />PPM is when the position o...
Basic Techniquesa) Variable Length Codingb) Fixed Length Coding<br />PCM, DM, ADM, DPCM etc.<br />PCM-Linear Pulse code mo...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />31<br /><ul><li>Advantages-1)Immunity to transmission noise
2)Regenerative repeaters-increases SNR
(occuresamplitude & phase distortion)
3)Encryption-privacy & security
4) Uniform representation of signal
Disadvantage: very large BW</li></li></ul><li>    Basic Block diagram<br />V. S. Hendre  Department of E&TC, TCOER, Pune<b...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />33<br />Digital info.<br />Format<br />Textual <br />info.<br />source<...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />34<br />Quantization Process<br />“A process of transforming the sample...
Operation of quantisation<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />35<br />X(t)<br />Xq(t)<br />VH<br />7<...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />36<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />37<br />Whenever x(t) is in the range 0, xq(t) maintains the constant ...
Qunatization example<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />38<br />Quant. levels<br />boundaries<br />x(...
PCM-conversion<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />39<br />PCM Sequence<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />40<br />Output<br />Xq(nTs)<br />Representation levels<br />Transfer ch...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />41<br />Two types of quantization: (a) midtread and                    ...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />42<br />Model of quantizing noise<br />Quantization error<br />Quantizi...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />43<br />Quantization Noise<br />Illustration of the quantization proces...
Transmission Bandwidth<br />N-no of bits/sample<br />Quantization levels Q=2N<br />Signaling rate=r=n.fs<br />BW (PCM)=(1/...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />45<br />Bandlimits fm-3.3KHz<br />Flat Top<br />PAM<br />Quantized PAM<...
PCM receiver<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />46<br />
ADC (Analog to Digital Converter)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />47<br />IC :0808/ 0809 Specifica...
No of bits per Sample: v or N = 8 bits
Quantization levels Q=2N  = 256
Step Size :
If Sampling Frequency is 8KHz
Bandwidth= ½  x N x Fs = 32 KHz</li></li></ul><li>Block diagram of regenerative repeaters<br />V. S. Hendre  Department of...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />49<br />s<br />Amplifier<br />i/p x(t)<br />output<br />C<br /><ul><li>...
Low o/p impd.</li></ul>Large load impd.<br />Sample & Hold Circuit<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />50<br />Output<br />Xq(nTs)<br />Representation levels<br />Signal to Q...
Signal to Quantization noise ratio: SNRq<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />51<br />If the range of a...
Signal to Quantization noise ratio: SNRq<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />52<br />
Signal to Quantization noise Ratio: SNRq<br />For quantizer<br />Noise power<br />Noise by r.v.      & its PDF <br />Mean ...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />54<br />Mean square value of r.v. x<br />Putting II)  into  I), mean sq...
Equn 1)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />55<br />=max. signal to quantisation noise ratio<br />* S...
 S/N = 3 x 22n x P
If input signal power is normalised, P≤1,
S/N ≤ 3 x 22n     ……v)normalised (S/N)q</li></li></ul><li>V. S. Hendre  Department of E&TC, TCOER, Pune<br />56<br />(S/N...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />57<br />Virtues, Limitations and Modifications of PCM<br />   Advantage...
PCM waveforms<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />58<br />Criteria for comparing and selecting PCM wav...
Uniform and non-uniform quantisation<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />59<br />Uniform (linear) quan...
Dis-advantages:Uniform Quantisation<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />60<br />1) let n=4 bits<br />	...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />61<br />1.0<br />Probability density function<br />0.5<br />2.0<br />1....
2) Statistical of speech amplitudes<br />Another way:   Crest Factor = Peak Value / RMS Value<br />For speech or music sig...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />63<br />Non-Uniform Quantisation<br />-Uses the input statistics to tun...
Nonuniform Quantizer<br />Used to reduce quantization error and increase the dynamic range when input signal is not unifor...
“Compressing-and-expanding” is called “companding.”<br />Nonuniform quantizer<br />Discrete<br />samples<br />Uniform<br /...
Compression Techniques<br />
Practical Implementation of µ-law compressor<br />
Output SNR of 8-bit PCM systems with and without companding.<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />69<br />compression+expansion        companding<br />Non-uniform quanti...
Companding curve<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />70<br />
Companding Curve<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />71<br />O/P. Voltage of Compander<br />Compressio...
Effect of companding<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />72<br />
Compression laws<br />Two Laws-’’ Law-United states, Canada,      <br />                            Japan (=225)<br />‘A...
SNR Performance of PCM with  Law<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />74<br />Fixed SNR-irrespective o...
Compression characteristic for  Law<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />75<br />As  µ   ∞,  Linear A...
‘A’ Law characteristics<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />76<br />Compression characteristics<br />A...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />77<br />Figure 3.14 Compression laws. (a) m-law. (b) A-law.<br />
Noise consideration in PCM systems      (Channel noise,  quantization noise)<br />V. S. Hendre  Department of E&TC, TCOER,...
Examples on PCM<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />79<br />A low pass signal of 3 KHz B.W. & amplitud...
Examples on PCM<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />80<br />ii) Bit Transmission Rate:<br />iii) (S/N)...
Examples on PCM<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />81<br />2. A compact disc recording system samples...
PCM with Noise<br />82<br />
Delta Modulation<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />83<br />PCM-drabacks-1)Large signalling rate<br /...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />84<br />For reduced step – ‘0’-transmitted<br />For increased step- ‘1’...
Waveform representation<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />85<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />86<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />87<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />88<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />89<br />“start up interval”-interval required to meet approximated sign...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />90<br />The modulator consists of a comparator, a quantizer, and an acc...
Slope Overload Condition<br />The slope overload distortion will occur if<br />
V. S. Hendre  Department of E&TC, TCOER, Pune<br />92<br />
Examples on DM<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />93<br />A delta modulated system is designed to ope...
Examples on DM<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />94<br />2. A 1KHz signal sampled by 8KHz, is to be ...
DM receiver<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />95<br />*When received binary 1-accumulator adds + to...
Adaptive Delta Modulation (ADM)<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />96<br />Step size -adaptive to va...
ADM-waveform<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />97<br />
ADM-receiver<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />98<br />
Why DM is not alternative for PCM for voice Signals?<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />99<br />Let u...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />100<br />Delta-Sigma modulation (sigma-delta modulation)<br />    -Delt...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />101<br />F>nyquist rate<br />1<br />Product modulator<br />output<br /...
A single period of the trigonometric sine function, sampled 100 times and represented as a PDM bitstream, is:0101011011110...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />103<br />
Applications<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />104<br />Data conversion systems<br />Frequency Synth...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />105<br />Differential Pulse-Code Modulation (DPCM)<br /><ul><li>PCM has...
encoded signal contains redundant information (audio & video –  </li></ul>adjucent samples ~same)<br /><ul><li>DPCM can e...
-Difference in adjucent samples (present & previous)-encoded-transmitted
Reduces overall bit rate & no. of bits required to transmit</li></li></ul><li>DPCM Transmitter<br />V. S. Hendre  Departme...
V. S. Hendre  Department of E&TC, TCOER, Pune<br />107<br />prediction<br />Unquanitsedi/p signal <br />Quantisation error...
DPCM receiver<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />108<br />
Comparision<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />109<br />
PCM with Noise<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />110<br />The reconstructed message contains two typ...
PCM with Noise<br />V. S. Hendre  Department of E&TC, TCOER, Pune<br />111<br />If we consider that the PCM word bits are ...
PCM with Noise<br />The random bit error can be obtained by mean square value<br />
PCM with Noise<br />113<br />
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Unit i-pcm-vsh

  1. 1. Digital Baseband Modulation & Waveform coding Techniques<br />Or<br />Source Coding Techniques<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />1<br />UNIT-I<br />
  2. 2. UNIT-I: Digital Baseband Modulation Techniques and Waveform Coding Techniques<br />Base band system, Formatting textual data, messages, characters & symbols,<br /> Formatting analog information, Sources of corruption, <br />PCM, Uniform and Non uniform quantization, <br />Baseband modulation, <br />Noise consideration in PCM systems, <br />DPCM, DM,ADM, LPC.<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />2<br />
  3. 3. INTRODUCTION<br />Formatting: is to insure that the message is compatible with Digital Signal Processing<br />Transmit Formatting: is a transformation from source information to digital symbols.<br />Source coding: data compression + formatting<br />Formatting<br />Character Coding<br />Sampling<br />Quantization<br />Pulse Code Modulation (PCM)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />3<br />
  4. 4. INTRODUCTION<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />4<br />Formatting<br />Character Coding<br />Sampling<br />Quantization<br />Pulse Code Modulation (PCM)<br />Source Coding<br />Predictive Coding, Block Coding<br />Variable Length Coding<br />Synthesis Coding<br />Lossless Compression<br />Lossy compression<br />Baseband Signaling<br />Line Codes/Data Formats<br />RZ,NRZ, Phase encoded, Multilevel binary, PAM, PPM ,PWM<br />
  5. 5. Baseband Systems<br />5<br />Signal Source / information source<br />Signal Sampling circuit<br />Source quantiser encoder<br />Channel encoder<br />modulator<br />Communication channel<br />AWGN<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />
  6. 6. 6<br />Digital info.<br />Format<br />Textual <br />info.<br />source<br />Pulse<br />modulate<br />Transmit<br />Encode<br />Sample<br />Quantize<br />Analog <br />info.<br />Channel<br />Pulse<br />waveforms<br />Bit stream<br />Format<br />Analog <br />info.<br />Low-pass<br />filter<br />Decode<br />Demodulate/<br />Detect<br />Receive<br />Textual <br />info.<br />sink<br />Digital info.<br />Baseband Systems<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />
  7. 7. Formatting Textual Data (Character Coding)<br />Original or baseband data is either textual or analog.<br />If data is alphanumeric text, it will be character encoded with some standard formats.<br />These formats are:<br />ASCII (American Standard Code for Information Interchange)<br />EBCDIC: Extended Binary Coded Decimal Interchange Code.<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />7<br />
  8. 8. ASCII Format (7 bit)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />8<br />
  9. 9. EBCDIC Format <br />V. S. Hendre Department of E&TC, TCOER, Pune<br />9<br />
  10. 10. Messages, Characters & Symbols <br />Textual message is first encoded in digital form by using ASCII or EBCDIC format.<br />This digital sequence of bits is called as bit stream or baseband signal.<br />Groups of ‘K’ bits can be combined to form new digits or Symbols.<br />Total no of symbols =M=2K .<br />A system using a symbol size of M is called as M-ary System.<br />M= 2- Binary System, M=3-Trinary System<br />M=4 –Quaternary System, M=5- 5ary system<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />10<br />
  11. 11. Ex: Messages, Characters & Symbols <br />V. S. Hendre Department of E&TC, TCOER, Pune<br />11<br />
  12. 12. Formatting Analog Information <br />If information is in Analog form then we can not be character encoded it as in textual form.<br />Here we need to convert it in Digital form by using the processes of Sampling & Quantization<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />12<br />
  13. 13. Sampling for Low Pass Signals<br />Sampling is the process of taking a periodic sample of the waveform to be transmitted.<br />Sampling of signal is the fundamental operation in digital comm. It is the process of conversing an analog signal (continuous time) into discrete time signal. <br />Statement for Low pass Sampling Theorem: <br /> A continuous time band limited signal can be completely represented in it sample form and recovered back if the sampling freq fs ≥ 2 w. when fs- sampling freq and w- is the max freq present in the signal.<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />13<br />Where fs = sampling frequency<br />fm(max) = maximum frequency of the modulating signal<br />
  14. 14. Sampling for Low Pass Signals<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />14<br />
  15. 15. Proof for Sampling Theorem<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />15<br />
  16. 16. V. S. Hendre Department of E&TC, TCOER, Pune<br />16<br />V (volt)<br />f (Hz)<br />fs<br />2fs<br />3fs<br />fm(max)<br />fs+fm(max)<br />fs-fm(max)<br />Sampling<br />Three basic condition of sampling process:<br />Sampling at fs=2fm(max)<br />
  17. 17. V. S. Hendre Department of E&TC, TCOER, Pune<br />17<br />V (volt)<br />Guardband<br />f (Hz)<br />fs<br />2fs<br />fm(max)<br />fs-fm(max)<br />fs+fm(max)<br />Sampling<br />Sampling at fs>2fm(max)<br />This sampling rate creates a guard band between fm(max) and the lowest frequency component fs-fm(max) of the sampling harmonics.<br />
  18. 18. V. S. Hendre Department of E&TC, TCOER, Pune<br />18<br />V (volt)<br />Aliasing distortion<br />f (Hz)<br />2fs<br />fs<br />3fs<br />fs-fm(max)<br />fm(max)<br />fs+fm(max)<br />Sampling<br />Sampling at fs<2fm(max)<br /> Aliasing: the distortion produced by the overlapping components from adjacent bands<br /> Aliasing occurs when a signal is sampled below its Nyquist rate<br />
  19. 19. Sampling<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />19<br />Aliasing effect in Time Domain<br />
  20. 20. Sampling<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />20<br />Sampling Rate: Practical Consideration<br />Voice Signals: Fmmax: 3.4 KHz<br /> Nyquist Criteria: 2 x 3.4K =6.8KHz<br /> Practical Sampling Rate: 8KHz.<br />2. High quality Music System:<br /> Max. Bandwidth : 20KHz<br /> Nyquist Criteria; 2 x 20K = 40 KHz<br /> Practical Sampling Rate:44.1 Ksamples/sec<br />3. Studio Quality Audio : Sampling Rate: 48.0 Ksamples/sec<br />Thus by an engineer’s version, Nyquist sampling Rate is<br />
  21. 21. Sampling<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />21<br />Sampling Rate: Practical Consideration<br />Voice Signals: Fmmax: 3.4 KHz<br /> Nyquist Criteria: 2 x 3.4K =6.8KHz<br /> Practical Sampling Rate: 8KHz.<br />2. High quality Music System:<br /> Max. Bandwidth : 20KHz<br /> Nyquist Criteria; 2 x 20K = 40 KHz<br /> Practical Sampling Rate:44.1 Ksamples/sec<br />3. Studio Quality Audio : Sampling Rate: 48.0 Ksamples/sec<br />Thus by an engineer’s version, Nyquist sampling Rate is<br />
  22. 22. Why Over Sample?<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />22<br /><ul><li> Oversampling is the most economic solution for the task of transforming an analog signal to a digital signal.
  23. 23. This is so because signal processing performed with high performance analog equipment is typically much more costly than using digital signal processing</li></ul>equipment to perform the same task.<br />Without Oversampling<br />1. The signal passes through a high performance analog lowpass filter to limit its bandwidth.<br />2. The filtered signal is sampled at the Nyquist rate for the (approximated) bandlimited signal. <br />3. The samples are processed by an analog-to-digital converter that maps the continuous-valued samples to a finite list of discrete output levels.<br />
  24. 24. Why Over Sample?<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />23<br />With Oversampling<br />1. The signal is passed through a low performance (less costly) analog low-pass filter (prefilter) to limit its bandwidth.<br />2. The pre-filtered signal is sampled at the (now higher) Nyquist rate for the (approximated) bandlimited signal.<br />3. The samples are processed by an analog-to-digital converter that maps the continuous-valued samples to a finite list of discrete output levels.<br />4. The digital samples are then processed by a high performance digital filter to<br />reduce the bandwidth of the digital samples.<br />5. The sample rate at the output of the digital filter is reduced in proportion to<br />the bandwidth reduction obtained by this digital filter.<br />
  25. 25. V. S. Hendre Department of E&TC, TCOER, Pune<br />24<br />Communication<br />System<br />Continuous Wave<br />Digital Wave<br />Analogue Pulse <br />Modulation<br />Digital Pulse <br />Modulation<br />PAM<br />PWM<br />PPM<br />Analogue Pulse Modulation Chart<br />
  26. 26. Analog Pulse Modulation (APM)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />25<br />In APM, the carrier signal is in the form of pulse form, and the modulated signal is where one of the characteristics either (amplitude, width, or position) is changed according to the modulating/audio signal.<br />Three common techniques of APM:<br />Pulse amplitude modulation (PAM)<br />Pulse Width Modulation (PWM)<br />Pulse Position Modulation (PPM)<br />
  27. 27. Waveforms for PAM, PWM and PPM<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />26<br />Modulating signal<br />carrier signal<br />PAM<br />(dual polarity)<br />PWM<br />PPM<br />
  28. 28. Pulse Amplitude Modulation (PAM)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />27<br />It is very similar to AM<br />The amplitude of a carrier signal is varied according to the amplitude of the modulating signal.<br />Two type PAM<br />Dual- polarity PAM<br />Single -polarity PAM <br />
  29. 29. Pulse Width Modulation (PWM)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />28<br />The technique of varying the width of the constant amplitude pulse proportional to the amplitude of the modulating signal.<br />PWM gives a better signal to noise performance than PAM<br />
  30. 30. Pulse Position Modulation (PPM)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />29<br />PPM is when the position of a constant width and constant amplitude pulse within prescribed time slot is varied according to the amplitude of the modulating signal. <br />
  31. 31. Basic Techniquesa) Variable Length Codingb) Fixed Length Coding<br />PCM, DM, ADM, DPCM etc.<br />PCM-Linear Pulse code modulation<br />Need-Analog PAM signaldigital<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />30<br />
  32. 32. V. S. Hendre Department of E&TC, TCOER, Pune<br />31<br /><ul><li>Advantages-1)Immunity to transmission noise
  33. 33. 2)Regenerative repeaters-increases SNR
  34. 34. (occuresamplitude & phase distortion)
  35. 35. 3)Encryption-privacy & security
  36. 36. 4) Uniform representation of signal
  37. 37. Disadvantage: very large BW</li></li></ul><li> Basic Block diagram<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />32<br />
  38. 38. V. S. Hendre Department of E&TC, TCOER, Pune<br />33<br />Digital info.<br />Format<br />Textual <br />info.<br />source<br />Pulse<br />modulate<br />Transmit<br />Encode<br />Sample<br />Quantize<br />Analog <br />info.<br />Channel<br />Pulse<br />waveforms<br />Bit stream<br />Format<br />Analog <br />info.<br />Low-pass<br />filter<br />Decode<br />Demodulate/<br />Detect<br />Receive<br />Textual <br />info.<br />sink<br />Digital info.<br />
  39. 39. V. S. Hendre Department of E&TC, TCOER, Pune<br />34<br />Quantization Process<br />“A process of transforming the sample amplitude x(nTs) into a discrete amplitude xq(nTs)<br /><ul><li>Amplitude quantizing: Mapping samples of a continuous amplitude waveform to a finite set of amplitudes.</li></ul>12<br />
  40. 40. Operation of quantisation<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />35<br />X(t)<br />Xq(t)<br />VH<br />7<br />q7<br />Quantization level<br /><br />qo<br />o<br />VL<br />=(VH-VL)/Q, Q:no of levels-signal is divided (Q=8), Q=2N, N=bits/sample<br />
  41. 41. V. S. Hendre Department of E&TC, TCOER, Pune<br />36<br />
  42. 42. V. S. Hendre Department of E&TC, TCOER, Pune<br />37<br />Whenever x(t) is in the range 0, xq(t) maintains the constant level qo<br />xq(t) makes a quantum jump of step size <br />Quantized signal-approximation of original signal<br />approximated signal is practically indistinguishable form original signal<br />Quantization removes additive noise<br /><br /> /2<br />
  43. 43. Qunatization example<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />38<br />Quant. levels<br />boundaries<br />x(nTs): sampled values<br />xq(nTs): quantized values<br />amplitude<br />x(t)<br /> 3.1867<br /> 2.2762<br /> 1.3657<br /><br /> 0.4552<br /> -0.4552<br /> -1.3657<br /> -2.2762<br /> -3.1867<br />Ts: sampling time<br />Actual<br />Sample <br />value<br />t<br />
  44. 44. PCM-conversion<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />39<br />PCM Sequence<br />
  45. 45. V. S. Hendre Department of E&TC, TCOER, Pune<br />40<br />Output<br />Xq(nTs)<br />Representation levels<br />Transfer characteristics of quantizer/quantizer curve<br /> 7/2<br /> 5/2<br />Maximum quantization error<br />/2<br /> 3/2<br /><br />-X(nTs)<br />Input<br />X(nTs)<br />/2<br /><br />Decision levels<br />3<br />4<br />0<br />2<br /> -/2<br />Overload levels<br /> -3/2<br /> -5/2<br /><br />Peak to peak excursion of the signal<br />Quantization error ()<br />/2<br />Input<br />X(nTs)<br /><br /> -/2<br />
  46. 46. V. S. Hendre Department of E&TC, TCOER, Pune<br />41<br />Two types of quantization: (a) midtread and (b) midrise.<br />13<br />
  47. 47. V. S. Hendre Department of E&TC, TCOER, Pune<br />42<br />Model of quantizing noise<br />Quantization error<br />Quantizing error: The difference between the input and output of a quantizer<br />Maximum quantisation error=<br />
  48. 48. V. S. Hendre Department of E&TC, TCOER, Pune<br />43<br />Quantization Noise<br />Illustration of the quantization process. <br />14<br />
  49. 49. Transmission Bandwidth<br />N-no of bits/sample<br />Quantization levels Q=2N<br />Signaling rate=r=n.fs<br />BW (PCM)=(1/2) x signaling rate<br /> (But ) <br />V. S. Hendre Department of E&TC, TCOER, Pune<br />44<br />
  50. 50. V. S. Hendre Department of E&TC, TCOER, Pune<br />45<br />Bandlimits fm-3.3KHz<br />Flat Top<br />PAM<br />Quantized PAM<br />P<br />C<br />M<br />N bit<br />q-level<br />Parallel to serial converter<br />Low pass<br />Filter<br />Sample & hold circuit<br />Quantiser<br />(uniform)<br />Binary encoder<br />Good SNR<br />8 bit<br />-approximation<br />-rounding off<br />-reduces additive noise <br />fc=fm<br />Fs>>2fm<br />@ 8KHz<br />R=64 kbps<br />Analog Speech signal<br />(300Hz- 3.3 KHz)<br />Pulse<br />Generator<br />Basic Block diagram<br />PCM Transmitter<br />X(t)<br />
  51. 51. PCM receiver<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />46<br />
  52. 52. ADC (Analog to Digital Converter)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />47<br />IC :0808/ 0809 Specifications<br /><ul><li>Max Input Voltage: 0 to 5V or -2.5V to +2.5V
  53. 53. No of bits per Sample: v or N = 8 bits
  54. 54. Quantization levels Q=2N = 256
  55. 55. Step Size :
  56. 56. If Sampling Frequency is 8KHz
  57. 57. Bandwidth= ½ x N x Fs = 32 KHz</li></li></ul><li>Block diagram of regenerative repeaters<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />48<br />Decision making Device<br />Amplitude Equaliser<br />Regenerated PCM wave<br />Distorted PCM wave<br />Timing Circuit<br />
  58. 58. V. S. Hendre Department of E&TC, TCOER, Pune<br />49<br />s<br />Amplifier<br />i/p x(t)<br />output<br />C<br /><ul><li>Unity gain
  59. 59. Low o/p impd.</li></ul>Large load impd.<br />Sample & Hold Circuit<br />
  60. 60. V. S. Hendre Department of E&TC, TCOER, Pune<br />50<br />Output<br />Xq(nTs)<br />Representation levels<br />Signal to Quantization noise ratio: SNRq<br /> 7/2<br /> 5/2<br />Maximum quantization error<br />/2<br /> 3/2<br /><br />-X(nTs)<br />Input<br />X(nTs)<br />/2<br /><br />Decision levels<br />3<br />4<br />0<br />2<br /> -/2<br />Overload levels<br /> -3/2<br /> -5/2<br /><br />Peak to peak excursion of the signal<br />Quantization error ()<br />/2<br />Input<br />X(nTs)<br /><br /> -/2<br />
  61. 61. Signal to Quantization noise ratio: SNRq<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />51<br />If the range of amplitude is from – Xmax to + Xmax<br />The step size <br />
  62. 62. Signal to Quantization noise ratio: SNRq<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />52<br />
  63. 63. Signal to Quantization noise Ratio: SNRq<br />For quantizer<br />Noise power<br />Noise by r.v. & its PDF <br />Mean square value<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />53<br />
  64. 64. V. S. Hendre Department of E&TC, TCOER, Pune<br />54<br />Mean square value of r.v. x<br />Putting II) into I), mean square value of noise voltage <br /> =<br />At R=1, noise power is normalized<br /> Normalized noise power/ quantization noise power = <br />
  65. 65. Equn 1)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />55<br />=max. signal to quantisation noise ratio<br />* S/N & n relation<br /><ul><li>If input x(t)-normalised, Mmax=1
  66. 66.  S/N = 3 x 22n x P
  67. 67. If input signal power is normalised, P≤1,
  68. 68. S/N ≤ 3 x 22n ……v)normalised (S/N)q</li></li></ul><li>V. S. Hendre Department of E&TC, TCOER, Pune<br />56<br />(S/N)q==>dB<br />
  69. 69. V. S. Hendre Department of E&TC, TCOER, Pune<br />57<br />Virtues, Limitations and Modifications of PCM<br /> Advantages of PCM<br /> 1. Robustness to noise and interference<br /> 2. Efficient regeneration <br /> 3. Efficient SNR and bandwidth trade-off<br /> 4. Uniform format <br /> 5. Secure <br />
  70. 70. PCM waveforms<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />58<br />Criteria for comparing and selecting PCM waveforms:<br />Spectral characteristics (power spectral density and bandwidth efficiency)<br />Bit synchronization capability<br />Error detection capability<br />Interference and noise immunity<br />Implementation cost and complexity <br />
  71. 71. Uniform and non-uniform quantisation<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />59<br />Uniform (linear) quantizing: step size -uniform<br />No assumption about amplitude statistics and correlation properties of the input.<br />Not using the user-related specifications<br />Robust to small changes in input statistic by not finely tuned to a specific set of input parameters<br />Simply implemented<br />Over complete range of signal max=|/2|<br />Application of linear quantizer:<br />Signal processing, graphic and display applications, process control applications<br />
  72. 72. Dis-advantages:Uniform Quantisation<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />60<br />1) let n=4 bits<br /> Q=2n=24=16 levels<br /> =2/q=(2/16)=(1/8) v<br /> max=|/2|=(1/16)<br /> If signal range=16 V, max=1 V is acceptable<br /> But it is very Harmful for signal amplitudes 2, 3 V….Lower<br /> Acceptable-signal amplitudes 15, 16… Higher<br /> Non-Uniform quantization<br />
  73. 73. V. S. Hendre Department of E&TC, TCOER, Pune<br />61<br />1.0<br />Probability density function<br />0.5<br />2.0<br />1.0<br />3.0<br />Normalized magnitude of speech signal<br />0.0<br />2) Statistical of speech amplitudes<br />In speech, weak signals are more frequent than strong ones.<br />Using equal step sizes (uniform quantizer) gives low for weak signals and high for strong signals.<br />Adjusting the step size of the quantizer by taking into account the speech statistics improves the SNR for the input range. <br />
  74. 74. 2) Statistical of speech amplitudes<br />Another way: Crest Factor = Peak Value / RMS Value<br />For speech or music signals Crest factor is very high.<br />
  75. 75. V. S. Hendre Department of E&TC, TCOER, Pune<br />63<br />Non-Uniform Quantisation<br />-Uses the input statistics to tune quantizer<br />parameters<br />-Larger SNR than uniform quantizing with same number of levels<br />-Non-uniform intervals in the dynamic range with same quantization noise variance<br />-Application of non-uniform quantizer:<br />Commonly used for speech <br />-for voice-amplitude values-concentrated near zero<br />-variable step size-directly not applicable (generates error)<br />-process:-signal amplification-at low level &<br /> -signal attenuation –at high level &<br /> - Uniform quantization<br />-overall effect-Non-Uniform Quantization<br />
  76. 76. Nonuniform Quantizer<br />Used to reduce quantization error and increase the dynamic range when input signal is not uniformly distributed over its allowed range of values.<br />allowed values<br />input<br />values for most<br />of time<br />time<br />
  77. 77. “Compressing-and-expanding” is called “companding.”<br />Nonuniform quantizer<br />Discrete<br />samples<br />Uniform<br />Quantizer<br />digital signals<br />Compressor<br /> • • • •<br />Channel<br /> • • • •<br />output<br />Decoder<br />Expander<br />received<br />digital signals<br />
  78. 78. Compression Techniques<br />
  79. 79. Practical Implementation of µ-law compressor<br />
  80. 80. Output SNR of 8-bit PCM systems with and without companding.<br />
  81. 81. V. S. Hendre Department of E&TC, TCOER, Pune<br />69<br />compression+expansion companding<br />Non-uniform quantization….process<br />At the transmitter Uniformly quantizing the “compressed” signal. <br />At the receiver, an inverse compression/expansion characteristic, called “expansion” is employed to avoid signal distortion. <br />Compress<br />Qauntize<br />Expand<br />Channel<br />Transmitter<br />Receiver<br />
  82. 82. Companding curve<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />70<br />
  83. 83. Companding Curve<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />71<br />O/P. Voltage of Compander<br />Compression<br />Expansion<br />I/P. Voltage of Compander<br />Expansion<br />Compression<br />
  84. 84. Effect of companding<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />72<br />
  85. 85. Compression laws<br />Two Laws-’’ Law-United states, Canada, <br /> Japan (=225)<br />‘A’ Law- Europe & India (A=87.6)<br />’’ Law Defn:<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />73<br />W1(t)-input to compressor, allowed value= 1<br />W2(t)-output of compressor<br />Appli: speech, music signals, PCM systems<br />
  86. 86. SNR Performance of PCM with  Law<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />74<br />Fixed SNR-irrespective of wide variations of signal levels among individual talkers<br />
  87. 87. Compression characteristic for  Law<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />75<br />As µ  ∞, Linear Amplification<br />Standard Value of µ=255<br />
  88. 88. ‘A’ Law characteristics<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />76<br />Compression characteristics<br />As A  ∞, Linear Amplification<br />Standard Value of A=87.6<br />
  89. 89. V. S. Hendre Department of E&TC, TCOER, Pune<br />77<br />Figure 3.14 Compression laws. (a) m-law. (b) A-law.<br />
  90. 90. Noise consideration in PCM systems (Channel noise, quantization noise)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />78<br />
  91. 91. Examples on PCM<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />79<br />A low pass signal of 3 KHz B.W. & amplitude over -5 volts to +5 volts range is sampled at Nyquist rate & converted to 8 bit PCM using uniform quantization. The mean squared value of message signal is 2 volt-squared. <br /> Calculate i) normalized power for quantization noise ii) Bit transmission rate iii) (S/N)Q in dB<br />Soln: Given : W=3KHz, VL =-5V, VH =5V, N=8<br />i) Normalized quantization noise:<br />
  92. 92. Examples on PCM<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />80<br />ii) Bit Transmission Rate:<br />iii) (S/N)Q in dB:<br />
  93. 93. Examples on PCM<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />81<br />2. A compact disc recording system samples each of the two stereo signals with 16 bit A/D converter at 44.1Kbps. Determine i) output S/N ratio for full scale sinusoid<br /> ii) The bit stream of digitized data is augmented by addition of error correcting bits, clock extraction bits etc., these additional bits represents 100% overhead. Determine output bit rate of the system.<br /> iii) The CD can record an hours worth of music. Determine no of bits recorded on CD.<br />Soln: i) Output (S/N) = (1.76+6*N) = 97.76 dB<br />ii) Bit rate of single channel: 16*44.1=705.6Kbps<br />For two channels :705.6*2=1.411Mbps<br />For additional 100% overhead<br />Final Bit rate = 1.411*2=2.8224Mbps<br />ii)This o/p bit rate represents 2.8224Mbps bits are coming per second (1 second). So, number of bits recorded in hour (3600 seconds) will be=2.8224Mbps x 3600=1.016 x 10^10 bits.<br />
  94. 94. PCM with Noise<br />82<br />
  95. 95. Delta Modulation<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />83<br />PCM-drabacks-1)Large signalling rate<br /> -2) Larger transmission BW<br />Delta modulation:- 1bit/sample<br />Present sample-compared with previous<br />Result-Increase/Decrease in amplitude<br />Input x(t)approximated , fixed step size <br />Diffn:x(t) & staircase approximated <br />2 levels:+ or -<br />If diffn:+ve, increased by one step  & has step with Ts=delay time<br />If diffn:-ve, decreased by one step  & has step with Ts=delay time<br />
  96. 96. V. S. Hendre Department of E&TC, TCOER, Pune<br />84<br />For reduced step – ‘0’-transmitted<br />For increased step- ‘1’-transmitted<br /> for each sample-one bit transmitted<br />Delta modulator/transmitter<br />
  97. 97. Waveform representation<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />85<br />
  98. 98. V. S. Hendre Department of E&TC, TCOER, Pune<br />86<br />
  99. 99. V. S. Hendre Department of E&TC, TCOER, Pune<br />87<br />
  100. 100. V. S. Hendre Department of E&TC, TCOER, Pune<br />88<br />
  101. 101. V. S. Hendre Department of E&TC, TCOER, Pune<br />89<br />“start up interval”-interval required to meet approximated signal to input signal<br />“Hunting” of approximated signal:-condition whenever input signal is almost constant or flat<br />Error (kTs) Granular Noise<br />When input signal increases or decreases too rapidly, approximated signal lags behind “Slope Overload error”<br />Advantages:1) transmits only 1 bit/sample<br /> signaling rate & transmission BW-reduced<br /> 2)transmitter & receiver –implementation –easy<br />Disadvantages:-1)Granular noise,2)slope overlaod<br /> Overcome-ADM<br />
  102. 102. V. S. Hendre Department of E&TC, TCOER, Pune<br />90<br />The modulator consists of a comparator, a quantizer, and an accumulator<br />Two types of quantization errors :<br />Slope overload distortion and granular noise<br />
  103. 103. Slope Overload Condition<br />The slope overload distortion will occur if<br />
  104. 104. V. S. Hendre Department of E&TC, TCOER, Pune<br />92<br />
  105. 105. Examples on DM<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />93<br />A delta modulated system is designed to operate at five times the nyquist rate for a signal with 3Khz B.W. Determine the max. amplitude of a 2KHz input sinusoid for which the delta mod doesn't have slope overload. Quantizing step size is 250mV<br />Soln: Given : W=3KHz, fm =2 KHz, fs =5 * 3 *2= 30KHz, <br />
  106. 106. Examples on DM<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />94<br />2. A 1KHz signal sampled by 8KHz, is to be encoded by using 1) 12 bit PCM 2) DM system. If 20 cycles of 1 KHz are digitized, state how many bits will be there in digital output signal in each case. State signaling rate and B.W. in each case.<br />Soln: 1) 12 bit PCM: Signaling Rate= v * fs=96Kbps<br /> B.W. = 48KHz <br />Tm = 1/1000, Ts =1/800, <br />Samples in one cycle= Tm/Ts = 8<br />In 20 cycles = 8*20 =160 samples<br />No of bits transmitted = 160 * 12 =1920<br />2) DM systems<br /> Signaling Rate: 8Kbps, B.W.=4KHz<br /> No of bits transmitted= 160bits<br />
  107. 107. DM receiver<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />95<br />*When received binary 1-accumulator adds + to previous o/p<br />*When received binary 0-accumulator subtracts  from previous o/p<br />
  108. 108. Adaptive Delta Modulation (ADM)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />96<br />Step size -adaptive to variations of input signal x(t)<br />Step size-reduced for slowly varying signal<br />Step size-increased for steep segment of signal <br />ADM transmitter<br />
  109. 109. ADM-waveform<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />97<br />
  110. 110. ADM-receiver<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />98<br />
  111. 111. Why DM is not alternative for PCM for voice Signals?<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />99<br />Let us consider 8 bit PCM,<br /> N=8, Q=256, <br />
  112. 112. V. S. Hendre Department of E&TC, TCOER, Pune<br />100<br />Delta-Sigma modulation (sigma-delta modulation)<br /> -Delta modulator with integrator<br /> -removes draw back of delta modulation<br /> -(Input to quantizer-approximation-derivative of input signal-demodulation-error)<br />Beneficial effects of using integrator:<br /> 1. Pre-emphasize the low-frequency content<br /> 2. Increase correlation between adjacent samples <br /> (reduce the variance of the error signal at the quantizer input )<br /> 3. Simplify receiver design<br />Because the transmitter has an integrator , the receiver consists simply of a low-pass filter. <br />(The accumulator in the conventional DM receiver is cancelled by the differentiator )<br />
  113. 113. V. S. Hendre Department of E&TC, TCOER, Pune<br />101<br />F>nyquist rate<br />1<br />Product modulator<br />output<br />+1<br />-ve i/p<br />+ve i/p<br />-1<br /> Two equivalent versions of delta-sigma modulation system.<br />
  114. 114. A single period of the trigonometric sine function, sampled 100 times and represented as a PDM bitstream, is:0101011011110111111111111111111111011111101101101010100100100000010000000000000000000001000010010101<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />102<br />
  115. 115. V. S. Hendre Department of E&TC, TCOER, Pune<br />103<br />
  116. 116. Applications<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />104<br />Data conversion systems<br />Frequency Synthesizers<br />SMPS<br />motor controls <br />Sony’s Super Audio CD (SACD) format<br />
  117. 117. V. S. Hendre Department of E&TC, TCOER, Pune<br />105<br />Differential Pulse-Code Modulation (DPCM)<br /><ul><li>PCM has the sampling rate higher than the Nyquist rate .
  118. 118. encoded signal contains redundant information (audio & video – </li></ul>adjucent samples ~same)<br /><ul><li>DPCM can efficiently remove this redundancy.
  119. 119. -Difference in adjucent samples (present & previous)-encoded-transmitted
  120. 120. Reduces overall bit rate & no. of bits required to transmit</li></li></ul><li>DPCM Transmitter<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />106<br />Q level<br />Principal of working: Prediction<br />
  121. 121. V. S. Hendre Department of E&TC, TCOER, Pune<br />107<br />prediction<br />Unquanitsedi/p signal <br />Quantisation error<br />Quantised version of signal<br />Original sample value<br />Quantisation error (+/-)<br />
  122. 122. DPCM receiver<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />108<br />
  123. 123. Comparision<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />109<br />
  124. 124. PCM with Noise<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />110<br />The reconstructed message contains two types of noise: 1) Quantization Noise 2) Decoding Noise<br />Decoding Noise: Random Noise added to PCM signal at the receiver causes regeneration errors that appears as erroneous digits in the codeword is called as decoding noise.<br />Expression for Decoding Noise power:<br />Let us consider a binary PCM with uniform quantization.<br />Let ‘v’ no of bits/samples & PCM is having very small bit error probability ‘Pe’.<br />Bit error probability: probability of a particular bit in error<br /> When Pe << 1, The Prob. of one error in given word is <br /> P= v Pe --------- (i) <br />
  125. 125. PCM with Noise<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />111<br />If we consider that the PCM word bits are given by<br /> bv-1, bv-2,……………….. b1, b0,<br />If there is error in mth bit , the decoded codeword is shifted by ±2m<br />For Ex. The transmitted codeword: 00001000<br />& error occurred at bo bit<br />Received codeword is :00001001<br />Decoded codeword is shifted by ±20 = ± i.e. by one step.<br />Thus Error in mth bit is given by:<br />m=±2m ……………..(ii)<br />
  126. 126. PCM with Noise<br />The random bit error can be obtained by mean square value<br />
  127. 127. PCM with Noise<br />113<br />
  128. 128. DM with Noise<br />114<br />
  129. 129. Linear Predictive Coding (LPC)<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />115<br />Digital encoding technique-different approach<br />Uses-transversal filter + auxillary components (to synthesize the waveform)<br />Transversal filter-one of the convenient & flexible device used for equalisation<br />Square up corners-for small amplitude higher harmonics<br />(Equalisation N/W:- Cures-linear distortion –amplitude & delay)<br />
  130. 130. V. S. Hendre Department of E&TC, TCOER, Pune<br />116<br />LPC Transmitter<br />LPC receiver<br />Decoder<br />Encoder<br />
  131. 131. Speech model<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />117<br />Frequency generators<br />-electrical equivalent to generate sound<br />Because -wide frequency spectrum <br />
  132. 132. V. S. Hendre Department of E&TC, TCOER, Pune<br />118<br />Complete LPC codeword-@80 bits/sample<br />-1 bit used to switch-voice/unvoiced<br />-6 bits-pitch freqn of voice<br />-few bits-represents error<br />Sampling rate-40-100 Hz, Bit rate=3-8 Kbps<br />
  133. 133. Digital Audio Recording<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />119<br />Disadvantages of analog audio storage<br />1)Wear & tear due to constant use & mechanical contacts with magnetic tape<br />2)Tapes stretch out & produces flutter<br />3)Dynamic range is limited @ 70dB (range required 100 dB to 120 dB)<br />4)Soft music is lost & loud music saturates the amplifier <br />
  134. 134. Advantages of CD Technology<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />120<br />Digital recording<br />Uses plastic disk @ 120mm diameter<br />20,000 tracks & width of each track-@0.5m<br />Spacing between adjucent tracks-1.6 m<br />Each track has-microscopic PITS<br />-Lands:regions betn the PITS<br />
  135. 135. V. S. Hendre Department of E&TC, TCOER, Pune<br />121<br />PITS & LANDS pattern on CD<br />Electrical signal<br />
  136. 136. V. S. Hendre Department of E&TC, TCOER, Pune<br />122<br />
  137. 137. V. S. Hendre Department of E&TC, TCOER, Pune<br />123<br />CD AUDIO RECORDING<br />
  138. 138. CD Playback<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />124<br />Job:1) Extract framing & sync. Information<br /> 2) Extract merging bits<br /> 3) Decode EFM signal<br /> 4) Extract control word bits<br />Sampling rate conversion<br />-Random error-air bubbles, PIT inaccuracies<br />-Burst error-scratches, fingerprints<br />16 bits DAC -expensive<br />-Incorrect bit-changed to opposite state<br />-If not possible-incorrect value-cancelled, its value-interpolated between neighbeuring samples<br />
  139. 139. ITU-Voice encoding & multimedia standards<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />125<br />International Telecommunication Union (united nations)<br />Publishes: Telecommunication Technology<br /> :regulatory & standards information<br />ITU standards<br />1) ITU-T: Telecommunication standardization sector<br /> :developes recommendations for wireless n/w.<br />2)ITU-R: Radio communication standardization sector<br /> :develops recommendations for wireless <br /> communications<br />3)ITU-D:standards for developing nations<br />
  140. 140. Voice encoding standards<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />126<br />
  141. 141. Multimedia /Multiplexing standards: video, data, multiplexing, signalling & encryption<br />V. S. Hendre Department of E&TC, TCOER, Pune<br />127<br />
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