McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Data Transmission Techniques Data to be transmitted is of two types 1.Analog data 2.Digital data Therefore, the data transmission is categorized into two types : 1.Analog Transmission 2.Digital Transmission

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Analog Transmission Analog (or analogue) transmission is a transmission method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable. It could be the transfer of an analog source signal, using an analog modulation method such as frequency modulation (FM) or amplitude modulation (AM), or no modulation at all.transmissionvoicevideocontinuous signal amplitudesignalmodulation frequency modulationamplitude modulation Another method is of analog transmission is known as passband data transmission using a digital modulation methods such as ASK, PSK and QAM, i.e. a sine wave modulated by a digital bit-stream, as analog transmission and as an analog signal.A passbanddigital modulation methodsanalog signal

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Digital Transmission Data transmission, digital transmission, or digital communications is the physical transfer of data (a digital bit stream or a digitized analog signal [1] ) over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibers, wireless communication channels, storage media and computer buses. The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal.datadigitalbit stream digitized [1]point-to-pointpoint-to-multipoint communicationchannelcopper wires optical fiberswirelessstorage mediacomputer buseselectromagnetic signalelectrical voltage radiowavemicrowaveinfrared

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 While analog transmission is the transfer of a continuously varying analog signal over an analog channel, digital communications is the transfer of discrete messages over a digital or an analog channel. The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying wave forms (passband transmission), using a digital modulation method.analog transmissionanalog signalline codebasebandpassbandmodulation Data transmitted may be digital messages originating from a data source, for example a computer or a keyboard. It may also be an analog signal such as a phone call or a video signal, digitized into a bit-stream for example using pulse-code modulation (PCM) or more advanced source coding (analog-to-digital conversion and data compression) schemes. This source coding and decoding is carried out by codec equipment.digitizedpulse-code modulationsource codinganalog-to-digital conversiondata compressioncodec

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-1 Data Transmission Conversion/Modulation Schemes

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-2 Digital to Digital Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 A baseband signal ("digital-over-digital" transmission): A sequence of electrical pulses or light pulses produced by means of a line coding scheme such as Manchester coding. This is typically used in serial cables, wired local area networks such as Ethernet, and in optical fiber communication. It results in a pulse amplitude modulated(PAM) signal, also known as a pulse train.baseband signalline codingManchester codingserial cableslocal area networks Ethernetpulse amplitude modulated(PAM)pulse train

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-3 Types of Digital to Digital Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Analog to Digital Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Pulse Amplitude Modulation (PAM) Pulse Code Modulation (PCM) –Sampling (means measuring the amplitude of the signal at an equal interval) –Sampling rate

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-16 WCB/McGraw-Hill PAM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-17 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Quantized PAM Signal

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-18 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Quantizing Using Sign and Magnitude

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Steps in PCM There are four steps used in PCM 1.PAM 2.Quantization 3.Binary Encoding 4.Digital to Digital encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-19 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20-continued WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20-continued WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20-continued From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Animation of PAM n/dcn/graphics/animations/05_20.swf

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Nyquist Theorem The Nyquist Theorem, also known as the sampling theorem, is a principle that is used in the digitization of analog signals. It is done by dividing the signals into the slices called as samples These samples are taken frequently. The number of samples taken per second is called the sampling rate or sampling frequency.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Suppose the highest frequency component, in hertz, for a given analog signal is f max. According to the Nyquist Theorem, the sampling rate must be at least 2f max, or twice the highest analog frequency component. The sampling in an analog-to-digital converter is actuated by a pulse generator (clock). If the sampling rate is less than 2f max, some of the highest frequency components in the analog input signal will not be correctly represented in the digitized output. When such a digital signal is converted back to analog form by a digital-to-analog converter, false frequency components appear that were not in the original analog signal. This undesirable condition is a form of distortion called as aliasing.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-21 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Nyquist Theorem

Example 5.3 : What sampling rate is needed for the signal with a bandwidth of 10,000 Hz ( 1,000 to 11,000 hz) ? SOLUTION : The sampling rate must be twice the highest frequency in the signal: Sampling rate = 2(11,000) = 22,000 samples/ seconds.

EXAMPLE 5.4 : A signal is sampled. Each sample requires at least 12 levels of precision ( +0 to +5 and -0 to -5). How many bits should be sent for each sample? SOLUTION : We need four bits ;one bit for the sign and three bits for the value. A three-bit value can represent 2 3 = 8 levels ( 000 to 111), which is more than what we need. A two – bit value is not enough since 2 2 =4. A four –bit value is too much because 2 4 = 16.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 EXAMPLE : We want to digitize the human voice. What is the bit rate assuming eight bits per sample? SOLUTION: The humans voice normally contains frequencies from 0 to 4000 Hz. So the sampling rate is Sampling rate = 4000 x 2 = 8000 samples/ seconds The bit rate can be calculated as : Bit rate= sampling rate x Number of bits per sample = 8000 x 8 = 64,000 bits/s = 64 kbps

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McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Digital To Analog Conversion A passband signal ("digital-over-analog" transmission): A modulated sine wave signal representing a digital bit-stream. Note that this is in some textbooks considered as analog transmission, but in most books as digital transmission. The signal is produced by means of a digital modulation method such as PSK, QAM or FSK. The modulation and demodulation is carried out by modem equipment. This is used in wireless communication, and over telephone network local- loop and cable-TV networks.passband signalmodulatedanalog transmissiondigital modulation methodPSKQAMFSK modem

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-22 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Digital to Analog Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-23 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-24 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 ASK

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-25 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Bandwidth for ASK

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 FSK Figure 5-27 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Bandwidth for FSK Figure 5-28 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 PSK Figure 5-29 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 PSK Constellation Figure 5-30 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., PSK Figure 5-31 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., PSK Characteristics Figure 5-32 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., PSK Characteristics Figure 5-33 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 PSK Bandwidth Figure 5-34 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., QAM and 8-QAM Constellations Figure 5-35 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., QAM Signal Figure 5-36 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., QAM Constellation Figure 5-37 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Bit Rate and Baud Rate Figure 5-38 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-38-continued WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Bit Rate and Baud Rate

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Analog To Analog Transmission

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-39 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Analog to Analog Modulation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-40 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-41 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Amplitude Modulation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-42 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 AM Bandwidth

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-43 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 AM Band Allocation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-44 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Frequency Modulation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-45 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 FM Bandwidth

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-46 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 FM Band Allocation

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McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Digital To Analog

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McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Analog To Analog