chapter 3 combi.pdf

ITT300 INTRODUCTION TO DATA COMMUNICATION AND NETWORKING CHAPTER 3 DATA AND SIGNAL Part 2 ADAPTED FROM: Behrouz A. Forouzan Lesson Outcomes At the end of this lesson, the students should be able to: Differentia...

ITT300 INTRODUCTION TO DATA COMMUNICATION AND NETWORKING CHAPTER 3 DATA AND SIGNAL Part 2 ADAPTED FROM: Behrouz A. Forouzan Lesson Outcomes At the end of this lesson, the students should be able to: Differentiate between analog and digital information and signal terms Discuss about the concepts of analog and digital signals Transmission of Digital signals Baseband Transmission Baseband transmission mean sending a digital signal over a channel without changing the digital signal to an analog signal. Baseband transmission requires that we have a low-pass channel, a channel with a bandwidth that start from zero. Bandwidths of two low-pass channels Baseband transmission using a dedicated medium Transmission of Digital signals (Cont..) Broadband Transmission Broadband transmission or modulation means changing the digital signal to an analog signal for transmission. Modulation allows us to use a bandpass channel, a channel with a bandwidth that does not start from zero. Note If the available channel is a bandpass channel, we cannot send the digital signal directly to the channel; we need to convert the digital signal to an analog signal before transmission.  Transmission Impairment (Changes in signal form) Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. What? The signal at the beginning of the medium is not the same as the signal at the end of the medium Attenuation Distortion 3 main causes of Causes of impairment impairment ? Noise Transmission Impairment cont. Attenuation Means loss of energy When signal travels through medium, it loss of its energy that is overcome the resistance of the medium. Some energy converted to heat. To compensate, amplifier used to amplify the signal To show that a signal has lost or gained strength, engineers use the unit of the decibel Transmission Impairment cont. Decibel(dB) To measure the relative strength of two signal or a signal at two different point. Signal negative mean signal is attenuated (the signal power is decrease) Signal positive signal is amplified(the signal power is increase)  Transmission Distortion Impairment cont. Means the signal change its form or shape Occurs in a composite signal made of different frequencies Each signal component has its own propagation speed through a medium, therefore, its own delay in arriving at the final destination Differences in delay may create a difference in phase if the delay is not exactly the same as the period duration *You can see here the phase in sender and receiver is different Signal components at the receiver have phases different from the sender – the shape is therefore not the same Transmission Noise Impairment Several types such as thermal noise, induced noise, crosstalk and impulse noise may corrupt the signal Thermal noise – random motion of electron in a wire which create an extra signal Induced noise – come form source such as motors and appliances Crosstalk – effect of one wire to another Impulse noise – a spike (a signal with high energy in a very short time) Transmission Impairment NOISE Signal-to-Noise (SNR) is used to calculate the ratio of the signal power to the noise power. Formula 𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑺𝒊𝒈𝒏𝒂𝒍 𝑷𝒐𝒘𝒆𝒓 SNR = 𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑵𝒐𝒊𝒔𝒆 𝑷𝒐𝒘𝒆𝒓 5/14/2024 13 Data Rate Limits How fast we can send data Data rate depends on: 1. The bandwidth available 2. The level of signal we use 3. The quality of the channel (level of noise) Two theoretical formulas were developed to calculate data rate: Nyquist Bit Rate Shannon Capacity  Data Rate Limits Noiseless channel: Nyquist Bit Rate The Nyquist bit rate Nyquist bit rate formula defines formula is a fundamental principle in theoretical maximum bit rate: digital communications that determines the maximum data rate for a Bit Rate = 2 x Bandwidth x log2 L noiseless channel. Bandwidth = BW of the channel L = number of signal level used to represent data BitRate = bit rate per second Example 1 Consider a noiseless channel with a bandwidth of 3000 Hz transmitting a signal with two signal levels. The maximum bit rate can be calculated as Bandwidth = 3000 Level = 2 BitRate = 2 x Bandwidth x log2 L Bit Rate = 2  3000  log2 2 = 6000 bps Example 2 Consider the same noiseless channel, transmitting a signal with four signal levels (for each level, we send two bits). The maximum bit rate can be calculated as: Bandwidth = 3000 Level = 4 BitRate = 2 x Bandwidth x log2 L Bit Rate = 2 x 3000 x log2 4 = 12,000 bps Data Rate Limits Noisy Channel: Shannon Capacity Highest data rate for noisy channel Capacity = Bandwidth x log2 ( 1 + SNR ) BW = bandwidth of the channel SNR = signal to noise ratio( statistical ratio of the power of the signal to the power of noise) Capacity = capacity in channel in bit per second Example 4 We can calculate the theoretical highest bit rate of a regular telephone line. A telephone line normally has a bandwidth of 3000 Hz (300 Hz to 3300 Hz). The signal-to-noise ratio is usually 3162. For this channel the capacity is calculated as Bandwidth= 3000; SNR = 3162 C = B log2 (1 + SNR) = 3000 log2 (1 + 3162) = 3000 log2 (3163) = 3000  11.63 = 34,890 bps Example 5 We have a channel with a 1 MHz bandwidth. The SNR for this channel is 63; what is the appropriate bit rate and signal level? First, we use the Shannon Then we use the Nyquist formula to formula to find our upper limit. find the number of signal levels. C = B log2 (1 + SNR) Bit Rate = 2 x Bandwidth x log2 L = 106 log2 (1 + 63) 6 Mbps = 2  1 MHz  log2 L ➔ L = 8 = 106 log2 (64) = 6 Mbps Performance Bandwidth The term can be used in two different contexts with two different measuring values. Bandwidth in Hertz – the range of frequencies contained in a composite signal or the range of frequencies a channel can pass. Eg: the bandwidth of a subscriber telephone line is 4 kHz Bandwidth in Bits per seconds – the number of bits per second that a channel, a link, or a network can transmit. Eg: bandwidth of a Fast Ethernet network is a maximum of 100 Mbps Performance Throughput The measurement of how fast we can send data through a network The number of bits that can pass the wall in one second The bandwidth is different with throughput The bandwidth is a potential measurement of a link; a throughput is an actual measurement of how fast we can send data Figure 3.20 Throughput Performance Latency (Delay) Defines how long it takes for an entire message to completely arrive at the destination from the time the first bit is sent out from the source Four components of latency: Propagation time Transmission time Queuing time Processing delay Performance Propagation Speed Measure the distance a signal or a bit can travel through a medium in one second Propagation Time The time required for a signal (or a bit) to travel from one point of the transmission medium to another Propagation or data spreading is somehow similar and equal to bandwidth performance that we have discuss just now. Performance Transmission Time In data communications we don’t send just 1 bit, we send a message (mean a lot of bit in 1 sec) The time required for transmission of a message depends on the size of the message and the bandwidth of the channel Performance Queuing Time The time needed for each intermediate or end device to hold the message before it can be processed The queuing time is not a fixed factor; it changes with the load imposed on the network When there is heavy traffic on the network, the queuing time increases  ITT300 INTRODUCTION TO DATA COMMUNICATION AND NETWORKING CHAPTER 3 DATA AND SIGNAL ADAPTED FROM: Behrouz A. Forouzan Lesson Outcomes At the end of this lesson, the students should be able to: Differentiate between analog and digital information and signal terms Discuss about the concepts of analog and digital signals  Analog and Digital Data Criteria ANALOG DIGITAL Signal Digital signals are Analog signal is a discrete (individually continuous signal which Information that is separate and distinct) represents physical continuous. signals generated by measurements. digital modulation. Example: Human voice Waves Denoted by square Denoted by sine waves waves Representation Uses continuous range Uses discrete or of values to represent discontinuous values to Information that has information represent information discrete states. Example Human voice in air, Computers, CDs, DVDs, Example: Data stored in analog electronic and other digital devices. electronic devices. computer, 0s and 1s  Analog vs Digital Criteria ANALOG DIGITAL Subjected to deterioration Can be noise-immune (weaken) by noise during without deterioration Data transmission transmission and write/read during transmission and cycle. write/read cycle. Less affected since noise More likely to get affected Response to Noise response are analog in reducing accuracy. nature. Digital signal processing Analog signal processing can be Bandwidth also an be done in real done in real time. time Analog hardware is not flexible. Digital hardware is flexible. Flexibility 4 Analog and Digital Signal Analog signals can have an infinite number of values in a range (for example voice, we can't determine the size of its signal) Digital signals can have only a limited number of values (for example either 8 bits or 12 bits) The simplest way to show signals is by plotting them on a pair of perpendicular axes The vertical axis represents the value or strength of a signal; the horizontal axis represents time Periodic and Non-Periodic Signals 1 cycle is repeated all over simultaneously Periodic Periodic signals Consists of continuous repetitive pattern within a time frame called period. The completion of one full pattern is called cycle. The cycle is not in the same pattern Non-periodic signals Non-periodic -Has no repetitive pattern -Can be decomposed into infinite number of periodic signals Periodic Analog Signals Only have 1 sine wave Simple Cannot be (sine decomposed into wave) simpler signals Sine wave There is more than 1 sine wave Composite Composed of multiple sine waves Composite Sine Wave Peak amplitude Characteristic Period or Phase/cycle Frequency Sine Wave Peak amplitude The value of its highest intensity, Measured by volts proportional to the energy it carries  Sine Wave Second Formula Period (P) The amount of time (in Inverse of frequency seconds) needs to P = 1/f complete one cycle First Formula Frequency (f) Also can be defined The number of cycles Inverse of period as rate of signal in a second (in Hertz) f = 1/P change with respect of time Period and frequency  Table 3.1 Units of periods and frequencies Unit Equivalent Unit Equivalent Seconds (s) 1s hertz (Hz) 1 Hz Milliseconds (ms) 10–3 s kilohertz (KHz) 103 Hz Microseconds (µs) 10–6 s megahertz (MHz) 106 Hz Nanoseconds (ns) 10–9 s gigahertz (GHz) 109 Hz Picoseconds (ps) 10–12 s terahertz (THz) 1012 Hz 11  Express a period of 100 ms in microseconds, and express the Example 1 corresponding frequency in kilohertz. Solution From Table 3.1 we find the equivalent of 1 ms. We make the following substitutions: 100 ms = 100  10-3 s = 100  10-3  10 s = 105 s Now we use the inverse relationship to find the frequency, changing hertz to kilohertz 100 ms = 100  10-3 s = 10-1 s / 0.1 s f = 1/P f = 1/10-1 = 10 Hz = 10  10-3 KHz = 10-2 KHz 12 Sine Wave Phase The Measured in Four types – position of degrees or radians 0 degrees, 90 the [360° is 2π rad] degrees, 180 waveform degrees, 270 relative to [1° is 2π/360 rad] degrees time zero [1 rad is 360/(2π)]  Image source: Data Communications And Networking, Forouzan Four sine waves with the same amplitude and frequency, but different phases  To plot you need this 3 component: Sine Wave 1) Amplitude 2) Phased 3) Frequency Time Domain The time-domain plot shows changes in signal amplitude with respect to time Phase is not explicitly shown on a time-domain plot Frequency Domain The frequency-domain plot shows the peak value and the frequency To show relationship between amplitude and frequency, use frequency domain plot The time domain and frequency domain of three sine waves Image source: Data Communications And Networking, Forouzan Composite Signal A signal made of many simple sine waves A composite signal can be periodic(have continuous repetitive pattern) or nonperiodic(have no continuous repetitive pattern) A periodic composite signal can be decomposed into a series of simple sine waves with discrete frequencies A nonperiodic composite signal can be decomposed into a combination of an infinite number of simple sine waves with continuous frequencies  A composite periodic signal The time and frequency domains of a non-periodic signal Image source: Data Communications And Networking, Forouzan Composite Signal Bandwidth The range of frequencies contained in a composite signal is its bandwidth B = highest frequency – lowest frequency The bandwidth of a composite signal is the difference between the highest and the lowest frequencies contained in that signal. The bandwidth of periodic and non- periodic composite signals  Bandwidth Terms Bandwidth in Bandwidth in bits per second hertz (Analog) (Digital) The range of frequencies in a composite signal or The speed of bit the range of frequencies transmission in a that a channel can pass channel or link Example 3 If a periodic signal is decomposed into five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz, what is the bandwidth? Draw the spectrum, assuming all components have a maximum amplitude of 10 V. Solution B = fh − fl = 900 − 100 = 800 Hz The spectrum has only five spikes, at 100, 300, 500, 700, and 900 22 Digital Signals Most digital signals are non- periodic – period and frequency is not appropriate Can be described by bit interval (instead of period) and bit rate (instead of frequency). Digital signal can be decomposed into an infinite number of sine waves Digital signal is a composite signal with an infinite bandwidth Two digital signals Digital Signals Information in digital signal will represent as 1s and 0s Two digital signals Digital Signals If Signal has L levels, Each level need log2 L bits No of bit per level = log2 no of levels Example: A digital signal has eight levels. How many bits are needed per level? = No of bit per level = log2 no of levels = log2 8 = 3 Each signal represented by 3 bits. Digital Signals Bit Rate, Bit Interval and Bit Length Bit interval(s) - the time required to send one single bit (1/bit rate) Bit rate(bps) – the number of bit intervals per second The bit rate is the number of bits in 1s, expresses in bits per second (bps) Bit length – the distances one bit occupy on the transmission medium  Terminology Recap Signal levels Data levels Bit interval (s) Bit rate (bps) The number of The number of The time The number of values allowed values used to required to bit intervals per in a particular represent data send one single second digital signal in a particular bit digital signal