Telecommunication Networks PDF

Telecommunication Networks Professor: Eduardo Rodríguez Lorenzo  Topics - What is a Network? - Network Effects - Network Topologies - Transmission Media - Radio (electromagnetic) Spectrum - Channel Capacity - Multiplexing - Network Econom...

Telecommunication Networks Professor: Eduardo Rodríguez Lorenzo  Topics - What is a Network? - Network Effects - Network Topologies - Transmission Media - Radio (electromagnetic) Spectrum - Channel Capacity - Multiplexing - Network Economics Networks 101  What are Networks? An Introduction to Networks A network is simply a collection of connected objects  Telecommunication Networks Telecommunication Networks are graphs designed to transmit signals (information) with: – optimal quality, – least energy consumption, – maximum capacity and – highest speed, … – at the least cost.  Network Effects Metcalfe's law states that the value of a telecommunications network is proportional to the square of the number of connected users of the system (n2)  The Internet Network Graph Routers connecting Autonomous Systems (independent networks) make up The Internet Internet Architecture: How it started… 1969: First message between computers in The ARPA Network 1974: Vinton Cerf and Bob Kahn (the Fathers of the Internet) publish "A Protocol for Packet Network Interconnection" which details the design of TCP. 1983: The Domain Name System (DNS) establishes the familiar.edu,.gov,.com,.mil,.org,.net, and.int system for naming websites. This is easier to remember than the previous designation for websites, such as 123.456.789.10. 1991: CERN introduces the World Wide Web to the public How it’s going… World Internet Topology  Information Transmission Media Signals transmission can be Wired: Coaxial cable Twisted-pair cable Fiber-optics … or Wireless Radio Frequency From Copper to Fiber Higher carrying capacity and wider transmission band ( x1000+ ) Less signal degradation No interference from light signals (as opposed to Electromagnetic Fields)  Radio Spectrum ▪ Hertz ▪ Frequency domain & Frequency Spectrum ▪ Information Signals and Carriers: Modulation ▪ Channels: Band, Bandwidth and Capacity ▪ Wireless Services  What is Frequency? A signal is information that changes over time. For example, audio, video, and voltage traces are all examples of signals. A frequency is the speed at which something repeats. For example, clocks tick at a frequency of one hertz (Hz), or one repetition per second. Power, in this case, just means the strength of each frequency. Sine Wave with increasing Frequency (f) Power 𝑡 = A · sin(2𝜋𝑓𝑡)  Sine Wave with increasing Frequency (f) Power 𝑡 = A · sin(2𝜋𝑓𝑡) 𝜆∙𝑓 =𝑐 c=3 ∙ 108 m/s (𝜆) wavelength (meters) A 1 𝑇= 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 𝑓 For Frequency = 5Hz, 5 Cycles (T) are completed every second Amplitude (A) is related to the Power carried by the Signal  Time Domain vs Frequency Domain Representation 1Hz=1 cycle per second 1KHz=1000Hz For periodic signals (those that repeat the sequence of values exactly after a fixed length of time), the Frequency Domain representation is a series of discrete values at each frequency present in the original signal Time Series (Signals) typically comprise multiple frequencies  Spectrum of Musical Notes: 3 Note Chord 293.66Hz 349.23Hz 493.88Hz Re Fa Ti  Spectrum of an Audio Signal Fourier Transform converts signal from time to frequency domain  Signal Modulation Information Signal travels modulated on a Higher Frequency Carrier Signal ▪ A Channel is defined by its Bandwidth (B), the difference between the upper and lower frequencies in the range ▪ Signal Modulation is critical to enable Transmission Media Sharing Signal Modulation: Information Signal x Carrier Signal  Carrier Frequency vs Channel Bandwidth 𝑓𝑐1 𝑓𝑐2 𝑓𝑐3 𝑓𝑐4 Each Carrier Frequency (𝑓𝑐𝑖 ) carries the Information Signal over a Channel Bandwidth Example: WiFi uses 𝑓𝑐 = 2.4GHz over Channels of up to 40MHz Wireless (Radio) Communications  mmWave Communications (95GHz to 3THz) 𝜆∙𝑓 = 𝑐 c=3 ∙ 108 m/s 𝑓 = 95𝐺𝐻𝑧 ⇒ 𝜆 =3.16mm The FCC has opened up experimental 6G spectrum licenses in 2019.The spectrum, which falls in the 95 gigahertz (GHz) to 3 terahertz (THz) range, will be open for experimental use to let engineers dreaming of the next generation of wireless begin their work. Channel Capacity and Multiplexing  Channel Capacity Nyquist Capacity for Noiseless Channels: [Bits/second (bps)] Shannon Capacity for Noisy Channels: [Bits/second (bps)]  SNR: Effects of Noise on Digital Signals Noise consists of a relatively modest level of background noise plus occasional larger spikes of noise. The digital data can be recovered from the signal by sampling the received waveform once per bit time. The noise is occasionally sufficient to change a 1 to a 0 or a 0 to a 1. Signal-to-Noise Ratio (SNR or S/N): The ratio of the power in a signal to the power contained in the noise at the receiver. For a given level of noise, a greater signal strength improves the ability to receive data correctly  Nyquist Capacity for Noiseless Channels: [Bits/second (bps)] In ideal conditions (noiseless channel) we can transmit twice the Bandwidth (B) bits per second (bps) and still be able to reconstruct the original signal. M represents the number of levels used by the digital modulation to encode bits. M acts as a multiplier that increases Channel Capacity. 16-QAM Digital Modulation 8-PSK Digital Modulation M=16 (16 symbols) M=8 (8 symbols)  Nyquist Capacity for Noiseless Channels [Bits/second (bps)] Example 1: IoT Radio System uses 20MHz for each Radio Channel and a 16- QAM Digital Modulation scheme (M = 16). What is the maximum Data Transmission Rate possible in noiseless conditions? 𝑀𝑎𝑥𝑖𝑚𝑢𝑚 𝐷𝑎𝑡𝑎 𝑇𝑟𝑎𝑛𝑠𝑚𝑖𝑠𝑠𝑖𝑜𝑛 𝑅𝑎𝑡𝑒 = 2 ∙ 20𝑀ℎ𝑧 ∙ log 2 16 = 160𝑀𝑏𝑝𝑠 Example 2: We need to send 265 kbps over a noiseless channel with a bandwidth of 20 kHz. How many signal levels do we need? 265𝑘𝑏𝑝𝑠 = 2 ∙ 20𝑘𝐻𝑧 ∙ log 2 𝑀 ⇒ 𝑀 = 26.625 = 98.7 𝑙𝑒𝑣𝑒𝑙𝑠  Shannon Capacity for Noisy Channels [Bits/second (bps)] Channels are always noisy. SNR measures the Signal to Noise ratio in 𝑃𝑜𝑤𝑒𝑟 𝑜𝑓 𝑆𝑖𝑔𝑛𝑎𝑙 the Channel, i.e., 𝑆𝑁𝑅 =. 𝑃𝑜𝑤𝑒𝑟 𝑜𝑓 𝑁𝑜𝑖𝑠𝑒 SNR is usually expressed in decibels (dBs): 𝑆𝑁𝑅 𝑑𝐵 = 10 ∙ log10 𝑆𝑁𝑅 𝑆𝑁𝑅 = 1000 ⇒ 𝑆𝑁𝑅 𝑑𝐵 = 30𝑑𝐵 ▪ The interpretation is that when the Power of the Signal equals the noise level in the Channel, the Maximum Error-Free Data Transmission Rate equals the Bandwidth used, i.e., for SNR=1 => Capacity = Bandwidth ▪ Error-Free Data Transmission Rate increases with Signal Power. Source Alphabet Msg Source Alphabet Msg  Shannon Capacity for Noisy Channels [Bits/second (bps)] Example 1: What is the maximum capacity for a Channel with a frequency bandwidth of 1kHz, and a SNR = 200? 𝐶 = 1𝑘𝐻𝑧 ∙ log 2 1 + 200 = 1000 ∙ 4.39 = 7.651𝑘𝑏𝑝𝑠 Example 2: A Voice over IP (VoIP) channel is assigned 3000Hz under SNRdB conditions of 40dB. What is the maximum bit rate supported for voice communications in this scenario? 𝑆𝑁𝑅 𝑑𝐵 = 40𝑑𝐵 = 10 ∙ log10 𝑆𝑁𝑅 ⇒ 𝑆𝑁𝑅 = 10000 𝐶 = 3𝑘𝐻𝑧 ∙ log 2 1 + 10000 = 3000 ∙ 13.29 = 40𝑘𝑏𝑝𝑠  Combining Shannon and Nyquist Capacity Formulas Example 1: Suppose that the spectrum of a channel is between 3 MHz and 4 MHz and SNRdB = 24 dB. Then: 𝐵 = 4𝑀𝐻𝑧 − 1𝑀𝐻𝑧 = 1𝑀𝐻𝑧 𝑆𝑁𝑅 𝑑𝐵 = 24𝑑𝐵 = 10 ∙ log10 𝑆𝑁𝑅 ⇒ 𝑆𝑁𝑅 = 251 Using Shannon’s formula: 𝐶 = 𝐵 ∙ 𝑙𝑜𝑔2 1 + 𝑆𝑁𝑅 𝐶 = 106 ∙ 𝑙𝑜𝑔2 1 + 251 ≈ 106 ∙ 8 = 8𝑀𝑏𝑝𝑠 Based on Nyquist’s formula, how many signal levels are required to achieve Shannon’s theoretical limit? 𝐶 = 2𝐵 ∙ 𝑙𝑜𝑔2 𝑀 ⇒ 106 ∙ 8 = 2 ∙ 106 ∙ 𝑙𝑜𝑔2 𝑀 4 = 𝑙𝑜𝑔2 𝑀 ⇒ 𝑀 = 16  Information Multiplexing: Frequency vs Time Multiplexing is a technique to combine multiple Digital Signals over a shared medium MUX DEMUX Frequency Division Multiplexing (FDM) 4 users optical, electromagnetic frequencies frequency divided into (narrow) frequency bands each user allocated its own band, can transmit at max rate of that narrow band time Time Division Multiplexing (TDM) time divided into slots frequency each user allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band, but only during its time slot(s) time Radio Features of different Communication Standards