IT438 Communication Technology Lecture Notes PDF

Fall Semester 2024-2025 IT438 Communication Technology Kamal Hamza, PhD Acknowledgement: This presentation contains some figures and text from Data Communications khamz...

Fall Semester 2024-2025 IT438 Communication Technology Kamal Hamza, PhD Acknowledgement: This presentation contains some figures and text from Data Communications [email protected] and Networks book by W. Stallings Signal Representation in the Frequency Domain In practice, an electromagnetic signal will be made up of many frequencies. For example, the signal: is made up sine waves of frequencies f1 and 3f1 The spectrum of a signal is the range of frequencies that it contains. IT438 Communication Technology 22 Signal Representation in the Frequency Domain (cont.) + = IT438 Communication Technology 23 Signal Representation in the Frequency Domain (cont.) Fourier analysis IT438 Communication Technology 24 Signal Representation in the Frequency Domain (cont.) If a signal includes a component of zero frequency, that component is a direct current (dc) or constant component. IT438 Communication Technology 25 Noise and Interference In practical communication systems signals are blurred by noise and interference: Time domain Frequency domain IT438 Communication Technology 26 Signal Bandwidth (cont.) Bandwidth is the difference between the upper and lower frequencies in a continuous band of frequencies. It is typically measured in unit of hertz (symbol Hz). IT438 Communication Technology 27 Signal Bandwidth (cont.) Bandwidth in Different Communication Systems: 1. Telecommunications (Audio): In traditional telephone systems, the bandwidth is typically limited to 300 Hz to 3400 Hz, which is sufficient for transmitting the human voice. This 3.1 kHz bandwidth filters out both very low and very high frequencies. 2. Radio Broadcasts: AM radio stations use bandwidths around 10 kHz per channel, while FM radio uses a much larger bandwidth (around 200 kHz) to transmit better quality sound. IT438 Communication Technology 28 Signal Bandwidth (cont.) Bandwidth in Different Communication Systems (Cont.): 3. Video and TV Transmission: Analog TV signals use bandwidths around 6 MHz. Digital video signals (e.g., HD video) use even more bandwidth, which is why they rely on advanced compression techniques. 4. Wi-Fi and 5G: a) Wi-Fi operates in the 2.4 GHz or 5 GHz frequency bands, with bandwidths typically ranging from 20 MHz to 160 MHz. Higher bandwidth means faster internet speeds. b) 5G technology operates at frequencies between 3 GHz and 100 GHz, with very large bandwidths available (up to several GHz), allowing it to carry massive amounts of data. IT438 Communication Technology 29 Signal Bandwidth (cont.) IT438 Communication Technology 30 Signal Bandwidth (cont.) IT438 Communication Technology 31  Fiber Optics Communication Technology Optical Transmission System Main components of an optical transmission system are: Optical fiber links Transmitters Receivers Amplifiers Network medium IT438 Communication Technology 1 Optical Fiber Links Light propagates by total internal reflection IT438 Communication Technology 2 Optical Fiber Links (cont.) Advantages of fiber optical links: 1. High Bandwidth Capacity Fiber optics can carry more data: Unlike copper cables, fiber optic cables have much higher bandwidth, which means they can transmit more data over longer distances without degradation. Speed: Modern fiber systems can easily handle data rates of 100 Gbps and higher. 2. Low Signal Attenuation (Loss) Long-distance transmission: Signals transmitted over fiber optic cables experience much less loss compared to copper cables. Improved efficiency: fiber optics are particularly suitable for large-scale communication networks, including long-distance telecommunication and undersea cables. IT438 Communication Technology 3 Optical Fiber Links (cont.) Advantages of fiber optical links (cont.): 3. Immunity to Electromagnetic Interference (EMI) Interference-free transmission: Fiber optic cables are immune to electromagnetic interference (EMI) because they transmit light instead of electrical signals. No cross-talk: In copper wires, nearby cables can interfere with each other, causing signal distortion. 4. Security Enhanced data security: Fiber optics offer greater security because it is difficult to tap into or intercept the light signals without disrupting the transmission. Tamper detection: Any attempt to physically tap into a fiber optic cable will cause noticeable disruption to the light transmission, which can be detected easily. IT438 Communication Technology 4 Optical Fiber Links (cont.) Advantages of fiber optical links (cont.): 5. Lightweight and Thin 6. Durability and Longevity 7. Reduced Latency 8. Scalability 9. Environmental Benefits 10. High Reliability IT438 Communication Technology 5 Optical Fiber Links (cont.) Types of optical fiber: 1. Single-mode fiber (SMF) 2. Multimode fiber (MMF) Feature Single-mode Fiber (SMF) Multimode Fiber (MMF) Core Size Small (8-10 microns) Larger (50-62.5 microns) Light Propagation Single light mode (direct path) Multiple light modes (bounces inside the core) Distance Long distances (up to 40 km or more) Short distances (up to 550 meters) Bandwidth Higher bandwidth, supports higher data rates Lower bandwidth, supports moderate data rates Cost More expensive to install and maintain Cheaper, simpler installation Application Long-haul telecom, WAN, high-speed data links LAN, data centers, short-range communication Attenuation/Dispersion Lower attenuation and dispersion Higher attenuation and modal dispersion IT438 Communication Technology 6 Attenuation Attenuation in optical fiber leads to a reduction of the signal power as the signal propagates over some distance. Attenuation (dB)= α × L Where: α = Attenuation coefficient (measured in dB/km). L = Length of the fiber (in kilometers). Attenuation must considered when determining the maximum distance that a signal can propagate. Caused by the fiber material, which absorbs and scatters light energy. IT438 Communication Technology 7  Dispersion Dispersion is the widening of a pulse duration as it travels through a fiber. Interference Different components of the light pulse arrive at the destination at different times. Affects the clarity and timing of the signal, limiting the data rate and causing errors when pulses overlap due to broadening. IT438 Communication Technology 8 Effect of Dispersion As a pulse widens, it can broaden enough to interfere with neighboring pulses (bits) on the fiber, leading to ISI. IT438 Communication Technology 9 Types of Dispersion 1. Modal Dispersion: Occurs in multimode fibers when different light paths (modes) travel at different speeds, causing pulse broadening. Mitigated by single-mode fibers or graded-index fibers. 2. Chromatic Dispersion: Affects both single-mode and multimode fibers as different wavelengths of light travel at different speeds, causing pulse spreading. Mitigated by lasers and dispersion-compensating fibers. IT438 Communication Technology 10  Types of Dispersion (cont.) 3. Polarization Mode Dispersion (PMD): Occurs in single-mode fibers when different polarization states travel at different speeds due to fiber imperfections. Mitigated with high-quality fibers or polarization-maintaining fibers. IT438 Communication Technology 11  Nonlinearities in Fiber Nonlinearities in fiber occur when the light intensity in the fiber becomes high enough to cause the fiber's refractive index to change or to induce other non-linear effects. It may lead to attenuation, distortion, and cross-channel interference. E.g.: Four-Wave Mixing (FWM) Cause: When multiple wavelengths of light interact within the fiber, new wavelengths are generated due to the non-linear mixing of signals. Effect: This creates additional wavelengths that interfere with the original signals, causing crosstalk and signal degradation. IT438 Communication Technology 12 Optical Couplers A coupler is a general term that covers all devices that combine light into or split light out of a fiber. Enabling signal sharing between different channels or users without the need for active electronics. A Splitter (1×N coupler) takes an input signal from one fiber and splits it into N output fibers. A Combiner (N×1 coupler) combines optical signals from multiple input fibers into a single output fiber. IT438 Communication Technology 13 Optical Couplers (cont.) Coupling ratio : describes how the input optical power is divided between the output ports of an optical coupler. Formula for Coupling Ratio: For a simple 1x2 optical coupler, the coupling ratio is defined as: 𝑃1 𝑃2 Coupling Ratio ( ) = 𝑜𝑟 𝑃1 + 𝑃2 𝑃1 + 𝑃2 Where: 𝑃1 = Power at output port 1. 𝑃2 ​ = Power at output port 2. IT438 Communication Technology 14 Optical Couplers (cont.) How to design a 1xN splitter? Couplers (2x1) can be used to design an 8-port splitter. IT438 Communication Technology 15