Communication Part 1

ece-1109 ECE-1109 Introduction to ECE

1. Introduction and Definitions

• Course & References: The material begins with an “Introduction of Communication Systems” by Prof. Dr. Monir Hossen. Reference books listed include works by Simon Haykin, B. P. Lathi, and G. K. Mithal.
• Telecommunication: Long-distance communication is technically called “Telecommunication,” where “Tele” means long distance.
• Core Components: Communication is technically defined as the summation of transmission, reception, and the processing of information by electric means.
• Historical Context: Radio communication saw great improvement during the Second World War. The field expanded widely after the invention of the transistor, integrated circuits (IC), other semiconductor devices, satellites, and fiber optics.
• Definition: Communication is the exchanging of information by speaking, writing, or using other media. Effective means include radio, mobile phones, telephone, and television. Transmission mediums can include phone lines, free space, cables, or computers.

2. Examples and Basic Components

• Examples: Systems include telephony, telegraphy, radio broadcasting, point-to-point & mobile communication, computer communication, radar, television broadcasting, radio telemetry, and radio aids to navigation and aircraft landing.
• 5 Basic Components:
  1. Data Source: Where data originates.
  2. Transmitter: Device used to transmit data.
  3. Transmission Medium: Cables or non-cable connecting devices.
  4. Receiver: Device used to receive data.
  5. Destination: Where the data will be placed.

3. Block Diagrams and System Components

The text outlines block diagrams for both Analog and Digital systems.

• Analog System: Consists of an Information Source, Processing Unit, Modulation, Amplifier, Antenna, Channel, RF Amplifier, De-Modulation, and Display Unit.
• Digital System Components:
  • Input Transducer: Converts physical input (e.g., sound) into an electrical signal (e.g., microphone) and includes an analog-to-digital converter.
  • Source Encoder: Compresses data into the minimum number of bits to utilize bandwidth effectively, removing redundant bits (zeros).
  • Channel Encoder: Adds redundant bits for error correction to counteract noise or signal alteration during transmission.
  • Digital Modulator: Modulates the signal by a carrier and converts the digital sequence to analog for transmission through the medium.
  • Channel: The medium allowing the analog signal to transmit from transmitter to receiver.
  • Digital Demodulator: The first step at the receiver end; it demodulates and converts the signal back from analog to digital to reconstruct it.
  • Channel Decoder: Detects the sequence and performs error corrections using the redundant bits added earlier.
  • Source Decoder: Recreates the source output by digitizing the signal again through sampling and quantizing.
  • Output Transducer: Converts the electrical signal back into its original physical form (e.g., loudspeaker).

4. Network Models and Spectrum Classifications

• OSI Model: The Open Systems Interconnection (OSI) model is introduced as a reference tool for understanding data communications between networked systems, consisting of 7 layers (Physical, Data link, Network, Transport, Session, Presentation, Application).
• RF Spectrum Classification: The text classifies the Radio Frequency spectrum by frequency, wavelength, propagation, and service:
  • VLF (10–30 KHz): Long-distance point-to-point (P2P) communication; low attenuation.
  • LF (30–300 KHz): Long-distance P2P and navigation; absorption is higher during the day.
  • MF (300–3000 KHz): Broadcasting and ship-to-shore; high daytime attenuation.
  • HF (3–30 MHz): Ionospheric propagation; used for broadcasting and P2P.
  • VHF (30–300 MHz): Tropospheric propagation; used for Radar, TV, FM broadcast, and short-distance communication.
  • UHF (300–3000 MHz): Tropospheric propagation; used for Facsimile, TV relay, and air navigation.
  • SHF (3000–30,000 MHz): Tropospheric propagation; used for Radar navigation and radio relay.

5. Regulatory Organizations

• International Telecommunication Union (ITU): A specialized UN agency established in 1865 (originally as the International Telegraph Union) to connect telegraphic networks. It manages global radio spectrum, satellite orbits, and technical standards.
• ITU Sectors:
  • ITU-T: Telecommunication Standardization Sector (formerly CCITT).
  • ITU-R: Radio Communication Standardization Sector (formerly CCIR), managing spectrum and satellite orbits.
  • ITU-D: Telecommunication Development Sector, focusing on developing countries.
• National Regulators:
  • Bangladesh: Bangladesh Telecommunication Regulatory Commission (BTRC).
  • USA: Federal Communications Commission (FCC).
  • India: Telecom Regulatory Authority of India.
  • Japan: Ministry of Internal Affairs and Communications.
  • UK: Office of Communications.

6. Need for Modulation

The text explains why high carrier frequencies and modulation are necessary:

• Antenna Height: For best results, antenna height should equal the wavelength ($v/f$). For a low-frequency signal like 20KHz, the required height would be 15,000 meters, which is impractical. High frequency carriers reduce the required antenna size.
• Signal Strength: Microphone signals are weak and low frequency, preventing long-distance travel; they require a high-frequency carrier.
• Other Reasons: Modulation permits wireless transmission, makes signals robust against noise, and matches signal frequency to channel bandwidth (e.g., microwave, satellite, or optical fiber ranges).

7. Modem

• Definition: A Modem (Modulator-Demodulator) modulates an analog carrier signal to encode digital information and demodulates it to decode the information.
• Goal: To produce a signal that can be transmitted easily and decoded to reproduce original digital data.
• Types: There are two types of modems: internal and external.

1. Data Communication Modes

The sources define three specific modes of data communication:

• Simplex: Communication is unidirectional. Only one device on a link can transmit; the other can only receive. Examples include keyboards, monitors, and television broadcasting.
• Half-duplex: Each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive (e.g., walkie-talkies, police radio, Citizens Band radio).
• Full-duplex: Both stations can transmit and receive simultaneously. Communication occurs in both directions all the time (e.g., Telephone networks, mobile communication).

2. Data Transmission Methods

The material outlines different methods for transmitting data:

• Parallel Transmission: 8 bits are sent together over eight lines,.
• Serial Transmission: Divided into three types:
  • Asynchronous: Data is sent as a byte or character with start and stop bits added. It is a half-duplex type that does not require synchronization, meaning there are gaps between data units.
  • Synchronous: Data is sent in blocks or frames without gaps. Synchronization between sender and receiver is compulsory. It is a full-duplex type, more efficient and reliable than asynchronous for transferring large amounts of data.
  • Isochronous: Used for real-time audio and video where delay differences (jitter) are not allowed. It ensures data arrives at a fixed rate. For example, TV transmission requires 30 frames per second without delays between frames.

3. Transmission Media

The physical layer uses transmission media to transport bits from a sender to a receiver using cables or air.

• Classes of Media: Media is categorized into Guided (wired) and Unguided (wireless).
• Guided Media: These provide a physical conduit from one device to another.

A. Twisted-Pair Cable

• Structure: Consists of conductors that are separately insulated and twisted together, often bundled into cables.
• Applications: The most common medium, used in telephone networks (subscriber loops), within buildings, Private Branch Exchange (PBX), and LANs (10Mbps or 100Mbps).
• Pros and Cons: Cheap and easy to work with, but has a low data rate and short range.
• Characteristics:
  • Analog: Requires amplifiers every 5km to 6km.
  • Digital: Requires repeaters every 2km or 3km. It has limited distance, bandwidth (1MHz), and data rate (100Mbps), and is susceptible to interference and noise.
• Crosstalk: “Near end crosstalk” occurs when a transmitted signal couples onto a receiving pair.
• Types:
  • Unshielded Twisted Pair (UTP): Ordinary telephone wire; cheapest and easiest to install but suffers from external EM interference.
  • Shielded Twisted Pair (STP): Features a metal braid or sheathing to reduce interference. It is more expensive and harder to handle due to weight and thickness.

B. Co-axial Cable

• Applications: The most versatile medium. Used for TV distribution (Aerial to TV, Cable TV), long-distance telephone transmission (can carry 10,000 voice calls simultaneously), and short-distance computer links/LANs. It is being replaced by fiber optics.
• Characteristics:
  • Analog: Amplifiers every few km (closer for higher frequencies); supports up to 500MHz.
  • Digital: Repeaters required every 1km (closer for higher data rates).

C. Optical Fiber

• Structure: Consists of a glass or plastic core, cladding, and a jacket. Light travels via reflection at the critical angle.
• Benefits: Greater capacity (data rates of hundreds of Gbps), smaller size and weight, lower attenuation, electromagnetic isolation, and greater repeater spacing (10s of km).
• Applications: Long-haul, metropolitan, and rural exchange trunks; subscriber loops; and LANs.
• Transmission Characteristics: Acts as a waveguide for $10^{14}$ to $10^{15}$ Hz (infrared and visible spectrum). Sources include Light Emitting Diodes (LED) which are cheaper and durable, or Injection Laser Diodes (ILD) which are more efficient and allow for Wavelength Division Multiplexing.
• Modes:
  • Multimode: Split into Step index and Graded index,.
  • Single mode:,.

Comparison of Guided Media

The sources provide a comparison table regarding frequency, attenuation, delay, and repeater spacing:

• Twisted Pair: 0 to 1 MHz range; high attenuation; ~2 km repeater spacing.
• Coaxial Cable: 0 to 500 MHz range; moderate attenuation; 1 to 9 km repeater spacing.
• Optical Fiber: 186 to 370 THz range; very low attenuation (0.2 to 0.5 dB/km); ~40 km repeater spacing.

4. Unguided Media (Wireless)

Unguided media transport electromagnetic waves without a physical conductor.

• Radio Wave: Used for multicast communications (radio, TV, paging). Highly regulated, uses omnidirectional antennas, and can penetrate walls.
• Microwave: Used for unicast communication (cellular phones, satellite, wireless LANs). Uses directional antennas (point-to-point line of sight). Higher frequencies cannot penetrate walls.
• Infrared: Used for short-range communication in closed areas using line-of-sight propagation.