ECEN 90 - Communications 2 Study Notes

ECEN 90 - Communications 2 Study Notes

• Course title: ECEN 90 - Communications 2
• Instructor: Lemuel G. Tatad
• Learning Objectives: After completing the chapter, students will be able to connect the concepts of bandwidth, bit rate, bit error rate, power, and complexity.

Introduction of Terms

• Bit rate: The rate at which data is processed or transferred. Measured in units per second. Units include bps, Kbps, Mbps, and Gbps, with higher units representing higher bit rates. Also known as data rate.
• Data Transfer Rate (DTR): The amount of digital data transferred in a given time.

Bit Rate Table

• A table showing various bit rate units, their corresponding symbols, multiples, decimal equivalents, and binary equivalents.

Introduction of Terms (Bandwidth)

• Bandwidth: Similar to maximum bit rate in a communication network. It's the transferring capacity of a communication channel or medium. It represents the maximum rate bits can be transferred from a source to a destination.
• It also indicates the amount of time required for transmitting or receiving data over a network.

Bandwidth vs. Bitrate Table

• A table comparing bandwidth and bitrate, explicitly defining each term, outlining units of measurement and highlighting that bit rate is always less than or equal to bandwidth.

Introduction of Terms (Bit Error Rate - BER)

• Bit Error Rate (BER): The number of bit errors divided by the total number of transmitted bits during a specific time interval. BER is a unitless performance measure, often expressed as a percentage.
• Errors occur due to noise, interference, distortion, or bit synchronization errors during digital transmission.

Introduction of Terms (BER Examples)

• An example of BER calculation is provided using a transmitted bit sequence (0110001011) and a received sequence (001010101).  The BER was calculated as 0.3 or 30%.

Introduction of Terms (Factors Affecting BER)

• Factors affecting BER include channel noise, interference, distortion, bit synchronization problems, attenuation, wireless multipath fading, etc.

Introduction of Terms (Improving BER)

• Methods to improve BER include optimizing transmit signal strength, selecting robust modulation/line coding scheme, implementing channel coding (e.g., forward error correction), employing equalization techniques to mitigate channel distortions, boosting signal strength through amplification and filtering, and reducing receiver noise.

Introduction of Terms (Baseband Binary PAM Transmission System Model)

• PAM (Pulse Amplitude Modulation): A method of transmitting digital data by varying the amplitude of discrete pulses.
• Binary PAM system uses two amplitudes to represent binary digits (0 and 1).
• PAM is efficient in terms of power and bandwidth utilization

System Components (Transmitter, Channel, Receiver)

• Detailed breakdown of the transmitter components (input sequence, pulse generator, transmitting filter)
• Breakdown of the channel (medium through which the signal is transmitted, often affected by noise)
• Breakdown of the receiver components (receiving filter, decision device)
• A diagram illustrating the components and their interactions in a Baseband binary PAM transmission system.

Intersymbol Interference (ISI)

• Intersymbol Interference (ISI): Occurs when a pulse spreads out to interfere with adjacent pulses at a sample instant.
• Causes of ISI include channel distortion, multipath propagation (wireless signals taking different paths), and bandwidth limitations.
• An example using polar NRZ (non-return to zero) line code, demonstrating how bandwidth limitations can spread (smear) pulses

Intersymbol Interference (ISI) - Nyquist Criterion

• Nyquist Criterion (Zero-ISI Transmission): A condition where pulses have no ISI when transmitted through a channel with sufficient bandwidth.
• A concise summary of the time domain and frequency domain conditions for eliminating ISI in a communication system
• Raised cosine-rolloff Nyquist filter is a solution that controls bandwidth to effectively minimize ISI.
• Nyquist Criterion difficulties with overall amplitude transfer characteristics being unrealistic and synchronization issues.

Intersymbol Interference (ISI) - Eye Diagram

• Eye Diagram: A graphical representation showing the degradation of signal quality during communication.
• How eye diagram width, optimum sampling time, and height of the opening are analyzed to determine the margin of signal quality over channel noise.

Optimum System Design for Noise Immunity

• The major objectives in designing for noise immunity are to carefully choose appropriate transmitting (H_T(f)) and receiving (H_R(f)) filters to minimize ISI in non-ideal communication channel, transmit pulse (G(f)), receive pulse(H(f)), in order to obtain the minimum achievable BER.

Optimum System Design for Noise Immunity (Assumptions)

• Practical significance includes ensuring input bits to a pulse generator are independent and equiprobable
• The transmit pulse (G(f)) is sufficiently narrow with respect to its Fourier transform that it does not change considerably across the relevant frequency bandwidth in question.
• Noise is additive white Gaussian noise(AWGN) with a specified power spectral density of N₀/2