Digital Communication #7. Line Coding Techniques: Difference Between Unipolar, Polar & Bipolar Line скачать в хорошем качестве

Digital Communication #7. Line Coding Techniques: Difference Between Unipolar, Polar & Bipolar Line

Digital Communication playlist.    • Digital Communication #3. Receiver End: Do...   For access to this presentation materials, membership is required: I need the Material PPT Sent me an email to Technologies.Discussion@gmail.com If you need the whole playlist material, send me email and we discuss. Give me some time to response. Thanks. Line coding is the process of converting digital data (bits) into a sequence of electrical or optical pulses (signals) suitable for transmission over a physical communication channel (e.g., a wire, fiber optic cable, or wireless medium). As a baseband transmission technique, it involves sending the signal without shifting it to a higher frequency band. In this process, a bit sequence is converted into a digital signal. The sender encodes digital data into this signal, and the receiver decodes the signal to recreate the original digital data. 1. Unipolar (On-Off Signaling) Concept: Uses only one voltage level (e.g., +V for '1', 0V for '0'). Example: NRZ (Non-Return-to-Zero) - Level is constant throughout the bit interval. Pros: Extremely simple. Cons: DC component present. No synchronization for long strings of 0s or 1s. Wasteful power. Rarely used in modern long-distance communication. Non return to zero (NRZ) - It is unipolar line coding scheme in which positive voltage defines bit 1 and the zero voltage defines bit 0. Signal does not return to zero at the middle of the bit thus it is called NRZ.  For example: Data =10110.  But this scheme uses more power as compared to polar scheme to send one bit per unit line resistance. Moreover, for continuous set of zeros or ones there will be self-synchronization and base line wandering problem. Polar (Two Equal but Opposite Voltage Levels) Uses two equal but opposite voltage levels (e.g., +V/2 for '1', -V/2 for '0'). a) NRZ-L (NRZ-Level) Voltage level depends on the bit. Common in early digital systems. b) NRZ-I (NRZ-Inverted) Transition at the start of a bit interval represents a '1'. No transition represents a '0'. Pros: Better synchronization than NRZ-L (a string of 1s causes frequent transitions). Cons: String of 0s still causes loss of sync. DC component possible. Used in: USB low-speed, magnetic recording. Polar schemes - In polar schemes, the voltages are on the both sides of the axis. NRZ-L and NRZ-I - These schemes are somewhat similar to unipolar NRZ but use two voltage levels. In NRZ-L (Non-Return-to-Zero, Level), the voltage level directly determines the bit value. Typically, a logic-level high (e.g., +V) represents a binary 1, and a logic-level low (e.g., -V) represents a binary 0. In NRZ-I (Non-Return-to-Zero, Inverted), a transition in the signal level (from high to low or low to high) occurs at the bit boundary only if the next bit to transmit is a logical 1. If the next bit is a logical 0, no transition occurs. Note: For the NRZ-I example, we assume the signal level before transmitting the data set "01001110" was positive (+V). Therefore, there is no transition at the start, and the first bit "0" begins at +V. Example: Data = 01001110. A comparison between NRZ-L and NRZ-I: Baseline wandering affects both schemes, but it is twice as severe in NRZ-L compared to NRZ-I. This difference arises because NRZ-I uses a transition at the bit boundary when the next bit to be transmitted is a logical 1. Similarly, the self-synchronization problem occurs in both for long sequences of 0’s, but for long sequences of 1’s, it is more severe in NRZ-L.