Evaluating the average probability of symbol error for different bandpass modulation schemes Comparing different modulation schemes based on their error signals to improve communications performance by increasing the robustness against channel impairments (noise, interference, fading, .) | Digital Communications I: Modulation and Coding Course Term 3 - 2008 Catharina Logothetis Lecture 9 Lecture 9 Last time we talked about: Evaluating the average probability of symbol error for different bandpass modulation schemes Comparing different modulation schemes based on their error performances. Lecture 9 Today, we are going to talk about: Channel coding Linear block codes The error detection and correction capability Encoding and decoding Hamming codes Cyclic codes Lecture 9 Block diagram of a DCS Format Source encode Format Source decode Channel encode Pulse modulate Bandpass modulate Channel decode Demod. Sample Detect Channel Digital modulation Digital demodulation Lecture 9 Channel coding: Transforming signals to improve communications performance by increasing the robustness against channel impairments (noise, interference, fading, .) Waveform coding: Transforming waveforms to better waveforms Structured sequences: Transforming data sequences into better sequences, . | Digital Communications I: Modulation and Coding Course Term 3 - 2008 Catharina Logothetis Lecture 9 Lecture 9 Last time we talked about: Evaluating the average probability of symbol error for different bandpass modulation schemes Comparing different modulation schemes based on their error performances. Lecture 9 Today, we are going to talk about: Channel coding Linear block codes The error detection and correction capability Encoding and decoding Hamming codes Cyclic codes Lecture 9 Block diagram of a DCS Format Source encode Format Source decode Channel encode Pulse modulate Bandpass modulate Channel decode Demod. Sample Detect Channel Digital modulation Digital demodulation Lecture 9 Channel coding: Transforming signals to improve communications performance by increasing the robustness against channel impairments (noise, interference, fading, .) Waveform coding: Transforming waveforms to better waveforms Structured sequences: Transforming data sequences into better sequences, having structured redundancy. -“Better” in the sense of making the decision process less subject to errors. What is channel coding? Lecture 9 Error control techniques Automatic Repeat reQuest (ARQ) Full-duplex connection, error detection codes The receiver sends feedback to the transmitter, saying that if any error is detected in the received packet or not (Not-Acknowledgement (NACK) and Acknowledgement (ACK), respectively). The transmitter retransmits the previously sent packet if it receives NACK. Forward Error Correction (FEC) Simplex connection, error correction codes The receiver tries to correct some errors Hybrid ARQ (ARQ+FEC) Full-duplex, error detection and correction codes Lecture 9 Why using error correction coding? Error performance vs. bandwidth Power vs. bandwidth Data rate vs. bandwidth Capacity vs. bandwidth A F B D C E Uncoded Coded Coding gain: For a given bit-error probability, the reduction in the Eb/N0 that can be realized through the use of code: Lecture 9 Channel
