tailieunhanh - Digital Communication I: Modulation and Coding Course-Lecture 2

Important features of digital communication systems Some basic concepts and definitions such as as signal classification, spectral density, random process, linear systems and signal first important step in any DCS: Transforming the information source to a form compatible with a digital syst | Digital Communications I: Modulation and Coding Course Term 3 – 2008 Catharina Logothetis Lecture 2 Lecture 2 Last time, we talked about: Important features of digital communication systems Some basic concepts and definitions such as as signal classification, spectral density, random process, linear systems and signal bandwidth. Lecture 2 Today, we are going to talk about: The first important step in any DCS: Transforming the information source to a form compatible with a digital system Lecture 2 Encode Transmit Pulse modulate Sample Quantize Demodulate/ Detect Channel Receive Low-pass filter Decode Pulse waveforms Bit stream Format Format Digital info. Textual info. Analog info. Textual info. Analog info. Digital info. source sink Formatting and transmission of baseband signal Lecture 2 Format analog signals To transform an analog waveform into a form that is compatible with a digital communication system, the following steps are taken: Sampling Quantization and encoding Baseband . | Digital Communications I: Modulation and Coding Course Term 3 – 2008 Catharina Logothetis Lecture 2 Lecture 2 Last time, we talked about: Important features of digital communication systems Some basic concepts and definitions such as as signal classification, spectral density, random process, linear systems and signal bandwidth. Lecture 2 Today, we are going to talk about: The first important step in any DCS: Transforming the information source to a form compatible with a digital system Lecture 2 Encode Transmit Pulse modulate Sample Quantize Demodulate/ Detect Channel Receive Low-pass filter Decode Pulse waveforms Bit stream Format Format Digital info. Textual info. Analog info. Textual info. Analog info. Digital info. source sink Formatting and transmission of baseband signal Lecture 2 Format analog signals To transform an analog waveform into a form that is compatible with a digital communication system, the following steps are taken: Sampling Quantization and encoding Baseband transmission Lecture 2 Sampling Time domain Frequency domain Lecture 2 Aliasing effect LP filter Nyquist rate aliasing Lecture 2 Sampling theorem Sampling theorem: A bandlimited signal with no spectral components beyond , can be uniquely determined by values sampled at uniform intervals of The sampling rate, is called Nyquist rate. Sampling process Analog signal Pulse amplitude modulated (PAM) signal Lecture 2 Quantization Amplitude quantizing: Mapping samples of a continuous amplitude waveform to a finite set of amplitudes. In Out Quantized values Average quantization noise power Signal peak power Signal power to average quantization noise power Lecture 2 Encoding (PCM) A uniform linear quantizer is called Pulse Code Modulation (PCM). Pulse code modulation (PCM): Encoding the quantized signals into a digital word (PCM word or codeword). Each quantized sample is digitally encoded into an l bits codeword where L in the number of quantization levels and Lecture 2 Quantization example t Ts: