McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Capítulo 5 Codificación y modulación

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Codificación Es necesario convertir los datos en forma de bits a señales antes de enviarlos a través del medio de transmisión. La conversión de una señal digital a analógica también se denomina modulación de una señal digital. La conversión de una señal analógica a otra analógica también se denomina modulación de una señal analógica.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-1 Different Conversion Schemes

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-2 Digital to Digital Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-3 Types of Digital to Digital Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Conversión digital a digital Unipolar, usa un único valor de nivel, que generalmente representa el ‘1’ y el ‘0’ mantiene la señal a 0. Polar, usa dos niveles de amplitud. Hay varias codificaciones: NRZ, RZ, bifásica, manchester y manchester diferencial. Bipolar, usa 3 niveles: positivo, cero y negativo. Tipos: Bipolar con Inversión de marca alternada (AMI), Bipolar con sustitución de 8 ceros (B8ZS) y Bipolar 3 de alta densidad (HDB3).

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-4 Unipolar Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-5 Types of Polar Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-6 NRZ-L and NRZ-I Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-7 RZ Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-8 Manchester and Diff. Manchester Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-9 Types of Bipolar Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-10 Bipolar AMI Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-11 B8ZS Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-12 HDB3 Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Resumen Digital a Digital

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-13 Solution to Example 5.1

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-14 Solution to Example 5.2

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Conversión de analógico a digital Se trata de digitalizar una señal analógica y consiste en muestrear periódicamente la señal analógica con infinitos valores continuos y transformar su valor en valores enteros discretos que posteriormente se convertirán en ceros y unos. De esta manera la señal analógica se transforma en pulsos digitales.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-15 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Analog to Digital Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Modulación por amplitud de pulsos (PAM) La señal analógica se muestrea con una determinada frecuencia y se genera una señal de pulsos discretos. PAM es el primer paso del método Modulación por codificación en pulsos (PCM)

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-16 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 PAM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-17 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Quantized PAM Signal

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Modulación por codificación en pulsos (PCM) PCM modifica los pulsos generados por PAM para obtener una señal completamente digital. PCM consta de 4 procesos: –PAM –Cuantificación –Cuantificación binaria, y –Codificación digital a digital. Según el teorema de Nyquist la tasa del muestreo debe ser al menos doble de la frecuencia más alta de la onda para no perder información significativa.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-18 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Quantizing Using Sign and Magnitude

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-19 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20-continued WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20-continued WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-20-continued WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 From Analog to PCM

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-21 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Nyquist Theorem

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Conversión de digital a analógico Los datos digitales deben ser modulados sobre una señal analógica (portadora) que ha sido manipulada para mostrar los valores correspondientes a los ceros y los unos de la señal digital. La modulación puede ser: –Modulación por desplazamiento de amplitud (ASK). –Modulación por desplazamiento de frecuencia (FSK). –Modulación por desplazamiento de fase (PSK). –Modulación de amplitud en cuadratura (QAM), que combina cambios en fase y en amplitud.

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-22 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Digital to Analog Encoding

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-23 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Modulación para datos digitales

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-24 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 ASK

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-25 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Bandwidth for ASK BW=(1+d) x N baudio

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 FSK Figure 5-27 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Bandwidth for FSK Figure 5-28 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 BW=(f c1 -f c0 ) + N baudio

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 PSK Figure 5-29 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 PSK Constellation Figure 5-30 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., PSK Figure 5-31 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., PSK Characteristics Figure 5-32 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., PSK Characteristics Figure 5-33 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 PSK Bandwidth Figure 5-34 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 BW=(1+d) x N baudio

McGraw-Hill©The McGraw-Hill Companies, Inc., QAM and 8-QAM Constellations Figure 5-35 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., QAM Signal Figure 5-36 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., QAM Constellation Figure 5-37 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Bit Rate and Baud Rate Figure 5-38 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-38-continued WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Bit Rate and Baud Rate

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Conversión de analógico a analógico La modulación analógica permite cambiar las características de una señal analógica. Hay tres modos de modulación: –Modulación en amplitud (AM) –Modulación en frecuencia (FM) –Modulación en fase (PM)

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-39 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Analog to Analog Modulation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-40 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-41 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Amplitude Modulation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-42 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 AM Bandwidth

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-43 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 AM Band Allocation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-44 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 Frequency Modulation

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-45 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 FM Bandwidth

McGraw-Hill©The McGraw-Hill Companies, Inc., 2001 Figure 5-46 WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998 FM Band Allocation