Curso: Normas Técnicas del ISDB-Tb 2/4 Modulación de fase (PM

Normas Técnicas del ISDB-Tb
Dic-2012
Modulación de fase (PM)
Curso:
Normas Técnicas del ISDB-Tb 2/4
Expositor:
Ing. Marcial López Tafur
05 Dic 2012
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Modulación de frecuencia (FM)
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Normas Técnicas del ISDB-Tb
Dic-2012
Modulación digital
Modulación digital
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Esquemas típicos de modulación
Espectro de la señal modulada
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Tecnología para la modulación digital
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Normas Técnicas del ISDB-Tb
Dic-2012
El formato I/Q
Tecnología para la modulación digital
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Lado de transmisión
Lado de recepción
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Lo básico de la modulación digital
Binary Amplitude Shift Keying
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Normas Técnicas del ISDB-Tb
Dic-2012
Aplicación del ASK
Binary o Bi-Phase Sift Keying
• One of the simplest forms of digital modulation is Binary or
Bi-Phase Shift Keying(BPSK).
• BPSK is used for deep space telemetry.
• The phase of a carrier signal with constant amplitude moves
between zero and 180 degrees between zero and 180
degrees .
• In I/Q format, there are two different states in I-axis.
• Since ASK is weak to a noise or an interference, ASK is not
used for long-distance communications, it is used by shortdistance communication.
• OOK (OnOff Keying) system is the same as ASK turn on and
turn off the continuous carrier of a constant frequency and
a constant amplitude. (It is used for low power
consumption radio equipment and known as Morse code.)
• Modulation is easy, then system is small, cheap and easy
to build, however the bandwidth after modulation is wide.
• 8 levels ASK is adopted for DTTB (Digital Terrestrial
Television Broadcasting) in the Unite d States.
M [bit/symbol] = log2{2} = 1
One bit per symbol
Bit rate = Symbol rate
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BPSK
Quadrature Phase Shift Keying (QPSK)
• Quadrature Phase Shift Keying (QPSK) is more common type of phase
modulation than BPSK.
• QPSK is effectively employed two independent BPSK systems (I and Q),
and therefore exhibits the same performance but twice the bandwidth
efficiency.
• QPSK can be filtered using raised cosine filters to achieve excellent out of
band suppression.
• Large envelope variations occur during phase transitions, thus requiring
linear amplification.
• BPSK is illustrated in the chart below. Notice the 180°
phase shifts indicated by the red line.
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QPSK
Quadrature Modulation
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Normas Técnicas del ISDB-Tb
Dic-2012
Tipos de QPSK
Modulador QPSK
• Conventional QPSK has transitions through zero. Because the
modulated signal can be off temporally, the PA must be linear
AMP with wide dynamic range.
• In Offset QPSK, I-signal (or Q-signal) is slowed for a half
symbol. So the QPSK signal has no transitions through zero.
• In π /4 QPSK , the set of constellation points are toggled each
symbol, so transitions through zero cannot occur.
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π/4 Shift QPSK
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Ventajas
– Phase transitions avoiding center of diagram, removes some
design constraints on amplifier.
– Amplitude fluctuations of π / 4–QPSK are between OQPSK
and non -offset QPSK
Sumario del QPSK
• QPSK is used extensively in applications including:
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CDMA (Code Division Multiple Access) cellular service,
Wireless local loop,
Iridium (a voice/data satellite system) ,
DVB-S (Digital Video Broadcasting - Satellite) and
ISDB - T (Mobile service).
• QPSK advantages are following:
• Symbol points are chosen as they can be easily
implemented using an I/Q modulator.
• There are four states because 22= 4. It is therefore a
more bandwidth-efficient type of modulation than
BPSK – potentially twice as efficient.
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Normas Técnicas del ISDB-Tb
Dic-2012
Binary Frequency Shift Keying
FSK
• En FSK, la frecuencia de la portadora se cambia como una
función de la señal modulante (data) que está siendo
transmitida. La amplitud no cambia.
• En Binary FSK (BFSK o 2FSK), un “ 1” es representado por una
frecuencia y un “ 0” es representado por otra frecuencia.
• Usually, the instantaneous frequency is shifted between
Information Carrier two discrete values termed “ mark
frequency ” and “ space frequency ”.
• Changing two kinds of oscillators (Fig1)
• – Controlling a VCO (Voltage Control Oscillator) (Fig2)
• Frequency changes continuously and this coherent
phase exhibits good spectral efficiency
• CPFSK “ Continuous Phase Frequency Shift Keying ”
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Implementación del FSK
Fig1 Cambio de osciladores
Sumario del FSK
• FSK is not susceptible to amplitude fluctuation.
• Class C amplifier can be used for power amplifier. (power
efficient)
• FSK modulator and demodulator are more complicated than
ASK, but are simpler than PSK.
• Bit error rate with the same C/N ratio is better than ASK and
is inferior to PSK.
• Used for the modem such as low-speed telephone lines.
• FSK (Frequency Shift Keying) is used in many applications
including cordless and paging systems.
• DECT: Digital Enhanced (formerly European) Cordless
Telephone
• CT-2: Cordless Telephone 2
Fig2 Cambio de Voltajes
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Minimum Shift Keying (MSK)
MSK
• MSK is the special case of FSK, whose modulation
index is 0.5.
• Because of the reduced bandwidth and coherent
detection possible at receiver, MSK is more practical
and widely used.
• MSK is used in the GSM ( Global System for Mobile
communications) European cellular standard
• Similarly to OQPSK, MSK is encoded with bits alternating
between quaternary components, with the Q component
delayed by half the symbol period.
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Normas Técnicas del ISDB-Tb
Dic-2012
Gaussian Filtered Minimum Shift Keying
(GMSK)
Multi-level (M-ary) APSK
Amplitude Phase Shift Keying
MSK with a Gaussian filter is termed GMSK (Gaussian filtered MSK).
The bandwidth of modulated signal is limited and remove the
interference with neighbor symbol by Gaussian filter.
• Limiting the bandwidth with the advantage of MSK
• Baseband signal (0/1) is converted into bipolar NRZ signal (-1/+1)
• NRZ signal is shaped by Gaussian filter
• FSK transmitter (modulation index: 0.5)
• Since Gaussian filter is not met Nyquist first standard, ISI occurs.
Diagrama de bloques conceptual
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Generación de una señal PSK de 8
niveles
Amplitude Phase Shift Keying (APSK)
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Quadrature Amplitude Modulation
(QAM)
Ruido en el canal de transmisión digital
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Normas Técnicas del ISDB-Tb
Dic-2012
Error debido al ruido Gaussiano
Patrones de errores concurrentes
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Bit Error Rate (BER) del BPSK
Relación entre la modulación PSK y el
ruido
Error performance in AWGN channel
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Normas Técnicas del ISDB-Tb
Dic-2012
TC8PSK (Trellis Coded 8PSK)
TC8PSK (Trellis Coding)
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Detección del DBPSK
Differential Binary Phase-Shift Keying
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Resumen
OFDM
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Normas Técnicas del ISDB-Tb
Dic-2012
Comparación de la duración de los símbolos
FFT e IFFT
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¿Por qué ortogonal?
¿Qué significa ortogonal?
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¿Qué es el intervalo de guardia?
Banda de frecuencia para el ISDB-T
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Normas Técnicas del ISDB-Tb
Dic-2012
Espectro de la señal OFDM
Espectro del UHF en Tokyo
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La modulación OFDM
Formas de onda y portadoras OFDM
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¿Qué es el QAM?
Ubicaciones del 64QAM (mapeo)
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Normas Técnicas del ISDB-Tb
Dic-2012
Ejemplo de recepción de 64QAM
Relación C/N – BER de 64QAM
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Multipath Echo Interferences
Signal Distortion by Multipath Echo
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¿Por qué la señal se distorsiona?
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Normas Técnicas del ISDB-Tb
Dic-2012
Pilot Carrier
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Equalizing
Placement of Pilot Carrier of ISDB-T
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Delay time- BER
Interleaving
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Normas Técnicas del ISDB-Tb
Dic-2012
Basic Configuration of ISDB-T Channel Coding
¿Por qué el Interleaving?
Frequency Interleaving
• In case of multi path echo interferences, specific
frequency area may be damaged in a mass.
• By frequency interleaving, it is able to fix the bit
error occurred in the specific frequency.
Time Interleaving
• In case of mobile reception, received power may
be under the threshold in a specific moment.
• By time interleaving, it is able to fix the bit errors
that has occurred during that moment.
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ISDB-T Channel Coding
Error Correction → for error on transmission
Interleavin g → for burst error on transmission
Pilot Carrier → for equalizing distorted signal
Guard Interval → for reducing multipath interference
IFFT → essential process for OFDM modulation
Framing, Multiplexing and others → regulated by
standard
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Resumen
Modulation Multi portadora
• Comparada con la modulación convencional de
una sola portadora .
• Longitud del símbolo grande
• Intervalo de Guardia
• Ecualización en el dominio de la frecuencia
Robusto contra el multi-trayecto
• Las Sub-portadoras son ortogonales una a la otra
Alta eficiencia espectral
Muchas gracias por su atención
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