D2 MAC PACKET SIGNAL

SUBMITTED BY V. SNEHA REDDY - VTU14772 Y. HAMSA VARSHINI - VTU 11625

D2 MAC PACKET SIGNAL

AAPPLICATIONS

PARAMETERS

FEATURES

INTRODUCTION

index

D2 MAC PACKET SIGNAL

INTRODUCTION

Section 1

• D2-MAC is a satellite television transmission standard, a member of Multiplexed Analogue Components family.
• Created to solve D-MAC's bandwidth problem on European cable systems.
• D2-MAC uses half the data rate of D-MAC (10.125 Mbit/s)
• D2-MAC has a reduced vision bandwidth, about 1/2 that of D-MAC.
• D2-MAC retains most of the quality of a D-MAC signal—but consumes only 5 MHz of bandwidth.

D2 MAC PACKET

FEATURES

Section 2

• A baseband time division multiplex in which the analogue picture signals are combined with duobinary encoded digital sound, synchronization and data signals;

• The capacity of the sound/data multiplex is about 1.5 Mbit/s, equivalent to four high quality 15 kHz sound channels with near instantaneous 14/10 bit companding (protected by one parity bit per sample). The spare data capacity can be used for other services;

• The single baseband representation of the time division multiplex signal is frequency modulated for satellite broadcasting.

D2 MAC PACKET SYSTEM FEATURES

• MAC transmits luminance and chrominance data separately in time rather than separately in frequency (as other analog television formats do, such as composite video).

• Audio, in a format similar to NICAM was transmitted digitally rather than as an FM sub-carrier.
• The MAC standard included a standard scrambling system, EuroCrypt, a precursor to the standard DVB-CSA encryption system.

TECHNICAL DETAILS

PARAMETERS

Section 3

GENERAL VIDEO PARAMETERS

LUMINANCE

CHROMINANCE

• The scanning frequency is the period of time required for one full scan of a complete line when the measuring object is sequentially scanned using a laser beam.
• Modems typically begin scanning frequencies at around 450 MHz because most DOCSIS downstream channels occur at relatively high frequencies (lower frequencies that are usually in use by television channels). Initial frequencies that are scanned are vendor specific and depend on modem brand and model.
• Several channel plans can be scanned. After a scanning cable modem encounters a digital signal that contains the appropriate DOCSIS control messages (a type of DOCSIS message called a clock sync message sent downstream 100 times a second) it identifies that frequency as a receive frequency.

SCANNING FREQUENCY

SCANING FREQUENCY

• In order to transmit the sound signal digitally, the C-MAC system which uses the BPSK or QPSK modulation was initially considered.
• But later on this idea was discarded because it requires a very large bandwidth of 12 MHz, instead of D2-MAC system which uses the duo-binary coding for sound was selected.
• The duo-binary coding is useful for reducing the bandwidth required for the digital sound.
• In D2-MAC system for the transmission luminance and colour difference signal TDM is used, the signals are not sent simultaneously but they are sent sequential one after another.

• In D2-MAC, the analog video and digital sound are multiplexed before modulation. The modulation of subcarrier will take place after that.
• It is possible to use AM/VSB for cable TV and FM for satellite broadcasting.
• The duo-binary uses three levels of signals instead of two and reduces the bandwidth requirement by 50%.

D2-Mac processing on a Philips satellite receiver from 1990

D2-MAC PROCESSING

The simultaneous PAL transmission of all TV-picture elements and the multiplexed transmission of the TV picture elements with D2-MAC.

• It is expected that in the future, the D2-MAC/packet system could beused for other applications, such as terrestrial broadcasting, point-to-point transmissions, video cassettes, etc.

• The D2-MAC/ packet system is suitable for satellite broadcasting wuth frequency modulation and for cable distribution withvestigial - sideband amplitude modulation, with full transparency.

APPLICATIONS

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