2 2 Wavelength division multiplexing

pcbinary June 27, 2021 0 Comments



Video processingEdit


In video editing and processing systems, multiplexing refers to the process ofinterleaving audio and video into one coherent data stream.In digital video, such a transport stream is normally a feature of a containerformat which may include metadata and other information, such as subtitles.The audio and video streams may have variable bit rate. Software that producessuch a transport stream and/or container is commonly called a statisticalmultiplexer or muxer. A demuxer is software that extracts or otherwise makesavailable for separate processing the components of such a stream orcontainer.

Digital broadcastingEdit


In digital television systems, several variable bit-rate data streams aremultiplexed together to a fixed bitrate transport stream by means ofstatistical multiplexing. This makes it possible to transfer several video andaudio channels simultaneously over the same frequency channel, together withvarious services. This may involve several standard definition television(SDTV) programmes (particularly on DVB-T, DVB-S2, ISDB and ATSC-C), or oneHDTV, possibly with a single SDTV companion channel over one 6 to 8 MHz-wideTV channel. The device that accomplishes this is called a statisticalmultiplexer. In several of these systems, the multiplexing results in an MPEGtransport stream. The newer DVB standards DVB-S2 and DVB-T2 has the capacityto carry several HDTV channels in one multiplex.[citation needed]In digital radio, a multiplex (also known as an ensemble) is a number of radiostations that are grouped together. A multiplex is a stream of digitalinformation that includes audio and other data.[9]On communications satellites which carry broadcast television networks andradio networks, this is known as multiple channel per carrier or MCPC. Wheremultiplexing is not practical (such as where there are different sources usinga single transponder), single channel per carrier mode is used.[citationneeded]

Analog broadcastingEdit


In FM broadcasting and other analog radio media, multiplexing is a termcommonly given to the process of adding subcarriers to the audio signal beforeit enters the transmitter, where modulation occurs. (In fact, the stereomultiplex signal can be generated using time-division multiplexing, byswitching between the two (left channel and right channel) input signals at anultrasonic rate (the subcarrier), and then filtering out the higherharmonics.) Multiplexing in this sense is sometimes known as MPX, which inturn is also an old term for stereophonic FM, seen on stereo systems since the1960s.

Video processing


Main article: Demultiplexer (media file)In video editing and processing systems, multiplexing refers to the process ofinterleaving audio and video into one coherent MPEG transport stream (TDM).In digital video, such a transport stream is normally a feature of a containerformat which may include metadata and other information, such as subtitles.The audio and video streams may have variable bit rate. Software that producessuch a transport stream and/or container is commonly called a statisticalmultiplexor or muxer. A demuxer is software that extracts or otherwise makesavailable for separate processing the components of such a stream orcontainer.

Digital broadcasting


In digital television and digital radio systems, several variable bit-ratedata streams are multiplexed together to a fixed bitrate transport stream bymeans of statistical multiplexing. This makes it possible to transfer severalvideo and audio channels simultaneously over the same frequency channel,together with various services.In the digital television systems, this may involve several standarddefinition television (SDTV) programmes (particularly on DVB-T, DVB-S2, ISDBand ATSC-C), or one HDTV, possibly with a single SDTV companion channel overone 6 to 8 MHz-wide TV channel. The device that accomplishes this is called astatistical multiplexer. In several of these systems, the multiplexing resultsin an MPEG transport stream. The newer DVB standards DVB-S2 and DVB-T2 has thecapacity to carry several HDTV channels in one multiplex. Even the originalDVB standards can carry more HDTV channels in a multiplex if the most advancedMPEG-4 compressions hardware is used.On communications satellites which carry broadcast television networks andradio networks, this is known as multiple channel per carrier or MCPC. Wheremultiplexing is not practical (such as where there are different sources usinga single transponder), single channel per carrier mode is used.Signal multiplexing of satellite TV and radio channels is typically carriedout in a central signal playout and uplink centre, such as SES PlatformServices in Germany, which provides playout, digital archiving, encryption,and satellite uplinks, as well as multiplexing, for hundreds of digital TV andradio channels.In digital radio, both the Digital Audio Broadcasting (DAB) Eureka 147 systemof digital audio broadcasting and the in-band on-channel HD Radio, FMeXtra,and Digital Radio Mondiale systems can multiplex channels. This is essentiallyrequired with DAB-type transmissions (where a multiplex is called a DABensemble), but is entirely optional with IBOC systems.

Analog broadcasting


In FM broadcasting and other analog radio media, multiplexing is a termcommonly given to the process of adding subcarriers to the audio signal beforeit enters the transmitter, where modulation occurs. (In fact, the stereomultiplex signal can be generated using time-division multiplexing, byswitching between the two (left channel and right channel) input signals at anultrasonic rate (the subcarrier), and then filtering out the higherharmonics.) Multiplexing in this sense is sometimes known as MPX, which inturn is also an old term for stereophonic FM, seen on stereo systems since the1960s.

2. Analog multiplexing


The most commonly used analog multiplexing techniques are frequency divisionmultiplexing (FDM) and wavelength division multiplexing.

2.2. Wavelength division multiplexing


Fiber-optic communications require a different kind of multiplexer called awavelength division multiplexer (WAD) [2, 4]. It is an analog multiplexingtechnique. It is designed for high data rate capability fiber cable. In thistechnique the bandwidth of the communication channel should be greater thanthe combined bandwidth of the individual channels. Here signals are convertedto light signals; each light which has different wavelengths is transmittedthrough the same fiber cable. WDM transmission system divides the opticalfiber bandwidth into a number of nonoverlapping optical wavelengths; these arereferred to as WDM channels. WDM mixes all incoming signals having differentwavelengths and are transmitted over a common channel. A demultiplexer doesthe reverse operation and separates the wavelengths. This multiplexingmechanism provides a much higher available transmission capacity.Figure 3 shows the representation of WDM system that consists of bothmultiplexer and demultiplexer.

2.6.1. OFDM transmitter


The block diagram depicting the OFDM transmitter is shown in Figure 12. ForOFDM transmitter, a serial stream of binary digits is considered as the input.The input is converted into N parallel streams using inverse multiplexing. Thetransformation of N parallel streams into the state-space mechanism isperformed by means of modulation techniques like quadrature amplitudemodulation (QAM) and phase shift keying (PSK).

2.6.2. Block diagram of OFDM transmitter


To provide a set of complex time-domain samples, IFFT is calculated for eachset of symbols. Later, the time-domain samples are quadrature mixed topassband in the normal way. By the use of digital-to-analog converters (DACs),the real and imaginary components are primarily converted to the analogdomain. Such analog signal helps to modulate corresponding cosine and sinewaves at the carrier frequency. Finally, those signals are summed up toprovide the transmission signal.

3. Digital multiplexer


Digital multiplexer [6, 7, 8] or data selector is a logic circuit that hasseveral input lines and a single output line. It also consists of dataselector switch which is used to select the inputs and permit the data intothe device to output.

5. Major digital modulation schemes


In analog communication we use different modulation schemes like amplitudemodulation, frequency modulation, phase modulation, etc. [9]. In digitalcommunication we use the following schemes:

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