Digital Television-Transmission and Reception

Digital satellite television: 

It consists of a network of satellites that broadcast digital data. The television signals are delivered by means of communication satellites and received by satellite dishes and set-top boxes. It provides users with a range of channels and services, often to areas that are not serviced by terrestrial or cable providers.

Satellite television, like other communications relayed by satellite, starts with a transmitting antenna located at an uplink facility which has very large uplink satellite dishes, as much as 9 to 12 metres. These dishes are pointed towards a specific satellite with the uplinked signals transmitted within a specific frequency range. This enables a transponder tuned to the frequency on board the satellite to receive the signal and ‘retransmit’ it back to earth at a different frequency band to avoid interference. From a technical perspective this is typically done in the C-band (4-8GHz) or the Ku-band (12-18GHz) or both.

The satellite receiver (such as the ones found  within homes) demodulates and converts the signals to the desired form such as audio (music), video (television), data (internet access), and so on. The coverage area of such a DTH network is determined by the footprint of the specific satellite being used. Fortunately, this is typically large enough to cover significant parts of continents or regions. 

The below illustration outlines a typical DTH satellite transmission:

With DTH services, customers can view and listen to content in high definition and are even able to customise their bouquet of services from the provider. 

DTH: 

DTH stands for Direct-To-Home. Direct-To-Home service is a digital satellite service that provides television services direct to home with a personal dish.

Components of DTH Technology:

DTH (Direct to Home) System consists of the following components:

• Dish Antenna

• LNBF (Low Noise Block Down Converter plus Feedhorn)

• Coaxial Cable

• Set Top Box

Dish Antenna: 

It is a Parabolic Reflector. It receives the signal and redirects it to the LNBF which works as receiver for signal transmitted by satellite Parabolic Reflector.

LNBF 

(Low Noise Block Down Converter Feedhorn): Small metal horn antenna on the Dish is called as Feedhorn. It collects the signal from dish and amplifies the signal bouncing off the dish and filters out the noise.

Coaxial Cable: 

It is the Cable that connects mini Dish and Set Top Box.

DTH Set Top Box:

 DTH Set Top Box, unlike the regular cable connection, decodes the encrypted transmission data and converts these signals into audio & video signal.

Digital TV receiver:

 A DTV receiver is a set-top box that permits the reception of digital television. Its components are very similar to a desktop PC. It is usually connected to the TV set or incorporated in the TV set. The main features of a DTV receiver may be classified as follows:

• decodes the incoming digital signal;

• verifies access rights and security levels;

• displays cinema quality pictures on the TV set;

• outputs digital surround sound;

• processes and renders Internet and interactive TV services.

The tuner in the box receives a digital signal from a cable, a satellite, or terrestrial network and isolates a particular channel. The signal is then forwarded to a demodulator and converted to binary format. Once in binary format, the demodulator will check for error and forward the binary signal to a demultiplexer that will extract audio, video, and data from the binary stream. Once the demultiplexer has finished with the signal, the decoders will transform the digital bits into a format suitable for viewing on the television set.

Components of DTV receiver:

Tuner:

 It selects the particular channel. (QAM tuner)

Modulator and demodulator

The function of the demodulator is to convert the analog signal to a digital bit stream. Then, it checks for errors and forward the bit stream to the demultiplexer. The modulator reverses the actions of a demodulator and its function is to deliver a signal to the return path tuner.

Demultiplexer and decryptor

The demultiplexer selects particular packets, decrypts, and forwards to a specific decoder.

Decoder:

(A video decoder) It transforms video packets into a sequence of pictures, which are displayed by the TV monitor. (An audio decoder) It decompresses the audio bit-stream.

Central processing unit:

The CPU is the brain of the DTV receiver. Functions provided by a CPU include:

• initializes the various hardware components;

• processes a range of Internet and interactive TV applications;

• monitors and manages hardware interrupts;

• fetches data and instructions from memory;

• runs various programs.

Digital Terrestrial Television (DTT):

 It is a technology for terrestrial television in which land-based (terrestrial) television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format.

DTT Transmitters

It refers to the transmission of TV signal in Digital mode using terrestrial transmitters. It facilitates better audio-video quality, multiple channels through single transmitter, better reception quality, programmes in Standard Definition (SD) and High Definition (HD) quality. DTT services can be received on fixed, Mobile and portable devices.

Two digital terrestrial television receiving antenna on the roof

DTT utilises conventional antennas (or aerials) instead of satellite dishes or cable connections to deliver video and audio services to customers. While the transmission of radio frequencies through airwaves is like analogue television, the biggest difference is that the multiplex transmitters enable the reception of multiple channels on a single frequency range. DTT is received via a digital set-top box that decodes the signal received via a standard aerial antenna. Unlike satellites, DTT networks comprise of several terrestrial transmitters each covering an area of approximately 80 to 120km radius from the transmitter. The actual coverage area is influenced by the power of the transmitter.

The advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, satellite, and telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, and potentially lower operating costs for broadcasters (after the initial upgrade costs).

 Closed-circuit television (CCTV):

 It is also known as video surveillance, is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point-to-point (P2P), point-to-multipoint (P2MP), or mesh wired or wireless links.

It comprises at least one camera transmitting data to a monitor or video recorder. The data transmitted can either be video and audio, or video only. 

Components of CCTV:

The complete closed circuit TV system (CCTV system) consists of:

• Security Cameras (Analog or Digital Camera)

• Cables (RJ45 or RJ59 Cables)

• Video recorders (DVR or NVR)

• Storage unit – typically Hard disk

• A display unit (Optional, such as a Monitor)

Both NVR and DVRs are responsible for video recording. DVR stands for Digital Video Recorder, whereas NVR stands for Network Video Recorder. The difference between NVR and DVR is how they process video data. DVR systems process the video data at the recorder, whereas NVR systems encode and process the video data at the camera, then stream it to the NVR recorder which is used for storage and remote viewing.

 CATV:

 Cable TV (CATV) stands for Cable Television, i.e., a method of providing consumers with access to television programs via coaxial cables or through optical fiber cable located in the subscribers’ premises. In CATV, the signals are sent through cables and not through the air. The television signals that come via cable are not disturbed by trees, buildings, or other hindrances.

CATV Architecture:

 TV Network companies beam their TV shows via satellites. Cable operators install control centres for cable network for aggregation of TV channels received from different satellites. They can mix this with content received from other sources such as broadband connections, local channels, etc., to form a bouquet of channels and then distribute to homes using coaxial cable (hence, the name cable TV) network installed either underground or hung over utility poles. To access the cable television services, one needs to subscribe to a cable company which will then connect a simple coaxial cable from the wall outlet to the television sets.

 

Today, cable television companies have found that fiber is the perfect choice for transmitting signals to multiple customer locations.

Video on demand (VoD)

 is a system that allows users to select and watch video content of their choice on their TVs or computers. Video on demand is one of the dynamic features offered by Internet Protocol TV. VoD provides users with a menu of available videos from which to choose. The video data is transmitted via Real-Time Streaming Protocol.

Video-on-demand has 3 core advantages. It allows viewers to:

1. Watch at any time. Users can play content whenever they want. Unlike “linear” TV programming, which only broadcasts in real-time, VOD doesn’t rely on a set schedule.

2. Control what they watch: Users have more opportunities to pick and choose what they watch, compared to traditional TV scheduling. 

3. Use media controls: Users can play, pause, rewind, fast forward, and completely control how they watch content. 

Different types of VOD content include: 

• Online tutoring. 

• Lessons and classes (music, dance, specialized skills).

• Fitness programs.

• Music and sporting events.

• Product demonstrations.

• College courses.

• Corporate team-building.

• Podcasts and interviews.

The majority of VOD users prefer to spend money on subscription plans. Some subscription services you probably recognize include.

• Netflix

• Amazon Prime 

• Disney+