ArtsAutosBooksBusinessEducationEntertainmentFamilyFashionFoodGamesGenderHealthHolidaysHomeHubPagesPersonal FinancePetsPoliticsReligionSportsTechnologyTravel

Advantages of Digital Broadcasting

Updated on September 10, 2009

Digital broadcasting is more than superb picture and sound quality, high definition picture, wide screen format, multichannel sound and more choice. There is one key factor that has significantly contributed to the success of digital broadcasting. This key property is the possibility that all transmitters within some area can transmit on the same frequency. This kind of operation is called a Single Frequency Network (SFN) and it significantly contributes to the efficient use of radiofrequency spectrum.

Most digital broadcasting transmission standards use COFDM - Coded Orthogonal Frequency Division Multiplex, a multi-carrier modulation scheme. The number of carries varies from 2k or 8k carriers in DVB-T system to many ten thousand carriers in the latest standards. The orthogonal frequency spacing of sub-carriers avoids inter-carrier interference, which permits each of the many thousand sub-carriers to carry from two bits of data in QPSK to eight bits in 256QAM. The “Coded” means that the transmitted data contains actual data and additional information for protection (FEC - Forward Error Correction).

Because of finite speed of radio waves at each reception point the propagation delay from various transmitters is different. Therefore, without some mechanism there would be interference receiving digital data from more than one transmitter operating on the same frequency.

The first part of the solution is that each subcarrier transmits its payload (symbol) during an elementary period of several hundred microseconds which is much longer than the multi-path propagation delay. The second part of the solution is that symbol time is prolonged with a “cyclic prefix”. This is called a guard interval.

During this guard interval time the same symbol with different reception times from different transmitters can be received without any interference. This is true until the difference in propagation delays is greater than the guard interval. This also means that short time echoes have no destructive effect on the reception. The length of the guard interval defines the size of the area where we can use SFN network. It is usually measured in tens of kilometers.

In order to operate within a Single Frequency Network, transmitters must transmit the same data and must be synchronized to transmit the same symbol at any time. The later is achieved by inserting synchronization packets into the transport stream. This allows each transmitter to wait until the indicated time to start broadcasting the particular packet. This time-synchronization method allows equalization of the distribution time through the network used to deliver the transport stream to each transmitting site.

The frequency of transmitters operating in SFN network must also be synchronized. Usually it is done with a GPS frequency and time reference. This allows the network to reach the accuracy and stability needed for SFN synchronization - better than 1 Hz in the frequency domain and 1 microsecond in the time domain.

Using single frequency networks means using only one frequency in particular area. This significantly reduces the number of frequencies needed to cover arbitrary territory. How important is this factor is evident, for example, near Italian border where a special agreement for dividing UHF channels has been developed.

Of course, the cost of the network is higher and usage of SFN repeaters (gap fillers) is very limited, but the overall gain of SFN networks is huge. The price we have to pay is lower than the price of the most valuable part of the system – the frequency.


Submit a Comment

No comments yet.


This website uses cookies

As a user in the EEA, your approval is needed on a few things. To provide a better website experience, uses cookies (and other similar technologies) and may collect, process, and share personal data. Please choose which areas of our service you consent to our doing so.

For more information on managing or withdrawing consents and how we handle data, visit our Privacy Policy at:

Show Details
HubPages Device IDThis is used to identify particular browsers or devices when the access the service, and is used for security reasons.
LoginThis is necessary to sign in to the HubPages Service.
Google RecaptchaThis is used to prevent bots and spam. (Privacy Policy)
AkismetThis is used to detect comment spam. (Privacy Policy)
HubPages Google AnalyticsThis is used to provide data on traffic to our website, all personally identifyable data is anonymized. (Privacy Policy)
HubPages Traffic PixelThis is used to collect data on traffic to articles and other pages on our site. Unless you are signed in to a HubPages account, all personally identifiable information is anonymized.
Amazon Web ServicesThis is a cloud services platform that we used to host our service. (Privacy Policy)
CloudflareThis is a cloud CDN service that we use to efficiently deliver files required for our service to operate such as javascript, cascading style sheets, images, and videos. (Privacy Policy)
Google Hosted LibrariesJavascript software libraries such as jQuery are loaded at endpoints on the or domains, for performance and efficiency reasons. (Privacy Policy)
Google Custom SearchThis is feature allows you to search the site. (Privacy Policy)
Google MapsSome articles have Google Maps embedded in them. (Privacy Policy)
Google ChartsThis is used to display charts and graphs on articles and the author center. (Privacy Policy)
Google AdSense Host APIThis service allows you to sign up for or associate a Google AdSense account with HubPages, so that you can earn money from ads on your articles. No data is shared unless you engage with this feature. (Privacy Policy)
Google YouTubeSome articles have YouTube videos embedded in them. (Privacy Policy)
VimeoSome articles have Vimeo videos embedded in them. (Privacy Policy)
PaypalThis is used for a registered author who enrolls in the HubPages Earnings program and requests to be paid via PayPal. No data is shared with Paypal unless you engage with this feature. (Privacy Policy)
Facebook LoginYou can use this to streamline signing up for, or signing in to your Hubpages account. No data is shared with Facebook unless you engage with this feature. (Privacy Policy)
MavenThis supports the Maven widget and search functionality. (Privacy Policy)
Google AdSenseThis is an ad network. (Privacy Policy)
Google DoubleClickGoogle provides ad serving technology and runs an ad network. (Privacy Policy)
Index ExchangeThis is an ad network. (Privacy Policy)
SovrnThis is an ad network. (Privacy Policy)
Facebook AdsThis is an ad network. (Privacy Policy)
Amazon Unified Ad MarketplaceThis is an ad network. (Privacy Policy)
AppNexusThis is an ad network. (Privacy Policy)
OpenxThis is an ad network. (Privacy Policy)
Rubicon ProjectThis is an ad network. (Privacy Policy)
TripleLiftThis is an ad network. (Privacy Policy)
Say MediaWe partner with Say Media to deliver ad campaigns on our sites. (Privacy Policy)
Remarketing PixelsWe may use remarketing pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to advertise the HubPages Service to people that have visited our sites.
Conversion Tracking PixelsWe may use conversion tracking pixels from advertising networks such as Google AdWords, Bing Ads, and Facebook in order to identify when an advertisement has successfully resulted in the desired action, such as signing up for the HubPages Service or publishing an article on the HubPages Service.
Author Google AnalyticsThis is used to provide traffic data and reports to the authors of articles on the HubPages Service. (Privacy Policy)
ComscoreComScore is a media measurement and analytics company providing marketing data and analytics to enterprises, media and advertising agencies, and publishers. Non-consent will result in ComScore only processing obfuscated personal data. (Privacy Policy)
Amazon Tracking PixelSome articles display amazon products as part of the Amazon Affiliate program, this pixel provides traffic statistics for those products (Privacy Policy)