Turbo and LDPC Codes for Digital Video Broadcasting

Abstract

The Digital Video Broadcasting (DVB) Project was founded in 1993 by the European Telecommunications Standards Institute (ETSI) with the goal of standardizing digital television services. Its initial standard for satellite delivery of digital television, dubbed DVB-S, used a concatenation of an outer (204,188) byte shortened Reed Solomon code and an inner constraint length 7, variable rate (r ranges from 1/2 to 7/8) convolutional code [7]. The same infrastructure used to deliver television via satellite can also be used to deliver Internet and data services to the subscriber. Internet over DVBS is a natural competitor against cable modem and DSL technology, and its universal coverage allows even the most remote areas to be served. Because DVB-S only provides a downlink, an uplink is also needed to enable interactive applications such as web browsing. The uplink and downlink need not be symmetric, since many Internet services require a faster downlink. One alternative for the uplink is to use a telephone modem, but this does not allow for always-on service, has modest data rates, and can be costly in remote areas. A more attractive alternative is for the subscriber equipment to transmit an uplink signal back to the satellite over the same antenna used for receiving the downlink signal. However, given the small antenna aperture and requirement for a low-cost, low-power amplifier, there is very little margin on the uplink and therefore strong FEC coding is desired. For this reason, the DVB Project has adopted turbo codes for the satellite return channel in its DVB-RCS (Return Channel over Satellite) standard [8]. At the same time that the DVB Project was developing turbo coding technology for the return channel, it was updating the downlink with modern coding technology. The latest standard, called DVB-S2, replaces the concatenated Reed-Solomon/convolutional coding approach of DVB-S with a concatenation of an outer BCH code and inner low density parity check (LDPC) code [9]. The result is a 30% increase in capacity over DVB-S. In this chapter, the coding strategies used by both DVB-RCS and DVB-S2 are discussed.