Scott L. Linfoot

Analysis of a DVB-T compliant receiver simulation under various multipath conditions

Since 1966, coded orthogonal frequency division multiplexing (COFDM) has been investigated to determine the possibility of reducing the overall throughput of a digitally modulated terrestrial television channel. In the investigations, many assumptions have emerged. One common misconception is that in a terrestrial environment, COFDM has an inherent immunity to multipath interference. A theoretical analysis of a multipath channel, along with simulation results has shown that this assumption does not hold the information is considered when including the radio frequency modulation and demodulation. This paper presents a background into the inception of COFDM, a mathematical analysis of the digitally modulated television signal under multipath conditions and the results of a European Digital Video Broadcasting-Terrestrial (DVB-T) compliant simulation model with MPEG-2 bitstreams transmitted under various multipath conditions.

Deterministic equalization and results of a DVB-T multipath equalizer for both 16-QAM and 64-QAM operation

Developments in the UK concerning the reception of digital terrestrial television (DTT) have indicated that, as it currently stands, DVB-T receivers may not be sufficient to maintain adequate quality of digital picture information to the consumer. There are many possible reasons why such large errors are being introduced into the system preventing reception failure. It has been suggested that one possibility is that the assumptions concerning the immunity to multipath that coded orthogonal frequency division multiplexing (COFDM) is expected to have, may not be entirely accurate. Previous research has shown that multipath can indeed have an impact on a DVB-T receiver performance. In the UK, proposals have been made to change the modulation from 64-QAM to 16-QAM to improve the immunity to multipath, but this paper demonstrates that the 16-QAM performance may again not be sufficient. To this end, this paper presents a deterministic approach to equalization such that a 64-QAM receiver with the simple equalizer presented has the same order of MPEG-2 BER performance as that of a 16-QAM receiver without equalization. Thus, alleviating the requirement in the broadcasters to migrate from 64-QAM to 16-QAM of course, by adding the equalizer to a 16-QAM receiver then the BER is also further improved and thus creating one more step to satisfying the consumers.

A soft decision 16-QAM demodulation algorithm for multipath affected DVB-T systems

In 1998, the United Kingdom started the worlds first commercial digital terrestrial television service. The system used was the European digital video broadcast-terrestrial (DVB-T) but due to technological constraints at the time, the system chosen was the 2K system - a system that uses 1705 carriers to convey the digital television services through a hostile terrestrial environment. Today, these constraints are no longer applicable but in order to maintain backwards compatibility to the older set top boxes, the 2K system is still used. The 2K system has the disadvantage of excluding the possibility of employing a single frequency network (SFN) - something that can help minimize the required bandwidth for television services. This paper demonstrates an observed phenomenon that explains why DVB-T fails to meet the required BER criteria and also shows how this phenomenon can be used in a computationally inexpensive technique for estimating the relative path attenuation of a multipath signal and how it can be used to estimate the parameters required for a soft decision QAM demapper.

A comparison of 64-QAM and 16-QAM DVB-T under long echo delay multipath conditions

In 2002, the commercial digital terrestrial television service in the United Kingdom had a technological revival. Since its first broadcast in 1998, there have been a number of reception issues concerning digital video broadcasting - terrestrial (DVB-T). As a result, the modulation method has changed in order to maximize the coverage and minimize errors. The consequence of changing the modulation method to a more robust system is that the overall throughput must suffer. Therefore, a trade-off between throughput and robustness must be made. This paper gives the detail of the results of experiments performed to ascertain the justification of changing the modulation method in DVB-T compliant system from 64-QAM to 16-QAM when transmitted at radio frequencies (RF) when subjected to multipath with long path delays as is normal in a single frequency network (SFN).

Correcting for local oscillator phase offset in a DVB-T compliant receiver under multipath conditions

In 1997, the UK implemented the worlds first commercial digital terrestrial television system. Under the ETS 300 744 standard, the chosen modulation method, COFDM, is assumed to be multipath resilient. Previous work has shown that this is not necessarily the case. It has been shown that the local oscillator required for demodulation from intermediate-frequency to baseband must be very accurate. This paper shows that under multipath conditions, standard methods for obtaining local oscillator phase lock may not be adequate. This paper demonstrates a set of algorithms designed for use with a simple local oscillator circuit which will allow correction for local oscillator phase offset to maintain a low bit error rate with multipath present.

A relative path attenuation approximation algorithm for DVB-T systems

In the United Kingdom and in fact throughout Europe, the chosen standard for digital terrestrial television is the European Telecommunications Standards Institute (ETSI) ETN 300 744 also known as digital video broadcasting - terrestrial (DVB-T). The modulation method under this standard was chosen to be orthogonal frequency division multiplex (OFDM) because of the apparent inherent capability for withstanding the effects of multipath. Within the DVB-T standard, the addition of pilot tones was included that can be used for many applications such as channel impulse response estimation or local oscillator phase and frequency offset estimation. This paper demonstrates a technique for an estimation of the relative path attenuation of a single multipath signal that can be used as a simple firmware update for a commercial set-top box. This technique can be used to help eliminate the effects of multipath.

A novel soft decision QAM demodulator for DVB-T for multipath system

In 1997, the United Kingdom started the worlds first commercial digital terrestrial television service. The system used was the European digital video broadcast - terrestrial (DVB-T) but due to technological constraints at the time, the system chosen was the 2K system - a system that uses 1705 carriers to convey the digital television services through a hostile terrestrial environment. Today, these constraints are no longer applicable but in order to maintain backwards compatibility to the older set top boxes, the 2K system is still used. The 2K system has the disadvantage of excluding the possibility of employing a single frequency network (SFN) - something that can help minimise the required bandwidth for television services. This paper will demonstrate a computationally inexpensive soft decision quadrature amplitude modulation technique that can reject the multipaths.

A study of COFDM in a terrestrial multipath environment

Coded orthogonal frequency division multiplexing (COFDM) has existed for many years but it was not until 1997 when the European Telecommunications Standards Institute proposed its use for the transmission of digital television through a terrestrial channel. Up to date, an assumption has been made concerning the resilience of COFDM in a multipath environment. This paper discusses this assumption, give results of a DVB-T compliant simulation and discuss the validity of this assumption based on the obtained results.