Email	Print Reprint
	add to:
	Del.icio.us Digg Google Furl	Slashdot Y! MyWeb Blink

To be successful, the tuner needs to have a broad dynamic range and the ability to discriminate the desired signal from adjacent TV channels or in-band interference, which could even be a mobile phone's normal transmissions. There is an added incentive for wireless providers to select handsets with high-quality mobile TV functionality. If the sensitivity and selectivity performance in the handset is of high-quality, then there is a potential to reduce the overall cost of the infrastructure. Sensitive handsets enable broader coverage ranges, and this could reduce the number of tower and broadcast sites.

Sensitivity
One challenge to mobile TV reliability is its operating environment. Depending on how far the handset is from the transmission site, it may receive a very large or very small signal, and both can be challenging for a tuner to target. To be successful, the tuner must have a broad dynamic range.

1. DVB-H tuners must tune over a wider frequency range, as illustrated here by the European UHF band. The tuner must retain high-signal integrity, while preserving battery life.
To ensure good quality reception, the receive system in the handset must be able to pick up a large signal, which could be -25 dBm or higher, as well as detect the smallest signal, amplify it, and pass it through the system in the presence of many other distorting signals that could be much stronger than the desired minimum signal level signal. The relative undesired signal power to the desired signal power ratio can be >45 dB (and as much as 56 dB for certain conditions). This means that the receiver needs to be able to amplify the desired signal in the presence of an interfering signal that is >45 dB higher. If it cannot do that, the tuner cannot deliver the performance necessary to ensure a quality end-user experience.

Selectivity
In addition to good sensitivity, the tuner must have the ability to discriminate the wanted signal from adjacent TV channels or other in-band interference, which could even be a mobile phone's own transmissions. Mobile phone receivers typically operate in narrow frequency bands of 20 to 30 MHz. To improve reliability in these systems, designers can put a filter in front of the receiver and effectively eliminate potential interferers across a broad spectrum.

2. Multiple interferers, including the cell phone power amplifier, impact mobile TV performance.

In contrast, a mobile TV receiver has a wider band. The first DVB-H tuners will need to tune across the UHF band IV-V frequencies (470 MHz to 750 MHz range) with 6-MHz, 7-MHz or 8-MHz channel bandwidth in Europe and the L-band 5-MHz channel (1670 MHz to 1675 MHz) range in North America. The situation is particularly challenging in Europe, where the spectrum is fragmented by country, and cellular transmitters are often spread into the same bands as mobile TV.

In response, the DVB-H standards committee has reduced the usable bandwidth for mobile TV within the allocated band up to 702 MHz, but there are a number of companies that would like to use the higher frequencies. Modifying the available spectrum is only a short-term fix, and a new tuning technology is required.

One way to improve tuning for mobile TV is to use on-chip filtering techniques. Developed by leveraging experience in cable set-top box, traditional television, and automotive TV systems, Microtune's ClearTune™ technology works in conjunction with the external filters that attenuate the out-of-band carriers by reducing a significant number of the in-band signals that cannot be stopped by external filters.

With a conventional receiver architecture, the low noise amplifier (LNA) saturates in the presence of strong in-band carriers. As soon as this occurs, the sensitivity of the receiver collapses. With a receiver using ClearTune technology, no sensitivity collapse occurs across the entire band of interest in DVB-H. This approach offers a major benefit, especially in the presence of a transmitted GSM carrier, which represents the biggest adjacent channel that a handset designer must contend with. Generally speaking, sensitivity can degrade by 3, 4, or 5 times simply due to the presence of a GSM carrier. In a practical application, this means that a subscriber can be watching mobile TV and, if an SMS is received or the handset polls the network, the TV signal can break up or the signal can be lost.

Previous Page | 1 | 2 | 3 Next Page

RELATED ARTICLES No Related Articles		TOP 5 ARTICLES No Top Articles.