What is DPD (Digital Pre-Distortion)?
This technique allows the power amplifier of a DAB transmitter to operate at a high level of perfection. The increase in perfection of the power amplifier results in an important feature and ensures that the amplifier delivers a very clean signal in all conditions. This is especially important to avoid generating interference in nearby DAB channels.
Of course, one also has the mandatory filter (behind the transmitter), but the better the signal from the transmitter, the better the result will be broadcast.
Given the requirement by some regulators that a transmitter signal complies with a “type 2 mask”, it makes sense to start from a good base. A transmitter with DPD technology can make all the difference here. Such a transmitter with a typical DAB filter should easily meet the “type 2 mask” requirement.
DPD technology requires a built-in high-quality DAB receiver that delivers the signal to the DPD circuit. The fast computing capability immediately adjusts the amplifier’s imperfections by calculating the imperfection’s inversion at the amplifier’s input. It requires many additional electronic components, such as microprocessors and chips developed for DPD. It, therefore, results in a much more expensive transmitter.
What are the differences?
With a transmitter without DPD, the transmitter will have to operate in a “power back-off” mode. Using a power amplifier with high consumption to generate a small transmit power is not ideal. It results in very low efficiency, in other words, a lot of power consumption for little transmit power.
Despite the “power back-off,” the transmitted DAB(+) signal will never reach the purity of the DPD-equipped transmitter. With a typical cavity filter, there is a risk that a “type 2 mask” filter cannot achieve the imposed specifications. Multiple successive filters (to still meet the type 2 mask) have the effect that the transmit power efficiency will drop even further.
In contrast, a DPD-equipped transmitter has much higher efficiency and will positively affect the transmitter site’s energy consumption and operational cost (OPEX). There will also be no problem meeting the requirement of a “type 2 mask” with a typical cavity filter. Purchasing such a transmitter will mean a more significant investment, though a lot of energy savings. We suggest a good business plan considering the Total Costs of Ownership (TCO).