1GP104

Digital Pre-Distortion

8.2 DPD in the SMW

The SMW is capable of applying AM-AM and/or AM-PM predistortion in realtime. The pre-distortion feature works with any baseband signal, i.e. with all digital standard signals (such as LTE, WLAN, etc.) and ARB waveforms. DPD works for all signal bandwidths, i.e. 160 MHz RF bandwidth at maximum. DPD is applied on each I/Q sample, i.e. from sample to sample.

The SMW applies memoryless DPD in an open loop system.

DPD can be activated via the

“I/Q Mod” block. AM-AM and AM-PM pre-distortions can be enabled separately or simultaneously. Either AM-AM or AM-PM predistortion can be applied first.

DPD alters the signal statistics and the signal level. The user can therefore define if the set mean RF level shall be the signal level before or after applying DPD. See section

8.2.1 for details.

The user can define the pre-distortion curve in the following ways:

 via table

 via polynomial

Table

The pre-distortion function is defined by a table of user-specific value pairs (up to

4000). There are two separate tables, one for AM-AM and one for AM-PM distortion. A linear interpolation can be applied in between the specified points to smoothen the curve. The specified delta power and delta phase values can be inverted. (Note that not every curve is mathematically invertible. The inverse function of the curve must be uniquely determinable. Therefore, only strictly monotonic increasing/decreasing data can be inverted.)

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Digital Pre-Distortion

See section 11.2 for details on the file format.

Polynomial

The pre-distortion function is defined by a polynomial. The order of the polynomial function can be selected

– up to 10 th

order is supported with definable polynomial coefficients.

In table mode, the user can load his own AM-AM and AM-PM tables or he can use the

FSW-K18 to directly generate and load the pre-distortion tables (see also section 7).

In the latter case, the AM-AM, AM-PM data measured with the FSW is approximated with a polynomial curve fit. (The parameters of the polynomial fit such as the order can be adjusted by the user.) These AM-AM and AM-PM curves are then inverted and saved as pre-distortion tables for direct use in the SMW.

Data points Ideal Fitted curve

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