Subband Filter Parameters (LTE)
The Filter properties are used to configure and apply subband filtering to the measurement. The subband filter is an FIR Finite Impulse Response filter that is applied to the measured signal before synchronization and demodulation in order to minimize the out of band emission and increase the spectrum efficiency.
| Parameter | Description |
|---|---|
|
Specify the characteristics of the subband signal by selecting a filter type. |
|
|
(default): No subband filter is applied. When the filter type is NONE, it means there is no subband filtering, which is the default setup for conventional LTE Long Term Evolution measurements. |
|
|
: The filter is designed by starting with an ideal sinc filter shape and then applying a window to the time-domain coefficients. The user specifies the Window Type, Window Length Mode, Passband BW, and Transition BW. Use Windowed Sinc to specify a filter for filtered OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. (F-OFDM) signals. |
|
|
: The filter is designed using the Remez-exchange method. The user specifies the Passband BW, Transition BW, Passband Ripple, and Stopband Attenuation. |
|
|
: The user provides a set of filter coefficients to apply. |
Filter Setting
Filter: Windowed Sinc
When Selection is set to Windowed Sinc, the filter impulse response is constructed by starting with an ideal sinc filter shape, and then applying a window.
| Parameter | Description |
|---|---|
|
Specify the window type for the windowed sinc filter. |
|
|
: A Uniform window type is applied. |
|
|
: A Hanning window type is applied (default). |
|
|
: A Hamming window type is applied. |
|
|
|
|
|
(default): The length (number of coefficients) is calculated automatically based on the Transition Bandwidth specified by the user. The Transition Bandwidth is specified as a fraction of the OFDM System Sample Frequency. |
|
|
: The length is specified directly by the Windowed Sinc Length parameter. |
|
|
Manually specify the windowed sinc length (number of coefficients) when Windowed Sinc Automatic Length is disabled. Default: 1 |
Filter: Remez or Windowed Sinc
Some filter parameters apply to both Remez and Windowed Sinc filtering.
| Parameter | Description |
|---|---|
|
Specify the pass bandwidth for either Remez or Windowed Sinc filtering as a fraction of the OFDM System Sample Frequency. Default: 0 Hz |
|
|
Specify the transition bandwidth for either Remez or Windowed Sinc filtering as a fraction of the OFDM System Sample Frequency. Default: 0 Hz |
Filter: Remez
When Selection is set to Remez, the filter impulse response is constructed using the Remez Exchange method.
| Parameter | Description |
|---|---|
|
Specify the peak-to-peak ripple of the pass-band in dB. Default: 0.0001 dB |
|
|
Specify the stop-band attenuation of the filter in dB. Default: -60 dB |
User Defined Filter Coefficients
When Subband Filter Type is set to User Defined, the filter coefficients as well as the sampling frequency for these coefficients are provided by the user. This choice provides the most flexibility, in case none of the other choices provide exactly what is desired.
| Parameter | Description |
|---|---|
|
Opens a user-created .csv file that contains Filter Length, Sampling Frequency, and filter coefficients and filter coefficients to match the number specified Filter Length. |
|
|
Saves the currently chosen subband filter's Filter Length, Sampling Frequency, and filter coefficients as a .csv file. |
See Also
LTE Demod Properties Dialog Box
