Customized Fir Filters; General; Custom Filters Programming - Safran CORTEX Series User Manual

3.3.2.2

Customized FIR Filters

3.3.2.2.1

General

The filtering is based on one FIR for I channel and one FIR for Q channel.
The FIR sampling rate is either:
 twice the symbol rate (symbol rate < 480 Msps)
 or four time the symbol rate (only if symbol rate < 240 Msps)
Example: for a QPSK / 100 Mbps (50 Msps) data stream, the FIR filter sampling rate can be set to 100
MHz or 200 MHz.
Two types of filters are available:
 symmetrical filter: 32 taps (even symmetrical FIR) or 31 taps (odd symmetrical FIR)
 asymmetrical filter: 16 taps on direct path I and Q plus 16 complex taps (Q to I and I to Q)
The I & D filter design is usually the best answer to matched filtering needs. However, custom filters
may improve the performances in some circumstances, like:
 reduction of adjacent channel interferences
 phase/amplitude equalization
3.3.2.2.2

Custom Filters Programming

Filter coefficients can be programmed from files on the hard disk. Up to 1000 files can be loaded to the
disk. Files are ASCII-coded and can be edited using Notepad or any other text editor.
Each file contains 16-bit data (in hexadecimal format):
Line 1: FIR type selection:
0000 for asymmetrical filter
0001 for even symmetrical filter
0002 for odd symmetrical filter
Bit 2 set to 1 enables the complex filter
Bit 3 set to 1 enables the complex filter
Line 2: Sampling rate selection:
0000 for 2 time the symbol rate
0001 for 4 time the symbol rate
Line 3: Direct FIR length
Line 4: Cross FIR length
Line 5: Cross FIR delay
Line 6: Reserved line
Line 7 to line 32: Direct coefficients (16 bit) on I
Line 33: Reserved line
Line 34 to line 41: Crossed coefficients Q to I for complex filter
Line 42: Reserved line
Line 43 to line 68: Direct coefficients (16 bit) on Q
Line 69: Reserved line
Line 70 to line 77: Crossed coefficients I to Q for complex filter
Access path to the filter files is: C:\Program Files\In-snec\crtxnt\FIR. Files are named fir_cust1 to
fir_cust1000.
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Ref. DTU 100782
Is.Rev 3.5
Date: June 1, 2021
Safran Data Systems
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