Selecting the Data Source
- Updated2025-10-08
- 6 minute(s) read
In general, the data source is set up using the Data Source tab. If you have selected a modulation scheme (refer to Selecting the Modulation Type) you will be able to select the Data Source tab. For a typical generic modulation scheme, the default screen is shown in the following image.
On this tab you can select the Data Source Type, which is the bit sequence that you want to modulate. The following sequences are supported:
- PRBS Sequences - The default option
- User Data Sequences
- Repeating Patterns
With the PRBS data source, you can select either one of eight preset PRBS sequences or a user-defined one using the PRBS Type drop-down list. The seed of the selected PRBS sequence can be toggled by clicking the left mouse button on the required bit.
For the pre-defined PRBS's, you cannot change the feedback mask or the PRBS length. If you want to change these select User Defined from the PRBS Type drop-down list. To enter or remove a feedback path, click on the appropriate tap mask square. To change the length of the PRBS, enter your required value into the Length text box. The maximum PRBS length supported is 32.
The Bit Encoding Method drop-down list enables you to select the bit encoding method that will be applied to the bit sequence. RFmx Waveform Creator supports 5-bit encoding methods: Differential, GSM Differential, Inverted, Manchester, and NRZ Inverted.
For this example, stay with the default settings but note that at this stage, you can decide on the Bit Encoding Method that you require.
PRBS Sequences
In RFmx Waveform Creator, a pseudo random binary sequence (PRBS) is generated using a linear feedback shift register (LFSR). The following figure shows a block diagram of a shift register with nine registers and two taps from which the feedback is obtained.
The characteristic polynomial that describes this sequence is f (x) = x9 + x4 + 1. The output is obtained by XORing the register values attached to the taps, feeding this back and shifting the registers by one as indicated in the preceding figure. An LFSR is defined by the location of feedback taps, the number of registers and the initial state of the registers. The output sequence will always be periodic because whatever the initial conditions of the shift register, after a finite number of shifts, the initial conditions will eventually be reproduced. The maximum number of different combinations is equal to 2N-1. An LFSR, whose output sequence has a period of 2N-1 is called a maximal length sequence. These sequences are also referred to pseudo random (PN) sequences.
Repeating Patterns
In RFmx Waveform Creator, a repeating pattern is a pattern of 1's and 0's that repeats until the required number of bits has been generated. You enter the pattern of your choice in the text box as shown in the bitmap below.
The example above shows a pattern of 01011. This pattern will repeat to generate a bit sequence of 01011010110101101011… until the required number of bits is generated. The maximum length of the repeating pattern is 16 bits. RFmx Waveform Creator does not allow you to define a longer sequence. The pattern must be entered as a binary sequence.
User Data Sequences
RFmx Waveform Creator allows you to input your own bit sequence as a data source. This is done by placing your required data into an ASCII file. The bits must be delimited by commas, spaces or tabs, line feeds or carriage returns. Values must be either 0 or 1. Any non-zero and/or non-delimited value will be set to 1 by the software.
You can select the Data Source tab and set the Source Type as User Data from File. you will be asked to enter a file name as indicated in the bitmap below.
Depending on the modulation scheme that you are working with the method to select a user data sequence will vary.
Bit Encoding
RFmx Waveform Creator helps you in encoding the bit sequence (data source) before modulating. There are five types of encoding are available.
Differential
where 
is an EXCLUSIVE OR operation.
GSM Differential
where is an EXCLUSIVE OR operation and
is the NOT of
x.
Inverted
where is the NOT of
x.
NRZ Inverted (Non return to zero inverted)
where is an EXCLUSIVE OR operation and
is the NOT of
x.
Manchester
Let bn be the binary input sequence of length n and dk+1 be the binary output sequence of length k+1 after encoding. dk and dk+1 are then defined as:
dk = bn
where k = 2n and
is the NOT of x.
Auto Cyclic Data
Enabling auto cyclic data ensures phase continuity. An additional number of symbols are added to the signal in order to make the signal phase continuous.