Configure the data source for a waveform with the bit sequence to modulate, bit encoding method, and PRBS type.

Use the Data Source tab to configure the data source.

Note To enable the Data Source tab, select a modulation type. For more information, refer to Selecting the Modulation Type.

The following figure shows a typical, generic modulation scheme.

Figure 1. Typical Generic Modulation Scheme
Data Source tab showing a typical generic modulation scheme
  • Data Source Type: select the bit sequence to modulate.
    • PRBS Sequences (default)
    • User Data Sequences
    • Repeating Patterns
  • Bit Encoding Method: select the bit encoding method to apply to the bit sequence. Leave at the default None, or select from the following 5-bit encoding methods:
    • Differential
    • GSM Differential
    • Inverted
    • Manchester
    • NRZ Inverted
  • PRBS Type: select a pre-defined PRBS sequence or select User Defined. To toggle the seed of the selected PRBS sequence, click on the required bit.

You cannot change the feedback mask or the PRBS length of a pre-defined PRBS sequence.

To change the feedback mask or the PRBS length of a user-defined sequence, set PRBS Type to User Defined:
  • To enter or remove a feedback path, click on the appropriate tap mask square.
  • To change the PRBS length, enter the value into the Length text box. The maximum PRBS length is 32.

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

Let bn be the binary input sequence at time n and dn be the binary output sequence at time n after encoding. dn is then defined as:

where is an EXCLUSIVE OR operation.

GSM Differential

Let bn be the binary input sequence at time n and dn be the binary output sequence at time n after encoding. dn is then defined as

where is an EXCLUSIVE OR operation and is the NOT of x.

Inverted

Let bn be the binary input sequence at time n and be dn the binary output sequence at time n after encoding. dn is then defined as

where is the NOT of x.

NRZ Inverted (Non return to zero inverted)

Let bn be the binary input sequence at time n and dn be the binary output sequence at time n after encoding. dn is then defined as

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

Auto‑cyclic data maintains phase continuity.

Adding an additional number of symbols to the signal makes the signal phase continuous.

Note This parameter is currently available only in FSK plugin.

SOQPSK Differential

Let b2i and b2i+1 be the user binary input bit pairs at time index i, and δ2i and δ2i+1 be the differentially encoded output bits.

The following equations define the encoded bits:
  • δ 2 i = b 2 i ⊕ δ 2 i - 1 ¯
  • δ 2 i + 1 = b 2 i + 1 ⊕ δ 2 i
where
  • ⊕ is an EXCLUSIVE OR operation
  • is the NOT of x