Communications Blockset

Representing Signals for Digital Modulation

All digital modulation blocks process only discrete-time signals. The data types of inputs and outputs are depicted in the figure below.

Note    If you are simulating baseband modulation and want to separate the in-phase and quadrature components of the complex modulated signal, then use the Complex to Real-Imag block in the Simulink Math Operations library.

Binary-Valued and Integer-Valued Signals

Some digital modulation blocks can accept either integers or binary representations of such integers. The corresponding demodulation blocks can output either integers or their binary representations. This section describes how modulation blocks process binary inputs; the case for demodulation blocks is the reverse.

If a modulator block's Input type parameter is set to Bit, then the block accepts binary representations of integers between 0 and M-1. It modulates each group of K bits, called a binary word. Also, these rules apply to the binary input mode:

• For baseband modulation, the input vector length must be an integer multiple of K. If the input is frame-based, then it must be a column vector.
• For passband modulation, the input must have length K and must be sample-based.

In binary input mode, the Constellation ordering (or Symbol set ordering, depending on the type of modulation) parameter indicates how the block maps a group of K input bits to a corresponding integer. If this parameter is set to Binary, then the block maps [u(1) u(2) ... u(K)] to the integer

and subsequently behaves as if this integer were the input value. Notice that u(1) is the most significant bit.

For example, if M = 8, Constellation ordering (or Symbol set ordering) is set to Binary, and the binary input word is [1 1 0], then the block internally converts [1 1 0] to the integer 6. The block produces the same output as in the case when the input is 6 and the Input type parameter is Integer.

If Constellation ordering (or Symbol set ordering) is set to Gray, then the block uses a Gray-coded arrangement. The explicit mapping is described in the algorithm section on the reference page for the M-PSK Modulator Baseband block.

Digital Modulation Features of the Blockset

Delays in Digital Modulation