Upsampled Signals and Rate Changes (Using the Communications Blockset)

Communications Blockset

Upsampled Signals and Rate Changes

Digital baseband modulation blocks can output an upsampled version of the modulated signal, while digital baseband demodulation blocks can accept an upsampled version of the modulated signal as input. Each block's Samples per symbol parameter, S, is the upsampling factor in both cases. It must be a positive integer. Depending on whether the signal is frame-based or sample-based, the block either changes the signal's vector size or its sample time, as the table below indicates. Only the OQPSK blocks deviate from the information in the table, in that S is replaced by 2S in the scaling factors.

Table 1-4: Processing of Upsampled Modulated Data (Except OQPSK Method)
Computation Type
Input Frame Status
Result

Modulation
Frame-based
Output vector length is S times the number of integers or binary words in the input vector. Output sample time equals the input sample time.

Modulation
Sample-based
Output vector is a scalar. Output sample time is 1/S times the input sample time.

Demodulation
Frame-based
Number of integers or binary words in the output vector is 1/S times the number of samples in the input vector. Output sample time equals the input sample time.

Demodulation
Sample-based
Output signal contains one integer or one binary word. Output sample time is S times the input sample time.
Furthermore, if S > 1 and the demodulator is from the AM, PM, or FM sublibrary, then the demodulated signal is delayed by one output sample period. There is no delay if S = 1 or if the demodulator is from the CPM sublibrary.

**Table 1-4: Processing of Upsampled Modulated Data (Except OQPSK Method)**
Computation Type	Input Frame Status	Result
Modulation	Frame-based	Output vector length is S times the number of integers or binary words in the input vector. Output sample time equals the input sample time.
Modulation	Sample-based	Output vector is a scalar. Output sample time is 1/S times the input sample time.
Demodulation	Frame-based	Number of integers or binary words in the output vector is 1/S times the number of samples in the input vector. Output sample time equals the input sample time.
Demodulation	Sample-based	Output signal contains one integer or one binary word. Output sample time is S times the input sample time. Furthermore, if S > 1 and the demodulator is from the AM, PM, or FM sublibrary, then the demodulated signal is delayed by one output sample period. There is no delay if S = 1 or if the demodulator is from the CPM sublibrary.

Digital passband blocks can also process upsampled data, but only as an intermediate internal format. For more information about this, see the description of the Baseband samples per symbol parameter on the reference page for any digital passband modulation block. Also note that passband blocks process only sample-based data, not frame-based data.

Illustrations of Size or Rate Changes

The following schematics illustrate how a baseband modulator (other than OQPSK) upsamples a triplet of frame-based and sample-based integers. In both cases, the Samples per symbol parameter is 2.

The following schematics illustrate how a demodulator (other than OQPSK or one from the CPM sublibrary) processes three doubly-sampled symbols using both frame-based and sample-based inputs. In both cases, the Samples per symbol parameter is 2. Notice that the sample-based schematic includes an output delay of one sample period.

Delays in Digital Modulation Examples of Digital Modulation