This model shows an end-to-end baseband communications system compliant with the U. S. MIL-STD-188-110B military standard. In particular, the model implements the data phase transmission, using a fixed-frequency serial (single-tone) waveform. This model supports these data rates: 150 bps, 300 bps, 600 bps, and 1200 bps. It also implements interleaver lengths of 0.6 s and 4.8 s.
The system described in this standard is intended for long-haul and tactical communications over HF (high frequency) channels. The system is compatible with the NATO standard STANAG 4539.
The communication system in this example performs these tasks:
Generation of random binary data.
Coding that depends on the data rate that you select in the Model Parameters block's dialog box. The Encoder block at the top level of the block diagram is a subsystem whose contents depend on the selected data rate. In all cases, this subsystem contains a convolutional encoder that uses a rate 1/2 code with constraint length 7. However, the subsystem can achieve rate 1/4 or 1/8 by following the encoder with a repetition operation.
Interleaving using a matrix specified by the standard.
Appending the training sequence, also referred to as the known data or the channel probe symbols. By contrast the unknown symbols are the data that the user wants to transmit.
Data scrambling, by adding the data to a randomizing sequence modulo 8.
Watterson channel model, implemented using the Multipath Rayleigh Fading Channel library block. Specifically, the block implements the moderate channel model described in , using a Gaussian Doppler spectrum.
Receiver equalization using an RLS equalizer. Internally, the equalizer subsystem scrambles the training sequence so as to compare corresponding data sets, introduces delays to align frame boundaries, and descrambles the equalized signal.
Channel symbol demapping.
Viterbi decoding. The decoder is a subsystem that mirrors the encoder subsystem. The decoder includes a reset port, because it is necessary to reset the Viterbi decoder after an initial delay period elapses.
Other Features of the Example. Inside the encoder subsystem is an icon labeled "Compare FEC Encoder." You can double-click it to open another Simulink model that compares the block diagram appearing in the standard with the single Convolutional Encoder block in the Communications System Toolbox™. The model illustrates that the two ways of modeling the convolutional code yield the same results.
Inside the Interleave Matrix subsystem is an icon labeled "Interleave Mapping." You can double-click it to open a plot that shows the mapping, which depends on your choices in the Model Parameters dialog box.
When you run the simulation, it displays these numerical or graphical results:
The bit error rate of the entire system.
The data rate at several points during the simulation. The source data rate is the one that you specify in the Model Parameters dialog box, while the last displayed data rate (before the Scrambler) is always 2400 bps. The other displayed data rates depend on your choices in the Model Parameters dialog box.
The channel impulse response. The plot shows the real part, imaginary part, and magnitude on the same set of axes.
The phase rotation of the signal due to the channel's strongest path.
Scatter plot of the signal before equalization.
Scatter plot of the signal after equalization.
The coding behavior in the standard depends on the data rate. This model varies the behavior of the coding and decoding subsystems depending on the Information Rate parameter that you select in the Model Parameters dialog box. Double-clicking the encoder or decoder icon enables you to see the contents of the subsystem based on the current value of the Information Rate parameter. When you change the Information Rate parameter, an initialization function associated with the Model Parameters block sets certain model parameters and also chooses the contents of the encoder and decoder subsystems.
 MIL-STD-188110B: Interoperability and Performance Standards for Data Modems, U. S. Department of Defense, 2000.
 ITU-R Recommendation 520-2: Use of High Frequency Ionospheric Channel Simulators, 1978/1982/1992.
The Communications System Toolbox example Defense Communications: US MIL-STD-188-110A Receiver shows a MIL-STD-188-110A receiver, with preamble detection, carrier synchronization, and symbol timing synchronization. It runs at a fixed rate of 1200 bps.