# Communication demos

This library contains some examples of digital communication systems and channel simulators.

- constellation
- A 16-QAM signal is sent through a baseband equivalent channel that simulates the following impairments: frequency offset, phase jitter and white Gaussian noise.
- DTMFCodec
- Dual-Tone Modulated Frequency Demo. Generate touch-tones and decode them based on the Goertzel Algorithm.
- Eye
- Plot an eye diagram for a binary antipodal signal with a raised-cosine pulse shape and user controlled noise.
- lmsDTMFCodec
- Dual-Tone Modulated Frequency Demo. Generate touch-tones and decode them based on the LMS Algorithm.
- LossySpeech
- Illustrate the effect on speech of a zero-substitution policy in a network with 48 byte packets and a variable loss probability. Note that this demo requires audio capability.
- LossySpeechPrevCell

Illustrate the effect on speech of a previous cell substitution policy in a network with 48 byte packets and a variable loss probability. Note that this demo requires audio capability.
- Modem
- Baseband model of a 16-QAM modem.
- pseudoRandom
- Generate a pseudo-random sequence of zeros and ones using a maximal-length shift register and test its randomness by estimating its autocorrelation.
- pulses
- Generate raised cosine and square-root raised cosine pulses and demonstrate matched filtering with the square-root raised cosine pulse.
- xmit2rec
- Simple 2-level PAM communication system (matched filtering at the receiver).
- xmit4rec
- Simple 4-level PAM communication system (no filtering at the receiver).

## Older communications demos

- qam
- Produce a 16-point quadrature amplitude modulated (QAM) signal and display the eye diagram for the in-phase part, the constellation, and the modulated transmitted signal.
- QAM4withDFE
- This is a model of a digital communication system that uses quadrature amplitude modulation (QAM) and a fractionally spaced decision feedback equalizer.
- codeDecode
- Encode and decode a 16-QAM signal using differential encoding for the quadrant and Gray coding for the point within the quadrant.
- PLLDemo
- Simulate a fourth-power optical phase-locked loop with laser phase noise and additive Gaussian white noise operating on a complex baseband envelope model of the signal.
- TelephoneChannelTest

Assuming a sampling rate of 8 kHz, a sinusoid at 500 Hz is transmitted through a simulation of a telephone channel with additive Gaussian noise, nonlinear distortion, and phase jitter.