The modem module implements a set of (mod)ulation/(dem)odulation schemes for encoding information into signals. For the analog modems, samples are encoded according to frequency or analog modulation. For the digital modems, data bits are encoded into symbols representing carrier frequency, phase, amplitude, etc.

http://liquidsdr.org/doc/modem/

This is the second of a two-part tutorial to derive bit error rate expressions for certain linear modulation schemes.

http://liquidsdr.org/blog/modem-ber-calc/

This is the first of a two-part tutorial to simulate bit error rates for linear modulation schemes.

http://liquidsdr.org/blog/modem-ber-sim/

Shown in the figure below is a compaarison of the transmitted spectrum for various combinations of parameters. Here is a basic example of the cpfksmod and cpfskdem objects.

http://liquidsdr.org/doc/cpfskmodem/

Frequency-shift keying (fsk) modem... Listed below is the full interface to... Here is a basic example of...

http://liquidsdr.org/doc/fskmodem/

The qpacketmodem object conveniently combines linear modulation with interleaving , two levels of forward error-correction coding, and a data integrity check. The object combines the packetizer object with symbol packing for modulation. Both hard-decision and soft-decision decoding are supported, assuming the forward error-correction codec supports it.

http://liquidsdr.org/doc/qpacketmodem/

The ampmodem object implements an analog amplitude modulation (AM) modulator/demodulator pair. Two basic transmission schemes are available: single side-band (SSB), and double side-band (DSB). For an input message signal , the double side-band transmitted signal is where is the carrier frequency, and is the modulation index.

http://liquidsdr.org/doc/ampmodem/

The freqmod and freqdem objects implement the analog frequency modulation (FM) modulator and demodulator, respectively, in liquid. Given an input message signal , the transmitted signal at complex baseband is where is the modulation factor.

http://liquidsdr.org/doc/freqmodem/

The framing module contains objects and methods for packaging data into manageable frames and packets. For convention, liquid refers to a "packet" as a group of binary data bytes (often with forward error-correction applied) that need to be communicated over a wireless link.

http://liquidsdr.org/doc/framing/

Version 1.3.0 is finally tagged in the Git repository.

http://liquidsdr.org/blog/liquid-dsp-1.3.0/

In the previous tutorials we have created only the basic building blocks for wireless communication. We have also used the basic framegen64 and framesync64 objects to transmit and receive simple framing data.

http://liquidsdr.org/doc/tutorial-ofdmflexframe/

This module provides interfaces for computing a vector dot product between two equally-sized vectors. Dot products are commonly used in digital signal processing for communications, particularly in filtering and matrix operations.

http://liquidsdr.org/doc/dotprod/

This is the main documentation page for liquid-dsp.

http://liquidsdr.org/doc/

This tutorial provides an overview of a very simple fininite impulse response least mean-squares equalizer simulation. This is part of my "DSP in 50 lines of C" series.

http://liquidsdr.org/blog/lms-equalizer/

The two objects gmksmod and gmskdem implement the Gauss minimum-shift keying (GMSK) modem in liquid. Notice that unlike the linear modem objects, the GMSK modulator and demodulator are split into separate objects.

http://liquidsdr.org/doc/gmskmodem/

The audio module in liquid provides several objects and functions for compressing, digitizing, and manipulating audio signals. This is particularly useful for encoding audio data for wireless communications. Continuously variable slope delta (CVSD) source encoding is used for data compression of audio signals.

http://liquidsdr.org/doc/cvsd/