C# QPSK DE-/MODULATOR

This repository is a working prototype of QPSK (Quadrature phase shift keying) modulator and Demodulator in C# (with channel impairment compensation: unstable transcievers LO, multipath,etc...)

Simulations:

SDR Test

moddemodoversdr.mp4

RF Simulation

testfulldemodchain.mp4

capabilities

• the modulator and demodulator both uses RRC for ISI mitagation, message framing to have consistent "packets",differential encoding for phase ambiguity, and TSC (for stabling receiver PLL & symbol sync before starting to send actual data)
• you may send raw data as byte[], raw text or string of bytes (0101...)
• FIR uses SIMD techniques, all models try to implement as much as possible data as span (faster for iteration)
• demod chain: Band-Edge FLL -> MF(RRC) -> Mueller muller (TED) + cubic lagrange interpolator -> Costas Loop -> decode message frame

Solution tree:

QPSK (main module):

• QPSKDeModulator
• QPSKModulator
• Band-Edge FLL (Frequency Locked loop)
• General FIRFilter with group delay
• general RRC FIR taps generator
• MuellerMuller TED (time error detector) + symbol sync based on TED with linear interpolator
• Costas Loop PLL (Phase Locked Loop)
• HelperFunctions for complex[] and float[] functions

TestBench

• ModDemodOverSDR - sdr over the air test (tested on USRP b205 mini) + ZMQ -> Gnuradio View of the results with data framing
• testFullDemodChain - simulation of an SDR and the demodulation chain using two unstable LO and each demodulation block seperatley + ZMQ -> Gnuradio View of the results
• testAtDataLevel -> simple test of the mod and demod blocks and check for bit-Errors with two unstable LO

dependencies:

• ZeroMQ
• MathNet
• PothosWare SoapySDR .NET bindings

N.B

this project is heavily based on the course of "Learn SDR with Prof Jason" by HarveyMuddPhysicsElectronicsLab