Single carrier modulations are widely used in modern wireless communication receivers for data transmission and reception. OLYMP Engineering LLC has developed Demodulation Library for FPGA that performs high speed BPSK, QPSK, 8PSK, 16PSK, 8QAM, 16QAM and OQPSK demodulation with symbol rate up to 40MSPS. Demodulation Library supports development for FPGA and Windows platforms, which allows developers to analyze, prototype algorithms, and application specific performance on Windows before compiling for FPGA. With LabVIEW and LabVIEW FPGA the marketing time is reduced drastically.
The PSK demodulator is mainly used to restore the shifted phases that are modulated at symbol rate to the carrier signals in the transmitter, and reinterpret the phase information back to symbols. The main components included in the Demodulation Library for FPGA are automatic gain control (AGC), matched filtering, carrier recovery, timing recovery, symbol decision and lock detection. This core can be dynamically programmable for MPSK=2, 4, 8 and 16 or MQAM=8 or 16 or OQPSK demodulation. Once the system locked, both demodulated In-Phase and Quadrature (I/Q) samples and hard-coded symbols are available at the outputs.
AGC and Matched Filtering
The AGC compensates any amplitude loss and maximizes the output dynamic range. It includes a gain error detector and a loop filter that responds to the long-term variation and adjusts the gain for the demodulator. In practical communication systems, pulse shaping is used to effectively compress the transmission bandwidth. One popular pulse shaping technique is to place a root-raised-cosine (RRC) filter in the transmitter and another matched filter in the receiver to create a raised-cosine (RC) filter. The symbol values can be completely recovered without ISI if the data is sampled in the middle of the symbol period.