Digital Receiver System

"We built our receiver system around NI FlexRIO modular FPGA hardware programmed with the NI LabVIEW FPGA Module, which helped us design the FPGA circuitry without needing to know VHDL coding. Through implementation of matching filter algorithms in FPGA, we achieved a significant increase in our processing performance."

The Challenge:

Developing a digital receiver system to conduct measurements and evaluate the performance of RF system using off-the-shelf products.

The Solution:

Using NI PXI Express modular instruments and NI LabVIEW to create a digital receiver system for pulse compression techniques.

Pulse compression is a signal processing technique often used to augment distance resolution as well as signal to noise ratio by modulating the transmitted pulse. Pulse compressions increase the transmitted average power while retaining the range resolution of a narrow pulse width. It has better discrimination of target echoes in clutter and is less susceptible to jamming.

Two basic types of pulse compression are linear FM and phase coding. Both encode the transmitted pulse with information that is compressed (decoded) in the receiver of the system. Pulse compression can compress pulses with durations of many microseconds down to a tenth of a microsecond. The ratio of transmitted pulse width to compressed pulse width is called the pulse-compression ratio.

Phase coding the transmitted pulse involves shifting the phase of the transmitter RF during the pulse width. A binary code is the normal method used to determine the phase shift. With a binary code, the binary bits can determine if the signal will shift to an in-phase condition or a 180-degree out-of-phase condition with respect to the reference. Pulse compression of the encoded waveform involves decoding the phase shifts and comparing this to the stored code. By making a bit-by-bit comparison of the received signal to the transmitted signal, we can determine target detection at the point when the bits match. This type of circuit is known as a matched filter.

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