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Application of DSP for Radar signal processing
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  • RADAR transmits radio signals at distant objects and analyzes reflection.
  • Data gathered can include the position and movement of the object, also radar can identify the object through its "signature" - the distinct reflection it generates.
  • There are many forms of RADAR - such as continuous CW), Doppler, ground penetrating or synthetic aperture; and they're used in many applications, from air traffic control to weather prediction.
  • In the moderm Radar systems digital ignal processing DSP is used extensively. At the transmitter end, it generates and shapes the transmission pulses, controls the antenna beam patter while at the receiver, DSP performs many complex tasks, including STAP (space time adaptive processing)- the removal of clutter, and beamforming (electronic guidance of direction).
  • The front end of the receiver for RADA is still often analog due the high frequencies involved. With fast ADC convertors - often multiple channel, complex IF signals are digitized. However, digital technology is coming closer to the antenna. We may also require fast digital interfaces to detect antenna position, or control other hardware.
  • The main task of a radar's signal processor is to make decisions. After a signal has been transmitted, the receiver starts receiving return signals, with those originating from near objects arriving first because time of arrival translates into target range.
  • The signal processor places a raster of range bins over the whole period of time, and now it has to make a decision for each of the range bins as to whether it contains an object or not.
  • This decision-making is severely hampered by noise. Atmospheric noise enters into the system through the antenna, and all the electronics in the radar's signal path produces noise too. enter image description here

7.3.1 Major blocks of Modern Radar System

  • The major components of modern radar are the antenna, the tracking computer and the signal generator.
  • The tracking computer in the modern radar does all the functions. By scheduling the appropriate antenna positions and transmitted signals as a function of time, keeps track of targets and running the display system.
  • Even if atmospheric attenuation can be neglected, the return from a distant object is incredibly weak. Target returns often are no stronger than twice the average noise level, sometimes even buried under it.
  • It is quite difficult to define a threshold for the decishold whether a given peak is noise or a real target. If the threshold is too high then existing targets are suppressed, that is, the probability of detection (PD) will drop.
  • If the threshold is too low then noise peaks will be reported as targets, that is, the probability of false alarms (PFA) will rise.
  • A common compromise is to have some 90$\%$ probability of detection and a false alarm rate of $10^{-6}$ . It maintains a given PFA known as CFAR, for Constant False Alarm Rate. Rather than keeping the threshold at a fixed point, CFAR circuitry inspects one range bin after the other and compares the signal level found there with the signal levels found in its neighboring bins. If the noise level is rather high in all of these (eg, because of precipitation) then the CFAR circuit will raise the threshold accordingly.
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