Analysis of control algorithms of adaptive network data transmission by local parameters
Scientific Research Institute of Precision Instruments, 51, Str., Dekabristov, Moscow, 127490, Russia
This paper discusses the design of the probing signal generator for spaceborne Synthetic Aperture Radar. Spaceborne SAR systems operate in conditions of interference signals influence (range and Doppler ambiguity, blind zones, etc.). The correct selection of pulse repetition frequency (PRF) of the probing signal allows reducing influence of noise on the echo-signal. In order to reduce the noise influence, the FPGA-based signal generator for spaceborne SAR is proposed.
Onboard memory blocks are mostly affected by space radiation (heavy charged particles). For this reason instead of Memory-based architecture an algorithm based on the Direct Digital Synthesizer architecture is presented. To increase the sampling rate up to 480 MHz the method of parallel processing is used (four 120 MHz channels for each I and Q quadrature).Thus achievable bandwidth equals 400 MHz (20 percent less than sampling rate), that allows to provide range resolution about 1 m (orbit altitude 514 km, angle of sight 20 degrees).
The special algorithm of PRF calculation is used. This algorithm takes into account blind zones distribution and nadir reflections on PRF – angle of sight plane. PRF values for the whole range of angles of sight are stored in FPGA memory.
The initial data for the signal generator are angle of sight, duty cycle and bandwidth. Angle of sight determines the working value of PRF. Duty cycle and working value of PRF determine the duration of the probe pulse. Bandwidth provides the required range resolution. Thus the probing signal generator provides desired characteristics of probing signal.
Keywords:synthetic aperture radar, programmable logic integrated circuit, digital signal processing
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