Implementation of a radar based on orthogonal frequency division multiplexing signals ensemble

 

A. A. Rodovich ¹, A. A. Seryakov ¹, P. N.Zakharov ¹, M. A. Polischuk ²

¹ M.V.Lomonosov Moscow State University, 119991 Moscow, Russia

² Bauman Moscow State Technical University, 105005 Moscow, Russia

 

The paper is received on July 7, 2016

 

Abstract. Use of OFDM signals with central frequency sweep in radars offers some advantages over conventional radiolocation systems based on chirp signals or short impulses, including increased time-domain resolution and dynamic range. The implementation of such a system is described in the article. The results of measurements demonstrating obtained range resolution of 10 cm are presented.

Increasing of the signal bandwidth is one of the main tendencies in radiolocation nowadays. Ultra-wideband location offers centimeter-range distance resolution and less sensitivity to jamming. If implemented using traditional approach with chirp or video or radio impulse ultra-wideband signals, the radar system experiences a number of problems, including less dynamic range due to the ADC (typical ENOB of 5-20 Gsps ADC is about 8-5 bits), requirements to the precision analog circuitry with linear phase and constant amplitude frequency response (otherwise ripples in time-domain signal appear), incompatibility with standard phase antenna arrays (PAR), limitations in time resolution due to RF switches for the short pulse approach.

A frequency-domain radar is free of the abovementioned problems. The measured quantity is the channel complex frequency response, which is then converted to analytic signal by FFT. This approach is quite similar to one used in vector network analyzers (VNAs) with time-domain option. However, the method is modified in this article for the use of OFDM signals instead of sinusoid signals used in VNAs. This allows orders of speed increase compared to sinusoid signals.

With OFDM signals ensemble, the dynamic range of the radar is kept high due to the use of 14-16 bits ADCs, the requirements to the analog circuitry are simple since the non-linearities are calibrated for each OFDM subcarrier, the PAR frequency dependence is taken into account using a specific phase shift on each subcarrier, and the RF switches limiting the time resolution are not used.

Keywords: radiolocation, OFDM.

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