Orthogonal multicarrier phased coded signal for netted radar systems

Orthogonal multicarrier radar waveforms have been designed for netted radar systems, where several radar stations are active simultaneously. The waveforms are phase-coded using orthogonal Golay complementary sets, derived from Reed Muller codes. These codes constrain the PMEPR of the signal to a maximum a 3 dB. Besides, ambiguity functions and cross-ambiguity functions with low sidelobes have been obtained. The possibility to encode data relative to the transmitter configuration (position, direction of the beam,...) in the radar waveform is also demonstrated.

I. Introduction

Multistatic or netted radars are a promising technology for future radar systems. Signal transmitted by several synchronous radar stations can be processed coherently to increase the Signal-to-Noise ratio at the receiver, and thus the detection performances. It means that each station can transmit a lower power, which makes them less expensive to build and less detectable by enemy radars [1]. Other advantages include angular diversity over the radar cross-section of the target and a better estimation of the angle of arrival through multilateration techniques [2]. The whole system can be synchronized through GPS (Global Positioning System) disciplined oscillators [3]. A major problems in netted radars is the design of orthogonal waveforms to reduce mutual interference between the signals. Recent works have focused on optimizing polyphase sequences to obtain good autocorrelation and cross-correlation properties [4]. However, the main drawback of polyphase sequences is their poor spectral efficiency, due to the fact the signal bandwidth is inversely proportional to the symbol period. In this paper, we investigate the use of Multicarrier-Phase-Coded (MCPC) signals, previously introduced by N. Levanon [5]. These waveforms use an Orthogonal Frequency Division Multiplexing (OFDM) structure, which make them well adapted for wideband applications. Secondly, the added dimension (i.e. the frequency) can be used to introduce some diversity between the transmitted signals. Finally, thanks to recent achievements in MIMO-OFDM communication systems, we can show that it is possible to encode the information relative to the transmitter configuration (position, direction of the beam, transmitted code, timing information,…) in the radar waveform. This property can be very useful for adaptive or mobile radar stations (e.g. airborne radars), whose configurations change over the time. In that case, channel coding is also required at the transmitter and the waveform needs to incorporate an error-correction code to prevent the data from being corrupted.