In this paper, a novel design scheme for radar signal is proposed. It is based on a modification of Costas codes design obtained by increasing the frequency separation of frequency hops beyond the orthogonality condition. This condition states that frequency separation between frequency hops should be at most equal to the inverse of bit duration of the code. Indeed, increasing frequency separation beyond this condition is sometimes needed in radar applications. However, this leads to the appearance of grating lobes near the main temporal lobe of the autocorrelation function. This paper proposes overcoming this problem using sub-pulse coding. The originality of the proposed approach consists in choosing for Costas sub-pulses other Costas codes instead of constant frequency ones in order to lower autocorrelation grating lobes that would normally appear when the orthogonality condition is not satisfied. Indeed, we show that, under some conditions on Costas signal parameters in the sub-pulse, good elimination of grating lobes is achieved.

Costas codes are a variant of pulse compression waveforms, largely studied for their attractive time-frequency properties. Their 'thumbtack-like' ambiguity function (AF) makes them highly suitable for delay and Doppler estimation, in radar and sonar applications. However, this behaviour depends heavily on the length of the code: the improvement in delay-Doppler resolutions and AF sidelobes level needs an increase in the size of the code. In this study, designs that allow good performance without increasing the size of the code are proposed. They are based on a modification of Costas codes by widening frequency separation between hops and replacing rectangular pulses by other waveforms. This will lead to a removal of autocorrelation function grating lobes that normally appear when frequency separation is increased. The originality of the work lies in the proposal of diversified pulse waveforms, such as phase codes, Slepian sequences, and other Costas codes, to encode main Costas pulses. A performance comparison of the proposed approaches is supplied. Such waveforms could also be of interest for applications where waveform diversity is desired

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We investigate the problem of sequence detection in a non linear channel for a contactless air interface. The work presented in this study is based on the the VHBR (Very High BitRate) amendments of the ISO 14443 international standard. We focused more particularly on the part of the standard extension that defines the phase modulation (PSK) from the Proximity Coupling Device (PCD) to the Passive Inductive Coupled Card (PICC). We propose an efficient detector to overcome both Inter Symbol Interference (ISI) due to the high data rates, and system non linearities introduced by the differential detection at the receiver side. The proposed detector is an adaptation of the Viterbi algorithm for constraint-ternary alphabet. Our numerical results show that a rate of 13.56 Mbps can be achieved using a 15-states sequence detector.