This study designs and analyses a new phase-coded spread-spectrum communication system where both phase-coded carrier and spreading factor are varied based on a chaotic behaviour in the communication process. This design aims to reduce the probability of interception of the considered system. Discrete values generated by a chaotic map are exploited to create a non-return-to-zero (NRZ)-chaos sequence and simultaneously make bit duration variable. The NRZ-chaos sequence is then modulated by binary phase-shift keying technique to produce the phased-coded carrier. Owing to chip duration being constant, the variation of bit duration also leads to the variation of spreading factor. Spectrum spreading in the transmitter is performed by multiplying directly the variable-duration bits with the phase-coded carrier. A coherent receiver relying on a direct correlator is used for recovering the data. Design of the transmitter and receiver as well as analysis of bit error probability for the proposed system in cases of single-user and multi-user under additive white Gaussian noise channel is presented. Simulation results are shown to confirm the operation of the designed structures and the obtained analytical performance.
This article presents a compact broadband dual‐polarized antenna for use in the sub‐6 GHz 5G applications. The antenna is a novel magneto‐electric (ME) dipole with microstrip‐line aperture‐coupled feed, that is, it is composed of two orthogonal microstrip‐lines coupled with four shorted patches through a crossed slot for the broadband dual‐polarized radiation. The electric and magnetic dipole modes are formed by the shorted patches and the gap between the patches, respectively. Therefore, the antenna achieves a low‐profile. To reduce the back radiation at the aperture‐coupled feed and remain the low‐profile, the antenna is backed by a high impedance surface. The final design with an overall size of 50 mm × 50 mm × 12.5 mm (0.5λmin × 0.5λmin × 0.125λmin) has been fabricated and measured. The measurements result in a bandwidth of 33% (3.02‐4.02 GHz) for voltage standing wave ratio <1.5 and an isolation of >25 dB among the two ports. Its bandwidth covers the specific 5G NR n78 band (3.3‐3.8 GHz). In addition, the antenna achieved a broadside gain of 7.9‐8.5 dBi, a front‐to‐back ratio of >18 dB, and a cross‐polarization level of <− 20 dB across the operational bandwidth.
This paper proposes a chaos-based secure direct-sequence/spread-spectrum (DS/SS) communication system which is based on a novel combination of the conventional DS/SS and chaos techniques. In the proposed system, bit duration is varied according to a chaotic behavior but is always equal to a multiple of the fixed chip duration in the communication process. Data bits with variable duration are spectrum-spread by multiplying directly with a pseudonoise (PN) sequence and then modulated onto a sinusoidal carrier by means of binary phase-shift keying (BPSK). To recover exactly the data bits, the receiver needs an identical regeneration of not only the PN sequence but also the chaotic behavior, and hence data security is improved significantly. Structure and operation of the proposed system are analyzed in detail. Theoretical evaluation of bit-error rate (BER) performance in presence of additive white Gaussian noise (AWGN) is provided. Parameter choice for different cases of simulation is also considered. Simulation and theoretical results are shown to verify the reliability and feasibility of the proposed system. Security of the proposed system is also discussed.
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