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The existing Beidou signal receiver has a low-noise amplifier scheme in the S-band, and the noise figure is between 1.5 dB～1.7 dB under the condition of meeting the gain requirements and the noise performance can be further optimized. The scheme studies a low noise amplifier(LNA) based on a high-bandwidth millimeter wave tube. The tube is based on NPN broadband silicon germanium RF transistor process. Amplifier uses two-stage conjugate matching to achieve the best balance between circuit noise and gain，and uses LDO circuit linear regulated output to minimize power supply noise. ADS software simulation, Altium designer board and actual measurement of Agilent noise analyzer show that it′s single-stage amplifier has a minimum noise figure of 0.4 dB. At 2.492 GHz, the maximum gain of the solution is 32 dB, and the corresponding noise figure is 1.23 dB. The low-noise amplifier scheme is applied to the front end of Beidou user receiver, which can effectively improve the system noise performance and improve the signal receiving efficiency.

In this paper, we propose a reference-modulated permutation index differential chaos shift keying (RM-PI-DCSK) over multipath fading channels. Due to quasi-orthogonal property between different permutated chaotic signals, the proposed scheme can remarkably suppress the inter-sequence interference to recover the desired information. Moreover, the proposed RM-PI-DCSK has one more modulation bit in the reference segment than the conventional permutation index differential chaos shift keying (PI-DCSK). Both the reference signal in the first time-slot and a permuted replica of the reference in the second time-slot are modulated for efficient transmission. The theoretical bit-error-rate (BER) performance and the highly consistent simulation results demonstrate that the proposed RM-PI-DCSK can achieve a performance gain 3 dB over the conventional PI-DCSK at a BER of $10^{-4}$ , and this gain becomes larger in a high-delay-spread channel. In particular, the performance superiority of the RM-PI-DCSK is further demonstrated in a typical ultra-wideband (UWB) channel with narrow-band interference. Therefore, this proposed scheme can be deemed as an efficient transmission alternative for chaotic-based wireless communications, such as in wireless local area network (WLAN) applications and indoor applications of the transmitted-reference UWB. [ABSTRACT FROM AUTHOR]