Ming-Seng Kao

Efficient acquisition algorithm for long pseudorandom sequence

In this paper, a novel method termed the phase coherence acquisition (PCA) is proposed for pseudorandom (PN) sequence acquisition. By employing complex phasors, the PCA requires only complex additions in the order of N, the length of the sequence, whereas the conventional method using fast Fourier transform (FFT) requires complex multiplications and additions both in the order of N log2N. To combat noise, the input and local sequences are partitioned and mapped into complex phasors in PCA. The phase differences between pairs of input and local phasors are used for acquisition; thus, complex multiplications are avoided. For more noise-robustness capability, the multilayer PCA is developed to extract the code phase step-by-step. The significant reduction of computational loads makes the PCA an attractive method, especially when the sequence length of N is extremely large, which becomes intractable for the FFT-based acquisition.

1-Bit High Accuracy Carrier Phase Discriminators

Asymptotic derivation of traditional 1-bit arctangent phase discriminator (APD) is derived, even though neighboring quantized samples are dependent. The results reveal that high accuracy can be achieved by an APD in low signal-to-noise ratio (SNR) applications using sufficient samples. For high- SNR applications a novel phase discriminator called noise-balanced digital phase discriminator (NB-DPD), which has a complementary asymptotic performance of APD, is proposed to achieve high accuracy. The threshold SNR 2.6 dB that is suggested to identify either APD or NB-DPD is adopted in a specific application. Finally the sampling, quantization, and environmental noise effects on convergence of the asymptotic performance are discussed, and the simulations are provided to verify the analytical results.

SNR-Aided Accurate Phase Estimation in 1-Bit Software-Defined Receiver

This work investigates the high-accuracy phase discriminator in 1-bit software-defined receiver (SDR) for three signal-to-noise ratio (SNR) ranges: low SNR, high SNR and moderate SNR. Unlike traditional approaches, our approach first distinguishes which SNR range an application falls into, and this SNR information is then utilized to select a proper phase discriminator to achieve high accuracy. For low-SNR applications, traditional arctangent phase discriminator (APD) is adopted and the analysis of asymptotic performance is derived. For high-SNR applications, the noise-balanced digital phase discriminator (NB-DPD) is adopted to improve accuracy [1]. Between them, for moderate-SNR applications, a novel SNR-aided phase discriminator (SNRaPD) is proposed. The analytical and simulation results verify the superiority of the proposed approach for applications in different SNR ranges. The determination of moderate SNR range is critical and discussed finally.

An approach attaining adjustable designated footprint

In satellite communications, the footprint is characterized by contour lines with specific receiving power. When data is delivered to the area within a specific footprint, called the designated footprint, illegal users outside the boundary of designated footprint (BDF) can still receive the signal with degraded power. In other words, illegal users can obtain the transmitted data with higher error probability. In this paper, we present a special two-stage serially concatenated (2-SC) coding scheme to more precisely define the designated footprint. Hence users outside the BDF are excluded from obtaining the data, i.e. they cannot correctly decode the data. The key technique, 2-SC coding scheme, achieves the brick-wall effect in error performance regarding bit energy-to-noise density ratio ( Eb / N0 ). The brick-wall effect has sharp cutoff at a critical Eb / N0 . When the transmitted data is protected by the 2-SC coding scheme, only the users within the designated footprint can successfully decode the data. Otherwise, for users outside the BDF with received Eb / N0 slightly less than critical Eb / N0 , even if the coding structure is known, they cannot correctly decode the data. Thus the BDF is sharply defined by the critical Eb / N0 . Moreover, by means of purposely-introduced error in the codewords, we can adjust the critical Eb / N0 and the BDF. We provide comprehensive analysis of the coding performance and further discuss the application of the proposed scheme to enhance secure satellite communications.