Marco Villanti

On the adaptive DVB-S2 physical layer: design and performance

The successful DVB standard has now evolved into the DVB-S2 standard, which promises to bring very significant capacity gains. The main DVB-S2 feature is its adaptive air interface, where coding and modulation techniques are varied flexibly to maximize performance and coverage. This article addresses the design of the entire DVB-S2 communication chain, considering practical algorithms for coding, modulation, predistortion, carrier and SNR estimation, frame synchronization, and data recovery. The design complexity is exacerbated by the fact that DVB-S2 foresees 28 different coding/modulation pairs, demanding specific optimization and variable frame length. The performance achieved considering all possible impairments is compared to the ideal performance achievable in the Gaussian channel in terms of integral degradation, which ranges from 0.4 to 2,5 dB in going from QPSK to 32-APSK.

Differential Post Detection Integration Techniques for Robust Code Acquisition

In this paper, the problem of code acquisition for spread-spectrum systems is investigated in the presence of frequency errors. The classic approach of noncoherent post detection integration (NCPDI) is contrasted with differential post detection integration (DPDI), presented in two different versions, namely DPDI-Real and DPDI-Abs, respectively, suited for fine and large frequency offsets. The differential schemes are characterized thoroughly introducing a novel analytical treatment that is validated by simulations. In order to fairly quantify the potential gains introduced by the differential solutions, specific detector parameter optimization is performed for each scheme. The interesting result is that the DPDI significantly outperforms the classic NCPDI approach for large frequency errors, and behaves close to it for small offsets. DPDI can, thus, be considered as a very robust PDI solution with moderate complexity.

Frame acquisition for continuous and discontinuous transmission in the forward link of satellite systems

This paper tackles the problem of frame acquisition for the forward link of satellite systems with continuous and discontinuous transmissions. Multi-dwell and single-dwell procedures with threshold crossing (TC) decision strategy are proposed and compared. To cope with the large frequency error, the detection is based on post-detection integration (PDI), which is presented in two alternatives: non-coherent and differential PDI. The main result of the paper is represented by the proposed analytical model that enables fine parameter optimization. The proposed approach being applicable to TDM/TDMA networks in general, the paper provides the designer with useful guidelines for the synchronization subsystem design.

Frame synchronization in frequency uncertainty

This paper addresses the problem of robust frame synchronization for TDM/TDMA systems in the presence of frequency errors, accomplished through data-aided recognition of the Unique Word (UW) preamble in the transmission flow. Robust detection design is performed applying, through approximations, the Maximum Likelihood (ML) criterion coupled to Post Detection Integration (PDI), to obtain a novel detector identified as Balanced-GPDI (B-GPDI). This new approach considerably outperforms other schemes available in the literature, at the cost of a moderate complexity increase. This is possible thanks to an optimized use of coherent accumulation, which enhances the correlation term in the decision variable, along with highly accurate modeling of the energy correction factor. To limit complexity increase and memory requirements, several approximations of the exact B-GPDI are proposed and discussed in the paper, to provide the designer with practical solutions that are still able to outperform other approaches in specific application scenarios. In particular, approximations for low and high Signal-to-Noise Ratio (SNR) are presented. Different application scenarios are considered in the paper for numerical analysis. In particular, the cases of forward link Continuous Transmission (CTX) and return link Burst Transmission (BTX) are addressed.

Differential and non-coherent post detection integration techniques for the return link of satellite W-CDMA systems

In the paper, the preamble structure of IMT-2000 SW-CDMA air radio interface is considered in the evaluation of the performance of different post detection integration techniques for code acquisition in the return link of a satellite W-CDMA system. In particular, non-coherent post detection integration (NCPDI) and two different options of differential post detection integration (DPDI) techniques, namely DPDI-abs and DPDI-real, are investigated in terms of missed detection and false alarm probabilities. AWGN and Rician channels are considered in the presence of a frequency error. Both analytical and simulation results are provided.

Enhanced Frame Synchronization for DVB-S2 System Under a Large of Frequency Offset

This paper investigates the possible robust technique of frame synchronization for DVB-S2 system. Basically, we focus on the improvement of correlation characteristic, instead of establishing the strategy of frame synchronization with optimal scenario due to variable transmission frame lengths of DVB-S2 standard. To cope with a large frequency offset as a maximum 20% value normalized to symbol rate, the differential generalized post detection integration scheme is newly proposed in the paper. The fruitful results of the paper are described by the suitable analytical approach through parameter optimization. The proposed scheme is shown to provide a good trade-off relation between complexity and performance and is verified in detail their improved performance.

Differential post detection integration technique in the return link of satellite CDMA systems

A performance evaluation is carried out of a differential post detection integration (DPDI) technique for code acquisition in the return link of a satellite CDMA system in the presence of Rician fading and non-ideal frequency recovery. In particular, the preamble structure of IMT-2000 SW-CDMA air radio interface is considered for evaluating the missed detection and false alarm probabilities. An analytical approach is used for a post detection integration length equal to one, whereas simulation results are provided both for validation purposes and for evaluation of more general cases. Finally, the achieved closed form expression for the false alarm probability allows the decision threshold to be computed analytically.

Design of distributed unique words for enhanced frame synchronization

A novel approach is introduced for the design of a unique word (UW) for frame synchronization in time division multiplexing/time division multiple access (TDM/TDMA) systems. In particular, the UW symbols are distributed in each frame in a specific pattern in order to optimize the UW autocorrelation properties. The distribution patterns are scalable, since they preserve their autocorrelation properties under truncation. The resulting frame structure enables the use of several types of UWs, including the silent-UW (SUW) and the unit-UW (UUW), that are novel approaches for which the optimal Bayes detector is derived. An analytical performance characterization is presented along with comparisons with state-of-the-art alternatives. We show that SUW can significantly outperform the classic UW in the presence of frequency offsets or whenever data interference is the main impairment to cope with, i.e. at moderate to high signal to noise ratios. Interestingly, this performance improvement comes with the further advantage of a considerable complexity reduction. Hence UUW is shown to provide both performance improvement and complexity reduction.

Robust Code Acquisition in the Presence of BOC Modulation for Future Galileo Receivers

The problem of code acquisition for the Galileo system is investigated in this paper. The effect of non-ideal sampling on the binary offset carrier (BOC) modulated signal is evaluated and a novel detection scheme, identified as Quadribranch, is proposed. Detection performance is investigated by analysis and simulations taking into account frequency errors and non ideal sampling with actual Galileo signals. The notable result is that Quadribranch is able to improve performance in terms of detection probability and mean acquisition time, and, differently from the conventional approach, allows to achieve robust code acquisition without oversampling.

Hierarchical code acquisition for dual band GNSS receivers

This paper tackles the problem of fast acquisition for dual band GNSS receiver. In particular, a novel technique is proposed based on the exploitation of the hierarchical structure of the Galileo E1 and E5 Open Service signals. The new procedure is based on the information exchange between the acquisition blocks of the two bands, and on the reduction of the uncertainty region in one band when the signal in the other one is already acquired. Numerical evaluation shows that the proposed method allows to achieve good performance in terms of Mean Acquisition Time with respect to classical stand alone acquisition while guaranteeing at the same time a significant complexity reduction.