Raffaella Pedone

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.

Generalized and Average Likelihood Ratio Testing for Post Detection Integration

In the context of spread spectrum communications, this paper investigates the use of likelihood ratio testing techniques for the design of post detection integration (PDI) methods for code acquisition in the presence of phase and frequency uncertainty. The proposed methods are derived as theoretical and pragmatic alternatives to the conventional approach based on noncoherent integration, which would be optimal in the absence of frequency uncertainty. Two competing alternatives are introduced to handle the unknown frequency error, respectively based on the generalized and average likelihood ratio tests, and identified as generalized PDI (GPDI) and average PDI (APDI). The GPDI versus APDI tradeoff is far from trivial and leads to numerous interesting insights, particularly with respect to the impact on performance of the frequency offset entity. Performance is also contrasted to that of conventional PDI techniques, i.e., noncoherent and differential PDI, to reveal significant gains in favor of the proposed methods.

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.

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.

Generalized and average post detection integration methods for code acquisition

In the context of spread spectrum systems, the paper focuses on post detection integration (PDI) for code acquisition in the presence of a frequency error. The PDI scheme is obtained through the theoretical likelihood ratio test (LRT) computation, and two approaches are considered: the generalized LRT, in the form of the special case STML-PDI (single term maximum likelihood-PDI); the average LRT (A2LLRT). The methods are developed in the AWGN channel but are applicable to fading channels, too. Possible applications are in cellular CDMA networks and in satellite navigation and positioning systems.

Maximum likelihood post detection integration methods for spread spectrum systems

In the context of spread spectrum systems, this paper illustrates a novel and improved method to implement post detection integration in a code acquisition scheme in the presence of an unknown frequency error. The method is developed in the AWGN channel but is applicable to fading channels, too. The novel method is obtained through the application of the maximum likelihood criterion. The result is compared with the classic noncoherent and differential post detection integration schemes, showing significant improvements. Possible applications are in cellular CDMA networks and in satellite navigation and positioning systems.

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.

Robust frame synchronization for the DVB-S2 system with large frequency offsets†

This paper tackles the problem of frame synchronization design for the Digital Video Broadcasting standard via Satellite (DVB-S2) system. In particular, the design of a novel frame detection scheme exhibiting robustness against large frequency errors is proposed. Post-detection integration (PDI) is exploited to provide coarse frame alignment with limited complexity with respect to classical approximate maximum likelihood (ML) solutions. The novel scheme, denoted as differential generalized post-detection integration, derives from a pragmatic adaptation of the well-known generalized PDI scheme (IEEE Trans. Commun. 2007; 55(11):2159–2171), which eliminates its inherent source of weakness in the presence of large frequency offsets, i.e. its non-differential component given by non-coherent PDI. The proposed approach manages to reduce the remarkable performance gap with respect to approximate ML techniques available in the literature (IEEE Trans. Commun. 2002; 50(7):1062–1065), providing the designer with an interesting performance/complexity trade-off. Performance is numerically evaluated in terms of receiver operating characteristics and mean acquisition time (MAT), handling the acquisition procedure according to a single-dwell approach. Both threshold crossing and MAX criterion are contrasted to identify the best design solution. Copyright