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.

This paper tackles the problem of time synchronization for the mobile extension of DVB-S2/RCS air interfaces. To increase robustness against other system interference, Direct Sequence Spread Spectrum (DS-SS) is selected, which calls for efficient code acquisition. Designed to operate jointly with frame synchronization, a novel high level control logic is proposed for code acquisition, along with robust detectors to cope with the large frequency uncertainty experienced at terminal start-up. The results show that the mean acquisition time is always limited to a few milliseconds, allowing fast acquisition even in the most challenging railway scenario.

This paper tackles the problem of unified frame and symbol timing synchronization for the return link of a DVB satellite system with Continuous Phase Modulation. Robust schemes are introduced to cope with the carrier frequency uncertainty affecting the received signal. The novel approach employs the same detector to recover the frame alignment and the symbol synchronism, based on Post Detection Integration strategy. It is shown that this unified approach is able to provide quasi-optimal performance limiting complexity at the same time.

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.

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.

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 synchronization is conventionally intended as "epoch recovery" of a symbols synchronous stream. But, what happens when symbol timing is unknown? A typical approach to this problem involves oversampling, which is computational intensive. This paper introduces a novel alternative approach whereby the detector is made aware of the emerging ISI due to imperfect symbol timing recovery in order to achieve the wanted performance with low computational complexity. The resulting sequence, identified as ISI-UW, is obtained as the combination of several conventional UW appropriately shifted in time. The adoption of this particular sequence structure allows to enhance performance in the worst case scenario, at the cost of a slight performance loss in the ideal case, and reveals to be an interesting low-complexity alternative to conventional oversampling techniques to cope with symbol timing fractional misalignments

Frame synchronization and frequency estimation have historically been completely separate problems in digital receiver design. Here, a common avenue is discovered and transformed into practical algorithms. The proposed approach is based on the adoption of a differential post detection integration (DPDI) scheme for the acquisition of the unique word marking the beginning of the frame. The DPDI decision variable can indeed be used also for frequency estimation purposes, with very limited complexity. The adoption of a modular preamble structure with a two stage detector is also proposed to improve performance and optimize the detector structure. Performance is studied through simulations and analysis, providing closed form expressions for the estimation error variance. Both simulations and analysis show that the proposed joint approach is able to provide estimation performance close to the Cramer-Rao bound, as well as practically error-free frame synchronization, with very limited complexity

This paper proposes a novel frame acquisition method for continuous transmissions in TDM/TDMA systems. The approach is based on a multi-dwell procedure, with approximate maximum likelihood criterion (MAX) applied in search mode, followed by a parallel threshold crossing (TC) verification stage. The particular case of single TC verification and the conventional all-TC procedures, which perform TC also in search mode, are considered for comparison. A thorough performance analysis is presented exploiting the flow-graph approach, along with numerical results. The proposed method allows achieving a gain in terms of mean frame acquisition time with respect to other solutions, with no significant complexity increase.

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.