Constellation Design in Four Dimensions under Average Power Constraint

in Proceedings on IEEE Symposium on Communications and Vehicular Technology in the Benelux (2015)

In this paper we address the problem of constellation design in four dimensional space (4D) under average power constraint. We compare the performance of best lattice constellations with those optimized ... [more ▼]

In this paper we address the problem of constellation design in four dimensional space (4D) under average power constraint. We compare the performance of best lattice constellations with those optimized without any constraint on their structure. Even though the lattice based constellations provide the best minimum distance, usually they do not allow for a good binary labelling. Therefore, in more realistic system scenarios, up to a 2 dB gain can be obtained by properly optimizing the constellation and the corresponding binary labelling. We also investigate the performance of 4D constellations obtained by the Cartesian product of two 2D constellations. [less ▲]

Performance Analysis of Noncoherent Frame Synchronization in Satellite Communications with Frequency Uncertainty

in Proceedings on IEEE Symposium on Communications and Vehicular Technology in the Benelux (2015)

Emerging markets for satellite communications, such as maritime and aeronautical applications, require reliable communications in challenging conditions and low-cost, low-complexity user terminals. In ... [more ▼]

Emerging markets for satellite communications, such as maritime and aeronautical applications, require reliable communications in challenging conditions and low-cost, low-complexity user terminals. In this perspective, the synchronization chain is a fundamental part of the receiver and its design becomes critical. When a quadricorrelator is used as first stage of the synchronization chain so as to perform a coarse frequency estimation, then a noncoherent algorithm for frame synchronization can be employed as second stage. A popular algorithm for frame synchronization is the post-detection integration (PDI), whose noncoherent version (NCPDI) is quite robust to non-negligible residual frequency offsets. In this paper we will assess the performance of NCPDI in presence of a random uniformly-distributed residual frequency offset and will find a closed-form approximation for the probability of detection. Moreover, we will optimize the design parameters of NCPDI for a system operating at very low signal-to-noise ratio (VL-SNR) by minimizing the probability of missed detection for a given probability of false alarm. [less ▲]

Low Complexity Predistortion and Equalization in Nonlinear Multicarrier Satellite Communications

in EURASIP Journal on Advances in Signal Processing (2015)

Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint amplification of multiple carriers using a single high-power amplifier (HPA) is being considered ... [more ▼]

Aiming to reduce the power/mass requirements in satellite transponders and to reduce mission costs, joint amplification of multiple carriers using a single high-power amplifier (HPA) is being considered. In this scenario, a careful investigation of the resulting power efficiency is essential as amplification is nonlinear, and multicarrier signals exhibit enlarged peak-to-average power ratio. Thus, operating the amplifier close to saturation vastly increases signal distortion resulting in a severe degradation of performance, especially for higher order modulations. This paper proposes a reduced-complexity digital predistortion (DPD) scheme at the transmitter and a corresponding equalizer (EQ) at the receiver to mitigate these nonlinear effects. Scenarios include both the forward as well as the return links. In particular, the paper exploits the MIMO Volterra representation and builds on a basis pursuit approach using a LASSO (least absolute shrinkage and selection operator) algorithm to achieve an efficient basis representation, avoiding large computational complexity, to describe the selection of predistorter/equalizer model. The work further compares and contrasts the two mitigation techniques taking various system aspects into consideration. The gains in performance and amplification efficiency demonstrated by the use of DPD/ EQ motivate their inclusion in next-generation satellite systems. [less ▲]

Spatial Multiplexing in Optical Feeder Links for High Throughput Satellites

in Spatial Multiplexing in Optical Feeder Links for High Throughput Satellites (2014, December 02)

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the ... [more ▼]

Optical feeder links are an attractive alternative to the RF feeder links in satellite communications (SatCom). In this paper, we present initial results from an optical feeder link study. We discuss the architecture of a geostationary earth orbit (GEO) satellite system based on optical feeder links. To mitigate the effects of cloud coverage, which is the main availability-limiting factor, Optical Ground Station (OGS) diversity is employed. Moreover, a spatial multiplexing scheme is considered. Assuming an ON-OFF channel model, the number of required OGSs to ensure availability and throughput requirements is analyzed [less ▲]

Performance Analysis of Fractionally Spaced Equalization in Non-linear Multicarrier Satellite Channels

in Proceedings of 32nd AIAA International Communications Satellite Systems Conference (ICSSC), (2014, August 05)

Joint amplification of multiple carriers with a single wideband high power amplifier (HPA) has been considered towards reusing the satellite resources among multiple links to reduce the mission cost. The ... [more ▼]

Joint amplification of multiple carriers with a single wideband high power amplifier (HPA) has been considered towards reusing the satellite resources among multiple links to reduce the mission cost. The non-linear characteristic of the HPA, especially near saturation, coupled with the on-board IMUX/ OMUX filters result in non-linear adjacent carrier interference (ACI) and inter-symbol interference (ISI) during multicarrier power amplification. To benefit from the advantages of multicarrier transmissions, on-ground techniques to mitigate the non-linear distortions need to be devised. These techniques include predistortion at the transmitter and equalization at the receiver. Several works have considered the use of multicarrier predistortion along with single carrier equalization. A symbol synchronous equalizer, while being simple to implement, may not necessarily provide for the optimum linear filter. Towards improving the performance, fractionally spaced equalizers (FSE) have been considered. Such receivers are shown to provide enhanced performance by effectively compensating for the group delay distortions. The objective of this work is to consider the use of FSE in the context of multicarrier transmissions over non-linear channels and illustrate their performance enhancements [less ▲]

Multicarrier LUT-based data predistortion for non-linear satellite channels

in Communications (ICC), 2014 IEEE International Conference on (2014, June)

Current satellite communication architectures can be potentially improved by applying multicarrier power amplification. Joint on-board amplification of multiple carriers reduces hardware and weight ... [more ▼]

Current satellite communication architectures can be potentially improved by applying multicarrier power amplification. Joint on-board amplification of multiple carriers reduces hardware and weight, enabling cost-efficient satellite architectures. However, on board power amplification is inherently a non-linear operation, whose distortion effects drastically increase when the high power amplifier (HPA) is operated in multiple carrier mode due to the generated inter-modulation products. In order to achieve the desired on-board power efficiency and to reduce the non-linear distortion, specific countermeasures need to be put in place. In this work we provide a novel data predistortion technique for multiple carriers satellite channel based on look up table (LUT) for high throughput applications. In contrast to known single carrier LUT techniques, the entries of the table are obtained by pursuing an analytical approach exploiting channel model and implementing recursive least squares techniques (RLS). A novel method to reduce the number of LUT entries based on LUT partitioning is proposed. Considerable performance gains over standard polynomial based predistortion are realized by the proposed technique. [less ▲]

Carrier Rate Optimization on the Return Link of Interactive Mobile Satellite Networks

in European Wireless 2014; 20th European Wireless Conference; Proceedings of (2014, May)

Emerging interactive satellite applications demand highly efficient transmission schemes. Narrow-band satellite return channels for mobile users have peculiar characteristics that make the optimal user ... [more ▼]

Emerging interactive satellite applications demand highly efficient transmission schemes. Narrow-band satellite return channels for mobile users have peculiar characteristics that make the optimal user-rate determination a hard problem. Carrier rate enhancement can only be enabled by increasing the user bandwidth and by the application of highly efficient coding schemes. However, with the system bandwidth held constant, gains from increased user bandwidth can be offset by interference from an adjacent user channels. Additional interference is caused by spurious emissions from adjacent channels; these arise from the spectral regrowth caused by the user terminal power amplifier when operated in high-efficiency region. On the other hand, efficient amplification is mandatory to achieve the required signal to noise ratio at the receiver. In this work we propose a combination of transmitter and receiver techniques to improve the user-rate while controlling the user power efficiency. [less ▲]

Timing and Frequency Synchronisation for Multiuser Detection on the Return Link of Interactive Mobile Satellite Networks

in Proceedings of the ICSSC conferrence (2013, October)

Synchronization, a key process in a communication system, can be very demanding, especially in burst mode transmissions. The estimation of timing, frequency and phase offsets is sensitive to the magnitude ... [more ▼]

Synchronization, a key process in a communication system, can be very demanding, especially in burst mode transmissions. The estimation of timing, frequency and phase offsets is sensitive to the magnitude of these offsets as well as the ambient interference and noise levels. The aggressive reuse of frequencies in a multibeam satellite system increases the co-channel interference significantly and motivates the need to revisit, and re-design if needed, the algorithms used for synchronization. This paper deals with such a scenario occurring on the return link of a mobile interactive satellite system and provides a set of synchronization sub-systems that allow for the design of a robust modem that can reap the benefits of sophisticated interference mitigation techniques. [less ▲]

Gateway Switching in Q/V Band Satellite Feeder Links

in IEEE Communications Letters (2013), 17(7), 1384-1387

A main challenge towards realizing the next generation Terabit/s broadband satellite communications (SatCom) is the limited spectrum available in the Ka band. An attractive solution is to move the feeder ... [more ▼]

A main challenge towards realizing the next generation Terabit/s broadband satellite communications (SatCom) is the limited spectrum available in the Ka band. An attractive solution is to move the feeder link to the higher Q/V band, where more spectrum is available. When utilizing the Q/V band, due to heavy rain attenuation, gateway diversity is considered a necessity to ensure the required feeder link availability. Although receive site diversity has been studied in the past for SatCom, there is much less maturity in terms of transmit diversity techniques. In this paper, a modified switch and stay combining scheme is proposed for a Q/V band feeder link, but its performance is also evaluated over an end-to-end satellite link. The proposed scheme is pragmatic and has close to optimal performance with notably lower complexity. [less ▲]

Non-parametric data predistortion for non-linear channels with memory

in Acoustics, Speech and Signal Processing (ICASSP), 2013 IEEE International Conference on (2013, May 26)

With the growing application of high order modulation techniques, the mitigation of the non-linear distortions introduced by the power amplification, has become a major issue in telecommunication. More ... [more ▼]

With the growing application of high order modulation techniques, the mitigation of the non-linear distortions introduced by the power amplification, has become a major issue in telecommunication. More sophisticated techniques to counteract the strong generated interferences need to be investigated in order to achieve the desired power and spectral efficiency. This work proposes a novel approach for the definition of a transmitter technique (predistortion) that outperforms the standard methods with respect to both performance and efficiency. [less ▲]