Bhavani Shankar

Applicability of MIMO to satellite communications

SUMMARY This paper presents achievements of an on-going activity where the applicability of MIMO to satellite communications with Digital Video Broadcasting – Satellite services to Handhelds as the key application is studied. The potential satellite and hybrid satellite-terrestrial MIMO scenarios are described, and the applicable MIMO schemes for each scenario are selected. The performance of the MIMO schemes was studied by performing comprehensive computer simulations, and the main results are presented in this paper. Copyright

Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels

Two key advances are envisaged for future missions: (a) spectrally efficienttransmission to meet the increasing demand and (b) sharing of satellite capacityamong different links to meet power/mass requirements. Joint amplification ofmultiple-carrier DVB-S2 signals using a single High-Power Amplifier (HPA) is aparticular application of satellite resource sharing. However, effects specific to sucha scenario that degrade power and spectral efficiencies include (a) an increasedAdjacent Channel Interference caused by non-linear characteristic of the HPA and(b) increased peak to average power ratio. The paper studies signal processingtechniques – digital pre-distortion (DPD) at the gateway and equalization (EQ) atthe User Terminal – to mitigate the non-linear effects and improve power as well asspectral efficiencies. While the algorithms for DPD and EQ are described inliterature, their use in multi-carrier scenario is novel and poses new challenges thatare investigated in the paper.

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

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.

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

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 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.

Sensitivity Analysis of Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels

Sensitivity Analysis of Multicarrier Digital Pre-distortion/ Equalization Techniques for Non-linear Satellite Channels

An iterative approach to nonconvex QCQP with applications in signal processing

This paper introduces a new iterative approach to solve or to approximate the solutions of the nonconvex quadratically constrained quadratic programs (QCQP). First, this constrained problem is transformed to an unconstrained problem using a specialized penalty-based method. A tight upper-bound for the alternative unconstrained objective is introduced. Then an efficient minimization approach to the alternative unconstrained objective is proposed and further studied. The proposed approach involves power iterations and minimization of a convex scalar function in each iteration, which are computationally fast. The important design problem of multigroup multicast beamforming is formulated as a nonconvex QCQP and solved using the proposed method.

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

ACI = Adjacent Channel Interference APSK = Amplitude Phase Shift Keying BER = Bit Error Rate BSS = Broadcast Satellite Services DPD = Digital Predistortion EQ = Equalization FSS = Fixed Satellite Services HPA = High Power Amplifier IBO = Input Back-Off IMD = Inter Modulation Distortions IMUX = Input MUX ISI = Inter-Symbol Interference L-TWTA = Linearized Travelling Wave Tube Amplifier OBO = Output Back-Off OMUX = Output MUX TD = Total Degradation TWTA = Travelling Wave Tube Amplifier

Enhancing mobile services with DVB-S2X superframing

DVB-S2X is the cornerstone for satellite communication standards forming the state-of-the-art of broadband satellite waveforms. In this paper we propose new application scenarios and advanced techniques, including a reference design implementing superframing, predistortion, a robust synchronization chain, and a plugand-play channel interleaver. We demonstrate by means of software simulations and hardware tests that the DVB-S2X can be a common technology enabler for land-mobile, aeronautical, and maritime satellite scenarios in addition to the more traditional VSAT scenario, even in very challenging conditions (e.g., very low SNR). Copyright c

Exploiting diversity in future generation satellite systems with optical feeder links

In this paper we exploit the transmitter micro diversity in the satellite communication systems with optical feeder links. Both analogue and digital transparent systems are studied. We consider up to four statistically independent transmitted optical beams with perfect or partial phase knowledge of the beams at the receiver. End-to-end simulation results for frame error rates are presented for a complete system including uplink, satellite payload and downlink. We compare our results with those of the DVB-S2 standard without the optical feeder link. Our results provide a complete view of gains and losses which can be obtained by micro diversity in both analogue and digital transparent satellite systems with optical feeder link. Given the system parameters, we also provide a detailed study of the transmitted power needed to achieve a target frame error rate and discuss the achieved bit rates in for each system scenario.

On-ground signal processing techniques enabling efficient amplification of multicarriers

Spectrally efficient transmission to meet the increasing demand and sharing of satellite capacity among different links to reduce mission costs are two key avenues charted for next-generation satellites. Joint amplification of multicarrier signals using a single high-power amplifier is an important aspect of satellite resource sharing. However, the inherent nonlinearity of the amplifier results in an increased adjacent-channel interference and peak-to-average power ratio that degrade power and spectral efficiencies while offsetting other potential benefits. This chapter describes signal processing techniques—predistortion at the gateway and equalization at the user terminal—that mitigate the interference and enable efficient joint onboard amplification.