Nonlinear Satellite Channels Research Articles

Symbol error rate calculation and data pre‐distortion for 16‐QAM transmission over nonlinear memoryless satellite channels

AbstractThis paper presents a simplified mathematical approach to evaluate the performance of any given circular constellation of 16‐level quadrature amplitude modulation (16‐QAM) in terms of symbol error rate (SER). Following this approach, with the aim to work with memoryless nonlinear satellite channels, a model is derived as a generalized form for both linear and nonlinear channels in the presence of down link additive white Gaussian noise (AWGN). The analysis provides means to calculate the optimal ring ratio (RR) and phase difference (PD) for several possible candidates of 16‐QAM circular constellations. The effects of RR and PD on the SER performance are investigated in the analysis. To overcome the nonlinear distortion, data pre‐distortion is taken into account in the study. The paper gives a general procedure for data pre‐distortion implementation for all circular 16‐QAM constellations. The analytical formulation has been extended for total degradation (TD) performance measure as a function of input back‐off (IBO) of the nonlinear amplifier. A SER performance‐comparison between different constellations for 16‐QAM systems has also been presented in this paper. The analytical results are validated by simulation. Copyright © 2006 John Wiley & Sons, Ltd.

Performance analysis of turbo-coded APSK modulations over nonlinear satellite channels

This paper investigates the performance of M-ary amplitude-phase shift keying (APSK) digital modulation over typical nonlinear satellite channels. The effect of the satellite nonlinearity is studied, and distortion pre- and post-compensation techniques for coded APSK are presented. Moreover, clock timing, signal amplitude and carrier phase recovery schemes are discussed. For the latter, a new class of non turbo decoder-aided closed-loop phase synchronizers featuring good performance and low complexity is studied. Finally, an end-to-end coded APSK system simulator inclusive of the satellite channel model and synchronization sub-systems is discussed and its performance compared to standard trellis-coded QAM concatenated with Reed-Solomon codes, showing a remarkable gain in both power and spectral efficiency. Coded APSK, recently selected for the new standard -DVB-S2- for digital video broadcasting and interactive broadband satellite services, is shown to represent a powerand spectral-efficient solution for satellite nonlinear channels.

DVB-S2: The Second Generation Standard for Satellite Broad-Band Services

DVB-S2 is the second-generation specification for satellite broad-band applications, developed by the Digital Video Broadcasting (DVB) Project in 2003. The system is structured as a toolkit to allow the implementation of the following satellite applications: TV and sound broadcasting, interactivity (i.e., Internet access), and professional services, such as TV contribution links and digital satellite news gathering. It has been specified around three concepts: best transmission performance approaching the Shannon limit, total flexibility, and reasonable receiver complexity. Channel coding and modulation are based on more recent developments by the scientific community: low density parity check codes are adopted, combined with QPSK, 8PSK, 16APSK, and 32APSK modulations for the system to work properly on the nonlinear satellite channel. The framing structure allows for maximum flexibility in a versatile system and also synchronization in worst case configurations (low signal-to-noise ratios). Adaptive coding and modulation, when used in one-to-one links, then allows optimization of the transmission parameters for each individual user,dependant on path conditions. Backward-compatible modes are also available,allowing existing DVB-S integrated receivers-decoders to continue working during the transitional period. The paper provides a tutorial overview of the DVB-S2 system, describing its main features and performance in various scenarios and applications.

Semi-random LDPC codes for CDMA communication over non-linear band-limited satellite channels

This paper considers the application of low-density parity check (LDPC) error correcting codes to code division multiple access (CDMA) systems over satellite links. The adapted LDPC codes are selected from a special class of semi-random (SR) constructions characterized by low encoder complexity, and their performance is optimized by removing short cycles from the code bipartite graphs. Relative performance comparisons with turbo product codes (TPC) for rate 1/2 and short-to-moderate block sizes show some advantage for SR-LDPC, both in terms of bit error rate and complexity requirements. CDMA systems using these SR-LDPC codes and operating over non-linear, band-limited satellite links are analysed and their performance is investigated for a number of signal models and codes parameters. The numerical results show that SR-LDPC codes can offer good capacity improvements in terms of supportable number of users at a given bit error performance.

Performance of non-uniform 16QAM modulation over linear and nonlinear channels

A technique of using a non-uniform 16QAM modulation combined with bit interleaved coded modulation and a new iterative decoding (BICM-ID) scheme is investigated. Simulation results of a parallel concatenated convolutional code shows a gain of 0.95 dB at a BER of 10−5 compared to conventional uniform 16QAM modulation in a linear channel. For a nonlinear satellite channel, this scheme offers a gain of 1.2 dB at the same BER compared to a uniform constellation.

Turbo-coded APSK modulations design for satellite broadband communications

This paper investigates the design of power and spectrally efficient coded modulations based on amplitude phase shift keying (APSK) modulation with application to satellite broadband communications. APSK represents an attractive modulation format for digital transmission over nonlinear satellite channels due to its power and spectral efficiency combined with its inherent robustness against nonlinear distortion. For these reasons APSK has been very recently introduced in the new standard for satellite Digital Video Broadcasting named DVB-S2. Assuming an ideal rectangular transmission pulse, for which no nonlinear inter-symbol interference is present and perfect pre-compensation of the nonlinearity, we optimize the APSK constellation. In addition to the minimum distance criterion, we introduce a new optimization based on the mutual information; this new method generates an optimum constellation for each spectral efficiency. To achieve power efficiency jointly with low bit error rate (BER) floor we adopt a powerful binary serially concatenated turbo-code coupled with optimal APSK modulations through bit-interleaved coded modulation. We derive tight approximations on the maximum-likelihood decoding error probability, and results are compared with computer simulations. The proposed coded modulation scheme is shown to provide a considerable performance advantage compared to current standards for satellite multimedia and broadcasting systems. Copyright © 2006 John Wiley & Sons, Ltd.

Performance of Predistorted APK Modulation for One- and Two-Link Nonlinear Power Amplifier Satellite Communication Channels

Digital satellite communications has been restricted to date to digital modulations having an efficiency of 2 bps/Hz; that is, filtered-quadrature phase-shift keying (QPSK) with close to a constant envelope. The main limitation to higher order digital modulations is the need for linearity of a high power amplifier both in the satellite and a terminal. Many years ago, Thomas et al. conducted a complete study of the use of higher order linear modulations on nonlinear satellite channels. However, pulse-shaping and predistortion were not treated. We consider these items for 16-point amplitude phase-shift keying (APK) modulation; that is, signal points assigned on concentric circles. A simple predistortion algorithm is given for APK modulations and symbol error-rate performance is determined for both one- and two-link nonlinear channels. Our best result is for an one-link channel and (5, 11) APK-5 points on an inner circle and 11 on the other, which, for predistortion on the nonlinear channel, loses only about 1 dB to 16-point quadrature amplitude modulation transmission on the linear channel.

Adaptive predistortion of COFDM signals for a mobile satellite channel

AbstractIn this paper, we consider the optimization of the performance of QPSK and 16‐QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non‐linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non‐linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non‐linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10−3 when compared to QPSK COFDM without the predistortion scheme and 16‐QAM COFDM provides a gain of 0.5 dB output back‐off and 1.2 dB signal to noise ratio at a BER of 3×10−5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10−4 for QPSK and 16‐QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd.

Comparative study of the performance of wavelets as shaping pulses for modulation over linear and non-linear channels

The use of orthonormal scaling functions, wavelets and wavelet packets for pulse shaping has been recently proposed in [1]–[9]. Because of their excellent spectral characteristics, such waveforms can be used for Wavelet Orthogonal Frequency Division Multiplexing (WOFDM) [2] and spectral shaping [10], [11]. In this paper we study the performance of the Meyer, Daubechies, biorthogonal Spline, Battle-Lemarie´ and modified Gaussian [12] families of wavelets for modulation over linear and non-linear channels, and we propose the use of wavelets for pulse shaping over FDM non-linear satellite channels and for multicarrier modulation on satellite and multipath channels. Simulation results indicate that in certain cases wavelet based shaping pulses could out-perform traditional techniques in extremely critical transmission conditions, such as interchannel interference impaired satellite transmission or transmission on multipath channels.

Performance analysis of extended OQPSK carrier phase recovery algorithm in satellite channel

This paper proposes a new extended decision-directed decision-estimated phase recovery algorithm based on maximum likelihood parameter estimation for OQPSK (offset QPSK). In this scheme, compared to the conventional one, the data dependent noise of the phase recovery loop is reduced by inserting a filter with 2 taps to the in-phase and quadrature channel respectively before the phase detector. The proposed scheme is compared to the conventional QPSK scheme with respect to BER (bit error rate) and phase error for roll-off factors of the baseband filter, output backoffs of the nonlinear satellite channel and loop bandwidth.

A QUASI‐CONSTANT ENVELOPE QUADRATURE OVERLAPPED MODULATION AND ITS PERFORMANCE OVER NON‐LINEAR BAND LIMITED SATELLITE CHANNELS

A new quadrature-overlapped modulation (QOTRC modulation) with a quasi-constant envelope is proposed in this paper. The new modulation possesses fast-decayed spectral side lobes. Bandwidth efficiency and detection efficiency of the new modulation under coherent detection over a band-limited non-linear satellite channel are studied and compared with those of MSK (a constant-envelope modulation) and SQORC (staggered quadrature-overlapped raised-cosine) modulations. The results obtained in this paper show that the new modulation can offer a satisfactory bit error rate (BER), which is comparable to or even better than that of MSK and much better than that of SQORC (a previously reported quadrature-overlapped modulation), depending on the signal-to-noise ratios (SNRs) and system bandwidth.

A QUASI-CONSTANT ENVELOPE QUADRATURE OVERLAPPED MODULATION AND ITS PERFORMANCE OVER NON-LINEAR BAND LIMITED SATELLITE CHANNELS

A new quadrature-overlapped modulation (QOTRC modulation) with a quasi-constant envelope is proposed in this paper. The new modulation possesses fast-decayed spectral side lobes. Bandwidth efficiency and detection efficiency of the new modulation under coherent detection over a band-limited non-linear satellite channel are studied and compared with those of MSK (a constant-envelope modulation) and SQORC (staggered quadrature-overlapped raised-cosine) modulations. The results obtained in this paper show that the new modulation can offer a satisfactory bit error rate (BER), which is comparable to or even better than that of MSK and much better than that of SQORC (a previously reported quadrature-overlapped modulation), depending on the signal-to-noise ratios (SNRs) and system bandwidth.

LTPSK: simple, bandwidth efficient modulation for multi-rate satellite channels

A constant envelope modulation called linear-transition phase shift keying (LTPSK) is examined as a candidate for use as a bandwidth and power efficient modulation on nonlinear satellite channels. This modulation is similar to differential phase shift keying (DPSK), but with phase transitions realized as a linear phase ramp between symbols to decrease spectral occupancy without introducing amplitude variation. The ratio of phase-transition time to symbol duration is referred to as the LTPSK mode. Spectral occupancy and BER performance with differential detection vary between that of DPSK and differential minimum shift keying (MSK), depending on the mode selected. By making the LTPSK mode proportional to the data rate, a simple LTPSK modulator and differential demodulator can support multiple data rates without the need for a bank of filters. The highest rate supported has the lowest ratio of spectral occupancy to data rate, and spectral occupancy is approximately constant for all rates, allowing efficient spectrum allocation with fixed frequency assignments. >

Analysis and design of an all-digital demodulator for trellis coded 16-QAM transmission over a nonlinear satellite channel

Although providing high spectral efficiency, sixteen-level quadrature amplitude modulation (16-QAM) is customarily considered a power-inefficient transmission technique for satellite communication systems, due to the considerable output back-off (OBO) of the optimum operating point of the nonlinear amplifier. The authors present a technique for the compensation of nonlinear distortions in the received signal constellation in an all-digital demodulator for rate-3/4 16-state trellis coded (TC) 16-QAM. They show that, by simple modifications to the metric computer in the Viterbi decoder, the optimum operating point of the amplifier can be moved much closer to saturation than in the conventional case, without any need for on-board amplifier linearization. The simulation results demonstrate a BER of 10/sup -5/ with a power saving of roughly 3.5 dB in a typical nonlinear channel, when compared to conventional uncoded 8-PSK. This figure includes all of the impairments produced by increased satellite amplifier OBO and by the presence of the subsystems for symbol timing recovery, carrier phase estimation and automatic gain control. >

Four-dimensional signaling for bandlimited channels

In this paper we discuss multidimensional signaling for transmission over the satellite channel, i.e., a bandlimited radio channel with nonlinearities. We derive a set of basis signals that are orthogonal and whose bandwidth occupancy is minimal, in the sense that they maximize the power inside a fixed frequency interval (/spl minus/B, B). Since we remove the assumption that the signals be confined in one symbol interval, the concept of orthogonality must be revisited. We design basis signals that satisfy the following requirements: (a) When passed through their matched filter, the sample sequence has no intersymbol interference; (b) when passed through the filter matched to another basis signal, the sample sequence has no interchannel interference, and (c) their bandwidth occupancy is minimum. The performance of four-dimensional signals designed according to this criterion is evaluated in terms of bandwidth occupancy and error probability over nonlinear satellite channels. Comparisons with two-dimensional modulation schemes (in particular QPSK) are also made. >

Trellis coded Q2PSK signals. I. AWGN and nonlinear satellite channels

Suitable bandwidth efficient coding techniques, to be combined with Q2PSK signals, are derived and analysed on AWGN and nonlinear channels. Five new Q2PSK TCs are presented. First, an expanded Q2PSK signal constellation has been used to design new 4D RI Q2PSK TCs. Partition of the 4D expanded Q2PSK signal space into 2D subspaces has allowed the utilisation of any 8-PSK TC to be implemented along Q2PSK signals. This novel division of the Q2PSK signal space has been utilised to implement double 8-PSK TCs designed by Ungerboeck and double convolutional codes over ring modulo-8 along Q2PSK signals. Finally, an unexpanded Q2PSK signal has been considered to implement and design 2/4 and 3/4 rate Q2PSK trellis codes. Performance evaluation of coded and uncoded Q2PSK signals on nonlinear satellite channels is reported, and the results obtained from computer simulations of coded and uncoded Q2PSK on nonlinear channels are presented, where different amplifier working situations have been considered.

Digital data transmission over nonlinear satellite channels

The M-ary PSK system over nonlinear satellite channels, in the presence of an arbitrary number of interferers and additive Gaussian noise on the uplink and downlink paths, is investigated. The effect of intersymbol interference due to the transmitter filter is also included. The bit error probabilities are obtained using the Gauss quadrature formula and a two-dimensional moment technique.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Spread SCPC/FDMA, spread TDMA/FDMA and SSMA/FDMA transmission through A non-linear satellite channel with an earth-station off-axis emission constraint

This paper analyses and compares possible access schemes to be used in satellite networks with a large number of small earth-stations. Basically, frequency division (FDMA), time division (TDMA), and spread spectrum multiple access (SSMA) are considered. For TDMA, one single carrier originated in one particular earth-station is transmitted in each sub-band and therefore a single-channel-per-carrier system results (SCPC/FDMA). For TDMA and SSMA, it is assumed that groups of earth-stations using either of these access schemes share the full available band in FDMA. The corresponding systems are thus TDMA/FDMA and SSMA/FDMA. Moreover, for SCPC/FDMA and TDMA/FDMA individual carriers may be spread to the extent that the available bandwidth is always fully occupied. Spectral efficiencies for these three access modes (Spread SCPC/FDMA, Spread TDMA/FDMA and SSMA/FDMA) are computed and compared for transmission through a non-linear satellite channel and optimum operating points for the non-linear amplifier are also determined. Comparisons are also performed for the situation in which transmitting earth-stations are bounded to obey an off-axis emission constraint.

Performance off 8-PSK trellis codes over nonlinear fading mobile satellite channels

In this paper a new analytical bound for large effective code length codes (ECL) is derived. The accuracy of the analytical bounds is validated by simulation. Based on the new bound a trellis code design procedure for fading channels is defined. A quasi-analytical technique for BER estimation on nonlinear channels is proposed. This method is used to estimate the performance degradation of nonlinear communication systems with the pilot tone.

Performance evaluation of pragmatic TCM codes through band-limited nonlinear satellite channel. a computer simulation approach

Most early communication satellite systems are power-limited; as improvements are made on launch vehicles and satellites become larger, the tendency has shifted from powerlimited to bandwidth-limited systems. In bandlimited nonlinear satellite applications, various papers have shown that respectable coding gains can be achieved by Ungerboeck TCM (trellis code modulation) codes, making them popular in this application owing to the advantage of performance improvement without bandwidth increase or transmitter power increase, and with the codes displaying their robustness to the nonlinearity and band-limiting that prevail in satellite channels. A recent paper by Viterbi proposed pragmatic codes which have a single coder and decoder for various bandwidth efficiencies and achieve a performance comparable to that of Ungerboeck codes on a linear Gaussian channel. These codes are punctured versions of the basic 1/2 rate convolutional code mapped into MPSK signal phase constellation. In this paper, the performance on band-limited nonlinear satellite channel of pragmatic 8PSK codes is studied with respect to equivalent Ungerboeck 8PSK codes. Computer simulation is used to estimate the coding gains achieved on these various codes, and lower bounds for bit error probability are estimated through formulas approximated by Forney. Signal space diagrams are also plotted to show the band-limiting effect, giving a better picture of the signal point dispersion phenomenon caused by severe band-limitation of the satellite channel.