Turbo-coded APSK modulations design for satellite broadband communications

Abstract

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 [1]. 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 channel capacity; 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 maximumlikelihood decoding error probability, and results are compared with computer simulations. In Ref.[2], the current analysis is complemented with the effects related to satellite nonlinear distortion effects with a band-limited transmission pulse and including demodulator timing,

Amplitude Phase Shift Keying Constellation Design and its Applications to Satellite Digital Video Broadcasting

“…In this case, we assume an (ideal) signal modulating a train of rectangular pulses, which do not create Inter-Symbol Interference (ISI) when passed through the HPA operated in the nonlinear region [De Gaudenzi et al, 2006a]. Under these conditions, the channel reduces to an Additive White Gaussian Noise (AWGN), where the modulation symbols are distorted following (2).…”

“…Thus, we are interested in finding an M-APSK constellation defined by the parameters ρ=( 1 , 2 ,…, nR ) and φ=(φ 1 ,φ 2 ,…,φ nR ) such that a given cost function f( X ) reaches a maximum. As discussed next, the cost function employed here is the mutual information of the AWGN channel [De Gaudenzi et al, 2006a;De Gaudenzi et al, 2006b;Liolis & Alagha, 2008] which, unlike the more classical optimization criterion of the minimum Euclidean distance referring to the high SNR asymptotic case, provides an optimum M-APSK constellation X for each coding www.intechopen.com…”

“…The concept of circular APSK modulation and its suitability for nonlinear channels was already proposed in 1970's [Thomas et al, 1974] but, at that time, it was concluded that APSK performs worse than PSK schemes for single carrier operation over nonlinear channel. However, based on the recent pioneering work of some of the authors reported in [De Gaudenzi et al, 2006a;De Gaudenzi et al, 2006b], this conclusion was reverted and thus APSK has become nowadays a state-of-the-art modulation scheme for advanced satellite communications. As an illustration, APSK has been recently adopted in the following commercial standards related to satellite digital video broadcasting:…”

“…The abovementioned standards have adopted the 16-and 32-APSK modulation schemes, whose constellation design has been described in [De Gaudenzi et al, 2006a;De Gaudenzi et al, 2006b]. These modulation schemes are mainly considered for professional applications where the satellite terminal sizing (i.e., antenna size and High Power Amplified (HPA)) allows for adequate Signal-to-Noise Ratio (SNR) at the receiver.…”

“…The reported results particularly in [Benedetto et al, 2005] were obtained as part of the ESA project "Modem for High Order Modulation Schemes" whose technical baseline has been recently proposed as potential standard for space telemetry related applications [CCSDS, 2007]. The APSK constellation design approaches considered in [De Gaudenzi et al, 2006a;De Gaudenzi et al, 2006b;Liolis & Alagha, 2008] follow two main optimization criteria: (i) maximization of the minimum Euclidean distance, and (ii) maximization of the channel mutual information. Unlike the former optimization criterion which refers to the high SNR asymptotic case, the latter provides an optimum M-APSK constellation for each SNR operating point.…”