Subcarrier Phase-shift Keying Research Articles

Performance analytics of adaptive subcarrier intensity modulated free-space optical communications over general Málaga turbulence links

In this paper, we study the performance analysis of free-space optical (FSO) system employing a constant-power variable-rate adaptive subcarrier intensity modulation (SIM) and utilizing phase-shift keying (PSK) over the Málaga atmospheric turbulence with pointing errors. According to a target bit-error rate (BER) and the instantaneous signal-to-noise ratio (SNR), the adaptive strategy adopts the subcarrier PSK modulation order. More precisely, we develop new analytical expressions for the average BER, the upper bound on ergodic channel capacity for non-adaptive modulation, and the attainable spectral efficiency (SE) of an adaptive SIM-FSO communication system. According to the simulation results, it is possible to achieve an increase in SE under weak-to-strong turbulence conditions without the need to increase the average optical power transmitted or compromise the BER requirements.

Adaptive subcarrier intensity modulation for free space optical communication

Increased capacity demands and radio frequency (RF) congestion impacts on current communication networks have brought greater attention to free-space optical (FSO) communication as a viable augmentation technology for terrestrial, aerial, and space-based communication infrastructure. As a complementary alternative to RF communication systems, FSO can support high link bandwidths and provide high data security without RF spectral constraints. The performance of FSO links, however, can be significantly impacted by receive power variation caused by propagation and scattering losses along with losses due to atmospheric turbulence. Depending on the FSO application, these loss mechanisms can dynamically change, impacting link performance at different time scales. We investigate subcarrier phase-shift keying (PSK) and quadrature amplitude modulation (QAM) intensity modulation that can be adapted to dynamically changing link conditions to optimize bandwidth utilization. Using custom subcarrier intensity modulation (SIM) modems, the performance of binary PSK (BPSK), QPSK, 8PSK, 16APSK, and 16-QAM waveforms is reported. The impact of adaptive equalization is also characterized, and the initial performance of a subcarrier multiplexed system is presented. This work represents the first experimental evaluation of SIM waveforms using a laboratory scintillation playback system based on scintillation recorded over real-world propagation paths.

SIMO subcarrier PSK FSO links with phase noise and non‐zero boresight pointing errors over turbulence channels

Terrestrial free-space optical (FSO) communication systems with subcarrier intensity modulation have experienced a particular research attention in the recent past. However, their performance strongly degrades in the presence of atmospheric turbulence, pointing errors, and phase noise impairments. In order to overcome these limitations, the authors consider a receiver diversity scheme of a typical subcarrier phase-shift keying (PSK) system and investigate the performance by means of the average symbol error probability (ASEP). They assume a wide range of turbulence conditions, non-zero boresight pointing errors, and phase noise strengths described through the gamma-gamma, Beckmann, and Tikhonov distributions, respectively. Novel approximate ASEP expressions are derived for single-input single-output and single-input multiple-output (SIMO) configurations. Appropriate numerical results are depicted and validated by Monte Carlo simulations.

Performance of Subcarrier PSK Systems Using PSAM Maximum Likelihood Estimation in Turbulence Channels

A pilot-symbol assisted subcarrier phase-shift keying (PSK) free-space optical communication system is studied with maximum likelihood (ML) phase estimation. Using the phase error probability density function of ML estimation phase error, we study the error rate performance of the subcarrier PSK system with carrier phase error in lognormal and Gamma–Gamma turbulence channels. The closed-form expressions are derived for the asymptotic signal-to-noise ratio (SNR) performance loss for the imperfectly synchronized systems over turbulence channels, and the analytical expressions are verified with numerical results. These expressions reveal how the subcarrier PSK systems with ML estimated phase error are influenced by the pilot length and the modulation order in large SNR regimes.

Subcarrier Phase-Shift Keying Systems With Phase Errors in Lognormal Turbulence Channels

We study the bit-error rate performance of different subcarrier phase-shift keying systems with carrier phase errors (CPE) in lognormal turbulence channels where the CPE is modeled as a Tikhonov random variable. The CPE induced asymptotic noise reference losses for the studied systems are quantified analytically by introducing the lognormal-Nakagami fading as an auxiliary channel model. The auxiliary channel method used in this study can be potentially applied to other performance analysis problems involving the lognormal channels.

Subcarrier Intensity Modulated MIMO Optical Communications in Atmospheric Turbulence

We investigate spatial diversity techniques for subcarrier phase-shift keying (PSK)-modulated optical wireless communication links over the Gamma–Gamma channels. Both repetition code and the Alamouti-type orthogonal space–time block code (OSTBC) are considered. Highly accurate series error rate expressions are derived by using a moment generating function approach with a series expansion of the modified Bessel function. Truncation error analyses and asymptotic error rate analyses are also presented. Our asymptotic analyses show that the diversity order of the studied system depends only on the effective number of small-scale cells of the scattering process in the atmosphere. Our performance analyses confirm that the repetition code outperforms OSTBC for subcarrier PSK-based systems over the Gamma–Gamma channels. The asymptotic performance loss of the Alamouti-coded system with respect to the repetition-coded system is also quantified analytically.

Adaptive Subcarrier PSK Intensity Modulation in Free Space Optical Systems

We propose an adaptive transmission technique for free space optical (FSO) systems, operating in atmospheric turbulence and employing subcarrier phase shift keying (S-PSK) intensity modulation. Exploiting the constant envelope characteristics of S-PSK, the proposed technique offers efficient utilization of the FSO channel capacity by adapting the modulation order of S-PSK, according to the instantaneous state of turbulence induced fading and a pre-defined bit error rate (BER) requirement. Novel expressions for the spectral efficiency and average BER of the proposed adaptive FSO system are presented and performance investigations under various turbulence conditions, turbulence models, and target BER requirements are carried out. Numerical results indicate that significant spectral efficiency gains are offered without increasing the transmitted average optical power or sacrificing BER requirements, especially in moderate-to-strong turbulence conditions. Furthermore, the proposed variable rate transmission technique is applied to multiple input multiple output (MIMO) FSO systems, providing additional improvement in the achieved spectral efficiency as the number of the transmit and/or receive apertures increases.

Optical Communication Using Subcarrier PSK Intensity Modulation Through Atmospheric Turbulence Channels

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper studies optical communications using subcarrier phase shift keying (PSK) intensity modulation through atmospheric turbulence channels. The bit error rate (BER) is derived for optical communication systems employing either on/off key (OOK) or subcarrier PSK intensity modulation. It is shown that at <formula formulatype="inline"><tex>${\hbox{BER}} =10^{-6}$</tex></formula> and a scintillation level of <formula formulatype="inline"><tex>$\sigma = 0.1$</tex></formula>, an optical communication system employing subcarrier BPSK is 3 dB better than a comparable system using fixed-threshold OOK. When <formula formulatype="inline"><tex> $\sigma =0.2$</tex></formula>, an optical communication system employing subcarrier BPSK achieves a <formula formulatype="inline"><tex>${\hbox{BER}} = 10^{-6}$</tex></formula> at <formula formulatype="inline"><tex> ${\hbox{SNR}} = 13.7$</tex></formula> dB, while the BER of a comparable system employing OOK can never be less than <formula formulatype="inline"><tex>$10^{-4}$</tex></formula>. Convolutional codes are discussed for optical communication through atmospheric turbulence channels. Interleaving is employed to overcome memory effect in atmospheric turbulence channels. An upper bound on BER is derived for optical communication systems employing convolutional codes and subcarrier BPSK modulation. </para>