In this paper, we present the true Cramer-Rao lower bounds (CRLBs) for estimation of phase offset common quadrature amplitude modulation (QAM), PSK, and PAM signals in AWGN channels. It is shown that same analysis also applies to QAM, FSK, CRLBs frequency estimation. The ratio modulated unmodulated derived all calculated specific cases interest. This useful determine limiting performance synchronization circuits coherent receivers without need simulate particular algorithms. hounds are...

The main drawback in communicating via the free space optical (FSO) channel is detrimental effect atmosphere has on a propagating laser beam. Atmospheric turbulence causes random fluctuations irradiance of received beam, commonly referred to as scintillation. This paper investigates use multiple lasers and apertures mitigate effects In particular, FSO multiple-input multiple-output (MIMO) with Q-ary pulse position modulation (QPPM) transmit repetition under assumption non-ideal...

We study the hybrid free-space optical (FSO) and radio-frequency (RF) channel from an information theoretic perspective. Since both links operate at vastly different carrier frequencies, we model as a pair of parallel channels. Moreover, since FSO signals higher rate than RF channel, incorporate this key feature in model. Both channels experience fading due to scintillation, which is slow compared typical signalling rates. Under framework, fundamental limits channel. In particular, analyse...

New Cramer-Rao lower bounds (CRBs) are derived for the estimation of phase offset, and frequency from a block random BPSK or QPSK symbols at low signal-to-noise (SNR) ratios. These compared to existing which apply unmodulated carrier (or known PSK symbols), performance some algorithms.

Optical data links through the atmosphere suffer from turbulence-induced signal scintillation. In a coaxially-symmetric bidirectional link scenario, variations of axial intensities at both ends are correlated. This relation can be used as an inherent feedback mechanism, with negligible delay, to enhance capacity transmission system. By experiment, we show correlation coefficient received signals reach values close one over long atmospheric distances, provided receiver apertures smaller than...

A statistical analysis of a decision-directed symbol timing algorithm for phase shift keyed modems is presented. The detector uses only one sample per period and suitable high speed which employ discrete-time synchronization methods. Expressions the detector’s mean value variance, as function offset, are derived compared to simulation results. includes effects decision errors occur at low signal-to-noise ratios eventually limit useful operating range decisiondirected modification described...

Free space optical (FSO) communication links experience different fading for longer terrestrial links, which may result in lognormal, Gamma-Gamma or exponentially distributed signals under weak, modarate and strong turbulence. Channel estimation is also corrupted by background electrical noise. In this paper, we measure the FSO distribution from experimental data collected a 1550nm, 12 km long link. Background noise statistics are found data. We consider of unknown parameters channel samples...

A large number of model probability density functions (PDFs) are used to analyze atmospheric scintillation statistics. We have analyzed data from two different experimental setups covering a range strengths determine which candidate PDFs best describe the data. The were fitted using method least squares. root-mean-squared fitting error was monitor goodness fit. results found depend strongly on strength. find that log normally modulated Rician and normal fit over encountered.

Free space optical (FSO) communication is an emerging technology which can fulfil the current demands of additional broadband channels. It offers enormous bandwidth, less expensive setup and highly secure links. But it has some potential drawbacks as well i.e. its links deteriorate significantly due to atmospheric turbulence weather conditions (fog or cloud). The detection incoming light signals in FSO communications done by photodiodes. most preferable photodiodes are photodetectors...

A novel transmission scheme for the forward link of a broadband satellite system that aims to avoid need feeder-link RF spectrum is described <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> . The hybrid uses one or more optical uplinks from hub station geostationary satellite, plus Ka band downlinks. approach retain advantages strong channel coding with high spectral efficiency, as used in recent high-speed digital video broadcast...

Narrowband satellite communications (SATCOM) in the ultra high frequency (UHF) band is an attractive option within military SATCOM (MILSATCOM) community. The UHF user terminals (UTs) are typically low cost, easily deployable and have broad beamwidths so that precise pointing to not a requirement for mobile users. At same time, some inherent disadvantages of limited bandwidth, inability apply re-use geo-stationary arc hence less capacity. multiple antenna technique, popularly referred as MIMO...

In MIMO-OFDM communications over channels subject to co-channel interference, beamforming (BF) is conventionally applied independently all subcarriers. Whilst this approach maximises mutual information, it highly computationally complex. Symbol-wise BF considerably reduces the complexity by carrying out in time domain. paper, we generalise symbol-wise take interference into account. Maximising information infeasible case and instead, propose a novel iterative algorithm that SINR before OFDM...

Up to 7 GHz of continuous bandwidth centred around 60 has been allocated worldwide for license free wireless communications. Highly attenuated due oxygen absorption and small in wavelength, this band is ideal extremely high data rate applications. These include numerous WPAN/WLAN applications such as home multimedia streaming. Traditional RF circuits used are based on expensive compound semiconductor technologies. However viable consumer applications, alternatives must be found. SiGe CMOS...

The 60 GHz band is an attractive candidate for wireless indoor communications as it offers a large amount of license free spectrum. Non-rich scattering situations, which commonly arise at due to the particular propagation conditions, result in relatively high spatial correlation. Spatial multiplexing, widely considered concept multiple-input multiple-output (MIMO) communications, can offer capacity gains if correlation low. In this paper, we demonstrate that multiplexing (SM) conjunction...

Free space optical communications through fading atmospheric channels can achieve improved throughput by using adaptive transmission techniques. This paper considers the use of symbol-rate and transmit-power methods. We an idealised model channel coding that assumes zero errors be achieved above some SNR threshold adjust rate power as varies to operate required threshold. Results are presented for two noise models appropriate non-coherent photodetection. Substantial performance gains...

In this letter, an efficient predistortion scheme is proposed to compensate imperfections in a satellite channel due the nonlinear power amplifier and output filter. The predistorter Wiener system consisting of linear components, which are trained independently. well suited systems where data bits generated onboard satellite. setup effectively compensates distortions has lower complexity compared with other strategies.

A novel extension of multiple symbol detection (MSD) non-coherent MPSK is presented in which the presence an arbitrary and unknown frequency offset considered. The resulting detector insensitive to present on received signal. near maximum-likelihood (ML), (FI-MSD) metric derived, its performance double differential (DD-MPSK) analysed by simulation. It shown that as observation length increased, approaches coherent detection. new removes need for explicit estimation removal prior detection,...

This paper presents the performance for turbo equalization of ISI caused by a nonlinear satellite channel. Mutual information transfer characteristics are used to highlight proposed and confirm convergence iterative scheme. An equivalent SNR model channel is presented which shows direct correspondence between linear channels. The equalizer based on soft interference cancellation approach has complexity with modulation order memory

Radio frequency (RF) spectrum is already too crowded for new broadband channels. Free space optical (FSO) communication an emerging technology which offers enormous bandwidth, low setup cost and highly secure link. However, FSO links may be deteriorated significantly by scintillation weather conditions (fog/cloud). Hybrid FSO-RF attractive alternate to handle the issues encountered in individual We propose a novel flexible adaptive hybrid (FAHOR) system reliable transmission under varying...

The true Cramer-Rao lower bound (CRLB) is derived and evaluated for the estimation of carrier phase Star 16-quadrature amplitude modulation (QAM) can be simply applied to frequency estimation. Different geometries are investigated by varying ring ratio (RR). For signal-to-noise ratios (SNRs) between 6-15 dB, CRLB with RR=3 than that Square 16-QAM. A modified estimator presented, which closely follows new CRLB. Investigation symbol error performance in short packet length reveals 16-QAM...

We consider least squares estimators of carrier phase and amplitude from a noisy communications signal that contains both pilot signals, known to the receiver, data unknown receiver. focus on signaling constellations have symbols evenly distributed complex unit circle, i.e., M-ary shift keying. show, under reasonably mild conditions distribution noise, estimator is strongly consistent asymptotically normally distributed. However, not consistent, but converges positive real number function...

Antennas are key components of inter-satellite links (ISLs). To achieve the necessary antenna gains with modest physical size, directional Ka or V Band antennas required that may be steered throughout duration ISL. This paper considers options for ISL on low-earth orbit satellites avoid any mechanical steering. A linear array phased feed elements is assumed, operating in conjunction a shaped reflector, allows beam to steered. Two types reflector described and promising results from geometric...

Free space optical (FSO) communication experiences severe fading due to scintillation in long-range links. Adaptive schemes based on channel variation can utilize the capacity efficiently. In this paper, we propose a truncated variable rate adaptive scheme for FSO channel. We determined improvement perfect side information (CSI) at transmitter and receiver using M-ary pulse position modulation (M-PAM) format. also an erroneous feedback one link of correlated bi-directional as transmitter....