The use of hybrid free-space optical (FSO)/radio-frequency (RF) links to provide robust, high-throughput communications, fixed infrastructure links, and their associated networks have been thoroughly investigated for both commercial and military applications. The extension of this paradigm to mobile, long-range networks has long been a desire by the military communications community for multigigabit mobile backbone networks. The FSO communications subsystem has historically been the primary limitation. The challenge has been addressing the compensation of propagation effects and dynamic range of the received optical signal. This paper will address the various technologies required to compensate for the effects referenced above. We will outline the effects FSO and RF links experience and how we overcome these degradations. Results from field experiments conducted, including those from the Air Force Research Laboratory Integrated RF/Optical Networked Tactical Targeting Networking Technologies (IRON-T2) program, will be presented.

Several expressions are derived for the probability density and cumulative distribution functions associated with the sum ofNsampled outputs of an analog cross correlator. The correlator inputs consist of deterministic signals having the same frequency with additive correlated stationary narrow-band Gaussian noise processes. Spectral symmetry of the noises is not assumed, and the noise components in each input channel have distinct variances. Wherever possible, comparisons of our results with previous work are discussed. The results derived are more general than previous work and, for the most part, functionally less complicated.

A general expression is derived for the probability density function (pdf) associated with the filtered output of an analog cross correlator, the inputs of which consist of deterministic signals having the same frequency plus correlated stationary Gaussian noise processes. The correlator is composed of input bandpass filters, a multiplier, and a zonal Iowpass filter. The noise components in each channel have distinct variances and obey no spectral symmetry condition. Using the derived expression for the pdf, the cumulative distribution function (cdf) under the same general conditions is calculated. All previous known special cases are subsequently deduced from the general expressions given here. The general results derived here are more suitable for numerical computations than comparable previous results found in the literature due to the fact that expressions here do not involve multiple infinite series. Lastly, asymptotic formulas are developed for both the pdf and cdf which may be helpful in certain calculations.

General expressions are derived for the characteristic function and probability density function of the output of a cross crrelator utilizing a hard clipper in one input channel. The inputs are assumed to beA_{1} \cos(\omega_{o}t)+n_{l}(t)andA_{2} \cos(\omega_{o}t+\phi)+n_{2}(t), wheren_{1}andn_{2}are independent narrowband Gaussian noises. From the characteristic function, which is expressed in the form of a Fourier series in the relative phase angle\phi, a double series involving cosines of multiples of\phiand Hermite polynomials of all orders is obtained as the probability density function of the output. Both the characteristic function and the density function pertain to the output at only a single instant of time. The first and second moments of the output are also calculated from the characteristic function, and lead to a closed-form expression for the output signal-to-noise ratio as a function of the input signal-to-noise ratios. Limiting cases of the output signal-to-noise ratio are computed and compared with similar cases involving the more conventional analog correlator without clippers and with the polarity-coincidence correlator.

A general expression is derived for the probability density function of the output of a cross-correlator, the inputs of which are assumed to consist of deterministic signals with a common frequency plus correlated stationary Gaussian noises. The correlator is composed of input bandpass filters, a multiplier, and postmultiplier low-pass filter. The general expression for the density function is later reduced to some special cases for comparison with previous results. Prior treatments of the problem, however, have omitted the case of correlated noise inputs except under more restrictive conditions.