Free-space laser communications systems experience fading due to quasi-static pointing error and tracking error that impairs communications performance. Under a block fading model we show that using forward error correcting codes and interleaving - a simple non-mechanical data processing technique - much of the harmful effect of tracking error on communications performance can be removed. Using the concepts of fading capacity and outage capacity, we provide analytical tools that quantify the effects of fading on communications performance with and without interleaving. A link budget based on this analysis includes three loss terms due to pointing and tracking error: 1) static loss, which is primarily a function of pointing error; 2) capacity loss, which is the power difference between fading capacity and fade-free capacity; and 3) finite interleaver loss, which is the power difference between the probability of outage curve and fading capacity. Assuming pulse-position modulation and a Poisson channel, we derive closed-form solutions for the probability of outage of interleaved systems using a Gaussian beam with circularly symmetric Gaussian tracking error.
[1]
Mohamed-Slim Alouini,et al.
Exponential-type bounds on the generalized Marcum Q-function with application to error probability analysis over fading channels
,
2000,
IEEE Trans. Commun..
[2]
Jon Hamkins,et al.
Deep-Space Optical Communications Downlink Budget: Modulation and Coding
,
2003
.
[3]
Shlomo Shamai,et al.
Information theoretic considerations for cellular mobile radio
,
1994
.
[4]
Carl W. Helstrom,et al.
Computing the generalized Marcum Q-function
,
1992,
IEEE Trans. Inf. Theory.
[5]
Chintha Tellambura,et al.
Cauchy-Schwarz bound on the generalized Marcum Q-function with applications
,
2001,
Wirel. Commun. Mob. Comput..
[6]
David Tse,et al.
Fundamentals of Wireless Communication
,
2005
.
[7]
Stephen S. Rappaport,et al.
Computing approximations for the generalized Q function and its complement (Corresp.)
,
1971,
IEEE Trans. Inf. Theory.