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Satellite Communications at Ka-Band and Above

The growing satellite communications market makes it more and more difficult to assign frequency resources in the commonly used frequency bands at 4/6 GHz and 11/14 GHz. Thus, frequency bands above 20 GHz are of increasing interest for future satellite communication links. In these bands, however, ice, clouds and rain can drastically reduce the received power level requiring appropriate system design and fade countermeasures.

Fade countermeasures such as the implementation of a static fade margin would be a waste of resources in Ka-band and above. This stimulates the development and application of more advanced fade mitigation techniques such as adaptive resource sharing, adaptive coding and modulation, adaptive data rate switching and adaptive beamforming. Since adaptive fade mitigation techniques are too complex to be optimised be paper work only, computer simulations are required for testing and optimisation. These simulations in turn require a rain fading channel model, i.e. a time-series generator, providing attenuation time-series whose statistics should be very similar to those of measured data. 
Such a rain fading channel simulator has been developed at DLR, Institute for Communications and Navigation. It outputs signal attenuation in dB as a function of time. The channel simulator is based on a 2nd order Markov chain whose transition probabilities can be derived from Gaussian distributions. A detailed descirption of the channel model can be found in
The channel model developed at DLR can be adjusted to different scenarios. This is done be extracting specific channel model parameters (SCMPs) from recorded data (at least 6 months of data should be available). SCMPs are available from the DLR measurement campaign carried out at Oberpfaffenhofen near Munich, Germany, in the years 1994 till 1997 with the 40 GHz beacon of the Italian satellite ITALSAT. In order to model seasonal and diurnal variations, SCMPs have been identified for the 4 seasons and for 4 day-time intervals ranging form 0:00 - 6:00 till 18:00 - 24:00.

Below a prototype of the channel model can be downloaded as MATLAB program. During the initialisation of the programm the following can be chosen: Station (type dlr or other in lower case letters), period (spring, summer, fall, and winter also in lower case letters), and number of days to be simulated (at least 10).

The channel simulator generates a time-series of attenuation (can also be extracted from the source code after line 108) and three figures:
(a) time-series of attenuation for the first 10 days,
(b) cumulative distribution of attenuation,
(c) probability to be in a fade exceeding the duration given at the abscissa and exceeding a fading depth given as parameter.

For downloading the MATLAB program, version 1.0, klick here.

Please note that due to the fact that the programme generates 1st and 2nd order statitics in parallel to the synthetic attenuation time-series, the programme runs considerably slower than it would be when only a time-series would be generated. To obtain statistically significant data, the simulation should run at least over 100 days.

In case of any questions please contact

Dr. Uwe-Carsten Fiebig, Tel.: +49 8153 282835, Email: uwe.fiebig@dlr.de

For further information of the DLR propagation measurement campaign with ITALSAT, click here.