A method to achieve clear-sky data-volume download in satellite links affected by tropospheric attenuation

Abstract

SUMMARYFor data downloading from satellites, the traditional approach of considering the complementary probability distribution, P(A trop ) of the total tropospheric attenuation A trop (dB), at a frequency, polarization, and elevation angle, may be too pessimistic, and it may lead to large overdesign. If the data volume downloaded in a given observation time T obs (a day, a week, a month, etc.), with a constant probability of symbol error, is more valuable than the instantaneous symbol, or bit rate (as it may be the case in Earth resources observation or in other services that allow long delays in communicating data), another approach can avoid overdesign, namely the various adaptive coding and modulation techniques. We study a particular time integral of A trop (t): (i) to define the average efficiency of a radio channel faded by the troposphere and (ii) to design a method that can theoretically achieve the same volume of data downloaded in clear-sky conditions (no troposphere), even if the radio link is faded by the troposphere. The average efficiency and its bounds can be calculated from the complementary probability distribution of A trop (t). We explicitly apply the theory to radio links faded by rain, by using the experimental rain-attenuation time series measured with satellite ITALSAT in a 37.8°slant path, at 18.7, 39.6, and 49.5 GHz at Spino d'Adda (Italy), and to those simulated with the synthetic storm technique. Based on the average efficiency, we define the method that can achieve in T obs , theoretically, the same data volume as in clear sky, directly applicable to quadrature phase-shift keying, multiple phase-shift keying, and Shannon capacity theorem. The method requires a fixed increase in power margin, and bandwidth, compared with clear-sky conditions, and delivers an average symbol rate equal to the maximum symbol rate obtainable when A trop (t) = 0. The method can also be used in terrestrial links at any frequency. We compare its theoretical performance with the traditional adaptive coding and modulation techniques and show that, even theoretically, these techniques cannot achieve unitary efficiency as, on the contrary, the novel method can do. Real-time satellite communications at frequencies above 10 GHz are characterized with the long-term probability distribution, P(A trop ), of total tropospheric attenuation A trop (dB) (a combination of attenuation due to rain, hail, snow, mist, water vapor, clouds, and oxygen), at a frequency, polarization, and elevation angle. This P(A trop ) refers to an average year, or to a shorter observation period, T obs , for example, a month, and is useful to calculate link budget and to assess link availability. The same approach holds for second-order statistics, such as fade duration and time derivative of fade (rate of change), which describe fading dynamics, especially with regard to rain attenuation, the most rapidly changing and less predictable tropospheric fade in slant paths. Fade duration statistics give information on the duration of continuous out...

A Small Power Margin and Bandwidth Expansion Allow Data Transmission During Rainfall Despite Large Attenuation: Application to GeoSurf Satellite Constellations at mm–Waves

“…delivering data with the mininum tolerated probability of symbol error. In [10], we have shown that in data channels this approach is too pessimistic and leads to large overdesign.…”

“…If the data volume downloadable during rainfall, with a constant probability of symbol error, is more valuable than the instantaneous symbol rate -e.g. in remote sensing and internet of things (IoT) using satellites -the method discussed in [10] can avoid overdesign. This method is usefull when: (a) data must be downloaded also when it is raining (e.g., because of satellite pass, or other technical or service constraints); (b) real-time communication is not strictly required.…”

“…The method is charaterized only by a single parameter, namely the mean efficiency 0 ≤ 𝜂 ≤ 1 of the link, suitably defined in [10] and recalled in Section 2. Theoretically, the method can achieve the same data volume down-loaded/up-loaded as if the link were in clear-sky conditions, and is directly applicable to QPSK, M-PSK and implements [10] Shannon's channel capacity.…”

“…In synthesis, according to the theory, a small power margin -regardless of instantaneous rain attenuation -and a small bandwidth expansion allow to deliver an average symbol rate equal to the symbol rate obtainable when 𝐴 = 0, therefore down-loading/up-loading the same data volume in the same interval, as if there were no rainfall. In [10] we have compared its theoretical performance with the Adaptive Coding and Modulation (ACM) techniques [11][12][13] and shown that, even theoretically, 2 these latter cannot achieve the maximum efficiency [14][15][16][17][18][19] as, on the contrary, the method theoretically does.…”

Performance of Micro-Scale Transmission & Reception Diversity Schemes in High Throughput Satellite Communication Networks

“…In order to increase the provided data rates in an efficient, cost-effective manner and taking into consideration the spectrum scarcity problem [5,6], next generation satellite communication systems are migrating to the Ka and Q/V bands and are expected to make extensive use of link adaptation strategies combined with multi-beam satellites and/or other relevant techniques [7][8][9][10][11][12][13][14]. Signal propagation at Ka-band frequencies and above is, nevertheless, highly affected by the various atmospheric phenomena causing degradation of the overall system performance.…”