Page 26 - ITU Journal: Volume 2, No. 1 - Special issue - Propagation modelling for advanced future radio systems - Challenges for a congested radio spectrum
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ITU Journal: ICT Discoveries, Vol. 2(1), December 2019



          3.   DATA ANALYSIS                                   of  the  noise  contribution  must  yet  be  carefully
                                                               addressed  due  to  CNR  variations  along  the  time;
          The raw experimental data is loaded together and     however, its contribution to the variance is small.
          preprocessed  by  a  dedicated  tool  to  perform  the
          preprocessing  [2].  This  step  aims  to  check  the   4.   RESULTS AND ANALYSIS
          quality of the data and to derive the attenuation by
          using  the  measured  copolar  levels  and  the      The  scintillation  is  usually  characterized  by  the
          estimated copolar levels that would be observed in   distribution  of  the  amplitude,    (dB),  or  by  the
          the absence of attenuation. All preprocessed time    standard deviation,  , computed in 1-minute time
                                                                                   
          series are stored in a single daily file.            windows. This last one is often calculated only for
          For the scintillation analysis, first, the preprocessed   dry periods, therefore, the periods with attenuation
          data files are loaded and the scintillation time series   larger than 0.5 dB at Ka-band and 1 dB at Q-band
          is  obtained  by  using  a  high  pass  filter,  based  on   were excluded from the statistical calculations. The
          raised  cosine  with  a  0.025  Hz  cut-off  frequency.   annual  and  monthly  statistics  here  presented
          Then, the wet refractivity,           , is calculated using   correspond  to  a  full  year,  from  June  2017  to
          the  temperature,  T(ºC),  relative  humidity,  H(%),   May 2018.
          and  pressure,  P(hPa),  all  integrated  with  a  10   4.1  Meteorological dependencies
          minutes integration time, according to [3]:
                                                               The  joint  distributions  of  the  hourly  averaged
                     = 72        + 3.75  10 5         (1)      scintillation standard deviation and meteorological
                        
                             +273           (  +273) 2
                                                               parameters were calculated.
          The water vapor pressure,   (hPa), is related with H   Fig.  1  presents  the  Q-band  scintillation  standard
          by                                                   deviation  versus  the  atmospheric  pressure.  The
                              =            (hPa)     (2)       higher  the  pressure  the  lower  the  scintillation
                               100                             variance.  High  pressure  means  usually  clear  sky,
          The  water  vapor  saturation  pressure,    ,  can  be   dry  and  stable  weather:  conditions  that  are  not
                                                  
          calculated from the temperature and the pressure     prone to atmospheric instability. As we can see the
          but the equations also found at [3], are omitted here   higher  the  scintillation  standard  deviation  is,  the
          for brevity.                                         more  sensitive  to  the  pressure.  The  scintillation
                                                               variance  is  higher  than  the  minimum  expected
          The  scintillation  variance  is  calculated  in  one-  value  due  to  measurement  noise  (see  Section  3),
          minute non-overlapping time windows. Finally, the    therefore, a residual scintillation is always present.
          scintillation  time  series  and  the  processed     The hourly correlation between the two-time series
          meteorological  data  are  stored  in  a  new  file.   is already not negligible. A similar plot is obtained
          Statistical  data  on  scintillation  parameters  is   for the Ka-band.
          derived  by  dedicated  tools  that  have  been
          developed in MATLAB.
          It must be pointed out that, due to the finite        ,
                                                        0
          the  Gaussian  noise  introduces  a  bias  on  the
          scintillation variance, given by [4]:

                                      −10       10 (      )
                  2
                   = 75.44  10 −      10      (dB )   (3)
                                                 2
                    
          where    = 8 Hz  is  the  sampling  bandwidth.  The
                   
          calculations,  using  the  values  in  Table  1,  gives
          respectively, 1.0E-3 and 3.0E-3 dB  for the Q and Ka
                                          2
          bands.
          The  measured  variance,  σ 2  ,  is  related  to  the
                                      
          atmospheric  induced  variance,  σ 2  ,  by  the
                                                  
          equation:

                               =            +     (dB )   (4)     Fig. 1 – Joint histogram (in log. units) of the scintillation
                                      2
                              2
                        2
                                           2
                                       
          The  variance  (or  standard  deviation)  presented    standard deviation at Q-band vs atmospheric pressure; the
                                                                              contours are log spaced
          throughout the paper, is σ . The accurate removal
                                  2
                                     
          10                                    © International Telecommunication Union, 2019
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