**FINAL REPORT ON EMWIN TESTING AT WALLOPS CDAS**

**September 6 to 14, 2006**

**Prepared by**

**Peter Woolner**

**Mitretek Systems**

**September 28, 2006**

**SUMMARY**

The tests described in this report were performed over the period
September 6 to 14, 2006 at the Wallops CDA Station by Philip Whaley of
NOAA/WCDAS, Dana Irvin of Avtec Systems, and Peter Woolner of Mitretek
Systems. The tests were performed using the same basic Avtec receive
software and IF Adapter as was used for similar tests in February and
November, 2005, but using a modified tracking loop subroutine to
maintain carrier lock when the RF front end downconverter local
oscillator drifted in frequency. The transmit equipment used was that
intended for operation when GOES-13 is put into service.

The test results show the prototype EMWIN-N system performance through
the GOES-N (now GOES-13) satellite transponder will be satisfactory with
an operating margin of about 5.5 dB for a receiver using a 1 meter
antenna. "Satisfactory" performance is defined as an average of one lost
frame per hour, or better. This is equal to about 1 frame missing or
with uncorrectable errors in ten thousand.

The EMWIN-N data distribution concept is considered to be successfully
proved and it is recommended NWS and NESDIS prepare to implement it when
GOES-13 becomes available for normal operations.

**TEST DESCRIPTION**

All tests were performed with the equipment configured as shown in
figure 1 below.

The tests used the same procedure that was used for the back-to-back
tests in February and November 2005, except the modulated signal was
routed through the EMWIN transponder on the GOES-13 satellite and the
data stream was provided by the NWS through a 19.2 kbps terrestrial
link. This data stream was input to the Avtec transmitter, consisting of
an Avtec PTP and a Comtech Data Modem CDM-550. The PTP removed the start
and stop bits from the data stream and inserted the Attached Sync Marker
and frame header bits. The Forward Error Correction (FEC) coding used
was a rate ½ Convolutional inner code concatenated with a RS (255,223)
outer code.

The modulator part of the CDM-550 used Offset Quadrature Phase Shift
Keyed modulation and the output was shaped to meet the requirements of
IESS 308e, figures 7 and 8, using a 6^th^ order Butterworth bandpass
filter to shape the incoming pulses. This produced an RF data rate of
35.94 kbps and an occupied bandwidth of 27.0 kHz. The modulator
frequency was set to 74.700 MHz and fed into a standard GOES transmit
system which translated it to an RF frequency of 2034.700 MHz and
amplified it to an uplink EIRP level of 76 dBmi.

The satellite transponder translates the EMWIN signal to 1692.700 MHz,
which was received with a 1.8 meter dish and downconverted to 139.200
MHz and fed into the test system as shown in figure 1. The level into
the Avtec receiver was set at -60 dBm and the noise generator output
level was adjusted as necessary to provide the desired E~B~/N~0~ values.
All measurements of C/N~0~ were made on the spectrum analyzer.

![](media/image1.wmf){width="6.020833333333333in"
height="3.6145833333333335in"}**Figure 1. Block Diagram of Test
Configuration**

For all tests, the frame sync parameters were set to Search Threshold =
0, Lock Threshold = 8, Check Frames = 0, and Flywheel Frames = 4.

At the start of each test the C/N~0~ was measured for an unmodulated
carrier using a spectrum analyzer with internal averaging set at 100.
The offset for the N~0~ part of the measurement was chosen at the
frequency that produced the lowest noise, but less than 20 kHz removed
from the EMWIN carrier, to keep this measurement within the transponder
bandwidth. The C/N~0~ was also measured at the end of each FER test and
averaged with the start value to provide the reference for that test.
The E~B~/N~0~ values were then calculated as:

E~B~/N~0~ = C/N~0~ -- 10\*LOG(15400) = C/N~0~ -- 41.9 dB/Hz

After each C/N~0~ start measurement, the modulation was reapplied and
the receiver was fully locked and receive frames were observed being
counted. The registers were zeroed and the test was allowed to run for a
pre-determined period of time. The numbers of frames transmitted and
received were recorded, plus the numbers of frames that are
uncorrectable by the RS code, Viterbi sync errors, frames missing, and
data frame sequence errors. This last item was used as a rough indicator
of the number of separate error events that had occurred.

The count of missing frames included the uncorrectable frames, as well
as those frames that were missed because the Attached Sync Marker could
not be correctly identified. Since either event will result in a frame
that is omitted from the data passed to the user, it was the total
number of missing frames that was recorded and used to derive the FER.
The FER was calculated by dividing the total number of missing frames by
the total number of transmitted frames. Frames transmitted count was
derived from the receiver monitor values by subtracting from the
received frames count the number of fill frames (if any) then adding the
total number of missing frames minus the uncorrectable frames.

For some of the tests it was found that only data frames were missing.
In these cases it was not necessary to subtract the number of fill
frames received from the total number of frames received.

The timing of the start of each test was controlled by manually setting
the receive monitor parameters to zero, after the system had shown it
was in lock. Each test was ended by freezing the receive monitor display
at the pre-determined time and capturing the values of the parameters
described above. They are shown in the table below.

**TEST RESULTS**

The following table shows the results of the tests of September 6 to 14,
2006, arranged basically in order of increasing E~B~/N~0~. Test numbers
not shown were omitted due to set up errors.

  ------ --------- ------------- ---------- ------------- --------- ----------
  Test   Eb/No     Total Frames  Sequence   Missing or    GOES-13   \~Errors
  Nbr    (dB/Hz)   Transmitted   Errors     Error Frames  FER       per Event

  8      4.20      7417          18         111           1.5E-02   6.17

  7      4.85      7370          12         44            6.0E-03   3.67

  6      5.00      7369          17         68            9.2E-03   4.00

  5      5.45      14170         15         26            1.8E-03   1.73

  9      5.60      15862         6          7             4.4E-4    1.17

  10     5.90      99936         24         101           1.0E-3    4.21

  14     6.70      56628         4          5             8.8E-5    1.25

  15     6.65      121062        3          3             2.5E-05   1.00

  11     8.00      31094         2          2             6.4E-05   1.00
  ------ --------- ------------- ---------- ------------- --------- ----------

The following chart is a plot of these results for E~B~/N~0~ versus FER,
plus the results from the previous back-to-back tests.

![](media/image2.wmf){width="5.999305555555556in"
height="4.064583333333333in"}**Chart 1. Frame Error Rate Test Results**

**DISCUSSION OF TEST RESULTS**

1.  When considered as an overall data set, the total of all the points
    shown in this chart is considered to be very strong evidence that
    the true performance curve for the prototype EMWIN system lies
    between the two dashed green lines.

2.  The data point at an E~B~/N~0~ of 8.0 dB is considered
    out-of-family. The other eight data points are all considered
    in-family, although the variation of these points was greater than
    expected.

3.  The greater than expected variation is attributed to changes in the
    absolute noise level that probably occurred during the relatively
    long intervals between the C/N~0~ measurements. Measurement that
    could have confirmed or refuted this postulate would have greatly
    extended the duration of the tests, so they were not made.

4.  Compared to the back-to-back measurements made previously, the
    measurements made through the satellite transponder have a noise
    level that is set by the ambient conditions outside of the
    controlled operations room. Any variations that are outside of the
    normal (or Gaussian) noise distribution are sources of error that
    will degrade the accuracy of this data set. Even when caused by
    natural phenomenon, they are a cause of inaccuracy unless they are
    incorporated in some way into the C/N~0~ measurements. This is one
    of the reasons why additional operating margin is recommended for
    links using a large amount of error correction coding.

5.  The worst case dashed green line is shown crossing the FER line of
    10^-4^ at E~B~/N~0~ value of 7.0 dB/Hz. The FER of 10^-4^ is
    approximately equal to an average of one frame missing or with
    uncorrectable errors per hour.

6.  The link calculations provided in appendix A show that this receive
    system performance results in a margin of 5.5 dB, which is much more
    than the recommended 2 dB minimum margin.

7.  This large operating margin could provide other possible commercial
    vendors of EMWIN receive systems with the potential to trade some of
    this margin for lower cost, simpler operation, greater robustness,
    etc.

**Overall Assessment:**

The prototype system has successfully proved the concept and processes
of the 19.2 kbps EMWIN-N data distribution system and shown that
excellent operating margin is available for receivers using a 1 meter
diameter antenna.

**Recommendation:**

NWS and NESDIS should accept the EMWIN-N data distribution system and
proceed with the implementation and transition to operation as soon as
the GOES-13 satellite is available.

**APPENDIX A. LINK CALCULATIONS**

  ---------------- ------------------------------------------- ------------- -----------
  **EMWIN-N LINK                                                             
  CALCULATIONS FOR                                                           
  GOES-13 PLT**                                                              

  **Ground Uplink                                              **Units**     **Value**
  Transmitter**                                                              

                   Uplink Frequency                            MHz           2034.70

  Transmit EIRP                                                dBmi          76.7

  Antenna Pointing                                             dB            0.5
  Loss                                                                       

  **Earth - To -                                                              
  Space**                                                                    

                   Path Distance (for 5 deg elevation)         km            41127

  Free Space Loss                                              dB            190.9

  Atmospheric                                                  dB            0.4
  Attenuation                                                                

  **S/C Receive                                                               
  Performance**                                                              

  Polarization                                                 dB            0.2
  Loss                                                                       

  U/L Incident                                                 dBmi          -115.3
  Power                                                                      

                   Antenna Gain (from 5 deg elevation)         dBi           14.8

  G/T (incl cable                                              dB/K          -14.2
  losses)                                                                    

  Boltzmann                                                    dBm/Hz/K      -198.6
  constant                                                                   

  Uplink Thermal                                               dB/Hz         69.1
  C/No                                                                       

  **S/C Transmit                                                              
  Performance**                                                              

                   Downlink Frequency                          MHz           1692.70

  Transmit EIRP                                                dBmi          46.2
  (to 5 deg                                                                  
  elevation)                                                                 

  **Space - To -                                                              
  Earth**                                                                    

                   Path Distance (for 5 deg elevation)         km            41127

  Free Space Loss                                              dB            189.3

  Atmospheric                                                  dB            0.4
  Attenuation                                                                

  **Ground                                                                    
  Downlink                                                                   
  Receiver**                                                                 

  Downlink                                                     dBmi          -143.5
  Incident Power                                                             

                   Pwr Flux Density Rqmt (EOC in 4 kHz)        dBW/m2        -154

                   Power Flux Density (EOC in 4 kHz)           dBW/m2        -155.9

  E/S G/T                                                      dB/K          -0.3

  Polarization                                                 dB            0.2
  Loss                                                                       

  Boltzmann                                                    dBm/Hz/K      -198.6
  constant                                                                   

  Downlink Thermal                                             dB/Hz         54.6
  C/No                                                                       

  **Eb/No Overall                                                             
  Calculation**                                                              

  Overall                                                      dB/Hz         54.4
  Composite C/No                                                             

  Uncoded Data                                                 dB-Hz         41.9
  Rate (15514 bps)                                                           
  in dB                                                                      

  Eb/No Calculated                                             dB            12.5

  **Required Eb/No                                                            
  Adjustments**                                                              

                   Required BER                                              1E-06

  Theoretical                                                  dB            10.6
  Eb/No with no                                                              
  coding                                                                     

  Theoretical                                                  dB            8.0
  coding gain                                                                

  Theoretical                                                  dB            2.6
  Eb/No with FEC                                                             
  coding                                                                     

  Ground Segment                                               dB            1.9
  Implementation                                                             
  Loss                                                                       

  Satellite                                                    dB            2.5
  Segment                                                                    
  Degradations                                                               

  Required Eb/No                                               dB            7.0

  **Eb/No MARGIN**                                             **dB**        **5.5**
  ---------------- ------------------------------------------- ------------- -----------