Table of Contents
Advertisement
CDM-750 Advanced High-Speed Trunking Modem
Forward Error Correction
10.2.1
Range of Data Rates
For the range of Data Rates, refer to
10.2.2
BER, QEF, Eb/No, Es/No Spectral Efficiency, and Occupied Bandwidth
Depending upon the operating mode, the DVB standard uses different modes of specifying
performance with a modem in IF Loop and Additive White Gaussian Noise (AWGN):
•
DVB-S (QPSK with Viterbi and Reed Solomon): BER = 2x10
Reed Solomon) and QEF after Reed Solomon at the specified Eb/No and includes a modem
implementation loss of 0.8 dB and the noise bandwidth increase due to the outer code
(10log 188/204 = 0,36 dB).
•
DVB-S2 standard: "Quasi Error Free" (QEF) is defined as "less than one uncorrected
error-event per transmission hour at the level of a 5 Mbit/s single TV service decoder",
approximately corresponding to a Transport Stream Packet Error Ratio equal to a
PER<10
size data.
•
Es/No vs. Eb/No: The DVB-S2 standard commonly refers to the use of Es/No instead of
Eb/No. When links operate at a constant symbol rate this is a good method for comparing
the performance of different modulation types and code rates.
The relation between the two quantities is given by:
•
Occupied Bandwidth: Occupied bandwidth is defined as the bandwidth between -10 dB
points of the power spectral density, which are approximately:
Occupied Bandwidth = 1.19
* Taken at the -10 dB points on the plot of power spectral density, the occupied bandwidth is 1.19 x Symbol
Rate for 35%, and 1.15 x Symbol Rate for 25%.
Figure 10-1 through Figure 10-4 illustrate the guaranteed error performance characteristics of
the CDM-750 while running with Normal frames (64,800 bits), Pilots ON. QPSK 1/4, 1/3, 2/5 are
shown for information only and are not available in the CDM-750.
Sect. 1.4 SUMMARY OF SPECIFICATIONS
-7
before demultiplexer. A packet is defined as block of 188 byte MPEG frame
Eb/No = Es/No – 10log(Spectral Efficiency)
Symbol Rate, for 35% Rolloff
x
= 1.15
x
= 1.12 x Symbol Rate, for 20% Rolloff
Symbol Rate, for 25% Rolloff
10–2
Revision 1
MN-CDM750
.
-4
after Viterbi (before
Advertisement
Table of Contents
