Rec. Itu-r bo. 1696




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Rec. ITU-R BO.1696

RECOMMENDATION ITU R BO.1696

Methodologies for determining the availability performance for digital multiprogramme broadcasting-satellite service systems, and their
associated feeder links operating in the planned bands

(Question ITU R 3/6)

(2005)

Scope


This Recommendation proposes methodologies for determining performance objectives for digital systems in the 11.7-12.7 GHz, and sets availability objectives for digital systems that are higher than those for analogue systems. Annex 1 to this Recommendation provides example implementations of the recommended methodologies, as well as exact and approximate solutions.
The ITU Radiocommunication Assembly,

considering

a) that digital multiprogramme systems are now in use in the broadcasting-satellite service (BSS);

b) that the performance of digital multiprogramme systems is important to administrations implementing such systems;

c) that the system availability performance provides an important reference point for evaluating the relative performance of an administration’s BSS assignment, should that assignment be implemented with a digital multiprogramme system;

d) that the reception characteristics of a digital multiprogramme system are significantly different from the reception characteristics of an analogue FM system;

e) that the existing Appendices 30 and 30A of the Radio Regulations performance objective of maintaining a C/N ratio equal to or better than 14 dB for 99% of the worst month is based on analogue FM transmission;

f) that, because of these factors, it is desirable to develop an availability performance objective specifically for digital multiprogramme systems;

g) that a methodology to determine availability performance for digital multiprogramme BSS systems must recognize the wide range of threshold C/N ratios at which these various systems operate;

h) that the development of a digital multiprogramme performance objective is not only useful for the planned BSS band, but also for other BSS bands, for example, the 17/21 GHz band,

further considering

a) that the performance of digital multiprogramme systems can be characterized by evaluating the system availability corresponding to the quasi-error-free (QEF) point1, which corresponds to high-picture quality reception,



recognizing

a) that although many operational digital multiprogramme BSS links have QEF link availability better than 99.5% of the worst month (or about 99.86% of an average year for most rain zones), the required availability is determined by specific system performance objectives;

b) that Recommendation ITU R BO.1516 – Digital multiprogramme television systems for use by satellites operating in the 11/12 GHz frequency range recommends, among other things, that one of the four transmission systems described in Annex 1 of that Recommendation be selected when implementing digital multiprogramme television services via satellite;

c) that Recommendation ITU R BO.1516 shows that the QEF C/N ratio values for these systems is spread over a wide range of values, and that trade-offs among primary digital link parameters can be used to meet performance objectives,



recommends

1 that administrations should use the methodologies provided in Annex 1 to this Recommendation to determine the system availability performance for digital multiprogramme BSS systems, and their associated feeder links, operating in the planned bands;

2 that digital multiprogramme systems should provide, as guidance, QEF performance for at least X% of the worst month;

3 that when implementing digital multiprogramme systems, a target C/N value of (minimum C/N + Z) dB should be maintained within the service area or coverage area for at least X% of the worst month. As guidance, 99.5% can be taken for the default value of X. The values of the minimum C/N are defined in Table 1 (also described in Table 2 of Recommendation ITU R BO.1516). The value Z is the additional degradation margin2.


TABLE 1

Minimum C/N for QEF operation (dB) (quoted from Table 2 of Recommendation ITU R BO.1516)

Modulation and coding

System A

System B

System C

System D

Modulation modes supported individually and on the same carrier

QPSK

QPSK

QPSK

8-PSK, QPSK, and BPSK

Performance requirement C/N (dB)

C/N for QEF(1)

C/N for QEF(2)

C/N for QEF(3)

C/N for QEF(4)

Modes Inner code













BPSK Conv.

1/2

Not used

Not used

No

0.2

QPSK Conv.

5/11

Not used

Not used

2.8/3.0

Not used

1/2

4.1

3.8

3.3/3.5

3.2

3/5

No

Not used

4.5/4.7

Not used

2/3

5.8

5

5.1/5.3

4.9

3/4

6.8

Not used

6.0/6.2

5.9

4/5

Not used

Not used

6.6/6.8

Not used

5/6

7.8

Not used

7.0/7.2

6.8

6/7

Not used

7.6

Not used

Not used

7/8

8.4

Not used

7.7/7.9

7.4

8-PSK Trellis

Not used

Not used

Not used

8.4

(1) At a BER < 10–10. The C/N values for System A refer to computer simulation results achieved on a hypothetical satellite chain, including input multiplex (IMUX), travelling wave tube amplifier (TWTA) and output multiplex (OMUX), with modulation roll-off of 0.35. They are based on the assumption of soft decision Viterbi decoding in the receiver. A bandwidth to symbol rate ratio of 1.28 has been adopted. The figures for C/N include a calculated degradation of 0.2 dB due to bandwidth limitations on IMUX and OMUX filters, 0.8 dB non-linear distortion on TWTA at saturation and 0.8 dB modem degradation. The figures apply to BER  2 × 10–4 before RS (204,188), which corresponds to QEF at the RS coder output. Degradation due to interference is not taken into account.

(2) At a BER of 1 × 10–12.

(3) Theoretical QPSK (2-bit per symbol) Es /N0, i.e. C/N as measured in Nyquist bandwidth (baud rate/2) for normal and truncated spectral shaping, respectively. Does not include hardware implementation margin or satellite transponder loss margin. Two values correspond to System C normal and truncated transmit spectral shaping, respectively.

(4) These values were derived from computer simulations and regarded as theoretical values. The values apply to BER  2 × 10–4 before RS (204,188) and using the Nyquist bandwidth. Does not include hardware implementation margin or satellite transponder loss margin.



Annex 1

Methodologies for determining the availability performance for digital


multiprogramme BSS systems, and their associated feeder links
operating in the planned bands

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