Comparison of different modulation schemes
(Theoretical W and S/N values at 106 BER; calculated values may
differ slightly due to different assumptions)
System
|
Variants
|
W
(dB)
|
S/N
(dB)
|
Nyquist
bandwidth
(bn)
|
|
Basic modulation schemes
|
FSK
|
2-state FSK with discriminator detection
3-state FSK (duo-binary)
4-state FSK
|
13.4
15.9
20.1
|
13.4
15.9
23.1
|
B
B
B/2
|
PSK
|
2-state PSK with coherent detection
4-state PSK with coherent detection
8-state PSK with coherent detection
16-state PSK with coherent detection
|
10.5
10.5
14.0
18.4
|
10.5
13.5
18.8
24.4
|
B
B/2
B/3
B/4
|
QAM
|
16-QAM with coherent detection
32-QAM with coherent detection
64-QAM with coherent detection
128-QAM with coherent detection
256-QAM with coherent detection
512-QAM with coherent detection
|
17.0
18.9
22.5
24.3
27.8
28.9
|
20.5
23.5
26.5
29.5
32.6
35.5
|
B/4
B/5
B/6
B/7
B/8
B/9
|
QPR
|
9-QPR with coherent detection
25-QPR with coherent detection
49-QPR with coherent detection
|
13.5
16.0
17.5
|
16.5
20.8
23.5
|
B/2
B/3
B/4
|
|
Basic modulation schemes with forward error correction
|
QAM
with block
codes(1)
|
16-QAM with coherent detection
32-QAM with coherent detection
64-QAM with coherent detection
128-QAM with coherent detection
256-QAM with coherent detection
512-QAM with coherent detection
|
13.9
15.6
19.4
21.1
24.7
25.8
|
17.6
20.6
23.8
26.7
29.8
32.4
|
B/4*(1 r)
B/5*(1 r)
B/6*(1 r)
B/7*(1 r)
B/8*(1 r)
B/9*(1 r)
|
QPR: quadrature partial response
(1) As an example, BCH error correction with a redundancy of 6.7% (r 6.7%) is used for calculations in this Table.
|
TABLE 1b
System
|
Variants
|
W
(dB)
|
S/N
(dB)
|
Nyquist
bandwidth
(bn)(1)
|
|
Coded modulation schemes
|
BCM(2)
|
96 BCM-4D (QAM one-step partition)
88 BCM-6D (QAM one-step partition)
16 BCM-8D (QAM one-step partition)
80 BCM-8D (QAM one-step partition)
128 BCM-8D (QAM two-step partition)
|
24.4
23.8
15.3
23.5
23.6
|
29.0
28.8
18.5
28.4
28.2
|
B/6
B/6
B/3,75
B/6
B/6
|
TCM(3)
|
16 TCM-2D
32 TCM-2D
128 TCM-2D
512 TCM-2D
64 TCM-4D
128 TCM-4D
512 TCM-4D
|
12.1
13.9
19.0
23.8
18.3
20.0
24.8
|
14.3
17.6
23.6
29.8
21.9
24.9
31.1
|
B/3
B/4
B/6
B/8
B/5.5
B/6.5
B/8.5
|
MLCM(4)
|
32 MLCM
64 MLCM
128 MLCM
|
14.1
18.1
19.6
|
18.3
21.7
24.5
|
B/4.5
B/5.5
B/6.5
|
QPR
with
AZD
|
9-QPR with coherent detection
25-QPR with coherent detection
49-QPR with coherent detection
|
11.5
14.0
15.5
|
14.5
18.8
21.5
|
B/2
B/3
B/4
|
BCM: block coded modulation
TCM: trellis coded modulation
MLCM: multi-level coded modulation
AZD: ambiguity zone detection
(1) The bit rate B does not include code redundancy.
(2) The block code length is half the number of the BCM signal dimensions.
(3) The performances depend upon the implemented decoding algorithm. In this example, an optimum decoder is used.
(4) In this example convolutional code is used for the lower two levels and block codes are used for the third level to give overall redundancies as for those of TCM-4D. Specifically, the redundancies are 3/2, 8/7 on the two convolutional coded levels and 24/23 on the block coded third level.
|
The actual signal-to-noise parameter is related to the average received signal level (RSL), for the relevant BER BER*, through the noise figure (NF) of the receiver and the bit rate relationship:
(4)
where:
k : Boltzmann constant
T : absolute temperature of the receiver (K).
Whilst the above mentioned signal-to-noise ratio (S/N) is useful for the comparison of different modulation methods, the real signal-to-noise ratio (allowing for all imperfections) needs to be considered in order to define real systems, specifically:
– S/N corresponding to the BER at which the severely errored seconds (SES) objective is defined by the relevant Recommendations on performance objectives;
– S/N corresponding to the BER at which the RBER objective is defined by the relevant Recommendations on performance objectives and that is needed to meet the errored seconds (ES) or errored blocks (EB) objectives.
The Nyquist bandwidth (bn) occupied by the modulated signal can also be used in comparing various modulation schemes. However this does not generally indicate the radio-frequency channel bandwidth that in practice must be allotted to a digitally modulated signal. This channel bandwidth is, in principle, a trade-off between the choice of modulation, inter-channel interference and network constraints and, in practice, is provided by the relevant ITU-R Recommendation on radio-frequency channel arrangements. It is expected to vary in the range 1.2 bn to 2 bn for various systems, except in the case of QPR which can transmit in a bandwidth equal to that of the Nyquist bandwidth (1 bn).
NOTE 1 – In coded modulation methods using a multi-state modulation format, redundant bits are inserted increasing the bit rate by a factor:
where z is a factor depending on the adopted coded modulation (z < 1).
In the meantime, the number of states are increased from 2n (that should have been used for uncoded modulation) to 2n1.
In this way, the actual symbol rate (bn) transmitted (related to the band occupancy) will become:
APPENDIX 2
TO ANNEX 1
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