Recommendation itu-r f. 1101 Characteristics of digital fixed wireless systems below about 17 ghz
Comparison of different modulation schemes
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ĐỒ ÁN MÔN TRUYỀN THÔNG DI ĐỘNG K2018, Ho ng Th Hu , Chuong 2 SV, Bai-4, VNU, document tailieudaihoc
| Comparison of different modulation schemes
(Theoretical W and S/N values at 106 BER; calculated values may differ slightly due to different assumptions)
TABLE 1b
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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