1、 Recommendation ITU-R S.1878(12/2010)Multi-carrier based transmissiontechniques for satellite systemsS SeriesFixed-satellite servicesii Rec. ITU-R S.1878 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spect
2、rum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication
3、Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent stateme
4、nts and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also ava
5、ilable online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellit
6、e services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time signals
7、and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any mean
8、s whatsoever, without written permission of ITU. Rec. ITU-R S.1878 1 RECOMMENDATION ITU-R S.1878 Multi-carrier based transmission techniques for satellite systems (Questions ITU-R 46-3/4 and ITU-R 73-2/4) (2010) Scope For the efficient use of frequency resources and high-speed data services, multi-c
9、arrier based transmission techniques are considered as promising technologies for providing future radiocommunication services. This Recommendation presents an overview of multi-carrier based transmission techniques over satellite links, briefly giving guidance for the utilization of multi-carrier c
10、ode division multiple access (MC-CDMA) and carrier interferometry orthogonal frequency division multiplexing (CI-OFDM) schemes for satellite radiocommunication systems. The ITU Radiocommunication Assembly, considering a) that satellites in the fixed-satellite service (FSS) and mobile-satellite servi
11、ce (MSS) are simultaneously used by many earth stations at different locations; b) that multicarrier-based multiple-access schemes such as orthogonal frequency division multiplexing frequency division multiple-access (OFDM-FDMA or OFDMA), MC-CDMA and multi-frequency TDMA (MF-TDMA) have been adopted
12、or are being considered to be adopted in many terrestrial and satellite system standards for future implementation; c) that although OFDM-type systems are largely used in terrestrial networks as a means for providing good spectral and energy efficiency over frequency selective channels, OFDM has hig
13、h peak to average power ratio (PAPR), which is problematic for the high power amplifier (HPA) in the satellite; d) that there is a need for a high degree of freedom especially for bursty (i.e. non-continuous and variable rate) and high-rate packet transmissions; e) that, in order to ensure the effic
14、ient use of frequency spectrum and orbits, it may be desirable to determine the optimum multiple-access characteristics; f) that the transmission characteristics of multiple-access systems, especially multi-carrier-based multiple-access systems, may be of importance in their interaction with one ano
15、ther, noting a) that Recommendation ITU-R S.1709 specifies MF-TDMA as an inbound traffic access format for global broadband satellite systems; b) that Recommendation ITU-R BO.1130 specifies coded OFDM (COFDM) as one of transmission techniques used for satellite digital sound broadcasting services to
16、 vehicular, portable and fixed receivers in the frequency range 1 400-2 700 MHz; c) that Report ITU-R S.2173 provides background material on multi-carrier transmissions over satellite links, including basic operational principles, application scenarios and the performance of multi-carrier-based tran
17、smissions over satellite links, analysed through computer simulation, 2 Rec. ITU-R S.1878 recommends 1 that Annex 1 should be used as guidance for planning the utilization of a CI-OFDM scheme for multi-carrier satellite radiocommunication systems; 2 that Annex 2 should be used as guidance for planni
18、ng the utilization of a MC-CDMA scheme for satellite radiocommunication systems; 3 that the subject techniques may even be used in combination provided that no basic incompatibility exists among them. Annex 1 CI-OFDM transmission in satellite radiocommunication systems 1 Introduction This Annex pres
19、ents a satellite radiocommunication system that makes use of CI-OFDM transmissions and its performance when compared with satellite radiocommunication systems using single-carrier and OFDM transmissions. 2 System model OFDM is a multi-carrier technology that is used to overcome the frequency selecti
20、ve nature of terrestrial radiocommunications environments. Apart from this advantage, there are several other advantages of OFDM that could be exploited by a satellite radiocommunication system. These advantages are listed in 5.2 of Report ITU-R S.2173. However, as mentioned in Report ITU-R S.2173,
21、OFDM has high peak to average power ratio (PAPR), which is problematic for the high power amplifier (HPA) in the satellite. CI-OFDM is a type of sub-carrier scrambling technology that can be implemented for an OFDM system at the cost of an additional fast Fourier transform (FFT) module at the transm
22、itter and receiver end of a radiocommunication system, in order to reduce the PAPR of OFDM signals. The detailed operational principles of CI-OFDM are well described in 6.3 of Report ITU-R S.2173. Figure 1 shows a satellite system employing CI-OFDM transmissions. The data source passes on vector mes
23、sage-words to an encoder, whose rate is set by the adaptive coding and modulation (ACM) controller. The encoded data is then passed on to a symbol mapper, whose output is passed to a multi-carrier signal generator (MSG). The MSG is composed of two blocks for simulation purposes: an OFDM signal gener
24、ator and a CI-OFDM signal generator. Only one MSG block is used during simulation. Each MSG generates a multi-carrier symbol from a collection of N symbols; where N is the number of subcarriers used for transmission. The output of the MSG is passed on to a HPA. The HPA output is then passed on to an
25、 analogue signal up-converter (U/C) that creates an analogue signal from the digital baseband symbols at a desired carrier frequency and sends it through the channel to the satellite. Given a bent-pipe satellite, the received signal is amplified and re-transmitted. A travelling-wave-tube amplifier (
26、TWTA) is often used for satellite transponders and symbol predistortion can be used by the multi-carrier satellite system (MCSS) to Rec. ITU-R S.1878 3 linearize the output of the TWTA. Note that many modern satellites are now being manufactured with linearized TWTAs (L-TWTA)s, and that the combinat
27、ion of a symbol precoder with a TWTA is essentially a L-TWTA. The receiver receives the transmitted analogue signal corrupted by noise and other impairments, and passes it on to either a signal sampler or channel estimator. The received signal is passed on to the channel estimator if pilot signals a
28、re transmitted. The channel estimator estimates the instantaneous carrier-to-noise ratio (CNR) through the channel and selects an appropriate modulation and coding combination (MODCOD). The MODCOD selection is then relayed back to ACM controller at the transmitter and used to set the appropriate mod
29、ulation and coding to be used in demodulating and decoding the received samples. When data is received by the receiver, the signals are passed on to the signal sampler, which creates a set of samples, sampled at the Nyquist rate, for the multi-carrier processing unit (MPU). The MPU is composed of tw
30、o modules for simulation: an OFDM processing unit and a CI-OFDM processing unit. The receiver uses the MPU module corresponding to the MSG module used by the transmitter. Each MPU produces a set of N symbol samples from a multi-carrier symbol sample. The MPU output is then passed on to a symbol dema
31、pper. The symbol demapper uses the average received constellations of each modulation and their respective error vector magnitudes to create hard- or soft-estimates for each transmitted bit, which are passed on to the decoder. The decoder outputs a decision on the transmitted data and passes it on t
32、o the data sink. FIGURE 1 Simulation block diagram of MCSS employing CI-OFDM transmissions U/C HPAD/CLNAData sourceEncoderSymbolmapperOFDMSig. genCI-OFDMSig. genAdaptative coding andmodulation controllerSignalsamplerOFDMProc. unitCI-OFDMProc. unitSignaldemapperChannelestimatorData sink DecoderMultic
33、arrier signalprocessingAdaptative coding andmodulation demodulatorMulticarrier signalgeneratorAdaptative codingand modulationMODCOD from receiverMODCOD to transmitterL-TWTA4 Rec. ITU-R S.1878 3 Performance results of CI-OFDM in a non-linear satellite channel Simulation results presented in this sect
34、ion are obtained using the system model described in 2 of this Annex. The DVB-S2 ACM scheme1is used by the system model with 100 belief propagation algorithm decoding iterations2. The baseband symbols are oversampled by a factor of 4 in order to obtain a proper representation of the modulated signal
35、 and 64 subcarriers are used to generate the multi-carrier symbols. The L-TWTA is that described in 10.3.1 of Report ITU-R S.2173. Channel and noise estimation and feedback from the receiver to transmitter are assumed to be error-free. The fairest way to evaluate the performance of a PAPR mitigation
36、 technique is by measuring the total degradation (TD) in packet error rate (PER) performance between a system with an ideal linear amplifier3 henceforth referred to as a linear amplifier and the system under study4, taking into account the degradation due to input back-off (IBO). Mathematically this
37、 is: TD (dB) = CNRnonlinear (dB) - CNRlinear (dB) + IBO dB (1) where CNRlinearand CNRnonlinearare the CNRs required to obtain a particular PER for the linear and nonlinear HPA respectively. Table 1 demonstrates the TD caused by passing a different DVB-S2 modulation through a L-TWTA, obtained at a PE
38、R of 103. Note that to properly compare the CNR of the linear HPA with the CNR of the system with L-TWTA, the equivalent CNR is: CNReq(dB) = CNR (dB)+ IBOoptdB (2) This conversion must be done to fairly compare the performance of both systems, operating at their maximal output power. The linear HPA
39、always operates at 0 dB IBO (HPA saturation), whereas the L-TWTA is not necessarily operated at saturation. Simulation results for the SCSS with L-TWTA specify that the optimal IBO5(IBOopt) at which to operate the L-TWTA is 0 dB6. For constant-envelope modulation such as M-ary PSK there is no degrad
40、ation; however the degradation for 16-APSK is negligible, while there is a noticeable degradation for 32-APSK. Table 1 demonstrates that a single-carrier satellite system (SCSS) can operate using the DVB-S2 with very little loss when compared to the theoretical system with linear amplifier. 1For mor
41、e information on DVB-S2 consult 9.2 of Report ITU-R S.2173. 2For more information on the belief propagation algorithm, please consult 7.4.4 of Report ITU-R S.2173. 3Note that an ideal linear amplifier has a linear transfer function and no saturation point. This means that the ideal linear amplifier
42、does not introduce noise due to clipping. 4The system under study could be a SCSS with nonlinear amplifier or a MCSS with or without PAPR reduction techniques. 5For more information on how to determine IBOopt, see 10.3.2 of Report ITU-R S.2173. 6This corroborates the results presented in 10.3.2 of R
43、eport ITU-R S.2173. Rec. ITU-R S.1878 5 TABLE 1 Degradation due to L-TWTA for a satellite system using various combinations of DVB-S2 MODCOD MODCOD Spectral Efficiency (bit/s/Hz) Linear Amp. L-TWTA CNReq (dB) PER = 103CNReq (dB) PER = 103TDL-TWTA(dB) QPSK 1/4 0.49 2.96 2.96 0 QPSK 2/5 0.79 0.64 0.64
44、 0 QPSK 1/2 0.99 1.13 1.13 0 QPSK 5/6 1.65 5.05 5.05 0 8-PSK 3/5 1.78 5.61 5.61 0 8-PSK 3/4 2.23 7.84 7.84 0 8-PSK 5/6 2.48 9.31 9.31 0 8-PSK 9/10 2.68 10.84 10.84 0 16-APSK 3/4 2.96 10.14 10.21 0.07 16-APSK 4/5 3.16 10.92 11.00 0.08 16-APSK 5/6 3.30 11.53 11.63 0.10 16-APSK 8/9 3.52 12.76 12.88 0.1
45、2 16-APSK 9/10 3.56 12.99 13.13 0.14 32-APSK 3/4 3.70 12.80 13.48 0.68 32-APSK 4/5 3.95 13.61 14.45 0.84 32-APSK 5/6 4.12 14.26 15.20 0.94 32-APSK 8/9 4.39 15.50 16.70 1.20 32-APSK 9/10 4.45 15.75 16.98 1.23 Table 2 demonstrates the TD performance loss for a MCSS using CI-OFDM transmissions when com
46、pared with a MCSS using OFDM transmissions. The change in TD for the MCSS systems is far more dramatic than when compared to the SCSS systems. This is because of the high PAPR of multi-carrier signals. It can also be observed that the MCSS with CI-OFDM transmissions has between 0.5 and 4.5 dB gain i
47、n terms of TD over the MCSS with OFDM transmissions depending on the MODCOD employed. Figure 2 demonstrates this behaviour by plotting TD with respect to the spectral efficiency (in bits per second per hertz (bit/s/Hz) of the DVB-S2 ACM scheme. Note that the results are presented in terms of CNReq a
48、s calculated in (2) for each MCSS system. Also note that the curves are plotted using the maximum spectral efficiency generated by all MODCODs at each CNReqfor a particular system. That is, if MODCOD x has higher spectral efficiency than MODCOD y, and MODCOD x has lower CNReqthan MODCOD y, then MODC
49、OD y is omitted from Fig. 2. MODCODs not included in Fig. 2 are underlined in Tables 1 and 2. It can be observed that the curve representing the MCSS using OFDM transmission has a much steeper ascent than the MCSS using CI-OFDM transmissions. In fact, up to a spectral efficiency of 3.6 bit/s/Hz, the MCSS with CI-OFDM transmissions has a TD less than 3 dB. This means that the MCSS with CI-OFDM transmissions could be employed for spectral efficiencies of up to 3.6 bit/s/Hz, at no more than double the required transmission power. 6 Rec. ITU-R S.1878 T
