1、 Report ITU-R M.2175(07/2010)Simultaneous dual linear polarization transmission technique using digital cross-polarization cancellationfor MSS systemsM SeriesMobile, radiodetermination, amateurand related satellites servicesii Rep. ITU-R M.2175 Foreword The role of the Radiocommunication Sector is t
2、o ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum 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 functio
3、ns of the Radiocommunication Sector are performed by World and Regional Radiocommunication 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 referen
4、ced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements 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
5、-R patent information database can also be found. Series of ITU-R Reports (Also available online at http:/www.itu.int/publ/R-REP/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (tel
6、evision) F Fixed service M Mobile, radiodetermination, amateur and related satellite 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 s
7、ervice systems SM Spectrum management Note: This ITU-R Report was approved in English by the Study Group 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 means whatsoever, witho
8、ut written permission of ITU. Rep. ITU-R M.2175 1 REPORT ITU-R M.2175 Simultaneous dual linear polarization transmission technique using digital cross-polarization cancellation for MSS systems*(Question ITU-R 83-6/4) (2010) TABLE OF CONTENTS Page 1 Introduction 2 2 Adaptive polarization division mul
9、tiplexing technique using V/H dual linear polarization . 4 3 Channel model 6 3.1 Without multi-path components . 7 3.2 With multi-path components 7 4 Feasibility of APDM technique 8 5 Considerations on interference among systems using APDM . 11 6 Conclusion 11 *When submitting to the Radiocommunicat
10、ion Bureau a satellite network intended to be operated with the technique described in this Report, administrations need to take into account that both orthogonal polarisations have to be included in the submission, in order for them to be appropriately coordinated. 2 Rep. ITU-R M.2175 1 Introductio
11、n Mobile-satellite communication services are now being offered all over the world. In order to share the limited frequency bandwidth among many MSS systems, a perpetual requirement is to improve the spectrum utilization efficiency. For this purpose, it is important to consider how to not only share
12、 the same frequency bandwidth between different systems but also improve spectrum utilization efficiency within an MSS system. Figure 1 shows a typical MSS system that employs circular polarization. Circular polarization is mainly adopted due to its polarization-tracking-free nature, which makes it
13、suitable for mobile services. In a typical system, right-hand circular polarization or left-hand circular polarization is selected. If a single user earth station sends at the bit rate of R (bit/s) with bandwidth of W (Hz) and user earth stations A and B make use of the satellite transponder, the to
14、tal bit rate is 2R with the bandwidth of 2 W in Fig. 1. FIGURE 1 Spectrum utilization in a circular polarization system without polarization tracking Another MSS system utilizes V/H dual linear polarization. Figure 2 shows an example of spectrum utilization in a V/H dual linear polarization system.
15、Each user earth station communicates using either V or H polarization. In Fig. 2, V polarization is assigned to user earth station A and H polarization is assigned to user earth station B. Since user earth station A and user earth station B share the same frequency bandwidth with different polarizat
16、ion, polarization tracking is required at each user earth station so as to eliminate cross-polarization interference on the other user earth station. In Fig. 2, if each user earth station sends at the bit rate of R with bandwidth of W, the total bit rate, 2R, is achieved with the bandwidth of W. Use
17、r earthstation AUser earthstation BSatelliteR.H.C. pol.Freq.AWWBase stationA BPolarization tracking freePolarization tracking freePolarization tracking freeTotal bandwidth : 2W (Hz)Total bit rate : 2R (bit/s)Bandwidth = W (Hz)Bit rate = R (bit/s)Bandwidth = W (Hz)Bit rate = R (bit/s)System featuresB
18、Right-hand circular polarization : R.H.C. pol. Freq.AWFreq.WBR.H.C. pol.R.H.C. pol.Rep. ITU-R M.2175 3 FIGURE 2 Spectrum utilization in a dual V/H linear polarization system with polarization tracking Compared to dual linear polarization, circular polarization excels in terms of its polarization-tra
19、cking-free nature which yields simple user earth stations. However, linear polarization offers double the spectrum utilization efficiency; 2R/W (bit/s/Hz) compared to 2R/2W (bit/s/Hz). This means that dual linear polarization makes better use of spectrum resources than circular polarization. It is t
20、rue that dual linear polarization is attractive from the viewpoint of spectrum utilization efficiency. However, in practice, accurate polarization tracking is difficult to realize, especially for mobile user earth stations with low-profile antennas. Figure 3 shows the degradation in spectrum utiliza
21、tion efficiency that occurs when the mobile user earth station experiences polarization misalignment. As shown, to handle this misalignment, the spectrum utilization efficiency of both user earth station A and user earth station B should be reduced to hold communication quality steady in the face of
22、 cross-polarization interference between user earth stations. Figure 3 also shows one solution to the problem of mutual interference: single linear polarization. This approach does not employ polarization multiplexing and so avoids the mutual interference between user earth stations. Its weakness is
23、 that it fails to increase the spectrum utilization efficiency. User AV pol.Bit rate = R (bit/s)SatelliteUser earthstation AFreq.Satellite V pol.SatelliteH pol.ABWFreq.Base stationBUser BH pol.User earthstation BFreq.AA BWWPrecisepolarization trackingPrecise polarization tracking Total bandwidth : W
24、 (Hz)Total bit rate : 2R (bit/s)Bandwidth = W (Hz) Bandwidth = W (Hz)Bit rate = R (bit/s)System featuresPrecisepolarization tracking4 Rep. ITU-R M.2175 FIGURE 3 Degradation in spectrum utilization efficiency due to imprecise polarization tracking 2 Adaptive polarization division multiplexing techniq
25、ue using V/H dual linear polarization The adaptive polarization division multiplexing (APDM) technique realizes a polarization-tracking-free MSS system with dual V/H linear polarization transmission. This technique offers improved spectrum utilization efficiency with a simple satellite tracking ante
26、nna. Figure 4 shows the concept of APDM. Each signal is divided into two blocks and conveyed independently using V or H linear polarization. The two signals are polarization multiplexed at the antenna of each user earth station. In Fig. 4, user earth station A sends at the bit rate of R with bandwid
27、th of W. Therefore, user earth station As signal is divided into two independent blocks, A1 and A2 (each W/2), and they are polarization multiplexed in the user earth station A. The signal of user earth station B is divided into B1 and B2 (each W/2) similarly. Note that the APDM station dispenses wi
28、th polarization tracking. Therefore, the polarization states of user earth station A and user earth station B are not aligned to those of the satellite as shown in Fig. 4. Thus, cross-polarization interference occurs between A1 and A2, and between B1 and B2 in the receiver. To counter this interfere
29、nce, a digital cross-polarization interference canceller is implemented in the user earth stations receiver as shown in Fig. 5. Figure 6 shows an example of the configurations of APDM transmitter and receiver. For realizing APDM, each transmitter must have a V/H dual modulator/frequency converter wi
30、th high-power amplifier. Each receiver, on Satellite V pol.SatelliteH pol.ABWFreq.Base stationA BImprecise polarizationtracking Total bandwidth : W (Hz)Total bit rate : less than 2R (bit/s)System featuresSatellite V pol.Satellite V pol.User A V pol.User B H pol.Polarization miss-alignmentin each use
31、r earth stationCross-polarization interferenceSatellite V pol.SatelliteH pol.AWFreq.Base stationAImprecise polarizationtrackingTotal bandwidth : W (Hz)Total bit rate : R (bit/s)System featuresWithout polarization multiplexingWith polarization multiplexingCross-polarization interferenceLow rate FEC,
32、etc（Dual linear pol.)（Single linear pol.)Rep. ITU-R M.2175 5 the other hand, needs to have a V/H dual low noise amplifier/frequency converter/demodulator with interference canceller. In Fig. 6, since modulator, demodulator and interference canceller are realized by digital circuits, they can be comp
33、actly implemented as integrated circuits. The major differences from the earth stations without APDM are the additional RF components, shown by the hatching in Fig. 6, that transmit/receive V/H dual polarized signals simultaneously. This polarization division multiplexing with digital cross-polariza
34、tion interference cancellation realizes polarization-tracking-free MSS systems using V/H dual linear polarization and facilitates broadband mobile-satellite communications services by achieving better spectrum utilization efficiency. FIGURE 4 Spectrum utilization in a dual V/H linear polarization sy
35、stem with APDM technique User AV pol.W/2User AH pol.User BV pol.A1WWUser earthstation ASatelliteFreq.Freq.ASatelliteV pol.W/2SatelliteH pol.W/2Freq.ABBSystem featuresPolarization tracking freeTotal bandwidth : W (Hz)Total bit rate : 2R (bit/s)User BH pol.B1User earthstation BBase stationwith digital
36、 cross-polarization interference cancellerA1 A2 A1A2Freq.Freq.B1 B2B2W/2A1A2B1B2Polarization tracking freePolarization tracking freeBandwidth = W (Hz)Bit rate = R (bit/s) Bandwidth = W (Hz)Bit rate = R (bit/s)6 Rep. ITU-R M.2175 FIGURE 5 APDM cross-polarization interference cancellation in the recei
37、ver FIGURE 6 Configuration of APDM transmitter and receiver 3 Channel model Due to the polarization-tracking-free-nature of APDM, its transmission channel triggers mutual coupling, V to V, H to H, V to H and H to V polarizations. To determine the basic properties of these mutual couplings, we introd
38、uce which denotes the polarization rotation angle between the transmitter (Tx) and receiver (Rx) as shown in Fig. 7. By using polarization rotation angle , XPI (cross-polarization isolation) is defined as: =cossinlog20log20log20)dB(HhVvXPI where v, h and V, H denote the amplitude of the cross polari
39、zation signal and that of the desired polarization signal, respectively. Cross-pol.Digitalcross-pol.interference cancellerFreq.Received V/H signalsReceiverFreq.De-mod.Freq.A1A2A2A1Freq.Freq.W/2W/2WA1A2ASat V pol.Sat H pol.CONV. : Frequency converterLNA : Low Noise AmplifierHPA : High Power Amplifier
40、OMT : Orthogonal Mode TransducerMOD : ModulatorDEM : DemodulatorMODMODCONV.CONV.HPAHPAS/P OMTDEMDEMLNALNAP/S OMTCONV.CONV.DigitalInterferenceCanceller(a) Transmitter(b) ReceiverDataDataDigital circuitDigital circuit: Additional RF componentRep. ITU-R M.2175 7 FIGURE 7 Polarization rotation between T
41、x and Rx 3.1 Without multi-path components Figure 8 a) shows the channel model without multi-path components. This condition is typically satisfied in bands above 6/4 GHz where most earth stations employ highly directional (pencil-beam) antennas. In general, the channel model is formed as a combinat
42、ion of the propagation path condition and the polarization rotation of the antenna. In other words, it is defined by a channel matrix that is the product of the propagation matrix and the antenna matrix as shown in Fig. 8. If each earth station uses a highly directional antenna, the multi-path compo
43、nent is negligible. As a result, the channel model simply consists of the polarization rotation of the antenna. In this model, cross-polarization cancellation can be carried out without performance degradation. 3.2 With multi-path components Figure 8 b) shows the channel model with multi-path compon
44、ents. This model is typical in the bands below 6/4 GHz where many of the earth stations employ omni-directional (or broad beam) antennas. Differently from the channel model in 3.1, the broad directionality of the omni-directional antenna in each earth station means that multi-path signals as well as
45、 direct-path signals are received. For example, a multi-path component that originates from the V polarization signal is superposed on its own direct-path component. At the same time, another multi-path component from the V polarization signal is mixed with the H polarization signal. The same situat
46、ion is true for the multi-path components from the H polarization signal. The resulting propagation matrix is shown in Fig. 8 b), where A, B, C and D are environment-dependent variables. These environment-dependent variables might affect the performance of cross-polarization cancellation. hHVv8 Rep.
47、 ITU-R M.2175 FIGURE 8 Channel models of dual V/H polarization signal transmission 4 Feasibility of APDM technique To confirm the basic feasibility of cross-polarization interference cancellation technique, an APDM modem module was developed and its performance was measured. Figure 9 shows the const
48、ellation before/after cross-polarization interference cancellation. Various types of interference canceller have been studied in the wireless communications field so far. In Fig. 9, the minimum mean squared error (MMSE) algorithm is used for the canceller. As shown in Fig. 9, cross-polarization inte
49、rference can be removed by a digital cross-polarization interference canceller. FIGURE 9 Cross-polarization interference cancellation Satellite Earth stationV+H+VHSatellite Earth stationPropagation matrixVH+VHAntenna matrixcos sinsin cos 1001cos sinsin cos A BCD Multi-path component(a) Without multi-path component(b) With multi-path componentPropagation matrixAntenna matrixCross-pol.Digitalcross-pol.interference cancellerFreq.Freq.Freq.A1A2A2A1Freq.W/2W/2A1A2Constellation before interference cancellationCo
