1、 Report ITU-R S.2150(09/2009)An interference reduction technique by adaptive-array earth station antennas for sharing between the fixed-satellite service and fixed/mobile services S SeriesFixed-satellite serviceRep. ITU-R S.2150 ii Foreword The role of the Radiocommunication Sector is to ensure the
2、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 functions of the Rad
3、iocommunication 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 referenced in Annex
4、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-R patent inf
5、ormation 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 (television) F Fi
6、xed 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 service system
7、s 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, without written pe
8、rmission of ITU. Rep. ITU-R S.2150 1REPORT ITU-R S.2150 An interference reduction technique by adaptive-array earth station antennas for sharing between the fixed-satellite service and fixed/mobile services (2009) Scope This Report describes an interference reduction technique using adaptive-array e
9、arth station antennas for sharing between the FSS and fixed/mobile services. This technique may be used to improve FSS link performance when sharing the same frequency band with other services. The Report contains the theoretical analysis and field test results as well as observations to provide gui
10、delines for the system design when employing the interference reduction technique. TABLE OF CONTENTS Page 1 Introduction 2 2 Overview of interference reduction technique using adaptive-array antennas . 3 3 Theoretical analysis on the performance of interference reduction . 4 4 Implementation of prot
11、otype interference reduction system 6 5 Field trials . 8 5.1 Overview of field trials . 8 5.2 Measurement of delay profiles . 11 5.3 Performance of interference reduction technique . 12 6 Summary . 17 7 Conclusion 20 7.1 Comparison with other interference reduction techniques . 20 7.2 Practicability
12、 of the interference reduction technique presented in this Report . 20 Rep. ITU-R S.2150 21 Introduction As one of the possible measures to improve link performance of the fixed-satellite service (FSS) systems, an interference reduction technique by adaptive-array antenna would be considered. In thi
13、s technique, as shown in Fig. 1, interference signals from stations of fixed/mobile services (i.e. base/fixed stations or mobile stations) are reduced at a FSS earth station antenna by digitally processing signals received at a main earth station antenna (denoted as “main antenna” hereafter) and sub
14、-antennas aligned around the main antenna. Each sub-antenna has the directivity in the horizontal plane and covers a part of the direction that interference signals arrive. FIGURE 1 Overall concept for interference reduction Report 2150-01Interferences from base/fixed stationsDesired signals in FSSd
15、own link (easily affectedby interferences)Earth stationantennaInterference signals frommobile stationsSub antennasIn this Report, the overview of interference reduction technique using adaptive-array antennas is presented firstly. Next, the theoretical analysis and implementation of prototype interf
16、erence reduction is discussed. Subsequently, test results of field trials conducted in a satellite teleport are presented. Finally, consideration of test results and system design guidelines are provided. It should be noted that this Report addresses only the technical aspects of the presented inter
17、ference reduction technique. As with any technology or interference reduction technique, there will be tradeoffs associated with balancing the complexity and cost of implementing the technique with the benefit derived from its implementation. Analysis of such tradeoffs is beyond the scope of this Re
18、port as such tradeoffs will be unique to every situation. The reader is advised that cost/benefit considerations are very important and should be carefully weighed when considering the possible implementation of such technologies. Rep. ITU-R S.2150 32 Overview of interference reduction technique usi
19、ng adaptive-array antennas Figure 2 depicts the principle of the interference reduction technique using adaptive-array antennas. A number of sub-antennas (N sub-antennas) are aligned around the main antenna. The number of interferers is assumed to be M in this case. At the main antenna, the interfer
20、ing signals (J01(t) to J0M(t): either from mobile stations or base/ fixed stations) are received in addition to the desired signal from a satellite s(t). The signal received at the main antenna, x0(t), is expressed by: )()()()(0010tJtJtstxM+= (1) At the sub-antennas (No. 1 to No. N), only the interf
21、ering signals are received and no desired signal is received since the antenna gain of sub-antennas towards the satellite is too low to sense the very weak signal from the satellite. As a result, the signal received at the k-th sub-antenna xk(t) is expressed by: )()()(1tJtJtxkMkk+= (2) Aggregated si
22、gnals received at the main and sub-antennas (= x0(t) + x1(t) + . + xN(t) are digitally processed by the “interference signal processor” (ISP) in Fig. 2. FIGURE 2 Principle of the interference reduction technique Report 2150-02D/CDesired signalInterferer No. 1Main antennaSub antenna No. 1Interference
23、signal processorDesiredsignal afterinterferencecancelledxout()tWeight calculationx0()tD/CLNAD/CLNASub antenna No. Nx1()tW1xN()tWNJMN()tJM1()tJ11()tJ1N()tJ0N()tJ01()ts()tInterferer No. MLNA: Low noise amplifierD/C: Down converterLNARep. ITU-R S.2150 4Consequently, the following signal is produced as
24、a desired signal after interference reduction: =+=Nkkkouttxwtxtx10)()()( (3) where wkis a weighting factor (or “weight”), that is adaptively computed by the interference signal processor, to multiply to the received signal at the k-th sub-antenna in order to minimize interference signals. 3 Theoreti
25、cal analysis on the performance of interference reduction Figure 3 shows a simple model to estimate the performance of interference reduction. By the principle of interference reduction technique, the system noise of the main antenna (i.e. the path for the desired signal) increases due to the additi
26、onal noise incurred by the sub-antenna even though the operation of “correlation” (or calculation of weight) in Fig. 3 is ideal. The residual noise after the interference reduction (i.e. the increment noise as to the original system thermal noise without interferences), r, is expressed by: 2211NINIr
27、 = (4) where I1, N1and S1represent the received levels of the interference signal, system thermal noise(excluding the interference) and desired signal at the main antenna and I2and N2represent those at the sub-antennas. The value r is regarded as a theoretical limit of the interference reduction tec
28、hnique in terms of incremental noise. FIGURE 3 Estimation of interference reduction performance Report 2150-03LNA1S0CorrelationMain antennaSub antennaOUTG0S1I1N1LNA2I2N2G1G2I0Table 1 shows an example set of parameters. Assuming that the propagation loss from the interferer to the main antenna is equ
29、ivalent to that to the sub-antenna, I1/I2is proportional to the ratio of antenna gain between the main and sub-antenna in the direction of the interference arrival Rep. ITU-R S.2150 5(i.e. G1/G2). N1/N2is proportional to the ratio of system noise between the main and sub-antennas. For receiving the
30、benefit of interference reduction, it is necessary to keep the value of G1/G2as small as possible. TABLE 1 Example parameters Category Item Value Note Interfering Frequency 3 900 MHz Note 1 signal Bandwidth 20 MHz Transmit e.i.r.p. No. 1 46 dBm For base stations Transmit e.i.r.p. No. 2 30 dBm For mo
31、bile stations Main antenna Antenna gain 10 dBi 48 (Ref. Recommendation ITU-R S.465) System noise temperature 100 K Sub-antenna Antenna gain 8 dBi System noise temperature 400 K NOTE 1 The purpose of 4 GHz band in Table 1 is to align the field trial described in 5 of this Report and the applicability
32、 of the technique is not limited to particular frequency bands. From the parameters shown in Table 1, the value of r is calculated as 12 dB, which corresponds to approximately 6% increase of the system noise floor of received FSS downlink. In this case, the G1/G2is 18 dB. Note that further improveme
33、nt could be expected since the antenna gain of the main antenna in the side-lobe region is typically better than 10 dBi in many cases. However, by the nature of interference reduction technique, it would be difficult to cancel the interference arriving from boresite direction of the main antenna. Fi
34、gure 4A/4B shows the relation between the distance to interferer and the I/N value and received level at the main antenna based on the parameters in Table 1. It is assumed that the interferer is either a mobile station or a base/ fixed station (single entry). Theoretically, the interference signal c
35、ould be cancelled with the residual noise determined by equation (4) above left. The difference between the input I/N (before interface reduction) and the residual I/N (after interface reduction) is defined as the “reduction gain” as illustrated in Fig. 4A. Naturally, the smaller the distance to int
36、erferer (or the larger received interference signal level), the larger the required reduction gain. For instance, it is seen from Fig. 4A that more than 40 dB reduction gain is required when the distance to interfering base station is within 2 000 m. The required reduction gain would have an influen
37、ce on the design of the interference signal processor (e.g. the number of bits in computation to determine the dynamic range and so forth). Furthermore, the maximum received level shown in Fig. 4B would be important in the system design to ensure the front-end LNA (Low noise amplifier) of the main a
38、ntenna is not saturated. Typically, the maximum permissible level at the LNA input is around 65 dBm in aggregation. Operational scenarios (distance to interferers and transmit power of interferer) should be determined taking into account these elements. Rep. ITU-R S.2150 6FIGURE 4A Relation between
39、distance to interferer and I/N at the main antenna Report 2150-04aDistance (m)Transmit of base stationTransmit of mobile stationResidual interference0 4 000 6 000 8 000 10 000 12 0002 00010.020.030.040.050.060.010.010.020.0IN/ atthemain antenna(dB)ReductiongainReductiongainFIGURE 4B Relation between
40、 distance to interferer and received level at the main antenna Report 2150-04bDistance (m)Transmit of base stationTransmit of mobile station0 4 000 6 000 8 000 10 0002 00090.070.060.050.0100.0110.0Receivedlevel(dBm)12 00080.04 Implementation of prototype interference reduction system In order to ver
41、ify the performance of interference reduction technique, the prototype interference reduction system is developed. The prototype system has the basic configuration shown in Fig. 2. The general diagram of the “interference signal processor” part is shown in Fig. 5. The signals from the main antenna a
42、nd sub-antennas (No. 1 to No. N) are fed into the processor for calculation of Rep. ITU-R S.2150 7weight values by systolic array. Delay taps (shown as boxes “D” in Fig. 5) are useful to correct relative delays between the main and sub-antennas since the path length from the interferer to the main a
43、ntenna differs from that to the sub-antennas in general. By nature, the performance of interference reduction would be degraded in presence of the above-mentioned relative delays. It should be noted that the computation amount by systolic array is proportional to the square of the number of input si
44、gnals. In Fig. 5, it is approximately proportional to the square of N*(1 + Nd) where Nd represents the number of delay taps for each sub-antenna. FIGURE 5 General diagram of interference signal processor Report 2150-05Input from themain antennaInput from thesub antenna No. 1Input from thesub antenna
45、 No. NDesired signalafter interferencecancellationDelay tapsDDDDDDDDDDSystolic array (calculation of weighting factor)Delay tapsIn implementing the prototype system, it is important to understand the nature of the desired and interfering signals as identified below: the received power of interfering
46、 signals can be much larger than that of the desired signal both at the main antenna and sub-antennas. At sub-antennas, the desired signal is not received or negligibly small; relative delays in the arrival time of interference signals between the main and sub-antennas may exist; due to motion of in
47、terferers and multipath fading effect, the received interference signals may vary quite rapidly; simultaneous interferences from multiple interferers may be present. Taking into account the above, two types of platform are adopted for the prototype system to evaluate the trade-off of key design elem
48、ents of interference signal processor as listed in Table 2. Rep. ITU-R S.2150 8TABLE 2 Platform of prototype interference reduction system Item Type-1 Type-2 Algorithm DCMP/RLS(1)DCMP/RLS(1)Device for computation CPU (DSP)/ Floating point computation FPGA/ Fixed point computation A/D converters cloc
49、k 120 MHz 120 MHz Update cycle of weights 270 s 8.33 ns No. of sub-antennas 10 7 Delay taps YES (6 delay taps for each sub-antenna) NO (delay fixed) (1)DCMP: Directional-constrained minimization of power, RLS: Recursive least square. Type-1 systems employ the DSP (Digital signal processor) for computation. Since the floating-point computation is used in this type, the results of calculation (i.e. weight values) are more accurate (less computational error). On the other hand, Type-2 systems employ FPGA (Field programmable gate arrays) for t
