1、 Rec. ITU-R M.1635 1 RECOMMENDATION ITU-R M.1635 General methodology for assessing the potential for interference between IMT-2000 or systems beyond IMT-2000 and other services (2003) Summary Consideration of the potential for interference between IMT-2000 and systems beyond IMT-2000 and other servi
2、ces is essential for administrations in planning the use of frequency bands where the mobile service exists on a co-primary basis with other services. Networks of IMT-2000 and systems beyond IMT-2000 are likely to accommodate significant numbers of cellular customers and hence networks will require
3、significant transmission capacity, involving the deployment of high-density infrastructures. This needs to be considered in analysis to assess sharing between IMT-2000 and systems beyond IMT-2000 and other services. This Recommendation provides recommendations for administrations for a methodology f
4、or assessing the potential for interference between IMT-2000 and systems beyond and other services under co-frequency as well as adjacent band conditions. The ITU Radiocommunication Assembly, considering a) that shared use of the frequency spectrum is supportive for the general objective of efficien
5、t use of the spectrum; b) that due to congestion in frequency bands suitable for broadband mobile service applications shared use of the spectrum with other services has to be considered as one possible option; c) that shared use of frequency bands by IMT-2000 and/or systems beyond IMT-2000 and othe
6、r services needs careful consideration of the coexistence conditions concerned; d) that reducing the necessary guardband to services operated in frequency bands adjacent to IMT-2000 to the greatest extent possible is a supportive measure to improve efficient use of the spectrum, recognizing a) that
7、IMT-2000 and its enhancements will continue to operate in the bands identified by the ITU at WARC-92 and WRC-2000; b) that the further development of systems beyond IMT-2000 may require spectrum in addition to that now identified for IMT-2000; 2 Rec. ITU-R M.1635 c) that the suitable frequency range
8、s for systems beyond IMT-2000 that support broadband wide area full mobility services may be, among others, the ones that are not far away from the existing frequency bands identified for IMT-2000; d) that the additional spectrum is requested especially in densely populated regions; e) that Recommen
9、dation ITU-R M.1461 provides a methodology for conducting sharing studies between the radiodetermination service and other services, recommends 1 that the procedures in Annex 1 be used for assessing the potential for interference between IMT-2000 and systems beyond IMT-2000 and systems in other serv
10、ices under co-frequency as well as adjacent band conditions taking into account other relevant ITU-R Recommendations on the subject of interference assessment concerning the services under consideration. Annex 1 General methodology for assessing the potential for interference between IMT-2000 or sys
11、tems beyond IMT-2000 and other services 1 Introduction Consideration of potential for interference between IMT-2000 and systems beyond IMT-2000 and other services is essential for administrations in planning the use of frequency bands where the mobile service exists on a co-primary basis with other
12、services or in adjacent frequency bands. This Annex describes the principles of a compatibility assessment methodology in order to perform sharing studies between the mobile service and other services in co-frequency and adjacent band scenarios. This methodology covers worst-case considerations as w
13、ell as a more representative approach, in order to get a full picture of the interference scenarios under consideration. Parts of the assessment procedures need to be based on a statistical methodology, well known as the Monte Carlo technique. The results may be focused on the cumulative distributio
14、ns of I/N or C/I at the receivers of the applications concerned, in order to demonstrate the probability of interference. The equations in this Annex describe a general calculation methodology. The units for the parameters in the equations must be consistent when they are applied to a specific study
15、. 2 Interference assessment methodology In order to perform sharing studies between mobile services and other services in co-frequency and adjacent band scenarios, simulation models need to be applied analysing the different parts of the interference path: transmitter, receiver, antennas, propagatio
16、n. Rec. ITU-R M.1635 3 On the other hand, it is necessary to operate with assumptions concerning future mature deployments of the mobile networks and applications in other services, in the phase before rolling out these networks. This allows at an early stage to achieve results which are as realisti
17、c as possible. Since interference scenarios between various applications may be analysed using this methodology, the concept of calculating the power spectral density at a victim receiver should be applied. This allows consideration of all kinds of modulation and bandwidth combinations, as well as t
18、he various requirements concerning the tolerable interference levels. The methodologies to model the different parts of the interference path should be based on ITU-R Recommendations to the extent possible. 2.1 Interference level at victim receiver 2.1.1 Assessing the power spectral density at a vic
19、tim receiver The power spectral density of an interfering signal at a victim receiver is a key element of the interference calculation process. Due to the large variety of interference spectra and receivers to be considered in assessing the potential of interference between the mobile service and ot
20、her services in co-frequency sharing as well as adjacent frequency band consideration, the concept of power spectral density calculation gives the most flexible approach. All kinds of combinations of frequency spectra and receiver selectivity may be applied in order to assess the potential for inter
21、ference between systems in the mobile service and other services. Thus the method for calculation of the interference power spectral density at the input of a victim receiver is the essential part in any compatibility assessment. The receiving power density spectrum at a victim receiver can be obtai
22、ned from the following algorithm: ),()()()()()(),(pfLRRfSPMGGfPpfPbRxTxRxRxTxTxRx= (1) where: PRx( f, p) : interfering power density spectrum at receiver PTx( f ) : transmitter output power spectral density GTx() : gain of the transmitting antenna in the direction of the receiver GRx() : gain of the
23、 receiving antenna in the direction of the transmitter PMRx() : polarization mismatch factor of receiving antenna S( f ) : selectivity of receiver RTx: feeder loss of transmitting antenna Rx: feeder loss of receiving antenna Lb( f, p) : attenuation due to propagation effects f : frequency p : percen
24、tage of time : angle between the transmitting antenna boresight and the receiving antenna : angle between receiving antenna boresight and the transmitting antenna 4 Rec. ITU-R M.1635 with the isolation between transmitter and receiver: ),()()()()(pfLRRPMGGpIbRxTxRxRxTxS= (2) where: IS ( p) : isolati
25、on between transmitter and receiver and the power spectrum at the output of the transmitter: )()( fMPfPETx out= (3) where: PTx( f ) : transmitter output power spectral density Pout: transmitter power output level ME ( f ) : modulation envelope of the transmitter output. The interfering power density
26、 spectrum is defined by: ()()()(),( fSpIfMPpfPSEoutRx= (4) This result represents the full picture of the interference level as a function of frequency and time percentage and thus allows assessment of all kinds of interference effects and scenarios in co-frequency as well as in adjacent band situat
27、ions. 2.1.2 Aggregation of interference from several sources Interference scenarios where several transmitters operate in the same frequency range and geographical area require methodologies for aggregating several interference signals suffered by a victim receiver. For assessing the overall interfe
28、rence prediction in such scenarios, the interfering signals should be aggregated by power: =NIRxIpfPpfP1),(),( (5) where: PI ( f, p) : aggregated interfering power density spectrum at receiver N : number of interfering signals. Rec. ITU-R M.1635 5 2.1.3 Effective interference power Some interference
29、 considerations require that the effective interference power in a certain part of the frequency spectrum has to be calculated. This effective power level is calculated by integrating the power spectral density over the bandwidth under consideration: fpfPpPffIInd),()(21= (6) where: PIn( p) : effecti
30、ve interference power at receiver f1: lower edge of considered bandwidth f2: upper edge of considered bandwidth which leads, if required, to the average interfering power density level in the frequency band under consideration: 12)()(ffpPpPInds= (7) where: Pds( p): average interfering power density.
31、 2.1.4 Calculation of peak interference level In interference scenarios where high gain antennas and/or rotating antennas have to be considered, the peak interference level is of interest in order to assess the probability aspects of interference levels. In such cases, the calculation procedure can
32、be simplified to the main beam coupling scenario of the transmitters and receivers under consideration. The peak interference power spectral density level at the input of the victim receiver can then be obtained from the following algorithm: ),()(),(pfLRRGGfPpfPbRxTxRxTxTxRx= (8) where: PRx( f, p) :
33、 interfering power density spectrum at receiver PTx( f ) : transmitter output power spectral density GTx: peak gain of the receiving antenna GRx: gain de crte de lantenne de rception RTx: feeder loss of transmitting antenna Rx: feeder loss of receiving antenna Lb( f, p) : attenuation due to propagat
34、ion effects f : frequency p : percentage of time. Applying free space propagation conditions leads to the worst-case scenario. 6 Rec. ITU-R M.1635 2.2 Transmitter model The transmitter emissions may be classified into the following categories: fundamental emission; harmonically related emissions; no
35、n-harmonically related emissions; broadband noise. A transmitter spectrum mask has to describe the power spectral density emitted by a transmitter. Due to the complex structure of the transmitter spectrum, a more generalized model should be applied in the interference assessment process. The fundame
36、ntal emission should be defined on the basis of a modulation envelope model with respect to the bandwidth of transmission covering 250% of the necessary bandwidth. Outside this frequency the relevant ITU-R Recommendations concerning the spurious emission levels should be applied. The attenuation rel
37、ative to the spectral density of the wanted emission has to be defined as a function of frequency offset. 2.3 Receiver model 2.3.1 Receiver susceptibility Receivers are designed to respond to certain types of electromagnetic signals within a predetermined frequency band. However, receivers also resp
38、ond to undesired signals having various modulation and frequency characteristics. Potentially interfering signals are considered to be in one of the following three basic categories: Co-channel interference refers to signals having frequencies that exist within the narrowest passband of the receiver
39、. Adjacent-channel interference refers to emissions having frequency components that exist within or near the widest receiver passband. Out-of-band interference refers to signals having frequency components which are outside of the widest receiver passband. From the standpoint of adjacent band inter
40、ference the radio-frequency (RF) selectivity is the most important parameter. This characteristic defines the frequency region over which interference may generally appear. On the other hand, the intermediate-frequency (IF) selectivity describes the ability of a receiver to discriminate against adja
41、cent channel interference. In combination with the transmitter spectrum mask the RF and IF selectivity are essential for the frequency separation considerations. If technical characteristics or measured data are not available, a good indicator for the selectivity characteristics of a receiver is giv
42、en by the ratio of 60 dB bandwidth to 3 dB bandwidth. Receivers with high selectivity may have a shape factor of 2; whereas receivers with low selectivity may have shape factors of greater than 8. Since the receiver IF selectivity describes the ability of a receiver to discriminate against signals i
43、n the widest passband of the receiver, it represents co-channel and adjacent channel interference. This selectivity should be defined by a mask with respect to the bandwidth of reception. For this purpose several combinations of bandwidth and susceptibility threshold levels in dB above sensitivity n
44、eed to be defined. The maximum value of attenuation of signals should be derived from the fundamental out-of-band selectivity neglecting spurious responses. Rec. ITU-R M.1635 7 2.3.2 Spurious response rejection In general, receivers are susceptible to out-of-band signals that can generate a spurious
45、 response in the receiver. A spurious response may be generated if the frequency of an interfering signal is such that the signal or one of its harmonics can mix with a local oscillator or one of its harmonics to produce an output in the receiver IF passband. The most critical frequency in that resp
46、ect is the image frequency of a receiver. For consideration of spurious response rejection the susceptibility threshold of the image frequency should be applied. If interference problems due to the image frequency are detected, further investigations are necessary focusing on the real spurious respo
47、nse characteristics of the receivers under consideration. However, this requires detailed information on these characteristics. 2.3.3 Receiver front-end desensitization Strong interference signals inside the RF bandwidth of a receiver may cause interference, even if the emission is outside the passb
48、and of the IF bandwidth. Strong undesired signals inside the RF passband may result in a reduction of gain for the desired signal due to non-linearities in the receiver front end. This effect leads to a reduced S/N ratio of the receiver concerned, if a certain saturation reference power level is exc
49、eeded (blocking or desensitization). The interference power level at the front end of a receiver should be calculated by equation (6) integrating over the RF bandwidth. 2.3.4 Receiver intermodulation Because of non-linearities within a receiver, two or more signals may intermodulate to produce signals at other frequencies. If these new frequencies are close enough to the received frequency band, they may cause interference since these signals are amplified and detected by the same mechanism which processes the desired signal. The pur
