1、 Recommendation ITU-R P.1407-5(09/2013)Multipath propagation andparameterization of its characteristicsP SeriesRadiowave propagationii Rec. ITU-R P.1407-5 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spec
2、trum 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 statem
4、ents 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 av
5、ailable 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 satelli
6、te 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, 2013 ITU 2013 All rights reserved. No part of this publication may be reproduced, by any mea
8、ns whatsoever, without written permission of ITU. Rec. ITU-R P.1407-5 1 RECOMMENDATION ITU-R P.1407-5 Multipath propagation and parameterization of its characteristics (Question ITU-R 203/3) (1999-2003-2005-2007-2009-2013) Scope Recommendation ITU-R P.1407 describes the nature of multipath propagati
9、on and defines the appropriate parameters for the statistical description of multipath effects, and provides examples of correlation effects among multiple propagation paths and their computation. The ITU Radiocommunication Assembly, considering a) the necessity of estimating the effects of multipat
10、h on services employing digital systems; b) that it is desirable to standardize the terminology and expressions used to characterize multipath, recommends 1 that, to describe the concepts of multipath in a consistent manner, the terms and definitions given in Annex 1 should be employed; 2 that the c
11、orrelation concepts of Annex 2 should be used to analyse the effects of multiple-input, multiple-output (MIMO) systems; 3 that for the generation of wideband channel, models in Annex 3 should be used to evaluate the performance of communication systems. Annex 1 1 Introduction In radio systems with l
12、ow antenna heights, there are often multiple indirect paths between the transmitter and receiver due to reflections from surrounding objects, in addition to the direct path when there is line-of-sight. Such multipath propagation is particularly significant in urban environments, where the sides of b
13、uildings and paved road surfaces provide strong reflections. As a result, the received signal consists of the summation of several components having various amplitudes, phase angles and directions of arrival. The resulting spatial variability of signal strength can be viewed as having two regimes: a
14、) rapid fading which varies over distances of the order of a wavelength due primarily to changes in phase angles of different signal components; b) slow fading which varies over larger distances due primarily to changes in shadowing loss by surrounding objects. In addition, the various signal compon
15、ents can be Doppler shifted by different amounts due to the movement of the mobile or of reflecting objects such as vehicles. 2 Rec. ITU-R P.1407-5 The multipath mobile channel can be characterized in terms of its impulse response which varies at a rate dependent on the speed of the mobile and/or th
16、e scatterers. Therefore, a receiver has to be able to cope with the signal distortion arising from echoes in the channel as well as the rapid changes in the nature of this distortion. Such characteristics of the mobile radio channel are described by the power delay profiles and the Doppler spectra w
17、hich are obtained from wideband channel sounding measurements. Signals transmitted to and from moving vehicles in urban or forested environments exhibit extreme variations in amplitude due to multiple scattering. Fades of 30 dB or more below the mean level are common. The instantaneous field strengt
18、h when measured over distances of a few tens of wavelengths is approximately Rayleigh-distributed. The mean values of these small sector distributions vary widely from area to area, depending on the height, density and distribution of hills, trees, buildings and other structures. Physically, multipa
19、th propagation parameters are multipath number, amplitude, path-length difference (delay), Doppler shift and arrival angle. These parameters can be characterized from a series of complex impulse responses over a short distance or time interval that can be used to estimate the delay-Doppler spread fu
20、nction representing the multipath phenomenon in the three dimensions of excess delay, Doppler frequency and power density. The delay-Doppler spread function defines a linear transversal filter whose output is the sum of multiple delayed, attenuated and Doppler-shifted replicas of the input signal. T
21、his formulation is useful for realizing a hardware simulator in the form of a dynamic transversal filter. The delay-Doppler spread function is used to estimate the power delay profile and the Doppler spectrum, which can be related to the coherence time of the channel. Alternatively, the Fourier tran
22、sform of the time variant complex impulse response results in the time variant complex frequency response whose amplitude vs frequency characteristics define the multipath frequency selectivity, which is related to the correlation bandwidth and whose time variability gives the fading characteristics
23、 at a particular frequency. Definitions of small-sector (or small-scale) channel parameters are given in 2, 3 and 4. Statistics of small-scale parameters are subsequently used to produce cumulative distribution functions (CDFs). The medium-scale CDF covers a particular route of measurement, which is
24、 of the order of tens to hundreds of metres. The combined data set from a number of medium-scale routes is considered to be a large-scale or global characterization, which is representative of the surveyed environment, e.g. hilly terrain, urban, suburban, indoor large rooms, corridors, etc. 2 Parame
25、ters of delay profiles 2.1 Definitions of power delay profiles The appropriate parameters for the statistical description of regarding multipath delay time can be computed from any of three types of power delay profiles: the instantaneous power delay profile; short-term power delay profile; or long-
26、term power delay profile, which are either time averages obtained when the receiver is stationary and represent variations in the environment, or spatial averages obtained when the receiver is in motion. Definitions of power delay profiles are given as shown in Fig. 1. The instantaneous power delay
27、profile is the power density of the impulse response at one moment at one point. The short-term (small-scale) power delay profile is obtained by spatially averaging the instantaneous power delay profiles over several tens of wavelengths within the range where the same multipath components are mainta
28、ined in order to suppress the variation of rapid fading. Alternatively, it can be obtained from the delay-Doppler spread function shown in Fig. 2A by Rec. ITU-R P.1407-5 3 taking the sum of the magnitude squared along the Doppler frequency shift axis, as illustrated in Fig. 2B. FIGURE 1 Definition o
29、f power delay profiles P.1407-01Instantaneouspower delay profileDistance (m)AveragingDelay timeAveragingMedianDelay timeLong-termenvelope path delay profilePathDelay timeShort-termpower delay profileLong-termenvelope delay profileDelay timeDistance (m)Delay timeDelay timePathLong-termpower path dela
30、y profileLong-termpower delay profilePowerFIGURE 2A Delay-Doppler spread function P.1407-02a5005010503020100(dB)Excess delay ( s)Doppler (Hz)4 Rec. ITU-R P.1407-5 FIGURE 2B Relative power vs. time response P.1407-02bTime ( s)0403530252015105051015Relativepower(dB)The long-term power delay profile is
31、 obtained by spatially averaging the short-term power delay profiles at approximately the same distance from the base station (BS) in order to suppress the variations due to shadowing. Long-term power delay profiles with a discrete excess delay time normalized by time resolution 1/B, where B is the
32、bandwidth, are defined as long-term power path delay profiles, instead of continuous power delay profiles. On the other hand, the long-term envelope delay profile is the median value of the short-term power delay profiles at approximately the same distance from the base station; it expresses the sha
33、pe of the delay profile at the area considered. 2.2 Definitions of statistical parameters The appropriate parameters for the statistical description regarding multipath delay time are given below. The average delay is the power weighted-average of the excess delays measured and is given by the first
34、 moment of the power delay profile (the square of the amplitude of the impulse response). The r.m.s. delay spread is the power weighted standard deviation of the excess delays and is given by the second moment of the power delay profile. It provides a measure of the variability of the mean delay. Th
35、e delay window is the length of the middle portion of the power delay profile containing a certain percentage (typically 90%) of the total energy found in that impulse response. The delay interval is defined as the length of the impulse response between two values of excess delay which mark the firs
36、t time the amplitude of the impulse response exceeds a given threshold, and the last time it falls below it. The number of multipath or signal components is the number of peaks in a power delay profile whose amplitude are within A dB of the highest peak and above the noise floor. Definitions of the
37、statistical parameters are given with reference to Figs 3A and 3B. Rec. ITU-R P.1407-5 5 2.2.1 Total energy The total energy, Pm, of the impulse response is: 30d)( = ttmttPP (1) where: P(t) : power density of the impulse response t : delay with respect to a time reference t0: instant when P(t) excee
38、ds the cut-off level for the first time t3: instant when P(t) exceeds the cut-off level for the last time. 2.2.2 Average delay time The average delay, TD, is given by the first moment of the power delay profile: aDeePPT =00d)(d)(2a) where: : excess time delay variable and is equal to t t0a: arrival
39、time of the first received multipath component (first peak in the profile) e= t3 t0. In discrete form with time resolution (= 1/B), equation (2a) becomes: MNiiNiiiDPPT =11)()(2b) i= (i 1) = (i 1)/B (i = 1, 2, , N) where i = 1 and N are the indices of the first and the last samples of the delay profi
40、le above the threshold level, respectively, and M is the index of the first received multipath component (first peak in the profile). The delays may be determined from the following relationship: iirt 3.3)s( = km (3) where riis the sum of the distances from the transmitter to the multipath reflector
41、, and from the reflector to the receiver, or is the total distance from the transmitter to receiver for tLOS. 6 Rec. ITU-R P.1407-5 2.2.3 r.m.s. delay spread The root mean square (r.m.s.) delay spread, S, is defined by the square root of the second central moment: =eePPTSaD002d)(d)()(4a) In discrete
42、 form with time resolution , equation (4a) becomes: =NiiNiiMDiPPTS112)()()(4b) 2.2.4 Delay window The delay window, Wq, is the length of the middle portion of the power delay profile containing a certain percentage, q, of the total power: Wq= (t2 t1) (5) whereby the boundaries t1and t2are defined by
43、: 3021100=d)( 100=d)(ttmttPqttPqttP (6) and the energy outside of the window is split into two equal parts mPq200100. 2.2.5 Delay interval The delay interval, Ith, is defined as the time difference between the instant t4when the amplitude of the power delay profile first exceeds a given threshold Pt
44、h, and the instant t5when it falls below that threshold for the last time: Ith= (t5 t4) (7) 2.2.6 Number of multipath components The number of multipath or signal components can be represented from the delay profile as the number of peaks whose amplitudes are within A dB of the highest peak and abov
45、e the noise floor, as shown in Fig. 3B. 2.2.7 Recommended parameters Delay windows for 50%, 75% and 90% power, delay intervals for thresholds of 9, 12 and 15 dB below the peak are recommended when analysing data. It is worth noting that the effects of noise and spurious signals in the system (from R
46、F to data processing) can be very significant. Therefore, it is important to determine the noise and/or spurious threshold of the systems accurately and to allow a safety margin on top of that. A safety margin of 3 dB is recommended, and in order to ensure the integrity of results, it is recommended
47、 that a minimum peak-to-spurious ratio of, for Rec. ITU-R P.1407-5 7 example, 15 dB (excluding the 3 dB safety margin) is used as an acceptance criterion before an impulse response is included in the statistics. The threshold used for the identification of the number of multipath components depends
48、on the dynamic range of the measuring equipment; a typical value is 20 dB below the peak level of the delay profile. FIGURE 3A P.1407-03aTime delay ( s)0800.5 1 1.5 27570656055Powerdensity(dBm)t0t4t1t2t5t3Power delay profile illustrating the following parameters: the delay window, W90, containing 90
49、% of the received power is marked between the two vertical dashed lines (t1and t2), the delay interval, I15, containing the signal above the level 15 dB below the peak, lies between t4and t5. t0and t3indicate the start and the end of the profile above the noise floor. FIGURE 3B Power delay profile indicating multipath components above threshold level P.1407-03bTime delay ( s)Relativepower(dB)Power delay profile0123450510152025A (dB)8 Rec. ITU-R P.1407-5 3 Paramete
