1、 Recommendation ITU-R P.1406-2 (07/2015) Propagation effects relating to terrestrial land mobile and broadcasting services in the VHF and UHF bands P Series Radiowave propagation ii Rec. ITU-R P.1406-2 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient
2、 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 Radiocommunication Sector are per
3、formed 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 1 of Resolution ITU-R 1. Forms
4、 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 information database can also be
5、found. Series of ITU-R Recommendations (Also available 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,
6、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 systems SM Spectrum manageme
7、nt SNG Satellite news gathering TF Time signals 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, 2015 ITU 2015 All rights reserved. No part of
8、 this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R P.1406-2 1 RECOMMENDATION ITU-R P.1406-2 Propagation effects relating to terrestrial land mobile and broadcasting services in the VHF and UHF bands (Question ITU-R 203/3) (1999-2007-2015) Scop
9、e This Recommendation provides information on various aspects of propagation which are likely to affect the terrestrial land mobile and broadcasting services. These aspects should be taken into account in the design and planning of such services. The ITU Radiocommunication Assembly, considering a) t
10、hat there is a need for information on aspects of propagation likely to affect terrestrial land mobile and broadcasting services, noting that Recommendation ITU-R P.2040 provides guidance on the effects of building material properties and structures on radiowave propagation, recommends 1 that the in
11、formation contained in Annex 1 should be taken into account in the design and planning of such services. Annex 1 1 Introduction This Recommendation provides information on various aspects of propagation which are likely to affect the terrestrial land mobile and broadcasting services. These aspects s
12、hould be taken into account in the design and planning of such services. 2 Attenuation due to land cover These losses are likely to be of great importance for the land mobile service. They will depend on the category of the terrain, the extent of vegetation, and on the location, density and height o
13、f buildings. Table 1 summarizes the applicability of the various available ITU-R Recommendations: 2 Rec. ITU-R P.1406-2 TABLE 1 Recommendations discussing land cover ITU-R P. Applicability 1546 Antenna height corrections 452 Clutter losses 833 Attenuation in vegetation (especially trees) 1058 Terrai
14、n databases 1146 Antenna height corrections 1812 Vegetation and clutter losses 1238 Planning of indoor radiocommunication systems 2040 Effects of building materials and structures 3 Signal strength variability 3.1 General The strength of the signal received will vary with both time and location. The
15、 signal may be composed of direct, diffracted, reflected, and refracted components. The quality of the reception will depend upon several factors such as the receiving environment, frequency shifts, time delays, and type of modulation. Similarly, unwanted transmissions may also be received from othe
16、r sources sharing the same frequencies as, or adjacent frequencies to, the wanted signal. These, too, will have to be taken into account in assessing the quality of service. These unwanted transmitters may be so distant from the receiver that the extent of the temporal variation created by the vario
17、us forms of abnormal propagation will need to be quantified. This may involve a situation in which the risk of interference has to be accepted for a defined percentage of time at various receiving locations in order to allow the network(s) to operate. In summary, the assessment of reception and the
18、definition of the service area involve the analysis of wanted and unwanted signals in both time and location domains, and the extent of the correlation between them. 3.2 Fading regimes A reduction in signal strength occurs when the receiver is in the shadow of trees or buildings or of terrain obstac
19、les or other objects. The signal then arrives at the receiver after being diffracted over or around these obstacles, or being reflected from other objects. If the size and shape of the obstacles are known, an attempt can be made to calculate from theory the additional path loss that they create. Oth
20、erwise, if only general information about the environment is available, an estimate of path loss can be made from measurements made in similar situations. In any case, on a sufficiently small scale, a theoretical estimate will not be possible, and an estimate based on measurements will be necessary.
21、 Such an estimate must be statistical in nature. Typically, it consists of a median path loss for a specified area, and a measure of its variance. The signal may vary explicitly with time because of atmospheric variations, but over distances of less than about 50 km, this kind of variation is relati
22、vely unimportant. More important in the land mobile service is spatial variability, which is seen as time variability by a moving receiver. It is convenient to divide spatial variability into two regimes, rapid fading due to multipath, which occurs on the scale of a few wavelengths, and slower fadin
23、g due to changes in shadowing. In analysing measurements, the two can be separated in the following way: a number of Rec. ITU-R P.1406-2 3 measurements should be made at equal intervals over a distance of about 40 wavelengths, and a median signal level or path loss found for this distance. About 36
24、such measurements are required to obtain a median accurate to within 1 dB with 90% probability. The distance between measurements should be at least 0.8 of a wavelength in order for adjacent measurements to be uncorrelated, a criterion that is satisfied with the conditions just given. This procedure
25、 is repeated for other distance intervals of 40 wavelengths until the area of interest is covered. Experience has shown that the distribution of these median values will be log-normal, and therefore their distribution can be characterized by their mean or median, and their standard deviation. This i
26、s the distribution of signal strength variations due to shadowing, with the multipath variation removed. 3.2.1 Shadowing A number of measurements have been made of signal-strength distribution due to shadowing. It is important to specify whether the area of interest is a large one, i.e. all paths of
27、 a given length around a base transmitter or all paths of a given length in a geographical region; or a small one, i.e. an area of dimensions of a few hundred metres over which the path profile and the general environment of the receiver do not change significantly. The signal variability will be gr
28、eater in a large area than in a small one. In rural areas, for all paths of a given length the standard deviation, L, of the location variability distribution may be estimated by: 000 3/f o rdB25000 3/f o rdB0063.069.06 2/1 hhhhLL (1) where: h: interdecile height variation (m) : wavelength (m) 300/f
29、 f: frequency (MHz). In flat urban areas, the standard deviation over a large area may be estimated by: L 5.25 + 0.42 log (f /100) + 1.01 log2 (f/100) dB (2) valid from 100 MHz to 3 000 MHz. The standard deviation of location variability over small areas is less well-known. It is thought to depend o
30、n land cover, but it is not clear what that dependence is. There is some evidence that the standard deviation decreases with increasing distance from the transmitter, but this is not always clear. A formula (3) roughly summarizes some measurements at UHF for distances up to 50 km and all types of la
31、nd cover, and which retains the frequency dependence of the formula (2), is: L 2.7 + 0.42 log (f /100) + 1.01 log2 (f/100) dB (3) A different empirical expression for such shadow fading is given in Recommendation ITU-R P.1546. 4 Rec. ITU-R P.1406-2 3.2.2 Multipath fading On a scale of a few waveleng
32、ths, signal variability is determined by multipath effects. As a minimum, it is to be expected that a ground reflected component will be present, and as a consequence, multipath effects are always observed in practice. Such multipath effects generally lead to the classification of a channel as being
33、 “Rayleigh” or “Ricean”. In the former case the received signal is the sum of many independently fading components, and can be represented by the Rayleigh distribution (see Recommendation ITU-R P.1057). Such a channel would be typical for a narrow band cellular mobile service operating in a cluttere
34、d urban environment, with no line-of-sight to the transmitter. The Ricean channel is associated with the situation where one of the components of the received signal, such as that associated with a line-of-sight path to the transmitter, has a power that is constant on the timescale of the multipath
35、fading. In this case, the overall signal fading can be modelled by the Nakagami-Rice distribution (see Recommendation ITU-R P.1057). This distribution is often formulated in terms of the parameter, K (the “Rice factor”) which is defined as the ratio between the power in the constant part of the sign
36、al and that in the random part. For K = 0, the distribution becomes Rayleigh. 3.3 Local reflections Radiowaves arriving at a mobile receiver may be reflected from the ground and from nearby objects such as buildings, trees and vehicles. The ground-reflected wave is coherent with the direct wave and
37、causes the received signal to vary with receiver antenna height. However, waves reflected from nearby objects have random amplitudes and phases. Constructive and destructive interference between the direct and various reflected waves creates an interference pattern in which the distance between mini
38、ma is at least one half wavelength. In urban or forested areas, there are many reflected waves, and the instantaneous field strength when measured over distances of a few tens of wavelengths follows approximately a Rayleigh distribution. The interference pattern gives rise to fast fading in a moving
39、 receiver, and reflections from moving vehicles can cause fading even in a stationary receiver. Fades of 30 dB or more below the mean level are common. Local reflections can also have the beneficial effect of filling in deep shadows to some degree. 3.4 Signal correlation The correlation in mean rece
40、ived power from different sources is important for the evaluations of carrier to interference ratio, C/I. Consider C as the desired carrier power (dB) with a mean Cm and a standard deviation C and I as the power (dB) from one interfering source with a mean Im and a standard deviation I then the mean
41、 C/I-ratio (C/I)m, becomes: (C/I)m = Cm Im dB (4) which is independent of the correlation. The standard deviation of the C/I ratio, C/I, becomes: ICICIC 222/ (5) Rec. ITU-R P.1406-2 5 where is the correlation coefficient. In the case of I C, equation (5) simplifies to: )1(2/ IC (6) The correlation c
42、oefficients derived from sample sets of received power data indicate that for reception from opposite directions no significant correlation is evident. When the angle of arrival difference at the mobile is small, significant correlations exist. Typical values of for co-sited sources are 0.8 to 0.9 i
43、n farmed and heavily wooded areas. In metropolitan areas the correlation is generally lower ( between 0.4 and 0.8). Usually correlations in mountainous areas are very low. However, values of 0.8 are observed in exceptional situations even in mountainous areas. 4 Delay spread Many types of radio syst
44、em, particularly those using digital techniques, are sensitive to multipath propagation introduced to the signal by the path characteristics. After the arrival of the direct signal, a number of reflected signals arrive causing this phenomenon. Based on the amplitudes and time delays of these signals
45、 a channel impulse response (CIR) can be derived. Several parameters describing the propagation channel can be extracted from the CIR, see Recommendation ITU-R P.1407. One of the important parameters is r.m.s. delay spread, S, as given in equations (3) and (4) of Recommendation ITU-R P.1407. A usefu
46、l measure of the extent of time spread is the multipath delay spread, Tm, where: Tm = 2 S (7) Which of the parameters discussed above are most useful in predicting system performance is dependent upon the particular modulation scheme involved. 4.1 Impact on system performance Depending on the ratio
47、between delay spread and symbol duration, different phenomena are responsible for the bit error ratio. Multipath signals yield a rapid phase variation in space and frequency. For modulation schemes using some sort of angular modulation, e. g. differential phase shift keying (DPSK), these phase varia
48、tions are responsible for the so-called irreducible errors, which remain, even at large signal-to-noise ratios. As long as the delay spread is smaller than the symbol duration, the irreducible errors depend more on the delay spread than on the exact shape of the impulse response. However, if the del
49、ay spread exceeds the symbol duration, intersymbol interference occurs, which depends more on the CIR shape. 4.2 Delayed signals due to local scatterers Signals with short delays are often observed in areas with a uniform distribution of local scatterers. Such signals typically occur in urban or suburban areas, where no line-of-sight situations to large reflectors at longer distances (mountains, hills) exist. The uniform distribution of the scattered signals usually yields
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