1、TIA STANDARD Radiowave Propagation - Path Loss - Measurement, Validation, Presentation and TIA-845 OCTOBER 2001 TELECOMMUNICATIONS INDUSTRY ASSOCIATION Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted withou
2、t license from IHS-,-,-NOTICE TWEIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and o
3、btaining with minimum delay the proper product for his particular need. Existence of such Standards and Publications shall not in any respect preclude any member or nonmember of TWEIA rom manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of
4、such Standards and Publications preclude their voluntary use by those other than TIARIA members, whether the standard is to be used either domestically or internationally. Standards and Publications are adopted by TIARIA in accordance with the American National Standards Institute (ANSI) patent poli
5、cy. By such action, TWEIA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard or Publication. This Standard does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It
6、 is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (From Standards Proposal No. 3-4820, formulated under the cognizance of the TIA TR-8.18 Subcommittee on Wireless Syste
7、ms Compatibility.) Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION 200 1 Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 PRICE: Please refer to current Catalog of EIA ELECTRONIC INDUSTRIES ALLIANCE STANDARDS and ENGINEERING PUBLICATIONS or call Global Engineering D
8、ocuments, USA and Canada (1-800-854-7179) International (303-397-7956) All rights reserved Printed in U. S.A. Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Copyright Telecommu
9、nications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted withou
10、t license from IHS-,-,-TIA-845 TABLE OF CONTENTS FOREWORD v INTRODUCTION . vi1 1.0 SCOPE 1 2.0 NORMATIVE REFERENCES . 1 3 .O DEFINITIONS however, this will partially be mitigated by the presence of multipath transmission. 4 Copyright Telecommunications Industry Association Provided by IHS under lice
11、nse with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TIA-845 At the base site, the optimum antenna arrangement is an omni-directional radiator located atop a mounting structure. However, side mounted antennas can be accommodated if the antennas position with
12、 respect to the tower and the towers geometry are well defined. The following antenna arrangements cannot be adequately characterized. Therefore, they shall not be used for research purposes : Variable down-tilt antennas Antennas mounted such that a portion extends above the tower and a portion is p
13、arallel to the antenna structure. Antennas within the near field of another antenna Because of the near-impossibility of determining the source transmitter, simulcast systems shall not be used as signal sources for measurements used for research purposes. 4.1.2 Receiver Considerations 4.1.2.1 Ge ne
14、ral Communications receivers frequently lack dynamic range at either the low end or the high end, or at both. To correct for the low-end problem, a pre-amplifier can be employed. To correct for the high-end problem, a programmable attenuator can be employed. Measuring receivers always put out signal
15、 strength in digital form. Communications receivers, on the other hand, output signal strength in either digital form as Received Signal Strength Indication (RSSI), or in analog form as limiter voltage. In the latter case, Digital Voltmeter (DVM) or an A/D converter must be employed to interface bet
16、ween the receiver output and the computer. See Figure 1. The best tool for making a signal measurement is a receiver designed specifically for that purpose. This type of receiver has numerous advantages and two disadvantages when compared to a communications receiver: A specialized measurement recei
17、ver is expensive. d2 iz *The near-field far-field boundary is given by 2-, where d is the effective length of the antenna and A is the wavelength. Antennas that are closely- spaced, yet outside the near field of any other antenna are compliant with this Standard, but are not recommended for research
18、 purposes. 5 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TIA-845 The measurement bandwidth is somewhat inflexible. This can be serious, since the measurement bandwidth must
19、accommodate the modulation from the transmitter. A communications receiver can also be used for making signal measurements. Although they do not have the many features provided by a measuring receiver, they are adequate for the job when properly applied and do have a small number of advantages over
20、measuring receivers, including low cost and having the exact bandwidth that is needed for the given application. Before using a communications receiver for this purpose, the user must ensure that the receivers output characteristic (either RSSI or limiter voltage) is monotonic. 4.1.2.2 Extending dyn
21、amic range If a communications receiver is to be used, consideration should be given to adding a low noise preamplifier to increase the measurable range at the low end. In implementing a preamplifier, care should be exercised such that intermodulation products are not produced, distorting the measur
22、ements. To address the opposite issue, saturation problems experienced at very strong signal levels, a programmable attenuator can be employed. When the computer sees that the signal strength is approaching saturation, it can switch a PIN diode coaxial switch that controls the attenuator. 4.1.2.3 Ca
23、libration issues A communications receiver should be calibrated to its antenna input port using a signal source whose absolute level accuracy is specified as within 5 0.5 dB. Coaxial cable losses shall be calibrated out. The calibration signal source shall have been calibrated within the time interv
24、al recommended by its manufacturer, but in no event more than one year prior to calibrating the test receiver. Prior to calibrating the receiver, the calibration signal source shall have been warmed up according to its manufacturers recommendation for guaranteed amplitude accuracy, but in no event f
25、or less than 30 minutes. Since communications receivers can have rather non-linear calibration curves, it is required that calibration points be taken at 1 dB intervals. Additionally, each point in the calibration table shall be the mean of at least 30 individual measurements. This latter requiremen
26、t is necessary because, at some points on the calibration curve, the signal level is close enough to the noise level that the noise will cause instability in the reading. Most measurement receivers are self-calibrating. Manufacturers recommendations should be followed in performing the calibration.
27、It should be noted that temperature and voltage variations can affect receiver calibration. The receiver should be tested for sensitivity to these variables. A 6 Copyright Telecommunications Industry Association Provided by IHS under license with EIANot for ResaleNo reproduction or networking permit
28、ted without license from IHS-,-,-TIA-845 regulated power supply may be required if the sensitivity to supply voltage variations is excessive. There is no practical means of addressing excessive sensitivity to temperature variation. 4.1.3 Position Information Considerations A source of position infor
29、mation is essential to a successful test. Position information is commonly derived from a Global Positioning System (GPS) receiver. The level of accuracy delivered by this system (122.5 meters at the 95fh percentile) may be adequate in some cases. However, it is strongly recommended that some form o
30、f DGPS (differential GPS) be employed when making measurements for research purposes. Some such systems give results as good as 11 meter. One notable DGPS system is the Wide Area Augmentation System (WAAS), supplied by the U.S. Federal Aviation Administration. It has 11 meter accuracy; however, beca
31、use the difference signals are transmitted from geo-synchronous satellites over the Atlantic and western Pacific, ground-based receivers located in the Northern and Western USA can have difficulty in receiving the differential signal. The U.S. Coast Guard Navigation Center provides somewhat less acc
32、urate DGPS information, on the order of 1 O meters rms. Over-the-air differential information is also available from private sources, sometimes broadcasting the information on a subsidiary carrier authorization (SCA) sub-carrier of an FM broadcasting station. Differential corrections can be processe
33、d either in real time or post-processed. Given that the speed calculations made by GPS receivers include a certain amount of hysteresis, a speed transducer, such as a Hall-effect device inserted in the speedometer cable or a “fifth wheel”, can be useful to provide more accurate speed information. 4.
34、2 Data Gathering It is required that the signal be transmitted from the base site and measured at a mobile receiver, rather than the opposite. This stems from two considerations: First, receivers located at base sites are typically more subject to signals that can produce desensitization and intermo
35、dulation interference than are those in mobile locations. Desensitization reduces the overall dynamic range available to be measured. Intermodulation interference can do so, as well. Intermodulation is also more apt to be intermittent, causing the receiver to become intermittently uncali brated. A s
36、econd reason for the preference for the base-to-mobile direction is that this mode of operation makes it practical to make multiple simultaneous geographically separated measurements by the use of mobile receivers mounted in multiple vehicles. 7 Copyright Telecommunications Industry Association Prov
37、ided by IHS under license with EIANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TIA-845 It is understood that there may exist a need for documenting data gathering methods in the mobile-to-base direction. Because of the multiplicity of issues involved and the unc
38、ertainty of the magnitude of the need, mobile-to-base measurements will be left for a later issue of this standard. 4.3 Data Reduction The output of the receiver used in making the measurement may take any of three forms; namely, a signal strength value (from a measuring receiver) and either a limit
39、er voltage or a received signal strength indication (RSSI) data stream (from a communications receiver). The outputs from the communications receiver must be converted into a signal strength value by making reference to a calibration curve. At this point, all antenna system gains and losses must be
40、factored in to result in an output value that gives the value that would appear at the output terminals of a dipole antenna. In accordance with user requirements, this can be converted to signal strength in dBi, field strength, power density, or (after taking into account transmitter ERP) into path
41、loss relative to dipoles or isotropic radiators. However, the value shown in the output file shall be expressed in dBm. Having diligently removed all systematic sources of error from the measurement system, the remaining measurement errors can be assumed to be uncorrelated random variables. The corr
42、esponding measurement uncertainties should be estimated and combined into an overall root sum of squares estimate for the overall measurement uncertainty. This quantity should be provided with the measured data. 8 Copyright Telecommunications Industry Association Provided by IHS under license with E
43、IANot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TIA-845 5 Before making data available publicly, that data shall be verified. As a minimum, the following measures shall be taken: DATA VE RIF I CATI ON 5.1 In terference Data measurements can be affected by interfe
44、rence. For example, an interfering signal resulting from an on-frequency station or from intermodulation products generated from an off frequency signal can artificially increase the measurement to a value higher than would be received from the desired value. The following methods have been found to
45、 be useful in avoiding or detecting interference: 5.1 .I Mon to ring If the channel is audibly monitored, it may be possible to identify interfered-with data. Frequently, an interfering signal will be obvious due to its audio characteristics or due to sounds made by the receiver in response to two o
46、r more received signals. To accentuate the ability to audibly identify interference, a unique modulation source can be placed on the desired carrier. Where interference is identified, the measurement equipment can be configured to either “flag” data that is suspected of being interfered-with or to r
47、emove such data upon operator intervention. See clause 6.3. 5.1.2 Bit Error Rate Another effective method of detecting interference is to place a data signal on the carrier being measured and to measure its Bit Error Rate (BER). In post- processing of the data, it can be determined when the BER is m
48、uch higher than would be expected of a signal of the measured strength. Such data should be regarded as suspect and, unless a reasonable explanation (e.9. strong multipath) can be made for why such an occurrence would occur in the absence of interference, it shall be flagged as “suspect” in the data
49、 file. See clause 6.3. 5.2 Unreasonably Strong Signals With very few exceptions, path loss will equal or exceed that calculated by the Free Space formula Friis 19461. Therefore, any measured data that appears to be stronger than would be predicted by that formula should be considered suspect. The link budget should be reviewed for errors and environmental issues should be considered to determine whether an anomalous propagat
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