1、 TSB-176-A March 2017Radiowave Propagation- Path Loss- Measurement and Validation NOTICE TIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of
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5、rements. It 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 Project No. TIA-PN-176-A, formulated under the cognizance of the TIA TR-8 Mobile and Personal Private
6、 Radio Standards, TR-8.18 Subcommittee on Wireless Systems Compatibility- Interference and Coverage). Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION Technology (b) there is no assurance that the Document will be approved by any Committee of TIA or any other body in its present or any other for
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19、UT SUCH LIMITATIONS. TIA TSB-176-A i TABLE OF CONTENTS DOCUMENT REVISION HISTORY ii FOREWORD . iii INTRODUCTION . iv 1.0 SCOPE 1 2.0 REFERENCES . 1 3.0 REFERENCES DEFINITIONS however, this will partially be mitigated by the presence of multipath transmission. For acceptance testing (as opposed to re
20、search) purposes, it is recommended that the antenna placement be identical (rather than similar) to the existing system and that the vehicle it is mounted on be similar in size and configuration to the existing system. Further information on acceptance testing is found in the current versions of TS
21、B88.3 and TSB-88.5. 1TIA TSB-171 provides a detailed background on mobile antennas with respect to the size of a vehicles roof dimensions and the effect of height of the vehicles roof AGL. Table 4 of TSB-171 summarizes the average gain (dBd) in the horizontal direction of a quarter wavelength radiat
22、or mounted in the center of a vehicles roof. See also TIA 329.2-C for the standard on vehicle antennas. TIA TSB-176-A 7 At the base site, the optimum antenna arrangement is an omni-directional radiator located atop a mounting structure2. However, side mounted antennas can be accommodated if the ante
23、nnas position with respect to the tower and the towers geometry are well defined. The following antenna arrangements cannot be adequately characterized. Therefore, they ought not be used for research purposes: Variable down-tilt antennas Antennas mounted such that a portion extends above the tower a
24、nd a portion is parallel to the antenna structure. Antennas within the near field3of another antenna Antennas that are obstructed by nearby tall buildings, trees, other towers, other antennas (microwave dishes), etc. Because of the near-impossibility of determining the source transmitter, simulcast
25、systems ought not be used as signal sources for measurements used for research purposes. 4.2.2 Receiver Considerations 4.2.2.1 General 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
26、employed. To correct for the high-end problem, a programmable attenuator can be employed. Measuring receivers always put out signal strength in digital form. Communications receivers, on the other hand, output signal strength in either digital form as Received Signal Strength Indication (RSSI), or i
27、n analog form as limiter voltage. In the latter case, employ a Digital Voltmeter (DVM) or an A/D converter to interface between 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 receive
28、r has numerous advantages and two disadvantages when compared to a communications receiver: 2See TIA 329.1-D for Base Antenna standards. See also TIA 845-B for a method of describing base antenna mounting configurations. 3*The near-field far-field boundary is given by 22d, where d is the effective l
29、ength of the antenna and is the wavelength. Antennas that are closely-spaced, yet outside the near field of any other antenna are in accord with this Bulletin, but are not recommended for research purposes. TIA TSB-176-A 8 A specialized measurement receiver is expensive. The measurement bandwidth is
30、 somewhat inflexible. This can be serious, since the measurement bandwidth is required to accommodate the modulation from the transmitter. However, if an unmodulated carrier is used, measurement bandwidth is unimportant. A communications receiver can also be used for making signal measurements. Alth
31、ough 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 measuring receivers, including low cost and having the exact bandwidth that is needed for the given application. Before using a
32、communications receiver for this purpose, the user ought to ensure that the receivers output characteristic (either RSSI or limiter voltage) is monotonic. 4.2.2.2 Extending dynamic range If a communications receiver is to be used, it is recommended that consideration be given to adding a low noise p
33、reamplifier to increase the measurable range at the low end. In implementing a preamplifier, exercise care such that significant intermodulation products are not produced, distorting the measurements. To address the opposite issue, saturation problems experienced at very strong signal levels, a prog
34、rammable 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. Capturing the activation of the attenuator allows the receivers calibration to be extended for processing. 4.2.2.3 Ca
35、libration issues Calibrate the communications receiver to its antenna input port using a signal source whose absolute level accuracy is specified as within 0.5 dB. Specify and calibrate out coaxial cable losses. Ensure that the calibration signal source has been calibrated within the time interval r
36、ecommended by its manufacturer, but in no event more than one year prior to calibrating the test receiver. Prior to calibrating the receiver, warm up the calibration signal source according to its manufacturers recommendation for guaranteed amplitude accuracy, but in no event for less than 30 minute
37、s. Since communications receivers can have rather non-linear calibration curves, it is recommended that calibration points be taken at 1 dB intervals. Additionally, each point in the calibration table ought to be the mean of at least 30 individual measurements. This latter recommendation is necessar
38、y because, at some points on the calibration curve, the signal level is close to TIA TSB-176-A 9 the thermal noise level, which can cause instability in the reading. Additionally, it is recommended that, to save time and effort, calibration measurements be automated through computer control of the m
39、easurement set-up. Most measurement receivers are self-calibrating. Follow the manufacturers recommendations in performing the calibration. Be sure the receiver and base transmitter frequencies are precisely matched to eliminate this potential error. It should be noted that temperature and voltage v
40、ariations can affect receiver calibration. It is recommended that the receiver be tested for sensitivity to these variables. A regulated power supply may be necessary if the sensitivity to supply voltage variations is excessive. There is no practical means of addressing excessive sensitivity to temp
41、erature variation. 4.2.3 Position Information Considerations A source of position information 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 (7.8 meters required, 3.6 meters m
42、easured, both at the 95th percentile 1) may be adequate in some cases. However, it is strongly recommended that some form of DGPS (differential GPS) be employed when making measurements for research purposes. Some such systems give results as good as 1 meter. One notable DGPS system is the Wide Area
43、 Augmentation System (WAAS), supplied by the U.S. Federal Aviation Administration. It has approximately 1 meter accuracy 2; however, because the difference signals are transmitted from geo-synchronous satellites some ground-based receivers might have difficulty in receiving the differential signal.
44、The U.S. Coast Guard Navigation Center provides somewhat less accurate DGPS information, 10 meters, at worst4. Differential corrections can be processed either in real time or post-processed. Given that the speed calculations made by GPS receivers include a certain amount of hysteresis, it is recomm
45、ended that real time speed information be collected by use of a fifth wheel speed sensor tool or interfacing to the vehicle OBD II interface with an appropriate, vehicle specific, 3rdparty speed sensor module that interfaces to the vehicle data bus. It is outside of the scope of this document to des
46、cribe details of interfacing to a vehicle data bus, 3rdparty speed sensor, or the data collection systems for the purposes of improving speed accuracy. 4http:/www.navcen.uscg.gov/?pageName=dgpsMain TIA TSB-176-A 10 Finally, location information in dense urban or other settings where appropriate view
47、 of GPS satellites is hampered, may require the use of 3rdparty dead reckoning tools (in conjunction with accurate speed calculations as noted previously) to gather accurate position information. It is outside of the scope of this document to describe details of implementing and interfacing to a dea
48、d reckoning 3rdparty tool. 4.3 Data Gathering It is only practical 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
49、produce desensitization and intermodulation 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 uncalibrated. A second 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
