1、L STD-CEPT ERC REPORT 77-ENGL 2000 II 232b414 001b524 454 W ERC REPORT 77 European Radiocommunications Committee (ERC) within the European Conference of Postal and Telecommunications Administrations (CEPT) FIELD STRENGTH MEASUREMENTS ALONG A ROUTE Naples, January 2000 STD-CEPT ERC REPORT 77ENGL 2000
2、 232b4L4 00Lb525 390 m b _ - ERC REPORT 77 Copyright 2000 the European Conference of Postal and Telecommunications Administrations (CEPI) STD.CEPT ERC REPORT 77-ENGL 2000 = 232b4L4 00Lb52b 227 ERC REPORT 77 INDEX TABLE FIELD STRENGTH MESUREMENTS ALONG A ROUTE GENERAL 1 THE RESULTS OF MOBILE FIELD ST
3、RENGTH MEASUREMENT 1 CALCULATION OF FIELD STRENGTH . 2 THE NECESSARY NUMBER OF MEASURING POINTS AND THE AVERAGING INTERVAL . (LEE METHOD) 2 THE VEHICLE SPEED 2 MEASURING ANTENNAS 3 TEST RECEIVER SETTINGS . 3 7.1 DYNAMIC RANGE: . 3 7.2 DETECTOR FUNCTIONS AND BANDWIDTHS FOR THE RESPECTIVE TYPES OF SIG
4、NAL: 3 8 NAVIGATION AND POSITIONING SYSTEMS . 4 DEAD RECKONING SYSTEM . 4 COMPLEX NAVIGATION SYSTEM . 4 8.1 8.3 8.2 GPS SYSTEM . 4 9 REQUIRED ACCURACY OF FIELD-STRENGTH MEASUREMENTS (REC . ITU-R SM.378) . 4 10 DATA COLLECTION AND PROCESSING 4 MEASUREMENT RESULT COLLECTING WITHOUT DATA REDUCTION (RAW
5、 FIELD STRENGTH DATA): 4 MEASUREMENT RESULT COLLECTING WITH DATA REDUCTION: . 5 10.2.1 Averaged values 5 10.2.2 Classification of results according to level exceeding probability . 5 11 DATA PRESENTATION: . 5 11.1 REPRESENTATION OF RAW DATA IN TABULAR FORM . 5 11.3 MAPPING . 6 TEST SYSTEM REQUIREMEN
6、TS . 8 10.1 10.2 11.2 PLOTTING M CARTESIAN CO-ORDINATES 5 12 STD-CEPT ERC REPORT 77-ENGL 2000 2326Y14 0016527 lb3 ERC REPORT 77 Page 1 FIELD STRENGTH MESUREMENTS ALONG A ROUTE 1 GENERAL Influenced by the local receiving conditions, the real values of the field strength can significantly differ from
7、their predicted values, therefore they must be checked by measurements. Field strength measurement along a route with co-ordinate registration by mobile means is the most time and cost-effective solution for establishing the radio field strength coverage of a large area for radio surveillance, or wh
8、en the task is to find and eliminate radio interference radiation. Registration of test results must be recorded along with their geographical co-ordinate data for locating the scenes of measurements and for mapping the results. Different colours on the final radio coverage map can indicate the meas
9、ured field strength levels, which were gathered on the most accessible roads of the area in question. It can be easily determined on the basis of the coloured map, whether that particular area is covered by the required field strength. Instead of measuring the actual field strength, there is sometim
10、es a requirement to measure the output voltage of a user antenna (the typical antenna for the service under investigation) in order to determine to what extent its output voltage exceeds the threshold value of a receiver used by that service, for radio coverage evaluation. Furthermore measuring only
11、 the carrier wave is not sufficient when testing a digital network system (such as GSM, DCS1800 or DAB) which is sensitive to the effects of reflected reception. In this case, besides measuring the signal level, a reception quality measurement made by the measurement of the bit-error ratio (BER) or
12、channel impulse response (CIR) measurement is also necessary to determine the performance evaluation of digital systems. Using automatically made calls; these measurements can be made on operationai GSM networks without any adverse effect. I 2 THE RESULTS OF MOBILE FIELD STRENGTH MEASUREMENT For mea
13、surement purposes along a route a continuous transmission is necessary. The field strength level, at a given point, not only depends on its distance from the transmitter, the frequency of transmission and the antenna heights but also on the long-term and short-term interferences caused by reflection
14、s of the natural environment (terrain configuration, vegetation) and the man-made environment. The received signal must be considered as the vector sum of the wanted signal and many reflected signals. Due to the effect of reflected signals, the field strength along a route shows severe fluctuation.
15、The rate of fluctuation increases at higher speed and at higher transmission frequencies. Since, the measurements are made on public roads the reflected signals coming from other vehicles cannot be foreseen. The field strength test results therefore very rarely match the results of measurements obta
16、ined at the same place, at a different time. If the measurement is performed by a single short time measurement using a peak or an average detector, it can coincide with the minimum or maximum value of reflection making the result false. Test results are also influenced by the chosen height of the r
17、eceiver antenna since its height probably differs from the antenna height of a subscriber or user. Other factors include the season, the weather, the vegetation and the wetness of surroundings. The difference between the maximum and minimum field strengths can reach some tens of decibels. Considerin
18、g the factors mentioned above, the results of mobile field strength measurements must be regarded as statistic- like results. STDaCEPT ERC REPORT 77-ENGL 2000 U 232b4L4 00Lb528 OTT - - - - ERC REPORT n freqWEY radio service distance of adjacent samples (0.8A) Page2 .- repetition time of samples at s
19、peed of 100 kmh 3 CALCULATION OF FIELD STRENGTH I (W) 80 With knowledge of the output voltage of the antenna (usually measured in dBpV), the antenna factor and the attenuation of antenna signal path, the field strength value can be calculated by the following equation: I (m) I (-1 VHF radio 3 108 e
20、= Y. + k + a, where; e electric field strength component in logarithmic form dB(pV/m) k antenna factor in logarithmic form dB(m-) a, VO output voltage of the antenna in logarithmic form dWV) attenuation of antenna signal path in logarithmic form dB . - 100 FM broadcasting 2.4 86 160 VHF radio 1.5 54
21、 450 NMT 450 0.53 19 900 GSM 900 0.27 9.7 t 1800 GSM i800/DECT 0.13 4.7 Using certain test receivers it is possible to read the field strength result directly in dBpV/m, by previously writing the summarised antenna factor and signal path attenuation into the memory of the receiver. 4 THE NECESSARY N
22、UMBER OF MEASURING POINTS AND THE AVERAGING INTERVAL. (Lee Method) For statistical evaluation a large number of measurement data points are necessary. Increasing the number of measuring points improves the reliability of the averaging, however beyond a certain confidence interval, it does not return
23、 a significant improvement. For statistical evaluation the number of sample points should be chosen in such a way that the results should display the process of slow changing in the field strength (effeot of long-term fading) and more or less they should also reflect the local (instantaneous) indivi
24、duality (effect of short-term fading) of the field strength distribution. According to calculations, 40A are considered to be the prop averaging length of raw data. For obtaining 1 dB confidence interval around the real mean value, the samples of test points should be chosen at each 0.8h (wavelength
25、), over 40A averaging interval. (SO measured values within 40 wavelength.). For a low frequency operation, an interval of 20h can be taken. 5 THE VEHICLE SPEED The vehicle speed should be appropriate for the wavelength, the simultaneously measured number of the tested signals and the applicable shor
26、test measuring time of the test receiver. Some examples: Simultaneous measurement at different frequencies takes longer time. (Practically, it takes approx. 0.2 sec for each measurement at three different frequencies.) _* . . . , u . . 6 MEASURING ANTENNAS Following the curves of the road by the mea
27、suring vehicle, the received signal comes from different angles to the test antenna, therefore the effect of the antenna diagram should be known on field strength test result. The antenna factor (“k“) accuracy should be within 1 dB. (Can be calibrated using the substitution method.) If the vehicle i
28、s equipped with a digital compass, the software directly provides the angular position of the antenna with respect to magnetic North. When measuring a vertically polarised signal, a vertical non-directional antenna can be used. For automatic horizontal measurement some kind of directional antenna is
29、 used. (This could be a dipole or at lower frequencies an active dipole with rotor which should be controlled via an RS-232 interface by the process controller. Alternatively, an antenna where the reception pattern can be electrically rotated could be used. The operating software should automaticall
30、y determine the best direction for the antenna. The deviation of the horizontal radiation diagram of the measuring antenna from a non-directional diagram should not exceed 3 dB. I During the measurement the chosen height of the test antenna is 1.5 . 3 metre. The result will be considered as being ca
31、rried out at a height of 3-metres. For reducing the falsification effects of reflections it is possible to use space diversity arrangement. In such a case the distance between the antennas is 1/2 A. This is more reasonable at higher frequencies where the two antennas can be easily placed close to ea
32、ch other. 7 TEST RECEIVER SETTINGS 7.1 Dynamic range: The operating dynamic range of the measuring receiver should be 2 60 dB. 7.2 Detector functions and bandwidths for the respective types of signal: When mobile field strength measurements are carried out, the instrument settings (e.g. measurement
33、bandwidth, detector type and measuring time) should be set depending on the characteristics and modulation mode of the tested signal. The bandwidth should be wide enough to receive the signal including the essential parts of the modulation spectrum. The table below gives a representative sample of s
34、ignal types in order to demonstrate the minimum bandwidths needed, together with the detector functions. 8 NAVIGATION AND POSITIONING SYSTEMS 8.1 Dead Reckoning System Using only a “traditional“ positioning system operated with gyroscope, mobile field strength measurements are more difficult because
35、 the starting point of the mobile measurement has to be registered manually, by using accurate maps during the test the position data occasionally has to be corrected. At other locations the determination of distance from the starting point is reckoned with the help of a distance-to-pulse transducer
36、 attached to a non-motor driven wheel of the test vehicle, while the mechanical gyroscope provides the heading information. Using software, the mobile measured results along with position data are stored on a computer disk. The location accuracy depends on the accuracy of the starting point registra
37、tion and the distance covered by the test vehicle. 8.2 GPSSystem The previous positioning system supplemented with GPS (or GLONASS) equipment, has allowed mobile field strength measurements to become simpler, automatic and significantly more efficient. A commerciaiised (SPS) GPS in itself can only g
38、ive accurate position data from a few 10 to 100 metres and does not operate accurately in tunnels, narrow streets or valleys. The required positioning accuracy of the measurements depends on the type of system being tested. An accuracy of 100 or 200 metres is quite sufficient when testing broadcasti
39、ng coverage of a TV or radio station. Testing a digital micro-cell system in an urban area requires an accuracy of positioning information within severai metres. In such a case differential GPS should be used in the positioning system. . 8.3 Complex Navigation System Taking into account that the GPS
40、 system does not work in certain environmental circumstances, recent navigation systems have therefore used GPS along with a newly developed fibre optic gyroscope (with no moving parts; therefore it does not require any run-up time) for occasionally making those corrections. Without the need for man
41、ual operator intervention, these navigation systems continuously provide; position and time data, heading and waypoint information, pitch and roll data (by using a 3-axis gyro sensor cluster). The standard version contains a single axis, fibre optic gyroscope. The positions of measurements, localid
42、by using any type of co-ordinate systems, combined with the additionai time and data information should be transferred to the process controller of the measuring system via a standard RS-232 computer interface. 9 REQUIRED ACCURACY OF FIELD-STRENGTH MEASUREMENTS (Rw. ITU-R SM.378) Below 30MHz 30 to 2
43、700 MHz f2dB f3dB 10 DATA COLLECTION AND PROCESSING Either the average, maximudminimum peak values, statistical evaluation or level exceeding probability of the results can be obtained by the following differentmeasuring and evaluation methods. 10.1 Measurement result coecting without data reduction
44、 (Raw field strength data): All digitised field-strength results in relation to distance should be held in the processors RAM and stored when the test vehicle is stopped. Due to the varying fading and reflection effects, a single test result is not reproducible, therefore can not represent directly
45、the field strength value of a test point. The raw data can be further procesised as desired. - STD*CEPT ERC REPORT 77-ENGL 2000 2326434 003b53L b94 ERC REPORT 77 Page 5 10.2 Measurement result collecting with data reduction: Taking into account that reproducible field strength test results can only
46、be calculated from a large number of raw data readings, the aim is to convert the raw data into reproducible results, by means of statistical processing. Furthermore, this efficient method also allows the amount of data to be reduced considerably. Some of the test receivers are able to perform inter
47、nal classification of test results over predefined user intervals. 10.2.1 Averaged values The volume of data can be reduced if the averaging happens during the data collection and only the arithmetic averaged values of the predefined number of test results are stored onto the hard disk and are indic
48、ated on the final map of radio coverage. The user can select the evaluation intervals of up to some 10,ooO measured samples, but each interval must contain at least 100 values. 10.2.2 Class8cation of results according to levei exceeding probability During measurements the results are classified acco
49、rding to exceeding probability, between 1 - 99 %. These percentage values represent the probability of overstepping for the applicable field-strength level. Their typical values are 1; 10; 50; 90 and 99%. The median value, 50 % is preferred for propagation studies. (The applicable field strength level is overstepped by 50 % of the measured values.) The results of the measurements are expressed in a value of field strength for the 50% of the locations. Usually the receiver requires about 50 ms for the evaluation of the classification, so during this time the trigger pulses are
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