Analysis on Radio Frequency Interferences

Transcription

1 Analysis on Radio Frequency Interferences 01 05/06/2002 G. Giovanni O. Benaglia ED DATE CHANGE NOTE APPRAISAL AUTHORITY ORIGINATOR Research Procedure on Interferences Z 3DB EAAA 1/14

2 Analysis on RF interferences on Alcatel s point-point Radio links NB. The analysis on interference carried out might, owing to the sensitivity of the tools being used, NOT permit to locate the interfering co-channels at fields lower than that of the sensitivity of the tools being implemented, and the signals that might still interfere with the useful traffic signal during particular conditions of propagation. Therefore, the fields displayed during the test must be considered as purely indicative. TABLE OF CONTENTS 1 INTRODUCTION TOOLS REQUESTED TEST DESCRIPTION CALCULATION OF THE INTERFERING FIELD LEVEL TOLERANCE VALUES TABLE LIST OF THE DOCUMENTS AND TESTS TO ENCLOSE RESULTS OF THE TEST AUXILIARY RESULTS OF THE TESTS AUXILIARY LIST OF THE TESTS AND AUXILIARY LIST OF NOTES AND AUXILIARY ACCEPTANCE Z 3DB EAAA 2/14

3 1 INTRODUCTION The aim of this document is of describing the interference test carried out in the various RF bands implemented by Alcatel s Radio Systems. 2 TOOLS REQUESTED - Spectrum Analyzer with the following characteristics: - Frequency Range - See max. frequency limit to measure. - Power supply - From battery. - Functions - Mask storing function. - Settings - Attenuation_ 0 db - RL - Reference Level_ -10 dbm - Es. Center Freq. 26 GHz - Span_ 112 / 360 MHz - RES BW_ 300 KHz - VID BW_ 300 Hz - Expected field sensitivity -85 dbm. - Amplifier operating in the frequency band being measured Gain = > 25dB NF = < 3.5dB - Antenna or horn antenna concerned with the frequency band being measured Gain 20dB Flare angle Cable guide adapter for the band being measured. - RF cable for the band being measured. NB. The spectrum sensitivity values indicated are obtained with a: Spectrum Analyzer type - HP 8563E Freq. Max 26GHz. As shown by the spectrum sensitivity values derived from the various examples indicated below, the cited sensitivity values variation is based on the characteristics of the instruments being implemented, on the settings and on the frequency used for the test (the highest the frequency the greater is the loss of the spectrum sensitivity). Therefore, by properly operating on the test setting values (see SPAN and RES BW ) it will be possible to optimize the background spectrum sensitivity. Note that the variation of these test settings corresponds to a SWP time variation Z 3DB EAAA 3/14

4 RES BW Variable to consider in the application of the interference calculation. Typical values read with a typical spectrum analyzer. Typical setting Type of Spectrum Analyzer: HP 8563E Freq. Max 26GHz -Center Freq 6 GHz 6 GHz 22 GHz 22 GHz 22 GHz - Attenuation 0 db 0 db 0 db 0 db 0 db - RL Ref. Level - 10 dbm - 10 dbm - 10 dbm - 10 dbm - 10 dbm - Span 112 / 360 MHz 112 / 360 MHz 112 / 360 MHz 112 /360 MHz 112 /360 MHz - RES BW 300 KHz 100 KHz 30 KHz 100 KHz 100 KHz - VID BW 300 Hz 300 Hz 300 Hz 300 Hz 300 Hz - SWP 3 sec. 9 sec. 32 sec. 9.4 sec. 30 sec. -Field sensitivity -90 dbm -95 dbm -95 dbm -90 dbm -90 dbm Z 3DB EAAA 4/14

5 3 TEST DESCRIPTION - Test drawing: RF Amplifier Spectrum Analyzer To reduce to a minimum the eventual loss induced by the RF cable on the link between the antenna and the amplifier/spectrum analyzer, a battery-powered analyzer is implemented compliant with the Safety Norms. set for tower operation. For the RF test use is made of a horn antenna with a flare angle of 30, and whose characteristics give: - 1 a satisfactory orientation. - 2 A 30 flare angle to reduce the amount of tests needed to cover the 360 needed to locate an interfering signal. The horn antenna must be mounted at a height that is equal to that set for the definite link. The interference test is inclusive of the detection of the current frequency band in 112MHz and 360MHz increments, in H and V polarisation. The bearing tests are split into : - Orientation tests (pointing the remote radio station) within the 30 angle. - Tests on the remaining 330, outside the section s 30 orientation angle. The different way of executing the tests is basically due to the no interference Span section. 112MHz in the remote station direction, and 360MHz in the remaining 330. See Start and Stop Frequency channelling adopted for the link being tested. N.B. The orientation tests within the 30 angle must be carried out throughout the frequency band and with H and V polarization in 112MHz ( Span ) increments. See Centr.Freq. start Ch 1 and stop Ch N' channelling for the link being tested Z 3DB EAAA 5/14

6 4 CALCULATION OF THE INTERFERING FIELD LEVEL The following is a description of the formula and limitations adopted to calculate the electromagnetic interfering level accepted at the antenna input: Pi = Pm - Ga + Ac G.Ampli. Pm = 10xLog RBW = (Spectrum Analyser RBW setting) Symbol Rate (Symbol Rate of the interfering signal) Piv = Pi - Pm Pm - Signal level measured by the analyser with 300kHz RBW Ga - Antenna gain Ac - RF signal loss produced by the RF cable between the antenna and the instrument G.Ampli. - Preamplifier gain Pi - Interference level assessed at the input of the antenna. (Measured with 300kHz RBW) Pm - Difference between the signal level read through the analyser and the true signal level Piv - True incoming interfering level (based on the type of interfering signal) Z 3DB EAAA 6/14

7 5 TOLERANCE VALUES TABLE Pi = Ps/Piv Maximum allowed co-channel interfering value referred to the Ps useful signal. Ps - Signal level wanted at the input of the antenna Maximum allowed co-channel interfering value See relevant Radio System Specifications Typical value Pi - 30 db Interference input direction Station: Measured value Piv= - dbm Station: Measured value Piv= - dbm The presence of interferences with values lower than those reported on the table can, in some cases, access the orientation point. In this case, owing to the high antenna gain their contribute to interference would no longer be considered unimportant. To prevent this from occurring, more restrictive limits should be reported on the table which would though, go beyond the sensitivity limits of the test instruments. Therefore, should such a condition arise, the solution indicated is that of searching among the free channels within the range. Should the channel necessarily be the one indicated and should it result to be interfered with, then proceed evaluating interference through the antenna that will be implemented on the link. The tests are stored on the spectrum analyser and then printed out thus offering a complete documentation. The documentation must be inclusive of the printouts of all the tests made with specific references: Spectrum Analyser setting Parameters Centre Frequency of each bearing. Start and Stop Band Frequency indication. Antenna pointing coordinate for each bearing. Remote station coordinate Z 3DB EAAA 7/14

8 Typical interference calculation Pi = Pm - Ga + Ac G.Amplif. = = dbm Pm = 10XLog RBW = 10XLog 300K = -1 9,3dB = -20dB (RBW of the Spectrum Analyser) Symbol Rate 25,4 Mb/s (Symbol Rate of a 128QAM STM1 signal) Piv = Pi - Pm = ( - 20 ) = - 97 dbm Pi = dbm; Interference value assessed at the input of the antenna (read with the Spectrum Analyser) Piv = - 97 dbm; True interference value assessed at the input of the antenna. NB: Therefore, assuming that : the useful signal of a SDH Radio System is considered valid up to approx. 75dBm fields, an interfering co-channel is considered as of no consequence for field of 30dBr below the useful signal level (-75 dbm). To this concern a specific test sensitivity is required. To reach this, apply an amplifier with a 25dB gain and NF lower than 3.5dB at the input of the Spectrum Analyser Z 3DB EAAA 8/14

9 6 LIST OF THE DOCUMENTS AND TESTS TO ENCLOSE Date of test execution Name of the site Address Type of structure Height of the antenna Azimuth of the link ( coordinate ) Frequency band Channelling measured with Start / Stop Freq.. Instrument used and date of calibration Antenna used and characteristics (flare angle and gain) Printout of the tests made with Vertical polarisation Printout of the tests made with Horizontal polarisation Z 3DB EAAA 9/14

10 7 RESULTS OF THE TEST NAME OF THE LOCAL RADIO STATION NAME OF THE REMOTE RADIO STATION Height of the antenna Azimuth of the link Frequency band Channelling measured with Start / Stop Freq.. Brand and type of Spectrum Analyser: Date of calibration Type of Antenna used: Diameter of the antenna Flare angle of the antenna Antenna gain Amplifier gain Printout of the tests made with Vertical polarisation Printout of the tests made with Horizontal polarisation / Date: Customer Operator: Alcatel Operator: Z 3DB EAAA 10/14

11 7.1. AUXILIARY Z 3DB EAAA 11/14

12 8 RESULTS OF THE TESTS NAME OF THE LOCAL RADIO STATION NAME OF THE REMOTE RADIO STATION Height of the antenna Azimuth of the link Frequency band Channelling measured with Start / Stop Freq. Brand and type of Spectrum Analyser: Date of calibration Type of Antenna used: Diameter of the antenna Flare angle of the antenna Antenna gain Amplifier gain Printout of the tests made with Vertical polarisation Printout of the tests made with Horizontal polarisation / Date: Customer Operator: Alcatel Operator: Z 3DB EAAA 12/14

13 8.1. AUXILIARY Z 3DB EAAA 13/14

14 9 LIST OF THE TESTS AND AUXILIARY 10 LIST OF NOTES AND AUXILIARY 11 ACCEPTANCE Date / / On behalf of CUSTOMER: On behalf of ALCATEL: END OF DOCUMENT Z 3DB EAAA 14/14