1、STD-CEPT ERC REPORT 35-ENGL 3992 E 2326434 00151s32 333 I ERC REPORT 15 v European Radiocommunications Committee (ERC) within the European Conference of Postai and Telecommunications Administrations (CEPT) COMPATIBILITY STUDY BETWEEN RADAR AND RLANs OPERATING AT FFU3QUENCIES AROUND 5.5 GHz Madrid, O
2、ctober 1992 STDnCEPT ERC REPORT 15-ENGL 1992 II 2326414 00151L3 058 I Copyright 1992 the European Conference of Postal and Telecommunications Admuiistrations (0 STD=CEPT ERC REPORT 35-ENGL 3992 I 2326434 00351i14 T94 I Interference Required C/I Receiver Threshold ERC REPORT 15 Page 1 level. Based on
3、 parameter for KAN at 17 GHz. Calculated from other assumed parameters. 20 dB -80 dBm COMPATIBILITY STUDY BETWEEN RADAR AND RLANs OPERATING AT FREQUENCIES AROUND 5.5 GHz 1 INTRODUCTION This reprt examines the prospect of Co-channel sharing between radar and Radio Local Area Networks (RLANs) operatin
4、g in the frequency bands around 5.5 GHz. Due to lack of information, the interference potential from the RLAN to the radar is not assessed. Results in this report show that if harmful interference to the RLAN is to be avoided no more than 6 radar can be permitted within a 50 km radius of any RLAN. 2
5、 ASSUMED WAN PARAMETERS At the time of writing (September 1992) very little information is available for the RLANs being proposed for sharing with radars at frequencies around 5.5 GHz. Under these circumstances some assumptions have been made regardhg the values of key RLAN parameters for use in the
6、 sharing study. These parameters are listed in the table below: PARAMETEN I VALUE I COMMENT Maximum eirp I 30dBm I Based on DECT Tx. Power of 24 dBm with an extra I I I 6 dB allowance for increased prop“ loss. Value I I I technology limited. I O dBi typical for mobile at 1 8 GHz. extra 2 dB for Ante
7、nna Gain IZdBi I I I higher frequency and to overcorn prop“ loss. Low I I cost antenna assumed. I Scaled fromDECT bandwidth and data rate ( 1.152 Channel Bandwidth I 20MHz I Mbitsk). Data rate of 1 5 Mbits/s assumed for RLAN. I Assumed interference level is equal to thermal noise Maximum Tolerable I
8、 -130 dBW/20 MHz The parameters given in the table are based on assumptions and they should be changed when information becomes available on the RLAN Characteristics and perfomce. 3 RADAR PERFORMANCE The following table (Table 2) gives information on the performance of example radar systems currentl
9、y operational in the band under investigation. The list of radars given is not exhaustive and is merely intended to provide some realistic examples for use in sharing calculation. The numbers and locations of the radars used are not available for use in this study. STD.CEPT ERC REPORT 35-ENGL 3992 I
10、 2326434 0035335 920 m WAR A B PEAKEIRP 98.6 dBW 26 dBW EMISSION 3MOOPON 15M5PON AN ERC REPORT 15 Page 2 C D E 60 dBW 93 dBw 97 dBw SOMOPON 14MOPON 3MOOPON I I I AIRBORNEUSE I NO I YES I NO I NO I NO Table 2. Radar parameters for use in sharing calculations. 4 METHODOLOGY The method used to calculat
11、e the potential for interference fromradar systems to the RLAN is based on estimates of the Minimum Couping Loss (MCL) required between radars and the RLAN. The MCL is defined as the minimum loss required to avoid adversely affecting receiver performance. This is measured between the antenna connect
12、or of the interfehg system and the antenna connector of the victimreceiver (i.e. feeder loss and antenna gain are not included). Quation 1 is used to that the MCL. L-L Equ. 1 MCL = P,+ 10 10g,o, Where, MCL Minimum Coupling Loss dB P, Bnoise BW, Transmitter Bandwidth (Radar) Hz I, It should be noted
13、that when the LAN receiver bandwidth is greater than the transmit bandwidth of the radar, the term 10 logl$mkJi3W, = O. Maximm Transmit Power, before antenna and feeders (Radar) dB Receiver Noise Bandwidth LAN) Hz Maximum Permissable Interference at Receiver, after antenna and feeder (KAN) dB Once t
14、he MCL has been calculated it may be converted to a required propagation loss by taking account of any antenna gain or feeder loss between the radar and the RLAN. Prop Loss = MCL + G, - Where, PropnLoss Required Propagation Loss G* L G, I4 Assuming free space propagation, then Equation 3 can be used
15、 to determine the required distance separation. + G, - L,+ Equ. 2 Gain of the radar antenna (see Table 2) Radar feeder loss (assumed = O dB) Gain of RLAN antenna (2 dBi) RLAN feeder loss (assumed = O dBi) - A. 1oProrrloss 4n 2o Equ. 3 d= Where all symbols have their previous meanings and, h Waveleng
16、th (evaluated at 5.5 GHz) d Required separation distance It should be noted that use of free space propagation formula to calculate required separation distances gives the worse case situation. ERC REPORT 15 Page 3 5 RESULTS Using the methodology outlined above and the parameters in Sections 2 and 3
17、 the foliowing table of results is produced. FEEDER LOSS see CCIR REC. 238 Table 3. Required distance separations for RLAN sharing with various radar system. If the distance to the radio horizon is taken as the limiting factor in determining the range over which a radar can cause interference to the
18、 RLAN, there is a potential interference zone of approximately 50 km around every land based radar and 350 km from the airborne radar. Details of the number of radars in the band are not known. However, given the transportable and airborne nature of radar usage in this band it should be assumed that
19、 there is a potential for interference from the radar to the RLAN. Further work is required to determine the precise interference environment of the band under investigation. 6 DURATION OF INTERFERENCE BURSTS In previous compatibility studies between RLANs and radar (e.g. Study at 17 GHz) advantage
20、was taken of the pulsed nature of the radar transmission and the RLANs ability to withstand interference so as to pennit sharing. A number of factors influence the period of time over which interference occurs to the RLAN as a result of the radar transmission. These include: radar Puise Width (PW),
21、the Pulse Repetition Frequency 0, the scanning nature of the radar and whether or not frequency hopping is employed by the radar information is not available on the latter two. The RLAN has to endure an interference burst of duration PW, PRF times per second. The effect of this on the RLAN design ca
22、n be seen from the worked example below. Worked Example - Interference from a single type A radar to an RLAN The RLAN performance will be constrained by two types of interference. These are interference from the radar and interference due to the systems own inherent performance limitations (Le. the
23、interference if no KAN were present). Interference due to radar From Table 2, it can be seen that a single radar of type A transmits bursts of 5 ps duration, 300 times per second. Taking an RLAN data rate of 15 Mbitsls and assuming no synchronisation between the radar and the RLAN gives: 76 bits in
24、errod5 ps, this occurs 300 times per second. 22.8 kbits/s are in error due to the radar transmission. Ihe distance to the radio horizon is calculated assuming a flat spherical earth and a radar pointing towards the horizon at a height of 30 m and an RLAN at a height of 50 m. Aircraft height of 6000
25、rn is assumed and an RLAN height of50 m. STD-CEPT ERC REPORT 35-ENGL L992 I 2326434 0035337 7T3 e ERC REPORT 15 Page 4 Interference due to RLAN system performance Assuming a system error (number of errors in normal RLAN operation without any radar interference present) rate of 1 in lo3 for the RLAN,
26、 and assuming that these errors are random. Gives an average error rate of: 15 kbitsls (Le. 1 error per 66.7 ps) Total error rate Equation 4 is used to evaluate the number of errors that occur per second. Error- = Error,. X PRP + Error, Equ. 4 Where, Error, Total number of errors per second Error- E
27、rror due to a single radar pulse PRF milse Repetition Frequency Error- Error due to inherent system performance Error, Given the error rate per radar, it is possible to evaluate the number of radars which can operate within a given radius of the RLAN, before the interference environment becomes such
28、 that the RLAN can no longer operate. Assuming that the lUAN can meet its performance targets with an error rate of 1 in 10 (same as for RUN at 17 GHz). Using Equation 5 and noting that the total acceptable error rate is 150 kbits/s. = 76 x 300 + 15 x lo3 = 37.8 kbitslslradar Error - Error, No. of r
29、adars = Errorm& Qu. 5 Where, No. of radars Eraccept ErroLYStm Errorradar Number of radars within the Radio Horizon Total acceptable error rate ( 150 kbits) Number of error due to RLAN operation when there is no radar interference ( 15 kbits) Number of errors due to radar transmission (300 X 76) Ther
30、efore, 150 x lo3- 15 x lo3 No. of radars = = 5.92 (5) .22.8 io3 From the above it can be seen that up to 5 radars could operate within a 50 !unradius of the RIAN. Table 4 shows the results for the other radars listed. Table 4. Performance degradation of RLAN sharing with various radar systems. 7 CON
31、CLUSIONS This report has studied the possibility of RIANS sharing with radar in the radiolocation bands around 5.5 GHz and has assessed the potential for interference from radar systems to RLANs. Using free space propagation formula, the required separation disiance between radars and tile RLAN is l
32、imited by the Radio Horizon (50 km for ground based radar and 340 km for airborne radar). However, this is the worse case and does not take into account terrain or building attenuation. Further calculations show that the RLAN could tolerate interference from between 5 and 14 STD-CEPT ERC REPORT 15-E
33、NGL L992 232b414 0015118 63T I ERC REPORT 15 Page 5 radars at a given tim. This is unlikely to reflect the majority of situations where RLANs will be used (mainiy urban areas at some distance from radar installations), and the distribution of radars will probably be less than 5 within 50 km Where an
34、 KAN is operating within line of sight of one or more radars, the system throughput will be reduced but still within acceptable limits. Ideally, further studies are required to provide FUAN equipment designers with an assessment of the interference enviromnt in the 5.5 GHz band. However, given that
35、radar system are mainiy used for defence purposes and the transportable character of the radar, some difficulties my be anticipated in obtaining a complete picture. This report has made no attempt to calculate the interference potential from the RLAN to the radar. Additionally, taking into account the relative power levels of radars and RLANs, radar systems will, in effect, create their own exclusion zones.
