1、I no spectrum spreading is assumed at this point. The radio LAN maximum Equivalent Isotropic Radiated Power IR) is scaled from that for DECT 3, which is 24 dBm in a 1.7 MHz bandwidth, according to the higher transmission loss at the higher frequency, the increased bandwidth and the reduced coverage.
2、 This gives a maximum EIRP of 30 dBm The radio LAN bandwidth is scaled from that for DECT, which is 1.7 MHz for a bit rate of 1.2 Mbits-1, according to the increase in bit rate to 15 Mbits-1. This gives a bandwidth of 20 MHi The radio LAN maximum tolerable interference is simply the thennai noise po
3、wer in the equivalent noise bandwidth of the radio LAN The required C/I is an approximate figure, yet to be confirmed by ETSI. The receiver threshold is calculated from the required CII and the maximum tolerable interference. The radio LAN antenna gain is 2 dBi, which is reasonable for a simple ante
4、nna, omni-directional in a horizontal plane (half wave dipole). However, radio LANs my use directional antennas to reduce time dispersion of signals by attenuating reflected components. In this case a maximum antenna gain can be calculated based on the maximum aperture available on a portable comput
5、er. The wavelength h, at 5 GHz, is approximately 6 cm and hence the maximum aperture diameter is around 12 cm or 2 h. The maximum directive gain for an aperture diameter, expressed in wavelengths Dk, is This gives a maximum directive gain of 16 dB and assuming 40% efficiency a maximum overall gain o
6、f 12 dB. However, regulatow conditions will probably impose a maximm EIRP of O dBW (30 dBm). G = 1 O log (: DA) (1) STD-CEPT ERC REPORT 14-ENGL 1792 111 232bYL4 0015108 790 m FREQUENCY OFFSET f 0 FROM BAND EDGE ERC REPORT 14 Page 2 MEASUREMENT BANDWIDTH Spurious Emission limit = 1 pW 10 MHZSfo -20.5
7、 dF3 ( 1 St) Ci -25.0 dB (2“d) -95 dBm 1- Bandwidth System Frequency Selectivity (Rejection) 150 kHz 40 dB (5.092 GHZ-5.250 GHz) 75 dB ( 5.250 GHz) I Thermal Noise Power I -123 dBm(l50 kHz) I I Antenna Gain I O dBi I 3.3 Interference Scenarios MLS systems operate at higher power levels for greater c
8、overage than radio LAN systems and hence interference problems should only occur in a near-far scenario when a radio LAN transmitter is close to an MLS receiver. There are two possible near-far scenarios: 1) Where a radio LAN on an aircraft is close to the aircraft MLS receiver. 2) Where many radio
9、LANs are in a multistorey building close to the aircraft approach path to the airport and hence close to the aircraft MLS receiver. Scenario (1) is the more likely scenario if radio LANs or portable computers with radio LAN cards are used by passengers on aircraft. However, the use of radio LAN syst
10、ems on aircraft could be prohibited avoiding this scenario completely. In this scenario the mwimum signai from the radio LAN transmitter to the MLS receiver could be either through propagation out of the aircraft and to the MLS via its antenna or through propagation along the body of the aircraft an
11、d to the MLS via its casing. The former should be easier to estimate as it simply involves a penetration loss and path loss. The latter requires detailed information about the Electromagnetic Compatibility PMC) specifications of the MLS equipment and casing. In either case the transmission loss is l
12、ikely to be similar involving a similar distance and a sidar additional loss. Scenario (2) is the less likely scenario because multistorey buildings are not built close to aircraft approach paths to airports for safety reasons. Such buildings are typically 1 km from the approach path. Also, at such
13、distances the MLS signal strength at the aircraft will be much greater than the minimum signal strength given in Table 3 which is calculated for the limit of the MLS coverage volume. At this ERC REPORT 14 Page 4 iimit of the MLS coverage volume the aircraft will be at a high altitude and any signals
14、 from radio LANs in buildings should be sufficiently attenuated by the large path loss. To investigate whether there is a potential interference problem in either of the above scenarios we must determine a radio LAN transmitter exclusion zone radius around an MLS receiver. The MCL and consequently t
15、he minhm separation distance are evaluated for MLS and radio LANs co-existing in the same and adjacent bands in the following sections. 3.4 MLS and Radio LANs in the Same Band The MCL for this scenario, based on the figures given in Table 3, is (values are in dBm): The transmission loss must be grea
16、ter than the calculated MCL. At 5.20 GHz the transmission loss is which reduces to MCL = 30 - 21.2 + 120 = 128.8 dB TL = 46.8 + I0 nlogd -G, -G, + A TL = 44.8 + I0 nlogd + A (5) (6) (7) using the parameters given previously. If free space propagation is assumed, the decay index n is 2, and additiona
17、i loss A is 3 dB The minimum separation distance d is 1.2 km Hence, in this case there is a senous potential problem and the use of radio LANs on aircraft would have to be prohibited and radio LAN exclusion zones would have to be imposed around airports. 3.5 MLS and Radio LANs in Adjacent Bands As s
18、tated previously, a thorough investigation of interference effects requires integration of the total interference. As this is not possible, the following calculations are based on the in-band adjacent band interference only It can be shown, by comparing the magnitudes of in-band and out-of-band inte
19、rference, that this is valid. The Radio Frequency (Rp) emissions of the radio LAN (outside the designated band) are -60 dBW, but the rejection of the MLS system of out-of-band signals is -40 dB system frequency selectivity plus -25 dB adjacent channel tolerance giving a total of -65 dB. Hence, the o
20、ut-of-band adjacent band interference is negligible compared to the in-band adjacent band interference. For the in-band adjacent band interference the interferer power Pi (the RF emission power outside the band designated for RLANs) is -60 dBW (-30 dBm). This assumes the worse case, i.e. that the sp
21、urious emissions are narrow band and the total power of -30 dBm falls within the MLS receiver bandwidth. Hence, the MCL for this scenario is (values are in dBm): The transmission loss must again be greater than the calculated MCL. Using equation 7 and the previous assumptions, n of 2 and A of 3, the
22、 minimum separation distance d is 129 m This is a pessimistic estimate for the exclusion zone radius as it is based on small values for the decay index n and additional loss A. If n is increased to 3 and A to 10 dB, which are more realistic figures considering that there will be no direct line of si
23、ght between the radio LAN and the MLS equipment, the minimum separation distance is 15 m This distance suggests that there would be no significant interference problem between radio LANs on an aircraft and the MLS equipment. If intelligent (automatically steerable) beam antennas are employed power c
24、ontrol will also be employed. When a link has not been Set-up the antenna will have an omni- directional pattern and power will be at its maximum (30 dBm) but when the link has been Set-up the antenna will have a directional pattern and the power will be controlled and hence the likelihood of maximu
25、m EIRP in the direction of MLS receivers is significantly reduced. In the above argmnts we have oniy considered one interfering radio LAN simply because it is unlikely that there will be mre than this being operated in close proximity to the MLS equipmnt on an aircraft in scenario (l), and hence we
26、do not need to consider the additive interference effects. MCL = - 30-(-120) = 90 dB (8) There may be a large number of potential interferers in scenario (2) but as we have shown from the minimum separation distances calculated, there should be no potential interference problem in scenario (2). This
27、 is illustrated in the following calculation. If we assume for example that there are 10 buildings within 1 km of the aircraft approach path and 10 radio LANs in each of these buildings giving a total of 100 radio LANs at 1 km The MCL for this example must be increased by 20 dB to 110 dB. The transm
28、ission loss must be greater than the calculated MCL. Using equation 7 and the previous STD-CEPT ERC REPORT 14-ENGL 1772 m 232b4L4 OOLSLLL 265 S ERC REPORT 14 Page 5 assumptions, n of 2 and A of 3, the minimum separation distance d is 1.3 km. Hence the MLS system could tolerate 100 radio LANs at 1.3
29、km and this is based on pessimistic propagation constants equivalent to every radio LAN having a clear line-of-sight obstructed only by a soft partition such as a window. Hence, there is no potential interference problem in scenario (2). 3.6 Interference Reduction with Spread Spectrum Techniques App
30、lying spread spectrum techniques to a narrow-band signal expands the bandwidth of the signal by the bandwidth expansion factor of Be and reduces the power spectral density of the signai by the processing gain Gp which is equal to the bandwidth expansion factor Be in dB. If spread spectrum techniques
31、 are applied to the 20 MHz bandwidth narrow-band radio LAN signai and the maxim available bandwidth is 100 MHz consequently the maximum available Be is 5, and Gp is 7 dB. The power spectral density of the entire signal is reduced by 7 dJ3. Hence, the application of spread spectrum would reduce the m
32、inimum separation distance from 11.2 km to 5.0 km for MLS and radio LANs h the same band. However, if the spurious emissions from spread spectrum radio LANs are considered as continuous wave emissions (i.e. not subject to spreading) the separation distance for adjacent band operation is the same (12
33、9 m) for both spread spectrum and non spread spectrum systems (ali figures are for a bandwidth of 20 MHz, n of 2 and A of 3 dB). So far we have not made a distinction between Direct Sequence (DS) and Frequency Hopping spread spectrum as the same reduction in power spectral density is achieved it wit
34、h both techniques. However, there may be a difference in the spectral roll-off and hence the level of adjacent band interference of DS and FH. This requires further investigation. 4. CONCLUSIONS This study has shown that MLS and radio LANS will not be able to co-exist in the same band but will be ab
35、le to co-exist in adjacent bands provided that there is a radio LAN exclusion zone of at least 15 m around the MLS equipment on an aircraft. However, it would be mre appropriate to impose a restriction prohibiting the use of radio LANs in aircraft to ensure that there would be no significant interfe
36、rence problem. It should be noted that the above minimum separation distances were calculated with pessimistic propagation paranieters and in practice the transmission losses could be much larger reducing the interference levels. Measurements are required to determine actual transmission losses in a
37、ircraft. The use of spectral spreading reduces interference and hence is advantageous. Also, there may be a difference in the spectral roil-off and hence the level of adjacent band interference of DS and FH spread spectrum This requires further investigation. It should be stressed that if there is a
38、ny significant change in radio LAN parameters from those used in this study the above mininnrm separation distances should be re-calculated. 5. REFERENCES i A report by T. WILKINSON and S.K. BARTON, University of Bradford, United Kingdom. 2 “Compatibility Study Between Radar and RLANs Operating at F
39、requencies Around 5.5 GHz, CEFT JPT FM7/SE ON RLANs, Radiocommunications Agency, VK, 16th January 1992. 3 ETSI, Radio Equipment and Systems, Digital European Cordless Telecommunications ETS 300175-2, Physical Layer. 4 PARSONS J.D, and GARDINER J.G., “Mobile Communication Systems“, Chapter 3, John Wi
40、ley and Sons 1989 5 WILKINSON T.A. and BARTON S.K.B., Radio Propagation in Buildings for Radio Local Area Networks“, Project Report 24/01/92. 6 ICA0 Standards and Recommended Practices relating to MLS Airborne Receivers, Annex 10 (source 7 CAP 208 (source UK Civil Aviation Authority). UK Civil Aviation Authority).
