Trong thực tế, tuy nhiên, chỉ có giá trị hữu hạn ACS và ACLR (xem Phần ). Giả sử giá trị của 33 dB và 45 dB, tương ứng, các khớp nối, C, giữa các tàu sân bay trở thành: C ¼ A10 Á log10 D10 A33 = 10 þ 10 A45 = 10 Þ dB ¼ 32:7 dB D3: 73Þ | WCDMA-GSM Co-planning Issues 297 antennas MHAs and feeder networks to be installed. In many networks sites will also be shared by at least two operators. Co-siting The term co-locating shall be used when BSs are installed at the same site. When sites are co-located and share feeders and antennas this shall be called cositing . Basically the same isolation requirements are still valid as in co-located sites but the means to achieve this could be different. Different kinds of sharing situations may be distinguished such as antenna and or feeder sharing or there could even be multi-mode BSs that share the same cabinets site support equipment transmission feeders and antennas. In the basic situation there would be an existing BS with the required site support equipment feeders and antennas and the operator installs a WCDMA BS on the same site. If the existing system is GSM1800 the attenuation of the feeder would be of the same order as in WCDMA but in the case of GSM900 the attenuation of the feeder should be checked and changed if needed. Single-mode antennas can be replaced by multi-mode antennas. One example is shown in Figure . Based upon the preceding discussion and the assumed NFs in Section the isolation between a WCDMA BS cabinet and a GSM900 BS cabinet should be at least 40 dB whereas the isolation between a WCDMA BS cabinet and a GSM1800 BS cabinet should be at least 45 dB. If the receiver NF is greater than that assumed . for an active distributed antenna system indoor solution - then the isolation requirement can be reduced. Figure Example of site feeder and antenna sharing. 298 Radio Network Planning and Optimisation for UMTS The way in which this isolation requirement is achieved depends upon the detailed site design. If a diplexer is being used to combine the WCDMA and GSM signals such that they can share the same feeders then the diplexor provides the majority of the isolation requirement. A diplexer typically offers 40 dB of .
