9Out-of-band interference

9 Out-of-band interference

(1) Out-of-band interference is difficult to predict, because the levels and frequencies of unwanted emissions depend on both the nearness and the operating frequencies of radiocommunications transmitters and radiocommunications receivers that are spectrally or geographically close. In addition, out-of-band interference: (a) can extend for many MHz either side of the frequency boundary of a spectrum licence; and (b) is dependent on the quality of the radiocommunications receiver as well as the levels of the radiocommunications transmitter’s emissions; and (c) is difficult to model accurately. (2) Emission limits are also used to manage out-of-band interference, but these do not provide protection along the frequency boundaries of a spectrum licence throughout the entire geographic area. Because of the nature of out-of-band interference, emission limits cannot be used to provide protection from out-of-band interference for radiocommunications devices that are located near each other.

Note: Example: Radiocommunications devices that are located near each other include devices located at multi-operator sites.

(3) Emission limits are not the sole mechanism used to manage out-of-band interference for devices in close proximity, because the interference modelling inaccuracy would require large probability margins to be added to those limits. Large probability margins would place severe constraints on the use of the spectrum because the upper and lower frequency limits of a spectrum licence extend throughout the geographic area. Emission limits to manage out-of-band interference throughout the geographic area cannot be used, because they would lead to a severe loss of utility of the spectrum on both sides of the frequency limits. (4) To avoid large probability margins, out-of-band interference is managed through interference management procedures based on a compatibility requirement for radiocommunications receivers. A minimum level of receiver performance is specified in Part 4 in conjunction with the compatibility requirement because the performance level of receivers: (a) affects the level of interference; and (b) can vary for receivers operating under spectrum licences.

Note: The minimum level of receiver performance is specified in Part 4. The compatibility requirement is set out in Part 5.

(5) High power radiolocation services are operated in the 3100 MHz to 3500 MHz frequency band by the Department of Defence, on an itinerant basis. These radiolocation services have the potential to disrupt the throughput of 3.4 GHz receivers, particularly on the uplink channel (base station receiver). The Department of Defence employs techniques to minimise the impact on in-band and adjacent band services. However, there may be occasions when interference cannot be fully mitigated by these techniques. In such a case, the interference may be due to receiver blocking, strong out-of-band emissions of the radar, or other susceptibilities within a fixed or mobile wireless network configuration. When planning service deployments, 3.4 GHz spectrum licensees should consider different engineering techniques to reduce the likelihood of an impact on their radiocommunications devices. Such techniques may include additional radiofrequency filtering, network redundancy, or resilience of network configuration where vulnerabilities to radar signal interference are identified. The ACMA intends to work with the Department of Defence to provide what additional information it can to assist spectrum licensees on this matter. Such information will generally only be given directly to existing or likely prospective spectrum licensees.