How to avoid harmful interference

Will harmful interference occur if Fixed Satellite Services (FSS) and Mobile Services share the C band?

The ITU-R study available on this website clearly explains the difficulties inherent in trying to deploy both terrestrial applications and FSS applications in the C band.  However, they are not the only studies which have been carried out to show the difficulty of allowing FSS and BWA applications to use the same band.

The Satellite Users Interference Reduction Group (SUIRG) conducted a field test on the compatibility of FSS and WiMAX services sharing the C band spectrum.  The test - conducted in the latter quarter of 2007 - demonstrated that WiMAX communications pose a significant interference threat to satellite signals using the C band frequency.

Calculations based on the initial measured data - and scaling with ITU criteria - resulted in a separation distance of 278 km to reduce the level of interference to meet required levels. Combining two analyses, from a flat non-blocking terrain to a wooded hilly terrain, results show that the criteria whereby FSS antennas cannot co-exist with WiMAX systems ranges from 50 to over 200 km dependent upon the local terrain and the WiMAX output levels.

The results of the test are a firm testament to the need for clearly defined regulatory action from all Administrations.

How should the results of WRC-07 be implemented to avoid harmful interference?

The existing sharing studies show how that a real problem exists - and the FSS community is carrying out more studies to more clearly show that a problem exists from ‘out-of-band’ as well as ‘in-band’ interference.  Administrations should take note of the Final Acts of WRC-07 – and the sentiments expressed that there should be no global IMT identification - in their regulatory decision making and ensure that their licensing arrangements provide protection for both existing and new FSS deployments.

Any new licensing in the C band should take into account existing efficient protection measures – both regulatory and technical – to protect FSS earth stations.  ITU Articles Nos. 9.17 & 9.18, 9.21 specifically deal with the issue and should be used in the regulatory process for the deployment of new terrestrial networks.  The licensing of any new services in the C band must at the very least safe-guard existing FSS services from harmful interference and allow the continued provision of those existing services.

Administrations should also be aware of deployments in neighbouring countries.  The ITU studies show that ubiquitous deployment of BWA services in a neighbouring country will significantly impair the ability of a neighbouring country to use a C band network.  Only a close watching of the regulatory activities of neighbouring countries can ensure that harmful interference is avoided.

All Administrations should be aware that this is an important decision and once you have taken it you can’t un-make it.  Once used for terrestrial services the C band will not be available for FSS applications.