The Future of C-Band
In Geneva, Switzerland, the World Radiocommunication Conference 2007 is currently underway — and at the center of the discussions is the future of C-Band (known colloquially as the "compromise band").
C-band is characterized by larger antennas and is preferred by a variety of full-time service providers. C-band is a portion of electromagnetic spectrum in the microwave range of frequencies ranging from 4 to 6 GHz — normally downlink 3.7–4.2 GHz, uplink 5.9–6.4 GHz.
From Satellite News (subscription required):
During the first week of the World Radiocommunication Conference (WRC-07), administrations from Asia, Africa, and Latin America made clear their broad and deep support for keeping the status quo for satellite services by calling for no change to the current use of the C band. This campaign, which exhorts the Conference not to identify international mobile telecommunications (IMT) systems in C-band has been gathering pace throughout the past year, driven by both national policy imperatives and the satellite industry.
In the weeks prior to the meeting, the number of countries expressing positions in support of protecting C-band for satellite use outnumbered those in favor of identifying C-band for IMT. Since the opening of the conference, support for protection of the whole band for satellite services has increased in strength from an already solid base. Governments have been assisted by the argumentation of regional and international satellite operators, spearheaded by SES Global, Inmarsat and Intelsat as well as regional operators such as Arabsat and Rascom, and network integrators such as Schlumberger, which all attended the WRC to rally their constituencies.
Advocates of no change in C-band allocations have come from many parts of the world, each with their particular reasons for supporting the position. These include concerns based on pre-existing interference between IMT-like technologies and satellite services which have, in some examples, ruptured Interpol’s communications in Gambia and caused severe problems to Bolivia’s direct-to-home satellite services during the 2006 FIFA World Cup. African governments have been at pains to emphasise the importance of C-band in areas that experience rain fade and the risk to satellite services if neighboring countries were to implement IMT. Asian governments, in clear allusions to recent tsunamis, have emphasised the role of satellite communications in disaster and emergency circumstances, as well as the growing demand for those services
Archived audio feeds of the discussion can be found here.
Proponents of keeping C-Band as it is have pointed to its value in providing a critical communications link during emergencies:
During the first week and a half of the 2007 World Radio Conference in Geneva, some 3000 attendees were given an opportunity to see how Radio Amateurs can provide Emergency and Disaster communications. A van, constructed and manned by German Radio amateurs, was parked in front of the main entrance of the conference centre for delegates to visit. IARU Emergency Communications coordinator Hans Zimmerman F5VKP also participated in the demonstration. The IARU flag was flown at the top of van’s extendable mast.
José Albuquerque, the Senior Director of Spectrum Engineering at Intelsat, also makes the case for C-Band:
Currently, there are some 160 satellites in the geostationary orbit using C-band frequencies for their downlink transmissions (see Figure 1). This is the equivalent of more than 3000 satellite transponders with a 36 MHz bandwidth with the potential for transmitting about 180 Gbit/s at any given instant. This infrastructure represents an investment in excess of USD 30 billion in spacecraft and launch costs alone, without taking into account investment in the ground segment made by users and satellite operators.
Deployment of IMT systems in these frequencies would drastically reduce the benefits that these resources have brought to users around the world, because fixed-satellite services and IMT systems cannot share frequencies in the same geographic area.
C-band frequencies are used for downlink satellite transmissions that provide a wide range of services in developed and developing countries, including critical applications such as distance learning, telemedicine and universal access services; backhaul services (telephony, Internet); very small aperture terminal (VSAT) data links such as bank transactions or corporate networks; distribution of television programmes; mobile-satellite service feeder links, and emergency links, including disaster recovery services and meteorological tracking. These services require the high reliability and broad geographic coverage that can only be delivered in the C-band….
It is not feasible to undertake co-frequency operation of FSS receiving Earth stations and transmitting fixed or mobile stations in IMT systems. ITU–R studies have concluded that separation distances of between tens of kilometres and a few hundred are required to ensure protection of FSS Earth stations. Considering that a typical city covers an area with radius of between 15 and 30 km, sharing between IMT systems and FSS receiving Earth stations is not realistic.
In addition, IMT transmitters can also interfere with FSS Earth stations operating in adjacent bands. Unwanted emissions generated by IMT transmitters falling within the FSS desired signal cannot be filtered and will therefore generate interference. Furthermore, signals generated by an IMT transmitter can be strong enough to saturate the low-noise amplifier (LNA) of the FSS receiver. In view of the significant difference between the levels of the desired signal (originating at the satellite transmitter about 36 000 km away) and the interfering signal (originating at the IMT transmitter only a few kilometres away), filtering the IMT signal to the required levels might become unfeasible.
The adjacent-band interference effects described above highlight the fact that identification of a portion of C-band frequencies for IMT systems, while keeping another contiguous portion for FSS use, is not free of interference problems and does not constitute a desirable approach.
The message from SES, in video form:
We’ll keep you updated on the fate of C-Band as it becomes clear (no pun intended).
