The rules for trading spectrum licences are defined in the Radiocommunications (Trading Rules for Spectrum Licences) Determination 2012. Effectively spectrum licences can be traded in part or whole to others by geographic area and bandwidth and can be divided or amalgamated.
To enable the efficient trading and allocation of spectrum licences the ACMA permits spectrum space to be bought and sold in terms of standard trading units.
Standard trading units (STUs)
A single STU is the smallest unit of spectrum space that a spectrum licence can be divided into. One or more STUs can be traded to another party, provided that the resulting new or varied licence meets the minimum contiguous bandwidth.
An STU can be thought of as a cube of spectrum space that covers a geographic area horizontally and bandwidth vertically. The geographic area of an STU is equal to a cell of the ACMA’s spectrum map grid, this is an area 5 minutes by 5 minutes of arc (approximately 9x9 km). The frequency bandwidth of an STU is set at 1 Hz for all spectrum licence bands.
A single STU may be too small to have much utility, but because of its regular shape, it can be stacked with neighbouring STUs vertically to provide increased bandwidth or horizontally to cover a larger area. These stacks form bodies of spectrum space that allow spectrum licences to be combined and subdivided according to market needs.
Minimum contiguous bandwidth (MCB)
Every spectrum licence band has a defined MCB which is specified in the Radiocommunications (Trading Rules for Spectrum Licences) Determination 2012. The concept of the MCB is to avoid situations where spectrum trading leads to licences that are too small to be practical, resulting in inefficient use of spectrum and unnecessary administrative costs.
Although an STU is the minimum bandwidth segment and geographic area of the spectrum that can be traded, trading may be restricted if an STU does not meet the MCB.
The choice of the MCB for a band sets the maximum number of frequency boundaries that are permitted within the spectrum. Small MCBs require more complex technical frameworks to manage interference across the larger number of possible frequency boundaries. The MCB must also be compatible with the necessary bandwidths of likely applications of the band to allow all of the licensed bandwidth to be used.