As we have seen in Chapter 4, most current radar arrays generate one inertialess beam that scans the radar's surveillance volume with the aid of the phase-shifters located in the T/R modules. As the beams derived by Butler matrices are staring, the matrices are unsuitable to meet the requirements and a comparison between DBFs and the beamformers we shall consider in this section will be undertaken at the end of this section.įor radar arrays the issues are more complex and application-dependent but some studies and proposals related to multiple-beam systems have been reported (e.g. The competing BFNs for this application are digital beamformers (DBFs), Butler matrices, and BFNs capable of deriving several agile beams simultaneously. The provision of reconfiguration in case a failure occurs in any radiated beam. The formation of nulls exactly onto the neighboring area where frequency reuse could create problems. Precise pointing of each beam to the target area despite possible deviations of the array system components and satellite attitude. In this context, the BFN is expected to provide the following functions : The use of active phased arrays on board the satellites is considered a viable means of enabling the radiation of high-power multiple beams. Satellite communications systems featuring multiple-beam LEO/MEO satellites have recently been proposed to meet the ever-growing demand for more communication channels.

Other applications that need high throughput and availability which can benefit from CR in DSS are machine to machine communications, Internet of the things and cloud computing. Typically these applications are related to the provision of fixed and mobile broadband multimedia services, for example, high definition (HD) broadcast and HD interactive multimedia.

In this sense, the applications that could benefit more from CR in DSS are those demanding high reliable throughput and availability which are the main benefits provided by CR DSS. As an illustration, a communication between an earth station and a lunar module through a satellite needs to be reliable, while transmissions from a control tower to airplanes must provide very low latencies. Satellite communication systems support a wide range of applications which need to satisfy a number and variety of requirements. Ricard Alegre-Godoy, in Cooperative and Cognitive Satellite Systems, 2015 12.2.3 Applications that could benefit from cognitive DSS

Satelite downlink