Dynamic Spectrum Access Decisions - George F. Elmasry

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networks can be deployed together and these networks will morph to the unique scenario needs while the waveform cognitive engines manage the configuration of links internal to the waveforms network and the master engines manager global routes.

       Making global dynamic route tables independent of route tables local to a network makes it possible for heterogeneous networks to be connected and optimized seamlessly.

      There are also disadvantages of this heterogeneous distributed cooperative DSA approach:

       The amount of DSA control traffic can grow exponentially as the number of nodes in a network increases and as the number of heterogeneous networks increases.

       Some nodes can go out‐of‐synch or temporarily lose connectivity and some information exchange control traffic can be lost. Retransmission of control traffic can further cause an already large volume of DSA control traffic to grow larger and can delay the adaptive route creation decisions.

       There are limits to global views of a large‐scale set of heterogeneous networks through distributed protocols. The master DSA agent in each gateway node will create a spectrum map that is less accurate than the spectrum map that can be created by a centralized arbitrator.

      To make different types of IP networks work seamlessly, Internet routing protocols faced similar challenges to what is described here for DSA challenges. This led to the creation of routing areas and gateway protocols such as the border gateway protocol (BGP). In some IP network design, certain routing configurations had to be left for a centralized network manager to decide. Similarly, the reliance on a distributed cooperative DSA for large‐scale heterogeneous networks will always show some limitations and lead us to consider the need for a centralized spectrum arbitrator to curb control traffic volume and arbitrate fairly between heterogeneous networks in certain cases while allowing a human (network manager) to monitor the cognitive network's health and set policies and rule sets. The network manager can change policies when needed.

Graph depicts the conceptual view of how control traffic volume depends on updating rate.

Schematic illustration of the use of a centralized DSA arbitrator in a hybrid DSA system of heterogeneous MANETs.

      Notice that the way a gateway can proxy a network spectrum utilization can depend on the gateway capabilities. This proxy approach can range from merely consolidating the network sensors' data into one message sent to the centralized arbitrator without fusion at the gateway node to performing extensive fusion at the gateway node and sending the centralized arbitrator a fused spectrum map. Factors such as SWaP limitations at the gateway node can guide the design of the gateway node fusion capabilities.

      With this type of hybrid DSA system, we have a mix of centralized spectrum allocation and distributed cooperative spectrum allocation within each network. Each network is assigned a pool of frequency bands to use based on the network's own distributed cooperative protocols while the centralized arbitrator changes the allocation of this pool of frequencies (redistributes frequency pools between all the networks) when its own spectrum map shows the need for such change.

      While the distributed cooperative hybrid system can work with a certain number of heterogeneous MANETs, as the number of networks in a large‐scale deployment increases, the need for a centralized arbitrator will increase. Notice that if the design elects that a gateway node would proxy a network spectrum map using extensive fusion, this could reduce the amount of DSA control traffic drastically. The gateway node can abstract the network spectrum map, fusing spectrum sensing information into very compressed messages sent to the centralized arbitrator.