Dynamic Spectrum Access Decisions. George F. Elmasry

4.6 can generalize the DLEP a step further by having the master DSA engine (higher tier engine) perform proactive sharing of the node's links capabilities over a “control plane” medium even when some of the available wireless links are not in use (i.e., in a large scale heterogeneous network, some MANET links have not been formed yet). In the gateway node, the master routing engine is able to receive (via the master DSA engine) location, status, capabilities, and spectrum resources utilization information from peer remote radios engines before all link establishment occurs and use this information to establish potential routes. The master DSA engine is able to use this information to perform spectrum resources deconfliction, link closure estimates, and bandwidth estimation before these links are established. The DSA master engine's ability to perform proactive sharing over different waveforms (mediums), through the master routing engine already established routes, gives the master routing engine the ability to ascertain potential data rates to neighbors on each network type prior to the establishment of all wireless links to these neighbors.

      Note that with this type of heterogeneous waveforms formation, the interface between the waveform DSA engine and the master DSA engine has to use unified wireless link metrics regardless of the waveform type which the waveform DSA engine represents. One waveform type may express the health of its wireless links in a different way from another waveform type. This multitiered architecture requires some normalization of the link health metrics calculated by the different waveforms in order for a routing engine to create an optimum global routing table without being skewed to use one waveform over another due to the lack of uniformity of link health metrics. This normalization should also allow the different networks to use different routing approaches internal to the formed MANET independent of global routes. One of the most important essences of creating true seamless efficient heterogeneous networks is to allow each network to use the best protocols for its internal routing and link health representation while requiring the different types of waveform DSA engines to adhere to a unified representation of the network metrics when it comes to global aspects.

      Let us illustrate how this hierarchical architecture can work with the case of a low bandwidth waveform that has global connectivity over a specific deployment. This low bandwidth waveform can be used to create a large RF footprint MANET that is used to establish the control plane over the deployed large‐scale heterogeneous hierarchical MANETs. In addition to the low bandwidth global network, the theater deployment has different types of higher bandwidth waveforms that will establish different types of networks (e.g., mesh networks, omnidirectional multiple access networks, LPI/LPD directional networks, etc.) where spectrum resources can be allocated dynamically within these networks and utilized globally by the master routing engine. Let us refer to these higher bandwidth networks links as offload links. The goal of DSA in this construct is to use these offload links dynamically and on‐demand considering the following:

      1 When data traffic to a node over the low bandwidth global network exceeds a defined threshold, the master routing engine will ask the master DSA engine to allocate resources over a specific higher bandwidth network. The master DSA engine will allocate the required spectrum resources by asking the corresponding waveform DSA engine to create a flow9 to that node. This action will create a new routing path for the master routing engine.

      2 When data traffic levels exceed the currently allocated bandwidth, the master routing engine will ask the master DSA engine to increment the allocated resources. The master DSA engine will ask the corresponding waveform DSA engine to acquire more bandwidth over the established offload data link. The current waveform DSA agent might adjust allocations or the master DSA engine might switch to another offload link on another network as necessary to meet the traffic volume needs. In either case, the master DSA engine will inform the master routing engine if the created routing path has increased bandwidth or if a new routing path is created with the required bandwidth.

      3 If traffic levels go below the currently allocated levels, bandwidth over the offload datalinks will be reduced, releasing some of the spectrum resources. Corresponding message flow to the two cases above will ensure the release of resources is known to all involved engines.

      4 If traffic levels go below a threshold, the flow over the offload data link will be torn down, releasing all resources back to the offload network.

      Notice the following:

       The low bandwidth global network is a lifeline to all nodes and is the start of the control plan. The control plane may use dynamic resource allocation (offload links) if needed.

       All offload networks spectrum become shared spectrum resources pools for allocating spectrum resources per traffic demand.

       The master routing engine is independent from the master DSA engine and the master routing engine has no say on how spectrum resources are to be allocated. This allows the inclusion of heterogeneous waveforms that use different resources allocation protocols within this heterogeneous hierarchical architecture. Each waveform can have a specific waveform DSA agent that works independently of other waveforms' DSA engines. One key aspect here is normalization of waveform metrics such that the master DSA agent uses unified resource allocation terms (e.g., flow) and the routing engines sees created routing paths in terms of unified data rate units (e.g., flow) and source destination pair. For the routing engines, a flow may be associated with a routing cost to allow the routing engine to ascertain the best route (path of multiple over‐the‐air hops).

      The use of such dynamic link establishment, link adaptation, and link teardown means the use of a dynamic reactive routing protocol creating route tables that get modified quickly. When there is a steady‐state period, the cognitive engines will be monitoring the allocated flow's health and exchanging information. Information exchange during steady‐state periods can include spectrum health awareness and mobile node geolocations. The shared information will allow the waveform DSA and routing engines to anticipate the need for changes¹⁰ local to the network and react in a timely manner. Shared information will also allow the master DSA and routing engines to anticipate the need for global changes and react in a timely manner.

      The master DSA engine is tightly coupled with the master routing engine in different ways. Consider the case when the master DSA engine is sharing spectrum awareness with its peer master DSA agents. The master DSA engine will rely on the dynamically created routes by the master routing engine and control traffic can become traffic demand on its own merit. If the global low‐bandwidth network cannot accommodate all control traffic volume, the offload network's spectrum resources would be used for control traffic.

The available resources on an established data link can change due to mobility, link stability, and link quality. For the cases where the waveform DSA engine learns new information about the link resources, the waveform DSA engine can inform the master DSA engine about any changes. One case of dynamically increasing link bandwidth due to mobility would be when a waveform switches to a lower forward error correction (FEC) mode, increasing throughput at close range while using the same amount of spectrum resources.¹¹ On the other hand, a case of decreased bandwidth is when the waveform must switch to a higher FEC mode due to increased range or jamming. With dynamic MANET, situational awareness must be shared between all cognitive engines, which can result in constant change of routing tables, constant changes in spectrum resource allocation and teardown, and consequently increase in control traffic load.¹²

      Let us summarize the advantages of this heterogeneous distributed cooperative DSA approach:

       Having a data plane that is independent of establishing offload links means the ability to exchange spectrum resources and link information before all networks are established.

       Waveform engines can be developed independent of each other as long as the exchange of waveform information is normalized between all types of waveforms.

       Waveforms can use their internal protocols for position awareness, antenna directionality, spectrum resources establishment, and teardown. Waveforms can decide how reactive routes local to the waveform network are established and torn down.

       A