Читать книгу Dynamic Spectrum Access Decisions - George F. Elmasry - Страница 108

Figure 6.12 shows a 5G spectrum fusion case where the macrocell is the only fusion center for spectrum sensing information. With this case, the following events can occur (notice that these events are continually occurring):

1 The SA continually senses spectrum and collects spectrum sensing information (without any fusion). It consolidates spectrum sensing information for all frequency bands.

2 The SA sends the consolidated spectrum sensing information to the macrocell.

3 Picocells and femtocells also send their consolidated spectrum sensing information to the macrocell.

4 The macrocell fusion center processes spectrum sensing information received from all SAs, all picocells, and all femtocells.

5 The macrocell fusion center creates fusion results and sends them to each SA, femtocell, and picocell.

6 An end user makes a spectrum service request from the SA.

7 The SA uses the fusion results from the macrocell and replies to the end user with a recommendation of which spectrum band(s) to use.

Figure 6.12 5G use of the macrocell as the fusion center.

This case can simply be described as a hybrid of distributed sensing and centralized fusion. Notice that this case can be morphed to the case where the SA, femtocells, and picocells perform a form of spectrum sensing information fusion and send the macrocell fusion center the results of its own local fusion. In either case, the macrocell fusion results are broadcasted to all lower hierarchy entities and the SA can't rely on its own local fusion results to respond to frequency band service requests from end users. Notice that even with the macrocell being the only place for fusion, the SAs, femtocells, and picocells perform a form of cooperative spectrum sensing.

If some SAs have limited energy and must conserve energy, the macrocell can select a subset of the SAs to perform spectrum sensing and collect sensing information. The macrocell algorithm has to consider the hidden node challenge discussed earlier in this book and select SAs that are geographically distributed to optimize sensing impact.