Читать книгу Dynamic Spectrum Access Decisions - George F. Elmasry - Страница 54

With a spectrum sensor performing a simple energy detection decision, this may be the end of the decision‐making process that can be made locally. The local decision fusion process would rely on the local hypotheses that differentiate if the frequency band being sensed is occupied or not. If a hypothesis is persistent for the presence or absence of a signal, the decision fusion will turn the hypotheses into a decision. However, if an augmented sensor is able to utilize a multisector antenna or antenna arrays, there could be further fusion steps before making a decision. An example of a further fusion step is to identify the direction of the interfering signal when the local process hypothesizes the presence of interference relying on the difference in the energy received per sector. This case is covered in Section 3.3.1.2 The more common case to perform further local decision fusion is for the same‐channel in‐band sensing in a MANET where the reception of the sensed communications signal can be mapped to an RF neighbor. This can make the spectrum sensor in the MANET node able to create a more detailed spectrum map (i.e., identify interference directionality) without using sectored antennas,¹⁷ as explained in Section 3.3.1.1

Notice that if the local fusion process stops without further fusion of spectrum sensing information, the higher hierarchical levels of decision making (e.g., distributed cooperative or centralized decision fusion) can make DSA decisions that are more optimum than that of the local decision‐making process. With hybrid DSA designs, fusion at the lower hierarchical level can always help reduce control traffic volume and make the overall decision‐making process more accurate even if the final decisions are left for the higher hierarchical level.¹⁸