Signal Processing for Cognitive Radios

12.6.2.2 Noisy Communication between CRs and the SSDC

In general, the error-free communications between nodes and the SSDC may not always be possible. While classical distributed detection and data fusion have mostly considered the case of error-free communications of local decisions to a fusion center, recent interest on wireless sensor networks had motivated the need to take into account the communications errors. As a result, there are many formulations of decision/data fusion at a fusion center where local decisions/data are forwarded to a fusion center over noisy channels [194-197,200]. In particular, there are optimal fusion rules and their performance analysis available for both AF types of local processing (i.e., sending direct local observations to the SSDC) and binary quantized local decisions (as we have assumed earlier). Different formulations have also considered different types of communications channels (e.g., AWGN, fading multipath, etc.), modulation schemes (BPSK, OOK, etc.), as well as multiple-access schemes (orthogonal, nonorthogonal, etc.). The important conclusion from these analysis is not surprising: When there are communications channel errors, the final fusion performance degrades. Essentially, each local decision is now corrupted not only by the local sensor observation noise but also by channel noise. In the following, we will discuss a simple formulation that shows the effect of communications noise on channel-state decisions made at the SSDC.

Let ...