Baseband Diversity for Hybrid Microwave Systems

A hybrid information carrier is defined as a carrier for partly analog and partly digital source information. Some of the reported schemes transmit 1.5 Mbits/s and 1200 frequency division multiplexing (FDM) channels, others 6.3 Mbits/s and 600 FDM channels, in the shared spectrum of the microwave baseband (BB). Baseband diversity (BBD) is frequently used in this type of system. As hybrid transmission is getting wider popularity, it is important to determine the requirements on hybrid BBD systems. Different block diagrams are considered and performance of realizable hybrid BBD units is discussed. The BBD has different configurations for different data rates. We discuss the reasons for this within the theoretical performance and practical limit of technology. The important functions of signal presence and noise evaluation occur in the BBD. A novel approach to noise evaluation in the BB of microwave systems is feasible with digital techniques. The analog noise and pilot detection are in its threshold for high noise condition and fast pilot sensing time requirement. The proposed scheme evaluates digitally the error probability , based on error detections, and works well in high noise conditions.