Multi-rate modulation for cognitive radio over land mobile satellite channel

Multiple transmission of heterogeneous multimedia services is a central aspect of satellite communication technology. In this framework, often the design of efficient communication systems is complicated by stringent bandwidth constraint. Due to the extensive use of predictive coding, compressed data exhibit different sensitivities to transmission errors which makes them suitable for unequal error protection (UEP) techniques. UEP mainly relies on differentiated error control coding which raises the robustness of data, but also increases the transmission bandwidth. Reed-Solomon (RS) or Turbo Codes (TC) are frequently used, but also more performing techniques, based on Rate-Compatible (RC) codes have been proposed by the research community. In multi-rate modulations (MRM) the properties of dy-homogeneous signals are exploited to transmit over multiple band frequencies and time scales. MRM have been proved on unknown channels in either bandwidth or time. These conditions occur in cognitive radio (CR) networks where opportunistic communications are set up while preserving primaries licensed users. In CR the uncertainty of transmission opportunity makes the use of error correcting codes not trivial. Therefore, to achieve robustness this work proposes unequal power allocation (UPA) over the symbols of MRM according to both data sensitivity to channel errors and spectrum availability. As optimization criterion the mean square error between the original and the decoded message, which has showed strong correlation with subjective perception, is used. To assess the effectiveness of the proposed scheme in realistic condition for CR satellite networks the Land Mobile Satellite (LMS) model is used to reproduce the memory associated with real channels.