Contradictions in Power Loading and Pilot Patterns in NC-OFDM Cognitive Radio Systems

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Cognitive Radio (CR) is seen as the next paradigm in radio communications and as a practical solution to the problem of spectrum scarcity. Non-Contiguous Orthogonal Frequency-Division Multiplexing (NC-OFDM) is a proposed implementation which allows the use of frequency bands to be placed arbitrarily close while maintaining the ability to disable those bands which are interfering with licensed users. This implementation poses challenges such as the optimal pilot pattern when pilots used for channel estimation need to be disabled to reduce interference as well as the Pilot-to-Data Power Ratio (PDPR) needed to maintain channel estimation accuracy. This paper discusses a theoretical problem with regard to the pilot pattern and power loading of pilot sub-channels when applied to a CR environment.