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Spectrum shaping: a new perspective on cognitive radio-part I: coexistence with coded legacy transmission

A new approach to cognitive radio based on the premise that the legacy link is not fully loaded by the legacy service is presented. The assumption implies that there is a non-negligible margin to accommodate a cognitive transmission; this accommodation is achieved by spectrum shaping of the cognitive user. Much prior work on cognitive systems captures the effect of interference by the interference power level. In contrast, the current work characterizes interference by its induced degradation on the legacy user. Despite ignorance of the legacy user's message, the spectrum shaped cognitive user can always operate at its full available power. As a result, logarithmic growth of the cognitive transmission rate is achievable. In Part I of this two-part paper, analysis is provided for both scalar and vector system models where the legacy system employs coded transmission (Part II examines analog legacy users). The logarithmic growth rates, i.e., the prelog coefficients, of cognitive transmission rates in the high-power regime, are established for both the scalar and vector system models considered.