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Transmitter non-linear components cause distortions when a signal with high Peak to Average Power Ratio (PAPR) is transmitted. High PAPR is a parameter commonly associated to the multi-carrier signals like Orthogonal Frequency Division Multiplexing (OFDM) and Software Radio (SWR). Since SWR is an enabling technology for Cognitive Radio (CR), the signals demonstrate high PAPR in CR context as well. Upon opportunistic spectrum access in CR, PAPR further increases as more carriers (secondary carriers) are added in an already large numbered multi-carrier signal (primary signal). This paper explores the PAPR variations on spectrum access in CR context. Also, the reduction of PAPR in SWR and CR is performed using Tone Reservation (TR). In TR, certain carriers of the data signal are reserved to create a peak reducing signal which on addition to the data signal reduces its peak power. These carriers are called peak reducing carriers (PRC). At first, PAPR is reduced for different SWR signal scenarios. Then the influence of bandwidth, position and power of PRC on he PAPR reduction performance is discussed. Finally, CR PAPR is reduced by presenting a joint pectrum access scheme which implies a part of secondary data carriers as PRC to reduce CR PAPR.