By analyzing the multi-hop cooperative diversity cognitive network in Underlay Sharing(US) mode, an approximate outage probability formulation and diversity order has been derived for decode-and-forward(DF) protocol in high signal-to-noise ratio. As DF protocol cannot achieve space diversity gain, modified multi-hop selective decode-and-forward(SDF) protocol is proposed and an approximate outage probability formulation and diversity order are deduced for SDF cognitive protocol to improve system performance. Theoretical analysis and simulation result show that the SDF protocol can decrease cogn...
