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In this letter, we consider hierarchical cooperative spectrum sensing based on two-threshold energy detection in cognitive radio networks. In order to solve the sensing failure problem in conventional two-threshold energy detection, soft combination of the observed energy value from different cognitive radio users is investigated. Encouraged by the performance gain of soft combination of energy falling between the two thresholds, we further propose a new softened hard combination scheme to reduce the communication overhead. Results show that the proposed method achieves a good tradeoff between sensing performance and communication overhead.