An electronic device in a wireless communication system, the electronic device comprising processing circuitry (901, 903, 905) configured to: evaluate availability of transmission opportunities of a secondary user in a cognitive radio system in wireless resources of the wireless communication system; identify a plurality of available transmission opportunities according to a result of the evaluating; rank the plurality of available transmission opportunities for at least one user terminal; and transmit a result of the ranking as rank information to the at least one user terminal, the rank information comprising wireless transmission priorities of the plurality of available transmission opportunities for the user terminal; wherein the processing circuitry is configured to evaluate availability of a transmission opportunity to be evaluated by calculating contiguous idle time duration statistic of a frequency band in which the transmission opportunity is located within a past predetermined time period, wherein the contiguous idle time duration statistic comprises one or more of the following parameters: an average time length of contiguous idle time durations of the frequency band in which the transmission opportunity is located within the time period; a time length of a contiguous idle time duration which occurs most frequently of the frequency band in which the transmission opportunity is located within the time period; a time length of a contiguous idle time duration in which a corresponding time point is located of the frequency band in which the transmission opportunity is located within the time period; and number of accumulated contiguous idle time durations of the frequency band in which the transmission opportunity is located within the time period. evaluate availability of transmission opportunities of a secondary user in a cognitive radio system in wireless resources of the wireless communication system; identify a plurality of available transmission opportunities according to a result of the evaluating; rank the plurality of available transmission opportunities for at least one user terminal; and transmit a result of the ranking as rank information to the at least one user terminal, the rank information comprising wireless transmission priorities of the plurality of available transmission opportunities for the user terminal; wherein the processing circuitry is configured to evaluate availability of a transmission opportunity to be evaluated by calculating contiguous idle time duration statistic of a frequency band in which the transmission opportunity is located within a past predetermined time period, wherein the contiguous idle time duration statistic comprises one or more of the following parameters: an average time length of contiguous idle time durations of the frequency band in which the transmission opportunity is located within the time period; a time length of a contiguous idle time duration which occurs most frequently of the frequency band in which the transmission opportunity is located within the time period; a time length of a contiguous idle time duration in which a corresponding time point is located of the frequency band in which the transmission opportunity is located within the time period; and number of accumulated contiguous idle time durations of the frequency band in which the transmission opportunity is located within the time period.