Long Term Evolution - Licensed Assist Access (LTELAA) was proposed in 3GPP TR 36.889 to support unlicensed data access assisted by licensed spectrum. However, owing to wide applications of unlicensed wireless technologies such as WiFi, we need to deal with coexistence and collision issues. In traditional LBT protocol, LTE-LAA UE performs CCA to sense whether a channel is idle or not and wait until the channel becomes clear before transmission. In this way, LTE-LAA UE may suffer a low probability of successful first-trial transmission and need to schedule for retransmissions. To tackle this problem, we proposed a spectrum map assisted unlicensed resource allocation scheme for LTE-LAA SBSs to enhance successful transmission probability. Once LTE-LAA UEs have more opportunities to access the unlicensed channels, they can save cost for licensed resources and improve the overall spectrum utilization efficiency. Simulation results show that the proposed scheme can improve the sum rates of LTE-LAA SBS and LTE-A MBS, and significantly reduce channel collisions with other WiFi APs and LTE-LAA UEs.