IEEE 802.16j-based wireless relay networks adopt time division multiple access, where time slots are assigned to communication links as transmission opportunities. When we employ adaptive modulation and coding for data transmission on wireless links, the transmission bitrate is affected by the signal to interference and noise ratio. Therefore, algorithms that assign time slots to links are important for enhancing the performance of relay networks. When we employ relay networks to access backhaul networks, the bottleneck link is likely to be located near the gateway node, and dominates the performance of the relay network. In this paper, we propose a time slot-adding algorithm to improve bottleneck link throughput in IEEE 802.16j relay networks. Although we employ an existing method for the initial assignment of time slots to links in the network, we introduce novel algorithm to add more time slots to the bottleneck link. Performance evaluations confirm that the proposed method improves data transfer throuzhput by up to around 30%.