Frequency scheduling for cascaded wireless relay networks with half duplex

This paper investigates the scheduling problem for K-hop frequency-division-duplex cascaded wireless relay networks, where the source, the relays, and the destination form a chain. Two scenarios are considered: 1) directed transmission, in which each relay node only transmits its radio wave to its neighboring downstream node; 2) undirected transmission, in which the radio wave can be received by the two neighboring upstream and downstream nodes, which causes hidden-terminal (HT) problem. The problem of frequency band allocation is formulated, which can be solved to maximize the network rate with decode-and-forward relay strategy. Optimal solution is derived based on a naive scheme, whose achievable rate shows a similar expression as that of time-division-duplex. We further show that the effect of half duplex and HT can be alleviated by increasing the spectrum efficiency of all relay hops when K > 3.