the problem-which resources are used best to support a particular UT (or RN because this is treated just like a UT). The scheduler takes care that, within a frame and inside a cell, there is no interference (i.e., no two senders are allowed to send at the same time on the same resource). There is one scheduler for the DL and one for the UL parts of the transmission. Both work independently. For the DL, the queue occupancy is known from the queues nearby; however, for the UL, there must be a signaling from the UT (or RN) to the BS telling about the number of bits and PDUs waiting inside the client stations. For QoS support, this information must be available per QoS class or priority. Relays simply work similarly. They receive resource requests from their UTs, schedule their DL and UL resources autonomously, and communicate their decision just like a BS toward its UT, within a resource map. The only difference from a BS is that the available resources on which the RN can decide make up a subset of all available resources on the link, and this subset has been assigned by the BS earlier. This resource parti- tioning is necessary SO that, within a cell, all resources are distinct and interference is mitigated. The following functions are located in a wireless resource scheduler, but only their relevance with regard to relaying is emphasized here. 8.4.2.1 Dynamic Subcarrier Assignment (DSA) DSA is a free decision of the scheduler responsible for the (single-hop) link. The set of available resources is given by the next-higher hierarchy leader, up to the BS. But the local decision is independent and can be based on CQI measurements, for example. 8.4.2.2 Adaptive Modulation and Coding (AMC) The PhyMode to use within each resource is also a link-local decision. The sched- uler knows an SINR estimation of the link and decides which PhyMode to take. This can be different for each subchannel if, for example, the channel is frequency dependent due to fading. Figure 8.11 shows such a frequency- and time-dependent channel. Due