iming (Radio Frame, TTI Frame) The BS always sets up the master frame (i.e., generates the timing schedule for the next period). Beginning with synchronization pilots, a broadcast channel (BCH), and a random/contention access channel, a number of regular frames follow. The BS also reserves some of the frames for the second hop, to be used in the responsibility of the relay. With stealth relaying, the BS does not even distinguish between relays and ordinary UTs because the relay reserves the radio resources needed for its second hop by pretending to have a huge uplink traffic demand. This was a method for older non-relay-aware systems. However, a central, relay-aware BS-controlled resource allocation is preferable in all cases for future systems. The preamble is typically also sent by relays because UTs are often not able to receive the BS preamble in the cover- age scenario. However, with transparent relays, only the BS sends the preamble. Resources for the second hop that are located within the resources granted to the RN in stealth mode make up the frame-in-frame concept [16]. Modern multihop systems incorporate interleaved multihop frames, where frames for the first and second hops alternate in time, all controlled by the BS. In Figure 8.7, the downlink frame format for one TTI frame is shown. Some people define a TTI frame to be 1 ms long, but the principal properties remain the same. The small- est granularity resource unit is a chunk, and 100 of them fit into this basic frame. Symbols used for signaling and synchronization are out of focus here (shown in gray) and the only impact is the overhead (resources not available for data through- put). Downlink and uplink transmissions happen simultaneously in the same frame raster. There are three ways to integrate relaying (i.e., the frames used for the second hop-or beyond): Time domain relaying. Resources for hop one and hop two are separated in time (sequentially). Frequency domain relaying. Resources for hop one and hop two are sepa- rated in frequency (neighb